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1

DEFF Research Database (Denmark)

Current models to predict heat, air and moisture (HAM) conditions in buildings assume constant boundary conditions for the temperature and relative humidity of the neighbouring air and for the surface heat and moisture transfer coefficients. These assumptions may introduce errors in the predicted HAM conditions. The paper focuses on the influence of the interior surface heat and moisture transfer coefficients, and investigates its effect on the hygrothermal performance. The parameter study showed that the magnitude of the convective surface transfer coefficients have a relatively large influence on the predicted hygrothermal conditions at the surface of a building component and on the heat and vapour exchange with the indoor environment.

Steskens, Paul Wilhelmus Maria Hermanus; Janssen, Hans

2009-01-01

2

Directory of Open Access Journals (Sweden)

Full Text Available This study investigates the effect of flow velocity and building surface temperature effects on Convective Heat Transfer Coefficient (CHTC from urban building surfaces by numerical simulation. The thermal effects produced by geometrical and physical properties of urban areas generate a relatively differential heating and uncomfortable environment compared to rural regions called as Urban Heat Island (UHI phenomena. The urban thermal comfort is directly related to the CHTC from the urban canopy surfaces. This CHTC from urban canopy surfaces expected to depend upon the wind velocity flowing over the urban canopy surfaces, urban canopy configurations, building surface temperature etc. But the most influential parameter on CHTC has not been clarified yet. Urban canopy type experiments in thermally stratified wind tunnel have normally been used to study the heat transfer issues. But, it is not an easy task in wind tunnel experiments to evaluate local CHTC, which vary on individual canyon surfaces such as building roof, walls and ground. Numerical simulation validated by wind tunnel experiments can be an alternative for the prediction of CHTC from building surfaces in an urban area. In our study, wind tunnel experiments were conducted to validate the low-Reynolds-number k-? model which was used for the evaluation of CHTC from surfaces. The calculated CFD results showed good agreement with experimental results. After this validation, the effects of flow velocity and building surface temperature effects on CHTC from urban building surfaces were investigated. It has been found that the change in velocity remarkably affects the CHTC from urban canopy surfaces and change in surface temperature has almost no effect over the CHTC from urban canopy surfaces.

Sivaraja Subramania Pillai

2013-06-01

3

Variation of Local Pool Boiling Heat Transfer Coefficient On 3-Degree Inclined Tube Surface

International Nuclear Information System (INIS)

Experimental studies on both subcooled and saturated pool boiling of water were performed to obtain local heat transfer coefficients on a 3 .deg. inclined tube of 50.8 mm diameter at atmospheric pressure. The local values were determined at every 45 .deg. from the very bottom to the uppermost of the tube periphery. The maximum and minimum local coefficients were observed at the azimuthal angles of 0 .deg. and 180 .deg., respectively, in saturated water. The locations of the maxima and the minima were dependent on the inclination angle of the tube as well as the degree of subcooling. The major heat transfer mechanisms were considered to be liquid agitation generated by the sliding bubbles and the creation of big size bubbles through bubble coalescence. As a way of quantifying the heat transfer coefficients, an empirical correlation was suggested

4

Variation of Local Pool Boiling Heat Transfer Coefficient On 3-Degree Inclined Tube Surface

Energy Technology Data Exchange (ETDEWEB)

Experimental studies on both subcooled and saturated pool boiling of water were performed to obtain local heat transfer coefficients on a 3 .deg. inclined tube of 50.8 mm diameter at atmospheric pressure. The local values were determined at every 45 .deg. from the very bottom to the uppermost of the tube periphery. The maximum and minimum local coefficients were observed at the azimuthal angles of 0 .deg. and 180 .deg., respectively, in saturated water. The locations of the maxima and the minima were dependent on the inclination angle of the tube as well as the degree of subcooling. The major heat transfer mechanisms were considered to be liquid agitation generated by the sliding bubbles and the creation of big size bubbles through bubble coalescence. As a way of quantifying the heat transfer coefficients, an empirical correlation was suggested.

Kang, Myeonggie [Andong National Univ., Andong (Korea, Republic of)

2013-12-15

5

International Nuclear Information System (INIS)

Convective heat transfer at exterior building surfaces has an impact on the design and performance of building components such as double-skin facades, solar collectors, solar chimneys and ventilated photovoltaic arrays, and also affects the thermal climate and cooling load in urban areas. In this study, an overview is given of existing correlations of the exterior convective heat transfer coefficient (CHTC) with the wind speed, indicating significant differences between these correlations. As an alternative to using existing correlations, the applicability of CFD to obtain forced CHTC correlations is evaluated, by considering a cubic building in an atmospheric boundary layer. Steady Reynolds-averaged Navier-Stokes simulations are performed and, instead of the commonly used wall functions, low-Reynolds number modelling (LRNM) is used to model the boundary-layer region for reasons of improved accuracy. The flow field is found to become quasi independent of the Reynolds number at Reynolds numbers of about 105. This allows limiting the wind speed at which the CHTC is evaluated and thus the grid resolution in the near-wall region, which significantly reduces the computational expense. The distribution of the power-law CHTC-U10 correlation over the windward and leeward surfaces is presented (U10 = reference wind speed at 10 m height). It is shown that these correlations can be accurately determined by simulations with relatively low wind spey simulations with relatively low wind speed values, which avoids the use of excessively fine grids for LRNM, and by using only two or three discrete wind speed values, which limits the required number of CFD simulations.

6

Cast impingement cooling geometries offer the gas turbine designer higher structural integrity and improved convective cooling when compared to traditional impingement cooling systems, which rely on plate inserts. In this paper, it is shown that the surface that forms the jets contributes significantly to the total cooling. Local heat transfer coefficient distributions have been measured in a model of an engine wall cooling geometry using the transient heat transfer technique. The method empl...

Gillespie, Drh; Wang, Z.; Ireland, Pt; Kohler, St

1998-01-01

7

Energy Technology Data Exchange (ETDEWEB)

Different approaches for the calculation of Direct Contact Condensation (DCC) using Heat Transfer Coefficients (HTC) based on the Surface Renewal Theory (SRT) are tested using the CFD simulation tool ANSYS CFX. The present work constitutes a preliminary study of the flow patterns and conditions observed using different HTC models. A complex 3D flow pattern will be observed in the CFD simulations as well as a strong coupling between the condensation rate and the two-phase flow dynamics. (orig.)

Wanninger, Andreas; Ceuca, Sabin Cristian; Macian-Juan, Rafael [Technische Univ. Muenchen, Garching (Germany). Dept. of Nuclear Engineering

2013-07-01

8

International Nuclear Information System (INIS)

Different approaches for the calculation of Direct Contact Condensation (DCC) using Heat Transfer Coefficients (HTC) based on the Surface Renewal Theory (SRT) are tested using the CFD simulation tool ANSYS CFX. The present work constitutes a preliminary study of the flow patterns and conditions observed using different HTC models. A complex 3D flow pattern will be observed in the CFD simulations as well as a strong coupling between the condensation rate and the two-phase flow dynamics. (orig.)

9

Turbulent Heat-Transfer Coefficients in the Vicinity of Surface Protuberances

Local turbulent heating rates were obtained in the vicinity of surface protuberances mounted on the cylinder section of a cone cylinder model at a Mach number of 3.12. Data were obtained at Reynolds number per foot of 4.5 and 6 million for an unswept cylinder, a 45 deg swept cylinder, a 45 deg elbow, and several 90 deg elbows. The unswept cylinder and the 90 deg elbows increased the local turbulent heating rates in the vicinity of the surface protuberances. The data of the 45 deg swept cylinder and the 45 deg elbow resulted in heating rates lower than those observed without surface protuberances. In general, sweeping a surface protuberance resulted in heating rates comparable or lower than those measured without surface protuberances.

Wisniewski, Richard J.

1958-01-01

10

Energy Technology Data Exchange (ETDEWEB)

A critical review of the assumptions, theoretical foundations, and supporting experimental evidence for the analytical procedures in current use for evaluation of the effects of artificial surface roughening on friction factor and Stanton number is provided. Recommendations are given concerning the application of these procedures to rough rod bundles. A new method is demonstrated for determination of the slope and intercept of the universal logarithmic dimensionless velocity distribution law for fully rough flow past roughened surfaces without the need for experimental measurement of the velocity profile. The slope is shown to vary with the nature of the roughened surface and to deviate significantly from the slope for turbulent flow past smooth walls in some cases. It is further shown that the intercept, which is a boundary condition equivalent to the roughness parameter for friction, is independent of the width of the velocity profile. A similar method is developed for determination of the slope and intercept of the temperature distribution law, but additional experimental investigation is required before the efficacy of this application can be conclusively established.

Hodge, S.A.; Sanders, J.P.; Klein, D.E.

1979-11-01

11

International Nuclear Information System (INIS)

A critical review of the assumptions, theoretical foundations, and supporting experimental evidence for the analytical procedures in current use for evaluation of the effects of artificial surface roughening on friction factor and Stanton number is provided. Recommendations are given concerning the application of these procedures to rough rod bundles. A new method is demonstrated for determination of the slope and intercept of the universal logarithmic dimensionless velocity distribution law for fully rough flow past roughened surfaces without the need for experimental measurement of the velocity profile. The slope is shown to vary with the nature of the roughened surface and to deviate significantly from the slope for turbulent flow past smooth walls in some cases. It is further shown that the intercept, which is a boundary condition equivalent to the roughness parameter for friction, is independent of the width of the velocity profile. A similar method is developed for determination of the slope and intercept of the temperature distribution law, but additional experimental investigation is required before the efficacy of this application can be conclusively established

12

International Nuclear Information System (INIS)

In fire engineering analysis, one of the open problem is the transfer of thermal parameters obtained by fire CFD model to FEM models for structural analysis. In this study the new useful concept of “Adiabatic Surface Temperature” or more commonly known as AST, introduced by Wickström, is investigated. The adiabatic surface temperature offers the opportunity to transfer both thermal information of the gas and the net heat flux to the solid phase model, obtained by CFD analysis. In this study two CFD analyses are carried out in order to evaluate the effect of emissivity and of convective heat transfer coefficient to determine the AST. First one CFD analysis simulating a fire scenario, “conjugate heat transfer”, with a square steel beam exposed to hot surface is carried out to calculate AST, heat convective coefficient and temperature field in the beam. Second one, a conductive analysis is carried out on “standalone beam” imposing a third type boundary condition on its boundaries assuming the AST, evaluated in the conjugate analysis, as external temperature. Different heat convective coefficients are imposed on the beam walls. The comparison between results obtained by means of the two proposed analyses shows the use of AST as transfer thermal parameter between CFD (Computational Fluid Dynamic) and FEM (Finite Element Method) models is appropriate when the convective heat transfer coefficient is properly evaluated. -- Highlights: ? An open problem is to transfer parameters obtained by thermal to structural models. ? The useful concept of “Adiabatic Surface Temperature” (AST) is investigated. ? The AST use is right for properly evaluated convective heat transfer coefficient

13

International Nuclear Information System (INIS)

The heat (mass) transfer characteristics on the blade surface of a first-stage turbine rotor cascade for power generation has been investigated by employing the naphthalene sublimation technique. A four-axis profile measurement system is successfully developed for the measurements of the local heat (mass) transfer coefficient on the curved blade surface. The experiment is carried out at the free-stream Reynolds number and turbulence intensity of 2.09x105 and 1.2%. The results on the blade surfaces show that the local heat (mass) transfer on the suction surface is strongly influenced by the endwall vortices, but that on the pressure surface shows a nearly two-dimensional nature. The pressure surface has a more uniform distribution of heat load than the suction one

14

Laser Measurement Of Convective-Heat-Transfer Coefficient

Coefficient of convective transfer of heat at spot on surface of wind-tunnel model computed from measurements acquired by developmental laser-induced-heat-flux technique. Enables non-intrusive measurements of convective-heat-transfer coefficients at many points across surfaces of models in complicated, three-dimensional, high-speed flows. Measurement spot scanned across surface of model. Apparatus includes argon-ion laser, attenuator/beam splitter electronic shutter infrared camera, and subsystem.

Porro, A. Robert; Hingst, Warren R.; Chriss, Randall M.; Seablom, Kirk D.; Keith, Theo G., Jr.

1994-01-01

15

An approximate transfer surface.

The principal defect in the Osgood (1949) transfer surface is the treatment of negative transfer. This may be corrected, although no surface can incorporate all the relevant transfer variables. The explanation and the scoring of negative transfer are discussed, with an emphasis on problems of skills learning. The conclusions reached are represented in the design of a new transfer surface. PMID:23952791

Dennis H, H

1976-03-01

16

Transfer coefficients for turbulent flow between parallel plates

International Nuclear Information System (INIS)

Average transfer coefficients in the turbulent forced convection entrance region between parallel plates, with asymmetrical conditions of the concentration profile, were determined experimentaly with the Naphthalene Sublimation Technique. In accordance with the analogy between heat and mass transfer, the tests correspond to a heat-transfer problem with uniform surface temperature at one plate and the other insulated. The Reynolds number ranges from 10900 to 91700. (Author)

17

Non intrusive measurement of the convective heat transfer coefficient

Energy Technology Data Exchange (ETDEWEB)

The efficiency of cooling methods in thermal systems such as radiators and heat exchangers must be improved in order to enhance performance. The evaluation of the heat transfer coefficients between a solid and a fluid is necessary for the control and the dimensioning of thermal systems. In this study, the pulsed photothermal method was used to measure the convective heat transfer coefficient on a solid-fluid interface, notably between an air flow and a heated slab mounted on a PVC flat plate. This configuration simulated the electronic air-cooling inside enclosures and racks. The influence of the deflector's inclination angle on the enhancement of heat transfer was investigated using 2 newly developed identification models. The first model was based on a constant heat transfer coefficient during the pulsed experiment, while the second, improved model was based on a variable heat transfer coefficient. The heat transfer coefficient was deduced from the evolution of the transient temperature induced by a sudden deposit of a luminous energy on the front face of the slab. Temperature evolutions were derived by infrared thermography, a camera for cartography and a detector for precise measurement in specific locations. The results show the improvement of measurement accuracies when using a model that considers the temporal evolution of the convective heat transfer coefficient. The deflection of air flow on the upper surface of the heated slab demonstrated better cooling of the slab by the deflection of air flow. 11 refs., 1 tab., 8 figs.

Rebay, M.; Mebarki, G.; Padet, J. [Reims Univ., Reims (France). Faculty of Science, GRESPI Thermomechanical Lab; Arfaoui, A. [Reims Univ., Reims (France). Faculty of Science, GRESPI Thermomechanical Lab; Tunis Univ., Tunis (Tunisia). Faculty of Science, EL MANAR, LETTM; Maad, B.R. [Tunis Univ., Tunis (Tunisia). Faculty of Science, EL MANAR, LETTM

2010-07-01

18

Effect of surfactants on liquid side mass transfer coefficients

In the present paper, the effect of liquid properties (surfactants) on bubble generation phenomenon, interfacial area and liquid side mass transfer coefficient was investigated. The measurements of surface tension (static and dynamic methods), of Critical Micelle Concentration (CMC) and of characteristic adsorption parameters such as the surface coverage ratio at equilibrium (se) were performed to understand the effects of surfactants on the mass transfer efficiency. Tap water and aqueous sol...

Painmanakul, Pisut; Loubiere, Karine; Roustan, Michel; Mietton-peuchot, Martine; Hebrard, Gilles

2005-01-01

19

Determination of the heat transfer coefficients in transient heat conduction

The determination of the space- or time-dependent heat transfer coefficient which links the boundary temperature to the heat flux through a third-kind Robin boundary condition in transient heat conduction is investigated. The reconstruction uses average surface temperature measurements. In both cases of the space- or time-dependent unknown heat transfer coefficient the inverse problems are nonlinear and ill posed. Least-squares penalized variational formulations are proposed and new formulae for the gradients are derived. Numerical results obtained using the nonlinear conjugate gradient method combined with a boundary element direct solver are presented and discussed.

Nho Hào, Dinh; Thanh, Phan Xuan; Lesnic, D.

2013-09-01

20

Determination of the heat transfer coefficients in transient heat conduction

International Nuclear Information System (INIS)

The determination of the space- or time-dependent heat transfer coefficient which links the boundary temperature to the heat flux through a third-kind Robin boundary condition in transient heat conduction is investigated. The reconstruction uses average surface temperature measurements. In both cases of the space- or time-dependent unknown heat transfer coefficient the inverse problems are nonlinear and ill posed. Least-squares penalized variational formulations are proposed and new formulae for the gradients are derived. Numerical results obtained using the nonlinear conjugate gradient method combined with a boundary element direct solver are presented and discussed. (paper)

21

Radiative Heat Transfer and Effective Transport Coefficients

The theory of heat transfer by electromagnetic radiation is based on the radiative transfer equation (RTE) for the radiation intensity, or equivalently on the Boltzmann transport equation (BTE) for the photon distribution. We focus in this review article, after a brief overview on different solution methods, on a recently introduced approach based on truncated moment expansion. Due to the linearity of the underlying BTE, the appropriate closure of the system of moment equations is entropy production rate minimization. This closure provides a distribution function and the associated effective transport coefficients, like mean absorption coefficients and the Eddington factor, for an arbitrary number of moments. The moment approach is finally illustrated with an application of the two-moment equations to an electrical arc.

Christen, Thomas; Gati, Rudolf

2010-01-01

22

Transfer coefficients in elliptical tubes and plate fin heat exchangers

International Nuclear Information System (INIS)

Mean transfer coefficients in elliptical tubes and plate fin heat exchangers were determined by application of heat and mass transfer analogy in conjunction with the naphthalene sublimation technique. The transfer coefficients are presented in a dimensionless form as functions of the Reynolds number. By using the least squares method analytical expressions for the transfer coefficients were determined with low scattering. (E.G.)

23

Local Pool Boiling Heat Transfer Coefficients on Near Horizontal Tubes

International Nuclear Information System (INIS)

They said that as the liquid is methanol the maximum local heat transfer coefficient (hb,max) was observed at the tube bottom while the maximum was at the tube sides as the boiling liquid was n-hexane. Cornwell and Einarsson reported that hb,max was observed at the tube bottom, as the boiling liquid was R113. Cornwell and Houston explained the reason of the difference in local heat transfer coefficients along the tube circumference with introducing effects of sliding bubbles on heat transfer. According to Gupta et al., the maximum and the minimum local heat transfer coefficients were observed at the bottom and top regions of the tube circumference, respectively, using a tube bundle and water. Kang also reported the similar results using a single horizontal tube and water. However, the maximum heat transfer coefficient was observed at the angle of 45 .deg. Sateesh et al. studied variations of hb along the tube periphery while controlling the inclination angle (?). They tested five inclination angles (i. e., ? =0 .deg, 30 .deg, 45 .deg, 60 .deg, and 90 .deg). The top wall superheat increases and bottom wall superheat decreases as the inclination is changed 90 .deg to 0 .deg from the horizontal. The cause for the tendency is thought as the bubble sliding length. Recently, Kang et al. studied pool boiling heat transfer on a 3-deg inclined tube for application to the design of the advanced power reactor plus. Since some more data is necessary, the present study is aimed to study variations in local pool boiling heat transfer coefficients on nearly horizontal tubes. Effects of the inclination angle on the changes of local pool boiling heat transfer coefficients on the outside surface of a 50.8 mm diameter tube have been investigated experimentally in the saturated water at atmospheric pressure. The azimuthal angles for the maximum and the minimum local coefficients are dependent on the inclination angle and the heat flux. The major mechanisms changing heat transfer on the surface are liquid agitation and bubble coalescence

24

Heat transfer coefficient between UO2 and Zircaloy-2

International Nuclear Information System (INIS)

This paper provides some experimental values of the heat-transfer coefficient between UO2 and Zircaloy-2 surfaces in contact under conditions of interfacial pressure, temperature, surface roughness and interface atmosphere, that are relevant to UO2/Zircaloy-2 fuel elements operating in pressurized-water power reactors. Coefficients were obtained from eight UO2/ Zircaloy-2 pairs in atmospheres of helium, argon, krypton or xenon, at atmosphere pressure and in vacuum. Interfacial pressures were varied from 50 to 550 kgf/cm2 while surface roughness heights were in the range 0.2 x 10-4 to 3.5 x 10-4 cm. The effect on the coefficients of cycling the interfacial pressure, of interface gas pressure and of temperature were examined. The experimental values of the coefficients were used to test the predictions of expressions for the heat-transfer between two solids in contact. For the particular UO2/ Zircaloy-2 pairs examined, numerical values were assigned to several parameters that related the surface roughnesses to either the radius of solid/solid contact spots or to the mean thickness of the interface voids and that accounted for the imperfect accommodation of the void gas on the test surfaces. (author)

25

International Nuclear Information System (INIS)

The heat (mass) transfer characteristics on the blade surface of a high-turning first-stage turbine rotor for power generation has been investigated by employing the naphthalene sublimation technique. A four-axis profile measurement system is developed successfully for the measurements of local sublimation depth on the curved surface. In the leading edge region, there is a good agreement between the present heat (mass) transfer data and the previous result on a turbine blade with a moderate turning angle, but come discrepancies are found in the mid-chord heat (mass) transfer between the two results. The local heat (mass) transfer on the present suction surface is greatly enhanced due to an earlier boundary transition, compared with that on a turbine blade with a moderate turning angle, meanwhile there is only a slight change in the pressures-side heat (mass) transfer between the two different turbine rotors. In general, the heat (mass) transfer augmentation by the endwall vortices is found much higher on the suction surface than on the pressure surface

26

Measuring Furnace/Sample Heat-Transfer Coefficients

Complicated, inexact calculations now unnecessary. Device called HTX used to simulate and measure transfer of heat between directional-solidification crystal-growth furnace and ampoule containing sample of crystalline to be grown. Yields measurement data used to calculate heat-transfer coefficients directly, without need for assumptions or prior knowledge of physical properties of furnace, furnace gas, or specimen. Determines not only total heat-transfer coefficients but also coefficients of transfer of heat in different modes.

Rosch, William R.; Fripp, Archibald L., Jr.; Debnam, William J., Jr.; Woodell, Glenn A.

1993-01-01

27

Radionuclide transfer to animal products: revised recommended transfer coefficient values

International Nuclear Information System (INIS)

A compilation has been undertaken of data which can be used to derive animal product transfer coefficients for radionuclides, including an extensive review of Russian language information. The resultant database has been used to provide recommended transfer coefficient values for a range of radionuclides to (i) cow, sheep and goat milk, (ii) meat (muscle) of cattle, sheep, goats, pigs and poultry and (iii) eggs. The values are used in a new IAEA handbook on transfer parameters which replaces that referred to as 'TRS 364'. The paper outlines the approaches and procedures used to identify and collate data, and assumptions used. There are notable differences between the TRS 364 'expected' values and the recommended values in the revised Handbook from the new database. Of the recommended values, three milk values are at least an order of magnitude higher than the TRS 364 values (Cr, Pu (cow) Pu (sheep)) and one milk value is lower (Ni (cow)). For meat, four values (Am, Cd, Sb (beef) I (pork)) are at least an order of magnitude higher than the TRS 364 values and eight values are at least an order of magnitude lower (Ru, Pu (beef), Ru, Sr, Zn (sheep), Ru, Sr (pork), Mn (poultry)). Many data gaps remain

28

Radionuclide transfer to animal products: revised recommended transfer coefficient values

Energy Technology Data Exchange (ETDEWEB)

A compilation has been undertaken of data which can be used to derive animal product transfer coefficients for radionuclides, including an extensive review of Russian language information. The resultant database has been used to provide recommended transfer coefficient values for a range of radionuclides to (i) cow, sheep and goat milk, (ii) meat (muscle) of cattle, sheep, goats, pigs and poultry and (iii) eggs. The values are used in a new IAEA handbook on transfer parameters which replaces that referred to as 'TRS 364'. The paper outlines the approaches and procedures used to identify and collate data, and assumptions used. There are notable differences between the TRS 364 'expected' values and the recommended values in the revised Handbook from the new database. Of the recommended values, three milk values are at least an order of magnitude higher than the TRS 364 values (Cr, Pu (cow) Pu (sheep)) and one milk value is lower (Ni (cow)). For meat, four values (Am, Cd, Sb (beef) I (pork)) are at least an order of magnitude higher than the TRS 364 values and eight values are at least an order of magnitude lower (Ru, Pu (beef), Ru, Sr, Zn (sheep), Ru, Sr (pork), Mn (poultry)). Many data gaps remain.

Howard, B.J. [Centre for Ecology and Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster LAI 4AP (United Kingdom)], E-mail: bjho@ceh.ac.uk; Beresford, N.A.; Barnett, C.L. [Centre for Ecology and Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster LAI 4AP (United Kingdom); Fesenko, S. [International Atomic Energy Agency, 1400 Vienna (Austria)

2009-03-15

29

Semi-empirical model for heat transfer coefficient in liquid metal turbulent flow

International Nuclear Information System (INIS)

The heat transfer by forced convection in a metal liquid turbulent flow for circular ducts is analyzed. An analogy between the momentum and heat in the wall surface, is determined, aiming to determine an expression for heat transfer coefficient in function of the friction coefficient. (E.G.)

30

Mass transfer coefficients in cross-flow ultrafiltration

Usually, in concentration polarization models, the mass transfer coefficient is an unknown parameter. Also, its variation with changing experimental circumstances is in question. In the literature, many relationships can be found to describe the mass transfer coefficient under various conditions, as well as various corrections for deviating behaviour during ultrafiltration. To obtain reliable mass transfer coefficient relations directly from experimental data, two methods were tested: a metho...

Berg, G. B. Den; Ra?cz, I. G.; Smolders, C. A.

1989-01-01

31

Overall mass-transfer coefficients in non-linear chromatography

DEFF Research Database (Denmark)

In case of mass transfer where concentration differences in both phases must be taken into account, one may define an over-all mass-transfer coefficient basd on the apparent over-all concentration difference. If the equilibrium relationship is linear, i.e. in cases where a Henry´s law relationship can be applied, the over-all mass-transfer coefficient will be concentration independent. However, in mass-transfer operations, a linear equilibrium relationship is in most cases not a valid approximation wherefore the over-all mass-transfer coefficient becomes strongly concentration dependent as shown in this paper. In this case one has to discard the use of over-all mass-transfer coefficients and calculate the rate of mass transfer from the two film theory using the appropriate non-linear relationship to calculate the equilibrium ratio at the interface between the two films.

Mollerup, JØrgen; Hansen, Ernst

1998-01-01

32

Heat transfer coefficient for F.E analysis in the warm forging process

Directory of Open Access Journals (Sweden)

Full Text Available Purpose: The Purpose of this paper is to obtain suitable convection and contact heat transfer coefficient forone-time finite element analysis in the warm forging process.Design/methodology/approach: To do this, the temperature of the tool used in the operation was measured witha thermocouple and repeated finite element analysis(FEA was performed using the experimentally calculatedcontact and cooling heat transfer coefficient. Also the surface temperature of the active tool was obtained bycomparing the measurement and analysis results and finally the contact heat transfer coefficient for one-time FEAwas completed by comparing the surface temperature between the repeated FEA and one-time FEA results.Findings: The acceptable convection heat transfer coefficients are from 0.3 to 0.8N/mm/s/K and the contactheat transfer coefficient of 6~9N/mm/s/K is appropriate for the warm forging process with flow-typelubrication conditions.Practical implications: A comparison of the temperatures from the repeated and one-time analysis allows anoptimum contact heat transfer coefficient for the one time finite element analysis to be determined.Originality/value: Several studies have been conducted with different conditions such as applied pressure andkind of lubricant, but no research has been conducted concerning the convection heat transfer coefficient in thewarm forging process. Also, comparative analysis concerning the reason for difference between experimentallydetermined contact heat transfer coefficient and practically adapted one has not been conducted, yet.

S.S. Kang

2007-01-01

33

Transfer coefficients for plate fin and elliptical tube heat exchangers

International Nuclear Information System (INIS)

In order to determine transfer coefficients for plate fin and elliptical tube exchangers, mass transfer experiments have been performed using the naphthalene sublimation technique. By means of the heat-mass transfer analogy, the results can be converted to heat transfer results. The transfer coefficients were compared with those for circular tube exchangers and the comparison revealed no major differences. This is a positive outcome, since the use of elliptical tubes may reduce substantially the pressure drop, without affecting the transfer characteristics.(Author)

34

International Nuclear Information System (INIS)

Tests were performed in a transient heat transfer tunnel in which the model under test was preheated prior to allowing room temperature air to be suddenly drawn over the model. The resulting movement of isothermal contours on the model is revealed using a surface coating of thermochromic liquid crystals that display distinctive colors at particular temperatures. A video record is obtained of a temperature and time data pair for all points on the model during a single test. Experiments on a duct model are reported in which the model was preheated using a hot air stream. A manner in which initial model temperature nonuniformities could be taken into account was investigated. The duct model was also tested with a steady-state measurement technique and results were compared with the transient measurements, but recognizing that differences existed between the upstream thermal boundary conditions. The steady-state and transient measurements were shown to be consistent with predicted values. The main advantage of this transient heat transfer technique using liquid crystals is that since the test model need not be actively heated, high-resolution measurements on surfaces with complex shapes may be obtained

35

International Nuclear Information System (INIS)

This paper is described for the measurement technique for local heat transfer coefficients using a copper sensor in rod bundles with mixing vanes. A copper sensor is defined as the device to measure the convective heat transfer coefficient using constant heat flux and surface temperatures. The copper sensor consists of a cartridge heater and four pieces of thermocouple. The copper sensors located at axial positions of rod bundles are able to measure the local heat transfer coefficients at its positions. The effect of local heated and full heated of copper sensors for rod bundles is investigated using CFD analysis. The decay of local heat transfer coefficients of locally heating condition such as a copper sensor is estimated to be higher value than that of fully heating condition. The calibration curve for local heat transfer coefficients measured is presented

36

Estimation of Volumetric Mass Transfer Coefficient in Bioreactor

Directory of Open Access Journals (Sweden)

Full Text Available This study is concentrated to investigate the effects of aeration and stirring speed on the volumetric mass transfer coefficient (KLa. A dynamic technique was used in estimating KLa values in order to achieve the aim of this study.This study was done in 10L bioreactor by using two medias:-1. Dionized water2. Xanthan solution (1 g /LMoreover, the research covered a comparison between the obtained values of KLa.The Xanthan solution was used because of its higher viscosity in comparison with water. It behaves similarly to the cultivation medium when organisms are cultivated in a bioreactor. Growth of organisms in the reactor leads to a change in the viscosity of the medium which affects the mass transfer.Two variables, the effect of air flow rate (3-20 L/min and the effect of stirring speed (250-700rpm on KLa value were studied. Other parameters such as temperature, liquid volume, and stirrer shape and stirrer position were held constant; the results demonstrated an increase in KLa ? value and mass transfer with increasing stirrer speed. Thus at higher speed, better dispersion of the bubbles was obtained. Therefore, that increased the surface / volume ratio which increased the mass transfer area i.e. KLa value.

Zainab Yaquob Atiya

2012-01-01

37

A new analytic global potential energy surface describing the hydroperoxyl radical system H((sup 2)S) + O2(X (sup 3)Sigma((sup -)(sub g))) (reversible reaction) HO2 ((X-tilde) (sup 2)A'') (reversible reaction) O((sup 3)P) + O H (X (sup 2)Pi) has been fitted using the ab initio complete active space SCF (self-consistent-field)/externally contracted configuration interaction (CASSCF/CCI) energy calculations of Walch and Duchovic. Results of quasiclassical trajectory studies to determine the rate coefficients of the forward and reverse reactions at combustion temperatures will be presented. In addition, vibrational energy levels were calculated using the quantum DVR-DGB (discrete variable representation-distributed Gaussian basis) method and the splitting due to H atom migration is investigated. The material of the proposed presentation was reviewed and the technical content will not reveal any information not already in the public domain and will not give any foreign industry or government a competitive advantage.

Dateo, Christopher E.; Arnold, James O. (Technical Monitor)

1994-01-01

38

A method of measuring local heat and mass transfer coefficients based on the wet-bulb temperature

International Nuclear Information System (INIS)

A new technique for measuring convective heat and mass transfer coefficients using the analogy between heat and mass transfer is presented. The method only requires measurements of free stream and surface temperatures and an imposed heat flux. Comparisons one made between heat transfer coefficients measured by this technique and those reported in the literature for similar convective situations

39

International Nuclear Information System (INIS)

In this study, we aimed to realize a parametric determination of the convective heat transfer coefficient of a gasoline engine on both the in-cylinder and jacket sides. The combustion products have been determined as a function of excess air coefficient. Cylinder temperature and pressure have been calculated with a simplistic model based on the First Law of Thermodynamics. The in-cylinder heat transfer coefficient is evaluated by using two different expressions; one a specific form of Annand's equation and the other the Woschni equation. Newton's convective heat transfer equation has been utilized to obtain the heat transfer coefficient between the engine block and the cooling water. This process is based on some temperature measurements at various locations in the cooling space, as the distance between the tip of the temperature sensor and the inner cylinder surface is varied for each location. We determined values of both coefficients for various engine parameters

40

Gas surface interactions and satellite drag coefficients

Information on gas-surface interactions in orbit has accumulated during the past 35 years. The important role played by atomic oxygen adsorbed on satellite surfaces has been revealed by the analysis of data from orbiting mass spectrometers and pressure gauges. Data from satellites of special design have yielded information on the energy accommodation and angular distributions of molecules reemitted from satellite surfaces. Consequently, it is now possible to calculate satellite drag coefficients from basic physical principles, utilizing parameters of gas-surface interactions measured in orbit. The results of such calculations are given. They show the drag coefficients of four satellites of different compact shapes in low-earth orbit with perigee altitudes in the range from about 150 to 300 km, where energy accommodation coefficients and diffuse angular distributions have been measured. The calculations are based on Sentman's analysis of drag forces in free-molecular flow. His model incorporates the random thermal motion of the incident molecules, and assumes that all molecules are diffusely reemitted The uncertainty caused by the assumption of diffuse reemission is estimated by using Schamberg's model of gas-surface interaction, which can take into account a quasi-specular component of the reemission. Such a quasi-specular component is likely to become more important at higher altitudes as the amount of adsorbed atomic oxygen decreases. A method of deducing accommodation coefficients and angular distributions at higher altitudes by comparing the simultaneous orbital decay of satellites of different shapes at a number of altitudes is suggested. The purpose is to improve thermospheric measurements and models, which are significantly affected by the choice of drag coefficients.

Moe, Kenneth; Moe, Mildred M.

2005-07-01

41

Heat transfer coefficient for F.E analysis in the warm forging process

Purpose: The Purpose of this paper is to obtain suitable convection and contact heat transfer coefficient forone-time finite element analysis in the warm forging process.Design/methodology/approach: To do this, the temperature of the tool used in the operation was measured witha thermocouple and repeated finite element analysis(FEA) was performed using the experimentally calculatedcontact and cooling heat transfer coefficient. Also the surface temperature of the active tool was obtained bycom...

Kang, S. S.; Kang, J. H.; Lee, K. O.

2007-01-01

42

Heat transfer coefficient determination for flow boiling in vertical and horizontal minichannels

The paper presents the results of boiling heat transfer research during FC-72 laminar flow along a minichannel of 1 mm depth, positioned vertically and horizontally, with an enhanced heating surface. One glass pane allows to determine the temperature of the heating wall by liquid crystal thermography. Calculations are aimed at the evaluation of one- and two-dimensional heat transfer approaches to determine the local heat transfer coefficient. In the one-dimensional approach only the direction...

Piasecka Magdalena; Maciejewska Beata

2014-01-01

43

Heat transfer coefficient in serpentine coolant passage for CCDTL

International Nuclear Information System (INIS)

A series of heat transfer experiments were conducted to refine the cooling passage design in the drift tubes of a coupled cavity drift tube linac (CCDTL). The experimental data were then compared to numerical models to derive relationships between heat transfer rates, Reynold's number, and Prandtl number, over a range of flow rates. Data reduction consisted of axisymmetric finite element modeling where the heat transfer coefficients were modified to match the experimental data. Unfortunately, the derived relationship is valid only for this specific geometry of the test drift tube. Fortunately, the heat transfer rates were much better (approximately 2.5 times) than expected

44

Experimental evaluation of heat transfer coefficients between radiant ceiling and room

DEFF Research Database (Denmark)

The heat transfer coefficients between radiant surfaces and room are influenced by several parameters: surfaces temperature distributions, internal gains, air movements. The aim of this paper is to evaluate the heat transfer coefficients between radiant ceiling and room in typical conditions of occupancy of an office or residential building. Internal gains were therefore simulated using heated cylinders and heat losses using cooled surfaces. Evaluations were developed by means of experimental tests in an environmental chamber. Heat transfer coefficient may be expressed separately for radiation and convection or as one total parameter, but this choice may lead to different considerations about thermal performance of the system. In order to perform correct evaluations, it is therefore extremely important to use the proper reference temperature. The obtained values confirm tendencies found in the literature, indicating limitations and possibilities of radiant ceiling systems improvement.

Causone, Francesco; Corgnati, Stefano P.

2009-01-01

45

Energy Technology Data Exchange (ETDEWEB)

The efficiency of energy utilization within coal-liquefaction process is of major significance to the commercialization of the process. Heat exchange equipment is also one of the major economic investments in new plants. Consequently, reliable heat transfer data are required for the economical design of heat exchange equipment. Since accurate heat transfer coefficients of coal slurries, especially with a gas phase present, cannot be accurately calculated from known physical data for the operational conditions found in the coal-liquefaction process, experimentally determined heat transfer coefficients under actual process conditions are needed. A liquefaction heat-transfer-coefficient measurement test unit for a nominal one-half-ton-per-day coal slurry was constructed, calibrated, and operated at ANL. This test unit was built to determine heat transfer coefficients needed for design of feed-heat and effluent-heat exchangers used in coal-liquefaction processes. The heat-transfer test module was substituted for the preheater and reactor used in the normal coal-liquefaction process. The heat transfer coefficient can be evaluated for the heat transfer between the three-phase feed and effluent fluids in turbulent flow and a heated or cooled stainless steel surface. A description is presented of the unit and its capabilities, calibration procedures and results, and preliminary operation and data analysis. Recommendations are made that should improve accuracy and ease of operation and data analysis of the test unit.

Mulcahey, T.P.; Lo, R.N.K.; Bump, T.R.; Mulcahey, M.E.; Fischer, J.; Cannon, T.F.; Brock, R.E.; Wilson, W.I.; Bowyer, D.

1979-06-01

46

DEFF Research Database (Denmark)

This paper reports the results of an investigation, based on fundamental fluid dynamics and mass transfer theory, carried out to obtain a general understanding of ammonia mass transfer from an emission surface. The effects of airflow and aqueous ammonium solution temperature on ammonia mass transfer are investigated by using computational fluid dynamics (CFD) modeling and by a mechanism modeling using dissociation constant and Henry's constant models based on the parameters measured in the experiments performed in a wind tunnel. The validated CFD model by experimental data is used to investigate the surface concentration distribution and mass transfer coefficient at different temperatures and velocities for which the Reynolds number is from 1.36 × 104 to 5.43 × 104 (based on wind tunnel length). The surface concentration increases as velocity decreases and varies greatly along the airflow direction on the emission surface. The average mass transfer coefficient increases with higher velocity and turbulence intensity. However, the mass transfer coefficient estimated by CFD simulation is consistently larger than the calculated one by the method using dissociation constant and Henry's constant models. In addition, the results show that the liquid-air temperature difference has little impact on the simulated mass transfer coefficient by CFD modeling, whereas the mass transfer coefficient increases with higher liquid temperature using the other method under the conditions that the liquid temperature is lower than the air temperature. Although there are differences of mass transfer coefficients between these two methods, the mass transfer coefficients determined by these two methods are significantly related.

Rong, Li; Nielsen, Peter V.

2010-01-01

47

Determining Overall Heat Transfer Coefficient and Shading Coefficient of Doubleskin Facade

The overall heat transfer coefficient (U?value) and the shading coefficient (SC?value) are substantial properties of double?skin façade. They are importantly required for energy?use estimation, particularly for heat load calculation of the air?conditioning system. The determination of the U?value and the SC?value of double?skin façade was done by numerical simulation employing FORTRAN for the one?year duration. By utilizing the least square method, the equat...

Mulyadi, Rosady

2011-01-01

48

3D measurements and numerical computations of heat transfer coefficients on spheres in an array

International Nuclear Information System (INIS)

The focus of this paper is to investigate the heat transfer coefficient distributions on the spheres in a three-dimensional (3-D) array. This arrangement is an essential geometry in pebble bed reactors (PBRs) that are generally adopted in the chemical and the nuclear engineering. Understanding the thermal-hydraulic characteristics of the pebbles is important for the design of reactors. Using the transient liquid crystal technique, an experimental device is set up to measure the transient wall temperature on the surface of spheres arranged in an array, as heated air flows across. Based on the measured temperature distributions on the sphere surfaces, the heat transfer coefficient can be derived. A 3-D transient computational fluid dynamics (CFD) model with different turbulence models is also developed and assessed using the measured heat transfer coefficient distributions. Five turbulence models are considered in this study: the standard k-? low-Re, AKN k-? low-Re, standard k-? two-layer, realizable k-? two-layer, and v2-bar-f turbulence models, respectively. Comparisons of the predicted heat transfer coefficient distributions and those in the experimental data reveal that the v2-bar-f turbulence model is more suitable for simulating flow and heat transfer characteristics in a sphere array. In addition, the beneficial effect of Rein on the heat transfer coefficient distribution is captured by both experimental measurements and CFD pth experimental measurements and CFD predictions. (authors)

49

Mass transfer coefficients determination from linear gradient elution experiments.

A procedure to estimate mass transfer coefficients in linear gradient elution chromatography is presented and validated by comparison with experimental data. Mass transfer coefficients are traditionally estimated experimentally through the van Deemter plot, which represents the HETP as a function of the fluid velocity. Up to now, the HETP was obtained under isocratic elution conditions. Unfortunately, isocratic elution experiments are often not suitable for large biomolecules which suffer from severe mass transfer hindrances. Yamamoto et al. were the first to propose a semi-empirical equation to relate HETPs measured from linear gradient elution experiments to those obtained under isocratic conditions [7]. Based on his pioneering work, the approach presented in this work aims at providing an experimental procedure supported by simple equations to estimate reliable mass transfer parameters from linear gradient elution chromatographic experiments. From the resolution of the transport model, we derived a rigorous analytical expression for the HETP in linear gradient elution chromatography. PMID:25497582

Pfister, David; Morbidelli, Massimo

2015-01-01

50

Boiling heat transfer intensity on small-size surface

Dependence of heat-release surface of heat carrier (water and ethanol) characteristic size, boundary conditions and thermophysical properties on boiling heat transfer intensity on small-size surface was investigated. Criterion equation for boiling heat transfer coefficients on small-size surface was obtained.

Alekseik O. S.; Yu, Kravets V.; Kopchevskaya I. A.

2012-01-01

51

Boiling heat transfer intensity on small-size surface

Directory of Open Access Journals (Sweden)

Full Text Available Dependence of heat-release surface of heat carrier (water and ethanol characteristic size, boundary conditions and thermophysical properties on boiling heat transfer intensity on small-size surface was investigated. Criterion equation for boiling heat transfer coefficients on small-size surface was obtained.

Alekseik O. S.

2012-02-01

52

Measurement of the convective heat-transfer coefficient

We propose an experiment for investigating how objects cool down toward the thermal equilibrium with its surrounding through convection. We describe the time dependence of the temperature difference of the cooling object and the environment with an exponential decay function. By measuring the thermal constant tau, we determine the convective heat-transfer coefficient, which is a characteristic constant of the convection system.

Conti, Rosaria; Gallitto, Aurelio Agliolo; Fiordilino, Emilio

2014-01-01

53

Estimation of convective heat transfer coefficients in industrial steam turbines

Energy Technology Data Exchange (ETDEWEB)

Steam turbines are increasingly being used in industries for duties other than base load operations, where fast start-ups, rapid load changes, and frequent shutdowns are involved. Generally, industrial steam turbines operate with constant inlet steam parameters and are partial admission turbines having the first turbine stage as an impulse stage and the subsequent turbine stages as reaction stages on drum-type rotors. During start-up, as control valves open, steam is admitted and passes through impulse blading, wheel chamber, and through the subsequent reaction stages. The turbine outer casing is horizontally split and the parting plane flanges have relatively thick sections. To limit thermal stresses which arise due to temperature differences in outer casings and rotors, the steam flow has to be increased gradually. The rate at which the steam flow is to be increased depends on the efficiency of heat transfer, i.e., the heat transfer coefficient, and hence knowledge of inside heat transfer coefficient is essential. The high heat transfer coefficients, h, at the beginning of cold start are attributable to condensation of steam at initial stages. The value of h decreased with lapse of time, and also its variation reduced considerably over time. Further, the h value varies more with location rather than with lapse of time. The variations observed in h show the complexity of heat transfer process and also bring out the fact that semi-empirical formulas, such as Gazley`s (1958), are not accurate for application in steam turbines. More studies need to be conducted on models of steam turbines to generate adequate data based on which a new correlation for the heat transfer coefficient h for start-up phase of operation could be proposed.

Adinarayana, N. [Bharat Heavy Electricals Ltd., Hyderabad (India); Sastri, V.M.K. [Indian Inst. of Tech., Madras (India). Heat Transfer Lab.

1996-05-01

54

Energy Technology Data Exchange (ETDEWEB)

The growth rate of a crystal in a supersaturated solution is limited by both reaction kinetics and the local concentration of solute. If the local mass transfer coefficient is too low, concentration of solute at the crystal-solution interface will drop below saturation, leading to a defect in the growing crystal. Here, mass transfer coefficients are calculated for a rotating crystal growing in a supersaturated solution of potassium diphosphate (KDP) in water. Since mass transfer is difficult to measure directly, the heat transfer coefficient of a scale model crystal in water is measured using temperature-sensitive paint (TSP). To the authors' knowledge this is the first use of TSP to measure temperatures in water. The corresponding mass transfer coefficient is then calculated using the Chilton- Colburn analogy. Measurements were made for three crystal sizes at two running conditions each. Running conditions include periodic reversals of rotation direction. Heat transfer coefficients were found to vary significantly both across the crystal faces and over the course of a rotation cycle, but not from one face to another. Mean heat transfer coefficients increased with both crystal size and rotation rate. Computed mass transfer coefficients were broadly in line with expectations from the full-scale crystal growth experiments. Additional experiments show that continuous rotation of the crystal results in about a 30% lower heat transfer compared to rotation with periodic reversals. The continuous rotation case also shows a periodic variation in heat transfer coefficient of about 15%, with a period about 1/20th of the rotation rate.

Bell, J H; Hand, L A

2005-04-21

55

In this paper, the research progress of the interfacial heat transfer in high pressure die casting (HPDC) is reviewed. Results including determination of the interfacial heat transfer coefficient (IHTC), influence of casting thickness, process parameters and casting alloys on the IHTC are summarized and discussed. A thermal boundary condition model was developed based on the two correlations: (a) IHTC and casting solid fraction and (b) IHTC peak value and initial die surface temperature. The ...

Cao Yongyou; Guo Zhipeng; Xiong Shoumei

2014-01-01

56

Experimental study of heat transfer coefficient in exhaust pipe

Energy Technology Data Exchange (ETDEWEB)

Exhaust gas from spark-ignition engines are one of the main sources of atmospheric pollution, especially in urban areas where traffic is dense. In order to comply with increasingly restrictive standards, the automobile industry must develop cleaning devices such as catalytic converters and particle filters. This experimental study examined the influence of a flow's intermittent character on the heat transfer coefficient within a bent exhaust pipe. A device was developed to estimate the heat transfer coefficient on the right channel or the bent portion of the exhaust line in a periodic intermittent flowing regime, as well as in a steady regime. The goal was to build a database of coefficient and augmentation factors (CAF) for the simulation of heat transfer in a variety of basic geometries found in spark-ignition engine exhaust lines. Parietal heat flux and wall temperature were estimated from temperature measurements using the Beck inverse algorithm. Estimates of gas temperature were derived by Tagawa's method, using temperature measurements in the intermittent gas flow with a two thermocouples probe. The results showed that intermittency intensifies heat transfer in the straight pipe as well as in the bent pipe. The augmentation factor within the straight pipe depends on the frequency. Peak intensification depends on the mechanical frequency of resonance on the tube. The augmentation factor for the bent pipe was found to be lower than in the straight pipe, and did not depend on the frequency. 22 refs., 7 figs.

Bourouga, B.; Bouloc, F. [Nantes Univ., Nantes (France). LTN/UMR; Anthoine, P. [Renault, Rueil Malmaison (France). Direction de la Mecanique

2010-07-01

57

Transfer coefficients of radionuclides from feed to livestock products

International Nuclear Information System (INIS)

The accumulation of data on radionuclide transfer are poor in Japan and those are limited to 90Sr, 137Cs and 131I released from the previous atomic bomb experiments. However, in Europe, intensive studies on environment RI level which affects the restriction of the intake for meats and milk products have been made as the measures against the environment radioactivity due to Chernobyl accident. The transfer coefficients of radionuclides to meats and milk products were estimated on a basis of the data published in the Science of the Total Environment vol.85(1989), Oxford University and CEC Radiation Protection, EUR 12608 EN, Luxembourg, 1990 in addition to the data on Exclusion of Radioactivity from foods, Environment Parameter, series No. 4. On the other hand, the transfer coefficients for Japanese were estimated using the concerned data from published reports and the environment radioactivity data reported by national and local government bodies. In this book, many new data of transfer coefficient are presented in tables along with the previous data collected by international nuclear energy agencies and respective national facilities concerned. (M.N.)

58

The heat transfer coefficient over the surface of a pedestal with fillet radii has been measured using thermochromic liquid crystals and the transient heat transfer method. The tests were performed at engine representative Reynolds numbers for a geometry typical of those used in turbine blade cooling systems. The heat conduction process that occurs in the engine was subsequently modeled numerically with a finite element discretization of the solid pedestal. The measured heat transfer coeffici...

Wang, Z.; Ireland, Pt; Jones, Tv

1993-01-01

59

Directory of Open Access Journals (Sweden)

Full Text Available An adequate supply of oxygen in aqueous solution becomes the focal point of interest when it comes to the growth and maintenance of most aerobic microbial and tissue cultures used for biochemical and pharmaceutical production. Unfortunately, oxygen mass transfer to the growth medium serves as a major growth limiting factor owing to it’s low solubility in aqueous solutions. (Approximately 10 ppm at ambient temperature and pressure. The reaction rate is such that as oxygen enters the liquid phase, it is immediately consumed to oxidize the sulfite so that the rate of oxidation equals that of the oxygen transfer. Oxygen must at first be transferred from gas bulk through a series of steps onto the surfaces of cells before it can be utilized. Therefore the enhancement of gas-liquid mass transfer during aerobic cultures and fermentations is always put into priority. The present study involves using the ‘Central Composite Design’, a statistical technique to determine the parametric conditions for the optimum volumetric mass transfer coefficient in a pilot scale (40L fermenter. The optimum volumetric mass transfer coefficient was found to lie outside the range of parameters studied and analytical expressions was obtained to predict the volumetric mass transfer coefficients for the parameter ranges studied using response surface methodology. The analytical expression was addressed to be significantly valid based on ANOVA results.

Rajesh Ghosh* and Sounak Bhattacherjee

2013-04-01

60

Uncertainty of evaluations of flow film boiling heat transfer coefficient

International Nuclear Information System (INIS)

The results of evaluations of the heat transfer coefficient (?s) for the flow film boiling (FFB) region received by two approaches, which are complemented each other are discussed here. In particular, they are as follows: 1) using empirical or semiempirical correlations, 2) developing the look-up tables (LUT). There is a need to distinguish two FFB heat transfer regime, such as 1) the post-dryout (PDO) heat transfer and 2) before critical heat flux (CHF) heat transfer. A new version of the LUT for ?s is presented at forced water flow in long tubes uniformly heated. It covers the following range of parameters: pressure 0.1/20 MPa; mass flux 250/3000 kg/m2·s; quality (-0.2)/2.2; heat flux 0.2/1.0 MW/m2; tube diameter 10 mm. The values of the FFB heat transfer coefficient in the LUT are marked by different methods depending on the used calculation method. Four methods were applied to develop the LUT for ?s, namely: 1) averaging experimental data, 2) calculations on the base of the Sergeev model, 3) using data from the LUT developed by Leung L. et al. (1997), 4) using both interpolation and extrapolation beyond the range of experimental data and theoretical evaluations. The calculated errors of the ?s values were obtained by comparison the LUT data with the experimental data stored in the database of the IPPE Thermophysical Data Center. (author)

61

Evaluation of heat transfer coefficient at direct contact condensation of cold water and steam

International Nuclear Information System (INIS)

The estimation of heat transfer coefficient at the direct contact condensation of cold water and steam is very hard, since the phenomena is unsteady and the interface moves complicately. Present research shows the heat transfer coefficient evaluated in the simulation analyses and experiments on the phenomena related to the Loss-of-Coolant Accident of light water reactors. At chugging the heat transfer coefficient was up to 106W/m2K. At condensation oscillation it was between 105-106 W/m2K. At jet region of cold water injected into steam flow it was around 105 W/m2K, and the surface of stratified flow it was between 104-5 x 104 W/m2K. (author)

62

Energy Technology Data Exchange (ETDEWEB)

An important task for the hydrogen isotopes separation by cryogenic distillation is to establish the shape and dimension of the column condenser and boiler in order to obtain the desired load and separation for the distillation column. In the paper we present the set-up experimental values for the heat transfer coefficient on various types of condensers. The heat transfer coefficients were determined by measurements on liquid hydrogen flow-rate condensed on the cold surface and temperature drop between the cooling liquid and the condensate. The experiments were made for different vapor pressures and certain temperatures of the cooling liquid from the condenser. As results we determined the condensation heat transfer coefficients for different shapes and geometries of the condensers as a function of the condensate film temperature drop. (authors)

Cristescu, I.; Zamfirache, M. [Institute of Cryogenics and Isotope Separations, Valcea (Romania)

2000-06-01

63

Measurement and modeling of interface heat transfer coefficients

International Nuclear Information System (INIS)

The results of preliminary work on the modeling and measurement of the heat transfer coefficients of metal/mold interfaces is reported. The system investigated is the casting of uranium in graphite molds. The motivation for the work is primarily to improve the accuracy of process modeling of prototype mold designs at the Los Alamos Foundry. The evolution in design of a suitable mold for unidirectional solidification is described, illustrating the value of simulating mold designs prior to use. Experiment indicated a heat transfer coefficient of 2 kW/m2/K both with and without superheat. It was possible to distinguish between solidification due to the mold and that due to radiative heat loss. This permitted an experimental estimate of the emissivity, epsilon = 0.2, of the solidified metal

64

INFLTB, Dosimetric Mass Energy Transfer and Absorption Coefficient

International Nuclear Information System (INIS)

1 - Description of program or function: INFLTB calculates mass energy transfer and mass energy absorption coefficients between 1 keV and 100 MeV for 29 elements and 14 mixtures and compounds of general dosimetric interest. Elements: hydrogen, helium, lithium, beryllium, carbon, graphite, nitrogen, oxygen, fluorine, neon, aluminum, silicon, sulfur, argon, calcium, titanium, iron, copper, germanium, krypton, molybdenum, tin, iodine, barium, gadolinium, tungsten, platinum, uranium, silver, lead. Mixtures and compounds: A-150 tissue-equivalent plastic, adipose tissue (ICRP), adipose tissue (ICRU, 1986), air, dry (near sea level), bone, compact (ICRU), bone, cortical (ICRP), bone, cortical (ICRU, 1986), calcium fluoride, calcium fluoride, ferrous sulfate (standard Fricke) dosimeter solution, ferrous sulfate ('super' Fricke) dosimeter solution, glass, borosilicate ('Pyrex', corning 7740), lithium fluoride, muscle, skeletal (ICRP), muscle, skeletal (ICRU, 1986), muscle, striated (ICRU), polyethylene, polymethyl methacrylate, 'Lucite', 'Perspex', 'Plexiglas', polystyrene, polytetrafluoroethylene, 'Teflon', water, liquid, water vapor, Te gas(methane). 2 - Method of solution: The mass energy transfer coefficient is calculated from the sum of the interaction cross sections (atomic photo effect, Compton scattering, and pair plus triplet production) multiplied by their respective average fractions of energy transferred to electrons and positrons. The mass energy absorption coefficitrons. The mass energy absorption coefficient is the product of the mass energy transfer coefficient and 1 - G, where G is the average fraction of the secondary electron (or positron) kinetic energy that is spent in Bremsstrahlung production and in-flight positron annihilation. 3 - Restrictions on the complexity of the problem: Photon source energies are limited to values between 1 keV and 100 MeV. Radiation yield files are available only for 29 element and 14 compounds and mixtures

65

Water mist effect on heat transfer coefficient in cooling of casting die

Directory of Open Access Journals (Sweden)

Full Text Available This project is showing investigation results of heat transfer process between cast iron die and environment during cooling of die in the temperature range 600÷100 C with compressed air, spray water and water mist streamed under pressure 0.35 0.45 MPa in air jet0.3 0.4 MPa .At the paper are shown results of cooling die’s flat wall using open cooling system. The temperature gradient was presented at die’s wallthickness and calculated thermal curve for cooling surface. The calculation results of heat transfer coefficient ? were presented between die and researched cooling factors and also mathematical models of ? coefficient depending on surface temperature. Revealed that coefficient ? has the biggest value’s range for die cooling with water mist under pressure 0.3/0.35 MPa.

R. W?adysiak

2008-10-01

66

Modeling the Effect of Internal Convection Currents on Heat Transfer Coefficient of Liquid Foods

The internal convection currents generated during the cooling process affect convective heat transfer coefficient from the surface of the container, these convection currents may increase the effective value of the surface film conductance (h). Therefore, in such situation the Nu-Re correlations, which are generally used to predict h-values, may not yield realistic results. In the present work, this effect has been investigated by using the empirical correlation developed through Temperature-...

SAJID ALI; RASHID ALI

2013-01-01

67

Resonant charge transfer at dielectric surfaces

We report on the theoretical description of secondary electron emission due to resonant charge transfer occurring during the collision of metastable nitrogen molecules with dielectric surfaces. The emission is described as a two step process consisting of electron capture to form an intermediate shape resonance and subsequent electron emission by decay of this ion, either due to its natural life time or its interaction with the surface. The electron capture is modeled using the Keldysh Green's function technique and the negative ion decay is described by a combination of the Keldysh technique and a rate equation approach. We find the resonant capture of electrons to be very efficient and the natural decay to be clearly dominating over the surface-induced decay. Secondary electron emission coefficients are calculated for aluminum oxide, magnesium oxide, silicon oxide, and diamond at several kinetic energies of the projectile. With the exception of magnesium oxide the coefficients turn out to be of the order of...

Marbach, Johannes; Fehske, Holger

2012-01-01

68

A correlation to the heat transfer coefficient in nucleate boiling

International Nuclear Information System (INIS)

Nucleate boiling heat transfer is a complex phenomenon, making the development of a correlation for the heat transfer coefficient rather cumbersome due to the number of physical parameters involved in it. Some authors have followed a pragmatic approach to the problem by correlating the heat transfer coefficient in terms of reduced primitive properties. Two of the most knowledgeable authors who have followed this approach are Gorenflo and Cooper. Comparisons have been performed among results from the correlations proposed by these researchers and experimental results obtained elsewhere for refrigerants R-11, R-113 and R-114. These comparisons have shown that Cooper's correlation is best fitted for halocarbon refrigerants. The correlation proposed by Gorenflo ads the difficulty of including a numerical factor specific for each fluid. Leiner modified Gorenflo's correlation to determine the numerical factor as a function of known physical parameters of the fluid. In present study, the form of this function has been investigated for halocarbon refrigerants. The obtained correlation is written in terms of the following parameters: reduced pressure, eccentric and compressibility factors at the critical state, and a dimensionless specific heat of the vapor phase. The correlation compares well with experimental results. (author)

69

Transfer coefficients of radionuclides secreted in milk of dairy cows

International Nuclear Information System (INIS)

This study simulated experimentally the transfer of radionuclides to milk of dairy cows on a worst-case situation using various radionuclides known to emanate from nuclear power stations and which have been detected on particulates. Two lactating Holstein cows were administered orally one gelatin capsule containing 10 radionuclides in water-soluble form per day for 14 consecutive days. Milk samples were collected and aliquots analyzed in a germanium lithium-drifted detector coupled to a 2048-multichannel gamma-ray analyzer to measure small amounts of complex mixtures of radionuclides. The transfer coefficients of the radionuclides were calculated when their secretion in milk reached or approached a plateau of concentration. The radionuclides and their transfer coefficients to milk were: chromium51 less than 0.01%; manganese54 0.033 +- 0.005%; cobalt60 0.01 +- 0.002%; iron59 0.0048 +- 0.002%; zinc65 0.31 +- 0.07%; selenium75 0.29 +- 0.1%; antimony125 0.011 +- 0.003%; iodine131 0.88 +- 0.05%; and cesium137 0.79 +- 0.08%

70

Modeling the Gas Transfer Coefficient and Gas Fluxes in Stratified Lakes

Lakes and reservoirs are now recognized as significant sources of climatically-active trace gases to the atmosphere. Estimates will be improved if fluxes are computed using gas transfer coefficients which take into account the turbulence at the air-water interface which moderates the transport rather than the wind-only based values which are typically used. Here, in an analysis of eddy covariance results from a weakly stratified lake, we demonstrate how buoyancy flux, that is, heat loss or heat gain, moderates changes in the magnitude of the gas transfer coefficient, k600, during low to moderate winds. Our analysis shows that i) k600 depends on wind speed and buoyancy flux ?, ii) higher values of k600 occur during windy periods with surface cooling than with surface heating, iii) under overnight low wind conditions k600 is more dependent on ? than wind speed, iv) not only the meteorological conditions at the time of measurement but also the inertia within the lake determine k600. Eddy covariance estimates of k600 compare well with predictions of k600 using a surface renewal model for which the inputs are wind speed and ?. Modeling of green house gas emissions will be improved via inclusion of buoyancy flux and wind shear in the gas transfer coefficient as well as consideration of controls on the frequency of events which transport waters with higher gas concentrations to surface waters. Regional and global fluxes of greenhouse gases from lakes may be considerably larger than current estimates.

MacIntyre, S.; Jonsson, A.; Jansson, M.; Aberg, J.; Turney, D. E.; Emery, B. M.; Simons, R. D.; Miller, S. D.

2010-12-01

71

DEFF Research Database (Denmark)

One of the operational challenges associated with membrane bioreactors (MBRs) is the fouling of the membranes. In tubular side-stream MBRs, fouling reduction can be achieved through controlling the hydrodynamics of the two-phase slug flow near the membrane surface. The two-phase slug flow induces higher shear stresses near the membrane surface, which generate high mass transfer coefficients from the surface to the bulk region. However, measuring the mass transfer coefficient is difficult in complex heterogeneous mixtures like activated sludge and existing techniques (e.g. electrochemical methods) cannot be applied directly. As an alternative, in this work, a multidisciplinary approach was selected, by exploiting dimensionless analysis using the Sherwood number. Mass transfer coefficients were measured at various superficial velocities of gas and liquid flow in a tubular system. Due to the variability of the mass transfer coefficient obtained for each experimental condition, the results were compiled into, mass transfer coefficient histograms (MTH) for analysis. A bimodal MTH was observed, with one peak corresponding to the mass transfer induced by the liquid flow, and the other peak induced by the gas flow. It was noted that coalescence of bubbles affects the MTH. Coalescence increased the “width” of the peaks (i.e. the estimate of the variability of the mass transfer coefficient) and the height of the peak (i.e. amount of time that a mass transfer coefficient of a given value is maintained). A semi-empirical relationship based on the Lévêque relationship for the Sherwood number (mass transfer coefficient) was formulated for the laminar regime. A test case comparison between water and activated sludge was performed based on full-scale airlift MBR operational conditions. It was found that the Sherwood number in the non-Newtonian case is 8% higher than that in the Newtonian case.

Ratkovich, Nicolas Rios; Berube, P.R.

2011-01-01

72

Confirmation of selected milk and meat radionuclide transfer coefficients. Progress report

International Nuclear Information System (INIS)

The objectives are to determine transfer coefficients to milk, beef and chicken of four radionuclides for which transfer coefficients were either indetermined or based upon secondary data. The radionuclides are 99Mo, 99Tc, 140Ba, and 131Te. The transfer coefficient for 133I to eggs was also determined, because again only limited data was available in the literature

73

Efficiency analysis of straight fin with variable heat transfer coefficient and thermal conductivity

Energy Technology Data Exchange (ETDEWEB)

In this study, one type of applicable analytical method, differential transformation method (DTM), is used to evaluate the efficiency and behavior of a straight fin with variable thermal conductivity and heat transfer coefficient. Fins are widely used to enhance heat transfer between primary surface and the environment in many industrial applications. The performance of such a surface is significantly affected by variable thermal conductivity and heat transfer coefficient, particularly for large temperature differences. General heat transfer equation related to the fin is derived and dimensionalized. The concept of differential transformation is briefly introduced, and then this method is employed to derive solutions of nonlinear equations. Results are evaluated for several cases such as: laminar film boiling or condensation, forced convection, laminar natural convection, turbulent natural convection, nucleate boiling, and radiation. The obtained results from DTM are compared with the numerical solution to verify the accuracy of the proposed method. The effects of design parameters on temperature and efficiency are evaluated by some figures. The major aim of the present study, which is exclusive for this article, is to find the effect of the modes of heat transfer on fin efficiency. It has been shown that for radiation heat transfer, thermal efficiency reaches its maximum value.

Sadri, Somayyeh; Raveshi, Mohammad Reza; Amiri, Shayan [K.N. Toosi University of Technology, Tehran (Iran, Islamic Republic of)

2012-04-15

74

Efficiency analysis of straight fin with variable heat transfer coefficient and thermal conductivity

International Nuclear Information System (INIS)

In this study, one type of applicable analytical method, differential transformation method (DTM), is used to evaluate the efficiency and behavior of a straight fin with variable thermal conductivity and heat transfer coefficient. Fins are widely used to enhance heat transfer between primary surface and the environment in many industrial applications. The performance of such a surface is significantly affected by variable thermal conductivity and heat transfer coefficient, particularly for large temperature differences. General heat transfer equation related to the fin is derived and dimensionalized. The concept of differential transformation is briefly introduced, and then this method is employed to derive solutions of nonlinear equations. Results are evaluated for several cases such as: laminar film boiling or condensation, forced convection, laminar natural convection, turbulent natural convection, nucleate boiling, and radiation. The obtained results from DTM are compared with the numerical solution to verify the accuracy of the proposed method. The effects of design parameters on temperature and efficiency are evaluated by some figures. The major aim of the present study, which is exclusive for this article, is to find the effect of the modes of heat transfer on fin efficiency. It has been shown that for radiation heat transfer, thermal efficiency reaches its maximum value

75

Evaluation of heat transfer coefficient at direct contact condensation of cold water and steam

International Nuclear Information System (INIS)

The research shows the heat transfer coefficient evaluated experimentally by assuming simple interface-shapes for complicated surface or by comparing the results of numerical analyses with the data of experiments related to LOCAs of LWRs. At chugging, the heat transfer coefficient reached up to 2 MW//m2 K). At condensation oscillation, it was between 105-106 W(m2 K). At jet region of cold water injected into steam flow in a pipe or stationary stream in a vessel, it was around 2X105 W/(m2 K), and at the surface of stratified flow, it was between 3x103-3x104 W/(m2 K). (orig./DG)

76

An experimental investigation into the performance of gas turbine engine component external cooling fins has been carried out using the transient liquid crystal technique in a low speed wind tunnel. Full fin surface local heat transfer coefficient distributions have been determined. Measurements with this level of resolution are not previously reported in the literature. In addition to the flat continuous fins, interrupted and corrugated fin geometries have been tested. These geometries enhan...

Robertson, Aj; Neely, Aj; Ireland, Pt; Harper, Lr

1997-01-01

77

Heat transfer coefficient determination for flow boiling in vertical and horizontal minichannels

Directory of Open Access Journals (Sweden)

Full Text Available The paper presents the results of boiling heat transfer research during FC-72 laminar flow along a minichannel of 1 mm depth, positioned vertically and horizontally, with an enhanced heating surface. One glass pane allows to determine the temperature of the heating wall by liquid crystal thermography. Calculations are aimed at the evaluation of one- and two-dimensional heat transfer approaches to determine the local heat transfer coefficient. In the one-dimensional approach only the direction of the flow in the channel is considered. In the two-dimensional approach the inverse problem in the heating wall and the direct problem in the glass barrier were solved by the finite element method with Trefftz functions as shape functions (FEMT. The developed flow boiling area was studied. Heat transfer coefficient values obtained for the horizontal minichannel were higher than those obtained for the vertical one. When the heat flux supplied to heating wall grows, the share of gas-phase increases leading to the heat transfer coefficient decreases. The same courses of the experiment were observed for the two applied methods, but the results obtained in the one-dimensional approach are considerably higher than in the two-dimensional one. One-dimensional approach seems to be less sensitive to measurement errors.

Piasecka Magdalena

2014-03-01

78

Heat transfer coefficient determination for flow boiling in vertical and horizontal minichannels

The paper presents the results of boiling heat transfer research during FC-72 laminar flow along a minichannel of 1 mm depth, positioned vertically and horizontally, with an enhanced heating surface. One glass pane allows to determine the temperature of the heating wall by liquid crystal thermography. Calculations are aimed at the evaluation of one- and two-dimensional heat transfer approaches to determine the local heat transfer coefficient. In the one-dimensional approach only the direction of the flow in the channel is considered. In the two-dimensional approach the inverse problem in the heating wall and the direct problem in the glass barrier were solved by the finite element method with Trefftz functions as shape functions (FEMT). The developed flow boiling area was studied. Heat transfer coefficient values obtained for the horizontal minichannel were higher than those obtained for the vertical one. When the heat flux supplied to heating wall grows, the share of gas-phase increases leading to the heat transfer coefficient decreases. The same courses of the experiment were observed for the two applied methods, but the results obtained in the one-dimensional approach are considerably higher than in the two-dimensional one. One-dimensional approach seems to be less sensitive to measurement errors.

Piasecka, Magdalena; Maciejewska, Beata

2014-03-01

79

Directory of Open Access Journals (Sweden)

Full Text Available In this paper, the research progress of the interfacial heat transfer in high pressure die casting (HPDC is reviewed. Results including determination of the interfacial heat transfer coefficient (IHTC, influence of casting thickness, process parameters and casting alloys on the IHTC are summarized and discussed. A thermal boundary condition model was developed based on the two correlations: (a IHTC and casting solid fraction and (b IHTC peak value and initial die surface temperature. The boundary model was then applied during the determination of the temperature field in HPDC and excellent agreement was found.

Cao Yongyou

2014-07-01

80

Determining convective heat transfer coefficient using phoenics software package

Energy Technology Data Exchange (ETDEWEB)

The two methods of determination of such important quantity of heat exchange on a body surface using PHOENICS are suggested in the presentation. The first method consists in a post-processing of results of conjugate heat transfer problem solved by PHOENICS. The second one is solving an inverse heat conduction problem for solid body using PHOENICS. Comparative characteristic of these two methods is represented. (author) 4 refs.

Kostikov, A.; Matsevity, Y. [Institute of Mechanical Engineering Problems of National Academy of Sciences of Ukraine, Kharkov (Ukraine)

1997-12-31

81

Measurement of Dynamic Friction Coefficient on the Irregular Free Surface

International Nuclear Information System (INIS)

A spent fuel storage cask must be estimated for a structural integrity when an earthquake occurs because it freely stands on ground surface without a restriction condition. Usually the integrity estimation for a seismic load is performed by a FEM analysis, the friction coefficient for a standing surface is an important parameter in seismic analysis when a sliding happens. When a storage cask is placed on an irregular ground surface, measuring a friction coefficient of an irregular surface is very difficult because the friction coefficient is affected by the surface condition. In this research, dynamic friction coefficients on the irregular surfaces between a concrete cylinder block and a flat concrete slab are measured with two methods by one direction actuator

82

Measurement of Heat Transfer Coefficients in an Agitated Vessel with Tube Baffles

Directory of Open Access Journals (Sweden)

Full Text Available Cooling or heating an agitated liquid is a very common operation in many industrial processes. A classic approach is to transfer the necessary heat through the vessel jacket. Another option, frequently used in the chemical and biochemical industries is to use the heat transfer area of vertical tube baffles. In large equipment, e.g. fermentor, the jacket surface is often not sufficient for large heat transfer requirements and tube baffles can help in such cases. It is then important to know the values of the heat transfer coefficients between the baffles and the agitated liquid. This paper presents the results of heat transfer measurements using the transient method when the agitated liquid is periodically heated and cooled by hot and cold water running through tube baffles. Solving the unsteady enthalpy balance, it is possible to determine the heat transfer coefficient. Our results are summarized by the Nusselt number correlations, which describe the dependency on the Reynolds number, and they are compared with other measurements obtained by a steady-state method.

M. Dostál

2010-01-01

83

Confirmation of selected milk and meat radionuclide-transfer coefficients

International Nuclear Information System (INIS)

The elements selected for study of their transfer coefficients to eggs, poultry meat, milk and beef were Mo, Tc, Te, and Ba. The radionuclides used in the study were the gamma-emitting radionuclides 99Mo, /sup 123m/Te and 133Ba. 133Ba was selected because 140Ba-140La is produced infrequently and availability was uncertain. 133Ba has a great advantage for our type of experiment because of its longer physical half-life. 99Tc is a pure beta-emitter and was used in the first three animal experiments because we could not obtain the gamma-emitting /sup 95m/Tc. A supply of this nuclide was recently obtained, however, for the second cow experiment

84

Geometric Dependence of the Scalar Transfer Efficiency over Rough Surfaces

We performed a series of wind-tunnel experiments under neutral conditions in order to create a comprehensive database of scalar transfer coefficients for street surfaces using regular block arrays representing an urban environment. The objective is to clarify the geometric dependence of scalar transfer phenomena on rough surfaces. In addition, the datasets we have obtained are necessary to improve the modelling of scalar transfer used for computational simulations of urban environments; further, we can validate the results obtained by numerical simulations. We estimated the scalar transfer coefficients using the salinity method. The various configurations of the block arrays were designed to be similar to those used in a previous experiment to determine the total drag force acting on arrays. Our results are summarized as follows: first, the results for cubical arrays showed that the transfer coefficients for staggered and square layouts varied with the roughness packing density. The results for the staggered layout showed the possibility that the mixing effect of air can be enhanced for the mid-range values of the packing density. Secondly, the transfer coefficients for arrays with blocks of non-uniform heights were smaller than those for arrays with blocks of uniform height under conditions of low packing density; however, as the packing density increased, the opposite tendency was observed. Thirdly, the randomness of rotation angles of the blocks in the array led to increasing values of the transfer coefficients under sparse packing density conditions when compared with those for cubical arrays.

Ikegaya, Naoki; Hagishima, Aya; Tanimoto, Jun; Tanaka, Yudai; Narita, Ken-ichi; Zaki, Sheikh Ahmad

2012-05-01

85

International Nuclear Information System (INIS)

The heat-transfer coefficients around a workpiece immersed in an electrically heated heat treatment fluidised bed were studied. A suspension probe designed to simulate a workpiece of complex geometry was developed to measure local total and radiative heat-transfer coefficients at a high bed temperature. The probe consisted of an energy-storage region separated by insulation from the fluidised bed, except for the measuring surface, and a multi-thermocouple measurement system. Experiments in the fluidised bed were performed for a fluidising medium of 120-mesh alumina, a wide temperature range of 110-1050 deg. C and a fluidising number range of 1.18-4.24. It was found that the workpiece surface temperature has a more significant effect on heat transfer than the bed temperature. The total heat-transfer coefficient at the upper surface of the workpiece sharply decreased at the start of heating, and then steadily increased as heating progressed, while a sharp decrease became a rapid increase and then a slow increase for the radiative heat-transfer coefficient. A great difference in the heat-transfer coefficients around the workpiece was observed

86

Modeling the Effect of Internal Convection Currents on Heat Transfer Coefficient of Liquid Foods

Directory of Open Access Journals (Sweden)

Full Text Available The internal convection currents generated during the cooling process affect convective heat transfer coefficient from the surface of the container, these convection currents may increase the effective value of the surface film conductance (h. Therefore, in such situation the Nu-Re correlations, which are generally used to predict h-values, may not yield realistic results. In the present work, this effect has been investigated by using the empirical correlation developed through Temperature-Time measurements at the centre of liquid food containers during cooling .The main concern of the present work is about considering the heat transfer behaviour for liquid foods for which a cylindrical shape container of brass metal have taken, in this work the transient Time-Temperature relation is utilized to calculate the value of convection heat transfer coefficient (h for each measured temperature at the centre of the cylinder (r¬¬o=0. Then after plotting the graph between ‘h’ and ‘T’ an expression between h and T is obtained, which is fed back in the programme developed with the help of finite difference method by which Time-Temperature variation is obtained. Experimental procedure was used to determine surface film conductance of cylindrical Apple and Orange juice container, calculated temperatures have been compared with the experimental results when the measured surface film conductance were used to solve the transient heat conduction equation in cylindrical coordinates. A consistently excellent agreement was observed.

SAJID ALI

2013-04-01

87

Evaluation of heat-transfer coefficient at direct-contact condensation of cold water and steam

International Nuclear Information System (INIS)

The estimation of the heat transfer coefficient at the direct-contact condensation of cold water and steam is a very hard task since the phenoma are essentially undsteady and the interface motion is so complicated that an exact estimation of its araea is almost impossible. The present study shows the heat transfer coefficient evaluated experimentally by assuming simple interface shapes for complicated surfaces and estimated those through comparison of the numerical analyses to the data of experiments related to the loss of coolant accidents of light water reactors. At chugging, the heat transfer coefficient reached up to 2 x 106 W/(m2 K). At condensation oscillation, it ranged between 105-106 W/(m2K). At a jet region of cold water injected into the steam flow in a pipe or the stationary steam in a vessel, the value was around 2 x 105 W/(m2 K), and at the surface of stratified flow, it was between 3 x 103-3x104 W/(m2 K). (orig.)

88

International Nuclear Information System (INIS)

The effect of the heat transfer coefficient at the casting-mold interface is of prime importance to improve the casting quality, especially for castings in metal molds. However, it is difficult to determine the values of heat transfer coefficient from experiments due to the influence of various factors, such as contacting pressure, oxides on surfaces, roughness of surfaces, coating material, coating thickness and gap formation caused by the deformation of casting and mold, etc. In the present paper, the interfacial heat transfer coefficient (IHTC) between the casting and metal mold is identified by using the method of inverse analysis based on measured temperatures, neural network with back-propagation algorithm and numerical simulation. Then, by applying the identified IHTC in finite element analysis, the comparison between numerical calculated and experimental results is made to verify the correctness of method. The results show that the numerical calculated temperatures are in good agreement with experimental ones. These demonstrate that the method of inverse analysis is a feasible and effective tool for determination of the casting-mold IHTC. In addition, it is found that the identified IHTC varies with time during the casting solidification and varies in the range of about 100-3200 Wm-2K-1. The characteristics of the time-varying IHTC have also been discussed.

89

Boiling Heat Transfer on Superhydrophilic, Superhydrophobic, and Superbiphilic Surfaces

With recent advances in micro- and nanofabrication, superhydrophilic and superhydrophobic surfaces have been developed. The statics and dynamics of fluids on these surfaces have been well characterized. However, few investigations have been made into the potential of these surfaces to control and enhance other transport phenomena. In this article, we characterize pool boiling on surfaces with wettabilities varied from superhydrophobic to superhydrophilic, and provide nucleation measurements. The most interesting result of our measurements is that the largest heat transfer coefficients are reached not on surfaces with spatially uniform wettability, but on biphilic surfaces, which juxtapose hydrophilic and hydrophobic regions. We develop an analytical model that describes how biphilic surfaces effectively manage the vapor and liquid transport, delaying critical heat flux and maximizing the heat transfer coefficient. Finally, we manufacture and test the first superbiphilic surfaces (juxtaposing superhydrophobic ...

Betz, Amy Rachel; Kim, Chang-Jin 'CJ'; Attinger, Daniel

2012-01-01

90

Determining heat transfer coefficients in radial flow through a polyethylene packed

Directory of Open Access Journals (Sweden)

Full Text Available A numerical-experimental methodology was used for determining interstitial heat transfer coefficients in water flowing through po-rous media where it was not in heat balance with the solid phase. Heat transfer coefficients were obtained through the single blow transient test method, combining experimental test equipment results with a mathematical model’s numerical solution. The partial differential equation system produced by the mathematical model was resolved by a numerical finite volume method-ba-sed methodology. Experimental tests and numerical solutions were satisfactorily carried out for different values from the fluid’s surface speed from the entrance to the bed and for different porosity values, finding that Nusselt numbers increased when Reynolds numbers also increased and that Nusselt numbers increased when porosity decreased. A 650 Reynolds number and 0.375 porosity gave a Nusselt number of up to 2.8.

Luís Patiño

2010-07-01

91

DMS gas transfer coefficients from algal blooms in the Southern Ocean

Directory of Open Access Journals (Sweden)

Full Text Available Air/sea dimethylsulfide (DMS fluxes and bulk air/sea gradients were measured over the Southern Ocean in February/March 2012 during the Surface Ocean Aerosol Production (SOAP study. The cruise encountered three distinct phytoplankton bloom regions, consisting of two blooms with moderate DMS levels, and a high biomass, dinoflagellate-dominated bloom with high seawater DMS levels (>15 nM. Gas transfer coefficients were considerably scattered at wind speeds above 5 m s?1. Bin averaging the data resulted in a linear relationship between wind speed and mean gas transfer velocity consistent with that previously observed. However, the wind speed-binned gas transfer data distribution at all wind speeds is positively skewed. The flux and seawater DMS distributions were also positively skewed, which suggests that eddy covariance-derived gas transfer velocities are consistently influenced by additional, log-normal noise. A~flux footprint analysis was conducted during a transect into the prevailing wind and through elevated DMS levels in the dinoflagellate bloom. Accounting for the temporal/spatial separation between flux and seawater concentration significantly reduces the scatter in computed transfer velocity. The SOAP gas transfer velocity data shows no obvious modification of the gas transfer-wind speed relationship by biological activity or waves. This study highlights the challenges associated with eddy covariance gas transfer measurements in biologically active and heterogeneous bloom environments.

T. G. Bell

2014-11-01

92

DMS gas transfer coefficients from algal blooms in the Southern Ocean

Air/sea dimethylsulfide (DMS) fluxes and bulk air/sea gradients were measured over the Southern Ocean in February/March 2012 during the Surface Ocean Aerosol Production (SOAP) study. The cruise encountered three distinct phytoplankton bloom regions, consisting of two blooms with moderate DMS levels, and a high biomass, dinoflagellate-dominated bloom with high seawater DMS levels (>15 nM). Gas transfer coefficients were considerably scattered at wind speeds above 5 m s-1. Bin averaging the data resulted in a linear relationship between wind speed and mean gas transfer velocity consistent with that previously observed. However, the wind speed-binned gas transfer data distribution at all wind speeds is positively skewed. The flux and seawater DMS distributions were also positively skewed, which suggests that eddy covariance-derived gas transfer velocities are consistently influenced by additional, log-normal noise. A~flux footprint analysis was conducted during a transect into the prevailing wind and through elevated DMS levels in the dinoflagellate bloom. Accounting for the temporal/spatial separation between flux and seawater concentration significantly reduces the scatter in computed transfer velocity. The SOAP gas transfer velocity data shows no obvious modification of the gas transfer-wind speed relationship by biological activity or waves. This study highlights the challenges associated with eddy covariance gas transfer measurements in biologically active and heterogeneous bloom environments.

Bell, T. G.; De Bruyn, W.; Marandino, C. A.; Miller, S. D.; Law, C. S.; Smith, M. J.; Saltzman, E. S.

2014-11-01

93

Heat transfer performance of metal fiber sintered surfaces

Boiling heat transfer performance on stainless steel metal fiber sintered surfaces is experimentally investigated with Freon 11 (R11) as the working fluid. The boiling heat transfer coefficient for the optimum surface structure gives a tenfold improvement over a smooth surface. The nondimensional specific parameter including all design parameters is introduced to explain the trend of the performance of various kinds of metal fiber sintered surfaces. Moreover, the metal fiber sintered surface clad with titanium film is suggested to be appropriate to an evaporator for Ocean Thermal Energy Conversion (OTEC) system.

Kajikawa, T.; Takazawa, H.; Mizuki, M.

1983-03-01

94

Mass transfer coefficients in a hanson mixer-settler extraction column

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english The volumetric overall mass transfer coefficients in a pilot plant Hanson mixer-settler extraction column of seven stages have been measured using toluene-acetone-water system. The effects of agitation speed and dispersed and continuous phases flow rates on volumetric overall mass transfer coefficie [...] nts have been investigated. The results show that the volumetric overall mass transfer coefficient increases with increase in agitation speed and reaches a maximum. After having reached its maximum, it falls with further increase in agitation speed. It was found that the volumetric overall mass transfer coefficient increases with increase in dispersed phase flow rate, while it decreases with increase in continuous phase flow rate. By using interfacial area, the overall mass transfer coefficients for continuous and dispersed phases are determined from volumetric coefficients. An empirical correlation for prediction of the continuous phase overall mass transfer coefficient is proposed in terms of Sherwood and Reynolds numbers. Also the experimental data of the column investigated are compared with data for various extraction columns. Comparison between theoretical models and experimental results for the dispersed phase mass transfer coefficient shows that these models do not have enough accuracy for column design. Using effective diffusivity in the Gröber equation results in more accurate prediction of overall mass transfer coefficient. The prediction of overall mass transfer coefficients from the presented equations is in good agreement with experimental results.

M., Torab-Mostaedi; S. J., Safdari; M. A., Moosavian; M. Ghannadi, Maragheh.

2008-09-01

95

Mass transfer coefficients in a hanson mixer-settler extraction column

Directory of Open Access Journals (Sweden)

Full Text Available The volumetric overall mass transfer coefficients in a pilot plant Hanson mixer-settler extraction column of seven stages have been measured using toluene-acetone-water system. The effects of agitation speed and dispersed and continuous phases flow rates on volumetric overall mass transfer coefficients have been investigated. The results show that the volumetric overall mass transfer coefficient increases with increase in agitation speed and reaches a maximum. After having reached its maximum, it falls with further increase in agitation speed. It was found that the volumetric overall mass transfer coefficient increases with increase in dispersed phase flow rate, while it decreases with increase in continuous phase flow rate. By using interfacial area, the overall mass transfer coefficients for continuous and dispersed phases are determined from volumetric coefficients. An empirical correlation for prediction of the continuous phase overall mass transfer coefficient is proposed in terms of Sherwood and Reynolds numbers. Also the experimental data of the column investigated are compared with data for various extraction columns. Comparison between theoretical models and experimental results for the dispersed phase mass transfer coefficient shows that these models do not have enough accuracy for column design. Using effective diffusivity in the Gröber equation results in more accurate prediction of overall mass transfer coefficient. The prediction of overall mass transfer coefficients from the presented equations is in good agreement with experimental results.

M. Torab-Mostaedi

2008-09-01

96

Calculation and Analysis of Heat Transfer Coefficients in a Circulating Fluidized Bed Boiler Furnace

A new way for the circulating fluidized bed (CFB) boiler research is proposed by the supervisory information system (SIS) in power plant level. The heat transfer coefficient in CFB boiler furnace is calculated and analyzed by the SIS calculation analysis in a commercial CFB boiler, the way how to calculate the heat transfer coefficient in SIS is introduced, and the heat transfer coefficient is accurately received by calculating a large amount of data from database. The relation about the heat transfer coefficient to unit load, bed temperature, bed velocity, and suspension density is analyzed; the linear relation could be accepted for the commercial CFB design. A new calculating and simple way for the heat transfer coefficient of CFB boiler is proposed for CFB boiler design. Using this research result, the reheat spray water flux larger than the design value in lots of commercial CFB boilers is analyzed; the main reason is the designed heat transfer coefficient smaller than the actual value.

Wang, Zhiwei; Yang, Jianhua; Li, Qinghai

97

International Nuclear Information System (INIS)

This paper investigates the nitrogen molecule interaction with surfaces at 2eV for a developed adsorbed layer. A molecular beam is obtained by exhausting nitrogen of 6000 K into vacuum. The momentum transfer coefficients are obtained by means of measuring the forces on plates of different materials in a flow. The mass flux indicatrices are measured, the surface roughness being measured electrochemically. The momentum transfere coefficients are shown to be stable with time, within the measured error. The simultaneous handling of the force and indicatrix data show their consitency. A model funciton of reflected molecules distribution is proposed on the basis of these measurements. The surface roughness increase results in a fall of the momentum transferred to the surface by reflected molecules. A number of approximate formulae is given

98

Estimation of grass to cow's milk transfer coefficients for emergency situations

International Nuclear Information System (INIS)

Several studies have been reported on soil to grass equilibrium transfer factors and grass to cow's milk transfer coefficients for 137Cs for the environs of different nuclear power plants of both India and other parts of the world. In such studies, the activity concentration of 137Cs is measured in grass collected from different places. Cow's milk samples are collected from nearby localities or from milk dairies and analyzed for 137Cs and the grass to cow's milk transfer coefficient is estimated. In situation where 137Cs is not present in measurable activity concentrations, its stable counterpart (Cs) is measured for the estimation of transfer coefficients. These transfer coefficient values are generally used in theoretical models to estimate the dose to the population for hypothetical situation of emergency. It should be noted that the transfer coefficients obtained for equilibrium conditions may not be totally applicable for emergency situation. However, studies aimed at evaluating transfer coefficients for emergency situations are sparse because nuclear power plants do not release 137Cs during normal operating situations and therefore simulating situation of emergency release is not possible. Hence, the only method to estimate the grass to milk transfer coefficient for emergency situation is to spike the grass with small quantity of stable Cs. This paper reports the results of grass to milk transfer coefficientults of grass to milk transfer coefficients for stable isotope of Cesium (Cs) for emergency situation

99

The conduction phenomenon in an insulated sphere is re-worked through a dimensionless approach, where the heat transfer coefficient dependence on the external radius and on the surface temperature, as in the case of forced and free convection, is taken into account. Assuming a power law variation of the convection coefficient [1, 2], and using the results of Sparrow [3], equations and graphs for the most important dimensionless parameters are presented. The developed equations show, for examp...

Branco, J. F.; Pinho, C. T.; Figueiredo, R. A.

2000-01-01

100

Heat transfer from rough surfaces

International Nuclear Information System (INIS)

The transformation of the friction data obtained with experiments in annuli can be performed either with the assumption of universal logarithmic velocity profile or of an universal eddy momentum diffusivity profile. For the roughness of practical interest both methods, when properly applied, give good results. For these roughnesses the transformed friction factors seem not to be unduly affected if one assumes a constant slope of the velocity profile equal to 2.5. All the transformation methods of the heat transfer data so far proposed predict too high wall temperatures in the central channels of a 19-rod bundle with three-dimensional roughness. Preliminary calculations show that the application of the superimposition principle with the logarithmic temperature profiles gives good results for the three-dimensional roughness as well. Although the measurements show that the slope of the logarithmic temperature profiles is different from 2.5, the assumption of a constant slope equal to 2.5 does not affect the transformed heat transfer data appreciably. For moderately high roughness ribs the turbulent Prandtl number, averaged over the cross section of a tube, is about the same (approx. 0.8) for rough as for smooth surfaces. The temperature effect on the heat transfer data with air cooling is stronger than originally assumed in the general correlation of Dalle Donne and Meyer. With helium cooling this temperature effect is even stronger. (orig.)

101

International Nuclear Information System (INIS)

In the scope of the Megawatt Pilot Experiment (MEGAPIE), i.e. a liquid metal target for a spallation neutron source, an experimental investigation (KILOPIE) of the target window cooling has to be performed. A reason to perform the KILOPIE experiment is that, in the area of the proton beam entry window, the values and distribution of the local convection heat transfer coefficient 'a' for MEGAPIE conditions are unknown. The liquid metal, in this case lead-bismuth eutectic (LBE), is simultaneously used as target material and coolant. A hemispherical flow geometry made of T91 steel is used for the mockup of the proton beam entry window in an experimental set-up for a determination of the local convection heat transfer coefficient 'a'. In KILOPIE two complementary methods are used for a determination of the local convection heat transfer coefficient 'a', the first one is the two dimensional Heat Emitting Temperature Sensitive Surface (2D-HETSS) method develop at PSI (Platnieks et al.) and the second is an improved two-dimensional and dynamic infrared thermography (2DD-IRT) method, also developed at PSI (Patorski et al.). In this paper only the methodology of improved 2DD-IRT will be presented. The experimental activities will be performed at the beginning of 2004 at Forschungszentrum Karlsruhe (FZK) using the THEADES loop of the KALLA laboratory and will be continued at Paul Scherrer Institute (PSI) using the new, consisting of two independent pumped circuits, PSI-LBE-Doub independent pumped circuits, PSI-LBE-Double-Loop. A specially tailored 0.053 mm thick Aluchrom YHf heating foil is used, which allows to apply a uniform and constant heat flux deposition on the outer surface of the hemispherical mockup-specimen of the target window. The optical non-contact IRT equipment measures the outer surface temperature of the mockup-specimen dish with a high space and time resolution, e.g. 1.25 mrad and 20 Hz. The 100 mm diameter of the mockup-specimen dish with approximately 5000 pixels, i.e. temperature measurement points, area of 1.6 mm2 is covering the area of interest, corresponding to the approx. 60 mm diameter of the proton beam footprint and results in temperature contour plots with good resolution. The dynamic capability of 2DD-IRT is essential for the investigation of the change of the local convection heat transfer coefficient 'a' especially during transient load cases, i.e. during changes of the flow rate of the coolant. The accuracy of the temperature measurement is ±1%. The knowledge of constant heat flux and temperature differences between inner surface and coolant allow a two-dimensional dynamic determination and visualization of the local convection heat transfer coefficient 'a'. In other words, the determination of the local convection heat transfer coefficient 'a' is a result of ratio of the known local heat flux from the Aluchrom YHf heating foil to the difference between the local inner surface temperature and the bulk temperature of the LBE coolant. (author)

102

Enhancement of pool boiling hear transfer on porous surface tube

International Nuclear Information System (INIS)

In this paper, the pool boiling heat transfer characteristics of a machined porous surface tube are investigated experimentally, considering the boiling operating condition of passive residual heat removal exchanger. The experiments have been carried out with high-pressure saturated steam condensation in tube as heating source and the results show that the porous surface tube has a considerable boiling heat transfer enhancing ability: the porous surface tube can increase the boiling heat transfer coefficient about 68%-75% and the wall superheat decreases about 1.5?; With the combined effect of condensation inside tube and boiling outside tube, the axial wall temperatures of heat transfer tube are neither uniform nor linear distribution, but represent some particular distribution characteristics. On the base of the experimental investigation, the enhanced mechanism of porous surface tube is also analyzed. (authors)

103

Investigation of Natural Convection Heat Transfer Coefficient on Extended Vertical Base Plates

Directory of Open Access Journals (Sweden)

Full Text Available In this research, Computational analysis of the laminar natural convection on vertical surfaces has been in-vestigated. Natural convection is observed when density gradients are present in a fluid acted upon by a gravitational field. Our example of this phenomenon is the heated vertical plate exposed to air, which, far from the plate, is motionless. The CFD simulations are carried out using fluent software. Governing equa-tions are solved using a finite volume approach. Coupling between the velocity and pressure is made with SIMPLE algorithm. The resultant system of discretized linear algebraic equations is solved with an alternat-ing direction implicit scheme. Then a configuration of rectangular fins is put in different ways on the surface and natural convection heat transfer coefficient on these no slope surfaces is studied and finally optimization is done.

D. Majidian

2011-05-01

104

Directory of Open Access Journals (Sweden)

Full Text Available The article deals with determination of energy transfer coefficient dependence from primary coil to secondary matching device coil on inductive load value. In the course of researches, the discharge pulses oscillograms have been registred, and the inductance of research inductors and the energy transfer coefficient from the primary matching device coil to the inductor– processing tool have been experimentally determined.

Gnatov, A.

2012-06-01

105

EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER ENHANCEMENT OVER THE DIMPLED SURFACE

Directory of Open Access Journals (Sweden)

Full Text Available Over the past couple of years the focus on using concavities or dimples provides enhanced heat transfer has been documented by a number of researchers. Dimples are used on the surface of internal flow passages because they produce substantial heat transfer augmentation. This project work is concerned with experimentalinvestigation of the forced convection heat transfer over the dimpled surface. The objective of the experiment is to find out the heat transfer and air flow distribution on dimpled surfaces and all the results obtained are compared with those from a flat surface. The varying parameters were i Dimple arrangement on the plate i.e.staggered and inline arrangement and ii Heat input iiiDimple density on the plate. Heat transfer coefficients and Nusselt number were measured in a channel with one side dimpled surface. Thespherical type dimples were fabricated, and the diameter and the depth of dimple were 6 mm and 3 mm, respectively. Channel height is 25.4mm, two dimple configurations were tested. The Reynolds number based on the channel hydraulic diameter was varied from 5000 to 15000.Study shown that thermal performance is increasing with Reynolds number. With the inline and staggered dimple arrangement, the heat transfer coefficients, Nusselt number and the thermal performance factors were higher for the staggered arrangement.

Dr. Sachin L. Borse

2012-08-01

106

Energy Technology Data Exchange (ETDEWEB)

Condensation in the presence of noncondensible gases plays an important role in the nuclear industry. The RELAP5/MOD3 thermal hydraulic code was used to study the ability of the code to predict this phenomenon. Two separate effects experiments were simulated using this code. These were the Massachusetts Institute of Technology`s (MIT) Pressurizer Experiment, the MIT Single Tube Experiment. A new iterative approach to calculate the interface temperature and the degraded heat transfer coefficient was developed and implemented in the RELAP5/MOD3 thermal hydraulic code. This model employs the heat transfer simultaneously. This model was found to perform much better than the reduction factor approach. The calculations using the new model were found to be in much better agreement with the experimental values.

Banerjee, S.; Hassan, Y.A. [Texas A& M Univ., College Station, TX (United States)

1995-09-01

107

Calculating the heat transfer coefficient of frame profiles with internal cavities

DEFF Research Database (Denmark)

Determining the energy performance of windows requires detailed knowledge of the thermal properties of their different elements. A series of standards and guidelines exist in this area. The thermal properties of the frame can be determined either by detailed two-dimensional numerical methods or by measurements in accordance to European or international standards. Comparing measured and calculated heat transfer coefficients for two typical frame profiles with cavities shows considerable differences. This investigation considers two typical frame profiles in aluminium and PVC with internal cavities. The heat transfer coefficient is determined by two-dimensional numerical calculations and by measurements. Calculations are performed in Therm (LBNL (2001)), which is developed at Lawrence Berkeley National Laboratory, USA. The calculations are performed in accordance with the future European standards and measurements have been performed at two German research institutes. The internal cavities have a large influence on the overall thermal performance of the frame profiles and the investigation shows that the applied method for modelling the heat transfer by radiation exchange in the internal cavities of the profiles is critical. The simple radiation model described in the pre European standard (prEN ISO 10077-2) does not yield valid results compared to measured values. Applying a more detailed, viewfactor based, grey surfaces enclosure model as described in the ISO standard (ISO/DIS 15099) gives a better correspondence between measured and calculated values. Hence, when determining the heat transfer coefficient of frame profiles with internal cavities by calculations, it is necessary to apply a more detailed radiation exchange model than described in the prEN ISO 10077-2 standard. The ISO-standard offers such an alternative.

Noyé, Peter Anders; Laustsen, Jacob Birck

2004-01-01

108

A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the load surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimental results agreed reasonably well with theoretical predictions of convective heat transfer of flat plate laminar boundary layers. The results indicate that this non-intrusive optical measurement technique has the potential to obtain high quality surface convective heat transfer measurements in high speed flowfields.

Porro, A. Robert; Keith, Theo G., Jr.; Hingst, Warren R.; Chriss, Randall M.; Seablom, Kirk D.

1991-01-01

109

International Nuclear Information System (INIS)

Transfer coefficients are commonly used as an approximation to the problem of quantifying the transit of radionuclides between an ecosystem's different characteristic receptor media. These coefficients are traditionally defined as the quotient between the specific activities of the receptor and the donor compartments. In the present study, the receptor were edible mushrooms and the donor the soil. However, not all the radioactive content of a soil is in a condition to be transferred. Instead, the fraction that is available will depend intimately on the capacity of the different compounds to which the radionuclides are associated to be taken up by the fungus. To analyse the cited capacity, we carried out a scheme of chemical speciation of the surface layer (0-5 cm) of the soils corresponding to two forest ecosystems (pine woods) that present a high productivity of mushrooms. This scheme consists of the sequential extraction of the available soil fraction (extractable with NH4OAc), that soluble in dilute acid (extractable with HCl 1M), that soluble in strong acid (extractable with HCl 6M), and the residue. We analysed the presence of different man-made (137Cs, 90Sr) and natural (40K, 226Ra) radionuclides in each of the soil fractions enumerated above and in two representative species of mushroom from the aforementioned two ecosystems: Hebeloma cylindrosporum and Lactarius deliciosus. Specifically, more than 75% of tliciosus. Specifically, more than 75% of the concentrations of 40K and 137Cs present in the soils studied were found bound to fractions not accessible to exchange reactions (the fraction soluble in strong acid and the residue). This implies that they are not associated to chemical compounds capable of being transferred to the fungi's fruiting bodies. Therefore, it is totally inappropriate to calculate the transfer coefficients in the usual way, since this uses the total activity found in the soil layer being considered. By way of example, for 40K the traditional method underestimates the transfer by approximately 2 orders of magnitude. We hence propose another approach, considering only the fraction of radionuclides present in the soil that are really in condition to be transferred. (author)

110

Directory of Open Access Journals (Sweden)

Full Text Available This paper explains the need for a database of cooling intensities for liquid quenchants, in order to predict the quench hardness, microstructure, stresses and distortion, when real engineering components of complex geometry are quenched. The existing laboratory procedures for cooling intensity evaluation, using small test specimens, and Lumped-Heat-Capacity Method for calculation of heat transfer coefficient, are presented. Temperature Gradient Method for heat transfer calculation in workshop conditions, when using the Liscic/Petrofer probe, has been elaborated. Critical heat flux densities and their relation to the initial heat flux density, is explained. Specific facilities for testing quenching intensity in workshop conditions, are shown. The two phase project of the International Federation for Heat Treatment and Surface Engineering (IFHTSE, as recently approved, is mentioned.

Božidar Liš?i?

2012-02-01

111

The determination of individual mass transfer coefficients in liquid-liquid extraction

Directory of Open Access Journals (Sweden)

Full Text Available An improved Lewis cell has been used as an efficient method to determine the mass transfer coefficient for any ternary multi-component system. In this paper the individual mass transfer coefficients were determined for three ternary systems: water-acetone-carbon tetrachloride water-acetone-chloroform and water-acetone-toluene, using the improved Lewis cell. Criteria! equations were developed to calculate the mass transfer coefficients when one or both (organic and aqueous phases were agitated and when solute transfer occurs in both directions.

Radu Tudose Z.

2003-01-01

112

Fouling of heat transfer surfaces

International Nuclear Information System (INIS)

There are many parameters affecting the fouling deposit on the heat transfer surface. These parameters include flow velocity, surface temperature, fluid bulk temperature, fluid characteristics, surface material and structure. The flow velocity is one of the most important parameters affecting the fouling rate and there is a rarity in literature covering this effect. Therefore, the purpose of the present work is to study the effect of flow velocity on the fouling rate. To carry out this study, an experimental test rig has been designed and constructed. The experimental loop has three 97% Cu-Ni test tubes of 2400 mm length and 16 mm inner diameter. Water with a solid particle concentration of 19 m/lit is used as a test fluid. The test fluid flows through the tubes which are heated by means of steam. The cooling water is arranged in a closed loop to keep constant solid particle concentration. The experiments are carried out under constant surface temperature by using the steam as a heating medium. These experiments have been carried out under different flow velocities (from 0.2 to 1.42 m/s). The experimental loop is a differential one and the runs have been operated for long time (about 200 hrs.) to attain the asymptotic fouling resistance. The obtained experimental results are analyzed, and the effect of flow velocity on the fouling rate and the asymptotic fouling resistance is plotted. From the discussion of these results, it is concluded that; both the fouling resistas concluded that; both the fouling resistance and the asymptotic fouling resistance decrease with increasing the flow velocity. The delay time is very small and is seen to approach zero in all the experimental work. The saw tooth effect has been obtained in all runs. Results have shown also essential.10 tabs.,4-8 figs.,71 refs

113

Directory of Open Access Journals (Sweden)

Full Text Available Heat transfer coefficients in the cooling cavities of turbine airfoils are greatly enhanced by the presence of discrete ribs on the cavity walls. These ribs introduce two heat transfer enhancing features: a significant increase in heat transfer coefficient by promoting turbulence and mixing, and an increase in heat transfer area. Considerable amount of data are reported in open literature for the heat transfer coefficients both on the rib surface and on the floor area between the ribs. Many airfoil cooling design software tools, however, require an overall average heat transfer coefficient on a rib-roughened wall. Dealing with a complex flow circuit in conjunction with 180Ã¢ÂˆÂ˜ bends, numerous film holes, trailing-edge slots, tip bleeds, crossover impingement, and a conjugate heat transfer problem; these tools are not often able to handle the geometric details of the rib-roughened surfaces or local variations in heat transfer coefficient on a rib-roughened wall. On the other hand, assigning an overall area-weighted average heat transfer coefficient based on the rib and floor area and their corresponding heat transfer coefficients will have the inherent error of assuming a 100% fin efficiency for the ribs, that is, assuming that rib surface temperature is the same as the rib base temperature. Depending on the rib geometry, this error could produce an overestimation of up to 10% in the evaluated rib-roughened wall heat transfer coefficient. In this paper, a correction factor is developed that can be applied to the overall area-weighted average heat transfer coefficient that, when applied to the projected rib-roughened cooling cavity walls, the net heat removal from the airfoil is the same as that of the rib-roughened wall. To develop this correction factor, the experimental results of heat transfer coefficients on the rib and on the surface area between the ribs are combined with about 400 numerical conduction models to determine an overall equivalent heat transfer coefficient that can be used in airfoil cooling design software. A well-known group method of data handling (GMDH scheme was then utilized to develop a correlation that encompasses most pertinent parameters including the rib geometry, rib fin efficiency, and the rib and floor heat transfer coefficients.

M. E. Taslim

2007-08-01

114

The volumetric overall mass transfer coefficients have been measured in a pulsed packed extraction column using diffusion model for two different liquid-liquid systems. The effects of operational variables such as pulsation intensity and dispersed and continuous phase flow rates on volumetric overall mass transfer coefficients have been investigated. Effective diffusivity is substituted for molecular diffusivity in the Gröber equation for prediction of dispersed phase overall mass transfer c...

Torab-mostaedi, M.; Safdari, J.

2009-01-01

115

Energy Technology Data Exchange (ETDEWEB)

Two-phase flow heat transfer has been exhaustively studied over recent years. However, in this field several questions remain unanswered. Heat transfer coefficient prediction related to nucleate and convective boiling have been studied using different approaches, numerical, analytical and experimental. In this work, an experimental analysis, data representation and heat transfer coefficient prediction on two-phase heat transfer on nucleate and convective boiling are presented. An empirical correlation is obtained based on genetic algorithms search engine over a dimensional analysis of the two-phase flow heat transfer problem. (author)

Picanco, Marco Antonio Silva [Regional University of Jaragua do Sul (UNERJ), SC (Brazil)], e-mail: mpicanco@unerj.br; Bandarra Filho, Enio Pedone [Federal University of Uberlandia (UFU), MG (Brazil). Fac. de Engenharia Mecanica], e-mail: bandarra@mecanica.ufu.br; Passos, Julio Cesar [Universidade Federal de Santa Catarina (UFSC), Florianopolis, SC (Brazil). Dept. de Engenharia Mecanica. Lab. de Engenharia de Processos e Tecnologia de Energia], e-mail: jpassos@emc.ufsc.br

2006-07-01

116

International Nuclear Information System (INIS)

Two-phase flow heat transfer has been exhaustively studied over recent years. However, in this field several questions remain unanswered. Heat transfer coefficient prediction related to nucleate and convective boiling have been studied using different approaches, numerical, analytical and experimental. In this work, an experimental analysis, data representation and heat transfer coefficient prediction on two-phase heat transfer on nucleate and convective boiling are presented. An empirical correlation is obtained based on genetic algorithms search engine over a dimensional analysis of the two-phase flow heat transfer problem. (author)

117

The usage of transfer coefficients to describe radionuclide transport from a cow's diet to its milk

International Nuclear Information System (INIS)

The terms 'transfer coefficient', 'transfer function' and 'transfer rate' are used to describe the transport of radionuclides from a cow's diet to her milk. Simple derivation of these parameters, their interpretations and interrelationships are given, and possible misinterpretations of published values due to imprecise definitions or incorrectly supplied or omitted units are reviewed. (author)

118

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

DEFF Research Database (Denmark)

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 temperature distribution of an average person. The measurements were performed in a room with controlled thermal environment. Air temperature was set at 26ºC for cooling and at 20ºC for heating. The radiant temperature asymmetry in horizontal and vertical direction was close to zero, i.e. mean radiant temperature was equal to the air temperature. The air velocity of the isothermal downward flow from the ceiling at height of 1.5 m above the floor (above the top of the head) was set in a range between still air and 0.73 m/s. Based on the analyses of the results relationships for determination 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<0.3 m/s, due to the natural convection were found. The results may be useful during design of air distribution in rooms, e.g. low impulse ventilation, diffuse ventilation, etc.

Kurazumi, Yoshihito; Rezgals, Lauris

2014-01-01

119

Evaluation of the heat transfer coefficient in thermal shock of alumina disks

International Nuclear Information System (INIS)

Disks of a high-purity commercial alumina powder were fabricated by slip casting, pre-calcined, sintered and machined with SiC paper (120 and 320 grit). The specimens were tested in thermal shock conditions from several temperatures (Ti) between 870 and 980 C using a high-velocity air jet at room temperature (T0). The temperature differential between the disk and the air jet was incremented in 10 C until crack propagation was detected. During the air impinging, the temperature was recorded on the lower specimen surface at the central point and at a peripheral one. The coefficient governing the convective heat transfer on the specimen surface, h, was estimated by fitting the calculated temperature profiles with those measured during the test. Three alternative models were proposed for the temperature calculations using a finite element analysis. (orig.)

120

Estimation of the sea surface drag coefficient based on wave data

The sea surface drag coefficient, an important parameter for the energy transfer process in wave prediction model, is generally expressed by a linear function of wind speed. However, it seems inadequate to apply these equations for strong wind conditions because these equations were deduced from the observational or the experimental data under wind speed of lower than 25m/s at fastest. To solve this problem, a wave prediction model ADWAM which includes a data assimilation method seems effe...

Yokota, M.; Hashimoto, N.; Kodama, M.; Amiya, R.

2013-01-01

121

Prediction of gas-liquid mass transfer coefficient in sparged stirred tank bioreactors.

Oxygen mass transfer in sparged stirred tank bioreactors has been studied. The rate of oxygen mass transfer into a culture in a bioreactor is affected by operational conditions and geometrical parameters as well as the physicochemical properties of the medium (nutrients, substances excreted by the micro-organism, and surface active agents that are often added to the medium) and the presence of the micro-organism. Thus, oxygen mass transfer coefficient values in fermentation broths often differ substantially from values estimated for simple aqueous solutions. The influence of liquid phase physicochemical properties on kLa must be divided into the influence on k(L) and a, because they are affected in different ways. The presence of micro-organisms (cells, bacteria, or yeasts) can affect the mass transfer rate, and thus kLa values, due to the consumption of oxygen for both cell growth and metabolite production. In this work, theoretical equations for kLa prediction, developed for sparged and stirred tanks, taking into account the possible oxygen mass transfer enhancement due to the consumption by biochemical reactions, are proposed. The estimation of kLa is carried out taking into account a strong increase of viscosity broth, changes in surface tension and different oxygen uptake rates (OURs), and the biological enhancement factor, E, is also estimated. These different operational conditions and changes in several variables are performed using different systems and cultures (xanthan aqueous solutions, xanthan production cultures by Xanthomonas campestris, sophorolipids production by Candida bombicola, etc.). Experimental and theoretical results are presented and compared, with very good results. PMID:16155951

Garcia-Ochoa, Felix; Gomez, Emilio

2005-12-20

122

International Nuclear Information System (INIS)

Hydrogen is expected to serve as a clean secondary energy, because it can be manufactured from water, used in a variety of energy end-use sectors as fuel, and returned to water after burning. For the realization of hydrogen energy system, development of efficient and economical hydrogen production methods is required to meet the future huge demand of hydrogen. The Iodine-Sulfur (IS) process is a promising candidate of such hydrogen production methods, in which water reacts with iodine and sulfur dioxide to produce hydrogen iodide and sulfuric acid (Bunsen reaction) and the produced acids are then decomposed to produce hydrogen and oxygen, respectively. This study is concerned with the development of IS process equipment named direct contact sulfuric acid concentrator, in which gaseous mixture produced by thermal decomposition of sulfuric acid contacts directly with sulfuric acid solution. In the concentrator, the high temperature heat of the decomposed gas is recovered and used to concentrate sulfuric acid solution and, at the same time, the undecomposed sulfuric acid is condensed and separated from the decomposition products of sulfur dioxide and oxygen. Although the concept is very attractive from the viewpoint of the development of compact and efficient sulfuric acid concentrator, little is known on the heat and mass transfer relevant to the concentrator. Therefore, experimental methods were discussed to acquire the gas-phase mass transfer coefficient required for se mass transfer coefficient required for the optimal design of the concentrator. Assuming the use of wetted-wall column and also of the sulfuric acid of azeotropic composition as the test solution which could eliminate the liquid-phase mass transfer resistance, the column specification and the measurement conditions were determined by which flooding could be avoided and surface wetting could be assured, as well. (author)

123

Experimental study of convective coefficient of mass transfer of avocado (Persia americana Mill.)

Energy Technology Data Exchange (ETDEWEB)

Most of all energy consumed worldwide comes from fossil fuels derived from petroleum. With the petroleum crisis in the 70 were sought new energy sources, among them renewable. One such source is biodiesel energy, organic matter originated from animal and/or vegetable. Among the various plant species is the avocado (Persia americana Mill.) showing great potential in the production of petroleum extracted from the pulp and the alcohol removed from the seed. The main obstacle for obtaining the petroleum is the high humidity found in the pulp, being necessary to the drying process, which involves the transfer of heat and mass. The aim of this study was to use the mathematical model represented by Newton's Law of Cooling to simulate the mass transfer on the surface of the avocado pulp during the drying process. The equation of the mathematical model was solved numerically and the method of least squares was identified convective coefficient of Mass Transfer. The dryer used in the experimental process was operated with air flow in the vertical, air flow average fixed 3m/s and temperatures of 50, 60 and 70 deg C. The scheme of the dryer used in the research is composed of the following equipment: centrifugal fan, which drives the air-drying; valve, which allows control of airflow; electrical resistance, used for heating air; the drying chamber, where enables measurement of temperature and relative humidity; support for smaller trays; trays smaller, where the samples of the pulp of the avocado are placed; exit of the air of drying for the environment. The result presented shows the ratio of moisture content as a function of temperature over time, where it is possible to also observe that how much bigger the temperature of drying, greater will be the convective coefficient of mass transfer of the avocado. (author)

Alves, Suerda Bezerra; Luiz, Marcia Ramos; Amorim, Joselma Araujo de; Gusmao, Rennam Pereira de; Gurgel, Jose Mauricio [Universidade Federal da Paraiba (LES/UFPB), Joao Pessoa, PB (Brazil). Lab. de Energia Solar

2010-07-01

124

Condensation heat transfer on two-tier superhydrophobic surfaces

We investigated water vapor condensation on a two-tier superhydrophobic surface in an environmental scanning electron microscope (ESEM) and in a customer-designed vapor chamber. We have observed continuous dropwise condensation (DWC) on the textured surface in ESEM. However, a film layer of condensate was formed on the multiscale texture in the vapor chamber. Due to the filmwise condensation, the condensation heat transfer coefficient of the superhydrophobic surface is lower than that of a flat hydrophobic surface especially under high heat flux situations. Our studies indicate that adaptive and prompt condensate droplet purging is the dominant factor for sustaining long-term DWC.

Cheng, Jiangtao; Vandadi, Aref; Chen, Chung-Lung

2012-09-01

125

Directory of Open Access Journals (Sweden)

Full Text Available The paper presents experimental research of thermal conductivity coefficients of the siliceous sand bed fluidized by air and an experimental investigation of the particle size influence on the heat transfer coefficient between fluidized bed and inclined exchange surfaces. The measurements were performed for the specific fluidization velocity and sand particle diameters d p=0.3, 0.5, 0.9 mm. The industrial use of fluidized beds has been increasing rapidly in the past 20 years owing to their useful characteristics. One of the outstanding characteristics of a fluidized bed is that it tends to maintain a uniform temperature even with nonuniform heat release. On the basis of experimental research, the influence of the process's operational parameters on the obtained values of the bed's thermal conductivity has been analyzed. The results show direct dependence of thermal conductivity on the intensity of mixing, the degree of fluidization, and the size of particles. In the axial direction, the coefficients that have been treated have values a whole order higher than in the radial direction. Comparison of experimental research results with experimental results of other authors shows good agreement and the same tendency of thermal conductivity change. It is well known in the literature that the value of the heat transfer coefficient is the highest in the horizontal and the smallest in the vertical position of the heat exchange surface. Variation of heat transfer, depending on inclination angle is not examined in detail. The difference between the values of the relative heat transfer coefficient between vertical and horizontal heater position for all particle sizes reduces by approximately 15% with the increase of fluidization rate.

B. Stojanovic

2009-06-01

126

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english The paper presents experimental research of thermal conductivity coefficients of the siliceous sand bed fluidized by air and an experimental investigation of the particle size influence on the heat transfer coefficient between fluidized bed and inclined exchange surfaces. The measurements were perfo [...] rmed for the specific fluidization velocity and sand particle diameters d p=0.3, 0.5, 0.9 mm. The industrial use of fluidized beds has been increasing rapidly in the past 20 years owing to their useful characteristics. One of the outstanding characteristics of a fluidized bed is that it tends to maintain a uniform temperature even with nonuniform heat release. On the basis of experimental research, the influence of the process's operational parameters on the obtained values of the bed's thermal conductivity has been analyzed. The results show direct dependence of thermal conductivity on the intensity of mixing, the degree of fluidization, and the size of particles. In the axial direction, the coefficients that have been treated have values a whole order higher than in the radial direction. Comparison of experimental research results with experimental results of other authors shows good agreement and the same tendency of thermal conductivity change. It is well known in the literature that the value of the heat transfer coefficient is the highest in the horizontal and the smallest in the vertical position of the heat exchange surface. Variation of heat transfer, depending on inclination angle is not examined in detail. The difference between the values of the relative heat transfer coefficient between vertical and horizontal heater position for all particle sizes reduces by approximately 15% with the increase of fluidization rate.

B., Stojanovic; J., Janevski; M., Stojiljkovic.

2009-06-01

127

Pool boiling heat transfer enhancement on porous surface tube

International Nuclear Information System (INIS)

The passive residual heat removal exchanger (PRHR HX), which is a key equipment of the passive residual heat removal system, is installed in an elevated pool. Its heat transfer performance affects security and economics of the reactor, and boiling heat transfer in the liquid surrounding the exchanger occurs when the liquid saturation temperature exceeded. The smooth tubes, which are widely used as heat transfer tubes in PRHR HX, can be replaced by some enhanced tubes to improve the boiling heat transfer capability. In this paper, the pool boiling heat transfer characteristics of smooth tube and a machined porous surface tube are investigated by using high-pressure steam condensing inside tube as heating source. Compared with smooth tube,the porous surface tube considerably enhances the boiling heat transfer, and shortens the time significantly before reaching the liquid saturation temperature. Its boiling heat transfer coefficient increases from 68% to 75%, and the wall superheat decreases by 1.5 degree C. Combining effect of condensation inside tube with boiling outside tube, the axial wall temperatures of heat transfer tube are neither uniform nor linear distribution. Based on these investigations, enhance mechanism of the porous surface tube is analyzed. (authors)

128

An Experimental Investigation of Heat Transfer Coefficients for Spiral Plate Heat Exchanger

Spiral plate heat exchangers play a vital role in cooling high density and high viscous fluids. This paper presents an experimental investigation of convective heat transfer co-efficient for electrolytes using spiral plate heat...

Kaliannan Saravanan; Rangasamy Rajavel

2009-01-01

129

Estimating the workpiece-backingplate heat transfer coefficient in friction stirwelding

Purpose - The purpose of this paper is to determine the magnitude and spatial distribution of the heat transfer coefficient between the workpiece and the backingplate in a friction stir welding process using inverse modelling. Design/methodology/approach - The magnitude and distribution of the heat transfer coefficient are the variables in an optimisation problem. The objective is to minimise the difference between experimentally measured temperatures and temperatures obtained using a 3D fini...

Larsen, Anders; Stolpe, Mathias; Hattel, Jesper Henri

2012-01-01

130

International Nuclear Information System (INIS)

Transfer coefficients have become virtually indispensible in the study of the fate of radioisotopes released from nuclear installations. These coefficients are used in equilibrium assessment models where they specify the degree of transfer in food chains of individual radioisotopes from soil to plant products and from feed or forage and drinking water to animal products and ultimately to man. Information on transfer coefficients for terrestrial food chain models is very piecemeal and occurs in a wide variety of journals and reports. To enable us to choose or determine suitable values for assessments, we have addressed the following aspects of transfer coefficients on a very broad scale: (1) definitions, (2) equilibrium assumption, which stipulates that transfer coefficients be restricted to equilibrium or steady rate conditions, (3) assumption of linearity, that is the idea that radioisotope concentrations in food products increase linearly with contamination levels in the soil or animal feed, (4) methods of determination, (5) variability, (6) generic versus site-specific values, (7) statistical aspects, (8) use, (9) sources of currently used values, (10) criteria for revising values, (11) establishment and maintenance of files on transfer coefficients, and (12) future developments. (auth)

131

Heat transfer in unwetted region under cooling of heated surfaces

International Nuclear Information System (INIS)

The results of experimental investigation of heat transfer coefficients in the unwetted region under cooling of heated surfaces are presented. Experiments were conducted using a tube at 7 and 16.7 MPa pressure, 500-3200 kg/(m2xc) mass flow rate and using four-rod bundle at 3.2-7.5 MPa pressure and 460-600 kg/(m2xc) mass flow rate. Thermal fluxes of the exothermic surface due to inner heat release were varied within the ranges from 0.12 up to 0.77 MW/m2. Flow rate relative enthalpy at the output did not exceed 0.2. Calculation technique for heat transfer coefficients regarding cooling under the comditions of back-annular flow is presented. Results of the calculation agree satisfactorily with experimental data

132

137Cs transfer coefficients from fodder to cow milk

International Nuclear Information System (INIS)

The transfer of 137Cs from the components of cows' diets to milk was followed in detail on 10 farms in the north-eastern region of Italy (Friuli-Venezia Giulia) from June to July 1988. Samples of milk, grass and other components of the cows' diet were collected regularly and analysed for radiocaesium content. The transfer factors, calculated for 137Cs after a four-week feeding period with contaminated silage, were higher (0.0064) than those calculated in 1987 in the same area (0.0030). This may be attributable to the fact that the 137Cs associated to the forage administrated to cows in 1988 was completely incorporated in the plant and thus more assimilable to the cattle. (Author)

133

The CO2 heat pump water heater ”ECO CUTE” which was commercialized in 2001 has a high potential for energy conservation and greenhouse abatement. The most important element apparatus is always the evaporator in order to develop smaller and higher performance equipment. In this paper, an experimental study has been conducted to measure the pure CO2 flow boiling heat transfer coefficient (99.999 % purity, without oil) in a horizontal smooth tube (outer diameter 6 mm, thickness 0.4 mm). The measured mean heat transfer coefficients are compared with calculated value with using previous experimental heat transfer correlation equations. These two values are different from each other. Mean heat transfer coefficients are measured with varying mass velocity, pressure and heat transfer lengths. The tube length is varied to 3.0 m, 4.0 m and 5.0 m, to distinguish the influence of mass velocity and that of heat flux to the heat transfer coefficient. The test conditions were: CO2 mass velocity from about 150 to about 700 kg?(m2s) (heat flux from about 10 to about 40 kW?m2), quality at inlet of test section is 0.17, CO2 super heat at outlet of test section is 5 K and saturation temperature of CO2 ranges from 0 to 10 °C. As a result, it has been understood that heat flux has a greater influence on the heat transfer coefficient.

Hashimoto, Katsumi; Kiyotani, Akihiro; Sasaki, Naoe

134

Pool boiling heat transfer from enhanced surfaces to dielectric fluids

International Nuclear Information System (INIS)

Pool boiling heat-transfer measurements were made using a 15.8 mm o.d. plain copper tube and three copper enhanced surfaces: a Union Carbide High Flux surface, a Hitachi Thermoexcell-E surface and a Wieland Gewa-T surface. The dielectric fluids were Freon-113 and Fluorinert FC-72, a perfluorinated organic compound manufactured to cool electronic equipment. Data were taken at atmospheric pressure, and at heat fluxes from 100 W/m2 to 200,000 W/m2. Prior to operation, each test surface was subjected to one of three aging procedures to observe the effect of surface past history upon boiling incipience. For Freon-113 the enhanced surfaces showed a two to tenfold increase in the heat-transfer coefficient when compared to a plain tube, whereas for FC-72 an increase of two to five was measured. The High Flux surface gave the best performance over the range of heat fluxes. The Gewa-T surface did not show as much of an enhancement at low fluxes as the other two surfaces, but at high fluxes its performance improved. In fact, it was the only surface tested which delayed the onset of film boiling with FC-72. The degree of superheat required to activate the enhanced surfaces was sensitive to both past history of the surface and to fluid properties

135

Modeling of the substrate and product transfer coefficients for ethanol fermentation

International Nuclear Information System (INIS)

The transfer phenomena of the substrate and product for ethanol fermentation with immobilized biocatalyst were investigated. Fermentation was carried out with a biocatalyst consisting of Ca-alginate gel in the form of two-layer spherical beads in anaerobic conditions. The determination of kinetic parameters was achieved by fitting bioreaction progress curves to the experimental data. The calculation of the diffusion coefficients was performed by numerical methods for experimental conditions. Finally, the glucose and ethanol transfer coefficients are defined and determined, using the effective diffusion coefficients. (Abstract Copyright [2008], Wiley Periodicals, Inc.)

136

Measurement of radon diffusion coefficients for Japanese surface soils

International Nuclear Information System (INIS)

The radon diffusion coefficient for soil, D, is a very important parameter used to estimate radon dose for uranium-bearing waste. Many Ds were measured in the uranium mill tailing remediation action project in the US, and a formula for the estimation of diffusion coefficient, Rogers's formula, was proposed. However, it is uncertain whether Rogers's formula is applicable to Japanese soils because most of them have come from volcanic ash and contain much water. This paper describes the development of a measurement apparatus for D using a lump response transient method and a step response transient method, and presents measured D values for Japanese surface soils. Measured alpha ray count curves are good in agreement with those of theory. This shows that radon transportation in soil can be described using Fick's law. Furthermore, the measured effective D values are good in agreement with those of Rogers's formula. This means that Rogers's formula can be applied to Japanese soils. (author)

137

The use of neural network to estimate mass transfer coefficient from the bottom of agitated vessel

In this study, the ability of the artificial neural network (ANN) to estimate the rate of mass transfer coefficient was compared against the mass transfer correlation obtained by dimensional analysis in terms of Sherwood, Schmidt and Reynolds numbers. The results showed that the ANN is better than the conventional mass transfer correlation in most cases and the best results are obtained at 3-7 neurons in the hidden layer.

ElShazly, Yehia M. S.

2014-09-01

138

Transient volumetric heat transfer coefficient prediction of a three-phase direct contact condenser

An experimental investigation for the time dependent volumetric heat transfer coefficient of the bubbles type, three-phase direct contact condenser has been carried out utilising a short column (70 cm in total height and 4 cm inner diameter). A 47 cm active height was chosen with five different mass flow rate ratios and three different initial dispersed phase temperatures. Vapour pentane and constant temperature tap water as dispersed and continuous phases were implemented. The results showed that the volumetric heat transfer coefficient decreases with increased time until it almost reaches its steady state conditions. A sharp decrease in the volumetric heat transfer coefficient was found at the beginning of the operation and, diminished over a short time interval. Furthermore, a positive effect of the mass flow rate ratios on the volumetric heat transfer coefficient was noted and this was more pronounced at the beginning of the operation. On the other hand, the volumetric heat transfer coefficient decreased with an increase in the continuous phase mass flow rate and there was no considerable effect of the initial dispersed phase temperatures, which confirms that latent heat transfer is dominant in the process.

Mahood, Hameed B.; Sharif, Adel O.; Thorpe, Rex B.

2015-02-01

139

Transient volumetric heat transfer coefficient prediction of a three-phase direct contact condenser

An experimental investigation for the time dependent volumetric heat transfer coefficient of the bubbles type, three-phase direct contact condenser has been carried out utilising a short column (70 cm in total height and 4 cm inner diameter). A 47 cm active height was chosen with five different mass flow rate ratios and three different initial dispersed phase temperatures. Vapour pentane and constant temperature tap water as dispersed and continuous phases were implemented. The results showed that the volumetric heat transfer coefficient decreases with increased time until it almost reaches its steady state conditions. A sharp decrease in the volumetric heat transfer coefficient was found at the beginning of the operation and, diminished over a short time interval. Furthermore, a positive effect of the mass flow rate ratios on the volumetric heat transfer coefficient was noted and this was more pronounced at the beginning of the operation. On the other hand, the volumetric heat transfer coefficient decreased with an increase in the continuous phase mass flow rate and there was no considerable effect of the initial dispersed phase temperatures, which confirms that latent heat transfer is dominant in the process.

Mahood, Hameed B.; Sharif, Adel O.; Thorpe, Rex B.

2014-07-01

140

Heat Transfer Variation on Protuberances and Surface Roughness Elements

In order to determine the effect of surface irregularities on local convective heat transfer, the variation in heat transfer coefficients on small (2-6 mm diam) hemispherical roughness elements on a flat plate has been studied in a wind funnel using IR techniques. Heat transfer enhancement was observed to vary over the roughness elements with the maximum heat transfer on the upstream face. This heat transfer enhancement increased strongly with roughness size and velocity when there was a laminar boundary layer on the plate. For a turbulent boundary layer, the heat transfer enhancement was relatively constant with velocity, but did increase with element size. When multiple roughness elements were studied, no influence of adjacent roughness elements on heat transfer was observed if the roughness separation was greater than approximately one roughness element radius. As roughness separation was reduced, less variation in heat transfer was observed on the downstream elements. Implications of the observed roughness enhanced heat transfer on ice accretion modeling are discussed.

Henry, Robert C.; Hansman, R. John, Jr.; Breuer, Kenneth S.

1995-01-01

141

Determining the surface roughness coefficient by 3D Scanner

Directory of Open Access Journals (Sweden)

Full Text Available Currently, several test methods can be used in the laboratory to determine the roughness of rock joint surfaces.However, true roughness can be distorted and underestimated by the differences in the sampling interval of themeasurement methods. Thus, these measurement methods produce a dead zone and distorted roughness profiles.In this paper a new rock joint surface roughness measurement method is presented, with the use of a camera-typethree-dimensional (3D scanner as an alternative to current methods. For this study, the surfaces of ten samples oftuff were digitized by means of a 3D scanner, and the results were compared with the corresponding Rock JointCoefficient (JRC values. Up until now such 3D scanner have been mostly used in the automotive industry, whereastheir use for comparison with obtained JRC coefficient values in rock mechanics is presented here for the first time.The proposed new method is a faster, more precise and more accurate than other existing test methods, and is apromising technique for use in this area of study in the future.

Karmen Fifer Bizjak

2010-12-01

142

Hydrodynamics and mass transfer coefficients for a modified Raschig ring packed column

The pressure drop, the liquid holdup, as well as the liquid film mass transfer coefficients (kL) for a modified Raschig packing, with turbulence promoters, used in absorption columns, were determined experimentally. The aim of this work is to verify the improved mass transfer properties of this new packing for the randomly and, particularly, for the arranged packed columns. The experiments were performed at gas velocities ranging from 800 to 2,000 m h-1 and liquid velocities scaling between 2.5 and 8.11 m h-1, ranges that cover most of the absorption column operation conditions. Experimental data and correlations for the pressure drop, the liquid holdup and the gas-liquid mass transfer coefficients (kL) for modified Raschig ring packed columns are presented. The influence of the gas and the liquid velocities on the column hydrodynamics and the mass transfer coefficients have been obtained experimentally and also, have been compared with literature data.

Mamaliga, I.; Sidor, D.; Condurat, C.; Iacob Tudose, E. T.

2014-10-01

143

International Nuclear Information System (INIS)

This paper presents a procedure for determining the transient heat transfer coefficient in cylindrical, thick-walled pressure parts. From theoretical considerations, the temperatures can be predicted at discrete locations throughout the wall, when input data such as thermocouple responses are known at one or several interior locations. Special emphasis is placed on the dynamic response of the thermometer, which measures the temperature, of the inside fluid, to enable exact determination of both heat transfer coefficient and fluid temperature. The transient response of a thermocouple in a convectional thermowell (pocket) is described by the first-order convective heat transfer model in which the rate of thermoelement temperature change is proportional to the instantaneous difference between the thermoelement and fluid temperatures. Several numerical examples show the effect of different time constants or thermal capacitances of thermometers on the calculated heat transfer coefficients and fluid temperatures. (orig.)

144

Effect of oxide layers on spray water cooling heat transfer at high surface temperatures

Energy Technology Data Exchange (ETDEWEB)

The influence of surface oxidation phenomena on spray water cooling heat transfer is an important issue in steel industry. In practical applications, spray cooling is regularly used for the cooling of steel surfaces from high temperatures with an (initial) oxide (scale) layer. This paper investigates the changes in the heat transfer due to the oxide layer and its removal during cooling. After a theoretical treatment of the principal effects of thin and stable layers, the heat transfer coefficient was measured by an automated cooling test stand (instationary method) for oxidized steel samples. The heat transfer is described by the concept of an effective heat transfer coefficient. Compared to the clean surface state, scale layers show a different effective heat transfer coefficient in the transition boiling regime. Additionally, the local delamination of the oxide, the formation of vapor gaps at the oxide-metal interface and the movement of scale plates makes the heat transfer more erratic. The heat transfer is therefore inhomogeneous and has to be described statistically. For water temperatures around 291 K, surface temperatures between 473 and 1173 K, i.e. {delta} T>180 K and water impact densities between V{sub S}=3 and 30 kg/(m{sup 2} s) the heat transfer coefficient {alpha} was measured. As sample material, different steel grades, oxidized in air for a specific time (0,.., 80 {mu}m scale layer) were used. The results are compared with the clean surface state. (author)

Wendelstorf, R.; Spitzer, K.-H.; Wendelstorf, J. [Clausthal University of Technology, Institute of Metallurgy, Robert Koch Str. 42, D-38678 Clausthal-Zellerfeld (Germany)

2008-09-15

145

Determination of heat transfer coefficients in plastic French straws plunged in liquid nitrogen.

The knowledge of the thermodynamic process during the cooling of reproductive biological systems is important to assess and optimize the cryopreservation procedures. The time-temperature curve of a sample immersed in liquid nitrogen enables the calculation of cooling rates and helps to determine whether it is vitrified or undergoes phase change transition. When dealing with cryogenic liquids, the temperature difference between the solid and the sample is high enough to cause boiling of the liquid, and the sample can undergo different regimes such as film and/or nucleate pool boiling. In the present work, the surface heat transfer coefficients (h) for plastic French straws plunged in liquid nitrogen were determined using the measurement of time-temperature curves. When straws filled with ice were used the cooling curve showed an abrupt slope change which was attributed to the transition of film into nucleate pool boiling regime. The h value that fitted each stage of the cooling process was calculated using a numerical finite element program that solves the heat transfer partial differential equation under transient conditions. In the cooling process corresponding to film boiling regime, the h that best fitted experimental results was h=148.12±5.4 W/m(2) K and for nucleate-boiling h=1355±51 W/m(2) K. These values were further validated by predicting the time-temperature curve for French straws filled with a biological fluid system (bovine semen-extender) which undergoes freezing. Good agreement was obtained between the experimental and predicted temperature profiles, further confirming the accuracy of the h values previously determined for the ice-filled straw. These coefficients were corroborated using literature correlations. The determination of the boiling regimes that govern the cooling process when plunging straws in liquid nitrogen constitutes an important issue when trying to optimize cryopreservation procedures. Furthermore, this information can lead to improvements in the design of cooling devices in the cryobiology field. PMID:25445573

Santos, M Victoria; Sansinena, M; Chirife, J; Zaritzky, N

2014-12-01

146

Validation of heat transfer coefficients for passive cooling

Energy Technology Data Exchange (ETDEWEB)

Experiments with 12 ft/sup 2/ water bags with wet and dry surfaces demonstrate that simple turbulent flow equations (e.g., h/sub c/ = C k/L Re/sup 0/ /sup 8/Pr/sup 0/ /sup 33/) describe convective and evaporative processes involved in the passive cooling of buildings. A passive test facility for humid climates is being built at Trinity University to test passive cooling and heating systems. Acquired data will be used to develop and validate design tools.

Loxsom, F.M.; Messer, C.; Doderer, E.; Cripe, A.; Allen, C.P.

1980-01-01

147

Estimation of grass to milk transfer coefficient for Strontium for emergency situations

International Nuclear Information System (INIS)

The grass to milk transfer coefficient is usually represented as Fm values. This paper reports the results of grass to cow milk transfer coefficients (Fm) for Strontium for emergency situation. An experimental grass field was developed in Kaiga region and 2 cows were adopted for collecting milk samples regularly. Grass was cut from the field and spiked with very low concentration of stable Strontium, taken in the form of Sr(No3)2, to simulate a sudden deposition of Strontium on grass and fed to the adopted cows. The milk samples were collected during normal milking periods (morning and evening) for several days and analyzed. The peak concentration of Sr in milk was observed during time period 12-36 hrs after the intake of spiked grass. The mean value of transfer coefficient was found to be 1.4 x 10-3 d L-1. The grass to milk transfer coefficient values observed under spiked conditions were similar to that observed for equilibrium transfer coefficient for Kaiga region. (author)

148

Estimation of Extract Yield and Mass Transfer Coefficient in Solvent Extraction of Lubricating Oil

Directory of Open Access Journals (Sweden)

Full Text Available An investigation was conducted to suggest relations for estimating yield and properties of the improved light lubricating oil fraction produced from furfural extraction process by using specified regression.Mass transfer in mixer-settler has been studied. Mass transfer coefficient of continuous phase, mass transfer coefficient of dispersed phase and the overall mass transfer coefficient extraction of light lubes oil distillate fraction by furfural are calculated in addition to all physical properties of individual components and the extraction mixtures.The effect of extraction variables were studied such as extraction temperature which ranges from 70 to 110°C and solvent to oil ratio which ranges from 1:1 to 4:1 (wt/wt were studied.The results of this investigation show that the extract yield E decreased with decreasing solvent to oil ratio in extract layer and increased with increasing temperature. The fraction of total solvent in the raffinate phase decreased with increasing oil to solvent ratio in raffinate layer and increased with increasing temperature. Solvent to oil ratio in extract layer decreased with increasing temperature and increased with increasing solvent to charge oil ratio at constant temperature. Oil to solvent ratio in raffinate decreased with increasing temperature and increased with increasing solvent to charge oil ratio at constant temperature.Estimated functions are the best modeling function for prediction extraction data at various operating conditions. Mass transfer coefficient of continuous phase kc and mass transfer coefficient of dispersed phase kd are increased with increasing temperature and solvent charge to oil ratio at constant temperature. The over all mass transfer coefficient Kod is increased with increasing temperature and solvent to charge oil ratio; while Kod a is increased with temperature and decreased with solvent to charge oil ratio.

Hussain K. Hussain

2010-01-01

149

Directory of Open Access Journals (Sweden)

Full Text Available The volumetric overall mass transfer coefficients have been measured in a pulsed packed extraction column using diffusion model for two different liquid-liquid systems. The effects of operational variables such as pulsation intensity and dispersed and continuous phase flow rates on volumetric overall mass transfer coefficients have been investigated. Effective diffusivity is substituted for molecular diffusivity in the Gröber equation for prediction of dispersed phase overall mass transfer coefficients. The enhancement factor is determined experimentally and therefrom an empirical correlation is derived for prediction of effective diffusivity as a function of Reynolds number, Schmidt number and viscosity ratio. Good agreement between prediction and experiments was found for all operating conditions that were investigated.

M. Torab-Mostaedi

2009-12-01

150

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english The volumetric overall mass transfer coefficients have been measured in a pulsed packed extraction column using diffusion model for two different liquid-liquid systems. The effects of operational variables such as pulsation intensity and dispersed and continuous phase flow rates on volumetric overal [...] l mass transfer coefficients have been investigated. Effective diffusivity is substituted for molecular diffusivity in the Gröber equation for prediction of dispersed phase overall mass transfer coefficients. The enhancement factor is determined experimentally and therefrom an empirical correlation is derived for prediction of effective diffusivity as a function of Reynolds number, Schmidt number and viscosity ratio. Good agreement between prediction and experiments was found for all operating conditions that were investigated.

M., Torab-Mostaedi; J., Safdari.

2009-12-01

151

Experimental studies of droplet heat transfer from hot metal surfaces

International Nuclear Information System (INIS)

The boiling of water droplets on hot metal surfaces is studied experimentally and mathematically in order to establish the conditions necessary for droplets to enter a film boiling mode. The subsurface temperature history within a plate undergoing droplet boiling on the surface is measured. A numerical model of the heat transfer in the plate is then used to deduce from these data the following characteristics of droplet boiling: (1) the effective heat transfer coefficient between water droplet and plate during the initial transient forming the spherical droplet, (2) the apparent time period needed to establish the droplet in the film boiling mode, and (3) the minimum plate surface temperature reached during the initial formation of the boiling droplet. The effective heat transfer coefficient, formation time, and minimum surface temperature are sufficient to develop a calculation method which predicts the minimum initial plate temperature necessary for a water droplet to enter film boiling. This numerical conduction model accounts for the influence of plate material, plate thickness, oxidation of the plate surface, the boundary condition on the plate lower surface, and the size of the droplet. The prediction method is successfully used to estimate the minimum film boiling temperature for brass, graphite, Pyrex, copper, aluminum, stainless steel, and Zircalloy II. The findings of the experiments and numerical studies are applied to the rewetting phase of a loss-of-coola to the rewetting phase of a loss-of-coolant-accident in a light water reactor. This application, in turn, provides explanations for some of the phenomena observed in studies of the prequench heat transfer within rod bundles including the effect of multiple droplet impacts

152

Heat and mass transfer across phase boundaries: Estimates of coupling coefficients

Heat and mass transport across phase boundaries are central in many engineering problems. The systematic description offered by classical non-equilibrium thermodynamics theory, when extended to surfaces, gives the interaction between the two fluxes in terms of coupling coefficients. It is shown in this paper that these coupling coefficients are large. The few experimental and computational results that are available confirm this. Neglect of coupling coefficients, which is common in most model...

Bedeaux, Dick; Kjelstrup, Signe

2008-01-01

153

Local Mass Transfer Coefficient for Idealized 2D Urban Street Canyon Models

Human activities in urban areas is one of the major sources of anthropogenic releases in the atmospheric boundary layer (ABL). The mechanism of urban morphology for the heat and mass transfer in built environment is thus an attractive topic in the research community. In this paper, a series of laboratory measurements is conducted to elucidate the mass transfer from hypothetical urban roughness constructed by idealized 2D street canyons. The experiments are carried out in the wind tunnel in the University of Hong Kong. The urban ABL structure inside the wind tunnel is controlled by placing small cubic Styrofoam blocks upstream of the test section. The street canyons are fabricated by movable rectangular acrylic blocks so that different building height to street width (aspect) ratios are examined. The height of building blocks is kept minimum to make sure that the urban ABL over the street canyons is high enough for fully developed turbulent flows. The prevailing wind is normal to the street axis, demonstrating the scenario of least pollutant removal from the street canyons to the urban ABL. The sample street canyon is covered by soaked filter papers to represent uniform mass concentrations on the building facades and ground surface. The wet bulb temperature of the filter papers is continuously monitored to ensure saturated conditions. Their weight before and after an experiment is used to measure the amount of water evaporated. Preliminary results illustrate the local mass transfer coefficient distribution for aspect ratios 1/4, 1/2, 1, and 2, which are comparable with those available in literuatre.

Leung, Ka Kit; Liu, Chun-Ho

2011-09-01

154

Transfer coefficient study of Sr-90 in the soil-grass-milk chain for Cuba

International Nuclear Information System (INIS)

One of the most important problems in modern radioecology is the lack of able information about the features of radionuclide migration in tropical and subtropical environment. The development of nuclear energy and the enhancing in the applications of nuclear techniques in those latitudes indicate that studies in this area are necessary. Cuba is carrying out studies on radioecological characterization of the principal food chains in the country. One of the objectives of these studies is to define the values of the transfer coefficients to be used in the evaluation programs for the assessment of the radiological impact of practices which involve ionizing radiation. This paper shows the results obtained in the determination of Sr-90 transfer coefficients in soil-grass-milk food chain in 'La Quebrada', a place near the Havana City where an important part of the milk that the citizens consume is produced. Transfer coefficients for Sr-90 were calculated on the basis of data collected during 5 years in the region. Soil-grass transfer coefficients are in the range 0.18-5 while grass-milk coefficients are in the range of 1.2x10-4 - 6x10-3 day/L. These values are in accordance with values reported by other authors in the literature. (authors). 4 refs., 2 tabs

155

International Nuclear Information System (INIS)

The determination of the heat transfer coefficient of the pins of the Spallation Neutron Source is a very important problem for the development of this facility, as data for thermal and structural studies. For this purpose, a test apparatus was built, in scale 1:1, for the simulation of the thermal and hydraulical conditions of the Neutron Source. This apparatus is a pin bank, with one of the pins electrically heated. Performance of measurements gave the values for the heat transfer coefficient, here presented in the Nusselt Number form, and its local distribution. Results show the linear dependence of Nusselt Number on Reynolds Number, for a constant heat production. (orig.)

156

Experimental determination of heat transfer coefficients in uranium zirconium hydride fuel rod

International Nuclear Information System (INIS)

This work presents the experiments and theoretical analysis to determine the temperature parameter of the uranium zirconium hydride fuel elements, used in the TRIGA IPR-R1 Research Nuclear Reactor. The fuel thermal conductivity and the heat transfer coefficient from the cladding to the coolant were evaluated experimentally. It was also presented a correlation for the gap conductance between the fuel and the cladding. In the case of nuclear fuels the heat parameters become functions of the irradiation as a result of change in the chemical and physical composition. The value of the heat transfer coefficients should be determined experimentally. (author)

157

International Nuclear Information System (INIS)

In this study, radiative and convective heat transfer coefficients at the ceiling are determined for a cooled ceiling room. Firstly, convective heat transfer is simulated numerically neglecting the radiative heat transfer at the surfaces (?f = ?w = ?c = 0), then, radiative heat transfer is calculated theoretically for different surface emissivities (?f = ?w = ?c = 0.5, 0.6, 0.7, 0.8 and 0.9) for different room dimensions (3 x 3 x 3, 4 x 3 x 4 and 6 x 3 x 4 m) and thermal conditions (Tf = 25 deg. C, Tw = 28-36 deg. C and Tc = 0-25 deg. C). Numerical data is compared with the results of correlations based on experimental data given in literature. New equations related to convective and total (including the effect of convection and radiation) heat transfer coefficients for ceiling are found in the current study

158

International Nuclear Information System (INIS)

In designing extraction columns many parameters must be considered such as mass transfer coefficients during formation, rising or falling and coalescence time, holdup, drop size and size distribution. Prediction of dispersed phase holdup is one of the most important parameter mentioned above. A laboratory spray column was constructed in our experimental works. Mass transfer coefficients, extraction percentage and local dispersed phase holdup were studied. Three physical systems with different physical properties and wide range of interfacial tensions, the most important physical property in our experiments, were used. It was found that the size of the mother drops produced by nozzles strongly depends on nozzle diameter. Most part of the mass transfer takes place in the nozzle tip and it increases as nozzles diameter decreases. Using multi orifices and single nozzles mass transfers were compared, taking into account the variation of dispersed phase hold up along the column

159

Energy Technology Data Exchange (ETDEWEB)

The four ITER partners propose to use binary beryllium pebble bed as neutron multiplier. Recently this solution has been adopted for the ITER blanket as well. In order to study the heat transfer in the blanket the effective thermal conductivity and the wall heat transfer coefficient of the bed have to be known. Therefore at Forschungszentrum Karlsruhe heat transfer experiments have been performed with a binary bed of beryllium pebbles and the results have been correlated expressing thermal conductivity and wall heat transfer coefficients as a function of temperature in the bed and of the difference between the thermal expansion of the bed and of that of the confinement walls. The comparison of the obtained correlations with the data available from the literature show a quite good agreement. (author)

Donne, M.D.; Piazza, G. [Forschungszentrum Karlsruhe GmbH Technik und Umwelt (Germany). Inst. fuer Neutronenphysik und Reaktortechnik; Goraieb, A.; Sordon, G.

1998-01-01

160

Lie point symmetry analysis is performed for an unsteady nonlinear heat diffusion problem modeling thermal energy storage in a medium with a temperature-dependent power law thermal conductivity and subjected to a convective heat transfer to the surrounding environment at the boundary through a variable heat transfer coefficient. Large symmetry groups are admitted even for special choices of the constants appearing in the governing equation. We construct one-dimensional optimal systems for the...

Moitsheki, Raseelo J.

2008-01-01

161

International Nuclear Information System (INIS)

Investigation of two-phase heat trnsfer in horizontal pipe flow have led to a new generalized correlation for the heat transfer coefficient. The proposed correlation equation is NUTP=3.04 [Pe]0.8 [Bo]0.6 This correlation was tested againts the existing and experimental data obtained on two-pahse heat transfer covering the entire possible flow regimes in a horizontal pipe flow. The correlation produces satisfactory result. (authors). 13 refs, 12 tabs, 2 figs

162

Convective and radiative heat transfer coefficients for individual human body segments.

Human thermal physiological and comfort models will soon be able to simulate both transient and spatial inhomogeneities in the thermal environment. With this increasing detail comes the need for anatomically specific convective and radiative heat transfer coefficients for the human body. The present study used an articulated thermal manikin with 16 body segments (head, chest, back, upper arms, forearms, hands, pelvis, upper legs, lower legs, feet) to generate radiative heat transfer coefficients as well as natural- and forced-mode convective coefficients. The tests were conducted across a range of wind speeds from still air to 5.0 m/s, representing atmospheric conditions typical of both indoors and outdoors. Both standing and seated postures were investigated, as were eight different wind azimuth angles. The radiative heat transfer coefficient measured for the whole-body was 4.5 W/m2 per K for both the seated and standing cases, closely matching the generally accepted whole-body value of 4.7 W/m2 per K. Similarly, the whole-body natural convection coefficient for the manikin fell within the mid-range of previously published values at 3.4 and 3.3 W/m2 per K when standing and seated respectively. In the forced convective regime, heat transfer coefficients were higher for hands, feet and peripheral limbs compared to the central torso region. Wind direction had little effect on convective heat transfers from individual body segments. A general-purpose forced convection equation suitable for application to both seated and standing postures indoors was hc = 10.3v0.6 for the whole-body. Similar equations were generated for individual body segments in both seated and standing postures. PMID:9195861

de Dear, R J; Arens, E; Hui, Z; Oguro, M

1997-05-01

163

International Nuclear Information System (INIS)

The effect of mechanical vibrations of a heated string on the heat transfer coefficient ? at various heat fluxes has been studied experimentally. An empirical relation between the coefficient ? and the vibration frequency and amplitude with unchanged q has been found

164

International Nuclear Information System (INIS)

Heat transfer of coolant flow through the automobile radiators is of great importance for the optimization of fuel consumption. In this study, the heat transfer performance of the automobile radiator is evaluated experimentally by calculating the overall heat transfer coefficient (U) according to the conventional ?-NTU technique. Copper oxide (CuO) and Iron oxide (Fe2O3) nanoparticles are added to the water at three concentrations 0.15, 0.4, and 0.65 vol.% with considering the best pH for longer stability. In these experiments, the liquid side Reynolds number is varied in the range of 50–1000 and the inlet liquid to the radiator has a constant temperature which is changed at 50, 65 and 80 °C. The ambient air for cooling of the hot liquid is used at constant temperature and the air Reynolds number is varied between 500 and 700. However, the effects of these variables on the overall heat transfer coefficient are deeply investigated. Results demonstrate that both nanofluids show greater overall heat transfer coefficient in comparison with water up to 9%. Furthermore, increasing the nanoparticle concentration, air velocity, and nanofluid velocity enhances the overall heat transfer coefficient. In contrast, increasing the nanofluid inlet temperature, lower overall heat transfer coefficient was recorded. -- Highlights: ? Overall heat transfer coefficient in the car radiator measured experimentally. ? Nanofluids showed greater heat transfer performance comparing with water. ? Increasing liquid and air Re increases the overall heat transfer coefficient. ? Increasing the inlet liquid temperature decreases the overall heat transfer coefficient

165

In this paper, convective heat transfer coefficient of Indian gooseberry (Emblica officinalis), in three different forms (shreds, slices and pieces), under forced convection mode has been determined. These forms were dried in laboratory drier. Values of constants C and n have been determined using experimental data and regression analysis for calculating values of convective heat transfer coefficient. It was found that the convective heat transfer coefficient varies with form of commodity bei...

Anwar, S. I.; Singh, R. D.

2012-01-01

166

Directory of Open Access Journals (Sweden)

Full Text Available In this paper photonic band gaps of 1D photonic crystal are compared by using transfer matrix method and Fresnel coefficients method. In Fresnel coefficients method, the refractive indices of each layer and incidence light angle to the surface are used for calculating Fresnel coefficients, and then the necessary and sufficient condition for a 100% reflection from the surface of double layer dielectrics is applied in such a way that reflection coefficient tends to unity so that photonic band gaps are determined. But in transfer matrix method there are some complications needed for solving quadratic partial differential equations and applying continuity of tangent components of fields and Bloch’s condition, though the results are the same

A Rahmatnezamabad

2014-11-01

167

Transfer coefficient of dense gaseous mixtures of charged and non-charged particles

International Nuclear Information System (INIS)

The Enskog-Landau kinetic equation for dense many-component systems of hard charged spheres is considered. Using the standard Chapman-Enskog method the normal solution to this equation in the first approximation is found. Numerical calculations for two- and three-component mixtures of neutral and charged particles are carried out on the basis of the found expressions for transfer coefficients

168

Based on several hypotheses about the process of supercritical carbon dioxide extraction, the onflow around the solute granule is figured out by the Navier-Stocks equation. In combination with the Higbie’s solute infiltration model, the link between the mass-transfer coefficient and the velocity of flow is found. The mass-transfer coefficient with the ultrasonical effect is compared with that without the ultrasonical effect, and then a new parameter named the ultrasonic-enhanced factor of mass-transfer coefficient is brought forward, which describes the mathematical model of the supercritical carbon dioxide extraction process enhanced by ultrasonic. The model gives out the relationships among the ultrasonical power, the ultrasonical frequency, the radius of solute granule and the ultrasonic-enhanced factor of mass-transfer coefficient. The results calculated by this model fit well with the experimental data, including the extraction of Coix Lacryma-jobi Seed Oil (CLSO) and Coix Lacryma-jobi Seed Ester (CLSE) from coix seeds and the extraction of Eicosapentaenoic Acid (EPA) and Docosahexaenoic Acid (DHA) from the alga by means of the ultrasonic-enhanced supercritical carbon dioxide extraction (USFE) and the supercritical carbon dioxide extraction (SFE) respectively. This proves the rationality of the ultrasonic-enhanced factor model. The model provides a theoretical basis for the application of ultrasonic-enhanced supercritical fluid extraction technique.

Luo, Benyi; Lu, Yigang

2008-10-01

169

Directory of Open Access Journals (Sweden)

Full Text Available The article presents the calculation of heat transfer coefficient during condensation of steam, the mathematical model of temperature distribution in the gas and liquid phases of the coolant and the model of the formation of the condensate film on the walls of the tubes.

Y.K.Sklifus

2012-12-01

170

Energy Technology Data Exchange (ETDEWEB)

This paper presented the characteristic of liquid desiccant dehumidification based on NTU-Le model. The results showed that the Lewis number Le had little effect on air outlet humidity ratio during desiccant solution dehumidification process. A new method called h{sub D}-Le separative evaluation method was developed for determining coupled heat and mass transfer coefficients between air and liquid desiccant, through which the heat and mass transfer coefficients between air and liquid desiccant were calculated to obtain from experimental inlet and outlet parameters of air and desiccant solution. The effects of the air volume flow rate, temperature, humidity ratio and the solution concentration, temperature on the Lewis number, heat and mass transfer coefficient were analyzed according to experimental data and the h{sub D}-Le separative evaluation method. Based on the computation results, it was concluded that the Lewis number greatly depended on the operation parameters and conditions of the air and desiccant. In addition, the correlations of the heat and mass transfer coefficients were developed. The additional 74 groups of experiments validated the developed correlations by comparison of air/solution parameters change with the calculation data. (author)

Yin, Yonggao; Zhang, Xiaosong [School of Energy and Environment, Southeast University, Nanjing (China)

2008-07-01

171

Simulation Study of Mass Transfer Coefficient in Slurry Bubble Column Reactor Using Neural Network

Directory of Open Access Journals (Sweden)

Full Text Available The objective of this study was to develop neural network algorithm, (Multilayer Perceptron, based correlations for the prediction overall volumetric mass-transfer coefficient (kLa, in slurry bubble column for gas-liquid-solid systems. The Multilayer Perceptron is a novel technique based on the feature generation approach using back propagation neural network. Measurements of overall volumetric mass transfer coefficient were made with the air - Water, air - Glycerin and air - Alcohol systems as the liquid phase in bubble column of 0.15 m diameter. For operation with gas velocity in the range 0-20 cm/sec, the overall volumetric mass transfer coefficient was found to decrease with increasing solid concentration. From the experimental work 1575 data points for three systems, were collected and used to predicate kLa. Using SPSS 17 software, predicting of overall volumetric mass-transfer coefficient (kLa was carried out and an output of 0.05264 sum of square error was obtained for trained data and 0.01064 for test data.

Safa A. Al-Naimi

2013-01-01

172

Soil plant transfer coefficient of 14C-carbofuran in brassica sp. vegetable agroecosystem

International Nuclear Information System (INIS)

The soil plant transfer coefficient or f factor of 14C-carbofuran pesticide was studied in outdoor lysimeter experiment consisting of Brassica sp. vegetable crop, riverine alluvial clayey soil and Bungor series sandy loam soil. Soil transfer coefficients at 0-10 cm soil depth were 4.38 ± 0.30, 5.76 ± 1.04, 0.99 ± 0.25 and 2.66 ± 0.71; from IX recommended application rate in alluvial soil, 2X recommended application rate in alluvial soil, IX recommended application rate in Bungor soil and 2X recommended application rate in Bungor soil, respectively. At 0-25 cm soil depth, soil plant transfer coefficients were 8.96 ± 0.91, 10.40 ± 2.63, 2.34 ± 0.68 and 619 ±1.40, from IX recommended application rate in alluvial soil, 2X recommended application rate in alluvial soil, IX recommended application rate in Bungor soil and 2X recommended application rate in Bungor soil, respectively. At 77 days after treatment (DAT), the soil plant transfer coefficient was significantly higher in riverine alluvial soil than Bungor soil whereas shoot and root growth was significantly higher in Bungor soil than in riverine alluvial soil. At both 0-10 cm Brassica sp. rooting depth and 0-25 cm soil depth, the soil plant transfer coefficient was significantly higher in 2X recommended application rate of 14C-carbofuran as compared to IX recommended application rate, in both Bungor and riverine alluvial soils. (Author)

173

International Nuclear Information System (INIS)

The present work is to improve our understanding and analysis of direct contact condensation on the gravity injection of CMTs and to measure the heat transfer coefficients around steam bubbles using the holographic interferometer and high speed camera. The condensation regime map associated with the downward injection of steam into water through the steam pipe is investigated to understand the mechanism of the direct contact condensation. The present map shows that the boundary of chugging and subsonic jetting with the larger diameter pipe is shifted to the larger steam mass flux. Steam cavity mode, not found in the literature, and the unique mode of downward injection for the present geometry, is observed at the low subcooled water temperature. With the holographic interferometry and the high speed camera, the heat transfer mechanism for the direct contact condensation in CMTs is understood and the heat transfer coefficients are measured. (orig.)

174

Identification of radon transfer velocity coefficient between liquid and gaseous phases

Radon transfer between a liquid phase and a gaseous phase is modelled by a Robin's condition (radon flux at the common interface is expressed as function of radon concentrations in the two phases). This condition involves two constants: Ostwald's coefficient ( ?) and the transfer velocity coefficient ( ?). Assuming the value of ? is known, a method is proposed to determinate the value of ?, by studying the radon transfer phenomenon at the laboratory scale. Knowing the initial radon concentrations, the experiment consists in measuring how long the radon flux passes through the common interface. In this stabilisation time radon transport is governed in each phase by diffusion and disintegration. Then, determination of ? is equivalent to solving an inverse problem formulated using measured data. A numerical procedure is developed to solve this problem. To cite this article: D.-G. Calugaru, J.-M. Crolet, C. R. Mecanique 330 (2002) 377-382.

Calugaru, Dan-Gabriel; Crolet, Jean-Marie

175

International Nuclear Information System (INIS)

A recent VAMP (Validation of Environmental Model Predictions) report collated values for aggregated transfer coefficients (Tag) which can describe the integrated transfer of radiocaesium to food products from semi-natural ecosystems. Further Tag data are presented for sheep and mushrooms which suggest that subdivision of Tag values to take soil type and seasonal variation into account is potentially valuable. For sheep, Tag values for organic soils are generally one to two orders of magnitude higher than those for sandy and clay soils. For most other semi-natural foodstuffs there are currently inadequate data to make such subdivisions. (author). 19 refs, 1 fig., 4 tabs

176

Radiant Heat Transfer in Reusable Surface Insulation

During radiant testing of mullite panels, temperatures in the insulation and support structure exceeded those predicted on the basis of guarded hot plate thermal conductivity tests. Similar results were obtained during arc tunnel tests of mullite specimens. The differences between effective conductivity and guarded hot plate values suggested that radiant transfer through the mullite was occurring. To study the radiant transport, measurements were made of the infrared transmission through various insulating materials and fibers of interest to the shuttle program, using black body sources over the range of 780 to 2000 K. Experimental data were analyzed and scattering coefficients were derived for a variety of materials, fiber diameters, and source temperature.

Hughes, T. A.; Linford, R. M. F.; Chmitt, R. J.; Christensen, H. E.

1973-01-01

177

Energy Technology Data Exchange (ETDEWEB)

An in-depth experimental study of heat transfer in ovens has provided basic data that is directly applicable to design. Heat transfer coefficients were measured for thermal loads having either black or highly reflective surface finishes. Approximately 100 different data runs were carried out. These heat transfer coefficients enabled the separation of the heat transfer into convective and radiative components, with radiation being the dominant transfer mechanism for blackened loads. The thermal response of the load to the presence of blockages situated either below or above the load was quantified. This response was only slightly affected by the blockages when they were empty of water, but major effects were observed when the blockages were water filled. Major effects were also encountered when the load was supported from below by cookie sheets. On the other hand, extensive investigation of various positions throughout the oven indicated a very weak effect of load position on the thermal response. (author)

Sparrow, E.M.; Abraham, J.P. [University of Minnesota, Minneapolis (United States). Laboratory of Heat Transfer Practice, Department of Mechanical Engineering

2002-08-01

178

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Full Text Available In this paper a numerical model will be adopted to analyze the heat transfer process during rapid solidification of a spherical sample placed on a metallic substrate cooled by water. The interfacial heat transfer coefficient between the sample and the substrate will be evaluated by matching model calculations with the surface temperature history recorded by a digital camera during solidification of a sample melted in an Arc-image furnace. .

Nikoli? Z.S.

2007-01-01

179

In this paper a numerical model will be adopted to analyze the heat transfer process during rapid solidification of a spherical sample placed on a metallic substrate cooled by water. The interfacial heat transfer coefficient between the sample and the substrate will be evaluated by matching model calculations with the surface temperature history recorded by a digital camera during solidification of a sample melted in an Arc-image furnace. .

Nikoli? Z.S.; Yoshimura M.; Araki S; Fujiwara T.

2007-01-01

180

Turbulent heat transfer from a sparsely vegetated surface - Two-component representation

The conventional calculation of heat fluxes from a vegetated surface involving the coefficient of turbulent heat transfer which increases logarithmically with surface roughness, is inappropriate such highly structured surfaces as desert scrub or open forest. An approach is developed here for computing sensible heat flux from sparsely vegetated surfaces, where the absorption of insolation and the transfer of absorbed heat to the atmosphere are calculated separately for the plants and for the soil. This approach is applied to a desert-scrub surface in the northern Sinai, for which the turbulent transfer coefficient of sensible heat flux from the plants is much larger than that from the soil below, as shown by an analysis of plant, soil, and air temperatures. The plant density is expressed as the sum of products (plant-height) x (plant-diameter) of plants per unit horizontal surface area. The solar heat absorbed by the plants is assumed to be transferred immediately to the airflow. The effective turbulent transfer coefficient k(g-eff) for sensible heat from the desert-scrub/soil surface computed under this assumption increases sharply with increasing solar zenith angle, as the plants absorb a greater fraction of the incoming irradiation. The surface absorptivity (the coalbedo) also increases sharply with increasing solar zenith angle, and thus the sensible heat flux from such complex surfaces is a much broader function of time of day than when computed under constant k(g-eff) and constant albedo assumptions.

Otterman, J.; Novak, M. D.; Starr, D. O'C.

1993-01-01

181

Integration Of Heat Transfer Coefficient In Glass Forming Modeling With Special Interface Element

International Nuclear Information System (INIS)

Numerical modeling of the glass forming processes requires the accurate knowledge of the heat exchange between the glass and the forming tools. A laboratory testing is developed to determine the evolution of the heat transfer coefficient in different glass/mould contact conditions (contact pressure, temperature, lubrication...). In this paper, trials are performed to determine heat transfer coefficient evolutions in experimental conditions close to the industrial blow-and-blow process conditions. In parallel of this work, a special interface element is implemented in a commercial Finite Element code in order to deal with heat transfer between glass and mould for non-meshing meshes and evolutive contact. This special interface element, implemented by using user subroutines, permits to introduce the previous heat transfer coefficient evolutions in the numerical modelings at the glass/mould interface in function of the local temperatures, contact pressures, contact time and kind of lubrication. The blow-and-blow forming simulation of a perfume bottle is finally performed to assess the special interface element performance

182

Integration Of Heat Transfer Coefficient In Glass Forming Modeling With Special Interface Element

Numerical modeling of the glass forming processes requires the accurate knowledge of the heat exchange between the glass and the forming tools. A laboratory testing is developed to determine the evolution of the heat transfer coefficient in different glass/mould contact conditions (contact pressure, temperature, lubrication…). In this paper, trials are performed to determine heat transfer coefficient evolutions in experimental conditions close to the industrial blow-and-blow process conditions. In parallel of this work, a special interface element is implemented in a commercial Finite Element code in order to deal with heat transfer between glass and mould for non-meshing meshes and evolutive contact. This special interface element, implemented by using user subroutines, permits to introduce the previous heat transfer coefficient evolutions in the numerical modelings at the glass/mould interface in function of the local temperatures, contact pressures, contact time and kind of lubrication. The blow-and-blow forming simulation of a perfume bottle is finally performed to assess the special interface element performance.

Moreau, P.; César de Sá, J.; Grégoire, S.; Lochegnies, D.

2007-05-01

183

Study for transfer coefficient of iodine from grass to cow milk

International Nuclear Information System (INIS)

Radioiodine (131I) is one of the radio nuclides likely to get released into the atmosphere in case of a reactor accident, though chances of such an accident are very remote due to stringent engineering safety features. During the short initial phase of accidental release of radioactivity, 131I is transferred through grass-cow milk pathway, leading to significant thyroid dose to those consuming milk, especially infant and children. Transfer coefficients are important for quick evaluation of environmental contamination, during both normal and abnormal operational phases of a nuclear facility. Transfer coefficient of iodine from grass to milk is defined as ratio of iodine concentration in milk (Bq.L-1) obtained at equilibrium for a constant rate of intake of iodine in (Bq.D-1). During normal operation conditions of nuclear power reactor, the release of radioactive iodine isotopes is are too low that they are not present in measurable concentrations in the environment. Hence, studies are to be performed using stable iodine to estimate the transfer coefficient. A method has been developed based on thermal neutron activation analysis (NAA) to estimate the stable iodine concentration present in grass and cow milk. The method involves pre-concentration from matrix, neutron activation and gamma spectrometry and these were standardized

184

Total and radiative heat transfer to an immersed surface in a gas-fluidized bed

International Nuclear Information System (INIS)

A high-temperature heat transfer probe capable of measuring both the total and radiative heat transfer coefficients between an immersed surface and the bed has been designed, fabricated, and tested. Measurements of these coefficients in beds of 559 and 751 ?m sand particles at temperatures up to 1,175K have been made using this probe. A thermal analysis of the probe is developed in order to ensure a reliable interpretation of the measured quantities. The dependence of the total and radiative heat transfer coefficients on such parameters as bed temperature, fluidizing air velocity, and mean bed particle size are investigated. The various models proposed to describe high-temperature heat transfer are evaluated from this perspective. The models capable of best simulating the heat transfer process with relative ease of computation are identified and evaluated using data generated in the study

185

Heat transfer phenomena of rarefied gas flows is discussed based on a literature survey of analytical and experimental rarefied gas dynamics. Subsonic flows are emphasized for the purposes of meteorological thermometry in the high atmosphere. The heat transfer coefficients for three basic geometries are given in the regimes of free molecular flow, transition flow, slip flow, and continuum flow. Different types of heat phenomena, and the analysis of theoretical and experimental data are presented. The uncertainties calculated from the interpolation rule compared with the available experimental data are discussed. The recovery factor for each geometry in subsonic rarefied flows is also given.

Chung, S.

1973-01-01

186

Directory of Open Access Journals (Sweden)

Full Text Available Lie point symmetry analysis is performed for an unsteady nonlinear heat diffusion problem modeling thermal energy storage in a medium with a temperature-dependent power law thermal conductivity and subjected to a convective heat transfer to the surrounding environment at the boundary through a variable heat transfer coefficient. Large symmetry groups are admitted even for special choices of the constants appearing in the governing equation. We construct one-dimensional optimal systems for the admitted Lie algebras. Following symmetry reductions, we construct invariant solutions.

Raseelo J. Moitsheki

2008-09-01

187

Energy Technology Data Exchange (ETDEWEB)

Visual experiments were employed to investigate heat transfer characteristics of steam on vertical titanium plates with/without surface modifications for different surface energies. Stable dropwise condensation and filmwise condensation were achieved on two surface modification titanium plates, respectively. Dropwise and rivulet filmwise co-existing condensation form of steam was observed on unmodified titanium surfaces. With increase in the surface subcooling, the ratio of area ({eta}) covered by drops decreased and departure diameter of droplets increased, resulting in a decrease in condensation heat transfer coefficient. Condensation heat transfer coefficient decreased sharply with the values of {eta} decreasing when the fraction of the surface area covered by drops was greater than that covered by rivulets. Otherwise, the value of {eta} had little effect on the heat transfer performance. Based on the experimental phenomena observed, the heat flux through the surface was proposed to express as the sum of the heat flux through the dropwise region and rivulet filmwise region. The heat flux through the whole surface was the weighted mean value of the two regions mentioned above. The model presented explains the gradual change of heat transfer coefficient for transition condensation with the ratio of area covered by drops. The simulation results agreed well with the present experimental data when the subcooling temperature is lower than 10 C. (author)

Baojin, Qi; Li, Zhang; Hong, Xu; Yan, Sun [State-Key Laboratory of Chemical Engineering, School of Mechanical and Power Engineering, East China University of Science and Technology, Shanghai 200237 (China)

2011-01-15

188

Directory of Open Access Journals (Sweden)

Full Text Available The evaporation heat transfer coefficient of the refrigerant R-134a in a vertical plate heat exchanger was investigated experimentally. The area of the plate was divided into several segments along the vertical axis. For each of the segments, the local value of the heat transfer coefficient was calculated and presented as a function of the mean vapor quality in the segment. Owing to the thermocouples installed along the plate surface, it was possible to determine the temperature distribution and vapor quality profile inside the plate. The influences of the mass flux, heat flux, pressure of system and the flow configuration on the heat transfer coefficient were also taken into account and a comparison with literature data was performed.

EMILA ŽIVKOVI?

2009-04-01

189

Vibration Analysis of a Framework Structure by Generalized Transfer Stiffness Coefficient Method

A generalized transfer stiffness coefficient method using graph theory is developed in order to improve the applicability of the transfer stiffness coefficient method. In the new method, an analytical model is expressed by a weighted signal-flow graph, and the graph is contracted according to the series and parallel contraction rules. The computational complexity and the memory requirement for the contraction process are both minimized by choosing the optimal contraction route. In addition, it is possible to develop a data-driving program that is applicable to various structures without updating the source program. An algorithm based on the present method is formulated for the in-plane longitudinal and flexural coupled free and forced vibration analyses of a two-dimensional framework structure. Furthermore, an overview for applying the method to a three-dimensional framework structure is briefly presented. The validity of the present algorithm is confirmed by the results of numerical computations.

Bonkobara, Yasuhiro; Kondou, Takahiro; Ayabe, Takashi; Choi, Myung-Soo

190

Experimental Estimation of Heat Transfer Coefficients Using Helical Coil in an Agitated Vessel

Directory of Open Access Journals (Sweden)

Full Text Available A mathematical model is developed to analyze the heating rates and compare the relation with experimental results obtained in our present study . Low shear rate concentration of sodium carboxymethal cellulose fluids with two different coil lengths 2.362m and 2.82m, diameter of the helical coil equal to 156mm, di=4.0mm and do=6.4mm were used to correlate overall heat transfer coefficients in an agitated vessel with four blade paddle impeller. The model is derived by using velocity flow field and energy equations in cylindrical coordinate for straight tube and later extended to helical coil. The new design relation for obtaining the individual heat transfer coefficient in terms of flow behavior index is equal to

Ashok Reddy K , Bhavanth Rao M ,Ram Reddy P

2012-04-01

191

Heat transfer coefficient between the flame and a radioactive material transport cask

International Nuclear Information System (INIS)

At the time of a full-scale fire experiment on a fire-resisting wooden building, a model radioactive material transport cask was placed within the flame of the fire. By measuring its temperatures and temperatures of the fire flame, the heat transfer coefficient etc. were observed. The specimen model cask is a three-layered structure; the outer steel shell, the inner stainless steel shell and a lead radiation shielding layer in between. (1) When the flame started to surround the cask, the heat flux from the flame into the cask was about 7 x 104 kcal/m2h, in agreement with that measured with a heat flow meter. (2) The total heat transfer coefficient from the flame into the cask, calculated from the temperature measurements in both, was about 150 - 200 kcal/m2h0C. (Mori, K.)

192

International Nuclear Information System (INIS)

Radioactive fission product release as the consequence of a severe accident with nuclear installations needs to be studied in considerable detail in order to predict the source term hazard with acceptable accuracy. As far as the research on the fission product behaviour in containments is concerned the international effort has been concentrated around two large experimental programmes, DEMONA and LACE. Results of the bench-mark on 'Post-test calculation of thermal-hydraulic behaviour in DEMONA experiment B3 with various computer codes used in CEC member states', show still considerable differences and uncertainties due to poor knowledge of global heat transfer coefficients for the wall condensation in containments. The objective of this study is to provide an estimate of the accuracy with which the coefficient for sensible heat transfer during wall condensation can be measured. (H.W.). 15 refs.; 7 figs.; 9 tabs

193

A study of the convection heat transfer coefficients of grinding fluids

By using hydrodynamic and thermal modelling, the variation of the convection heat transfer coefficient (CHTC) of the process fluids within the grinding zone has been investigated. Experimental measurements of CHTC for different grinding fluids have been undertaken and show that the CHTC depends on the grinding wheel speed and the fluid film thickness within the contact zone. The film thickness is determined by grinding wheel speed, porosity, grain size, fluid type, flow rate...

Jin, T.; Stephenson, David J.

2008-01-01

194

Approximate evaluation method of thermal transient stress under variable heat transfer coefficient

International Nuclear Information System (INIS)

The new approximate evaluation method was proposed for thermal transient stress under variable heat transfer coefficient. The proposed method uses Green functions and convolution integral. The proposed method was applied to the calculations of thermal transient stresses of a skirt-structure and a tube-sheet structure of IHX (intermediate heat exchanger) in commercialized fast reactor. It was verified that the proposed method gave good estimations for thermal transient stresses of those structures. (author)

195

Effect of Mass on Convective Heat Transfer Coefficient During Onion Flakes Drying

Directory of Open Access Journals (Sweden)

Full Text Available In this present study an open sun and greenhouse drying of onion flakes has been performed to study the effect of mass on convective heat transfer coefficient. Three sets of experiments with total quantity of onion as 300, 600 and 900 g were done. The onion was continuously dried for 33 h both in open sun and in the roof type even span greenhouse with floor area of 1.2 x 0.78 m2. Experiments were carried out during the months of October to December 2003 at IIT Delhi (28°35`N 72°12`E. Experiments were started at 8 am. The data obtained from experimentation under open sun and greenhouse conditions have been used to determine values of the constant `C` and exponent `n` by regression analysis and consequently, convective heat transfer coefficient. It is observed that there is a significant effect of mass on convective heat transfer coefficient for open as well as greenhouse drying. It is also observed that the rate of moisture evaporation in case of greenhouse drying is more than that in open sun drying during the off sunshine hours due to the stored energy inside the greenhouse. The experimental observations were analyzed in terms of percentage uncertainty also.

G.N. Tiwari

2006-01-01

196

Heat transfer coefficient, two-phase flow boiling of HFC134a

International Nuclear Information System (INIS)

Evaporation of HFC134a inside smooth, horizontal tubes is studied. Tests are made with pure refrigerant and with oil-refrigerant mixtures. Heat flux has varied from 2 kW/m2 to 10 kW/m2. The inner diameter of the tubes are 12 mm. Two evaporators are used, 4 and 10 m long. Oil content is varied from 0 to 2.5 mass percentage (synthetic oil, EXP-0275). Oil free HFC134a is found to have higher heat transfer coefficient than HCF22 at the same heat flux, as well as mass flux. The effect of oil in the refrigerant depends on the flux. At 2 and 4 kW/m2, the heat transfer coefficient has a maximum value for an oil content of around 0.5 mass percentage. No increase at all is registered for a heat flux of 6 kW/m2. Heat transfer coefficients for pure refrigerant are also compared to existing correlations. Pierre's correlation predict values with a reasonable accuracy

197

Effects of cooling and internal wave motions on gas transfer coefficients in a boreal lake

Directory of Open Access Journals (Sweden)

Full Text Available Lakes and other inland waters contribute significantly to regional and global carbon budgets. Emissions from lakes are often computed as the product of a gas transfer coefficient, k 600 , and the difference in concentration across the diffusive boundary layer at the air–water interface. Eddy covariance (EC techniques are increasingly being used in lacustrine gas flux studies and tend to report higher values for derived k 600 than other approaches. Using results from an EC study of a small, boreal lake, we modelled k 600 using a boundary-layer approach that included wind shear and cooling. During stratification, fluxes estimated by EC occasionally were higher than those obtained by our models. The high fluxes co-occurred with winds strong enough to induce deflections of the thermocline. We attribute the higher measured fluxes to upwelling-induced spatial variability in surface concentrations of CO2 within the EC footprint. We modelled the increased gas concentrations due to the upwelling and corrected our k 600 values using these higher CO2 concentrations. This approach led to greater congruence between measured and modelled k values during the stratified period. k 600 has a well-resolved and ~cubic relationship with wind speed when the water column is unstratified and the dissolved gases well mixed. During stratification and using the corrected k 600 , the same pattern is evident at higher winds, but k 600 has a median value of ~7 cm h?1 when winds are less than 6 m s?1, similar to observations in recent oceanographic studies. Our models for k 600 provide estimates of gas evasion at least 200% higher than earlier wind-based models. Our improved k 600 estimates emphasize the need for integrating within lake physics into models of greenhouse gas evasion.

Jouni J. Heiskanen

2014-05-01

198

International Nuclear Information System (INIS)

Program FREG series calculate temperature distribution in a fuel rod and the stored energy based on the distribution. The temperature distribution is calculated accordance with the fuel rod irradiation history. The temperature in the fuel rod is severely influenced with gap heat transfer coefficients between fuel pellet surface and cladding inner surface. Enphasis is placed on how to find the gap heat transfer coefficients. FREG-4 is a version-up program of FREG-3. Major modification from FREG-3 is handlings of fission product gas release, which have influences on the gap heat transfer. FREG-4 distingushed fission-product isotopes remained in pellets and fission-product gaseous isotopes released from the pellets, and considers that the released isotopes are transported for plenums to balance whole fuel rod internal pressure and transformed into another isotopes due to decay and the nuetron absorptions. The present report describes modified models from FREG-3 and user's manual for FREG-4. (author)

199

Comparison of boiling heat transfer coefficient and pressure drop correlations for evaporators

International Nuclear Information System (INIS)

Evaporator design is an important aspect for the HVAC industry. As the demand for more efficient and compact heat exchangers increase, researches on estimation of two-phase flow heat transfer and pressure drop gain importance. Due to complexity of the hydrodynamic and heat transfer of the two-phase flow, there are many experimental studies available for refrigerants int he literature. In this study, a model for boiling heat transfer in a horizontal tube has been developed and the simulation results are compared with experimental ones published in the literature. In these comparisons, heat transfer coefficient is calculated by using Kattan-Thome-Favrat (1998), Shah (1982), Kandilikar (1990), Chaddock and Brunemann (1967) correlations under different operational conditions such as saturation pressure, mass flux, the type of refrigerant and two phase flow pattern. Besides that flow pattern has also been considered in the simulation by using Thome and El Hajal (2002) model. For pressure drop Lockhart-Martinelli (1949), Mueller-Steinhagen-Hack (1986) and Groennerund (1979) correlations are used in simulations. Local vapor quality change at each experimental condition through the model is determined. Roughness is an important parameter for frictional pressure drop. Friction coefficient is determined by using Churchill (1977) model. (author)

200

The influence of a heat transfer coefficient probe on fluid flow near wall

Directory of Open Access Journals (Sweden)

Full Text Available Good knowledge of the convective boundary condition is necessary for finite element analysis of thermal deformation behavior in machine tools. There are a number of correlation equations for natural and forced convection and several correlations for mixed convection. Due to a relatively wide range of dimensions, temperatures and speeds, all regimes of convective heat transfer can be observed in machine tools, including the transition region between laminar and turbulent free convection, characterized by Rayleigh number values ranging between Ra = 108 – 109. Since convection in machine tools is highly influenced by external and internal factors, the heat transfer coefficient characterizing convective heat transfer and its changes has to be evaluated experimentally. An experimental technique for evaluating the heat transfer coefficient on the wall and its changes between the wall and the ambient air, based on an active sensor, is being developed. Since the probe dimensions are not negligible, given the fluid motion structures near the wall which are induced by buoyancy or by forced flow, the influence of the probe has to be considered. Paper deals with latest experimental results and summarizes previous work.

Mareš Martin

2012-04-01

201

Immersion Condensation on Oil-Infused Heterogeneous Surfaces for Enhanced Heat Transfer

Enhancing condensation heat transfer is important for broad applications from power generation to water harvesting systems. Significant efforts have focused on easy removal of the condensate, yet the other desired properties of low contact angles and high nucleation densities for high heat transfer performance have been typically neglected. In this work, we demonstrate immersion condensation on oil-infused micro and nanostructured surfaces with heterogeneous coatings, where water droplets nucleate immersed within the oil. The combination of surface energy heterogeneity, reduced oil-water interfacial energy, and surface structuring enabled drastically increased nucleation densities while maintaining easy condensate removal and low contact angles. Accordingly, on oil-infused heterogeneous nanostructured copper oxide surfaces, we demonstrated approximately 100% increase in heat transfer coefficient compared to state-of-the-art dropwise condensation surfaces in the presence of non-condensable gases. This work offers a distinct approach utilizing surface chemistry and structuring together with liquid-infusion for enhanced condensation heat transfer.

Xiao, Rong; Miljkovic, Nenad; Enright, Ryan; Wang, Evelyn N.

2013-06-01

202

This paper examines a parameterization of a quasi-geostrophic eddy transport that takes into account the time variation of eddy transfer coefficients according to Green's (1970) theory. It was found that, in the original eddy transfer relationship of Green, connecting the integral of the northward eddy entropy flux through midlatitudes with the second power of the difference in 500-mb entropy across the region of baroclinic activity, a value of 4 for the exponent is obtained when the temperature gradients at 500 mb are used. When the gradients at 1000 mb are used, an exponent of 1.5 is obtained. The differences in the powers in the eddy transfer relation were explored in a two-level zonally averaged model. It was found that an appropriate choice of power may be of special importance if the model is devised to simulate the seasonal climate cycle or to test astronomical changes inducing different seasonalities.

Neeman, Binyamin U.; Ohring, George; Joseph, Joachim H.

1989-01-01

203

Prediction of the heat transfer coefficient for ice slurry flows in a horizontal pipe

Energy Technology Data Exchange (ETDEWEB)

In this study, heat transfer for ice slurry flows was investigated. For the experiments, ice slurry was made from 9% ethanol-water solution flow in a 20 mm internal diameter, 1000 mm long horizontal copper tube. The ice slurry was heated by a cylindrical electrical resistance. Experiments of the melting process were conducted with changing the ice slurry mass flux rate and the heat flux. The enthalpy-porosity formulation was used to predict the ice slurry temperature and the local values of heat transfer coefficient in the exchanger. Measurements and data acquisition of ice slurry temperature and mass flow rate at the inlet and outlet are performed. It was found that the heat transfer rates increase with the mass flow rate, the ice fraction and the heat flux density. However, the effect of ice fraction appears not to be significant at high mass flow rates. In addition, the correlation proposed by Christensen and Kauffeld gives good agreement with numerical results. (author)

Kousksou, T.; Jamil, A.; Zeraouli, Y. [Laboratoire de Thermique Energetique et Procedes, Avenue de l' Universite, BP 1155, 64013 Pau Cedex (France); El Rhafiki, T. [Laboratoire de Thermique Energetique et Procedes, Avenue de l' Universite, BP 1155, 64013 Pau Cedex (France); Laboratoire d' Energetique, Mecanique des Fluides et Sciences des Materiaux, Universite AbdelMalek Essaidi, 90000 Tetouan (Morocco)

2010-06-15

204

Experimental investigation of scale formation at heat transfer surface in PWR secondary system

International Nuclear Information System (INIS)

In the secondary system of steam generators (SGs) of PWR plants, iron is brought from feedwater and some of it is brought out with blow down of SGs, then others build upon an equipment in the SGs. The iron deposit onto heat transfer surface and form a scale, and increases heat transfer resistance. Then it may affect heat transfer performance. The secondary water chemistry in Japanese PWR plants is operated under the AVT condition (NH3 and N2H4). Feedwater usually contains very low concentration of iron. The study was performed jointly by 5 Japanese utilities and Japanese plant manufacturer of PWR plant, as a title of ''The study on secondary water chemistry to retard deposition onto the secondary side surface of heat transfer tube of SG''. This paper presents investigated results of relationship between feedwater chemistry and scale formation onto heat transfer surface, and heat transfer coefficient. (authors). 6 figs., 2 tabs., 6 refs

205

International Nuclear Information System (INIS)

Although the heat transfer problem of pressurized supercritical water (SCW) flows in around tube has been studied for decades, the subject is still considerably of interest nowadays. This is partly because of the expanded investigation of using SCW for nuclear engineering applications like SCWR which is generation IV reactor and promising advanced nuclear systems because of their high thermal efficiency(i.e., about 45% as opposed to about 33% efficiency for current light water reactors LWRs) and considerable plant simplification. Literature survey shows that heat transfer coefficient (HTC) is sharply enhanced near the pseudo critical temperature. As the heat flux increases, the peak of the HTC decreases. When the heat flux reaches to some high values, heat transfer deterioration (HTD) occurs. CFD code with various turbulence models are being used to evaluate HTC. Modeling of Yamagata's experiment has been carried out for evaluation of HTC using CFD code FLUENT with standard k? turbulence model, nonequilibrium wall function,viscous heating, full buoyancy effect and including wall roughness effect.In this paper model constants for standard k? model have been derived. In the Yamagata experiment, investigations were made for HTC to supercritical water flowing vertically upward in vertical tubes of 10 and 7.5mm internal diameter, at pressures 22.6, 24.5 and 29.5 MPa, bulk temperature from 230 to 540 oC, heat flux 233, 465, 698 and 930kW/m2 and mass 5, 698 and 930kW/m2 and mass flux 1200 kg/m2.s. Two dimensional axisymmetry grid generation has been done using GAMBIT. Inbuilt boundary conditions in the FLUENT are invoked for mass flow rate at inlet,pressure outlet at the outlet of the tube and wall at the cylindrical surface where heat flux is given. Thermo-physical properties are taken from the (IAPWSIF97) and piecewise linear variation are given in the FLUENT for 30 temperature points. Bulk fluid temperature is obtained using user defined function. HTC are obtained based on heat flux, surface temperature and bulk fluid temperature. The calculated HTC is compared with the experimental results and also compared with the results of the other authors. It is observed in both experimental and code calculated values that peak HTC decreases for increase in heat flux for constant mass flux and it is also noticed that peak HTC decreases with the increase in system pressure for constant heat flux. However, it is noticed that magnitude of peak HTC calculated by code is higher than the experimental data especially for higher heat flux and rate of decrease of peak HTC with increase in heat flux is lesser with compared to experimental results. It is observed that peak HTC increases with increase in wall roughness of the tube. It is also observed that HTC calculated by FLUENTcode is in good agreement with the HTC calculated by other authors using CFD code with various turbulence models. (author)

206

Radiative transfer through arrays of discrete surfaces

International Nuclear Information System (INIS)

Radiant transport involving arrays of discrete surfaces constitutes one of the major unresolved problems in the field of radiation heat transfer. This paper discusses the requirements for experimental validation of a general Monte Carlo solution to this class of problems. This work is a collaborative effort between Oregon State University, where the experimental portion is being accomplished, and the Pacific Northwest Laboratory, which is responsible for the Monte Carlo simulation. The design and calibration of a simple, compact, and flexible instrument for direct measurement of bidirectional reflectance are presented in some detail. The capability to measure full bidirectional reflectance, as provided by this instrument, is essential to an accurate portrayal of surface properties in a Monte Carlo simulation. Measured data for a common flat white paint are presented and clearly demonstrate the need for accurate and complete surface property information. Applications include volumetric air heating solar central receivers, ceramic fabrics, and fibrous insulation

207

The hydrodynamic characteristics and the overall volumetric oxygen transfer coefficient of a new multi-environment bioreactor which is an integrated part of a wastewater treatment system, called BioCAST, were studied. This bioreactor contains several zones with different environmental conditions including aerobic, microaerophilic and anoxic, designed to increase the contaminant removal capacity of the treatment system. The multi-environment bioreactor is designed based on the concept of airlift reactors where liquid is circulated through the zones with different environmental conditions. The presence of openings between the aerobic zone and the adjacent oxygen-depleted microaerophilic zone changes the hydrodynamic properties of this bioreactor compared to the conventional airlift designs. The impact of operating and process parameters, notably the hydraulic retention time (HRT) and superficial gas velocity (U(G)), on the hydrodynamics and mass transfer characteristics of the system was examined. The results showed that liquid circulation velocity (V(L)), gas holdup (?) and overall volumetric oxygen transfer coefficient (k(L)a(L)) increase with the increase of superficial gas velocity (U(G)), while the mean circulation time (t(c)) decreases with the increase of superficial gas velocity. The mean circulation time between the aerobic zone (riser) and microaerophilic zone (downcomer) is a stronger function of the superficial gas velocity for the smaller openings (1/2 in.) between the two zones, while for the larger opening (1 in.) the mean circulation time is almost independent of U(G) for U(G) ? 0.023 m/s. The smaller openings between the two zones provide higher mass transfer coefficient and better zone generation which will contribute to improved performance of the system during treatment operations. PMID:23142846

Behzadian, Farnaz; Yerushalmi, Laleh; Alimahmoodi, Mahmood; Mulligan, Catherine N

2013-08-01

208

International Nuclear Information System (INIS)

Flow Accelerated Corrosion (FAC) requires considerable attention in plant piping management, for its potential of catastrophic pipe rupture of main piping systems. For plant integrity and safety, pipe wall inspection must be conducted with proper prediction of FAC susceptible area and thinning rate. In view of fluid dynamics, the most essential factor to be considered is mass transfer at the inner surface of the pipe. Mass transfer coefficients are determined by fluid properties and piping geometry, however, no universal correlation exists, which is adaptable to various types of piping elements. It would be very useful if the coefficients can be obtained by a common method with inputs of general hydraulic properties. In this study, FAC experiments were conducted with a contracted rectangular duct under PWR condensate water condition. Also, numerical calculations were done to obtain hydraulic features in the duct of the experiment. The modeling of mass transfer coefficient was progressed, in parallel, based on Chilton-Colburn analogy and utilizing 'Effective Friction velocity' and 'Effective Reynolds number' from the hydraulics in the viscous layer along the wall. By considering the turbulent velocity of the viscous layer into the mass transfer coefficient, the correlation with the FAC thinning rate improved, effectively. Future works will be to quantify the turbulence effect and the surface roughness effect to the thinning rate. (author)e. (author)

209

Effect of pressure on heat transfer coefficient at the metal/mold interface of A356 aluminum alloy

DEFF Research Database (Denmark)

The aim of this paper is to correlate interfacial heat transfer coefficient (IHTC) to applied external pressure, in which IHTC at the interface between A356 aluminum alloy and metallic mold during the solidification of casting under different pressures were obtained using the inverse heat conduction problem (IHCP) method. The method covers the expedient of comparing theoretical and experimental thermal histories. Temperature profiles obtained from thermocouples were used in a finite difference heat flow program to estimate the transient heat transfer coefficients. The new simple formula was presented for correlation between external pressure and heat transfer coefficient. Acceptable agreement with data in literature shows the accuracy of the proposed formula.

Fardi Ilkhchy, A.; Jabbari, Masoud

2012-01-01

210

Energy Technology Data Exchange (ETDEWEB)

This paper attempts to formulate Overall Thermal Transfer Value (OTTV) coefficients for Composite, Hot-Dry and Warm-Humid climates, the three main tropical climates in India. Four existing air-conditioned office buildings - two mid-rise and two high-rise were modeled as case studies using eQuest v.3.6, which is a DoE2.2, based building energy simulation tool. Based on the study of building envelope, loads, operation and HVAC system characteristics of these case study buildings, a hypothetical high-rise, 16 storey office building, octagonal in plan was created for parametric studies. 98 types of opaque exterior wall constructions and 93 types of glass constructions were varied sequentially in parametric runs to obtain results for hourly wall conduction, glass conduction and glass radiation heat flow in eight orientations for each of the climate type. These hourly results were processed to obtain annual heat gain intensities for each parametric case for all three modes of heat transfer. Regression analysis was used to obtain the OTTV coefficients -TD{sub eq}, DT and SF for the three climates. A new OTTV equation is obtained and presented. The set of coefficients obtained were verified by calculating the OTTV for the four case study buildings, for various parametric runs. The computed OTTV for the four case study buildings exhibits good linear correlation with the annual space cooling plus heating energy use in three climates. (author)

Devgan, Seema; Jain, A.K.; Bhattacharjee, B. [Department of Civil Engineering, Indian Institute of Technology, Hauz khas, New Delhi 110016 (India)

2010-10-15

211

Correlations for heat transfer coefficients in open gaps with respect to mixed convection

International Nuclear Information System (INIS)

Published results on mixed convection phenomena have been applied to determine the convective heat transfer between the cover gas and the open gaps in the roof of SNR 2. It has been reported in the literature that heat transfer coefficients for forced flow conditions in vertical heated or cooled pipes are modified by buoyancy effects. In the ''aiding'' condition, where buoyancy and flow act in the same direction, heat transfer is enhanced. In the ''opposing'' case heat transfer is reduced. This applies for laminar flow; the reverse is true for turbulent flow. The literature indicates furthermore that: the Reynolds number indicating turbulent flow can be as low as 30 for mixed convection; the criterion for the onset of mixed convection is given by the Richardson number Ri=Gr/Re2 > 0,002. The published results have been modified in consistency with the open gaps in the SNR 2 reactor roof. Several heat transfer correlations have been evaluated and their suitability examined. (author)

212

Energy Technology Data Exchange (ETDEWEB)

Even a small amount of noncondensable gas can reduce the condensation heat transfer considerably. In the condenser tube, the condensate flows as an annular liquid film adjacent to the tube wall, while the vapor/noncondensable gas mixture flows in the core region. Consequently, the noncondensable gas layer that forms adjacent to the liquid/gas interface reduces the heat transfer capability. Several correlations were developed to evaluate steam condensation heat transfer with noncondensable gas in a vertical condenser tube. In this study, two empirical correlations proposed by Vierow and Schrock and Kuhn are considered and a new correlation is developed to improve the accuracy of prediction. In these correlations, the local heat transfer coefficient is simply expressed in the form of a 'degradation factor,' defined as the ratio of the experimental heat transfer coefficient to a reference heat transfer coefficient.

Lee, Kwon-Yeong; Kim, Moo Hwan [Pohang University of Science and Technology, Pohang (Korea, Republic of)

2006-07-01

213

Heat transfer in an unwetted zone in hot-surface cooling

International Nuclear Information System (INIS)

Pin cladding overheating may occur because of increasing power or reduction in coolant flow rate, which perturb normal working conditions. Conditions return to normal after the perturbation only if the heat output in a pin corresponds to the heat removed by the coolant. It is necessary to calculate the heat transfer at all stages in such a situation to provide nuclear safety. At present, little is known about heat transfer when hot pins are cooled by underheated water or steam-water mixtures with low steam contents in particular because measurements are difficult. Under stationary conditions, the high critical heat fluxes mean that the temperatures in the transfer surfaces beyond the crisis zone become too high, which leads to failure. When measurements are made with hot surfaces cooling, the relatively high transfer coefficients at high mass flow rates mean that the cooling lasts only some seconds. As the cooling time shortens, the equipment specifications tighten, and there is a marked increase in the error in determining the transfer coefficients. To overcome these difficulties, a hot-spot method has been proposed, which under stationary conditions gives a flow structure as in nonstationary cooling. However, it is impossible to estimate the amount of heat transferred to the flow from the hot spot, so it is virtually impossible to calculate the two-phase flow parameters. The authors have made measurements on the heat-transfer coefficients in the unwetted zone when tr coefficients in the unwetted zone when the hot surface is cooled by pressurized water at high mass speeds. The relatively high heat deposition rate in the working section produced quasistationary cooling conditions, which enabled them to determine the transfer coefficients with acceptable accuracy

214

International Nuclear Information System (INIS)

Highlights: ? Mass transfer coefficient does not depend on biomass concentration. ? The pulp density has a negative effect on mass transfer coefficient. ? The pulp density is the unique factor that affects maximum OUR. ? In this work, Neale’s correlation is corrected for prediction of mass transfer coefficient. ? Biochemical reaction is a limiting factor in the uranium bioleaching process. - Abstract: In this work, the volumetric oxygen mass transfer coefficient and the oxygen uptake rate (OUR) were studied for uranium ore bioleaching process by Acidthiobacillus ferrooxidans in a stirred tank reactor. The Box-Bohnken design method was used to study the effect of operating parameters on the oxygen mass transfer coefficient. The investigated factors were agitation speed (rpm), aeration rate (vvm) and pulp density (% weight/volume) of the stirred tank reactor. Analysis of experimental results showed that the oxygen mass transfer coefficient had low dependence on biomass concentration but had higher dependence on the agitation speed, aeration rate and pulp density. The obtained biological enhancement factors were equal to ones in experiments. On the other hand, the obtained values for Damkohler number (Da < 0.468) indicated that the process was limited by the biochemical reaction rate. Experimental results obtained for oxygen mass transfer coefficient were correlated with the empirical relations proposed by Garcia-Ochoa and Gomez (2009) and Neale and Pinches (1994). Due to the high relative error in the correlation of Neale and Pinches, that correlation was corrected and the coefficient of determination was calculated to be 89%. The modified correlation has been obtained based on a wide range of operating conditions, which can be used to determine the mass transfer coefficient in a bioreactor

215

International Nuclear Information System (INIS)

The paper reports and analysis of the influence of errors in measuring the temperature and isotopic concentrations in experimental determination of mass and heat transfer coefficient. The calculation model for this coefficient is presented as well as the result obtained from an experimental installation of water distillation. The experimental distillation column of an 108 mm inner diameter was filled with an B ordered packing up to a 14 m height. In such a column temperature, vapor concentrations, pressures and reflux rates were measured in 12 points. A table with measured and calculated values is given. Large errors in this quantities made lead to either sub- or super evaluation of the packing performances. Under-evaluation may lead to investment cost increases while super-evaluation may lead to a production capacity decrease

216

Energy Technology Data Exchange (ETDEWEB)

Thermal accommodation coefficients have been derived for a variety of gas-surface combinations using an experimental apparatus developed to measure the pressure dependence of the conductive heat flux between parallel plates at unequal temperature separated by a gas-filled gap. The heat flux is inferred from temperature-difference measurements across the plates in a configuration where the plate temperatures are set with two carefully controlled thermal baths. Temperature-controlled shrouds provide for environmental isolation of the opposing test plates. Since the measured temperature differences in these experiments are very small (typically 0.3 C or less over the entire pressure range), high-precision thermistors are used to acquire the requisite temperature data. High-precision components have also been utilized on the other control and measurement subsystems in this apparatus, including system pressure, gas flow rate, plate alignment, and plate positions. The apparatus also includes the capability for in situ plasma cleaning of the installed test plates. Measured heat-flux results are used in a formula based on Direct Simulation Monte Carlo (DSMC) code calculations to determine the thermal accommodation coefficients. Thermal accommodation coefficients have been determined for three different gases (argon, nitrogen, helium) in contact with various surfaces. Materials include metals and alloys such as aluminum, gold, platinum, and 304 stainless steel. A number of materials important to fabrication of Micro Electro Mechanical Systems (MEMS) devices have also been examined. For most surfaces, coefficient values are near 0.95, 0.85, and 0.45 for argon, nitrogen, and helium, respectively. Only slight differences in accommodation as a function of surface roughness have been seen. Surface contamination appears to have a more significant effect: argon plasma treatment has been observed to reduce thermal accommodation by as much as 0.10 for helium. Mixtures of argon and helium have also been examined, and the results have been compared to DSMC simulations incorporating thermal-accommodation values from single-species experiments.

Gallis, Michail A.; Castaneda, Jaime N.; Rader, Daniel John; Torczynski, John Robert; Trott, Wayne Merle

2010-10-01

217

Energy Technology Data Exchange (ETDEWEB)

Condensation (vapor to liquid phase change) is encountered in various industrial processes, in steam engine systems, refrigerating machineries and heat pumps. Vapor condensation on a cooled surface leads to two types of phenomena: the film condensation and the dropwise condensation which have different heat transfer properties. This article treats of the film condensation on smooth surfaces and on its application to the condensation inside and outside cylindrical tubes: 1 - basic considerations about condensation: condensation coefficient, heat transfer coefficients; 2 - film condensation of pure vapor: condensation of pure stagnating vapor (Nusselt theory, condensation on a tube bundle, flooding effect, waves influence on the film surface, approach using 2D boundary layer equations, Sparrow and Greg analysis), condensation outside a smooth tube (condensation on the outer surface, general equations, laminar flow without pressure gradient, flow with pressure gradient), condensation inside smooth tubes (vertical tube, horizontal tube), influence of rotation. (J.S.)

Panday, P. [Universite de Technologie de Belfort-Monbeliard, 90 (France)

2006-01-15

218

International Nuclear Information System (INIS)

Water heat transfer experiments were carried out in a uniformly heated annulus with a wide range of pressure conditions. The local heat transfer coefficients for saturated water flow boiling have been measured just before the occurrence of the Critical Heat Flux(CHF) along the length of the heated section. The trends of the measured heat transfer coefficients were quite different from the conventional understanding for the heat transfer of saturated flow boiling. The discrepancy was explained from the nucleate boiling in the liquid film of annular flow under high heat flux conditions

219

Mass Transfer Coefficient During Cathodic Protectionof Low Carbon Steel in Seawater

The aim of this research is to calculate mass transfer coefficient, kd, during cathodic protection of low carbon steel in neutral seawater (3.5% W/V NaCl in distilled water with pH = 7). Two types of cathodic protection were used:First: Sacrificial anode cathodic protection (SACP) were a pipeline of steel carrying seawater using zinc as a sacrificial anode and with variable temperatures ranged (0 ? 45oC) and volumetric flow rate ranged (5 ? 900 lit/hr). It was found that the kd increa...

Ameel Mohammed Rahman; Anees Abdullah Khadom; Hameed, Khalid W.

2009-01-01

220

Effect of Mass on Convective Heat Transfer Coefficient During Onion Flakes Drying

In this present study an open sun and greenhouse drying of onion flakes has been performed to study the effect of mass on convective heat transfer coefficient. Three sets of experiments with total quantity of onion as 300, 600 and 900 g were done. The onion was continuously dried for 33 h both in open sun and in the roof type even span greenhouse with floor area of 1.2 x 0.78 m2. Experiments were carried out during the months of October to December 2003 at IIT Delhi (28°35`N 72°1...

Tiwari, G. N.; Anil Kumar

2006-01-01

221

Effect of Mixed Working Fluid Composition on Binary Cycle Condenser Heat Transfer Coefficients

Energy Technology Data Exchange (ETDEWEB)

Effect of Mixed Working Fluid Composition on Binary Cycle Condenser Heat Transfer Coefficients Dan Wendt, Greg Mines Idaho National Laboratory The use of mixed working fluids in binary power plants can provide significant increases in plant performance, provided the heat exchangers are designed to take advantage of these fluids non-isothermal phase changes. In the 1980's testing was conducted at DOE's Heat Cycle Research Facility (HCRF) where mixtures of different compositions were vaporized at supercritical pressures and then condensed. This testing had focused on using the data collected to verify that Heat Transfer Research Incorporated (HTRI) codes were suitable for the design of heat exchangers that could be used with mixtures. The HCRF data includes mixture compositions varying from 0% to 40% isopentane and condenser tube orientations of 15{sup o}, 60{sup o}, and 90{sup o} from horizontal. Testing was performed over a range of working fluid and cooling fluid conditions. Though the condenser used in this testing was water cooled, the working fluid condensation occurred on the tube-side of the heat exchanger. This tube-side condensation is analogous to that in an air-cooled condenser. Tube-side condensing heat transfer coefficient information gleaned from the HCRF testing is used in this study to assess the suitability of air-cooled condenser designs for use with mixtures. Results of an air-cooled binary plant process model performed with Aspen Plus indicate that that the optimal mixture composition (producing the maximum net power for the scenario considered) is within the range of compositions for which data exist. The HCRF data is used to assess the impact of composition, tube orientation, and process parameters on the condensing heat transfer coefficients. The sensitivity of the condensing coefficients to these factors is evaluated and the suitability of air-cooled condenser designs with mixtures is assessed. This paper summarizes the evaluation of the HCRF data and discusses the next steps in the project evaluation of air-cooled condenser designs that can take advantage of the performance gains possible with these fluids.

Dan Wendt; Greg Mines

2011-10-01

222

This paper describes a new method to determine the equivalent heat transfer coefficients, i.e., radial and azimuthal, in CICC’s with parallel cooling channels. The method is based on the measurement of the steady state temperature response to a step heating. The experiment is modelled by a set of transport equations for the temperature distribution that contain explicitly the parametric dependence on the transverse heat transfer coefficients. The equations are solved analytically and the values of the equivalent transverse heat transfer coefficients are obtained as the best fit of the experimental temperature distributions. We show the results obtained with the method by application to a short length sample experiment in the SULTAN test facility using an ITER-type CICC with special instrumentation, and with heaters to generate a variety of heat slugs. The values of heat transfer coefficient are consistent with expected values, based in particular on the theory of dispersion in porous media.

Marinucci, C; Bruzzone, P; Stepanov, B

2007-01-01

223

A review of measured values of the milk transfer coefficient (fsub(m)) for iodine

International Nuclear Information System (INIS)

Most published assessments of the environmental transport of iodine have used a value of 1 X 10-2 days per litre (d/1) for the transfer coefficient (fsub(m)) which relates the concentration per litre of milk to the daily amount of the element ingested by a cow. However, the USNRC has recommended (USNRC 77) a value of 0.6 X 10-2 d/1 for the transfer of iodine to cow's milk and 6 X 10-2 d/1 for goat's milk. A literature survey of published values of fsub(m) leads to a recommendation which deviates from the values chosen by the USNRC. An fsub(m) of 0.5 d/1 for goat's milk and an fsub(m) of 1 X 10-2 for cow's milk appear to be more appropriate. (author)

224

Assessment of Real Heat Transfer Coefficients through Shell and Tube and Plate Heat Exchangers

Directory of Open Access Journals (Sweden)

Full Text Available The purpose of this paper is to present a procedure used in the assessment of the real heat transfer characteristic of shell and tube and plate heat exchangers. The theoretical fundamentals of the procedure are introduced as well as the measured data collection and processing. The theoretical analysis is focused on the adoption of criterial equations which, subjected to certain verification criteria presented in the paper, provide the most credible value of the convection heat transfer coefficients inside the circular and flat tubes. In the end two case studies are presented, one concerning a shell and tube heat exchanger operational at INCERC Thermal Substation and the other concerning a plate heat exchanger tested on the Laboratory Stand of the Department of Building Services and Efficient Use of Energy in Buildings of INCERC Bucharest.

Dan CONSTANTINESCU

2011-07-01

225

International Nuclear Information System (INIS)

The heat transfer of enhancement condensation of the vapor over the surface of an axisymmetric cylinder has been first studied theoretically in this paper. The problems of an axisymmetric cylinder are transformed into plate problems. The effects of some parameters on heat transfer coefficients of the vapor condensation over the surface of an axisymmetric cylinder have been discussed here. The heat transfer of the vapor condensation over an elliptical cylinder and an axisymmetric wing-shape cylinder has compared with the heat transfer of the vapor condensation over a tube surface. The conclusion is that the heat transfer of the vapor condensation over an elliptical cylinder and an axisymmetric wing-shape cylinder is greater than that over tubes

226

Heat and mass transfer rates during flow of dissociated hydrogen gas over graphite surface

To improve upon the performance of chemical rockets, the nuclear reactor has been applied to a rocket propulsion system using hydrogen gas as working fluid and a graphite-composite forming a part of the structure. Under the boundary layer approximation, theoretical predictions of skin friction coefficient, surface heat transfer rate and surface regression rate have been made for laminar/turbulent dissociated hydrogen gas flowing over a flat graphite surface. The external stream is assumed to be frozen. The analysis is restricted to Mach numbers low enough to deal with the situation of only surface-reaction between hydrogen and graphite. Empirical correlations of displacement thickness, local skin friction coefficient, local Nusselt number and local non-dimensional heat transfer rate have been obtained. The magnitude of the surface regression rate is found low enough to ensure the use of graphite as a linear or a component of the system over an extended period without loss of performance.

Nema, V. K.; Sharma, O. P.

1986-01-01

227

International Nuclear Information System (INIS)

An experimental study was conducted to determine the two-phase heat transfer coefficient in an air-water, non-boiling vertical system. Enhancement of the heat transfer coefficient in this two-phase flow system was observed in both upward and downward flow directions. The correlation of void fraction profile and water velocity profile in bubbly flow was discussed and its influence on heat transfer behavior was examined. An explanation for the heat transfer mechanism in slug flow was postulated from the observed hydrodynamic phenomenon. Correlations based on the Sieder-Tate type equation was established to collapse, within /plus or minus/15%, the experimentally determined two-phase heat transfer coefficient utilizing a two-phase Reynolds number based on a liquid phase Reynolds number corrected for liquid holdup. 24 refs

228

Pool Boiling Heat Transfer on the Inside Surface of an Inclined Tube

International Nuclear Information System (INIS)

The present study is aimed at the determination of heat transfer characteristics on the inside surface of a tube while changing the inclination angle. Changes in pool boiling heat transfer coefficients on the inside surface of a 16.2 mm internal diameter has been studied experimentally at atmospheric pressure. Experiments were performed at six different inclination angles to investigate variations in the heat transfer coefficients due to the inclination angle change. Results for 30 .deg.???90 .deg. are almost same whereas the result for ? =15 .deg. is different from the other angles. To predict the heat transfer coefficients an empirical correlation has been developed as ?b 1/(A + Blnq). The developed correlation can predict the measured experimental data within ±4% error bound. Pool boiling is closely related with the design of passive type heat exchangers, which have been investigated in nuclear power plants to achieve safety functions in case of no power supply. Since the space for the installation of a heat exchanger is usually limited, developing more efficient heat exchangers is important. Several researchers have published results for the pool boiling on the outside surface. Jung et al. experimented boiling heat transfer in R-11 to investigate heat transfer mechanisms on the inside surface of a circular cylindrical tank. They simulated the surface by a flat plate. Somewhat detailed study on the inclination angle itself was previously done by Nishikawa et al. by using the combination of a plate and water. Jabardo and Filho performed an experimental study of forced convective boiling of refrigerants in a 12.7 mm internal diameter tube to investigate effects of physical parameters over the variations in local surface temperature. However, mechanisms of pool boiling are much different from those of the forced convective boiling. Kang investigated pool boiling heat transfer of water on the inside surface of a horizontal tube at atmospheric pressure. Experiments were performed at four different azimuthal angles to investigate variations in local heat transfer coefficients along the tube periphery. The local coefficient changes much along the tube periphery and the minimum was observed at the tube bottom. Summarizing the previous works, it is identified that the study for pool boiling heat transfer on the inside surface of a tube is very rare

229

Pool Boiling Heat Transfer on the Inside Surface of an Inclined Tube

Energy Technology Data Exchange (ETDEWEB)

The present study is aimed at the determination of heat transfer characteristics on the inside surface of a tube while changing the inclination angle. Changes in pool boiling heat transfer coefficients on the inside surface of a 16.2 mm internal diameter has been studied experimentally at atmospheric pressure. Experiments were performed at six different inclination angles to investigate variations in the heat transfer coefficients due to the inclination angle change. Results for 30 .deg.???90 .deg. are almost same whereas the result for ? =15 .deg. is different from the other angles. To predict the heat transfer coefficients an empirical correlation has been developed as ?{sub b} 1/(A + Blnq{sup )}. The developed correlation can predict the measured experimental data within ±4% error bound. Pool boiling is closely related with the design of passive type heat exchangers, which have been investigated in nuclear power plants to achieve safety functions in case of no power supply. Since the space for the installation of a heat exchanger is usually limited, developing more efficient heat exchangers is important. Several researchers have published results for the pool boiling on the outside surface. Jung et al. experimented boiling heat transfer in R-11 to investigate heat transfer mechanisms on the inside surface of a circular cylindrical tank. They simulated the surface by a flat plate. Somewhat detailed study on the inclination angle itself was previously done by Nishikawa et al. by using the combination of a plate and water. Jabardo and Filho performed an experimental study of forced convective boiling of refrigerants in a 12.7 mm internal diameter tube to investigate effects of physical parameters over the variations in local surface temperature. However, mechanisms of pool boiling are much different from those of the forced convective boiling. Kang investigated pool boiling heat transfer of water on the inside surface of a horizontal tube at atmospheric pressure. Experiments were performed at four different azimuthal angles to investigate variations in local heat transfer coefficients along the tube periphery. The local coefficient changes much along the tube periphery and the minimum was observed at the tube bottom. Summarizing the previous works, it is identified that the study for pool boiling heat transfer on the inside surface of a tube is very rare.

Kang, Myeong Gie [Andong National Univ., Andong (Korea, Republic of)

2013-10-15

230

The role of surface energy coefficients and nuclear surface diffuseness in the fusion of heavy-ions

We discuss the effect of surface energy coefficients as well as nuclear surface diffuseness in the proximity potential and ultimately in the fusion of heavy-ions. Here we employ different versions of surface energy coefficients. Our analysis reveals that these technical parameters can influence the fusion barriers by a significant amount. A best set of these parameters is also given that explains the experimental data nicely.

Dutt, Ishwar; Puri, Rajeev K.

2010-01-01

231

Correcting the microscopic coefficient of surface tension of associated liquids

A correction to the association of saturation vapor molecules is introduced into the theory of microscopic surface tension proposed by Sinanoglu. It is determined that the calculated solubility of benzene in water coincides with the one measured using this correction.

Ar'ev, I. A.

2014-01-01

232

Transfer coefficient of 137Cs from feed to cow milk in tropical region Kaiga (India)

International Nuclear Information System (INIS)

In the transport model for the prediction of the concentration of 137Cs in milk, the transfer coefficient from feed to milk, Fm, is an important parameter. Site-specific transfer coefficient from feed to cow's milk, for 137Cs in the Kaiga environment, a nuclear power station site in India, determined over a period of 10 y is presented in this paper. The value is determined from 137Cs concentration in milk and grass samples of the Kaiga region and the result ranged from 6.43 E-03 to 1.09 E-02 d l-1 with a geometric mean value of 8.0 E-03 d l-1. The result is compared with that for 40K, determined concurrently at the same region and ranged from 3.06 E-03 to 3.48 E-03 d l-1 with a geometric mean value of 3.26 E-03 d l-1. This parameter is quite useful in decision-making for implementing countermeasures during a large area contamination with 137Cs in tropical areas like Kaiga. (authors)

233

Volumetric mass transfer coefficient and hydrodynamic study of a new self-inducing turbine

International Nuclear Information System (INIS)

Highlights: • Experimental study of a new self inducing turbine. • Hydrodynamic parameters study of the generated flow. • Experimental study of the evolution of kLa and we give an empirical correlation. • Comparing our results to a previous research [17]. • Find a good agreements, with better performances of our turbine. - Abstract: The self-inducing turbines are among mobile agitations which present a very interesting potential in terms of energy in the field of wastewater treatment by activated sludge. Often, the reactions involved in this type of contactors are limited by the gas–liquid mass transfer. The objective of this experimental work is the determination of the oxygenation capacity of a new self-inducing turbine, a holed hollow cylinder, having a thickness of W = 1.5 cm and a diameter D = 9 cm, with 6 holes having a diameter of 0.5 cm each. During this experimental work, we evaluated the volumetric mass transfer coefficient kLa, which is directly related to the oxygenation capacity (OC) and this for various rotational speeds of the turbine as well as for various submergences. We finally succeeded to find an empirical correlation for our new self inducing turbine. The most common method used to estimate experimentally the coefficient kLa is the technique of dynamic oxygenation and deoxygenation. We finally concluded that this new turbine had a satisfying aeration capacity, which increases with the increase of the rotational speed, and decreases when increasing the submergence of the impeller

234

International Nuclear Information System (INIS)

Extensive studies on transfer of 131I through grass-cow-milk pathway after the Chernobyl accident were reported. But, under nor mal operational conditions of a power reactor, 131I is not present in measurable concentration in environmental matrices around a nuclear power generating station. Hence, database on 131I transfer coefficients for grass-cow-milk pathway in equilibrium conditions in the environment of a nuclear power plant are sparse. One of method to estimate the equilibrium transfer coefficient is to use stable iodine, which is present naturally in very low levels in the environmental matrices. By measuring the concentration of stable iodine concentration in grass and cow milk, the grass-to-milk transfer coefficient of iodine can be estimated. Since the metabolism of stable and radioiodine is same, the data obtained for transfer coefficient of stable iodine could be used for predicting the transfer for radioiodine to cow milk. The measurement of stable iodine in the environmental sample is very challenging because of its extremely low concentration. Neutron Activation Analysis (NAA) can be used to estimate stable iodine in the environment matrices after suitably optimizing the condition to minimize interferences. This paper presents the results of a systematic study on the transfer coefficients for grass-cow milk pathway of iodine in normal (equilibrium) situations as well as for a postulated (simulated) emergency condition in Kaiga region

235

Electron transfer in gas surface collisions

International Nuclear Information System (INIS)

In this thesis electron transfer between atoms and metal surfaces in general is discussed and the negative ionization of hydrogen by scattering protons at a cesiated crystalline tungsten (110) surface in particular. Experimental results and a novel theoretical analysis are presented. In Chapter I a theoretical overview of resonant electron transitions between atoms and metals is given. In the first part of chapter II atom-metal electron transitions at a fixed atom-metal distance are described on the basis of a model developed by Gadzuk. In the second part the influence of the motion of the atom on the atomic charge state is incorporated. Measurements presented in chapter III show a strong dependence of the fraction of negatively charged H atoms scattered at cesiated tungsten, on the normal as well as the parallel velocity component. In chapter IV the proposed mechanism for the parallel velocity effect is incorporated in the amplitude method. The scattering process of protons incident under grazing angles on a cesium covered surface is studied in chapter V. (Auth.)

236

Reactions involving electron transfer at semiconductor surfaces

International Nuclear Information System (INIS)

Rapid isotopic equilibration was observed upon contacting an equimolar mixture of (16O2 + 18O2) at 295 or 77 K with oxygen-deficient surfaces of pure and doped zinc oxides from which light was excluded at all stages. Kinetic expressions for opposing second-order reactions accurately described variations in mole fraction of 16O2, 16O18O and 18O2 in the gas phase during the approach to full isotopic equilibration at 295 or 77 K. Rate constants thereby derived for this R0-type exchange did not correlate with reported concentrations of conduction-band electrons for the zinc oxides, indicating that the rate-determining process for exchange was not collective-electron type charge transfer at the oxygen-deficient surfaces in the absence of illumination. Surfaces could be rendered inactive by extensive preoxidation in 16O2 at 650 K in the dark, but heating for 2 h periods in the dark under continuous evacuation restored activity to a progressively increasing extent at temperatures of 400 to 650 K. Preadsorption of H2O, H2 or (CH3)2CHOH at 295 K strongly inhibited activity. An explanation of the observed results is developed. (author)

237

In this paper detailed experimental measurements and computational predictions of heat transfer coefficient distributions in a large scale perspex model of a novel integrally cast blade cooling geometry are reported. In a gas turbine blade, the cooling passage investigated is integrally cast into the blade wall, providing good thermal contact with the outer surface of the turbine blade. Flow enters the racetrack passage through the root of the blade and exits to a central plenum through a ser...

Ieronymidis, I.; Gillespie, Drh; Ireland, Pt; Kingston, R.

2006-01-01

238

Determination of the pressure drop and the heat transfer coefficient in a gas-solid two-phase flow

International Nuclear Information System (INIS)

An experimental study was developed for a vertical gas solid two phase flow with heat transfer by analysing the gradient of both static pressure and temperature alongside the system. The measurements were used to produce the isothermal hydrodynamic entry lenght and the gas-solid heat transfer coefficient as well as the influence of the solid particle. (Author)

239

Temperature measurement by thermocouples is prone to errors due to conduction and radiation losses and therefore has to be corrected for precise measurement. The temperature dependent emissivity of the thermocouple wires is measured by the use of thermal infrared camera. The measured emissivities are found to be 20%-40% lower than the theoretical values predicted from theory of electromagnetism. A transient technique is employed for finding the heat transfer coefficients for the lead wire and the bead of the thermocouple. This method does not require the data of thermal properties and velocity of the burnt gases. The heat transfer coefficients obtained from the present method have an average deviation of 20% from the available heat transfer correlations in literature for non-reacting convective flow over cylinders and spheres. The parametric study of thermocouple error using the numerical code confirmed the existence of a minimum wire length beyond which the conduction loss is a constant minimal. Temperature of premixed methane-air flames stabilised on 16 mm diameter tube burner is measured by three B-type thermocouples of wire diameters: 0.15 mm, 0.30 mm, and 0.60 mm. The measurements are made at three distances from the burner tip (thermocouple tip to burner tip/burner diameter = 2, 4, and 6) at an equivalence ratio of 1 for the tube Reynolds number varying from 1000 to 2200. These measured flame temperatures are corrected by the present numerical procedure, the multi-element method, and the extrapolation method. The flame temperatures estimated by the two-element method and extrapolation method deviate from numerical results within 2.5% and 4%, respectively. PMID:23464237

Hindasageri, V; Vedula, R P; Prabhu, S V

2013-02-01

240

A methodology to assess transient contact heat transfer coefficient using contact boiling test data

International Nuclear Information System (INIS)

One of the passive safety features present in CANDU reactors is the heavy-water moderator surrounding the fuel channels. During some postulated loss-of-coolant accidents (LOCAs), pressure tubes (PTs) will deform radially into contact with associated calandria tubes (CTs). The contacted tubes form a radial heat removal path that is additional to the heat removal capability of the heat transport system. The stored heat and the decay heat from the fuel channel are transferred through the CT to the moderator, which acts as a heat sink. To demonstrate the effectiveness of the moderator as a heat sink and to ensure the integrity of the fuel channel, the transient contact heat transfer coefficient (CHTC) between the PT and CT after PT/CT contact is needed for safety analysis. Since the early 1980s, several series of experiments have been conducted at AECL Whiteshell Laboratories to assess contact boiling heat transfer that occurs when a pressurized PT deforms through a CO2 annulus gas gap into contact with a CT in a tank of heated water. Such contact boiling tests, in which full-scale PT and CT sections were used, provide sufficient data (i.e., test section temperatures, applied heater power and internal pressure) to infer the transient PT/CT CHTC based on the principles of heat transfer. A methodology has been developed to assess the transient PT/CT CHTC. The simulation model implements a negative feedback method by comparing contact boiling test data with the coring contact boiling test data with the corresponding transient simulation results. The effectiveness and applicability of such a CHTC simulation model has been demonstrated with several test cases. The results show that the model has the capability to capture CHTC transient characteristics from the input data including the rapid changes in PT and CT temperatures upon initial contact and associated rapid changes in contact heat transfer coefficients. The PT/CT CHTC is an important parameter for determining fuel channel behaviour, which changes significantly during the course of a LOCA. With the methodology developed here the PT/CT CHTC transient can be determined using contact boiling test data to meet the needs of safety analysis. (author)

241

Hydromagnetic convective heat transfer at a stretching surface with heat generation or absorption

International Nuclear Information System (INIS)

The problem of steady, laminar , hydromagnetic convective heat transfer at a stretching surface with heat generation or absorption is considered. the sheet is linearly stretched in the presence of a uniform free stream of constant velocity and temperature. the effects of free convection and heat generation or absorption are also considered. the governing partial differential equations for this investigation are transformed into ordinary differential equations . the resulting equations are solved numerically by a perturbation technique and the obtained results are compared favorably with previously published work. A parametric study is performed to illustrate the influence of the Prandtl number, Hartmann number, heat generation/absorption coefficient, and the surface mass transfer coefficient on the profiles of the velocity components and temperature. numerical results for the skin friction coefficient and the Nusselt number functions have been studied for various parametric conditions

242

Fundamental understanding of interfacial electron transfer (ET) among electrolyte/DNA/solid-surface will facilitate the design for electrical detection of DNA molecules. In this report, the electron transfer characteristics of synthetic DNA (sequence from pathogenic Cryptosporidium parvum) self-assembled on a gold surface was electrochemically studied. The effects of immobilization order on the interface ET related parameters such as diffusion coefficient (D0), surface coverage (?R), and mon...

Mcewen, Gerald D.; Chen, Fan; Zhou, Anhong

2009-01-01

243

Heat transfer coefficient calculation for analysis of ITER shield block using CFX and ANSYS

International Nuclear Information System (INIS)

Highlights: ? Benchmark HTC modeling in CFX and compare this modeling with empirical formulas. ? Given the error formulas derived from theory. ? Benchmark HTC modeling in ANSYS and the results is consistent with the conclusion of error estimate from theory. - Abstract: In thermal-mechanical analysis of ITER shield block using ANSYS code, it needs the real heat transfer coefficient (HTC) values which are computed by CFX. Because two kinds of HTC values can be gotten from CFX and which has some difference with ANSYS, so it is necessary to estimate the error caused by HTC transferred from CFX to ANSYS. In this paper, HTC values got from CFX was firstly benchmarked with the results got from empirical formulas, then estimated the error caused by HTC transferred from theory and gave the expressions of the error, thirdly benchmark work of ANSYS results in 4 cases was done, then compared the error with former error estimated formula derived from theory. In the end, conclusions will be given based on above benchmark works.

244

Free-stream turbulence effect on the heat (mass) transfer characteristics on a turbine rotor surface

International Nuclear Information System (INIS)

The heat (mass) transfer characteristics on the blade surface of a first-stage turbine rotor cascade has been investigated by employing the naphthalene sublimation technique. A four-axis profile measurement system is employed for the measurements of the local heat (mass) transfer coefficient on the curved blade surface. The experiments are carried out for two free-stream turbulence intensities of 1.2% and 14.7%. The high free-stream turbulence results in more uniform distributions of heat load on the both pressure and suction surfaces and in an early boundary-layer separation on the suction surface. The heat (mass) transfer enhancement on the suction surface due to the endwall vortices is found to be relatively small under the high free-stream turbulence

245

Vaporization heat transfer of dielectric liquids on enhanced surfaces covered with screen wicks

Experiments were conducted to investigate the vaporization heat transfer characteristics for the dielectric liquid FC-72 on several wicking surfaces which may be used in flat-plate heat pipes. The wicking materials studied included microstructure enhanced surfaces and coarse surfaces covered with screen meshes. Experimental data for q versus deltaT curves and critical heat fluxes were obtained for the two different operating conditions of a heat pipe, evaporation, and shallow pool boiling. When the liquid level was above the heated surface, the height of the liquid level above the surface was varied from 0 to 10 mm. When the liquid level was below the heated surface, the distance from the liquid level to the edge of the surface was adjusted from 0 to 15 mm. Experimental results revealed that for shallow pool boiling when the heated surface was covered with a wire screen mesh, the heat transfer coefficient increased at lower heat fluxes but the critical heat flux (CHF) decreased for all the surfaces tested. In the case of evaporation, both CHF and the heat transfer coefficient increased as the microstructure surfaces were covered with screen meshes.

Gu, C. B.; Chow, L. C.; Pais, M. R.; Baker, K.

1993-01-01

246

Distribution coefficient Kd in surface soils collected in Aomori prefecture

International Nuclear Information System (INIS)

Soil-solution distribution coefficients (Kds), which are the ratio of an element concentration in a soil solid phase to that in a solution phase, for 32 elements in Andosols, Wet Andosols and Gleyed Andosols collected throughout Aomori Prefecture were determined. A dried soil sample was mixed with a 10-fold amount of pure water in a PPCO centrifuge tube, and then gently shaken for 24 h. The Kd values were obtained by measurement of element concentrations in solid and solution phases (batch method). The Kd values in this work were up to three orders of magnitude higher than the IAEA reported values, and their 95% confidence intervals were within two orders of magnitude. Most Kd values of elements were decreasing with increasing electrical conductivity of the solution phase. The Kd of Ca had a good correlation with that of Sr. However, the correlation between the Kds of K and Cs was not good. The Kd values were also determined by another method. The soil solutions were separated from the fresh soil samples by means of high speed centrifuging. The Kd values were calculated from the element concentration in solid phase and soil solution (centrifugation method). The Kd values obtained by the centrifugation method agreed within one order of magnitude with those by the batch method, and both variation patterns in elements correlated well. (author)

247

A thin film heat transfer gauge is applied to the measurement of heat transfer coefficients in the interaction regions of incident shock waves and fully developed turbulent boundary layers. It was developed to measure heat flux with high spatial resolution and fast response for wind tunnels with long flow duration. To measure the heat transfer coefficients in the interaction region in detail, experiments were performed under the conditions of Mach number = 4, total pressure = 1.2 MPa, 0.59 to approximately 0.65. Reynolds number = 1.3 to approximately 1.5 x 10 to the 7th power and incident shock angles from 17.8 to 22.8 degrees. The results show that the heat transfer coefficient changes complicatedly in the interaction region. At the beginning the interaction region, the heat transfer coefficient decreases at first, reaches its minimum value at the point where the pressure begins to increase, and then increases sharply. When the boundary layer begins to separate, even a small separation bubble causes significant changes in the heat transfer coefficient, while the pressure does not show any changes which suggests that the boundary layer begins to separate.

Hayashi, M.; Sakurai, A.; Aso, S.

1986-01-01

248

High-pressure die cast B390 alloy was prepared on a 350 ton cold chamber die casting machine. The metal/die interfacial heat transfer coefficient of the alloy was investigated. Considering the filling process, a "finger"-shaped casting was designed for the experiments. This casting consisted of five plates with different thicknesses (0.05 inch or 1.27 mm to 0.25 inch or 6.35 mm) as well as individual ingates and overflows. Experiments under various operation conditions were conducted, and temperatures were measured at various specific locations inside the die. Based on the results, the interfacial heat transfer coefficient and heat flux were determined by solving the inverse heat transfer problem. The influence of the mold-filling sequence, sensor locations, as well as processing parameters including the casting pressure, die temperature, and fast/slow shot speeds on the heat transfer coefficient were discussed.

Cao, Yongyou; Guo, Zhipeng; Xiong, Shoumei

2012-07-01

249

International Nuclear Information System (INIS)

High-pressure die cast B390 alloy was prepared on a 350 ton cold chamber die casting machine. The metal/die interfacial heat transfer coefficient of the alloy was investigated. Considering the filling process, a 'finger'-shaped casting was designed for the experiments. This casting consisted of five plates with different thicknesses (0.05 inch or 1.27 mm to 0.25 inch or 6.35 mm) as well as individual ingates and overflows. Experiments under various operation conditions were conducted, and temperatures were measured at various specific locations inside the die. Based on the results, the interfacial heat transfer coefficient and heat flux were determined by solving the inverse heat transfer problem. The influence of the mold-filling sequence, sensor locations, as well as processing parameters including the casting pressure, die temperature, and fast/slow shot speeds on the heat transfer coefficient were discussed.

250

Heat/Mass transfer measurement on concave surface in rotating jet impingement

International Nuclear Information System (INIS)

The objective of this paper is to investigate the heat/mass transfer characteristics on a concave surface for rotating impinging jets. The jet with Reynolds number of 5,000 is applied to the concave surface and the flat surface, respectively. The rotating experiments have been carried out at the rotating speed of 560RPM which is corresponding to Ro number of 0.075. The two jet orientation (front and trailing orientation) are considered. Detailed heat/mass transfer coefficients on the target plate were measured using a naphthalene sublimation method. The result indicates that the rotation leads to change in local heat/mass transfer distributions and the slight increase in the Sh level. The front orientation induces asymmetric Sh distributions, whereas the trailing orientation shows the shifted heat/mass transfer feature due to rotation-induced flow behavior. The crossflow effect on heat/mass transfer is also observed as the stream wise direction increases. Compared to flat surface, the heat/mass transfer on the concave surface is enhanced with increasing the spanwise direction due to the curvature effect, providing the higher averaged Sh value. It is proved that the difference of surface geometry affects somewhat the local and averaged heat/mass transfer regardless of rotation condition

251

Flux surface averaging of the diffusion coefficient in electron cyclotron resonance heating

International Nuclear Information System (INIS)

The single particle model has been used to describe electron cyclotron resonance heating. Fielding's (1980) method of calculating the diffusion coefficient has been simplified and extended to include the effect of finite beam width. It is shown how this effect and the effect of the rotational transform lead to a spreading of the resonance over a wider class of particles and how the diffusion coefficient should be averaged over a magnetic surface or surfaces. (author)

252

Connection coefficients for cold plasma wave propagation near metallic surfaces

International Nuclear Information System (INIS)

Sheaths tend to form when immersing metallic objects in plasmas. As it avoids the need to capture the sheath details, which occur on the Debye length scale while antennas are typically various orders of magnitude larger, the sheath boundary condition due to D'Ippolito and Myra (2006 Phys. Plasmas 13 102508, 2008 Phys. Plasmas 15 102501) offers antenna designers a major reduction in the numerical problem size they face. The sheath boundary condition was derived by making a number of simplifying assumptions to enable finding an analytical approximation of the conditions rapidly oscillating waves have to satisfy beyond the sheath that forms close to such objects. This paper discusses the solution of the cold plasma wave equation for sheath relevant density profiles, e.g. highlighting the role of the orientation of the static magnetic field and of oblique incidence, and underlining the impact the density profile has on the wave physics. It illustrates that the cross-talk between the waves impinging on and those excited at the wall and in the sheath sensitively depends on a number of parameters. The 2 × 2 connection coefficient matrix that is numerically obtained captures the sheath region fast time scale wave physics for a given density profile. When supplemented with a satisfactory model for the slow time scale variation it is a numerical tool that permits upgrading the realism of the fast time scale wave physics contained in the sheath boundary condition and that can h sheath boundary condition and that can help delimiting the range of applicability of simplified models, and assessing if a sufficiently general set of boundary conditions to describe the effect of the sheath can at all be constructed. (paper)

253

frictional strength of faults is a critical factor that contributes to continuous fault slip and earthquake occurrence. Frictional strength can be reduced by the presence of sheet-structured clay minerals. In this study, two important factors influencing the frictional coefficient of minerals were quantitatively analyzed by a newly developed computational method based on a combination of first-principles study and thermodynamics. One factor that helps reduce the frictional coefficient is the low adhesion energy between the layers under dry conditions. Potassium ions on mica surfaces are easily exchanged with sodium ions when brought into contact with highly concentrated sodium-halide solutions. We found that the surface ion exchange with sodium ions reduces the adhesion energy, indicating that the frictional coefficient can be reduced under dry conditions. Another factor is the lubrication caused by adsorbed water films on mineral surfaces under wet conditions. Potassium and sodium ions on mica surfaces have a strong affinity for water molecules. In order to remove the adsorbed water molecules confined between mica surfaces, a differential compressive stress of the order of tens of gigapascals was necessary at room temperature. These water molecules inhibit direct contact between mineral surfaces and reduce the frictional coefficient. Our results imply that the frictional coefficient can be modified through contact with fluids depending on their salt composition. The low adhesion energy between fault-forming minerals and the presence of an adsorbed water film is a possible reason for the low frictional coefficient observed at continuous fault slip zones.

Sakuma, Hiroshi

2013-12-01

254

Estimation of overall heat transfer coefficient of cooling system in RF capacitive hyperthermia

Directory of Open Access Journals (Sweden)

Full Text Available The study presented in this article involves the estimation of the overall heat transfer coefficient of cooling system in RF capacitive hyperthermia treatment using inverse problem based on the conjugate gradient method to provide improved distribution of temperature. The temperature data computed numerically from the direct problem using the finite difference time domain method are used to simulate the temperature measurements. The effects of the errors and sensor positions upon the precision of the estimated results are also considered. The results show that a reasonable estimation of the unknown can be obtained. Finally, measurements in a tissue-equivalent phantom are employed to appraise the reliability of the presented method. The comparison of computed data with measurements shows a good agreement between numerical and experimental results.

Mohammad Hasan Zahmatkesh

2013-05-01

255

Distribution coefficient and transfer factor of stable iodine in agricultural soils in Aomori, Japan

International Nuclear Information System (INIS)

Soil-to-solution distribution coefficient (Kd) and soil-to-plant transfer factor (TF) were determined for agricultural soils and selected plants in Aomori Prefecture, Japan, by means of analysis of stable I in soil and plant samples. The concentration of I in the soil samples varied between 0.52 and 82.8 mg kg-1 (geometric mean of 4.4 mg kg-1). The Kd, which was defined as the ratio of I concentration in soil to that in water extracted from the soil, was 1.5 x 103 in geometric mean (L/kg). The TF value was defined as the ratio of I concentration in plant to that in soil. Geometric means of the TF on dry weight base obtained in this study were 3.2 x 10-2 for komatsuna, 2.0 x 10-2 for Japanese radish and 2.3 x 10-2 for pasture grass. (author)

256

Directory of Open Access Journals (Sweden)

Full Text Available A procedure based on the Artificial Bee Colony algorithm for solving the two-phase axisymmetric one-dimensional inverse Stefanproblem with the third kind boundary condition is presented in this paper. Solving of the considered problem consists in reconstruction of the function describing the heat transfer coefficient appearing in boundary condition of the third kind in such a way that the reconstructed values of temperature would be as closed as possible to the measurements of temperature given in selected points of the solid. A crucial part of the solution method consists in minimizing some functional which will be executed with the aid of one of the swarm intelligence algorithms - the ABC algorithm.

E. Hetmaniok

2012-12-01

257

Effect factors of heat transfer coefficient between hollow glass microsphere and furnace atmosphere

International Nuclear Information System (INIS)

In order to achieve an effective control of the heat transfer coefficient (hq) between microsphere and furnace atmosphere in the fabrication of hollow glass micro-sphere by sol-gel technology, the effects of component percentage, temperature and total pressure of gas mixture on hq are studied. Further, the influences of diameter and wall thickness of hollow glass microsphere on hq are also investigated. The results show that in the range of component percentage, temperature and pressure of gas mixture commonly used in the fabrication of hollow glass microsphere by sol-gel technology, the temperature and total pressure of gas mixture and the wall thickness of hollow glass microsphere have little influence on hq, but hq significantly increases with the volume fraction of helium in the furnace atmosphere and significantly decreases with increasing of microsphere diameter. (authors)

258

Measurement of the transfer coefficient for radiocesium transport from a sheep's diet to its milk

International Nuclear Information System (INIS)

The rate of increase and decay of radio contamination secreted in sheep's milk, resulting from a constant level of radiocesium in the animals' diet, was investigated. Ten lactating ewes were used in the experiment. For a period of 12 d the animals fed on contaminated grass, resulting in a daily radiocesium intake of 832 Bq per animal. They were subsequently returned to a contamination-free diet and were monitored for another 9 d. Throughout the period of the experiment, 134Cs and 137Cs concentrations in the animals' milk were measured daily with an 18% efficiency, high-resolution Ge detector. The data were in satisfactory agreement with the predictions of a simple two-compartment theory. The transfer coefficient, describing the steady-state equilibrium in this model, was measured as fm = 0.058 +/- 0.007 dL-1

259

Reorientational angle distribution and diffusion coefficient for nodal and cylindrical surfaces

We present a catalogue of diffusion coefficients and reorientational angle distribution (RAD) for various periodic surfaces, such as I-WP, F-RD, S, and S1 nodal surfaces; cylindrical structures like simple, undulated, and spiral cylinders, and a three-dimensional interconnected-rod structures. The results are obtained on the basis of a simulation algorithm for a diffusion on a surface given by the general equation ?(r)=0 [Ho?yst et al., Phys Rev. E 60, 302 (1999)]. I-WP, S, and S1 surfaces have a spherelike RAD, while F-RD has a cubelike RAD. The average of the second Legendre polynomial with RAD function for all nodal surfaces, except the F-RD nodal surface, decays exponentially with time for short times. The decay time is related to the Euler characteristic and the area per unit cell of a surface. This analytical formula, first proposed by B. Halle, S. Ljunggren, and S. Lidin in J. Chem. Phys. 97, 1401 (1992), is checked here on nodal surfaces, and its range of validity is determined. RAD function approaches its stationary limit exponentially with time. We determine the time to reach stationary state for all surfaces. In the case of the value of the effective diffusion coefficient the mean curvature and a connectivity between parts of surfaces have the main influence on it. The surfaces with low mean curvature at every point of the surface are characterized by high-diffusion coefficient. However if a surface has globally low mean curvature with large regions of nonzero mean curvature (negative and positive) the effective diffusion coefficient is low, as for example, in the case of undulated cylinders. Increasing the connectivity, at fixed curvatures, increases the diffusion coefficient.

Plewczy?ski, D.; Ho?yst, R.

2000-12-01

260

DEFF Research Database (Denmark)

A membrane inlet mass spectrometer (MIMS) was used in combination with a developed computer model to study and improve management of a biofilter (BF) treating malodorous ventilation air from a meat rendering facility. The MIMS was used to determine percentage removal efficiencies (REs) of selected sulfur gases and to provide toluene retention profiles for the model to determine the air velocity and overall mass-transfer coefficient of toluene. The mass-transfer coefficient of toluene was used as a reference for determining the mass transfer of sulfur gases. By presenting the model to scenarios of a filter bed with a consortium of effective sulfur oxidizers, the most likely mechanism for incomplete removal of sulfur compounds from the exhaust air was elucidated. This was found to be insufficient mass transfer and not inadequate bacterial activity as anticipated by the manager of the BF. Thus, knowing the relationship between mass-transfer coefficients and air velocity for a given type of BF allows for an improved dimensioning and managing of this and similar BFs. This research demonstrates that it is possible to estimate mass-transfer coefficients and air velocity in BFs using MIMS in combination with computer modeling. Udgivelsesdato: February

Nielsen, Anders Michael; Nielsen, Lars Peter

2009-01-01

261

Simulation of Convective Heat-Transfer Coefficient in a Buried Exchanger

Directory of Open Access Journals (Sweden)

Full Text Available This study presents analytical models allowing to study a forced convection laminar flow in non-established dynamic and thermic regimes. We treated a flow in a bitubular exchanger in permanent thermal contact with a semi-infinite medium, such as the ground. The wall temperature as well as the wall heat flux evolve in the course of time until a quasi-steady mode. The theoretical method is original because it uses Green's functions method to determine the analytical solutions of the heat propagation equation on the wall during the heating phase. These analytical solutions allow to identify the temperature distribution versus time. The complexity of the system geometry as well as the infinity of the medium surrounding the exchanger make the traditional methods of numerical resolution unable to solve the problem. We used, to solve it, the finite volume method coupled with the finite element method at the boundary. We studied the effect of Reynolds number, the fluid entry temperature and the transfer duration on the axial evolution of the heat transfer coefficient. We illustrated also the profile of the temperature field in the fluid medium.

Taoufik Mnasri

2008-01-01

262

Condensation Heat Transfer Performance of Nano- Engineered Cu Surfaces

We investigated condensate mobility and resulting heat transfer performance on Cu based water repellent surfaces including hydrophobic, superhydrophobic and oil-infused surfaces. We observed the transient microscale condensation behaviours up to 3 hours with controlling the supersaturation level at 1.64. We experimentally characterized the nucleation density, droplet size distribution and growth rate, and then incorporated them into the developed condensation heat transfer model to compare the condensation heat transfer performance of each surface. Due to the spontaneous coalescence induced jumping, superhydrophobic surface can maintain the high heat transfer performance while other surfaces show a gradual decrease in heat transfer performance due to the increase in the thermal resistance across the growing droplets. We also quantified each thermal resistance values from the vapor to the surface through the droplets to find out the relative importance of each thermal resistance term.

Kim, Hyunsik; Nam, Youngsuk

2014-11-01

263

Energy Technology Data Exchange (ETDEWEB)

Tube-side heat transfer coefficients for single-phase flow, evaporation, and condensation are presented for propane (R-290), isobutane (R-600a), and a 50/50 mixture (by weight) of propane and isobutane. Heat transfer coefficients have been presented for smooth tubes based on the standard correlations available in the literature for pure refrigerants. The correlations for evaporation and condensation have previously been verified for R-12 and other refrigerants. The correlations for evaporation and condensation have previously been verified for R-12 and other refrigerants. The mass flux of the refrigerant is varied over a wide range that is typically encountered in residential, commercial, and automotive applications. Evaporation temperatures of {minus}6.7 C (20 F) and 4.4 C (40 F) and condensation temperatures of 37.8 C (100 F) and 48.9 C (120 F) have been used for this investigation. The heat transfer coefficients for hydrocarbons (R-290, R-600a, R-290/R-600a) have been compared with R-12 and R-134a. The REFPROP computer program developed by the National Institute of Standards and Technology (NIST) has been used to determine the thermodynamic properties for R-290, R-600a, and R-290/R-600a. This study shows that the heat transfer coefficients for hydrocarbons are significantly higher than those for both R-12 and R-134a. For the range of refrigerant temperatures and mass flux studied, single-phase vapor heat transfer coefficients for hydrocarbons are greater by 234% to 259% in comparison to R-12 and are greater by 167% to 181% in comparison to R-134a. The single-phase liquid heat transfer coefficients for hydrocarbons are greater by 193% to 245% in comparison to R-12; and are greater by 155% to 198% in comparison to R-134a. Average evaporative heat transfer coefficients for hydrocarbons are greater by 194% to 238% in comparison to R-12 and are greater by 157% to 192% in comparison to R-134a. Finally, average condensing coefficients are greater by 220% to 233% in comparison to R-12 and are greater by 177% to 187% in comparison to R-134a. Tables 3 through 6 show a summary of the heat transfer coefficient enhancement of the hydrocarbons in comparison to both R-12 and R-134a.

Mathur, G.D. [Zexel USA Corp., Decatur, IL (United States)

1998-12-31

264

Ultrasonic Heat Transfer Enhancement with Obstacle in Front of Heating Surface

Heat transfer enhancement using a horn-type transducer was carried out in the natural convection region while a flat plate was used as a wall-like obstacle in front of the heating surface. Three types of plate were used as obstacles: acrylic, aluminum, and Styrofoam. A horn tip of 6 mm diameter and 60.7 kHz was used as the ultrasonic transducer. The acoustic cavitation jet induced by the ultrasonic vibration exhibited the same tendency as the axisymmetric free jet. The acoustic jet from the horn tip was shut out by the flat plate; however, the ultrasound passed through the flat plate and transferred the flow effect and agitation effect to the area behind the plate. By applying ultrasonic vibration, the heat transfer coefficient of the heating surface behind the flat plate was increased by up to threefold. The heat transfer coefficient decreased as the thickness of the flat plate increased. The heat transfer coefficient was the highest for the acrylic plate, then the aluminum plate, and lowest for the Styrofoam plate.

Nomura, Shinfuku; Nakagawa, Masafumi; Mukasa, Shinobu; Toyota, Hiromichi; Murakami, Koichi; Kobayashi, Ryousuke

2005-06-01

265

Determination of surface tension coefficient of liquids by diffraction of light on capillary waves

International Nuclear Information System (INIS)

This paper describes a simple technique for determining the coefficient of the surface tension of liquids, based on laser light diffraction on capillary waves. Capillary waves of given frequency are created by an exciter needle acting on the surface of liquid and represent a reflective diffraction grating, the constant of which (the wavelength of capillary waves) can be determined based on a known incidence angle of light (grazing angle). We obtain the coefficient of the surface tension of liquids by applying the dispersion relation for capillary waves and analyze the difficulties that arise when setting up and conducting the experiment in detail. (paper)

266

Energy Technology Data Exchange (ETDEWEB)

Highlights: ? Measured subcooled boiling pressure drop and local heat transfer coefficient in horizontal tubes. ? Infra-red thermal imaging is used for wall temperature measurement. ? Developed correlations for pressure drop and local heat transfer coefficient. -- Abstract: Horizontal flow is commonly encountered in boiler tubes, refrigerating equipments and nuclear reactor fuel channels of pressurized heavy water reactors (PHWR). Study of horizontal flow under low pressure and low flow (LPLF) conditions is important in understanding the nuclear core behavior during situations like LOCA (loss of coolant accidents). In the present work, local heat transfer coefficient and pressure drop are measured in a horizontal tube under LPLF conditions of subcooled boiling. Geometrical parameters covered in this study are diameter (5.5 mm, 7.5 mm and 9.5 mm) and length (550 mm, 750 mm and 1000 mm). The operating parameters varied are mass flux (450–935 kg/m{sup 2} s) and inlet subcooling (29 °C, 50 °C and 70 °C). Infra-red thermography is used for the measurement of local wall temperature to estimate the heat transfer coefficient in single phase and two phase flows with water as the working medium at atmospheric pressure. Correlation for single phase diabatic pressure drop ratio (diabatic to adiabatic) as a function of viscosity ratio (wall temperature to fluid temperature) is presented. Correlation for pressure drop under subcooled boiling conditions as a function of Boiling number (Bo) and Jakob number (Ja) is obtained. Correlation for single phase heat transfer coefficient in the thermal developing region is presented as a function of Reynolds number (Re), Prandtl number (Pr) and z/d (ratio of axial length of the test section to diameter). Correlation for two phase heat transfer coefficient under subcooled boiling condition is developed as a function of boiling number (Bo), Jakob number (Ja) and Prandtl number (Pr)

Baburajan, P.K. [Atomic Energy Regulatory Board, Mumbai (India); Bisht, G.S. [Indian Institute of Technology, Bombay (India); Gupta, S.K. [Atomic Energy Regulatory Board, Mumbai (India); Prabhu, S.V., E-mail: svprabhu@iitb.ac.in [Indian Institute of Technology, Bombay (India)

2013-02-15

267

Directory of Open Access Journals (Sweden)

Full Text Available In this study, a completely randomized experiment was designed with five irrigation treatments and three replicates. The irrigation programs were raw wastewater (T1, treated wastewater (T2, a combination of 50% raw wastewater and 50% fresh water (T3, a combination of 50% treated wastewater and 50% fresh water (T4, and fresh water (T5. The experiments were run within a greenhouse. The lysimeters were built up in September 2009 and they were filled with a two layer soil. The upper (30 cm and lower (40 cm layers were sandy loam and sandy clay loam, respectively. The results showed that the effects of watering treatments on transfer coefficients of heavy metals from soil to shoots (except Cd and tubers of potato (except Zn and Cu were significant (p <0.01. Maximum and minimum transfer coefficients of heavy metals were observed in the (T1 and (T5 treatments, respectively. Also, the transfer coefficients of Cd from soil to shoots were lower than tubers. In the case of Zn, Cu and Pb, transfer coefficients from soil to tubers were lower than shoots. In this study, the maximum transfer coefficients to shoots were Cd (0.331-0.463, Zn (0.383-0.230, Cu (0.173-0.386 and Pb (0.003-0.057, respectively. Maximum transfer coefficients toward tubers (except T5 were Cd (0.439-0.572, Cu (0.081-0.138, Zn (0.170-0.217 and Pb (0-0.017, respectively. The combination of wastewater and fresh water use in short-term irrigation might be feasible, but a heavy metal monitoring program is necessary.

N. Parsafar

2014-02-01

268

International Nuclear Information System (INIS)

The influence of the rhodium self-powered detector transition regime in the RBMK-1000 reactor on correction coefficients taking into account fuel and emitter material burnups is considered. It is shown that application of the known correction coefficients dependence on burnup after the detector transfer into another fuel channel is possible only taking into account the channel power generation and time-integrated current produced by the detector for the moment of transition. 4 refs., 3 figs

269

Heat and mass transfer to flowing bodies of surface water

International Nuclear Information System (INIS)

The most important limiting quantities for heat transfer from a river to its environment are the thermal radiation, the free convection and the forced convection due to wind. For a sure preliminary calculation of the heat emission of a flowing body of water it is necessary to know exactly the decisive heat- and mass transfer coefficients and their dependence on wind velocity. Measurements have been effected at a power plant channel in Pleidelsheim/Neckar. The measuring technique, arrangement of the measuring points and measuring devices are shown in detail as well as the theoretical basis for the analysis of the measurements. Balancing calculations lead to relations representing, in the form of extended exponential functions, the dependence of the transfer coefficients on wind velocity. As against the transfer coefficients so far used for calculating the thermal load plans, much higher values have been obtained. This is of considerable practical importance insofar as a flowing water obviously emits the received foreign heat quicker than assumed until now. Because of the importance of the radiation a new intermittent measuring method has been developed enabling the determination of the different radiation fluxes as well as the heat- and mass transfer coefficients. (orig.)

270

Impact of External Pressure on the Heat Transfer Coefficient during Solidification of Al-A356 Alloy

DEFF Research Database (Denmark)

In this paper the interfacial heat transfer coefficient (IHTC) is correlated to applied external pressure, in which IHTC at the interface between A356 aluminum alloy and metallic mold during the solidification of the casting under different pressures were obtained using the Inverse Heat Conduction Problem (IHCP) method. The method covers the expedient of comparing theoretical and experimental thermal histories. Temperature profiles obtained from thermocouples were used in a finite difference heat flow program to estimate the transient heat transfer coefficients. The new simple formula was presented and compared with data in literature which shows acceptable agreement.

Jabbari, Masoud; Ilkhchy, A.Fardi

271

International Nuclear Information System (INIS)

In this paper, a sensitivity analysis on the overall heat transfer coefficient has been carried out as a function of operation temperature and pressure. The sulfur-iodine (SI) cycle and Westinghouse sulfur hybrid cycle, combined with a very high temperature gas-cooled reactor (VHTR), are well-known as feasible technologies for hydrogen production. The SI process consists of a Bunsen reactor; H2SO4, SO3, and HIx decomposers; and a HI pre-heater. The overall heat transfer coefficient of the process heat exchanger (PHE) used in the SI process is a very important factor when sizing the PHE

272

The forced convection heat transfer coefficient and friction factor are determined for the flow of water and nanofluid in a vertical packed bed column. The analysis is undertaken in the laminar and transition Reynolds number range. The column is filled with spherical glass beads as the bed material. The heat transfer coefficients with Al2O3 nanofluid increased by 12% to 15% with the increase of volume concentration from 0.02% to 0.5% compared with water. The experimental values of axial tempe...

Srinivasa Rao, G.; Sharma, K. V.; Chary, S. P.; Rahman, M. M.; Kadirgama, K.; Noor, M. M.

2011-01-01

273

International Nuclear Information System (INIS)

An experimental study on forced convection in a four-cusp duct simulating a typical nuclear reactor channel degraded by accident is presented. Transfer coefficients were obtained by using the analogy between heat and mass tranfer, with the naphtalene sublimation technique. The experiment consisted in forcing air past a four-cusp naphthalene moulded duct. Mass transfer coefficients were determined in nondimensional form as Sherwood number. Experimental curves correlating the Sherwood number with a nondimensional length, x+, were obtained for Reynolds number varying from 891 to 30.374. This range covers typical flow rates that are expected to exist in a degraded nuclear reactor core. (Author)

274

International Nuclear Information System (INIS)

The effects of liquid sprayed density on the pressure drop and mass transfer coefficient were discussed in a hydrogen-water liquid phase catalytic bed of ?24 mm x 1000 mm, which was filled with the mixture of hydrophobic catalyst and packing. The pressure drop (?p) increases obviously with the liquid sprayed density (l) in higher gas velocity and slightly with l in lower gas velocity. When the gas velocity is lower, l and entrained liquid (?) have little effect on the mass transfer coefficient (Kya). While the gas velocity is higher, Kya increases with l, ? has effect on Kya. (authors)

275

International Nuclear Information System (INIS)

In this paper, a study of convective mass transfer coefficient and rate of moisture removal from cabbage and peas for open sun drying and inside greenhouse drying has been performed as a function of climatic parameters. The hourly data for the rate of moisture removal, crop temperature, relative humidity inside and outside the greenhouse and ambient air temperature for complete drying have been recorded. The experiments were conducted after the crop harvesting season from September to December 2001. These data were used for determination of the coefficient of convective mass transfer and then for development of the empirical relation of convective mass transfer coefficient with drying time under natural and forced modes. The empirical relations with convective mass transfer for open and greenhouse drying have been compared. The convective mass transfer coefficient was lower for drying inside the greenhouse with natural mode as compared to open sun drying. Its value was doubled under the forced mode inside the greenhouse drying compared to natural convection in the initial stage of drying

276

International Nuclear Information System (INIS)

For the future upgrade of inner vessel components (CIEL project) a guard limiter for plasma ramp-up and disruption protection will be installed on the high field side of the vacuum vessel. Among transient heat loads, this structure has to sustain a moderate heat flux in the range of ?0.5 MW/m2 during quasi steady state operation (1000 s). A bolted carbon-carbon (C-C) tile is preferred compared with a brazed tile solution due to the expected moderate heat fluxes, costs and the possibility of rapid replacement of individual tiles. Large flat tile assemblies require a sufficient soft and conductive compliant layer enclosed between tile and heat sink in order to avoid thermal contact loss of the assembly during heat loads and therefore minimising the tile surface temperature. The global heat transfer coefficient (Hgl) under vacuum at low contact pressures (0.5-1.5 MPa) between C-C and CuCrZr heat sink substrata has been measured in the experimental device, installation of contact heat transfer measurements (ITTAC), using different compliant materials. It appears that the best compliant layer is a graphite sheet (PAPYEX), compared with copper-felt/foam material. As an example, a Hgl number of ?104 W/m2 K at an average contact pressure of 0.5 MPa has been measured near room temperature between C-C (SEP N11) and CuCrZr substrata using a 0.5-mm thick PAPYEX layer. Thermohydraulic calculations (2D) of the guard limitercalculations (2D) of the guard limiter design show an expected tile surface temperature of about 550 deg. C in steady state regime for an incident heat flux of 0.5 MW/m2

277

This work studies the forced convection problem in internal flow between concentric annular ducts, with radial fins at the internal tube surface. The finned surface heat transfer is analyzed by two different approaches. In the first one, it is assumed one-dimensional heat conduction along the internal tube wall and fins, with the convection heat transfer coefficient being a known parameter, determined by an uncoupled solution. In the other way, named conjugated approach, the mathematical mode...

Andrade, Cla?udia R.; Zaparoli, Edson L.

2000-01-01

278

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english This work is aimed at modeling the heat transfer mechanism in a fluidized bed of grass seeds (Brachiaria brizantha) for supporting further works on simulating the drying of these seeds in such a bed. The three-phase heat transfer model, developed by Vitor et al. (2004), is the one used for this prop [...] osal. This model is modified to uncouple one of the four adjusted model parameters from the gas temperature. Using the first set of experiments, carried out in a laboratory scale batch fluidized bed, the four adjusted model parameters are determined, generating the heat transfer coefficient between particles and gas phase, as well as the heat transfer coefficient between the column wall and ambient air. The second set of experiments, performed in the same unit at different conditions, validates the modified model.

A. C., Rizzi Jr.; M. L., Passos; J. T., Freire.

2009-09-01

279

A mathematical model is presented to study the Soret and Dufour effects on the convective heat and mass transfer in stagnation-point flow of viscous incompressible fluid towards a shrinking surface. Suitable similarity transformations are used to convert the governing partial differential equations into self-similarity ordinary differential equations that are then numerically solved by shooting method. Dual solutions for temperature and concentration are obtained in the presence of Soret and Dufour effects. Graphical representations of the heat and mass transfer coefficients, the dimensionless thermal and solute profiles for various values of Prandtl number, Lewis number, Soret number and Dufour number are demonstrated. With Soret number the mass transfer coefficient which is related to mass transfer rate increases for both solutions and the heat transfer coefficient (related to heat transfer rate) for both solutions becomes larger with Dufour number. The Prandtl number causes reduction in heat and the mass transfer coefficients and similarly with the Lewis number mass transfer coefficient decreases. Also, double crossing over is found in dual dimensionless temperature profiles for increasing Soret number and in dual dimensionless concentration profiles for the increase in Dufour number. Due to the larger values of Dufour number the thermal boundary layer increases and for Prandtl number increment it decreases; whereas, the solute boundary layer thickness reduces with increasing values of Prandtl number and Lewis number.

Bhattacharyya, Krishnendu; Layek, G. C.; Seth, G. S.

2014-09-01

280

Methamphetamine residue dermal transfer efficiencies from household surfaces.

Methamphetamine contamination from illegal production operations poses a potential health concern for emergency responders, child protective services, law enforcement, and children living in contaminated structures. The objective of this study was to evaluate dermal transfer efficiencies of methamphetamine from contaminated household surfaces. These transfer efficiencies are lacking for methamphetamine, and would be beneficial for use in exposure models. Surfaces were contaminated using a simulated smoking method in a stainless steel chamber. Household surfaces were carpet, painted drywall, and linoleum. Dermal transfer efficiencies were obtained using cotton gloves for two hand conditions, dry or saliva moistened (wet). In addition, three contact scenarios were evaluated for both hand conditions: one, two, or three contacts with contaminated surfaces. Dermal transfer efficiencies were calculated for both hand conditions and used as inputs in a Stochastic Human Exposure and Dose Simulation model (SHEDS-Multimedia, Office of Research and Development, United States Environmental Protection Agency, Research Triangle Park, N.C.). Results of this study showed that average dermal transfer efficiencies of methamphetamine ranged from 11% for dry hands to 26% for wet hands. There was a significantly higher wet transfer as compared to dry transfer for all surfaces. For wet hands, dermal transfer depended on surface type with higher transfer from carpet and linoleum as compared to drywall. Based on our estimates of dermal transfer efficiency, a surface contamination clearance level of 1.5 ?g/100 cm(2) may not ensure absorbed doses remain below the level associated with adverse health effects in all cases. Additional dermal transfer studies should be performed using skin surrogates that may better predict actual skin transfer. PMID:24579754

Van Dyke, Mike; Martyny, John W; Serrano, Kate A

2014-01-01

281

An effusive molecular beam technique is described to measure alkane dissociative sticking coefficients, S(Tg, Ts; ?), on metal surfaces for which the impinging gas temperature, Tg, and surface temperature, Ts, can be independently varied, along with the angle of incidence, ?, of the impinging gas. Effusive beam experiments with Tg = Ts = T allow for determination of angle-resolved dissociative sticking coefficients, S(T; ?), which when averaged over the cos (?)/? angular distribution appropriate to the impinging flux from a thermal ambient gas yield the thermal dissociative sticking coefficient, S(T). Nonequilibrium S(Tg, Ts; ?) measurements for which Tg ? Ts provide additional opportunities to characterize the transition state and gas-surface energy transfer at reactive energies. A resistively heated effusive molecular beam doser controls the Tg of the impinging gas striking the surface. The flux of molecules striking the surface from the effusive beam is determined from knowledge of the dosing geometry, chamber pressure, and pumping speed. Separate experiments with a calibrated leak serve to fix the chamber pumping speed. Postdosing Auger electron spectroscopy is used to measure the carbon of the alkyl radical reaction product that is deposited on the surface as a result of alkane dissociative sticking. As implemented in a typical ultrahigh vacuum chamber for surface analysis, the technique has provided access to a dynamic range of roughly 6 orders of magnitude in the initial dissociative sticking coefficient for small alkanes on Pt(111).

Cushing, G. W.; Navin, J. K.; Valadez, L.; Johánek, V.; Harrison, I.

2011-04-01

282

International Nuclear Information System (INIS)

The three-surface theorem for uniformly elliptic differential inequalities with nonpositive coefficient of zero-order term in some domain D is a subset of Rn becomes trivial if the maximum of u on two separate boundary surfaces of D is nonpositive. We give a method in this paper for obtaining a nontrivial estimate of the maximum of u on a family of closed surfaces. (author). 2 refs

283

International Nuclear Information System (INIS)

FREG-3 predicts the temperature distribution in a fuel rod and the stored energy based on the distribution. The temperature distribution is calculated in accordance with fuel-rod irradiation history under normal operating conditions. An important factor in obtaining the temperature distribution is the gap heat transfer coefficient between pellet outer surface and cladding inner surface. To obtain the proper coefficient, the program incorporates submodels and correlations. Purpose of the program is to evaluate stored energy in the fuel rod preceding the initiation of the LOCA. The estimated stored energy is a significant key parameter in safety evaluation of the fuel rod. The program can also be used as the best estimate code, if calculation models or correlations are appropriately chosen. The calculation procedure and the models used are described. (auth.)

284

Energy Technology Data Exchange (ETDEWEB)

Self-induced thermocapillary convection and its significance with regard to film boiling heat transfer from a vertical saturated surface is discussed. Utilizing a simplified geometrical model, an analytical expression (multiplier factor) for the vapor film thickness and heat transfer coefficient corrected by thermocapillary phenomena was derived. The above equation is a new theoretical viewpoint for the enhancement in the heat transfer coefficient observed in the experimental data in the viscous regime and agree qualitatively with available experimental measurements made on R113 coolant.

Arias, F.J. [Department of Physics and Nuclear Engineering, Technical University of Catalonia (UPC), Barcelona, 08028 Catalonia (Spain)], E-mail: frariasm7@fis.ub.edu

2009-10-15

285

International Nuclear Information System (INIS)

Self-induced thermocapillary convection and its significance with regard to film boiling heat transfer from a vertical saturated surface is discussed. Utilizing a simplified geometrical model, an analytical expression (multiplier factor) for the vapor film thickness and heat transfer coefficient corrected by thermocapillary phenomena was derived. The above equation is a new theoretical viewpoint for the enhancement in the heat transfer coefficient observed in the experimental data in the viscous regime and agree qualitatively with available experimental measurements made on R113 coolant.

286

Studying heat transfer enhancement for water boiling on a surface with micro- and nanorelief

We present the results from a study of heat transfer enhancement for bulk water boiling at atmospheric pressure on a surface with micro- and nanorelief, including a relief formed from silicon carbide and aluminum oxide nanoparticles. Horizontally oriented steel tube 1.2 mm in diameter and copper plate 15 × 3 mm in size were selected as test sections. The process was recorded by means of a video camera, and the values of heat transfer, critical heat fluxes, and contact angles were measured. The use of surface with micro- and nanorelief makes it possible to obtain a significantly higher critical heat flux and boiling heat transfer coefficient owing to a change of surface wettability. The results of investigations can find use in compact heat exchangers, refrigerating plants, heat pipes, in the mirrors of high-capacity lasers, in the targets and resonators of charged particle accelerators and for external cooling of reactor vessels under emergency conditions.

Kuzma-Kichta, Yu. A.; Lavrikov, A. V.; Shustov, M. V.; Chursin, P. S.; Chistyakova, A. V.; Zvonarev, Yu. A.; Zhukov, V. M.; Vasil'eva, L. T.

2014-03-01

287

Pressure-induced absorption coefficients for radiative transfer calculations in Titan's atmosphere

International Nuclear Information System (INIS)

The semiempirical theory of Birnbaum and Cohen (1976) is used to calculate the FIR pressure-induced absorption (PIA) spectra of N2, CH4, N2 + Ar, N2 + CH4, and N2 + H2 under conditions like those in the Titan troposphere. The results are presented graphically and compared with published data from laboratory measurements of PIA in the same gases and mixtures (Dagg et al., 1986; Dore et al., 1986). Good agreement is obtained, with only a slight underestimation of PIA at 300-400/cm in the case of CH4. The absorption coefficients are presented in tables, and it is suggested that the present findings are of value for evaluating the effects of tropospheric clouds on the Titan FIR spectrum and studying the greenhouse effect near the Titan surface. 24 references

288

Gas holdup and overall volumetric oxygen transfer coefficient in airlift contactors.

The two major types of airlift contactors, concentric-tube and external-loop, were investigated for their gas holdup (riser and downcomer) and overall mass transfer characteristics. Results obtained in batch charges of tap water and 0.15 kmol/m(3) NaCl solution are reported for external-loop airlift contactors having downcomer-to-riser cross-sectional area ratios, A(d)/A(r), ranging from 0.11

Bello, R A; Robinson, C W; Moo-Young, M

1985-03-01

289

Relationship between coefficient of friction and surface roughness of wafer in nanomachining process

Fixed abrasive polishing technology can obtain a nanoscale surface and is one of the future nano machining directions. The coefficient of friction between the pad and the wafer in the polishing process can influence on the surface quality of the wafer. The relationship between the coefficient of friction and surface roughness of the wafer was investigated to improve the efficiency and surface quality. Based on the Florida model, the adhesion, asperity plough and abrasive plough from the pad in the polishing process was analyzed. The friction force per unit area was calculated by the properties of the pad and wafer. Based on the rod model, the actual contact area was calculated by the surface roughness and the properties of the pad and wafer. The relational model between the surface roughness of the wafer and the friction coefficient was established. The model was verified by the experiments of fixed abrasive polishing of BK7 glass. When the friction coefficient is less than 1.9, the data of the experiment and theory match very well in the comparison process.

Li, Jun; Xia, Lei; Li, Pengpeng; Zhu, Yongwei; Sun, Yuli; Zuo, Dunwen

2013-08-01

290

International Nuclear Information System (INIS)

The 18O-exchange reaction between 18O2 gas and nickel oxide was followed with a microbalance in the temperature range of 300-7000C. The plots of weight gain vs.tsup(1/2) resulted in a curve having two straight portions. From the data in the first straight line the surface diffusion coefficients of oxygen for NiO were determined and were expressed as Dsub(s)=5.04 x 10-16 exp (-10.2x103 (cal/mol)/RT)(cm2/s). The surface layer thickness was calculated from the weight change of the specimen at the end of the first line: delta=1.42x103 exp(-7.02 x103/RT)(A). The grain boundary diffusion coefficient of oxygen at 7000C calculated from the second slow line was almost identical to the surface diffusion coefficient. (orig.)

291

Mass Transfer Coefficient During Cathodic Protectionof Low Carbon Steel in Seawater

Directory of Open Access Journals (Sweden)

Full Text Available The aim of this research is to calculate mass transfer coefficient, kd, during cathodic protection of low carbon steel in neutral seawater (3.5% W/V NaCl in distilled water with pH = 7. Two types of cathodic protection were used:First: Sacrificial anode cathodic protection (SACP were a pipeline of steel carrying seawater using zinc as a sacrificial anode and with variable temperatures ranged (0 ? 45oC and volumetric flow rate ranged (5 ? 900 lit/hr. It was found that the kd increases with increasing temperature and volumetric flow rate of seawater, where kd ranged (0.24×10-6 ? 41.6×10-6 m/s.Second: Impressed current cathodic protection (ICCP technique adopting a rotating vertical steel cylinder in seawater with variable temperatures ranged (0 ? 45oC and rotating velocity ranged (0 ? 400 rpm. It was found that the kd increases with increasing temperature and rotating velocity, where kd ranged (7.25×10-6 ? 36.82×10-6 m/s.

Ameel Mohammed Rahman

2009-01-01

292

An Experimental Investigation of Heat Transfer Coefficients for Spiral Plate Heat Exchanger

Directory of Open Access Journals (Sweden)

Full Text Available Spiral plate heat exchangers play a vital role in cooling high density and high viscous fluids. This paper presents an experimental investigation of convective heat transfer co-efficient for electrolytes using spiral plate heat exchanger. The test section consists of a Plate of width 0.3150 m, thickness 0.001 m and mean hydraulic diameter of 0.01 m. The mass flow rate of hot fluid is varying from 0.4 kg sec-1 to 0.8 kg sec-1 and the mass flow rate of cold fluid varies from 0.3 kg sec-1 to 0.8 kg sec-1. Experiments have been conducted by varying the mass flow rate, temperature and pressure of cold fluid, keeping the mass flow rate of hot fluid constant. The effects of relevant parameters on spiral plate heat exchanger are investigated. The data obtained from the experimental study are compared with the theoretical data. Besides, a new correlation for the nusselt number that can be used for practical applications is proposed.

Kaliannan Saravanan

2009-02-01

293

Surface heat transfer due to sliding bubble motion

International Nuclear Information System (INIS)

The presence of a rising bubble in a fluid can greatly enhance heat transfer from adjacent heated surfaces such as in shell and tube heat exchangers and chemical reactors. One specific case of this is when a bubble impacts and slides along the surface. The result is heat transfer enhancement by two main mechanisms: first, the bubble itself acting as a bluff body, and second, the wake generated behind the bubble leads to increasing mixing. The current research is concerned with measuring the heat transfer from a submerged heated surface that is subject to a sliding bubble flow. An ohmically heated 25 ?m thick stainless steel foil, submerged in a water tank, forms the test surface. An air bubble is injected onto the lower surface of the test plate, it slides along its length and the effects are monitored by two methods. Thermochromic liquid crystals (TLC's) are used in conjunction with a high speed camera to obtain a time varying 2D temperature map of the test surface. A second synchronised camera mounted below the foil records the bubble motion. Tests are performed at angles of 10 deg., 20 deg. and 30 deg. to the horizontal. This paper reports on the enhancement of the heat transfer due to the bubble. It has been found that the angle made between the heated surface and the horizontal influences heat transfer by changing the bubble's motion. In general, a steeper angle leads to a higher bubble velocity, which results in greater heat transfer enhancementheat transfer enhancement

294

Flux surface averaging on the diffusion coefficient in electron cyclotron resonance heating

International Nuclear Information System (INIS)

The single particle model has been used to describe electron cyclotron resonance heating. Fielding's method of calculating the diffusion coefficient has been simplified and extended to include the effect of finite beam width. It is shown how this effect and the effect of the rotational transform lead to a spreading of the resonance over a wider class of particles and how the diffusion coefficient should be average over a magnetic surface or surfaces. The spreading of the resonance due to these effects is expected to increase the threshold for saturation of the heating to occur

295

International Nuclear Information System (INIS)

Reductive-extraction is one of the main process of pyro-chemical reprocessing for metallic fuel. Mass transfer coefficient of rare earth elements was evaluated in LiCl-KCl/Cd system at 450 and 500 degree C. The interface between the salt and the Cd was agitated with a fun turbine blade at 30 to 500 rpm. In case of 300 or 500 rpm, the system reached at equilibrium condition within 10 minutes. The evaluated mass transfer coefficient was 0.0008 to 0.05 cm/sec, which depended on the agitation speed or Reynolds number. The mass transfer coefficients became larger at 500 degree C than at 450 degree C, and in case of upward stream than in case of downward stream. Evaluation of recovery yield and separation efficiency of each solute were carried out in single-stage continuous-flow extraction and in multi-stages counter-current extraction in LiCl-KCl/Cd system. The mass transfer coefficients obtained in these experiments should be enough for separation and recovery in pyro-reprocessing by using counter-current extraction with 6 stages in case that the flow rare of both salt and Cd controlled within 2%/min. (author)

296

Heat transfer enhancement and surface thermostabilization for pool boiling on porous structures

The scope of the article includes the description of the experimental setup, methodology of the experimental studies, the study results for pool boiling heat transfer coefficient encountered on sintered capillary porous coverings. The results of own studies presented here refer to the boiling in a large volume on copper fibrous coverings. Hysteresis type I, II and III were described. Several examples of capillary porous surface coverings applications in purposely chosen complex boiling heat t...

Wojcik Tadeusz Michal

2012-01-01

297

An effort is made to explain and improve the understanding of the mechanisms behind the thermo-hydraulic performance of perforated extended surfaces used in compact heat exchangers in the laminar flow regime (Re D = 400-2500). A transient liquid crystal technique, which uses Helium as operating fluid, together with digital image photographic processing have been used to provide measurements of local heat transfer coefficients for this geometry. This work has found that through the use of perf...

Adams, Jc; Ireland, Pt; Oswald, J.

2003-01-01

298

Rough surfaces with enhanced heat transfer for electronics cooling by direct metal laser sintering

Experimental evidences are reported on the potential of direct metal laser sintering (DMLS) in manufacturing flat and finned heat sinks with a remarkably enhanced convective heat transfer coefficient, taking advantage of artificial roughness in fully turbulent regime. To the best of our knowledge, this is the first study where artificial roughness by DMLS is investigated in terms of such thermal performances. On rough flat surfaces, we experience a peak of 73 % for the convective heat transfe...

Calignano, Flaviana; Asinari, Pietro; Chiavazzo, Eliodoro; Manfredi, Diego Giovanni; Ventola, Luigi

2014-01-01

299

International Nuclear Information System (INIS)

Measurements of friction factor and heat transfer coefficients for two rods of 18.9 mm 0.D. with two-dimensional roughness, each in two different outer smooth tubes have been performed in turbulent and laminar flow. The turbulent flow results indicate that the flow was not thermally fully established, the isothermal data however agree reasonably well with our previously obtained general correlation. Laminar flow results can be correlated best when the Reynolds and Greatz numbers are evaluated at the temperature average between the temperature of the inner rod surface and of the outer smooth surface of the annulus, the average being weighted over the two surfaces. (orig.)

300

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background One of the current shortcomings of radiofrequency (RF tumor ablation is its limited performance in regions close to large blood vessels, resulting in high recurrence rates at these locations. Computer models have been used to determine tissue temperatures during tumor ablation procedures. To simulate large vessels, either constant wall temperature or constant convective heat transfer coefficient (h have been assumed at the vessel surface to simulate convection. However, the actual distribution of the temperature on the vessel wall is non-uniform and time-varying, and this feature makes the convective coefficient variable. Methods This paper presents a realistic time-varying model in which h is a function of the temperature distribution at the vessel wall. The finite-element method (FEM was employed in order to model RF hepatic ablation. Two geometrical configurations were investigated. The RF electrode was placed at distances of 1 and 5 mm from a large vessel (10 mm diameter. Results When the ablation procedure takes longer than 1–2 min, the attained coagulation zone obtained with both time-varying h and constant h does not differ significantly. However, for short duration ablation (5–10 s and when the electrode is 1 mm away from the vessel, the use of constant h can lead to errors as high as 20% in the estimation of the coagulation zone. Conclusion For tumor ablation procedures typically lasting at least 5 min, this study shows that modeling the heat sink effect of large vessels by applying constant h as a boundary condition will yield precise results while reducing computational complexity. However, for other thermal therapies with shorter treatment using a time-varying h may be necessary.

Pinheiro Cleber

2008-07-01

301

Estimation of the friction coefficient between wheel and rail surface using traction motor behaviour

The friction coefficient between a railway wheel and rail surface is a crucial factor in maintaining high acceleration and braking performance of railway vehicles thus monitoring this friction coefficient is important. Restricted by the difficulty in directly measuring the friction coefficient, the creep force or creepage, indirect methods using state observers are used more frequently. This paper presents an approach using a Kalman filter to estimate the creep force and creepage between the wheel and rail and then to identify the friction coefficient using the estimated creep force-creepage relationship. A mathematic model including an AC motor, wheel and roller is built to simulate the driving system. The parameters are based on a test rig at Manchester Metropolitan University. The Kalman filter is designed to estimate the friction coefficient based on the measurements of the simulation model. Series of residuals are calculated through the comparison between the estimated creep force and theoretical values of different friction coefficient. Root mean square values of the residuals are used in the friction coefficient identification.

Zhao, Y.; Liang, B.; Iwnicki, S.

2012-05-01

302

Estimation of the friction coefficient between wheel and rail surface using traction motor behaviour

International Nuclear Information System (INIS)

The friction coefficient between a railway wheel and rail surface is a crucial factor in maintaining high acceleration and braking performance of railway vehicles thus monitoring this friction coefficient is important. Restricted by the difficulty in directly measuring the friction coefficient, the creep force or creepage, indirect methods using state observers are used more frequently. This paper presents an approach using a Kalman filter to estimate the creep force and creepage between the wheel and rail and then to identify the friction coefficient using the estimated creep force-creepage relationship. A mathematic model including an AC motor, wheel and roller is built to simulate the driving system. The parameters are based on a test rig at Manchester Metropolitan University. The Kalman filter is designed to estimate the friction coefficient based on the measurements of the simulation model. Series of residuals are calculated through the comparison between the estimated creep force and theoretical values of different friction coefficient. Root mean square values of the residuals are used in the friction coefficient identification.

303

A gas turbine airfoil contains multiple coolant passageways. These passages usually have rib roughened wall surfaces in order to increase the heat transfer from the blade to the cooling air. Auxiliary power and compressed air is very valuable in a gas turbine, therefore low pumping power requirements are crucial. The thermal performance of three different coolant channel geometries with three different rib sizes was investigated. Heat transfer calculations were performed for Reynolds numbers ranging from 6,000 to 40,000. The performance characteristics were calculated through the use of the convective heat transfer coefficient and the friction factor. In this study, the most desirable characteristics are a high heat transfer coefficient and minimal pumping power requirements. The thermal performance of each case was determined by comparing the average Nusselt numbers to the friction factor ratio. The resulting value was then plotted against the Reynolds number for each case. The trending data indicated thermal efficiency decreases with an increasing Reynolds number for all cases. The picture data shows increased thermal efficiency at larger distances from the nose portion of the cavity. In addition, thermal efficiency was higher at the half distance of the rib pitch while areas close to the ribs saw a lower thermal efficiency. The following experimental data will show that Rig 2 and 3 are the most thermally efficient geometries, with Rig 2 requiring lower pumping power and Rig 3 having a higher average Nusselt number.

Hagan, Peter

304

Directory of Open Access Journals (Sweden)

Full Text Available The paper presents the FEM method for determination of boiling heat transfer coefficient in cooling liquid flow in a rectangular minichannel with asymmetric heating. Experimental research has focused on the transition from single phase forced convection to nucleate boiling, i.e. the zone of boiling incipience. The “boiling front” location has been determined from the temperature distribution of the heated wall obtained from liquid crystal thermography. The main part of the test section has been a minichannel of pre-set depth from 0.7 to 2.0 mm, of different spatial orientations. Local values of heat transfer coefficient have been determined following the solution of the two-dimensional inverse heat transfer problem. This problem has been solved with the use of Trefftz functions. Trefftz functions have been used to construct base functions in the finite element method (FEMT.

Maciejewska Beata

2012-04-01

305

International Nuclear Information System (INIS)

The importance of azimuthal temperature variation upon the diametral strain of PWR zircaloy cladding at fuel pin failure is discussed and causes of temperature gradients are considered. A correlation between the surface heat-transfer coefficient profile and the pitch-to-diameter ratio of the pin bundle has been incorporated in the ADVICE computer code. This enables the code to calculate the temperature distribution in a segment of the fuel pin and hence to predict the deformation of the fuel cladding, both before and after contact with adjacent rods. The code also predicts the bowing of the cladding and relative movement between the fuel pellet and the cladding. Two postulated loss-of-coolant flow histories have been studied using the ADVICE code, and estimates of the deformation histories and the failure strains are presented. In the first case the cladding failed while in the alpha phase and the failure strain was limited by temperature gradients caused by unstable bowing. In the second, the cladding started to change phase before cladding substantial deformation had occurred and it hardly bowed at all. In this case, the cladding temperature remained relatively uniform and a higher failure strain was predicted. (author)

306

Two systems have been developed to study boiling heat transfer on the microscale. The first system utilizes a 32 x 32 array of diodes to measure the local temperature fluctuations during boiling on a silicon wafer heated from below. The second system utilizes an array of 96 microscale heaters each maintained at constant surface temperature using electronic feedback loops. The power required to keep each heater at constant temperature is measured, enabling the local heat transfer coefficient to be determined. Both of these systems as well as some preliminary results are discussed.

Kim, J.; Bae, S. W.; Whitten, M. W.; Mullen, J. D.; Quine, R. W.; Kalkur, T. S.

1999-01-01

307

Heat transfer enhancement and surface thermostabilization for pool boiling on porous structures

Directory of Open Access Journals (Sweden)

Full Text Available The scope of the article includes the description of the experimental setup, methodology of the experimental studies, the study results for pool boiling heat transfer coefficient encountered on sintered capillary porous coverings. The results of own studies presented here refer to the boiling in a large volume on copper fibrous coverings. Hysteresis type I, II and III were described. Several examples of capillary porous surface coverings applications in purposely chosen complex boiling heat transfer processes have been presented based on Wojcik and Poniewski patents.

Wojcik Tadeusz Michal

2012-04-01

308

Experimental study on augmentation of nucleate boiling heat transfer on nano porous surfaces

Energy Technology Data Exchange (ETDEWEB)

Nucleate boiling broadly occurs in thermal hydraulic and safety systems of nuclear power plant (NPP). Heat transfer performance of nucleate boiling is closely related to efficiency and safety of NPPs. Hence, there have been numerous researches to effectively enhance nucleate boiling heat transfer performance. A number of recent studies have reported significant enhancements in nucleate boiling heat transfer coefficient (NBHTC) and critical heat flux (CHF) by fabricating nano/microscale structures on a boiling surface. Wei et al. showed that both NBHTC and CHF can be significantly enhanced with micro pin finned structures. They explained enhancement of NBHTC and CHF that occurred by increase in effective heat transfer area due to micro pin finned structures. Ahn et al. reported 100% enhancement in CHF on a boiling surface with nano/micro hybrid structures. They analyzed CHF enhancement that was caused by improvement of surface wettability on Nano/micro hybrid structures. In this study, an ordered nano porous surface was prepared using anodized aluminum oxide (AAO) technique and nucleate boiling heat transfer performance was examined in a pool with FC 72. Furthermore, the pool boiling result on the nano porous surface was interpreted based on heterogeneous bubble nucleation theory from a cavity.

Park, Young Jae; Kim, Hyung Dae [Kyung Hee Univ., Seoul (Korea, Republic of)

2012-10-15

309

Effect of Lubricant Viscosity and Surface Roughness on Coefficient of Friction in Rolling Contact

Directory of Open Access Journals (Sweden)

Full Text Available The main objective of this paper is to investigate the effect of surface roughness and lubricant viscosity on coefficient of friction in silicon nitride- steel rolling contact. Two samples of silicon nitride with two different values of surface roughness were tested against steel counter face. The test was performed on four ball tester in presence of lubricant with two different values of viscosity. Taguchi technique a methodology in design of experiment implemented to plan the experimentation and same is utilized to evaluate the interacting effect of surface roughness and lubricant viscosity. Analysis of experimental results presents a strong interaction between surface roughness and lubricant viscosity on coefficient of friction in rolling contact.

S.G. Ghalme

2013-12-01

310

International Nuclear Information System (INIS)

Detailed studies were carried out to establish site-specific soil to grass transfer factors (Fv) and grass to cow milk transfer coefficients (Fm) for radioactive cesium (137Cs) and stable cesium (Cs) for Kaiga region, where a nuclear power station has been in operation for more than 10 years. The study included adopted cows, cows of local farmers, and cows from the dairy farm. A grass field was developed specifically for the study and 2 local breed cows were adopted and allowed to graze in this grass field. The soil and grass samples were collected regularly from this field and analyzed for the concentrations of 137Cs and stable Cs to evaluate the soil to grass Fv values. The milk samples from the adopted cows were analyzed for the 137Cs and stable Cs concentrations to evaluate Fm values. For comparison, studies were also carried out in dominant grazing areas in different villages around the nuclear power plant and the cows of local farmers which graze in these areas were identified and milk samples were collected and analyzed regularly. The geometric mean values of Fv were found to be 1.1 × 10?1 and 1.8 × 10?1 for 137Cs and stable Cs, respectively. The Fm of 137Cs had geometric mean values of 1.9 × 10?2 d L?1 and 4.6 × 10?2 d L?1, respectively, for adopted Cows 1 and 2; 1.7 × 10?2 d L?1 for the cows of local farmers, and 4.0 × 10?3 d L?1 for the dairy farm cows. The geometric mean values of Fm for stable Cs were similar to those of 137Cs. The Fm value for the dairy farm cows was an order of magnitude lower than those for local breed cows. The Fm values observed for the local breed cows were also an order of magnitude higher when compared to the many values reported in the literature and in the IAEA publication. Possible reasons for this higher Fm values were identified. The correlation between Fv and Fm values for 137Cs and stable Cs and their dependence on the potassium content (40K and stable K) in the soil and grass were also studied. In order to estimate the ingestion dose accurate data of the dietary habits of the population was necessary and this data was collected through a well planned demographic survey. The internal doses to a child due to the ingestion of 137Cs along with the milk of the local cows and from the dairy farm were found to be 0.29 ?Sv y?1 and 0.04 ?Sv y?1,while that to an adult were 0.39 ?Sv y?1 and 0.05 ?Sv y?1, respectively. -- Highlights: • This is a detailed study on Fv and Fm for 137Cs and stable Cs around the Kaiga nuclear power plant, India. • The geometric mean values of Fv were found to be 1.1 × 10?1 and 1.8 × 10?1 for 137Cs and stable Cs, respectively. • The Fm value for 137Cs for the local breed cows was estimated to be 2.4 × 10?2 d L?1. • The Fm value for dairy farm cows (4.0 × 10?3 d L?1) was an order of magnitude lower than those for local breed cows. • The reasons for the higher Fm values for 137Cs for the local breed cows are identified

311

A theoretical and experimental approach was used to perform a systematic analysis to find the optimal parameters of a textured surface for the purpose of reducing the coefficient of static friction. A textured surface implies using laser, mechanical, or in this case chemical means to produce regularly shaped and spaced depressions (or dimples) in metallic contacts. This research focused on high load metallic contact, such as in a hydraulic gerotor or geroler displacement machine. The theoreti...

Brandt, Daniel S.

2012-01-01

312

Coefficient of friction between carbon steel and perlite concrete surfaces. Test report

International Nuclear Information System (INIS)

The results of coefficient of friction, ?, tests conducted on perlite blocks and carbon steel plates under various conditions are discussed. Variables included in the test entailed the use of lubricants (i.e. water and simulated radioactive waste solution) abrasives (120 grit, 60 grit, 40 grit sand paper) applied to the surfaces of the perlite block and carbon steel plates

313

Effects of surface structure in meson transfer reactions

International Nuclear Information System (INIS)

We discuss some effects occuring when mesons are transferred from hydrogen to the atoms of other elements in solids. The relationship between the mesic X-ray intensities and the surface structure is studied. (orig.)

314

MASS TRANSFER COEFFICIENTS FOR A NON-NEWTONIAN FLUID AND WATER WITH AND WITHOUT ANTI-FOAM AGENTS

International Nuclear Information System (INIS)

Mass transfer rates were measured in a large scale system, which consisted of an 8.4 meter tall by 0.76 meter diameter column containing one of three fluids: water with an anti-foam agent, water without an anti-foam agent, and AZ101 simulant, which simulated a non-Newtonian nuclear waste. The testing contributed to the evaluation of large scale mass transfer of hydrogen in nuclear waste tanks. Due to its radioactivity, the waste was chemically simulated, and due to flammability concerns oxygen was used in lieu of hydrogen. Different liquids were used to better understand the mass transfer processes, where each of the fluids was saturated with oxygen, and the oxygen was then removed from solution as air bubbled up, or sparged, through the solution from the bottom of the column. Air sparging was supplied by a single tube which was co-axial to the column, the decrease in oxygen concentration was recorded, and oxygen measurements were then used to determine the mass transfer coefficients to describe the rate of oxygen transfer from solution. Superficial, average, sparging velocities of 2, 5, and 10 mm/second were applied to each of the liquids at three different column fill levels, and mass transfer coefficient test results are presented here for combinations of superficial velocities and fluid levels

315

Heat transfer to curved surfaces from heat generating pools

International Nuclear Information System (INIS)

Experiments were conducted on heat transfer from internally heated ZnSO4-H2O pools to curved surfaces. These experiments extended existing data for nonboiling pools to higher Rayleigh numbers. The data for convective downward heat transfer from nonboiling pools to a curved surface were reasonably close to the Mayinger correlation extrapolated to higher Rayleigh numbers and lower ratios of pool depth to radius of curvature. Sideward heat transfer to a surface could be described by Nu=0.7Ra/sup 0.2/. Insulating the upper pool surface from the atmosphere had no effect on either sideward or downward heat transfer. An investigation was also made on effects of curvature on heat transfer from boiling pools. Nusselt numbers for sideward heat transfer were proportional to a boiling Reynolds number based on superficial vapor velocity to the 0.275 power and quite close to the correlation for a pool with flat vertical walls. Downward boiling heat transfer to a curved surface was proportional to the Reynolds number to the 0.1 power

316

Data Qualification Report For DTN: MO0012RIB00065.002, Parameter Values For Transfer Coefficients

International Nuclear Information System (INIS)

A data-qualification evaluation was conducted on Reference Information Base (RIB) data set MOO0 12RIB00065.002, ''Parameter Values for Transfer Coefficients''. The corroborating data method was used to evaluate the data. This method was selected because it closely matches the literature-review method followed to select parameter values. Five criteria were considered when the corroborating method was used: adequacy of the corroborative literature, sufficiency of value-selection criteria, implementation of the selection criteria, documentation of the process, and whether the analysis was conducted in accordance with applicable quality assurance (QA) procedures. Three criteria were used when a literature review was not conducted: appropriate logic used to select parameters, documentation of the process, and whether the analysis was conducted in accordance with applicable QA procedures. The RIB data item, the associated Analysis and Model Report (AMR), the corroborative literature, and the results of an audit revision O/ICN--0 of the AMR were examined. All calculations and the selection process for all values were repeated and confirmed. The qualification team concluded: (1) A sufficient quantity of corroborative literature was reviewed and no additional literature was identified that should have been considered. (2) The selection criteria were sufficient and resulted in valid parameter values. (3) The process was well defined, adequately documented in the AMR, and correctly followed. (4) The analysis was developed in accordance with applicable QA procedures. No negative findings were documented that resulted in questions about the quality of the data. The qualification team therefore recommends that the qualification status of RIB data set MO0012RIB00065.002 be changed to qualified

317

Liquid crystal measurements of heat transfer and surface shear stress

Liquid crystals have become an accurate and convenient means of measuring surface temperature and heat transfer for the gas turbine and heat transfer research communities. The measurement of surface shear stress using liquid crystals is finding increasing favour with aerodynamicists and developments in these techniques ensure that liquid crystals will continue to provide key thermal and shear stress data in the future. The increasing use of three-dimensional finite element computational model...

Ireland, Pt; Jones, Tv

2000-01-01

318

Directory of Open Access Journals (Sweden)

Full Text Available Due to the Magnetohydrodynamic (MHD effect, which degrades heat transfer coefficients by pulsation suppression of external magnetic field, on the electrically conducting flow, the wall with non-uniform electrical conductivity is employed in a free surface MHD-flow system for heat transfer enhancement. The non-uniform electrical conductivity distribution of the channel wall may create alternate Lorentz forces along spanwise direction, which can effectively produce flow disturbance, promote mixture, reduce the thickness of boundary layer, and enhance heat transfer. So the heat transfer performances enhanced by some conducting strips aligned with the mean flow direction on the insulating wall of free surface MHD-flow are simulated numerically in this paper. The flow behaviors, heat transfer coefficients, friction factors and pressure drops are presented under different Hartmann numbers. Results show that, in the range of Hartmann numbers between 30 - 100, the wall with non-uniform conductivity can achieve heat transfer enhancements (Nu/Nu0 of about 1.2 to 1.6 relative to the insulating wall, with negligible friction augmentation. This research indicates that the modules with three or five conducting strips can obtain better enhancement effect in our research. Particularly, the heat transfer augmentation increases monotonically with increasing Hartmann numbers. Therefore, the enhancement purpose for high Hartman number MHD-flow is marked, which may remedy the depressing heat transfer coefficients by MHD effect.

H. L. Huang, B. Li

2010-11-01

319

Unsteady convection flow and heat transfer over a vertical stretching surface.

This paper investigates the effect of thermal radiation on unsteady convection flow and heat transfer over a vertical permeable stretching surface in porous medium, where the effects of temperature dependent viscosity and thermal conductivity are also considered. By using a similarity transformation, the governing time-dependent boundary layer equations for momentum and thermal energy are first transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by the numerical shooting technique with fourth-fifth order Runge-Kutta scheme. Numerical results show that as viscosity variation parameter increases both the absolute value of the surface friction coefficient and the absolute value of the surface temperature gradient increase whereas the temperature decreases slightly. With the increase of viscosity variation parameter, the velocity decreases near the sheet surface but increases far away from the surface of the sheet in the boundary layer. The increase in permeability parameter leads to the decrease in both the temperature and the absolute value of the surface friction coefficient, and the increase in both the velocity and the absolute value of the surface temperature gradient. PMID:25264737

Cai, Wenli; Su, Ning; Liu, Xiangdong

2014-01-01

320

Improvement of dropwise condensation heat transfer using hydrophobic nano porous surfaces

Energy Technology Data Exchange (ETDEWEB)

Recently interest of passive system in thermal hydraulic safety system of nuclear power plants has been increased. Passive residual heat removal system (PRHRS) is applied to SMART and APR+ for providing the sufficient cooling capacity against accident conditions. PRHRS is a device for removing the decay heat that cools steam through condensation heat transfer in emergency tank. Condensation is one of most important heat transfer methods in almost industry including the PRHRS. Condensation is classified, according to shape of condensate, into drop-wise condensation and film wise condensation. Drop-wise condensation (DWC) exhibits a significantly higher heat transfer coefficient than film wise condensation (FWC). Whether DWC or FWC occurs in a heat transfer surface is strongly affected by wettability of a surface. It is known that DWC is appears on low wettability surfaces while FWC is appears on high wettability one. In this study, nano-porous hydrophobic surfaces were prepared and tested for the improvement of dropwise condensation heat transfer performance.

Kim, Sang Eun; Kim, Hyun Dae [Kyung Hee Univ., Seoul (Korea, Republic of)

2012-10-15

321

Improvement of dropwise condensation heat transfer using hydrophobic nano porous surfaces

International Nuclear Information System (INIS)

Recently interest of passive system in thermal hydraulic safety system of nuclear power plants has been increased. Passive residual heat removal system (PRHRS) is applied to SMART and APR+ for providing the sufficient cooling capacity against accident conditions. PRHRS is a device for removing the decay heat that cools steam through condensation heat transfer in emergency tank. Condensation is one of most important heat transfer methods in almost industry including the PRHRS. Condensation is classified, according to shape of condensate, into drop-wise condensation and film wise condensation. Drop-wise condensation (DWC) exhibits a significantly higher heat transfer coefficient than film wise condensation (FWC). Whether DWC or FWC occurs in a heat transfer surface is strongly affected by wettability of a surface. It is known that DWC is appears on low wettability surfaces while FWC is appears on high wettability one. In this study, nano-porous hydrophobic surfaces were prepared and tested for the improvement of dropwise condensation heat transfer performance

322

Temperature dependence of volume and surface symmetry energy coefficients of nuclei

International Nuclear Information System (INIS)

The thermal evolution of the energies and free energies of a set of spherical and near-spherical nuclei spanning the whole periodic table are calculated in the subtracted finite-temperature Thomas-Fermi framework with the zero-range Skyrme-type KDE0 and the finite-range modified Seyler-Blanchard interaction. The calculated energies are subjected to a global fit in the spirit of the liquid-drop model. The extracted parameters in this model reflect the temperature dependence of the volume symmetry and surface symmetry coefficients of finite nuclei, in addition to that of the volume and surface energy coefficients. The temperature dependence of the surface symmetry energy is found to be very substantial whereas that of the volume symmetry energy turns out to be comparatively mild.

323

Temperature dependence of volume and surface symmetry energy coefficients of nucle

The thermal evolution of the energies and free energies of a set of spherical and near-spherical nuclei spanning the whole periodic table are calculated in the subtracted finite-temperature Thomas- Fermi framework with the zero-range Skyrme-type KDE0 and the finite-range modified Seyler-Blanchard interaction. The calculated energies are subjected to a global fit in the spirit of the liquid-drop model. The extracted parameters in this model reflect the temperature dependence of the volume symmetry and surface symmetry coefficients of finite nuclei, in addition to that of the volume and surface energy coefficients. The temperature dependence of the surface symmetry energy is found to be very substantial whereas that of the volume symmetry energy turns out to be comparatively mild.

De, J N; Agrawal, B K

2012-01-01

324

The Ohio State 1991 geopotential and sea surface topography harmonic coefficient models

The computation is described of a geopotential model to deg 360, a sea surface topography model to deg 10/15, and adjusted Geosat orbits for the first year of the exact repeat mission (ERM). This study started from the GEM-T2 potential coefficient model and it's error covariance matrix and Geosat orbits (for 22 ERMs) computed by Haines et al. using the GEM-T2 model. The first step followed the general procedures which use a radial orbit error theory originally developed by English. The Geosat data was processed to find corrections to the a priori geopotential model, corrections to a radial orbit error model for 76 Geosat arcs, and coefficients of a harmonic representation of the sea surface topography. The second stage of the analysis took place by doing a combination of the GEM-T2 coefficients with 30 deg gravity data derived from surface gravity data and anomalies obtained from altimeter data. The analysis has shown how a high degree spherical harmonic model can be determined combining the best aspects of two different analysis techniques. The error analysis was described that has led to the accuracy estimates for all the coefficients to deg 360. Significant work is needed to improve the modeling effort.

Rapp, Richard H.; Wang, Yan Ming; Pavlis, Nikolaos K.

1991-01-01

325

International Nuclear Information System (INIS)

The mass energy absorption, the mass energy transfer and mass absorption coefficients have been widely used for problems and applications involving dose calculations. Direct measurements of the coefficients are difficult, and theoretical computations are usually employed. In this paper, analytical equations are presented for determining the mass energy transfer and mass absorption coefficients for gamma rays with an incident energy range between 0.4 and 10 MeV in nitrogen, silicon, carbon, copper and sodium iodide. The mass absorption and mass energy transfer coefficients for gamma rays were calculated, and the results obtained were compared with the values reported in the literature

326

Energy Technology Data Exchange (ETDEWEB)

The mass energy absorption, the mass energy transfer and mass absorption coefficients have been widely used for problems and applications involving dose calculations. Direct measurements of the coefficients are difficult, and theoretical computations are usually employed. In this paper, analytical equations are presented for determining the mass energy transfer and mass absorption coefficients for gamma rays with an incident energy range between 0.4 and 10 MeV in nitrogen, silicon, carbon, copper and sodium iodide. The mass absorption and mass energy transfer coefficients for gamma rays were calculated, and the results obtained were compared with the values reported in the literature.

Gurler, O. [Physics Department, Faculty of Arts and Sciences, Uludag University, Gorukle Campus, 16059 Bursa (Turkey)], E-mail: ogurler@uludag.edu.tr; Oz, H. [Physics Department, Faculty of Arts and Sciences, Uludag University, Gorukle Campus, 16059 Bursa (Turkey); Yalcin, S. [Education Faculty, Kastamonu University, 37200 Kastamonu (Turkey); Gundogdu, O. [Department of Physics, University of Surrey, Guildford GU2 7XH (United Kingdom); NCCPM, Medical Physics, Royal Surrey County Hospital, GU2 7XX (United Kingdom)

2009-01-15

327

Energy Technology Data Exchange (ETDEWEB)

In the present study, the effect of delta-wing vortex generators(DWVG) on the local heat transfer of the plate fin-oval tube was experimentally analyzed for Reynolds numbers for 2000, 2500 and 3200. The local heat transfer coefficient of the fin surface for four type DWVGs was measured by the naphthalene sublimation technique. As the results, the distribution of the heat transfer coefficient at rear of DWVGs showed longitudinal contours for common flow down DWVGs and wavy contours for common flow up DWVGs. The distribution showed many cell type contours at near wall and downstream for all DWVGs. Compared to case without DWVGs in present experimental tests, all DWVGs showed the best enhancement of heat transfer at Re=2000. Of 4 cases of DWVGs, D type showed the best enhancement of heat transfer.

Shin, Seok Won; Chung, In Kee; Kim, Soo Youn [Yeungnam University, Gyeongsan (Korea, Republic of)

2009-10-15

328

International Nuclear Information System (INIS)

In the present study, the effect of delta-wing vortex generators(DWVG) on the local heat transfer of the plate fin-oval tube was experimentally analyzed for Reynolds numbers for 2000, 2500 and 3200. The local heat transfer coefficient of the fin surface for four type DWVGs was measured by the naphthalene sublimation technique. As the results, the distribution of the heat transfer coefficient at rear of DWVGs showed longitudinal contours for common flow down DWVGs and wavy contours for common flow up DWVGs. The distribution showed many cell type contours at near wall and downstream for all DWVGs. Compared to case without DWVGs in present experimental tests, all DWVGs showed the best enhancement of heat transfer at Re=2000. Of 4 cases of DWVGs, D type showed the best enhancement of heat transfer

329

Transfer coefficients of 137Cs via the forage-cow-milk pathway in Aomori Prefecture of Japan

International Nuclear Information System (INIS)

The transfer of radiocesium to foodstuff of cattle is very serious, because it contributes significantly to internal exposure resulting from the intake of 137Cs through the feed-cow-milk pathway. The transfer coefficient from feed to milk (Fm) is widely used to predict the dose to man from the radioactivity released to the biosphere. A commercial fuel reprocessing plant is under construction in Rokkasho-mura/Aomori Prefecture, the northeastern district of Japan. To figure out Fm under conventional farming conditions, therefore, transfer of 137Cs deposited in the environment in cooperation with two daily farms in this region. Transfer factors for 137Cs from feed to cow's milk have been obtained from data acquired from biweekly routine monitoring program under the two dissimilar farming conditions. The one dairy farm condition is mainly composed of high hay ration and the other is high concentrate ration. As a result of the experiments, 137Cs activity of milk correlated significantly with that of feed. The mean transfer coefficients of 137Cs to milk were calculated to be 0.0037 and 0.0063 (d/l), respectively. (author)

330

Boiling heat transfer coefficients and pressure drop of R-22 and its alternatives, which are R32/R125a/ R134 (23%/25%/52%) and R32/R125a (50%/50%), flowing inside smooth and grooved tubes have been determined with the conditions similar to those in small refrigerators. The range of mass flow rates examined is between 0.0025 and 0.0125 kg/s. The data have been taken at the evaporator temperatures of -35 to -4 oC and at the condenser temperatures of 40 to 50 oC. The boiling heat transfer coeffi...

Uthen Kuntha; Tanongkiat Kiatsiriroat

2002-01-01

331

DEFF Research Database (Denmark)

Theoretical and experimental investigations to date have assumed that bridge cables can be modeled as ideal circular cylinders and the associated aerodynamic coefficients are invariant with the wind angle-of-attack. On the other hand, bridge cables are normally characterized by local alterations of their inherent surface roughness and shape, which might present a significant disturbance for the surrounding wind flow. The present study focuses on the experimental determination, based on static wind tunnel tests, of the aerodynamic coefficients of full-scale bridge cable section models both perpendicular and inclined to the flow, for varying wind angles-of-attack. The wind tunnel test results demonstrate that the aerodynamic coefficients of bridge cables can be significantly affected by the wind angle-of-attack.

Matteoni, G.; Georgakis, C.T.

2012-01-01

332

International Nuclear Information System (INIS)

The computation and analysis of the heat transfer coefficient correction factor the shell and tube type of the Kartini reactor's heat exchanger (HE) has been carried out. The computation of the correction factor was done by measuring of the actual dimension of HE. As known that the shell and tube type of the Kartini reactor's has been opera-ted for more than 15 years. Due to the scraping and rusting occur at the buffle, the total heat transfer coefficient correction factor Ft was decrease. At the later computation, it is found that it's value is 0,4669 or differ of 0,1331 compared to the prediction standard value. So far, if the rusting and scraping of the secondary water coolant to the buffle is linear to the earlier HE's operation time, it is predicted that the function of the buffle will crisis approximately in the year of 2002/2003 or 7,5 years again

333

The paper presents the FEM method for determination of boiling heat transfer coefficient in cooling liquid flow in a rectangular minichannel with asymmetric heating. Experimental research has focused on the transition from single phase forced convection to nucleate boiling, i.e. the zone of boiling incipience. The “boiling front” location has been determined from the temperature distribution of the heated wall obtained from liquid crystal thermography. The main part of the test section ha...

Maciejewska Beata; Piasecka Magdalena

2012-01-01

334

Fouling of roughened stainless steel surfaces during convective heat transfer to aqueous solutions

International Nuclear Information System (INIS)

The deterioration of heat transfer performance due to fouling is the prime cause for higher energy consumption and inefficiency in many industrial heat exchangers such as those in power plants, refineries, food and dairy industries. Fouling is also a very complex process in which many geometrical, physical and operating parameters are involved with poorly understood interaction. Among them, the surface roughness is an important surface characteristic that would greatly influence crystallisation fouling mechanisms and hence deposition morphology and stickability to the surface. In this work, the effect of the surface roughness of AISI 304 BA stainless steel surfaces on fouling of an aqueous solution with inverse solubility behaviour has been investigated under convective heat transfer. Several experiments have been performed on roughened surfaces ranging from 0.18 to 1.55 ?m for different bulk concentrations and heat fluxes. The EDTA titration method was used to measure the concentration of the calcium sulphate salt in order to maintain it at constant value during each fouling run. Experimental results show that the heat transfer coefficient of very rough surfaces (1.55 ?m) decreases more rapidly than that of 0.54 ?m. Several facts contribute to this behaviour notably (1) increased of primary heterogeneous nucleation rate on the surfaces; (2) reduction of local shear stress in the valleys and (3) reduced removal rate of the crystals from the surfaces where the roughstals from the surfaces where the roughness elements protrude out of the viscous sub-layer. The results also show linear and proportional variation of the fouling rate and heat flux within the range of operating conditions. In addition, the deposition process in terms of fouling rate could only be affected at lower surface contact angles. Such results would particularly be of interest for new surface treatment technologies which aim at altering the surface texture

335

International Nuclear Information System (INIS)

In order to predict and mitigate flow accelerated corrosion (FAC) of carbon steel piping in PWR and BWR secondary systems, computer program packages for evaluating FAC have been developed by coupling one through three dimensional (1-3D) computational flow dynamics (CFD) models and corrosion models. To evaluate corrosive conditions, e.g., oxygen concentration and electrochemical corrosion potential (ECP) along the flow path, flow pattern and temperature in each elemental volume were obtained with 1D computational flow dynamics (CFD) codes. Precise flow turbulence and mass transfer coefficients at the structure surface were calculated with 3D CFD codes to determine wall thinning rates. One of the engineering options is application of k-? calculation as a 3D CFD code, which has limitation of detail evaluation of flow distribution at very surface of large scale piping. A combination of k-? calculation and wall function was proposed to evaluate precise distribution of mass transfer coefficients with reasonable CPU volume and computing time and, at the same time, reasonable accuracy. (author)

336

An Experimental Study on the Pool Boiling Heat Transfer on a Square Surface

International Nuclear Information System (INIS)

An experimental study was carried out to identify the various regimes of natural convective boiling and to determine the Critical Heat Flux (CHF) on a square surface. The basic knowledge on the boiling heat transfer and CHF on the square surface is necessary for various engineering problems, such as the design of compact heat exchangers, cooling of CPU chips, and design of the external cooling mechanism for the reactor during the severe accidents in the nuclear power plants. The heater block made of copper with cartridge heaters in it is submerged in a water tank with windows for visualization. The heater surface has dimension of 70mm x 70mm and the maximum heat flux capacity is about 1.8MW/m2. The boiling heat transfer coefficient for the various flow regimes up to CHF has been measured for upward facing surface, vertical surface, and nearly horizontal downward facing surfaces. The temperatures of the heater block are measured by the thermocouples imbedded in the heater block. As the heat flux increases from 100kW/m2 to 1.0MW/m2, the heat-transfer regime changes from the nucleate boiling to the CHF. Near 1.0MW/m2, the heat transfer regime suddenly changed from nucleate boiling to film boiling and it resulted in a rapid heat up of the heater block. The various boiling patterns on the vertical surface, upward facing surface, and downward facing surface are observed by a high speed video camera whose frame rate is 1000fps. An eo camera whose frame rate is 1000fps. An explosive vapor generation on the heated surface, whose size and frequency are characterized by the heat flux and inclination angle, is observed

337

An experimental study on the pool boiling heat transfer on a square surface

International Nuclear Information System (INIS)

An experimental study was carried out to identify the various regimes of natural convective boiling and to determine the Critical Heat Flux (CHF) on a square surface. The basic knowledge on the boiling heat transfer and CHF on the square surface is necessary for various engineering problems, such as the design of compact heat exchangers, cooling of CPU chips, and design of the external cooling mechanism for the reactor during the severe accidents in the nuclear power plants. The heater block made of copper with cartridge heaters in it is submerged in a water tank with windows for visualization. The heater surface has dimension of 70 mm x 70 mm and the maximum heat flux capacity is about 1.8 MW/m2. The boiling heat transfer coefficient for the various flow regimes up to CHF has been measured for upward facing surface, vertical surface, and nearly horizontal downward facing surfaces. The temperatures of the heater block are measured by the thermocouples imbedded in the heater block. As the heat flux increases from 100 kW/m2 to 1.0 MW/m2, the heat-transfer regime changes from the nucleate boiling to the CHF. Near 1.0 MW/m2, the heat transfer regime suddenly changed from nucleate boiling to film boiling and it resulted in a rapid heat up of the heater block. The various boiling patterns on the vertical surface, upward facing surface, and downward facing surface are observed by a high speed video camera whose frame rate is 1000 fed video camera whose frame rate is 1000 fps. An explosive vapor generation on the heated surface, whose size and frequency is characterized by the heat flux and inclination angle, is observed

338

In certain regions of turbine aerofoils, cooling system designers need to cool the blades with convection systems that provide high heat transfer coefficients. The present research has investigated a circular cooling passage with tangential injection suitable for a blade leading edge. The heat transfer coefficients are measured using the conventional transient heat transfer, liquid crystal technique. The results are compared to the data from steady state experiments performed by Hedlund et al...

Ling, Jpcw; Ireland, Pt; Harvey, Nw

2006-01-01

339

International Nuclear Information System (INIS)

A new measurement method for measuring the mean fuel temperature as well as the fuel-to-coolant heat transfer coefficient of fast breeder reactor subassemblies (SA) is reported. The method is based on the individual heat balance of fuel SA's after fast reactor shut-downs and uses only the plants normal SA outlet temperature and neutron power signals. The method was used successfully at the french breeder prototype Super Phenix 1. The mean SA fuel temperature as well as the heat transfer coefficient of all SPX SA's have been determined at power levels between 15 and 90% of nominal power and increasing fuel burn-up from 3 to 83 EFPD (Equivalent of Full Power-Days). The measurements also provided fuel and whole SA time constants. The estimated accuracy of measured fuel parameters is in the order of 10%. Fuel temperatures and SA outlet temperature transients were also calculated with the SPX1 systems code DYN2 for exactly the same fuel and reactor operating parameters as in the experiments. Measured fuel temperatures were higher than calculated ones in all cases. The difference between measured and calculated core mean values increases from 50 K at low power to 180 K at 90% n.p. This is about the double of the experimental error margins. Measured SA heat transfer coefficients are by nearly 20% lower than corresponding heat transfer parameters used in the calculations. Discrepancies found between measured and calculated results also indicate that either the transient heat transfer in the gap between fuel and cladding (gap conductance) might not be exactly reproduced in the computer code or that the gap in the fresh fuel was larger than assumed in the calculations. (orig.)

340

Anomalous changes of Fermi surface and Hall coefficient at quantum critical point

International Nuclear Information System (INIS)

Motivated by the Hall-effect experiments in YbRh2Si2, we study the ground state and Fermi surface (FS) of a Kondo lattice model in a two-dimensional square lattice with variational Monte Carlo method. We have found the simultaneous occurrence of the antiferromagnetic transition and the FS reconstruction (topological transition) without the breakdown of the Kondo screening. This phase transition is accompanied by the jump of the Hall coefficient and considered to be consistent with the experiment

341

Sustained frictional instabilities on nanodomed surfaces: Stick-slip amplitude coefficient

DEFF Research Database (Denmark)

Understanding the frictional properties of nanostructured surfaces is important because of their increasing application in modern miniaturized devices. In this work, lateral force microscopy was used to study the frictional properties between an AFM nanotip and surfaces bearing well-defined nanodomes comprising densely packed prolate spheroids, of diameters ranging from tens to hundreds of nanometers. Our results show that the average lateral force varied linearly with applied load, as described by Amontons' first law of friction, although no direct correlation between the sample topographic properties and their measured friction coefficients was identified. Furthermore, all the nanodomed textures exhibited pronounced oscillations in the shear traces, similar to the classic stick-slip behavior, under all the shear velocities and load regimes studied. That is, the nanotextured topography led to sustained frictional instabilities, effectively with no contact frictional sliding. The amplitude of the stick-slip oscillations, ?f, was found to correlate with the topographic properties of the surfaces and scale linearly with the applied load. In line with the friction coefficient, we define the slope of this linear plot as the stick-slip amplitude coefficient (SSAC). We suggest that such stick-slip behaviors are characteristics of surfaces with nanotextures and that such local frictional instabilities have important implications to surface damage and wear. We thus propose that the shear characteristics of the nanodomed surfaces cannot be fully described by the framework of Amontons' laws of friction and that additional parameters (e.g., ?f and SSAC) are required, when their friction, lubrication, and wear properties are important considerations in related nanodevices. © 2013 American Chemical Society.

Quignon, Benoit; Pilkington, Georgia A.

2013-01-01

342

This paper focuses on the derivation of a general position-dependent diffusion coefficient to describe the two-dimensional (2D) diffusion in a narrow and smoothly asymmetric channel of varying cross section and non-straight midline embedded in a flat or on a curved surface. We consider the diffusion of non-interacting point-like Brownian particles under no external field. In order to project the 2D diffusion equation into an effective one-dimensional generalized Fick-Jacobs equation in both, flat and curved manifolds using the generalization of the mapping procedure introduced by Kalinay and Percus. The expression obtained is the more general position-dependent diffusion coefficient for 2D narrow channels that lies in a plane, which contains all the well-known previous results both symmetric and asymmetric channels as special cases. In a straightforward manner, previously defining the corresponding Fick-Jacobs equation on a curved surface, this result can be generalized to the case of a narrow 2D channel embedded on a no-flat smooth surface where the full position-dependent diffusion coefficient is modified according to the metric elements that accounts for the curvature of the surface. In addition, the equations for the mean first-passage time are obtained for asymmetrical channels on curved surfaces. As an example we shall solve this equation for the case of an asymmetric channel defined by straight walls embedded on a cylindrical surface having a reflecting wall at the origin and an absorbent one at distance ?L.

Pineda, I.; Chacón-Acosta, G.; Dagdug, L.

2014-12-01

343

Sustained frictional instabilities on nanodomed surfaces: stick-slip amplitude coefficient.

Understanding the frictional properties of nanostructured surfaces is important because of their increasing application in modern miniaturized devices. In this work, lateral force microscopy was used to study the frictional properties between an AFM nanotip and surfaces bearing well-defined nanodomes comprising densely packed prolate spheroids, of diameters ranging from tens to hundreds of nanometers. Our results show that the average lateral force varied linearly with applied load, as described by Amontons' first law of friction, although no direct correlation between the sample topographic properties and their measured friction coefficients was identified. Furthermore, all the nanodomed textures exhibited pronounced oscillations in the shear traces, similar to the classic stick-slip behavior, under all the shear velocities and load regimes studied. That is, the nanotextured topography led to sustained frictional instabilities, effectively with no contact frictional sliding. The amplitude of the stick-slip oscillations, ?f, was found to correlate with the topographic properties of the surfaces and scale linearly with the applied load. In line with the friction coefficient, we define the slope of this linear plot as the stick-slip amplitude coefficient (SSAC). We suggest that such stick-slip behaviors are characteristics of surfaces with nanotextures and that such local frictional instabilities have important implications to surface damage and wear. We thus propose that the shear characteristics of the nanodomed surfaces cannot be fully described by the framework of Amontons' laws of friction and that additional parameters (e.g., ?f and SSAC) are required, when their friction, lubrication, and wear properties are important considerations in related nanodevices. PMID:24219790

Quignon, Benoit; Pilkington, Georgia A; Thormann, Esben; Claesson, Per M; Ashfold, Michael N R; Mattia, Davide; Leese, Hannah; Davis, Sean A; Briscoe, Wuge H

2013-12-23

344

DEFF Research Database (Denmark)

Prediction of chloride ingress into concrete is an important part of durability design of reinforced concrete structures exposed to chloride containing environment. This paper presents the state-of-the art: an analytical model which describes chloride profiles in concrete as function of depth and time, and where both the surface chloride concentration and the diffusion coefficient are allowed to vary in time; the Mejlbro-Poulsen model is the general solution to Fick’s 2nd law. The paper also presents conversion formulas for the four decisive but rather abstract parameters to parameters, which makes physical sense for the design engineer, i.e. the achieved chloride diffusion coefficients at 1 year and 100 years, D1 and D100 respectively, and the corresponding achieved chloride concentrations at the exposed concrete surface, C1 and C100. Data from field exposure supports the assumption of time dependent surface chloride concentrations and the diffusion coefficients. Model parameters for Portland cement concretes with and without silica fume and fly ash in marine atmospheric and submerged South Scandinavian environment are suggested in a companion paper based on 10 years field exposure data.

Frederiksen, Jens Mejer; Geiker, Mette Rica

2008-01-01

345

Effect of surface impurities on the hydrogen recombination coefficient of first-wall materials

International Nuclear Information System (INIS)

The ''hydrogen recombination coefficient'' kR was evaluated for such metals as stainless steel, vanadium and nickel from experimental data of the permeation rate of ion- and gas-driven hydrogen isotopes. The measured values of kR were found to decrease with increasing the surface concentration of certain impurity elements; oxygen for stainless steel, sulfur for vanadium and nickel as was determined by Auger electron spectroscopy. They were also compared to theoretical models and the role of surface impurities on the hydrogen recombination process was discussed with respect to these models. (orig.)

346

Effect of surface impurities on the hydrogen recombination coefficient of first-wall materials

The "hydrogen recombination coefficient" kR was evaluated for such metals as stainless steel, vanadium and nickel from experimental data of the permeation rate of ion- and gas-driven hydrogen isotopes. The measured values of kR were found to decrease with increasing the surface concentration of certain impurity elements; oxygen for stainless steel, sulfur for vanadium and nickel as was determined by Auger electron spectroscopy. They were also compared to theoretical models and the role of surface impurities on the hydrogen recombination process was discussed with respect to these models.

Yamawaki, M.; Yamaguchi, K.; Tanaka, S.; Namba, T.; Kiyoshi, T.; Takahashi, Y.

1989-04-01

347

International Nuclear Information System (INIS)

Highlights: • Infra-red thermographic study of Taylor bubble train flow in square mini-channel. • Design of experiments for measurement of local streamwise Nusselt number. • Minimizing conjugate heat transfer effects and resulting errors in data reduction. • Benchmarking against single-phase flow and three-dimensional computations. • Local heat transfer enhancement up to two times due to Taylor bubble train flow. -- Abstract: In mini/micro confined internal flow systems, Taylor bubble train flow takes place within specific range of respective volume flow ratios, wherein the liquid slugs get separated by elongated Taylor bubbles, resulting in an intermittent flow situation. This unique flow characteristic requires understanding of transport phenomena on global, as well as on local spatio-temporal scales. In this context, an experimental design methodology and its validation are presented in this work, with an aim of measuring the local heat transfer coefficient by employing high-resolution InfraRed Thermography. The effect of conjugate heat transfer on the true estimate of local transport coefficients, and subsequent data reduction technique, is discerned. Local heat transfer coefficient for (i) hydrodynamically fully developed and thermally developing single-phase flow in three-side heated channel and, (ii) non-boiling, air–water Taylor bubble train flow is measured and compared in a mini-channel of square cross-section (5 mm × 5 mm; Dh = 5 mm, Bo ? 3.4) machined on a stainless steel substrate (300 mm × 25 mm × 11 mm). The design of the setup ensures near uniform heat flux condition at the solid–fluid interface; the conjugate effects arising from the axial back conduction in the substrate are thus minimized. For benchmarking, the data from single-phase flow is also compared with three-dimensional computational simulations. Depending on the employed volume flow ratio, it is concluded that enhancement of nearly 1.2–2.0 times in time-averaged local streamwise Nusselt number can be obtained by Taylor bubble train flow, as compared to fully developed single-phase flow. This enhancement is attributed to the intermittent intrusion of Taylor bubbles in the liquid flow which drastically changes the local fluid temperature profiles. It is important to maintain proper boundary conditions during the experiment while estimating local heat transfer coefficient, especially in mini-micro systems

348

Heat transfer characteristics of a back-corrugated absorber surface for solar air collectors

The present study experimentally examines a back-corrugated absorber-convector comprised of a rectangularly corrugated plate attached to the back side of a flat absorber plate with a high temperature, high strength adhesive. The upper surface is subjected to a heat flux from a blanket-type electric heater simulating solar irradiation. The corrugated plate configuration creates two parallel airflow channel types. The two channels have different geometries and, therefore, may have different heat transfer characteristics. An apparatus was designed to determine the local convective heat transfer coefficients along each of the channels. The results show that the back-corrugated absorber-convector has much better thermal performance than the simple flat-plate absorber-convector, mainly because of the increased connective heat transfer area.

Shockey, K. A.; Pearson, J. T.; Dewitt, D. P.

1981-11-01

349

Surface diffusion coefficient of Au atoms on single layer graphene grown on Cu

Energy Technology Data Exchange (ETDEWEB)

A 5?nm thick Au film was deposited on single layer graphene sheets grown on Cu. By thermal processes, the dewetting phenomenon of the Au film on the graphene was induced so to form Au nanoparticles. The mean radius, surface-to-surface distance, and surface density evolution of the nanoparticles on the graphene sheets as a function of the annealing temperature were quantified by scanning electron microscopy analyses. These quantitative data were analyzed within the classical mean-field nucleation theory so to obtain the temperature-dependent Au atoms surface diffusion coefficient on graphene: D{sub S}(T)=[(8.2±0.6)×10{sup ?8}]exp[?(0.31±0.02(eV)/(at) )/kT]?cm{sup 2}/s.

Ruffino, F., E-mail: francesco.ruffino@ct.infn.it; Cacciato, G.; Grimaldi, M. G. [Dipartimento di Fisica ed Astronomia-Universitá di Catania, via S. Sofia 64, 95123 Catania, Italy and MATIS IMM-CNR, via S. Sofia 64, 95123 Catania (Italy)

2014-02-28

350

Energy Technology Data Exchange (ETDEWEB)

Transient boiling heat transfer data are reported for two different heater surface geometries submerged in liquid nitrogen. During the early part of the transient heat pulse, the heat transfer coefficient for both geometries generally agrees with values predicted from classical transient pure conduction equations. This agreement persists until the onset of convection.

Giarratano, P.J.

1984-08-01

351

The maximum coefficient of friction that can be supported at the shoe and floor interface without a slip is usually called the available coefficient of friction (ACOF) for human locomotion. The probability of a slip could be estimated using a statistical model by comparing the ACOF with the required coefficient of friction (RCOF), assuming that both coefficients have stochastic distributions. An investigation of the stochastic distributions of the ACOF of five different floor surfaces under dry, water and glycerol conditions is presented in this paper. One hundred friction measurements were performed on each floor surface under each surface condition. The Kolmogorov-Smirnov goodness-of-fit test was used to determine if the distribution of the ACOF was a good fit with the normal, log-normal and Weibull distributions. The results indicated that the ACOF distributions had a slightly better match with the normal and log-normal distributions than with the Weibull in only three out of 15 cases with a statistical significance. The results are far more complex than what had heretofore been published and different scenarios could emerge. Since the ACOF is compared with the RCOF for the estimate of slip probability, the distribution of the ACOF in seven cases could be considered a constant for this purpose when the ACOF is much lower or higher than the RCOF. A few cases could be represented by a normal distribution for practical reasons based on their skewness and kurtosis values without a statistical significance. No representation could be found in three cases out of 15. PMID:24268803

Chang, Wen-Ruey; Matz, Simon; Chang, Chien-Chi

2014-05-01

352

International Nuclear Information System (INIS)

The paper presents a new heat transfer correlation of water at supercritical pressure after review on existing heat transfer correlations. The new correlation is optimized by genetic algorithms based on existing test data. Based on current results, we conclude that genetic algorithms are effective to search a global optimized correlation but it is important to carefully select representative and authentic test data to reach an optimized solution and special attention needs to be paid on the deteriorated heat transfer region in the design of supercritical water reactor because it can not be predicted well by any correlations reviewed. (orig.)

353

The paper presents a new heat transfer correlation of water at supercritical pressure after review on existing heat transfer correlations. The new correlation is optimized by genetic algorithms based on existing test data. Based on current results, we conclude that genetic algorithms are effective to search a global optimized correlation but it is important to carefully select representative and authentic test data to reach an optimized solution and special attention needs to be paid on the deteriorated heat transfer region in the design of supercritical water reactor because it can not be predicted well by any correlations reviewed.

Yu, Jiyang; Jia, Baoshan; Wu, Dan; Wang, Daling

2009-04-01

354

Directory of Open Access Journals (Sweden)

Full Text Available The morphological features of the surface in both micro and macro levels are important factors governing the tribological behavior of the contacting surfaces. Surface hardness is also an important factor which governs the friction and wear behaviors of the contacting surfaces. Surface morphology of a tool is an important factor as it primarily controls the tribological behavior at the interface which in turn controls the surface finish of products. In the present investigation a pin-on-plate sliding tester was used to identify the effect of surface morphology and hardness on co-efficient of friction and transfer layer which characterizes the tribological behavior. The morphology of mild steel (EN8 plate surfaces were modified by employing three different surface modification methods like grinding (silicon carbide wheel polishing, shot blasting and electric discharge machining methods. Surface roughness parameters which characterize the morphology of the steel plates were measured using a three dimensional optical profilometer. Role of hardness is studied by employing lead, copper and Aluminum (Al6082 pins which were slid against steel plates. Experiments were conducted for plate inclination angles of 1, 1.5,2 and 2.5 degrees. Normal load was varied from 1 to 150N during the tests. Experiments were conducted under dry condition in ambient environment. Scanning electron microscope was used to study the formation of transfer layer on plate and pin surfaces. It was observed that the co-efficient of friction and transfer layer formation were found to depend on the surface morphology of the harder surface. The quantum of transfer layer formation on the surfaces is found to increase with increase in surface roughness

Mr.M Basavaraju

2013-09-01

355

International Nuclear Information System (INIS)

This document presents tables of diet-to-milk transfer coefficients for radioactive and stable isotopes in the cow. The values are based on an extensive literature review of the secretion of radioisotopes in milk and the concentrations of radioactive or stable isotopes in milk and feed. Transfer coefficients were compiled and tabulated for isotopes of more than 70 elements. The values are summarized in a table of elemental transfer coefficients and also organized into separate tables that reveal their elemental systematics and the effects of physical and chemical form

356

Serrating Nozzle Surfaces for Complete Transfer of Droplets

A method of ensuring the complete transfer of liquid droplets from nozzles in microfluidic devices to nearby surfaces involves relatively simple geometric modification of the nozzle surfaces. The method is especially applicable to nozzles in print heads and similar devices required to dispense liquid droplets having precise volumes. Examples of such devices include heads for soft printing of ink on paper and heads for depositing droplets of deoxyribonucleic acid (DNA) or protein solutions on glass plates to form microarrays of spots for analysis. The main purpose served by the present method is to ensure that droplets transferred from a nozzle have consistent volume, as needed to ensure accuracy in microarray analysis or consistent appearance of printed text and images. In soft printing, droplets having consistent volume are generated inside a print head, but in the absence of the present method, the consistency is lost in printing because after each printing action (in which a drop is ejected from a nozzle), a small residual volume of liquid remains attached to the nozzle. By providing for complete transfer of droplets (and thus eliminating residual liquid attached to the nozzle) the method ensures consistency of volume of transferred droplets. An additional benefit of elimination of residue is prevention of cross-contamination among different liquids printed through the same nozzle a major consideration in DNA microarray analysis. The method also accelerates the printing process by minimizing the need to clean a printing head to prevent cross-contamination. Soft printing involves a hydrophobic nozzle surface and a hydrophilic print surface. When the two surfaces are brought into proximity such that a droplet in the nozzle makes contact with the print surface, a substantial portion of the droplet becomes transferred to the print surface. Then as the nozzle and the print surface are pulled apart, the droplet is pulled apart and most of the droplet remains on the print surface. The basic principle of the present method is to reduce the liquid-solid surface energy of the nozzle to a level sufficiently below the intrinsic solid-liquid surface energy of the nozzle material so that the droplet is not pulled apart and, instead, the entire droplet volume becomes transferred to the print surface. In this method, the liquid-solid surface energy is reduced by introducing artificial surface roughness in the form of micromachined serrations on the inner nozzle surface (see figure). The method was tested in experiments on soft printing of DNA solutions and of deionized water through 0.5-mm-diameter nozzles, of which some were not serrated, some were partially serrated, and some were fully serrated. In the nozzles without serrations, transfer was incomplete; that is, residual liquids remained in the nozzles after printing. However, in every nozzle in which at least half the inner surface was serrated, complete transfer of droplets to the print surface was achieved.

Kim, Chang-Jin " CJ" Yi, Uichong

2010-01-01

357

Reactions involving electron transfer at semiconductor surfaces

International Nuclear Information System (INIS)

Comparisons are made between the changes in isotopic composition of isotopically pre-equilibrated (i.p.eq.) and isotopically non-equilibrated (i.n.eq.) gaseous oxygen in contact with prereduced or preoxidised samples of ZnO and TiO2 at room temperature. In the absence of illumination a place exchange (p.x.) process predominated in the oxygen isotope exchange (o.i.e.) detectable at low pressures, ca. 8 x 10-3 Torr, of i.p.eq. O2 upon contact with preoxidised samples, whereas a homophase, R0-type o.i.e. process predominated for i.n.eq. (16O2 + 18O2) contacted with prereduced samples at pressures of ca. 10-1 Torr. The latter R0 activity was removed by preoxidation but light restored it with quantum efficiency > 6 for pure ZnO and > 30 for lithium-doped ZnO. A mechanism is described to account for the correspondingly high turnover achieved on each site photoactivated by light. For i.p.eq. O2 exposed to intense illumination in contact with prereduced or preoxidised ZnO, a heterophase R1-type process, accompanied by a faster R0-type process, predominated and reasons for this are considered. Residual hydroxyls affect the ratio of o.i.e. processes on TiO2 surfaces. (author)

358

Directory of Open Access Journals (Sweden)

Full Text Available Boiling heat transfer coefficients and pressure drop of R-22 and its alternatives, which are R32/R125a/ R134 (23%/25%/52% and R32/R125a (50%/50%, flowing inside smooth and grooved tubes have been determined with the conditions similar to those in small refrigerators. The range of mass flow rates examined is between 0.0025 and 0.0125 kg/s. The data have been taken at the evaporator temperatures of -35 to -4 oC and at the condenser temperatures of 40 to 50 oC. The boiling heat transfer coefficients of the refrigerants in the grooved tubes are higher than those in the smooth tubes and R-22 shows the best performance for both tubes. The heat transfer correlations have also been developed. In case of the pressure drop, the twophase friction multiplier ?G 2 increases with Martinelli parameter and there is no effect of the tube roughness and the types of the refrigerants.

Uthen Kuntha

2002-04-01

359

Directory of Open Access Journals (Sweden)

Full Text Available In this research, an experimental study was conducted to high light the impact of the exterior shape of a cylindrical body on the forced and free convection heat transfer coefficients when the body is hold in the entrance of an air duct. The impact of changing the body location within the air duct and the air speed are also demonstrated. The cylinders were manufactured with circular, triangular and square sections of copper for its high thermal conductivity with appropriate dimensions, while maintaining the surface area of all shapes to be the same. Each cylinder was heated to a certain temperature and put inside the duct at certain locations. The temperature of the cylinder was then monitored. The heat transfer coefficient were then calculated for forced convection for several Reynolds number (4555-18222.The study covered free convection impact for values of Rayleigh number ranging between (1069-3321. Imperical relationships were obtained for all cases of forced and free convection and compared with equations of circular cylindrical shapes found in literature. These imperical equations were found to be in good comparison with that of other sources.

Sundus Hussein Abd

2012-01-01

360

In this paper, we study the influence of Platinum (100) surface morphology on the Tangential Momentum Accommodation Coefficient (TMAC) with Argon usingMolecular Dynamics method (MD). The coefficient is computed directly by beaming Ar atoms into the surfaces and measuring the relative momentum changes. The wall is maintained at a constant temper-ature and its interaction with the gas atoms is governed by the Kulginov potential [1]. To capture correctly the surface effect of the walls and atoms...

Tung Pham, T.; To, Q. D.; Lauriat, G.; Le?onard, C.; Vo, V. H.

2012-01-01

361

International Nuclear Information System (INIS)

Physical sputtering yields from the carbon surface irradiated by the boundary plasma are obtained with the use of a Monte Carlo simulation code ACAT. The yields are calculated for many random initial energy and angle values of incident protons or deuterons with a Maxwellian velocity distribution, and then averaged. Here the temperature of the boundary plasma, the sheath potential and the angle ? between the magnetic field line and the surface normal are taken into account. A new fitting formula for an arrangement of the numerical data of sputtering yield is introduced, in which six fitting parameters are determined from the numerical results and listed. These results provide a way to estimate the erosion of carbon materials irradiated by boundary plasma. The particle reflection coefficients for deuterons and their neutrals from a carbon surface are also calculated by the same code and presented together with, for comparison, that for the case of monoenergetic normal incidence. (author)

362

Directory of Open Access Journals (Sweden)

Full Text Available Hot and cold forming of metals is carried out in industry for manufacturing engineering components. Such manufacturing processes employ dies, whose surface condition is one of the factors which characterize the surface finish of engineering components. The surface finish of engineering components is largely influenced by the tribological phenomenon at die and components interface. Lubrication, morphology and hardness of die surface are found to control surface finish of the products. In the present investigation a pin-on-plate sliding tester was used to identify the effect of surface morphology, lubrication and hardness on co-efficient of friction and transfer layer which characterizes the tribological behaviour. The morphology of mild steel (EN8 plate surfaces were modified by employing three different surface modification methods like grinding (silicon carbide wheel polishing, shot blasting and electric discharge machining methods. Surface roughness parameters which characterize the morphology of the steel plates were measured using a three dimensional optical profilometer. Role of hardness is studied by employing lead, copper and Aluminum (Al6082 pins which were slid against steel plates. Experiments were conducted for plate inclination angles of 1, 1.5,2 and 2.5 degrees. Normal load was varied from 1 to 150N during the tests. Experiments were conducted under lubricated condition in ambient environment. Scanning electron microscope was used to study the formation of transfer layer on plate and pin surfaces. It was observed that the co-efficient of friction and transfer layer formation were found to depend on the surface morphology of the harder surface under lubricated condition. The quantum of transfer layer formation on the surfaces is found to increase with increase in surface roughness.

Dr.S Ranganatha

2013-09-01

363

The charge transfer rate coefficient for the reaction N(2+)(2p(sup 2)P(sup 0)) + He yields products is measured by recording the time dependence of the N(2+) ions stored in an ion trap. A cylindrical radio-frequency ion trap was used to store N(2+) ions produced by laser ablation of a solid titanium nitride target. The decay of the ion signals was analyzed by single exponential least-squares fits to the data. The measured rate coefficient is 8.67(0.76) x 10(exp -11)sq cm/s. The N(2+) ions were at a mean energy of 2.7 eV while He gas was at room temperature, corresponding to an equivalent temperature of 3.9 x 10(exp 3) K. The measured value is in good agreement with a recent calculation.

Fang, Z.; Kwong, Victor H. S.

1997-01-01

364

Experimental &Theoretical Analysis Of Heat Transfer Augmentation From Dimpled Surface

Directory of Open Access Journals (Sweden)

Full Text Available In the present work the heat transfer characteristics and the pressure drop of the forced convection apparatus of six dimpled plates is studied. Six test plates with varying dimple densities; by varying the input voltage Nusselt No. variation was recorded. It is found that Nusselt No. increases as the dimple density increases .Also it was found that percentage increase in Nusselt No. is greater for staggered dimple arrangement. The sample experimental results obtained are presented in graphical forms as shown in Figure shows the calculated results based on the observations to show the comparative Nusselt numbers enhancements with that obtained with different parameters combinations. Dimpled typical technique that offers a higher heat transfer increase at the cost of mild pressure drop penalty. This study investigates the heat transfer characteristics of Plate with dimpled surface. Over the past couple of years the focus on using concavities or dimples provides enhanced heat transfer has been documented by a number of researchers.

Dhananjay R.Giram

2013-09-01

365

Radiation induced surface activation on heat transfer enhancement

International Nuclear Information System (INIS)

Improving the limit of boiling heat transfer or critical heat flux requires that the cooling liquid can contact the heating surface, or a high-wettability, highly hydrophilic heating surface, even if a vapor bubble layer is generated on the surface. From this basis, we investigated surface wettability and heat transfer phenomena using metal oxides irradiated by ?-rays. First, contact angle, an indicator of macroscopic wettability, of a water droplet on metal oxide at room temperature was measured by image processing of the images obtained by a CCD video camera. The results showed that the surface wettability on metal oxide pieces of titanium, zircaloy No. 4 SUS-304, and copper was improved significantly by the Radiation Induced Surface Activation (RISA) phenomenon. Highly hydrophilic conditions of the test pieces were achieved after 500-kGy irradiation by 60Co ?-rays. After the end of irradiation, the contact angle decreased. Second, to delineate the effect of Radiation Induced Surface Activation (RISA) on heat transferring phenomena, the Leidenfrost condition and quenching of metal oxides irradiated by ?-rays were investigated in this study. In the Leidenfrost experiment, when the temperature of the heating surface reached the wetting limit temperature, water-solid contact vanished because a stable vapor film existed between the droplet and the metal surface; i.e., a Leidenfrost condition obtained. The wetting limit temperature increased with integratedt temperature increased with integrated irradiation dose. After irradiation, the wet length and the duration of contact increased, and the contact angle decreased. In the quenching test, high surface wettability, or a highly hydrophilic condition, of a simulated fuel rod made of SUS was achieved, and the quenching velocities were increased up to 20 30% after 300 kGy 60Co ?-ray irradiation. (author)

366

Directory of Open Access Journals (Sweden)

Full Text Available This study investigates the frequency bifurcation phenomena of a typical voltage-fed resonant converter based on mutual induction model. It is found that the Zero Current Switching (ZCS operating frequency has the bifurcation region as the coupling coefficient varies due to the distance. The expression for the bifurcation boundary is derived and analyzed. Such results are very useful for guiding the design of practical Inductively Coupled Power Transfer (ICPT systems especially in applications which have the requirement of the position flexibility. Analytical results are verified both via MATLAB simulations and experimental prototype.

Zhihui Wang

2013-01-01

367

Study of Pool Boiling Heat Transfer on Various Surfaces with Variation of Flow Velocity

International Nuclear Information System (INIS)

In this study, a smooth flat surface, low fin, Turbo-B, and Thermo excel-E surfaces are used to examine the effect of the flow velocity on the pool boiling heat transfer coefficients (HTSC) and critical heat fluxes (Chefs). HTSC and Chefs are measured on a smooth square heater of 9.53 ? 9.53 m2 at 60 .deg. C in a pool of pure water at various fluid velocities of 0, 0.1, 0.15, and 0.2 m/s. Test results show that for all surfaces, Chefs obtained with flow are higher than those obtained without flow. Chefs of the low fin surface are higher than those of the Turbo-B and Thermo excel-E surfaces due largely to the increase in surface area and sufficient fin spaces for the easy removal of bubbles. Chefs of the low fin surface show even 5 times higher Chefs as compared to the plain surface. On the other hand, both Turbo-B and Thermo excel-E surfaces do not show satisfactory results because their pore sizes are too small and water bubbles easily cover them. At low heat fluxes of less than 50 k W/m2, HTSC increase as the flow velocity increases for all surfaces. In conclusion, a low fin geometry is good for application to steam generators in nuclear power plants

368

Pattern recognition of surface electromyography signal based on wavelet coefficient entropy

Directory of Open Access Journals (Sweden)

Full Text Available This paper introduced a novel, simple and ef-fective method to extract the general feature of two surface EMG (electromyography signal patterns: forearm supination (FS surface EMG signal and forearm pronation (FP surface EMG signal. After surface EMG (SEMG signal was decomposed to the fourth resolution level with wavelet packet transform (WPT, its whole scaling space (with frequencies in the interval (0Hz, 500Hz] was divided into16 frequency bands (FB. Then wavelet coefficient entropy (WCE of every FB was calculated and corre-spondingly marked with WCE(n (from the nth FB, n=1,2,…16. Lastly, some WCE(n were chosen to form WCE feature vector, which was used to distinguish FS surface EMG signals from FP surface EMG signals. The result showed that the WCE feather vector consisted of WCE(7 (187.25Hz, 218.75Hz and WCE(8 (218.75Hz, 250Hz can more effectively recog-nize FS and FP patterns than other WCE feature vector or the WPT feature vector which was gained by the combination of WPT and principal components analysis.

Ying Gao

2009-09-01

369

Nucleate pool-boiling heat transfer - I. Review of parametric effects of boiling surface

International Nuclear Information System (INIS)

The objective of this paper is to assess the state-of-the-art of heat transfer in nucleate pool-boiling. Therefore, the paper consists of two parts: part I reviews and examines the effects of major boiling surface parameters affecting nucleate-boiling heat transfer, and part II reviews and examines the existing prediction methods to calculate the nucleate pool-boiling heat transfer coefficient (HTC). A literature review of the parametric trends points out that the major parameters affecting the HTC under nucleate pool-boiling conditions are heat flux, saturation pressure, and thermophysical properties of a working fluid. Therefore, these effects on the HTC under nucleate pool-boiling conditions have been the most investigated and are quite well established. On the other hand, the effects of surface characteristics such as thermophysical properties of the material, dimensions, thickness, surface finish, microstructure, etc., still cannot be quantified, and further investigations are needed. Particular attention has to be paid to the characteristics of boiling surfaces. (author)

370

Volumetric mass transfer coefficients characterising VOC absorption in water/silicone oil mixtures

The physical absorption of three Volatile Organic Compounds (dimethyldisulphide (DMDS), dimethylsulphide (DMS) and toluene) in "water/silicone oil" systems at a constant flow rate for mixtures of different compositions (f = 0, 5, 10, 15, 20 and 100%) was investigated using a dynamic absorption method. The results indicate that silicone oil addition leads to a dramatic decrease in KLa which can be related to the change in the partition coefficient (Hmix). They confirm the results obtained for ...

Dumont, Eric; Darracq, Guillaume; Couvert, Annabelle; Couriol, Catherine; Amrane, Abdeltif; Thomas, Diane; Andres, Yves; Le Cloirec, Pierre

2013-01-01

371

Directory of Open Access Journals (Sweden)

Full Text Available The aim of this study is to characterize thermal insulating local material, kapok, from a study in 3 dimensions in Cartesian coordinate and in dynamic frequency regime. From a study a 3 dimensional the heat transfer through a material made of wool kapok (thermal conductivity: &lambda = 0,035 W/m/K; density: &rho = 12, 35 kg/m3; thermal diffusivity: &alpha = 17, 1.10-7 m2 /s is presented. The evolution curves of temperature versus convective heat transfer coefficient have helped highlight the importance of pulse excitation and the depth in the material. The thermal impedance is studied from representations of Nyquist and Bode diagrams allowing characterizing the thermal behavior from thermistors. The evolution of the thermal impedance with the thermal capacity of the material is presented.

M. Dieng

2013-02-01

372

Directory of Open Access Journals (Sweden)

Full Text Available An experimental study has been conducted to examine the effects of macroscale, microscale, and nanoscale surface modifications in water pool boiling heat transfer and to determine the different heat transfer enhancing mechanisms at different scales. Nanostructured surfaces are created by acid etching, while microscale and macroscale structured surfaces are synthesized through a sintering process. Six structures are studied as individual and collectively integrated surfaces from nanoscale through microscale to macroscale: polished plain, flat nanostructured, flat porous, modulated porous, nanostructured flat porous, and nanostructured modulated porous. Boiling performance is measured in terms of critical heat flux (CHF and heat transfer coefficient (HTC. Both HTC and CHF have been greatly improved on all modified surfaces compared to the polished baseline. Hierarchical multiscale surfaces of integrated nanoscale, microscale, and macroscale structures have been proven to have the most significant improvements on HTC and CHF. The CHF and HTC of the hierarchical multiscale modulated porous surface have achieved the most significant improvements of 350% and 200% over the polished plain surface, respectively. Experimental results are compared to the predictions of a variety of theoretical models with an attempt to reveal the different heat transfer enhancing mechanisms at different scales. It is concluded that models for the structured surfaces at all scales need to be further developed to be able to have good quantitative predictions of CHFs on structured surfaces.

Russell P. Rioux

2014-11-01

373

Mass transfer in bioreactors has been examined. In the present work, dynamic methods are used for the determination of KLa values for water, model media and a fermentation broth (Candida utilis) in an airlift reactor. The conventional dynamic method is applied at the end of the microbial process in order to avoid an alteration in the metabolism of the microorganisms. New dynamic methods are used to determine KLa in an airlift reactor during the microbial growth of Candida utilis on glucose. One of the methods is based on the continuous measurement of carbon dioxide production while the other method is based on the relationship between the oxygen transfer and biomass growth rates. These methods of determining KLa does not interfere with the microorganisms action. A theoretical mass transfer model has been used for KLa estimation for the systems described above. Some differences between calculated and measured values are found for fermentation processes due to the model is developed for two-phase air-water systems. Nevertheless, the average deviation between the predicted values and those obtained from the relationship between oxygen transfer and biomass production rates are lower than 25% in any case.

Tobajas, M.; García-Calvo, E.

374

Surface transfer doping of diamond with a molecular heterojunction

Surface conductivity and C1s core level measurements were employed to show that surface transfer doping of hydrogen-terminated diamond C(100) can be achieved with a molecular heterojunction formed with C60F48 and an intralayer of zinc-tetraphenylporphyrin. Measurement of the shift in the diamond Fermi energy shows that the zinc-tetraphenylporphyrin (ZnTPP) layer modifies the C60F48-diamond interaction, modulating the extent of charge transfer between the diamond and the fluorofullerene. In contrast to the case of C60F48 acceptors, the presence of a ZnTPP layer prevents the formation of air-induced surface conductivity, showing that the intralayer acts to selectively separate these two doping channels.

Langley, D. P.; Smets, Y.; Stark, C. B.; Edmonds, M. T.; Tadich, A.; Rietwyk, K. J.; Schenk, A.; Wanke, M.; Wu, Q.-H.; Barnard, P. J.; Ley, L.; Pakes, C. I.

2012-01-01

375

EPMA-EDS surface measurements of interdiffusion coefficients between miscible metals in thin films

Energy Technology Data Exchange (ETDEWEB)

A new technique is developed to study interdiffusion between two miscible metals. The technique is applied to the Ni-Pd system. It consists in measuring the change of apparent surface composition of a Pd substrate coated with an 800 nm Ni thin film during annealing at a given temperature. The measurement is carried out in-situ inside the chamber of a SEM (scanning electron microscope) by EPMA-EDS (electron probe microanalysis-energy dispersive X-ray spectroscopy). The experimental data are processed using a model that mixes the Fick's diffusion equations and the electron probe microanalysis equation. This process allows the determination of the mean interdiffusion coefficient at a given annealing temperature. The main advantages of the technique are the possible determination of interdiffusion coefficients in thin films and at very low temperature (down to 430 deg. C, i.e. {approx}0.4 T{sub m}), which is not achievable with other techniques conventionally used for the study of interdiffusion. The Ni-Pd mean interdiffusion coefficient is shown to follow an Arrhenius law (D-tilde{sub c}=6.32x10{sup -3} exp((178.8kJmol{sup -1})/(RT) )cm{sup 2}s{sup -1}) between 430 deg. C and 900 deg. C, in relatively good agreement with previous interdiffusion measurements made on the Ni-Pd system at higher temperature.

Christien, F., E-mail: frederic.christien@univ-nantes.fr [Laboratoire Genie des Materiaux et Procedes Associes, Universite de Nantes, Polytech' Nantes, Rue Christian Pauc, BP 50609, F-44306 Nantes Cedex 3 (France); Pierson, J.F. [Laboratoire de Science et Genie des Surfaces (UMR CNRS 7570), Ecole des Mines, Parc de Saurupt F-54042 NANCY Cedex France (France); Hassini, A. [Laboratoire Genie des Materiaux et Procedes Associes, Universite de Nantes, Polytech' Nantes, Rue Christian Pauc, BP 50609, F-44306 Nantes Cedex 3 (France); Capon, F. [Laboratoire de Science et Genie des Surfaces (UMR CNRS 7570), Ecole des Mines, Parc de Saurupt F-54042 NANCY Cedex France (France); Le Gall, R.; Brousse, T. [Laboratoire Genie des Materiaux et Procedes Associes, Universite de Nantes, Polytech' Nantes, Rue Christian Pauc, BP 50609, F-44306 Nantes Cedex 3 (France)

2010-01-01

376

EPMA-EDS surface measurements of interdiffusion coefficients between miscible metals in thin films

International Nuclear Information System (INIS)

A new technique is developed to study interdiffusion between two miscible metals. The technique is applied to the Ni-Pd system. It consists in measuring the change of apparent surface composition of a Pd substrate coated with an 800 nm Ni thin film during annealing at a given temperature. The measurement is carried out in-situ inside the chamber of a SEM (scanning electron microscope) by EPMA-EDS (electron probe microanalysis-energy dispersive X-ray spectroscopy). The experimental data are processed using a model that mixes the Fick's diffusion equations and the electron probe microanalysis equation. This process allows the determination of the mean interdiffusion coefficient at a given annealing temperature. The main advantages of the technique are the possible determination of interdiffusion coefficients in thin films and at very low temperature (down to 430 deg. C, i.e. ?0.4 Tm), which is not achievable with other techniques conventionally used for the study of interdiffusion. The Ni-Pd mean interdiffusion coefficient is shown to follow an Arrhenius law (D-tildec=6.32x10-3 exp((178.8kJmol-1)/(RT) )cm2s-1) between 430 deg. C and 900 deg. C, in relatively good agreement with previous interdiffusion measurements made on the Ni-Pd system at higher temperature.

377

Scientific Electronic Library Online (English)

Full Text Available SciELO Cuba | Language: Spanish Abstract in spanish La pérdida de eficiencia del proceso de enfriamiento del licor amoniacal, mediante el uso de intercambiadores de calor de placas, está asociada a imprecisiones en la estimación de los coeficientes de transferencia de calor y la acumulación de incrustaciones en la superficie de intercambio. El objeti [...] vo de la investigación es determinar los coeficientes de transferencia de calor y la influencia de las incrustaciones en la pérdida de eficiencia de la instalación. Mediante un procedimiento iterativo se estableció la ecuación del número de Nusselt y su relación con el número de Reynolds y Prandtl. Se utilizó un diseño experimental multifactorial. Los resultados predicen el conocimiento de los coeficientes para el cálculo del número de Nusselt en ambos fluidos. Los valores de los coeficientes del licor amoniacal son inferiores, ello se debe a la presencia de componentes gaseosos. La ecuación obtenida muestra correspondencia con el modelo de Buonapane, el error comparativo es del 3,55 %. Abstract in english The loss of efficiency of the ammonia liquor cooling process, by means of the plate heat exchanger, is associated to the incorrect estimate of the heat transfer coefficients and the accumulation of inlays in the exchange surface. The objective of the investigation is to determine the transfer coeffi [...] cients and the influence of the inlays in the efficiency loss of the installation. By means of an iterative procedure was obtained the Nusselt number equation and the relationship with the Reynolds and Prandtl number, for it was used it a design experimental multifactorial. The results predict the knowledge of the coefficients for the calculation of the Nusselt number for both fluids. The ammonia liquor coefficients values are inferior, due to the presence of gassy components. The obtained equation shows correspondence with the Buonapane pattern, the comparative error is 3,55 %.

Enrique, Torres-Tamayo; Yoalbys, Retirado-Medianeja; Ever, Góngora-Leyva.

2014-04-01

378

International Nuclear Information System (INIS)

Nature of physical problem solved: AUTOJOM is a computer program that will generate the coefficients of any quadratic equation used to define conic volumes and also the coefficients of the planes needed to define parallelepipeds, wedges, and pyramids. JOMREAD is a computer code to check any 3D geometry composed of and constructed with quadratic surfaces

379

A Survey of Ballistic Transfers to the Lunar Surface

In this study techniques are developed which allow an analysis of a range of different types of transfer trajectories from the Earth to the lunar surface. Trajectories ranging from those obtained using the invariant manifolds of unstable orbits to those derived from collision orbits are analyzed. These techniques allow the computation of trajectories encompassing low-energy trajectories as well as more direct transfers. The range of possible trajectory options is summarized, and a broad range of trajectories that exist as a result of the Sun's influence are computed and analyzed. The results are then classified by type, and trades between different measures of cost are discussed.

Anderson, Rodney L.; Parker, Jeffrey S.

2011-01-01

380

Heat transfer and pressure drop characteristics in the annulus of concentric helical coils heat exchangers were experimentally investigated. The effects of coil curvature ratio, flow configuration, number of turns and addition of surfactant were investigated. Five test coils were designed and manufactured to study the effect of different parameters on heat transfer and pressure drop. The liquids used in the present study were water and oleyl-dihydroxy-etheyl-amine-oxide (ODEAO, C22H45NO3 = 371) non-ionic aqua surfactant solution flowing through the annulus side. The inner side Reynolds number range 11,000-27,000 and the annulus side range 5,000-19,000. The results showed that the annulus Nusselt number decreases as annulus curvature ratio increases and increases when number of turns decrease. Moreover, the friction factor increases with the curvature ratio and also increases as number of turns decreases. Both Nusselt number and friction factor decrease when ODEAO concentration increases.

Gomaa, Abdalla; Aly, Wael I. A.; Omara, M.; Abdelmagied, Mahmoud

2014-04-01

381

International Nuclear Information System (INIS)

The diet-milk transfer coefficient, Fm (Bq L-1 output in milk divided by Bq d-1 intake to the animal) was studied for eight radionuclides that previously had been given little attention. The Fm values for cows and goats, respectively, were: 2.3 x 10(-5) and 1.5 x 10(-4) for /sup 99m/Tc, 1.4 x 10(-4) and 8.5 x 10(-4) for /sup 95m/Tc, 1.1 x 10(-2) for 99Tc (goats only); 1.7 x 10(-3) and 9 x 10(-3) for 99Mo; 4.8 x 10(-4) and 4.4 x 10(-3) for /sup 123m/Te; 4.8 x 10(-4) and 4.6 x 10(-3) for 133Ba; 5.5 x 10(-7) and 5.5 x 10(-6) for 95Zr; and 4.1 x 10(-7) and 6.4 x 10(-6) for 95Nb. The goat/cow transfer coefficient ratios for milk were approximately 10, but the goat/cow ratios for meat varied by three orders of magnitude

382

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english This work shows the experimental study of a continuous gas-solid fluidized bed with an immersed tube where cold water is heated by fluidized solid particles presenting inlet temperature from 450 to 700°C. Experiments were carried out in order to verify the influence of solid particle flow rate and d [...] istance between baffles immersed in a shallow fluidized bed. The solid material was 254µm diameter silica sand particles, fluidized by air in a 0.90m long and 0.15m wide heat exchanger. The measurements were taken at steady state conditions for solid mass flow rate from 10 to 100 kg/h, in a heat exchanger with the presence of 5 or 8 baffles. Bed temperature measurements along the length of the heat exchanger were experimentally obtained and heat balances for differential control volumes of the heat exchanger were made in order to obtain the axial profile of the bed-to-tube heat transfer coefficient. The results showed that heat transfer coefficient increases with the solid particle mass flow rate and with the presence of baffles, suggesting that these are important factors to be considered in the design of such heat exchanger.

Araí A. Bernárdez, Pécora; Maria Regina, Parise.

2006-09-01

383

Directory of Open Access Journals (Sweden)

Full Text Available This work shows the experimental study of a continuous gas-solid fluidized bed with an immersed tube where cold water is heated by fluidized solid particles presenting inlet temperature from 450 to 700degreesC. Experiments were carried out in order to verify the influence of solid particle flow rate and distance between baffles immersed in a shallow fluidized bed. The solid material was 254µm diameter silica sand particles, fluidized by air in a 0.90m long and 0.15m wide heat exchanger. The measurements were taken at steady state conditions for solid mass flow rate from 10 to 100 kg/h, in a heat exchanger with the presence of 5 or 8 baffles. Bed temperature measurements along the length of the heat exchanger were experimentally obtained and heat balances for differential control volumes of the heat exchanger were made in order to obtain the axial profile of the bed-to-tube heat transfer coefficient. The results showed that heat transfer coefficient increases with the solid particle mass flow rate and with the presence of baffles, suggesting that these are important factors to be considered in the design of such heat exchanger.

Pécora Araí A. Bernárdez

2006-01-01

384

Directory of Open Access Journals (Sweden)

Full Text Available The objective of this research was to study the effects of process variables on the volumetric mass transfer coefficient of oxygen, KLa, in a stirred bioreactor using the static gassing-out method. In this study, various process conditions were chosen, including 3 parameters, namely, concentration of glucose in medium (10, 15 and 20 g/l, air flow rate (1, 1.25, 1.5 and 1.75 vvm, and agitation rate (300, 400, 500 and 600 rpm. From the results, it was found that the KLa increased with increasing air flow rate and/or speed of agitation, but decreased with increasing concentration of glucose in medium. The maximum KLa occurred when the concentration of glucose in medium was the least (10 g/l, with an air flow rate of 1.75 vvm, and an agitation rate of 600 rpm. Correlations have been developed for the estimation of volumetric mass transfer coefficients at various process conditions for medium with different glucose concentrations. The exponent values representing dependence of KLa on the process conditions were then compared with literature values.

Kongdej LIMPAIBOON

2013-12-01

385

International Nuclear Information System (INIS)

The present thesis describes an apparative arrangement for the measurement of the n-p polarization-transfer coefficient Dt at a mean neutron energy of 25.5 MeV and the possibility for the determination of the 3S1-3D1 mixing parameter. Extensive Monte Carlo programs were developed for the optimization of the experimental arrangement and for the determination of the polarimeter properties. An unpolarized test measurement is presented as well as the course of the data evaluation discussed. A first polarized measurement yielded because of a cup current of only 30 nA as well as some technical problems at the isochronous cyclotron yet no evident result concerning Dt. At a polarized beam current of 500 nA to be expected and a mean neutron polarization of Pn=0.45 the n-p polarization-transfer coefficient Dt can be determined in a four-week beam-time to +-0.025 from which a fixation of the 3S1-3D1 mixing parameter to +-1.0 degrees results. (orig.)

386

Many-particle surface diffusion coefficients near first-order phase transitions at low temperatures

We analyze the chemical and jump surface diffusion coefficients, Dc and DJ, near a first-order phase transition at which two phases coexist and the surface coverage, ?, jumps between single-phase values ?-* and ?+*. Contrary to other studies, we consider temperatures that are sufficiently subcritical. Using the local equilibrium approximation, we obtain approximate analytical formulas for the dependences of Dc and DJ on the coverage and system size, N, near such a transition. In the two-phase regime, when ? ranges between ?-* and ?+*, the diffusion coefficients behave as the sums of two hyperbolas, Dc?A-/N|?-?-*|+A+/N|?-?+*| and DJ?A-|?-?+*|/?+A+|?-?-*|/?. This behavior rapidly changes as the system goes from the two-phase regime to either of the single-phase regimes (when ? goes below ?-* or above ?+*). The crossover behavior of Dc(?) and DJ(?) between the two-phase and single-phase regimes is described by rather complex formulas involving the Lambert function. We consider a lattice-gas model on a triangular lattice to illustrate these general results, applying them to four specific examples of transitions exhibited by the model.

Medved', Igor; Trník, Anton

2012-07-01

387

Evaluation of Heat and Mass Transfer Coefficients for R134a/DMF Bubble Absorber

The Vapour Absorption Refrigeration System (VARS) has generated renewed interest and is being viewed as one of the alternatives for vapour compression refrigeration due to its potential for waste heat utilization. To improve the efficiency of these systems, it is necessary to study heat and mass transfer processes in absorption system components. The absorber, one of the crucial components in VARS is considered for study. Experimental investigation is carried out to study heat and mass transf...

Suresh, M.; Mani, A.

2011-01-01

388

The influence of a heat transfer coefficient probe on fluid flow near wall

Good knowledge of the convective boundary condition is necessary for finite element analysis of thermal deformation behavior in machine tools. There are a number of correlation equations for natural and forced convection and several correlations for mixed convection. Due to a relatively wide range of dimensions, temperatures and speeds, all regimes of convective heat transfer can be observed in machine tools, including the transition region between laminar and turbulent free convection, char...

Mareš Martin; Horejš Otakar; Kohút Peter

2012-01-01

389

DEFF Research Database (Denmark)

Night-time ventilation is a promising approach to reduce the energy needed for cooling buildings without reducing thermal comfort. Nevertheless actual building simulation tools have showed their limits in predicting accurately the efficiency of night-time ventilation, mainly due to inappropriate models for convection. In a full-scale test room, the heat transfer was investigated during 12 h of discharge by night-time ventilation. A total of 34 experiments have been performed, with different ventilation types (mixing and displacement), air change rates, temperature differences between the inlet air and the room, and floor emissivities. This extensive experimental study enabled a detailed analysis of the convective and radiative flow at the different surfaces of the room. The experimentally derived convective heat transfer coefficients (CHTC) have been compared to existing correlations. For mixing ventilation, existing correlations did not predict accurately the convective heat transfer at the ceiling due to differences in the experimental conditions. But the use of local parameters of the air flow showed interesting results to obtain more adaptive CHTC correlations. For displacement ventilation, the convective heat transfer was well predicted by existing correlations. Nevertheless the change of floor emissivity influenced the CHTC at the surface of interest.

Le Dreau, Jerome; Heiselberg, Per

2013-01-01

390

Local pool boiling heat transfer on a 3 Degree inclined tube surface

Energy Technology Data Exchange (ETDEWEB)

Mechanisms of pool boiling heat transfer have been studied for a long time. Recently, it has been widely investigated in nuclear power plants for the purpose of acquiring inherent safety functions in case of no power supply. To design more efficient heat exchangers, effects of several parameters on heat transfer must be studied in detail. One of the major issues is variation in local heat transfer coefficients on a tube. Lance and Myers reported that the type of boiling liquid can change the trend of local heat transfer coefficients along the tube periphery. Lance and Myers said that as the liquid is methanol the maximum local heat transfer coefficient was observed at the tube bottom while the maximum was at the tube sides as the boiling liquid was n hexane. Corn well and Einarsson reported that the maximum local heat transfer coefficient was observed at the tube bottom, as the boiling liquid was R113. Corn well and Houston explained the reason of the difference in local heat transfer coefficients along the tube circumference with introducing effects of sliding bubbles on heat transfer. According to Gu pta et al., the maximum and the minimum local heat transfer coefficients were observed at the bottom and top regions of the tube circumference, respectively, using a tube bundle and water. Kang also reported the similar results using a single horizontal tube and water. However, the maximum heat transfer coefficient was observed at the angle of 45 deg. Sateesh et al. investigated variations in local heat transfer coefficients along a tube periphery as the inclination angle was changed. Summarizing the published results, some parts are still remaining to be investigated in detail. Although pool boiling analysis on a nearly horizontal tube is necessary for the design of the advanced power reactor plus, no previous results are published yet. Therefore, the present study is aimed to study variations in local pool boiling heat transfer coefficients for a 3 degree inclined tube submerged in subcooled or saturated water.

Kang, Myeong Gie [Andong National Univ., Kyungbuk (Korea, Republic of)

2012-10-15

391

Diffusion along interface and grain boundaries provides an efficient pathway and may control chemical transport in rocks as well as their mechanical strength. Besides the significant relevance of these diffusion processes for various geologic processes, experimental data are still very limited (e.g., Dohmen & Milke, 2010). Most of these data were measured using polycrystalline materials and the formalism of LeClaire (1951) to fit integrated concentration depth profiles. To correctly apply this formalism, certain boundary conditions of the diffusion problem need to be fulfilled, e.g., surface diffusion is ignored, and furthermore the lattice diffusion coefficient has to be known from other studies or is an additional fitting parameter, which produces some ambiguity in the derived grain boundary diffusion coefficients. We developed an experimental setup where we can measure the lattice and grain boundary diffusion coefficients simultaneously but independent and demonstrate the relevance of surface diffusion for typical grain boundary diffusion experiments. We performed Mg2SiO4 bicrystal diffusion experiments, where a single grain boundary is covered by a thin-film of pure Ni2SiO4 acting as diffusant source, produced by pulsed laser deposition. The investigated grain boundary is a 60° (011)/[100]. This specific grain boundary configuration was modeled using molecular dynamics for comparison with the experimental observations in the transmission electron microscope (TEM). Both, experiment and model are in good agreement regarding the misorientation, whereas there are still some disagreements regarding the strain fields along the grain boundary that are of outmost importance for the strengths of the material. The subsequent diffusion experiments were carried out in the temperature range between 800° and 1450° C. The inter diffusion profiles were measured using the TEMs energy dispersive x-ray spectrometer standardized using the Cliff-Lorimer equation and EMPA measurements. To evaluate the obtained diffusion profiles we adapted the isolated grain boundary model, first proposed by Fisher (1951) to match several observations: (i) Anisotropic diffusion in forsterite, (ii) fast diffusion along the grain boundary, (iii) fast diffusion on the surface of the sample. The latter process is needed to explain an additional flux of material from the surface into the grain boundary. Surface and grain boundary diffusion coefficients are on the order of 10000 times faster than diffusion in the lattice. Another observation was that in some regions the diffusion profiles in the lattice were greatly extended. TEM observations suggest here that surface defects (nano-cracks, ect.) have been present, which apparently enhanced the diffusion through the bulk lattice. Dohmen, R., & Milke, R. (2010). Diffusion in Polycrystalline Materials: Grain Boundaries, Mathematical Models, and Experimental Data. Reviews in Mineralogy and Geochemistry, 72(1), 921-970. Fisher, J. C. (1951). Calculations of Diffusion Penetration Curves for Surface and Grain Boundary Diffusion. Journal of Applied Physics, 22(1), 74-77. Le Claire, A. D. (1951). Grain boundary diffusion in metals. Philosophical Magazine A, 42(328), 468-474.

Marquardt, Katharina; Dohmen, Ralf; Wagner, Johannes

2014-05-01

392

Local heat transfer characteristics of array impinging jets with channel flow on the concave surface

International Nuclear Information System (INIS)

In this study, the effect of channel flow in the concave surface on local heat transfer characteristics of array jets was investigated experimentally. A TLC method is employed to determine local heat transfer coefficients on the target plate and also flow visualization has been conducted to investigate the behavior of a row of impinging jets and array of impinging jets. Two different array patterns of impinging array jets devices are tested for Reynolds number(Re=10,000). In a row of impinging jets, secondary vortex is strongly maintained by main vortex at nozzle-to-plate distance of H/d=2. Therefore, the Nusselt number slowly decreased at the mid-way region between adjacent jets. In array jets, the local maximum Nusselt number region move further in the downstream direction due to the increase of channel flow velocity

393

As pressure increases and approaches the critical pressure, density difference between liquid and vapor becomes small, latent heat of condensation approaches zero and other physical properties show remarkably different behaviors from those at lower pressure. Therefore it is expected that condensation heat transfer near the critical pressure differs from that at lower pressure. An experimental study of natural convection condensation on a vertical cylinder surface was carried out using Carbon Dioxide as a working fluid in the pressure range of 5.0 to 7.1 MPa. Filmwise condensation was observed, and heat transfer coefficients were obtained from measuring condensate volume and compared with Nusselt's theory and with experimental results under usual pressure conditions.

Ishihara, Isao; Matsumoto, Ryosuke; Ebihara, Tsutomu; Maegoya, Akira

394

Surface roughness effects on heat transfer in Couette flow

International Nuclear Information System (INIS)

A cell theory for viscous flow with rough surfaces is applied to two basic illustrative heat transfer problems which occur in Couette flow. Couette flow between one adiabatic surface and one isothermal surface exhibits roughness effects on the adiabatic wall temperature. Two types of rough cell adiabatic surfaces are studied: (1) perfectly insulating (the temperature gradient vanishes at the boundary of each cell); (2) average insulating (each cell may gain or lose heat but the total heat flow at the wall is zero). The results for the roughness on a surface in motion are postulated to occur because of fluid entrainment in the asperities on the moving surface. The symmetry of the roughness effects on thermal-viscous dissipation is discussed in detail. Explicit effects of the roughness on each surface, including combinations of roughness values, are presented to enable the case where the two surfaces may be from different materials to be studied. The fluid bulk temperature rise is also calculated for Couette flow with two ideal adiabatic surfaces. The effect of roughness on thermal-viscous dissipation concurs with the viscous hydrodynamic effect. The results are illustrated by an application to lubrication. (Auth.)

395

Flow patterns and corresponding local heat transfer coefficients in a pulsating heat pipe

A Pulsating Heat Pipe (PHP) is a passive two-phase heat transfer device for handling moderate to high heat fluxes, typically suited for power electronics and similar applications. It usually consists of a meandering capillary tube, closed end-to-end in a loop, evacuated and then partially filled with a working fluid. The internal flow patterns in a PHP are a function of the applied heat flux. At low heat flux levels, an oscillating slug flow pattern is prevalent but once the heat power increa...

Mameli, Mauro; Marengo, Marco; Khandekar, Sameer

2011-01-01

396

Determining the moderator temperature coefficient by fitting the noise analysis transfer function

International Nuclear Information System (INIS)

Previous researchers have established that the value of the moderator temperature coefficient (MTC) of reactivity is contained in correlations between fluctuations of the neutron flux and core-exit coolant temperature. Both the root-mean-square method and the frequency response function (FRF) technique are used to determine the absolute magnitude of the MTC. Normally, these methods are used in conjunction with the phase angle technique, which is used to ascertain the MTC sign; however, a recent study has determined that a boundary exists on the range of MTC values for which the phase angle from noise analysis can be used. This paper describes a fitting method to determine both the MTC sign and magnitude in a single analysis in order to overcome such limitations

397

This thesis experimentally investigates the enhancement of single-phase heat transfer, frictional loss and pressure drop characteristics in a Single Heater Element Loop Tester (SHELT). The heater element simulates a single fuel rod for Pressurized Nuclear reactor. In this experimental investigation, the effect of the outer surface roughness of a simulated nuclear rod bundle was studied. The outer surface of a simulated fuel rod was created with a three-dimensional (Diamond-shaped blocks) surface roughness. The angle of corrugation for each diamond was 45 degrees. The length of each side of a diamond block is 1 mm. The depth of each diamond block was 0.3 mm. The pitch of the pattern was 1.614 mm. The simulated fuel rod had an outside diameter of 9.5 mm and wall thickness of 1.5 mm and was placed in a test-section made of 38.1 mm inner diameter, wall thickness 6.35 mm aluminum pipe. The Simulated fuel rod was made of Nickel 200 and Inconel 625 materials. The fuel rod was connected to 10 KW DC power supply. The Inconel 625 material of the rod with an electrical resistance of 32.3 kO was used to generate heat inside the test-section. The heat energy dissipated from the Inconel tube due to the flow of electrical current flows into the working fluid across the rod at constant heat flux conditions. The DI water was employed as working fluid for this experimental investigation. The temperature and pressure readings for both smooth and rough regions of the fuel rod were recorded and compared later to find enhancement in heat transfer coefficient and increment in the pressure drops. Tests were conducted for Reynold's Numbers ranging from 10e4 to 10e5. Enhancement in heat transfer coefficient at all Re was recorded. The maximum heat transfer co-efficient enhancement recorded was 86% at Re = 4.18e5. It was also observed that the pressure drop and friction factor increased by 14.7% due to the increased surface roughness.

Najeeb, Umair

398

Nonadiabatic effects in charge transfer in atom-surface scattering

International Nuclear Information System (INIS)

Using a recently developd many-body theory, we investigate the velocity dependence of charge transfer in atom-surface scattering. We show that under certain conditions, intra-atomic correlation effects can introduce nontrivial sources of nonadiabaticity. For situations where a sharp Kondo resonance is formed near the Fermi energy, the system can exhibit strong nonadiabatic effects even at low velocities. This nonadiabatic behavior is caused by the relatively long-time scale for the formation or survival of the Kondo peak

399

Surface Bloch waves mediated heat transfer between two photonic crystals

We theoretically investigate the non-radiative heat transfer between two photonic crystals separated by a small gap in non-equilibrium thermal situation. We predict that the surface Bloch states coupling supported by these media can make heat exchanges larger than those measured at the same separation distance between two massive homogeneous materials made with the elementary components of photonic crystals. These results could find broad applications in near-field technologies.

Ben-Abdallah, Philippe; Pryamikov, Andrey

2010-01-01

400

Energy Technology Data Exchange (ETDEWEB)

This paper presents the experimental results of the local heat transfer for falling film evaporation of water sheet by solving the inverse heat conduction problem. It is shown that the local heat transfer coefficients increase by increasing the air flow velocity, the film liquid flow rate or decreasing the inlet bulk film temperature. Correlations for the mean heat transfer coefficients in the absence of superimposed flow for the stagnation region, the thermally developed region and the bottom of the heated cylinder are proposed. (orig.)

Louahlia-Gualous, H.; Omari, L. El.; Panday, P.K.; Artioukhine, E [Universite de Technologie Belfort-Montbeliard, Belfort (France)

2005-10-01

401

Flow and heat transfer regimes during quenching of hot surfaces

International Nuclear Information System (INIS)

Reflooding experiments have been performed to study flow and heat transfer regimes in a heated annular vertical channel under supercooled inlet conditions. A gamma densitometer was employed to determine the void fraction as a function of the distance from the quench front. Surface heat fluxes were determined by fast measurements of the temperature spatial distribution. Two quench front is shown to lie in the transition boiling region which spreads into the dry and wet segments of the heated surface. (authors) 5 refs, 3 figs

402

Heat transfer to droplets impinging upon superheated surfaces

International Nuclear Information System (INIS)

Transient surface temperature traces were obtained for a block when impinged upon by a water droplet under different experimental conditions. The temperature measurement relied on successful electro-plating over a surface thermal probe. Instantaneous heat flux from the metal block to the impacting droplet was derived through inverse conduction calculation. Four relevant parameters (degree of wall superheat, degree of droplet subcooling, impinging velocity and droplet size) were experimentally tested to study their effects on the droplet quenching process. The experimental data indicates the following: (1) for a dynamic impingement, the occurrence of liquid contact with a solid beyond Leidenfrost temperature was experimentally confirmed. (2) Heat transfer between droplet and wall surface were significantly affected by the degrees of wall superheat and droplet subcooling. The effects of impinging velocity and droplet size were obscure in the test ranges. (3) Boiling curves were established for this special droplet quenching process. It consisted of two regions: a nucleate-boiling-like region and a transition region. In the nucleate-boiling-like region, the heat transfer rate varied with wall superheat only and was close to Miyasaka et al.'s subcooled pool boiling data. In the transition region, heat transfer depended on both wall superheat and droplet subcooling

403

Improvement of Reactor Fuel Element Heat Transfer by Surface Roughness

Energy Technology Data Exchange (ETDEWEB)

In heat exchangers with a limited surface temperature such as reactor fuel elements, rough heat transfer surfaces may give lower pumping power than smooth. To obtain data for choice of the most advantageous roughness for the superheater elements in the Marviken reactor, measurements were made of heat transfer and pressure drop in an annular channel with a smooth or rough test rod in a smooth adiabatic shroud. 24 different roughness geometries were tested. The results were transformed to rod cluster geometry by the method of W B Hall, and correlated by the friction and heat transfer similarity laws as suggested by D F Dipprey and R H Sabersky with RMS errors of 12.5 % in the friction factor and 8.1 % in the Stanton number. The relation between the Stanton number and the friction factor could be described by a relation of the type suggested by W Nunner, with a mean error of 3.1 % and an RMS error of 11.6 %. Application of the results to fuel element calculations is discussed, and the great gains in economy which can be obtained with rough surfaces are demonstrated by two examples.

Kjellstroem, B.; Larsson, A.E.

1967-04-15

404

International Nuclear Information System (INIS)

The paper shows the results of a study on the influence of the changes of the heat transfer coefficient ''k'' on the exergetic losses in some selected equipment components of the thermal system and on the alternations of unit electric power. The changes of the ''k'' may be due to the fouling of the heat exchange surfaces or errors in the design. This research concerned with two feed-water heaters (low- and high-pressure) and the steam reheater situated behind the moisture separator. The research was conducted for the range of the ratio ? (of actual to the design value of ''k'') from 0.5 to 1.5 of its value assumed in the design. The mathematical model considers off-design operating conditions in the whole thermal system, which result from the change of the coefficient ''k'' in the selected parts of the thermal system. The decomposition method and Seild's multilevel iterative process were used to solve the problem. The research proved that the capacity of the unit during operation may differ from the design value - 1000 MW - from ten to twenty MW due to alternations of the operation value of ''k'' from the design one. (author). 5 refs, 5 figs