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Sample records for single-phase forced convection

  1. On the prediction of single-phase forced convection heat transfer in narrow rectangular channels

    International Nuclear Information System (INIS)

    Ghione, Alberto; Noel, Brigitte; Vinai, Paolo; Demazière, Christophe

    2014-01-01

    In this paper, selected heat transfer correlations for single-phase forced convection are assessed for the case of narrow rectangular channels. The work is of interest in the thermal-hydraulic analysis of the Jules Horowitz Reactor (JHR), which is a research reactor under construction at CEA-Cadarache (France). In order to evaluate the validity of the correlations, about 300 tests from the SULTAN-JHR database were used. The SULTAN-JHR program was carried out at CEA-Grenoble and it includes different kinds of tests for two different vertical rectangular channels with height of 600 mm and gap of 1.51 and 2.16 mm. The experimental conditions range between 2 - 9 bar for the pressure; 0.5 - 18 m/s for the coolant velocity and 0.5 - 7.5 MW/m 2 for the heat flux (whose axial distribution is uniform). Forty-two thermocouples and eight pressure taps were placed at several axial locations, measuring wall temperature and pressure respectively. The analysis focused on turbulent flow with Reynolds numbers between 5.5 x 10 3 - 2.4 x 10 5 and Prandtl numbers between 1.5 - 6. It was shown that standard correlations as the Dittus-Boelter and Seider-Tate significantly under-estimate the heat transfer coefficient, especially at high Reynolds number. Other correlations specifically designed for narrow rectangular channels were also taken into account and compared. The correlation of Popov-Petukhov in the form suggested by Siman-Tov still under-estimates the heat transfer coefficient, even if slight improvements could be seen. A better agreement for the tests with gap equal to 2.16 mm could be found with the correlation of Ma and the one of Liang. However the heat transfer coefficient when the gap is equal to 1.51 mm could not be predicted accurately. Furthermore these correlations were based on data at low Reynolds numbers (up to 13000) and low heat flux, so the use of them for SULTAN-JHR may be questionable. According to the authors’ knowledge, existing models of heat transfer

  2. Effects of rolling on single-phase water forced convective heat transfer characteristics

    International Nuclear Information System (INIS)

    Guo Yanming; Gao Puzhen; Huang Zhen

    2010-01-01

    A series of single-phase forced circulation tests in a vertical tube with rolling motion were performed in order to investigate effects of rolling motion on thermal-hydraulic characteristics. The amplitudes of the rolling motion in the tests were 10 degree, 15 degree and 20 degree. The rolling periods were 7.5 s, 10 s, 15 s and 20 s. The Reynolds number was from 6000 to 15000. Heat transfer in the test tube is bated by the rolling motion. As the test-bed rolling more acutely, the heat transfer coefficient of the test tube becomes smaller when the mass flow rate in the test tube is a constant. The heat transfer coefficient calculated by the formula which is for stable state doesn't fit very well with that from experiments. At last a formula for calculating heat transfer in rolling motion was introduced. (authors)

  3. Single-phase liquid flow forced convection under a nearly uniform heat flux boundary condition in microchannels

    KAUST Repository

    Lee, Man; Lee, Yi-Kuen; Zohar, Yitshak

    2012-01-01

    A microchannel heat sink, integrated with pressure and temperature microsensors, is utilized to study single-phase liquid flow forced convection under a uniform heat flux boundary condition. Utilizing a waferbond-and-etch- back technology, the heat source, temperature and pressure sensors are encapsulated in a thin composite membrane capping the microchannels, thus allowing experimentally good control of the thermal boundary conditions. A three-dimensional physical model has been constructed to facilitate numerical simulations of the heat flux distribution. The results indicate that upstream the cold working fluid absorbs heat, while, within the current operating conditions, downstream the warmer working fluid releases heat. The Nusselt number is computed numerically and compared with experimental and analytical results. The wall Nusselt number in a microchannel can be estimated using classical analytical solutions only over a limited range of the Reynolds number, Re: both the top and bottom Nusselt numbers approach 4 for Re < 1, while the top and bottom Nusselt numbers approach 0 and 5.3, respectively, for Re > 100. The experimentally estimated Nusselt number for forced convection is highly sensitive to the location of the temperature measurements used in calculating the Nusselt number. © 2012 IOP Publishing Ltd.

  4. Single-phase liquid flow forced convection under a nearly uniform heat flux boundary condition in microchannels

    KAUST Repository

    Lee, Man

    2012-02-22

    A microchannel heat sink, integrated with pressure and temperature microsensors, is utilized to study single-phase liquid flow forced convection under a uniform heat flux boundary condition. Utilizing a waferbond-and-etch- back technology, the heat source, temperature and pressure sensors are encapsulated in a thin composite membrane capping the microchannels, thus allowing experimentally good control of the thermal boundary conditions. A three-dimensional physical model has been constructed to facilitate numerical simulations of the heat flux distribution. The results indicate that upstream the cold working fluid absorbs heat, while, within the current operating conditions, downstream the warmer working fluid releases heat. The Nusselt number is computed numerically and compared with experimental and analytical results. The wall Nusselt number in a microchannel can be estimated using classical analytical solutions only over a limited range of the Reynolds number, Re: both the top and bottom Nusselt numbers approach 4 for Re < 1, while the top and bottom Nusselt numbers approach 0 and 5.3, respectively, for Re > 100. The experimentally estimated Nusselt number for forced convection is highly sensitive to the location of the temperature measurements used in calculating the Nusselt number. © 2012 IOP Publishing Ltd.

  5. Assessment of thermal conductivity, viscosity and specific heat of nanofluids in single phase laminar indernal forced convection

    NARCIS (Netherlands)

    Vanapalli, Srinivas; ter Brake, Hermanus J.M.

    2013-01-01

    Nanofluids are considered for improving the heat exchange in forced convective flow. In literature, the benefit of nanofluids compared to the corresponding base fluid is represented by several figures-of-merit in which the heat transfer benefit and the cost of pumping the fluid are considered. These

  6. Stability characteristics of a single-phase free convection loop

    Science.gov (United States)

    Creveling, H. F.; De Paz, J. F.; Baladi, J. Y.; Schoenhals, R. J.

    1975-01-01

    Experiments investigating the stability characteristics of a single-phase free convection loop are reported. Results of the study confirm the contention made by previous workers that instabilities near the thermodynamic critical point can occur for ordinary fluids as well as those with unusual behavior in the near-critical region. Such a claim runs counter to traditional beliefs, but it is supported by the observation of such instabilities for water at atmospheric pressure and moderate temperatures in the present work.

  7. Theoretical study to determine the heat transfer by forced convection coefficient in an empirical correlation in single phase, for annular channels

    International Nuclear Information System (INIS)

    Herrera A, E.

    1994-01-01

    In the heat transfer studies by forced convection, we have few data about behavior of the fluids in an annular channel heated by a concentric pipe, such date is necessary to know the heat transfer coefficient that establish the interchange of energy and the thermic properties of the fluid with the geometry of the flow. In this work the objective, was to compare some empirical correlations that we needed for determinate the heat transfer coefficient for annular channels, where we obtained similar at the theoretical results of an experiment made by Miller and Benforado. It is important to know such coefficients because we can determinate the heat quantity transmitted to a probe zone, in which we simulate a nuclear fuel element that developed huge heat quantity that must be dispersed in short time. We give theoretical data of the heat forced transfer convection and we analyzed the phenomena in annular channels given some empirical correlations employed by some investigators and we analyzed each one. (Author)

  8. Single-phase convective heat transfer in rod bundles

    International Nuclear Information System (INIS)

    Holloway, Mary V.; Beasley, Donald E.; Conner, Michael E.

    2008-01-01

    The convective heat transfer for turbulent flow through rod bundles representative of nuclear fuel rods used in pressurized water reactors is examined. The rod bundles consist of a square array of parallel rods that are held on a constant pitch by support grids spaced axially along the rod bundle. Split-vane pair support grids, which create swirling flow in the rod bundle, as well as disc and standard support grids are investigated. Single-phase convective heat transfer coefficients are measured for flow downstream of support grids in a rod bundle. The rods are heated using direct resistance heating, and a bulk axial flow of air is used to cool the rods in the rod bundle. Air is used as the working fluid instead of water to reduce the power required to heat the rod bundle. Results indicate heat transfer enhancement for up to 10 hydraulic diameters downstream of the support grids. A general correlation is developed to predict the heat transfer development downstream of support grids. In addition, circumferential variations in heat transfer coefficients result in hot streaks that develop on the rods downstream of split-vane pair support grids

  9. Single-phase convective heat transfer in rod bundles

    Energy Technology Data Exchange (ETDEWEB)

    Holloway, Mary V. [Mechanical Engineering Department, United States Naval Academy, 590 Holloway Rd., Annapolis, MD 21402 (United States)], E-mail: holloway@usna.edu; Beasley, Donald E. [Mechanical Engineering Department, Clemson University, Clemson, SC 29634 (United States); Conner, Michael E. [Westinghouse Nuclear Fuel, 5801 Bluff Road, Columbia, SC 29250 (United States)

    2008-04-15

    The convective heat transfer for turbulent flow through rod bundles representative of nuclear fuel rods used in pressurized water reactors is examined. The rod bundles consist of a square array of parallel rods that are held on a constant pitch by support grids spaced axially along the rod bundle. Split-vane pair support grids, which create swirling flow in the rod bundle, as well as disc and standard support grids are investigated. Single-phase convective heat transfer coefficients are measured for flow downstream of support grids in a rod bundle. The rods are heated using direct resistance heating, and a bulk axial flow of air is used to cool the rods in the rod bundle. Air is used as the working fluid instead of water to reduce the power required to heat the rod bundle. Results indicate heat transfer enhancement for up to 10 hydraulic diameters downstream of the support grids. A general correlation is developed to predict the heat transfer development downstream of support grids. In addition, circumferential variations in heat transfer coefficients result in hot streaks that develop on the rods downstream of split-vane pair support grids.

  10. Comparison of numerical results with experimental data for single-phase natural convection in an experimental sodium loop

    International Nuclear Information System (INIS)

    Ribando, R.J.

    1979-01-01

    A comparison is made between computed results and experimental data for single-phase natural convection in an experimental sodium loop. The tests were conducted in the Thermal-Hydraulic Out-of-Reactor Safety (THORS) Facility, an engineering-scale high temperature sodium facility at the Oak Ridge National Laboratory used for thermal-hydraulic testing of simulated LMFBR subassemblies at normal and off-normal operating conditions. Heat generation in the 19 pin assembly during these tests was typical of decay heat levels. Tests were conducted both with zero initial forced flow and with a small initial forced flow. The bypass line was closed in most tests, but open in one. The computer code used to analyze these tests [LONAC (LOw flow and NAtural Convection)] is an ORNL-developed, fast running, one-dimensional, single-phase finite difference model for simulating forced and free convection transients in the THORS loop

  11. Comparison of numerical results with experimental data for single-phase natural convection in an experimental sodium loop. [LMFBR

    Energy Technology Data Exchange (ETDEWEB)

    Ribando, R.J.

    1979-01-01

    A comparison is made between computed results and experimental data for a single-phase natural convection test in an experimental sodium loop. The test was conducted in the Thermal-Hydraulic Out-of-Reactor Safety (THORS) facility, an engineering-scale high temperature sodium loop at the Oak Ridge National Laboratory (ORNL) used for thermal-hydraulic testing of simulated Liquid Metal Fast Breeder Reactor (LMFBR) subassemblies at normal and off-normal operating conditions. Heat generation in the 19 pin assembly during the test was typical of decay heat levels. The test chosen for analysis in this paper was one of seven natural convection runs conducted in the facility using a variety of initial conditions and testing parameters. Specifically, in this test the bypass line was open to simulate a parallel heated assembly and the test was begun with a pump coastdown from a small initial forced flow. The computer program used to analyze the test, LONAC (LOw flow and NAtural Convection) is an ORNL-developed, fast-running, one-dimensional, single-phase, finite-difference model used for simulating forced and free convection transients in the THORS loop.

  12. Comparison of numerical results with experimental data for single-phase natural convection in an experimental sodium loop

    International Nuclear Information System (INIS)

    Ribando, R.J.

    1979-01-01

    A comparison is made between computed results and experimental data for a single-phase natural convection test in an experimental sodium loop. The test was conducted in the Thermal-Hydraulic Out-of-Reactor Safety (THORS) facility, an engineering-scale high temperature sodium loop at the Oak Ridge National Laboratory (ORNL) used for thermal-hydraulic testing of simulated Liquid Metal Fast Breeder Reactor (LMFBR) subassemblies at normal and off-normal operating conditions. Heat generation in the 19 pin assembly during the test was typical of decay heat levels. The test chosen for analysis in this paper was one of seven natural convection runs conducted in the facility using a variety of initial conditions and testing parameters. Specifically, in this test the bypass line was open to simulate a parallel heated assembly and the test was begun with a pump coastdown from a small initial forced flow. The computer program used to analyze the test, LONAC (LOw flow and NAtural Convection) is an ORNL-developed, fast-running, one-dimensional, single-phase, finite-difference model used for simulating forced and free convection transients in the THORS loop

  13. On the development of a grid-enhanced single-phase convective heat transfer correlation

    International Nuclear Information System (INIS)

    Miller, D.J.; Cheung, F.B.; Bajorek, S.M.

    2011-01-01

    A new single-phase convective heat transfer augmentation correlation has been developed using single phase steam cooling experimental data obtained from the Penn State/NRC Rod Bundle Heat Transfer (RBHT) facility. Experimental data obtained from the RBHT single phase steam cooling tests have been evaluated and new findings identified. Previous rod bundle tests showed the importance of spacer grid on the local heat transfer, and that the augmentation in heat transfer downstream of a grid decays exponentially. The RBHT data also shows that the Reynolds number affects the rate at which this augmentation decays. The new correlation includes the strong dependence of heat transfer on both the Reynolds number and the grid blockage ratio. While the effects of both parameters were clearly evident in the RBHT experimental data, existing correlations do not account for the Reynolds number effect. The developed correlation incorporates Reynolds number in the decay curve of heat transfer. The newly developed correlation adequately accounts for the dependence of the heat transfer augmentation decay rate on the local flow Reynolds number. (author)

  14. A note on similarity in single-phase and porous-medium natural convection

    International Nuclear Information System (INIS)

    Lyall, H.G.

    1981-03-01

    The similarity laws for single-phase and porous-medium natural convection are developed. For single-phase flow Nu = Nu(Ra) implies that inertial effects are negligible, while Nu = Nu(Ra.Pr) implies that viscous effects are. The first correlation is adequate for Pr>10, while the second applies for Pr<0.01. For intermediate values of Pr, a more general correlation, Nu = Nu(Ra,Pr) is necessary. For a porous-medium, if inertial effects and dispersion are negligible, Nu* = Nu*(Ra*). However dispersion will only be negligible if the ratio of grain size d to the width of the region L is very small (d/L<< l). If this condition does not hold it is necessary to model d/L. If inertial effects are significant, i.e. the Reynolds number is too large for Darcy's law to apply, a group containing the effective Prandtl number, Pr*, also needs to be modelled for similarity. (author)

  15. Experimental study on the convective heat transfer enhancement in single-phase steam flow by a support grid

    International Nuclear Information System (INIS)

    Kim, Byoung Jae; Kim, Kihwan; Kim, Dong-Eok; Youn, Young-Jung; Park, Jong-Kuk; Moon, Sang-Ki; Song, Chul-Hwa

    2014-01-01

    Highlights: • The convective heat transfer enhancement by support grids is investigated. • Experiments were performed in a square array 2 × 2 rod bundle. • The enhancement was affected not only by the blockage ratio also by the Reynolds number. • For low Reynolds numbers, the enhancement depends on the Reynolds number (Re). • For high Reynolds numbers, the enhancement is nearly independent of Re. - Abstract: Single-phase flow occurs in the fuel rod bundle of a pressurized water reactor, during the normal operation period or at the early stage of the reflood phase in a loss-of-coolant accident scenario. In the former period, the flow is single-phase water flow, but in the latter case, the flow is single-phase steam flow. Support grids are required to maintain a proper geometry configuration of fuel rods within nuclear fuel assemblies. This study was conducted to elucidate the effects of support grids on the convective heat transfer in single-phase steam flow. Experiments were made in a square array 2 × 2 rod bundle. The four electrically-heating rods were maintained by support grids with mixing vanes creating a swirl flow. Two types of support grids were considered in this study. The two types are geometrically similar except the blockage ratio by different mixing vane angles. For all test runs, 2 kW power was supplied to each rod. The working fluid was superheated steam with Re = 2,301–39,594. The axial profile of the rod surface temperatures was measured, and the convective heat transfer enhancement by the presence of the support grids was examined. The peak heat transfer enhancement was a function of not only the blockage ratio but also the Reynolds number. Given the same blockage ratio, the heat transfer enhancement was sensitive to the Reynolds number in laminar flow, whereas it was nearly independent of the Reynolds number in turbulent flow

  16. Experimental research on single phase convection heat transfer in micro-fin tube

    International Nuclear Information System (INIS)

    Fan Guangming; Sun Zhongning; Zhu Sheng

    2011-01-01

    An experimental investigation of heat transfer and flow resistance characteristics of single phase water in three micro-fin tubes with different fin height was conducted. At the same time, the efficiency of micro-fin tubes within the experimental scope was evaluated and the optimal working region was determined. Based on the experimental data in the optimal working region, correlations for predicting the heat transfer and flow resistance were also given by multiple regression method. The result indicates that the micro-fin tubes can greatly enhance the single-phase heat transfer in turbulent flow, and the increase of heat transfer coefficient is higher than the increase of flow resistance. The accuracy of the correlation is very high, of which the deviation from the experimental value is very small. (authors)

  17. Experimental research of inclined-micro-fin flat tube on single phase convection heat transfer

    International Nuclear Information System (INIS)

    Fan Guangming; Sun Zhongning; Wang Meng

    2011-01-01

    The experimental research of heat transfer and flow resistance characteristics of single phase water in four inclined-micro-fin flat tubes with different physical dimensions was conducted. At the same time,suitable criteria were selected to evaluate the efficiency of inclined-micro-fin flat tubes within the experimental scope and the optimal working region was determined. The results indicate that inclined-micro-fin flat tubes can greatly enhance the single-phase heat transfer in turbulent flow and the maximum heat transfer coefficient attains to 5.9 times of that in smooth tube. The quantities of heat transfer for inclined-micro-fin flat tubes are three times higher than that of smooth tube with the same of heat exchange area and pump power. (authors)

  18. Nucleate pool boiling, film boiling and single-phase free convection at pressures up to the critical state. Part I: Integral heat transfer for horizontal copper cylinders

    Energy Technology Data Exchange (ETDEWEB)

    Gorenflo, Dieter; Baumhoegger, Elmar; Windmann, Thorsten; Herres, Gerhard [Institut fuer Energie- und Verfahrenstechnik, Universitaet Paderborn, Warburger Str. 100, D-33098 Paderborn (Germany)

    2010-11-15

    Transcritical working cycles for refrigerants have led to increased interest in heat transfer near the Critical State. In general, experimental results for this region differ significantly from those far from it because some fluid properties vary much more there than at a greater distance. In this paper, measurements for two-phase and single-phase free convective heat transfer from an electrically heated copper tube with 25 mm O.D. to refrigerant R125 are discussed for fluid states very close to the Critical Point and far from it. It is shown that heat transfer for film boiling slightly below and for free convection slightly above the critical pressure is very similar. The new - and also previous - experimental data for nucleate boiling, film boiling, and single-phase free convection are compared with calculated results between atmospheric and critical pressure. It can be concluded that the Principle of Corresponding States in its simplest form is very well suited to transfer the results to other refrigerants. In Part II, particular attention will be given to a minimum superheat for nucleate boiling and a maximum superheat for film boiling and single-phase free convection within the circumferential variation of the isobaric wall superheat on the lower parts of the tube. (author)

  19. Cryogenic forced convection refrigerating system

    International Nuclear Information System (INIS)

    Klee, D.J.

    1988-01-01

    This patent describes the method of refrigerating products by contact with a refrigerating gas which comprises introducing product into a refrigeration zone, contacting the product with the refrigerating gas for a sufficient time to refrigerate it to the appropriate extent and removing the refrigerated product. The improvement for producing the refrigeration gas from a liquid cryogen such that essentially all of the liquid cryogen is fully vaporized before contacting the product comprises: (a) introducing the liquid cryogen, selected from the group consisting of liquid air and liquid nitrogen, at elevated pressure into an ejector as the motive fluid to accelerate a portion of a warm refrigerating gas through the ejector while mixing the cryogen and gas to effect complete vaporization of the liquid cryogen and substantial cooling of the portion of the refrigerating gas resulting in a cold discharge gas which is above the liquefaction temperature of the cryogen; (b) introducing the cold discharge gas into a forced circulation pathway of refrigerating gas and producing a cold refrigerating gas which contacts and refrigerates product and is then at least partially recirculated; (c) sensing the temperature of the refrigerating gas in the forced circulation pathway and controlling the introduction of liquid cryogen with regard to the sensed temperature to maintain the temperature of the discharge gas above the liquefacton temperature of the cryogen utilized

  20. Numerical Analyses of a single-phase natural convection system for Molten Flibe using MARS-FLIBE code

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Sarah; Bang, In Cheol [Ulsan National Institute of Science and Technology, Ulsan (Korea, Republic of)

    2014-10-15

    These advantages make the MSR attractive and to be one of the six candidates for the Generation IV Reactor. Therefore, the researches related to the MSR are being conducted. To analyze the molten salt-cooled systems in the laboratory, this study generated the properties of molten salt using MARS-LMR. In this research, the implemented salts were Flibe (LiF-BeF{sub 2}) in a molar mixture that is 66% LiF and 34% BeF{sub 2}, respectively. Table 1 indicates the comparison of thermal properties of various coolants in nuclear power plants. Molten salt was added to the MARS-LMR code to support the analysis of Flibe-cooled systems. The molten salt includes LiF-BeF{sub 2} in a molar mixture that is 66% LiF and 34% BeF{sub 2}, respectively. MARS-LMR code for liquid metals uses the soft sphere model based on Monte Carlo calculations for particles interacting with pair potentials. Although MARS was originally intended for a safety analysis of light water reactor, Flibe properties were newly added to this code as so-called MARS-FLIBE which is applicable for Flibe-cooled systems. By using this thermodynamic property table file, the thermal hydraulic systems of Flibe can be simulated for numerical and parametric studies. In this study, the natural convection phenomena in the rectangular natural convection loop and IVR-ERVC in APR 1400 were simulated. Through the simulations in Flibe-cooled systems, the temperature distribution and mass flowrate of Flibe can be calculated and the heat transfer coefficients of Flibe in natural convection loop will be calculated by adding the related heat transfer correlations in the MARS-FLIBE code. MARS-FLIBE code will be used to predict and design of Flibe-cooled systems.

  1. Forced convection heat transfer in He II

    International Nuclear Information System (INIS)

    Kashani, A.

    1986-01-01

    An investigation of forced convection heat transfer in He II is conducted. The study includes both experimental and theoretical treatments of the problem. The experiment consists of a hydraulic pump and a copper flow tube, 3 mm in ID and 2m long. The system allows measurements of one-dimensional heat and mass transfer in He II. The heat transfer experiments are performed by applying heat at the midpoint along the length of the flow tube. Two modes of heat input are employed, i.e., step function heat input and square pulse heat input. The heat transfer results are discussed in terms of temperature distribution in the tube. The experimental temperature profiles are compared with numerical solutions of an analytical model developed from the He II energy equation. The bath temperature is set at three different values of 1.65, 1.80, and 1.95 K. The He II flow velocity is varied up to 90 cm/s. Pressure is monitored at each end of the flow tube, and the He II pressure drop is obtained for different flow velocities. Results indicate that He II heat transfer by forced convention is considerably higher than that by internal convection. The theoretical model is in close agreement with the experiment. He II pressure drop and friction factor are very similar to those of an ordinary fluid

  2. Suppression of saturated nucleate boiling by forced convective flow

    International Nuclear Information System (INIS)

    Bennett, D.L.; Davis, M.W.; Hertzler, B.L.

    1980-01-01

    Tube-side forced convective boiling nitrogen and oxygen and thin film shell-side forced convective boiling R-11 data demonstrate a reduction in the heat transfer coefficient associated with nucleate boiling as the two-phase friction pressure drop increases. Techniques proposed in the literature to account for nucleate boiling during forced convective boiling are discussed. The observed suppression of nucleate boiling for the tube-side data is compared against the Chen correlation. Although general agreement is exhibited, supporting the interactive heat transfer mechanism theory, better agreement is obtained by defining a bubble growth region within the thermal boundary layer. The data suggests that the size of the bubble growth region is independent of the friction drop, but is only a function of the physical properties of the boiling liquid. 15 refs

  3. Transition from boiling to two-phase forced convection

    International Nuclear Information System (INIS)

    Maroti, L.

    1985-01-01

    The paper presents a method for the prediction of the boundary points of the transition region between fully developed boiling and two-phase forced convection. It is shown that the concept for the determination of the onset of fully developed boiling can also be applied for the calculation of the point where the heat transfer is effected again by the forced convection. Similarly, the criterion for the onset of nucleate boiling can be used for the definition of the point where boiling is completely suppressed and pure two-phase forced convection starts. To calculate the heat transfer coefficient for the transition region, an equation is proposed that applies the boundary points and a relaxation function ensuring the smooth transition of the heat transfer coefficient at the boundaries

  4. Reynolds analogy for subcooled surface boiling under forced convection

    International Nuclear Information System (INIS)

    Avdeev, A.A.

    1982-01-01

    For the case of subcooled surface boiling under forced convection the analytic expression of analogy between the heat transfer and carry pulse (Reynolds analogy) is derived. It is concluded that the obtained dependence creates the basis for solution of a series of problems of surface boiling physics. On the basis of the performed analysis the method of coordinate calculation of the origin of intensive vapour generation is developed and the formula for calculation of the broken-off-bubble radius under forced convection is derived [ru

  5. Investigation of the transition from forced to natural convection in the research reactor Munich II

    International Nuclear Information System (INIS)

    Skreba, S.; Adamek, J.; Unger, H.

    1999-01-01

    The new research reactor Munich II (FRM-II), which is under construction at the Technical University Munich, Germany, makes use of a newly developed compact reactor core consisting of a single fuel element, which is assembled of two concentric pipes. Between the fuel element's inner and outer pipe 113 involutely bent fuel plates are placed rotationally symmetric, forming 113 cooling channels of a constant width of 2.2 mm. After a shut down of the reactor, battery supported cooling pumps are started by the reactor safety system in order to remove the decay heat by a downwards directed forced flow. Three hours after they have been started, the cooling pumps are shut down and so-called 'natural convection flaps' are opened by their own weight. Through a flow path, which is provided by the opening of the natural convection flaps, the decay heat is given off to the water in the reactor pool after the direction of the flow has changed and an upwards directed natural convection flow has developed. At the Department for Nuclear and New Energy Systems of the Ruhr-University Bochum, Germany, a test facility has been built in order to confirm the concept of the decay heat removal in the FRM-II, to acquire data of single and two phase natural convection flows and to detect the dry out in a narrow channel. The thermohydraulics of the FRM-II are simulated by an electrically heated test section, which represents one cooling channel of the fuel element. At first experiments have been performed, which simulated the transition from forced to natural convection in the core of the FRM-II, both at normal operation and at a complete loss of the decay heat removal pumps. In case of normal operation, the transition from forced to natural convection takes place single phased. If a complete loss of the active decay heat removal system occurs, the decay heat removal is ensured by a quasi-steady two phase flow. In a second test series minimum heat flux densities leading to pressure pulsations

  6. A Correlation for Forced Convective Boiling Heat Transfer of Refrigerants in a Microfin Tube

    Science.gov (United States)

    Momoki, Satoru; Yu, Jian; Koyama, Shigeru; Fujii, Tetsu; Honda, Hiroshi

    The experimental study is reported on the forced convective boiling of pure refrigerants HCFC22, HFC134a and HCFC123 flowing in a horizontal microfin tube. The local heat transfer coefficient defined based on the actual inside surface area is measured in the ranges of mass velocity of 200 to 400 kg/m2s, heat flux of 5 to 64 kW/m2 and reduced pressure of 0.07 to 0.24. Using the Chen-type model, a new correlation for microfin tubes is proposed considering the enhancement effect of microfins on both the convective heat transfer and the nucleate boiling components. In the convective heat transfer component, the correlation to predict the heat transfer coefficient of liquid-only flow is determined from preliminary experiments on single-phase flow in microfin tubes, and the two-phase flow enhancement factor is determined from the present experimental data. For the nucleate boiling component, the correlation of Takamatsu et al. for smooth tube is modified. The prediction of the present correlation agrees well with present experimental data, and is available for several microfin tubes which were tested by other researchers.

  7. Eulerian-Eulerian two-phase numerical simulation of nanofluid laminar forced convection in a microchannel

    International Nuclear Information System (INIS)

    Kalteh, Mohammad; Abbassi, Abbas; Saffar-Avval, Majid; Harting, Jens

    2011-01-01

    In this paper, laminar forced convection heat transfer of a copper-water nanofluid inside an isothermally heated microchannel is studied numerically. An Eulerian two-fluid model is considered to simulate the nanofluid flow inside the microchannel and the governing mass, momentum and energy equations for both phases are solved using the finite volume method. For the first time, the detailed study of the relative velocity and temperature of the phases are presented and it has been observed that the relative velocity and temperature between the phases is very small and negligible and the nanoparticle concentration distribution is uniform. However, the two-phase modeling results show higher heat transfer enhancement in comparison to the homogeneous single-phase model. Also, the heat transfer enhancement increases with increase in Reynolds number and nanoparticle volume concentration as well as with decrease in the nanoparticle diameter, while the pressure drop increases only slightly.

  8. Forced convection mixing transients in the MITR core tank

    International Nuclear Information System (INIS)

    Hu, Lin-Wen; Meyer, J.E.; Bernard, J.A.

    1995-01-01

    This paper reports the results of forced convection mixing transient experiments that were studied in the core tank of the 5-MW Massachusetts Institute of Technology (MIT) nuclear reactor as part of the studies being conducted to support a facility upgrade to 10 MW

  9. Multiphase forces on bend structures – critical gas fraction for transition single phase gas to multiphase flow behaviour

    NARCIS (Netherlands)

    Belfroid, S.P.C.; Nennie, E.D.; Lewis, M.

    2016-01-01

    Piping structures are generally subjected to high dynamic loading due to multiphase forces. In particular subsea structures are very vulnerable as large flexibility is required to cope for instance with thermal stresses. The forces due to multiphase flow are characterized by a broadband spectrum

  10. Forced convective post CHF heat transfer and quenching

    International Nuclear Information System (INIS)

    Nelson, R.A.

    1980-01-01

    This paper discusses mechanisms in the post-CHF region which provide understanding and qualitative prediction capability for several current forced convective heat transfer problems. In the area of nuclear reactor safety, the mechanisms are important in the prediction of fuel rod quenches for the reflood phase, blowdown phase, and possibly some operational transients with dryout. Results using the mechanisms to investigate forced convective quenching are presented. Data reduction of quenching experiments is discussed, and the way in which the quenching transient may affect the results of different types of quenching experiments is investigated. This investigation provides an explanation of how minimum wall superheats greater than the homogeneous nucleation temperature result, as well as how these may appear to be either hydrodynamically or thermodynamically controlled. Finally, the results of a parametric study of the effects of the mechanisms upon the LOFT L2-3 hotpin calculation are presented

  11. Transient heat transfer for forced convection flow of helium gas

    International Nuclear Information System (INIS)

    Liu, Qiusheng; Fukuda, Katsuya; Sasaki, Kenji; Yamamoto, Manabu

    1999-01-01

    Transient heat transfer coefficients for forced convection flow of helium gas over a horizontal cylinder were measured using a forced convection test loop. The platinum heater with a diameter of 1.0 mm was heated by electric current with an exponential increase of Q 0 exp(t/τ). It was clarified that the heat transfer coefficient approaches the steady-state one for the period τ over 1 s, and it becomes higher for the period of τ shorter than 1 s. The transient heat transfer shows less dependent on the gas flowing velocity when the period becomes very shorter. Semi-empirical correlations for steady-state and transient heat transfer were developed based on the experimental data. (author)

  12. Single-Phase PLLs

    DEFF Research Database (Denmark)

    Golestan, Saeed; Guerrero, Josep M.; Quintero, Juan Carlos Vasquez

    2017-01-01

    Single-phase phase-locked loops (PLLs) are popular for the synchronization and control of single-phase gridconnected converters. They are also widely used for monitoring and diagnostic purposes in the power and energy areas. In recent years, a large number of single-phase PLLs with different stru......-PLLs). The members of each category are then described and their pros and cons are discussed. This work provides a deep insight into characteristics of different single-phase PLLs and, therefore, can be considered as a reference for researchers and engineers....

  13. Various aspects of magnetic field influence on forced convection

    Directory of Open Access Journals (Sweden)

    Pleskacz Lukasz

    2016-01-01

    Full Text Available Flows in the channels of various geometry can be found everywhere in industrial or daily life applications. They are used to deliver media to certain locations or they are the place where heat may be exchanged. For Authors both points of view are interesting. The enhancement methods for heat transfer during the forced convection are demanded due to a technological development and tendency to miniaturization. At the same time it is also worth to find mechanisms that would help to avoid negative effects like pressure losses or sedimentation in the channel flows. This paper shows and discuss various aspects of magnetic field influence on forced convection. A mathematical model consisted of the mass, momentum and energy conservation equations. In the momentum conservation equation magnetic force term was included. In order to calculate this magnetic force Biot-Savart’s law was utilized. Numerical analysis was performed with the usage of commonly applied software. However, userdefined functions were implemented. The results revealed that both temperature and velocity fields were influenced by the strong magnetic field.

  14. Forced and free convection hydromagnetic flow past a vertical flat plate

    International Nuclear Information System (INIS)

    Abdelkhalek, M.M.

    2004-01-01

    The effects of magnetic field and temperature heat source on the free and forced convection flow past an infinite vertical plate is studied analytically. Solutions of the reduced equation appropriate in the forced convection and free convection regime are obtained using perturbation technique. The expression for the velocity field, skin friction and Nusselt number have been obtained

  15. An experimental study on single phase convection heat transfer and pressure drop in two brazed plate heat exchangers with different chevron shapes and hydraulic diameters

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Man Bae; Park, Chang Yong [Seoul National University of Science and Technology, Seoul (Korea, Republic of)

    2017-05-15

    An experimental study on heat transfer and pressure drop characteristics was performed at single phase flow in two Brazed plate heat exchangers (BPHEs) with different geometries. The corrugation density of one of the BPHE (Type II) was two times as high as that of the other BPHE (Type I). The hydraulic diameter of the type II BPHE was 2.13 mm, which was 38 % smaller than that of the type I BPHE. Also, the cross section shape of the flow channels for the type II BPHE was different from that for conventional BPHEs due to the unusual corrugation patterns and brazing points. The experimental conditions for temperatures were varied from 4.6 °C to 49.1 °C, and for mass flow rates were changed from 0.07 kg/s to 1.24 kg/s. The measured results showed that pressure drop in the type II BPHE was about 110 % higher than that in the type I BPHE. Nu of the type II was higher than that of the type I BPHE and the enhancement became larger with the increase of Re at the ranges above 800. New correlations for fF and Nu were proposed by this study and their prediction accuracy could be improved by considering the surface enlargement factor in the correlations. The performance evaluation of the two BPHEs was performed by (j/f{sub F}1{sup /3}) which represented the ratio of heat transfer and pressure drop performance. Also, a new parameter, the capacity compactness of PHE, was proposed and it presented the PHE capacity per unit volume and unit log mean temperature difference. The comparison showed that the two BPHEs had similar values of the (j/f{sub F}1{sup /3}), whereas they had significantly different values of the capacity compactness. The capacity compactness of the type II BPHE was 1.5 times higher than that for the type I BPHE.

  16. An experimental study on single phase convection heat transfer and pressure drop in two brazed plate heat exchangers with different chevron shapes and hydraulic diameters

    International Nuclear Information System (INIS)

    Kim, Man Bae; Park, Chang Yong

    2017-01-01

    An experimental study on heat transfer and pressure drop characteristics was performed at single phase flow in two Brazed plate heat exchangers (BPHEs) with different geometries. The corrugation density of one of the BPHE (Type II) was two times as high as that of the other BPHE (Type I). The hydraulic diameter of the type II BPHE was 2.13 mm, which was 38 % smaller than that of the type I BPHE. Also, the cross section shape of the flow channels for the type II BPHE was different from that for conventional BPHEs due to the unusual corrugation patterns and brazing points. The experimental conditions for temperatures were varied from 4.6 °C to 49.1 °C, and for mass flow rates were changed from 0.07 kg/s to 1.24 kg/s. The measured results showed that pressure drop in the type II BPHE was about 110 % higher than that in the type I BPHE. Nu of the type II was higher than that of the type I BPHE and the enhancement became larger with the increase of Re at the ranges above 800. New correlations for fF and Nu were proposed by this study and their prediction accuracy could be improved by considering the surface enlargement factor in the correlations. The performance evaluation of the two BPHEs was performed by (j/f F 1 /3 ) which represented the ratio of heat transfer and pressure drop performance. Also, a new parameter, the capacity compactness of PHE, was proposed and it presented the PHE capacity per unit volume and unit log mean temperature difference. The comparison showed that the two BPHEs had similar values of the (j/f F 1 /3 ), whereas they had significantly different values of the capacity compactness. The capacity compactness of the type II BPHE was 1.5 times higher than that for the type I BPHE.

  17. Forced convection and subcooled flow boiling heat transfer in asymmetrically heated ducts of T-section

    International Nuclear Information System (INIS)

    Abou-Ziyan, Hosny Z.

    2004-01-01

    This paper presents the results of an experimental investigation of heat transfer from the heated bottom side of tee cross-section ducts to an internally flowing fluid. The idea of this work is derived from the cooling of critical areas in the cylinder heads of internal combustion engines. Fully developed single phase forced convection and subcooled flow boiling heat transfer data are reported. Six T-ducts of different width and height aspect ratios are tested with distilled water at velocities of 1, 2 and 3 m/s for bulk temperatures of 60 and 80 deg. C, while the heat flux was varied from about 80 to 700 kW/m 2 . The achieved data cover Reynolds numbers in the range of 5.22 x 10 4 to 2.36 x 10 5 , Prandtl numbers in the range from 2.2 to 3.0, duct width aspect ratio between 2.19 and 3.13 and duct height aspect ratio from 0.69 to 2.0. The results revealed that the increase in either the width or height aspect ratio of the T-ducts enhances the convection heat transfer coefficients and the boiling heat fluxes considerably. The following comparisons are provided for coolant velocity of 2 m/s, bulk temperature of 60 deg. C, wall superheat of 20 K and wall to bulk temperature difference of 20 K. As the width aspect ratio increases by 43%, the convection heat transfer coefficient and the boiling heat flux increase by 27% and 39%, respectively. An increase in the height aspect ratio by 290% enhances the convection heat transfer coefficient and the boiling heat fluxes by 82% and 103%, respectively. When the coolant velocity changes from 1 to 2 m/s, the heat transfer coefficient increases by 60% and the boiling heat flux rises by 62-98% for the various tested ducts. The convection heat transfer coefficient increases by 12% and the boiling heat flux decreases by 31% as the bulk fluid temperature rises from 60 to 80 deg. C. A correlation was developed for Nusselt number as a function of Reynolds number, Prandtl number, viscosity ratio and some aspect ratios of the T-duct

  18. Mechanistic modeling of CHF in forced-convection subcooled boiling

    International Nuclear Information System (INIS)

    Podowski, M.Z.; Alajbegovic, A.; Kurul, N.; Drew, D.A.; Lahey, R.T. Jr.

    1997-05-01

    Because of the complexity of phenomena governing boiling heat transfer, the approach to solve practical problems has traditionally been based on experimental correlations rather than mechanistic models. The recent progress in computational fluid dynamics (CFD), combined with improved experimental techniques in two-phase flow and heat transfer, makes the use of rigorous physically-based models a realistic alternative to the current simplistic phenomenological approach. The objective of this paper is to present a new CFD model for critical heat flux (CHF) in low quality (in particular, in subcooled boiling) forced-convection flows in heated channels

  19. Reassessment of forced convection heat transfer correlations for refrigerant-12

    International Nuclear Information System (INIS)

    Celata, G.P.; Cuomo, M.; D'Annibale, F.; Farello, G.E.; Setaro, T.

    1986-01-01

    In the frame of a Refrigerant-12 experiment on postulated accidental transients in Pressurized Water Reactors under way at Heat Transfer Laboratory (ENEA Casaccia Research Center), an assessment of the main correlation available in scientific literature, for the different heat transfer regions encountered when a liquid is boiled in a confined heated channel, has been performed. Considering a vertical tube uniformly heated over its length with CHF at the exit, the following heat transfer regimes may be individuated: convective heat transfer to liquid, subcooled boiling, saturated nucleate boiling, forced convective heat transfer through liquid film (annular flow regime) and thermal crisis. From the comparison of computed values with an original ENEA dataset, the best correlations in predicting Refrigerant-12 data have been individuated. In a few cases, though preserving the original structure of the correlations, mainly developed for water, it was necessary to adjust some coefficients by means of best-fit procedures through our experimental data. The work has been performed in the frame of the ENEA Thermal Reactor Department Safety Research Project

  20. Forced heat convection in annular spaces; Convection forcee de la chaleur dans les espaces annulaires

    Energy Technology Data Exchange (ETDEWEB)

    Pelce, J [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1960-02-15

    This report deals with the experimental study of forced heat convection in annular spaces through which flow of air is passing when a uniform heat flux is dissipated across the inner wall. These observations took place chiefly in the region where thermal equilibrium are not yet established. Amongst other things it became apparent that, both in the region where thermal equilibrium conditions are on the way to establishment and where they are already established, the following relationship held good: the longitudinal temperature gradient, either on the wall or in the fluid stream, is proportional to the heat flux dissipated q, and inversely proportional to the average flow rate V: dT/dx = B (q/V). From this result the next step is to express the variations of the local convection coefficient {alpha} (or of the Margoulis number M) in a relationship of the form: 1/M = {psi}(V) + F(x). If this relationship is compared with the classical empirical relationship {alpha} = KV{sup n} (where n is close to 0.8), the relationship: 1/M = {xi}V{sup 1-n} + F(x) is obtained ({xi} is a constant for a given annular space); from this it was possible to coordinate the whole set of experimental results. (author) [French] Il s'agit precisement de l'etude experimentale de la convection forcee de la chaleur dans des espaces annulaires parcourus par de l'air en ecoulement turbulent, lorsqu'on dissipe a travers la paroi interieure un flux de chaleur uniforme. Ces observations ont eu lieu principalement dans la region ou le regime thermique n'est pas encore etabli. Il est apparu, entre autre, qu'il existait, tant dans la region ou le regime thermique est en voie d'etablissement qu'en regime etabli, la relation suivante: le gradient longitudinal des temperatures, que ce soit sur la paroi ou dans l'ecoulement fluide, est proportionnel au flux de la chaleur dissipee q, et inversement proportionnel a la vitesse moyenne V de l'ecoulement: dT/dx = B (q/V). Ce resultat a pour consequence de traduire

  1. Comparative analysis of heat transfer correlations for forced convection boiling

    International Nuclear Information System (INIS)

    Guglielmini, G.; Nannei, E.; Pisoni, C.

    1978-01-01

    A critical survey was conducted of the most relevant correlations of boiling heat transfer in forced convection flow. Most of the investigations carried out on partial nucleate boiling and fully developed nucleate boiling have led to the formulation of correlations that are not able to cover a wide range of operating conditions, due to the empirical approach of the problem. A comparative analysis is therefore required in order to delineate the relative accuracy of the proposed correlations, on the basis of the experimental data presently available. The survey performed allows the evaluation of the accuracy of the different calculating procedure; the results obtained, moreover, indicate the most reliable heat transfer correlations for the different operating conditions investigated. This survey was developed for five pressure range (up to 180bar) and for both saturation and subcooled boiling condition

  2. Heat transfer during forced convection condensation inside horizontal tube

    Energy Technology Data Exchange (ETDEWEB)

    Tandon, T.N. [M.M.M. Engineering College, Gorakhpur, Uttar Pradesh (India). Dept. of Mechanical Engineering; Varma, H.K.; Gupta, C.P. [Roorkee Univ., Uttar Pradesh (India). Dept. of Mechanical and Industrial Engineering

    1995-03-01

    This paper presents the results of an experimental investigation on heat transfer behaviour during forced convection condensation inside a horizontal tube for wavy, semi-annular and annular flows. A qualitative study was made of the effect of various parameters - refrigerant mass flux, vapour quality, condensate film temperature drop and average vapour mass velocity - on average condensing-heat transfer coefficient. Akers-Rosson correlations have been found to predict the heat transfer coefficients within {+-} 25% for the entire range of data. A closer examination of the data revealed that the nature of the relation for the heat transfer coefficient changes from annular and semi-annular flow to wavy flow. Akers-Rosson correlations with changed constant and power have been recommended for the two flow regimes. (author)

  3. Silk cocoon drying in forced convection type solar dryer

    International Nuclear Information System (INIS)

    Singh, Panna Lal

    2011-01-01

    The thin layer silk cocoon drying was studied in a forced convection type solar dryer. The drying chamber was provided with several trays on which the cocoons loaded in thin layer. The hot air generated in the solar air heater was forced into drying chamber to avoid the direct exposure of sunlight and UV radiation on cocoons. The drying air temperature varied from 50 to 75 o C. The cocoon was dried from the initial moisture content of about 60-12% (wb). The drying data was fitted to thin layer drying models. Drying behaviour of the silk cocoon was best fitted with the Wang and Singh drying model. Good agreement was obtained between predicted and experimental values. Quality of the cocoons dried in the solar dryer was at par with the cocoons dried in the conventional electrical oven dryer in term of the silk yield and strength of the silk. Saving of electrical energy was about 0.75 kWh/kg cocoons dried. Economic analysis indicated that the NPV of the solar dryer was higher and more stable (against escalation rate of electricity) as compare to the same for electrical oven dryer. Due to simplicity in design and construction and significant saving of operational electrical energy, solar cocoon dryer seems to be a viable option.

  4. Forced convective melting at an evolving ice-water interface

    Science.gov (United States)

    Ramudu, Eshwan; Hirsh, Benjamin; Olson, Peter; Gnanadesikan, Anand

    2015-11-01

    The intrusion of warm Circumpolar Deep Water into the ocean cavity between the base of ice shelves and the sea bed in Antarctica causes melting at the ice shelves' basal surface, producing a turbulent melt plume. We conduct a series of laboratory experiments to investigate how the presence of forced convection (turbulent mixing) changes the delivery of heat to the ice-water interface. We also develop a theoretical model for the heat balance of the system that can be used to predict the change in ice thickness with time. In cases of turbulent mixing, the heat balance includes a term for turbulent heat transfer that depends on the friction velocity and an empirical coefficient. We obtain a new value for this coefficient by comparing the modeled ice thickness against measurements from a set of nine experiments covering one order of magnitude of Reynolds numbers. Our results are consistent with the altimetry-inferred melting rate under Antarctic ice shelves and can be used in climate models to predict their disintegration. This work was supported by NSF grant EAR-110371.

  5. Visualization of bubble behaviors in forced convective subcooled flow boiling

    International Nuclear Information System (INIS)

    Inaba, Noriaki; Matsuzaki, Mitsuo; Kikura, Hiroshige; Aritomi, Masanori; Komeno, Toshihiro

    2007-01-01

    Condensation characteristics of vapor bubble after the departure from a heated section in forced convective subcooled flow boiling were studied visually by using a high speed camera. The purpose of the present study was to measure two-phase flow parameters in subcooled flow boiling. These two-phase flow parameters are void fraction, interfacial area concentration and Sauter mean diameter, which express bubble interface behaviors. The experimental set-up was designed to measure the two-phase flow parameters necessary for developing composite equations for the two fluid models in subcooled flow boiling. In the present experiments, the mass flux, liquid subcooling and the heater were varied within 100-1000kg/m 2 s, 2-10K and 100-300kW/m 2 respectively. Under these experimental conditions, the bubble images were obtained by a high-speed camera, and analyzed paying attention to the condensation of vapor bubbles. These two-phase parameters were obtained by the experimental data, such as the bubble parameter, the bubble volume and the bubble surface. In the calculation process of the two phase flow parameters, it was confirmed that these parameters are related to the void fraction. (author)

  6. Turbulent forced convection of nanofluids downstream an abrupt expansion

    Science.gov (United States)

    Kimouche, Abdelali; Mataoui, Amina

    2018-03-01

    Turbulent forced convection of Nanofluids through an axisymmetric abrupt expansion is investigated numerically in the present study. The governing equations are solved by ANYS 14.0 CFD code based on the finite volume method by implementing the thermo-physical properties of each nanofluid. All results are analyzed through the evolutions of skin friction coefficient and Nusselt number. For each nanofluid, the effect of both volume fraction and Reynolds number on this type of flow configuration, are examined. An increase on average Nusselt number with the volume fraction and Reynolds number, are highlighted and correlated. Two relationships are proposed. The first one, determines the average Nusselt number versus Reynolds number, volume fraction and the ratio of densities of the solid particles to that of the base fluid ( \\overline{Nu}=f(\\operatorname{Re},φ, ρ_s/ρ_f) ). The second one varies according Reynolds number, volume fraction and the conductivities ratio of solid particle to that of the base fluid ( \\overline{Nu}=f(\\operatorname{Re},φ, k_s/k_f) ).

  7. A study of forced convective subcooled flow boiling

    International Nuclear Information System (INIS)

    Serizawa, Akimi; Kenning, D.B.R.

    1979-01-01

    Based on a simple nucleation model, parameter survey technique is used to derive a predictive correlation for boiling initiation under forced convection. Results are expressed by a semi-empirical equation which considers effects of the flow turbulence on interfacial heat transfer coefficient for evaporation and condensation of vapour bubbles during their growth. This correlation agrees within +-25% with a variety of experimental water data presently available. The bubble departure diameter and the subcooling-dependence of active nucleation sites were examined, using experimental data available. Results are expressed by empirical equations. Finally, an analytical model is presented to predict conditions for the point of net vapour generation. The model is based on the formation and growth of a bubble boundary layer adjacent to the heated wall. It is shown that the point of net vapour generation is determined by the liquid subcooling at the boiling initiation and the subcooling-dependences of bubble departure diameter and bubble flux. The result implies that the bubble ejection from bubble layer is a possible mechanism for the significant void increase even at high velocities. (author)

  8. Development and performance evaluation of forced convection potato solar dryer

    International Nuclear Information System (INIS)

    Khan, M.A.; Sabir, M.S.; Iqbal, M.

    2011-01-01

    This research paper deals with the design development and testing of a forced convection solar dryer, for drying and converting to flour of high moisture content vegetables like potatoes. The angle of solar collector was made adjustable for the absorption of maximum solar radiation by the absorber plate. The air flow rate was controlled by adjustable gate valve to find the optimum flow rate for dehydration of the product. The penetration of solar radiation raised the temperature of the absorber plate of the dryer to 110 deg. C during the operation under stagnation or no load conditions. The maximum air temperature attained in the solar air heater, under this condition was 80 deg. C. The dryer was loaded with 12 Kg of blanched potato chips having an initial moisture content of 89.75%, and the final desired moisture content of 6.95% was achieved within five hours without losing the color of potato chips, while the moisture contents reduction was from 89.75% to 33.75% for five hours in open sun drying under shade. The drying cost for 1 Kg of potatoes was calculated as Rs. 245 and it was Rs. 329 in the case of an electric dryer. The life span of the solar dryer was assumed to be 20 years. The cumulative present worth of annual savings over the life of the solar dryer was calculated for blanched potato chips drying, and it turned out be Rs.163177.67/- which was much higher than the capital cost of the dryer (Rs. 25000). The payback period was calculated as 0.89 years, which was also very small considering the life of the system (20 years). (author)

  9. Experimental StudyHigh Altitude Forced Convective Cooling of Electromechanical Actuation Systems

    Science.gov (United States)

    2016-01-01

    34 Massachusetts Institute of Technology , 1989. [3] FedBizOps.Gov, " Integrated Vehicle Energy Technology (INVENT) Development Program for the 6th...AFRL-RQ-WP-TR-2016-0043 EXPERIMENTAL STUDY—HIGH ALTITUDE FORCED CONVECTIVE COOLING OF ELECTROMECHANICAL ACTUATION SYSTEMS Evan M. Racine...TITLE AND SUBTITLE EXPERIMENTAL STUDY—HIGH ALTITUDE FORCED CONVECTIVE COOLING OF ELECTROMECHANICAL ACTUATION SYSTEMS 5a. CONTRACT NUMBER In-house

  10. Effect of Buoyancy on Forced Convection Heat Transfer in Vertical Channels - a Literature Survey

    Energy Technology Data Exchange (ETDEWEB)

    Bhattacharyya, A

    1965-03-15

    This report contains a short resume of the available information from various sources on the effect of free convection flow on forced convection heat transfer in vertical channels. Both theoretical and experimental investigations are included. Nearly all of the theoretical investigations are concerned with laminar flow with or without internal heat generation. More consistent data are available for upward flow than for downward flow. Curves are presented to determine whether free convection or forced convection mode of heat transfer is predominant for a particular Reynolds number and Rayleigh number. At Re{sub b} > 10{sup 5} free convection effects are negligible. Downward flow through a heated channel at low Reynolds number is unstable. Under similar conditions the overall heat transfer coefficient for downward flow tends to be higher than that for upward flow.

  11. Forced-convection boiling tests performed in parallel simulated LMR fuel assemblies

    International Nuclear Information System (INIS)

    Rose, S.D.; Carbajo, J.J.; Levin, A.E.; Lloyd, D.B.; Montgomery, B.H.; Wantland, J.L.

    1985-01-01

    Forced-convection tests have been carried out using parallel simulated Liquid Metal Reactor fuel assemblies in an engineering-scale sodium loop, the Thermal-Hydraulic Out-of-Reactor Safety facility. The tests, performed under single- and two-phase conditions, have shown that for low forced-convection flow there is significant flow augmentation by thermal convection, an important phenomenon under degraded shutdown heat removal conditions in an LMR. The power and flows required for boiling and dryout to occur are much higher than decay heat levels. The experimental evidence supports analytical results that heat removal from an LMR is possible with a degraded shutdown heat removal system

  12. Convective Heat Transfer Coefficients of the Human Body under Forced Convection from Ceiling

    DEFF Research Database (Denmark)

    Kurazumi, Yoshihito; Rezgals, Lauris; Melikov, Arsen Krikor

    2014-01-01

    The average convective heat transfer coefficient for a seated human body exposed to downward flow from above was determined. Thermal manikin with complex body shape and size of an average Scandinavian female was used. The surface temperature distribution of the manikin’s body was as the skin...... of the convective heat transfer coefficient of the whole body (hc [W/(m2•K)]) was proposed: hc=4.088+6.592V1.715 for a seated naked body at 20ºC and hc=2.874+7.427V1.345 for a seated naked body at 26ºC. Differences in the convective heat transfer coefficient of the whole body in low air velocity range, V

  13. Thermal and hydrodynamic characteristics of forced and mixed convection flow through vertical rectangular channels

    Directory of Open Access Journals (Sweden)

    Hanafi Abdalla S.

    2008-01-01

    Full Text Available This paper presents experimental and numerical studies for the case of turbulent forced and mixed convection flow of water through narrow vertical rectangular channel. The channel is composed of two parallel plates which are heated at a uniform heat flux, whereas, the other two sides of the channel are thermally insulated. The plates are of 64 mm in width, 800 mm in height, and separated from each other at a narrow gap of 2.7 mm. The Nusselt number distribution along the flow direction normalized by the Nusselt number for the case of turbulent forced convection flow is obtained experimentally with a comparison with the numerical results obtained from a commercial computer code. The quantitative determination of the nor- malized Nusselt number with respect to the dimension-less number Z = (Gr/Re21/8Pr0.5 is presented with a comparison with previous experimental results. Qualitative results are presented for the normalized temperature and velocity profiles in the transverse direction with a comparison between the forced and mixed convection flow for both the cases of upward and downward flow directions. The effect of the axial locations and the parameter Gr/Re on the variation of the normalized temperature profiles in the transverse direction for both the regions of forced and mixed convection and for both of the upward and downward flow directions are obtained. The normalized velocity profiles in the transverse directions are also determined at different inlet velocity and heat fluxes for the previous cases. It is found that the normalized Nusselt number is greater than one in the mixed convection region for both the cases of upward and downward flow and correlated well with the dimension-less parameter Z for both of the forced and mixed convection regions. The temperature profiles increase with increasing the axial location along the flow direction or the parameter Gr/Re for both of the forced and mixed convection regions, but this increase is

  14. Modeling a forced to natural convection boiling test with the program LOOP-W

    International Nuclear Information System (INIS)

    Carbajo, J.J.

    1984-01-01

    Extensive testing has been conducted in the Simulant Boiling Flow Visualization (SBFV) loop in which water is boiled in a vertical transparent tube by circulating hot glycerine in an annulus surrounding the tube. Tests ranged from nonboiling forced convection to oscillatory boiling natural convection. The program LOOP-W has been developed to analyze these tests. This program is a multi-leg, one-dimensional, two-phase equilibrium model with slip between the phases. In this study, a specific test, performed at low power where non-boiling forced convection was changed to boiling natural convection and then to non-boiling again, has been modeled with the program LOOP-W

  15. Assessment of RANS and LES Turbulence Modeling for Buoyancy-Aided/Opposed Forced and Mixed Convection

    Science.gov (United States)

    Clifford, Corey; Kimber, Mark

    2017-11-01

    Over the last 30 years, an industry-wide shift within the nuclear community has led to increased utilization of computational fluid dynamics (CFD) to supplement nuclear reactor safety analyses. One such area that is of particular interest to the nuclear community, specifically to those performing loss-of-flow accident (LOFA) analyses for next-generation very-high temperature reactors (VHTR), is the capacity of current computational models to predict heat transfer across a wide range of buoyancy conditions. In the present investigation, a critical evaluation of Reynolds-averaged Navier-Stokes (RANS) and large-eddy simulation (LES) turbulence modeling techniques is conducted based on CFD validation data collected from the Rotatable Buoyancy Tunnel (RoBuT) at Utah State University. Four different experimental flow conditions are investigated: (1) buoyancy-aided forced convection; (2) buoyancy-opposed forced convection; (3) buoyancy-aided mixed convection; (4) buoyancy-opposed mixed convection. Overall, good agreement is found for both forced convection-dominated scenarios, but an overly-diffusive prediction of the normal Reynolds stress is observed for the RANS-based turbulence models. Low-Reynolds number RANS models perform adequately for mixed convection, while higher-order RANS approaches underestimate the influence of buoyancy on the production of turbulence.

  16. Combined Lorentz force and ultrasound Doppler velocimetry in a vertical convection liquid metal flow

    Science.gov (United States)

    Zürner, Till; Vogt, Tobias; Resagk, Christian; Eckert, Sven; Schumacher, Jörg

    2017-11-01

    We report experimental studies on turbulent vertical convection flow in the liquid metal alloy gallium-indium-tin. Flow measurements were conducted by a combined use of local Lorentz force velocimetry (LLFV) and ultrasound Doppler velocimetry (UDV). It is known that the forced convection flow in a duct generates a force on the LLFV magnet system, that grows proportional to the flow velocity. We show that for the slower flow of natural convection LLFV retains this linear dependence in the range of micronewtons. Furthermore experimental results on the scaling of heat and momentum transport with the thermal driving are presented. The results cover a range of Rayleigh numbers 3 ×105 Deutsche Forschungsgemeinschaft under Grant No. GRK 1567.

  17. Forced convective and subcooled flow boiling heat transfer to pure water and n-heptane in an annular heat exchanger

    International Nuclear Information System (INIS)

    Peyghambarzadeh, S.M.; Sarafraz, M.M.; Vaeli, N.; Ameri, E.; Vatani, A.; Jamialahmadi, M.

    2013-01-01

    Highlights: ► The cooling performance of water and n-heptane is compared during subcooled flow boiling. ► Although n-heptane leaves the heat exchanger warmer it has a lower heat transfer coefficient. ► Flow rate, heat flux and degree of subcooling have direct effect on heat transfer coefficient. ► The predictions of some correlations are evaluated against experimental data. - Abstract: In this research, subcooled flow boiling heat transfer coefficients of pure n-heptane and distilled water at different operating conditions have been experimentally measured and compared. The heat exchanger consisted of vertical annulus which is heated from the inner cylindrical heater with variable heat flux (less than 140 kW/m 2 ). Heat flux is varied so that two different flow regimes from single phase forced convection to nucleate boiling condition are created. Meanwhile, liquid flow rate is changed in the range of 2.5 × 10 −5 –5.8 × 10 −5 m 3 /s to create laminar up to transition flow regimes. Three subcooling levels including 10, 20 and 30 °C are also considered. Experimental results demonstrated that subcooled flow boiling heat transfer coefficient increases when higher heat flux, higher liquid flow rate and greater subcooling level are applied. Furthermore, influence of the operating conditions on the bubbles generation on the heat transfer surface is also discussed. It is also shown that water is better cooling fluid in comparison with n-heptane

  18. [Constitutive correlations for wire-wrapped subchannel analysis under forced and mixed convection conditions]. Part II

    International Nuclear Information System (INIS)

    Cheng, S.K.; Todreas, N.E.

    1984-08-01

    A new version of the ENERGY series code, ENERGY-IV, was written for predicting coolant temperature distributions in wire-wrapped rod assemblies used in the Liquid Metal Fast Breeder Reactor. The ENERGY-IV Code is applicable to both steady-state forced and mixed convection operation for a single isolated assembly. (The SUPERENERGY Code, [Basehore (1980)] is applicable to core wide forced convection analysis.) ENERGY-IV is an empirical code designed to be fast running. Hence the core designer can use it as an inexpensive thermal hydraulic design or diagnosis tool

  19. Modelling of subcooled boiling and DNB-type boiling crisis in forced convection

    International Nuclear Information System (INIS)

    Bricard, Patrick

    1995-01-01

    This research thesis aims at being a contribution to the modelling of two phenomena occurring during a forced convection: the axial evolution of the vacuum rate, and the boiling crisis. Thus, the first part of this thesis addresses the prediction of the vacuum rate, and reports the development of a modelling of under-saturated convection in forced convection. The author reports the development and assessment of two-fluid one-dimensional model, the development of a finer analysis based on an averaging of local equations of right cross-sections in different areas. The second part of this thesis addresses the prediction of initiation of a boiling crisis. The author presents generalities and motivations for this study, reports a bibliographical study and a detailed analysis of mechanistic models present in this literature. A mechanism of boiling crisis is retained, and then further developed in a numerical modelling which is used to assess some underlying hypotheses [fr

  20. Rotating turbulent Rayleigh-Bénard convection subject to harmonically forced flow reversals

    NARCIS (Netherlands)

    Geurts, B.J.; Kunnen, R.P.J.

    2014-01-01

    The characteristics of turbulent flow in a cylindrical Rayleigh–B´enard convection cell which can be modified considerably in case rotation is included in the dynamics. By incorporating the additional effects of an Euler force, i.e., effects induced by nonconstant rotation rates, a remarkably strong

  1. Rotating turbulent Rayleigh–Bénard convection subject to harmonically forced flow reversals

    NARCIS (Netherlands)

    Geurts, Bernardus J.; Kunnen, Rudie P.J.

    2014-01-01

    The characteristics of turbulent flow in a cylindrical Rayleigh–Bénard convection cell which can be modified considerably in case rotation is included in the dynamics. By incorporating the additional effects of an Euler force, i.e., effects induced by non-constant rotation rates, a remarkably strong

  2. Combined free and forced convection flow in a rotating channel with ...

    African Journals Online (AJOL)

    user

    free and forced convection flow of a viscous incompressible electrically conducting fluid in a .... The boundary conditions (10) and (11), in dimensionless form, become ...... On hydromagnetic Flow and heat transfer in a rotating fluid past an infinite porous ... Electrically Conducting Fluid in Non-Rotating and Rotating Media”.

  3. Body-force-driven multiplicity and stability of combined free and forced convection in rotating curved ducts: Coriolis force

    Science.gov (United States)

    Yang, T.; Wang, L.

    A numerical study is made on the fully developed bifurcation structure and stability of forced convection in a rotating curved duct of square cross-section. Solution structure is determined as variation of a parameter that indicates the effect of rotation (Coriolis-force-driven multiplicity). Three solutions for the flows in a stationary curved duct obtained in the work of Yang and Wang [1] are used as initial solutions of continuation calculations to unfold the solution branches. Twenty-one solution branches are found comparing with five obtained by Selmi and Nandakumar [2]. Dynamic responses of the multiple solutions to finite random disturbances are examined by the direct transient computation. Results show that characteristics of physically realizable fully developed flows changes significantly with variation of effect of rotation. Fourteen sub-ranges are identified according to characteristics of physically realizable solutions. As rotation effect changes, possible physically realizable fully-developed flows can be stable steady 2-cell state, stable multi-cell state, temporal periodic oscillation between symmetric/asymmetric 2-cell/4-cell flows, temporal oscillation with intermittency, temporal chaotic oscillation and temporal oscillation with pseudo intermittency. Among these possible physically realizable fully developed flows, stable multi-cell state and stable steady 2-cell state exist as dual stable. And oscillation with pseudo intermittency is a new phenomenon. In addition to the temporal oscillation with intermittency, sudden shift from stationary stable solution to temporal chaotic oscillation is identified to be another way of onset of chaos.

  4. Sensitivity of tropical convection in cloud-resolving WRF simulations to model physics and forcing procedures

    Science.gov (United States)

    Endo, S.; Lin, W.; Jackson, R. C.; Collis, S. M.; Vogelmann, A. M.; Wang, D.; Oue, M.; Kollias, P.

    2017-12-01

    Tropical convection is one of the main drivers of the climate system and recognized as a major source of uncertainty in climate models. High-resolution modeling is performed with a focus on the deep convection cases during the active monsoon period of the TWP-ICE field campaign to explore ways to improve the fidelity of convection permitting tropical simulations. Cloud resolving model (CRM) simulations are performed with WRF modified to apply flexible configurations for LES/CRM simulations. We have enhanced the capability of the forcing module to test different implementations of large-scale vertical advective forcing, including a function for optional use of large-scale thermodynamic profiles and a function for the condensate advection. The baseline 3D CRM configurations are, following Fridlind et al. (2012), driven by observationally-constrained ARM forcing and tested with diagnosed surface fluxes and fixed sea-surface temperature and prescribed aerosol size distributions. After the spin-up period, the simulations follow the observed precipitation peaks associated with the passages of precipitation systems. Preliminary analysis shows that the simulation is generally not sensitive to the treatment of the large-scale vertical advection of heat and moisture, while more noticeable changes in the peak precipitation rate are produced when thermodynamic profiles above the boundary layer were nudged to the reference profiles from the forcing dataset. The presentation will explore comparisons with observationally-based metrics associated with convective characteristics and examine the model performance with a focus on model physics, doubly-periodic vs. nested configurations, and different forcing procedures/sources. A radar simulator will be used to understand possible uncertainties in radar-based retrievals of convection properties. Fridlind, A. M., et al. (2012), A comparison of TWP-ICE observational data with cloud-resolving model results, J. Geophys. Res., 117, D05204

  5. Entropy Generation Analysis and Performance Evaluation of Turbulent Forced Convective Heat Transfer to Nanofluids

    Directory of Open Access Journals (Sweden)

    Yu Ji

    2017-03-01

    Full Text Available The entropy generation analysis of fully turbulent convective heat transfer to nanofluids in a circular tube is investigated numerically using the Reynolds Averaged Navier–Stokes (RANS model. The nanofluids with particle concentration of 0%, 1%, 2%, 4% and 6% are treated as single phases of effective properties. The uniform heat flux is enforced at the tube wall. To confirm the validity of the numerical approach, the results have been compared with empirical correlations and analytical formula. The self-similarity profiles of local entropy generation are also studied, in which the peak values of entropy generation by direct dissipation, turbulent dissipation, mean temperature gradients and fluctuating temperature gradients for different Reynolds number as well as different particle concentration are observed. In addition, the effects of Reynolds number, volume fraction of nanoparticles and heat flux on total entropy generation and Bejan number are discussed. In the results, the intersection points of total entropy generation for water and four nanofluids are observed, when the entropy generation decrease before the intersection and increase after the intersection as the particle concentration increases. Finally, by definition of Ep, which combines the first law and second law of thermodynamics and attributed to evaluate the real performance of heat transfer processes, the optimal Reynolds number Reop corresponding to the best performance and the advisable Reynolds number Read providing the appropriate Reynolds number range for nanofluids in convective heat transfer can be determined.

  6. Characteristic of The RSG-Gas Oxide Fuel Element Temperature Under Forced Convection And Natural Convection Mode

    International Nuclear Information System (INIS)

    Sudarmono

    2000-01-01

    One of the methods used for fuel element plate temperature measurement in RSG-Gas is a direct measurement. Evaluation on the measurement results were done by using HEATHYDE and NATCON code, which was then compared to the safety margin criteria. Results of thermalhydraulic measurement on transitional core both under forced and natural convection were compared with the results of calculations using the two codes. Measurement result for maximum fuel element plate temperature at typical working core of 30 MW, was 121 o C. The deviation between calculation and measurement result was under 9.75 %. Under normal operation, safety margin on DNB and OFI are 3.56 and 2.60, respectively. Natcon calculation result showed that the typical working core under the natural circulation mode, an onset of nucleate boiling (ONB)occurred at a core power level of 826 kW (2.8% of the nominal power)

  7. Numerical analysis of laminar forced convection in a spherical annulus

    International Nuclear Information System (INIS)

    Tuft, D.B.

    1980-01-01

    Calculations of steady laminar incompressible fluid-flow and heat transfer in a spherical annulus are presented. Steady pressures, temperatures, velocities, and heat transfer coefficients are calculated for an insulated outer sphere and a 0 0 C isothermal inner sphere with 50 0 C heated water flowing in the annulus. The inner sphere radius is 13.97 cm, the outer sphere radius is 16.83 cm and the radius ratio is 1.2. The transient axisymmetric equations of heat, mass, and momentum conservation are solved numerically in spherical coordinates. The transient solution is carried out in time until steady state is achieved. A variable mesh is used to improve resolution near the inner sphere where temperature and velocity gradients are steep. It is believed that this is the first fully two-dimensional analysis of forced flow in a spherical annulus. Local and bulk Nusselt numbers are presented for Reynolds numbers from 4.4 to 440. Computed bulk Nusselt numbers ranged from 2 to 50 and are compared to experimental results from the literature. Inlet flow jetting off the inner sphere and flow separation are predicted by the analysis. The location of wall jet separation was found to be a function of Reynolds number, indicating the location of separation depends upon the ratio of inertia to viscous forces. Wall jet separation has a pronounced effect on the distribution of local heat flux. The area between inlet and separation was found to be the most significant area for heat transfer. Radial distributions of azimuthal velocity and temperature are presented for various angles beginning at the inlet. Inner sphere pressure distribution is presented and the effect on flow separation is discussed

  8. Observations of Convectively Coupled Kelvin Waves forced by Extratropical Wave Activity

    Science.gov (United States)

    Kiladis, G. N.; Biello, J. A.; Straub, K. H.

    2012-12-01

    It is well established by observations that deep tropical convection can in certain situations be forced by extratropical Rossby wave activity. Such interactions are a well-known feature of regions of upper level westerly flow, and in particular where westerlies and equatorward wave guiding by the basic state occur at low enough latitudes to interact with tropical and subtropical moisture sources. In these regions convection is commonly initiated ahead of upper level troughs, characteristic of forcing by quasi-geostrophic dynamics. However, recent observational evidence indicates that extratropical wave activity is also associated with equatorial convection even in regions where there is a "critical line" to Rossby wave propagation at upper levels, that is, where the zonal phase speed of the wave is equal to the zonal flow speed. A common manifestation of this type of interaction involves the initiation of convectively coupled Kelvin waves, as well as mixed Rossby-gravity (MRG) waves. These waves are responsible for a large portion of the convective variability within the ITCZ over the Indian, Pacific, and Atlantic sectors, as well as within the Amazon Basin of South America. For example, Kelvin waves originating within the western Pacific ITCZ are often triggered by Rossby wave activity propagating into the Australasian region from the South Indian Ocean extratropics. At other times, Kelvin waves are seen to originate along the eastern slope of the Andes. In the latter case the initial forcing is sometimes linked to a low-level "pressure surge," initiated by wave activity propagating equatorward from the South Pacific storm track. In yet other cases, such as over Africa, the forcing appears to be related to wave activity in the extratropics which is not necessarily propagating into low latitudes, but appears to "project" onto the Kelvin structure, in line with past theoretical and modeling studies. Observational evidence for extratropical forcing of Kelvin and MRG

  9. Laminar forced convective heat transfer to near-critical water in a tube

    International Nuclear Information System (INIS)

    Lee, Sang Ho

    2003-01-01

    Numerical modeling is carried out to investigate forced convective heat transfer to near-critical water in developing laminar flow through a circular tube. Due to large variations of thermo-physical properties such as density, specific heat, viscosity, and thermal conductivity near thermodynamic critical point, heat transfer characteristics show quite different behavior compared with pure forced convection. With flow acceleration along the tube unusual behavior of heat transfer coefficient and friction factor occurs when the fluid enthalpy passes through pseudocritical point of pressure in the tube. There is also a transition behavior from liquid-like phase to gas-like phase in the developing region. Numerical results with constant heat flux boundary conditions are obtained for reduced pressures from 1.09 to 1.99. Graphical results for velocity, temperature, and heat transfer coefficient with Stanton number are presented and analyzed

  10. Forced convection heat transfer correlation for finned plates in a duct

    International Nuclear Information System (INIS)

    Chae, Myeong-Seon; Moon, Je-Young; Chung, Bum-Jin

    2014-01-01

    Forced convection heat transfer experiments were conducted for plate-fin in a duct using various fin spacing, fin height, duct width, Reynolds number for Prandtl numbers 2,014. Based upon analogy concept, mass transfer rate were measured instead of heat transfer rates. The heat transfer rates were enhanced with the increase of fin height and decrease of fin spacing as they increase the heat transfer area. Meanwhile, heat transfer rates were impaired with the increase of the duct width as the bypass flows increased to tip clearance region. Forced convection heat transfer correlations were developed for laminar and turbulent flow conditions and for narrow and wide ducts. The work draws attention to the tip clearance on the heat transfer of the finned plate in a duct. (author)

  11. The effect of internal ribbing on forced convective heat transfer in circular-sectioned tubes

    International Nuclear Information System (INIS)

    Farhadi Rahmat-Abadi, K.; Morris, W. D.

    2003-01-01

    This paper presents the results of an experimental examination of the effect of internal circumferential ribs on forced convection in circular-sectioned tubes. The work is relevant to the internal cooling of gas turbine rotor blades. The influence of rib geometry is investigated for three different rib configurations and simple design-type, empirical equations are developed for estimating heat transfer at rib and mid-rib locations. It is demonstrated that heat transfer may be improved by up to three fold in relation to fully developed forced convection in smooth-walled tubes. The geometric parameters which have been used for the experiments are typical of those currently applied to gas turbine blade cooling designs

  12. Experimental and theoretical study on forced convection film boiling heat transfer

    International Nuclear Information System (INIS)

    Liu, Qiusheng

    2001-01-01

    Theoretical solutions of forced convection film boiling heat transfer from horizontal cylinders in saturated liquids were obtained based on a two-phase laminar boundary layer film boiling model. It was clarified that author's experimental data for the cylinders with the nondimensional diameters, D, of around 1.3 in water and in Freon-113 agreed with the values of theoretical numerical solutions based on the two-phase laminar boundary layer model with the smooth vapor-liquid interface except those for low flow velocities. A forced convection film boiling heat transfer correlation including the radiation contribution from the cylinders with various diameters in saturated and subcooled liquids was developed based on the two-phase laminar boundary layer film boiling model and the experimental data for water and Freon-113 at wide ranges of flow velocities, surface superheats, system pressures and cylinder diameters. (author)

  13. Analysis of forced convective transient boiling by homogeneous model of two-phase flow

    International Nuclear Information System (INIS)

    Kataoka, Isao

    1985-01-01

    Transient forced convective boiling is of practical importance in relation to the accident analysis of nuclear reactor etc. For large length-to-diameter ratio, the transient boiling characteristics are predicted by transient two-phase flow calculations. Based on homogeneous model of two-phase flow, the transient forced convective boiling for power and flow transients are analysed. Analytical expressions of various parameters of transient two-phase flow have been obtained for several simple cases of power and flow transients. Based on these results, heat flux, velocity and time at transient CHF condition are predicted analytically for step and exponential power increases, and step, exponential and linear velocity decreases. The effects of various parameters on heat flux, velocity and time at transient CHF condition have been clarified. Numerical approach combined with analytical method is proposed for more complicated cases. Solution method for pressure transient are also described. (author)

  14. Theoretical and experimental studies on transient forced convection heat transfer of helium gas

    International Nuclear Information System (INIS)

    Liu, Qiusheng; Fukuda, Katsuya; Shibahara, Makoto

    2008-01-01

    Forced convection transient heat transfer for helium gas at various periods of exponential increase of heat input to a horizontal cylinder and a plate (ribbon) one was experimentally and theoretically studied. In the experimental studies, the authors measured heat flux, surface temperature, and transient heat transfer coefficients for forced convection flow of helium gas over a horizontal cylinder and a plate (ribbon) one under wide experimental conditions. Empirical correlations for quasi-steady-state heat transfer and transient heat transfer were obtained based on the experimental data. In the theoretical study, transient heat transfer was numerically solved based on a turbulent flow model. The values of numerical solution for surface temperature and heat flux were compared and discussed with authors' experimental data. (author)

  15. Evaluation of forced-convection nucleate boiling detection by acoustic emission

    International Nuclear Information System (INIS)

    Wells, R.P.; Paterson, J.A.

    1981-10-01

    Acoustic Emission techniques are being investigated for use as protection systems in neutral beam accelerators and water cooled beam dumps. For this purpose, the characteristics of the boiling curve for forced-convection surface boiling have been compared to the Acoustic Emission (AE) produced. Results indicate that AE, in the form of count-rate, is a sensitive indicator of nucleate boiling incipience and is relatively insensitive to flow velocity in the 0 to 12 m/s range

  16. Burnout in boiling heat transfer. Part II: subcooled and low quality forced-convection systems

    International Nuclear Information System (INIS)

    Bergles, A.E.

    1977-01-01

    Recent experimental and analytical developments regrading burnout in subcooled and low quality forced-convection systems are reviewed. Much data have been accumulated which clarify the parametric trends and lead to new design correlations for water and a variety of other coolants in both simple and complex geometries. A number of critical experiments and models have been developed to attempt to clarify the burnout mechanism(s) in simpler geometries and power transients

  17. Burnout in boiling heat transfer. Part III. High-quality forced-convection systems

    International Nuclear Information System (INIS)

    Bergles, A.E.

    1979-01-01

    This is the final part of a review of burnout during boiling heat transfer. The status of burnout in high-quality forced-convection systems is reviewed, and recent developments are summarized in detail. A general guide to the considerable literature is given. Parametric effects and correlations for water in circular and noncircular ducts are presented. Other topics discussed include transients, steam-generator applications, correlations for other fluids, fouling, and augmentation

  18. Experiment of forced convection heat transfer using microencapsulated phase-change-material slurries

    International Nuclear Information System (INIS)

    Kubo, Shinji; Akino, Norio; Tanaka, Amane; Nagashima, Akira.

    1997-01-01

    The present study describes an experiment on forced convective heat transfer using a water slurry of Microencapsulated Phase-change-material. A normal paraffin hydrocarbon is microencapsulated by melamine resin, melting point of 28.1degC. The heat transfer coefficient and pressure drop in a circular tube were evaluated. The heat transfer coefficient using the slurry in case with and without phase change were compared to in case of using pure water. (author)

  19. The influence of terrain forcing on the initiation of deep convection over Mediterranean islands

    Science.gov (United States)

    Barthlott, Christian; Kirshbaum, Daniel

    2013-04-01

    The influence of mountainous islands on the initiation of deep convection is investigated using the Consortium for Small-scale Modeling (COSMO) model. The study day is 26 August 2009 on which moist convection occurred over both the Corsica and Sardinia island in the Mediterranean Sea. Sensitivity runs with systematically modified topography are explored to evaluate the relative importance of the land-sea contrast and the terrain height for convection initiation. Whereas no island precipitation is simulated when the islands are completely removed, all simulations that represent these land surfaces develop convective precipitation. Although convection initiates progressively earlier in the day over taller islands, the precipitation rates and accumulations do not show a fixed relationship with terrain height. This is due to the competing effects of different physical processes. First, whereas the forcing for low-level ascent increases over taller islands, the boundary-layer moisture supply decreases, which diminishes the conditional instability and precipitable water. Second, whereas taller islands enhance the inland propagation speeds of sea-breeze fronts, they also mechanically block these fronts and prevent them from reaching the island interior. As a result, the island precipitation is rather insensitive to island terrain height except for one particular case in which the island precipitation increases considerably due to an optimal superposition of the sea breeze and upslope flow. These results demonstrate the complexity of interactions between sea breezes and orography and reinforce that an adequate representation of detailed topographic features is necessary to account for thermally induced wind systems that initiate deep convection.

  20. Hydrogen transfer in Pb–Li forced convection flow with permeable wall

    Energy Technology Data Exchange (ETDEWEB)

    Fukada, Satoshi, E-mail: sfukada@nucl.kyushu-u.ac.jp; Muneoka, Taiki; Kinjyo, Mao; Yoshimura, Rhosuke; Katayama, Kazunari

    2015-10-15

    Highlights: • The paper presents experimental and analytical results of Pb–Li eutectic alloy forced convection flow. • Analytical results are in good agreement with ones of hydrogen permeation in Pb–Li forced convection flow. • The results are useful for the design of liquid blanket of fusion reactors. - Abstract: Transient- or steady-state hydrogen permeation from a primary fluid of Li{sub 17}Pb{sub 83} (Pb–Li) through a permeable tube of Inconel-625 alloy to a secondary Ar purge is investigated experimentally under a forced convection flow in a dual cylindrical tube system. Results of the overall hydrogen permeation flux are correlated in terms of diffusivity, solubility and an average axial velocity of Pb–Li and diffusivity and solubility of the solid wall. Analytical solutions under proper assumptions are derived to simulate the transient- and steady-state rates of the overall hydrogen permeation, and close agreement is obtained between experiment and analysis. Two things are clarified from the comparison: (i) how the steady-state permeation rate is affected by the mass-transfer properties and the average velocity of Pb–Li and the properties of Inconel-625, and (ii) how its transient behavior is done by the diffusivity of the two materials. The results obtained here will give important information to estimate or to analyze the tritium transfer rate in fluidized Pb–Li blankets of DEMO or the future commercial fusion reactors.

  1. Investigation of forced convection heat transfer of supercritical pressure water in a vertically upward internally ribbed tube

    International Nuclear Information System (INIS)

    Wang Jianguo; Li Huixiong; Guo Bin; Yu Shuiqing; Zhang Yuqian; Chen Tingkuan

    2009-01-01

    In the present paper, the forced convection heat transfer characteristics of water in a vertically upward internally ribbed tube at supercritical pressures were investigated experimentally. The six-head internally ribbed tube is made of SA-213T12 steel with an outer diameter of 31.8 mm and a wall thickness of 6 mm and the mean inside diameter of the tube is measured to be 17.6 mm. The experimental parameters were as follows. The pressure at the inlet of the test section varied from 25.0 to 29.0 MPa, and the mass flux was from 800 to 1200 kg/(m 2 s), and the inside wall heat flux ranged from 260 to 660 kW/m 2 . According to experimental data, the effects of heat flux and pressure on heat transfer of supercritical pressure water in the vertically upward internally ribbed tube were analyzed, and the characteristics and mechanisms of heat transfer enhancement, and also that of heat transfer deterioration, were also discussed in the so-called large specific heat region. The drastic changes in thermophysical properties near the pseudocritical points, especially the sudden rise in the specific heat of water at supercritical pressures, may result in the occurrence of the heat transfer enhancement, while the covering of the heat transfer surface by fluids lighter and hotter than the bulk fluid makes the heat transfer deteriorated eventually and explains how this lighter fluid layer forms. It was found that the heat transfer characteristics of water at supercritical pressures were greatly different from the single-phase convection heat transfer at subcritical pressures. There are three heat transfer modes of water at supercritical pressures: (1) normal heat transfer, (2) deteriorated heat transfer with low HTC but high wall temperatures in comparison to the normal heat transfer, and (3) enhanced heat transfer with high HTC and low wall temperatures in comparison to the normal heat transfer. It was also found that the heat transfer deterioration at supercritical pressures was

  2. Forced and thermocapillary convection in silicon Czochralski crystal growth in semispherical crucible

    Energy Technology Data Exchange (ETDEWEB)

    Mokhtari, F [Physics Department, Faculty of Science, University of Mouloud Mammeri, Tizi Ouzou (Algeria); Bouabdallah, A; Zizi, M [LTSE Laboratory, University of Science and Technology USTHB. BP 32 Elalia, Babezzouar, Algiers (Algeria); Hanchi, S [UER Mecanique/ E.M.P B.P 17, Bordj El Bahri, Algiers (Algeria); Alemany, A, E-mail: abouab2002@yahoo.f [Laboratoire EPM, CNRS, Grenoble (France)

    2010-03-01

    In order to understand the influence of a semispherical crucible geometry combined with different convection modes as a thermocapillary convection, natural convection and forced convection, induced by crystal rotation, on melt flow pattern in silicon Czochralski crystal growth process, a set of numerical simulations are conducted using Fluent Software. We solve the system of equations of heat and momentum transfer in classical geometry as cylindrical and modified crystal growth process geometry as cylindro-spherical. In addition, we adopt hypothesis adapted to boundary conditions near the interface and calculations are executed to determine temperature, pressure and velocity fields versus Grashof and Reynolds numbers. The analysis of the obtained results led to conclude that there is advantage to modify geometry in comparison with the traditional one. The absence of the stagnation regions of fluid in the hemispherical crucible corner and the possibility to control the melt flow using the crystal rotation enhances the quality of the process comparatively to the cylindrical one. The pressure field is strongly related to the swirl velocity.

  3. Forced and thermocapillary convection in silicon Czochralski crystal growth in semispherical crucible

    International Nuclear Information System (INIS)

    Mokhtari, F; Bouabdallah, A; Zizi, M; Hanchi, S; Alemany, A

    2010-01-01

    In order to understand the influence of a semispherical crucible geometry combined with different convection modes as a thermocapillary convection, natural convection and forced convection, induced by crystal rotation, on melt flow pattern in silicon Czochralski crystal growth process, a set of numerical simulations are conducted using Fluent Software. We solve the system of equations of heat and momentum transfer in classical geometry as cylindrical and modified crystal growth process geometry as cylindro-spherical. In addition, we adopt hypothesis adapted to boundary conditions near the interface and calculations are executed to determine temperature, pressure and velocity fields versus Grashof and Reynolds numbers. The analysis of the obtained results led to conclude that there is advantage to modify geometry in comparison with the traditional one. The absence of the stagnation regions of fluid in the hemispherical crucible corner and the possibility to control the melt flow using the crystal rotation enhances the quality of the process comparatively to the cylindrical one. The pressure field is strongly related to the swirl velocity.

  4. Experimental study of cooling BIPV modules by forced convection in the air channel

    International Nuclear Information System (INIS)

    Kaiser, A.S.; Zamora, B.; Mazón, R.; García, J.R.; Vera, F.

    2014-01-01

    Highlights: • An experimental setup for studying the effects of forced convection on cell temperature. • The induced velocity within the forced convection channel significantly affects the PV cooling. • Correlations for the Ross coefficient, module temperature, efficiency, and power output. • Prediction of the thermal behavior of the PV module in BIPV configurations. - Abstract: The efficiency of photovoltaic systems depends mainly on the cell temperature. Frequently, the PV collectors are installed on the top of the building. One cost effective method to regulate the temperature of rooftop integrated photovoltaic panels is to provide an open air channel beneath the panel. The cell temperature of these PV modules is very much influenced by the capability of ventilating this channel. The ventilation may be modified by different factors such as the wind velocity, the air gap size, and the forced convection induced by a fan or by a conventional air conditioning system. This paper describes an experimental setup to study the influence of the air gap size and the forced ventilation on the cell temperature (and consequently on the electrical efficiency of the PV module) of a BIPV configuration, for different values of the incident solar radiation, ambient temperatures, and aspect ratios, as well as for several forced ventilation conditions. Semi empirical correlations for the Ross coefficient, module temperature, electrical efficiency, and power output are proposed, showing a good agreement with respect to experimental measurements. A critical channel aspect ratio close to 0.11 can be considered to minimize overheating of PV devices. For a duct velocity V v = 6 m/s, a power output increase of 19% is observed over the natural ventilation case (V v = 0.5 m/s)

  5. Evaluation of T-111 forced-convection loop tested with lithium at 13700C

    International Nuclear Information System (INIS)

    DeVan, J.H.; Long, E.L. Jr.

    1975-04-01

    A T-111 alloy (Ta--8 percent W--2 percent Hf) forced-convection loop containing molten lithium was operated 3000 h at a maximum temperature of 1370 0 C. Flow velocities up to 6.3 m/s were used. The results obtained in this forced-convection loop are very similar to those observed in lower velocity thermal-convection loops of T-111 containing lithium. Weight changes were determined at 93 positions around the loop. The maximum dissolution rate occurred at the maximum wall temperature of the loop and was less than 1.3 μ m/year. Mass transfer of hafnium, nitrogen, and, to a lesser extent, carbon occurred from the hotter to cooler regions. Exposed surfaces in the highest temperature region were found to be depleted in hafnium to a depth of 60 μ m with no detectable change in tungsten content. There was some loss in room-temperature tensile strength for specimens exposed to lithium at 1370 0 C, attributable to depletion of hafnium and nitrogen and to attendant grain growth. (U.S.)

  6. Regimes of Axisymmetric Flow and Scaling Laws in a Rotating Annulus with Local Convective Forcing

    Directory of Open Access Journals (Sweden)

    Susie Wright

    2017-07-01

    Full Text Available We present a numerical study of axisymmetric flow in a rotating annulus in which local thermal forcing, via a heated annular ring on the outside of the base and a cooled circular disk in the centre of the top surface, drives convection. This new configuration is a variant of the classical thermally-driven annulus, where uniform heating and cooling are applied through the outer and inner sidewalls respectively. The annulus provides an analogue to a planetary circulation and the new configuration, with its more relaxed vertical thermal boundary conditions, is expected to better emulate vigorous convection in the tropics and polar regions as well as baroclinic instability in the mid-latitude baroclinic zone. Using the Met Office/Oxford Rotating Annulus Laboratory (MORALS code, we have investigated a series of equilibrated, two dimensional axisymmetric flows across a large region of parameter space. These are characterized in terms of their velocity and temperature fields. When rotation is applied several distinct flow regimes may be identified for different rotation rates and strengths of differential heating. These regimes are defined as a function of the ratio of the horizontal Ekman layer thickness to the non-rotating thermal boundary layer thickness and are found to be similar to those identified in previous annulus experiments. Convection without rotation is also considered and the scaling of the heat transport with Rayleigh number is calculated. This is then compared with existing work on the classical annulus as well as horizontal and Rayleigh-Bénard convection. As with previous studies on both rotating and non-rotating convection the system’s behaviour is found to be aspect ratio dependent. This dependence is seen in the scaling of the non-rotating Nusselt number and in transitions between regimes in the rotating case although further investigation is required to fully explain these observations.

  7. Forced and free convection flow with viscous dissipation effects: The method of parametric differentiation

    International Nuclear Information System (INIS)

    Hossain, M.A.; Arbad, O.

    1988-07-01

    Effect of buoyancy force in a laminar uniform forced convection flow past a semi-infinite vertical plate has been analyzed near the leading edge, taking into account the viscous dissipation. The coupled non-linear locally similar equations, which govern the flow, are solved by the method of parametric differentiation. Effects of the buoyancy force and the heat due to viscous dissipation on the flow and the temperature fields as well as on the wall shear-stress and the heat transfer at the surface of the plate are shown graphically for the values of the Prandtl number σ ranging from 10 -1 to 1.0. (author). 20 refs, 3 figs, 2 tabs

  8. Numerical simulation of forced convection in a duct subjected to microwave heating

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, J.; Kuznetsov, A.V. [North Carolina State University, Department of Mechanical and Aerospace Engineering, Campus Box 7910, Raleigh, NC (United States); Sandeep, K.P. [North Carolina State University, Department of Food Science, Raleigh, NC (United States)

    2007-01-15

    In this paper, forced convection in a rectangular duct subjected to microwave heating is investigated. Three types of non-Newtonian liquids flowing through the duct are considered, specifically, apple sauce, skim milk, and tomato sauce. A finite difference time domain method is used to solve Maxwell's equations simulating the electromagnetic field. The three-dimensional temperature field is determined by solving the coupled momentum, energy, and Maxwell's equations. Numerical results show that the heating pattern strongly depends on the dielectric properties of the fluid in the duct and the geometry of the microwave heating system. (orig.)

  9. Experimental study of drying kinetics by forced convection of aromatic plants

    Energy Technology Data Exchange (ETDEWEB)

    Belghit, A; Boutaleb, B C [Laboratoire de Mecanique des Fluides et Energetique, Marrakech (Morocco). Faculte des Sciences Semlalia; Kouhila, M [Laboratoire d' Energie Solaire, Marrakech (Morocco). Ecole Normale Superieure

    2000-08-01

    This paper has the objectives to determine the isotherms of sorption and the drying kinetics of verbena, which is the most consumed aromatic plant in Morocco. The experiments undertaken consist of examining the effects of drying air velocity, temperature of drying air and air moisture content on the drying kinetics of verbena in a laboratory drying tunnel working by forced convection. The results verified, with good reproducibility, that temperature is the main factor in controlling the rate of drying. The expression of the drying rate is determined empirically from the characteristic curve of drying. (author)

  10. Forced convective transition boiling: review of literature and comparison of prediction methods

    International Nuclear Information System (INIS)

    Groeneveld, D.C.; Fung, K.K.

    1976-06-01

    This report reviews the published information on transition boiling heat transfer under forced convective conditions. It was found that transition boiling data have been obtained only within a limited range of conditions and many data are considered unreliable. The data do not permit the derivation of a correlation; however the parametric trends can be isolated from the data. Several authors have proposed correlations valid in the transition boiling region. Most of the correlations are valid only within a narrow range of conditions. A comparison with the data shows that in general agreement is poor. Hsu's correlation is tentatively recommended for low flows and pressures. (author)

  11. Bifurcation and stability of forced convection in tightly coiled ducts: multiplicity

    International Nuclear Information System (INIS)

    Wang Liqiu; Pang, Ophelia; Cheng Lin

    2005-01-01

    A numerical study is made on the fully developed bifurcation structure of the forced convection in tightly coiled ducts of square cross-section. In addition to the examination of structural changes of three known solution branches found in loosely coiled ducts, three new solution branches are found. These new branches are isolated from the three known branches. The flows on these new branches are in a symmetric 4-cell state, a symmetric 8-cell state, an asymmetric 2-cell state, an asymmetric 5-cell state, an asymmetric 7-cell state, or an asymmetric 8-cell structure

  12. Heat transfer with water in forced convection without boiling in small diameter tubes

    International Nuclear Information System (INIS)

    Ricque, Roger; Siboul, Roger

    1969-01-01

    This note presents the measurements performed for the establishment of an empirical heat transfer law for water in forced convection without boiling in small diameter tubes (2 and 4 mm), with high flow velocity and strong heat flux, and for relatively low fluid temperatures. A correlation of experimental points is obtained with a very small maximum dispersion: Nu fl = 0,0092 Re fl 0,88 Pr 0,5 (μ fl /μ p ) 0,14 . A correlation for the fiction coefficient is also presented [fr

  13. Burnout in boiling heat transfer. II. Subcooled and low-quality forced-convection systems

    International Nuclear Information System (INIS)

    Bergles, A.E.

    1977-01-01

    Recent experimental and analytical developments regarding burnout in subcooled and low-quality forced-convection systems are reviewed. Many data have been accumulated which clarify the parametric trends and lead to new design correlations for water and a variety of other coolants in both simple and complex geometries. A number of critical experiments and models have been developed to attempt to clarify the burnout mechanism(s) in simpler geometries. Other topics discussed include burnout with power transients and techniques to augment burnout. 86 references

  14. In-situ detection of convection and rotation striations by growth interface electromotive force spectrum

    Science.gov (United States)

    Zhu, Yunzhong; Tang, Feng; Yang, Xin; Yang, Mingming; Ma, Decai; Zhang, Xiaoyue; Liu, Yang; Lin, Shaopeng; Wang, Biao

    2018-04-01

    Nanoscale growth striations, induced by the crystal rotation and melt convection, are in-situ detected by the growth interface electromotive force (GEMF) spectrum during Czochralski (CZ) crystal growth. Specifically, the intensity and period of rotation and convection striations could be precisely revealed under different rotation rates. This is because the GEMF spectrum is affected by the combination effort of temperature difference in crystal rotation path and the melt flow in growth interface. Furthermore, the spectrum analysis (Fourier transform) reveals remarkable characteristics of periodic flow oscillation. More interestingly, in different rotation rates, the corresponding convection period and intensity show particular regularity that could barely be observed in semitransparent and high-temperature melt. Therefore, the GEMF spectrum reflects the subtle changes of a growing crystal that is far beyond the detecting precision of sensors in current CZ equipment. On the basis of this paper and our previous work, the real-time feedback of multiscale striations is established. GEMF spectrum could be a promising approach to reveal striation formation mechanism and optimize crystal quality.

  15. Experimental Investigation of Temperature Distribution along the Length of Uniform Area Fin for Forced and Free Convection

    Science.gov (United States)

    Kannojiya, Vikas; Sharma, Riya; Gaur, Rahul; Jangra, Anil; Yadav, Pushpender; Prajapati, Pooja

    2018-03-01

    The overheating of an industrial component sometimes may leads to system failure. The convection heat transfer from a heated surface can be effectively enhanced by employing fins on that surface. This Paper emphasizes on the experimental investigation of temperature distribution along the length of pin shaped fin. The analysis is performed on a 100 mm long fin made up of brass with 19.6 mm diameter having thermal conductivity as 111 W/m.K. Temperature at different section of the fin along its length is evaluated experimentally and theoretically. The influence of convection mode viz natural & forced convection and variable heat input on the temperature distribution is evaluated. The result outcomes are then compared with the widely accepted analytical relations. A comparison of convective heat transfer coefficient for uniform and non-uniform area fin is also presented. The results by experimental and analytical method are found to be in good agreement for free convection phenomenon.

  16. Numerical simulation for aspects of homogeneous and heterogeneous reactions in forced convection flow of nanofluid

    Science.gov (United States)

    Hayat, Tasawar; Shah, Faisal; Khan, Muhammad Ijaz; Alsaedi, Ahmed

    2018-03-01

    Mixed convection stagnation point flow of nanofluid by a vertical permeable circular cylinder has been addressed. Water is treated as ordinary liquid while nanoparticles include aluminium oxide, copper and titanium dioxide. Homogeneous-heterogeneous reactions are considered. The nonlinear higher order expressions are changed into first ordinary differential equations and then solved by built-in-Shooting method in mathematica. The results of velocity, temperature, concentration, skin friction and local Nusselt number are discussed. Our results demonstrate that surface drag force and heat transfer rate are enhanced linearly for higher estimation of curvature parameter. Further surface drag force decays for aluminium oxide and it enhances for copper nanoparticle. Heat transfer rate enhances with increasing all three types of nanoparticles. In addition, the lowest heat transfer rate is obtained in case of titanium dioxide when compared with copper and aluminium oxide.

  17. MHD forced and free convection boundary layer flow near the leading edge

    International Nuclear Information System (INIS)

    Hossain, M.A.; Ahmed, M.

    1988-07-01

    Magnetohydrodynamic forced and free convection flow of an electrically conducting viscous incompressible fluid past a vertical flat plate with uniform heat flux in the presence of a magnetic field acting normal to the plate that moves with the fluid has been studied near the leading edge of the plate. The coupled non-linear equations are solved by the method of superposition for the values of the Prandtl number ranges from 0.01 to 10.0. The velocity and the temperature profiles are presented graphically and the values of the wall shear-stress as well as the heat transfer rate are presented in tabular form showing the effect of the buoyancy force and the applied magnetic field. To show the accuracy of the present method some typical values are compared with the available one. (author). 17 refs, 3 figs, 2 tabs

  18. Study of nitrogen injection to enhance forced convection for gas fast reactors

    International Nuclear Information System (INIS)

    Tauveron, N.; Dor, I.; Bentivoglio, F.

    2011-01-01

    Highlights: → The present study concerns the use of blowers in case of nitrogen injection. It is a well-known fact that heavier gases (than helium) enhance natural circulation. The use of such heavier gases (nitrogen is considered here) can also enhance forced convection. → A specific work on the impact of the use of alternative gas on blower behaviour is presented. → These developments are used in a simplified system analysis and in a complete transient behaviour analysis in depressurised situations computed with the CATHARE2 code. - Abstract: In the frame of the international forum GenIV, the gas fast reactor is considered as a promising concept, combining the benefits of fast spectrum and high temperature, using helium as coolant. In the current preliminary viability GFR studies safety system relies on blowers in case of depressurised conditions. The present study concerns the use of blowers in case of nitrogen injection. It is a well-known fact that heavier gases (than helium) enhance natural circulation. The use of such gases (nitrogen is considered) can also enhance forced convection. A specific work on the impact of the use of alternative gas on blower behaviour is presented. Transient behaviours in depressurised situations are computed with the CATHARE2 code and analyzed.

  19. Performance of a forced convection solar drier integrated with gravel as heat storage material

    Energy Technology Data Exchange (ETDEWEB)

    Mohanraj, M. [Dr Mahalingam College of Engineering and Technology, Pollachi (India). Dept. of Mechanical Engineering; Chandrasekar, P. [Swinburne Univ. of Technology, Sarawak (Malaysia). School of Engineering Sciences

    2009-07-01

    Sun drying is the most common method used in India to dry agricultural products such as grains, fruits and vegetables. The rate of drying depends on solar radiation, ambient temperature, wind velocity, relative humidity, initial moisture content, type of crops, crop absorptivity and mass product per unit exposed area. However, this method of spreading the crop in a thin layer on the ground has several disadvantages. This paper reported on a study that focused on developing a forced convection solar drier integrated with heat storage materials for drying various agricultural crops. The indirect forced convection solar drier, integrated with gravel as a sensible heat material, was used to dry pineapple slices under conditions similar to those found in Pollachi, India. The performance of the system was discussed along with the drying characteristics, drying rate, and specific moisture extraction rate. The results showed that the moisture content (wet basis) of pineapple was reduced from about 87.5 to 14.5 per cent (equilibrium moisture content) in about 29 hours in the bottom tray and 32 hours in the top tray. The thermal efficiency of the solar air heater was also reviewed. 9 refs., 5 figs.

  20. Experimental and theoretical analysis of a hybrid solar thermoelectric generator with forced convection cooling

    Science.gov (United States)

    Sundarraj, Pradeepkumar; Taylor, Robert A.; Banerjee, Debosmita; Maity, Dipak; Sinha Roy, Susanta

    2017-01-01

    Hybrid solar thermoelectric generators (HSTEGs) have garnered significant research attention recently due to their potential ability to cogenerate heat and electricity. In this paper, theoretical and experimental investigations of the electrical and thermal performance of a HSTEG system are reported. In order to validate the theoretical model, a laboratory scale HSTEG system (based on forced convection cooling) is developed. The HSTEG consists of six thermoelectric generator modules, an electrical heater, and a stainless steel cooling block. Our experimental analysis shows that the HSTEG is capable of producing a maximum electrical power output of 4.7 W, an electrical efficiency of 1.2% and thermal efficiency of 61% for an average temperature difference of 92 °C across the TEG modules with a heater power input of 382 W. These experimental results of the HSTEG system are found to be in good agreement with the theoretical prediction. This experimental/theoretical analysis can also serve as a guide for evaluating the performance of the HSTEG system with forced convection cooling.

  1. Evaluating a tobacco-curing oven using a forced-convection heat exchanger USCO — MADR

    Directory of Open Access Journals (Sweden)

    Néstor Enrique Cerquera Peña

    2010-01-01

    Full Text Available A traditional oven for curing tobacco leaves was redesigned (based on existing infrastructure; a forced-convection heat exchan- ger system was implemented in it which worked with coffee hulls as fuel. This oven (called a forced-convection tobacco leaf curing oven was evaluated during the harvesting season. It was found that temperature and relative humidity inside the furnace could be controlled with this assembly during the three stages involved in curing tobacco leaves. The equipment used performed excellently when using coffee hulls as fuel, having the following approximate consumption during curing: 8.92 kilograms per hour during the yellowing stage, 17.75 kilograms per hour during the leaf drying and color fixation phase and 19.29 kilograms per hour during the stem drying stage. Comparative analysis of the oven’s operating costs along with the proposed adjustments to be made to it would allow its implementation as a promising alternative in the existing tobacco chain.

  2. The Impact of Convective Fluid Inertia Forces on Operation of Tilting-Pad Journal Bearings

    Directory of Open Access Journals (Sweden)

    Thomas Hagemann

    2017-01-01

    Full Text Available This paper presents a combination of experimental data, CFD analyses, and bearing code predictions on emergence of convective inertia fluid forces within the lube oil flow of tilting-pad journal bearings. Concordantly, experimental data and CFD analyses show a significant rise of local pressure at the transition between inlet and leading edge of tilting-pad, especially for high-speed applications with surface speeds up to 100 m/s. This effect can be related to convective inertia forces within fluid flow as cross-sections and flow character rapidly change at the pad entrance. An energy-based approach is implemented in the bearing code in order to provide enhanced boundary conditions for Reynolds equation considering this effect. As a result, predictions of bearing code achieved significant improved correlation with measured pressure distributions and CFD-data. Further, beside the local influence, a nonnegligible impact on characteristic parameters of bearing operation such as maximum temperature and stiffness and damping coefficients is observed. Finally, the results are critically analyzed and requirements to gain more distinct and reliable data are specified.

  3. An experimental study of forced convective flow boiling CHF in nanofluid

    International Nuclear Information System (INIS)

    Ahn, Hoseon; Kim, Seontae; Jo, Hangjin; Kim, Dongeok; Kang, Soonho; Kim, Moohwan

    2008-01-01

    Recently the enhancement of CHF (critical heat flux) in nanofluids under the pool boiling condition is known as a result of nanoparticle deposition on the heating surface. The deposition phenomenon of nanoparticles on the heating surface is induced dominantly by the vigorous boiling on the heating surface. Considering the importance of flow boiling conditions in various practical heat transfer applications, an experimental study was performed to verify whether or not the enhancement of CHF in nanofluids exists in a forced convective flow boiling condition. The nanofluid used in this research was Al 2 O 3 -water dispersed by the ultra-sonic vibration method in very low concentration (0.01% Vol). A heater specimen was made of a copper block easily detachable to look into the surface condition after the experiment. The heating method was a thermal-heating made with a conductive material. The flow channel took a rectangular type (10mm x 10mm) and had a length of 1.2 m to assure a hydrodynamically fully-developed region. In result, CHF in the nanofluid under the forced convective flow boiling condition has been enhanced distinctively along with the effect of flow rates. To reason the CHF increase in the nanofluids, the boiling surface was investigated thoroughly with the SEM image. (author)

  4. An investigation of transition boiling mechanisms of subcooled water under forced convective conditions

    Energy Technology Data Exchange (ETDEWEB)

    Kwang-Won, Lee; Sang-Yong, Lee

    1995-09-01

    A mechanistic model for forced convective transition boiling has been developed to investigate transition boiling mechanisms and to predict transition boiling heat flux realistically. This model is based on a postulated multi-stage boiling process occurring during the passage time of the elongated vapor blanket specified at a critical heat flux (CHF) condition. Between the departure from nucleate boiling (DNB) and the departure from film boiling (DFB) points, the boiling heat transfer is established through three boiling stages, namely, the macrolayer evaporation and dryout governed by nucleate boiling in a thin liquid film and the unstable film boiling characterized by the frequent touches of the interface and the heated wall. The total heat transfer rates after the DNB is weighted by the time fractions of each stage, which are defined as the ratio of each stage duration to the vapor blanket passage time. The model predictions are compared with some available experimental transition boiling data. The parametric effects of pressure, mass flux, inlet subcooling on the transition boiling heat transfer are also investigated. From these comparisons, it can be seen that this model can identify the crucial mechanisms of forced convective transition boiling, and that the transition boiling heat fluxes including the maximum heat flux and the minimum film boiling heat flux are well predicted at low qualities/high pressures near 10 bar. In future, this model will be improved in the unstable film boiling stage and generalized for high quality and low pressure situations.

  5. Characterization of Radial Curved Fin Heat Sink under Natural and Forced Convection

    Science.gov (United States)

    Khadke, Rishikesh; Bhole, Kiran

    2018-02-01

    Heat exchangers are important structures widely used in power plants, food industries, refrigeration, and air conditioners and now widely used in computing systems. Finned type of heat sink is widely used in computing systems. The main aim of the design of the heat sink is to maintain the optimum temperature level. To achieve this goal so many geometrical configurations are implemented. This paper presents a characterization of radially curved fin heat sink under natural and forced convection. Forced convection is studied for the optimization of temperature for better efficiency. The different alternatives in geometry are considered in characterization are heat intensity, the height of the fin and speed of the fan. By recognizing these alternatives the heat sink is characterized by the heat flux usually generated in high-end PCs. The temperature drop characteristics across height and radial direction are presented for the constant heat input and air flow in the heat sink. The effect of dimensionless elevation height (0 ≤ Z* ≤ 1) and Elenbaas Number (0.4 ≤ El ≤ 2.8) of the heat sink were investigated for study of the Nusselt number. Based on experimental characterization, process plan has been developed for the selection of the similar heat sinks for desired output (heat dissipation and temperature distribution).

  6. Visualization study for forced convection heat transfer of supercritical carbon dioxide near pseudo-boiling point

    International Nuclear Information System (INIS)

    Sakurai, K.; Ko, H.S.; Okamoto, K.; Madarame, H.

    2001-01-01

    For development of new reactor, supercritical water is expected to be used as coolant to improve thermal efficiency. However, the thermal characteristics of supercritical fluid is not revealed completely because its difficulty for experiment. Specific phenomena tend to occur near the pseudo-boiling point which is characterised by temperature corresponding to the saturation point in ordinary fluid. Around this point, the physic properties such as density, specific heat and thermal conductivity are drastically varying. Although there is no difference between gas and liquid phases in supercritical fluids, phenomena similar to boiling (with heat transfer deterioration) can be observed round the pseudo-boiling point. Experiments of heat transfer have been done for supercritical fluid in forced convective condition. However, these experiments were mainly realised inside stainless steel cylinder pipes, for which flow visualisation is difficult. Consequently, this work has been devoted to the development of method allowing the visualisation of supercritical flows. The experiment setup is composed of main loop and test section for the visualisation. Carbon dioxide is used as test fluid. Supercritical carbon dioxide flows upward in rectangular channel and heated by one-side wall to generate forced convection heat transfer. Through window at mid-height of the test section, shadowgraphy was applied to visualize density gradient distribution. The behavior of the density wave in the channel is visualized and examined through the variation of the heat transfer coefficient. (author)

  7. Experimental study on forced convection boiling heat transfer on molten alloy

    International Nuclear Information System (INIS)

    Nishimura, Satoshi; Ueda, Nobuyuki; Nishi, Yoshihisa; Furuya, Masahiro; Kinoshita, Izumi

    1999-01-01

    In order to clarify the characteristics of forced convection boiling heat transfer on molten metal, basic experiments have been carried out with subcooled water flowing on molten Wood's alloy pool surface. In these experiments, water flows horizontally in a rectangular duct. A cavity filled with Wood's alloy is present in a portion of the bottom of the duct. Wood's alloy is heated by a copper conductor at the bottom of the cavity. The experiments have been carried out with various velocities and subcoolings of water, and temperature of Wood's alloy. Boiling curves on the molten alloy surface were obtained and compared with that on a solid heat transfer surface. It is observed that the boiling curve on molten alloy is in a lower superheat region than the boiling curve on a solid surface. This indicates that the heat transfer performance of forced convection boiling on molten alloy is enhanced by increase of the heat transfer area, due to oscillation of the surface and fragmentation of molten alloy

  8. Study on hydrogen isotope behavior in Pb-Li forced convection flow with permeable wall

    Energy Technology Data Exchange (ETDEWEB)

    Yoshimura, Ryosuke; Fukada, Satoshi, E-mail: sfukada@nucl.kyushu-u.ac.jp; Muneoka, Taiki; Kinjo, Mao; Katayama, Kazunari

    2016-12-15

    Highlights: • Transient- and steady-state hydrogen permeation from Li-Pb forced convection flow through permeable tube to outside Ar purge gas was investigated at 600 °C. • It was found that the overall permeation rates were limited by diffusion in the Li-Pb boundary layer developed from the flow inlet. • The effect of the boundary layer was correlated in terms of mass transfer coefficient. The values of mass transfer coefficients at 600 °C were compared with those of 400 °C and 500 °C obtained beforehand. - Abstract: Transient- and steady-state hydrogen permeation from Li-Pb forced convection flow in a permeable tube to outside Ar purge gas was investigated between 400–600 °C. The values of the steady-state permeation rate increased with the increase of the Li-Pb flow rate. It was found that the overall permeation rates were limited by diffusion in a Li-Pb boundary layer developed from flow inlet. The effect of the boundary layer was correlated in terms of the mass-transfer coefficient. The values of the mass-transfer coefficient at 600 °C were compared with those of 400 °C and 500 °C obtained beforehand. Judged from these data of mass-transfer coefficients, it can be predicted that the effect of boundary layer varies with the increase of Li-Pb flow rate at different temperature conditions.

  9. Investigation of combined free and forced convection in a 2 x 6 rod bundle during controlled flow transients

    International Nuclear Information System (INIS)

    Bates, J.M.; Khan, E.U.

    1980-10-01

    An experimental study was performed to obtain local fluid velocity and temperature measurements in the mixed (combined free and forced) convection regime for specific flow coastdown transients. A brief investigation of steady-state flows for the purely free-convection regime was also completed. The study was performed using an electrically heated 2 x 6 rod bundle contained in a flow housing. In addition a transient data base was obtained for evaluating the COBRA-WC thermal-hydraulic computer program

  10. Instability of single-phase natural circulation

    International Nuclear Information System (INIS)

    Xie Heng; Zhang Jinling; Jia Dounan

    1997-01-01

    The author has investigated the instability of single-phase flows in natural circulation loops. The momentum equation and energy equation are made dimensionless according to some definitions, and some important dimensionless parameters are gotten. The authors decomposed the mean mass flowrate and temperature into a steady solution and a small disturbance equations. Through solving the disturbance equations, the authors get the neutral stability curves. The authors have studied the effect of the two parameters which represent the ratio of buoyancy force to the friction loss in the loop on the stability of loops. The authors also have studied the effect of the difference of height between the center of heat source and the heat sink on the stability

  11. Study and Application of Forced Convection in Road Bus Heating System

    Directory of Open Access Journals (Sweden)

    Scheila Sandi Biazus

    2015-03-01

    Full Text Available This work deals with a replacing the heating system of intercity buses, made by long heat exchangers distributed on the sides of the passenger saloon by small and compact ones that use forced convection to heat dissipation. At the beginning the calculation was made of the heat capacity of a heat exchanger with the parameters defined by the supplier, and then conducted an analysis of change in these parameters in order to improve its efficiency. The method for examining the heat exchanger is based on the correlations available in the convection flow inside and outside to determine the respective convective coefficients, and therefore the overall coefficient of heat transfer. Following, the heat exchanger in its original form, was tested on bench. Thus, from the thermal load of the bus model studied, the amount of exchangers required has been defined to satisfy the thermal comfort of passengers. Field tests of the heating systems with new heat exchangers were performed to obtain actual data of the proposed system. The original factory system showed to be efficient in meeting the needs thermal load and economically viable, such that the critical thermal load can be met with ten heaters installed along the body. Furthermore, this system offers the possibility of varying the parameters to best fit to the project, where the flow variation of the fans or the spacing between the fins of the heat exchanger decreases the amount of heaters required. At the same time, the system showed the need for further study to assess its distribution along the passenger saloon in order to meet a best uniformity temperature distribution.

  12. A block-iterative nodal integral method for forced convection problems

    International Nuclear Information System (INIS)

    Decker, W.J.; Dorning, J.J.

    1992-01-01

    A new efficient iterative nodal integral method for the time-dependent two- and three-dimensional incompressible Navier-Stokes equations has been developed. Using the approach introduced by Azmy and Droning to develop nodal mehtods with high accuracy on coarse spatial grids for two-dimensional steady-state problems and extended to coarse two-dimensional space-time grids by Wilson et al. for thermal convection problems, we have developed a new iterative nodal integral method for the time-dependent Navier-Stokes equations for mechanically forced convection. A new, extremely efficient block iterative scheme is employed to invert the Jacobian within each of the Newton-Raphson iterations used to solve the final nonlinear discrete-variable equations. By taking advantage of the special structure of the Jacobian, this scheme greatly reduces memory requirements. The accuracy of the overall method is illustrated by appliying it to the time-dependent version of the classic two-dimensional driven cavity problem of computational fluid dynamics

  13. Experimental-theoretical analysis of laminar internal forced convection with nanofluids

    Energy Technology Data Exchange (ETDEWEB)

    Cerqueira, Ivana G.; Cotta, Renato M. [Lab. of Transmission and Technology of Heat-LTTC. Mechanical Eng. Dept. - POLI and COPPE/UFRJ, Rio de Janeiro, RJ (Brazil)], E-mail: cotta@mecanica.coppe.ufrj.br; Mota, Carlos Alberto A. [Conselho Nacional de Pesquisas - CNPq, Brasilia, DF (Brazil)], e-mail: carlosal@cnpq.br; Nunes, Jeziel S. [INPI, Rio de Janeiro, RJ (Brazil)], e-mail: jeziel@inpi.gov.br

    2010-07-01

    This work reports fundamental experimental-theoretical research related to heat transfer enhancement in laminar channel flow with nanofluids, which are essentially modifications of the base fluid with the dispersion of metal oxide nanoparticles. The theoretical work was performed by making use of mixed symbolic-numerical computation (Mathematica 7.0 platform) and a hybrid numerical-analytical methodology (Generalized Integral Transform Technique - GITT) in accurately handling the governing partial differential equations for the heat and fluid flow problem formulation with temperature dependency in all the thermophysical properties. Experimental work was also undertaken based on a thermohydraulic circuit built for this purpose, and sample results are presented to verify the proposed model. The aim is to illustrate detailed modeling and robust simulation attempting to reach an explanation of the controversial heat transfer enhancement observed in laminar forced convection with nanofluids. (author)

  14. Simulation of forced convection in non-Newtonian fluid through sandstones

    Science.gov (United States)

    Gokhale, M. Y.; Fernandes, Ignatius

    2017-11-01

    Numerical simulation is carried out to study forced convection in non-Newtonian fluids flowing through sandstones. Simulation is carried out using lattice Boltzmann method (LBM) for both shear-thinning and shear-thickening, by varying the power law index from 0.5 to 1.5 in Carreau-Yasuda model. Parameters involved in LBM and Carreau model are identified to achieve numerical convergence. Permeability and porosity are varied in the range of 10-10-10-6 and 0.1-0.7, respectively, to match actual geometrical properties of sandstone. Numerical technology is validated by establishing Darcy's law by plotting the graph between velocity and pressure gradient. Consequently, investigation is carried out to study the influence of material properties of porous media on flow properties such as velocity profiles, temperature profiles, and Nusselt number.

  15. Electrochemical characterization of tenoxicam using a bare carbon paste electrode under stagnant and forced convection conditions

    International Nuclear Information System (INIS)

    Guzmán-Hernández, D.S.; Ramírez-Silva, M.T.; Palomar-Pardavé, M.; Corona-Avendaño, S.; Galano, Annia; Rojas-Hernández, A.; Romero-Romo, M.

    2012-01-01

    Highlights: ► Tenoxicam electrochemical oxidation was studied from aqueous solution with a CPE. ► Both stagnant and forced convection conditions were considered. ► We found tenoxicam electrochemical oxidation is a mass transfer-controlled process. ► An EC mechanism was found where the electrodic and chemical kinetics are fast. ► It was found that in this case n = 2 and E 1/2 = 0.770 V. ► Calculated D was 4.09 × 10 −6 cm 2 s −1 which compares with theoretically estimated. - Abstract: From potentiostatic current transients and voltammetry studies, carried out under both stagnant and forced convection conditions, the tenoxicam electrochemical behavior on a bare carbon paste rotating disk electrode was assessed in an aqueous solution (pH = 0.403). It was found that tenoxicam's electrochemical oxidation is a mass transfer-controlled process where a current peak is clearly formed at around 0.74 V when the potential scan was varied in the positive direction. However, when the potential was switched to the negative direction, up to the initial potential value, no reduction peak was formed. Tenoxicam's electrochemical oxidation follows an EC mechanism where the electrodic and chemical kinetics are fast. From sample-current voltammetry both the number of electrons, n, that tenoxicam losses during its electro-oxidation and its half-wave potential, E 1/2 , were determined to be 2 and 0.770 V vs. Ag/AgCl, respectively. Moreover, from differential pulse voltammetry plots it was confirmed that effectively in this case n = 2. Considering 2 electrons and both the Randles-Sevcik and Cotrell equations, the tenoxicam's diffusion coefficient, D, was determined to be (3.745 ± 0.077) × 10 −6 and (4.116 ± 0.086) × 10 −6 cm 2 s −1 , respectively. From linear sweep voltammetry plots recorded under forced convection conditions, it was found that Levich's equation describes adequately the limiting current recorded as a function of the electrode rotation rate, from

  16. A numerical investigation of laminar forced convection in a solar collector with non-circular duct

    Directory of Open Access Journals (Sweden)

    Teleszewski Tomasz Janusz

    2017-01-01

    Full Text Available This paper presents a two-dimensional numerical study to investigate laminar flow in a flat plate solar collector with non-circular duct (regular polygonal, elliptical, and Cassini oval shape featuring forced convection with constant axial wall heat flux and constant peripheral wall temperature (H1 condition. Applying the velocity profile obtained for the duct laminar flow, the energy equation was solved exactly for the constant wall heat flux using the Boundary Element Method (BEM. Poiseuille and Nusselt numbers were obtained for flows having a different number of geometrical factors. The results are presented and discussed in the form of tables and graphs. The area goodness factor and volume goodness factor are calculated. The predicted correlations for Poiseuille and Nusselt numbers may be a very useful resource for the design and optimization of solar collectors with non-circular ducts.

  17. Experiments on forced convection form a horizontal heated plate in a packed bed of glass spheres

    Energy Technology Data Exchange (ETDEWEB)

    Renken, K.J. (Univ. of Wisconsin, Milwaukee (USA)); Poulikakos, D. (Univ. of Illinois, Chicago (USA))

    1989-02-01

    This paper presents an experimental investigation of boundary-layer forced convective heat transfer from a flat isothermal plate in a packed bed of spheres. Extensive experimental results are reported for the thermal boundary-layer thickness, the temperature field, and the local wall heat flux (represented by the local Nusselt number). Theoretical findings of previous investigations using the Darcy flow model as well as a general model for themomentum equation accouting for flow inertia and macroscopic shear wtih and without variable porosity are used to evaluate the theoretical models. Several trends are revealed regarding the conditions of validity of these flow models. Overall the general flow model including variable porosity appears to perform better, even through the need for serious improvements in modeling becomes apparent.

  18. Analysis of Forced Convection Heat Transfer for Axial Annular Flow of Giesekus Viscoelastic Fluid

    Energy Technology Data Exchange (ETDEWEB)

    Mohseni, Mehdi Moayed; Rashidi, Fariborz; Movagar, Mohammad Reza Khorsand [Amirkabir University of Technology, Tehran (Iran, Islamic Republic of)

    2015-02-15

    Analytical solutions for the forced convection heat transfer of viscoelastic fluids obeying the Giesekus model are obtained in a concentric annulus under laminar flow for both thermal and hydrodynamic fully developed conditions. Boundary conditions are assumed to be (a) constant fluxes at the walls and (b) constant temperature at the walls. Temperature profiles and Nusselt numbers are derived from dimensionless energy equation. Subsequently, effects of elasticity, mobility parameter and viscous dissipation are discussed. Results show that by increasing elasticity, Nusselt number increases. However, this trend is reversed for constant wall temperature when viscous dissipation is weak. By increasing viscous dissipation, the Nusselt number decreases for the constant flux and increases for the constant wall temperature. For the wall cooling case, when the viscous dissipation exceeds a critical value, the generated heat overcomes the heat which is removed at the walls, and fluid heats up longitudinally.

  19. A theoretical study of the spheroidal droplet evaporation in forced convection

    Energy Technology Data Exchange (ETDEWEB)

    Li, Jie, E-mail: leejay1986@163.com; Zhang, Jian

    2014-11-07

    In many applications, the shape of a droplet may be assumed to be an oblate spheroid. A theoretical study is conducted on the evaporation of an oblate spheroidal droplet under forced convection conditions. Closed-form analytical expressions of the mass evaporation rate for an oblate spheroid are derived, in the regime of controlled mass-transfer and heat-transfer, respectively. The variation of droplet size during the evaporation process is presented in the regime of shrinking dynamic model. Comparing with the droplets having the same surface area, an increase in the aspect ratio enhances the mass evaporation rate and prolongs the burnout time. - Highlights: • Fully algebraic solutions for the spheroidal droplet evaporation rate is obtained. • We examine the effect of aspect ratio on the droplet evaporation. • We propose a calculation method of Nusselt number for spheroidal droplet.

  20. Study of turbulent natural-circulation flow and low-Prandtl-number forced-convection flow

    International Nuclear Information System (INIS)

    Chung, K.S.; Thompson, D.H.

    1980-01-01

    Calculational methods and results are discussed for the coupled energy and momentum equations of turbulent natural circulation flow and low Prandtl number forced convection flow. The objective of this paper is to develop a calculational method for the study of the thermal-hydraulic behavior of coolant flowing in a liquid metal fast breeder reactor channel under natural circulation conditions. The two-equation turbulence model is used to evaluate the turbulent momentum transport property. Because the analogy between momentum transfer and heat transfer does not generally hold for low Prandtl number fluid and natural circulation flow conditions, the turbulent thermal conductivity is calculated independently using equations similar to the two-equation turbulence model. The numerical technique used in the calculation is the finite element method

  1. Thermally developing forced convection and the corresponding thermal stresses in a porous plate channel

    Institute of Scientific and Technical Information of China (English)

    YANG Xiao; LIU Xuemei

    2007-01-01

    Based on the Darcy fluid model, by considering the effects of viscous dissipation due to the interaction between solid skeleton and pore fluid flow and thermal conduction in the direction of the fluid flow, the thermally developing forced convection of the local thermal equili- brium and the corresponding thermal stresses in a semi- infmite saturated porous plate channel are investigated in this paper. The expressions of temperature, local Nusselt number and corresponding thermal stresses are obtained by means of the Fourier series, and the distributions of the same are also shown. Furthermore, influences of the Péclet number (Pe) and Brinkman number (Br) on temperature, Nusselt number (Nu) and thermal stress are revealed numerically.

  2. A theoretical study of the spheroidal droplet evaporation in forced convection

    International Nuclear Information System (INIS)

    Li, Jie; Zhang, Jian

    2014-01-01

    In many applications, the shape of a droplet may be assumed to be an oblate spheroid. A theoretical study is conducted on the evaporation of an oblate spheroidal droplet under forced convection conditions. Closed-form analytical expressions of the mass evaporation rate for an oblate spheroid are derived, in the regime of controlled mass-transfer and heat-transfer, respectively. The variation of droplet size during the evaporation process is presented in the regime of shrinking dynamic model. Comparing with the droplets having the same surface area, an increase in the aspect ratio enhances the mass evaporation rate and prolongs the burnout time. - Highlights: • Fully algebraic solutions for the spheroidal droplet evaporation rate is obtained. • We examine the effect of aspect ratio on the droplet evaporation. • We propose a calculation method of Nusselt number for spheroidal droplet

  3. A numerical investigation of laminar forced convection in a solar collector with non-circular duct

    Science.gov (United States)

    Janusz Teleszewski, Tomasz

    2017-11-01

    This paper presents a two-dimensional numerical study to investigate laminar flow in a flat plate solar collector with non-circular duct (regular polygonal, elliptical, and Cassini oval shape) featuring forced convection with constant axial wall heat flux and constant peripheral wall temperature (H1 condition). Applying the velocity profile obtained for the duct laminar flow, the energy equation was solved exactly for the constant wall heat flux using the Boundary Element Method (BEM). Poiseuille and Nusselt numbers were obtained for flows having a different number of geometrical factors. The results are presented and discussed in the form of tables and graphs. The area goodness factor and volume goodness factor are calculated. The predicted correlations for Poiseuille and Nusselt numbers may be a very useful resource for the design and optimization of solar collectors with non-circular ducts.

  4. Thermo-electrochemical model for forced convection air cooling of a lithium-ion battery module

    International Nuclear Information System (INIS)

    Tong, Wei; Somasundaram, Karthik; Birgersson, Erik; Mujumdar, Arun S.; Yap, Christopher

    2016-01-01

    Highlights: • Coupled thermal-electrochemical model for a Li-ion battery module resolving every functional layer in all cells. • Parametric analysis of forced convection air cooling of Li-ion battery module with a detailed multi-scale model. • Reversing/reciprocating airflow for Li-ion battery module thermal management provides uniform temperature distribution. - Abstract: Thermal management is critical for safe and reliable operation of lithium-ion battery systems. In this study, a one-dimensional thermal-electrochemical model of lithium-ion battery interactively coupled with a two-dimensional thermal-fluid conjugate model for forced convection air cooling of a lithium-ion battery module is presented and solved numerically. This coupled approach makes the model more unique and detailed as transport inside each cell in the battery module is solved for and thus covering multiple length and time scales. The effect of certain design and operating parameters of the thermal management system on the performance of the battery module is assessed using the coupled model. It is found that a lower temperature increase of the battery module can be achieved by either increasing the inlet air velocity or decreasing the distance between the cells. Higher air inlet velocity, staggered cell arrangement or a periodic reversal airflow of high reversal frequency results in a more uniform temperature distribution in the module. However, doing so increases the parasitic load as well as the volume of the battery module whence a trade-off should be taken into account between these parameters.

  5. Performance of a Forced-Convection Greenhouse Dryer for Fish Drying

    Directory of Open Access Journals (Sweden)

    Martunis Martunis

    2013-04-01

    Full Text Available ABSTRACT. This research present experimental performance of a forced convection greenhouse dryer for drying of fish. The greenhouse dryer was installed at Aceh province, Indonesia. It has a concrete floor with the area of 6×4 m2. The roof of dryer is built in semi-cylindrical shape and covered with transparent polycarbonate sheets. Two axial flow fans powered by a 50-watt solar cell module was used to generate forced convection for ventilating the dryer.To investigate its performance, the dryer was used to dry two batches of fish. The Results showed that to dry 50 kg fish with initial moisture 68 % required 11 hours. Incontrast, to dry the same amount of fish using sun drying take a time about 2 days. The air temperature inside greenhouse dryer at noon in the clear day was 45-55°C. Kinerja Pengering Rumah Kaca Dengan Metode Konveksi Paksa Untuk Pengeringan Ikan ABSTRAK. Penelitian ini memperlihatkan hasil percobaan terhadap kinerja pengering rumah kaca dengan metode konveksi udara secara paksa pada pengeringan ikan. Penelitian pengering rumah kaca ini dilakukan di Propinsi Aceh, Indonesia. Pengering ini berlantaikan beton dengan luas sebesar 6x4 m2. .Atapnya dibuat berbentuk semi-selinder dan ditutup dengan lembaran plastik transparan berbahan polikarbonat. Dua buah kipas dengan aliran udara secara aksial dipasang dengan sumber daya berasal dari panel surya sebesar 50 Watt dan dipakai untuk menghasilkan konveksi udara paksa pada ventilasi pengering. Untuk menginvestigasi kinerja rumah kaca ini, pengering ini digunakan untuk mengeringkan dua tumpukan ikan. Hasilnya menunjukkan bahwa untuk mengeringkan sebanyak 50 kg ikan dengan kadar air awalnya sebesar 68% membutuhkan waktu selama 11 jam. Sebaliknya, dengan menggunakan sinar matahari secara langsung, untuk mengeringkan ikan dengan jumlah yang sama, maka waktu yang dibutuhkan lebih lama yaitu sekitar 2 hari. Suhu udara di dalam rumah pengering tepat pada siang hari yang cerah berkisar antara 45

  6. NUMERICAL STUDY OF DEVELOPING LAMINAR FORCED CONVECTION OF A NANOFLUID HEAT TRANSFER IN AN ANNULAR HORIZONTAL PIPE

    Directory of Open Access Journals (Sweden)

    M BENKHEDDA

    2014-12-01

    Full Text Available This study reports numerical simulation for 3D laminar forced convection of a nanofluid flow in horizontal annulus with constant heat flux at the outer cylinder will the inner cylinder is considered adiabatic. The numerical model is carried out by solving the governing equation of continuity, momentum and energy using take account for thee finite volume method, with the assistance of SIMPLER algorithm. The results shows that for the Reynolds numbers and Prandtl fixed, the dimensionless velocity profile for the laminar forced convection of a nanofluid consisting of water does not vary with the volume concentration of nanoparticles while the effect of the concentration of nanoparticles on the temperature of the mass is significant nanofluid. These results are consistent with those found in the literature. In general the use of nanofluid with a volume concentration of nanoparticles causes a increase in the coefficient of heat transfer by convection.

  7. Experimental investigation of forced-convection in a finned rhombic tube of the flat-plate solar collectors

    DEFF Research Database (Denmark)

    Taherian, Hessam; Yazdanshenas, Eshagh

    2006-01-01

    Due to scarcity of literature on forced-convection heat transfer in a solar collector with rhombic cross-section absorbing tubes, a series of experiments was arranged and conducted to determine heat transfer coefficient. In this study, a typical rhombic cross-section finned tube of flat...

  8. Dynamical and statistical phenomena of circulation and heat transfer in periodically forced rotating turbulent Rayleigh-Bénard convection

    NARCIS (Netherlands)

    Sterl, S.H.; Li, H.M.; Zhong, J.Q.

    2016-01-01

    In this paper, we present results from an experimental study into turbulent Rayleigh-Bénard convection forced externally by periodically modulated unidirectional rotation rates. We find that the azimuthal rotation velocity θ(t) and thermal amplitude δ(t) of the large-scale circulation (LSC) are

  9. Forcings and feedbacks on convection in the 2010 Pakistan flood: Modeling extreme precipitation with interactive large-scale ascent

    Science.gov (United States)

    Nie, Ji; Shaevitz, Daniel A.; Sobel, Adam H.

    2016-09-01

    Extratropical extreme precipitation events are usually associated with large-scale flow disturbances, strong ascent, and large latent heat release. The causal relationships between these factors are often not obvious, however, the roles of different physical processes in producing the extreme precipitation event can be difficult to disentangle. Here we examine the large-scale forcings and convective heating feedback in the precipitation events, which caused the 2010 Pakistan flood within the Column Quasi-Geostrophic framework. A cloud-revolving model (CRM) is forced with large-scale forcings (other than large-scale vertical motion) computed from the quasi-geostrophic omega equation using input data from a reanalysis data set, and the large-scale vertical motion is diagnosed interactively with the simulated convection. Numerical results show that the positive feedback of convective heating to large-scale dynamics is essential in amplifying the precipitation intensity to the observed values. Orographic lifting is the most important dynamic forcing in both events, while differential potential vorticity advection also contributes to the triggering of the first event. Horizontal moisture advection modulates the extreme events mainly by setting the environmental humidity, which modulates the amplitude of the convection's response to the dynamic forcings. When the CRM is replaced by either a single-column model (SCM) with parameterized convection or a dry model with a reduced effective static stability, the model results show substantial discrepancies compared with reanalysis data. The reasons for these discrepancies are examined, and the implications for global models and theoretical models are discussed.

  10. Preliminary experimentally-validated forced and mixed convection computational simulations of the Rotatable Buoyancy Tunnel

    International Nuclear Information System (INIS)

    Clifford, Corey E.; Kimber, Mark L.

    2015-01-01

    Although computational fluid dynamics (CFD) has not been directly utilized to perform safety analyses of nuclear reactors in the United States, several vendors are considering adopting commercial numerical packages for current and future projects. To ensure the accuracy of these computational models, it is imperative to validate the assumptions and approximations built into commercial CFD codes against physical data from flows analogous to those in modern nuclear reactors. To this end, researchers at Utah State University (USU) have constructed the Rotatable Buoyancy Tunnel (RoBuT) test facility, which is designed to provide flow and thermal validation data for CFD simulations of forced and mixed convection scenarios. In order to evaluate the ability of current CFD codes to capture the complex physics associated with these types of flows, a computational model of the RoBuT test facility is created using the ANSYS Fluent commercial CFD code. The numerical RoBuT model is analyzed at identical conditions to several experimental trials undertaken at USU. Each experiment is reconstructed numerically and evaluated with the second-order Reynolds stress model (RSM). Two different thermal boundary conditions at the heated surface of the RoBuT test section are investigated: constant temperature (isothermal) and constant surface heat flux (isoflux). Additionally, the fluid velocity at the inlet of the test section is varied in an effort to modify the relative importance of natural convection heat transfer from the heated wall of the RoBuT. Mean velocity, both in the streamwise and transverse directions, as well as components of the Reynolds stress tensor at three points downstream of the RoBuT test section inlet are compared to results obtained from experimental trials. Early computational results obtained from this research initiative are in good agreement with experimental data obtained from the RoBuT facility and both the experimental data and numerical method can be used

  11. A numerical model of the shortbread baking process in a forced convection oven

    International Nuclear Information System (INIS)

    Kokolj, Uroš; Škerget, Leopold; Ravnik, Jure

    2017-01-01

    Highlights: • The evaporation of water had a significant effect on the temperature field. • The numerical model associated the grade of browning with the temperature field. • The results of the numerical and experimental grade of browning are comparable. • The difference between the measured and simulated temperature at the oven was 2.8 K. - Abstract: The objective of all manufacturers and users of ovens is to achieve uniform browning of various baked foods. In recent years, manufacturers have found it difficult to achieve this, due to the rapid appearance of new trends and due to progressively shorter development times. In this paper, we present the development and validation of a time-dependent 3D computational fluid dynamics model, which enables the numerical prediction of the baking performance and grade of browning of a forced convection oven. Flow and heat transfer of hot air in an oven, where a round heating element and a fan are both operating, are simulated. Radiative and convective heat transfer is taken into account. We found, that it is necessary to include water evaporation in the model. The numerical model was validated by performing experimental measurements of temperature and by performing baking tests of shortbread. After baking, the grade of browning was measured for the shortbread. To determine the grade of browning, the method of identification of colour contrasts was used, based on the colour space CIE L"∗a"∗b. Based on the results, we proposed a linear model, which enabled the prediction of the grade of browning based on the results of the fluid dynamics simulation.

  12. The diurnal interaction between convection and peninsular-scale forcing over South Florida

    Science.gov (United States)

    Cooper, H. J.; Simpson, J.; Garstang, M.

    1982-01-01

    One of the outstanding problems in modern meterology is that of describing in detail the manner in which larger scales of motion interact with, influence and are influenced by successively smaller scales of motion. The present investigation is concerned with a study of the diurnal evolution of convection, the interaction between the peninsular-scale convergence and convection, and the role of the feedback produced by the cloud-scale downdrafts in the maintenance of the convection. Attention is given to the analysis, the diurnal cycle of the network area-averaged divergence, convective-scale divergence, convective mass transports, and the peninsular scale divergence. The links established in the investigation between the large scale (peninsular), the mesoscale (network), and the convective scale (cloud) are found to be of fundamental importance to the understanding of the initiation, maintenance, and decay of deep precipitating convection and to its theoretical parameterization.

  13. Conceptual Design of Forced Convection Molten Salt Heat Transfer Testing Loop

    Energy Technology Data Exchange (ETDEWEB)

    Manohar S. Sohal; Piyush Sabharwall; Pattrick Calderoni; Alan K. Wertsching; S. Brandon Grover

    2010-09-01

    This report develops a proposal to design and construct a forced convection test loop. A detailed test plan will then be conducted to obtain data on heat transfer, thermodynamic, and corrosion characteristics of the molten salts and fluid-solid interaction. In particular, this report outlines an experimental research and development test plan. The most important initial requirement for heat transfer test of molten salt systems is the establishment of reference coolant materials to use in the experiments. An earlier report produced within the same project highlighted how thermophysical properties of the materials that directly impact the heat transfer behavior are strongly correlated to the composition and impurities concentration of the melt. It is therefore essential to establish laboratory techniques that can measure the melt composition, and to develop purification methods that would allow the production of large quantities of coolant with the desired purity. A companion report describes the options available to reach such objectives. In particular, that report outlines an experimental research and development test plan that would include following steps: •Molten Salts: The candidate molten salts for investigation will be selected. •Materials of Construction: Materials of construction for the test loop, heat exchangers, and fluid-solid corrosion tests in the test loop will also be selected. •Scaling Analysis: Scaling analysis to design the test loop will be performed. •Test Plan: A comprehensive test plan to include all the tests that are being planned in the short and long term time frame will be developed. •Design the Test Loop: The forced convection test loop will be designed including extensive mechanical design, instrument selection, data acquisition system, safety requirements, and related precautionary measures. •Fabricate the Test Loop. •Perform the Tests. •Uncertainty Analysis: As a part of the data collection, uncertainty analysis will

  14. The sensitivity of tropical convective precipitation to the direct radiative forcings of black carbon aerosols emitted from major regions

    Directory of Open Access Journals (Sweden)

    C. Wang

    2009-10-01

    Full Text Available Previous works have suggested that the direct radiative forcing (DRF of black carbon (BC aerosols are able to force a significant change in tropical convective precipitation ranging from the Pacific and Indian Ocean to the Atlantic Ocean. In this in-depth analysis, the sensitivity of this modeled effect of BC on tropical convective precipitation to the emissions of BC from 5 major regions of the world has been examined. In a zonal mean base, the effect of BC on tropical convective precipitation is a result of a displacement of ITCZ toward the forcing (warming hemisphere. However, a substantial difference exists in this effect associated with BC over different continents. The BC effect on convective precipitation over the tropical Pacific Ocean is found to be most sensitive to the emissions from Central and North America due to a persistent presence of BC aerosols from these two regions in the lowermost troposphere over the Eastern Pacific. The BC effect over the tropical Indian and Atlantic Ocean is most sensitive to the emissions from South as well as East Asia and Africa, respectively. Interestingly, the summation of these individual effects associated with emissions from various regions mostly exceeds their actual combined effect as shown in the model run driven by the global BC emissions, so that they must offset each other in certain locations and a nonlinearity of this type of effect is thus defined. It is known that anthropogenic aerosols contain many scattering-dominant constituents that might exert an effect opposite to that of absorbing BC. The combined aerosol forcing is thus likely differing from the BC-only one. Nevertheless, this study along with others of its kind that isolates the DRF of BC from other forcings provides an insight of the potentially important climate response to anthropogenic forcings particularly related to the unique particulate solar absorption.

  15. Effect of Thermophysical Properties on Coupled Heat and Mass Transfer in Porous Material during Forced Convective Drying

    Directory of Open Access Journals (Sweden)

    Wei Cai

    2014-06-01

    Full Text Available The convective drying kinetics of porous medium was investigated numerically. A mathematical model for forced convective drying was established to estimate the evolution of moisture content and temperature inside multilayered porous medium. The set of coupled partial differential equations with the specified boundary and initial conditions were solved numerically using a MATLAB code. An experimental setup of convective drying had been constructed and validated the theoretical model. The temperature and moisture content of the potato samples were dynamically measured and recorded during the drying process. Results indicate that thermal diffusion coefficient has significant positive impact on temperature distribution and mass diffusion coefficient might directly affect the moisture content distribution. Soret effect has a significant impact on heat flux and temperature distribution in the presence of large temperature gradient.

  16. Thermal convection in a closed cavity in zero-gravity space conditions with stationary magnetic forces

    International Nuclear Information System (INIS)

    Lyubimova, T; Mailfert, A

    2013-01-01

    The paper deals with the investigation of thermo-magnetic convection in a paramagnetic liquid subjected to a non-uniform magnetic field in weightlessness conditions. Indeed, in zero-g space conditions such as realized in International Space Station (ISS), or in artificial satellite, or in free-flight space vessels, the classical thermo-gravitational convection in fluid disappears. In any cases, it may be useful to restore the convective thermal exchange inside fluids such as liquid oxygen. In this paper, the restoration of heat exchange by the way of creation of magnetic convection is numerically studied.

  17. Forced Convection Heat Transfer of a sphere in Packed Bed Arrangement

    International Nuclear Information System (INIS)

    Lee, Dong-Young; Chung, Bum-Jin

    2016-01-01

    This paper analysis and discuss the forced convective heat transfer from heated single sphere, which is buried in unheated packed bed, depending on Re d with porosity. The present work determines the test matrix for the packed bed experiment. And this study discuss difference of heat transfer according to the location of heated sphere and compared heated bed with heated sphere in packed bed and compared FCC (Face Centered Cubic), HCP (Hexagonal Closed Packed) structured packed bed with random packed. This paper is to discuss and make the plan to experiment the heat transfer for depending on location of heated single sphere in unheated packed bed, to compare single sphere in packed bed with heated packed bed and to compare the structured packed bed with random packed bed. The Nu d increase as heated single sphere is close to the wall and bottom because of increasing porosity and enhancing eddy motion respectively. The existing experiment of heated sphere in packed bed do not consider the preheating effect which decrease heat transfer on downstream. The heat transfer rate of structured packed bed is different from random packed bed because of unsteady flow in random packed bed. In this study, mass transfer experiments will replace heat transfer experiments based on analogy concept. An electroplating system is adopted using limiting current technique

  18. Forced convective heat transfer in boundary layer flow of Sisko fluid over a nonlinear stretching sheet.

    Science.gov (United States)

    Munir, Asif; Shahzad, Azeem; Khan, Masood

    2014-01-01

    The major focus of this article is to analyze the forced convective heat transfer in a steady boundary layer flow of Sisko fluid over a nonlinear stretching sheet. Two cases are studied, namely (i) the sheet with variable temperature (PST case) and (ii) the sheet with variable heat flux (PHF case). The heat transfer aspects are investigated for both integer and non-integer values of the power-law index. The governing partial differential equations are reduced to a system of nonlinear ordinary differential equations using appropriate similarity variables and solved numerically. The numerical results are obtained by the shooting method using adaptive Runge Kutta method with Broyden's method in the domain[Formula: see text]. The numerical results for the temperature field are found to be strongly dependent upon the power-law index, stretching parameter, wall temperature parameter, material parameter of the Sisko fluid and Prandtl number. In addition, the local Nusselt number versus wall temperature parameter is also graphed and tabulated for different values of pertaining parameters. Further, numerical results are validated by comparison with exact solutions as well as previously published results in the literature.

  19. Desorption isotherms, drying characteristics and qualities of glace tropical fruits undergoing forced convection solar drying

    Energy Technology Data Exchange (ETDEWEB)

    Jamradloedluk, Jindaporn; Wiriyaumpaiwong, Songchai [Mahasarakham Univ. Khamriang, Kantarawichai, Mahasarakham (Thailand)

    2008-07-01

    Solar energy, a form of sustainable energy, has a great potential for a wide variety of applications because it is abundant and accessible, especially for countries located in the tropical region. Drying process is one of the prominent techniques for utilization of solar energy. This research work proposes a forced convection solar drying of osmotically pretreated fruits viz. mango, guava, and pineapple. The fruit cubes with a dimension of 1cm x 1cm x 1cm were immersed in 35% w./w. sucrose solution prior to the drying process. Drying kinetics, color and hardness of the final products obtained from solar drying were investigated and compared with those obtained from open air-sun drying. Desorption isotherms of the osmosed fruits were also examined and five mathematical models were used to fit the desorption curves. Experimental results revealed that solar drying provided higher drying rate than natural sun drying. Color of glace fruit processed by solar drying was more intense, indicated by lower value of lightness and higher value of yellowness, than that processed by sun drying. Hardness of the products dehydrated by both drying methods, however, was not significantly different (p>0.05). Validation of the mathematical models developed showed that the GAB model was most effective for describing desorption isotherms of osmotically pretreated mango and pineapple whereas Peleg's model was most effective for describing desorption isotherms of osmotically pretreated guava. (orig.)

  20. Experimental and numerical studies on the treatment of wet astronaut trash by forced-convection drying

    Science.gov (United States)

    Arquiza, J. M. R. Apollo; Morrow, Robert; Remiker, Ross; Hunter, Jean B.

    2017-09-01

    During long-term space missions, astronauts generate wet trash, including food containers with uneaten portions, moist hygiene wipes and wet paper towels. This waste produces two problems: the loss of water and the generation of odors and health hazards by microbial growth. These problems are solved by a closed-loop, forced-convection, heat-pump drying system which stops microbial activity by both pasteurization and desiccation, and recovers water in a gravity-independent porous media condensing heat exchanger. A transient, pseudo-homogeneous continuum model for the drying of wet ersatz trash was formulated for this system. The model is based on the conservation equations for energy and moisture applied to the air and solid phases and includes the unique trash characteristic of having both dry and wet solids. Experimentally determined heat and mass transfer coefficients, together with the moisture sorption equilibrium relationship for the wet material are used in the model. The resulting system of differential equations is solved by the finite-volume method as implemented by the commercial software COMSOL. Model simulations agreed well with experimental data under certain conditions. The validated model will be used in the optimization of the entire closed-loop system consisting of fan, air heater, dryer vessel, heat-pump condenser, and heat-recovery modules.

  1. Constitutive correlations for wire-wrapped subchannel analysis under forced and mixed convection conditions. Part 1

    International Nuclear Information System (INIS)

    Cheng, S.K.; Todreas, N.E.

    1984-08-01

    A simple subchannel analysis method based on the ENERGY series of codes, ENERGY-IV, has been established for predicting the temperature field in a single isolated wire-wrapped Liquid Metal Fast Breeder Reactor (LMFBR) subassembly under steady state forced and mixed convection conditions. The ENERGY-IV is a totally empirical code employed for fast running purposes and requires well calibrated lead length averaged input parameters to achieve satisfactory predictions. These input parameters were identified to be the inlet flow split parameters, the subchannel friction factors, the interchannel mixing parameters, the conduction shape factor, and the transverse velocity at the edge gap. Experiments were performed in a 37-pin wire-wrapped rod bundle with a geometry between that of a typical LMFBR fuel subassembly and blanket subassembly for filling the gap in the available data base for the input parameters. The isokinetic extraction method for measuring subchannel velocity, the pitot-static probe for measuring pressure drop, and the salt tracer injection method for estimating the interchannel mixing, were used in these experiments

  2. Modeling and analysis of a robust thermal control system based on forced convection thermal switches

    Science.gov (United States)

    Williams, Andrew D.; Palo, Scott E.

    2006-05-01

    There is a critical need, not just in the Department of Defense (DOD) but the entire space industry, to reduce the development time and overall cost of satellite missions. To that end, the DOD is actively pursuing the capability to reduce the deployment time of a new system from years to weeks or even days. The goal is to provide the advantages space affords not just to the strategic planner but also to the battlefield commanders. One of the most challenging aspects of this problem is the satellite's thermal control system (TCS). Traditionally the TCS must be vigorously designed, analyzed, tested, and optimized from the ground up for every satellite mission. This "reinvention of the wheel" is costly and time intensive. The next generation satellite TCS must be modular and scalable in order to cover a wide range of applications, orbits, and mission requirements. To meet these requirements a robust thermal control system utilizing forced convection thermal switches was investigated. The problem was investigated in two separate stages. The first focused on the overall design of the bus. The second stage focused on the overarching bus architecture and the design impacts of employing a thermal switch based TCS design. For the hot case, the fan provided additional cooling to increase the heat transfer rate of the subsystem. During the cold case, the result was a significant reduction in survival heater power.

  3. Numerical investigation of forced convection heat transfer in unsteady flow past a row of square cylinders

    International Nuclear Information System (INIS)

    Chatterjee, Dipankar; Biswas, Gautam; Amiroudine, Sakir

    2009-01-01

    This paper presents the unsteady laminar forced convection heat transfer from a row of five isothermal square cylinders placed in a side-by-side arrangement at a Reynolds number of 150. The numerical simulations are performed using a finite volume code based on the PISO algorithm in a collocated grid system. Special attention is paid to investigate the effect of the spacing between the cylinders on the overall transport processes for the separation ratios (spacing to size ratio) between 0.2 and 10. No significant interaction between the wakes is observed for spacing greater than four times the diameter at this Reynolds number. However, at smaller spacing, the wakes interact in a complicated manner resulting different thermo-hydrodynamic regimes. The vortex structures and isotherm patterns obtained are systematically presented and discussed for different separation ratios. In addition, the mean and instantaneous drag and lift coefficients, mean and local Nusselt number and Strouhal number are determined and discussed for various separation ratios. A new correlation is derived for mean Nusselt number as a function of separation ratio for such flows.

  4. Forced Convection Heat Transfer of a sphere in Packed Bed Arrangement

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Dong-Young; Chung, Bum-Jin [Kyung Hee University, Yongin (Korea, Republic of)

    2016-10-15

    This paper analysis and discuss the forced convective heat transfer from heated single sphere, which is buried in unheated packed bed, depending on Re{sub d} with porosity. The present work determines the test matrix for the packed bed experiment. And this study discuss difference of heat transfer according to the location of heated sphere and compared heated bed with heated sphere in packed bed and compared FCC (Face Centered Cubic), HCP (Hexagonal Closed Packed) structured packed bed with random packed. This paper is to discuss and make the plan to experiment the heat transfer for depending on location of heated single sphere in unheated packed bed, to compare single sphere in packed bed with heated packed bed and to compare the structured packed bed with random packed bed. The Nu{sub d} increase as heated single sphere is close to the wall and bottom because of increasing porosity and enhancing eddy motion respectively. The existing experiment of heated sphere in packed bed do not consider the preheating effect which decrease heat transfer on downstream. The heat transfer rate of structured packed bed is different from random packed bed because of unsteady flow in random packed bed. In this study, mass transfer experiments will replace heat transfer experiments based on analogy concept. An electroplating system is adopted using limiting current technique.

  5. A forced convective heat transfer model for two-phase hydrogen systems

    International Nuclear Information System (INIS)

    Pasch, J.; Anghaie, S.

    2007-01-01

    A consistent event in the use of hydrogen in nuclear thermal propulsion is film boiling, in which the wall heat is so large that liquid can not exist at the wall. Instead, vapor interfaces with the wall and liquid flows in the core of the duct. To better understand heat transfer under these conditions, a select set of hydrogen test data from these conditions are analyzed. This paper presents the results of an extensive literature search for film boiling heat transfer models. A representative cross-section of these models is then applied to the data. The heat transfer coefficient data were found difficult to predict and highly dependent upon the flow regime. Pre-critical heat flux correlations completely fail to predict the heat transfer of inverted film boiling conditions. Pool boiling models for inverted film boiling also are inappropriate. Current force convection models for inverted film boiling, while far better than the previous two classes of models, still generate large predictive errors. It is recommended that for the inverted annular film boiling flow regime the modified equilibrium bulk Dittus-Boelter model be used. For agitated inverted annular film boiling and dispersed film boiling regimes associated with positive equilibrium qualities, the Hendricks model should be used. (A.C.)

  6. Regressed relations for forced convection heat transfer in a direct injection stratified charge rotary engine

    Science.gov (United States)

    Lee, Chi M.; Schock, Harold J.

    1988-01-01

    Currently, the heat transfer equation used in the rotary combustion engine (RCE) simulation model is taken from piston engine studies. These relations have been empirically developed by the experimental input coming from piston engines whose geometry differs considerably from that of the RCE. The objective of this work was to derive equations to estimate heat transfer coefficients in the combustion chamber of an RCE. This was accomplished by making detailed temperature and pressure measurements in a direct injection stratified charge (DISC) RCE under a range of conditions. For each specific measurement point, the local gas velocity was assumed equal to the local rotor tip speed. Local physical properties of the fluids were then calculated. Two types of correlation equations were derived and are described in this paper. The first correlation expresses the Nusselt number as a function of the Prandtl number, Reynolds number, and characteristic temperature ratio; the second correlation expresses the forced convection heat transfer coefficient as a function of fluid temperature, pressure and velocity.

  7. Model Based Analysis of Forced and Natural Convection Effects in an Electrochemical Cell

    Directory of Open Access Journals (Sweden)

    D Brunner

    2017-03-01

    Full Text Available High purity copper, suitable for electrical applications, can only be obtained by electro-winning. The hallmark of this process is its self-induced natural convection through density variations of the electrolyte at both anode and cathode. In order to do this, first the full dynamic complexity of the process needs to be understood. Thus an OpenFoam®-based 2D model of the process has been created. This finite-volume multiphysics approach solves the laminar momentum and copper-ion species conservation equations, as well as local copper-ion conversion kinetics. It uses a Boussinesq approximation to simulate the species-momentum coupling, namely natural draft forces induced by variations of the spatial copper concentration within the fluid. The model shows good agreement with benchmark-cases of real-life electrochemical cells found in literature. An additional flow was imposed at the bottom of a small scale electrochemical cell in order to increase the ionic transport and thereby increase the overall performance of the cell. In a small scale electrochemical cell in strictly laminar flow, the overall performance could be increased and stratification decreased.

  8. Forced convective boiling of water inside helically coiled tube. Characteristics of oscillation of dryout point

    International Nuclear Information System (INIS)

    Nagai, Niro; Sugiyama, Kenta; Takeuchi, Masanori; Yoshikawa, Shinji; Yamamoto, Fujio

    2006-01-01

    The helically coiled tube of heat exchanger is used for the evaporator of prototype fast breeder reactor 'Monju'. This paper aims at the grasp of two-phase flow phenomena of forced convective boiling of water inside helical coiled tube, especially focusing on oscillation phenomena of dryout point. A glass-made helically coiled tube was used to observe the inside water boiling behavior flowing upward, which was heated by high temperature oil outside the tube. This oil was also circulated through a glass made tank to provide the heat source for water evaporation. The criterion for oscillation of dryout point was found to be a function of inlet liquid velocity and hot oil temperature. The observation results suggest the mechanism of dryout point oscillation mainly consists of intensive nucleate boiling near the dryout point and evaporation of thin liquid film flowing along the helical tube. In addition, the oscillation characteristics were experimentally confirmed. As inlet liquid velocity increases, oscillation amplitude also increases but oscillation cycle does not change so much. As hot oil temperature increases, oscillation amplitude and cycle gradually decreases. (author)

  9. Kinetics modeling of the drying of sunflower stem (Helianthus annuus L.) in a forced convection tunnel

    Science.gov (United States)

    López, R.; Vaca, M.; Terres, H.; Lizardi, A.; Morales, J.; Flores, J.; Chávez, S.

    2015-01-01

    The sunflower is an annual plant native to the Americas. It possesses a large inflorescence (flowering head), and its name is derived from the flower's shape and image, which is often used to capture the sun. The plant has a rough, broad, hairy stem, coarsely toothed, with rough leaves, and circular flower heads. The sunflower seeds are appreciated for their oil, which has become a widespread cooking ingredient. Leaves of the sunflower can be used as cattle feed, while the stems contain a fiber that may be used in paper production. Recently this flower has been used in phytoremediation of soils, contaminated with heavy metals. Sunflower has been probed as an efficient phytoextractor of chromium, lead, aluminum, zinc, cadmium from soil. In this work we present the experimental results of the drying of the sunflower stem, cut in 100 mm longitudinal sections, with diameters in the range of 11-18 mm. The aim was to obtain a dry and easy-to-handle final product, since these plants were originally cultivated in order to extract heavy metals from a polluted soil. The dried stems could then be easily confined or sent to recycle premises to concentrate the metals. The drying process was done in forced convection within a hot air tunnel. The used temperature was 60 °C, the velocity of air was 3 m/s and the required times were 8 hours. The initial average wet mass was 28 g and the final value was 5 g, resulting in the aimed product.

  10. Controlling the structure of forced convective flow by means of rotating magnetic-field inductors

    International Nuclear Information System (INIS)

    Sorkin, M.Z.; Mozgirs, O.Kh.

    1993-01-01

    The forced convective flow generated by a rotating magnetic-field inductor is used in a melt as a means of controlling the transfer of mass and heat in the case of directed crystallization. An obvious advantage in using a rotating field is the generation of azimuthal twisting of the fluid, this providing for an evening out of the crystallization conditions in the azimuthal direction under nonsymmetrical boundary conditions in an actual technological process. From the standpoint of affecting the crystallization processes it would be preferable to use an inductor which would allow alteration of the intensity and of the direction of the meridional flow. Mixing in the form of velocity pulsations generated by the inductor within the melt would be if interest from the standpoint of affecting the crystallization processes, in particular to intensify the crystallization purification. The authors propose the use of a double magnetohydrodynmic rotator which consists of two rotating magnetic-field inductors, separated in altitude, with separate power supplies. The supply of power to the inductors with various current loads allows the generation of a controllable nonuniformity in field distribution and in the azimuthal velocity through the altitude and thus allows control of both the intensity and configuration of the meridional flows. The dual rotator makes it possible to purposefully control the structure of the meridional flows and the pulsation component of velocity and can be recommended for use in processes of directed crystallization as well as in crystallization purification. 4 refs., 3 figs

  11. Control of dynamical self-assembly of strongly Brownian nanoparticles through convective forces induced by ultrafast laser

    Science.gov (United States)

    Ilday, Serim; Akguc, Gursoy B.; Tokel, Onur; Makey, Ghaith; Yavuz, Ozgun; Yavuz, Koray; Pavlov, Ihor; Ilday, F. Omer; Gulseren, Oguz

    We report a new dynamical self-assembly mechanism, where judicious use of convective and strong Brownian forces enables effective patterning of colloidal nanoparticles that are almost two orders of magnitude smaller than the laser beam. Optical trapping or tweezing effects are not involved, but the laser is used to create steep thermal gradients through multi-photon absorption, and thereby guide the colloids through convective forces. Convective forces can be thought as a positive feedback mechanism that helps to form and reinforce pattern, while Brownian motion act as a competing negative feedback mechanism to limit the growth of the pattern, as well as to increase the possibilities of bifurcation into different patterns, analogous to the competition observed in reaction-diffusion systems. By steering stochastic processes through these forces, we are able to gain control over the emergent pattern such as to form-deform-reform of a pattern, to change its shape and transport it spatially within seconds. This enables us to dynamically initiate and control large patterns comprised of hundreds of colloids. Further, by not relying on any specific chemical, optical or magnetic interaction, this new method is, in principle, completely independent of the material type being assembled.

  12. Heat transfer in a sodium-to-sodium heat exchanger under conditions of combined force and free convection

    International Nuclear Information System (INIS)

    Jackson, J.D.; Axcell, B.P.; Johnston, S.E.

    1987-01-01

    A combined experimental and theoretical investigation of heat transfer in a vertical tube and annulus, countercurrent flow heat exchanger is reported. The working fluid was liquid sodium. Included in the range of conditions covered were those which are of interest in connection with the low flow rate operation of fast reactor intermediate heat exchanger systems. The heat transfer process ranged from that of pure forced convection to combined forced and free convection. By changing the direction of fluid flow or the direction of heat flow four different configurations were studied. In two cases the convection process was buoyancy aided and in the other two it was buoyancy opposed. Results are presented showing the influence of flow rate and temperature difference on overall heat transfer coefficient for each case. A theoretical model of turbulent flow and heat transfer incorporating influences of buoyancy was used to produce results for the range of conditions covered in the experiments. The predictions of overall heat transfer coefficient were found to be in reasonable general agreement with the measurements. It was clear from these calculations that the influence of buoyancy on heat transfer stemmed largely, under the conditions of the present experiment, from the modification of the convection process due to the distortion of the velocity field. This led to an enhancement of the heat transfer for the buoyancy-aided process and an impairment for the buoyancy-opposed process. The contribution of the turbulent diffusion of heat was relatively small. (author)

  13. PERFORMANCE OF A FORCED CONVECTION SOLAR DRIER INTEGRATED WITH GRAVEL AS HEAT STORAGE MATERIAL FOR CHILI DRYING

    Directory of Open Access Journals (Sweden)

    M. MOHANRAJ

    2009-09-01

    Full Text Available An indirect forced convection solar drier integrated with different sensible heat storage maternal has been developed and tested its performance for drying chili under the metrological conditions of Pollachi, India. The system consists of a flat plate solar air heater with heat storage unit, a drying chamber and a centrifugal blower. Drying experiments have been performed at an air flow rate of 0.25 kg/s. Drying of chili in a forced convection solar drier reduces the moisture content from around 72.8% (wet basis to the final moisture content about 9.1% in 24 h. Average drier efficiency was estimated to be about 21%. The specific moisture extraction rate was estimated to be about 0.87 kg/kWh.

  14. Forced, combined and natural convections of water in a vertical nine-rod bundle with a square lattice and P/C = 1.5

    International Nuclear Information System (INIS)

    El-Genk, M.S.; Su, Bingjing; Guo, Zhanxiong

    1992-01-01

    Heat transfer correlations are developed for forced turbulent and laminar, combined, and natural convections of water in a uniformly heated, square arranged, nine-rod bundle having a P/D ratio of 1.5. In all correlations, the heated equivalent diameter is used in all the dimensionless quantities, and the water physical properties are evaluated at the water bulk temperature. In the experiments, Re is varied from 300 to 2.5 X 10 4 , Pr from 4 to 9, Ra q from 3 x 10 6 to 3 x 10 8 for natural convection and from 5 x 10 7 to 7 , 10 8 for combined convection, and Ri from 0.04 to 100. In both upflow and downflow experiments, the transition from forced turbulent to forced laminar convection occurs at Re T = 6,700; while the transition from forced laminar to buoyancy assisted combined convection occurs at Ri = 2.0. Results show that the rod arrangement in the bundle has little effect on the values of Nu in the forced and natural convection regimes. In general, Nu values for the square arranged rod bundle are less than 8% higher and less than 10% lower than those for a triangularly arranged rod bundle in the forced and natural convection regimes, respectively. 16 refs., 7 figs

  15. Turbulent Convection Insights from Small-Scale Thermal Forcing with Zero Net Heat Flux at a Horizontal Boundary.

    Science.gov (United States)

    Griffiths, Ross W; Gayen, Bishakhdatta

    2015-11-13

    A large-scale circulation, a turbulent boundary layer, and a turbulent plume are noted features of convection at large Rayleigh numbers under differential heating on a single horizontal boundary. These might be attributed to the forcing, which in all studies has been limited to a unidirectional gradient over the domain scale. We instead apply forcing on a length scale smaller than the domain, and with variation in both horizontal directions. Direct numerical simulations show turbulence throughout the domain, a regime transition to a dominant domain-scale circulation, and a region of logarithmic velocity in the boundary layer, despite zero net heat flux. The results show significant similarities to Rayleigh-Bénard convection, demonstrate the significance of plume merging, support the hypothesis that the key driver of convection is the production of available potential energy without necessarily supplying total potential energy, and imply that contributions to domain-scale circulation in the oceans need not be solely from the large-scale gradients of forcing.

  16. Forced convection flow boiling and two-phase flow phenomena in a microchannel

    Science.gov (United States)

    Na, Yun Whan

    2008-07-01

    The present study was performed to numerically analyze the evaporation phenomena through the liquid-vapor interface and to investigate bubble dynamics and heat transfer behavior during forced convective flow boiling in a microchannel. Flow instabilities of two-phase flow boiling in a microchannel were studied as well. The main objective of this research is to investigate the fundamental mechanisms of two-phase flow boiling in a microchannel and provide predictive tools to design thermal management systems, for example, microchannel heat sinks. The numerical results obtained from this study were qualitatively and quantitatively compared with experimental results in the open literature. Physical and mathematical models, accounting for evaporating phenomena through the liquid-vapor interface in a microchannel at constant heat flux and constant wall temperature, have been developed, respectively. The heat transfer mechanism is affected by the dominant heat conduction through the thin liquid film and vaporization at the liquid-vapor interface. The thickness of the liquid film and the pressure of the liquid and vapor phases were simultaneously solved by the governing differential equations. The developed semi-analytical evaporation model that takes into account of the interfacial phenomena and surface tension effects was used to obtain solutions numerically using the fourth-order Runge-Kutta method. The effects of heat flux 19 and wall temperature on the liquid film were evaluated. The obtained pressure drops in a microchannel were qualitatively consistent with the experimental results of Qu and Mudawar (2004). Forced convective flow boiling in a single microchannel with different channel heights was studied through a numerical simulation to investigate bubble dynamics, flow patterns, and heat transfer. The momentum and energy equations were solved using the finite volume method while the liquid-vapor interface of a bubble is captured using the VOF (Volume of Fluid

  17. Similarity Solution for Combined Free-Forced Convection Past a Vertical Porous Plate in a Porous Medium with a Convective Surface Boundary Condition

    Directory of Open Access Journals (Sweden)

    Garg P.

    2016-12-01

    Full Text Available This paper studies the mathematical implications of the two dimensional viscous steady laminar combined free-forced convective flow of an incompressible fluid over a semi infinite fixed vertical porous plate embedded in a porous medium. It is assumed that the left surface of the plate is heated by convection from a hot fluid which is at a temperature higher than the temperature of the fluid on the right surface of the vertical plate. To achieve numerical consistency for the problem under consideration, the governing non linear partial differential equations are first transformed into a system of ordinary differential equations using a similarity variable and then solved numerically under conditions admitting similarity solutions. The effects of the physical parameters of both the incompressible fluid and the vertical plate on the dimensionless velocity and temperature profiles are studied and analysed and the results are depicted both graphically and in a tabular form. Finally, algebraic expressions and the numerical values are obtained for the local skin-friction coefficient and the local Nusselt number.

  18. Kinetics modeling of the drying of sunflower stem (Helianthus annuus L.) in a forced convection tunnel

    International Nuclear Information System (INIS)

    López, R; Vaca, M; Terres, H; Lizardi, A; Morales, J; Flores, J; Chávez, S

    2015-01-01

    The sunflower is an annual plant native to the Americas. It possesses a large inflorescence (flowering head), and its name is derived from the flower's shape and image, which is often used to capture the sun. The plant has a rough, broad, hairy stem, coarsely toothed, with rough leaves, and circular flower heads. The sunflower seeds are appreciated for their oil, which has become a widespread cooking ingredient. Leaves of the sunflower can be used as cattle feed, while the stems contain a fiber that may be used in paper production. Recently this flower has been used in phytoremediation of soils, contaminated with heavy metals. Sunflower has been probed as an efficient phytoextractor of chromium, lead, aluminum, zinc, cadmium from soil. In this work we present the experimental results of the drying of the sunflower stem, cut in 100 mm longitudinal sections, with diameters in the range of 11-18 mm. The aim was to obtain a dry and easy-to-handle final product, since these plants were originally cultivated in order to extract heavy metals from a polluted soil. The dried stems could then be easily confined or sent to recycle premises to concentrate the metals. The drying process was done in forced convection within a hot air tunnel. The used temperature was 60 °C, the velocity of air was 3 m/s and the required times were 8 hours. The initial average wet mass was 28 g and the final value was 5 g, resulting in the aimed product

  19. Determination of blade-to-coolant heat-transfer coefficients on a forced-convection, water-cooled, single-stage turbine

    Science.gov (United States)

    Freche, John C; Schum, Eugene F

    1951-01-01

    Blade-to-coolant convective heat-transfer coefficients were obtained on a forced-convection water-cooled single-stage turbine over a large laminar flow range and over a portion of the transition range between laminar and turbulent flow. The convective coefficients were correlated by the general relation for forced-convection heat transfer with laminar flow. Natural-convection heat transfer was negligible for this turbine over the Grashof number range investigated. Comparison of turbine data with stationary tube data for the laminar flow of heated liquids showed good agreement. Calculated average midspan blade temperatures using theoretical gas-to-blade coefficients and blade-to-coolant coefficients from stationary-tube data resulted in close agreement with experimental data.

  20. The GeoFlow experiment-spherical Rayleigh-Benard convection under the influence of an artificial central force field

    International Nuclear Information System (INIS)

    Gellert, M; Beltrame, P; Egbers, C

    2005-01-01

    Spherical Rayleigh-Benard convection under the influence of an artificial central force field produced by the so-called dielectrophoretic effect is studied as a simplified model of the flow in the outer earth core. The fluid motion there is most probably driving the earth's dynamo and the energy source for the earth's magnetic field. Studying convective flows in earth-like geometry could lead to a deeper understanding of the basics of these processes. This research is a preparatory study for the experiments on the International Space Station (ISS). A bifurcation-theoretical approach shows the existence of heteroclinic cycles between spherical modes (l, l + 1) for the non-rotating system. This behavior depends strong on the radius ratio of the spheres and will be hard to detect in the experiment. For slow rotations interactions of the azimuthal modes (m, m + 1) found in numerical simulations for supercritical states are supposed to be experimentally observable

  1. Thermodynamic investigation and optimization of laminar forced convection in a rotating helical tube heat exchanger

    International Nuclear Information System (INIS)

    Shi, Zhongyuan; Dong, Tao

    2014-01-01

    Highlights: • Variation of total entropy generation is investigated parametrically. • Pareto solution sets for heat transfer and flow friction components are obtained. • Dominant irreversibility component and impact of key variables are discussed. - Abstract: Based on the second law of thermodynamics, an entropy generation investigation is carried out under given dimensionless parameters, i.e. heat exchanger duty, heat flux, with respect to heat transfer and frictional pressure drop in a rotating helical tube heat exchanger with laminar convective flow. The entropy generation from heat transfer across a finite temperature difference – Ψ h decreases with increasing Dean number which represents the impact of centrifugal force induced secondary flow in enhancing heat transfer. Another aspect of increasing Dean number is that intensified momentum transfer in the radial direction also raises the entropy generation from frictional pressure drop – Ψ f , the superposed effect of which yields a decreasing–increasing trend of the total entropy generation-Ψ, a local minimum located in between. The rotation of the helical tube in streamwise (co-rotation) or counter streamwise (counter-rotation) direction leads to a decrease in Ψ h and a increase in Ψ f which complicates the situation that whether or where the minimum of total entropy generation exists is dependent on whether Ψ is dominated by Ψ h or Ψ f or somewhere in between. No difference is discerned between pairs of cases with constant wall temperature and uniform wall heat flux but the same set of variables and parameters. A multi-objective optimization targeting Ψ h and Ψ f simultaneously is implemented using the non-dominated sorting genetic algorithm II (NSGA II). Five solution sets are selected and compared with the conventional optimization in regard of Ψ distinguishing the Ψ h -dominated region from the Ψ f -dominated region, the dimensionless variable η 1 is found to be the most suitable

  2. Single phase induction motor with starting performance

    Energy Technology Data Exchange (ETDEWEB)

    Popescu, M.; Demeter, E. [Research Institute for Electrical Machines, ICPE-ME, Bucharest (Romania); Navrapescu, V. [University `Politehnica` Bucharest, Electrical Engineering Faculty Splaiul Independentei, Bucharest (Romania)

    1997-12-31

    The paper presents problems related to a special type of single phase induction motor. The main novelty consists in the use of a conducting (aluminium casted) shell distributed on the periferic region of the rotor. As a result the starting performance, as well as the rated ones, is much improved in comparison with the conventional construction. (orig.) 4 refs.

  3. Preparation of single phase molybdenum boride

    International Nuclear Information System (INIS)

    Camurlu, Hasan Erdem

    2011-01-01

    Highlights: → Formation of Mo and a mixture of molybdenum boride phases take place in preparation of molybdenum borides. → It is intricate to prepare single phase molybdenum borides. → Formation of single phase MoB from MoO 3 + B 2 O 3 + Mg mixtures has not been reported previously. → Single phase MoB was successfully prepared through a combination of mechanochemical synthesis and annealing process. - Abstract: The formation of MoB through volume combustion synthesis (VCS), and through mechanochemical synthesis (MCS) followed by annealing has been investigated. MoO 3 , B 2 O 3 and Mg were used as reactants while MgO and NaCl were introduced as diluents. Products were leached in dilute HCl solution and were subjected to X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) examinations. Mo was the major phase component in the VCS products under all the experimental conditions. Mo 2 B, MoB, MoB 2 and Mo 2 B 5 were found as minor phases. Products of MCS contained a mixture of Mo 2 B, MoB, MoB 2 and Mo. After annealing the MCS product at 1400 deg. C for 3 h, single phase α-MoB was obtained.

  4. Laminar forced convective/conductive heat transfer by finite element method

    International Nuclear Information System (INIS)

    Kushwaha, H.S.; Kakodkar, A.

    1982-01-01

    The present study is directed at developing a finite element computer program for solution of decoupled convective/conductive heat transfer problems. Penalty function formulation has been used to solve momentum equations and subsequently transient energy equation is solved using modified Crank-Nicolson method. The optimal upwinding scheme has been employed in energy equation to remove oscillations at high Peclet number. (author)

  5. The effect of Coriolis force on nonlinear convection in a porous medium

    Directory of Open Access Journals (Sweden)

    D. H. Riahi

    1994-01-01

    Full Text Available Nonlinear convection in a porous medium and rotating about vertical axis is studied in this paper. An upper bound to the heat flux is calculated by the method initiated first by Howard [6] for the case of infinite Prandtl number.

  6. A critical review of predictive models for the onset of significant void in forced-convection subcooled boiling

    International Nuclear Information System (INIS)

    Dorra, H.; Lee, S.C.; Bankoff, S.G.

    1993-06-01

    This predictive models for the onset of significant void (OSV) in forced-convection subcooled boiling are reviewed and compared with extensive data. Three analytical models and seven empirical correlations are considered in this review. These models and correlations are put onto a common basis and are compared, again on a common basis, with a variety of data. The evaluation of their range of validity and applicability under various operating conditions are discussed. The results show that the correlations of Saha-Zuber seems to be the best model to predict OSV in vertical subcooled boiling flow

  7. The Impact of the Aerosol Direct Radiative Forcing on Deep Convection and Air Quality in the Pearl River Delta Region

    Science.gov (United States)

    Liu, Z.; Yim, Steve H. L.; Wang, C.; Lau, N. C.

    2018-05-01

    Literature has reported the remarkable aerosol impact on low-level cloud by direct radiative forcing (DRF). Impacts on middle-upper troposphere cloud are not yet fully understood, even though this knowledge is important for regions with a large spatial heterogeneity of emissions and aerosol concentration. We assess the aerosol DRF and its cloud response in June (with strong convection) in Pearl River Delta region for 2008-2012 at cloud-resolving scale using an air quality-climate coupled model. Aerosols suppress deep convection by increasing atmospheric stability leading to less evaporation from the ground. The relative humidity is reduced in middle-upper troposphere due to induced reduction in both evaporation from the ground and upward motion. The cloud reduction offsets 20% of the aerosol DRF. The weaker vertical mixing further increases surface aerosol concentration by up to 2.90 μg/m3. These findings indicate the aerosol DRF impact on deep convection and in turn regional air quality.

  8. R-HPDC Process with Forced Convection Mixing Device for Automotive Part of A380 Aluminum Alloy

    Directory of Open Access Journals (Sweden)

    Bing Zhou

    2014-04-01

    Full Text Available The continuing quest for cost-effective and complex shaped aluminum castings with fewer defects for applications in the automotive industries has aroused the interest in rheological high pressure die casting (R-HPDC. A new machine, forced convection mixing (FCM device, based on the mechanical stirring and convection mixing theory for the preparation of semisolid slurry in convenience and functionality was proposed to produce the automotive shock absorber part by R-HPDC process. The effect of barrel temperature and rotational speed of the device on the grain size and morphology of semi-solid slurry were extensively studied. In addition, flow behavior and temperature field of the melt in the FCM process was investigated combining computational fluid dynamics simulation. The results indicate that the microstructure and pore defects at different locations of R-HPDC casting have been greatly improved. The vigorous fluid convection in FCM process has changed the temperature field and composition distribution of conventional solidification. Appropriately increasing the rotational speed can lead to a uniform temperature filed sooner. The lower barrel temperature leads to a larger uniform degree of supercooling of the melt that benefits the promotion of nucleation rate. Both of them contribute to the decrease of the grain size and the roundness of grain morphology.

  9. Properties of forced convection experimental with silicon carbide based nano-fluids

    Science.gov (United States)

    Soanker, Abhinay

    -fluids. The nano-fluid properties were tested at three different volume concentrations; 0.55%, 1% and 1.6%. Thermal conductivity was measured for the three-volume concentration as function of temperature. Thermal conductivity enhancement increased with the temperature and may be attributed to increased Brownian motion of colloidal particles at higher temperatures. Measured thermal conductivity values are compared with results obtained by theoretical model derived in this work. Effect of temperature and volume concentration on viscosity was also measured and reported. Viscosity increase and related consequences are important issues for the use of nano-fluids. Extensive measurements of heat transfer and pressure drop for forced convection in circular pipes with nano-fluids was also conducted. Parameters such as heat transfer coefficient, Nusselt number, pressure drop and a thermal hydraulic performance factor that takes into account the gains made by increase in thermal conductivity as well as penalties related to increase in pressure drop are evaluated for laminar and transition flow regimes. No significant improvement in heat transfer (Nusselt number) compared to its based fluid was observed. It is also observed that the values evaluated for the thermal-hydraulic performance factor (change in heat transfer/change in pressure drop) was under unity for many flow conditions indicating poor overall applicability of SiC based nano-fluids.

  10. Design of Test Loops for Forced Convection Heat Transfer Studies at Supercritical State

    Science.gov (United States)

    Balouch, Masih N.

    Worldwide research is being conducted to improve the efficiency of nuclear power plants by using supercritical water (SCW) as the working fluid. One such SCW reactor considered for future development is the CANDU-Supercritical Water Reactor (CANDU-SCWR). For safe and accurate design of the CANDU-SCWR, a detailed knowledge of forced-convection heat transfer in SCW is required. For this purpose, two supercritical fluid loops, i.e. a SCW loop and an R-134a loop are developed at Carleton University. The SCW loop is designed to operate at pressures as high as 28 MPa, temperatures up to 600 °C and mass fluxes of up to 3000 kg/m2s. The R-134a loop is designed to operate at pressures as high as 6 MPa, temperatures up to 140 °C and mass fluxes in the range of 500-6000 kg/m2s. The test loops designs allow for up to 300 kW of heating power to be imparted to the fluid. Both test loops are of the closed-loop design, where flow circulation is achieved by a centrifugal pump in the SCW loop and three parallel-connected gear pumps in the R-134a loop, respectively. The test loops are pressurized using a high-pressure nitrogen cylinder and accumulator assembly, which allows independent control of the pressure, while simultaneously dampening pump induced pressure fluctuations. Heat exchangers located upstream of the pumps control the fluid temperature in the test loops. Strategically located measuring instrumentation provides information on the flow rate, pressure and temperature in the test loops. The test loops have been designed to accommodate a variety of test-section geometries, ranging from a straight circular tube to a seven-rod bundle, achieving heat fluxes up to 2.5 MW/m2 depending on the test-section geometry. The design of both test loops allows for easy reconfiguration of the test-section orientation relative to the gravitational direction. All the test sections are of the directly-heated design, where electric current passing through the pressure retaining walls of the

  11. Dual reciprocity boundary element analysis for the laminar forced heat convection problem in concentric annulus

    International Nuclear Information System (INIS)

    Choi, Chang Yong

    1999-01-01

    This paper presents a study of the Dual Reciprocity Boundary Element Method (DRBEM) for the laminar heat convection problem in a concentric annulus with constant heat flux boundary condition. DRBEM is one of the most successful technique used to transform the domain integrals arising from the nonhomogeneous term of the poisson equation into equivalent boundary only integrals. This recently developed and highly efficient numerical method is tested for the solution accuracy of the fluid flow and heat transfer study in a concentric annulus. Since their exact solutions are available, DRBEM solutions are verified with different number of boundary element discretization and internal points. The results obtained in this study are discussed with the relative error percentage of velocity and temperature solutions, and potential applicability of the method for the more complicated heat convection problems with arbitrary duct geometries

  12. Predictions of the effect of stratification on superimposed forced and free convection between vertical parallel plates for various boundary conditions

    International Nuclear Information System (INIS)

    Cowan, G.H.; Irvine, T.J. Jr.; Quarini, G.L.

    1983-01-01

    The velocity and temperature equations for laminar buoyancy and forced convection flows between vertical flat parallel plates are presented. The thermal boundary conditions on the plate define the buoyancy driven field, while the channel Reynolds number defines the forced flow field. Specific examples relating to tall narrow channels with laminar convention and to closed high ratio cavities (as may be found in the proposed active and passive insulation systems for sodium cooled fast reactors) are presented. The analysis is limited to the laminar flow regimes, whilst some reactor situations are likely to be turbulent, hence a proposal for a simple extension of this analysis to the turbulent regime is made. It is shown how the analysis can be made to apply to fluids of various Prandtl numbers. (author)

  13. Analysis of optimal Reynolds number for developing laminar forced convection in double sine ducts based on entropy generation minimization principle

    International Nuclear Information System (INIS)

    Ko, T.H.

    2006-01-01

    In the present paper, the entropy generation and optimal Reynolds number for developing forced convection in a double sine duct with various wall heat fluxes, which frequently occurs in plate heat exchangers, are studied based on the entropy generation minimization principle by analytical thermodynamic analysis as well as numerical investigation. According to the thermodynamic analysis, a very simple expression for the optimal Reynolds number for the double sine duct as a function of mass flow rate, wall heat flux, working fluid and geometric dimensions is proposed. In the numerical simulations, the investigated Reynolds number (Re) covers the range from 86 to 2000 and the wall heat flux (q'') varies as 160, 320 and 640 W/m 2 . From the numerical simulation of the developing laminar forced convection in the double sine duct, the effect of Reynolds number on entropy generation in the duct has been examined, through which the optimal Reynolds number with minimal entropy generation is detected. The optimal Reynolds number obtained from the analytical thermodynamic analysis is compared with the one from the numerical solutions and is verified to have a similar magnitude of entropy generation as the minimal entropy generation predicted by the numerical simulations. The optimal analysis provided in the present paper gives worthy information for heat exchanger design, since the thermal system could have the least irreversibility and best exergy utilization if the optimal Re can be used according to practical design conditions

  14. Vertical microphysical profiles of convective clouds as a tool for obtaining aerosol cloud-mediated climate forcings

    Energy Technology Data Exchange (ETDEWEB)

    Rosenfeld, Daniel [Hebrew Univ. of Jerusalem (Israel)

    2015-12-23

    Quantifying the aerosol/cloud-mediated radiative effect at a global scale requires simultaneous satellite retrievals of cloud condensation nuclei (CCN) concentrations and cloud base updraft velocities (Wb). Hitherto, the inability to do so has been a major cause of high uncertainty regarding anthropogenic aerosol/cloud-mediated radiative forcing. This can be addressed by the emerging capability of estimating CCN and Wb of boundary layer convective clouds from an operational polar orbiting weather satellite. Our methodology uses such clouds as an effective analog for CCN chambers. The cloud base supersaturation (S) is determined by Wb and the satellite-retrieved cloud base drop concentrations (Ndb), which is the same as CCN(S). Developing and validating this methodology was possible thanks to the ASR/ARM measurements of CCN and vertical updraft profiles. Validation against ground-based CCN instruments at the ARM sites in Oklahoma, Manaus, and onboard a ship in the northeast Pacific showed a retrieval accuracy of ±25% to ±30% for individual satellite overpasses. The methodology is presently limited to boundary layer not raining convective clouds of at least 1 km depth that are not obscured by upper layer clouds, including semitransparent cirrus. The limitation for small solar backscattering angles of <25º restricts the satellite coverage to ~25% of the world area in a single day. This methodology will likely allow overcoming the challenge of quantifying the aerosol indirect effect and facilitate a substantial reduction of the uncertainty in anthropogenic climate forcing.

  15. Analytical prediction of friction factors and Nusselt numbers of turbulent forced convection in rod bundles with smooth and rough surfaces

    International Nuclear Information System (INIS)

    Su Jian; Silva Freire, Atila P.

    2002-01-01

    A simple analytical method was developed for the prediction of the friction factor, f, of fully developed turbulent flow and the Nusselt number, Nu, of fully developed turbulent forced convection in rod bundles arranged in square or hexagonal arrays. The friction factor equation for smooth rod bundles was presented in a form similar to the friction factor equation for turbulent flow in a circular pipe. An explicit equation for the Nusselt number of turbulent forced convection in rod bundles with smooth surface was developed. In addition, we extended the analysis to rod bundles with rough surface and provided a method for the prediction of the friction factor and the Nusselt number. The method was based on the law of the wall for velocity and the law of the wall for the temperature, which were integrated over the entire flow area to yield algebraic equations for the prediction of f and Nu. The present method is applicable to infinite rod bundles in square and hexagonal arrays with low pitch to rod diameter ratio, P/D<1.2

  16. Thermal response of core and central-cavity components of a high-temperature gas-cooled reactor in the absence of forced convection coolant flow

    International Nuclear Information System (INIS)

    Whaley, R.L.; Sanders, J.P.

    1976-09-01

    A means of determining the thermal responses of the core and the components of a high-temperature gas-cooled reactor after loss of forced coolant flow is discussed. A computer program, using a finite-difference technique, is presented together with a solution of the confined natural convection. The results obtained are reasonable and demonstrate that the computer program adequately represents the confined natural convection

  17. Two-phase pressure drop and heat transfer of sodium at forced convection

    International Nuclear Information System (INIS)

    Grieb, G.

    1989-04-01

    Experiments with sodium for the two-phase pressure drop in vertical tubes with upward flow (internal diameters 6 and 9 mm) performed at the Joint Research Centre (JRC) of the European Communities in Ispra, Italy, and at the Nuclear Research Centre in Karlsruhe (KfK) were evaluated and analysed. Furthermore, experiments for the single-phase and two-phase heat transfer in the grid spaced twelve-rod bundle (p d /d =1.3, rod diameter 8 mm) with flow in axial direction performed at the JRC were evaluated and analysed. The pressure drop measurements were carried out at moderate to high mass flow rates (30 to 4500 kg/(m 2 s)) and at moderate pressures (50 to 300 kPa, density ratio ρ f /ρ g = 950 to 5400). The measurements for the single-phase heat transfer at high heat fluxes (0.16 to 1.6 MW/m 2 ) were carried out in the Reynolds number region (3100 2 s)) and at high heat fluxes (0.46 to 1.6 MW/m 2 ) within the temperature range from 870 to 970 0 C. For the subsequent calculation of the experiments relating to the two-phase pressure drop a computer program was developed, which is based on the so-called slip model. It requires a friction pressure loss correlation and a slip correlation. The tested correlations were not suitable for describing the experimental measurements. Accordingly, simplified equations of momentum were used to develop a new slip correlation for the case of annular flow together with the annular-mist flow, the most important two-phase flow regimes for sodium in the measurement range. After the inception of the entrainment - transition from the annular flow to the annular-mist flow - an even larger fraction of liquid enters the vapour core in the form of droplets, as the vapour quality increases. An equation was formulated for the slip in this region and adapted to the experiments via coefficients. (orig./GL) [de

  18. Numerical simulation of forced convection over a periodic series of rectangular cavities at low Prandtl number

    International Nuclear Information System (INIS)

    Stalio, E.; Angeli, D.; Barozzi, G.S.

    2011-01-01

    Highlights: → We investigate laminar convective heat transfer in channels with periodic cavities. → Heat transfer rates are lower than for the flat channel. → This is ascribed to the steady circulating motion within the cavities. → Diffusion in a low Prandtl number fluid can locally overcome the heat transfer decrease due to advection only for isothermal boundary conditions. - Abstract: Convective heat transfer in laminar conditions is studied numerically for a Prandtl number Pr = 0.025, representative of liquid lead-bismuth eutectic (LBE). The geometry investigated is a channel with a periodic series of shallow cavities. Finite-volume simulations are carried out on structured orthogonal curvilinear grids, for ten values of the Reynolds number based on the hydraulic diameter between Re m = 24.9 and Re m = 2260. Flow separation and reattachment are observed also at very low Reynolds numbers and wall friction is found to be remarkably unequal at the two walls. In almost all cases investigated, heat transfer rates are smaller than the corresponding flat channel values. Low-Prandtl number heat transfer rates, investigated by comparison with Pr = 0.71 results, are large only for uniform wall temperature and very low Re. Influence of flow separation on local heat transfer rates is discussed, together with the effect of different thermal boundary conditions. Dependency of heat transfer performance on the cavity geometry is also considered.

  19. Thermal modeling of the forced convection Sandwich Greenhouse drying system for rubber sheets

    International Nuclear Information System (INIS)

    Tanwanichkul, B.; Thepa, S.; Rordprapat, W.

    2013-01-01

    Highlights: • Sandwich Greenhouse is designed for better quality and efficiency of rubber sheet drying. • Thermal models are developed to predict the convection heat transfer coefficient. • The models are validated and show good agreement with the actual experimental data. • The proposed greenhouse can maintain 40–60 °C, suitable for rubber sheet drying. • This greenhouse can bring down the moisture content to 2.8% in fewer than 2 days. - Abstract: In this paper, a novel “Sandwich Greenhouse” for rubber sheet drying is proposed. Using solar energy as the only heat source instead of traditional smoke house that requires firewood, it eliminates shortcomings such as skilled labor monitoring requirement, possible fire hazard, and darken-color rubber sheets due to soot particle contamination. Our greenhouse is specially designed to retain solar energy within, while minimizing the heat loss to the outside environment. The mathematical models are developed to predict the convection mass transfer coefficient and to study the thermal behavior during the drying of rubber sheets under our proposed greenhouse design. Validated with experimental observations, the models show good agreement with the actual experimental data. The experiment demonstrates an effectiveness of our proposed Sandwich Greenhouse, as the temperature of the rubber sheet is 15 °C and 5 °C higher than the ambient temperature during the daytime and nighttime, respectively. As a result, the moisture content of the rubber sheets can decrease from 36.4% to 2.8% in fewer than 2 days

  20. Heat transfer in pool boiling liquid neon, deuterium and hydrogen, and critical heat flux in forced convection of liquid neon

    International Nuclear Information System (INIS)

    Astruc, J.M.

    1967-12-01

    In the first part, free-convection and nucleate pool boiling heat transfer (up to burn-out heat flux) between a platinum wire of 0.15 mm in diameter in neon, deuterium and hydrogen has been studied at atmospheric pressure. These measurements were continued in liquid neon up to 23 bars (Pc ≅ 26.8 b). Film boiling heat transfer coefficients have been measured in pool boiling liquid neon at atmospheric pressure with three heating wires (diameters 0.2, 0.5, 2 mm). All the results have been compared with existing correlations. The second part is devoted to measurements of the critical heat flux limiting heat transfer with small temperature differences between the wall and the liquid neon flowing inside a tube (diameters 3 x 3.5 mm) heated by joule effect on 30 cm of length. Influences of flow stability, nature of electrical current, pressure, mass flow rate and subcooling are shown. In conclusion, the similarity of the heat transfer characteristics in pool boiling as well as in forced convection of liquid neon and hydrogen is emphasized. (author) [fr

  1. Non-Equilibrium Thermodynamic Analysis of Double Diffusive, Nanofluid Forced Convection in Catalytic Microreactors with Radiation Effects

    Directory of Open Access Journals (Sweden)

    Lilian Govone

    2017-12-01

    Full Text Available This paper presents a theoretical investigation of the second law performance of double diffusive forced convection in microreactors with the inclusion of nanofluid and radiation effects. The investigated microreactors consist of a single microchannel, fully filled by a porous medium. The transport of heat and mass are analysed by including the thick walls and a first order, catalytic chemical reaction on the internal surfaces of the microchannel. Two sets of thermal boundary conditions are considered on the external surfaces of the microchannel; (1 constant temperature and (2 constant heat flux boundary condition on the lower wall and convective boundary condition on the upper wall. The local thermal non-equilibrium approach is taken to thermally analyse the porous section of the system. The mass dispersion equation is coupled with the transport of heat in the nanofluid flow through consideration of Soret effect. The problem is analytically solved and illustrations of the temperature fields, Nusselt number, total entropy generation rate and performance evaluation criterion (PEC are provided. It is shown that the radiation effect tends to modify the thermal behaviour within the porous section of the system. The radiation parameter also reduces the overall temperature of the system. It is further demonstrated that, expectedly, the nanoparticles reduce the temperature of the system and increase the Nusselt number. The total entropy generation rate and consequently PEC shows a strong relation with radiation parameter and volumetric concentration of nanoparticles.

  2. Numerical study of magnetic field effect on nano-fluid forced convection in a channel

    Energy Technology Data Exchange (ETDEWEB)

    Heidary, H., E-mail: Heidary_ha@aut.ac.ir [Department of Mechanical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran (Iran, Islamic Republic of); Hosseini, R. [Department of Mechanical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran (Iran, Islamic Republic of); Pirmohammadi, M., E-mail: Pirmohamadi@pardisiau.ac.ir [Department of Mechanical Engineering, Pardis Branch, Islamic Azad University, Pardis New City, Tehran (Iran, Islamic Republic of); Kermani, M.J. [Department of Mechanical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran (Iran, Islamic Republic of)

    2015-01-15

    In this study heat transfer and fluid flow analysis in a straight channel utilizing nano-fluid is numerically studied, while flow field is under magnetic field. Usage of nano-particles in base fluid and also applying magnetic field transverse to fluid velocity are two ways recommended in this paper to enhance heat exchange in straight duct. The fluid temperature at the channel inlet (T{sub in}) is taken less than that of the walls (T{sub w}). With assuming thermal equilibrium state of both the fluid phase and nano-particles and ignoring the slip velocity between the phases, single phase approach is used for modeling of nano-fluid. The governing equations are numerically solved in the domain by the control volume approach based on the SIMPLE technique. Numerical studies are performed over a range of Reynolds number, nano-fluid volume fraction and Hartmann number. The influence of these parameters is investigated on the local and average Nusselt numbers. Computations show excellent agreement with the literature. From this study, it is concluded that heat transfer in channels can enhance up to 75% due to the presence of nano-particles and magnetic field in channels. In industrial applications for cooling or heating purposes, the recommended ways in this paper, can provide helpful guidelines to the manufacturers to enhance efficiencies without heat exchanger area increase. - Highlights: • Addition of 10% nano-particles (copper here) can enhance the heat exchange by 26%. • Presence of magnetic field with Ha=30 in pure fluid can enhance the heat exchange by 50%. • Presence of magnetic field and nanofluid with Ha=30 and ϕ=0.1, can enhance the heat exchange by 76%. • Increasing Re{sub H} from 50 to 1000, the average Nu number can increase by a factor of ≈3.

  3. Variability of radiatively forced diurnal cycle of intense convection in the tropical west pacific

    Energy Technology Data Exchange (ETDEWEB)

    Gray, W.M.; Sheaffer, J.D.; Thorson, W.B. [Colorado State Univ., Fort Collins, CO (United States)

    1996-04-01

    Strong differences occur in daytime versus nighttime (DVN) net radiative cooling in clear versus cloudy areas of the tropical atmosphere. Daytime average cooling is approximately -0.7{degrees}C/day, whereas nighttime net tropospheric cooling rates are about -1.5{degrees}C/day, an approximately two-to-one difference. The comparatively strong nocturnal cooling in clear areas gives rise to a diurnally varying vertical circulation and horizontal convergence cycle. Various manifestations of this cyclic process include the observed early morning heavy rainfall maxima over the tropical oceans. The radiatively driven DVN circulation appears to strongly modulate the resulting diurnal cycle of intense convection which creates the highest, coldest cloudiness over maritime tropical areas and is likely a fundamental mechanism governing both small and large scale dynamics over much of the tropical environment.

  4. Experimental determination of heat transfer critical conditions in water forced convection at low pressure in a circular channel

    International Nuclear Information System (INIS)

    Fernandes, M.P.

    1973-02-01

    An experimental determination was made of heat transfer critical conditions in a circular channel, uniformly heated, and internally cooled by water in ascending forced convection, under a pressure slightly above atmospheric pressure. Measurements were made of water flow, pressure, electric power temperature and heating, and a systematic analysis was made of the system's parameters. The values obtained for the heat critical flux are circa 50% lower than those predicted by Becker and Biasi and this is accounted to flowing instabilities of thermo-hydrodynamic nature. It is suggested that the flowing channels of circuits aiming at the study of the boiling crisis phenomenon be expanded in its upper extremity, and that the coolant circulation be kept through a pump with a pressure X flow characteristic as vertical as possible

  5. Experimental study of pistachio drying behavior in a mixed-mode PV operated forced convection solar dryer

    Energy Technology Data Exchange (ETDEWEB)

    Zangiabadi, B [Univ. of Stavanger, Stavanger (Norway); Ameri, M; Mahmoudabadi, M M [Shahid Bahonar Univ., Kerman (Iran, Islamic Republic of)

    2008-07-01

    According to FAO statistics, Iran is the largest exporter of pistachios. Kerman province -south east of Iran- has approximately 200000 hectares of pistachio orchards, which provides practically 80% of whole country production of pistachios. After harvesting the pistachio, nuts must be washed to prevent staining. Therefore the nuts have almost 40% moisture content and it must be decreased to storage moisture of 6% or below. Simply decreasing in the moisture content of the products is called drying. In some areas where the environment conditions meet the minimum standard, solar drying can be an alternative approach for drying agricultural products. This work deals with the design, construction and testing a mixed-mode forced convection PV operated solar dryer. (orig.)

  6. A comparative design study of PB-BI cooled reactor cores with forced and natural convection cooling

    International Nuclear Information System (INIS)

    Mizuno, Tomoyasu; Enuma, Yasuhiro; Tanji, Mikio

    2003-01-01

    A comparative core design study is performed on Pb-Bi cooled reactors with forced and natural convection (FC and NC) cooling. Major interests of the study are core performance and core safety features. The designed core concepts with nitride fuel achieve reasonable breeding capability. The results of unprotected event analyses such as UTOP and ULOF show that both of concepts have possible features to withstand unprotected events due to negative reactivity feedback by Doppler effect, control rod drive line expansion, etc. These results lead to a conclusion that both of concepts have possible capability as one of future promising core concepts. A FC cooling core concept has more advantage if fuel recycle viewpoint is emphasized. (author)

  7. Forced convection on a heated horizontal flat plate with finite thermal conductivity in a non-Darcian porous medium

    Energy Technology Data Exchange (ETDEWEB)

    Luna, N. [Direccion de Operacion Petrolera, Direccion General de Exploracion y Explotacion de Hidrocarburos, Secretaria de Energia, 03100 Mexico DF (Mexico); Mendez, F. [Facultad de Ingenieria, UNAM, 04510 Mexico DF (Mexico)

    2005-07-01

    The steady-state analysis of conjugated heat transfer process for the hydrodynamically developed forced convection flow on a heated flat plate embedded in a porous medium is studied. The governing equations for the fluid-saturated porous medium are solved analytically using the integral boundary layer approximation. This integral solution is coupled to the energy equation for the flat plate, where the longitudinal heat conduction effects are taken into account. The resulting equations are then reduced to an integro-differential equation which is solved by regular perturbation techniques and numerical methods. The analytical and numerical predictions for the temperature profile of the plate and appropriate local and average Nusselt numbers are plotted for finite values of the conduction parameter, {alpha}, which represents the presence of the longitudinal heat conduction effects. (authors)

  8. A dry-spot model of critical heat flux and transition boiling in pool and subcooled forced convection boiling

    International Nuclear Information System (INIS)

    Ha, Sang Jun

    1998-02-01

    A new dry-spot model for critical heat flux (CHF) is proposed. The new concept for dry area formation based on Poisson distribution of active nucleation sites and the critical active site number is introduced. The model is based on the boiling phenomena observed in nucleate boiling such as Poisson distribution of active nucleation sites and formation of dry spots on the heating surface. It is hypothesized that when the number of bubbles surrounding one bubble exceeds a critical number, the surrounding bubbles restrict the feed of liquid to the microlayer under the bubble. Then a dry spot of vapor will form on the heated surface. As the surface temperature is raised, more and more bubbles will have a population of surrounding active sites over the critical number. Consequently, the number of the spots will increase and the size of dry areas will increase due to merger of several dry spots. If this trend continues, the number of effective sites for heat transport through the wall will diminish, and CHF and transition boiling occur. The model is applicable to pool and subcooled forced convection boiling conditions, based on the common mechanism that CHF and transition boiling are caused by the accumulation and coalescences of dry spots. It is shown that CHF and heat flux in transition boiling can be determined without any empirical parameter based on information on the boiling parameters such as active site density and bubble diameter, etc., in nucleate boiling. It is also shown that the present model well represents actual phenomena on CHF and transition boiling and explains the mechanism on how parameters such as flow modes (pool or flow) and surface wettability influence CHF and transition boiling. Validation of the present model for CHF and transition boiling is achieved without any tuning parameter always present in earlier models. It is achieved by comparing the predictions of CHF and heat flux in transition boiling using measured boiling parameters in nucleate

  9. Forced convective boiling heat transfer of water in vertical rectangular narrow channel

    International Nuclear Information System (INIS)

    Chen, Chong; Gao, Pu-zhen; Tan, Si-chao; Chen, Han-ying; Chen, Xian-bing

    2015-01-01

    Highlights: • Chen correlation cannot well predict the coefficient of rectangular channel. • Kim and Mudawar correlation is the best one among the Chen type correlations. • Lazarek and Black correlation predicted 7.0% of data within the ±30% error band. • The new correlation can well predict the coefficient with a small MAE of 14.4%. - Abstract: In order to research the characteristics of boiling flows in a vertical rectangular narrow channel, a series of convective boiling heat transfer experiments are performed. The test section is made of stainless steel with an inner diameter of 2 × 40 mm and heated length of 1100 mm. The 3194 experimental data points are obtained for a heat flux range of 10–700 kW/m 2 , a mass flux range of 200–2400 kg/m 2 s, a system pressure range of 0.1–2.5 MPa, and a quality range of 0–0.8. Eighteen prediction models are used to predict the flow boiling heat transfer coefficient of the rectangular narrow channel and the predicted value is compared against the database including 3194 data points, the results show that Chen type correlations and Lazarek and Black type correlations are not suitable for the rectangular channel very much. The Kim and Mudawar correlation is the best one among the 18 models. A new correlation is developed based on the superposition concept of nucleate boiling and convective boiling. the new correlation is shown to provide a good prediction against the database, evidenced by an overall MAE of 14.4%, with 95.2% and 98.6% of the data falling within ±30% and ±35% error bands, respectively

  10. A methodology to determine boundary conditions from forced convection experiments using liquid crystal thermography

    Science.gov (United States)

    Jakkareddy, Pradeep S.; Balaji, C.

    2017-02-01

    This paper reports the results of an experimental study to estimate the heat flux and convective heat transfer coefficient using liquid crystal thermography and Bayesian inference in a heat generating sphere, enclosed in a cubical Teflon block. The geometry considered for the experiments comprises a heater inserted in a hollow hemispherical aluminium ball, resulting in a volumetric heat generation source that is placed at the center of the Teflon block. Calibrated thermochromic liquid crystal sheets are used to capture the temperature distribution at the front face of the Teflon block. The forward model is the three dimensional conduction equation which is solved within the Teflon block to obtain steady state temperatures, using COMSOL. Match up experiments are carried out for various velocities by minimizing the residual between TLC and simulated temperatures for every assumed loss coefficient, to obtain a correlation of average Nusselt number against Reynolds number. This is used for prescribing the boundary condition for the solution to the forward model. A surrogate model obtained by artificial neural network built upon the data from COMSOL simulations is used to drive a Markov Chain Monte Carlo based Metropolis Hastings algorithm to generate the samples. Bayesian inference is adopted to solve the inverse problem for determination of heat flux and heat transfer coefficient from the measured temperature field. Point estimates of the posterior like the mean, maximum a posteriori and standard deviation of the retrieved heat flux and convective heat transfer coefficient are reported. Additionally the effect of number of samples on the performance of the estimation process has been investigated.

  11. Dynamical and statistical phenomena of circulation and heat transfer in periodically forced rotating turbulent Rayleigh-Bénard convection

    Science.gov (United States)

    Sterl, Sebastian; Li, Hui-Min; Zhong, Jin-Qiang

    2016-12-01

    In this paper, we present results from an experimental study into turbulent Rayleigh-Bénard convection forced externally by periodically modulated unidirectional rotation rates. We find that the azimuthal rotation velocity θ ˙(t ) and thermal amplitude δ (t ) of the large-scale circulation (LSC) are modulated by the forcing, exhibiting a variety of dynamics including increasing phase delays and a resonant peak in the amplitude of θ ˙(t ) . We also focus on the influence of modulated rotation rates on the frequency of occurrence η of stochastic cessation or reorientation events, and on the interplay between such events and the periodically modulated response of θ ˙(t ) . Here we identify a mechanism by which η can be amplified by the modulated response, and these normally stochastic events can occur with high regularity. We provide a modeling framework that explains the observed amplitude and phase responses, and we extend this approach to make predictions for the occurrence of cessation events and the probability distributions of θ ˙(t ) and δ (t ) during different phases of a modulation cycle, based on an adiabatic approach that treats each phase separately. Last, we show that such periodic forcing has consequences beyond influencing LSC dynamics, by investigating how it can modify the heat transport even under conditions where the Ekman pumping effect is predominant and strong enhancement of heat transport occurs. We identify phase and amplitude responses of the heat transport, and we show how increased modulations influence the average Nusselt number.

  12. Load compensation for single phase system using series active filter

    African Journals Online (AJOL)

    user

    Keywords: Active power filter (APF), current source type of harmonic load ... Single phase active filters could attract less attention than three phase due to its low ..... Generalised single-phase p-q theory for active power filtering: simulation and.

  13. A zonally symmetric model for the monsoon-Hadley circulation with stochastic convective forcing

    Science.gov (United States)

    De La Chevrotière, Michèle; Khouider, Boualem

    2017-02-01

    Idealized models of reduced complexity are important tools to understand key processes underlying a complex system. In climate science in particular, they are important for helping the community improve our ability to predict the effect of climate change on the earth system. Climate models are large computer codes based on the discretization of the fluid dynamics equations on grids of horizontal resolution in the order of 100 km, whereas unresolved processes are handled by subgrid models. For instance, simple models are routinely used to help understand the interactions between small-scale processes due to atmospheric moist convection and large-scale circulation patterns. Here, a zonally symmetric model for the monsoon circulation is presented and solved numerically. The model is based on the Galerkin projection of the primitive equations of atmospheric synoptic dynamics onto the first modes of vertical structure to represent free tropospheric circulation and is coupled to a bulk atmospheric boundary layer (ABL) model. The model carries bulk equations for water vapor in both the free troposphere and the ABL, while the processes of convection and precipitation are represented through a stochastic model for clouds. The model equations are coupled through advective nonlinearities, and the resulting system is not conservative and not necessarily hyperbolic. This makes the design of a numerical method for the solution of this system particularly difficult. Here, we develop a numerical scheme based on the operator time-splitting strategy, which decomposes the system into three pieces: a conservative part and two purely advective parts, each of which is solved iteratively using an appropriate method. The conservative system is solved via a central scheme, which does not require hyperbolicity since it avoids the Riemann problem by design. One of the advective parts is a hyperbolic diagonal matrix, which is easily handled by classical methods for hyperbolic equations, while

  14. Domain switching in single-phase multiferroics

    Science.gov (United States)

    Jia, Tingting; Cheng, Zhenxiang; Zhao, Hongyang; Kimura, Hideo

    2018-06-01

    Multiferroics are a time-honoured research subject by reason for their tremendous application potential in the information industry, such as in multi-state information storage devices and new types of sensors. An outburst of studies on multiferroicity has been witnessed in the 21st century, although this field has a long research history since the 19th century. Multiferroicity has now become one of the hottest research topics in condensed matter physics and materials science. Numerous efforts have been made to investigate the cross-coupling phenomena among ferroic orders such as ferroelectricity, (anti-)ferromagnetism, and ferroelasticity, especially the coupling between electric and magnetic orderings that would account for the magnetoelectric (ME) effect in multiferroic materials. The magnetoelectric properties and coupling behavior of single phase multiferroics are dominated by their domain structures. It was also noted that, however, the multiferroic materials exhibit very complicated domain structures. Studies on domain structure characterization and domain switching are a crucial step in the exploration of approaches to the control and manipulation of magnetic (electric) properties using an electric (magnetic) field or other means. In this review, following a concise outline of our current basic knowledge on the magnetoelectric (ME) effect, we summarize some important research activities on domain switching in single-phase multiferroic materials in the form of single crystals and thin films, especially domain switching behavior involving strain and the related physics in the last decade. We also introduce recent developments in characterization techniques for domain structures of ferroelectric or multiferroic materials, which have significantly advanced our understanding of domain switching dynamics and interactions. The effects of a series of issues such as electric field, magnetic field, and stress effects on domain switching are been discussed as well. It

  15. Experimental Investigation of Solar Drying for Orange Peels by Forced convection

    International Nuclear Information System (INIS)

    Ben Slama, Romdhane; Mechlouch, Fethi; Ben Daoud, Houcine

    2009-01-01

    Solar drier does not degrade any more the dried products with the manner of the products dried at the natural sun. The drying unit is composed mainly of a solar air collector and an enclosure of drying. The transformation of the solar radiation into heat is done thanks to the solar collector whose effectiveness is increased by the addition of suitable baffles in the mobile air vein. The efficiency of the collector reaches then 80. The hot air on the outlet side of the collector arrives in the enclosure of drying where the heat transfer with the product to be dried is done by convection. The kinetics drying study shows that in addition to the dependence of the temperature and air velocity of drying, the speed of drying also depends on fragmentation on the product to dry, and mainly, of the product surface in contact with the drying air. Thus, the hygrometry is reduced from 76 to 13 pour cent in one day.. The total efficiency of the drier reached 28 pour cent

  16. Combined free and forced convection flow of a second order liquid through porous parallel walls

    International Nuclear Information System (INIS)

    Mishra, S.P.

    1977-01-01

    An analysis of the flow of a second order fluid through porous parallel walls with heat transfer under the influence of buoyancy forces is carried out. Solutions for the velocity and temperature fields have been obtained by an iterative procedure. The flow phenomena have been characterized by parameters like: R (cross flow Reynolds number), Λ (elastic parameter), G (Grashof number), σ (Prandtl number) and the effects of these numbers on the flow characteristics have been presented in several graphs and tables. (author)

  17. Theoretical and experimental studies on transient heat transfer for forced convection flow of helium gas over a horizontal cylinder

    International Nuclear Information System (INIS)

    Liu Qiusheng; Katsuya Fukuda; Zhang Zheng

    2005-01-01

    Forced convection transient heat transfer for helium gas at various periods of exponential increase of heat input to a horizontal cylinder (heater) was theoretically and experimentally studied. In the theoretical study, transient heat transfer was numerically solved based on a turbulent flow model. It was clarified that the surface superheat and heat flux increase exponentially as the heat generation rate increases with the exponential function. The temperature distribution near the cylinder becomes larger as the surface temperature increases. The values of numerical solution for surface temperature and heat flux agree well with the experimental data for the cylinder diameter of 1 mm. However, the heat flux shows difference from the experimental values for the cylinder diameters of 0.7 mm and 2.0 mm. In the experimental studies, the authors measured heat flux, surface temperature, and transient heat transfer coefficients for forced convection flow of helium gas over horizontal cylinders under wide experimental conditions. The platinum cylinders with diameters of 1.0 mm, 0.7 mm, and 2.0 mm were used as test heaters and heated by electric current with an exponential increase of Q 0exp (t/τ) . The gas flow velocities ranged from 2 to 10 m/s, the gas temperatures ranged from 303 to 353 K, and the periods ranged from 50 ms to 20 s. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period τ longer than about 1 s, and it becomes higher for the period shorter than around 1 s. The transient heat transfer shows less dependence on the gas flowing velocity when the period becomes very shorter. The heat transfer shifts to the quasi-steady-state heat transfer for longer periods and shifts to the transient heat transfer for shorter periods at the same flow velocity. It also approaches the quasi-steady-state one for higher flow velocity at the same period. The transient heat transfer coefficients show significant dependence on

  18. A one-dimensional model of the semiannual oscillation driven by convectively forced gravity waves

    Science.gov (United States)

    Sassi, Fabrizio; Garcia, Rolando R.

    1994-01-01

    A one-dimensional model that solves the time-dependent equations for the zonal mean wind and a wave of specified zonal wavenumber has been used to illustrate the ability of gravity waves forced by time-dependent tropospheric heating to produce a semiannual oscillation (SAO) in the middle atmosphere. When the heating has a strong diurnal cycle, as observed over tropical landmasses, gravity waves with zonal wavelengths of a few thousand kilometers and phase velocities in the range +/- 40-50 m/sec are excited efficiently by the maximum vertical projection criterion (vertical wavelength approximately equals 2 x forcing depth). Calculations show that these waves can account for large zonal mean wind accelerations in the middle atmosphere, resulting in realistic stratopause and mesopause oscillations. Calculations of the temporal evolution of a quasi-conserved tracer indicate strong down-welling in the upper stratosphere near the equinoxes, which is associated with the descent of the SAO westerlies. In the upper mesosphere, there is a semiannual oscillation in tracer mixing ratio driven by seasonal variability in eddy mixing, which increases at the solstices and decreases at the equinoxes.

  19. A visual study of forced convection boiling. Part I: Results for a flat vertical heater

    International Nuclear Information System (INIS)

    Kirby, G.J.; Staniforth, R.; Kinneir, J.H.

    1965-03-01

    This report presents the first results of a visual study of the hydrodynamics of boiling in channels and of burnout. It was found that the bubbles formed did not diffuse into the main stream at high heat fluxes, but remained close to the heater. Consequently severe coalescence took place, resulting in the formation of large regularly shaped bubbles. An analysis of the forces acting on these bubbles is given; this accounts qualitatively for the observed behaviour. The above bubble formations result from the addition of heat at a wall so that clearly isothermal models, such as those using air-water mixtures, cannot give a true representation of the flow pattern. Attempts to view the heater surface at burnout were frustrated by poor visibility through the boiling mixture. (author)

  20. Experimental investigation on TBAB clathrate hydrate slurry flows in a horizontal tube: Forced convective heat transfer behaviors

    Energy Technology Data Exchange (ETDEWEB)

    Wenji, Song [Guangzhou Institute of Energy Conversion, CAS, No. 2 Nengyuan Road, Tianhe District, Guangzhou 510640 (China); Key Laboratory of Renewable Energy and Gas Hydrate, CAS, No. 2 Nengyuan Road, Tianhe District, Guangzhou 510640 (China); Graduate School of Chinese Academy of Sciences, Beijing 100039 (China); Rui, Xiao; Chong, Huang; Shihui, He; Kaijun, Dong; Ziping, Feng [Guangzhou Institute of Energy Conversion, CAS, No. 2 Nengyuan Road, Tianhe District, Guangzhou 510640 (China); Key Laboratory of Renewable Energy and Gas Hydrate, CAS, No. 2 Nengyuan Road, Tianhe District, Guangzhou 510640 (China)

    2009-11-15

    Tetra-n-butyl-ammonium bromide (TBAB) clathrate hydrate slurry (CHS) is one kind of secondary refrigerants, which is promising to be applied into air-conditioning or latent-heat transportation systems as a thermal storage or cold carrying medium for energy saving. It is a solid-liquid two phase mixture which is easy to produce and has high latent heat and good fluidity. In this paper, the heat transfer characteristics of TBAB slurry were investigated in a horizontal stainless steel tube under different solid mass fractions and flow velocities with constant heat flux. One velocity region of weakened heat transfer was found. Moreover, TBAB CHS was treated as a kind of Bingham fluids, and the influences of the solid particles, flow velocity and types of flow on the forced convective heat transfer coefficients of TBAB CHS were investigated. At last, criterial correlations of Nusselt number for laminar and turbulent flows in the form of power function were summarized, and the error with experimental results was within {+-}20%. (author)

  1. Augmentation of forced-convection heat transfer by applying electric fields to disturb flow near a wall

    International Nuclear Information System (INIS)

    Nariai, H.; Ishiguro, H.; Nagata, S.; Yabe, A.

    1991-01-01

    This paper reports on the augmentation effect of electrohydrodynamically (EHD) induced flow disturbance on forced-convection heat transfer in a channel that was experimentally investigated in order to determine the applicability of the enhanced heat transfer into a low- pressure drop heat exchanger, such as a high-performance oil cooler. The investigation is mainly based on the study carried out on the unique point where the flow is disturbed actively and controllably by applying electric fields between the wall and array of wire electrodes installed near the wall along the main stream. The liquid mixture of refrigerant R113 (96 wt %) and ethanol (4 wt %), called Fronsorubu AE, was selected as a working fluid. Heat transfer was found to be promoted intensely in the turbulent flow as well as in the laminar flow, up to a factor of about twenty-three in the case of laminar flow. It is noteworthy that the rate of increase in heat transfer coefficient is larger compared to that in the pressure drop. From a measurement of velocities by a laser Doppler velocimeter, it was made clear that the electrohydrodynamically induced flow disturbance brings about large heat transfer coefficients

  2. Numerical investigation of laminar forced convection heat transfer in rectangular channels with different block geometries using nano-fluids

    Directory of Open Access Journals (Sweden)

    Foroutani Saeed

    2017-01-01

    Full Text Available This research investigates the laminar steady-forced convection heat transfer of a Cu-water nanofluid in a 2-D horizontal channel with different block geometries attached to the bottom wall. The block geometries assumed in this research are triangular and curve blocks. The governing equations associated with the required boundary conditions are solved using finite volume method based on the SIMPLE technique and the effects of Reynolds number, nanofluid volume fraction, block geometry, and the numbers of blocks on the local and average Nusselt numbers are explored. The obtained results show that nanoparticles can effectively enhance the heat transfer in a channel. Furthermore, the local and average Nusselt number distribution is strongly dependent on the block geometry. As observed, the heat transfer augments with the increase in the Reynolds number and nanofluid volume fraction for both block geometries. It is also concluded that the average Nusselt number of the curve block is higher than that of the triangular block for different Reynolds numbers which declares the importance of the block geometry in the heat transfer enhancement.

  3. Effect of Magnetic Field on Entropy Generation Due to Laminar Forced Convection Past a Horizontal Flat Plate

    Directory of Open Access Journals (Sweden)

    Moh'd A. Al-Nimr

    2004-06-01

    Full Text Available Magnetic field effect on local entropy generation due to steady two-dimensional laminar forced convection flow past a horizontal plate was numerically investigated. This study was focused on the entropy generation characteristics and its dependency on various dimensionless parameters. The effect of various dimensionless parameters, such as Hartmann number (Ha, Eckert number (Ec, Prandtl number (Pr, Joule heating parameter (R and the free stream temperature parameter (θ∞ on the entropy generation characteristics is analyzed. The dimensionless governing equations in Cartesian coordinate were solved by an implicit finite difference technique. The solutions were carried out for Ha2=0.5-3, Ec=0.01-0.05, Pr=1-5 and θ∞=1.1-2.5. It was found that, the entropy generation increased with increasing Ha, Ec and R. While, increasing the free stream temperature parameter, and Prandtl number tend to decrease the local entropy generation.

  4. Impact of forced convective radiative heat and mass transfer mechanisms on 3D Carreau nanofluid: A numerical study

    Science.gov (United States)

    Khan, M.; Irfan, M.; Khan, W. A.

    2017-12-01

    Nanoliquids retain remarkable features that have fascinated various researchers owing to their utilization in nanoscience and nanotechnology. We will present a mathematical relation for 3D forced convective heat and mass transfer mechanism of a Carreau nanoliquid over a bidirectional stretched surface. Additionally, the features of heat source/sink and nonlinear thermal radiation are considered for the 3D Carreau nanoliquid. The governing nonlinear PDEs are established and altered into a set of nonlinear ODEs by utilizing a suitable conversion. A numerical approach, namely the bvp4c is adopted to resolve the resultant equations. The achieved outcomes are schemed and conferred in detail for somatic parameters. It is realized that amassed values of Brownian motion parameter Nb lead to enhance the temperature of the Carreau nanoliquid while quite conflicting behavior is being noticed for the concentration of the Carreau nanoliquid. Moreover, it is also noted that the influence of heat source δ > 0 is relatively antithetic to heat sink δ communication with these results.

  5. Phenomenological and statistical analyses of turbulence in forced convection with temperature-dependent viscosity under non-Boussinesq condition.

    Science.gov (United States)

    Yahya, S M; Anwer, S F; Sanghi, S

    2013-10-01

    In this work, Thermal Large Eddy Simulation (TLES) is performed to study the behavior of weakly compressible Newtonian fluids with anisotropic temperature-dependent viscosity in forced convection turbulent flow. A systematic analysis of variable-viscosity effects, isolated from gravity, with relevance to industrial cooling/heating applications is being carried out. A LES of a planar channel flow with significant heat transfer at a low Mach number was performed to study effects of fluid property variation on the near-wall turbulence structure. In this flow configuration the top wall is maintained at a higher temperature (T hot ) than the bottom wall (T cold ). The temperature ratio (R θ = T hot /T cold ) is fixed at 1.01, 2 and 3 to study the effects of property variations at low Mach number. Results indicate that average and turbulent fields undergo significant changes. Compared with isothermal flow with constant viscosity, we observe that turbulence is enhanced in the cold side of the channel, characterized by locally lower viscosity whereas a decrease of turbulent kinetic energy is found at the hot wall. The turbulent structures near the cold wall are very short and densely populated vortices but near the hot wall there seems to be a long streaky structure or large elongated vortices. Spectral study reveals that turbulence is completely suppressed at the hot side of the channel at a large temperature ratio because no inertial zone is obtained (i.e. index of Kolmogorov scaling law is zero) from the spectra in these region.

  6. Burnout experiment in subcooled forced-convection boiling of water for beam dumps of a high power neutral beam injector

    International Nuclear Information System (INIS)

    Horiike, Hiroshi; Kuriyama, Masaaki; Morita, Hiroaki

    1982-01-01

    Experimental studies were made on burnout heat flux in highly subcooled forced-convection boiling of water for the design of beam dumps of a high power neutral beam injector for Japan Atomic Energy Research Institute Tokamak-60. These dumps are composed of many circular tubes with two longitudinal fins. The tube was irradiated with nonuniformly distributed hydrogen ion beams of 120 to 200 kW for as long as 10 s. The coolant water was circulated at flow velocities of 3 to 7.5 m/s at exit pressures of 0.4 to 0.9 MPa. The burnout and film-boiling data were obtained at local heat fluxes of 8 to 15 MW/m 2 . These values were as high as 2.5 times larger than those for the circumferentially uniform heat flux case with the same parameters. These data showed insensitivity to local subcooling as well as to pressure, and simple burnout correlations were derived. From these results, the beam dumps have been designed to receive energetic beam fluxes of as high as 5 MW/m 2 with a margin of a factor of 2 for burnout

  7. Numerical study on turbulent forced convective heat transfer using nanofluids TiO2 in an automotive cooling system

    Directory of Open Access Journals (Sweden)

    Adnan M. Hussein

    2017-03-01

    Full Text Available The limited thermal properties of liquids have led to the addition of solid nanoparticles to liquids in many industrial applications. In this paper, the friction factor and forced convection heat transfer of TiO2 nanoparticles dispersed in water in a car radiator was numerically determined. Four different nanofluid volume concentrations (1%, 2%, 3% and 4% were used, and the resulting thermal properties were evaluated. The Reynolds number and inlet temperature ranged from 10000 to 100000 and from 60 to 90 °C, respectively. The results showed that the friction factor decreases as the Reynolds number increases and increases as the volume concentration increases. Additionally, the Nusselt number increases as the Reynolds number and volume concentration of the nanofluid increases. The TiO2 nanofluid at low concentrations can enhance the heat transfer efficiency up to 20% compared with that of pure water. There was good agreement among the CFD analysis and experimental data available in the literature.

  8. Theoretical models to predict the transient heat transfer performance of HIFAR fuel elements under non-forced convective conditions

    International Nuclear Information System (INIS)

    Green, W.J.

    1987-04-01

    Simple theoretical models have been developed which are suitable for predicting the thermal responses of irradiated research fuel elements of markedly different geometries when they are subjected to loss-of-coolant accident conditions. These models have been used to calculate temperature responses corresponding to various non-forced convective conditions. Comparisons between experimentally observed temperatures and calculated values have shown that a suitable value for surface thermal emissivity is 0.35; modelling of the fuel element beyond the region of the fuel plate needs to be included since these areas account for approximately 25 per cent of the thermal power dissipated; general agreement between calculated and experimental temperatures for both transient and steady-state conditions is good - the maximum discrepancy between calculated and experimental temperatures for a HIFAR Mark IV/V fuel element is ∼ 70 deg C, and for an Oak Ridge Reactor (ORR) box-type fuel element ∼ 30 deg C; and axial power distribution does not significantly affect thermal responses for the conditions investigated. Overall, the comparisons have shown that the models evolved can reproduce experimental data to a level of accuracy that provides confidence in the modelling technique and the postulated heat dissipation mechanisms, and that these models can be used to predict thermal responses of fuel elements in accident conditions that are not easily investigated experimentally

  9. Drying of prickly pear cactus cladodes (Opuntia ficus indica) in a forced convection tunnel

    Energy Technology Data Exchange (ETDEWEB)

    Lopez, R.; de Ita, A.; Vaca, M. [Universidad Autonoma Metropolitana-Azcapotzalco, DePt. de Energia, Area de Termofluidos, Av. San Pablo 180, Col. Reynosa Tamaulipas, Del. Azcapotzalco, C.P. 02200, Mexico D.F. (Mexico)

    2009-09-15

    In this work we evaluated the kinetics of drying of Opuntia's cladodes observing two conditions: complete cladode with the protective cuticle of the intact product and with reduced cuticle (partially removed), using a drying tunnel with forced flow. The temperature of the air was set at 35, 45, and 60 C with velocities of 1.5 and 3.0 m/s. The conditions of the environment were controlled and maintained at 22 C and 30% of relative humidity. The results show that the drying time was considerably reduced when approximately 30% of the cuticle that protects the product was removed. Additionally, the temperature had greater influence than the velocity of the air. The numerical model that best describes the behavior of the drying process is the double logarithmic one, with the imposed restrictions of r close to the unit, the lowest possible {chi}{sup 2} and the RSEM tending to zero. The characteristic drying function of the product resulted in a third-grade exponential curve, where r and SD were the corresponding selection criteria. (author)

  10. Drying of prickly pear cactus cladodes (Opuntia ficus indica) in a forced convection tunnel

    International Nuclear Information System (INIS)

    Lopez, R.; Ita, A. de; Vaca, M.

    2009-01-01

    In this work we evaluated the kinetics of drying of Opuntia's cladodes observing two conditions: complete cladode with the protective cuticle of the intact product and with reduced cuticle (partially removed), using a drying tunnel with forced flow. The temperature of the air was set at 35, 45, and 60 deg. C with velocities of 1.5 and 3.0 m/s. The conditions of the environment were controlled and maintained at 22 deg. C and 30% of relative humidity. The results show that the drying time was considerably reduced when approximately 30% of the cuticle that protects the product was removed. Additionally, the temperature had greater influence than the velocity of the air. The numerical model that best describes the behavior of the drying process is the double logarithmic one, with the imposed restrictions of r close to the unit, the lowest possible χ 2 and the RSEM tending to zero. The characteristic drying function of the product resulted in a third-grade exponential curve, where r and SD were the corresponding selection criteria.

  11. Correlation of Normal Gravity Mixed Convection Blowoff Limits with Microgravity Forced Flow Blowoff Limits

    Science.gov (United States)

    Marcum, Jeremy W.; Olson, Sandra L.; Ferkul, Paul V.

    2016-01-01

    The axisymmetric rod geometry in upward axial stagnation flow provides a simple way to measure normal gravity blowoff limits to compare with microgravity Burning and Suppression of Solids - II (BASS-II) results recently obtained aboard the International Space Station. This testing utilized the same BASS-II concurrent rod geometry, but with the addition of normal gravity buoyant flow. Cast polymethylmethacrylate (PMMA) rods of diameters ranging from 0.635 cm to 3.81 cm were burned at oxygen concentrations ranging from 14 to 18% by volume. The forced flow velocity where blowoff occurred was determined for each rod size and oxygen concentration. These blowoff limits compare favorably with the BASS-II results when the buoyant stretch is included and the flow is corrected by considering the blockage factor of the fuel. From these results, the normal gravity blowoff boundary for this axisymmetric rod geometry is determined to be linear, with oxygen concentration directly proportional to flow speed. We describe a new normal gravity 'upward flame spread test' method which extrapolates the linear blowoff boundary to the zero stretch limit in order to resolve microgravity flammability limits-something current methods cannot do. This new test method can improve spacecraft fire safety for future exploration missions by providing a tractable way to obtain good estimates of material flammability in low gravity.

  12. Characterization of Single Phase and Two Phase Heat and Momentum Transport in a Spiraling Radial Inow Microchannel Heat Sink

    Science.gov (United States)

    Ruiz, Maritza

    Thermal management of systems under high heat fluxes on the order of hundreds of W/cm2 is important for the safety, performance and lifetime of devices, with innovative cooling technologies leading to improved performance of electronics or concentrating solar photovoltaics. A novel, spiraling radial inflow microchannel heat sink for high flux cooling applications, using a single phase or vaporizing coolant, has demonstrated enhanced heat transfer capabilities. The design of the heat sink provides an inward swirl flow between parallel, coaxial disks that form a microchannel of 1 cm radius and 300 micron channel height with a single inlet and a single outlet. The channel is heated on one side through a conducting copper surface, and is essentially adiabatic on the opposite side to simulate a heat sink scenario for electronics or concentrated photovoltaics cooling. Experimental results on the heat transfer and pressure drop characteristics in the heat sink, using single phase water as a working fluid, revealed heat transfer enhancements due to flow acceleration and induced secondary flows when compared to unidirectional laminar fully developed flow between parallel plates. Additionally, thermal gradients on the surface are small relative to the bulk fluid temperature gain, a beneficial feature for high heat flux cooling applications. Heat flux levels of 113 W/cm2 at a surface temperature of 77 deg C were reached with a ratio of pumping power to heat rate of 0.03%. Analytical models on single phase flow are used to explore the parametric trends of the flow rate and passage geometry on the streamlines and pressure drop through the device. Flow boiling heat transfer and pressure drop characteristics were obtained for this heat sink using water at near atmospheric pressure as the working fluid for inlet subcooling levels ranging from 20 to 80 deg C and mean mass flux levels ranging from 184-716 kg/m. 2s. Flow enhancements similar to singlephase flow were expected, as well

  13. Estimation of radiative forcing and chore length of shallow convective clouds (SCC) based on broadband pyranometer measurement network

    Science.gov (United States)

    Shi, H.

    2017-12-01

    We presented a method to identify and calculate cloud radiative forcing (CRF) and horizontal chore length (L) of shallow convective clouds (SCC) using a network of 9 broadband pyranometers. The analyzing data was collected from the SCC campaign during two years summers (2015 2016) at Baiqi site over Inner Mongolia grassland. The network of pyranometers was operated across a spatial domain covering 42.16-42.30° N and 114.83-114.98° E. The SCC detection method was verified by observer reports and cameras, which showed that the detection method and human observations were in agreement about 75 %. The differences between the SCC detection method and human observations can be responsible for following factors: 1) small or dissipating clouds can be neglected for the value of 1 min of temporal resolution of pyranometer; 2) human observation recorded weather conditions four times every day; 3) SCC was indistinguishable from coexistence of SCC and Cirrus (Ci); 4) the SCC detection method is weighted toward clouds crossing the sun's path, while the human observer can view clouds over the entire sky. The deviation of L can be attributed to two factors: 1) the accuracy of wind speed at height of SCC and the ratio of horizontal and vertical length play a key role in determine values of L; 2) the effect of variance of solar zenith angle can be negligible. The downwelling shortwave CRF of SCC was -134.1 Wm-2. The average value of L of SCC was 1129 m. Besides, the distribution of normalized cloud chore length agreed well with power-law fit.

  14. Using C-Band Dual-Polarization Radar Signatures to Improve Convective Wind Forecasting at Cape Canaveral Air Force Station and NASA Kennedy Space Center

    Science.gov (United States)

    Amiot, Corey G.; Carey, Lawrence D.; Roeder, William P.; McNamara, Todd M.; Blakeslee, Richard J.

    2017-01-01

    The United States Air Force's 45th Weather Squadron (45WS) is the organization responsible for monitoring atmospheric conditions at Cape Canaveral Air Force Station and NASA Kennedy Space Center (CCAFS/KSC) and issuing warnings for hazardous weather conditions when the need arises. One such warning is issued for convective wind events, for which lead times of 30 and 60 minutes are desired for events with peak wind gusts of 35 knots or greater (i.e., Threshold-1) and 50 knots or greater (i.e., Threshold-2), respectively (Roeder et al. 2014).

  15. Current Harmonics from Single-Phase Grid-Connected Inverters

    DEFF Research Database (Denmark)

    Yang, Yongheng; Zhou, Keliang; Blaabjerg, Frede

    2016-01-01

    Environmental conditions and operational modes may significantly impact the distortion level of the injected current from single-phase grid-connected inverter systems, such as photovoltaic (PV) inverters, which may operate in cloudy days with a maximum power point tracking, in a non-unity power...... factor, or in the low voltage ride through mode with reactive current injection. In this paper, the mechanism of the harmonic current injection from grid-connected single-phase inverter systems is thus explored, and the analysis is conducted on single-phase PV systems. In particular, the analysis...... is focused on the impacts of the power factor and the feed-in grid current level on the quality of the feed-in grid current from single-phase inverters. As a consequence, an internal model principle based high performance current control solution is tailor-made and developed for single-phase grid-connected...

  16. Simplified thermal-hydraulic analysis of single phase natural circulation circuit with two heat exchangers

    Energy Technology Data Exchange (ETDEWEB)

    Pinheiro, Larissa Cunha; Su, Jian, E-mail: larissa@lasme.coppe.ufrj.br, E-mail: sujian@lasme.coppe.ufrj.br [Coordenacao dos Programas de Pos-Graduacao em Engenharia (COPPE/UFRJ), Rio de Janeiro, RJ (Brazil). Programa de Engenhraria Nuclear; Cotta, Renato Machado, E-mail: cotta@mecanica.coppe.ufrj.br [Coordenacao dos Programas de Pos-Graduacao em Engenharia (POLI/COPPE/UFRJ), Rio de Janeiro, RJ (Brazil). Dept. de Engenharia Mecanica

    2015-07-01

    Single phase natural circulation circuits composed of two convective heat exchangers and connecting tubes are important for the passive heat removal from spent fuel pools (SFP). To keep the structural integrity of the stored spent fuel assemblies, continuously cooling has to be provided in order to avoid increase at the pool temperature and subsequent uncovering of the fuel and enhanced reaction between water and metal releasing hydrogen. Decay heat can achieve considerably high amounts of energy e.g. in the AP1000, considering the emergency fuel assemblies, the maximum heat decay will reach 13 MW in the 15th day (Westinghouse Electric Company, 2010). A highly efficient alternative to do so is by means of natural circulation, which is cost-effective compared to active cooling systems and is inherently safer since presents less associated devices and no external work is required. Many researchers have investigated safety and stability aspects of natural circulation loops (NCL). However, there is a lack of literature concerning the improvement of NCL through a standard unified methodology, especially for natural circulation circuits with two heat exchangers. In the present study, a simplified thermal-hydraulic analysis of single phase natural circulation circuit with two heat exchanges is presented. Relevant dimensionless key groups were proposed to for the design and safety analysis of a scaled NCL for the cooling of spent fuel storage pool with convective cooling and heating. (author)

  17. Simulation of the phenomenon of single-phase and two-phase natural circulation

    International Nuclear Information System (INIS)

    Castrillo, Lazara Silveira

    1998-02-01

    Natural convection phenomenon is often used to remove the residual heat from the surfaces of bodies where the heat is generated e.g. during accidents or transients of nuclear power plants. Experimental study of natural circulation can be done in small scale experimental circuits and the results can be extrapolated for larger operational facilities. The numerical analysis of transients can be carried out by using large computational codes that simulate the thermohydraulic behavior in such facilities. The computational code RELAP5/MOD2, (Reactor Excursion and Leak Analysis Program) was developed by U.S. Nuclear Regulatory Commissions's. Division of Reactor Safety Research with the objective of analysis of transients and postulated accidents in the light water reactor (LWR) systems, including small and large ruptures with loss of coolant accidents (LOCA's). The results obtained by the simulation of single-phase and two-phase natural circulation, using the RELAP5/MOD2, are presented in this work. The study was carried out using the experimental circuit built at the 'Departamento de Engenharia Quimica da Escola Politecnica da Universidade de Sao Paulo'. In the circuit, two experiments were carried out with different conditions of power and mass flow, obtaining a single-phase regime with a level of power of 4706 W and flow of 5.10 -5 m 3 /s (3 l/min) and a two-phase regime with a level of power of 6536 W and secondary flow 2,33.10 -5 m 3 /s (1,4 l/min). The study allowed tio evaluate the capacity of the code for representing such phenomena as well as comparing the transients obtained theoretically with the experimental results. The comparative analysis shows that the code represents fairly well the single-phase transient, but the results for two-phase transients, starting from the nodalization and calibration used for the case single-phase transient, did not reproduce faithfully some experimental results. (author)

  18. Improvement of Torque Production in Single-Phase Induction Motors

    African Journals Online (AJOL)

    OLUWASOGO

    PID controller. Simulation results show the starting torque of the motor increased by 75% under the developed drive .... The model equations of the capacitor-run single phase induction .... process using the MATLAB pidtool command (Control.

  19. A Novel Single Phase Hybrid Switched Reluctance Motor Drive System

    DEFF Research Database (Denmark)

    Liang, Jianing; Xu, Guoqing; Jian, Linni

    2011-01-01

    In this paper, a novel single phase hybrid switched reluctance motor(SRM) drive system is proposed. It integrated a single phase hybrid SRM and a novel single phase boost converter. This motor can reduce the number of phase switch. And the permanent magnet which is used in the motor can improve...... the performance and efficiency of SR motor. However, the inherent characteristic of this motor is that the negative torque is very sensitive with the excitation current near the turn-on angle. The slow excitation current limits the torque generation region and reduces the average torque. Therefore, a novel single...... phase boost converter is applied to improve the performance of this motor. It is easy to generate a double dclink voltage and dc-link voltage and switch both of them. The voltage of boost capacitor is self balance, so the protective circuit is not need to consider. The fast excitation mode helps hybrid...

  20. Load compensation for single phase system using series active filter ...

    African Journals Online (AJOL)

    Load compensation for single phase system using series active filter. ... KK Mishra, R Gupta ... load varies from time to time, the non linear load ranging from voltage source type harmonic load (VSHL) dominant to current source type harmonic ...

  1. Experimental and Numerical Investigation of Forced Convection Heat Transfer in Heat Sink with Rectangular Plates at Varying Inclinations on Vertical Base

    Science.gov (United States)

    Patil, Harshal Bhauso; Dingare, Sunil Vishnu

    2018-03-01

    Heat exchange upgrade is a vital territory of research area. Utilization of reasonable systems can bring about noteworthy specialized points of interest coming about reserve funds of cost. Rectangular plates are viewed as best balance arrangement utilized for heat exchange improvement. This gives an enlargement strategy to heat exchange with beginning of limit layer and vortex development. To assess and look at the rate of heat exchange enhancement by rectangular plate fins with differing inclinations (0°-30°-60°), shifting Re and heat supply under forced convection are the principle destinations of this study. The study is done by fluctuating introductions of fins with various inclinations, input heat supply and Re under forced convection. The coefficient of heat transfer increments observed with the expansion in air speed for all the examined designs. The coefficient of the heat transfer is discovered higher at the edge of introduction of fins at 30° for inline arrangement and 0° for staggered arrangement. Looking at both the arrangements, it is discovered that the heat transfer coefficient in 0° fin staggered arrangement is about 17% higher than 30° inline arrangement and 76% higher than the vertical plate fin. For plate fin heat sink, boundary layer formation and growth results in decrease of the coefficient of heat transfer in forced convection. This issue is overcome by accommodating some rectangular fins on the plate fin. It brings about increment of heat transfer coefficient of the RPFHS under the states of trial factors. As indicated by past research, it is discovered that examination of the plate fin heat sink with various sorts of fins for horizontal orientation is done yet but this investigation expects to discover the upgrade of transfer coefficient of plate fin heat sink for its vertical position with rectangular plates at different inclinations under the shifting scopes of heat input supply, fin arrangements and Reynolds number (Re).

  2. Long-term unsteadiness and large-scale structures in Rayleigh-Bénard convection with and without electromagnetic forcing

    NARCIS (Netherlands)

    Verdoold, J.

    2010-01-01

    This dissertation focuses on turbulent thermal convection, which occurs in a wide range of (geo)physical situations, like in the atmosphere, the oceans, the interior of stars or planets, and engineering applications, like metal casting or crystal growth processes. In this work, a special type of

  3. Experimental investigation of the effect of an electric field on heat transfers at boiling point for a high-resistivity water in forced convection

    International Nuclear Information System (INIS)

    Morin, Henri; Verdier, Jacques

    1964-10-01

    The enhancement of heat exchanges with boiling water in forced convection in an annular duct is studied when applying an electric field between the two walls of the duct. At the local boiling and at saturation temperature, for a water resistivity comprised between 0.5 and 1 M Ω cm, with fields on the cylindrical interior surface of the canal comprised between 4 and 8 kV/cm, significant enhancements of the exchanged heat fluxes are noticed, 2.5 to 10 time superior to exchanges without electric field. When heating, heat fluxes may be increased from two to three times [fr

  4. Development of a single-phase thermosiphon for cold collection and storage of radiative cooling

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Dongliang; Martini, Christine Elizabeth; Jiang, Siyu; Ma, Yaoguang; Zhai, Yao; Tan, Gang; Yin, Xiaobo; Yang, Ronggui

    2017-11-01

    A single-phase thermosiphon is developed for cold collection and storage of radiative cooling. Compared to the conventional nocturnal radiative cooling systems that use an electric pump to drive the heat transfer fluid, the proposed single-phase thermosiphon uses the buoyancy force to drive heat transfer fluid. This solution does not require electricity, therefore improving the net gain of the radiative cooling system. A single-phase thermosiphon was built, which consists of a flat panel, a cold collection tank, a water return tube, and a water distribution tank. Considering that outdoor radiative cooling flux is constantly changing (i.e. uncontrollable), an indoor testing facility was developed to provide a controllable cooling flux (comparable to a radiative cooling flux of 100 W/m2) for the evaluation of thermosiphon performance. The testing apparatus is a chilled aluminum flat plate that has a controlled air gap separation relative to the flat panel surface of the thermosiphon to emulate radiative cooling. With an average of 105 W/m2 cooling flux, the 18 liters of water in the thermosiphon was cooled to an average temperature of 12.5 degrees C from an initial temperature of 22.2 degrees C in 2 h, with a cold collection efficiency of 96.8%. The results obtained have demonstrated the feasibility of using a single-phase thermosiphon for cold collection and storage of radiative cooling. Additionally, the effects of the thermosiphon operation conditions, such as tilt angle of the flat panel, initial water temperature, and cooling energy flux, on the performance have been experimentally investigated. Modular design of the single-phase thermosiphon gives flexibility for its scalability. A radiative cooling system with multiple thermosiphon modules is expected to play an important role in cooling buildings and power plant condensers.

  5. Analysis of coolability of the control rods of a Savannah River Site production reactor with loss of normal forced convection cooling

    International Nuclear Information System (INIS)

    Easterling, T.C.; Hightower, N.T.; Smith, D.C.; Amos, C.N.

    1992-01-01

    An analytical study of the coolability of the control rods in the Savannah River Site (SRS) K-Production Reactor under conditions of loss of normal forced convection cooling has been performed. The study was performed as part of the overall safety analysis of the reactor supporting its restart. The analysis addresses the buoyancy-driven flow over the control rods that occurs when forced cooling is lost, and the limit of critical heat flux that sets the acceptance criteria for the study. The objective of the study is to demonstrate that the control rods will remain cooled at powers representative of those anticipated for restart of the reactor. The study accomplishes this objective with a very tractable simplified analysis for the modest restart power. In addition, a best-estimate calculation is performed, and the results are compared to results from sub-scale scoping experiments. 5 refs

  6. The Single-Phase ProtoDUNE Technical Design Report

    Energy Technology Data Exchange (ETDEWEB)

    Abi, B. [Univ. of Padova (Italy); et al.

    2017-06-21

    ProtoDUNE-SP is the single-phase DUNE Far Detector prototype that is under construction and will be operated at the CERN Neutrino Platform (NP) starting in 2018. ProtoDUNE-SP, a crucial part of the DUNE effort towards the construction of the first DUNE 10-kt fiducial mass far detector module (17 kt total LAr mass), is a significant experiment in its own right. With a total liquid argon (LAr) mass of 0.77 kt, it represents the largest monolithic single-phase LArTPC detector to be built to date. It's technical design is given in this report.

  7. Forced convection of ammonia. 2. part.: gaseous ammonia - very high wall temperatures (1000 to 3000 K); Convection forcee de l'ammoniac. 2. partie: ammoniac gazeux - cas de tres hautes temperatures de paroi (1000 a 3000{sup 0} K)

    Energy Technology Data Exchange (ETDEWEB)

    Perroud, P.; Rebiere, J.; Strittmatter, R. [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires

    1969-07-01

    Heat transfer coefficients and pressure drop of gaseous ammonia in forced convection are experimentally determined. The fluid flows (mass flow rate 0.6 to 2.4 g/s) in a long tungsten tube (d{sub i} = 2.8 mm, d{sub e} = 5.1 mm, L = 700 mm) electrically heated. The temperature of the wall reaches 3000 deg. K and the fluid 2500 deg. K; maximum heat flux 530 w/cm{sup 2}. Ammonia is completely dissociated and the power necessary for dissociation reaches 30 per cent of the total power exchanged. Inlet pressure varies between 6 and 16 bars and the maximum pressure drop in the tube reaches 15 bars. Two regimes of dissociation have been shown: catalytic and homogeneous and the variation of dissociation along the length of the tube is studied. The measured heat transfer coefficients may be about 10 times these calculated by the means of classical formulae. A correlation of experimental results using enthalpy as a driving force for heat transmission is presented. Pressure drops may be calculated by the means of a classical friction factor. (authors) [French] On determine experimentalement les coefficients d'echange thermique et les pertes de charge de l'ammoniac gazeux en convection forcee. Le fluide circule avec un debit en masse compris entre 0.6 et 2.4 g/s (G = 10 a 40 g/cm{sup 2}.s) dans un tube long en tungstene (d{sub i} = 2.8 mm, d{sub e} = 5.1 mm, L = 700 mm), chauffe electriquement. La temperature de paroi atteint 3000 deg. K, celle du fluide 2500 deg. K et le flux de chaleur maximal est de 530 W/cm{sup 2}. L'ammoniac se dissocie completement, la puissance correspondant a la dissociation atteint 30 pour cent de la puissance totale echangee. La pression d'entree varie entre 6 et 16 bars et la chute de pression maximale dans le canal est de 15 bars. On distingue deux regimes de dissociation, catalytique et homogene, et on etudie la variation du taux de dissociation en fonction de la longueur du tube. Les coefficients d'echange thermique mesures

  8. Forced convection of ammonia. 2. part.: gaseous ammonia - very high wall temperatures (1000 to 3000 K); Convection forcee de l'ammoniac. 2. partie: ammoniac gazeux - cas de tres hautes temperatures de paroi (1000 a 3000{sup 0} K)

    Energy Technology Data Exchange (ETDEWEB)

    Perroud, P; Rebiere, J; Strittmatter, R [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires

    1969-07-01

    Heat transfer coefficients and pressure drop of gaseous ammonia in forced convection are experimentally determined. The fluid flows (mass flow rate 0.6 to 2.4 g/s) in a long tungsten tube (d{sub i} = 2.8 mm, d{sub e} = 5.1 mm, L = 700 mm) electrically heated. The temperature of the wall reaches 3000 deg. K and the fluid 2500 deg. K; maximum heat flux 530 w/cm{sup 2}. Ammonia is completely dissociated and the power necessary for dissociation reaches 30 per cent of the total power exchanged. Inlet pressure varies between 6 and 16 bars and the maximum pressure drop in the tube reaches 15 bars. Two regimes of dissociation have been shown: catalytic and homogeneous and the variation of dissociation along the length of the tube is studied. The measured heat transfer coefficients may be about 10 times these calculated by the means of classical formulae. A correlation of experimental results using enthalpy as a driving force for heat transmission is presented. Pressure drops may be calculated by the means of a classical friction factor. (authors) [French] On determine experimentalement les coefficients d'echange thermique et les pertes de charge de l'ammoniac gazeux en convection forcee. Le fluide circule avec un debit en masse compris entre 0.6 et 2.4 g/s (G = 10 a 40 g/cm{sup 2}.s) dans un tube long en tungstene (d{sub i} = 2.8 mm, d{sub e} = 5.1 mm, L = 700 mm), chauffe electriquement. La temperature de paroi atteint 3000 deg. K, celle du fluide 2500 deg. K et le flux de chaleur maximal est de 530 W/cm{sup 2}. L'ammoniac se dissocie completement, la puissance correspondant a la dissociation atteint 30 pour cent de la puissance totale echangee. La pression d'entree varie entre 6 et 16 bars et la chute de pression maximale dans le canal est de 15 bars. On distingue deux regimes de dissociation, catalytique et homogene, et on etudie la variation du taux de dissociation en fonction de la longueur du tube. Les coefficients d'echange thermique mesures peuvent etre environ 10

  9. Single-phase multi-dimensional thermohydraulics direct numerical simulation code DINUS-3. Input data description

    Energy Technology Data Exchange (ETDEWEB)

    Muramatsu, Toshiharu [Power Reactor and Nuclear Fuel Development Corp., Oarai, Ibaraki (Japan). Oarai Engineering Center

    1998-08-01

    This report explains the numerical methods and the set-up method of input data for a single-phase multi-dimensional thermohydraulics direct numerical simulation code DINUS-3 (Direct Numerical Simulation using a 3rd-order upwind scheme). The code was developed to simulate non-stationary temperature fluctuation phenomena related to thermal striping phenomena, developed at Power Reactor and Nuclear Fuel Development Corporation (PNC). The DINUS-3 code was characterized by the use of a third-order upwind scheme for convection terms in instantaneous Navier-Stokes and energy equations, and an adaptive control system based on the Fuzzy theory to control time step sizes. Author expect this report is very useful to utilize the DINUS-3 code for the evaluation of various non-stationary thermohydraulic phenomena in reactor applications. (author)

  10. Numerical Simulation of a Single-Phase Closed-Loop Thermo-Siphon in LORELEI Test Device

    International Nuclear Information System (INIS)

    Gitelman, D.; Shenha, H.; Gonnier, Ch.; Tarabelli, D.; Sasson, A.; Weiss, Y.; Katz, M.

    2014-01-01

    The LORELEI experimental setup in the Jules Horowitz Reactor (JHR) is dedicated for the study of fuel during a Loss of Coolant Accident (LOCA). The main objective of the LORELEI(2) (Light-Water One-Rod Equipment for LOCA Experimental Investigation) is to study the thermal-mechanical behavior of fuel during such an accident and to produce a short half-life fission products source term. In order to study those phenomena, the fuel sample will experience a transient neutron flux field, which in turn will generate a Linear Heat Generation Rate (LHGR) and determine the temperature of the fuel and its cladding, simulating the behavior of the fuel and the cladding during a LOCA accident. In order to reproduce a LOCA-type transient sequence, the experimental test device will be located on a displacement device. The displacement device moves the test device in the flux field in order to generate a representing LHGR in the fuel or temperature of its cladding. The LOCA-type transient sequence has four major features: „h An adiabatic heating of the fuel up to the ballooning and burst occurrence. „h High temperature plateau which will promote clad oxidation. „h Passive precooling by thermal inertia. „h Water re-flooding and quenching. The challenge in the thermo-hydraulic design of the LORELEI test section is in defining a one closed water capsule design that can operate as a thermo-siphon at re-irradiation phase and also can reproduce all LOCA-type transient sequence phases. This design should be validated and verified to fill all safety and regulation requirements. This work aims to investigate fluid flow behavior of a single-phase thermo-siphon in the LORELEI test device, as part of the conceptual design and optimization study. The complexity of the flow field in the LORELEI test device, as a closed-loop thermo-siphon, is due to the opposing forces in the device - buoyancy forces and natural convection flow generated (mainly) by the fuel power in the hot channel

  11. An equivalent ground thermal test method for single-phase fluid loop space radiator

    Directory of Open Access Journals (Sweden)

    Xianwen Ning

    2015-02-01

    Full Text Available Thermal vacuum test is widely used for the ground validation of spacecraft thermal control system. However, the conduction and convection can be simulated in normal ground pressure environment completely. By the employment of pumped fluid loops’ thermal control technology on spacecraft, conduction and convection become the main heat transfer behavior between radiator and inside cabin. As long as the heat transfer behavior between radiator and outer space can be equivalently simulated in normal pressure, the thermal vacuum test can be substituted by the normal ground pressure thermal test. In this paper, an equivalent normal pressure thermal test method for the spacecraft single-phase fluid loop radiator is proposed. The heat radiation between radiator and outer space has been equivalently simulated by combination of a group of refrigerators and thermal electrical cooler (TEC array. By adjusting the heat rejection of each device, the relationship between heat flux and surface temperature of the radiator can be maintained. To verify this method, a validating system has been built up and the experiments have been carried out. The results indicate that the proposed equivalent ground thermal test method can simulate the heat rejection performance of radiator correctly and the temperature error between in-orbit theory value and experiment result of the radiator is less than 0.5 °C, except for the equipment startup period. This provides a potential method for the thermal test of space systems especially for extra-large spacecraft which employs single-phase fluid loop radiator as thermal control approach.

  12. Convective environment in pre-monsoon and monsoon conditions over the Indian subcontinent: the impact of surface forcing

    Directory of Open Access Journals (Sweden)

    L. Thomas

    2018-05-01

    Full Text Available Thermodynamic soundings for pre-monsoon and monsoon seasons from the Indian subcontinent are analysed to document differences between convective environments. The pre-monsoon environment features more variability for both near-surface moisture and free-tropospheric temperature and moisture profiles. As a result, the level of neutral buoyancy (LNB and pseudo-adiabatic convective available potential energy (CAPE vary more for the pre-monsoon environment. Pre-monsoon soundings also feature higher lifting condensation levels (LCLs. LCL heights are shown to depend on the availability of surface moisture, with low LCLs corresponding to high surface humidity, arguably because of the availability of soil moisture. A simple theoretical argument is developed and showed to mimic the observed relationship between LCLs and surface moisture. We argue that the key element is the partitioning of surface energy flux into its sensible and latent components, that is, the surface Bowen ratio, and the way the Bowen ratio affects surface buoyancy flux. We support our argument with observations of changes in the Bowen ratio and LCL height around the monsoon onset, and with idealized simulations of cloud fields driven by surface heat fluxes with different Bowen ratios.

  13. Numerical investigation of double diffusive buoyancy forces induced natural convection in a cavity partially heated and cooled from sidewalls

    Directory of Open Access Journals (Sweden)

    Rasoul Nikbakhti

    2016-03-01

    Full Text Available This paper deals with a numerical investigation of double-diffusive natural convective heat and mass transfer in a cavity filled with Newtonian fluid. The active parts of two vertical walls of the cavity are maintained at fixed but different temperatures and concentrations, while the other two walls, as well as inactive areas of the sidewalls, are considered to be adiabatic and impermeable to mass transfer. The length of the thermally active part equals half of the height. The non-dimensional forms of governing transport equations that describe double-diffusive natural convection for two-dimensional incompressible flow are functions of temperature or energy, concentration, vorticity, and stream-function. The coupled differential equations are discretized via FDM (Finite Difference Method. The Successive-Over-Relaxation (SOR method is used in the solution of the stream function equation. The analysis has been done for an enclosure with different aspect ratios ranging from 0.5 to 11 for three different combinations of partially active sections. The results are presented graphically in terms of streamlines, isotherms and isoconcentrations. In addition, the heat and mass transfer rate in the cavity is measured in terms of the average Nusselt and Sherwood numbers for various parameters including thermal Grashof number, Lewis number, buoyancy ratio and aspect ratio. It is revealed that the placement order of partially thermally active walls and the buoyancy ratio influence significantly the flow pattern and the corresponding heat and mass transfer performance in the cavity.

  14. A Transformer-less Single Phase Inverter For photovoltaic Systems

    DEFF Research Database (Denmark)

    Mostaan, Ali; Alizadeh, Ebrahim; Qu, Ying

    2017-01-01

    A single phase transformer-less inverter is introduced in this paper. The negative polarities of the input voltage and output terminal have common ground. Therefore, the leakage current problem that is common in PV systems is eliminated naturally. In addition, the proposed inverter has fewer comp...

  15. Dynamics Assessment of Advanced Single-Phase PLL Structures

    DEFF Research Database (Denmark)

    Golestan, Saeed; Monfarad, Mohammad; Freijedo, Francisco D.

    2013-01-01

    Recently, several advanced phase locked loop (PLL) techniques have been proposed for single-phase applications. Among these, the Park-PLL, and the second order generalized integrator (SOGI) based PLL are very attractive, owing to their simple digital implementation, low computational burden...

  16. experimental implementation of single-phase, three-level, sinusoidal

    African Journals Online (AJOL)

    Page 1 ... of many multilevel inverter configurations. This paper presents an experimental report of a simplified topology for single-phase, SPWM, three-level voltage source inverter wit R-L load. To keep the power circuit ... employed in many industrial applications such as variable speed drives, uninterruptible power sup-.

  17. An Asymmetrical Space Vector Method for Single Phase Induction Motor

    DEFF Research Database (Denmark)

    Cui, Yuanhai; Blaabjerg, Frede; Andersen, Gert Karmisholt

    2002-01-01

    Single phase induction motors are the workhorses in low-power applications in the world, and also the variable speed is necessary. Normally it is achieved either by the mechanical method or by controlling the capacitor connected with the auxiliary winding. Any above method has some drawback which...

  18. Solar-Based Boost Differential Single Phase Inverter | Eya | Nigerian ...

    African Journals Online (AJOL)

    Solar-Based Boost Differential Single Phase Inverter. ... Solar-based boost differential inverter is reduced down to 22.37% in closed loop system with the aid of Proportional –integral-Differential (PID) ... The dc power source is photovoltaic cell.

  19. A single phase photovoltaic inverter control for grid connected system

    Indian Academy of Sciences (India)

    This paper presents a control scheme for single phase grid connected photovoltaic (PV) system operating under both grid connected and isolated grid mode. The control techniques include voltage and current control of grid-tie PV inverter. During grid connected mode, grid controls the amplitude and frequency of the PV ...

  20. A simple output voltage control scheme for single phase wavelet ...

    African Journals Online (AJOL)

    DR OKE

    of the wavelet modulated (WM) scheme is that a single synthesis function, derived ... a single-phase H-bridge voltage-source (VS) inverter using MATLAB simulations. ... reconstruction process has been suggested to device a new class of ...

  1. Single-phase convection heat transfer characteristics of pebble-bed channels with internal heat generation

    International Nuclear Information System (INIS)

    Meng Xianke; Sun Zhongning; Xu Guangzhan

    2012-01-01

    Graphical abstract: The core of the water-cooled pebble bed reactor is the porous channels which stacked with spherical fuel elements. The gaps between the adjacent fuel elements are complex because they are stochastic and often shift. We adopt electromagnetic induction heating method to overall heat the pebble bed. By comparing and analyzing the experimental data, we get the rule of power distribution and the rule of heat transfer coefficient with particle diameter, heat flux density, inlet temperature and working fluid's Re number. Highlights: ► We adopt electromagnetic induction heating method to overall heat the pebble bed to be the internal heat source. ► The ball diameter is smaller, the effect of the heat transfer is better. ► With Re number increasing, heat transfer coefficient is also increasing and eventually tends to stabilize. ► The changing of heat power makes little effect on the heat transfer coefficient of pebble bed channels. - Abstract: The reactor core of a water-cooled pebble bed reactor includes porous channels that are formed by spherical fuel elements. This structure has notably improved heat transfer. Due to the variability and randomness of the interstices in pebble bed channels, heat transfer is complex, and there are few studies regarding this topic. To study the heat transfer characters of pebble bed channels with internal heat sources, oxidized stainless steel spheres with diameters of 3 and 8 mm and carbon steel spheres with 8 mm diameters are used in a stacked pebble bed. Distilled water is used as a refrigerant for the experiments, and the electromagnetic induction heating method is used to heat the pebble bed. By comparing and analyzing the experimental results, we obtain the governing rules for the power distribution and the heat transfer coefficient with respect to particle diameter, heat flux density, inlet temperature and working fluid Re number. From fitting of the experimental data, we obtain the dimensionless average heat transfer coefficient correlation criteria and find that the deviation between the fitted results and the experimental results is 12% or less.

  2. Optimal selection of annulus radius ratio to enhance heat transfer with minimum entropy generation in developing laminar forced convection of water-Al2O3 nanofluid flow

    Institute of Scientific and Technical Information of China (English)

    Siavashi Majid; Jamali Mohammad

    2017-01-01

    Heat transfer and entropy generation of developing laminar forced convection flow of water-Al2O3 nanofluid in a concentric annulus with constant heat flux on the walls is investigated numerically. In order to determine entropy generation of fully developed flow, two approaches are employed and it is shown that only one of these methods can provide appropriate results for flow inside annuli. The effects of concentration of nanoparticles, Reynolds number and thermal boundaries on heat transfer enhancement and entropy generation of developing laminar flow inside annuli with different radius ratios and same cross sectional areas are studied. The results show that radius ratio is a very important decision parameter of an annular heat exchanger such that in each Re, there is an optimum radius ratio to maximize Nu and minimize entropy generation. Moreover, the effect of nanoparticles concentration on heat transfer enhancement and minimizing entropy generation is stronger at higher Reynolds.

  3. An experimental comparison between forced convection burn-out in freon 12 flowing vertically upwards through uniformly and non-uniformly heated round tubes

    International Nuclear Information System (INIS)

    Stevens, G.F.; Elliott, D.F.; Wood, R.W.

    1965-05-01

    Some correlations of forced convection burn-out data are based on the approximate linearity of the relationship between burn-out heat flux and the channel-averaged quality at the burn-out point. These correlations perform satisfactorily on data obtained from uniformly heated configurations. Therefore the further inference is sometimes made that the burn-out heat flux is uniquely related to the quality, and that the burn-out in non-uniformly heated configurations can be calculated from measurements made with uniform heating. This report presents burn-out data for Freon 12 flowing vertically upwards through both uniformly and non-uniformly heated round tubes. This data shows that the quality at burn-out does depend on the heat flux profile, and that the inference mentioned above is not justified. (author)

  4. Overview of Single-Phase Grid-Connected Photovoltaic Systems

    DEFF Research Database (Denmark)

    Yang, Yongheng; Blaabjerg, Frede

    2017-01-01

    A continuous booming installation of solar photovoltaic (PV) systems has been witnessed worldwide. It is mainly driven by the imperative demand of “clean” power generation from renewables. Grid-connected PV systems will thus become an even more active player in the future mixed power systems, which...... systems. This chapter thus gives an overview of the advancement of power electronics converters in single-phase grid-connected PV systems, being commonly used in residential applications. Demands to single-phase grid-connected PV systems and the general control strategies are also addressed...... are linked together by a vast of power electronics converters and the power grid. In order to achieve a reliable and efficient power generation from PV systems, more stringent demands have been imposed on the entire PV system. It, in return, advances the development of the power converter technology in PV...

  5. Permanent split capacitor single phase electric motor system

    Science.gov (United States)

    Kirschbaum, H.S.

    1984-08-14

    A permanent split capacitor single phase electric motor achieves balanced operation at more than one operating point by adjusting the voltage supplied to the main and auxiliary windings and adjusting the capacitance in the auxiliary winding circuit. An intermediate voltage tap on an autotransformer supplies voltage to the main winding for low speed operation while a capacitive voltage divider is used to adjust the voltage supplied to the auxiliary winding for low speed operation. 4 figs.

  6. Observing Convective Aggregation

    Science.gov (United States)

    Holloway, Christopher E.; Wing, Allison A.; Bony, Sandrine; Muller, Caroline; Masunaga, Hirohiko; L'Ecuyer, Tristan S.; Turner, David D.; Zuidema, Paquita

    2017-11-01

    Convective self-aggregation, the spontaneous organization of initially scattered convection into isolated convective clusters despite spatially homogeneous boundary conditions and forcing, was first recognized and studied in idealized numerical simulations. While there is a rich history of observational work on convective clustering and organization, there have been only a few studies that have analyzed observations to look specifically for processes related to self-aggregation in models. Here we review observational work in both of these categories and motivate the need for more of this work. We acknowledge that self-aggregation may appear to be far-removed from observed convective organization in terms of time scales, initial conditions, initiation processes, and mean state extremes, but we argue that these differences vary greatly across the diverse range of model simulations in the literature and that these comparisons are already offering important insights into real tropical phenomena. Some preliminary new findings are presented, including results showing that a self-aggregation simulation with square geometry has too broad distribution of humidity and is too dry in the driest regions when compared with radiosonde records from Nauru, while an elongated channel simulation has realistic representations of atmospheric humidity and its variability. We discuss recent work increasing our understanding of how organized convection and climate change may interact, and how model discrepancies related to this question are prompting interest in observational comparisons. We also propose possible future directions for observational work related to convective aggregation, including novel satellite approaches and a ground-based observational network.

  7. Single-phase high-entropy alloys. An overview

    Energy Technology Data Exchange (ETDEWEB)

    Kozak, Roksolana; Steurer, Walter [ETH Zurich (Switzerland). Lab. of Crystallography; Sologubenko, Alla [ETH Zurich (Switzerland). Lab. of Nanotechnology

    2015-02-01

    The term 'high-entropy alloys (HEAs)' first appeared about 10 years ago defining alloys composed of n=5-13 principal elements with concentrations of approximately 100/n at.% each. Since then many equiatomic (or near equiatomic) single- and multi-phase multicomponent alloys were developed, which are reported for a combination of tunable properties: high hardness, strength and ductility, oxidation and wear resistance, magnetism, etc. In our paper, we focus on probably single-phase HEAs (solid solutions) out of all HEAs studied so far, discuss ways of their prediction, mechanical properties. In contrast to classical multielement/multiphase alloys, only single-phase multielement alloys (solid solutions) represent the basic concept underlying HEAs as mixing-entropy stabilized homogenous materials. The literature overview is complemented by own studies demonstrating that the alloys CrFeCoNi, CrFeCoNiAl{sub 0.3} and PdFeCoNi homogenized at 1300 and 1100 C, respectively, for 1 week are not single-phase HEAs, but a coherent mixture of two solid solutions.

  8. The influence of nanoparticle migration on forced convective heat transfer of nanofluid under heating and cooling regimes.

    Science.gov (United States)

    Kozlova, Sofya V; Ryzhkov, Ilya I

    2014-09-01

    In this paper, laminar convective heat transfer of water-alumina nanofluid in a circular tube with uniform heat flux at the tube wall is investigated. The investigation is performed numerically on the basis of two-component model, which takes into account nanoparticle transport by diffusion and thermophoresis. Two thermal regimes at the tube wall, heating and cooling, are considered and the influence of nanoparticle migration on the heat transfer is analyzed comparatively. The intensity of thermophoresis is characterized by a new empirical model for thermophoretic mobility. It is shown that the nanoparticle volume fraction decreases (increases) in the boundary layer near the wall under heating (cooling) due to thermophoresis. The corresponding variations of nanofluid properties and flow characteristics are presented and discussed. The intensity of heat transfer for the model with thermophoresis in comparison to the model without thermophoresis is studied by plotting the dependence of the heat transfer coefficient on the Peclet number. The effectiveness of water-alumina nanofluid is analyzed by plotting the average heat transfer coefficient against the required pumping power. The analysis of the results reveals that the water-alumina nanofluid shows better performance in the heating regime than in the cooling regime due to thermophoretic effect.

  9. Effect of microscale protrusions on local fluid flow and mass transport in the presence of forced convection

    Energy Technology Data Exchange (ETDEWEB)

    Matzen, Gehard W. [Univ. of California, Berkeley, CA (United States)

    1997-01-01

    Three-dimensional creeping flow around single, axisymmetric protrusions is studied numerically using the boundary-integral technique. Emphasis is placed upon cylindrical protrusions on plane walls for various height-to-radius (h-to-a) aspect ratios, but cones and sections of spheres protruding from plane walls are also briefly examined. The presented items include shear-stress distributions, shear-stress contours, extents of the fluid-flow disturbance, total forces and torques on the cylinders, streamlines, and skin-friction lines. Also included is a discussion of flow topology around axisymmetric geometries. No flow reversal is observed for cylindrical protrusions with aspect ratios greater than 2.4 to 2.6. At higher aspect ratios, the fluid tends to be swept around cylindrical protrusions with little vertical motion. At lower aspect ratios, the strength of the recirculation increases, and the recirculation region becomes wider in the transverse direction and narrower in the flow direction. Also, the recirculation pattern begins to resemble the closed streamline patterns in two-dimensional flow over square ridges. However, unlike two-dimensional flow, closed streamline patterns are not observed. For arbitrary axisymmetric geometries, the extent of the fluid-flow disturbance can be estimated with the total force that is exerted on the protrusion. When the same force is exerted on protrusions with different aspect ratios, the protrusion with the higher aspect ratio tends to have a greater disturbance in the flow direction and a smaller disturbance in the transverse direction. The total force exerted on cylindrical protrusions with rounded corners is only slightly lower than the total force exerted on cylindrical protrusions with sharp corners.

  10. Investigation on a Novel Discontinuous Pulse-Width Modulation Algorithm for Single-phase Voltage Source Rectifier

    DEFF Research Database (Denmark)

    Qu, Hao; Yang, Xijun; Guo, Yougui

    2014-01-01

    Single-phase voltage source converter (VSC) is an important power electronic converter (PEC), including single-phase voltage source inverter (VSI), single-phase voltage source rectifier (VSR), single-phase active power filter (APF) and single-phase grid-connection inverter (GCI). Single-phase VSC...

  11. Noninvasive estimation of transmitral pressure drop across the normal mitral valve in humans: importance of convective and inertial forces during left ventricular filling

    Science.gov (United States)

    Firstenberg, M. S.; Vandervoort, P. M.; Greenberg, N. L.; Smedira, N. G.; McCarthy, P. M.; Garcia, M. J.; Thomas, J. D.

    2000-01-01

    OBJECTIVES: We hypothesized that color M-mode (CMM) images could be used to solve the Euler equation, yielding regional pressure gradients along the scanline, which could then be integrated to yield the unsteady Bernoulli equation and estimate noninvasively both the convective and inertial components of the transmitral pressure difference. BACKGROUND: Pulsed and continuous wave Doppler velocity measurements are routinely used clinically to assess severity of stenotic and regurgitant valves. However, only the convective component of the pressure gradient is measured, thereby neglecting the contribution of inertial forces, which may be significant, particularly for nonstenotic valves. Color M-mode provides a spatiotemporal representation of flow across the mitral valve. METHODS: In eight patients undergoing coronary artery bypass grafting, high-fidelity left atrial and ventricular pressure measurements were obtained synchronously with transmitral CMM digital recordings. The instantaneous diastolic transmitral pressure difference was computed from the M-mode spatiotemporal velocity distribution using the unsteady flow form of the Bernoulli equation and was compared to the catheter measurements. RESULTS: From 56 beats in 16 hemodynamic stages, inclusion of the inertial term ([deltapI]max = 1.78+/-1.30 mm Hg) in the noninvasive pressure difference calculation significantly increased the temporal correlation with catheter-based measurement (r = 0.35+/-0.24 vs. 0.81+/-0.15, pforces are significant components of the maximal pressure drop across the normal mitral valve. These can be accurately estimated noninvasively using CMM recordings of transmitral flow, which should improve the understanding of diastolic filling and function of the heart.

  12. Potential of enhancing a natural convection loop with a thermomagnetically pumped ferrofluid

    Energy Technology Data Exchange (ETDEWEB)

    Aursand, Eskil; Gjennestad, Magnus Aa.; Lervåg, Karl Yngve, E-mail: karl.lervag@sintef.no; Lund, Halvor

    2016-11-01

    The feasibility of using a thermomagnetically pumped ferrofluid to enhance the performance of a natural convection cooling loop is investigated. First, a simplified analytical estimate for the thermomagnetic pumping action is derived, and then design rules for optimal solenoid and ferrofluid are presented. The design rules are used to set up a medium-scale (1 m, 10–1000 W) case study, which is modeled using a previously published and validated model (Aursand et al. [1]). The results show that the thermomagnetic driving force is significant compared to the natural convection driving force, and may in some cases greatly surpass it. The results also indicate that cooling performance can be increased by factors up to 4 and 2 in the single-phase and two-phase regimes, respectively, even when taking into the account the added heat from the solenoid. The performance increases can alternatively be used to obtain a reduction in heat-sink size by up to 75%. - Highlights: • We consider a thermomagnetically pumped ferrofluid for heat transfer. • The performance of the thermomagnetic pump is compared to natural convection. • The flow is simulated using a two-phase flow model. • The thermomagnetic driving force improves heat transfer significantly.

  13. Liquid Salts as Media for Process Heat Transfer from VHTR's: Forced Convective Channel Flow Thermal Hydraulics, Materials, and Coating

    Energy Technology Data Exchange (ETDEWEB)

    Sridharan, Kumar; Anderson, Mark; Allen, Todd; Corradini, Michael

    2012-01-30

    on Cr-carbide on the graphite surface. Ni-electroplating dramatically reduced corrosion of alloys, although some diffusion of Fe and Cr were observed occur through the Ni plating. A pyrolytic carbon and SiC (PyC/SiC) CVD coating was also investigated and found to be effective in mitigating corrosion. The KCl-MgCl2 molten salt was less corrosive than FLiNaK fluoride salts for corrosion tests performed at 850oC. Cr dissolution in the molten chloride salt was still observed and consequently Ni-201 and Hastelloy N exhibited the least depth of attack. Grain-boundary engineering (GBE) of Incoloy 800H improved the corrosion resistance (as measured by weight loss and maximum depth of attack) by nearly 50% as compared to the as-received Incoloy 800H sample. Because Cr dissolution is an important mechanism of corrosion, molten salt electrochemistry experiments were initiated. These experiments were performed using anodic stripping voltammetry (ASV). Using this technique, the reduction potential of Cr was determined against a Pt quasi-reference electrode as well as against a Ni(II)-Ni reference electrode in molten FLiNaK at 650 oC. The integrated current increased linearly with Cr-content in the salt, providing for a direct assessment of the Cr concentration in a given salt of unknown Cr concentration. To study heat transfer mechanisms in these molten salts over the forced and mixed convection regimes, a forced convective loop was constructed to measure heat transfer coefficients, friction factors and corrosion rates in different diameter tubes in a vertical up flow configuration in the laminar flow regime. Equipment and instrumentation for the forced convective loop was designed, constructed, and tested. These include a high temperature centrifugal pump, mass flow meter, and differential pressure sensing capabilities to an uncertainty of < 2 Pa. The heat transfer coefficient for the KCl-MgCl2 salt was measured in two different diameter channels (0.083 and 0.370Ã). In the 0

  14. Thermal-Hydraulic Analyses of Transients in an Actinide-Burner Reactor Cooled by Forced Convection of Lead Bismuth

    Energy Technology Data Exchange (ETDEWEB)

    Davis, Cliff Bybee

    2003-09-01

    The Idaho National Engineering and Environmental Laboratory (INEEL) and the Massachusetts Institute of Technology (MIT) are investigating the suitability of lead or lead–bismuth cooled fast reactors for producing low-cost electricity as well as for actinide burning. The current analysis evaluated a pool type design that relies on forced circulation of the primary coolant, a conventional steam power conversion system, and a passive decay heat removal system. The ATHENA computer code was used to simulate various transients without reactor scram, including a primary coolant pump trip, a station blackout, and a step reactivity insertion. The reactor design successfully met identified temperature limits for each of the transients analyzed.

  15. Computational simulation of flow and heat transfer in single-phase natural circulation loops

    International Nuclear Information System (INIS)

    Pinheiro, Larissa Cunha

    2017-01-01

    Passive decay heat removal systems based on natural circulation are essential assets for the new Gen III+ nuclear power reactors and nuclear spent fuel pools. The aim of the present work is to study both laminar and turbulent flow and heat transfer in single-phase natural circulation systems through computational fluid dynamics simulations. The working fluid is considered to be incompressible with constant properties. In the way, the Boussinesq Natural Convection Hypothesis was applied. The model chosen for the turbulence closure problem was the k -- εThe commercial computational fluid dynamics code ANSYS CFX 15.0 was used to obtain the numerical solution of the governing equations. Two single-phase natural circulation circuits were studied, a 2D toroidal loop and a 3D rectangular loop, both with the same boundary conditions of: prescribed heat flux at the heater and fixed wall temperature at the cooler. The validation and verification was performed with the numerical data provided by DESRAYAUD et al. [1] and the experimental data provided by MISALE et al. [2] and KUMAR et al. [3]. An excellent agreement between the Reynolds number (Re) and the modified Grashof number (Gr_m), independently of Prandtl Pr number was observed. However, the convergence interval was observed to be variable with Pr, thus indicating that Pr is a stability governing parameter for natural circulation. Multiple steady states was obtained for Pr = 0,7. Finally, the effect of inclination was studied for the 3D circuit, both in-plane and out-of-plane inclinations were verified for the steady state laminar regime. As a conclusion, the Re for the out-of-plane inclination was in perfect agreement with the correlation found for the zero inclination system, while for the in-plane inclined system the results differ from that of the corresponding vertical loop. (author)

  16. Investigation of effect of single phase electrical faults at LOFT

    International Nuclear Information System (INIS)

    Yeates, J.A.

    1978-01-01

    This LTR presents the general basic engineering facts related to an open phase fault in a three phase power system commonly referred to as a single phase condition. It describes the probable results to electrical motors and describes the LOFT system design factors which minimize the likelihood of such a fault occurring at LOFT. It recognizes that the hazard of such a fault is a realistic threat and notes the types of relays designed to provide protection. Recommendations are made to perform a detailed engineering study to determine the most advantageous protective relay design, and to implement such a design by installation of the necessary devices and controls

  17. Ultrafast Switching Superjunction MOSFETs for Single Phase PFC Applications

    DEFF Research Database (Denmark)

    Hernandez Botella, Juan Carlos; Petersen, Lars Press; Andersen, Michael A. E.

    2014-01-01

    This paper presents a guide on characterizing state-of-the-art silicon superjunction (SJ) devices in the 600V range for single phase power factor correction (PFC) applications. The characterization procedure is based on a minimally inductive double pulse tester (DPT) with a very low intrusive...... current measurement method, which enables reaching the switching speed limits of these devices. Due to the intrinsic low and non-linear capacitances in vertical SJ MOSFETs, special attention needs to be paid to the gate drive design to minimize oscillations and limit the maximum at turn off. This paper...

  18. Critical flow rate in a single phase flow. Blocking concept

    International Nuclear Information System (INIS)

    Giot, Michel

    1978-01-01

    After referring to the phenomena accompanying the appearance of a critical flow rate in a nozzle and presenting equations governing single phase flows, the critical condition is defined. Several particular cases are then examined; the horizontal and vertical isentropic flow, Fanno's flow and Raleigh's and the isothermal flow. The entropy deviation is calculated on either side of a normal impact. To conclude, the link existing between the concepts of critical flow and the propagation rate of small perturbations is demonstrated. To do so, the method of perturbations, that of Prandtl and that of characteristic directions are applied in turn [fr

  19. Control of Single-Stage Single-Phase PV inverter

    DEFF Research Database (Denmark)

    Ciobotaru, Mihai; Teodorescu, Remus; Blaabjerg, Frede

    2005-01-01

    In this paper the issue of control strategies for single-stage photovoltaic (PV) inverter is addressed. Two different current controllers have been implemented and an experimental comparison between them has been made. A complete control structure for the single-phase PV system is also presented......-forward; - and the grid current controller implemented in two different ways, using the classical proportional integral (PI) and the novel proportional resonant (PR) controllers. The control strategy was tested experimentally on 1.5 kW PV inverter....

  20. A numerical modeling study of the interaction between the tides and the circulation forced by high-latitude plasma convection

    International Nuclear Information System (INIS)

    Mikkelsen, I.S.; Larsen, M.F.

    1991-01-01

    A spectral, time-varying thermospheric general circulation model has been used to study the nonlinear interaction at high latitudes between the tides propagating into the thermosphere from below and the circulation induced by magnetospheric forcing and in situ solar heating. The model is discrete in the vertical with 27 layers spaced by half a scale height. In the horizontal, the fields are expanded in a series of spherical harmonics using a triangular truncation at wave number 31, equivalent to a homogeneous global resolution with a minimum wavelength of 1,270 km. A hypothetical uniform grid point model would require a horizontal spacing of 417 km to describe the same minimum wavelength. In the high-latitude F region the tides affect the dusk vortex of the neutral flow very little, but the dawn vortex is either suppressed or amplified dependent upon the universal time and tidal phase. In the E region neutral flow, both the dusk and dawn vortices are shifted in local time by the tides, again as a function of universal time and tidal phase. At dusk a nonlinear amplification of the sunward winds occurs for certain combination of parameters, and at dawn the winds may be completely suppressed. Below 120 km altitude the magnetospheric forcing creates a single cyclonic vortex which is also sensitive to the high-latitude tidal structure

  1. Benchmarking of thermalhydraulic loop models for lead-alloy-cooled advanced nuclear energy systems. Phase I: Isothermal forced convection case

    International Nuclear Information System (INIS)

    2012-06-01

    Under the auspices of the NEA Nuclear Science Committee (NSC), the Working Party on Scientific Issues of the Fuel Cycle (WPFC) has been established to co-ordinate scientific activities regarding various existing and advanced nuclear fuel cycles, including advanced reactor systems, associated chemistry and flowsheets, development and performance of fuel and materials and accelerators and spallation targets. The WPFC has different expert groups to cover a wide range of scientific issues in the field of nuclear fuel cycle. The Task Force on Lead-Alloy-Cooled Advanced Nuclear Energy Systems (LACANES) was created in 2006 to study thermal-hydraulic characteristics of heavy liquid metal coolant loop. The objectives of the task force are to (1) validate thermal-hydraulic loop models for application to LACANES design analysis in participating organisations, by benchmarking with a set of well-characterised lead-alloy coolant loop test data, (2) establish guidelines for quantifying thermal-hydraulic modelling parameters related to friction and heat transfer by lead-alloy coolant and (3) identify specific issues, either in modelling and/or in loop testing, which need to be addressed via possible future work. Nine participants from seven different institutes participated in the first phase of the benchmark. This report provides details of the benchmark specifications, method and code characteristics and results of the preliminary study: pressure loss coefficient and Phase-I. A comparison and analysis of the results will be performed together with Phase-II

  2. Cell structures caused by settling particles in turbulent Rayleigh-Bénard convection

    Science.gov (United States)

    Lee, Changhoon; Park, Sangro

    2016-11-01

    Turbulent thermal convection is an important phenomenon frequently found in nature and industrial processes, often with laden particles. In the last several decades, the vast majority of studies have addressed single phase convective flow with focus on the scaling relation of flow parameters associated with heat transfer. Particle-laden Rayleigh-Bénard convection, however, has not been sufficiently studied. In this study, modulation of cell structures by settling particles in turbulent Rayleigh-Bénard convection in a doubly periodic square channel is investigated using direct numerical simulation with a point particle approach. Flow parameters are fixed at Rayleigh number=106, Prandtl number=0.7, the aspect ratio=6, and Froude number=0.19. We report from the simulations that settling heavy particles modulate irregular large-scale thermal plume structures into organized polygonal cell structures. Different shapes of flow structures are obtained for different particle diameters and mass loadings. We found that polygonal cell structures arise due to asymmetric feedback force exerted by particles onto hot and cold plumes. Increasing the number of particles augments the asymmetry and the polygonal cell structures become smaller, eventually going to the hexagonal structures.

  3. Modelling a single phase voltage controlled rectifier using Laplace transforms

    Science.gov (United States)

    Kraft, L. Alan; Kankam, M. David

    1992-01-01

    The development of a 20 kHz, AC power system by NASA for large space projects has spurred a need to develop models for the equipment which will be used on these single phase systems. To date, models for the AC source (i.e., inverters) have been developed. It is the intent of this paper to develop a method to model the single phase voltage controlled rectifiers which will be attached to the AC power grid as an interface for connected loads. A modified version of EPRI's HARMFLO program is used as the shell for these models. The results obtained from the model developed in this paper are quite adequate for the analysis of problems such as voltage resonance. The unique technique presented in this paper uses the Laplace transforms to determine the harmonic content of the load current of the rectifier rather than a curve fitting technique. Laplace transforms yield the coefficient of the differential equations which model the line current to the rectifier directly.

  4. Visualization of Two Phase Natural Convection Flow in a Vertical Pipe using the Sulfuric Acid - Copper Sulfate Electroplating System

    Energy Technology Data Exchange (ETDEWEB)

    Ohk, Seung-Min; Chae, Myeong-Seon; Chung, Bum-Jin [Kyung Hee Univ., Yongin (Korea, Republic of)

    2014-10-15

    The passive containment cooling system (PCCS) driven by natural forces convection gain draws research interests after Fukushima NPP accident. The PCCS was classified into three categories: Containment pressure suppression, Containment passive heat removal/pressure suppression systems and Passive containment spray. Among the types of containment passive heat removal/pressure suppression systems, the system composed of an internal heat exchanger and an external coolant tank is considered. In a severe accident condition, the heat from the containment atmosphere is transferred to the outer surface of the heat exchanger by the convection and condensation of the mixture of steam and gases. On the other hand, the heat is transferred to external pool by single phase or two phase natural convection inside of heat exchanger pipes. The study aimed at investigating the influence of the diameter (D) and height (H) of the heat exchanger pipes on the single phase and two phase natural convection heat transfer. As the initial stage of the study, the two phase natural convection flow inside a vertical pipe is visualized. In order to achieve the aim with ample test rig, a sulfuric acid - cooper sulfate electroplating system was employed based on the analogy between heat and mass transfer. The reduction of hydrogen ion at the cathode surface at high potential was used to simulate the boiling phenomena. This study tried to visualize the boiling heat transfer inside a vertical pipe using a cupric acid-copper sulfate (H{sub 2}SO{sub 4}-CuSO{sub 4}) electroplating system. This seems to be successful so far. However further study has to be done to compare the result with real two phase flow situation. The surface tension and surface characteristics are to be tuned to simulate the real situation.

  5. Developing the laminar MHD forced convection flow of water/FMWNT carbon nanotubes in a microchannel imposed the uniform heat flux

    Energy Technology Data Exchange (ETDEWEB)

    Karimipour, Arash; Taghipour, Abdolmajid [Department of Mechanical Engineering, Najafabad Branch, Islamic Azad University, Najafabad (Iran, Islamic Republic of); Malvandi, Amir, E-mail: amirmalvandi@aut.ac.ir [Department of Mechanical Engineering, Neyshabur Branch, Islamic Azad University, Neyshabur (Iran, Islamic Republic of)

    2016-12-01

    This paper aims to investigate magnetic field and slip effects on developing laminar forced convection of nanofluids in the microchannels. A novel mixture of water and FMWNT carbon nanotubes is used as the working fluid. To do this, fluid flow and heat transfer through a microchannel is simulated by a computer code in FORTRAN language. The mixture of FMWNT carbon nanotubes suspended in water is considered as the nanofluid. Slip velocity is supposed as the hydrodynamic boundary condition while the microchannel's lower wall is insulated and the top wall is under the effect of a constant heat flux. Moreover, the flow field is subjected to a magnetic field with a constant strength. The results are presented as the velocity, temperature and Nusselt number profiles. It is observed that nanofluid composed of water and carbon nanotubes (FMWNT) can work well to increase the heat transfer rate along the microchannel walls. Furthermore, it is indicated that imposing the magnetic field is very effective at the thermally developing region. In contrast, the magnetic field effect at fully developed region is insignificant, especially at low values of Reynolds number. - Highlights: • Simulation of water/FMWNT carbon nanotubes flow in a microchannel. • The effects of magnetic field strength on nanofluid's slip velocity. • The effects of Ha, Re, ϕ and slip coefficient on averaged Nusselt number. • Magnetic field effect at developing flow region is significant.

  6. Influence of Lorentz force, Cattaneo-Christov heat flux and viscous dissipation on the flow of micropolar fluid past a nonlinear convective stretching vertical surface

    Science.gov (United States)

    Gnaneswara Reddy, Machireddy

    2017-12-01

    The problem of micropolar fluid flow over a nonlinear stretching convective vertical surface in the presence of Lorentz force and viscous dissipation is investigated. Due to the nature of heat transfer in the flow past vertical surface, Cattaneo-Christov heat flux model effect is properly accommodated in the energy equation. The governing partial differential equations for the flow and heat transfer are converted into a set of ordinary differential equations by employing the acceptable similarity transformations. Runge-Kutta and Newton's methods are utilized to resolve the altered governing nonlinear equations. Obtained numerical results are compared with the available literature and found to be an excellent agreement. The impacts of dimensionless governing flow pertinent parameters on velocity, micropolar velocity and temperature profiles are presented graphically for two cases (linear and nonlinear) and analyzed in detail. Further, the variations of skin friction coefficient and local Nusselt number are reported with the aid of plots for the sundry flow parameters. The temperature and the related boundary enhances enhances with the boosting values of M. It is found that fluid temperature declines for larger thermal relaxation parameter. Also, it is revealed that the Nusselt number declines for the hike values of Bi.

  7. 30 CFR 77.806 - Connection of single-phase loads.

    Science.gov (United States)

    2010-07-01

    ... COAL MINES Surface High-Voltage Distribution § 77.806 Connection of single-phase loads. Single-phase loads, such as transformer primaries, shall be connected phase to phase in resistance grounded systems. ...

  8. 30 CFR 77.905 - Connection of single-phase loads.

    Science.gov (United States)

    2010-07-01

    ... COAL MINES Low- and Medium-Voltage Alternating Current Circuits § 77.905 Connection of single-phase loads. Single-phase loads shall be connected phase-to-phase in resistance grounded systems. ...

  9. Experimental and numerical thermohydraulic study of a supercritical helium loop in forced convection under pulsed heat loads

    International Nuclear Information System (INIS)

    Lagier, Benjamin

    2014-01-01

    Future fusion reactor devices such as ITER or JT-60SA will produce thermonuclear fusion reaction in plasmas at several millions of degrees. The confinement in the center of the chamber is achieved by very intense magnetic fields generated by superconducting magnets. These coils have to be cooled down to 4.4 K through a forced flow of supercritical helium. The cyclic behavior of the machines leads to pulsed thermal heat loads which will have to be handled by the refrigerator. The HELIOS experiment built in CEA Grenoble is a scaled down model of the helium distribution system of the tokamak JT-60SA composed of a saturated helium bath and a supercritical helium loop. The thesis work explores HELIOS capabilities for experimental and numerical investigations on three heat load smoothing strategies: the use of the saturated helium bath as an open thermal buffer, the rotation speed variation of the cold circulator and the bypassing of the heated section. The developed model describes well the physical evolutions of the helium loop (pressure, temperature, mass flow) submitted to heat loads observed during experiments. Advanced controls have been tested and validated to improve the stability of the refrigerator and to optimize the refrigeration power. (author) [fr

  10. Experimental studies in a single-phase parallel channel natural circulation system. Preliminary results

    International Nuclear Information System (INIS)

    Bodkha, Kapil; Pilkhwal, D.S.; Jana, S.S.; Vijayan, P.K.

    2016-01-01

    Natural circulation systems find extensive applications in industrial engineering systems. One of the applications is in nuclear reactor where the decay heat is removed by natural circulation of the fluid under off-normal conditions. The upcoming reactor designs make use of natural circulation in order to remove the heat from core under normal operating conditions also. These reactors employ multiple vertical fuel channels with provision of on-power refueling/defueling. Natural circulation systems are relatively simple, safe and reliable when compared to forced circulation systems. However, natural circulation systems are prone to encounter flow instabilities which are highly undesirable for various reasons. Presence of parallel channels under natural circulation makes the system more complicated. To examine the behavior of parallel channel system, studies were carried out for single-phase natural circulation flow in a multiple vertical channel system. The objective of the present work is to study the flow behavior of the parallel heated channel system under natural circulation for different operating conditions. Steady state and transient studies have been carried out in a parallel channel natural circulation system with three heated channels. The paper brings out the details of the system considered, different cases analyzed and preliminary results of studies carried out on a single-phase parallel channel system.

  11. Hydrogen and helium recycling from a JxB-force convected liquid metal Ga{sub 67}In{sub 20.5}Sn{sub 12.5} under steady state plasma bombardment

    Energy Technology Data Exchange (ETDEWEB)

    Hirooka, Yoshi, E-mail: hirooka.yoshihiko@nifs.ac.jp [National institute for Fusion Science, Oroshi, Toki, Gifu 509-5292 (Japan); Graduate University for Advanced Studies, Oroshi, Toki, Gifu 509-5292 (Japan); Bi, Hailin [Graduate University for Advanced Studies, Oroshi, Toki, Gifu 509-5292 (Japan); Shimada, Michiya [Japan Atomic Energy Agency, Rokkasho, Kamikita, Aomori 039-3212 (Japan); Ono, Masa [Princeton Plasma Physics Laboratory, Princeton, NJ 08543 (United States)

    2017-04-15

    A series of first-of-a-kind laboratory-scale experiments on the JxB-force convected liquid metal divertor concept have been carried out in the temperature range from room temperature to ∼200 °C, employing a eutectic alloy: Ga{sub 67}In{sub 20.5}Sn{sub 12.5}, the melting point of which is 10.5 °C. The electrical current conducted through the alloy is set at about 70A and the magnetic field is set at about 700 G. It has reproducibly been observed that hydrogen as well as helium particle recycling is noticeably reduced under steady state plasma bombardment when the liquid is convected by the JxB force.

  12. Structure and single-phase regime of boron carbides

    International Nuclear Information System (INIS)

    Emin, D.

    1988-01-01

    The boron carbides are composed of twelve-atom icosahedral clusters which are linked by direct covalent bonds and through three-atom intericosahedral chains. The boron carbides are known to exist as a single phase with carbon concentrations from about 8 to about 20 at. %. This range of carbon concentrations is made possible by the substitution of boron and carbon atoms for one another within both the icosahedra and intericosahedral chains. The most widely accepted structural model for B 4 C (the boron carbide with nominally 20% carbon) has B/sub 11/C icosahedra with C-B-C intericosahedral chains. Here, the free energy of the boron carbides is studied as a function of carbon concentration by considering the effects of replacing carbon atoms within B 4 C with boron atoms. It is concluded that entropic and energetic considerations both favor the replacement of carbon atoms with boron atoms within the intericosahedral chains, C-B-C→C-B-B. Once the carbon concentration is so low that the vast majority of the chains are C-B-B chains, near B/sub 13/C 2 , subsequent substitutions of carbon atoms with boron atoms occur within the icosahedra, B/sub 11/C→B/sub 12/. Maxima of the free energy occur at the most ordered compositions: B 4 C,B/sub 13/C 2 ,B/sub 14/C. This structural model, determined by studying the free energy, agrees with that previously suggested by analysis of electronic and thermal transport data. These considerations also provide an explanation for the wide single-phase regime found for boron carbides

  13. Single-phase heat transfer enhancement in micro/minichannels using nanofluids: Theory and applications

    International Nuclear Information System (INIS)

    Hussien, Ahmed A.; Abdullah, Mohd Z.; Al-Nimr, Moh’d A.

    2016-01-01

    Highlights: • Review recent experimental and numerical studies on heat transfer in micro/minichannels and nanofluids. • Display the new applications of using nanofluids and micro/minichannels to enhance thermal performance. • Explain the factors affecting the thermal conductivity enhancement ratio of nanofluids. • The challenges of using the mini/microchannels and nanofluids. - Abstract: New cooling techniques are being explored for the dissipation of heat fluxes. Many recent studies on heat transfer in micro/minichannels (M/MCs) with nanofluids have focused on combining the advantages of both, for the purpose of obtaining higher single-phase enhancement of heat transfer. Developing of many applications such as cooling electronic device, solar cell, and automotive technology is highly demanded now a day to obtain high efficiency and reduce the operating cost. This review article summarizes recent studies, with a focus on two main topics: The first part contains the main concepts such as scaling effects of M/MCs, physical properties and convective heat transfer. The second part displays the main recent applications of M/MCs with nanofluids with the challenges to be widely used. The purpose of this article to provide exhaustive and comprehensive review of updated works published in this new area, with general conclusions.

  14. Design and analysis of linear oscillatory single-phase permanent magnet generator for free-piston stirling engine systems

    Science.gov (United States)

    Kim, Jeong-Man; Choi, Jang-Young; Lee, Kyu-Seok; Lee, Sung-Ho

    2017-05-01

    This study focuses on the design and analysis of a linear oscillatory single-phase permanent magnet generator for free-piston stirling engine (FPSE) systems. In order to implement the design of linear oscillatory generator (LOG) for suitable FPSEs, we conducted electromagnetic analysis of LOGs with varying design parameters. Then, detent force analysis was conducted using assisted PM. Using the assisted PM gave us the advantage of using mechanical strength by detent force. To improve the efficiency, we conducted characteristic analysis of eddy-current loss with respect to the PM segment. Finally, the experimental result was analyzed to confirm the prediction of the FEA.

  15. Design and analysis of linear oscillatory single-phase permanent magnet generator for free-piston stirling engine systems

    Directory of Open Access Journals (Sweden)

    Jeong-Man Kim

    2017-05-01

    Full Text Available This study focuses on the design and analysis of a linear oscillatory single-phase permanent magnet generator for free-piston stirling engine (FPSE systems. In order to implement the design of linear oscillatory generator (LOG for suitable FPSEs, we conducted electromagnetic analysis of LOGs with varying design parameters. Then, detent force analysis was conducted using assisted PM. Using the assisted PM gave us the advantage of using mechanical strength by detent force. To improve the efficiency, we conducted characteristic analysis of eddy-current loss with respect to the PM segment. Finally, the experimental result was analyzed to confirm the prediction of the FEA.

  16. A novel single-phase flux-switching permanent magnet linear generator used for free-piston Stirling engine

    Science.gov (United States)

    Zheng, Ping; Sui, Yi; Tong, Chengde; Bai, Jingang; Yu, Bin; Lin, Fei

    2014-05-01

    This paper investigates a novel single-phase flux-switching permanent-magnet (PM) linear machine used for free-piston Stirling engines. The machine topology and operating principle are studied. A flux-switching PM linear machine is designed based on the quasi-sinusoidal speed characteristic of the resonant piston. Considering the performance of back electromotive force and thrust capability, some leading structural parameters, including the air gap length, the PM thickness, the ratio of the outer radius of mover to that of stator, the mover tooth width, the stator tooth width, etc., are optimized by finite element analysis. Compared with conventional three-phase moving-magnet linear machine, the proposed single-phase flux-switching topology shows advantages in less PM use, lighter mover, and higher volume power density.

  17. On the phenomenon of the reversal of the cooling current in the hot pipes of a swimming-pool type pile cooled by forced convection; Sur un phenomene de renversement du courant de refrigeration dans les canaux chauds d'une pile piscine refroidie en convection forcee

    Energy Technology Data Exchange (ETDEWEB)

    Boure, J [Commissariat a l' Energie Atomique, Grenoble (France).Centre d' Etudes Nucleaires

    1961-07-01

    It is shown, for a swimming-pool type pile cooled by forced convection (general flow downwards), that a permanently stable regime with downward flow in all the channels is not possible when the flow is below a critical value for a given power. In the hot channels the natural convection then becomes preponderant, the direction of the flow is reversed and a permanently stable regime exists for which the flow is upwards in the hot channels. Calculations are made, with simplifying hypotheses in the case of Melusine. (author) [French] Pour une pile piscine refrigeree en convection forcee (ecoulement global descendant), on montre qu'un regime permanent stable avec ecoulement descendant dans tous les canaux est impossible lorsque le debit est inferieur a une valeur critique pour une puissance donnee. Dans les canaux chauds, la convection naturelle l'emporte alors, le sens du courant s'inverse et un regime permanent stable existe, pour lequel le courant est ascendant dans les canaux chauds. On fait les calculs, avec des hypotheses simplificatrices, dans le cas de Melusine. (auteur)

  18. AN EXPERIMENTAL STUDY FOR HEAT TRANSFER ENHANCEMENT BY LAMINAR FORCED CONVECTION FROM HORIZONTAL AND INCLINED TUBE HEATED WITH CONSTANT HEAT FLUX, USING TWO TYPES OF POROUS MEDIA

    Directory of Open Access Journals (Sweden)

    Thamir K. Jassem

    2015-02-01

    Full Text Available An experimental forced laminar study was presented in this research for an air flowing through a circular channel for different angles ( ,30o,45o,60o, the channel was heated at constant heat flux , the channel also was packed with steel and glass spheres respectively . The tests were done for three values of Peclets number (2111.71,3945.42,4575.47 with changing the heat flux for each case and five times for each number.The results showed that the dimensionless temperature distribution  will decrease with increasing the dimensionless channel length for all cases with changing Peclet number, heat flux and inclination angles, and its lowest value will be for glass spheres at highest flux, while at lower flux for , and the decreasing in dimensionless temperature was closed for both types of packed at other inclination angles.The study declared that the local Nusselt number decreases with increasing the dimensionless length of the channel for both packeds and for different applied heat flux, also through this study it was declared that the average Nusselt increases as Peclet number increases for both packed. Its value for the glass spheres is greater than the steel spheres with percentage (98.3% at small Peclet, and percentage (97.2% at large Peclet number for the horizontal tube, and (98.3% at small Peclet number and (97.8% at large Peclet number at  .Through this study its was found that average Nusselt number increases along the channel as the heat flux increases, because the bulk temperature will increase as the flow proceeds toward the end of the channel , so the heat transfer coefficient will increase.  It was declared from this study that in the case of the steel packed the heat transfer will occur mainly by conduction, while in the case of glass packed the heat transfer will occur mainly by laminar forced convection, where the lowest Nusselt number (Nu=3.8 was found when the pipe is horizontal and lowest heat flux and lowest Peclet number.  

  19. Numerical Study of Developing Laminar Forced Convection Flow of Water/CuO Nanofluid in a Circular Tube with a 180 Degrees Curve

    OpenAIRE

    Hamed K. Arzani; Hamid K. Arzani; S.N. Kazi; A. Badarudin

    2016-01-01

    Numerical investigation into convective heat transfer of CuO-Water based nanofluid in a pipe with return bend under laminar flow conditions has been done. The impacts of Reynolds number and the volume concentration of nanoparticles on the flow and the convective heat transfer behaviour are investigated. The results indicate that the increase in Reynolds number leads to the enhancement of average Nusselt number, and the increase in specific heat in the presence of the nanofluid results in impr...

  20. Force convective solar drying system

    International Nuclear Information System (INIS)

    Ruslan, M.H.; Othman, M.Y.; Baharuddin Yatim; Kamaruzzaman Sopian; Ibarahim, Z.

    2006-01-01

    This paper presents design and performance of V-groove back-pass solar collector for solar drying system. In this study three V-groove back-pass solar collector each with dimension of 4.6 m x 1.0 m x 0.15 m have been fabricated for solar drying system. An outdoor test at mean solar intensity for 600-800 Wm -2 by using 0.15m 3 s -1 of air flow rate which also been suggested by (Zeroul et al. 1994) was carried out at Solar Research Energy Park. Universiti Kebangsaan Malaysia. Analysis on the collector performance based on daily data was reported that the value of FR ) e and FRUL was 0.709 ± 0.001 and 5.89 ± 0.31 Wm -2o C -1 respectively with 60-70 o C of output temperature (Ruslan et al. 2001). The three V-groove collectors each with dimension 4.6 m x 0.15 m were connected in series array mounted on the roof of a solar assisted drying system. By using two electric fans of 85W and 2700 rpm each, the speed of air was regulated at 0.11 kgs -1 to 0.31 kgs -1 using a voltage regulator. Performance of the collector based on the thermal analysis showed that at mean daily solar radiation 700 Wm -2 , the output temperature of 52 o C to 73 o C could be achieved using 0.11-0.31 kgs -1 of flow rate. Thermal analysis also showed that the efficiencies of 45% to 61% could be obtains using the same flow rate and solar radiation. Analysis of daily data showed that for radiation from 300 Wm -2 to 1000 Wm -2 the power generated from the collector was within 1.5 kW to 8.9 kW. The study concluded that the levels of the levels of the solar radiation and flow rate used influenced the performance of the collector

  1. A grid-connected single-phase photovoltaic micro inverter

    Science.gov (United States)

    Wen, X. Y.; Lin, P. J.; Chen, Z. C.; Wu, L. J.; Cheng, S. Y.

    2017-11-01

    In this paper, the topology of a single-phase grid-connected photovoltaic (PV) micro-inverter is proposed. The PV micro-inverter consists of DC-DC stage with high voltage gain boost and DC-AC conversion stage. In the first stage, we apply the active clamp circuit and two voltage multipliers to achieve soft switching technology and high voltage gain. In addition, the flower pollination algorithm (FPA) is employed for the maximum power point tracking (MPPT) in the PV module in this stage. The second stage cascades a H-bridge inverter and LCL filter. To feed high quality sinusoidal power into the grid, the software phase lock, outer voltage loop and inner current loop control method are adopted as the control strategy. The performance of the proposed topology is tested by Matlab/Simulink. A PV module with maximum power 300W and maximum power point voltage 40V is applied as the input source. The simulation results indicate that the proposed topology and the control strategy are feasible.

  2. Self-assembled single-phase perovskite nanocomposite thin films.

    Science.gov (United States)

    Kim, Hyun-Suk; Bi, Lei; Paik, Hanjong; Yang, Dae-Jin; Park, Yun Chang; Dionne, Gerald F; Ross, Caroline A

    2010-02-10

    Thin films of perovskite-structured oxides with general formula ABO(3) have great potential in electronic devices because of their unique properties, which include the high dielectric constant of titanates, (1) high-T(C) superconductivity in cuprates, (2) and colossal magnetoresistance in manganites. (3) These properties are intimately dependent on, and can therefore be tailored by, the microstructure, orientation, and strain state of the film. Here, we demonstrate the growth of cubic Sr(Ti,Fe)O(3) (STF) films with an unusual self-assembled nanocomposite microstructure consisting of (100) and (110)-oriented crystals, both of which grow epitaxially with respect to the Si substrate and which are therefore homoepitaxial with each other. These structures differ from previously reported self-assembled oxide nanocomposites, which consist either of two different materials (4-7) or of single-phase distorted-cubic materials that exhibit two or more variants. (8-12) Moreover, an epitaxial nanocomposite SrTiO(3) overlayer can be grown on the STF, extending the range of compositions over which this microstructure can be formed. This offers the potential for the implementation of self-organized optical/ferromagnetic or ferromagnetic/ferroelectric hybrid nanostructures integrated on technologically important Si substrates with applications in magnetooptical or spintronic devices.

  3. Inertial piezoelectric linear motor driven by a single-phase harmonic wave with automatic clamping mechanism

    Science.gov (United States)

    He, Liangguo; Chu, Yuheng; Hao, Sai; Zhao, Xiaoyong; Dong, Yuge; Wang, Yong

    2018-05-01

    A novel, single-phase, harmonic-driven, inertial piezoelectric linear motor using an automatic clamping mechanism was designed, fabricated, and tested to reduce the sliding friction and simplify the drive mechanism and power supply control of the inertial motor. A piezoelectric bimorph and a flexible hinge were connected in series to form the automatic clamping mechanism. The automatic clamping mechanism was used as the driving and clamping elements. A dynamic simulation by Simulink was performed to prove the feasibility of the motor. The finite element method software COMSOL was used to design the structure of the motor. An experimental setup was built to validate the working principle and evaluate the performance of the motor. The prototype motor outputted a no-load velocity of 3.178 mm/s at a voltage of 220 Vp-p and a maximum traction force of 4.25 N under a preload force of 8 N. The minimum resolution of 1.14 μm was achieved at a driving frequency of 74 Hz, a driving voltage of 50 Vp-p, and a preload force of 0 N.

  4. FIELD IMPLEMENTATION OF A WINSOR TYPE I SURFACTANT/ALCOHOL MIXTURE FOR IN SITU SOLUBILIZATION OF A COMPLEX LNAPL AS A SINGLE-PHASE MICROEMULSION

    Science.gov (United States)

    A Winsor Type I surfactant/alcohol mixture was used as an in situ flushing agent to solubilize a muticomponent nonaqueous phase liquid (NAPL) as a single-phase microemulsion (SPME) in a hydraulically isolated test cell at Hill Air Force Base (AFB), Utah. The surfactant (polyoxye...

  5. Heat Convection

    Science.gov (United States)

    Jiji, Latif M.

    Professor Jiji's broad teaching experience lead him to select the topics for this book to provide a firm foundation for convection heat transfer with emphasis on fundamentals, physical phenomena, and mathematical modelling of a wide range of engineering applications. Reflecting recent developments, this textbook is the first to include an introduction to the challenging topic of microchannels. The strong pedagogic potential of Heat Convection is enhanced by the follow ing ancillary materials: (1) Power Point lectures, (2) Problem Solutions, (3) Homework Facilitator, and, (4) Summary of Sections and Chapters.

  6. European developments in single phase turbulence for innovative reactors

    Energy Technology Data Exchange (ETDEWEB)

    Roelofs, F., E-mail: roelofs@nrg.eu [NRG, Petten (Netherlands); Rohde, M. [DUT, Delft (Netherlands); and others

    2011-07-01

    Thermal-hydraulics is recognized as a key scientific subject in the development of different innovative nuclear reactor systems. From the thermal-hydraulic point of view, different innovative reactors are mainly characterized by their coolants (gas, water, liquid metals and molten salt). They result in specific behavior of flow and heat transfer, which requires specific models and advanced analysis tools. However, many common thermal-hydraulic issues are identified among various innovative nuclear systems. In Europe, such cross-cutting thermal-hydraulics topics are the motivation for the THINS (Thermal-Hydraulics of Innovative Nuclear Systems) project which is sponsored by the European Commission from 2010 to 2014. This paper describes the ongoing developments in an important part of this project devoted to single phase turbulence issues. To this respect, the two main issues have been identified: Non-unity Prandtl number turbulence. In case of liquid metals, molten salts or supercritical fluids, the commonly applied constant turbulent Prandtl number concept is not applicable and robust engineering turbulence models are needed. This paper will report on the progress achieved with respect to the development and validation of turbulence models available in commonly used engineering tools. The paper also reports about the supporting experiments and direct numerical simulations; and, Temperature fluctuations possibly leading to thermal fatigue in innovative reactors. The status is described of a fundamental experiment dealing with the mixing of different density gases in a rectangular channel, an experiment in a more complex geometry of a small mixing plenum using a supercritical fluid, and direct numerical simulations of conjugate heat transfer on temperature fluctuations in liquid metal. (author)

  7. European developments in single phase turbulence for innovative reactors

    International Nuclear Information System (INIS)

    Roelofs, F.; Rohde, M.

    2011-01-01

    Thermal-hydraulics is recognized as a key scientific subject in the development of different innovative nuclear reactor systems. From the thermal-hydraulic point of view, different innovative reactors are mainly characterized by their coolants (gas, water, liquid metals and molten salt). They result in specific behavior of flow and heat transfer, which requires specific models and advanced analysis tools. However, many common thermal-hydraulic issues are identified among various innovative nuclear systems. In Europe, such cross-cutting thermal-hydraulics topics are the motivation for the THINS (Thermal-Hydraulics of Innovative Nuclear Systems) project which is sponsored by the European Commission from 2010 to 2014. This paper describes the ongoing developments in an important part of this project devoted to single phase turbulence issues. To this respect, the two main issues have been identified: Non-unity Prandtl number turbulence. In case of liquid metals, molten salts or supercritical fluids, the commonly applied constant turbulent Prandtl number concept is not applicable and robust engineering turbulence models are needed. This paper will report on the progress achieved with respect to the development and validation of turbulence models available in commonly used engineering tools. The paper also reports about the supporting experiments and direct numerical simulations; and, Temperature fluctuations possibly leading to thermal fatigue in innovative reactors. The status is described of a fundamental experiment dealing with the mixing of different density gases in a rectangular channel, an experiment in a more complex geometry of a small mixing plenum using a supercritical fluid, and direct numerical simulations of conjugate heat transfer on temperature fluctuations in liquid metal. (author)

  8. Effects of rolling on characteristics of single-phase water flow in narrow rectangular ducts

    International Nuclear Information System (INIS)

    Xing Dianchuan; Yan Changqi; Sun Licheng; Xu Chao

    2012-01-01

    Highlights: ► Mass flow rate and friction pressure drop with different pressure head are compared. ► The effect of pressure head on flow fluctuation is considered theoretically. ► Time-mean and real-time friction pressure drop in different rolling motion are studied. ► Rolling motion influences the fluctuation of friction pressure drop in two aspects. ► New correlation for frictional coefficient in rolling motion is achieved. - Abstract: Experimental and theoretical studies of rolling effects on characteristics of single-phase water flow in narrow rectangular ducts are performed under ambient temperature and pressure. Two types of pressure head are supplied by elevate water tank and pump respectively. The results show that the frictional pressure drop under rolling condition fluctuates periodically, with its amplitude decaying as mean Reynolds number increase and the rolling amplitude decrease, while the amplitude is nearly invariable with rolling period. Rolling motion influences the fluctuation amplitude of frictional pressure drop in two aspects, on the one hand, rolling reduced periodical pulsing flow leads to the fluctuation of the frictional pressure drop, on the other hand, additional force acting on fluid near the wall due to the rolling motion makes local frictional resistance oscillate periodically. The mass flow rate oscillates periodically in rolling motion with the pressure head supplied by water tank, while its fluctuation is so weak that could be neglected for the case of the pressure head supplied by pump. An empirical correlation for the frictional coefficient under rolling condition is achieved, and the experimental data is well correlated. A mathematical model is also developed to study the effect of pressure head on mass flow rate fluctuation in rolling motion. The fluctuation amplitude of the mass flow rate decreases rapidly with a higher pressure head. Comparing with the vertical condition, rolling motion nearly has no effects on

  9. An experimental investigation into the deployment of 3-D, finned wing and shape memory alloy vortex generators in a forced air convection heat pipe fin stack

    International Nuclear Information System (INIS)

    Aris, M.S.; McGlen, R.; Owen, I.; Sutcliffe, C.J.

    2011-01-01

    Forced air convection heat pipe cooling systems play an essential role in the thermal management of electronic and power electronic devices such as microprocessors and IGBT's (Integrated Gate Bipolar Transistors). With increasing heat dissipation from these devices, novel methods of improving the thermal performance of fin stacks attached to the heat pipe condenser section are required. The current work investigates the use of a wing type surface protrusions in the form of 3-D delta wing tabs adhered to the fin surface, thin wings punched-out of the fin material and TiNi shape memory alloy delta wings which changed their angles of attack based on the fin surface temperature. The longitudinal vortices generated from the wing designs induce secondary mixing of the cooler free stream air entering the fin stack with the warmer fluid close to the fin surfaces. The change in angle of the attack of the active delta wings provide heat transfer enhancement while managing flow pressure losses across the fin stack. A heat transfer enhancement of 37% compared to a plain fin stack was obtained from the 3-D tabs in a staggered arrangement. The punched-out delta wings in the staggered and inline arrangements provided enhancements of 30% and 26% respectively. Enhancements from the active delta wings were lower at 16%. However, as these devices reduce the pressure drop through the fin stack by approximately 19% in the de-activate position, over the activated position, a reduction in fan operating cost may be achieved for systems operating with inlet air temperatures below the maximum inlet temperature specification for the device. CFD analysis was also carried out to provide additional detail of the local heat transfer enhancement effects. The CFD results corresponded well with previously published reports and were consistent with the experimental findings. - Highlights: → Heat transfer enhancements of heat pipe fin stacks was successfully achieved using fixed and active delta

  10. Equivalence of two models in single-phase multicomponent flow simulations

    KAUST Repository

    Wu, Yuanqing

    2016-02-28

    In this work, two models to simulate the single-phase multicomponent flow in reservoirs are introduced: single-phase multicomponent flow model and two-phase compositional flow model. Because the single-phase multicomponent flow is a special case of the two-phase compositional flow, the two-phase compositional flow model can also simulate the case. We compare and analyze the two models when simulating the single-phase multicomponent flow, and then demonstrate the equivalence of the two models mathematically. An experiment is also carried out to verify the equivalence of the two models.

  11. Equivalence of two models in single-phase multicomponent flow simulations

    KAUST Repository

    Wu, Yuanqing; Sun, Shuyu

    2016-01-01

    In this work, two models to simulate the single-phase multicomponent flow in reservoirs are introduced: single-phase multicomponent flow model and two-phase compositional flow model. Because the single-phase multicomponent flow is a special case of the two-phase compositional flow, the two-phase compositional flow model can also simulate the case. We compare and analyze the two models when simulating the single-phase multicomponent flow, and then demonstrate the equivalence of the two models mathematically. An experiment is also carried out to verify the equivalence of the two models.

  12. Prediction of the single-phase turbulent mixing rate between two parallel subchannels using a subchannel geometry factor

    International Nuclear Information System (INIS)

    Sadatomi, M.; Kawahara, A.; Sato, Y.

    1996-01-01

    This paper presents a simple method for predicting the single-phase turbulent mixing rate between adjacent subchannels in nuclear fuel bundles. In this method, the mixing rate is computed as the sum of the two components of turbulent diffusion and convective transfer. Of these, the turbulent diffusion component is calculated using a newly defined subchannel geometry factor F* and the mean turbulent diffusivity for each subchannel which is computed from Elder's equation. The convective transfer component is evaluated from a mixing Stanton number correlation obtained empirically in this study. In order to confirm the validity of the proposed method, experimental data on turbulent mixing rate were obtained using a tracer technique under adiabatic conditions with three test channels, each consisting of two subchannels. The range of Reynolds number covered was 5000-66 000. From comparisons of the predicted turbulent mixing rates with the experimental data of other investigators as well as the authors, it has been confirmed that the proposed method can predict the data in a range of gap clearance to rod diameter ratio of 0.02-0.4 within about ±25% for square array bundles and about ±35% for triangular array bundles. (orig.)

  13. new topology for single-phase, three-level, spwm vsi with lc filter

    African Journals Online (AJOL)

    level PWM inverter. However, this is not the case with single-phase PWM inverters. In these days, the popular single-phase inverters adopt the full-bridge type using approximate sinusoidal modulation technique. The output voltage in them has two values: zero and pos- itive supply dc voltage levels in the positive half cycle.

  14. Torque Analysis With Saturation Effects for Non-Salient Single-Phase Permanent-Magnet Machines

    DEFF Research Database (Denmark)

    Lu, Kaiyuan; Ritchie, Ewen

    2011-01-01

    The effects of saturation on torque production for non-salient, single-phase, permanent-magnet machines are studied in this paper. An analytical torque equation is proposed to predict the instantaneous torque with saturation effects. Compared to the existing methods, it is computationally faster......-element results, and experimental results obtained on a prototype single-phase permanent-magnet machine....

  15. Experimental investigation of natural convection in a core of a marine reactor in rolling motion

    International Nuclear Information System (INIS)

    Murata, Hiroyuki; Sawada, Ken-ichi; Kobayashi, Michiyuki

    2000-01-01

    A series of single-phase natural circulation experiments in a simulated marine reactor mounted on a rolling bed was performed and the average Nusselt number in the core was evaluated in order to investigate effects of the rolling motion on the heat transfer in the core. Heat transfer with an upright attitude is well correlated with the Rayleigh number and is slightly lower than El-Genk's correlation. Heat transfer in the core is not affected by the inclination angle because the inclination of the present experiment is not large enough to cause any remarkable changes in the flow pattern of the core. Heat transfer in the core is enhanced by the rolling motion which is thought to cause internal flow in the core. Heat transfer during the rolling motion is correlated with the Richardson number for rolling motion, Ri R , and is classified into three regimes: (1) region A (0.05 R ≤0.3) where heat transfer is dominated by the inertial force due to the rolling motion; (2) region B (0.3 R ≤2) where heat transfer is affected by the combined effect of the inertial force and natural convection; and (3) region C (Ri R >2) where heat transfer is affected only by the natural convection. (author)

  16. Secagem de fatias de abóboras (Cucurbita moschata, L. por convecção natural e forçada Drying of pumpkin (Cucurbita moschata, L. slices by natural and forced convection

    Directory of Open Access Journals (Sweden)

    Soraia Vilela Borges

    2008-12-01

    Full Text Available A abóbora (Cucurbita moschata, L. é uma importante fonte de provitamina A, de baixo custo, e sob a forma desidratada oferece diferentes opções de utilização e consumo. Secagens por convecção natural e forçada foram comparadas quanto ao grau de secagem atingido e encolhimento, em função da temperatura, velocidade de ar e dimensões do produto. Os resultados obtidos mostraram que o uso de fatias com volume de 6,25 cm³ em secador por convecção forçada a 50 °C e à velocidade de 5,5 x 10-4 ms-1 resultaram em produtos de menor encolhimento, sendo recomendadas estas condições.Besides its low price, Pumpkin (Cucurbita moschata, L. is an important source of provitamin-A, and when dehydrated it offers different options of utilizations and consumption. Natural and forced convection drying were compared according to the drying degree shrinkage as a function of temperature, and air velocity and product dimensions. The obtained results showed that slices with the volume of 6.25 cm³ in forced convection oven at 50 °C and at the velocity of 5.5 x 10-4 ms-1 resulted in a lower shrinkage products, so these conditions were recommended.

  17. A single-phase axially-magnetized permanent-magnet oscillating machine for miniature aerospace power sources

    Directory of Open Access Journals (Sweden)

    Yi Sui

    2017-05-01

    Full Text Available A single-phase axially-magnetized permanent-magnet (PM oscillating machine which can be integrated with a free-piston Stirling engine to generate electric power, is investigated for miniature aerospace power sources. Machine structure, operating principle and detent force characteristic are elaborately studied. With the sinusoidal speed characteristic of the mover considered, the proposed machine is designed by 2D finite-element analysis (FEA, and some main structural parameters such as air gap diameter, dimensions of PMs, pole pitches of both stator and mover, and the pole-pitch combinations, etc., are optimized to improve both the power density and force capability. Compared with the three-phase PM linear machines, the proposed single-phase machine features less PM use, simple control and low controller cost. The power density of the proposed machine is higher than that of the three-phase radially-magnetized PM linear machine, but lower than the three-phase axially-magnetized PM linear machine.

  18. A single-phase axially-magnetized permanent-magnet oscillating machine for miniature aerospace power sources

    Science.gov (United States)

    Sui, Yi; Zheng, Ping; Cheng, Luming; Wang, Weinan; Liu, Jiaqi

    2017-05-01

    A single-phase axially-magnetized permanent-magnet (PM) oscillating machine which can be integrated with a free-piston Stirling engine to generate electric power, is investigated for miniature aerospace power sources. Machine structure, operating principle and detent force characteristic are elaborately studied. With the sinusoidal speed characteristic of the mover considered, the proposed machine is designed by 2D finite-element analysis (FEA), and some main structural parameters such as air gap diameter, dimensions of PMs, pole pitches of both stator and mover, and the pole-pitch combinations, etc., are optimized to improve both the power density and force capability. Compared with the three-phase PM linear machines, the proposed single-phase machine features less PM use, simple control and low controller cost. The power density of the proposed machine is higher than that of the three-phase radially-magnetized PM linear machine, but lower than the three-phase axially-magnetized PM linear machine.

  19. International symposium on transient convective heat transfer: book of abstracts

    International Nuclear Information System (INIS)

    1996-01-01

    The international symposium on convective heat transfer was held on 19-23 August 1996, in Cesme, Izmir, Turkey. The spesialists discussed forced convection, heat exchangers, free convection and multiphase media and phase change at the meeting. Almost 53 papers were presented in the meeting

  20. National Convective Weather Diagnostic

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Current convective hazards identified by the National Convective Weather Detection algorithm. The National Convective Weather Diagnostic (NCWD) is an automatically...

  1. Experimental research on single-phase heat transfer characteristics in a vertical circular tube under marine conditions

    International Nuclear Information System (INIS)

    Du Sijia; Zhang Hong; Jia Baoshan

    2011-01-01

    Experiments have been conducted to study the heat transfer characteristics of single-phase forced circulation when the test tube was under different marine conditions. The experiments measured the wall temperature of test tube to calculate the heat transfer coefficients at different circumferential places. When the test tube was under inclined conditions, the heat transfer coefficient increased at downside and decreased at upside of test tube because of buoyancy effect. When the test tube was under rolling conditions, the heat transfer coefficients fluctuated with the rolling motions, and the Coriolis force dominated the heat transfer fluctuation during the rolling motion. CFD method was used to simulate the heat transfer phenomena under marine conditions, and the results were accord to the experimental phenomena. (authors)

  2. Experimental study on single-phase convection heat transfer characteristics of pebble bed channels with internal heat generation

    International Nuclear Information System (INIS)

    Meng Xianke; Sun Zhongning; Zhou Ping; Xu Guangzhan

    2012-01-01

    The water-cooled pebble bed reactor core is the porous channels stacked with spherical fuel elements, having evident effect on enhancing heat transfer. Owing to the variability and randomness characteristics of it's interstice, pebble bed channels have a very complex heat transfer situation and have little correlative research. In order to research the heat transfer characters of pebble bed channels with internal heat source, electromagnetic induction heating method was adopted for overall heating the pebble bed which was composed of 8 mm diameter steel balls, and the internal heat transfer characteristics were researched. By comparing and analyzing the experimental data, the rule of power distribution and heat transfer coefficient with heat flux density, inlet temperature and working fluid's Re were got. According to the experimental data fitting, the dimensionless average heat transfer coefficient correlation criteria was got. The fitting results are good agreement with the experimental results within 12% difference. (authors)

  3. Convective heat transfer in single-phase flow in a vertical tube subjected to axial low frequency oscillations

    Energy Technology Data Exchange (ETDEWEB)

    Pendyala, Rajashekhar; Jayanti, Sreenivas; Balakrishnan, A.R. [Indian Institute of Technology Madras, Department of Chemical Engineering, Chennai, Tamil Nadu (India)

    2008-05-15

    The effect of oscillations on the heat transfer in a vertical tube has been studied experimentally. A vertical tube was mounted on a plate and the whole plate was subjected to oscillations in the vertical plane using a mechanical oscillator to provide low frequency oscillations. A section of the tube in the middle is subjected to a constant heat flux. The effect of the oscillations on the heat transfer coefficient has been examined. It was found that the heat transfer coefficient increased with oscillations in the laminar regime. In turbulent flow regime (Re > 2,100) it is found that the effect of oscillations did not show any change. A correlation has been developed for enhancement of the local Nusselt number in terms of the effective acceleration and Reynolds number. Using this, an expression has been proposed to calculate the mean Nusselt number as a function of the tube length. (orig.)

  4. Transient Mixed Convection Validation for NGNP

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Barton [Utah State Univ., Logan, UT (United States); Schultz, Richard [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2015-10-19

    The results of this project are best described by the papers and dissertations that resulted from the work. They are included in their entirety in this document. They are: (1) Jeff Harris PhD dissertation (focused mainly on forced convection); (2) Blake Lance PhD dissertation (focused mainly on mixed and transient convection). This dissertation is in multi-paper format and includes the article currently submitted and one to be submitted shortly; and, (3) JFE paper on CFD Validation Benchmark for Forced Convection.

  5. Transient Mixed Convection Validation for NGNP

    International Nuclear Information System (INIS)

    Smith, Barton; Schultz, Richard

    2015-01-01

    The results of this project are best described by the papers and dissertations that resulted from the work. They are included in their entirety in this document. They are: (1) Jeff Harris PhD dissertation (focused mainly on forced convection); (2) Blake Lance PhD dissertation (focused mainly on mixed and transient convection). This dissertation is in multi-paper format and includes the article currently submitted and one to be submitted shortly; and, (3) JFE paper on CFD Validation Benchmark for Forced Convection.

  6. Single-phase liquid jet impingement heat transfer

    International Nuclear Information System (INIS)

    Webb, B.W.; Ma, C.F.

    1995-01-01

    Impinging liquid jets have been demonstrated to be an effective means of providing high heat/mass transfer rates in industrial transport processes. When a liquid jet strikes a surface, thin hydrodynamic and thermal boundary layers from in the region directly beneath due to the jet deceleration and the resulting increase in pressure. The flow is then forced to accelerate in a direction parallel to the target surface in what is termed the wall jet or parallel flow zone. The thickness of the hydrodynamic and thermal boundary layers in the stagnation region may be of the order of tens of micrometers. Consequently, very high heat/mass transfer coefficients exist in the stagnation zone directly under the jet. Transport coefficients characteristic of parallel flow prevail in the wall jet region. The high heat transfer coefficients make liquid jet impingement an attractive cooling option where high heat fluxes are the norm. Some industrial applications include the thermal treatment of metals, cooling of internal combustion engines, and more recently, thermal control of high-heat-dissipation electronic devices. Both circular and planar liquid jets have attracted research attention. 180 refs., 35 figs., 11 tabs

  7. A Novel Model Predictive Control for Single-Phase Grid-Connected Photovoltaic Inverters

    DEFF Research Database (Denmark)

    Zangeneh Bighash, Esmaeil; Sadeghzadeh, Seyed Mohammad; Ebrahimzadeh, Esmaeil

    2017-01-01

    Single-phase grid-connected inverters with LCL filter are widely used to connect photovoltaic systems to the utility grid. Among the existing control schemes, predictive control methods are faster and more accurate but also more complicated to implement. Recently, the Model Predictive Control (MPC......) algorithm for single-phase inverter has been presented, where the algorithm implementation is straightforward. In the MPC approach, all switching states are considered in each switching period to achieve the control objectives. However, since the number of switching states in single-phase inverters is small......, the inverter output current has a high Total Harmonic Distortions (THD). In order to reduce this, this paper presents an improved MPC for single-phase grid-connected inverters. In the proposed approach, the switching algorithm is changed and the number of the switching states is increased by means of virtual...

  8. Standard Specification for Sampling Single-Phase Geothermal Liquid or Steam for Purposes of Chemical Analysis

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    1983-01-01

    1.1 This specification covers the basic requirements for equipment to be used for the collection of uncontaminated and representative samples from single-phase geothermal liquid or steam. Geopressured liquids are included. See Fig 1.

  9. POD-Galerkin Model for Incompressible Single-Phase Flow in Porous Media

    KAUST Repository

    Wang, Yi; Yu, Bo; Sun, Shuyu

    2017-01-01

    Fast prediction modeling via proper orthogonal decomposition method combined with Galerkin projection is applied to incompressible single-phase fluid flow in porous media. Cases for different configurations of porous media, boundary conditions

  10. Prediction of heat transfer coefficients for forced convective boiling of N2-hydrocarbon mixtures at cryogenic conditions using artificial neural networks

    Science.gov (United States)

    Barroso-Maldonado, J. M.; Belman-Flores, J. M.; Ledesma, S.; Aceves, S. M.

    2018-06-01

    A key problem faced in the design of heat exchangers, especially for cryogenic applications, is the determination of convective heat transfer coefficients in two-phase flow such as condensation and boiling of non-azeotropic refrigerant mixtures. This paper proposes and evaluates three models for estimating the convective coefficient during boiling. These models are developed using computational intelligence techniques. The performance of the proposed models is evaluated using the mean relative error (mre), and compared to two existing models: the modified Granryd's correlation and the Silver-Bell-Ghaly method. The three proposed models are distinguished by their architecture. The first is based on directly measured parameters (DMP-ANN), the second is based on equivalent Reynolds and Prandtl numbers (eq-ANN), and the third on effective Reynolds and Prandtl numbers (eff-ANN). The results demonstrate that the proposed artificial neural network (ANN)-based approaches greatly outperform available methodologies. While Granryd's correlation predicts experimental data within a mean relative error mre = 44% and the S-B-G method produces mre = 42%, DMP-ANN has mre = 7.4% and eff-ANN has mre = 3.9%. Considering that eff-ANN has the lowest mean relative error (one tenth of previously available methodologies) and the broadest range of applicability, it is recommended for future calculations. Implementation is straightforward within a variety of platforms and the matrices with the ANN weights are given in the appendix for efficient programming.

  11. Reducing Electromagnetic Interference in a Grid Tied Single Phase Power Inverter

    Science.gov (United States)

    2016-09-01

    With the growing demand for a reliable electrical grid, backup power supplies and energy management systems are a necessity. Systems such as server...ELECTROMAGNETIC INTERFERENCE IN A GRID TIED SINGLE PHASE POWER INVERTER by Jason Hassan Valiani September 2016 Thesis Advisor: Giovanna Oriti...3. REPORT TYPE AND DATES COVERED Master’s thesis 4. TITLE AND SUBTITLE REDUCING ELECTROMAGNETIC INTERFERENCE IN A GRID TIED SINGLE PHASE POWER

  12. Convective heat transfer in foams under laminar flow in pipes and tube bundles.

    Science.gov (United States)

    Attia, Joseph A; McKinley, Ian M; Moreno-Magana, David; Pilon, Laurent

    2012-12-01

    The present study reports experimental data and scaling analysis for forced convection of foams and microfoams in laminar flow in circular and rectangular tubes as well as in tube bundles. Foams and microfoams are pseudoplastic (shear thinning) two-phase fluids consisting of tightly packed bubbles with diameters ranging from tens of microns to a few millimeters. They have found applications in separation processes, soil remediation, oil recovery, water treatment, food processes, as well as in fire fighting and in heat exchangers. First, aqueous solutions of surfactant Tween 20 with different concentrations were used to generate microfoams with various porosity, bubble size distribution, and rheological behavior. These different microfoams were flowed in uniformly heated circular tubes of different diameter instrumented with thermocouples. A wide range of heat fluxes and flow rates were explored. Experimental data were compared with analytical and semi-empirical expressions derived and validated for single-phase power-law fluids. These correlations were extended to two-phase foams by defining the Reynolds number based on the effective viscosity and density of microfoams. However, the local Nusselt and Prandtl numbers were defined based on the specific heat and thermal conductivity of water. Indeed, the heated wall was continuously in contact with a film of water controlling convective heat transfer to the microfoams. Overall, good agreement between experimental results and model predictions was obtained for all experimental conditions considered. Finally, the same approach was shown to be also valid for experimental data reported in the literature for laminar forced convection of microfoams in rectangular minichannels and of macrofoams across aligned and staggered tube bundles with constant wall heat flux.

  13. Synthesis of single-phase L10-FeNi magnet powder by nitrogen insertion and topotactic extraction.

    Science.gov (United States)

    Goto, Sho; Kura, Hiroaki; Watanabe, Eiji; Hayashi, Yasushi; Yanagihara, Hideto; Shimada, Yusuke; Mizuguchi, Masaki; Takanashi, Koki; Kita, Eiji

    2017-10-16

    Tetrataenite (L1 0 -FeNi) is a promising candidate for use as a permanent magnet free of rare-earth elements because of its favorable properties. In this study, single-phase L1 0 -FeNi powder with a high degree of order was synthesized through a new method, nitrogen insertion and topotactic extraction (NITE). In the method, FeNiN, which has the same ordered arrangement as L1 0 -FeNi, is formed by nitriding A1-FeNi powder with ammonia gas. Subsequently, FeNiN is denitrided by topotactic reaction to derive single-phase L1 0 -FeNi with an order parameter of 0.71. The transformation of disordered-phase FeNi into the L1 0 phase increased the coercive force from 14.5 kA/m to 142 kA/m. The proposed method not only significantly accelerates the development of magnets using L1 0 -FeNi but also offers a new synthesis route to obtain ordered alloys in non-equilibrium states.

  14. Network model of free convection within internally heated porous media

    International Nuclear Information System (INIS)

    Conrad, P.W.

    1977-01-01

    A hypothetical core-disruptive accident (HCDA) in a liquid metal fast breeder reactor (LMFBR) may result in the formation of an internally heated debris bed. Considerable attention has been given to postulated mechanisms by which such beds may be cooled. It is the purpose of the work described to demonstrate a method for computing the heat transfer from such a bed to the overlying sodium pool due to single-phase, free convection

  15. Thermo-electro-hydrodynamic convection under microgravity: a review

    Energy Technology Data Exchange (ETDEWEB)

    Mutabazi, Innocent; Yoshikawa, Harunori N; Fogaing, Mireille Tadie; Travnikov, Vadim; Crumeyrolle, Olivier [Laboratoire Ondes et Milieux Complexes, UMR 6294, CNRS-Université du Havre, CS 80450, F-76058 Le Havre Cedex (France); Futterer, Birgit; Egbers, Christoph, E-mail: Innocent.Mutabazi@univ-lehavre.fr [Department of Aerodynamics and Fluid Mechanics, Brandenburg University of Technology Cottbus-Senftenberg, Cottbus (Germany)

    2016-12-15

    Recent studies on thermo-electro-hydrodynamic (TEHD) convection are reviewed with focus on investigations motivated by the analogy with natural convection. TEHD convection originates in the action of the dielectrophoretic force generated by an alternating electric voltage applied to a dielectric fluid with a temperature gradient. This electrohydrodynamic force is analogous to Archimedean thermal buoyancy and can be regarded as a thermal buoyancy force in electric effective gravity. The review is concerned with TEHD convection in plane, cylindrical, and spherical capacitors under microgravity conditions, where the electric gravity can induce convection without any complexities arising from geometry or the buoyancy force due to the Earth’s gravity. We will highlight the convection in spherical geometry, comparing developed theories and numerical simulations with the GEOFLOW experiments performed on board the International Space Station (ISS). (paper)

  16. A heat exchanger between forced flow helium gas at 14 to 18 K and liquid hydrogen at 20 K circulated by natural convection

    International Nuclear Information System (INIS)

    Green, M.A.; Ishimoto, S.; Lau, W.; Yang, S.

    2003-01-01

    The Muon Ionization Cooling Experiment (MICE) has three 350-mm long liquid hydrogen absorbers to reduce the momentum of 200 MeV muons in all directions. The muons are then re-accelerated in the longitudinal direction by 200 MHz RF cavities. The result is cooled muons with a reduced emittance. The energy from the muons is taken up by the liquid hydrogen in the absorber. The hydrogen in the MICE absorbers is cooled by natural convection to the walls of the absorber that are in turn cooled by helium gas that enters at 14 K. This report describes the MICE liquid hydrogen absorber and the heat exchanger between the liquid hydrogen and the helium gas that flows through passages in the absorber wall

  17. Numerical Investigation of Thermal Radiation and Viscous Effects on Entropy Generation in Forced Convection Blood Flow over an Axisymmetric Stretching Sheet

    Directory of Open Access Journals (Sweden)

    Mohammad Yaghoub Abdollahzadeh Jamalabadi

    2016-05-01

    Full Text Available Numerical and analytical investigation of the effects of thermal radiation and viscous heating on a convective flow of a non-Newtonian, incompressible fluid in an axisymmetric stretching sheet with constant temperature wall is performed. The power law model of the blood is used for the non-Newtonian model of the fluid and the Rosseland model for the thermal radiative heat transfer in an absorbing medium and viscous heating are considered as the heat sources. The non-dimensional governing equations are transformed to similarity form and solved numerically. A parameter study on entropy generation in medium is presented based on the Second Law of Thermodynamics by considering various parameters such as the thermal radiation parameter, the Brinkman number, Prandtl number, Eckert number.

  18. Thermal boundary condition effects on forced convection heat transfer. Application of a numerical solution of an adjoint problem; Kyosei tairyu netsudentatsu mondai ni okeru netsuteki kyokai joken no eikyo. Zuihan mondai no suchi kai wo mochiita kosatsu

    Energy Technology Data Exchange (ETDEWEB)

    Momose, K.; Saso, K.; Kimoto, H. [Osaka University, Osaka (Japan). Faculty of Engineering Science

    1997-11-25

    We propose a numerical solution for the adjoint operator of a forced convection heat transfer problem to evaluate mean heat transfer characteristics under arbitrary thermal conditions. Using the numerical solutions of the adjoint problems under Dirichlet and Neumann conditions, both of which can be computed using a conventional CFD code, the influence function of the local surface temperature on the total heat transfer and that of the local surface heat flux on the mean surface temperature are obtained. As a result, the total heat fluxes for arbitrary surface temperature distributions and the mean surface temperatures for arbitrary surface heat flux distributions can be calculated using these influence functions. The influence functions for a circular cylinder and for an in-line square rod array are presented. 14 refs., 9 figs., 1 tab.

  19. Experimental study of the effect of an electric field on thermal exchanges under forced convection with gaseous carbon anhydride in presence of the radiation of the Melusine pile; Etude experimentale de l'effet d'un champ electrique sur les echanges thermiques en convection forcee avec l'anhydride carbonique gazeux en presence du rayonnement de la pile Melusine

    Energy Technology Data Exchange (ETDEWEB)

    Perroud, P.; Rebiere, J.; Verdier, J.

    1961-01-21

    Previous studies showed that, under free or forced convection, the application of a non-uniform electric field with a sufficient intensity at the neighbourhood of the heating elements resulted in a significant improvement of the thermal exchange coefficient under some flow rate and pressure conditions. But these improvements first required the creation of ions in the gas (shock ionization and existence of a corona effect above a sufficient voltage). This document therefore report further studies performed at the neighbourhood of the Melusine atomic pile which would provide ionizing radiations of much greater intensity. The objectives were, on the one hand, a global verification of work hypotheses imagined for the exchange improvement mechanism, and, on the other hand, to obtain data on the conditions under which this exchange improvement mechanism could be used in channels of a reactor. The authors present the instrumentation (measurement cells, gas circuit, heating circuit, high voltage circuit), describe how physical values are measured (pressure, gas flow rate, temperature of the heating element, gas temperature, high voltage). They describe how they compare powers exchanged under forced convection between dioxide carbon and a heated wire with or without external ionizing radiations, and report the various performed calculations (power supplied to the gas, temperature shift, Nusselt and Reynolds numbers). They report and discuss experimental results obtained outside the pile without ionizing radiations, and within the pile in presence of a ionizing radiation [French] Les essais ont ete effectues dans les conditions suivantes: nombres de Reynolds variant de 20.000 a 80.000, pression de 11 a 21 kg/cm{sup 2}, temperatures moyennes de l'element chauffant de 200 a 600 deg. C, tension electrique de 0 a 30 kV eff et intensite maximum du rayonnement γ, 3x10{sup 7} roentgen/h. On a confirme, hors pile, que l'augmentation de la puissance echangee, au dessus du seuil d

  20. Boundary Layer Control of Rotating Convection Systems

    Science.gov (United States)

    King, E. M.; Stellmach, S.; Noir, J.; Hansen, U.; Aurnou, J. M.

    2008-12-01

    Rotating convection is ubiquitous in the natural universe, and is likely responsible for planetary processes such magnetic field generation. Rapidly rotating convection is typically organized by the Coriolis force into tall, thin, coherent convection columns which are aligned with the axis of rotation. This organizational effect of rotation is thought to be responsible for the strength and structure of magnetic fields generated by convecting planetary interiors. As thermal forcing is increased, the relative influence of rotation weakens, and fully three-dimensional convection can exist. It has long been assumed that rotational effects will dominate convection dynamics when the ratio of buoyancy to the Coriolis force, the convective Rossby number, Roc, is less than unity. We investigate the influence of rotation on turbulent Rayleigh-Benard convection via a suite of coupled laboratory and numerical experiments over a broad parameter range: Rayleigh number, 10310; Ekman number, 10-6≤ E ≤ ∞; and Prandtl number, 1≤ Pr ≤ 100. In particular, we measure heat transfer (as characterized by the Nusselt number, Nu) as a function of the Rayleigh number for several different Ekman and Prandtl numbers. Two distinct heat transfer scaling regimes are identified: non-rotating style heat transfer, Nu ~ Ra2/7, and quasigeostrophic style heat transfer, Nu~ Ra6/5. The transition between the non-rotating regime and the rotationally dominant regime is described as a function of the Ekman number, E. We show that the regime transition depends not on the global force balance Roc, but on the relative thicknesses of the thermal and Ekman boundary layers. The transition scaling provides a predictive criterion for the applicability of convection models to natural systems such as Earth's core.

  1. Influence of single-phase heat transfer correlations on safety analysis of research reactors with narrow rectangular fuel channels

    International Nuclear Information System (INIS)

    Rawashdeh, A.; Altamimi, R.; Lee, B.; Chung, Y. J.; Park, S.

    2013-01-01

    The influence of different single-phase heat transfer correlations on the fuel temperature and minimum critical heat flux ratio (MCHFR) during a typical accident of a 5 MW research reactor is investigated. A reactor uses plate type fuel, of which the cooling channels have a narrow rectangular shape. RELAP5/MOD3.3 tends to over-predict the Nusselt number (Nu) at a low Reynolds number (Re) region, and therefore the correlation set is modified to properly describe the thermal behavior at that region. To demonstrate the effect of Nu at a low-Re region on an accident analysis, a two-pump failure accident was chosen as a sample problem. In the accident, the downward core flow decreases by a pump coast-down, and then reverses upward by natural convection. During the pump coast-down and flow reversal, the flow undergoes a laminar flow regime which has a different Nu with respect to the correlation sets. Compared to the results by the original RELAP5/MOD3.3, the modified correlation set predicts the fuel temperature to be a little higher than the original value, and the MCHFR to be a little lower than the original value. Although the modified correlation set predicts the fuel temperature and the MCHFR to be less conservative than those calculated from the original correlation of RELAP5/MOD3.3, the maximum fuel temperature and the MCHFR still satisfy the safety acceptance criteria

  2. Single-phase ProtoDUNE, the Prototype of a Single-Phase Liquid Argon TPC for DUNE at the CERN Neutrino Platform

    CERN Document Server

    Cavanna, F; Touramanis, C

    2017-01-01

    ProtoDUNE-SP is the single-phase DUNE Far Detector prototype that is under construction and will be operated at the CERN Neutrino Platform (NP) starting in 2018. It was proposed to the CERN SPSC in June 2015 (SPSC-P-351) and was approved in December 2015 as experiment NP04 (ProtoDUNE). ProtoDUNE-SP, a crucial part of the DUNE effort towards the construction of the first DUNE 10-kt fiducial mass far detector module (17 kt total LAr mass), is a significant experiment in its own right. With a total liquid argon (LAr) mass of 0.77 kt, it represents the largest monolithic single phase LArTPC detector to be built to date. It is housed in an extension to the EHN1 hall in the North Area, where the CERN NP is providing a new dedicated charged-particle test beamline. ProtoDUNE-SP aims to take its first beam data before the LHC long shutdown (LS2) at the end of 2018. ProtoDUNE-SP prototypes the designs of most of the single-phase DUNE far detector module (DUNE-SP) components at a 1:1 scale, with an extrapolation of abo...

  3. Searching for Next Single-Phase High-Entropy Alloy Compositions

    Directory of Open Access Journals (Sweden)

    David E. Alman

    2013-10-01

    Full Text Available There has been considerable technological interest in high-entropy alloys (HEAs since the initial publications on the topic appeared in 2004. However, only several of the alloys investigated are truly single-phase solid solution compositions. These include the FCC alloys CoCrFeNi and CoCrFeMnNi based on 3d transition metals elements and BCC alloys NbMoTaW, NbMoTaVW, and HfNbTaTiZr based on refractory metals. The search for new single-phase HEAs compositions has been hindered by a lack of an effective scientific strategy for alloy design. This report shows that the chemical interactions and atomic diffusivities predicted from ab initio molecular dynamics simulations which are closely related to primary crystallization during solidification can be used to assist in identifying single phase high-entropy solid solution compositions. Further, combining these simulations with phase diagram calculations via the CALPHAD method and inspection of existing phase diagrams is an effective strategy to accelerate the discovery of new single-phase HEAs. This methodology was used to predict new single-phase HEA compositions. These are FCC alloys comprised of CoFeMnNi, CuNiPdPt and CuNiPdPtRh, and HCP alloys of CoOsReRu.

  4. Coordinated single-phase control scheme for voltage unbalance reduction in low voltage network.

    Science.gov (United States)

    Pullaguram, Deepak; Mishra, Sukumar; Senroy, Nilanjan

    2017-08-13

    Low voltage (LV) distribution systems are typically unbalanced in nature due to unbalanced loading and unsymmetrical line configuration. This situation is further aggravated by single-phase power injections. A coordinated control scheme is proposed for single-phase sources, to reduce voltage unbalance. A consensus-based coordination is achieved using a multi-agent system, where each agent estimates the averaged global voltage and current magnitudes of individual phases in the LV network. These estimated values are used to modify the reference power of individual single-phase sources, to ensure system-wide balanced voltages and proper power sharing among sources connected to the same phase. Further, the high X / R ratio of the filter, used in the inverter of the single-phase source, enables control of reactive power, to minimize voltage unbalance locally. The proposed scheme is validated by simulating a LV distribution network with multiple single-phase sources subjected to various perturbations.This article is part of the themed issue 'Energy management: flexibility, risk and optimization'. © 2017 The Author(s).

  5. Numerical simulations of convectively excited gravity waves

    International Nuclear Information System (INIS)

    Glatzmaier, G.A.

    1983-01-01

    Magneto-convection and gravity waves are numerically simulated with a nonlinear, three-dimensional, time-dependent model of a stratified, rotating, spherical fluid shell heated from below. A Solar-like reference state is specified while global velocity, magnetic field, and thermodynamic perturbations are computed from the anelastic magnetohydrodynamic equations. Convective overshooting from the upper (superadiabatic) part of the shell excites gravity waves in the lower (subadiabatic) part. Due to differential rotation and Coriolis forces, convective cell patterns propagate eastward with a latitudinally dependent phase velocity. The structure of the excited wave motions in the stable region is more time-dependent than that of the convective motions above. The magnetic field tends to be concentrated over giant-cell downdrafts in the convective zone but is affected very little by the wave motion in the stable region

  6. Scaling Analysis of the Single-Phase Natural Circulation: the Hydraulic Similarity

    International Nuclear Information System (INIS)

    Yu, Xin-Guo; Choi, Ki-Yong

    2015-01-01

    These passive safety systems all rely on the natural circulation to cool down the reactor cores during an accident. Thus, a robust and accurate scaling methodology must be developed and employed to both assist in the design of a scaled-down test facility and guide the tests in order to mimic the natural circulation flow of its prototype. The natural circulation system generally consists of a heat source, the connecting pipes and several heat sinks. Although many applauding scaling methodologies have been proposed during last several decades, few works have been dedicated to systematically analyze and exactly preserve the hydraulic similarity. In the present study, the hydraulic similarity analyses are performed at both system and local level. By this mean, the scaling criteria for the exact hydraulic similarity in a full-pressure model have been sought. In other words, not only the system-level but also the local-level hydraulic similarities are pursued. As the hydraulic characteristics of a fluid system is governed by the momentum equation, the scaling analysis starts with it. A dimensionless integral loop momentum equation is derived to obtain the dimensionless numbers. In the dimensionless momentum equation, two dimensionless numbers, the dimensionless flow resistance number and the dimensionless gravitational force number, are identified along with a unique hydraulic time scale, characterizing the system hydraulic response. A full-height full-pressure model is also made to see which model among the full-height model and reduced-height model can preserve the hydraulic behavior of the prototype. From the dimensionless integral momentum equation, a unique hydraulic time scale, which characterizes the hydraulic response of a single-phase natural circulation system, is identified along with two dimensionless parameters: the dimensionless flow resistance number and the dimensionless gravitational force number. By satisfying the equality of both dimensionless numbers

  7. Scaling Analysis of the Single-Phase Natural Circulation: the Hydraulic Similarity

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Xin-Guo; Choi, Ki-Yong [KAERI, Daejeon (Korea, Republic of)

    2015-05-15

    These passive safety systems all rely on the natural circulation to cool down the reactor cores during an accident. Thus, a robust and accurate scaling methodology must be developed and employed to both assist in the design of a scaled-down test facility and guide the tests in order to mimic the natural circulation flow of its prototype. The natural circulation system generally consists of a heat source, the connecting pipes and several heat sinks. Although many applauding scaling methodologies have been proposed during last several decades, few works have been dedicated to systematically analyze and exactly preserve the hydraulic similarity. In the present study, the hydraulic similarity analyses are performed at both system and local level. By this mean, the scaling criteria for the exact hydraulic similarity in a full-pressure model have been sought. In other words, not only the system-level but also the local-level hydraulic similarities are pursued. As the hydraulic characteristics of a fluid system is governed by the momentum equation, the scaling analysis starts with it. A dimensionless integral loop momentum equation is derived to obtain the dimensionless numbers. In the dimensionless momentum equation, two dimensionless numbers, the dimensionless flow resistance number and the dimensionless gravitational force number, are identified along with a unique hydraulic time scale, characterizing the system hydraulic response. A full-height full-pressure model is also made to see which model among the full-height model and reduced-height model can preserve the hydraulic behavior of the prototype. From the dimensionless integral momentum equation, a unique hydraulic time scale, which characterizes the hydraulic response of a single-phase natural circulation system, is identified along with two dimensionless parameters: the dimensionless flow resistance number and the dimensionless gravitational force number. By satisfying the equality of both dimensionless numbers

  8. Forced convection heat transfer in rectangular ducts - general case of wall resistances and peripheral conduction for ventilation cooling of nuclear waste repositories [ heat transfer and nuclear disposal

    Energy Technology Data Exchange (ETDEWEB)

    Lyczkowski, R. W.; Solbrig, C. W.; Gidaspow, D.

    1980-01-01

    A numerical solution for laminar flow heat transfer between a flowing gas and its containing rectangular duct has been obtained for many different boundary conditions which may arise in nuclear waste repository ventilation corridors. The problem has been solved for the cases of insulation on no walls, one wall, two walls, and three walls with various finite resistances on the remaining walls. Simplifications are made to decouple the convective heat transfer problem for the far field conduction problem, but peripheral conduction is retained. Results have been obtained for several duct aspect ratios in the thermal entrance and in the fully developed regions, including the constant temperature cases. When one wall is insulated and the other three are at constant temperature, the maximum temperature occurs in the fluid rather than on the insulated wall. This maximum moves toward the insulated wall with increasing axial distance. Nusselt numbers for the same constant flux on all four walls with peripheral conduction lie in a narrow band bounded by zero and infinite peripheral conduction cases. A dimensionless wall conduction group of four can be considered infinite for the purpose of estimating fully developed Nusselt numbers to within an accuracy of 3%. A decrease in wall and bulk temperatures by finite wall conduction has been demonstrated for the case of a black body radiation boundary condition. Nusselt numbers for the case of constant temperature on the top and bottom walls and constant heat flux on the side walls exhibited unexpected behavior.

  9. Forced convection heat transfer in rectangular ducts - general case of wall resistances and peripheral conduction for ventilation cooling of nuclear waste repositories

    International Nuclear Information System (INIS)

    Lyczkowski, R.W.; Solbrig, C.W.; Gidaspow, D.

    1982-01-01

    A numerical solution for laminar flow heat transfer between a flowing gas and its containing rectangular duct has been obtained for many different boundary conditions which may arise in nuclear waste repository ventilation corridors. The problem has been solved for the cases of insulation on no walls, one wall, two walls, and three walls with various finite resistances on the remaining walls. Simplifications are made to decouple the convective heat transfer problem from the far field conduction problem, but peripheral conduction is retained. Results have been obtained for several duct aspect ratios in the thermal entrance and in the fully developed regions, including the constant temperature cases. When one wall is insulated and the other three are at constant temperature, the maximum temperature occurs in the fluid rather than on the insulated wall. This maximum moves toward the insulated wall with increasing axial distance. Nusselt numbers for the same constant flux on all four walls with peripheral conduction lie in a narrow band bounded by zero and infinite peripheral conduction cases. A dimensionsless wall conduction group of four can be considered infinite for the purpose of estimating fully developed Nusselt numbers to within an accuracy of 3%. A decrease in wall and bulk temperatures by finite wall conduction has been demonstrated for the case of a black body radiation boundary condition. Nusselt numbers for the case of constant temperature on the top and bottom walls and constant heat flux on the side walls exhibited unexpected behavior. (orig.)

  10. Forced convection heat transfer in rectangular ducts - general case of wall resistances and peripheral conduction for ventilation cooling of nuclear waste repositories

    International Nuclear Information System (INIS)

    Lyczkowski, R.W.; Solbrig, C.W.; Gidaspow, D.

    1980-01-01

    A numerical solution for laminar flow heat transfer between a flowing gas and its containing rectangular duct has been obtained for many different boundary conditions which may arise in nuclear waste repository ventilation corridors. The problem has been solved for the cases of insulation on no walls, one wall, two walls, and three walls with various finite resistances on the remaining walls. Simplifications are made to decouple the convective heat transfer problem for the far field conduction problem, but peripheral conduction is retained. Results have been obtained for several duct aspect ratios in the thermal entrance and in the fully developed regions, including the constant temperature cases. When one wall is insulated and the other three are at constant temperature, the maximum temperature occurs in the fluid rather than on the insulated wall. This maximum moves toward the insulated wall with increasing axial distance. Nusselt numbers for the same constant flux on all four walls with peripheral conduction lie in a narrow band bounded by zero and infinite peripheral conduction cases. A dimensionless wall conduction group of four can be considered infinite for the purpose of estimating fully developed Nusselt numbers to within an accuracy of 3%. A decrease in wall and bulk temperatures by finite wall conduction has been demonstrated for the case of a black body radiation boundary condition. Nusselt numbers for the case of constant temperature on the top and bottom walls and constant heat flux on the side walls exhibited unexpected behavior

  11. Forced convection heat transfer in rectangular ducts - general case of wall resistances and peripheral conduction for ventilation cooling of nuclear waste repositories

    Energy Technology Data Exchange (ETDEWEB)

    Lyczkowski, R W [Institute of Gas Technology, Chicago, IL (USA); Solbrig, C W [EG and G Idaho, Inc., Idaho Falls (USA); Gidaspow, D [Illinois Inst. of Tech., Chicago (USA). Dept. of Chemical Engineering

    1982-02-01

    A numerical solution for laminar flow heat transfer between a flowing gas and its containing rectangular duct has been obtained for many different boundary conditions which may arise in nuclear waste repository ventilation corridors. The problem has been solved for the cases of insulation on no walls, one wall, two walls, and three walls with various finite resistances on the remaining walls. Simplifications are made to decouple the convective heat transfer problem from the far field conduction problem, but peripheral conduction is retained. Results have been obtained for several duct aspect ratios in the thermal entrance and in the fully developed regions, including the constant temperature cases. When one wall is insulated and the other three are at constant temperature, the maximum temperature occurs in the fluid rather than on the insulated wall. This maximum moves toward the insulated wall with increasing axial distance. Nusselt numbers for the same constant flux on all four walls with peripheral conduction lie in a narrow band bounded by zero and infinite peripheral conduction cases. A dimensionsless wall conduction group of four can be considered infinite for the purpose of estimating fully developed Nusselt numbers to within an accuracy of 3%. A decrease in wall and bulk temperatures by finite wall conduction has been demonstrated for the case of a black body radiation boundary condition. Nusselt numbers for the case of constant temperature on the top and bottom walls and constant heat flux on the side walls exhibited unexpected behavior.

  12. Reliability Evaluation of a Single-phase H-bridge Inverter with Integrated Active Power Decoupling

    DEFF Research Database (Denmark)

    Tang, Junchaojie; Wang, Haoran; Ma, Siyuan

    2016-01-01

    it with the traditional passive DC-link solution. The converter level reliability is obtained by component level electro-thermal stress modeling, lifetime model, Weibull distribution, and Reliability Block Diagram (RBD) method. The results are demonstrated by a 2 kW single-phase inverter application.......Various power decoupling methods have been proposed recently to replace the DC-link Electrolytic Capacitors (E-caps) in single-phase conversion system, in order to extend the lifetime and improve the reliability of the DC-link. However, it is still an open question whether the converter level...... reliability becomes better or not, since additional components are introduced and the loading of the existing components may be changed. This paper aims to study the converter level reliability of a single-phase full-bridge inverter with two kinds of active power decoupling module and to compare...

  13. High Quality Model Predictive Control for Single Phase Grid Connected Photovoltaic Inverters

    DEFF Research Database (Denmark)

    Zangeneh Bighash, Esmaeil; Sadeghzadeh, Seyed Mohammad; Ebrahimzadeh, Esmaeil

    2018-01-01

    Single phase grid-connected inverters with LCL filter are widely used to connect the photovoltaic systems to the utility grid. Among the presented control schemes, predictive control methods are faster and more accurate but are more complex to implement. Recently, the model-predictive control...... algorithm for single-phase inverter has been presented, where the algorithm implementation is straightforward. In the proposed approach, all switching states are tested in each switching period to achieve the control objectives. However, since the number of the switching states in single-phase inverter...... is low, the inverter output current has a high total harmonic distortions. In order to reduce the total harmonic distortions of the injected current, this paper presents a high-quality model-predictive control for one of the newest structure of the grid connected photovoltaic inverter, i.e., HERIC...

  14. Benchmarking of Grid Fault Modes in Single-Phase Grid-Connected Photovoltaic Systems

    DEFF Research Database (Denmark)

    Yang, Yongheng; Blaabjerg, Frede; Zou, Zhixiang

    2013-01-01

    Pushed by the booming installations of singlephase photovoltaic (PV) systems, the grid demands regarding the integration of PV systems are expected to be modified. Hence, the future PV systems should become more active with functionalities of Low Voltage Ride-Through (LVRT) and grid support...... phase systems under grid faults. The intent of this paper is to present a benchmarking of grid fault modes that might come in future single-phase PV systems. In order to map future challenges, the relevant synchronization and control strategies are discussed. Some faulty modes are studied experimentally...... and provided at the end of this paper. It is concluded that there are extensive control possibilities in single-phase PV systems under grid faults. The Second Order General Integral based PLL technique might be the most promising candidate for future single-phase PV systems because of its fast adaptive...

  15. Laminar Mixed Convection Heat Transfer Correlation for Horizontal Pipes

    International Nuclear Information System (INIS)

    Chae, Myeong Seon; Chung, Bum Jin

    2013-01-01

    This study aimed at producing experimental results and developing a new heat transfer correlation based upon a semi-empirical buoyancy coefficient. Mixed convection mass transfers inside horizontal pipe were investigated for the pipe of various length-to-diameters with varying Re. Forced convection correlation was developed using a very short cathode. With the length of cathode increase and Re decrease, the heat transfer rates were enhanced and becomes higher than that of forced convection. An empirical buoyancy coefficient was derived from correlation of natural convection and forced convection with the addition of L/D. And the heat transfer correlation for laminar mixed convection was developed using the buoyancy coefficient, it describes not only current results, but also results of other studies. Mixed convection occurs when the driving forces of both forced and natural convections are of comparable magnitude (Gr/Re 2 ∼1). It is classical problem but is still an active area of research for various thermal applications such as flat plate solar collectors, nuclear reactors and heat exchangers. The effect of buoyancy on heat transfer in a forced flow is varied by the direction of the buoyancy force. In a horizontal pipe the direction of the forced and buoyancy forces are perpendicular. The studies on the mixed convections of the horizontal pipes were not investigated very much due to the lack of practical uses compared to those of vertical pipes. Even the definitions on the buoyancy coefficient that presents the relative influence of the forced and the natural convections, are different by scholars. And the proposed heat transfer correlations do not agree

  16. Synchronization in single-phase grid-connected photovoltaic systems under grid faults

    DEFF Research Database (Denmark)

    Yang, Yongheng; Blaabjerg, Frede

    2012-01-01

    The highly increasing penetration of single-phase photovoltaic (PV) systems pushes the grid requirements related to the integration of PV power systems to be updated. These upcoming regulations are expected to direct the grid-connected renewable generators to support the grid operation and stabil......The highly increasing penetration of single-phase photovoltaic (PV) systems pushes the grid requirements related to the integration of PV power systems to be updated. These upcoming regulations are expected to direct the grid-connected renewable generators to support the grid operation...

  17. Single phase cascaded H5 inverter with leakage current elimination for transformerless photovoltaic system

    DEFF Research Database (Denmark)

    Guo, Xiaoqiang; Jia, X.; Lu, Z.

    2016-01-01

    Leakage current reduction is one of the important issues for the transformelress PV systems. In this paper, the transformerless single-phase cascaded H-bridge PV inverter is investigated. The common mode model for the cascaded H4 inverter is analyzed. And the reason why the conventional cascade H4...... inverter fails to reduce the leakage current is clarified. In order to solve the problem, a new cascaded H5 inverter is proposed to solve the leakage current issue. Finally, the experimental results are presented to verify the effectiveness of the proposed topology with the leakage current reduction...... for the single-phase transformerless PV systems....

  18. Challenges in thermal design of industrial single-phase power inverter

    Directory of Open Access Journals (Sweden)

    Ninković Predrag

    2016-01-01

    Full Text Available This paper presents the influence of thermal aspects in design process of an industrial single-phase inverter, choice of its topology and components. Stringent design inputs like very high overload level, demand for natural cooling and very wide input voltage range have made conventional circuit topology inappropriate therefore asking for alternative solution. Different power losses calculations in semiconductors are performed and compared, outlining the guidelines how to choose the final topology. Some recommendations in power magnetic components design are given. Based on the final project, a 20kVA single-phase inverter for thermal power plant supervisory and control system is designed and commissioned.

  19. Single-Phase Hybrid Switched Reluctance Motor for Low-Power Low-Cost Applications

    DEFF Research Database (Denmark)

    Lu, Kaiyuan; Rasmussen, Peter Omand; Jakobsen, Uffe

    2011-01-01

    This paper presents a new single-phase, Hybrid Switched Reluctance (HSR) motor for low-cost, low-power, pump or fan drive systems. Its single-phase configuration allows use of a simple converter to reduce the system cost. Cheap ferrite magnets are used and arranged in a special flux concentration...... manner to increase effectively the torque density and efficiency of this machine. The efficiency of this machine is comparable to the efficiency of a traditional permanent magnet machine in the similar power range. The cogging torque, due to the existence of the permanent magnetic field, is beneficially...

  20. An Open-Loop Grid Synchronization Approach for Single-Phase Applications

    DEFF Research Database (Denmark)

    Golestan, Saeed; Guerrero, Josep M.; Quintero, Juan Carlos Vasquez

    2018-01-01

    in the presence of frequency drifts. This is particularly true in single-phase applications, where the lack of multiple independent input signals makes the implementation of the synchronization technique difficult. The aim of this paper is to develop an effective OLS technique for single-phase power and energy...... applications. The proposed OLS method benefits from a straightforward implementation, a fast dynamic response (a response time less than two cycles of the nominal frequency), and a complete immunity against the DC component in the grid voltage. In addition, the designed OLS method totally blocks (significantly...

  1. Fractional single-phase-lagging heat conduction model for describing anomalous diffusion

    Directory of Open Access Journals (Sweden)

    T.N. Mishra

    2016-03-01

    Full Text Available The fractional single-phase-lagging (FSPL heat conduction model is obtained by combining scalar time fractional conservation equation to the single-phase-lagging (SPL heat conduction model. Based on the FSPL heat conduction model, anomalous diffusion within a finite thin film is investigated. The effect of different parameters on solution has been observed and studied the asymptotic behavior of the FSPL model. The analytical solution is obtained using Laplace transform method. The whole analysis is presented in dimensionless form. Numerical examples of particular interest have been studied and discussed in details.

  2. Modeling and Stability Assessment of Single-Phase Grid Synchronization Techniques

    DEFF Research Database (Denmark)

    Golestan, Saeed; Guerrero, Josep M.; Vasquez, Juan

    2018-01-01

    (GSTs) is of vital importance. This task is most often based on obtaining a linear time-invariant (LTI) model for the GST and applying standard stability tests to it. Another option is modeling and dynamics/stability assessment of GSTs in the linear time-periodic (LTP) framework, which has received...... a very little attention. In this letter, the procedure of deriving the LTP model for single-phase GSTs is first demonstrated. The accuracy of the LTP model in predicting the GST dynamic behavior and stability is then evaluated and compared with that of the LTI one. Two well-known single-phase GSTs, i...

  3. Southern Ocean Convection and tropical telleconnections

    Science.gov (United States)

    Marinov, I.; Cabre, A.; Gnanadesikan, A.

    2014-12-01

    We show that Southern Ocean (SO) temperatures in the latest generation of Earth System Models exhibit two major modes of variation, one driven by deep convection, the other by tropical variability. We perform a CMIP5 model intercomparison to understand why different climate models represent SO variability so differently in long, control simulations. We show that multiyear variability in Southern Ocean sea surface temperatures (SSTs) can in turn influence oceanic and atmospheric conditions in the tropics on short (atmospheric) time-scales. We argue that the strength and pattern of SO-tropical teleconnections depends on the intensity of SO deep convection. Periodic convection in the SO is a feature of most CMIP5 models under preindustrial forcing (deLavergne et al., 2014). Models show a wide distribution in the spatial extent, periodicity and intensity of their SO convection, with some models convecting most of the time, and some showing very little convection. In a highly convective coupled model, we find that multidecadal variability in SO and global SSTs, as well as SO heat storage are driven by Weddell Sea convective variability, with convective decades relatively warm due to the heat released from the deep southern ocean and non-convective decades cold due to the subsurface storage of heat. Furthermore, pulses of SO convection drive SST and sea ice variations, influencing absorbed shortwave and emitted longwave radiation, wind, cloud and precipitation patterns, with climatic implications for the low latitudes via fast atmospheric teleconnections. We suggest that these high-low latitude teleconnection mechanisms are relevant for understanding hiatus decades. Additionally, Southern Ocean deep convection varied significantly during past, natural climate changes such as during the last deglaciation. Weddell Sea open convection was recently weakened, likely as a consequence of anthropogenic forcing and the resulting surface freshening. Our study opens up the

  4. Preliminary Numerical Analysis of Convective Heat Transfer Loop Using MARS Code

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Yongjae; Seo, Gwang Hyeok; Jeun, Gyoodong; Kim, Sung Joong [Hanyang Univ., Seoul (Korea, Republic of)

    2014-05-15

    be provided with expected results for the single-phase and forced convective phenomena. For the future study, different materials for the heating part are considered, such as other metals or silicon carbide (SiC) tube, which is a candidate material of fuel claddings for current and next-generation reactors.

  5. Preliminary Numerical Analysis of Convective Heat Transfer Loop Using MARS Code

    International Nuclear Information System (INIS)

    Lee, Yongjae; Seo, Gwang Hyeok; Jeun, Gyoodong; Kim, Sung Joong

    2014-01-01

    be provided with expected results for the single-phase and forced convective phenomena. For the future study, different materials for the heating part are considered, such as other metals or silicon carbide (SiC) tube, which is a candidate material of fuel claddings for current and next-generation reactors

  6. National Convective Weather Forecast

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The NCWF is an automatically generated depiction of: (1) current convection and (2) extrapolated signficant current convection. It is a supplement to, but does NOT...

  7. Single Phase Transformer-less Buck-Boost Inverter with Zero Leakage Current for PV Systems

    DEFF Research Database (Denmark)

    Mostaan, Ali; Abdelhakim, Ahmed; N. Soltani, Mohsen

    2017-01-01

    In this paper, a novel single-stage single-phase transformer-less buck-boost inverter is proposed, in which a reduced number of passive components is used. The proposed inverter combines the conventional buck, boost, and buck-boost converters in one converter in order to obtain a sinusoidal output...

  8. An efficiency improved single-phase PFC converter for electric vehicle charger applications

    DEFF Research Database (Denmark)

    Zhu, Dexuan; Tang, Yi; Jin, Chi

    2013-01-01

    This paper presents an efficiency improved single-phase power factor correction (PFC) converter with its target application to plug-in hybrid electric vehicle (PHEV) charging systems. The proposed PFC converter features sinusoidal input current, three-level output characteristic, and wide range...

  9. Design and Implementation of Wireless Energy Meter System for Monitoring the Single Phase Supply

    OpenAIRE

    U. V, Prashanth B.

    2013-01-01

    Wireless energy meter is a system developed to serve as a basic single-phase energy meter with advanced functionalities such as Peak hour setting, Peak load setting Wireless reading transmission; further the system eliminates the role of a Meter Reader.

  10. Multi-scale Modeling of Compressible Single-phase Flow in Porous Media using Molecular Simulation

    KAUST Repository

    Saad, Ahmed Mohamed

    2016-01-01

    potential model that accounts for the molecular quadrupole moment of fluids with non-spherical molecules such as CO2. The potential model was used to simulate the thermodynamic equilibrium properties for single-phase and two-phase systems using the canonical

  11. Dynamics Assessment of Grid-Synchronization Algorithms for Single-Phase Grid-Connected Converters

    DEFF Research Database (Denmark)

    Han, Yang; Luo, Mingyu; Guerrero, Josep M.

    2015-01-01

    Several advanced phase-lock-loop (PLL) algorithms have been proposed for single-phase power electronic systems. Among these algorithms, the orthogonal signal generators (OSGs) are widely utilized to generate a set of in-quadrature signals, owing to its benefit of simple digital implementation and...

  12. Comparative Performance Evaluation of Orthogonal-Signal-Generators-Based Single-Phase PLL Algorithms

    DEFF Research Database (Denmark)

    Han, Yang; Luo, Mingyu; Zhao, Xin

    2016-01-01

    The orthogonal signal generator based phase-locked loops (OSG-PLLs) are among the most popular single-phase PLLs within the areas of power electronics and power systems, mainly because they are often easy to be implement and offer a robust performance against the grid disturbances. The main aim o...

  13. Novel Motion Sensorless Control of Single Phase Brushless D.C. PM Motor Drive, with experiments

    DEFF Research Database (Denmark)

    Lepure, Liviu Ioan; Boldea, Ion; Andreescu, Gheorghe Daniel

    2010-01-01

    A motion sensorless control for single phase permanent magnet brushless d.c. (PM-BLDC) motor drives, based on flux integration and prior knowledge of the PM flux/position characteristic is proposed here and an adequate correction algorithm is adopted, in order to increase the robustness to noise...

  14. Single-Phase 3L PR Controlled qZS Inverter Connected to the Distorted Grid

    DEFF Research Database (Denmark)

    Makovenko, Elena; Husev, Oleksandr; Roncero-Clemente, Carlos

    2016-01-01

    This paper presents a single-phase three-level NPC qZS inverter connected to a distorted grid using PID and PR regulators. A case study system along with the control strategy are described. Tuning approaches for PID and PR regulators are addressed and validated by means of simulation results...

  15. Potential pitfalls of single phasing operation in a three phase distribution network

    Energy Technology Data Exchange (ETDEWEB)

    Narayanan, V S

    1986-07-01

    Finding it difficult to cope with the increased demand for electric power, some electricity boards have resorted to single phasing techniques in distribution system. This practice is harmful to the equipment in the power system. Some of the potential dangers associated with this undesirable practice are briefly discussed.

  16. PI and repetitive control for single phase inverter based on virtual rotating coordinate system

    Science.gov (United States)

    Li, Mengqi; Tong, Yibin; Jiang, Jiuchun; Liang, Jiangang

    2018-03-01

    Microgrid technology developed rapidly and nonlinear loads were connected increasingly. A new control strategy was proposed for single phase inverter when connected nonlinear loads under island condition. PI and repetitive compound controller was realized under synchronous rotating coordinate system and acquired high quality sinusoidal voltage output without voltage spike when loads step changed. Validity and correctness were verified by simulation using MATLAB/Simulink.

  17. 16 channel WDM regeneration in a single phase-sensitive amplifier through optical Fourier transformation

    DEFF Research Database (Denmark)

    Guan, Pengyu; Da Ros, Francesco; Lillieholm, Mads

    2016-01-01

    We demonstrate simultaneous phase regeneration of 16-WDM DPSK channels using optical Fourier transformation and a single phase-sensitive amplifier. The BERs of 16-WDM×10-Gbit/s phase noise degraded DPSK signals are improved by 0.4-1.3 orders of magnitude...

  18. Forest resources of southeast Alaska, 2000: results of a single-phase systematic sample.

    Science.gov (United States)

    Willem W.S. van Hees

    2003-01-01

    A baseline assessment of forest resources in southeast Alaska was made by using a single-phase, unstratified, systematic-grid sample, with ground plots established at each grid intersection. Ratio-of-means estimators were used to develop population estimates. Forests cover an estimated 48 percent of the 22.9-million-acre southeast Alaska inventory unit. Dominant forest...

  19. Zero-Voltage Ride-Through Capability of Single-Phase Grid-Connected Photovoltaic Systems

    Directory of Open Access Journals (Sweden)

    Zhen Zhang

    2017-03-01

    Full Text Available Distributed renewable energy systems play an increasing role in today’s energy paradigm. Thus, intensive research activities have been centered on improving the performance of renewable energy systems, including photovoltaic (PV systems, which should be of multiple-functionality. That is, the PV systems should be more intelligent in the consideration of grid stability, reliability, and fault protection. Therefore, in this paper, the performance of single-phase grid-connected PV systems under an extreme grid fault (i.e., when the grid voltage dips to zero is explored. It has been revealed that combining a fast and accurate synchronization mechanism with appropriate control strategies for the zero-voltage ride-through (ZVRT operation is mandatory. Accordingly, the representative synchronization techniques (i.e., the phase-locked loop (PLL methods in the ZVRT operation are compared in terms of detection precision and dynamic response. It shows that the second-order generalized integrator (SOGI-PLL is a promising solution for single-phase systems in the case of fault ride-through. A control strategy by modifying the SOGI-PLL scheme is then introduced to single-phase grid-connected PV systems for ZVRT operation. Simulations are performed to verify the discussions. The results have demonstrated that the proposed method can help single-phase PV systems to temporarily ride through zero-voltage faults with good dynamics.

  20. Modeling and Control of a Single-Phase Marine Cooling System

    DEFF Research Database (Denmark)

    Hansen, Michael; Stoustrup, Jakob; Bendtsen, Jan Dimon

    2013-01-01

    This paper presents two model-based control design approaches for a single-phase marine cooling system. Models are derived from first principles and aim at describing significant system dynamics including nonlinearities and transport delays, while keeping the model complexity low. The two...

  1. Single phase inverter for a three phase power generation and distribution system

    Science.gov (United States)

    Lindena, S. J.

    1976-01-01

    A breadboard design of a single-phase inverter with sinusoidal output voltage for a three-phase power generation and distribution system was developed. The three-phase system consists of three single-phase inverters, whose output voltages are connected in a delta configuration. Upon failure of one inverter the two remaining inverters will continue to deliver three-phase power. Parallel redundancy as offered by two three-phase inverters is substituted by one three-phase inverter assembly with high savings in volume, weight, components count and complexity, and a considerable increase in reliability. The following requirements must be met: (1) Each single-phase, current-fed inverter must be capable of being synchronized to a three-phase reference system such that its output voltage remains phaselocked to its respective reference voltage. (2) Each single-phase, current-fed inverter must be capable of accepting leading and lagging power factors over a range from -0.7 through 1 to +0.7.

  2. protoDUNE-Single Phase and protDUNE-DualPhase

    CERN Multimedia

    Brice, Maximilien

    2016-01-01

    At the EHN1 two big 8m x 8m x8m detector prototypes (protoDUNE-Single Phase and protDUNE-DualPhase) are being constructed. The aim is to test technologies and detector performances for DUNE, a new generation of LBN neutr

  3. Benchmarking of grid fault modes in single-phase grid-connected photovoltaic systems

    DEFF Research Database (Denmark)

    Yang, Yongheng; Blaabjerg, Frede; Zou, Zhixiang

    2012-01-01

    Pushed by the booming installations of single-phase photovoltaic (PV) systems, the grid demands regarding the integration of PV systems are expected to be modified. Hence, the future PV systems should become more active with functionalities of low voltage ride-through (LVRT) and the grid support...

  4. Frequency Adaptive Repetitive Control of Grid-Tied Single-Phase PV Inverters

    DEFF Research Database (Denmark)

    Zhou, Keliang; Yang, Yongheng; Blaabjerg, Frede

    2015-01-01

    . This paper thus explores a frequency adaptive repetitive control strategy for grid converters, which employs fractional delay filters in order to adapt to the change of the grid frequency. Case studies with experimental results of a single-phase grid-connected PV inverter system are provided to verify...

  5. The Effect of Grain Size on Mechanical Instability in Single-Phase Li-Alloy Anodes

    National Research Council Canada - National Science Library

    Wolfenstine, Jeff

    2000-01-01

    .... The results of this study suggest that decreasing the particle and/or grain size is not a practical approach to solving the mechanical instability problem of single phase Li alloys that are intended to be used as anodes in Li-ion batteries.

  6. Lyapunov-Based Control Scheme for Single-Phase Grid-Connected PV Central Inverters

    NARCIS (Netherlands)

    Meza, C.; Biel, D.; Jeltsema, D.; Scherpen, J. M. A.

    A Lyapunov-based control scheme for single-phase single-stage grid-connected photovoltaic central inverters is presented. Besides rendering the closed-loop system globally stable, the designed controller is able to deal with the system uncertainty that depends on the solar irradiance. A laboratory

  7. Decoupling of fluctuating power in single-phase systems through a symmetrical half-bridge circuit

    DEFF Research Database (Denmark)

    Tang, Yi; Blaabjerg, Frede; Loh, Poh Chiang

    2014-01-01

    Single-phase AC/DC or DC/AC systems inherently subject to harmonic disturbance which is caused by the well-known double line frequency ripple power. This issue can be eased through the installation of bulky electrolytic capacitors in the dc-link, but such passive filtering approach may inevitably...

  8. A Direct Maximum Power Point Tracking Method for Single-Phase Grid Connected PV Inverters

    DEFF Research Database (Denmark)

    EL Aamri, Faicel; Maker, Hattab; Sera, Dezso

    2018-01-01

    in dynamic conditions, especially in low irradiance when the measurement of signals becomes more sensitive to noise. The proposed MPPT is designed for single-phase single-stage grid-connected PV inverters, and is based on estimating the instantaneous PV power and voltage ripples, using second...

  9. Pressure Drop Correlations of Single-Phase and Two-Phase Flow in Rolling Tubes

    International Nuclear Information System (INIS)

    Xia-xin Cao; Chang-qi Yan; Pu-zhen Gao; Zhong-ning Sun

    2006-01-01

    A series of experimental studies of frictional pressure drop for single phase and two-phase bubble flow in smooth rolling tubes were carried out. The tube inside diameters were 15 mm, 25 mm and 34.5 mm respectively, the rolling angles of tubes could be set as 10 deg. and 20 deg., and the rolling periods could be set as 5 s, 10 s and 15 s. Combining with the analysis of single-phase water motion, it was found that the traditional correlations for calculating single-phase frictional coefficient were not suitable for the rolling condition. Based on the experimental data, a new correlation for calculating single-phase frictional coefficient under rolling condition was presented, and the calculations not only agreed well with the experimental data, but also could display the periodically dynamic characteristics of frictional coefficients. Applying the new correlation to homogeneous flow model, two-phase frictional pressure drop of bubble flow in rolling tubes could be calculated, the results showed that the relative error between calculation and experimental data was less than ± 25%. (authors)

  10. Hybrid Control Method for a Single Phase PFC using a Low Cost Microcontroller

    DEFF Research Database (Denmark)

    Jakobsen, Lars Tønnes; Nielsen, Nils; Wolf, Christian

    2005-01-01

    This paper presents a hybrid control method for single phase boost PFCs. The high bandwidth current loop is analog while the voltage loop is implemented in an 8-bit microcontroller. The design focuses on minimizing the number of calculations done in the microcontroller. A 1kW prototype has been...

  11. A Generic Topology Derivation Method for Single-phase Converters with Active Capacitive DC-links

    DEFF Research Database (Denmark)

    Wang, Haoran; Wang, Huai; Zhu, Guorong

    2016-01-01

    capacitive DCDC- link solutions, but important aspects of the topology assess-ment, such as the total energy storage, overall capacitive energy buffer ratio, cost, and reliability are still not available. This paper proposes a generic topology derivation method of single-phase power converters...

  12. Flux Concentration and Pole Shaping in a Single Phase Hybrid Switched Reluctance Motor Drive

    DEFF Research Database (Denmark)

    Jakobsen, Uffe; Lu, Kaiyuan

    2010-01-01

    The single phase hybrid switched reluctance motor (HSRM) may be a good candidate for low-cost drives used for pump applications. This paper presents a new design of the HSRM with improved starting torque achieved by stator pole shaping, and a better arrangement of the embedded stator permanent...

  13. Modelling and simulation of multiple single - phase induction motor in parallel connection

    Directory of Open Access Journals (Sweden)

    Sujitjorn, S.

    2006-11-01

    Full Text Available A mathematical model for parallel connected n-multiple single-phase induction motors in generalized state-space form is proposed in this paper. The motor group draws electric power from one inverter. The model is developed by the dq-frame theory and was tested against four loading scenarios in which satisfactory results were obtained.

  14. Reversibility of magnetic field driven transition from electronic phase separation state to single-phase state in manganites: A microscopic view

    Science.gov (United States)

    Liu, Hao; Lin, Lingfang; Yu, Yang; Lin, Hanxuan; Zhu, Yinyan; Miao, Tian; Bai, Yu; Shi, Qian; Cai, Peng; Kou, Yunfang; Lan, Fanli; Wang, Wenbin; Zhou, Xiaodong; Dong, Shuai; Yin, Lifeng; Shen, Jian

    2017-11-01

    Electronic phase separation (EPS) is a common phenomenon in strongly correlated oxides. For colossal magnetoresistive (CMR) manganites, the EPS is so pronounced that not only does it govern the CMR behavior, but also raises a question whether EPS exists as a ground state for systems or a metastable state. While it has been well known that a magnetic field can drive the transition of the EPS state into a single-phase state in manganites, the reversibility of this transition is not well studied. In this work we use magnetic force microscopy (MFM) to directly visualize the reversibility of the field driven transition between the EPS state and the single-phase state at different temperatures. The MFM images correspond well with the global magnetic and transport property measurements, uncovering the underlying mechanism of the field driven transition between the EPS state and the single-phase state. We argue that EPS state is a consequence of system quenching whose response to an external magnetic field is governed by a local energy landscape.

  15. Behaviors and transitions along the path to magnetostrophic convection

    Science.gov (United States)

    Grannan, A. M.; Vogt, T.; Horn, S.; Hawkins, E. K.; Aggarwal, A.; Aurnou, J. M.

    2017-12-01

    The generation of magnetic fields in planetary and stellar interiors are believed to be controlled primarily by turbulent convection constrained by Coriolis and Lorentz forces in their electrically conducting fluid layers. Yet relatively few laboratory experiments are capable of investigating the different regimes of turbulent magnetohydrodynamic convection. In this work, we perform one laboratory experiment in a cylinder at a fixed heat flux using the liquid metal gallium in order to investigate, sequentially: Rayleigh-Bènard convection without any imposed constraints, magnetoconvection with a Lorentz constraint imposed by vertical magnetic field, rotating convection with a Coriolis constraint imposed by rotation, and finally the magnetostrophic convective regime where both Coriolis and Lorentz are imposed and equal. Using an array of internal and external temperature probes, we show that each regime along the path to magnetostrophic convection is unique. The behaviors and transitions in the dominant modes of convection as well as their fundamental frequencies and wavenumbers are investigated.

  16. Simulation of the phenomenon of single-phase and two-phase natural circulation; Simulacao do fenomeno de circulacao natural mono e bifasica

    Energy Technology Data Exchange (ETDEWEB)

    Castrillo, Lazara Silveira

    1998-02-01

    Natural convection phenomenon is often used to remove the residual heat from the surfaces of bodies where the heat is generated e.g. during accidents or transients of nuclear power plants. Experimental study of natural circulation can be done in small scale experimental circuits and the results can be extrapolated for larger operational facilities. The numerical analysis of transients can be carried out by using large computational codes that simulate the thermohydraulic behavior in such facilities. The computational code RELAP5/MOD2, (Reactor Excursion and Leak Analysis Program) was developed by U.S. Nuclear Regulatory Commissions's. Division of Reactor Safety Research with the objective of analysis of transients and postulated accidents in the light water reactor (LWR) systems, including small and large ruptures with loss of coolant accidents (LOCA's). The results obtained by the simulation of single-phase and two-phase natural circulation, using the RELAP5/MOD2, are presented in this work. The study was carried out using the experimental circuit built at the 'Departamento de Engenharia Quimica da Escola Politecnica da Universidade de Sao Paulo'. In the circuit, two experiments were carried out with different conditions of power and mass flow, obtaining a single-phase regime with a level of power of 4706 W and flow of 5.10{sup -5} m{sup 3}/s (3 l/min) and a two-phase regime with a level of power of 6536 W and secondary flow 2,33.10{sup -5} m{sup 3}/s (1,4 l/min). The study allowed tio evaluate the capacity of the code for representing such phenomena as well as comparing the transients obtained theoretically with the experimental results. The comparative analysis shows that the code represents fairly well the single-phase transient, but the results for two-phase transients, starting from the nodalization and calibration used for the case single-phase transient, did not reproduce faithfully some experimental results. (author)

  17. Heat transfer measurements in a forced convection loop with two molten-fluoride salts: LiF--BeF2--ThF2--UF4 and eutectic NaBF4--NaF

    International Nuclear Information System (INIS)

    Silverman, M.D.; Huntley, W.R.; Robertson, H.E.

    1976-10-01

    Heat transfer coefficients were determined experimentally for two molten-fluoride salts [LiF-BeF 2 -ThF 2 -UF 4 (72-16-12-0.3 mole %) and NaBF 4 -NaF (92-8 mole %] proposed as the fuel salt and coolant salt, respectively, for molten-salt breeder reactors. Information was obtained over a wide range of variables, with salt flowing through 12.7-mm-OD (0.5-in.) Hastelloy N tubing in a forced convection loop (FCL-2b). Satisfactory agreement with the empirical Sieder-Tate correlation was obtained in the fully developed turbulent region at Reynolds moduli above 15,000 and with a modified Hausen equation in the extended transition region (Re approx.2100-15,000). Insufficient data were obtained in the laminar region to allow any conclusions to be drawn. These results indicate that the proposed salts behave as normal heat transfer fluids with an extended transition region

  18. Steady, three-dimensional, internally heated convection

    International Nuclear Information System (INIS)

    Schubert, G.; Glatzmaier, G.A.; Travis, B.

    1993-01-01

    Numerical calculations have been carried out of steady, symmetric, three-dimensional modes of convection in internally heated, infinite Prandtl number, Boussinesq fluids at a Rayleigh number of 1.4x10 4 in a spherical shell with inner/outer radius of 0.55 and in a 3x3x1 rectangular box. Multiple patterns of convection occur in both geometries. In the Cartesian geometry the patterns are dominated by cylindrical cold downflows and a broad hot upwelling. In the spherical geometry the patterns consist of cylindrical cold downwellings centered either at the vertices of a tetrahedron or the centers of the faces of a cube. The cold downflow cylinders are immersed in a background of upwelling within which there are cylindrical hot concentrations (plumes) and hot halos around the downflows. The forced hot upflow return plumes of internally heated spherical convection are fundamentally different from the buoyancy-driven plumes of heated from below convection

  19. A New Power Calculation Method for Single-Phase Grid-Connected Systems

    DEFF Research Database (Denmark)

    Yang, Yongheng; Blaabjerg, Frede

    2013-01-01

    A new method to calculate average active power and reactive power for single-phase systems is proposed in this paper. It can be used in different applications where the output active power and reactive power need to be calculated accurately and fast. For example, a grid-connected photovoltaic...... system in low voltage ride through operation mode requires a power feedback for the power control loop. Commonly, a Discrete Fourier Transform (DFT) based power calculation method can be adopted in such systems. However, the DFT method introduces at least a one-cycle time delay. The new power calculation...... method, which is based on the adaptive filtering technique, can achieve a faster response. The performance of the proposed method is verified by experiments and demonstrated in a 1 kW single-phase grid-connected system operating under different conditions.Experimental results show the effectiveness...

  20. 100-nm thick single-phase wurtzite BAlN films with boron contents over 10%

    KAUST Repository

    Li, Xiaohang

    2017-01-11

    Growing thicker BAlN films while maintaining single-phase wurtzite structure and boron content over 10% has been challenging. In this study, we report on the growth of 100 nm-thick single-phase wurtzite BAlN films with boron contents up to 14.4% by MOCVD. Flow-modulated epitaxy was employed to increase diffusion length of group-III atoms and reduce parasitic reactions between the metalorganics and NH3. A large growth efficiency of ∼2000 μm mol−1 was achieved as a result. Small B/III ratios up to 17% in conjunction with high temperatures up to 1010 °C were utilized to prevent formation of the cubic phase and maintain wurtzite structure.

  1. 100-nm thick single-phase wurtzite BAlN films with boron contents over 10%

    KAUST Repository

    Li, Xiaohang; Wang, Shuo; Liu, Hanxiao; Ponce, Fernando A.; Detchprohm, Theeradetch; Dupuis, Russell D.

    2017-01-01

    Growing thicker BAlN films while maintaining single-phase wurtzite structure and boron content over 10% has been challenging. In this study, we report on the growth of 100 nm-thick single-phase wurtzite BAlN films with boron contents up to 14.4% by MOCVD. Flow-modulated epitaxy was employed to increase diffusion length of group-III atoms and reduce parasitic reactions between the metalorganics and NH3. A large growth efficiency of ∼2000 μm mol−1 was achieved as a result. Small B/III ratios up to 17% in conjunction with high temperatures up to 1010 °C were utilized to prevent formation of the cubic phase and maintain wurtzite structure.

  2. Stability analysis of single-phase thermosyphon loops by finite difference numerical methods

    International Nuclear Information System (INIS)

    Ambrosini, W.

    1998-01-01

    In this paper, examples of the application of finite difference numerical methods in the analysis of stability of single-phase natural circulation loops are reported. The problem is here addressed for its relevance for thermal-hydraulic system code applications, in the aim to point out the effect of truncation error on stability prediction. The methodology adopted for analysing in a systematic way the effect of various finite difference discretization can be considered the numerical analogue of the usual techniques adopted for PDE stability analysis. Three different single-phase loop configurations are considered involving various kinds of boundary conditions. In one of these cases, an original dimensionless form of the governing equations is proposed, adopting the Reynolds number as a flow variable. This allows for an appropriate consideration of transition between laminar and turbulent regimes, which is not possible with other dimensionless forms, thus enlarging the field of validity of model assumptions. (author). 14 refs., 8 figs

  3. Microcontroller Based SPWM Single-Phase Inverter For Wind Power Application

    Directory of Open Access Journals (Sweden)

    Khin Ohmar Lin

    2017-04-01

    Full Text Available In this paper microcontroller based sinusoidal pulse width modulation SPWM single-phase inverter is emphasized to constant frequency conversion scheme for wind power application. The wind-power generator output voltage and frequency are fluctuated due to the variation of wind velocity. Therefore the AC output voltage of wind-generator is converted into DC voltage by using rectifier circuit and this DC voltage is converted back to AC voltage by using inverter circuit. SPWM technique is used in inverter to get nearly sine wave and reduce harmonic content. The rating of inverter is 500W single-phase 220V 50 Hz. The required SPWM timing pulses for the inverter are generated from the PIC16F877A microcontroller. Circuit simulation was done by using Proteus 7 Professional and MATLABR 2008 software. The software for microcontroller is implemented by using MPASM assembler.

  4. Hybrid Three-Phase/Single-Phase Microgrid Architecture with Power Management Capabilities

    DEFF Research Database (Denmark)

    Sun, Qiuye; Zhou, Jianguo; Guerrero, Josep M.

    2015-01-01

    With the fast proliferation of single-phase distributed generation (DG) units and loads integrated into residential microgrids, independent power sharing per phase and full use of the energy generated by DGs have become crucial. To address these issues, this paper proposes a hybrid microgrid...... architecture and its power management strategy. In this microgrid structure, a power sharing unit (PSU), composed of three single-phase back-to-back (SPBTB) converters, is proposed to be installed at the point of common coupling (PCC). The aim of the PSU is mainly to realize the power exchange and coordinated...... control of load power sharing among phases, as well as to allow fully utilization of the energy generated by DGs. Meanwhile, the method combining the modified adaptive backstepping-sliding mode control approach and droop control is also proposed to design the SPBTB system controllers. With the application...

  5. A High Power Density Single-Phase PWM Rectifier With Active Ripple Energy Storage

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Ruxi [Virginia Polytechnic Institute and State University (Virginia Tech); Wang, Fei [ORNL; Boroyevich, Dushan [Virginia Polytechnic Institute and State University (Virginia Tech); Burgos, Rolando [ABB; Lai, Rixin [General Electric; Ning, Puqi [ORNL; Rajashekara, Kaushik [Rolls Royce

    2011-01-01

    It is well known that single-phase pulse width modulation rectifiers have second-order harmonic currents and corresponding ripple voltages on the dc bus. The low-frequency harmonic current is normally filtered using a bulk capacitor in the bus, which results in low power density. However, pursuing high power density in converter design is a very important goal in the aerospace applications. This paper studies methods for reducing the energy storage capacitor for single-phase rectifiers. The minimum ripple energy storage requirement is derived independently of a specific topology. Based on theminimum ripple energy requirement, the feasibility of the active capacitor s reduction schemes is verified. Then, we propose a bidirectional buck boost converter as the ripple energy storage circuit, which can effectively reduce the energy storage capacitance. The analysis and design are validated by simulation and experimental results.

  6. A Synchronization Method for Single-Phase Grid-Tied Inverters

    DEFF Research Database (Denmark)

    Hadjidemetriou, Lenos; Kyriakides, Elias; Yang, Yongheng

    2016-01-01

    The controllers of single-phase grid-tied inverters require improvements to enable distribution generation systems to meet the grid codes/standards with respect to power quality and the fault ride through capability. In that case, the response of the selected synchronization technique is crucial...... for the performance of the entire grid-tied inverter. In this paper, a new synchronization method with good dynamics and high accuracy under a highly distorted voltage is proposed. This method uses a Multi-Harmonic Decoupling Cell (MHDC), which thus can cancel out the oscillations on the synchronization signals due...... to the harmonic voltage distortion while maintaining the dynamic response of the synchronization. Therefore, the accurate and dynamic response of the proposed MHDC-PLL can be beneficial for the performance of the whole single-phase grid-tied inverter....

  7. A continuous and prognostic convection scheme based on buoyancy, PCMT

    Science.gov (United States)

    Guérémy, Jean-François; Piriou, Jean-Marcel

    2016-04-01

    A new and consistent convection scheme (PCMT: Prognostic Condensates Microphysics and Transport), providing a continuous and prognostic treatment of this atmospheric process, is described. The main concept ensuring the consistency of the whole system is the buoyancy, key element of any vertical motion. The buoyancy constitutes the forcing term of the convective vertical velocity, which is then used to define the triggering condition, the mass flux, and the rates of entrainment-detrainment. The buoyancy is also used in its vertically integrated form (CAPE) to determine the closure condition. The continuous treatment of convection, from dry thermals to deep precipitating convection, is achieved with the help of a continuous formulation of the entrainment-detrainment rates (depending on the convective vertical velocity) and of the CAPE relaxation time (depending on the convective over-turning time). The convective tendencies are directly expressed in terms of condensation and transport. Finally, the convective vertical velocity and condensates are fully prognostic, the latter being treated using the same microphysics scheme as for the resolved condensates but considering the convective environment. A Single Column Model (SCM) validation of this scheme is shown, allowing detailed comparisons with observed and explicitly simulated data. Four cases covering the convective spectrum are considered: over ocean, sensitivity to environmental moisture (S. Derbyshire) non precipitating shallow convection to deep precipitating convection, trade wind shallow convection (BOMEX) and strato-cumulus (FIRE), together with an entire continental diurnal cycle of convection (ARM). The emphasis is put on the characteristics of the scheme which enable a continuous treatment of convection. Then, a 3D LAM validation is presented considering an AMMA case with both observations and a CRM simulation using the same initial and lateral conditions as for the parameterized one. Finally, global

  8. Removal of Direct Current Link Harmonic Ripple in Single Phase Voltage Source Inverter Systems Using Supercapacitors

    Science.gov (United States)

    2016-09-01

    Khaligh, “Optimization of sizing and battery cycle life in battery/ultracapacitor hybrid energy storage systems for electric vehicle applications...depth cycling operation in photovoltaic system ,” in 22nd International Conference “Mixed Design of Integrated Circuits and Systems ,” Toruń, Poland...CURRENT LINK HARMONIC RIPPLE IN SINGLE-PHASE VOLTAGE SOURCE INVERTER SYSTEMS USING SUPERCAPACITORS by Gabriel D. Hernandez September 2016

  9. Geometric relationships for homogenization in single-phase binary alloy systems

    Science.gov (United States)

    Unnam, J.; Tenney, D. R.; Stein, B. A.

    1978-01-01

    A semiempirical relationship is presented which describes the extent of interaction between constituents in single-phase binary alloy systems having planar, cylindrical, or spherical interfaces. This relationship makes possible a quick estimate of the extent of interaction without lengthy numerical calculations. It includes two parameters which are functions of mean concentration and interface geometry. Experimental data for the copper-nickel system are included to demonstrate the usefulness of this relationship.

  10. Single-phase flow and flow boiling of water in horizontal rectangular microchannels

    OpenAIRE

    Mirmanto

    2013-01-01

    This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University The current study is part of a long term experimental project devoted to investigating single-phase flow pressure drop and heat transfer, flow boiling pressure drop and heat transfer, flow boiling instability and flow visualization of de-ionized water flow in microchannels. The experimental facility was first designed and constructed by S. Gedupudi (2009) and in the present study; ...

  11. Single-phase DECT with VNCT compared with three-phase CTU in patients with haematuria

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jung Jae; Park, Byung Kwan; Kim, Chan Kyo [Sungkyunkwan University School of Medicine, Department of Radiology, Samsung Medical Center, Seoul (Korea, Republic of)

    2016-10-15

    To retrospectively evaluate the diagnostic performance of single-phase dual-energy CT (DECT) with virtual non-contrast CT (VNCT) compared with three-phase CT urography (CTU) in patients with haematuria. A total of 296 patients underwent three-phase CTU (NCT at 120 kVp; nephrographic phase and excretory phase DECTs at 140 kVp and 80 kVp) owing to haematuria. Diagnostic performances of CT scans were compared for detecting urothelial tumours and urinary stones. Dose-length product (DLP) was compared in relation to single-phase DECT and three-phase CTU Dose-length product (DLP) was compared in relation to single-phase DECT and three-phase CTU. Sensitivity and specificity for tumour were 95 % (19/20) and 98.9 % (273/276) on CTU, 95 % (19/20) and 98.2 % (271/276) on nephrographic phase DECT, and 90 % (18/20) and 98.2 % (271/276) on excretory phase DECT (P > 0.1). Of the 148 stones detected on NCT, 108 (73 %) and 100 (67.6 %) were detected on nephrographic phase and excretory phase VNCTs, respectively. The mean size of stones undetected on nephrographic and excretory VNCTs was measured as 1.5 ± 0.5 mm and 1.6 ± 0.6 mm, respectively. The mean DLPs of three-phase CTU, nephrographic phase DECT and excretory phase DECT were 1076 ± 248 mGy . cm, 410 ± 98 mGy . cm, and 360 ± 87 mGy . cm, respectively (P < 0.001). Single-phase DECT has a potential to replace three-phase CTU for detecting tumours with a lower radiation dose. (orig.)

  12. Influence of microstructure on low cycle fatigue in some single phase and biphasic stainless steels

    Energy Technology Data Exchange (ETDEWEB)

    Stolarz, J. [Ecole Nationale Superieure des Mines, Centre SMS, URA CNRS 1884, Saint-Etienne (France)

    2004-07-01

    This overview deals with the effects of microstructural parameters in different single phase and biphasic stainless steels on short crack behaviour and on fatigue life in the low cycle regime. The effect of the grain size is investigated in a single phase austenitic stainless steel. Under plastic strain control, the fatigue life increases when the grain size decreases. The results are discussed by analysing the distributions of crack depths as a function of the grain size. The second type of material is a metastable austenitic steel which partially transforms into martensite during LCF at temperatures between -50 C and +120 C. The grain size of the initially single phase austenitic microstructure has a combined influence on the volume fraction of martensite produced during fatigue and on the fatigue life. In this case, the grain size effect is still considerable but totally indirect because all fatigue cracks grow exclusively in the martensite. The cyclic behaviour analysis in biphasic alloys in which two phases undergo plastic deformation during LCF is considerably more complex because the conventional concept of microstructural barriers cannot be applied. The possible damage patterns in a pair of grains with different mechanical properties are discussed on the example of a solution treated and aged superduplex austenitic-ferritic stainless steel (SDSS). The hardening of one phase (ferrite) through ageing at 475 C changes the cyclic behaviour of the initial ''quasi single phase'' microstructure. Consequently, the fatigue life under plastic strain control decreases compared with the solution treated SDSS. The discussion is focussed on LCF damage mechanisms at the microstructure size scale with a particular accent put on the propagation of short cracks in the bulk. All the microstructures exhibit some common features with respect to the behaviour of short cracks. In particular a strong effect of microstructural barriers in the bulk and the

  13. SINGLE-PHASE AND TWO-PHASE SECONDARY COOLANTS: SIMULATION AND EVALUATION OF THEIR THERMOPHYSICAL PROPERTIES

    Directory of Open Access Journals (Sweden)

    Pedro Samuel Gomes Medeiros

    2011-09-01

    Full Text Available This paper makes a comparative analysis of the thermophysical properties of ice slurry with conventional single-phase secondary fluids used in thermal storage cooling systems. The ice slurry is a two-phase fluid consisting of water, antifreeze and ice crystals. It is a new technology that has shown great energy potential. In addition to transporting energy as a heat transfer fluid, it has thermal storage properties due to the presence of ice, storing coolness by latent heat of fusion. The single-phase fluids analyzed are water-NaCl and water-propylene glycol solutions, which also operate as carrier fluids in ice slurry. The presence of ice changes the thermophysical properties of aqueous solutions and a number of these properties were determined: density, thermal conductivity and dynamic viscosity. Data were obtained by software simulation. The results show that the presence of 10% by weight of ice provides a significant increase in thermal conductivity and dynamic viscosity, without causing changes in density. The rheological behavior of ice slurries, associated with its high viscosity, requires higher pumping power; however, this was not significant because higher thermal conductivity allows a lower mass flow rate without the use of larger pumps. Thus, the ice slurry ensures its high potential as a secondary fluid in thermal storage cooling systems, proving to be more efficient than single-phase secondary fluids.

  14. Interaction of externally-driven acoustic waves with compressible convection

    International Nuclear Information System (INIS)

    Jones, P.; Merryfield, W.

    1992-01-01

    Two-dimensional numerical simulations are used to examine the interaction of acoustic waves with a compressible convecting fluid. Acoustic waves are forced at the lower boundary of the computational domain and propagate through a three-layer system undergoing vigorous penetrative convection. Energy exchange between the wave and the fluid is analyzed using a work integral formulation

  15. Primary Issues of Mixed Convection Heat Transfer Phenomena

    Energy Technology Data Exchange (ETDEWEB)

    Chae, Myeong-Seon; Chung, Bum-Jin [Kyung Hee University, Yongin (Korea, Republic of)

    2015-10-15

    The computer code analyzing the system operating and transient behavior must distinguish flow conditions involved with convective heat transfer flow regimes. And the proper correlations must be supplied to those flow regimes. However the existing safety analysis codes are focused on the Light Water Reactor and they are skeptical to be applied to the GCRs (Gas Cooled Reactors). One of the technical issues raise by the development of the VHTR is the mixed convection, which occur when the driving forces of both forced and natural convection are of comparable magnitudes. It can be encountered as in channel of the stacked with fuel elements and a decay heat removal system and in VHTR. The mixed convection is not intermediate phenomena with natural convection and forced convection but independent complicated phenomena. Therefore, many researchers have been studied and some primary issues were propounded for phenomena mixed convection. This paper is to discuss some problems identified through reviewing the papers for mixed convection phenomena. And primary issues of mixed convection heat transfer were proposed respect to thermal hydraulic problems for VHTR. The VHTR thermal hydraulic study requires an indepth study of the mixed convection phenomena. In this study we reviewed the classical flow regime map of Metais and Eckert and derived further issues to be considered. The following issues were raised: (1) Buoyancy aided an opposed flows were not differentiated and plotted in a map. (2) Experimental results for UWT and UHF condition were also plotted in the same map without differentiation. (3) The buoyancy coefficient was not generalized for correlating with buoyancy coefficient. (4) The phenomenon analysis for laminarization and returbulization as buoyancy effects in turbulent mixed convection was not established. (5) The defining to transition in mixed convection regime was difficult.

  16. Experimental study of laminar mixed convection in a rod bundle with mixing vane spacer grids

    Energy Technology Data Exchange (ETDEWEB)

    Mohanta, Lokanath, E-mail: lxm971@psu.edu [Department of Mechanical and Nuclear Engineering, Pennsylvania State University, University Park, PA 16802 (United States); Cheung, Fan-Bill [Department of Mechanical and Nuclear Engineering, Pennsylvania State University, University Park, PA 16802 (United States); Bajorek, Stephen M.; Tien, Kirk; Hoxie, Chris L. [Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001 (United States)

    2017-02-15

    Highlights: • Investigated the heat transfer during mixed laminar convection in a rod bundle with linearly varying heat flux. • The Nusselt number increases downstream of the inlet with increasing Richardson number. • Developed an enhancement factor to account for the effects of mixed convection over the forced laminar heat transfer. - Abstract: Heat transfer by mixed convection in a rod bundle occurs when convection is affected by both the buoyancy and inertial forces. Mixed convection can be assumed when the Richardson number (Ri = Gr/Re{sup 2}) is on the order of unity, indicating that both forced and natural convection are important contributors to heat transfer. In the present study, data obtained from the Rod Bundle Heat Transfer (RBHT) facility was used to determine the heat transfer coefficient in the mixed convection regime, which was found to be significantly larger than those expected assuming purely forced convection based on the inlet flow rate. The inlet Reynolds (Re) number for the tests ranged from 500 to 1300, while the Grashof (Gr) number varied from 1.5 × 10{sup 5} to 3.8 × 10{sup 6} yielding 0.25 < Ri < 4.3. Using results from RBHT test along with the correlation from the FLECHT-SEASET test program for laminar forced convection, a new correlation ​is proposed for mixed convection in a rod bundle. The new correlation accounts for the enhancement of heat transfer relative to laminar forced convection.

  17. Some developments and applications of LES of single phase turbulent flows for nuclear industry

    International Nuclear Information System (INIS)

    Frederic Ducros; Valerie Barthel; Ulrich Bieder; Alexandre Chatelain; Younes Benarafa; Olivier Cioni; Gauthier Fauchet; Philippe Emonot; Patrick Quemere; Bernard Menant; Nicolas Tauveron; Simone Vandroux; Christophe Calvin

    2005-01-01

    Full text of publication follows: The turbulence modelling is an important issue concerning the predictive capability of the CFD codes applied to nuclear reactor safety (NRS), in particular for single-phase flows. Common features of these unsteady high Reynolds number turbulent flows are various regimes (laminar, transitional, fully turbulent) developing in arbitrary complex geometries involving a large extend of standard flow configurations (attached and detached boundary layers, mixing layers, jets in cavity, in cross flows, jet impingement) eventually submitted to buoyancy forces, to dilatation effects and leading to mixing of constituents and temperatures. NRS issues are most of the time related to the eventual knowledge of parietal quantities such as temperature (mean and fluctuating), leading to consider the wall region as a crucial one and to deal with coupled problems. All these features can lead to consider different approaches for turbulence modelling: more or less standard 'Reynolds Average Navier-Stokes equations' closures, Large Eddy Simulations, both of them considered with or without wall functions, with or without large implicit time stepping etc. The development and industrialization of LES as a target of providing 'reference simulations' for NRS are parts of the Trio-U project, developed at CEA for several years [1]. First, the paper presents the current status of LES implementation and some insights on the R and D effort concerning the turbulence modelling. The R and D strategy will be introduced as a result of both the extra-nuclear community know-how on LES and several years of applications of LES for nuclear issues at CEA. It will be shown that LES can be considered as a good candidate to deal with the previous mentioned issues. A large emphasis will be devoted to the R and D on approximate wall conditions, including first the checking of the consistency of standard and advanced wall conditions with LES approach, second specific works dealing

  18. A hybrid convection scheme for use in non-hydrostatic numerical weather prediction models

    Directory of Open Access Journals (Sweden)

    Volker Kuell

    2008-12-01

    Full Text Available The correct representation of convection in numerical weather prediction (NWP models is essential for quantitative precipitation forecasts. Due to its small horizontal scale convection usually has to be parameterized, e.g. by mass flux convection schemes. Classical schemes originally developed for use in coarse grid NWP models assume zero net convective mass flux, because the whole circulation of a convective cell is confined to the local grid column and all convective mass fluxes cancel out. However, in contemporary NWP models with grid sizes of a few kilometers this assumption becomes questionable, because here convection is partially resolved on the grid. To overcome this conceptual problem we propose a hybrid mass flux convection scheme (HYMACS in which only the convective updrafts and downdrafts are parameterized. The generation of the larger scale environmental subsidence, which may cover several grid columns, is transferred to the grid scale equations. This means that the convection scheme now has to generate a net convective mass flux exerting a direct dynamical forcing to the grid scale model via pressure gradient forces. The hybrid convection scheme implemented into the COSMO model of Deutscher Wetterdienst (DWD is tested in an idealized simulation of a sea breeze circulation initiating convection in a realistic manner. The results are compared with analogous simulations with the classical Tiedtke and Kain-Fritsch convection schemes.

  19. CONVECTION IN CONDENSIBLE-RICH ATMOSPHERES

    Energy Technology Data Exchange (ETDEWEB)

    Ding, F. [Department of the Geophysical Sciences, University of Chicago, Chicago, IL 60637 (United States); Pierrehumbert, R. T., E-mail: fding@uchicago.edu [Department of Physics, University of Oxford, Oxford OX1 3PU (United Kingdom)

    2016-05-01

    Condensible substances are nearly ubiquitous in planetary atmospheres. For the most familiar case—water vapor in Earth’s present climate—the condensible gas is dilute, in the sense that its concentration is everywhere small relative to the noncondensible background gases. A wide variety of important planetary climate problems involve nondilute condensible substances. These include planets near or undergoing a water vapor runaway and planets near the outer edge of the conventional habitable zone, for which CO{sub 2} is the condensible. Standard representations of convection in climate models rely on several approximations appropriate only to the dilute limit, while nondilute convection differs in fundamental ways from dilute convection. In this paper, a simple parameterization of convection valid in the nondilute as well as dilute limits is derived and used to discuss the basic character of nondilute convection. The energy conservation properties of the scheme are discussed in detail and are verified in radiative-convective simulations. As a further illustration of the behavior of the scheme, results for a runaway greenhouse atmosphere for both steady instellation and seasonally varying instellation corresponding to a highly eccentric orbit are presented. The latter case illustrates that the high thermal inertia associated with latent heat in nondilute atmospheres can damp out the effects of even extreme seasonal forcing.

  20. Bio-inspired piezoelectric linear motor driven by a single-phase harmonic wave with an asymmetric stator.

    Science.gov (United States)

    Pan, Qiaosheng; Miao, Enming; Wu, Bingxuan; Chen, Weikang; Lei, Xiujun; He, Liangguo

    2017-07-01

    A novel, bio-inspired, single-phase driven piezoelectric linear motor (PLM) using an asymmetric stator was designed, fabricated, and tested to avoid mode degeneracy and to simplify the drive mechanism of a piezoelectric motor. A piezoelectric transducer composed of two piezoelectric stacks and a displacement amplifier was used as the driving element of the PLM. Two simple and specially designed claws performed elliptical motion. A numerical simulation was performed to design the stator and determine the feasibility of the design mechanism of the PLM. Moreover, an experimental setup was built to validate the working principles, as well as to evaluate the performance, of the PLM. The prototype motor outputs a no-load speed of 233.7 mm/s at a voltage of 180 V p-p and a maximum thrust force of 2.3 N under a preload of 10 N. This study verified the feasibility of the proposed design and provided a method to simplify the driving harmonic signal and structure of PLMs.

  1. A radiographic study of external apical root resorption in patients treated with single-phase fixed orthodontic therapy.

    Science.gov (United States)

    Agarwal, S S; Chopra, S S; Kumar, Prasanna; Jayan, B; Nehra, K; Sharma, Mohit

    2016-12-01

    External apical root resorption (EARR) is one of the most common iatrogenic consequences of orthodontic tooth movement. Many factors like gender, duration, orthodontic force and duration of orthodontic treatment have been implicated to cause EARR. Pre- and post-treatment OPGs of 60 orthodontic patients (30 males and 30 females) who had undergone treatment with a single phase of fixed orthodontic therapy were randomly selected from institutional archives. The root apices were evaluated for EARR by a single operator on an radiograph viewing box at a standardized source of light using a four-grade ordinal scale. Anterior EARR was measured on the maxillary and mandibular canines. Posterior EARR was measured on premolars, mesiobuccal and distobuccal roots of maxillary first molars and mesial and distal roots of mandibular first molars. The results were compiled and subjected to statistical analysis. The cases in which the patients underwent therapeutic extraction had a relatively higher amount of EARR compared to the cases in which the patients were treated by non-extraction therapy ( P  orthodontic treatment ( P  > 0.05). Therapeutic extraction is an important determinant of post-treatment EARR. Gender and duration of orthodontic treatment may not be important variables in the causation of EARR according to the findings of this study. However, longitudinal studies with larger sample size are required to validate the results of this study.

  2. Effect of duration of the pause single-phase auto-reclosing on electro-power transmission capacitance

    Directory of Open Access Journals (Sweden)

    Krasil'nikova Tatyana

    2017-01-01

    Full Text Available This paper discusses the problem associated with accidents in the aerial line (AL ultra-high voltage (UHV due to its big length. In lines with a voltage of 500-1150 kV the overwhelming proportion of trips (98% is caused by single-phase short circuit (SPSC. A substantial portion (70% single-phase short circuits is erratic arc accidents which can be successfully eliminated in a high-speed auto-reclosing (HSAR or single-phase auto-reclosing (SPAR. Success single-phase auto-reclosing (SPAR at liquidation by single-phase short circuit (SPSC, on the one hand, is determined by the characteristics of the secondary arc current, and on the other hand the effectiveness of ways to reduce secondary arc current and recovery voltage development. The minimum dead time, at a HSAR it is usually taken as 0.5 s., at single-phase autoreclosing (SPAR it depends on the current value of the arc support is in the range of 0.5-3.0 s. The article shows high efficiency of use single-phase auto reclosing (SPAR at liquidation SPSC in a single-chain AL voltage of 500 kV, the dependence of the bandwidth of transmission in maintaining the dynamic stability from the length of the pause SPAR.

  3. A new lattice Boltzmann equation to simulate density-driven convection of carbon dioxide

    KAUST Repository

    Allen, Rebecca

    2013-01-01

    The storage of CO2 in fluid-filled geological formations has been carried out for more than a decade in locations around the world. After CO2 has been injected into the aquifer and has moved laterally under the aquifer\\'s cap-rock, density-driven convection becomes an important transport process to model. However, the challenge lies in simulating this transport process accurately with high spatial resolution and low CPU cost. This issue can be addressed by using the lattice Boltzmann equation (LBE) to formulate a model for a similar scenario when a solute diffuses into a fluid and density differences lead to convective mixing. The LBE is a promising alternative to the traditional methods of computational fluid dynamics. Rather than discretizing the system of partial differential equations of classical continuum mechanics directly, the LBE is derived from a velocity-space truncation of the Boltzmann equation of classical kinetic theory. We propose an extension to the LBE, which can accurately predict the transport of dissolved CO2 in water, as a step towards fluid-filled porous media simulations. This is achieved by coupling two LBEs, one for the fluid flow and one for the convection and diffusion of CO2. Unlike existing lattice Boltzmann equations for porous media flow, our model is derived from a system of moment equations and a Crank-Nicolson discretization of the velocity-truncated Boltzmann equation. The forcing terms are updated locally without the need for additional central difference approximation. Therefore our model preserves all the computational advantages of the single-phase lattice Boltzmann equation and is formally second-order accurate in both space and time. Our new model also features a novel implementation of boundary conditions, which is simple to implement and does not suffer from the grid-dependent error that is present in the standard "bounce-back" condition. The significance of using the LBE in this work lies in the ability to efficiently

  4. Natural convection in porous media with heat generation

    International Nuclear Information System (INIS)

    Hardee, H.C. Jr.; Nilson, R.H.

    1976-12-01

    Heat transfer characteristics of a fluid saturated porous media are investigated for the case of uniform internal heat generation with cooling from above. Analytical models of conduction and single phase cellular convection show good agreement with previous Rayleigh number correlations and with experimental data obtained by Joule heating of salt water in a sand bed. An approximate dryout criterion is also derived for two phase boiling heat transfer in a fixed bed which is neither channeled nor fluidized. Correlation of dryout data using this criterion is encouraging, especially considering the analytical rather than correlational basis of the criterion

  5. Strongly coupled single-phase flow problems: Effects of density variation, hydrodynamic dispersion, and first order decay

    Energy Technology Data Exchange (ETDEWEB)

    Oldenburg, C.M.; Pruess, K. [Lawrence Berkeley Laboratory, Berkeley, CA (United States)

    1995-03-01

    We have developed TOUGH2 modules for strongly coupled flow and transport that include full hydrodynamic dispersion. T2DM models tow-dimensional flow and transport in systems with variable salinity, while T32DMR includes radionuclide transport with first-order decay of a parent-daughter chain of radionuclide components in variable salinity systems. T2DM has been applied to a variety of coupled flow problems including the pure solutal convection problem of Elder and the mixed free and forced convection salt-dome flow problem. In the Elder and salt-dome flow problems, density changes of up to 20% caused by brine concentration variations lead to strong coupling between the velocity and brine concentration fields. T2DM efficiently calculates flow and transport for these problems. We have applied T2DMR to the dispersive transport and decay of radionuclide tracers in flow fields with permeability heterogeneities and recirculating flows. Coupling in these problems occurs by velocity-dependent hydrodynamic dispersion. Our results show that the maximum daughter species concentration may occur fully within a recirculating or low-velocity region. In all of the problems, we observe very efficient handling of the strongly coupled flow and transport processes.

  6. Accurate prediction of complex free surface flow around a high speed craft using a single-phase level set method

    Science.gov (United States)

    Broglia, Riccardo; Durante, Danilo

    2017-11-01

    compare the hydrodynamic forces and the attitudes assumed at different velocities. A very good agreement between numerical and experimental results demonstrates the reliability of the single-phase level set approach for the predictions of high Froude numbers flows.

  7. Total robotic radical rectal resection with da Vinci Xi system: single docking, single phase technique.

    Science.gov (United States)

    Tamhankar, Anup Sunil; Jatal, Sudhir; Saklani, Avanish

    2016-12-01

    This study aims to assess the advantages of Da Vinci Xi system in rectal cancer surgery. It also assesses the initial oncological outcomes after rectal resection with this system from a tertiary cancer center in India. Robotic rectal surgery has distinct advantages over laparoscopy. Total robotic resection is increasing following the evolution of hybrid technology. The latest Da Vinci Xi system (Intuitive Surgical, Sunnyvale, USA) is enabled with newer features to make total robotic resection possible with single docking and single phase. Thirty-six patients underwent total robotic resection in a single phase and single docking. We used newer port positions in a straight line. Median distance from the anal verge was 4.5 cm. Median robotic docking time and robotic procedure time were 9 and 280 min, respectively. Median blood loss was 100 mL. One patient needed conversion to an open approach due to advanced disease. Circumferential resection margin and longitudinal resection margins were uninvolved in all other patients. Median lymph node yield was 10. Median post-operative stay was 7 days. There were no intra-operative adverse events. The latest Da Vinci Xi system has made total robotic rectal surgery feasible in single docking and single phase. With the new system, four arm total robotic rectal surgery may replace the hybrid technique of laparoscopic and robotic surgery for rectal malignancies. The learning curve for the new system appears to be shorter than anticipated. Early perioperative and oncological outcomes of total robotic rectal surgery with the new system are promising. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

  8. Fabrication of single phase 2D homologous perovskite microplates by mechanical exfoliation

    Science.gov (United States)

    Li, Junze; Wang, Jun; Zhang, Yingjun; Wang, Haizhen; Lin, Gaoming; Xiong, Xuan; Zhou, Weihang; Luo, Hongmei; Li, Dehui

    2018-04-01

    The two-dimensional (2D) Ruddlesden-Popper type perovskites have attracted intensive interest for their great environmental stability and various potential optoelectronic applications. Fundamental understanding of the photophysical and electronic properties of the 2D perovskites with pure single phase is essential for improving the performance of the optoelectronic devices and designing devices with new architectures. Investigating the optical and electronic properties of these materials with pure single phase is required to obtain pure single phase 2D perovskites. Here, we report on an alternative approach to fabricate (C4H9NH3)2(CH3NH3) n-1Pb n I3n+1 microplates with pure single n-number perovskite phase for n  >  2 by mechanical exfoliation. Micro-photoluminescence and absorption spectroscopy studies reveal that the as-synthesized 2D perovskite plates for n  >  2 are comprised by dominant n-number phase and small inclusions of hybrid perovskite phases with different n values, which is supported by excitation power dependent photoluminescence. By mechanical exfoliation method, 2D perovskite microplates with the thickness of around 20 nm are obtained, which surprisingly have single n-number perovskite phase for n  =  2-5. In addition, we have demonstrated that the exfoliated 2D perovskite microplates can be integrated with other 2D layered materials such as boron nitride, and are able to be transferred to prefabricated electrodes for photodetections. Our studies not only provide a strategy to prepare 2D perovskites with a single n-number perovskite phase allowing us to extract the basic optical and electronic parameters of pure phase perovskites, but also demonstrate the possibility to integrate the 2D perovskites with other 2D layered materials to extend the device’s functionalities.

  9. A PWM strategy for acoustic noise reduction for grid-connected single-phase inverters

    Energy Technology Data Exchange (ETDEWEB)

    Shao, R.; Guo, Z.; Chang, L. [New Brunswick Univ., Fredericton, NB (Canada). Dept. of Electrical and Computer Engineering

    2006-07-01

    This paper presented a newly proposed and improved pulse width modulation (PWM) strategy for grid-connected single-phase inverters. Small distributed generators using energy from renewable resources such as PV and wind systems typically use grid-connected single-phase inverters as voltage source inverters for good acoustic performance. PWM is generally applied in these inverters in order to achieve good waveforms of output current as required by interconnection standards. In routine simultaneous switching PWM methods, the current ripples through the inverter output filter inductor are at the carrier switching frequency, which is one of the major causes for inverter acoustic noise. The new PWM strategy effectively alleviates acoustic noise and improves output power quality. It is based on the principle of evenly splitting the switching of Insulated Gate Bipolar Transistors (IGBT) in each switching cycle among all IGBTs of the full bridge, thereby using a non-simultaneous mode of PWM which doubles the output current ripple frequency. This increases the inductor current ripple frequency to twice the carrier frequency. It is therefore possible to increase the current ripple frequency, or noise frequency into the range of ultrasonic which is inaudible to the human ear, without increasing the inverter's switching frequency to which the inverter's switching loss is proportional. In addition, this new PWM scheme can reduce the output current harmonics distortion and dc link current ripples. As such, lower capacitance in dc link capacitors and lower inductance of output inductor are needed. The improved PWM scheme was verified in a 3 kW grid-connected single-phase inverter. It was shown that the PWM strategy can be readily implemented with a digital signal processing microcontroller. 8 refs., 11 figs.

  10. Computational simulation of flow and heat transfer in single-phase natural circulation loops; Simulacao computacional de escoamento e transferencia de calor em circuitos de circulacao natural monofasica

    Energy Technology Data Exchange (ETDEWEB)

    Pinheiro, Larissa Cunha

    2017-07-01

    Passive decay heat removal systems based on natural circulation are essential assets for the new Gen III+ nuclear power reactors and nuclear spent fuel pools. The aim of the present work is to study both laminar and turbulent flow and heat transfer in single-phase natural circulation systems through computational fluid dynamics simulations. The working fluid is considered to be incompressible with constant properties. In the way, the Boussinesq Natural Convection Hypothesis was applied. The model chosen for the turbulence closure problem was the k -- εThe commercial computational fluid dynamics code ANSYS CFX 15.0 was used to obtain the numerical solution of the governing equations. Two single-phase natural circulation circuits were studied, a 2D toroidal loop and a 3D rectangular loop, both with the same boundary conditions of: prescribed heat flux at the heater and fixed wall temperature at the cooler. The validation and verification was performed with the numerical data provided by DESRAYAUD et al. [1] and the experimental data provided by MISALE et al. [2] and KUMAR et al. [3]. An excellent agreement between the Reynolds number (Re) and the modified Grashof number (Gr{sub m}), independently of Prandtl Pr number was observed. However, the convergence interval was observed to be variable with Pr, thus indicating that Pr is a stability governing parameter for natural circulation. Multiple steady states was obtained for Pr = 0,7. Finally, the effect of inclination was studied for the 3D circuit, both in-plane and out-of-plane inclinations were verified for the steady state laminar regime. As a conclusion, the Re for the out-of-plane inclination was in perfect agreement with the correlation found for the zero inclination system, while for the in-plane inclined system the results differ from that of the corresponding vertical loop. (author)

  11. Reliability-Oriented Design and Analysis of Input Capacitors in Single-Phase Transformer-less Photovoltaic Inverters

    DEFF Research Database (Denmark)

    Wang, Huai; Yang, Yongheng; Blaabjerg, Frede

    2013-01-01

    While 99% efficiency has been reported, the target of 20 years of service time imposes new challenge to cost-effective solutions for grid-connected photovoltaic (PV) inverters. Aluminum electrolytic capacitors are the weak-link in terms of reliability and lifetime in single-phase PV systems....... A reliability-oriented design guideline is proposed in this paper for the input capacitors in single-phase transformer-less PV inverters. The guideline ensures that the service time requirement is to be accomplished under different power levels and ambient temperature profiles. The theoretical analysis has been...... demonstrated by a 1 kW single-phase PV inverter....

  12. Sunspots and the physics of magnetic flux tubes. VI - Convective propulsion. VII - Heat flow in a convective downdraft

    Science.gov (United States)

    Parker, E. N.

    1979-01-01

    The effect of negative aerodynamic drag in an ideal fluid subject to convective instability is considered. It is shown that a cylinder moving in such a fluid is propelled forward in its motion by the convective forces and that the characteristic acceleration time is comparable to the onset time of convective motions in the fluid. It is suggested that convective propulsion plays an important role in the dynamics of flux tubes extending through the surface of the sun. The suppression of the upward heat flow in a Boussinesq convective cell with free upper and lower boundaries by a downdraft is then analyzed. Application to the solar convection zone indicates that downdrafts of 1 to 2 km/s at depths of 1000 to 4000 km beneath the visible surface of the sun are sufficient to reduce the upward heat flux to a small fraction of the ambient value.

  13. Indirect Control of a low power Single-Phase Active Power Filter

    Directory of Open Access Journals (Sweden)

    SILVIU EPURE

    2010-12-01

    Full Text Available This paper deals with a low power, single phase active filter used to compensate nonlinear loads. The filter uses the indirect control method and it is based on a particular connection between filter, polluting load and grid to avoid timeconsuming mathematic operations or signal processing computations and assures good rejection of harmonic currents injected by the nonlinear load into the grid. A scale model was first simulated in Simulink and then physically implemented. The paper presents simulation and experimental results, and highlight problems encountered during experiments.

  14. A Novel Flying Capacitor Transformerless Inverter for Single-Phase Grid Connected Solar Photovoltaic System

    DEFF Research Database (Denmark)

    Siwakoti, Yam Prasad; Blaabjerg, Frede

    2016-01-01

    This paper proposes a new single-phase flying capacitor transformerless PV inverter for grid-connected photovoltaic (PV) systems. The neutral of the grid can be directly connected to the negative terminal of the source (PV). It consists of four power switches, one diode, one capacitor and a small...... and some topologies, which requires two times of the peak ac-voltage magnitude) and, (5) the flying capacitor charges every switching cycle, which reduces the size of the required capacitor with switching frequency. In addition, industry standard half bridge module can be used in the new inverter without...

  15. S4 Grid-Connected Single-Phase Transformerless Inverter for PV Application

    DEFF Research Database (Denmark)

    Ardashir, Jaber Fallah; Siwakoti, Yam Prasad; Sabahi, Mehran

    2016-01-01

    This paper introduces a new single-phase transformerless inverter for grid-connected photovoltaic systems with low leakage current. It consists of four power switches, two diodes, two capacitors and a filter at the output stage. The neutral of the grid is directly connected to the negative terminal...... size, low cost, flexible grounding configuration and higher efficiency. The operating principle and analysis of the proposed circuit are presented in details. Experimental results of a 500 W prototype are demonstrated to validate the proposed topology and the overall concept. The results obtained...... clearly verify the performance of the proposed inverter and its practical application for grid-connected PV systems....

  16. Low voltage ride-through of single-phase transformerless photovoltaic inverters

    DEFF Research Database (Denmark)

    Yang, Yongheng; Blaabjerg, Frede; Wang, Huai

    2013-01-01

    Transformerless photovoltaic (PV) inverters are going to be more widely adopted in order to achieve high efficiency, as the penetration level of PV systems is continuously booming. However, problems may arise in highly PV-integrated distribution systems. For example, a sudden stoppage of all PV...... discussed. The selected inverters are the full-bridge inverter with bipolar modulation, full-bridge inverter with DC bypass and the Highly Efficient and Reliable Inverter Concept (HERIC). A 1 kW single-phase grid-connected PV system is analyzed to verify the discussions. The tests confirmed that, although...

  17. H-Bridge Transformerless Inverter with Common Ground for Single-Phase Solar-Photovoltaic System

    DEFF Research Database (Denmark)

    Siwakoti, Yam Prasad; Blaabjerg, Frede

    2017-01-01

    This paper proposes a new single-phase H-Bridge transformerless inverter with common ground for grid-connected photovoltaic systems (hereafter it is called ‘Siwakoti-H’ inverter). The inverter works on the principle of flying capacitor and consists of only four power switches (two reverse blocking...... IGBT's (RB-IGBT) and two MOSFET's), a capacitor and a small filter at the output stage. The proposed topology share a common ground with the grid and the PV source. A Unipolar Sinusoidal Pulse-Width Modulation (SPWM) technique is used to modulate the inverter to minimize switching loss, output current...

  18. Pressure drop and heat transfer of lithium single-phase flow under transverse magnetic field

    International Nuclear Information System (INIS)

    Takahashi, Minoru; Aritomi, Masanori; Inoue, Akira; Matsuzaki, Mitsuo

    1996-01-01

    Pressure drop and heat transfer characteristics of a lithium single-phase flow in a rectangular channel was investigated experimentally in the presence of a magnetic field. Friction loss coefficient under non-magnetic field and skin friction coefficient under magnetic field agreed well with the Blasius formula and a simple analytical expression, respectively. Nusselt number under non-magnetic field was slightly lower than the correlation by Hartnett and Irvine. Heat transfer was enhanced by increasing magnetic field above the Hartmann number of about 200. (author)

  19. A review of single-phase grid-connected inverters for photovoltaic modules

    DEFF Research Database (Denmark)

    Kjaer, Soren Baekhoej; Pedersen, John Kim; Blaabjerg, Frede

    2005-01-01

    -phase grid; 3) whether they utilizes a transformer (either line or high frequency) or not; and 4) the type of grid-connected power stage. Various inverter topologies are presented, compared, and evaluated against demands, lifetime, component ratings, and cost. Finally, some of the topologies are pointed out......This review focuses on inverter technologies for connecting photovoltaic (PV) modules to a single-phase grid. The inverters are categorized into four classifications: 1) the number of power processing stages in cascade; 2) the type of power decoupling between the PV module(s) and the single...

  20. Single phase and two-phase flow pressure losses through restrictions, expansions and inserts

    International Nuclear Information System (INIS)

    Glenat, P.; Solignac, P.

    1984-11-01

    We give a selection of methods to predict pressure losses through retrictions, expansions and inserts. In single phase flow, we give the classical method based on the one-dimensional momentum and mass balances. In two-phase flow, we propose the method given by Harshe et al. and an empirical approach suggested by Chisholm. We notice the distinction between long and short inserts depends upon wether or not the vena contracta lies within insert. Finally, we propose three correlations to calculate void fraction through the singularities which have been considered [fr

  1. Fixed switching frequency applied in single-phase boost AC to DC converter

    International Nuclear Information System (INIS)

    Chen, T.-C.; Ren, T.-J.; Ou, J.-C.

    2009-01-01

    The fixed switching frequency control for a single-phase boost AC to DC converter to achieve a sinusoidal line current and unity power factor is proposed in this paper. The relation between the line current error and the fixed switching frequency was developed. For a limit line current error, the minimum switching frequency for a boost AC to DC converter can be achieved. The proposed scheme was implemented using a 32-bit digital signal processor TMS320C32. Simulations and experimental results demonstrate the feasibility and fast dynamic response of the proposed control strategy.

  2. An empirical relationship for homogenization in single-phase binary alloy systems

    Science.gov (United States)

    Unnam, J.; Tenney, D. R.; Stein, B. A.

    1979-01-01

    A semiempirical formula is developed for describing the extent of interaction between constituents in single-phase binary alloy systems with planar, cylindrical, or spherical interfaces. The formula contains two parameters that are functions of mean concentration and interface geometry of the couple. The empirical solution is simple, easy to use, and does not involve sequential calculations, thereby allowing quick estimation of the extent of interactions without lengthy calculations. Results obtained with this formula are in good agreement with those from a finite-difference analysis.

  3. A Study on Energy Saving of Single Phase Induction Motor By Voltage Control

    Energy Technology Data Exchange (ETDEWEB)

    Bae, Jong Moon [Pusan College of Information Technolgy, Pusan (Korea); Kim, Joon Hong [Dong Myong College, Pusan (Korea)

    2001-06-01

    This paper describes a simple effective method for energy saving of AC motors having a widely variable load. The proposed method is based on an optimal efficiency control which is operated by voltage-current pattern such as to maintain the maximum efficiency on the efficiency-output characteristics of the motor, TRIAC voltage control characteristics. The parameters of simplified voltage-current pattern can be determined approximately and reliably from the rated voltage and current of the motor. Experiments are focused on a single phase capacitor motor, the optimal energy saving are proved by proposed method. (author). 8 refs., 15 figs.

  4. Power quality improvement of single-phase photovoltaic systems through a robust synchronization method

    DEFF Research Database (Denmark)

    Hadjidemetriou, Lenos; Kyriakides, Elias; Yang, Yongheng

    2014-01-01

    An increasing amount of single-phase photovoltaic (PV) systems on the distribution network requires more advanced synchronization methods in order to meet the grid codes with respect to power quality and fault ride through capability. The response of the synchronization technique selected...... is crucial for the performance of PV inverters. In this paper, a new synchronization method with good dynamics and accurate response under highly distorted voltage is proposed. This method uses a Multi-Harmonic Decoupling Cell (MHDC), which cancels out the oscillations on the synchronization signals due...

  5. DQ reference frame modeling and control of single-phase active power decoupling circuits

    DEFF Research Database (Denmark)

    Tang, Yi; Qin, Zian; Blaabjerg, Frede

    2015-01-01

    . This paper presents the dq synchronous reference frame modeling of single-phase power decoupling circuits and a complete model describing the dynamics of dc-link ripple voltage is presented. The proposed model is universal and valid for both inductive and capacitive decoupling circuits, and the input...... of decoupling circuits can be either dependent or independent of its front-end converters. Based on this model, a dq synchronous reference frame controller is designed which allows the decoupling circuit to operate in two different modes because of the circuit symmetry. Simulation and experimental results...... are presented to verify the effectiveness of the proposed modeling and control method....

  6. A New Synchronous Reference Frame-Based Method for Single-Phase Shunt Active Power Filters

    DEFF Research Database (Denmark)

    Monfared, Mohammad; Golestan, Saeed; Guerrero, Josep M.

    2013-01-01

    This paper deals with the design of a novel method in the synchronous reference frame (SRF) to extract the reference compensating current for single-phase shunt active power filters (APFs). Unlike previous works in the SRF, the proposed method has an innovative feature that it does not need...... the fictitious current signal. Frequency-independent operation, accurate reference current extraction and relatively fast transient response are other key features of the presented strategy. The effectiveness of the proposed method is investigated by means of detailed mathematical analysis. The results confirm...

  7. Control Method of Single-phase Inverter Based Grounding System in Distribution Networks

    DEFF Research Database (Denmark)

    Wang, Wen; Yan, L.; Zeng, X.

    2016-01-01

    of neutral-to-ground voltage is critical for the safety of distribution networks. An active grounding system based on single-phase inverter is proposed to achieve this objective. Relationship between output current of the system and neutral-to-ground voltage is derived to explain the principle of neutral......The asymmetry of the inherent distributed capacitances causes the rise of neutral-to-ground voltage in ungrounded system or high resistance grounded system. Overvoltage may occur in resonant grounded system if Petersen coil is resonant with the distributed capacitances. Thus, the restraint...

  8. Single Phase Current-Source Active Rectifier for Traction: Control System Design and Practical Problems

    Directory of Open Access Journals (Sweden)

    Jan Michalik

    2006-01-01

    Full Text Available This research has been motivated by industrial demand for single phase current-source active rectifier dedicated for reconstruction of older types of dc machine locomotives. This paper presents converters control structure design and simulations. The proposed converter control is based on the mathematical model and due to possible interaction with railway signaling and required low switching frequency employs synchronous PWM. The simulation results are verified by experimental tests performed on designed laboratory prototype of power of 7kVA

  9. Reaction kinetics of oxygen on single-phase alloys, oxidation of nickel and niobium alloys

    International Nuclear Information System (INIS)

    Lalauze, Rene

    1973-01-01

    This research thesis first addresses the reaction kinetics of oxygen on alloys. It presents some generalities on heterogeneous reactions (conventional theory, theory of jumps), discusses the core reaction (with the influence of pressure), discusses the influence of metal self-diffusion on metal oxidation kinetics (equilibrium conditions at the interface, hybrid diffusion regime), reports the application of the hybrid diffusion model to the study of selective oxidation of alloys (Wagner model, hybrid diffusion model) and the study of the oxidation kinetics of an alloy forming a solid solution of two oxides. The second part reports the investigation of the oxidation of single phase nickel and niobium alloys (phase α, β and γ)

  10. Dispersed single-phase-step Michelson interferometer for Doppler imaging using sunlight.

    Science.gov (United States)

    Wan, Xiaoke; Ge, Jian

    2012-09-15

    A Michelson interferometer is dispersed with a fiber array-fed spectrograph, providing 59 Doppler sensing channels using sunlight in the 510-570 nm wavelength region. The interferometer operates at a single-phase-step mode, which is particularly advantageous in multiplexing and data processing compared to the phase-stepping mode of other interferometer spectrometer instruments. Spectral templates are prepared using a standard solar spectrum and simulated interferometer modulations, such that the correlation function with a measured 1D spectrum determines the Doppler shift. Doppler imaging of a rotating cylinder is demonstrated. The average Doppler sensitivity is ~12 m/s, with some channels reaching ~5 m/s.

  11. Single-Phase Phase-Locked Loop Based on Derivative Elements

    DEFF Research Database (Denmark)

    Guan, Qingxin; Zhang, Yu; Kang, Yong

    2017-01-01

    High-performance phase-locked loops (PLLs) are critical for power control in grid-connected systems. This paper presents a new method of designing a PLL for single-phase systems based on derivative elements (DEs). The quadrature signal generator (QSG) is constructed by two DEs with the same...... PLL to achieve high performance when the grid frequency changes rapidly. This paper presents the model of the PLL and a theoretical performance analysis with respect to both the frequency-domain and time-domain behavior. The error arising from the discretization process is also compensated, ensuring...

  12. Benchmarking of small-signal dynamics of single-phase PLLs

    DEFF Research Database (Denmark)

    Zhang, Chong; Wang, Xiongfei; Blaabjerg, Frede

    2015-01-01

    Phase-looked Loop (PLL) is a critical component for the control and grid synchronization of grid-connected power converters. This paper presents a benchmarking study on the small-signal dynamics of three commonly used PLLs for single-phase converters, including enhanced PLL, second......-order generalized integrator based PLL, and the inverse-PLL. First, a unified small-signal model of those PLLs is established for comparing their dynamics. Then, a systematic design guideline for parameters tuning of the PLLs is formulated. To confirm the validity of theoretical analysis, nonlinear time...

  13. Control of single-phase islanded PV/battery minigrids based on power-line signaling

    DEFF Research Database (Denmark)

    Quintana, Pablo; Guerrero, Josep M.; Dragicevic, Tomislav

    2014-01-01

    should be utilized as efficiently as possible. This paper proposes a coordinated control strategy based on power-line signaling (PLS), instead of common communications, for a single-phase minigrid in which each unit can operate in different operation modes taking into account the resource limitation...... types of renewable energy sources (RES) and energy storage systems (ESS). Specifically, the recharging process of secondary battery, the most prominent ESS, should be done in a specific manner to preserve its life-time, microgrid line voltage must be kept within the bounds and the energy offered by RES...

  14. Energy efficient power electronic controller for a capacitor-run single-phase induction motor

    International Nuclear Information System (INIS)

    Saravana Ilango, G.; Samidurai, K.; Roykumar, M.; Thanushkodi, K.

    2009-01-01

    At present the speed control of a capacitor-run single-phase induction motor is being achieved by using triac based voltage regulators. This paper proposes a new scheme; an electronic transformer acts as a voltage regulator. Performance comparison is made between these two schemes in this paper. It is found that the proposed scheme has superior operating and performance characteristics. Experimental results show that apart from improvement in performance with respect to power factor and total harmonic distortion an appreciable amount of energy saving is also obtained in the electronic transformer based scheme.

  15. Novel Position and Speed Estimator for PM Single Phase Brushless D.C. Motor Drives

    DEFF Research Database (Denmark)

    Lepure, Liviu I.; Andreescu, Gheorghe-Daniel; Iles, Doris

    2010-01-01

    A novel position and speed estimator for single phase permanent magnet brushless d.c. (PMBLDC) motor drives, based on flux integration and prior knowledge of ΨPM (θ) is proposed here and an adequate correction algorithm is adopted in order to increase the robustness to noise and to reduce...... the sensitivity to accuracy of flux linkage estimation. A speed and current close loop control is employed based on the Hall signal and the motor is controlled at different speeds in order to validate the proposed estimation algorithm with satisfying results. The position correction effect is analyzed...

  16. Improved state observers for sensorless single phase BLDC-PM motor drives

    DEFF Research Database (Denmark)

    Lepure, Liviu L.; Boldea, Ion; Andreescu, Gheorghe Daniel

    2010-01-01

    Two methods of extracting the rotor position and speed for a sensorless single phase BLDC-PM motor drive by measuring only the phase current are presented here. Both methods are based on a generated orthogonal flux system. The first method extracts the position information by using the tan−1...... function and then an improved observer is created by adding a 4th order harmonic term in the estimated position, while the second method uses a phase locked loop structure. The proposed state observers are detailed using simulation results and then validated by experimental results....

  17. Boiling of subcooled water in forced convection

    International Nuclear Information System (INIS)

    Ricque, R.; Siboul, R.

    1970-01-01

    As a part of a research about water cooled high magnetic field coils, an experimental study of heat transfer and pressure drop is made with the following conditions: local boiling in tubes of small diameters (2 and 4 mm), high heat fluxes (about 1000 W/cm 2 ), high coolant velocities (up to 25 meters/s), low outlet absolute pressures (below a few atmospheres). Wall temperatures are determined with a good accuracy, because very thin tubes are used and heat losses are prevented. Two regimes of boiling are observed: the establishment regime and the established boiling regime and the inception of each regime is correlated. Important delays on boiling inception are also observed. The pressure drop is measured; provided the axial temperature distribution of the fluid and the axial distributions of the wall temperatures, in other words the axial distribution of the heat transfer coefficients under boiling and non boiling conditions, at the same heat flux or the same wall temperatures, are taken in account, then total pressure drop can be correlated, but probably under certain limits of void fraction only. Using the same parameters, it seems possible to correlate the experimental values on critical heat flux obtained previously, which show very important effect of length and hydraulic diameter of the test sections. (authors) [fr

  18. Lattice BGK simulation of natural convection

    International Nuclear Information System (INIS)

    Chen, Yu; Ohashi, Hirotada; Akiyama, Mamoru

    1995-01-01

    Recently a new thermal lattice Bhatnagar-Gross-Krook fluid model was suggested by the authors. In this study, this new model was applied into the numerical simulation of natural convection, namely the Rayleigh Benard flow. The critical number for the onset of convective phenomenon was numerically measured and compared with that of theoretical prediction. A gravity dependent deviation was found in the numerical simulation, which is explained as an unavoidable consequence of the incorporation of gravity force in the lattice BGK system. (author)

  19. Design of Controller for Reducing In-Rush Current of Single-Phase Induction Motor

    Energy Technology Data Exchange (ETDEWEB)

    Park, Su Kang; Baek, Hyung Lae; Lee, Sang Il [Chosun University, Kwangju (Korea)

    2001-05-01

    During an AC motor's start-up accelerating period, a large amount of current is required to reach to the rating speed. This is called in-rush current. This peak in-rush current can be more than about several times the operating or steady-state current in the full load rating of the motor. In-rush current is present in both and electronic ballasts. The main area of concern is the tripping of circuit breaker and fuses which can affect electrical system components From this, we can see that the electrical power controllers will be rather concerned, since they have to supply the actual current necessary to start the motor. This paper presents a new method to reducing in-rush current and energy saving of the single-phase induction motor used in air-conditioner. It can be obtained that proposed system is low cost and small size as compared with other controller. Experiments are focused on a capacitor starting single-phase induction motor. The optimal power saving and in-rush current limiting by phase angle control are verified by experimental results. Also, auxiliary winding was controlled by electronic starting switch. (author). 10 refs., 13 figs., 2 tabs.

  20. Common-Ground-Type Transformerless Inverters for Single-Phase Solar Photovoltaic Systems

    DEFF Research Database (Denmark)

    Siwakoti, Yam Prasad; Blaabjerg, Frede

    2018-01-01

    This paper proposes a family of novel flying capacitor transformerless inverters for single-phase photovoltaic (PV) systems. Each of the new topologies proposed is based on a flying capacitor principle and requires only four power switches and/or diodes, one capacitor, and a small filter at the o......This paper proposes a family of novel flying capacitor transformerless inverters for single-phase photovoltaic (PV) systems. Each of the new topologies proposed is based on a flying capacitor principle and requires only four power switches and/or diodes, one capacitor, and a small filter...... at the output stage. A simple unipolar sinusoidal pulse width modulation technique is used to modulate the inverter to minimize the switching loss, output current ripple, and the filter requirements. In general, the main advantages of the new inverter topologies are: 1) the negative polarity of the PV...... description of the operating principle with modulation techniques, design guidelines, and comprehensive comparisons is presented to reveal the properties and limitations of each topology in detail. Finally, experimental results of 1-kVA prototypes are presented to prove the concept and theoretical analysis...

  1. A Standalone Solar Photovoltaic Power Generation using Cuk Converter and Single Phase Inverter

    Science.gov (United States)

    Verma, A. K.; Singh, B.; Kaushika, S. C.

    2013-03-01

    In this paper, a standalone solar photovoltaic (SPV) power generating system is designed and modeled using a Cuk dc-dc converter and a single phase voltage source inverter (VSI). In this system, a dc-dc boost converter boosts a low voltage of a PV array to charge a battery at 24 V using a maximum power point tracking control algorithm. To step up a 24 V battery voltage to 360 V dc, a high frequency transformer based isolated dc-dc Cuk converter is used to reduce size, weight and losses. The dc voltage of 360 V is fed to a single phase VSI with unipolar switching to achieve a 230 Vrms, 50 Hz ac. The main objectives of this investigation are on efficiency improvement, reduction in cost, weight and size of the system and to provide an uninterruptible power to remotely located consumers. The complete SPV system is designed and it is modeled in MATLAB/Simulink. The simulated results are presented to demonstrate its satisfactory performance for validating the proposed design and control algorithm.

  2. Numerical investigation of refrigeration machine compressor operation considering single-phase electric motor dynamic characteristics

    Science.gov (United States)

    Baidak, Y.; Smyk, V.

    2017-08-01

    Using as the base the differential equations system which was presented in relative units for generalized electric motor of hermetic refrigeration compressor, mathematical model of the software for dynamic performance calculation of refrigeration machine compressors drive low-power asynchronous motors was developed. Performed on its ground calculations of the basic model of two-phase electric motor drive of hermetic compressor and the proposed newly developed model of the motor with single-phase stator winding, which is an alternative to the industrial motor winding, have confirmed the benefits of the motor with innovative stator winding over the base engine. Given calculations of the dynamic characteristics of compressor drive motor have permitted to determine the value of electromagnetic torque swinging for coordinating compressor and motor mechanical characteristics, and for taking them into consideration in choosing compressor elements construction materials. Developed and used in the process of investigation of refrigeration compressor drive asynchronous single-phase motor mathematical and software can be considered as an element of computer-aided design system for design of the aggregate of refrigeration compression unit refrigerating machine.

  3. Validation of CATHENA MOD-3.5/Rev0 for single-phase water hammer

    International Nuclear Information System (INIS)

    Beuthe, T.G.

    2000-01-01

    This paper describes work performed to validate the system thermalhydraulics code CATHENA MOD-3.5c/Rev0 for single-phase water hammer. Simulations were performed and are compared quantitatively against numerical tests and experimental results from the Seven Sisters Water Hammer Facility to demonstrate CATHENA can predict the creation and propagation of pressure waves when valves are opened and closed. Simulations were also performed to show CATHENA can model the behaviour of reflected and transmitted pressure waves at area changes, dead ends, tanks, boundary conditions, and orifices in simple and more complex piping systems. The CATHENA results are shown to calculate pressure and wave propagation speeds to within 0.2% and 0.5% respectively for numerical tests and within 3.3% and 5% for experimental results respectively. These results are used to help validate CATHENA for use in single-phase water hammer analysis. They also provide assurance that the fundamental parameters needed to successfully model more complex forms of water hammer are accounted for in the MOD-3.5c/Rev0 version of CATHENA, and represent the first step in the process to validate the code for use in modelling two-phase water hammer and condensation-induced water hammer. (author)

  4. Fabrication and Characterization of Single Phase α-Alumina Membranes with Tunable Pore Diameters

    Science.gov (United States)

    Masuda, Tatsuya; Asoh, Hidetaka; Haraguchi, Satoshi; Ono, Sachiko

    2015-01-01

    Nanoporous and single phase α-alumina membranes with pore diameters tunable over a wide range of approximately 60–350 nm were successfully fabricated by optimizing the conditions for anodizing, subsequent detachment, and heat treatment. The pore diameter increased and the cell diameter shrunk upon crystallization to α-alumina by approximately 20% and 3%, respectively, in accordance with the 23% volume shrinkage resulting from the change in density associated with the transformation from the amorphous state to α-alumina. Nevertheless, flat α-alumina membranes, each with a diameter of 25 mm and a thickness of 50 μm, were obtained without thermal deformation. The α-alumina membranes exhibited high chemical resistance in various concentrated acidic and alkaline solutions as well as when exposed to high temperature steam under pressure. The Young’s modulus and hardness of the single phase α-alumina membranes formed by heat treatment at 1250 °C were notably decreased compared to the corresponding amorphous membranes, presumably because of the nodular crystallite structure of the cell walls and the substantial increase in porosity. Furthermore, when used for filtration, the α-alumina membrane exhibited a level of flux higher than that of the commercial ceramic membrane. PMID:28788005

  5. Fabrication and Characterization of Single Phase α-Alumina Membranes with Tunable Pore Diameters

    Directory of Open Access Journals (Sweden)

    Tatsuya Masuda

    2015-03-01

    Full Text Available Nanoporous and single phase α-alumina membranes with pore diameters tunable over a wide range of approximately 60–350 nm were successfully fabricated by optimizing the conditions for anodizing, subsequent detachment, and heat treatment. The pore diameter increased and the cell diameter shrunk upon crystallization to α-alumina by approximately 20% and 3%, respectively, in accordance with the 23% volume shrinkage resulting from the change in density associated with the transformation from the amorphous state to α-alumina. Nevertheless, flat α-alumina membranes, each with a diameter of 25 mm and a thickness of 50 μm, were obtained without thermal deformation. The α-alumina membranes exhibited high chemical resistance in various concentrated acidic and alkaline solutions as well as when exposed to high temperature steam under pressure. The Young’s modulus and hardness of the single phase α-alumina membranes formed by heat treatment at 1250 °C were notably decreased compared to the corresponding amorphous membranes, presumably because of the nodular crystallite structure of the cell walls and the substantial increase in porosity. Furthermore, when used for filtration, the α-alumina membrane exhibited a level of flux higher than that of the commercial ceramic membrane.

  6. A Nonadaptive Window-Based PLL for Single-Phase Applications

    DEFF Research Database (Denmark)

    Golestan, Saeed; Guerrero, Josep M.; Quintero, Juan Carlos Vasquez

    2018-01-01

    The rectangular window filter, typically known as the moving average filter (MAF), is a quasi-ideal low-pass filter that has found wide application in designing advanced single-phase phase-locked loops (PLLs). Most often, the MAF is employed as an in-loop filter within the control loop of the sin......The rectangular window filter, typically known as the moving average filter (MAF), is a quasi-ideal low-pass filter that has found wide application in designing advanced single-phase phase-locked loops (PLLs). Most often, the MAF is employed as an in-loop filter within the control loop...... response is avoided. Nevertheless, the PLL implementation complexity considerably increases as MAFs are frequency-adaptive and, therefore, they require an additional frequency detector for estimating the grid frequency. To reduce the implementation complexity while maintaining a good performance, using...... a nonadaptive MAF-based QSG with some error compensators is suggested in this letter. The effectiveness of the resultant PLL, which is briefly called the nonadaptive MAF-based PLL, is verified using experimental results....

  7. Experimental study of single-phase pressure drops in coarse particle beds

    Energy Technology Data Exchange (ETDEWEB)

    Clavier, R., E-mail: remi.clavier@irsn.fr [IRSN Cadarache, Saint Paul-lez-Durance (France); Chikhi, N., E-mail: nourdine.chikhi@irsn.fr [IRSN Cadarache, Saint Paul-lez-Durance (France); Fichot, F., E-mail: florian.fichot@irsn.fr [IRSN Cadarache, Saint Paul-lez-Durance (France); Quintard, M., E-mail: Michel.Quintard@imft.fr [Université de Toulouse, Allée Camille Soula, F-31400 Toulouse (France); INPT, UPS, Allée Camille Soula, F-31400 Toulouse (France); IMFT (Institut de Mécanique des Fluides de Toulouse), Allée Camille Soula, F-31400 Toulouse (France); CNRS, F-31400 Toulouse (France)

    2017-02-15

    Motivated by uncertainty reduction in nuclear debris beds coolability, experiments have been conducted on the CALIDE facility in order to investigate single-phase pressure losses in representative debris beds, i.e., high sphericity (>80%) particle beds with small size dispersion (from 1 mm to 10 mm), for which no validated model exists. In this paper, experimental results are presented and analyzed in order to identify a simple correlation for single-phase flow pressure losses generated in this kind of porous media in reflooding flowing conditions, which cover Darcy to weakly turbulent regimes. In the literature, it has been observed that their behavior can be accurately described by a Darcy–Forchheimer law, involving the sum of a linear term and a quadratic non-linear deviation, with respect to the filtration velocity. Expressions for the coefficients of the linear and quadratic terms are determined by assessing the possibility to evaluate equivalent diameters, i.e., characteristic lengths allowing correct predictions of the linear and quadratic terms by the Ergun equation. It has been observed that the Sauter diameter of particles allows a very precise prediction of the linear term, while the quadratic term can be predicted using the product of the Sauter diameter and a sphericity coefficient as an equivalent diameter.

  8. MECHANICAL CHARACTERISTICS OF THREE-PHASE INDUCTION MOTORS WITH SINGLE-PHASE POWER SUPPLY

    Directory of Open Access Journals (Sweden)

    V.S. Malyar

    2016-06-01

    Full Text Available Aim. Development of a method for calculating mechanical characteristics of three-phase induction motors with single-phase power supply. Methods. The developed algorithm is based on the high-adequacy mathematical model of motor and projection method for solving the boundary problem for equations of electrical circuits balance presented in the three-phase coordinate system. As a result of asymmetry of power supply to the stator windings, in steady state, flux-linkage and current change according to the periodic law. They are determined by solving the boundary problem. Results. The developed mathematical model allows determining periodic dependence of coordinates as a function of slip and, based on them, mechanical characteristics of motors. Academic novelty. The developed method relies on a completely new mathematical approach to calculation of stationary modes of nonlinear electromagnetic circuits, which allows obtaining periodic solution in a timeless domain. Practical value. Using the developed calculation algorithm, one can select capacitance required to start an induction motor with single-phase power supply and calculate static mechanical characteristics at a given capacitance.

  9. FUZZY LOGIC BASED OPTIMIZATION OF CAPACITOR VALUE FOR SINGLE PHASE OPEN WELL SUBMERSIBLE INDUCTION MOTOR

    Directory of Open Access Journals (Sweden)

    R. Subramanian

    2011-01-01

    Full Text Available Purpose – The aim of this paper is to optimize the capacitor value of a single phase open well submersible motor operating under extreme voltage conditions using fuzzy logic optimization technique and compared with no-load volt-ampere method. This is done by keeping the displacement angle (a between main winding and auxiliary winding near 90o, phase angle (f between the supply voltage and line current near 0o. The optimization work is carried out by using Fuzzy Logic Toolbox software built on the MATLAB technical computing environment with Simulink software. Findings – The optimum capacitor value obtained is used with a motor and tested for different supply voltage conditions. The vector diagrams obtained from the experimental test results indicates that the performance is improved from the existing value. Originality/value – This method will be highly useful for the practicing design engineers in selecting the optimum capacitance value for single phase induction motors to achieve the best performance for operating at extreme supply voltage conditions.

  10. An experimental study of mixed convection

    International Nuclear Information System (INIS)

    Saez, Manuel

    1998-01-01

    The aim of our study is to establish a reliable data base for improving thermal-hydraulic codes, in the field of turbulent flows with buoyancy forces. The flow considered is mixed convection in the Reynolds and Richardson number range: Re=10"3 to 6*10"4 and Ri=10"-"4 to 1. Experiments are carried out in an upward turbulent flow between vertical parallel plates at different wall temperatures. Part 1 gives a detailed data base of turbulent mixed flow of free and forced convection. Part II presents the installation and the calibration system intended for probes calibration. Part III describes the measurement technique (constant-temperature probe and cold-wire probe) and the method for measuring the position of the hot-wire anemometer from the wall surface. The measurement accuracy is within 0.001 mm in the present system. Part IV relates the development of a method for near wall measurements. This correction procedure for hot-wire anemometer close to wall has been derived on the basis of a two-dimensional numerical study. The method permits to obtain a quantitative correction of the wall influence on hot-wires and takes into account the velocity profile and the effects the wall material has on the heat loss. Part V presents the experimental data obtained in the channel in forced and mixed convection. Results obtained in the forced convection regime serve as a verification of the measurement technique close to the wall and give the conditions at the entrance of the test section. The effects of the buoyancy force on the mean velocity and temperature profiles are confirmed. The buoyancy strongly affects the flow structure and deforms the distribution of mean velocity. The velocity profiles are asymmetric. The second section of part V gives an approach of analytical wall functions with buoyancy forces, on the basis of the experimental data obtained in the test section. (author) [fr

  11. Parametric modulation of thermomagnetic convection in magnetic fluids.

    Science.gov (United States)

    Engler, H; Odenbach, S

    2008-05-21

    Previous theoretical investigations on thermal flow in a horizontal fluid layer have shown that the critical temperature difference, where heat transfer changes from diffusion to convective flow, depends on the frequency of a time-modulated driving force. The driving force of thermal convection is the buoyancy force resulting from the interaction of gravity and the density gradient provided by a temperature difference in the vertical direction of a horizontal fluid layer. An experimental investigation of such phenomena fails because of technical problems arising if buoyancy is to be changed by altering the temperature difference or gravitational acceleration. The possibility of influencing convective flow in a horizontal magnetic fluid layer by magnetic forces might provide us with a means to solve the problem of a time-modulated magnetic driving force. An experimental setup to investigate the dependence of the critical temperature difference on the frequency of the driving force has been designed and implemented. First results show that the time modulation of the driving force has significant influence on the strength of the convective flow. In particular a pronounced minimum in the strength of convection has been found for a particular frequency.

  12. Convective heat transfer

    CERN Document Server

    Kakac, Sadik; Pramuanjaroenkij, Anchasa

    2014-01-01

    Intended for readers who have taken a basic heat transfer course and have a basic knowledge of thermodynamics, heat transfer, fluid mechanics, and differential equations, Convective Heat Transfer, Third Edition provides an overview of phenomenological convective heat transfer. This book combines applications of engineering with the basic concepts of convection. It offers a clear and balanced presentation of essential topics using both traditional and numerical methods. The text addresses emerging science and technology matters, and highlights biomedical applications and energy technologies. What’s New in the Third Edition: Includes updated chapters and two new chapters on heat transfer in microchannels and heat transfer with nanofluids Expands problem sets and introduces new correlations and solved examples Provides more coverage of numerical/computer methods The third edition details the new research areas of heat transfer in microchannels and the enhancement of convective heat transfer with nanofluids....

  13. Preliminary Study of Single-Phase Natural Circulation for Lab-scaled Molten Salt Application

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Yukyung; Kang, Sarah; Kim, In Guk; Seo, Seok Bin; Bang, In Cheol [UNIST, Ulsan (Korea, Republic of); Park, Seong Dae [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2015-10-15

    Advanced reactors such as MSR (FHR), VHTR and AHTR utilized molten salt as a coolant for efficiency and safety which has advantages in higher heat capacity, lower pumping power and scale compared to liquid metal. It becomes more necessary to study on the characteristics of molten salt. However, due to several characteristics such as high operating temperature, large-scale facility and preventing solidification, satisfying that condition for study has difficulties. Thus simulant fluid was used with scaling method for lab-scale experiment. Scaled experiment enables simulant fluid to simulate fluid mechanics and heat transfer behavior of molten salt on lower operating temperature and reduced scale. In this paper, as a proof test of the scaled experiment, simplified single-phase natural circulation loop was designed in a lab-scale and applied to the passive safety system in advanced reactor in which molten salt is considered as a major coolant of the system. For the application of the improved safety system, prototype was based on the primary loop of the test-scale DRACS, the main passive safety system in FHR, developed at the OSU. For preliminary experiment, single-phase natural circulation under low power was performed. DOWTHERM A and DOWTHERM RP were selected as simulant candidates. Then, study of feasibility with simulant was conducted based on the scaling law for heat transfer characteristics and geometric parameters. Additionally, simulation with MARS code and ANSYS-CFX with the same condition of natural circulation was carried out as verification. For the accurate code simulation, thermo-physical properties of DOWTHERM A and RP were developed and implemented into MARS code. In this study, single-phase natural circulation experiment was performed with simulant oil, DOWTHERM RP, based on the passive safety system of FHR. Feasibility of similarity experiment for molten salt with oil simulant was confirmed by scaling method. In addition, simulation with two

  14. Analytical prediction of the electromagnetic torques in single-phase and two-phase ac motors

    Energy Technology Data Exchange (ETDEWEB)

    Popescu, M.

    2004-07-01

    The single-phase and two-phase versions of AC motors can be modelled by means of the two-axis (d-q) theory with sufficient accuracy when the equivalent circuit parameters are correctly estimated. This work attempts to present a unified approach to the analytical prediction of the electromagnetic torque of these machines. Classical d-q axes formulation requires that the reference frame should be fixed on the frame where the asymmetries arise, i.e. the stator and rotor. The asynchronous torques that characterize the induction motors are modelled in a stationary reference frame, where the d-q axes coincide with the physical magnetic axes of the stator windings. For the permanent magnet motors, that may exhibit asymmetries on both stator and rotor, the proposed solution includes: a series of frame transformations, followed by symmetrical components decomposition. As in single-phase and two-phase systems the homopolar component is zero; each symmetrical component - negative and positive - is further analysed using d-q axes theory. The superposition principle is employed to consider the magnets and rotor cage effects. The developed models account for the most important asymmetries of the motor configuration. These are, from the stator point of view, different distribution, conductors' dimensions and number of effective turns, non-orthogonal magnetic axes windings and from the rotor point of view, asymmetrical rotor cage, variable reluctance, and permanent magnets effect. The time and space harmonics effect is ignored. Test data are compared with the computed data in order to observe how the simplifying assumptions affect the level of accuracy. The analytical prediction methods make possible torque computation according to the nature of the torque being computed, namely, induction, reluctance and excitation (permanent magnet). The results are available for quasi steady-state, steady-state (rated or synchronous speed) and dynamic analyses. All the developed

  15. Pressure drop-flow rate curves for single-phase steam in Combustion Engineering type steam generator U-tubes during severe accidents

    Energy Technology Data Exchange (ETDEWEB)

    Fynan, Douglas A.; Ahn, Kwang-Il, E-mail: kiahn@kaeri.re.kr

    2016-12-15

    Highlights: • Pressure drop-flow rate curves for superheated steam in U-tubes were generated. • Forward flow of hot steam is favored in the longer and taller U-tubes. • Reverse flow of cold steam is favored in short U-tubes. • Steam generator U-tube bundle geometry and tube diameter are important. • Need for correlation development for natural convention heat transfer coefficient. - Abstract: Characteristic pressure drop-flow rate curves are generated for all row numbers of the OPR1000 steam generators (SGs), representative of Combustion Engineering (CE) type SGs featuring square bend U-tubes. The pressure drop-flow rate curves are applicable to severe accident natural circulations of single-phase superheated steam during high pressure station blackout sequences with failed auxiliary feedwater and dry secondary side which are closely related to the thermally induced steam generator tube rupture event. The pressure drop-flow rate curves which determine the recirculation rate through the SG tubes are dependent on the tube bundle geometry and hydraulic diameter of the tubes. The larger CE type SGs have greater variation of tube length and height as a function of row number with forward flow of steam favored in the longer and taller high row number tubes and reverse flow favored in the short low row number tubes. Friction loss, natural convection heat transfer coefficients, and temperature differentials from the primary to secondary side are dominant parameters affecting the recirculation rate. The need for correlation development for natural convection heat transfer coefficients for external flow over tube bundles currently not modeled in system codes is discussed.

  16. Actively convected liquid metal divertor

    International Nuclear Information System (INIS)

    Shimada, Michiya; Hirooka, Yoshi

    2014-01-01

    The use of actively convected liquid metals with j × B force is proposed to facilitate heat handling by the divertor, a challenging issue associated with magnetic fusion experiments such as ITER. This issue will be aggravated even more for DEMO and power reactors because the divertor heat load will be significantly higher and yet the use of copper would not be allowed as the heat sink material. Instead, reduced activation ferritic/martensitic steel alloys with heat conductivities substantially lower than that of copper, will be used as the structural materials. The present proposal is to fill the lower part of the vacuum vessel with liquid metals with relatively low melting points and low chemical activities including Ga and Sn. The divertor modules, equipped with electrodes and cooling tubes, are immersed in the liquid metal. The electrode, placed in the middle of the liquid metal, can be biased positively or negatively with respect to the module. The j × B force due to the current between the electrode and the module provides a rotating motion for the liquid metal around the electrodes. The rise in liquid temperature at the separatrix hit point can be maintained at acceptable levels from the operation point of view. As the rotation speed increases, the current in the liquid metal is expected to decrease due to the v × B electromotive force. This rotating motion in the poloidal plane will reduce the divertor heat load significantly. Another important benefit of the convected liquid metal divertor is the fast recovery from unmitigated disruptions. Also, the liquid metal divertor concept eliminates the erosion problem. (letter)

  17. Factors that affect the calibration of turbines in single-phase flow

    Energy Technology Data Exchange (ETDEWEB)

    Piper, T. C.

    1977-05-01

    Basic turbine operation in single-phase flow is related. Causes and relative magnitudes of retarding torque are given for two sizes of turbines when used for water flow measurement. An equation for slip caused by retarding torques is given. Evaluation of turbine slip behavior at the turbine low flow region shows that bearing retarding torques, change in flow patterns, or other effects can predominate in the relatively large changes in the calibration ''constant'' that occurs there. Fluid lubricity is singled out as an important fluid property in certain types of bearings and flow. Temperature induced changes in turbine size are shown to cause calibration changes if a turbine is used at a temperature significantly different than that at which it was calibrated.

  18. POD-Galerkin Model for Incompressible Single-Phase Flow in Porous Media

    KAUST Repository

    Wang, Yi

    2017-01-25

    Fast prediction modeling via proper orthogonal decomposition method combined with Galerkin projection is applied to incompressible single-phase fluid flow in porous media. Cases for different configurations of porous media, boundary conditions and problem scales are designed to examine the fidelity and robustness of the model. High precision (relative deviation 1.0 x 10(-4)% similar to 2.3 x 10(-1)%) and large acceleration (speed-up 880 similar to 98454 times) of POD model are found in these cases. Moreover, the computational time of POD model is quite insensitive to the complexity of problems. These results indicate POD model is especially suitable for large-scale complex problems in engineering.

  19. Condition monitoring of shaft of single-phase induction motor using optical sensor

    Science.gov (United States)

    Fulzele, Asmita G.; Arajpure, V. G.; Holay, P. P.; Patil, N. M.

    2012-05-01

    Transmission type of optical technique is developed to sense the condition of rotating shafts from a distance. A parallel laser beam is passed tangential over the surface of rotating shaft of a single phase induction motor and its flickering shadow is received on a photo sensor. Variations in sensor voltage output are observed on a digital storage oscilloscope. It is demonstrated that this signal carries information about shaft defects like miss alignment, play and impacts in bearings along with surface deformities. Mathematical model of signals corresponding to these shaft defects is developed. During the development and testing of the sensor, effects of reflections are investigated, sensing phenomenon is simulated, frequency response of the sensor is obtained and its performance is compared with conventional accelerometer.

  20. Reactive Power Injection Strategies for Single-Phase Photovoltaic Systems Considering Grid Requirements

    DEFF Research Database (Denmark)

    Yang, Yongheng; Wang, Huai; Blaabjerg, Frede

    2014-01-01

    .g. Germany and Italy. Those advanced features can be provided by next generation PV systems, and will be enhanced in the future to ensure an even efficient and reliable utilization of PV systems. In light of this, Reactive Power Injection (RPI) strategies for single-phase PV systems are explored...... in this paper. The RPI possibilities are: a) constant average active power control, b) constant active current control, c) constant peak current control and d) thermal optimized control strategy. All those strategies comply with the currently active grid codes, but are with different objectives. The proposed...... RPI strategies are demonstrated firstly by simulations and also tested experimentally on a 1 kW singe-phase grid-connected system in LVRT operation mode. Those results show the effectiveness and feasibilities of the proposed strategies with reactive power control during LVRT operation. The design...

  1. Benchmarking of Constant Power Generation Strategies for Single-Phase Grid-Connected Photovoltaic Systems

    DEFF Research Database (Denmark)

    Sangwongwanich, Ariya; Yang, Yongheng; Blaabjerg, Frede

    2018-01-01

    strategies based on: 1) a power control method (P-CPG), 2) a current limit method (I-CPG) and 3) the Perturb and Observe algorithm (P&O-CPG). However, the operational mode changes (e.g., from the maximum power point tracking to a CPG operation) will affect the entire system performance. Thus, a benchmarking...... of the presented CPG strategies is also conducted on a 3-kW single-phase grid-connected PV system. Comparisons reveal that either the P-CPG or I-CPG strategies can achieve fast dynamics and satisfactory steady-state performance. In contrast, the P&O-CPG algorithm is the most suitable solution in terms of high...

  2. Internal friction and lattice anomalies of single-phase Hg-1223

    International Nuclear Information System (INIS)

    Zhang, Q.M.; Nanjing Univ.; Shao, H.M.; Nanjing Univ.; Huang, Y.N.; Nanjing Univ.; Shen, H.M.; Nanjing Univ.; Wang, Y.N.; Nanjing Univ.

    1997-01-01

    Internal friction in the kHz range has been performed for single-phase HgBa 2 Ca 2 Cu 3 O 8+δ with the critical temperature T c = 120 K. The results indicate that two peaks of internal friction appear near 150 and 250 K. X-ray diffraction exhibits a lattice parameter stepping at tens of Kelvin above T c . The Grueneisen parameter γ is estimated from the value of thermal expansion coefficients obtained from X-ray diffraction measurements. The discussion suggests that the anomaly at 150 K is caused by lattice instabilities and the other one near 250 K may be associated with a Neel transition. (orig.)

  3. Reliability assessment of single-phase grid-connected PV microinverters considering mission profile and uncertainties

    DEFF Research Database (Denmark)

    Zare, Mohammad Hadi; Mohamadian, Mustafa; Wang, Huai

    2017-01-01

    Microinverters usually connect a PV panel to a Single-phase power grid. In such system, the input power is constant while the output power oscillates twice the line frequency. Thus, the input and output power differences should be stored in a storage component, which is typically an electrolytic ...... irritation of two different places on the micro inverter lifetime is studied....... capacitor. However, electrolytic capacitors are usually blamed for their short lifetime. Recently, some active power decoupling methods are introduced in the literature which can takes advantage of high reliable film capacitors. However, some extra switches and diodes are added to the microinverter which...... can influence the microinverter lifetime. This paper investigates the microinverter reliability according to mission profile where it is installed. To get more accurate results, uncertainties in both lifetime model and manufacturing process are considered. The effect of ambient temperature and solar...

  4. Model Building of Photovoltaic Array with MPPT Function and Research on Single Phase Grid Connected

    Directory of Open Access Journals (Sweden)

    Li Zhengzhou

    2016-01-01

    Full Text Available With the continued development of solar photovoltaic technology, research on distributed grid connected photovoltaic system has become a research focus in the field of photovoltaic grid power plant and the computer simulation technology is an effective technology means in the study. On the basis of the photovoltaic array output characteristic equation, the photovoltaic array maximum power control simulation model based on M function is established by using MATLAB/Simulink and the simulation model of single phase grid connected photovoltaic array is proposed. It overcomes the shortcomings of the process of building the model of the PV array by using Simulink component library and provides the basic guarantee for the realization of system simulation, guiding theory research and system design.

  5. Adaptive Hysteresis Band Current Control for Transformerless Single-Phase PV Inverters

    DEFF Research Database (Denmark)

    Vázquez, Gerardo; Rodriguez, Pedro; Ordoñez, Rafael

    2009-01-01

    Current control based on hysteresis algorithms are widely used in different applications, such as motion control, active filtering or active/reactive power delivery control in distributed generation systems. The hysteresis current control provides to the system a fast and robust dynamic response......, and requires a simple implementation in standard digital signal platforms. On the other hand, the main drawback of classical hysteresis current control lies in the fact that the switching frequency is variable, as the hysteresis band is fixed. In this paper a variable band hysteresis control algorithm...... different single-phase PV inverter topologies, by means of simulations performed with PSIM. In addition, the behavior of the thermal losses when using each control structure in such converters has been studied as well....

  6. Reliable Grid Condition Detection and Control of Single-Phase Distributed Power Generation Systems

    DEFF Research Database (Denmark)

    Ciobotaru, Mihai

    standards addressed to the grid-connected systems will harmonize the combination of the DPGS and the classical power plants. Consequently, the major tasks of this thesis were to develop new grid condition detection techniques and intelligent control in order to allow the DPGS not only to deliver power...... to the utility grid but also to sustain it. This thesis was divided into two main parts, namely "Grid Condition Detection" and "Control of Single-Phase DPGS". In the first part, the main focus was on reliable Phase Locked Loop (PLL) techniques for monitoring the grid voltage and on grid impedance estimation...... techniques. Additionally, a new technique for detecting the islanding mode has been developed and successfully tested. In the second part, the main reported research was concentrated around adaptive current controllers based on the information provided by the grid condition detection techniques. To guarantee...

  7. Rotor Design for an Efficient Single-Phase Induction Motor for Refrigerator Compressors

    Directory of Open Access Journals (Sweden)

    Hyun-Jin Ahn

    2016-03-01

    Full Text Available This article describes a rotor making technology for the production of high-efficiency single-phase induction motors (SPIMs to be used in refrigerator compressors. Rotors can have different aluminum fill factors according to the fabrication method. In order to examine the association between the fill factor and the efficiency of the rotor, we analyzed the distribution of magnetic flux density using the finite element method (FEM. Next, we made prototype rotors by conventional casting methods and by the proposed casting method and compared their fill factors. In addition, SPIMs were made using the rotors, and their efficiencies were measured using a dynamometer. Moreover, the SPIMs were put to use in a compressor, for testing, and for each SPIM the refrigerating capacity of the compressor was measured with a calorimeter. Based on the results of the FEM analysis of the magnetic flux density and the experiments, the reliability and validity of the proposed method were proven.

  8. Compact ASD Topologies for Single-Phase Integrated Motor Drives with Sinusoidal Input Current

    DEFF Research Database (Denmark)

    Klumpner, Christian; Blaabjerg, Frede; Thoegersen, Paul

    2005-01-01

    of the induction motor as a boost inductor for a PFC (Power Factor Correction) stage controlled by the inverter zero-sequence voltage component. By determining how much energy is possible to store in a corner inductor, it is proven that integrating the magnetics into the stator yoke is a feasible solution......, investigating the physical removal of power inductors from the converter enclosure in conjunction with reducing the number of semiconductor active devices. There are two ways to do that: to integrate the inductors in the unused area of the stator yoke of the motor or to use the leakage inductance....... Topologies of single-phase converters that take advantage of the motor leakage inductance are analyzed. The installed power in silicon active devices of these topologies is compared with a standard situation, showing that this will involve higher cost. As the iron core of the inductors is not suitable...

  9. Factors that affect the calibration of turbines in single-phase flow

    International Nuclear Information System (INIS)

    Piper, T.C.

    1977-05-01

    Basic turbine operation in single-phase flow is related. Causes and relative magnitudes of retarding torque are given for two sizes of turbines when used for water flow measurement. An equation for slip caused by retarding torques is given. Evaluation of turbine slip behavior at the turbine low flow region shows that bearing retarding torques, change in flow patterns, or other effects can predominate in the relatively large changes in the calibration ''constant'' that occurs there. Fluid lubricity is singled out as an important fluid property in certain types of bearings and flow. Temperature induced changes in turbine size are shown to cause calibration changes if a turbine is used at a temperature significantly different than that at which it was calibrated

  10. Reversible control of magnetic interactions by electric field in a single-phase material.

    Science.gov (United States)

    Ryan, P J; Kim, J-W; Birol, T; Thompson, P; Lee, J-H; Ke, X; Normile, P S; Karapetrova, E; Schiffer, P; Brown, S D; Fennie, C J; Schlom, D G

    2013-01-01

    Intrinsic magnetoelectric coupling describes the interaction between magnetic and electric polarization through an inherent microscopic mechanism in a single-phase material. This phenomenon has the potential to control the magnetic state of a material with an electric field, an enticing prospect for device engineering. Here, we demonstrate 'giant' magnetoelectric cross-field control in a tetravalent titanate film. In bulk form, EuTiO(3), is antiferromagnetic. However, both anti and ferromagnetic interactions coexist between different nearest europium neighbours. In thin epitaxial films, strain was used to alter the relative strength of the magnetic exchange constants. We not only show that moderate biaxial compression precipitates local magnetic competition, but also demonstrate that the application of an electric field at this strain condition switches the magnetic ground state. Using first-principles density functional theory, we resolve the underlying microscopic mechanism resulting in G-type magnetic order and illustrate how it is responsible for the 'giant' magnetoelectric effect.

  11. Modelling and Simulation of Single-Phase Series Active Compensator for Power Quality Improvement

    Science.gov (United States)

    Verma, Arun Kumar; Mathuria, Kirti; Singh, Bhim; Bhuvaneshwari, G.

    2017-10-01

    A single-phase active series compensator is proposed in this work to reduce harmonic currents at the ac mains and to regulate the dc link voltage of a diode bridge rectifier (DBR) that acts as the front end converter for a voltage source inverter feeding an ac motor. This ac motor drive is used in any of the domestic, commercial or industrial appliances. Under fluctuating ac mains voltages, the dc link voltage of the DBR depicts wide variations and hence the ac motor is used at reduced rating as compared to its name-plate rating. The active series compensator proposed here provides dual functions of improving the power quality at the ac mains and regulating the dc link voltage thus averting the need for derating of the ac motor.

  12. An investigation of subchannel analysis models for single-phase and two-phase flow

    Energy Technology Data Exchange (ETDEWEB)

    Hwang, Dae Hyun

    1996-01-01

    The governing equations and lateral transport modelings of subchannel analysis code, which is the most widely used tool for the analysis of thermal hydraulics fields in reactor cores, have been thoroughly investigated in this study. The procedure for the derivation of subchannel integral balance equations from the local instantaneous phase equations was investigated by stages. The characteristics of governing equations according to the treatment of phase velocity were studies, and the equations based on the drift-flux equilibrium formulation have been derived. Turbulent mixing and void drift modeling, which affect considerably to the accuracy of subchannel analysis code, have been reviewed. In addition, some representative modelings of single-phase and two-phase turbulent mixing models have been introduced. (author). 5 tabs., 4 figs., 16 refs.

  13. Rapid synthesis of single-phase bismuth ferrite by microwave-assisted hydrothermal method

    Energy Technology Data Exchange (ETDEWEB)

    Cao, Wenqian [College of Materials Science and Engineering, China Jiliang University, 258 Xueyuan Street, Xiasha Higher Education District, Hangzhou 310018, Zhejiang Province (China); Chen, Zhi, E-mail: zchen0@gmail.com [College of Materials Science and Engineering, China Jiliang University, 258 Xueyuan Street, Xiasha Higher Education District, Hangzhou 310018, Zhejiang Province (China); Gao, Tong; Zhou, Dantong; Leng, Xiaonan; Niu, Feng [College of Materials Science and Engineering, China Jiliang University, 258 Xueyuan Street, Xiasha Higher Education District, Hangzhou 310018, Zhejiang Province (China); Zhu, Yuxiang [College of Materials Science and Engineering, China Jiliang University, 258 Xueyuan Street, Xiasha Higher Education District, Hangzhou 310018, Zhejiang Province (China); Tianjin Key Laboratory of Marine Resources and Chemistry, Tianjin University of Science and Technology, Tianjin (China); Qin, Laishun, E-mail: qinlaishun@yeah.net [College of Materials Science and Engineering, China Jiliang University, 258 Xueyuan Street, Xiasha Higher Education District, Hangzhou 310018, Zhejiang Province (China); Wang, Jiangying; Huang, Yuexiang [College of Materials Science and Engineering, China Jiliang University, 258 Xueyuan Street, Xiasha Higher Education District, Hangzhou 310018, Zhejiang Province (China)

    2016-06-01

    This paper describes on the fast synthesis of bismuth ferrite by the simple microwave-assisted hydrothermal method. The phase transformation and the preferred growth facets during the synthetic process have been investigated by X-ray diffraction. Bismuth ferrite can be quickly prepared by microwave hydrothermal method by simply controlling the reaction time, which is further confirmed by Fourier Transform infrared spectroscopy and magnetic measurement. - Graphical abstract: Single-phase BiFeO{sub 3} could be realized at a shortest reaction time of 65 min. The reaction time has strong influences on the phase transformation and the preferred growth facets. - Highlights: • Rapid synthesis (65 min) of BiFeO{sub 3} by microwave-assisted hydrothermal method. • Reaction time has influence on the purity and preferred growth facets. • FTIR and magnetic measurement further confirm the pure phase.

  14. Influence of modulation method on using LC-traps with single-phase voltage source converters

    DEFF Research Database (Denmark)

    Wang, Xiongfei; Min, Huang; Bai, Haofeng

    2015-01-01

    The switching-frequency LC-trap filter has recently been employed with high-order passive filters for Voltage Source Inverters (VSIs). This paper investigates the influence of modulation method on using the LC-traps with single-phase VSIs. Two-level (bipolar) and three-level (unipolar) modulations...... that include phase distortion and alternative phase opposition distortion methods are analyzed. Harmonic filtering performances of four LC-trap-based filters with different locations of LC-traps are compared. It is shown that the use of parallel-LC-traps in series with filter inductors, either grid...... or converter side, has a worse harmonic filtering performance than using series-LC-trap in the shunt branch. Simulations and experimental results are presented for verifications....

  15. Flux distribution in single phase, Si-Fe, wound transformer cores

    International Nuclear Information System (INIS)

    Loizos, George; Kefalas, Themistoklis; Kladas, Antonios; Souflaris, Thanassis; Paparigas, Dimitris

    2008-01-01

    This paper shows experimental results of longitudinal flux density and its harmonics at the limb, the yoke and the corner as well as normal flux in the step lap joint of a single phase, Si-Fe, wound transformer core. Results show that the flux density as well as the harmonics content is higher in the inner (window) side of the core and reduces gradually towards the outer side. Variations of flux density distribution between the limb and the corner or the yoke of the core were observed. A full record of normal flux around the step lap region of the model core was also obtained. Longitudinal and normal flux findings will enable the development of more accurate numerical models that describe the magnetic behavior of magnetic cores

  16. Green synthesis of isopropyl myristate in novel single phase medium Part I: Batch optimization studies.

    Science.gov (United States)

    Vadgama, Rajeshkumar N; Odaneth, Annamma A; Lali, Arvind M

    2015-12-01

    Isopropyl myristate finds many applications in food, cosmetic and pharmaceutical industries as an emollient, thickening agent, or lubricant. Using a homogeneous reaction phase, non-specific lipase derived from Candida antartica, marketed as Novozym 435, was determined to be most suitable for the enzymatic synthesis of isopropyl myristate. The high molar ratio of alcohol to acid creates novel single phase medium which overcomes mass transfer effects and facilitates downstream processing. The effect of various reaction parameters was optimized to obtain a high yield of isopropyl myristate. Effect of temperature, agitation speed, organic solvent, biocatalyst loading and batch operational stability of the enzyme was systematically studied. The conversion of 87.65% was obtained when the molar ratio of isopropyl alcohol to myristic acid (15:1) was used with 4% (w/w) catalyst loading and agitation speed of 150 rpm at 60 °C. The enzyme has also shown good batch operational stability under optimized conditions.

  17. Single-phase sodium pump model for LMFBR thermal-hydraulic analysis

    International Nuclear Information System (INIS)

    Madni, I.K.; Cazzoli, E.G.; Agrawal, A.K.

    1979-01-01

    A single-phase, homologous pump model has been developed for simulation of safety-related transients in LMFBR systems. Pump characteristics are modeled by homologous head and torque relations encompassing all regimes of operation. These relations were derived from independent model test results with a centrifugal pump of specific speed equal to 35 (SI units) or 1800 (gpm units), and are used to analyze the steady-state and transient behavior of sodium pumps in a number of LMFBR plants. Characteristic coefficients for the polynomials in all operational regimes are provided in a tabular form. The speed and flow dependence of head is included through solutions of the impeller and coolant dynamic equations. Results show the model to yield excellent agreement with experimental data in sodium for the FFTF prototype pump, and with vendor calculations for the CRBR pump. A sample pipe rupture calculation is also performed to demonstrate the necessity for modeling the complete pump characteristics

  18. Zero-voltage ride-through capability of single-phase grid-connected photovoltaic systems

    DEFF Research Database (Denmark)

    Zhang, Zhen; Yang, Yongheng; Ma, Ruiqing

    2017-01-01

    Distributed renewable energy systems play an increasing role in today’s energy paradigm. Thus, intensive research activities have been centered on improving the performance of renewable energy systems, including photovoltaic (PV) systems, which should be of multiple-functionality. That is, the PV...... systems should be more intelligent in the consideration of grid stability, reliability, and fault protection. Therefore, in this paper, the performance of single-phase grid-connected PV systems under an extreme grid fault (i.e., when the grid voltage dips to zero) is explored. It has been revealed...... that combining a fast and accurate synchronization mechanism with appropriate control strategies for the zero-voltage ride-through (ZVRT) operation is mandatory. Accordingly, the representative synchronization techniques (i.e., the phase-locked loop (PLL) methods) in the ZVRT operation are compared in terms...

  19. A self-regulating valve for single-phase liquid cooling of microelectronics

    International Nuclear Information System (INIS)

    Donose, Radu; De Volder, Michaël; Peirs, Jan; Reynaerts, Dominiek

    2011-01-01

    This paper reports on the design, optimization and testing of a self-regulating valve for single-phase liquid cooling of microelectronics. Its purpose is to maintain the integrated circuit (IC) at constant temperature and to reduce power consumption by diminishing flow generated by the pump as a function of the cooling requirements. It uses a thermopneumatic actuation principle that combines the advantages of zero power consumption and small size in combination with a high flow rate and low manufacturing costs. The valve actuation is provided by the thermal expansion of a liquid (actuation fluid) which, at the same time, actuates the valve and provides feed-back sensing. A maximum flow rate of 38 kg h −1 passes through the valve for a heat load up to 500 W. The valve is able to reduce the pumping power by up to 60% and it has the capability to maintain the IC at a more uniform temperature.

  20. Analytical Determining Of The Steinmetz Equivalent Diagram Elements Of Single-Phase Transformer

    Directory of Open Access Journals (Sweden)

    T. Aly Saandy

    2015-08-01

    Full Text Available This article presents to an analytical calculation methodology of the Steinmetz Equivalent Diagram Elements applied to the prediction of Eddy current loss in a single-phase transformer. Based on the electrical circuit theory the active and reactive powers consumed by the core are expressed analytically in function of the electromagnetic parameters as resistivity permeability and the geometrical dimensions of the core. The proposed modeling approach is established with the duality parallel series. The equivalent diagram elements empirically determined by Steinmetz are analytically expressed using the expressions of the no loaded transformer consumptions. To verify the relevance of the model validations both by simulations with different powers and measurements were carried out to determine the resistance and reactance of the core. The obtained results are in good agreement with the theoretical approach and the practical results.

  1. Analytical Modeling Of The Steinmetz Coefficient For Single-Phase Transformer Eddy Current Loss Prediction

    Directory of Open Access Journals (Sweden)

    T. Aly Saandy

    2015-08-01

    Full Text Available Abstract This article presents to an analytical calculation methodology of the Steinmetz coefficient applied to the prediction of Eddy current loss in a single-phase transformer. Based on the electrical circuit theory the active power consumed by the core is expressed analytically in function of the electrical parameters as resistivity and the geometrical dimensions of the core. The proposed modeling approach is established with the duality parallel series. The required coefficient is identified from the empirical Steinmetz data based on the experimented active power expression. To verify the relevance of the model validations both by simulations with two in two different frequencies and measurements were carried out. The obtained results are in good agreement with the theoretical approach and the practical results.

  2. Adaptive nonlinear control of single-phase to three-phase UPS system

    Directory of Open Access Journals (Sweden)

    Kissaoui M.

    2014-01-01

    Full Text Available This work deals with the problems of uninterruptible power supplies (UPS based on the single-phase to three-phase converters built in two stages: an input bridge rectifier and an output three phase inverter. The two blocks are joined by a continuous intermediate bus. The objective of control is threefold: i power factor correction “PFC”, ii generating a symmetrical three-phase system at the output even if the load is unknown, iii regulating the DC bus voltage. The synthesis of controllers has been reached by two nonlinear techniques that are the sliding mode and adaptive backstepping control. The performances of regulators have been validated by numerical simulation in MATLAB / SIMULINK.

  3. Time domain spectral phase encoding/DPSK data modulation using single phase modulator for OCDMA application.

    Science.gov (United States)

    Wang, Xu; Gao, Zhensen; Kataoka, Nobuyuki; Wada, Naoya

    2010-05-10

    A novel scheme using single phase modulator for simultaneous time domain spectral phase encoding (SPE) signal generation and DPSK data modulation is proposed and experimentally demonstrated. Array- Waveguide-Grating and Variable-Bandwidth-Spectrum-Shaper based devices can be used for decoding the signal directly in spectral domain. The effects of fiber dispersion, light pulse width and timing error on the coding performance have been investigated by simulation and verified in experiment. In the experiment, SPE signal with 8-chip, 20GHz/chip optical code patterns has been generated and modulated with 2.5 Gbps DPSK data using single modulator. Transmission of the 2.5 Gbps data over 34km fiber with BEROCDMA) and secure optical communication applications. (c) 2010 Optical Society of America.

  4. Adaptive fuzzy sliding control of single-phase PV grid-connected inverter.

    Science.gov (United States)

    Fei, Juntao; Zhu, Yunkai

    2017-01-01

    In this paper, an adaptive fuzzy sliding mode controller is proposed to control a two-stage single-phase photovoltaic (PV) grid-connected inverter. Two key technologies are discussed in the presented PV system. An incremental conductance method with adaptive step is adopted to track the maximum power point (MPP) by controlling the duty cycle of the controllable power switch of the boost DC-DC converter. An adaptive fuzzy sliding mode controller with an integral sliding surface is developed for the grid-connected inverter where a fuzzy system is used to approach the upper bound of the system nonlinearities. The proposed strategy has strong robustness for the sliding mode control can be designed independently and disturbances can be adaptively compensated. Simulation results of a PV grid-connected system verify the effectiveness of the proposed method, demonstrating the satisfactory robustness and performance.

  5. An LLCL Power Filter for Single-Phase Grid-Tied Inverter

    DEFF Research Database (Denmark)

    Wu, Weimin; He, Yuanbin; Blaabjerg, Frede

    2012-01-01

    This paper presents a new topology of higher order power filter for grid-tied voltage-source inverters, named the LLCL filter, which inserts a small inductor in the branch loop of the capacitor in the traditional LCL filter to compose a series resonant circuit at the switching frequency. Particul......This paper presents a new topology of higher order power filter for grid-tied voltage-source inverters, named the LLCL filter, which inserts a small inductor in the branch loop of the capacitor in the traditional LCL filter to compose a series resonant circuit at the switching frequency...... to the inverter system control. The parameter design criteria of the proposed LLCL filter is also introduced. The comparative analysis and discussions regarding the traditional LCL filter and the proposed LLCL filter have been presented and evaluated through experiment on a 1.8-kW-single-phase grid-tied inverter...

  6. Modelling of the modified-LLCL-filter-based single-phase grid-tied Aalborg inverter

    DEFF Research Database (Denmark)

    Liu, Zifa; Wu, Huiyun; Liu, Yuan

    2017-01-01

    Owing to less conduction and switching power losses, the recently proposed Aalborg inverter has high efficiency within a wide range of input DC voltage for single-phase DC/AC power conversion. In theory, the conduction power losses can be further decreased, if an LLCL-filter is adopted instead...... of an LCL-filter for a voltage source inverter, mainly due to the reduced inductance. The Aalborg inverter shows the characteristic of a current source inverter, when working in the `boost' state. Whether the LLCL-filter can meet the control requirement of this type inverter needs to be further explored....... In this study, the small signal analysis for the modified-LLCL-filter-based Aalborg inverter is addressed. Through the modelling, it can be proven that compared with the LCL-filter, the modified-LLCL-filter causes no extra control challenge for the Aalborg inverter, and therefore more inductance in the power...

  7. Rapid synthesis of single-phase bismuth ferrite by microwave-assisted hydrothermal method

    International Nuclear Information System (INIS)

    Cao, Wenqian; Chen, Zhi; Gao, Tong; Zhou, Dantong; Leng, Xiaonan; Niu, Feng; Zhu, Yuxiang; Qin, Laishun; Wang, Jiangying; Huang, Yuexiang

    2016-01-01

    This paper describes on the fast synthesis of bismuth ferrite by the simple microwave-assisted hydrothermal method. The phase transformation and the preferred growth facets during the synthetic process have been investigated by X-ray diffraction. Bismuth ferrite can be quickly prepared by microwave hydrothermal method by simply controlling the reaction time, which is further confirmed by Fourier Transform infrared spectroscopy and magnetic measurement. - Graphical abstract: Single-phase BiFeO_3 could be realized at a shortest reaction time of 65 min. The reaction time has strong influences on the phase transformation and the preferred growth facets. - Highlights: • Rapid synthesis (65 min) of BiFeO_3 by microwave-assisted hydrothermal method. • Reaction time has influence on the purity and preferred growth facets. • FTIR and magnetic measurement further confirm the pure phase.

  8. A Rotor Flux and Speed Observer for Sensorless Single-Phase Induction Motor Applications

    Directory of Open Access Journals (Sweden)

    Massimo Caruso

    2012-01-01

    Full Text Available It is usual to find single-phase induction motor (SPIM in several house, office, shopping, farm, and industry applications, which are become each time more sophisticated and requiring the development of efficient alternatives to improve the operational performance of this machine. Although the rotor flux and rotational speed are essential variables in order to optimize the operation of a SPIM, the use of conventional sensors to measure them is not a viable option. Thus, the adoption of sensorless strategies is the more reasonable proposal for these cases. This paper presents a rotor flux and rotational speed observer for sensorless applications involving SPIMs. Computer simulations and the experimental results are used to verify the performance of the proposed observer.

  9. Conceptual Design of a Single Phase 33 MVA HTS Transformer with a Tertiary Winding

    International Nuclear Information System (INIS)

    Lee, S. W.; Kim, W. S.; Hahn, S. Y.; Hwang, Y. I.; Choi, K. D.

    2006-01-01

    We have proposed a 3 phase, 100 MVA, 154 kV class HTS transformer substituting for a 60 MVA conventional transformer. The power transformer of 154 kV class has a tertiary winding besides primary and secondary windings. So the HTS transformer should have the 3rd superconducting winding. In this paper, we designed conceptually the structure of the superconducting windings of a single phase 33 MVA transformer. The electrical characteristics of the HTS transformer such as % impedance and AC loss vary with the arrangement of the windings and gaps between windings. We analyzed the effects of the winding parameters, evaluated the cost of each design, and proposed a suitable HTS transformer model for future power distribution system.

  10. Calculation of single phase AC and monopolar DC hybrid corona effects

    International Nuclear Information System (INIS)

    Zhao, T.; Sebo, S.A.; Kasten, D.G.

    1996-01-01

    Operating a hybrid HVac and HVdc line is an option for increasing the efficiency of power transmission and overcoming the difficulties in obtaining a new right-of-way. This paper proposes a new calculation method for the study of hybrid line corona. The proposed method can be used to calculate dc corona losses and corona currents in dc or ac conductors for single phase ac and monopolar dc hybrid lines. Profiles of electric field strength and ion current density at ground level can be estimated. The effects of the presence of an energized ac conductor on dc conductor corona and dc voltage on ac conductor corona are included in the method. Full-scale and reduced-scale experiments were utilized to investigate the hybrid line corona effects. Verification of the proposed calculation method is given

  11. Single-phase pump model for analysis of LMFBR heat transport systems

    International Nuclear Information System (INIS)

    Madni, I.K.; Cazzoli, E.

    1978-05-01

    A single-phase pump model for transient and steady-state analysis of LMFBR heat transport systems is presented. Fundamental equations of the model are angular momentum balance to determine transient impeller speed and mass balance (including thermal expansion effects) to determine the level of sodium in the pump tank. Pump characteristics are modeled by homologous head and torque relations. All regions of pump operation are represented with reverse rotation allowed. The model also includes option for enthalpy rise calculations and pony motor operation. During steady state, the pump operating speed is determined by matching required head with total load in the circuit. Calculated transient results are presented for pump coastdown and double-ended pipe break accidents. The report examines the influence of frictional torque and specific speed on predicted response for the pump coastdown to natural circulation transient. The results for a double-ended pipe break accident indicate the necessity of including all regions of operation for pump characteristics

  12. Harmonics Suppression for Single-Phase Grid-Connected Photovoltaic Systems in Different Operation Modes

    DEFF Research Database (Denmark)

    Yang, Yongheng; Zhou, Keliang; Blaabjerg, Frede

    2013-01-01

    -connected PV inverters may be severely affected in different operation modes. In this paper, a detailed analysis is conducted to reveal the relationship between the harmonics level with the power factor and the current level in the PV systems. A current control solution which employs an Internal Model...... Principle (IMP) is proposed to suppress the harmonic currents injected into the grid. Experiments are carried out to verify the analysis and the performance of the proposed control method. It is demonstrated that the proposed method presents an effective solution to harmonics suppression for single......-phase grid-connected PV systems in different operation modes. Especially, it can remove higher order harmonics effectively leading to a better power quality compared to the Proportional plus Multi-Resonant Controller, and it has less computational burden....

  13. On Thermodynamics Problems in the Single-Phase-Lagging Heat Conduction Model

    Directory of Open Access Journals (Sweden)

    Shu-Nan Li

    2016-11-01

    Full Text Available Thermodynamics problems for the single-phase-lagging (SPL model have not been much studied. In this paper, the violation of the second law of thermodynamics by the SPL model is studied from two perspectives, which are the negative entropy production rate and breaking equilibrium spontaneously. The methods for the SPL model to avoid the negative entropy production rate are proposed, which are extended irreversible thermodynamics and the thermal relaxation time. Modifying the entropy production rate positive or zero is not enough to avoid the violation of the second law of thermodynamics for the SPL model, because the SPL model could cause breaking equilibrium spontaneously in some special circumstances. As comparison, it is shown that Fourier’s law and the CV model cannot break equilibrium spontaneously by analyzing mathematical energy integral.

  14. Numerical simulation of single-phase and multiphase non-Darcy flowin porous and fractured reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Yu-Shu

    2000-06-02

    A numerical method as well as a theoretical study of non-Darcy fluid flow of through porous and fractured reservoirs is described. The non-Darcy flow is handled in a three-dimensional, multiphase flow reservoir simulator, while the model formulation incorporates the Forchheimer equation for describing single-phase or multiphase non-Darcy flow and displacement. The numerical scheme has been verified by comparing its results against those of analytical methods. Numerical solutions are used to obtain some insight into the physics of non-Darcy flow and displacement in reservoirs. In addition, several type curves are provided for well-test analyses of non-Darcy flow to demonstrate a methodology for modeling this type of flow in porous and fractured rocks, including flow in geothermal reservoirs.

  15. A Robust DC-Split-Capacitor Power Decoupling Scheme for Single-Phase Converter

    DEFF Research Database (Denmark)

    Yao, Wenli; Loh, Poh Chiang; Tang, Yi

    2017-01-01

    Instead of bulky electrolytic capacitors, active power decoupling circuit can be introduced to a single-phase converter for diverting second harmonic ripple away from its dc source or load. One possible circuit consists of a half-bridge and two capacitors in series for forming a dc-split capacitor......, instead of the usual single dc-link capacitor bank. Methods for regulating this power decoupler have earlier been developed, but almost always with equal capacitances assumed for forming the dc-split capacitor, even though it is not realistic in practice. The assumption should, hence, be evaluated more...... thoroughly, especially when it is shown in the paper that even a slight mismatch can render the power decoupling scheme ineffective and the IEEE 1547 standard to be breached. A more robust compensation scheme is, thus, needed for the dc-split capacitor circuit, as proposed and tested experimentally...

  16. Multi-scale Modeling of Compressible Single-phase Flow in Porous Media using Molecular Simulation

    KAUST Repository

    Saad, Ahmed Mohamed

    2016-05-01

    In this study, an efficient coupling between Monte Carlo (MC) molecular simulation and Darcy-scale flow in porous media is presented. The cell-centered finite difference method with a non-uniform rectangular mesh were used to discretize the simulation domain and solve the governing equations. To speed up the MC simulations, we implemented a recently developed scheme that quickly generates MC Markov chains out of pre-computed ones, based on the reweighting and reconstruction algorithm. This method astonishingly reduces the required computational time by MC simulations from hours to seconds. In addition, the reweighting and reconstruction scheme, which was originally designed to work with the LJ potential model, is extended to work with a potential model that accounts for the molecular quadrupole moment of fluids with non-spherical molecules such as CO2. The potential model was used to simulate the thermodynamic equilibrium properties for single-phase and two-phase systems using the canonical ensemble and the Gibbs ensemble, respectively. Comparing the simulation results with the experimental data showed that the implemented model has an excellent fit outperforming the standard LJ model. To demonstrate the strength of the proposed coupling in terms of computational time efficiency and numerical accuracy in fluid properties, various numerical experiments covering different compressible single-phase flow scenarios were conducted. The novelty in the introduced scheme is in allowing an efficient coupling of the molecular scale and Darcy scale in reservoir simulators. This leads to an accurate description of the thermodynamic behavior of the simulated reservoir fluids; consequently enhancing the confidence in the flow predictions in porous media.

  17. Single-phase dual-energy CT urography in the evaluation of haematuria.

    Science.gov (United States)

    Ascenti, G; Mileto, A; Gaeta, M; Blandino, A; Mazziotti, S; Scribano, E

    2013-02-01

    To assess the value of a single-phase dual-energy computed tomography (DECT) urography protocol with synchronous nephrographic-excretory phase enhancement and to calculate the potential dose reduction by omitting the unenhanced scan. Eighty-four patients referred for haematuria underwent CT urography using a protocol that included single-energy unenhanced and dual-energy contrast-enhanced with synchronous nephrographic-excretory phase scans. DECT-based images [virtual unenhanced (VUE), weighted average, and colour-coded iodine overlay] were reconstructed. Opacification degree by contrast media of the upper urinary tract, and image quality of virtual unenhanced images were independently evaluated using a four-point scale. The diagnostic accuracy in detecting urothelial tumours on DECT-based images was determined. The dose of a theoretical dual-phase single-energy protocol was obtained by multiplying the effective dose of the unenhanced single-energy acquisition by two. Radiation dose saving by omitting the unenhanced scan was calculated. The degree of opacification was scored as optimal or good in 86.9% of cases (k = 0.72); VUE image quality was excellent or good in 83.3% of cases (k = 0.82). Sensitivity, specificity, positive predictive value, and negative predictive value for urothelial tumours detection were 85.7, 98.6, 92.3, and 97.1%. Omission of the unenhanced scan led to a mean dose reduction of 42.7 ± 5%. Single-phase DECT urography with synchronous nephrographic-excretory phase enhancement represents an accurate "all-in-one'' approach with a radiation dose saving up to 45% compared with a standard dual-phase protocol. Copyright © 2012 The Royal College of Radiologists. All rights reserved.

  18. Single-phase dual-energy CT urography in the evaluation of haematuria

    International Nuclear Information System (INIS)

    Ascenti, G.; Mileto, A.; Gaeta, M.; Blandino, A.; Mazziotti, S.; Scribano, E.

    2013-01-01

    Aim: To assess the value of a single-phase dual-energy computed tomography (DECT) urography protocol with synchronous nephrographic–excretory phase enhancement and to calculate the potential dose reduction by omitting the unenhanced scan. Materials and methods: Eighty-four patients referred for haematuria underwent CT urography using a protocol that included single-energy unenhanced and dual-energy contrast-enhanced with synchronous nephrographic–excretory phase scans. DECT-based images [virtual unenhanced (VUE), weighted average, and colour-coded iodine overlay] were reconstructed. Opacification degree by contrast media of the upper urinary tract, and image quality of virtual unenhanced images were independently evaluated using a four-point scale. The diagnostic accuracy in detecting urothelial tumours on DECT-based images was determined. The dose of a theoretical dual-phase single-energy protocol was obtained by multiplying the effective dose of the unenhanced single-energy acquisition by two. Radiation dose saving by omitting the unenhanced scan was calculated. Results: The degree of opacification was scored as optimal or good in 86.9% of cases (k = 0.72); VUE image quality was excellent or good in 83.3% of cases (k = 0.82). Sensitivity, specificity, positive predictive value, and negative predictive value for urothelial tumours detection were 85.7, 98.6, 92.3, and 97.1%. Omission of the unenhanced scan led to a mean dose reduction of 42.7 ± 5%. Conclusion: Single-phase DECT urography with synchronous nephrographic–excretory phase enhancement represents an accurate “all-in-one’’ approach with a radiation dose saving up to 45% compared with a standard dual-phase protocol.

  19. Synthesis and characterization of single-phase Mn-doped ZnO

    Science.gov (United States)

    Chattopadhyay, S.; Dutta, S.; Banerjee, A.; Jana, D.; Bandyopadhyay, S.; Chattopadhyay, S.; Sarkar, A.

    2009-05-01

    Different samples of Zn 1-xMn xO series have been prepared using conventional solid-state sintering method. We identified up to what extent doping will enable us to synthesize single-phase polycrystalline Mn-doped ZnO sample, which is one of the prerequisites for dilute magnetic semiconductor, and we have analyzed its some other physical aspects. In synthesizing the samples, proportion of Mn varies from 1 to 5 at%. However, the milling time varied (6, 12, 24, 48 and 96 h) only for 2 at% Mn-doped samples while for other samples (1, 3, 4 and 5 at% Mn doped) the milling time has been fixed to 96 h. Room-temperature X-ray diffraction (XRD) data reveal that all of the prepared samples up to 3 at% of Mn doping exhibit wurtzite-type structure, and no segregation of Mn and/or its oxides has been found. The 4 at% Mn-doped samples show a weak peak of ZnMn 2O 4 apart from the other usual peaks of ZnO and the intensity of this impurity peak has been further increased for 5 at% of Mn doping. So beyond 3 at% doping, single-phase behavior is destroyed. Band gap for all the 2 at% Mn-doped samples has been estimated to be between 3.21 and 3.19 eV and the reason for this low band gap values has been explained through the grain boundary trapping model. The room-temperature resistivity measurement shows an increase of resistivity up to 48 h of milling and with further milling it saturates. The defect state of these samples has been investigated using the positron annihilation lifetime (PAL) spectroscopy technique. Here all the relevant lifetime parameters of positron i.e. free annihilation ( τ1) at defect site ( τ2) and average ( τav) increases with milling time.

  20. Synthesis and characterization of single-phase Mn-doped ZnO

    International Nuclear Information System (INIS)

    Chattopadhyay, S.; Dutta, S.; Banerjee, A.; Jana, D.; Bandyopadhyay, S.; Chattopadhyay, S.; Sarkar, A.

    2009-01-01

    Different samples of Zn 1-x Mn x O series have been prepared using conventional solid-state sintering method. We identified up to what extent doping will enable us to synthesize single-phase polycrystalline Mn-doped ZnO sample, which is one of the prerequisites for dilute magnetic semiconductor, and we have analyzed its some other physical aspects. In synthesizing the samples, proportion of Mn varies from 1 to 5 at%. However, the milling time varied (6, 12, 24, 48 and 96 h) only for 2 at% Mn-doped samples while for other samples (1, 3, 4 and 5 at% Mn doped) the milling time has been fixed to 96 h. Room-temperature X-ray diffraction (XRD) data reveal that all of the prepared samples up to 3 at% of Mn doping exhibit wurtzite-type structure, and no segregation of Mn and/or its oxides has been found. The 4 at% Mn-doped samples show a weak peak of ZnMn 2 O 4 apart from the other usual peaks of ZnO and the intensity of this impurity peak has been further increased for 5 at% of Mn doping. So beyond 3 at% doping, single-phase behavior is destroyed. Band gap for all the 2 at% Mn-doped samples has been estimated to be between 3.21 and 3.19 eV and the reason for this low band gap values has been explained through the grain boundary trapping model. The room-temperature resistivity measurement shows an increase of resistivity up to 48 h of milling and with further milling it saturates. The defect state of these samples has been investigated using the positron annihilation lifetime (PAL) spectroscopy technique. Here all the relevant lifetime parameters of positron i.e. free annihilation (τ 1 ) at defect site (τ 2 ) and average (τ av ) increases with milling time.