Directory of Open Access Journals (Sweden)
James A. Parsons
2001-01-01
Full Text Available The effect of channel rotation on jet impingement cooling by arrays of circular jets in twin channels was studied. Impinging jet flows were in the direction of rotation in one channel and opposite to the direction of rotation in the other channel. The jets impinged normally on the smooth, heated target wall in each channel. The spent air exited the channels through extraction holes in each target wall, which eliminates cross flow on other jets. Jet rotation numbers and jet Reynolds numbers varied from 0.0 to 0.0028 and 5000 to 10,000, respectively. For the target walls with jet flow in the direction of rotation (or opposite to the direction of rotation, as rotation number increases heat transfer decreases up to 25% (or 15% as compared to corresponding results for non-rotating conditions. This is due to the changes in flow distribution and rotation induced Coriolis and centrifugal forces.
Energy Technology Data Exchange (ETDEWEB)
Sarh, B.; Gokalp, I.; Sanders, H. [Centre National de la Recherche Scientifique (CNRS), 45 - Orleans-la-Source (France)
1997-12-31
In the framework of the studies carried out by the LCSR on variable density flows and diffusion turbulent flames, this paper deals with the study of the influence of density variation on the characteristics of a heated rectangular turbulent jet emerging in a stagnant surrounding atmosphere and more particularly on the determination of turbulent viscosity. The dynamical field is measured using laser-Doppler anemometry while the thermal field is measured using cold wire anemometry. A numerical predetermination of the characteristics of this jet, based on a k-{epsilon} modeling, is carried out. (J.S.) 6 refs.
Directory of Open Access Journals (Sweden)
Calisir Tamer
2015-01-01
Full Text Available Thermal control of electronic components is a continuously emerging problem as power loads keep increasing. The present study is mainly focused on experimental and numerical investigation of impinging jet cooling of 18 (3 × 6 array flash mounted electronic components under a constant heat flux condition inside a rectangular channel in which air, following impingement, is forced to exit in a single direction along the channel formed by the jet orifice plate and impingement plate. Copper blocks represent heat dissipating electronic components. Inlet flow velocities to the channel were measured by using a Laser Doppler Anemometer (LDA system. Flow field observations were performed using a Particle Image Velocimetry (PIV and thermocouples were used for temperature measurements. Experiments and simulations were conducted for Re = 4000 – 8000 at fixed value of H = 10 × Dh. Flow field results were presented and heat transfer results were interpreted using the flow measurement observations. Numerical results were validated with experimental data and it was observed that the results are in agreement with the experiments.
Flow Characteristics of Rectangular Underexpanded Impinging Jets
Institute of Scientific and Technical Information of China (English)
Minoru YAGA; Yoshio KINJO; Masumi TAMASHIRO; Kenyu OYAKAWA
2006-01-01
In this paper, the flow fields of underexpanded impinging jet issued from rectangular nozzles of aspect ratio 1,3 and 5 are numerically and experimentally studied. Two dimensional temperature and pressure distributions are measured by using infrared camera and the combination of a pressure scanning device and a stepping motor, respectively. The variation of the stagnation pressure on the impinging plate reveals that a hystcretic phenomenon exists during the increasing and decreasing of the pressure ratio for the aspect ratio of 3.0 and 5.0. It is also found that the nozzle of aspect ratio 1.0 caused the largest total pressure loss pc/p0 = 0.27 at the pressure ratio of p0/pb, = 6.5, where pc is the stagnation center pressure on the wall, p0 the upstream stagnation pressure, pb the ambient pressure. The other two nozzles showed that the pressure loss pc / p0=0.52 and 0.55 were achieved by the nozzles of the aspect ratio 3,0 and 5.0, respectively. The comparison between the calculations and experiments is fairly good, showing the three dimensional streamlines and structures of the shock waves in the jets. However, the hysteresis of the pressure variations observed in the experiments between the pressure ratio of 3.5 and 4.5 cannot be confirmed in the calculations.
Diffusion of heat from a finite, rectangular, plane heat source
International Nuclear Information System (INIS)
Ferreri, J.C.; Caballero, C.H.
1985-01-01
Non-dimensional results for the temperature field originating in a rectangular, finite, plane heat source with infinitesimal thickness are introduced. The source decays in time, zero decay being a particular case. Results are useful for obtaining an aproximation of the maximum temperature of a system holding an internal heat source. The range selected for the parameters is specially useful in the case of a nuclear waste repository. The application to the case of mass diffussion arises from analogy. (Author) [es
Yu, Roger Ho Zhen; Ismail, Mohd Azmi bin; Ramdan, Muhammad Iftishah; Mustaffa, Nur Musfirah binti
2017-03-01
Synthetic Jet generates turbulence flow in cooling the microelectronic devices. In this paper, the experiment investigation of the cooling performance of pneumatic synthetic jet with single slot rectangular orifices at low frequency motion is presented. The velocity profile at the end of the orifice was measured and used as characteristic performance of synthetic jet in the present study. Frequencies of synthetic jet and the compressed air pressure supplied to the pneumatic cylinder (1bar to 5bar) were the parameters of the flow measurement. The air velocity of the synthetic jet was measured by using anemometer air flow meter. The maximum air velocity was 0.5 m/s and it occurred at frequency motion of 8 Hz. The optimum compressed air supplied pressure of the synthetic jet study was 4 bar. The cooling performance of synthetic jet at several driven frequencies from 0 Hz to 8 Hz and heat dissipation between 2.5W and 9W were also investigate in the present study. The results showed that the Nusselt number increased and thermal resistance decreased with both frequency and Reynolds number. The lowest thermal resistance was 5.25°C/W and the highest Nusselt number was 13.39 at heat dissipation of 9W and driven frequency of 8Hz.
International Nuclear Information System (INIS)
Collard, T.H.
1982-01-01
A jet pump system is shown that utilizes waste heat to provide heating and/or cooling. Waste heat diverted through a boiler causes a refrigerant to evaporate and expand for supersonic discharge through a nozzle thereby creating a vacuum in an evaporator coil. The vacuum draws the refrigerant in a gaseous state into a condensing section of a jet pump along with refrigerant from a reservoir in a subcooled liquid form. This causes condensation of the gas in a condensation section of the jet pump, while moving at constant velocity. The change in momentum of the fluid overcomes the system high side pressure. Some of the condensate is cooled by a subcooler. Refrigerant in a subcooled liquid state from the subcooler is fed back into the evaporator and the condensing section with an adequate supply being insured by the reservoir. The motive portion of the condensate is returned to the boiler sans subcooling. By proper valving start-up is insured, as well as the ability to switch from heating to cooling
Critical heat flux correlation for thin rectangular channels
International Nuclear Information System (INIS)
Tanaka, Futoshi; Mishima, Kaichiro; Hibiki, Takashi
2007-01-01
The effect of heated length on Critical heat flux (CHF) in thin rectangular channels was studied based on CHF data obtained under atmospheric pressure. CHF in small channels has been widely studied in the past decades but most of the studies are related to CHF in round tubes. Although basic mechanisms of burnout in thin rectangular channels are similar to tubes, applicability of CHF correlations for tubes to rectangular channels are questionable since CHF in rectangular channels are affected by the existence of non-heated walls and the non-circular geometry of channel circumference. Several studies of CHF in thin rectangular channels have been reported in relation to thermal hydraulic design of research reactors and neutron source targets and CHF correlations have been proposed, but the studies mostly focus on CHFs under geometrical conditions of the application of interest. In his study, existing CHF data obtained in thin rectangular channels were collected and the effect of heated length on CHF was examined. Existing CHF correlations were verified with positive quality flow CHF data but none of the correlations successfully reproduced the CHF for a wide range of heated length. A new CHF correlation for qualify region applicable to a wide range of heated length was developed based on the collected data. (author)
Influence of a circular jet arrangement in a rectangular tank on flow and suspended sediment release
Althaus, Jenzer; Isabella, Jolanda Maria
2011-01-01
With the objective of high sediment release out of a rectangular tank the performance of a circular jet arrangement has been investigated. Therefore, experiments with four jets arranged in a horizontal circle placed in water with quasi homogeneous sediment concentration were conducted. The induced circulation was analysed by measuring the flow field. The influence of the flow circulation on suspension and on sediment release through the water intake was studied and discussed. The offbottom cl...
Azimuthal critical heat flux in narrow rectangular channels
Energy Technology Data Exchange (ETDEWEB)
Kim, Yong Hoon; Noh, Sang Woo; Kim, Sung Joong; Suh, Kune Y. [Seoul National University, Seoul (Korea, Republic of)
2003-07-01
Tests were conducted to examine the critical heat flux (CHF) on the one-dimensional downward heating rectangular channel having a narrow gap by changing the orientation of the copper test heater assembly in a pool of saturated water under the atmospheric pressure. The test parameters include both the gap sizes of 1, 2, 5 and 10mm, and the surface orientation angles from the downward-facing position (180{sup o}) to the vertical position (90{sup o}), respectively. Also, the CHF experiments were performed for pool boiling with varying heater surface orientations in the unconfined space at the atmospheric pressure using the rectangular test section. It was observed that the CHF generally decreases as the surface inclination angle increases and as the gap size decreases. In consistency with several studies reported in the literature, it was found that there exists a transition angle above which the CHF changes with a rapid slope. An engineering correlation is developed for the CHF during natural convective boiling in the inclined, confined rectangular channels with the aid of dimensional analysis.
FLOW VISUALIZATION OF RECTANGULAR SLOT AIR JET IMPINGEMENT ON FLAT SURFACES
Satheesha V *1, B. K. Muralidhra2, Abhilash N3, C. K. Umesh4
2018-01-01
Jet impingement near the mid-chord of the gas turbine blade is treated as a flat plate. Experimental and numerical investigations are carried out for a single slot air jet impinging on flat surface for two different rectangular slots of dimension (3mm x 65 mm) and (5mm x 65 mm). Experimentation is done to study the flow pattern topography on the flat target plate, with varying the flow rate from 20 LPM to 50 LPM by varying the nozzle to plate distance from 9 mm to 24 mm for slot jet of 3mm an...
Near field vorticity distributions from a sharp-edged rectangular jet
International Nuclear Information System (INIS)
Vouros, Alexandros P.; Panidis, Thrassos; Pollard, Andrew; Schwab, Rainer R.
2015-01-01
Highlights: • Axial mean vorticity equation terms are calculated from experimental data. • Appearance of ridges, dumbbell shape and saddleback velocity profiles is highlighted. • Explanations are provided using terms from the vorticity equation. - Abstract: Experimental results on the near field development of a free rectangular jet with aspect ratio 10 are presented. The jet issues from a sharp-edged orifice attached to a rectangular settling chamber at Re h ∼ 23,000, based on slot width, h. Measurements on cross plane grids were obtained with a two-component hot wire anemometry probe, which provided information on the three dimensional characteristics of the flow field. Two key features of this type of jet are mean axial velocity profiles presenting two off axis peaks, commonly mentioned as saddleback profiles, and a predominant dumbbell shape as described by, for example, a contour of the axial mean velocity. The saddleback shape is found to be significantly influenced by the vorticity distribution in the transverse plane of the jet, while the dumbbell is traced to two terms in the axial mean vorticity transport equation that diffuse fluid from the centre of the jet towards its periphery. At the farthest location where measurements were taken, 30 slot widths from the jet exit, the flow field resembles that of an axisymmetric jet
El-Amin, Mohamed; Sun, Shuyu
2010-01-01
In most of real-world applications, such as the case of heat stores, inlet is not kept at a constant temperature but it may vary with time during charging process. In this paper, a vertical water jet injected into a rectangular storage tank is measured experimentally and simulated numerically. Two cases of study are considered; one is a hot water jet with uniform inlet temperature (UIT) injected into a cold water tank, and the other is a cold water jet with non-uniform inlet temperature (NUIT) injected into a hot water tank. Three different temperature differences and three different flow rates are studied for the hot water jet with UIT which is injected into a cold water tank. Also, three different initial temperatures with constant flow rate as well as three different flow rates with constant initial temperature are considered for the cold jet with NUIT which is injected into a hot water tank. Turbulence intensity at the inlet as well as Reynolds number for the NUIT cases are therefore functions of inlet temperature and time. Both experimental measurements and numerical calculations are carried out for the same measured flow and thermal conditions. The realizable k-ε model is used for modeling the turbulent flow. Numerical solutions are obtained for unsteady flow while pressure, velocity, temperature and turbulence distributions inside the water tank are analyzed. The simulated results are compared to the measured results, and they show a good agreement at low temperatures. © 2010 IEEE.
El-Amin, Mohamed
2010-12-01
In most of real-world applications, such as the case of heat stores, inlet is not kept at a constant temperature but it may vary with time during charging process. In this paper, a vertical water jet injected into a rectangular storage tank is measured experimentally and simulated numerically. Two cases of study are considered; one is a hot water jet with uniform inlet temperature (UIT) injected into a cold water tank, and the other is a cold water jet with non-uniform inlet temperature (NUIT) injected into a hot water tank. Three different temperature differences and three different flow rates are studied for the hot water jet with UIT which is injected into a cold water tank. Also, three different initial temperatures with constant flow rate as well as three different flow rates with constant initial temperature are considered for the cold jet with NUIT which is injected into a hot water tank. Turbulence intensity at the inlet as well as Reynolds number for the NUIT cases are therefore functions of inlet temperature and time. Both experimental measurements and numerical calculations are carried out for the same measured flow and thermal conditions. The realizable k-ε model is used for modeling the turbulent flow. Numerical solutions are obtained for unsteady flow while pressure, velocity, temperature and turbulence distributions inside the water tank are analyzed. The simulated results are compared to the measured results, and they show a good agreement at low temperatures. © 2010 IEEE.
Numerical modelling of unsteady flow behaviour in the rectangular jets with oblique opening
Directory of Open Access Journals (Sweden)
James T. Hart
2016-09-01
Full Text Available Vortex shedding in a bank of three rectangular burner-jets was investigated using a CFD model. The jets were angled to the wall and the whole burner was recessed into a cavity in the wall; the ratio of velocities between the jets varied from 1 to 3. The model was validated against experimentally measured velocity profiles and wall pressure tapings from a physical model of the same burner geometry, and was generally found to reproduce the mean flow field faithfully. The CFD model showed that vortex shedding was induced by a combination of an adverse pressure gradient, resulting from the diffuser-like geometry of the recess, and the entrainment of fluid into the spaces separating the jets. The asymmetry of the burner, a consequence of being angled to the wall, introduced a cross-stream component into the adverse pressure gradient that forced the jets to bend away from their geometric axes, the extent of which depended upon the jet velocity. The vortex shedding was also found to occur in different jets depending on the jet velocity ratio.
Taha, T.J.; Lefferts, Leonardus; van der Meer, Theodorus H.
2016-01-01
An experimental heat transfer investigation was carried out to examine the influence of carbon nanotubes (CNTs) layer deposits on the convective heat transfer performance inside rectangular microchannels. Successful synthesis of vertically aligned CNTs was achieved using a catalytic vapor deposition
Experimental study of critical heat flux in inclined rectangular gap
International Nuclear Information System (INIS)
Kim, S.J.; Kim, Y.H.; Noh, S.W.; Suh, K.Y.; Rempe, J.L.; Cheung, F.B.; Kim, S.B.
2003-01-01
In the TMI-2 accident, the lower part of the reactor pressure vessel was overheated and then rather rapidly cooled down, as was later found out in a vessel investigation project. This accounted for the possibility of gap cooling feasibility. For this reason, a great deal of investigations was performed to determine the critical heat flux (CHF) from the standpoint of in-vessel retention (IVR). As part of a joint Korean-U.S. International Nuclear Energy Research Initiative (INERI) project, Tests were conducted to examine the critical heat flux (CHF) on the one-dimensional downward heating rectangular channel having a narrow gap by changing the orientation of the copper test heater assembly in a pool of saturated water under the atmospheric pressure. The test parameters include both the gap sizes of 1, 2, 5 and 10 mm, and the surface orientation angles from the downward-facing position (180deg) to the vertical position (90deg), respectively. It was observed that the CHF generally decreases as the surface inclination angle increases and as the gap size decreases. However, in downward-facing position (180deg), somewhat differing results were detected relative to previous reports. For a certain gap size having a similar dimension with vapor layer thickness, more efficient heat transfer was detected and this may be interpreted by characteristic property such as the vapor layer thickness of water. In consistency with several studies reported in the literature, it was found that there exists a transition angle above that the CHF changes with a rapid slope. (author)
Heated water jet in coflowing turbulent stream
International Nuclear Information System (INIS)
Shirazi, M.A.; McQuivey, R.S.; Keefer, T.N.
1974-01-01
Effects of ambient turbulence on temperature and salinity distributions of heated water and neutrally buoyant saltwater jets were studied for a wide range of densimetric jet Froude numbers, jet discharge velocities, and ambient turbulence levels in a 4-ft-wide channel. Estimates of vertical and lateral diffusivity coefficients for heat and for salt were obtained from salinity and temperature distributions taken at several stations downstream of the injection point. Readily usable correlations are presented for plume center-line temperature, plume width, and trajectory. The ambient turbulence affects the gross behavior characteristics of the plume. The effects vary with the initial jet Froude number and the jet to ambient velocity ratio. Heat and salinity are transported similarly and the finite source dimensions and the initial jet characteristics alter the numerical value of the diffusivity
Electromagnetic flow control of a bifurcated jet in a rectangular cavity
International Nuclear Information System (INIS)
Kalter, R.; Tummers, M.J.; Kenjereš, S.; Righolt, B.W.; Kleijn, C.R.
2014-01-01
Highlights: • Self-sustained oscillations in a thin cavity with submerged nozzle were observed. • The self-sustained oscillations were influenced by applying a Lorentz force. • A POD was applied to study the distribution of kinetic energy. • The large scale fluctuations can be enhanced or suppressed by the Lorentz force. • The turbulence fluctuations are not affected by the Lorentz force. - Abstract: The effect of Lorentz forcing on self-sustained oscillations of turbulent jets (Re = 3.1 × 10 3 ) issuing from a submerged bifurcated nozzle into a thin rectangular liquid filled cavity was investigated using free surface visualization and time-resolved particle image velocimetry (PIV). A Lorentz force is produced by applying an electrical current across the width of the cavity in conjunction with a magnetic field. As a working fluid a saline solution is used. The Lorentz force can be directed downward (F L L >0), to weaken or strengthen the self-sustained jet oscillations. The low frequency self-sustained jet oscillations induce a free surface oscillation. When F L L >0 the free surface oscillation amplitude is enhanced by a factor of 1.5. A large fraction of the turbulence kinetic energy k=1/2 u i ′ u i ′‾ is due to the self-sustained jet oscillations. A triple decomposition of the instantaneous velocity was used to divide the turbulence kinetic energy into a part originating from the self-sustained jet oscillation k osc and a part originating from the higher frequency turbulent fluctuations k turb . It follows that the Lorentz force does not influence k turb in the measurement plane, but the distribution of k osc can be altered significantly. The amount of energy contained in the self-sustained oscillation is three times lower when F L L >0
Mechanism of occurrence of self-exciting sloshing in rectangular vessel by plane jet flow
International Nuclear Information System (INIS)
Fukaya, Masashi; Okamoto, Koji; Madarame, Haruki
1996-01-01
FBRs have free liquid surfaces in reactor vessels and others, and it is expected that the flow velocity of liquid sodium coolant heightens accompanying the reduction of the reactor size. In the field where free liquid surface and high velocity flow exist, there is the possibility that various unstable phenomena occur on the liquid surface by the interference of the free liquid surface and flow. One example is the self-exciting sloshing by flow. In order to elucidate the mechanism of occurrence of the phenomena in a simple system, the experimental and analytical examinations were carried out on the self-exciting sloshing of free liquid surface in a rectangular vessel by plane jet flow. The basic oscillation characteristics of self-exciting sloshing were examined, and the physical quantities that control the occurrence of self-exciting sloshing were investigated by examining the effect in the case of changing the shapes of vessels. The experiments on the self-exciting sloshing in the case of vertical, horizontal and oblique plane jet flows are reported. The model for the occurrence of oscillation, in which the interaction of sloshing and jet variation was simplified, is proposed, and the verification of the model is reported. (K.I.)
Directory of Open Access Journals (Sweden)
Yasuhisa Shinmoto
2017-11-01
Full Text Available The use of immiscible liquids for cooling of surfaces with high heat generation density is proposed based on the experimental verification of its superior cooling characteristics in fundamental systems of pool boiling and flow boiling in a tube. For the purpose of practical applications, however, heat transfer characteristics due to flow boiling in narrow rectangular channels with different small gap sizes need to be investigated. The immiscible liquids employed here are FC72 and water, and the gap size is varied as 2, 1, and 0.5 mm between parallel rectangular plates of 30 mm × 175 mm, where one plate is heated. To evaluate the effect of gap size, the heat transfer characteristics are compared at the same inlet velocity. The generation of large flattened bubbles in a narrow gap results in two opposite trends of the heat transfer enhancement due to thin liquid film evaporation and of the deterioration due to the extension of dry patch in the liquid film. The situation is the same as that observed for pure liquids. The latter negative effect is emphasized for extremely small gap sizes if the flow rate ratio of more-volatile liquid to the total is not reduced. The addition of small flow rate of less-volatile liquid can increase the critical heat flux (CHF of pure more-volatile liquid, while the surface temperature increases at the same time and assume the values between those for more-volatile and less-volatile liquids. By the selection of small flow rate ratio of more-volatile liquid, the surface temperature of pure less-volatile liquid can be decreased without reducing high CHF inherent in the less-volatile liquid employed. The trend of heat transfer characteristics for flow boiling of immiscible mixtures in narrow channels is more sensitive to the composition compared to the flow boiling in a round tube.
Low-dimensional and Data Fusion Techniques Applied to a Rectangular Supersonic Multi-stream Jet
Berry, Matthew; Stack, Cory; Magstadt, Andrew; Ali, Mohd; Gaitonde, Datta; Glauser, Mark
2017-11-01
Low-dimensional models of experimental and simulation data for a complex supersonic jet were fused to reconstruct time-dependent proper orthogonal decomposition (POD) coefficients. The jet consists of a multi-stream rectangular single expansion ramp nozzle, containing a core stream operating at Mj , 1 = 1.6 , and bypass stream at Mj , 3 = 1.0 with an underlying deck. POD was applied to schlieren and PIV data to acquire the spatial basis functions. These eigenfunctions were projected onto their corresponding time-dependent large eddy simulation (LES) fields to reconstruct the temporal POD coefficients. This reconstruction was able to resolve spectral peaks that were previously aliased due to the slower sampling rates of the experiments. Additionally, dynamic mode decomposition (DMD) was applied to the experimental and LES datasets, and the spatio-temporal characteristics were compared to POD. The authors would like to acknowledge AFOSR, program manager Dr. Doug Smith, for funding this research, Grant No. FA9550-15-1-0435.
Ion heat transport studies in JET
DEFF Research Database (Denmark)
Mantica, P; Angioni, C; Baiocchi, B
2011-01-01
Detailed experimental studies of ion heat transport have been carried out in JET exploiting the upgrade of active charge exchange spectroscopy and the availability of multi-frequency ion cyclotron resonance heating with 3He minority. The determination of ion temperature gradient (ITG) threshold a...
Huixing Li; Yu Liu
2016-01-01
In order to investigate the characteristics of boiling heat transfer for hydrocarbon mixture refrigerant in plate-fin heat exchanger which is used in the petrochemical industry field, a model was established on boiling heat transfer in vertical rectangular channel. The simulated results were compared with the experimental data from literature. The results show that the deviation between the simulated results and experimental data is within ±15%. Meanwhile, the characteristic of boiling heat t...
Energy Technology Data Exchange (ETDEWEB)
Triplett, C.E.
1996-12-01
This thesis presents the results of an experimental investigation of natural convection heat transfer in a staggered array of heated cylinders, oriented horizontally within a rectangular enclosure. The main purpose of this research was to extend the knowledge of heat transfer within enclosed bundles of spent nuclear fuel rods sealed within a shipping or storage container. This research extends Canaan`s investigation of an aligned array of heated cylinders that thermally simulated a boiling water reactor (BWR) spent fuel assembly sealed within a shipping or storage cask. The results are presented in terms of piecewise Nusselt-Rayleigh number correlations of the form Nu = C(Ra){sup n}, where C and n are constants. Correlations are presented both for individual rods within the array and for the array as a whole. The correlations are based only on the convective component of the heat transfer. The radiative component was calculated with a finite-element code that used measured surface temperatures, rod array geometry, and measured surface emissivities as inputs. The correlation results are compared to Canaan`s aligned array results and to other studies of natural convection in horizontal tube arrays.
International Nuclear Information System (INIS)
Triplett, C.E.
1996-12-01
This thesis presents the results of an experimental investigation of natural convection heat transfer in a staggered array of heated cylinders, oriented horizontally within a rectangular enclosure. The main purpose of this research was to extend the knowledge of heat transfer within enclosed bundles of spent nuclear fuel rods sealed within a shipping or storage container. This research extends Canaan's investigation of an aligned array of heated cylinders that thermally simulated a boiling water reactor (BWR) spent fuel assembly sealed within a shipping or storage cask. The results are presented in terms of piecewise Nusselt-Rayleigh number correlations of the form Nu = C(Ra) n , where C and n are constants. Correlations are presented both for individual rods within the array and for the array as a whole. The correlations are based only on the convective component of the heat transfer. The radiative component was calculated with a finite-element code that used measured surface temperatures, rod array geometry, and measured surface emissivities as inputs. The correlation results are compared to Canaan's aligned array results and to other studies of natural convection in horizontal tube arrays
International Nuclear Information System (INIS)
Sugano, Y.
1980-01-01
The transient thermal stresses in an orthotropic finite rectangular plate due to arbitrary surface heat-generations on two edges are studied by means of the Airy stress function. The purposes of this paper are to present a method of determing the transient thermal stresses in an orthographic rectangular plate with four edges of distinct thermal boundary condition of the third kind which exactly satisfy the traction-free conditions of shear stress over all boundaries including four corners of the plate, and to consider the effects of the anisotropies of material properties and the convective heat transfer on the upper and lower surfaces on the thermal stress distribution. (orig.)
Directory of Open Access Journals (Sweden)
Huixing Li
2016-05-01
Full Text Available In order to investigate the characteristics of boiling heat transfer for hydrocarbon mixture refrigerant in plate-fin heat exchanger which is used in the petrochemical industry field, a model was established on boiling heat transfer in vertical rectangular channel. The simulated results were compared with the experimental data from literature. The results show that the deviation between the simulated results and experimental data is within ±15%. Meanwhile, the characteristic of boiling heat transfer was investigated in vertical rectangular minichannel of plate-fin heat exchanger. The results show that the boiling heat transfer coefficient increases with the increase in quality and mass flux and is slightly impacted by the heat flux. This is because that the main boiling mechanism is forced convective boiling while the contribution of nucleate boiling is slight. The correlation of Liu and Winterton is in good agreement with the simulation results. The deviation between correlation calculations and simulation results is mostly less than ±15%. These results will provide some constructive instructions for the understanding of saturated boiling mechanism in a vertical rectangular minichannel and the prediction of heat transfer performance in plate-fin heat exchanger.
Heat transfer in a compact heat exchanger containing rectangular channels and using helium gas
Olson, D. A.
1991-01-01
Development of a National Aerospace Plane (NASP), which will fly at hypersonic speeds, require novel cooling techniques to manage the anticipated high heat fluxes on various components. A compact heat exchanger was constructed consisting of 12 parallel, rectangular channels in a flat piece of commercially pure nickel. The channel specimen was radiatively heated on the top side at heat fluxes of up to 77 W/sq cm, insulated on the back side, and cooled with helium gas flowing in the channels at 3.5 to 7.0 MPa and Reynolds numbers of 1400 to 28,000. The measured friction factor was lower than that of the accepted correlation for fully developed turbulent flow, although the uncertainty was high due to uncertainty in the channel height and a high ratio of dynamic pressure to pressure drop. The measured Nusselt number, when modified to account for differences in fluid properties between the wall and the cooling fluid, agreed with past correlations for fully developed turbulent flow in channels. Flow nonuniformity from channel-to-channel was as high as 12 pct above and 19 pct below the mean flow.
Natural convection heat transfer in a rectangular pool with volumetric heat sources
International Nuclear Information System (INIS)
Lee, Seung Dong; Lee, Kang Hee; Suh, Kune Y.
2003-01-01
Natural convection plays an important role in determining the thermal load from debris accumulated in the reactor vessel lower head during a severe accident. The heat transfer within the molten core material can be characterized by buoyancy-induced flows resulting from internal heating due to decay of fission products. The thermo-fluid dynamic characteristics of the molten pool depend strongly on the thermal boundary conditions. The spatial and temporal variation of heat flux on the pool wall boundaries and the pool superheat are mainly characterized by the natural convection flow inside the molten pool. In general, natural convection involving internal heat generation is delineated in terms of the modified Rayleigh number, Ra', which quantifies the internal heat source and hence the strength of buoyancy. The test section is of rectangular cavity whose length, width, and height are 500 mm, 80 mm, and 250 mm, respectively. A total of twenty-four T-type thermocouples were installed in the test loop to measure temperature distribution. Four T-type thermocouples were utilized to measure temperatures on the boundary. A direct heating method was adopted in this test to simulate the uniform heat generation. The experiments covered a range of Rayleigh number, Ra, between 4.87x10 7 and 2.32x10 14 and Prandtl number, Pr, between 0.7 and 3.98. Tests were conducted with water and air as simulant. The upper and lower boundary conditions were maintained at a uniform temperature of 10degC. (author)
Investigating the Structures of Turbulence in a Multi-Stream, Rectangular, Supersonic Jet
Magstadt, Andrew S.
Supersonic flight has become a standard for military aircraft, and is being seriously reconsidered for commercial applications. Engine technologies, enabling increased mission capabilities and vehicle performance, have evolved nozzles into complex geometries with intricate flow features. These engineering solutions have advanced at a faster rate than the understanding of the flow physics, however. The full consequences of the flow are thus not known, and using predictive tools becomes exceedingly difficult. Additionally, the increasing velocities associated with supersonic flight exacerbate the preexisting jet noise problem, which has troubled the engineering community for nearly 65 years. Even in the simplest flows, the full consequences of turbulence, e.g. noise production, are not fully understood. For composite flows, the fluid mechanics and acoustic properties have been studied even less sufficiently. Before considering the aeroacoustic problem, the development, structure, and evolution of the turbulent flow-field must be considered. This has prompted an investigation into the compressible flow of a complex nozzle. Experimental evidence is sought to explain the stochastic processes of the turbulent flow issuing from a complex geometry. Before considering the more complicated configuration, an experimental campaign of an axisymmetric jet is conducted. The results from this study are presented, and guide research of the primary flow under investigation. The design of a nozzle representative of future engine technologies is then discussed. Characteristics of this multi-stream rectangular supersonic nozzle are studied via time-resolved schlieren imaging, stereo PIV measurements, dynamic pressure transducers, and far-field acoustics. Experiments are carried out in the anechoic chamber at Syracuse University, and focus primarily on the flow-field. An extensive data set is generated, which reveals a detailed view of a very complex flow. Shear, shock waves, unequal
Critical heat flux of subcooled flow boiling in narrow rectangular channels
International Nuclear Information System (INIS)
Kureta, Masatoshi; Akimoto, Hajime
1999-01-01
In relation to the high-heat-load devices such as a solid-target cooling channel of a high-intensity neutron source, burnout experiments were performed to obtain critical heat flux (CHF) data systematically for vertical upward flow in one-side heated rectangular channels. One of the objectives of this study was to study an extensibility of existing CHF correlations and models, which were proposed for a round tube, to rectangular channels for design calculation. Existing correlations and models were reviewed and compared with obtained data. Sudo's thin liquid layer dryout model, Griffel correlation and Bernath correlation were in good agreement with the experimental data for short-heated-length and low inlet water temperature conditions. (author)
Screech Tones from Rectangular Jets with Spanwise Oblique Shock-Cell Structures
Raman, Ganesh
1996-01-01
Understanding screech is especially important for the design of advanced aircraft because screech can cause sonic fatigue failure of aircraft structures. Although the connection between shock-cell spacing and screech frequency is well understood, the relation between non-uniformities in the shock-cell structures and the resulting amplitude, mode, and steadiness of screech have remained unexplored. This paper addresses the above issues by intentionally producing spanwise (larger nozzle dimension) variations in the shock-cell structures and studying the resulting spanwise screech mode. The spanwise oblique shock-cell structures were produced using imperfectly expanded convergent-divergent rectangular nozzles (aspect ratio = 5) with nonuniform exit geometries. Three geometries were studied: (a) a nozzle with a spanwise uniform edge, (b) a nozzle with a spanwise oblique (single bevelled) edge, and (c) a nozzle that had two spanwise oblique (double bevelled) cuts to form an arrowhead-shaped nozzle. For all nozzles considered, the screech mode was antisymmetric in the transverse (smaller nozzle dimension) direction allowing focus on changes in the spanwise direction. Three types of spanwise modes were observed: symmetric (1), antisymmetric (2), and oblique (3). The following significant results emerged: (1) for all cases the screech mode corresponds with the spanwise shock-cell structure, (2) when multiple screech modes are present, the technique presented here makes it possible to distinguish between coexisting and mutually exclusive modes, (3) the strength of shocks 3 and 4 influences the screech source amplitude and determines whether screech is unsteady. The results presented here offer hope for a better understanding of screech and for tailoring shock-containing jets to minimize fatigue failure of aircraft components.
Present status of heat transfer in narrow gap rectangular channel
International Nuclear Information System (INIS)
Sudo, Yukio; Kaminaga, Masanori
1990-01-01
In the safety evaluation for research nuclear reactors, at the time of abnormal transient change and accidents, after the tripping of a primary coolant pump, such event that the flow direction of coolant in a core reverses from steady downward flow to rising flow is supposed. In this case, the coexisting convection field, in which free convection and forced convection coexist, arises in place of forced convection, and especially in the research reactors using plate type fuel like JRR-3, it is important to grasp the heat transfer characteristics in the coexisting convection field in a narrow channel. Jackson et al. proposed the heat transfer correlation equation which can be applied to wide conditions including the coexisting convection zone, but its applicability to a narrow channel has not been confirmed. Based on the experimental results, in this study, the effect that the decrease of gap exerts to the convection heat transfer characteristics reported so far was investigated. The experiment and the results are reported. In this experiment on the coexisting convection zone in a narrow gap, the effect of main flow acceleration arose sufficiently large as compared with the effect of buoyancy, and heat transfer was promoted. (K.I.)
Kostichev, P. I.; Poddubnyi, I. I.; Razuvanov, N. G.
2017-11-01
In some DEMO blanket designs liquid metal flows in vertical ducts of rectangular cross-section between ceramic breeder units providing their cooling. Heat exchange in these conditions is governed by the influence of magnetic field (coplanar) and by buoyancy effects that depend on the flow orientation to the gravity vector (downward and upward flow). Magnetohydrodynamic and heat transfer of liquid metal in vertical rectangular ducts is not well researched. Experimental study of buoyancy effects in rectangular duct with coplanar magnetic field for one-sided heat load and downward and upward flowsis presented in this paper. The detail research with has been done on mercury MHD close loop with using of the probe technique allow to discover several advantageous and disadvantageous effects. The intensive impact of buoyancy force has been observed in a few regime of downward flow which has been laminarized by magnetic field. Due to the development in the flow of the secondary large-scale vortices heat transfer improved and the temperature fluctuations of the abnormally high intensity have been fixed. On the contrary, in the upward flow the buoyancy force stabilized the flow which lead to decreasing of the turbulence heat transfer ratio and, consequently, deterioration of heat transfer.
Review of Critical Heat Flux Correlations for Upward Flow in a Vertical Thin Rectangular Channel
Energy Technology Data Exchange (ETDEWEB)
Choi, Gil Sik; Chang, Soon Heung [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)
2014-05-15
From the view point of safety, this type of fuel has higher resistance to earthquake and external impact. The cross section of coolant flow channel in the reactor core composed with the plate fuel is a thin rectangular shape. Thermal-hydraulic characteristics of this thin rectangular channel are different with those of general circular rod fuel bundle flow channel. Accordingly it could be thought that the CHF correlation in a thin rectangular channel is different with that in a circular channel, for which a large number of researches on CHF prediction have been carried out. The objective of this paper is to review previous researches on CHF in a thin rectangular channel, summarize the important conclusion and propose the new simple CHF correlation, which is based on the data set under high pressure and high flow rate condition. The researches on CHF in rectangular channel have been partially carried out according to the pressure, heated surface number, heated surface wettability effect, flow driving force and flow direction conditions. From the literature researches on CHF for upward flow in a vertical thin rectangular channel, some CHF prediction methods were reviewed and compared. There is no universal correlation which can predict CHF at all conditions, but generally, Katto empirical correlation is known to be useful at high pressure and high flow rate. The new simple correlation was developed from the restricted data set, the CHF prediction capacity of which is better than that of Katto. Even though the prediction consistency of the new simple correlation is lower, MAE and RMS error decreased quite. For the more development of the new simple CHF correlation, the more advanced regression analysis method and theoretical analysis should be studied in future.
Review of Critical Heat Flux Correlations for Upward Flow in a Vertical Thin Rectangular Channel
International Nuclear Information System (INIS)
Choi, Gil Sik; Chang, Soon Heung
2014-01-01
From the view point of safety, this type of fuel has higher resistance to earthquake and external impact. The cross section of coolant flow channel in the reactor core composed with the plate fuel is a thin rectangular shape. Thermal-hydraulic characteristics of this thin rectangular channel are different with those of general circular rod fuel bundle flow channel. Accordingly it could be thought that the CHF correlation in a thin rectangular channel is different with that in a circular channel, for which a large number of researches on CHF prediction have been carried out. The objective of this paper is to review previous researches on CHF in a thin rectangular channel, summarize the important conclusion and propose the new simple CHF correlation, which is based on the data set under high pressure and high flow rate condition. The researches on CHF in rectangular channel have been partially carried out according to the pressure, heated surface number, heated surface wettability effect, flow driving force and flow direction conditions. From the literature researches on CHF for upward flow in a vertical thin rectangular channel, some CHF prediction methods were reviewed and compared. There is no universal correlation which can predict CHF at all conditions, but generally, Katto empirical correlation is known to be useful at high pressure and high flow rate. The new simple correlation was developed from the restricted data set, the CHF prediction capacity of which is better than that of Katto. Even though the prediction consistency of the new simple correlation is lower, MAE and RMS error decreased quite. For the more development of the new simple CHF correlation, the more advanced regression analysis method and theoretical analysis should be studied in future
Burnout in a high heat flux boiling system with forced supply of liquid through a plane jet
International Nuclear Information System (INIS)
Katto, Yoshiro; Ishii, Kazunori.
1978-01-01
As for pool boiling, the non-dimensional formula for the burnout heat flux of a simple, basic boiling system has been obtained. On the other hand, in forced convection boiling, the studies on the burnout in forced flow boiling in a channel have been continued, but the derivation of a non-dimensional formula applicable generally is far away from the realization because the phenomena are too complex. Accordingly, in this study, the result of the experiment on the burnout of a boiling system to which liquid is supplied by the plane jet flowing out of a thin rectangular nozzle installed near the front edge of a rectangular heating surface is reported. The experimental apparatus is described, and the experiment was carried out in the ranges of two jet thicknesses at the nozzle outlet, two incident angles of jet and from 1.5 to 15 m/s of jet velocity. Burnout occurs under the situation of sufficiently developed nuclear boiling. A part of the liquid supplied from a plane jet is blown apart by the vapor blowing out of the nuclear boiling liquid layer covering the heating surface in the nuclear boiling with sufficiently developed high heat flux. However, the nuclear boiling liquid layer itself continues to exist on the heating surface till burnout occurs. Only the entering velocity of the plane jet affects burnout heat flux. (Kako, I.)
Comparison of air-standard rectangular cycles with different specific heat models
International Nuclear Information System (INIS)
Wang, Chao; Chen, Lingen; Ge, Yanlin; Sun, Fengrui
2016-01-01
Highlights: • Air-standard rectangular cycle models are built and investigated. • Finite-time thermodynamics is applied. • Different dissipation models and variable specific heats models are adopted. • Performance characteristics of different cycle models are compared. - Abstract: In this paper, performance comparison of air-standard rectangular cycles with constant specific heat (SH), linear variable SH and non-linear variable SH are conducted by using finite time thermodynamics. The power output and efficiency of each cycle model and the characteristic curves of power output versus compression ratio, efficiency versus compression ratio, as well as power output versus efficiency are obtained by taking heat transfer loss (HTL) and friction loss (FL) into account. The influences of HTL, FL and SH on cycle performance are analyzed by detailed numerical examples.
International Nuclear Information System (INIS)
Zhang Yanlai; Rao Zhonghao; Wang Shuangfeng; Zhang Zhao; Li Xiuping
2012-01-01
Highlights: ► It gives heat transfer characteristics in a rectangular heat storage tank as the basic unit for reservoir of thermal storage. ► Onset of natural convection gets easier for the MPCMS with a higher mass concentration. ► It enhances the heat transfer ability of natural convection for the MPCMS. ► Obtained the relationship between Ra and Nu of the MPCMS. - Abstract: The main purpose of this experiment is to evaluate natural convection heat transfer characteristics of microencapsulated PCM (phase change material) slurry (MPCMS) during phase change process in a rectangular heat storage tank heated from the bottom and cooled at the top. The microencapsulated PCM is several material compositions of n-paraffin waxes (mainly nonadecane) as the core materials, outside a layer of a melamine resin wrapped. In the present study, its slurry is used mixing with water. And the specific heat capacity with latent heat shows a peak value at the temperature of about T = 31 °C. We investigate the influences of the phase change process of the MPCMS on natural convection heat transfer. The experimental results indicate that phase change process of the MPCMS promote natural convection heat transfer. The local maximum heat transfer enhancement occurs at approximately T H = 34 °C corresponding to the heated plate temperature. With high mass concentration C m , the onset of natural convection gets easier for the MPCMS. The temperature gradient is larger near top plate and bottom plate of a rectangular heat storage tank. Heat transfer coefficient increases with the phase change of the PCM. And it summarizes that the phase change process of the PCM promote the occurrence of natural convection.
International Nuclear Information System (INIS)
Choi, Hang Seok; Park, Tae Seon
2013-01-01
Highlights: ► With changing aspect ratio, the effect of secondary flows on the turbulent heat transfer is scrutinized by a LES. ► The conditional sampling technique of instantaneous near-wall streamwise vortices is developed. ► Clockwise and counter-clockwise rotating streamwise vortices are sampled and discussed with the wall heat transfer. ► The hot-sweep motions of CW and CCW vortices clearly appear with increasing aspect ratio. -- Abstract: The effect of aspect ratio of rectangular duct on the turbulent flow and heat transfer is very important for its engineering applications. But the turbulent thermal fields have not been fundamentally scrutinized in spite of its engineering significance especially for cooling device. Hence, in the present study, large eddy simulation is applied to the turbulent flow and heat transfer in rectangular ducts with varying aspect ratio. The turbulent statistics of the flow and thermal quantities are calculated and the characteristics of wall Nusselt number are investigated for each rectangular duct. Especially, to scrutinize near-wall streamwise vortices, a conditional sampling technique is developed and adopted. Clockwise and counter-clockwise rotating streamwise vortices are sampled and the probability density function of the vortex circulation Reynolds number and wall Nusselt number are calculated. From the results, the time-averaged secondary flow caused by instantaneous vortical motions has a great effect on the heat and momentum transport of the flow in the rectangular ducts. Hence, the wall Nusselt number is enhanced near the downwash flow region of the secondary flow. However, with increasing the aspect ratio, the effects of the hot-sweep flow of the clockwise and counter-clockwise rotating vortices become equally dominant near the wall normal bisector of the ducts. During time averaging process, these two counter-rotating vortices are canceled out each other diminishing a secondary flow but they still enhance the
Study on critical heat flux based on wavelet transform in rectangular narrow channels
International Nuclear Information System (INIS)
Zhou Tao; Ju Zhongyun; Zhang Lei; Li Jingjing; Sheng Cheng; Xiao Zejun
2014-01-01
Critical heat flux is very important for the safety of nuclear reactor, and observing temperature rise rate is a feasible method. The wavelet transform is used to analyze the CHF temperature rise curves in rectangular narrow channels, which can remove relative weaker interference and effectively judge CHF. Rectangular narrow channel can strengthen heat transfer and reduce CHF, whose characteristics are proved by temperature rise curves analyzed by wavelet transform. Respectively applying Daubechies function and Haar function is to guarantee the accuracy of the wavelet analysis, and Daubechies function is more accurate than Haar function in the detail signal processing from results. While the wavelet analysis and experimental results are compared and found in good agreement with the experimental results. (authors)
Study on critical heat flux based on wavelet transform in rectangular narrow channels
International Nuclear Information System (INIS)
Zhou Tao; Ju Zhongyun; Zhang Lei; Li Jingjing; Sheng Cheng; Xiao Zejun
2014-01-01
Critical heat flux is very important for nuclear reactor safety, and observing temperature rise rate is a feasible method. Through using the wavelet transform to analyze the CHF temperature rise curves in rectangular narrow channels, it can remove relative weaker interference and effectively judge CHF. Rectangular narrow channel can strengthen heat transfer and reduce CHF, whose characteristics are proved by, temperature rise curves analyzed by wavelet transform. Respectively applying Daubechies function and Haar function is for guarantee the accuracy of the wavelet analysis, and Daubechies function is more accurate than Haar function in the detail signal processing from results. While the wavelet analysis and experimental results are compared and found in good agreement with the experimental results. (authors)
Forced convective boiling heat transfer of water in vertical rectangular narrow channel
International Nuclear Information System (INIS)
Chen, Chong; Gao, Pu-zhen; Tan, Si-chao; Chen, Han-ying; Chen, Xian-bing
2015-01-01
Highlights: • Chen correlation cannot well predict the coefficient of rectangular channel. • Kim and Mudawar correlation is the best one among the Chen type correlations. • Lazarek and Black correlation predicted 7.0% of data within the ±30% error band. • The new correlation can well predict the coefficient with a small MAE of 14.4%. - Abstract: In order to research the characteristics of boiling flows in a vertical rectangular narrow channel, a series of convective boiling heat transfer experiments are performed. The test section is made of stainless steel with an inner diameter of 2 × 40 mm and heated length of 1100 mm. The 3194 experimental data points are obtained for a heat flux range of 10–700 kW/m 2 , a mass flux range of 200–2400 kg/m 2 s, a system pressure range of 0.1–2.5 MPa, and a quality range of 0–0.8. Eighteen prediction models are used to predict the flow boiling heat transfer coefficient of the rectangular narrow channel and the predicted value is compared against the database including 3194 data points, the results show that Chen type correlations and Lazarek and Black type correlations are not suitable for the rectangular channel very much. The Kim and Mudawar correlation is the best one among the 18 models. A new correlation is developed based on the superposition concept of nucleate boiling and convective boiling. the new correlation is shown to provide a good prediction against the database, evidenced by an overall MAE of 14.4%, with 95.2% and 98.6% of the data falling within ±30% and ±35% error bands, respectively
A Green's function solution for a rectangular heat source on an infinite plate
International Nuclear Information System (INIS)
Bainbridge, B.L.
1989-01-01
The applications associated with a rectangular heat source on an infinite plate range from integrated circuits to thin film heat flux sensors on thin substrates. The particular problem from which the solution is developed concerns the use of a resistive strip for monitoring currents generated in circuits exposed to electromagnetic fields. The Green's function formulation is solved by using early and late time approximations for which analytical solutions can be derived. In this paper expressions are developed for three sets of boundary conditions and compared to the experimental performance of a physical device
Premature and stable critical heat flux for downward flow in a narrow rectangular channel
International Nuclear Information System (INIS)
Lee, Juhyung; Chang, Soon Heung; Jeong, Yong Hoon; Jo, Daeseong
2014-01-01
It has been recommended that RRs and MTRs be designed to have sufficient margins for CHF and the onset of FI as well, since unstable flow could leads to premature CHF under very low wall heat flux in comparison to stable CHF. Even the fact and previous studies, however, the understanding of relationship among FI, premature CHF and stable CHF is not sufficient to date. In this regards, subcooled flow boiling in a vertical rectangular channel was experimentally investigated to enhance the understanding of the CHF and the effect of the two-phase flow instability on it under low pressure conditions, especially for downward flow which was adopted for Jordan Research and Training Reactor (JRTR) and Kijang research reactor (KJRR) to achieve easier fuel and irradiation rig loading. In this study, CHF for downward flow of water under low pressure in narrow rectangular channel was experimentally investigated. For conditions such as downward flow, narrow rectangular channel and low pressure, it has been deduced from literature that flow instability could largely influence on triggering CHF at lower heat flux, i. e. premature CHF. Total 54 CHF data, which includes premature and stable data was obtained for various fluid conditions and system configurations including inlet stiffness. The upper and lower boundaries of CHF were newly proposed based on the experiment
Energy Technology Data Exchange (ETDEWEB)
Kim, Sin-Yeob; Shin, Dong-Ho; Park, Goon-Cherl; Cho, Hyoung Kyu [Seoul National Univ., Seoul (Korea, Republic of); Kim, Chan-Soo [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2016-10-15
VHTR being developed at Korea Atomic Energy Research Institute adopts an air-cooled Reactor Cavity Cooling System (RCCS) incorporating rectangular riser channels to remove the afterheat emitted from the reactor vessel. Because the performance of RCCS is determined by heat removal rate through the RCCS riser, it is important to understand the heat transfer phenomena in the RCCS riser to ensure the safety of the reactor. In the mixed convection, due to the buoyance force induced by temperature and density differences, local flow structure and heat transfer mode near the heated wall have significantly dissimilar characteristics from both forced convection and free convection. In this study, benchmark calculation was conducted to reproduce the previous statements that V2F turbulence model can capture the mixed convection phenomena with the Shehata's experimental data. Then, the necessity of the model validation for the mixed convection phenomena was confirmed with the CFD analyses for the geometry of the prototype RCCS riser. For the purpose of validating the turbulence models for mixed convection phenomena in the heated rectangular riser duct, validation plan with three experimental tests was introduced. Among them, the flow visualization test facility with preserved cross-section geometry was introduced and a preliminary test result was shown.
MHD and heat transfer benchmark problems for liquid metal flow in rectangular ducts
International Nuclear Information System (INIS)
Sidorenkov, S.I.; Hua, T.Q.; Araseki, H.
1994-01-01
Liquid metal cooling systems of a self-cooled blanket in a tokamak reactor will likely include channels of rectangular cross section where liquid metal is circulated in the presence of strong magnetic fields. MHD pressure drop, velocity distribution and heat transfer characteristics are important issues in the engineering design considerations. Computer codes for the reliable solution of three-dimensional MHD flow problems are needed for fusion relevant conditions. Argonne National Laboratory and The Efremov Institute have jointly defined several benchmark problems for code validation. The problems, described in this paper, are based on two series of rectangular duct experiments conducted at ANL; one of the series is a joint ANL/Efremov experiment. The geometries consist of variation of aspect ratio and wall thickness (thus wall conductance ratio). The transverse magnetic fields are uniform and nonuniform in the axial direction
Progress in understanding heat transport at JET
International Nuclear Information System (INIS)
Mantica, P.; Garbet, X.; Angioni, C.
2005-01-01
This paper reports recent progress in understanding heat transport mechanisms either in conventional or advanced tokamak scenarios in JET. A key experimental tool has been the use of perturbative transport techniques, both by ICH power modulation and by edge cold pulses. The availability of such results has allowed careful comparison with theoretical modelling using 1D empirical or physics based transport models, 3D fluid turbulence simulations or gyrokinetic stability analysis. In conventional L- and H-mode plasmas the issue of temperature profile stiffness has been addressed. JET results are consistent with the concept of a critical inverse temperature gradient length above which transport is enhanced by the onset of turbulence. A threshold value R/L Te ∼5 has been found for the onset of stiff electron transport, while the level of electron stiffness appears to vary strongly with plasma parameters, in particular with the ratio of electron and ion heating: electrons become stiffer when ions are strongly heated, resulting in larger R/L Ti values. This behaviour has also been found theoretically, although quantitatively weaker than in experiments. In plasmas characterized by Internal Transport Barriers (ITB), the properties of heat transport inside the ITB layer and the ITB formation mechanisms have been investigated. The plasma current profile is found to play a major role in ITB formation. The effect of negative magnetic shear on electron and ion stabilization is demonstrated both experimentally and theoretically using turbulence codes. The role of rational magnetic surfaces in ITB triggering is well assessed experimentally, but still lacks a convincing theoretical explanation. Attempts to trigger an ITB by externally induced magnetic reconnection using saddle coils have shown that MHD islands in general do not produce a sufficient variation of ExB flow shear to lead to ITB formation. First results of perturbative transport in ITBs show that the ITB is a narrow
On the prediction of single-phase forced convection heat transfer in narrow rectangular channels
International Nuclear Information System (INIS)
Ghione, Alberto; Noel, Brigitte; Vinai, Paolo; Demazière, Christophe
2014-01-01
In this paper, selected heat transfer correlations for single-phase forced convection are assessed for the case of narrow rectangular channels. The work is of interest in the thermal-hydraulic analysis of the Jules Horowitz Reactor (JHR), which is a research reactor under construction at CEA-Cadarache (France). In order to evaluate the validity of the correlations, about 300 tests from the SULTAN-JHR database were used. The SULTAN-JHR program was carried out at CEA-Grenoble and it includes different kinds of tests for two different vertical rectangular channels with height of 600 mm and gap of 1.51 and 2.16 mm. The experimental conditions range between 2 - 9 bar for the pressure; 0.5 - 18 m/s for the coolant velocity and 0.5 - 7.5 MW/m 2 for the heat flux (whose axial distribution is uniform). Forty-two thermocouples and eight pressure taps were placed at several axial locations, measuring wall temperature and pressure respectively. The analysis focused on turbulent flow with Reynolds numbers between 5.5 x 10 3 - 2.4 x 10 5 and Prandtl numbers between 1.5 - 6. It was shown that standard correlations as the Dittus-Boelter and Seider-Tate significantly under-estimate the heat transfer coefficient, especially at high Reynolds number. Other correlations specifically designed for narrow rectangular channels were also taken into account and compared. The correlation of Popov-Petukhov in the form suggested by Siman-Tov still under-estimates the heat transfer coefficient, even if slight improvements could be seen. A better agreement for the tests with gap equal to 2.16 mm could be found with the correlation of Ma and the one of Liang. However the heat transfer coefficient when the gap is equal to 1.51 mm could not be predicted accurately. Furthermore these correlations were based on data at low Reynolds numbers (up to 13000) and low heat flux, so the use of them for SULTAN-JHR may be questionable. According to the authors’ knowledge, existing models of heat transfer
International Nuclear Information System (INIS)
Seki, Nobuhiro; Fukusako, Shoichiro; Inaba, Hideo
1978-01-01
In the present study the behavior of heat transfer in a rectangular cavity with one isothermal vertical wall heated and the other cooled is investigated. Heat transfer coefficients on the vertical walls are measured for fluids with Prandtl number Pr of 3 to 40,000 in case of aspect-ratio H/W from 5 to 47.5 and their correlated results are presented for laminar, transition and turbulent regions, respectively. It is shown that the present arrangement (Nu sub(H) - Ra sub(H)) using the height of cavity as a representative length may significantly be useful in the various heat transfer modes accompanied with flow patterns of them. (auth.)
Laminar turbulent transition in heated free jet
International Nuclear Information System (INIS)
Krejci, L.; Marsik, F.; Nenicka, V.
1998-01-01
The evolution of heat and mass transfer in the initial region of a transitional plasma plume is investigated and discussed. The results show that these transport processes are controlled and limited by the plume shear layer instability. The process of laminar-turbulent transition is consecutively controlled by the plume core shear layer instability where interrelation of the effective thickness of the shear temperature and density layers play decisive role. When the absolute instability occurs the resonances in the jet and arc chamber must be taken into account. These processes are manifested in three events. Between the first and second phase, there is a maximum of arc heater exit average enthalpy. The other two thresholds occur at maximum and minimum stagnation heat flux from the plume core. It seems that these processes also influence the thermal energy production in the arc chamber cavity. (author)
DEFF Research Database (Denmark)
Jensen, Michael Vincent; Walther, Jens Honore
2013-01-01
was investigated at a jet Reynolds number of 1.66 × 105 and a temperature difference between jet inlet and wall of 1600 K. The focus was on the convective heat transfer contribution as thermal radiation was not included in the investigation. A considerable influence of the turbulence intensity at the jet inlet...... to about 100% were observed. Furthermore, the variation in stagnation point heat transfer was examined for jet Reynolds numbers in the range from 1.10 × 105 to 6.64 × 105. Based on the investigations, a correlation is suggested between the stagnation point Nusselt number, the jet Reynolds number......, and the turbulence intensity at the jet inlet for impinging jet flows at high jet Reynolds numbers. Copyright © 2013 Taylor and Francis Group, LLC....
Electron heating in JET by ICRH
International Nuclear Information System (INIS)
Cordey, J.G.; Christiansen, J.P.; Core, W.G.F.; Cotrell, G.A.; Eriksson, L.G.; Kovanen, M.A.; Lomas, P.; Start, D.F.H.; Taroni, A.; Tibone, F.
1991-01-01
Several ICRH experiments carried out on JET during the period 1988-90 have been directed specifically at raising the electron temperature to a high value by maximizing the total input power per particle (P tot /n). It has been found that the electron temperature saturates around 12-14 keV in sharp contrast to NBI ion heating experiments in which ion temperatures exceed 25 keV. Initial calculations suggested that this saturation was due to strongly enhanced transport in the central region. It is shown in this paper that the saturation is due to a lack of heating in the plasma center. The power input to electrons in an ICRF minority heating scheme is mainly via collisional transfer from the minority fast ions and a main problem is to maintain a peaked profile of fast ions. In the present experiments the highest fast ion energy content 4MJ has been achieved with a He 3 minority scheme, the equivalent fast ion toroidal β is 8%; electron temperatures in the range 11-14 keV are attained in these pulses. There are several possible physical effects that can give rise to the broadening of the fast ion radial profile: sawteeth, fishbones, fast ion finite orbit effects and Alfven or drift wave turbulence driven by the large gradients of fast ion pressure (discussed in section IV). The existence of such phenomena in many JET pulses means that the calculation of the power input profile by codes which contain purely classical collisional processes can be misleading. Hence an alternative approach is developed in section II; the measured fast ion energy is used directly to evaluate the power input to the central region; the scaling of the electron temperature with the actual power per particle can therefore be determined (section III). (author) 6 refs., 5 figs
Critical heat flux for free convection boiling in thin rectangular channels
International Nuclear Information System (INIS)
Cheng, Lap Y.; Tichler, P.R.
1991-01-01
A review of the experimental data on free convection boiling critical heat flux (CHF) in vertical rectangular channels reveals three mechanisms of burnout. They are the pool boiling limit, the circulation limit, and the flooding limit associated with a transition in flow regime from churn to annular flow. The dominance of a particular mechanism depends on the dimensions of the channel. Analytical models were developed for each free convection boiling limit. Limited agreement with data is observed. A CHF correlation, which is valid for a wide range of gap sizes, was constructed from the CHFs calculated according to the three mechanisms of burnout. 17 refs., 7 figs
Oscillating-flow loss test results in rectangular heat exchanger passages
Wood, J. Gary
1991-01-01
Test results of oscillating flow losses in rectangular heat exchanger passages of various aspect ratios are given. This work was performed in support of the design of a free-piston Stirling engine (FPSE) for a dynamic space power conversion system. Oscillating flow loss testing was performed using an oscillating flow rig, which was based on a variable stroke and variable frequency linear drive motor. Tests were run over a range of oscillating flow parameters encompassing the flow regimes of the proposed engine design. Test results are presented in both tabular and graphical form and are compared against analytical predictions.
Solution of the two- dimensional heat equation for a rectangular plate
Directory of Open Access Journals (Sweden)
Nurcan BAYKUŞ SAVAŞANERİL
2015-11-01
Full Text Available Laplace equation is a fundamental equation of applied mathematics. Important phenomena in engineering and physics, such as steady-state temperature distribution, electrostatic potential and fluid flow, are modeled by means of this equation. The Laplace equation which satisfies boundary values is known as the Dirichlet problem. The solutions to the Dirichlet problem form one of the most celebrated topics in the area of applied mathematics. In this study, a novel method is presented for the solution of two-dimensional heat equation for a rectangular plate. In this alternative method, the solution function of the problem is based on the Green function, and therefore on elliptic functions.
Stability and contraction of a rectangular liquid metal jet in a vacuum environment
International Nuclear Information System (INIS)
Konkachbaev, A.I.; Morley, N.B.; Gulec, K.; Sketchley, T.
2000-01-01
Hydrodynamic similarity criteria and experimental data are reported here from experiments underway at UCLA that simulate the slab jets of the HYLIFE-II inertial fusion reactor. The current experimental setup produces a 2x20 mm slab jet, and reaches a maximum Reynolds number 5x10 4 , corresponding to a jet velocity of 12 m/s. A high-speed camera is used to obtain and analyze data. Two major phenomena are observed, the inversion (axis-switching) of the slab jet owing to surface tension and corner vortices; and surface waves due to turbulent velocity profile relaxation. The main purpose of this series of experiments is the study of the rapid inversion (almost 50% of the jet over the length of interest) seen in previous experiments. It is shown here that this was due to secondary flows caused by features of orifice nozzle design. Current experiments show an inversion length considerably in excess of analytic correlations based on 2-D inviscid theory. For parameters approaching HYLIFE-II jets, inversion length is shown to be more than several hundred non-dimensional lengths
Microwave pre-heating of natural rubber using a rectangular wave guide (MODE: TE10
Directory of Open Access Journals (Sweden)
Doo-ngam, N.
2007-11-01
Full Text Available This paper presents an application of microwave radiation for pre-heating of natural rubbercompounding with various sulphur contents. The natural rubber-compounding was pre-heated by microwave radiation using a rectangular wave guide system (MODE: TE10 operating at frequency of 2.45 GHz in which the power can vary from 0 to 1500 W. In the present work, the influence of power input, sample thickness, and sulphur content were examined after applying microwave radiation to the rubber samples. Results are discussed regarding the thermal properties, 3-D network, dielectric properties and chemical structures. From the result, firstly, it was found that microwave radiation can be applied to pre-heating natural rubber-compounding before the vulcanization process. Secondly, microwave radiation was very useful for pre-heating natural rubber-compounding that has a thickness greater than 5mm. Thirdly, crosslinking in natural rubber-compounding may occurs after pre-heating by microwave radiation though Fourier Transform Infrared Spectroscopy(FTIR. Finally, there a little effect of sulphur content on temperature profiles after applying microwave radiation to the natural rubber-compounding. Moreover, natural rubber-compounding without carbon black showed a lower heat absorption compared with natural rubbercompounding filled carbon black. This is due to the difference in dielectric loss factor. This preliminary result will be useful information in terms of microwave radiation for pre-heating natural rubber-compounding and rubber processing in industry.
Two dimensional heat transfer problem in flow boiling in a rectangular minichannel
Directory of Open Access Journals (Sweden)
Hożejowska Sylwia
2015-01-01
Full Text Available The paper presents mathematical modelling of flow boiling heat transfer in a rectangular minichannel asymmetrically heated by a thin and one-sided enhanced foil. Both surfaces are available for observations due to the openings covered with glass sheets. Thus, changes in the colour of the plain foil surface can be registered and then processed. Plain side of the heating foil is covered with a base coat and liquid crystal paint. Observation of the opposite, enhanced surface of the minichannel allows for identification of the gas-liquid two-phase flow patterns and vapour quality. A two-dimensional mathematical model of heat transfer in three subsequent layers (sheet glass, heating foil, liquid was proposed. Heat transfer in all these layers was described with the respective equations: Laplace equation, Poisson equation and energy equation, subject to boundary conditions corresponding to the observed physical process. The solutions (temperature distributions in all three layers were obtained by Trefftz method. Additionally, the temperature of the boiling liquid was obtained by homotopy perturbation method (HPM combined with Trefftz method. The heat transfer coefficient, derived from Robin boundary condition, was estimated in both approaches. In comparison, the results by both methods show very good agreement especially when restricted to the thermal sublayer.
Effect of the configuration of the corner in a narrow rectangular channel on flow and heat transfer
International Nuclear Information System (INIS)
Xu Jianjun; Chen Bingde; Wang Xiaojun
2009-01-01
In order to further understand the effect of the configuration of the corner in a narrow rectangular channel on flow and heat transfer, flow field and temperature field in a narrow rectangular channel were numerical simulated by using CFD code CFX10.0. The results show under the condition of equal quantity of heat of solid which is obtained by decreasing the solid of the corner, the distributions of inside wall temperature for the orthogonal and circular type configurations of the corner are almost the same as that of the archetypal configuration, and those can simulate heat transfer of the archetypal con- figuration. Under the condition of equal Re, secondary flow and friction pressure of the orthogonal type configuration are almost the same as those of the circular type configuration, which shows that the circular type configuration of the corner in a narrow channel can substituted for the archetypal configuration to simulate flow and heat transfer in a narrow rectangular channel. (authors)
Directory of Open Access Journals (Sweden)
Fengming Wang
2012-12-01
Full Text Available The flow and heat transfer characteristics inside a rectangular channel embedded with pin fins were numerically and experimentally investigated. Several differently shaped pin fins (i.e., circular, elliptical, and drop-shaped with the same cross-sectional areas were compared in a staggered arrangement. The Reynolds number based on the obstructed section hydraulic diameter (defined as the ratio of the total wetted surface area to the open duct volume available for flow was varied from 4800 to 8200. The more streamlined drop-shaped pin fins were better at delaying or suppressing separation of the flow passing through them, which decreased the aerodynamic penalty compared to circular pin fins. The heat transfer enhancement of the drop-shaped pin fins was less than that of the circular pin fins. In terms of specific performance parameters, drop-shaped pin fins are a promising alternative configuration to circular pin fins.
Khan, Md Imran; Billah, Md. Mamun; Rahman, Mohammed Mizanur; Hasan, Mohammad Nasim
2017-12-01
Numerical simulation of steady two-dimensional heat transfer in a rectangular channel with a centered variable speed cylinder has been performed in this paper. In this setup, an isoflux heater is placed at the bottom wall of the channel while the upper wall is kept isothermal with a low temperature. The cylinder's peripheral speed to maximum inlet fluid velocity ratio (ξ) is varied from 0.5 to 1.5 for both clockwise and anticlockwise rotational cases. Air has been considered as working fluid while other system parameters such as Grashof and Reynolds numbers are varied. The effects of rotational speed, Grashof and Reynolds numbers on the streamline pattern, isothermal lines, local and average Nusselt number are analyzed and presented. It is observed the cylinder's rotational direction and speed has a significant effect on the flow pattern, temperature distribution as well as heat transfer characteristics.
International Nuclear Information System (INIS)
Sturgis, J.C.; Mudawar, I.
1999-01-01
An experimental study was undertaken to examine the enhancement in critical heat flux (CHF) provided by streamwise curvature. Curved and straight rectangular flow channels were fabricated with identical 5.0 x 2.5 mm cross sections and heated lengths of 101.6 mm in which the heat was applied to only one wall--the concave wall (32.3 mm radius) in the curved channel and a side wall in the straight. Tests were conducted using FC-72 liquid with mean inlet velocity and outlet subcooling of 0.25 to 10 m s -1 and 3 to 29 C, respectively. Centripetal acceleration for curved flow reached 315 times earth's gravitational acceleration. Critical heat flux was enhanced due to flow curvature at all conditions but the enhancement decreased with increasing subcooling. For near-saturated conditions, the enhancement was approximately 60% while for highly subcooled flow it was only 20%. The causes for the enhancement were identified as (1) increased pressure on the liquid-vapor interface at wetting fronts, (2) buoyancy forces and (3) increased subcooling at the concave wall. Flow visualization tests were conducted in transparent channels to explore the role of buoyancy forces in enhancing the critical heat flux. These forces were observed to remove vapor from the concave wall and distribute it throughout the cross section. Vapor removal was only effective at near-saturated conditions, yielding the observed substantial enhancement in CHF relative to the straight channel
Hydrodynamics and Heat Transfer in Flow over Rectangular Ribs on the Initially Smooth Surface
Directory of Open Access Journals (Sweden)
V. N. Afanasiev
2017-01-01
Full Text Available An efficiency of the heat exchange equipment and reducing their weight and size parameters can be considerably improved by using the optimal methods of heat transfer enhancement, which include a two-dimensional roughness, i.e. ribs, backward-facing steps, cavities, etc. deposited on the heat transfer surface. Their shape, sizes and positional relationship have a significant impact on the structure of the boundary layer and its exchange processes.As known, the most affordable and effective method of controlled influence on the structure of turbulent flow is to create a separation zone or other organized vortex structure in it. In order to successfully use the separation zone, it is necessary to know the mechanism of their interaction with the main turbulent flow and the mechanism of the process in separation zone itself. Heat transfer enhancement is provided mainly due to roughness impact on hydrodynamics of turbulent flow, if the rib height h does not exceed the thickness of the viscous sublayer, since heat transfer enhancement arises from breaking and destruction of viscous sublayer produced by the roughness ribs and emerging vortex zones – sources of turbulence. Usually, the height of ribs y+ ≈ 50, and the distance between them along the streamlined surface is 10-20 times greater. The coefficient of friction also increases, but if the height of ribs is sufficiently small and most of them are in the sublayer, the increase of the friction factor will not exceed the increase of the heat transfer coefficient.The paper presents results of experimental investigation of hydrodynamics and heat transfer in the separation zone before and after a rib and in the area of two rectangular ribs with the height of y+ £ 60. The ribs are placed on the flat plate and heated according to the law of qw = const. The structure of turbulent boundary layer from the standpoint of the universal logarithmic law of velocity distribution has been experimentally
Single-phase liquid jet impingement heat transfer
International Nuclear Information System (INIS)
Webb, B.W.; Ma, C.F.
1995-01-01
Impinging liquid jets have been demonstrated to be an effective means of providing high heat/mass transfer rates in industrial transport processes. When a liquid jet strikes a surface, thin hydrodynamic and thermal boundary layers from in the region directly beneath due to the jet deceleration and the resulting increase in pressure. The flow is then forced to accelerate in a direction parallel to the target surface in what is termed the wall jet or parallel flow zone. The thickness of the hydrodynamic and thermal boundary layers in the stagnation region may be of the order of tens of micrometers. Consequently, very high heat/mass transfer coefficients exist in the stagnation zone directly under the jet. Transport coefficients characteristic of parallel flow prevail in the wall jet region. The high heat transfer coefficients make liquid jet impingement an attractive cooling option where high heat fluxes are the norm. Some industrial applications include the thermal treatment of metals, cooling of internal combustion engines, and more recently, thermal control of high-heat-dissipation electronic devices. Both circular and planar liquid jets have attracted research attention. 180 refs., 35 figs., 11 tabs
Intraseasonal relationships between tropical heating and extratropical jets
Neith, Michael T.
1992-01-01
Approved for public release; distribution is unlimited Intraseasonal variations of the northern midlatitude circulation and their relationships with the global tropical heating field are investigated using climate model fields. The greatest intraseasonal variance in the midlatitude flow is found in the vicinity of the time mean jets, and in the areas immediately downstream of these jet exits. The model kinetic energy field associated with these jets shows a clear 30-60 day variation and ...
International Nuclear Information System (INIS)
Sridhar, S.; Faghri, M.; Lessmann, R.C.
1990-01-01
Experiments have been carried out to study thermal wake effects in arrays of rectangular blocks encountered in electronic equipment. Data were obtained for a series of channel heights and flow velocities. The temperature rise due to wake effects behind a single heated module was found to be fairly independent of the channel height and the position of the heated block, for a given approach velocity. The adiabatic temperature rise data for a module due to a heated element immediately upstream of it for different inter-module spacings were found to correlate well in terms of a new parameter called the surface packing density. This paper reports that it was reported by the authors in an earlier paper that both the adiabatic heat transfer coefficient nd pressure-drop data for regular in-line arrays correlated well in terms of a composite geometric parameter called the column packing density. These experiments have been extended to a higher Reynolds number. Empirical correlations are presented here for friction factor and Nusselt number in terms of the volume packing density, and for the thermal wake effects in terms of the surface packing density. Data from literature for arrays with widely different geometric parameters are shown to agree with these correlations
Heat transfer and friction characteristics in steam cooled rectangular channels with rib turbulators
Energy Technology Data Exchange (ETDEWEB)
Gong, Jianying; Gao, Tieyu; Li, Guojun [Xi' an Jiaotong University, Xi' an (China)
2014-01-15
We studied the heat transfer and friction characteristics in steam-cooled rectangular channels with rib turbulators on W side or H side walls in the Reynolds number (Re) range of 10000-80000. Each of the test channels was welded by four stainless steel plates to simulate the actual geometry and heat transfer structure of blade/vane internal cooling passage. The length of the channel L was 1000 mm, the cross section of the channel was 40 mm X 80 mm, and the pitch-to-rib height ratio p/e was kept at 10. The channel blockage ratio (W/H) was 0.047. Results showed that the Nusselt number (Nu) distributions displayed different trends at the entrance region with the increase of Re for the rib turbulators on the W side walls. The heat transfer performance of the rib turbulators on the H side walls was about 24- 27% higher than that on the W side walls at the same pumping power. In addition, semi-empirical correlations for the two cases, rib turbulators on W side walls and rib turbulators on H side walls, were developed based on the heat transfer results, which could be used in the design of the internal cooling passage of new generation steam-cooled gas turbine blade/vane.
Heat Transfer Augmentation in Gas Turbine Blade Rectangular Passages Using Circular Ribs with Fins
Directory of Open Access Journals (Sweden)
Mohammed W. Al-Jibory
2017-11-01
Full Text Available In this paper, an experimental system was designed and built to simulate conditions in the gas turbine blade cooling and run the experimental part. Boundary conditions are: inlet coolant air temperature is 300K with Reynolds numbers (Re=7901 .The surrounding constant hot air temperatures was (673 K.The numerical simulations were done by using software FLUENT version (14.5, in this part, it was presented the effect of using circular ribs having middle fin fitted in rectangular passage channel on fluid flow and heat transfer characteristics. Ribs used with pitch-rib height of 10, rectangular channel of (30x60 mm cross section, 1.5 mm duct thickness and 0.5 m long. The temperature, velocity distribution contours, cooling air temperature distribution at the duct centerline, the inner wall surface temperature of the duct, and thermal performance factor are presented in this paper. it can be seen that the duct with all ribs with middle fins was the better case which leads to increase the coolant air temperature by (10.22 % and decrease the inner wall temperature by (6.15 % . The coolant air flow velocity seems to be accelerated and decelerated through the channel in the presence of ribs, so it was shown that the thermal performance factor along the duct is larger than 1, this is due to the fact that the ribs create turbulent conditions and increasing thermal surface area, and thus increasing heat transfer coefficient than the smooth channel.
Heat and mass transfers in the jets; Transferts de chaleur et de masse dans les jets
Energy Technology Data Exchange (ETDEWEB)
NONE
2001-07-01
This day on the heat and mass transfers in the jets, was organized by the SFT (French Society of Thermic) to present the state of the art in the domain. Fifteen presentations allowed the participants to discuss about turbulent flows, simulation of fluid flow and jets impacts. (A.L.B.)
Single phase flow pressure drop and heat transfer in rectangular metallic microchannels
International Nuclear Information System (INIS)
Sahar, Amirah M.; Özdemir, Mehmed R.; Fayyadh, Ekhlas M.; Wissink, Jan; Mahmoud, Mohamed M.; Karayiannis, Tassos G.
2016-01-01
Numerical simulations were performed using Fluent 14.5 to investigate single phase flow and conjugate heat transfer in copper rectangular microchannels. Two different configurations were simulated: (1) single channel with hydraulic diameter of 0.561 mm and (2) multichannel configuration consisting of inlet and outlet manifolds and 25 channels with hydraulic diameter of 0.409 mm. In the single channel configuration, four numerical models were investigated namely, 2D thin-wall, 3D thin-wall (heated from the bottom), 3D thin-wall (three side heated) and 3D full conjugate models. In the multichannel configuration, only 3D full conjugate model was used. The simulation results of the single channel configuration were validated using experimental data of water as a test fluid while the results of the multichannel configuration were validated using experimental data of R134a refrigerant. In the multichannel configuration, flow distribution among the channels was also investigated. The 3D thin-wall model simulation was conducted at thermal boundary conditions similar to those assumed in the experimental data reduction (uniform heat flux) and showed excellent agreement with the experimental data. However, the results of the 3D full conjugate model demonstrated that there is a significant conjugate effect and the heat flux is not uniformly distributed along the channel resulting in significant deviation compared to the experimental data (more than 50%). Also, the results demonstrated that there is a significant difference between the 3D thin-wall and full conjugate models. The simulation of the multichannel configuration with an inlet manifold having gradual decrease in cross sectional area achieved very reasonable uniform flow distribution among the channels which will provide uniform heat transfer rates across the base of the microchannels.
Mansoor, Mohammad M.
2012-02-01
A 3D-conjugate numerical investigation was conducted to predict heat transfer characteristics in a rectangular cross-sectional micro-channel employing simultaneously developing single-phase flows. The numerical code was validated by comparison with previous experimental and numerical results for the same micro-channel dimensions and classical correlations based on conventional sized channels. High heat fluxes up to 130W/cm 2 were applied to investigate micro-channel thermal characteristics. The entire computational domain was discretized using a 120×160×100 grid for the micro-channel with an aspect ratio of (α=4.56) and examined for Reynolds numbers in the laminar range (Re 500-2000) using FLUENT. De-ionized water served as the cooling fluid while the micro-channel substrate used was made of copper. Validation results were found to be in good agreement with previous experimental and numerical data [1] with an average deviation of less than 4.2%. As the applied heat flux increased, an increase in heat transfer coefficient values was observed. Also, the Reynolds number required for transition from single-phase fluid to two-phase was found to increase. A correlation is proposed for the results of average Nusselt numbers for the heat transfer characteristics in micro-channels with simultaneously developing, single-phase flows. © 2011 Elsevier Ltd.
Analytical solutions of heat transfer for laminar flow in rectangular channels
Directory of Open Access Journals (Sweden)
Rybiński Witold
2014-12-01
Full Text Available The paper presents two analytical solutions namely for Fanning friction factor and for Nusselt number of fully developed laminar fluid flow in straight mini channels with rectangular cross-section. This type of channels is common in mini- and microchannel heat exchangers. Analytical formulae, both for velocity and temperature profiles, were obtained in the explicit form of two terms. The first term is an asymptotic solution of laminar flow between parallel plates. The second one is a rapidly convergent series. This series becomes zero as the cross-section aspect ratio goes to infinity. This clear mathematical form is also inherited by the formulae for friction factor and Nusselt number. As the boundary conditions for velocity and temperature profiles no-slip and peripherally constant temperature with axially constant heat flux were assumed (H1 type. The velocity profile is assumed to be independent of the temperature profile. The assumption of constant temperature at the channel’s perimeter is related to the asymptotic case of channel’s wall thermal resistance: infinite in the axial direction and zero in the peripheral one. It represents typical conditions in a minichannel heat exchanger made of metal.
Experimental study of heat transfer in a heat exchanger with rectangular channels
International Nuclear Information System (INIS)
Hammami, Mahmoud; Ben Said, Akrem; Ben Maad, Rejeb; Rebay, Mourad
2009-01-01
This paper presents the results of an experimental study related to characterisation of a mini channel heat exchanger. Such heat exchanger may be used in water cooling of electronic components. The results obtained show the efficiency of this exchanger even with very low water flow rates. Indeed, in spite of the importance of the extracted heat fluxes which can reach about 50Kw/m 2 , the temperature of the cooled Aluminium bloc remained always lower than the tolerated threshold of 80 degree in electronic cooling. Moreover, several thermal characteristics such as equivalent thermal resistance of the exchanger, the average internal convective heat transfer coefficient and the increase in the temperature of the cooling water have been measured. The results presented have been obtained with in q uinconce r ectangular mini-channel heat exchanger, with a hydraulic diameter D h = 2mm. NOMENCLATURE h D Hydraulic diameter (mm). int
Enhanced heat sink with geometry induced wall-jet
Energy Technology Data Exchange (ETDEWEB)
Hossain, Md. Mahamudul, E-mail: sohel0991@gmail.com; Tikadar, Amitav; Bari, Fazlul; Morshed, A. K. M. M. [Department of Mechanical Engineering Bangladesh University of Engineering and Technology, Dhaka-1000. Bangladesh (Bangladesh)
2016-07-12
Mini-channels embedded in solid matrix have already proven to be a very efficient way of electronic cooling. Traditional mini-channel heat sinks consist of single layer of parallel channels. Although mini-channel heat sink can achieve very high heat flux, its pumping requirement for circulating liquid through the channel increase very sharply as the flow velocity increases. The pumping requirements of the heat sink can be reduced by increasing its performance. In this paper a novel approach to increase the thermal performance of the mini-channel heat sink is proposed through geometry induced wall jet which is a passive technique. Geometric irregularities along the channel length causes abrupt pressure change between the channels which causes cross flow through the interconnections thus one channel faces suction and other channel jet action. This suction and jet action disrupts boundary layer causing enhanced heat transfer performance. A CFD model has been developed using commercially available software package FLUENT to evaluate the technique. A parametric study of the velocities and the effect of the position of the wall-jets have been performed. Significant reduction in thermal resistance has been observed for wall-jets, it is also observed that this reduction in thermal resistance is dependent on the position and shape of the wall jet.
Zeeshan, Mohd; Hazarika, Saheera Azmi; Nath, Sujit; Bhanja, Dipankar
2017-07-01
In the present work, a 3-D numerical investigation has been performed to explore the effect of attack angles on the thermal-hydraulic performance of fin and tube heat exchanger (FTHE) using rectangular winglet pairs (RWPs). RWPs are placed adjacent to the tubes and three attack angels are considered for the study i.e. 5°, 15° and 25°. The effect of attack angles are examined on the heat transfer characteristics as well as in pressure drop penalty with airside Reynolds number Rea ranges from 500 to 900. Two performance evaluation criteria namely PEC1 i.e. area goodness factor (j/f) and PEC2 i.e. heat transfer rate per unit fan power consumption (Q/Pf) are considered for the performance evaluation. Furthermore, MOORA method is applied to obtain the performance order of FTHE configurations by taking PEC1 and PEC2 as beneficial attributes and fan power Pf as a non-beneficial attribute, keeping equal importance to each attribute. The results show that 5° attack angle provides the better performance in terms of PEC1 as heat transfer coefficient is increased by 27.70% at Rea=500 and 32.73% at Rea=900 respectively with 13.01% increased pressure drop penalty at Rea=500 and 14.26% at Rea=900 respectively. In terms of PEC2, though the 5° attack angle provides the high values of Q/Pf factor among the 15° and 25° attack angles, but it is found insignificant to replace the baseline configuration i.e. plain fin and tube heat exchanger configuration without vortex generators. Moreover, in MOORA optimization analysis also, it is found that 5° attack angle provides the better thermal-hydraulic performance.
Patil, Harshal Bhauso; Dingare, Sunil Vishnu
2018-03-01
Heat exchange upgrade is a vital territory of research area. Utilization of reasonable systems can bring about noteworthy specialized points of interest coming about reserve funds of cost. Rectangular plates are viewed as best balance arrangement utilized for heat exchange improvement. This gives an enlargement strategy to heat exchange with beginning of limit layer and vortex development. To assess and look at the rate of heat exchange enhancement by rectangular plate fins with differing inclinations (0°-30°-60°), shifting Re and heat supply under forced convection are the principle destinations of this study. The study is done by fluctuating introductions of fins with various inclinations, input heat supply and Re under forced convection. The coefficient of heat transfer increments observed with the expansion in air speed for all the examined designs. The coefficient of the heat transfer is discovered higher at the edge of introduction of fins at 30° for inline arrangement and 0° for staggered arrangement. Looking at both the arrangements, it is discovered that the heat transfer coefficient in 0° fin staggered arrangement is about 17% higher than 30° inline arrangement and 76% higher than the vertical plate fin. For plate fin heat sink, boundary layer formation and growth results in decrease of the coefficient of heat transfer in forced convection. This issue is overcome by accommodating some rectangular fins on the plate fin. It brings about increment of heat transfer coefficient of the RPFHS under the states of trial factors. As indicated by past research, it is discovered that examination of the plate fin heat sink with various sorts of fins for horizontal orientation is done yet but this investigation expects to discover the upgrade of transfer coefficient of plate fin heat sink for its vertical position with rectangular plates at different inclinations under the shifting scopes of heat input supply, fin arrangements and Reynolds number (Re).
International Nuclear Information System (INIS)
Gori, Fabio; Petracci, Ivano; Angelino, Matteo
2014-01-01
Highlights: • Flow with Negligible Disturbances, or first type, with length L ND = L 1 . • Flow with Small Disturbances, or second type, with length L SD . • Total length, L ND + L SD = L 2 , is in agreement with average Undisturbed flow, L U . • Flow with Coherent Vortices, or third type, with length L CV . • Total length, L ND + L SD + L CV = L 3 , is in agreement with average Potential core, L P . - Abstract: The paper is aimed at investigating the influence of the Reynolds number on the instant flow evolution of a rectangular free jet of air in the range of Reynolds numbers from Re = 35,300 to Re = 2,200, where the Reynolds number, Re, is defined according to the hydraulic diameter, D, of a rectangular slot of height H, equal to about D = 2H. The Particle Image Velocimetry (PIV) technique allows obtaining the instant PIV visualizations on the central symmetry section of the rectangular jet. The visual inspection of the instant frames with one and two vortices, except for Re = 35,300 where only one vortex images are detected, shows that after the jet exit is present the Flow with Constant Instant Height, with a length L CIH which increases with the decrease of the Reynolds number, from a ratio L CIH /H equal to L CIH /H = 0.9 at Re = 35,300 to L CIH /H = 4.0 at Re = 2,200. The instant PIV measurements, carried out at several distances from the jet exit, show that the variations of the ratio U/U ‾ 0 of the centerline instant velocity, U, to the exit average velocity, U ‾ 0 , remain below ±4% for a length L CIV , defining the Flow with Constant Instant Velocity on the centerline. The ratio L CIV /H increases from L CIV /H = 1.1 at Re = 35,300 to L CIV /H = 4.1 at Re = 2,200 and is quite similar to L CIH /H. The instant PIV measurements of the centerline turbulence intensity, Tu, show that its variations remain below ±4% for a length L CIT , defining the Flow with Constant Instant Turbulence on the centerline. The ratio L CIT /H is equal to L CIV /H
Increasing heat transfer of non-Newtonian nanofluid in rectangular microchannel with triangular ribs
Shamsi, Mohammad Reza; Akbari, Omid Ali; Marzban, Ali; Toghraie, Davood; Mashayekhi, Ramin
2017-09-01
In this study, computational fluid dynamics and the laminar flow of the non-Newtonian fluid have been numerically studied. The cooling fluid includes water and 0.5 wt% Carboxy methyl cellulose (CMC) making the non-Newtonian fluid. In order to make the best of non-Newtonian nanofluid in this simulation, solid nanoparticles of Aluminum Oxide have been added to the non-Newtonian fluid in volume fractions of 0-2% with diameters of 25, 45 and 100 nm. The supposed microchannel is rectangular and two-dimensional in Cartesian coordination. The power law has been used to speculate the dynamic viscosity of the cooling nanofluid. The field of numerical solution is simulated in the Reynolds number range of 5 nanoparticles as well as the use for nanoparticles with smaller diameters lead to greater heat transfer. Among all the studied forms, the triangular rib from with an angle of attack 30° has the biggest Nusselt number and the smallest pressure drop along the microchannel. Also, an increase in the angle of attack and as a result of a sudden contact between the fluid and the ribs and also a reduction in the coflowing length (length of the rib) cause a cut in heat transfer by the fluid in farther parts from the solid wall (tip of the rib).
Critical heat flux of forced flow boiling in a narrow one-side heated rectangular flow channel
Energy Technology Data Exchange (ETDEWEB)
Limin, Zheng [Shanghai Nuclear Engineering Research and Design Inst., SH (China); Iguchi, Tadashi; Kureta, Masatoshi; Akimoto, Hajime
1997-08-01
The present work deals with the critical heat flux (CHF) under subcooled flow boiling in a narrow one-side uniformly heated rectangular flow channel. The range of interest of parameters such as pressure, flow velocity and subcooling is around 0.1 MPa, 5-15 ms{sup -1} and 50degC, respectively. The rectangular flow channel used is 50 mm long, 12 mm in width and 0.2 to 3 mm in height. Test conditions were selected by combination of the following parameters: Gap=0.2-3.0 mm (D{sub hy}=0.3934-4.8 mm); flow length, 50.0 mm; water mass flux, 4.94-14.82 Mgm{sup -2}s{sup -1} (water flow velocity, 5-15 ms{sup -1}); exit pressure, 0.1 MPa; inlet temperature, 50degC, inlet coolant subcooling, 50degC. Over 40 CHF stable data points were obtained. CHF increased with the gap and flow velocity in a non-linear fashion. HTC increased with flow velocity and decreasing gap. Based on the experimental results, an empirical correlation was developed, indicating the dependence of CHF on the gap and flow velocity. All of data points predicted within {+-}18% error band for the present experimental data. On the other hand, another similitude-based correlation was also developed, indicating the dependence of Boiling number (Bo) on Reynolds number (Re) and the variable of Gap/La, where La is a characteristic length known as Laplace capillary constant. For the limited present experimental data, all of data points were predicted within {+-}16%. (author)
Critical heat flux of forced flow boiling in a narrow one-side heated rectangular flow channel
International Nuclear Information System (INIS)
Zheng Limin; Iguchi, Tadashi; Kureta, Masatoshi; Akimoto, Hajime.
1997-08-01
The present work deals with the critical heat flux (CHF) under subcooled flow boiling in a narrow one-side uniformly heated rectangular flow channel. The range of interest of parameters such as pressure, flow velocity and subcooling is around 0.1 MPa, 5-15 ms -1 and 50degC, respectively. The rectangular flow channel used is 50 mm long, 12 mm in width and 0.2 to 3 mm in height. Test conditions were selected by combination of the following parameters: Gap=0.2-3.0 mm (D hy =0.3934-4.8 mm); flow length, 50.0 mm; water mass flux, 4.94-14.82 Mgm -2 s -1 (water flow velocity, 5-15 ms -1 ); exit pressure, 0.1 MPa; inlet temperature, 50degC, inlet coolant subcooling, 50degC. Over 40 CHF stable data points were obtained. CHF increased with the gap and flow velocity in a non-linear fashion. HTC increased with flow velocity and decreasing gap. Based on the experimental results, an empirical correlation was developed, indicating the dependence of CHF on the gap and flow velocity. All of data points predicted within ±18% error band for the present experimental data. On the other hand, another similitude-based correlation was also developed, indicating the dependence of Boiling number (Bo) on Reynolds number (Re) and the variable of Gap/La, where La is a characteristic length known as Laplace capillary constant. For the limited present experimental data, all of data points were predicted within ±16%. (author)
Turbulent flow and heat transfer from a slot jet impinging on a moving plate
International Nuclear Information System (INIS)
Chattopadhyay, Himadri; Saha, Sujoy K.
2003-01-01
The flow field due to an impinging jet over a moving surface at a moderately high Reynolds number, emanating from a rectangular slot nozzle has been computed using the large eddy simulation technique. A dynamic subgrid-scale stress model has been used for the small scales of turbulence. The velocity of the impinging surface perpendicular to the jet velocity has been varied up to two times the jet velocity at the nozzle exit. Turbulence quantities such as kinetic energy, production rate of turbulent kinetic energy and the Reynolds stresses are calculated for different surface velocities. It has been observed that, while the turbulent kinetic energy increases with increasing velocity of the impinging surface, production rate of turbulence initially increases with increasing surface velocity and then comes down. By analyzing the components of turbulent production it was found that P 33 is the dominant term up to the surface velocity of one unit and when the surface velocity is two times the jet velocity at the nozzle exit, the major contribution to turbulence production comes from P 13 and partly from P 11 . Heat transfer from the plate initially increases with non-dimensional surface velocity up to 1.2 and then comes down
International Nuclear Information System (INIS)
Felker, B.; Calderon, M.O.; Chargin, A.K.
1983-01-01
The electron-cyclotron-resonant heating (ECRH) systems of rectangular waveguides on Tandem Mirror Experiment-Upgrade (TMX-U) operated with a overall efficiency of 50%, each system using a 28-GHz, 200-kW pulsed gyrotron. We designed and built four circular-waveguide systems with greater efficiency and greater power-handling capabilities to replace the rectangular waveguides. Two of these circular systems, at the 5-kG second-harmonic heating locations, have a total transmission efficiency of >90%. The two systems at the 10-kG fundamental heating locations have a total transmission efficiency of 80%. The difference in efficiency is due to the additional components required to launch the microwaves in the desired orientation and polarization with respect to magnetic-field lines at the 10-kG points. These systems handle the total power available from each gyrotron but do not have the arcing limitation problem of the rectangular waveguide. Each system requires several complex components. The overall physical layout and the design considerations for the rectangular and circular waveguide components are described here
Energy Technology Data Exchange (ETDEWEB)
Felker, B.; Calderon, M.O.; Chargin, A.K.; Coffield, F.E.; Lang, D.D.; Rubert, R.R.; Pedrotti, L.R.; Stallard, B.W.; Gallagher, N.C. Jr.; Sweeney, D.W.
1983-11-18
The electron-cyclotron-resonant heating (ECRH) systems of rectangular waveguides on Tandem Mirror Experiment-Upgrade (TMX-U) operated with a overall efficiency of 50%, each system using a 28-GHz, 200-kW pulsed gyrotron. We designed and built four circular-waveguide systems with greater efficiency and greater power-handling capabilities to replace the rectangular waveguides. Two of these circular systems, at the 5-kG second-harmonic heating locations, have a total transmission efficiency of >90%. The two systems at the 10-kG fundamental heating locations have a total transmission efficiency of 80%. The difference in efficiency is due to the additional components required to launch the microwaves in the desired orientation and polarization with respect to magnetic-field lines at the 10-kG points. These systems handle the total power available from each gyrotron but do not have the arcing limitation problem of the rectangular waveguide. Each system requires several complex components. The overall physical layout and the design considerations for the rectangular and circular waveguide components are described here.
Heat transfer and flow structure evaluation of a synthetic jet emanating from a planar heat sink
International Nuclear Information System (INIS)
Manning, Paul; Persoons, Tim; Murray, Darina
2014-01-01
Direct impinging synthetic jets are a proven method for heat transfer enhancement, and have been subject to extensive research. However, despite the vast amount of research into direct synthetic jet impingement, there has been little research investigating the effects of a synthetic jet emanating from a heated surface, this forms the basis of the current research investigation. Both single and multiple orifices are integrated into a planar heat sink forming a synthetic jet, thus allowing the heat transfer enhancement and flow structures to be assessed. The heat transfer analysis highlighted that the multiple orifice synthetic jet resulted in the greatest heat transfer enhancements. The flow structures responsible for these enhancements were identified using a combination of flow visualisation, thermal imaging and thermal boundary layer analysis. The flow structure analysis identified that the synthetic jets decreased the thermal boundary layer thickness resulting in a more effective convective heat transfer process. Flow visualisation revealed entrainment of local air adjacent to the heated surface; this occurred from vortex roll-up at the surface of the heat sink and from the highly sheared jet flow. Furthermore, a secondary entrainment was identified which created a surface impingement effect. It is proposed that all three flow features enhance the heat transfer characteristics of the system.
Prediction of radiant heat flux from horizontal propane jet fire
International Nuclear Information System (INIS)
Zhou, Kuibin; Liu, Jiaoyan; Jiang, Juncheng
2016-01-01
Highlights: • Line source model for the radiant heat flux from horizontal jet fire is proposed. • A review on the difference between horizontal and vertical jet fires is conducted. • Effects of lift-off distance and flame shape are discussed for the line source model. • Line source model gives encouraging results relative to the validity of model system. - Abstract: Jet fires are often reported to occur in process industry with lots of hazardous heat energy released. A line source model describing the flame emissive power and subsequent heat flux radiated from a horizontal propane jet fire is evaluated through a testing against experimental fire data and comparison against other models. By a review on the jet flame behavior, the correlations of the lift-off distance, flame length and radiative fraction are proposed to close the line source model in theory. It is found that the fuel jet direction holds a considerable effect on the flame behavior by comparison between horizontal and vertical jet fires. Results indicate that the lift-off distance and the flame shape influence the model prediction to some extent. Comparison of model predictions against data collected in the near field and predictions from the point source model and multipoint source model gives encouraging results relative to the validity of model system.
International Nuclear Information System (INIS)
M Hadi Kusuma; Mulya Juarsa; Anhar Riza Antariksawan
2013-01-01
Boiling heat transfer phenomena on rectangular narrow gap was related to the safety of nuclear reactors. Research done in order to study the safety of nuclear reactors in particular relating to boiling heat transfer and useful on the improvement of next-generation reactor designs. The research focused on calculation of the heat flux during the cooling process in rectangular narrow gap size 1.0 mm. with initial temperatures 200°C. 400°C, and 600°C, also the flow rates of cooling water 0,1 liters/second. 0,2 liters/second. and 0,3 liters/second. Experiments carried out by injecting water at a certain flow rate with the water temperature 85°C. Transient temperature measurement data recorded by the data acquisition system. Transient temperature measurement data is used to calculate the flux of heat gain is then used to obtain the heat transfer coefficient. This research aimed to obtain the correlation between critical heat flux and heat transfer coefficient to changes in temperatures and water flow rates for bilaterally-heated cases on rectangular narrow gap. The results obtained for a constant cooling water flow rate, critical heat flux will increase when hot plate temperature also increased. While on a constant hot plate temperature, coefficient heat transfer will increase when cooling water flow rate also increased. Thus it can be said that the cooling water flow rate and temperature of the hot plate has a significant effect on the critical heat flux and heat transfer coefficient resulted in quenching process of vertical rectangular narrow gap with double-heated cases. (author)
Application of dynamic response analysis to JET heat pulse data
International Nuclear Information System (INIS)
Griguoli, A.; Sips, A.C.C.
1993-09-01
The plasma dynamic response can be used to study transport processes in a tokamak plasma. A method has been developed for the application of dynamic response analysis to study perturbations away from the plasma equilibrium. In this report perturbations on the electron temperature following a sawtooth collapse in the center of the plasma are considered. The method has been used to find mathematical description of a series of heat pulses at the Joint European Torus project (JET). From the plasma dynamic response, the time constants which characterise the heat pulse are obtained. These time constants are compared to the transport coefficients found in previous analysis of the JET heat pulse data. Various methods are discussed for applying dynamic response analysis to JET heat pulse data. (author)
International Nuclear Information System (INIS)
Claesson, J.; Probert, T.
1996-01-01
The temperature field in rock due to a large rectangular grid of heat releasing canisters containing nuclear waste is studied. The solution is by superposition divided into different parts. There is a global temperature field due to the large rectangular canister area, while a local field accounts for the remaining heat source problem. The global field is reduced to a single integral. The local field is also solved analytically using solutions for a finite line heat source and for an infinite grid of point sources. The local solution is reduced to three parts, each of which depends on two spatial coordinates only. The temperatures at the envelope of a canister are given by a single thermal resistance, which is given by an explicit formula. The results are illustrated by a few numerical examples dealing with the KBS-3 concept for storage of nuclear waste. 8 refs
Directory of Open Access Journals (Sweden)
Kadhum Audaa Jehhef
2015-09-01
Full Text Available Anumerical solutions is presented to investigate the effect of inclination angle (θ , perforation ratio (m and wall temperature of the plate (Tw on the heat transfer in natural convection from isothermal square flat plate up surface heated (with and without concentrated hole. The flat plate with dimensions of (128 mm length × (64 mm width has been used five with square models of the flat plate that gave a rectangular perforation of (m=0.03, 0.06, 0.13, 0.25, 0.5. The values of angle of inclination were (0o, 15o 30o 45o 60o from horizontal position and the values of wall temperature (50oC, 60 oC, 70 oC, 90 oC, 100oC. To investigate the temperature, boundary layer thickness and heat flux distributions; the numerical computation is carried out using a very efficient integral method to solve the governing equation. The results show increase in the temperature gradient with increase in the angle of inclination and the high gradient and high heat transfer coefficients located in the external edges of the plate, for both cases: with and without holed plate. There are two separation regions of heat transfer in the external edge and the internal edges. The boundary layer thickness is small in the external edge and high in the center of the plate and it decreases as the inclination angle of plate increases. Theoretical results are compared with previous result and it is found that the Nusslet numbers in the present study are higher by (22 % than that in the previous studies. And the results show good agreement in range of Raleigh number from 105 to 106.
Linear Stability Analysis of Flow in an Internally Heated Rectangular Duct
Energy Technology Data Exchange (ETDEWEB)
Uhlmann, M.
2004-07-01
The linear stability of flow in a vertical rectangular duct subject to homogeneous internal heating, constant-temperature no-slip walls and a driving pressure gradient is investigated numerically. A full Chebyshevbased Galerkin method is found to be more reliable than a collocation method, both including the elimination of the pressure and the stream wise velocity from the system of equations and making use of the full symmetry properties. A classification of the mean flow-obtained as a function of Grashof and Reynolds numbers and the geometrical aspect ratio in terms of its inflectional properties is proposed. It is found that the flow loses stability at all aspects rations for a combination of finite thermal buoyancy and pressure forces with opposed sings. In the square duct, the unstable region coincides with the range where additional inflection lines are observed the mean velocity profile. Unstable eigenfunctions are obtained for all basic symmetry modes and their structure can be described as slightly elongated pockets of cross-stream-vertical motion, training each other along the stream wise direction. (Author) 22 refs.
Energy Technology Data Exchange (ETDEWEB)
Lyczkowski, R. W. [Institute of Gas Technology, Chicago, IL (United States); Solbrig, C. W. [Commonwealth Edison Co., Chicago, IL (United States); Gidaspow, D. [Illinois Inst. of Technology, Chicago, IL (United States)
1980-01-01
A numerical solution for laminar flow heat transfer between a flowing gas and its containing rectangular duct has been obtained for many different boundary conditions. The problem has been solved for the cases of insulation on no walls, one wall, two walls, and three walls with various finite resistances on the remaining walls. Results have been obtained for several duct aspect ratios in the thermal entrance and in the fully developed regions, including the constant temperature cases. When one wall is insulated and the other three are at constant temperature, the maximum temperature occurs in the fluid rather than on the insulated wall. This maximum moves toward the insulated wall with increasing axial distance. Nusselt numbers for the same constant flux on all four walls with peripheral conduction lie in a narrow band bounded by zero and infinite peripheral conduction cases. A dimensionless wall conduction group of four can be considered infinite for the purpose of estimating fully developed Nusselt numbers to within an accuracy of 3%. A decrease in wall and bulk temperatures by finite wall conduction has been demonstrated for the case of a black body radiation boundary condition.
International Nuclear Information System (INIS)
Wang Junfeng; Huang Yanping; Wang Yanlin
2011-01-01
Highlights: → Specific points on the demand curve and flow patterns are visually studied. → Bubbly, churn, and annular flows were observed. → Onset of flow instability and bubbly-churn transition occurs at the same time. → The evolution of specific points and flow pattern transitions were examined. - Abstract: A simultaneous visualization and measurement study on some specific points on demand curves, such as onset of nucleate boiling (ONB), onset of significant void (OSV), onset of flow instability (OFI), and two-phase flow patterns in a single-side heated narrow rectangular channel, having a width of 40 mm and a gap of 3 mm, was carried out. New experimental approaches were adopted to identify OSV and OFI in a narrow rectangular channel. Under experimental conditions, the ONB could be predicted well by the Sato and Matsumura model. The OSV model of Bowring can reasonably predict the OSV if the single-side heated condition is considered. The OFI was close to the saturated boiling point and could be described accurately by Kennedy's correlation. The two-phase flow patterns observed in this experiment could be classified into bubbly, churn, and annular flow. Slug flow was never observed. The OFI always occurred when the bubbles at the channel exit began to coalesce, which corresponded to the beginning of the bubbly-churn transition in flow patterns. Finally, the evolution of specific points and flow pattern transitions were examined in a single-side heated narrow rectangular channel.
International Nuclear Information System (INIS)
Probert, T.; Claesson, Johan
1997-04-01
In the KBS-3 concept canisters containing nuclear waste are deposited along parallel tunnels over a large rectangular area deep below the ground surface. The temperature field in rock due to such a rectangular grid of heat-releasing canisters is studied. An analytical solution for this problem for any heat source has been presented in a preceding paper. The complete solution is summarized in this paper. The solution is by superposition divided into two main parts. There is a global temperature field due to the large rectangular canister area, while a local field accounts for the remaining heat source problem. In this sequel to the first report, the local solution is discussed in detail. The local solution consists of three parts corresponding to line heat sources along tunnels, point heat sources along a tunnel and a line heat source along a canister. Each part depends on two special variables only. These parts are illustrated in dimensionless form. Inside the repository the local temperature field is periodic in the horizontal directions and has a short extent in the vertical direction. This allows us to look at the solution in a parallelepiped around a canister. The solution in the parallelepiped is valid for all canisters that are not too close to the repository edges. The total temperature field is calculated for the KBS-3 case. The temperature field is calculated using a heat release that is valid for the first 10 000 years after deposition. The temperature field is shown in 23 figures in order to illustrate different aspects of the complex thermal process
International Nuclear Information System (INIS)
Choi, Gil Sik; Chang, Soon Heung; Jeong, Yong Hoon
2016-01-01
A study, on the theoretical method to predict the critical heat flux (CHF) of saturated upward flow boiling water in vertical narrow rectangular channels, has been conducted. For the assessment of this CHF prediction method, 608 experimental data were selected from the previous researches, in which the heated sections were uniformly heated from both wide surfaces under the high pressure condition over 41 bar. For this purpose, representative previous liquid film dryout (LFD) models for circular channels were reviewed by using 6058 points from the KAIST CHF data bank. This shows that it is reasonable to define the initial condition of quality and entrainment fraction at onset of annular flow (OAF) as the transition to annular flow regime and the equilibrium value, respectively, and the prediction error of the LFD model is dependent on the accuracy of the constitutive equations of droplet deposition and entrainment. In the modified Levy model, the CHF data are predicted with standard deviation (SD) of 14.0% and root mean square error (RMSE) of 14.1%. Meanwhile, in the present LFD model, which is based on the constitutive equations developed by Okawa et al., the entire data are calculated with SD of 17.1% and RMSE of 17.3%. Because of its qualitative prediction trend and universal calculation convergence, the present model was finally selected as the best LFD model to predict the CHF for narrow rectangular channels. For the assessment of the present LFD model for narrow rectangular channels, effective 284 data were selected. By using the present LFD model, these data are predicted with RMSE of 22.9% with the dryout criterion of zero-liquid film flow, but RMSE of 18.7% with rivulet formation model. This shows that the prediction error of the present LFD model for narrow rectangular channels is similar with that for circular channels.
Heat loss prediction of a confined premixed jet flame using a conjugate heat transfer approach
Gövert, S.; Mira, D.; Zavala-Ake, M.; Kok, J.B.W.; Vázquez, M.; Houzeaux, G.
2017-01-01
The presented work addresses the investigation of the heat loss of a confined turbulent jet flame in a lab-scale combustor using a conjugate-heat transfer approach and large-eddy simulation. The analysis includes the assessment of the principal mechanisms of heat transfer in this combustion chamber:
Prediction of critical heat flux in narrow rectangular channels using an artificial neural network
International Nuclear Information System (INIS)
Zhou Lei; Yan Xiao; Huang Yanping; Xiao Zejun; Yu Jiyang
2011-01-01
The concept of Critical heat flux (CHF) and its importance are introduced and the meaning to research CHF in narrow rectangular channels independently is emphasized. This paper is the first effort to predict CHF in NRCs using aritificial neural network. The mathematical structure of the artificial neural network and the error back-propagation algorithm are introduced. To predict CHF, the four dimensionless groups are inputted to the neural network and the output is the dimensionless CHF. As the hidden nodes increased, the training error decreases while the testing error decreases firstly and then transition occurs. Based on this, the hidden nodes are set as 5 and the trained network predicts all of the training and testing data points with RMS=0.0016 and μ=1.0003, which is better than several well-known existing correlations. Based on the trained network, the effect of several parameters on CHF are simulated and discussed. CHF increases almost linearly as the inlet subcooling increases. And larger mass flux enhances the effect of the inlet subcooling. CHF increases with the mass flux increasing. And the effect seems to be a little stronger for relatively low system pressure. CHF decreases almost linearly as the system pressure increases for the fixed inlet condition. The slope of the curve also increases with higher mass flux. This observation is limited to the ranges of the experimental database. CHF decreases as the heated length is increased and the gradients of the curves become very sharp for relatively short channel. CHF increases slightly with the diameter increasing with the variance of the gap limited within 1 to 3 mm. For relatively low mass flux, the effect of the equivalent diameter on CHF is insignificant. As the width of the channel is large enough, the effect of the gap is quite the same as that of the equivalent diameter. A BPNN is successfully trained based on near 500 CHF data points in NRCs, which has much better performances than the
Characterization of local heat fluxes around ICRF antennas on JET
Energy Technology Data Exchange (ETDEWEB)
Campergue, A.-L. [Ecole Nationale des Ponts et Chaussées, F77455 Marne-la-Vallée (France); Jacquet, P.; Monakhov, I.; Arnoux, G.; Brix, M.; Sirinelli, A. [Euratom/CCFE Association, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Bobkov, V. [Max-Planck-Institut für Plasmaphysik, EURATOM-Assoziation, Garching (Germany); Milanesio, D. [Politecnico di Torino, Department of Electronics, Torino (Italy); Colas, L. [CEA, IRFM, F-13108 Saint-Paul-Lez-Durance (France); Collaboration: JET-EFDA Contributors
2014-02-12
When using Ion Cyclotron Range of Frequency (ICRF) heating, enhanced power deposition on Plasma-Facing Components (PFCs) close to the antennas can occur. Experiments have recently been carried out on JET with the new ITER-Like-Wall (ILW) to characterize the heat fluxes on the protection of the JET ICRF antennas, using Infra-Red (IR) thermography measurement. The measured heat flux patterns along the poloidal limiters surrounding powered antennas were compared to predictions from a simple RF sheath rectification model. The RF electric field, parallel to the static magnetic field in front of the antenna, was evaluated using the TOPICA code, integrating a 3D flattened model of the JET A2 antennas. The poloidal density variation in front of the limiters was obtained from the mapping of the Li-beam or edge reflectometry measurements using the flux surface geometry provided by EFIT equilibrium reconstruction. In many cases, this simple model can well explain the position of the maximum heat flux on the different protection limiters and the heat-flux magnitude, confirming that the parallel RF electric field and the electron plasma density in front of the antenna are the main driving parameters for ICRF-induced local heat fluxes.
Chyczewski, Thomas Stanley, Jr.
factors (such as initial disturbance amplitude, corner vortices and modal excitation) that can significantly influence the jet development. A comprehensive analysis of the effect of these factors is provided. The method has been implemented and optimized on the CM-5 using the data parallel paradigm. These optimizations are quite effective and result in an efficient parallel algorithm. The code is written in CMFortran, which is a dialect of High Performance Fortran (HPF), and can be easily ported to the latest generation parallel processors. The supersonic flow from a cold, ideally expanded rectangular orifice is calculated to validate the code. The geometry (jet aspect ratio of 3) and flow conditions (M _{jet}=1.54,Re_{jet}=25,000) are selected to match those of a rectangular jet experiment that has recently concluded at The Pennsylvania State University. Detailed information on the experimental setup as well as experimental results have been provided. The results presented in this thesis indicate that the direct simulation approach is capable of predicting many of the features of supersonic rectangular jets. This includes the evolution of large scale turbulent structures and the noise they radiate to the far field.
Lower hybrid resonance heating of the JET plasma
International Nuclear Information System (INIS)
Brambilla, M.; Lallia, P.; Nguyen Trong, K.
1975-10-01
A preliminary proposition is presented to apply high power L.H.R. heating to the JET plasma, using a phased weveguide array (the Grill). The frequency is first choosen in order to locate the energy absorption region well within the plasma. The theory of the grill as a launching structure is then used to define the most appropriate Grill parameters compatible with the access available on the JET. Finally, a source and circuit realization capable of launching 10MW to the plasma is proposed [fr
Ice slurry flow and heat transfer during flow through tubes of rectangular and slit cross-sections
Directory of Open Access Journals (Sweden)
Niezgoda-Żelasko Beata
2014-09-01
Full Text Available The paper presents the results of experimental research of pressure drop and heat transfer coefficients of ice slurry during its flow through tubes of rectangular and slit cross-sections. Moreover, the work discusses the influence of solid particles, type of motion and cross-section on the changes in the pressure drop and heat transfer coefficient. The analysis presented in the paper allows for identification of the criterial relations used to calculate the Fanning factor and the Nusselt number for laminar and turbulent flow, taking into account elements such as phase change, which accompanies the heat transfer process. Ice slurry flow is treated as a generalized flow of a non-Newtonian fluid.
International Nuclear Information System (INIS)
Chen, K.S.; Chen, Y.Y.; Tsai, S.T.
1990-01-01
An experimental study is presented for the heat transfer performance of a rectangular, two-phase, natural-circulation loop with water-steam as the working fluid. Local temperature measurements of the core fluid and the wall were made, and the overall heat transfer coefficients of the evaporator, the condenser, and the loop system were obtained and correlated in terms of the fluid properties, heat flux conditions, and the liquid charge level. An overheat phenomenon at very low charge level was also observed. Result of a preliminary analysis shows that if the liquid charge level is below the fractional volume of the connecting tube between the condenser and the evaporator, an overheat phenomenon will occur
CARS Temperature Measurements in a Combustion-Heated Supersonic Jet
Tedder, S. A.; Danehy, P. M.; Magnotti, G.; Cutler, A. D.
2009-01-01
Measurements were made in a combustion-heated supersonic axi-symmetric free jet from a nozzle with a diameter of 6.35 cm using dual-pump Coherent Anti-Stokes Raman Spectroscopy (CARS). The resulting mean and standard deviation temperature maps are presented. The temperature results show that the gas temperature on the centerline remains constant for approximately 5 nozzle diameters. As the heated gas mixes with the ambient air further downstream the mean temperature decreases. The standard deviation map shows evidence of the increase of turbulence in the shear layer as the jet proceeds downstream and mixes with the ambient air. The challenges of collecting data in a harsh environment are discussed along with influences to the data. The yield of the data collected is presented and possible improvements to the yield is presented are discussed.
Numerical Investigation of Jet Impingement Heat Transfer on a Flat plate
Directory of Open Access Journals (Sweden)
Asem Nabadavis
2016-12-01
Full Text Available The numerical investigation emphasizes on studying the heat transfer characteristics when a high velocity air jet impinges upon a flat plate having constant heat flux. Numerical analysis has been conducted by solving conservation equations of momentum, mass and energy with two equations based k- ε turbulence model to determine the wall temperature and Nu of the plate considering the flow to be incompressible. It was found from the investigation that the heat transfer rate increases with the increase of Reynolds number of the jet (Rej. It was also found that there is an optimum value for jet distance to nozzle diameter ratio (H/d for maximum heat transfer when all the other parameters were kept fixed. Similar results as above were found when two jets of air were used instead of one jet keeping the mass flow rate constant. For a two jets case it was also found that heat transfer rate over the surface increases when the jets are inclined outward compared to vertical and inward jets and also there exists an optimum angle of jet for maximum heat transfer. Further investigation was carried out for different jetto-jet separation distance for a twin jet impingement model where it was noted that heat transfer is more distributed in case of larger values of L and the rate of heat transfer increases as the separation between the jet increases till a certain point after which the rate of heat transfer decreases.
International Nuclear Information System (INIS)
Hideto Niikura; Kazuo Soga; Ken-ichiro Sugiyama; Akira Yamaguchi
2005-01-01
In a steam generator using liquid sodium, water intensely reacts with sodium when it leaks out from a heat transfer tube. It is important to evaluate the influence of sodium-water reaction to surrounding tubes and the shell. Hence, it has been desired to develop the simulation code for the evaluation of sodium-water reaction. From this viewpoint, the Japan Nuclear Cycle is now developing the SERAPHIM code. We reported a preliminary study to establish an experimental method for a single heated rod immersed in sodium pool with steam jet impingement planned in the near future as well as to obtain a preliminary data to verify the adequacy of SERAPHIM code. We first measured local and mean heat transfer coefficients around a horizontal single heated rod immersed in a water pool and a sodium pool with a limited volume in the experimental apparatus. It was confirmed that the mean heat transfer coefficients fairly agreed with the existing data for natural convection in water and sodium. Secondary we measured local and mean heat transfer coefficients around a horizontal single heated rod with Ar gas jet impingement immersed in the limited water pool and in the limited sodium pool. It was clearly observed that the local heat transfer coefficients in the sodium pool keep almost the same values in every angle regardless of increase in Ar gas jet velocity varied from about 8.7m/s to about 78m/s. On the other hand, it was confirmed in the water pool that local heat transfer coefficients on the forward stagnation side exposed in the Ar gas jet impingement increase with increasing the jet velocity while the local heat transfer coefficients on the opposite surface keep almost same values regardless of increase in the velocity. (authors)
International Nuclear Information System (INIS)
Lamsaadi, M.; Naimi, M.; Hasnaoui, M.
2006-01-01
A combined analytical and numerical study is conducted for two dimensional, steady state, buoyancy driven flows of non-Newtonian power law fluids confined in a shallow rectangular cavity submitted to uniform fluxes of heat along both its short vertical sides, while its long horizontal walls are considered adiabatic. The effect of the non-Newtonian behavior on the fluid flow and heat transfer characteristics is examined. An approximate theoretical solution is developed on the basis of the parallel flow assumption and validated numerically by solving the full governing equations
International Nuclear Information System (INIS)
Beckermann, C.; Ramadhyani, S.; Viskanta, R.
1986-01-01
A numerical and experimental study is performed to analyze the steady-state natural convection fluid flow and heat transfer in a vertical rectangular enclosure that is partially filled with a vertical layer of a fluid-saturated porous medium. The flow in the porous layer is modeled utilizing the Brinkman-Forchheimer-extended Darcy equations. The numerical model is verified by conducting a number of experiments with spherical glass beads as the porous medium and water and glycerin as the fluids in rectangular test-cells. The agreement between the flow visualization results and temperature measurements and the numerical model is, in general, good. It is found that the amount of fluid penetrating from the fluid region into the porous layer depends strongly on the Darcy (Da) and Rayleigh (Ra) numbers. For a relatively low product of Ra x Da, the flow takes place primarily in the fluid layer, and heat transfer in the porous layer is by conduction only. On the other hand, fluid penetrating into a relatively highly permeable porous layer has a significant impact on the natural convection flow patterns in the entire enclosure
Ji, Songsong; Yang, Yibo; Pang, Gang; Antoine, Xavier
2018-01-01
The aim of this paper is to design some accurate artificial boundary conditions for the semi-discretized linear Schrödinger and heat equations in rectangular domains. The Laplace transform in time and discrete Fourier transform in space are applied to get Green's functions of the semi-discretized equations in unbounded domains with single-source. An algorithm is given to compute these Green's functions accurately through some recurrence relations. Furthermore, the finite-difference method is used to discretize the reduced problem with accurate boundary conditions. Numerical simulations are presented to illustrate the accuracy of our method in the case of the linear Schrödinger and heat equations. It is shown that the reflection at the corners is correctly eliminated.
International Nuclear Information System (INIS)
Wang Junfeng; Huang Yanping; Wang Yanlin; Song Mingliang
2012-01-01
Highlights: ► Flow regimes were visually investigated in a heated narrow rectangular channel. ► Bubbly, churn, and annular flow were observed. Slug flow was never observed. ► Flow regime transition boundary could be predicted by existing criteria. ► Churn zone in present flow regime maps were poorly predicted by existing criteria. - Abstract: Flow regimes are very important in understanding two-phase flow resistance and heat transfer characteristics. In present work, two-phase flow regimes for steam–water flows in a single-side heated narrow rectangular channel, having a width of 40 mm and a gap of 3 mm, were visually studied at relatively low pressure and low mass flux condition. The flow regimes observed in this experiment could be classified into bubbly, churn and annular flow. Slug flow was never observed at any of the conditions in our experiment. Flow regime maps at the pressure of 0.7 MPa and 1.0 MPa were developed, and then the pressure effect on flow regime transition was analyzed. Based on the experimental results, the comparisons with some existing flow regime maps and transition criteria were conducted. The comparison results show that the bubbly transition boundary and annular formation boundary of heated steam–water flow were consistent with that of adiabatic air–water flow. However, the intermediate flow pattern between bubbly and annular flow was different. Hibiki and Mishima criteria could predict the bubbly transition boundary and annular formation boundary satisfactorily, but it poorly predicted churn zone in present experimental data.
Convective heat transfer around vertical jet fires: An experimental study
Energy Technology Data Exchange (ETDEWEB)
Kozanoglu, Bulent, E-mail: bulentu.kozanoglu@udlap.mx [Universidad de las Americas, Puebla (Mexico); Zarate, Luis [Universidad Popular Autonoma del Estado de Puebla (Mexico); Gomez-Mares, Mercedes [Universita di Bologna (Italy); Casal, Joaquim [Universitat Politecnica de Catalunya (Spain)
2011-12-15
Highlights: Black-Right-Pointing-Pointer Experiments were carried out to analyze convection around a vertical jet fire. Black-Right-Pointing-Pointer Convection heat transfer is enhanced increasing the flame length. Black-Right-Pointing-Pointer Nusselt number grows with higher values of Rayleigh and Reynolds numbers. Black-Right-Pointing-Pointer In subsonic flames, Nusselt number increases with Froude number. Black-Right-Pointing-Pointer Convection and radiation are equally important in causing a domino effect. - Abstract: The convection heat transfer phenomenon in vertical jet fires was experimentally analyzed. In these experiments, turbulent propane flames were generated in subsonic as well as sonic regimes. The experimental data demonstrated that the rate of convection heat transfer increases by increasing the length of the flame. Assuming the solid flame model, the convection heat transfer coefficient was calculated. Two equations in terms of adimensional numbers were developed. It was found out that the Nusselt number attains greater values for higher values of the Rayleigh and Reynolds numbers. On the other hand, the Froude number was analyzed only for the subsonic flames where the Nusselt number grows by this number and the diameter of the orifice.
Ezzaraa, K.; Bahlaoui, A.; Arroub, I.; Raji, A.; Hasnaoui, M.; Naïmi, M.
2018-05-01
In this work, we investigated numerically heat transfer by mixed convection coupled to thermal radiation in a vented rectangular enclosure uniformly heated from below with a constant heat flux. The fresh fluid is admitted into the cavity by injection or suction, by means of two openings located on the lower part of both right and left vertical sides. Another opening is placed on the middle of the top wall to ensure the ventilation. Air, a radiatively transparent medium, is considered to be the cooling fluid. The inner surfaces, in contact with the fluid, are assumed to be gray, diffuse emitters and reflectors of radiation with identical emissivities. The effects of some pertinent parameters such as the Reynolds number, 300 ≤ Re ≤ 5000, and the emissivity of the walls, 0 ≤ ɛ ≤ 0.85, on flow and temperature patterns as well as on the heat transfer rate within the enclosure are presented for the two ventilation modes (injection and suction). The results indicate that the flow and thermal structures are affected by the thermal radiation for the two modes of imposed flow. However, the suction mode is found to be more favorable to the heat transfer in comparison with the injection one.
An Empirical Temperature Variance Source Model in Heated Jets
Khavaran, Abbas; Bridges, James
2012-01-01
An acoustic analogy approach is implemented that models the sources of jet noise in heated jets. The equivalent sources of turbulent mixing noise are recognized as the differences between the fluctuating and Favre-averaged Reynolds stresses and enthalpy fluxes. While in a conventional acoustic analogy only Reynolds stress components are scrutinized for their noise generation properties, it is now accepted that a comprehensive source model should include the additional entropy source term. Following Goldstein s generalized acoustic analogy, the set of Euler equations are divided into two sets of equations that govern a non-radiating base flow plus its residual components. When the base flow is considered as a locally parallel mean flow, the residual equations may be rearranged to form an inhomogeneous third-order wave equation. A general solution is written subsequently using a Green s function method while all non-linear terms are treated as the equivalent sources of aerodynamic sound and are modeled accordingly. In a previous study, a specialized Reynolds-averaged Navier-Stokes (RANS) solver was implemented to compute the variance of thermal fluctuations that determine the enthalpy flux source strength. The main objective here is to present an empirical model capable of providing a reasonable estimate of the stagnation temperature variance in a jet. Such a model is parameterized as a function of the mean stagnation temperature gradient in the jet, and is evaluated using commonly available RANS solvers. The ensuing thermal source distribution is compared with measurements as well as computational result from a dedicated RANS solver that employs an enthalpy variance and dissipation rate model. Turbulent mixing noise predictions are presented for a wide range of jet temperature ratios from 1.0 to 3.20.
Recent {sup 3}He radio frequency heating experiments on JET
Energy Technology Data Exchange (ETDEWEB)
Van Eester, D. [Association Euratom-Belgian State, LPP-ERM/KMS, TEC, Brussels (Belgium); Imbeaux, F.; Joffrin, E. [Association Euratom-CEA Cadarache, 13 - Saint-Paul-lez-Durance (France)] [and others
2003-07-01
Various ITER relevant experiments using {sup 3}He in a majority D plasma were performed in the recent JET campaigns. Two types can be distinguished: dedicated studies of the various RF heating scenarios which rely on the presence of {sup 3}He, and physics studies using RF heating as a working tool to provide a tunable heat source. As the success of a number of these experiments depended on the capability to keep the {sup 3}He concentration fixed, real time control of the {sup 3}He concentration was developed and used. This paper presents a brief overview of the results obtained, zooms in on some of the more interesting recent findings and discusses some of the theoretical background. (authors)
Ion heating in minority ICRH experiments on JET
International Nuclear Information System (INIS)
Start, D.F.H.; Bhatnagar, V.; Bures, M.
1991-06-01
Bulk ion heating by high power H-minority ICRH has been demonstrated in JET during both pellet enhanced performance H-mode experiments (PEP + H - mode) and in density limit studies. In the PEP + H - mode plasmas the electron and ion temperatures both reached 10 keV at an electron density of 7 x 10 19 /m 3 . According to Fokker-Planck calculations the power from the minority was transfered almost equally to the electrons and majority ions as a result of both the high electron density, n e , and the high minority density, n h , (n h /n e ≅ 0.15). For the first time with ICRH on JET a central ion temperature greater than the central electron temperature was achieved. In the density limit experiments which involved strong gas puffing into limiter discharges, there was strong evidence of a transfer from electron heating to ion heating as the electron density was ramped up to 8 x 10 19 /m 3 . (Author)
Experimental and Computational Study of Underexpanded Jet Impingement Heat Transfer
Rufer, Shann J.; Nowak, Robert J.; Daryabeigi, Kamran; Picetti, Donald
2009-01-01
An experiment was performed to assess CFD modeling of a hypersonic-vehicle breach, boundary-layer flow ingestion and internal surface impingement. Tests were conducted in the NASA Langley Research Center 31-Inch Mach 10 Tunnel. Four simulated breaches were tested and impingement heat flux data was obtained for each case using both phosphor thermography and thin film gages on targets placed inside the model. A separate target was used to measure the surface pressure distribution. The measured jet impingement width and peak location are in good agreement with CFD analysis.
Multiple flow patterns and heat transfer in confined jet impingement
International Nuclear Information System (INIS)
Li Xianchang; Gaddis, J. Leo; Wang Ting
2005-01-01
The flow field of a 2-D laminar confined impinging slot jet is investigated. Numerical results indicate that there exist two different solutions in some range of geometric and flow parameters. The two steady flow patterns are obtained under identical boundary conditions but only with different initial flow fields. Two different exit boundary conditions are investigated with two commercial software packages to eliminate artificial or computational effects. The different flow patterns are observed to significantly affect the heat transfer. A flow visualization experiment is carried out to verify the computational results and both flow patterns are observed. The bifurcation mechanism is interpreted and discussed
Heat transfers in a low-pressure arc-jet
Energy Technology Data Exchange (ETDEWEB)
Dudeck, M [Centre National de la Recherche Scientifique (CNRS), 92 - Meudon-Bellevue (France); Kaminska, A [Politechnika Poznanska, Poznan (Poland)
1995-03-01
In the framework of low-pressure arc-jet applications to thermodynamical condition simulation for reentry vehicles at hypersonic speed, an analytical study has been carried out concerning the thermodynamical conditions of a plasma in an arc-source for plasmatron usual operating conditions. After a review of gas physical properties, the gas flow in the plasmatron with a divergent nozzle is modelled; temperature profiles in the arc and in the divergent and the wall heat flux are then computed. Results are given. 8 refs., 6 figs.
International Nuclear Information System (INIS)
Sugano, Yoshihiro; Nakanishi, Takanori; Ito, Masahiko; Saito, Koichi.
1982-01-01
Recently, anisotropic materials have been used widely for reactor core elements and fast flying objects, therefore, the problem of thermal stress in anisotropic bodies has been studied actively. In this study, the unsteady plane thermal stress in an orthotropic rectangular thin plate heated by the temperature of ambient medium was analyzed, taking the heat transfer on both surfaces into account. The influence that the anisotropy of material constants and the heat transfer on both surfaces exert on the temperature and thermal stress of the plate was examined. Moreover, in order to investigate into the effect of the aspect ratio of the plate on the temperature and thermal stress, the unsteady distributions of temperature and thermal stress in an orthotropic semi-infinite band, of which the end surfaces are heated by ambient medium, were analyzed. The numerical calculation was carried out, and the results are shown. Before, it was difficult to satisfy the boundary condition related to shearing stress, accordingly, the analysis has not been performed, but in this study, it was shown that the analysis is possible. (Kako, I.)
Jet Impingement Heat Transfer at High Reynolds Numbers and Large Density Variations
DEFF Research Database (Denmark)
Jensen, Michael Vincent; Walther, Jens Honore
2010-01-01
Jet impingement heat transfer from a round gas jet to a flat wall has been investigated numerically in a configuration with H/D=2, where H is the distance from the jet inlet to the wall and D is the jet diameter. The jet Reynolds number was 361000 and the density ratio across the wall boundary...... layer was 3.3 due to a substantial temperature difference of 1600K between jet and wall. Results are presented which indicate very high heat flux levels and it is demonstrated that the jet inlet turbulence intensity significantly influences the heat transfer results, especially in the stagnation region....... The results also show a noticeable difference in the heat transfer predictions when applying different turbulence models. Furthermore calculations were performed to study the effect of applying temperature dependent thermophysical properties versus constant properties and the effect of calculating the gas...
Awasarmol, Umesh Vandeorao; Pise, Ashok T.
2018-02-01
The main objective of this experimental work is to investigate and compare heat transfer enhancement of alternate dwarf fin array at different angles of inclination. In this study, the steady state heat transfer from the full length fin arrays and alternate dwarf fin arrays are measured in natural convection and radiation environment. Largest increase in the Nusselt number was achieved with alternate dwarf fin at angle of orientation 90°, which shows about 28% enhanced heat transfer coefficient as opposed to the full-length fin array with 25% saving in material. In case of non-black FAB, contribution of radiation heat transfer is found to be very small nearly within 1% of the heater input. After coating lamp black contribution of radiation heat transfer is found to increase to about 3-4% of the heater input in the range of temperatures considered in this study.
Directory of Open Access Journals (Sweden)
I. G. Zorina
2016-01-01
Full Text Available To use the renewable power sources such as solar, wind, biogas, and others is complicated because of their sporadic supply. Thus and so, energy accumulation makes the user independent on the operating mode of the power source.Some of the heat accumulation methods can be realized with accumulators using phase transitions and based on the heat storage materials that change their state of aggregation during storage and rejection of thermal energy. In comparison with the gravel or liquid heat accumulators these devices are compact and provide high density of stored energy. To intensify heat exchange in such devices, are used highly heat-conductive metallic inсlusions of different shape, capsular laying or heat storage materials placed in the form of inserts, extended heat exchange surfaces, etc.Heat transfer of accumulator using phase transitions is calculated through solving a nonlinear Stefan problem. For calculation, are, usually, used various sufficiently time-consuming methods.The paper presents a heat transfer calculation when changing the aggregation state of substance. Its recommendation is to use the analytical dependences that allow calculation of heat exchange characteristics with charging phase transition accumulators of a capsular type in which a heat storage material is in cross-inserts.It is assumed that heat transfer in the coolant flow is one-dimensional, thermal and physical properties of heat storage material and coolant are constant, and heat transfer in the accumulator using phase transitions is quasi-stationary.
The effect of nozzle collar on signle phase and boiling heat transfer by planar impinging jet
International Nuclear Information System (INIS)
Shin, Chang Hwan; Yim, Seong Hwan; Cho, Hyung Hee; Wu, Seong Je
2005-01-01
The water jet impingement cooling is one of the techniques to remove the heat from high heat flux equipment. Local heat transfer of the confined water impinging jet and the effect of nozzle collar to enhance the heat transfer are investigated in the free surface jet and submerged jet. Boiling is initiated from the farthest downstream and increase of the wall temperature is reduced with developing boiling, forming the flat temperature distributions. The reduction in the nozzle-to-surface distance for H/W≤1 causes significant increases and distribution changes of heat transfer. Developed boiling reduces the differences of heat transfer for various conditions. The nozzle collar is employed at the nozzle exit. The distances from heated surface to nozzle collar, H c are 0.25W, 0.5W and 1.0W. The liquid film thickness is reduced and the velocity of wall jet increases as decreased spacing of collar to heated surface. Heat transfer is enhanced for region from the stagnation to x/W∼8 in the free surface jet and to x/W∼5 in the submerged jet. For nucleate boiling region of further downstream, the heat transfer by the nozzle collar is decreased in submerged jet comparing with higher velocity condition. It is because the increased velocity by collar is de-accelerated downstream
Energy Technology Data Exchange (ETDEWEB)
Gong, Jianying; Li, Guojun; Gao, Tieyu [Xian Jiaotong University, Xian (China)
2014-09-15
The present experiment compares the heat transfer and friction characteristics in steam cooled and air cooled rectangular channels (simulating a gas turbine blade cooling passage) with two opposite rib-roughened walls. The Reynolds number (Re) whose length scale is the hydraulic diameter of the passage is set within the range of 10000-60000. The channel length is 1000 mm. The pitch-to-rib height ratio, the channel aspect ratio and the channel blockage ratio is 10, 0.5 and 0.047, respectively. It is found that the average Nu, the average friction coefficient, and the heat transfer performance of both steam and air in the ribbed channels show almost the same change trend with the increase of Re. Under the same test conditions, the average Nu of steam is 30.2% higher than that of air, the average friction coefficient is 18.4% higher, and the heat transfer performances of steam on the ribbed and the smooth walls are 8.4% and 7.3% higher than those of air, respectively. In addition, semi-empirical correlations for the two test channels are developed, which can predict the Nu under the given test condition. The correlations can be used in the design of the internal cooling passage of new generation steam cooled gas turbine blade/vane.
International Nuclear Information System (INIS)
Bakkas, M.; Amahmid, A.; Hasnaoui, M.
2006-01-01
In this paper, we perform a numerical investigation of laminar steady natural convection flows in a two-dimensional horizontal channel containing heating rectangular blocks, periodically mounted on its lower wall. The blocks are heated at a constant temperature, T H ' and connected with adiabatic surfaces. The upper wall of the channel is maintained at a cold temperature T C ' . The parameters governing the problem are the Rayleigh number (10 2 = 6 ), the geometric parameter C (0.25=< C=l'/H'=<0.75) and the relative height of the blocks (1/8=< B=h'/H'=<1/2). The effect of the computational domain choice on the multiplicity of solutions is also investigated. The results obtained using air (Pr=0.72) as the working fluid show that the parameters B and C have a significant effect on the fluid flow and temperature fields. The symmetry of the flow is not always maintained although the boundary conditions for this problem are symmetrical, and the difference between two multiple solutions in terms of heat transfer may reach 34% for a given set of the governing parameters
Heat transfer in a vertical rectangular duct filled with a porous matrix ...
African Journals Online (AJOL)
International Journal of Engineering, Science and Technology. Journal Home ... The flow nature using different nanoparticles is also studied. ... Silver nanoparticle attains the maximum heat transfer rate when compared to other nanoparticles.
Fundamental ion cyclotron resonance heating of JET deuterium plasmas
International Nuclear Information System (INIS)
Krasilnikov, A V; Amosov, V N; Kaschuck, Yu A; Van Eester, D; Lerche, E; Ongena, J; Bonheure, G; Biewer, T; Crombe, K; Ericsson, G; Giacomelli, L; Hellesen, C; Hjalmarsson, A; Esposito, B; Marocco, D; Jachmich, S; Kiptily, V; Leggate, H; Mailloux, J; Kallne, J
2009-01-01
Radio frequency heating of majority ions is of prime importance for understanding the basic role of auxiliary heating in the activated D-T phase of ITER. Majority deuterium ion cyclotron resonance heating (ICRH) experiments at the fundamental cyclotron frequency were performed in JET. In spite of the poor antenna coupling at 25 MHz, this heating scheme proved promising when adopted in combination with D neutral beam injection (NBI). The effect of fundamental ICRH of a D population was clearly demonstrated in these experiments: by adding ∼25% of heating power the fusion power was increased up to 30-50%, depending on the type of NBI adopted. At this power level, the ion and electron temperatures increased from T i ∼ 4.0 keV and T e ∼ 4.5 keV (NBI-only phase) to T i ∼ 5.5 keV and T e ∼ 5.2 keV (ICRH + NBI phase), respectively. The increase in the neutron yield was stronger when 80 keV rather than 130 keV deuterons were injected in the plasma. It is shown that the neutron rate, the diamagnetic energy and the electron as well as the ion temperature scale roughly linearly with the applied RF power. A synergistic effect of the combined use of ICRF and NBI heating was observed: (i) the number of neutron counts measured by the neutron camera during the combined ICRF + NBI phases of the discharges exceeded the sum of the individual counts of the NBI-only and ICRF-only phases; (ii) a substantial increase in the number of slowing-down beam ions was detected by the time of flight neutron spectrometer when ICRF power was switched on; (iii) a small D subpopulation with energies slightly above the NBI launch energy was detected by the neutral particle analyzer and γ-ray spectroscopy.
International Nuclear Information System (INIS)
Rawashdeh, A.; Altamimi, R.; Lee, B.; Chung, Y. J.; Park, S.
2013-01-01
The influence of different single-phase heat transfer correlations on the fuel temperature and minimum critical heat flux ratio (MCHFR) during a typical accident of a 5 MW research reactor is investigated. A reactor uses plate type fuel, of which the cooling channels have a narrow rectangular shape. RELAP5/MOD3.3 tends to over-predict the Nusselt number (Nu) at a low Reynolds number (Re) region, and therefore the correlation set is modified to properly describe the thermal behavior at that region. To demonstrate the effect of Nu at a low-Re region on an accident analysis, a two-pump failure accident was chosen as a sample problem. In the accident, the downward core flow decreases by a pump coast-down, and then reverses upward by natural convection. During the pump coast-down and flow reversal, the flow undergoes a laminar flow regime which has a different Nu with respect to the correlation sets. Compared to the results by the original RELAP5/MOD3.3, the modified correlation set predicts the fuel temperature to be a little higher than the original value, and the MCHFR to be a little lower than the original value. Although the modified correlation set predicts the fuel temperature and the MCHFR to be less conservative than those calculated from the original correlation of RELAP5/MOD3.3, the maximum fuel temperature and the MCHFR still satisfy the safety acceptance criteria
On the challenge of plasma heating with the JET metallic wall
Mayoral, M. L.; Bobkov, V.; Czarnecka, A.; Day, I.; Ekedahl, A.; Jacquet, P.; Goniche, M.; King, R.; Kirov, K.; Lerche, E.; J. Mailloux,; Van Eester, D.; Asunta, O.; Challis, C.; Ciric, D.; Coenen, J. W.; Colas, L.; Giroud, C.; Graham, M.; Jenkins, I.; Joffrin, E.; Jones, T.; King, D.; Kiptily, V.; Klepper, C. C.; Maggi, C.; Maggiora, R.; Marcotte, F.; Matthews, G.; Milanesio, D.; Monakhov, I.; Nightingale, M.; Neu, R.; Ongena, J.; T. Puetterich,; Riccardo, V.; Rimini, F.; Strachan, J.; Surrey, E.; Thompson, V.; van Rooij, G. J.
2014-01-01
The major aspects linked to the use of the JET auxiliary heating systems: NBI, ICRF and LHCD, in the new JET ITER-like wall are presented. We show that although there were issues related to the operation of each system, efficient and safe plasma heating was obtained with room for higher power. For
1983-12-01
PROPOSED SOLUTIONS Many papers have been published outlining alternative methods of thermally controlling microelectronic devices. Hannemann [3] describes...Workshop, NSF Grant ENG-7701297, Directions of Heat Transfer in Electronic Equipment, Fy R. C. Chu, 1977. 3. Hannemann , R., "Electronic System Thermal
The effects of imperfect insulator coatings on MHD and heat transfer in rectangular duct
International Nuclear Information System (INIS)
Ying, A.Y.; Gaizer, A.A.
1994-01-01
In self cooled liquid metal blankets, the use of an insulator coating to reduce the flow of the eddy current to the structure leads to a significant reduction in MHD pressure drop. Furthermore, this insulating layer alters the velocity structure by reducing the potential difference between the side wall and boundary layer. The questions which arise are: (1) How the imperfections in the insulator coating affect the velocity profiles and their consequent impacts on heat transfer performance?; and, (2) How much crack can lead to an unacceptable MHD pressure drop? The dynamics of the crack healing in an insulator coating duct is one of the important subjects requiring study. The purpose of this work is to present numerical simulations of fully developed MHD flow and developing heat transfer characteristics in imperfectly insulated ducts, and to quantify the influences of crack locations, sizes and resistivities on 2-D MHD pressure drops. Comparisons of finite element solutions of pressure drops in partially insulated ducts with analytical solutions obtained from a circuit analogy show excellent agreement. In addition, the remarkable side layer velocity profile observed in a laminar MHD flow of a conducting duct gradually diminishes as the resistance of the insulating layer increases. The average side wall Nusselt number drops by a factor of 2 as the duct becomes fully insulated
Analysis of the Onset of Flow Instability in rectangular heated channel using drift flux model
International Nuclear Information System (INIS)
El-Hadjen, H.; Balistrou, M.; Hamidouche, T.; Bousbia-Salah, A.
2005-01-01
Two-phase flow excursion (Ledinegg) instability in boiling channels is of great concern in the design and operation of numerous practical systems especially in Research Reactors. Such instability can lead to significant reduction in channel flow, thereby causing premature burnout of the heated channel before the CHF point. The present work focuses on a simulation of pressure drop in forced convection boiling in vertical narrow and parallel uniformly heated channels. The objective is to determine the point of Onset of Flow Instability (OFI) by varying input flow rate. The axial void distribution is also provided. The numerical model is based on the finite difference method which transforms the partial differential conservation equation of mass, momentum and energy, in algebraic equations. Closure relationships based upon the drift flux model and other constitutive equations are considered to determine the channel pressure drop under steady state boiling conditions. The model validation is performed by confronting the calculations with the Oak Ridge National Laboratory thermal Hydraulic Test Loop (THTL) experimental data set. Further verification of this model is performed by code- to code verification using the results of RELAP5/Mod 3.2 code. (author)
International Nuclear Information System (INIS)
Unal, C.; Bohl, W.R.; Pasamehmetoglu, K.O.
1999-01-01
Complex ladder-like structures recently have been considered as the target design for accelerator applications. The decay heat, during a postulated beyond design-basis loss-of-coolant accident in the target where all normal and emergency cooling fails, is removed mainly by radiation heat transfer. Modeling of the radiation transport in complex ladder-like structures has several challenges and limitations when the standard net-radiation model is used. This paper proposes a simplified lumped, or 'hot-rung' model, that considers the worst elements and utilizes the standard net-radiation method. The net-radiation model would under-predict structure temperatures if surfaces were subject to non-uniform radiosity. The proposed model was assessed to suggest corrections to account for the non-uniform radiosity. The non-uniform radiosity effect causes the proposed hot-rung model to under-predict the center-rung temperatures by ∼4-74 C when all parametrics, including temperatures up to 1500 C, were considered. These temperatures are small. The proposed model predicted that an important effect of decreasing the emissivity was smoothing of non-isothermal effects. The radiosity effects are more pronounced when there are strong temperature gradients. Uniform rung temperatures tend to decrease the radiosity effects. We concluded that a relatively simple model that is conservative with respect to radiosity effects could be developed. (orig.)
Heat transfer and pressure drop in rectangular channels with crossing fins (a Review)
Sokolov, N. P.; Polishchuk, V. G.; Andreev, K. D.; Rassokhin, V. A.; Zabelin, N. A.
2015-06-01
Channels with crossing finning find wide use in the cooling paths of high-temperature gas turbine blade systems. At different times, different institutions carried out experimental investigations of heat transfer and pressure drop in channels with coplanar finning of opposite walls for obtaining semiempirical dependences of Nusselt criteria (dimensionless heat-transfer coefficients) and pressure drop coefficients on the operating Reynolds number and relative geometrical parameters (or their complexes). The shape of experimental channels, the conditions of experiments, and the used variables were selected so that they would be most suited for solving particular practical tasks. Therefore, the results obtained in processing the experimental data have large scatter and limited use. This article considers the results from experimental investigations of different authors. In comparing the results, additional calculations were carried out for bringing the mathematical correlations to the form of dependences from the same variables. Generalization of the results is carried out. In the final analysis, universal correlations are obtained for determining the pressure drop coefficients and Nusselt number values for the flow of working medium in channels with coplanar finning.
International Nuclear Information System (INIS)
Gori, Fabio; Petracci, Ivano; Angelino, Matteo
2013-01-01
Highlights: • Zone of flow establishment contains a newly identified undisturbed region of flow. • In the undisturbed region of flow the velocity profile is similar to the exit one. • In undisturbed region of flow the height of average PIV visualizations is constant. • In the undisturbed region of flow the turbulence on the centerline is equal to exit. • Length of undisturbed region of flow decreases with Reynolds number increase. -- Abstract: The paper presents average flow visualizations and measurements, obtained with the Particle Image Velocimetry (PIV) technique, of a submerged rectangular free jet of air in the range of Reynolds numbers from Re = 35,300 to Re = 2200, where the Reynolds number is defined according to the hydraulic diameter of a rectangular slot of height H. According to the literature, just after the exit of the jet there is a zone of flow, called zone of flow establishment, containing the region of mixing fluid, at the border with the stagnant fluid, and the potential core, where velocity on the centerline maintains a value almost equal to the exit one. After this zone is present the zone of established flow or fully developed region. The goal of the paper is to show, with average PIV visualizations and measurements, that, before the zone of flow establishment is present a region of flow, never mentioned by the literature and called undisturbed region of flow, with a length, L U , which decreases with the increase of the Reynolds number. The main characteristics of the undisturbed region is the fact that the velocity profile maintains almost equal to the exit one, and can also be identified by a constant height of the average PIV visualizations, with length, L CH , or by a constant turbulence on the centerline, with length L CT . The average PIV velocity and turbulence measurements are compared to those performed with the Hot Film Anemometry (HFA) technique. The average PIV visualizations show that the region of constant height has
Conceptual study of lower hybrid frequency heating of the J.E.T. plasma
International Nuclear Information System (INIS)
Tonon, G.; Bernard, M.; Brambilla, M.
1981-04-01
The aim of this report is to bring up the conclusions of the conceptual study of the J.E.T. plasma heating by lower hybrid waves. While giving an overall view of potential use for lower hybrid heating (LHH) in the J.E.T. plasma, this study deals more specificaly with the following concerns: up-to-date status of LHH theory and experiment; the physics of LHH on J.E.T.: RF requirements and expected results from numerical computations; the J.E.T. LHH coupling structure; the 10 MW RF generator; the associated RF diagnostics; the time schedule and the cost estimates
Heat loads on plasma facing components during disruptions on JET
International Nuclear Information System (INIS)
Arnoux, G.; Riccardo, V.; Fundamenski, W.; Loarte, A.; Huber, A.
2009-01-01
For the first time, fast measurements of heat loads on the main chamber plasma facing components (about 1 ms time resolution) during disruptions are taken on JET. The timescale of energy deposition during the thermal quench is estimated and compared with the timescale of the core plasma collapse measured with soft x-ray diagnostic. The energy deposition time is 3-8 times longer than the plasma energy collapse during density limit disruptions or radiative limit disruptions. This factor is rather in the range 1.5-4 for vertical displacement events. The heat load profiles measured during the thermal quench show substantial broadening of the power footprint on the upper dump plate. The scrape-off layer power width is increased by a factor of 3 for the density limit disruptions. The far scrape-off layer is characterized by a steeper gradient which could be explained by shadowing of the dump plate by other main chamber plasma facing components such as the outer limiter.
International Nuclear Information System (INIS)
Ohta, Takahiro; Kamo, Kazuhiko; Asada, Seiji; Terasaki, Toshio
2009-01-01
The new process called L-SIP (outer surface irradiated Laser Stress Improvement Process) is developed to improve the tensile residual stress of the inner surface near the butt welded joints of pipes in the compression stress. The temperature gradient occurs in the thickness of pipes in heating the outer surface rapidly by laser beam. By the thermal expansion difference between the inner surface and the outer surface, the compression stress occurs near the inner surface of pipes. In this paper, the theoretical equation for the temperature distributions of pipes heated by moving rectangular Gauss distribution heat source on the outer surface is derived. The temperature histories of pipes calculated by theoretical equation agree well with FEM analysis results. According to the theoretical equation, the controlling parameters of temperature distributions and histories are q/2a y , vh, a x /h and a y /h, where q is total heat input, a y is heat source length in the axial direction, a x is Gaussian radius of heat source in the hoop direction, ν is moving velocity, and h is thickness of the pipe. The essential variables for L-SIP, which are defined on the basis of the measured temperature histories on the outer surface of the pipe, are Tmax, F 0 =kτ 0 /h 2 , vh, W Q and L Q , where Tmax is maximum temperature on the monitor point of the outer surface, k is thermal diffusivity coefficient, τ 0 is the temperature rise time from 100degC to maximum temperature on the monitor point of the outer surface, W Q is τ 0 x ν, and L Q is the uniform temperature length in the axial direction. It is verified that the essential variables for L-SIP match the controlling parameters by the theoretical equation. (author)
Energy Technology Data Exchange (ETDEWEB)
Lyczkowski, R. W.; Solbrig, C. W.; Gidaspow, D.
1980-01-01
A numerical solution for laminar flow heat transfer between a flowing gas and its containing rectangular duct has been obtained for many different boundary conditions which may arise in nuclear waste repository ventilation corridors. The problem has been solved for the cases of insulation on no walls, one wall, two walls, and three walls with various finite resistances on the remaining walls. Simplifications are made to decouple the convective heat transfer problem for the far field conduction problem, but peripheral conduction is retained. Results have been obtained for several duct aspect ratios in the thermal entrance and in the fully developed regions, including the constant temperature cases. When one wall is insulated and the other three are at constant temperature, the maximum temperature occurs in the fluid rather than on the insulated wall. This maximum moves toward the insulated wall with increasing axial distance. Nusselt numbers for the same constant flux on all four walls with peripheral conduction lie in a narrow band bounded by zero and infinite peripheral conduction cases. A dimensionless wall conduction group of four can be considered infinite for the purpose of estimating fully developed Nusselt numbers to within an accuracy of 3%. A decrease in wall and bulk temperatures by finite wall conduction has been demonstrated for the case of a black body radiation boundary condition. Nusselt numbers for the case of constant temperature on the top and bottom walls and constant heat flux on the side walls exhibited unexpected behavior.
Impingement heat/mass transfer to hybrid synthetic jets and other reversible pulsating jets
Czech Academy of Sciences Publication Activity Database
Trávníček, Zdeněk; Vít, T.
2015-01-01
Roč. 85, June (2015), s. 473-487 ISSN 0017-9310 R&D Projects: GA ČR GA14-08888S Institutional support: RVO:61388998 Keywords : impinging jet * reversible pulsating jet * synthetic jet Subject RIV: JU - Aeronautics, Aerodynamics, Aircrafts Impact factor: 2.857, year: 2015 http://www.sciencedirect.com/science/article/pii/S001793101500143X
Experimental study on boiling heat transfer to an impinging jet on a hot block
International Nuclear Information System (INIS)
Kamata, Choko
1997-01-01
Previous studies on boiling heat transfer by impinging jets are mainly concerned with the impinging point by using small heat transfer surfaces of about 20 mm. An experimental study of the boiling heat transfer to an impinging water jet on a massive hot block is made. The upward heating surface is made of copper. Its diameter and nozzle diameter are 80 mm and 2.2 mm, respectively. The velocity of the impinging jet was varied from 0.6 to 2.1 m/s. Saturated water normally impinged on the heating surface, flowed radially, and subsequently dispersed into the atmosphere. The present study clarifies that heat transfer characteristics vary with the temperature of heat transfer surface, and also with the distance from the impinging point. (author)
Development of pulsating twin jets mechanism for mixing flow heat transfer analysis.
Gitan, Ali Ahmed; Zulkifli, Rozli; Abdullah, Shahrir; Sopian, Kamaruzzaman
2014-01-01
Pulsating twin jets mechanism (PTJM) was developed in the present work to study the effect of pulsating twin jets mixing region on the enhancement of heat transfer. Controllable characteristics twin pulsed jets were the main objective of our design. The variable nozzle-nozzle distance was considered to study the effect of two jets interaction at the mixing region. Also, the phase change between the frequencies of twin jets was taken into account to develop PTJM. All of these factors in addition to the ability of producing high velocity pulsed jet led to more appropriate design for a comprehensive study of multijet impingement heat transfer problems. The performance of PTJM was verified by measuring the pulse profile at frequency of 20 Hz, where equal velocity peak of around 64 m/s for both jets was obtained. Moreover, the jet velocity profile at different pulsation frequencies was tested to verify system performance, so the results revealed reasonable velocity profile configuration. Furthermore, the effect of pulsation frequency on surface temperature of flat hot plate in the midpoint between twin jets was studied experimentally. Noticeable enhancement in heat transfer was obtained with the increasing of pulsation frequency.
International Nuclear Information System (INIS)
Bakkas, M.; Amahmid, A.; Hasnaoui, M.
2008-01-01
Two-dimensional laminar steady natural convection in a horizontal channel with the upper wall maintained cold at a constant temperature and the lower one provided with rectangular heating blocks, periodically distributed, has been studied numerically. The blocks are connected with adiabatic segments and their surfaces are assumed to release a uniform heat flux. The study is performed using air as the working fluid (Pr = 0.72). The spacing between the blocks is maintained constant (C = l'/H' = 0.5) while the Rayleigh number and the relative height of the blocks are respectively varied in the ranges 10 2 ≤ Ra ≤ 2 x 10 6 and 1/8 ≤ B = h'/H' ≤ 1/2. The effect of the computational domain length on the multiplicity of solutions is investigated. Flow and temperature fields are also produced for various combinations of the governing parameters. It is demonstrated that, depending on the length of the computational domain and the governing parameters, different flow structures can be obtained
Khanjian, Assadour; Habchi, Charbel; Russeil, Serge; Bougeard, Daniel; Lemenand, Thierry
2018-05-01
Convective heat transfer enhancement can be achieved by generating secondary flow structures that are added to the main flow to intensify the fluid exchange between hot and cold regions. One method involves the use of vortex generators to produce streamwise and transverse vortices superimposed to the main flow. This study presents numerical computation results of laminar convection heat transfer in a rectangular channel whose bottom wall is equipped with one row of rectangular wing vortex generators. The governing equations are solved using finite volume method by considering steady state, laminar regime and incompressible flow. Three-dimensional numerical simulations are performed to study the effect of the angle of attack α of the wing on heat transfer and pressure drop. Different values are taken into consideration within the range 0° heat transfer enhancement, Nusselt number and the friction factor are studied on both local and global perspectives. Also, the location of the generated vortices within the channel is studied, as well as their effect on the heat transfer enhancement throughout the channel for all α values . Based on both local and global analysis, our results show that the angle of attack α has a direct impact on the heat transfer enhancement. By increasing its value, it leads to better enhancement until an optimal value is reached, beyond which the thermal performances decrease.
The improvement of the heat transfer model for sodium-water reaction jet code
International Nuclear Information System (INIS)
Hashiguchi, Yoshirou; Yamamoto, Hajime; Kamoshida, Norio; Murata, Shuuichi
2001-02-01
For confirming the reasonable DBL (Design Base Leak) on steam generator (SG), it is necessary to evaluate phenomena of sodium-water reaction (SWR) in an actual steam generator realistically. The improvement of a heat transfer model on sodium-water reaction (SWR) jet code (LEAP-JET ver.1.40) and application analysis to the water injection tests for confirmation of propriety for the code were performed. On the improvement of the code, the heat transfer model between a inside fluid and a tube wall was introduced instead of the prior model which was heat capacity model including both heat capacity of the tube wall and inside fluid. And it was considered that the fluid of inside the heat exchange tube was able to treat as water or sodium and typical heat transfer equations used in SG design were also introduced in the new heat transfer model. Further additional work was carried out in order to improve the stability of the calculation for long calculation time. The test calculation using the improved code (LEAP-JET ver.1.50) were carried out with conditions of the SWAT-IR·Run-HT-2 test. It was confirmed that the SWR jet behavior on the result and the influence to the result of the heat transfer model were reasonable. And also on the improved code (LEAP-JET ver.1.50), user's manual was revised with additional I/O manual and explanation of the heat transfer model and new variable name. (author)
Studies of heating efficiencies and models of RF-sheaths for the JET antennae
International Nuclear Information System (INIS)
Hedin, J.
1996-02-01
A theoretical model for the appearance of RF-sheaths is developed to see if this can explain the expected lower heating efficiencies of the new A 2 antennae at JET. The equations are solved numerically. A general method for evaluation of the experimental data of the heating efficiencies of the new antennae at JET is developed and applied for discharges with and without the bumpy limiter on the D antennae. 8 refs, 26 figs
Observations of rotation in JET plasmas with electron heating by ion cyclotron resonance heating
DEFF Research Database (Denmark)
Hellsten, T.; Johnson, T. J.; Van Eester, D.
2012-01-01
The rotation of L-mode plasmas in the JET tokamak heated by waves in the ion cyclotron range of frequencies (ICRF) damped on electrons, is reported. The plasma in the core is found to rotate in the counter-current direction with a high shear and in the outer part of the plasma with an almost......, electron absorption of the fast magnetosonic wave by transit time magnetic pumping and electron Landau damping (TTMP/ELD) is the dominating absorption mechanism. Inverted mode conversion is done in (He-3)-H plasmas where the mode converted waves are essentially absorbed by electron Landau damping. Similar...... rotation profiles are seen when heating at the second harmonic cyclotron frequency of He-3 and with mode conversion at high concentrations of He-3. The magnitude of the counter-rotation is found to decrease with an increasing plasma current. The correlation of the rotation with the electron temperature...
Directory of Open Access Journals (Sweden)
Xi-yue Liu
2017-01-01
Full Text Available A simplified approach which utilizes an isotropic porous medium model has been widely adopted for modeling the flow through a compact heat exchanger. With respect to situations where the compact heat exchangers are partially installed inside a channel, such as the application of recuperators in an intercooled recuperative engine, the use of an isotropic porous medium model needs to be carefully assessed because the flow passing through the heat exchanger is very complicated. For this purpose, in this study the isotropic porous medium model is assessed together with specific pressure–velocity relationships for flow field modeling inside a rectangular channel with a built-in double-U-shaped tube bundle heat exchanger. Firstly, experiments were conducted using models to investigate the relationship between the pressure drop and the inlet velocity for a specific heat exchanger with different installation angles inside a rectangular channel. Secondly, a series of numerical computations were carried out using the isotropic porous medium model and the pressure–velocity relationship was then modified by introducing correction coefficients empirically. Finally, a three-dimensional (3-D direct computation was made using a computational fluid dynamics (CFD method for the comparison of detailed flow fields. The results suggest that the isotropic porous medium model is capable of making precise pressure drop predictions given the reasonable pressure–velocity relationship but is unable to precisely simulate the detailed flow features.
Time-varying Entry Heating Profile Replication with a Rotating Arc Jet Test Article
Grinstead, Jay Henderson; Venkatapathy, Ethiraj; Noyes, Eric A.; Mach, Jeffrey J.; Empey, Daniel M.; White, Todd R.
2014-01-01
A new approach for arc jet testing of thermal protection materials at conditions approximating the time-varying conditions of atmospheric entry was developed and demonstrated. The approach relies upon the spatial variation of heat flux and pressure over a cylindrical test model. By slowly rotating a cylindrical arc jet test model during exposure to an arc jet stream, each point on the test model will experience constantly changing applied heat flux. The predicted temporal profile of heat flux at a point on a vehicle can be replicated by rotating the cylinder at a prescribed speed and direction. An electromechanical test model mechanism was designed, built, and operated during an arc jet test to demonstrate the technique.
Gas and heat dynamics of a micro-scaled atmospheric pressure plasma reference jet
International Nuclear Information System (INIS)
Kelly, Seán; Golda, Judith; Schulz-von der Gathen, Volker; Turner, Miles M
2015-01-01
Gas and heat dynamics of the ‘Cooperation on Science and Technology (COST) Reference Microplasma Jet’ (COST-jet), a European lead reference device for low temperature atmospheric pressure plasma application, are investigated. Of particular interest to many biomedical application scenarios, the temperature characteristics of a surface impacted by the jet are revealed. Schlieren imaging, thermocouple measurements, infrared thermal imaging and numerical modelling are employed. Temperature spatial profiles in the gas domain reveal heating primarily of the helium fraction of the gas mixture. Thermocouple and model temporal data show a bounded exponential temperature growth described by a single characteristic time parameter to reach ∼63% or (1-1/e) fraction of the temperature increase. Peak temperatures occurred in the gas domain where the carrier jet exits the COST-jet, with values ranging from ambient temperatures to in excess of 100 °C in ‘α-mode’ operation. In a horizontal orientation of the COST-jet a curved trajectory of the helium effluent at low gas flows results from buoyant forces. Gas mixture profiles reveal significant containment of the helium concentrations for a surface placed in close proximity to the COST-jet. Surface heating of a quartz plate follows a similar bounded exponential temporal temperature growth as device heating. Spatial profiles of surface heating are found to correlate strongly to the impacting effluent where peak temperatures occur in regions of maximum surface helium concentration. (paper)
Gas and heat dynamics of a micro-scaled atmospheric pressure plasma reference jet
Kelly, Seán; Golda, Judith; Turner, Miles M.; Schulz-von der Gathen, Volker
2015-11-01
Gas and heat dynamics of the ‘Cooperation on Science and Technology (COST) Reference Microplasma Jet’ (COST-jet), a European lead reference device for low temperature atmospheric pressure plasma application, are investigated. Of particular interest to many biomedical application scenarios, the temperature characteristics of a surface impacted by the jet are revealed. Schlieren imaging, thermocouple measurements, infrared thermal imaging and numerical modelling are employed. Temperature spatial profiles in the gas domain reveal heating primarily of the helium fraction of the gas mixture. Thermocouple and model temporal data show a bounded exponential temperature growth described by a single characteristic time parameter to reach ∼63% or (1-1/e) fraction of the temperature increase. Peak temperatures occurred in the gas domain where the carrier jet exits the COST-jet, with values ranging from ambient temperatures to in excess of 100 °C in ‘α-mode’ operation. In a horizontal orientation of the COST-jet a curved trajectory of the helium effluent at low gas flows results from buoyant forces. Gas mixture profiles reveal significant containment of the helium concentrations for a surface placed in close proximity to the COST-jet. Surface heating of a quartz plate follows a similar bounded exponential temporal temperature growth as device heating. Spatial profiles of surface heating are found to correlate strongly to the impacting effluent where peak temperatures occur in regions of maximum surface helium concentration.
International Nuclear Information System (INIS)
Takase, K.; Hasan, M.Z.
1995-01-01
Convective heat transfer in MHD laminar flow through rectangular channels in the plasma-facing components of a fusion reactor has been analyzed numerically to investigate the effects of channel aspect ratio, defined as the ratio of the lengths of the plasma-facing side to the other side. The adverse effect of the nonuniformity of surface heat flus on Nusselt number (Nu) at the plasma-facing side can be alleviated by increasing the aspect ratio of a rectangular duct. At the center and corner of the plasma-facing side of a square duct, the Nu of non-MHD flow are 6.8 and 2.2, respectively, for uniform surface heat flux. In the presence of a strong magnetic field, Nu at the center and corner increases to 22 and 3.6, respectively. However, when the heat flux is highly nonuniform, as in the plasma-facing components, Nu decreases from 22 to 3.1 at the center and from 3.6 to 3.1 at the corner. When the aspect ratio is increased to 4, Nu at the center and corner increase to 5 and 4.7. Along the circumference of a rectangular channel, there are locations where the wall temperature is equal to or less than the bulk coolant temperature, thus making the Nu with conventional definition infinity or negative. The ratio between Nu of MHD flow and Nu of non-MHD flow for various aspect ratios is constant in the region of Hartmann number of more than 200 at least. On the other hand, its ratio increases monotonously with increasing the aspect ratio
Novel two-phase jet impingement heat sink for active cooling of electronic devices
International Nuclear Information System (INIS)
Oliveira, Pablo A. de; Barbosa, Jader R.
2017-01-01
Highlights: • Novel jet-based heat sink integrates the evaporator and the expansion device. • The system was tested with a small-scale oil-free R-134a compressor. • The thermodynamic performance of the cooling system was evaluated experimentally. • The single-jet maximum cooling capacity was 160 W, with a COP of 2.3 and a η 2nd of 8%. • Maximum heat transfer coefficient of 15 kW m −2 K −1 and surface temperature of 30 °C. - Abstract: This work presents a compact vapor compression cooling system equipped with a small-scale oil-free R-134a compressor and a jet-impingement-based heat sink that integrates the evaporator and the expansion device into a single unit. At the present stage of the development, a single orifice was used to generate the high-speed two-phase impinging jet on the heated surface. The effects of the compressor piston stroke, applied thermal load and orifice diameter on the system performance were quantified. The thermodynamic performance of the system was evaluated in terms of the temperature of the heated surface, impinging jet heat transfer coefficient, several system thermal resistances, coefficient of performance, second-law efficiency and second-law ratio. The coefficient of performance of the new refrigeration system increased with the cooling capacity, justifying its application in the removal of large thermal loads. The maximum system cooling capacity with a single jet was approximately 160 W, which was achieved with an orifice diameter of 500 μm and operation at a full compressor piston stroke. This condition corresponded to a COP of 2.3, a second-law efficiency of 8.0%, a jet impingement heat transfer coefficient above 15 kW m −2 K −1 and a heater surface temperature of approximately 30 °C.
White, Molly E.; Hyatt, Andrew J.
2016-01-01
The Orion Multi-Purpose Crew Vehicle (MPCV) Reaction Control System (RCS) is critical to guide the vehicle along the desired trajectory during re--entry. However, this system has a significant impact on the convective heating environment to the spacecraft. Heating augmentation from the jet interaction (JI) drives thermal protection system (TPS) material selection and thickness requirements for the spacecraft. This paper describes the heating environment from the RCS on the afterbody of the Orion MPCV during Orion's first flight test, Exploration Flight Test 1 (EFT-1). These jet plumes interact with the wake of the crew capsule and cause an increase in the convective heating environment. Not only is there widespread influence from the jet banks, there may also be very localized effects. The firing history during EFT-1 will be summarized to assess which jet bank interaction was measured during flight. Heating augmentation factors derived from the reconstructed flight data will be presented. Furthermore, flight instrumentation across the afterbody provides the highest spatial resolution of the region of influence of the individual jet banks of any spacecraft yet flown. This distribution of heating augmentation across the afterbody will be derived from the flight data. Additionally, trends with possible correlating parameters will be investigated to assist future designs and ground testing programs. Finally, the challenges of measuring JI, applying this data to future flights and lessons learned will be discussed.
Minority and mode conversion heating in (He-3)-H JET plasmas
Van Eester, D.; Lerche, E.; Johnson, T. J.; Hellsten, T.; Ongena, J.; Mayoral, M. L.; Frigione, D.; Sozzi, C.; Calabro, G.; Lennholm, M.; Beaumont, P.; Blackman, T.; Brennan, D.; Brett, A.; Cecconello, M.; Coffey, I.; Coyne, A.; Crombe, K.; Czarnecka, A.; Felton, R.; Johnson, M. G.; Giroud, C.; Gorini, G.; Hellesen, C.; Jacquet, P.; Kazakov, Y.; Kiptily, V.; Knipe, S.; Krasilnikov, A.; Lin, Y.; Maslov, M.; Monakhov, I.; Noble, C.; Nocente, M.; Pangioni, L.; Proverbio, I.; Stamp, M.; Studholme, W.; Tardocchi, M.; Versloot, T. W.; Vdovin, V.; Whitehurst, A.; Wooldridge, E.; Zoita, V.
2012-01-01
Radio frequency (RF) heating experiments have recently been conducted in JET (He-3)-H plasmas. This type of plasmas will be used in ITER's non-activated operation phase. Whereas a companion paper in this same PPCF issue will discuss the RF heating scenario's at half the nominal magnetic
Minority and mode conversion heating in (3He)–H JET plasmas
Eester, van D.; Versloot, T.W.; et al, [No Value
2012-01-01
Radio frequency (RF) heating experiments have recently been conducted in JET (3He)–H plasmas. This type of plasmas will be used in ITER’s non-activated operation phase. Whereas a companion paper in this same PPCF issue will discuss the RF heating scenario’s at half the nominal magnetic field, this
Experimental study of curvature effects on jet impingement heat transfer on concave surfaces
Directory of Open Access Journals (Sweden)
Ying Zhou
2017-04-01
Full Text Available Experimental study of the local and average heat transfer characteristics of a single round jet impinging on the concave surfaces was conducted in this work to gain in-depth knowledge of the curvature effects. The experiments were conducted by employing a piccolo tube with one single jet hole over a wide range of parameters: jet Reynolds number from 27000 to 130000, relative nozzle to surface distance from 3.3 to 30, and relative surface curvature from 0.005 to 0.030. Experimental results indicate that the surface curvature has opposite effects on heat transfer characteristics. On one hand, an increase of relative nozzle to surface distance (increasing jet diameter in fact enhances the average heat transfer around the surface for the same curved surface. On the other hand, the average Nusselt number decreases as relative nozzle to surface distance increases for a fixed jet diameter. Finally, experimental data-based correlations of the average Nusselt number over the curved surface were obtained with consideration of surface curvature effect. This work contributes to a better understanding of the curvature effects on heat transfer of a round jet impingement on concave surfaces, which is of high importance to the design of the aircraft anti-icing system.
Heat flux characteristics in an atmospheric double arc argon plasma jet
International Nuclear Information System (INIS)
Tu Xin; Yu Liang; Yan Jianhua; Cen Kefa; Cheron, Bruno
2008-01-01
In this study, the axial evolution of heat flux excited by a double arc argon plasma jet impinging on a flat plate is determined, while the nonstationary behavior of the heat flux is investigated by combined means of the fast Fourier transform, Wigner distribution, and short-time Fourier transform. Two frequency groups (<1 and 2-10 kHz) are identified in both the Fourier spectrum and the time-frequency distributions, which suggest that the nature of fluctuations in the heat flux is strongly associated with the dynamic behavior of the plasma arc and the engulfment of ambient air into different plasma jet regions
International Nuclear Information System (INIS)
Song, Junghyun; Jeong, Yong Hoon; Lee, Juhyung; Chang, Soon Heung
2014-01-01
Research reactor is the nuclear reactor serves neutron source for many research fields such as neutron scattering, non-destructive testing, radioisotope treatment and so on. Due to that characteristic of research reactor, as many people work around the research reactor, research reactor should be designed to have much more conservative margin for normal operation. Boiling heat transfer is the one of the most efficient type in heat transfer modes, however, research reactor needs to avoid onset of nucleate boiling (ONB) in normal operation as IAEA recommend for research reactors to have enough ONB margin to maintain the normal operation state in 'IAEA-TECDOC-233' (1980) for the same reason explained above. Jordan Research and Training Reactor (JRTR) operates under downward flow in narrow rectangular channel in fuel assembly. There isn't sufficient heat transfer data under downward flow condition and only few ONB prediction correlation as well. In the present work, not only a new ONB prediction model would be developed, but also comparison between heat transfer data with several heat transfer correlations could be shown. In addition, as Sudo and Omar S. proposed differently about the Nusselt number behaviors in upward and downward convective heat transfer, the study of convective heat transfer should be conducted continuously to determine it exactly. In this paper, single-phase heat transfer data is analyzed by several heat transfer correlations before developing ONB prediction correlation. In this study, an experiment on the single-phase heat transfer was conducted. As shown in Fig. 5, comparison between experimental data and existing correlations shows quite huge difference as about 40%. Additional experiments on single-phase heat transfer at low heat flux are necessary to clarify the tendency of Nusselt number among heat flux and to develop new correlation for single-phase heat transfer
Putnam, L. E.; Mercer, C. E.
1986-01-01
An investigation has been conducted in the Langley 16-Foot Transonic Tunnel to measure the flow field in and around the jet exhaust from a nonaxisymmetric nozzle configuration. The nozzle had a rectangular exit with a width-to-height ratio of 2.38. Pitot-pressure measurements were made at five longitudinal locations downstream of the nozzle exit. The maximum distance downstream of the exit was about 5 nozzle heights. These measurements were made at free-stream Mach numbers of 0.00, 0.60, and 1.20 with the nozzle operating at a ratio of nozzle total pressure to free-stream static pressure of 4.0. The jet exhaust was simulated with high-pressure air that had an exit total temperature essentially equal to the free-stream total temperature.
Liquid jet impingement cooling with diamond substrates for extremely high heat flux applications
International Nuclear Information System (INIS)
Lienhard V, J.H.
1993-01-01
The combination of impinging jets and diamond substrates may provide an effective solution to a class of extremely high heat flux problems in which very localized heat loads must be removed. Some potential applications include the cooling of high-heat-load components in synchrotron x-ray, fusion, and semiconductor laser systems. Impinging liquid jets are a very effective vehicle for removing high heat fluxes. The liquid supply arrangement is relatively simple, and low thermal resistances can be routinely achieved. A jet's cooling ability is a strong function of the size of the cooled area relative to the jet diameter. For relatively large area targets, the critical heat fluxes can approach 20 W/mm 2 . In this situation, burnout usually originates at the outer edge of the cooled region as increasing heat flux inhibits the liquid supply. Limitations from liquid supply are minimized when heating is restricted to the jet stagnation zone. The high stagnation pressure and high velocity gradients appear to suppress critical flux phenomena, and fluxes of up to 400 W/mm 2 have been reached without evidence of burnout. Instead, the restrictions on heat flux are closely related to properties of the cooled target. Target properties become an issue owing to the large temperatures and large temperature gradients that accompany heat fluxes over 100 W/mm 2 . These conditions necessitate a target with both high thermal conductivity to prevent excessive temperatures and good mechanical properties to prevent mechanical failures. Recent developments in synthetic diamond technology present a possible solution to some of the solid-side constraints on heat flux. Polycrystalline diamond foils can now be produced by chemical vapor deposition in reasonable quantity and at reasonable cost. Synthetic single crystal diamonds as large as 1 cm 2 are also available
Heating, current drive and energetic particles studies on JET in preparation of ITER operation
International Nuclear Information System (INIS)
Noterdaeme, J.-M.; Budny, R.; Cardinali, A.
2003-01-01
This paper summarizes the recent work on JET in the three areas of heating, current drive and energetic particles. The achievements have extended the possibilities of JET, have a direct connection to ITER operation and provide new and interesting physics. Toroidal rotation profiles of plasmas heated far off axis with little or no refueling or momentum input are hollow with only small differences on whether the power deposition is located on the low field side or on the high field side. With LH current drive the magnetic shear was varied from slightly positive to negative. The improved coupling (through the use of plasma shaping and CD 4 ) allowed up to 3.4 MW of P LH in ITB plasmas with more than 15MW of combined NBI and ICRF heating. The q profile with negative magnetic shear and the ITB could be maintained for the duration of the high heating pulse (8s). Fast ions have been produced in JET with ICRF to simulate alpha particles: by using third harmonic 4 He heating, beam injected 4 He at 120 kV were accelerated to energies above 2 MeV, taking advantage of the unique capability of JET to use NBI with 4 He and to confine MeV class ions. ICRF heating was used to replicate the dynamics of alpha heating and the control of an equivalent Q=10 'burn' was simulated. (author)
Experimental study of a water-mist jet issuing normal to a heated flat plate
Directory of Open Access Journals (Sweden)
Vouros Andreas
2016-01-01
Full Text Available A parametric experimental study on the development of a round jet spray impacting a smooth, heated, flat plate has been accomplished. The main objective of this effort was to provide information characterizing the flow structure of a developing mist jet, issuing vertically towards an upward facing, horizontal heated plate, by means of simultaneous droplet size and velocity measurements. Phase Doppler Anemometry was used, providing also information on liquid volume flux. The fine spray of small atomized droplets (0.5-5.0 μm, was generated using a medical nebulizer. Two low Reynolds number jets (Re=2952, 3773 issuing from a cylindrical pipe have been tested. The distance between the jets’ exit and the plate was 50 cm. A stainless steel non-magnetic flat plate of dimensions 1000x500x12mm3 was used as target wall. Constant heat flux boundary conditions were established during measurements. Results indicate that the heat flux from the plate is influencing the evolution of the spray jet, diminishing its velocity and turbulence. Average droplet sizes are affected little by the heat flux, although for the non-heated sprays, droplet sizes increase at locations very close to the plate. A significant effect on droplet volume flow rate is also reported.
Heat pulse analysis in JET and relation to local energy transport models
International Nuclear Information System (INIS)
Haas, J.C.M. de; Lopes Cardozo, N.J.; Han, W.; Sack, C.; Taroni, A.
1989-01-01
The evolution of a perturbation T e of the electron temperature depends on the linearised expression of the heat flux q e and may be not simply related to the local value of the electron heat conductivity χ e . It is possible that local heat transport models predicting similar temperature profiles and global energy confinement properties, imply a different propagation of heat pulses. We investigate here this possibility for the case of two models developed at JET. We also present results obtained at JET on a set of discharges covering the range of currents from 2 to 5 MA. Only L-modes, limiter discharges are considered here. Experimental results on the scaling of χ HP , the value of χ e related to heat pulse propagation, are compared with those of χ HP derived from the models. (author) 7 refs., 2 figs., 2 tabs
Impinging jets - a short review on strategies for heat transfer enhancement
Nastase, Ilinca; Bode, Florin
2018-02-01
In industrial applications, heat and mass transfer can be considerably increased using impinging jets. A large number of flow phenomena will be generated by the impinging flow, such as: large scale structures, large curvature involving strong shear and normal stresses, stagnation in the wall boundary layers, heat transfer with the impinged wall, small scale turbulent mixing. All these phenomena are highly unsteady and even if nowadays a substantial number of studies in the literature are dedicated, the impinging jets are still not fully understood due to the highly unsteady nature and more over due to great difficulty of performing detailed numerical and experimental investigations.
Analysis of Heat Transfer in Cooling of a Hot Plate by Planar Impingement Jet
International Nuclear Information System (INIS)
Ahn, Dae Hwan; Kim, Dong Sik
2009-01-01
Water jet impingement cooling is used to remove heat from high-temperature surfaces such as hot steel plates in the steel manufacturing process (thermo-mechanical cooling process; TMCP). In those processes, uniform cooling is the most critical factor to ensure high strength steel and good quality. In this study, experiments are performed to measure the heat transfer coefficient together with the inverse heat conduction problem (IHCP) analysis for a plate cooled by planar water jet. In the inverse heat transfer analysis, spatial and temporal variations of heat transfer coefficient, with no information regarding its functional form, are determined by employing the conjugate gradient method with an adjoint problem. To estimate the two dimensional distribution of heat transfer coefficient and heat flux for planar waterjet cooling, eight thermo-couple are installed inside the plate. The results show that heat transfer coefficient is approximately uniform in the span-wise direction in the early stage of cooling. In the later stage where the forced-convection effect is important, the heat transfer coefficient becomes larger in the edge region. The surface temperature vs. heat flux characteristics are also investigated for the entire boiling regimes. In addition, the heat transfer rate for the two different plate geometries are compared at the same Reynolds number
Real time plasma control experiments using the JET auxiliary plasma heating systems as the actuator
International Nuclear Information System (INIS)
Zornig, N.H.
1999-01-01
The role of the Real Time Power Control system (RTPC) in the Joint European Torus (JET) is described in depth. The modes of operation are discussed in detail and a number of successful experiments are described. These experiments prove that RTPC can be used for a wide range of experiments, including: (1) Feedback control of plasma parameters in real time using Ion Cyclotron Resonance Heating (ICRH) or Neutral Beam Heating (NBH) as the actuator in various JET operating regimes. It is demonstrated that in a multi-parameter space it is not sufficient to control one global plasma parameter in order to avoid performance limiting events. (2) Restricting neutron production and subsequent machine activation resulting from high performance pulses. (3) The simulation of α-particle heating effects in a DT-plasma in a D-only plasma. The heating properties of α-particles are simulated using ICRH-power, which is adjusted in real time. The simulation of α-particle heating in JET allows the effects of a change in isotopic mass to be separated from α-particle heating. However, the change in isotopic mass of the plasma ions appears to affect not only the global energy confinement time (τ E ) but also other parameters such as the electron temperature at the plasma edge. This also affects τ E , making it difficult to make a conclusive statement about any isotopic effect. (4) For future JET experiments a scheme has been designed which simulates the behaviour of a fusion reactor experimentally. The design parameters of the International Thermonuclear Experimental Reactor (ITER) are used. In the proposed scheme the most relevant dimensionless plasma parameters are similar in JET and ITER. It is also shown how the amount of heating may be simulated in real time by RTPC using the electron temperature and density as input parameters. The results of two demonstration experiments are presented. (author)
International Nuclear Information System (INIS)
Frainer, V.J.
1979-01-01
A solution of the time-transient Heat Transfer Differential Equation in rectangular coordinates is presented, leading to a model which describes the temperature drop with time in rectangular bars. It is similar to an other model for cilindrical bars which has been previously developed in the Laboratory of Mechanical Metallurgy of UFRGS. Following these models, a generalization has been made, which permits cooling time evaluation for all profiles. These results are compared with experimental laboratory data in the 1200 to 800 0 C range. Some other existing models were also studied which have the purpose of studing the same phenomenon. Their mathematical forms and their evaluated values are analyzed and compared with experimental ones. (Author) [pt
Czech Academy of Sciences Publication Activity Database
Frassinetti, L.; Saarelma, S.; Lomas, P.; Nunes, I.; Rimini, F.; Beurskens, M.N.A.; Bílková, Petra; Boom, J.E.; De La Luna, E.; Delabie, E.; Drewelow, P.; Flanagan, J.; Garzotti, L.; Giroud, C.; Hawks, N.; Joffrin, E.; Kempenaars, M.; Kim, H.-T.; Kruezi, U.; Loarte, A.; Lomanowski, B.; Lupelli, I.; Meneses, L.; Maggi, C.F.; Menmuir, S.; Peterka, Matěj; Rachlew, E.; Romanelli, M.; Stefanikova, E.
2017-01-01
Roč. 59, č. 1 (2017), č. článku 014014. ISSN 0741-3335. [EPS 2016: Conference on Plasma Physics/43./. Leuven, 04.07.2016-08.07.2016] EU Projects: European Commission(XE) 633053 - EUROfusion Institutional support: RVO:61389021 Keywords : JET-ILW * dimensionless scaling * pedestal * confinement * pedestal stability * heat transport Subject RIV: BL - Plasma and Gas Discharge Physics OBOR OECD: Fluids and plasma physics (including surface physics) Impact factor: 2.392, year: 2016 http://dx.doi.org/10.1088/0741-3335/59/1/014014
ISOTROPIC HEATING OF GALAXY CLUSTER CORES VIA RAPIDLY REORIENTING ACTIVE GALACTIC NUCLEUS JETS
International Nuclear Information System (INIS)
Babul, Arif; Sharma, Prateek; Reynolds, Christopher S.
2013-01-01
Active galactic nucleus (AGN) jets carry more than sufficient energy to stave off catastrophic cooling of the intracluster medium (ICM) in the cores of cool-core clusters. However, in order to prevent catastrophic cooling, the ICM must be heated in a near-isotropic fashion and narrow bipolar jets with P jet = 10 44–45 erg s –1 , typical of radio AGNs at cluster centers, are inefficient in heating the gas in the transverse direction to the jets. We argue that due to existent conditions in cluster cores, the supermassive black holes (SMBHs) will, in addition to accreting gas via radiatively inefficient flows, experience short stochastic episodes of enhanced accretion via thin disks. In general, the orientation of these accretion disks will be misaligned with the spin axis of the black holes (BHs) and the ensuing torques will cause the BH's spin axis (and therefore the jet axis) to slew and rapidly change direction. This model not only explains recent observations showing successive generations of jet-lobes-bubbles in individual cool-core clusters that are offset from each other in the angular direction with respect to the cluster center, but also shows that AGN jets can heat the cluster core nearly isotropically on the gas cooling timescale. Our model does require that the SMBHs at the centers of cool-core clusters be spinning relatively slowly. Torques from individual misaligned disks are ineffective at tilting rapidly spinning BHs by more than a few degrees. Additionally, since SMBHs that host thin accretion disks will manifest as quasars, we predict that roughly 1-2 rich clusters within z < 0.5 should have quasars at their centers.
Thermal performance analysis of optimized hexagonal finned heat sinks in impinging air jet
Energy Technology Data Exchange (ETDEWEB)
Yakut, Kenan, E-mail: kyakut@atauni.edu.tr [Department of Mechanical Engineering, Faculty of Engineering, Atatürk University, 25100, Erzurum (Turkey); Yeşildal, Faruk, E-mail: fayesildal@agri.edu.tr [Department of Mechanical Engineering, Faculty of Patnos Sultan Alparslan Natural Sciences and Engineering, Ağrı İbrahim Çeçen University, 04100, Ağrı (Turkey); Karabey, Altuğ, E-mail: akarabey@yyu.edu.tr [Department of Machinery and Metal Technology, Erciş Vocational High School, Yüzüncü Yıl University, 65400, Van (Turkey); Yakut, Rıdvan, E-mail: ryakut@kafkas.edu.tr [Department of Mechanical Engineering, Faculty of Engineering and Architecture, Kafkas University, 36100, Kars (Turkey)
2016-04-18
In this study, thermal performance analysis of hexagonal finned heat sinks which optimized according to the experimental design and optimization method of Taguchi were investigated. Experiments of air jet impingement on heated hexagonal finned heat sinks were carried out adhering to the L{sub 18}(2{sup 1*}3{sup 6}) orthogonal array test plan. Optimum geometries were determined and named OH-1, OH-2. Enhancement efficiency with the first law of thermodynamics was analyzed for optimized heat sinks with 100, 150, 200 mm heights of hexagonal fin. Nusselt correlations were found out and variations of enhancement efficiency with Reynolds number presented in η–Re graphics.
International Nuclear Information System (INIS)
Stieglitz, Robert; Daubner, Markus; Batta, A.; Lefhalm, C.-H.
2007-01-01
The MEGAPIE target installed at the Paul-Scherrer Institute is an example of a spallation target using eutectic liquid lead-bismuth (Pb 45 Bi 55 ) both as coolant and neutron source. An adequate cooling of the target requires a conditioning of the flow, which is realized by a main flow transported in an annular gap downwards, u-turned at a hemispherical shell into a cylindrical riser tube. In order to avoid a stagnation point close to the lowest part of the shell a jet flow is superimposed to the main flow, which is directed towards to the stagnation point and flows tangentially along the shell. The heated jet experiment conducted in the THEADES loop of the KALLA laboratory is nearly 1:1 representation of the lower part of the MEGAPIE target. It is aimed to study the cooling capability of this specific geometry in dependence on the flow rate ratio (Q main /Q jet ) of the main flow (Q main ) to the jet flow (Q jet ). Here, a heated jet is injected into a cold main flow at MEGAPIE relevant flow rate ratios. The liquid metal experiment is accompanied by a water experiment in almost the same geometry to study the momentum field as well as a three-dimensional turbulent numerical fluid dynamic simulation (CFD). Besides a detailed study of the envisaged nominal operation of the MEGAPIE target with Q main /Q jet = 15 deviations from this mode are investigated in the range from 7.5 ≤ Q main /Q jet ≤ 20 in order to give an estimate on the safe operational threshold of the target. The experiment shows that, the flow pattern establishing in this specific design and the turbulence intensity distribution essentially depends on the flow rate ratio (Q main /Q jet ). All Q main /Q jet -ratios investigated exhibit an unstable time dependent behavior. The MEGAPIE design is highly sensitive against changes of this ratio. Mainly three completely different flow patterns were identified. A sufficient cooling of the lower target shell, however, is only ensured if Q main /Q jet ≤ 12
Choi, Byungchul; Chung, Suk-Ho
2012-01-01
and then increased as the jet velocity increased. Based on the mechanism in which the autoignited laminar lifted flame is stabilized by ignition delay time, the liftoff height can be influenced not only by the heat loss, but also by the preferential diffusion between
Buoyancy effects laminar slot jet impinging on a surface with constant heat flux
International Nuclear Information System (INIS)
Shokouhmand, H.; Esfahanian, V.; Masoodi, R.
2004-01-01
The two-dimensional laminar air jet issuing from a nozzle of half which terminates at height above a flat plate normal to the jet is numerically on the flow and thermal structure of the region near impingement. The impinging surface is maintained at a constant heat flux condition. The full Navier-Stocks and energy equations are solved by a finite difference method to evaluate the velocity profiles and temperature distribution. The governing parameters and their ranges are: Reynolds number Re, 10-50, Grashof number Gr, 0-50, Richardson number Ri=Gr/ Re 2 , Non dimensional nozzle height H,2-3. Results of the free streamline, local friction factor and heat transfer coefficient are graphically presented. It is found that enhancement of the heat transfer rate is substantial for high Richardson number conditions. Although the laminar jet impingement for isothermal condition has been already studied, however the constant heat flux has not been studied enough. the present paper will analyze a low velocity air jet, Which can be used for cooling of a simulated electronics package
International Nuclear Information System (INIS)
Anderson, A.; Eriksson, L.G.; Lisak, M.
1986-01-01
The present report summarizes the work performed within the contract JT4/9008, the aim of which is to derive analytical models for ion velocity distributions resulting from ICRF heating on JET. The work has been performed over a two-year-period ending in August 1986 and has involved a total effort of 2.4 man years. (author)
Directory of Open Access Journals (Sweden)
Raj Kumar
2016-05-01
Full Text Available In this work, the effect of angle of attack ( α a of the discrete V-pattern baffle on thermohydraulic performance of rectangular channel has been studied experimentally. The baffle wall was constantly heated and the other three walls of the channel were kept insulated. The experimentations were conducted to collect the data on Nusselt number ( N u b and friction factor ( f b by varying the Reynolds number (Re = 3000–21,000 and angle of attack ( α a from 30° to 70°, for the kept values of relative baffle height ( H b / H = 0 . 50 , relative pitch ratio ( P b / H = 1 . 0 , relative discrete width ( g w / H b = 1 . 5 and relative discrete distance ( D d / L v = 0 . 67 . As compared to the smooth wall, the V-pattern baffle roughened channel enhances the Nusselt number ( N u b and friction factor ( f b by 4.2 and 5.9 times, respectively. The present discrete V-pattern baffle shapes with angle of attack ( α a of 60° equivalent to flow Reynolds number of 3000 yields the greatest thermohydraulic performance. Discrete V-pattern baffle has improved thermal performance as compared to other baffle shapes’ rectangular channel.
Mitigation of divertor heat loads by strike point sweeping in high power JET discharges
Silburn, S. A.; Matthews, G. F.; Challis, C. D.; Frigione, D.; Graves, J. P.; Mantsinen, M. J.; Belonohy, E.; Hobirk, J.; Iglesias, D.; Keeling, D. L.; King, D.; Kirov, K.; Lennholm, M.; Lomas, P. J.; Moradi, S.; Sips, A. C. C.; Tsalas, M.; Contributors, JET
2017-12-01
Deliberate periodic movement (sweeping) of the high heat flux divertor strike lines in tokamak plasmas can be used to manage the heat fluxes experienced by exhaust handling plasma facing components, by spreading the heat loads over a larger surface area. Sweeping has recently been adopted as a routine part of the main high performance plasma configurations used on JET, and has enabled pulses with 30 MW plasma heating power and 10 MW radiation to run for 5 s without overheating the divertor tiles. We present analysis of the effectiveness of sweeping for divertor temperature control on JET, using infrared camera data and comparison with a simple 2D heat diffusion model. Around 50% reduction in tile temperature rise is obtained with 5.4 cm sweeping compared to the un-swept case, and the temperature reduction is found to scale slower than linearly with sweeping amplitude in both experiments and modelling. Compatibility of sweeping with high fusion performance is demonstrated, and effects of sweeping on the edge-localised mode behaviour of the plasma are reported and discussed. The prospects of using sweeping in future JET experiments with up to 40 MW heating power are investigated using a model validated against existing experimental data.
Mitigation of divertor heat loads by strike point sweeping in high power JET discharges
International Nuclear Information System (INIS)
Silburn, S A; Matthews, G F; Challis, C D; Belonohy, E; Iglesias, D; Keeling, D L; King, D; Kirov, K; Lomas, P J; Frigione, D; Graves, J P; Mantsinen, M J; Hobirk, J; Lennholm, M; Moradi, S; Sips, A C C; Tsalas, M
2017-01-01
Deliberate periodic movement (sweeping) of the high heat flux divertor strike lines in tokamak plasmas can be used to manage the heat fluxes experienced by exhaust handling plasma facing components, by spreading the heat loads over a larger surface area. Sweeping has recently been adopted as a routine part of the main high performance plasma configurations used on JET, and has enabled pulses with 30 MW plasma heating power and 10 MW radiation to run for 5 s without overheating the divertor tiles. We present analysis of the effectiveness of sweeping for divertor temperature control on JET, using infrared camera data and comparison with a simple 2D heat diffusion model. Around 50% reduction in tile temperature rise is obtained with 5.4 cm sweeping compared to the un-swept case, and the temperature reduction is found to scale slower than linearly with sweeping amplitude in both experiments and modelling. Compatibility of sweeping with high fusion performance is demonstrated, and effects of sweeping on the edge-localised mode behaviour of the plasma are reported and discussed. The prospects of using sweeping in future JET experiments with up to 40 MW heating power are investigated using a model validated against existing experimental data. (paper)
Directory of Open Access Journals (Sweden)
Abhijit Paul
2016-09-01
Full Text Available Present article illustrates a computational study of three-dimensional steady state heat transfer and high turbulent flow characteristics through a rectangular duct with constant heat fluxed upper wall and single rectangular cross-sectioned baffle insertion at different angles. RNG k–ɛ model along with standard wall function based computations has been accomplished applying the finite volume method, and SIMPLE algorithm has been executed for solving the governing equations. For a Reynolds number, Re of 10,000 to 50,000, Prandtl Number, Pr of 0.707 and baffle angle, α of 30°, 60°, 90°, 120°, 150°, computational studies are executed, centred onto the hydraulic diameter, Dh, test section and hydrodynamic entry length of the duct. Flow field has been solved using Ansys Fluent 14.0 software. Study exposes that baffled rectangular duct has a higher average Nusselt number, Nu and Darcy friction factor, f compared to a smooth rectangular duct. Nu as well as f are found to be maximum at 90° baffle angle. Results illustrate that both α and Re play a significant role in heat transfer as well as flow characteristics and also effects TEF. The correctness of the results attained in this study is corroborated by comparing the results with those existing in the literature for smooth rectangular duct within a precision of ±2% for f and ±4% for Nu.
International Nuclear Information System (INIS)
Aziz, Abdul; Beers-Green, Arlen B.
2009-01-01
This paper investigates the performance and optimum design of a longitudinal rectangular fin attached to a convectively heated wall of finite thickness. The exposed surfaces of the fin lose heat to the environmental sink by simultaneous convection and radiation. The tip of the fin is assumed to lose heat by convection and radiation to the same sink. The analysis and optimization of the fin is conducted numerically using the symbolic algebra package Maple. The temperature distribution, the heat transfer rates, and the fin efficiency data is presented illustrating how the thermal performance of the fin is affected by the convection-conduction number, the radiation-conduction number, the base convection Biot number, the convection and radiation Biot numbers at the tip, and the dimensionless sink temperature. Charts are presented showing the relationship between the optimum convection-conduction number and the optimum radiation-conduction number for different values of the base convection Biot number and dimensionless sink temperature and fixed values of the convection and radiation Biot numbers at the tip. Unlike the few other papers which have applied the Adomian's decomposition and the differential quadrature element method to this problem but give illustrative results for specific fin geometry and thermal variables, the present graphical data are generally applicable and can be used by fin designers without delving into the mathematical details of the computational techniques.
Excitation of global Alfven Eigenmodes by RF heating in JET
Energy Technology Data Exchange (ETDEWEB)
Kerner, W; Borba, D; Gormezano, C; Huysmans, G; Porcelli, F; Start, D [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking; Fasoli, A [Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP); Sharapov, S [Kurchatov Institute, Moscow (Russian Federation)
1994-07-01
The alpha-particle confinement of future D-T experiments at JET can be severely degraded by Global Alfven Eigenmodes (AE). Scenarios for the excitation of Alfven Eigenmodes in usual (e.g. D-D) plasmas are proposed, which provide a MHD diagnostic and allow the study of the transport of super-Alfvenic ions. Active studies with separate control of TAE amplitude and energetic particle destabilization, measuring the plasma response, give more information than passive studies, in particular concerning the damping mechanisms. The TAE excitation can be achieved by means of the saddle coil and the ICRH antenna. The experimental method is introduced together with a theoretical model for RF excitation. (authors). 6 refs., 3 figs.
International Nuclear Information System (INIS)
Al Mers, A.; Mimet, A.
2006-01-01
We propose a new procedure using 1 D additive correction strategy (AC), for resolution of tow dimensional problem of heat and mass transfer in field reactor of adsorption cooling machine. The reactor contains a porous medium constituted of activated carbon reacting by adsorption with ammonia. The present paper demonstrated how the new procedure of the (AC) propose here can be used, in the case of non-rectangular domain and strongly anisotropic coefficients, to improve the convergence rate of different iterative solvers currently used: Point Gauss-Seidel (GS), the line Gauss-Seidel (LGS), strongly implicit procedure (SIP) and the strongly implicit solver (SIS). Results shows that for different solvers, the performance of the additive correction strategy is efficiently improved by using the new procedure.(Author)
International Nuclear Information System (INIS)
Fujii, Kota; Yamada, Masahiko
2013-01-01
Ice slurries are now commonly used as cold thermal storage materials, and have the potential to be applied to other engineering fields such as quenching metals to control properties, emergency cooling systems, and preservation of food and biomaterials at low temperatures. Although ice slurries have been widely utilized because of their high thermal storage densities, previous studies have revealed that the latent heat of ice particles is not completely released on melting because of insufficient contact between the ice particles and a heated surface. In this study, an injection flow that was bifurcated from the main flow of an ice slurry was employed to promote melting heat transfer of ice particles on a horizontal heated surface. The effects of injection angle and injection flow rate on local heat transfer coefficients and heat transfer coefficient ratios were determined experimentally. The results show that from two to three times higher heat transfer coefficients can be obtained by using large injection flow rates and injection angles. However, low injection angles improved the utilization rate of the latent heat of ice near the injection point by approximately a factor of two compared to that without injection. -- Highlights: • Melting of ice slurries were enhanced by the injection under constant total flow rate. • Contribution of ice particles and their latent heat to heat transfer was investigated. • Effect of velocity ratio of injection to that of main flow was examined. • Effect of the angle of injection flow to the main flow was also examined. • Appropriate conditions for the use of latent heat of ice and heat transfer did not coincide
Jafarimoghaddam, Amin; Aberoumand, Sadegh
2017-01-01
The present study aims to experimentally investigate heat transfer performance of rectangular and semicircular tubes in the presence of Ag / water nanofluids. The nanoparticles of Ag (silver) were used in seven different volume concentrations of 0.03%, 0.07%, 0.1%, 0.2%, 0.4%, 1% and 2%. The experiment was conducted in relatively low Reynolds numbers of 301 to 740. A heater with the power of 200 W was used to keep the outer surface of the tubes under a constant heat flux condition. In addition, the rectangular tube has been designed within the same length as the semicircular one and also within the same hydraulic diameter. Moreover, the average nanoparticles size was 20 nm. The outcome results of the present empirical work indicate that, for all the examined Reynolds numbers, the semicircular tube has higher convective heat transfer coefficient for all the utilized volume concentrations of Ag nanoparticles. The possible reasons behind this advantage are discussed through the present work mainly by taking the boundary effect on Brownian motions into account. Coming to this point that the conventional design for cooling system of photovoltaic cells is a heat sink with the rectangular graves, it is discussed that using a semicircular design may have the advantage over the rectangular one in convective heat transfer coefficient enhancement and hence a better cooling performance for these solar cells.
Directory of Open Access Journals (Sweden)
Amin Jafarimoghaddam
Full Text Available The present study aims to experimentally investigate heat transfer performance of rectangular and semicircular tubes in the presence of Ag / water nanofluids. The nanoparticles of Ag (silver were used in seven different volume concentrations of 0.03%, 0.07%, 0.1%, 0.2%, 0.4%, 1% and 2%. The experiment was conducted in relatively low Reynolds numbers of 301 to 740. A heater with the power of 200 W was used to keep the outer surface of the tubes under a constant heat flux condition. In addition, the rectangular tube has been designed within the same length as the semicircular one and also within the same hydraulic diameter. Moreover, the average nanoparticles size was 20 nm. The outcome results of the present empirical work indicate that, for all the examined Reynolds numbers, the semicircular tube has higher convective heat transfer coefficient for all the utilized volume concentrations of Ag nanoparticles. The possible reasons behind this advantage are discussed through the present work mainly by taking the boundary effect on Brownian motions into account. Coming to this point that the conventional design for cooling system of photovoltaic cells is a heat sink with the rectangular graves, it is discussed that using a semicircular design may have the advantage over the rectangular one in convective heat transfer coefficient enhancement and hence a better cooling performance for these solar cells.
An analysis of JET fast-wave heating and current drive experiments directly related to ITER
Energy Technology Data Exchange (ETDEWEB)
Bhatnagar, V P; Eriksson, L; Gormezano, C; Jacquinot, J; Kaye, A; Start, D F.H. [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking
1994-07-01
The ITER fast-wave system is required to serve a variety of purposes, in particular, plasma heating to ignition, current profile and burn control and eventually, in conjunction with other schemes, a central non-inductive current drive (CD) for the steady-state operation of ITER. The ICRF heating and current drive data that has been obtained in JET are analyzed in terms of dimensionless parameters, with a view to ascertaining its direct relevance to key ITER requirements. The analysis is then used to identify areas both in physics and technological aspects of ion-cyclotron resonance heating (ICRH) and CD that require further experimentation in ITER-relevant devices such as JET to establish the required data base. (authors). 12 refs., 8 figs.
An analysis of JET fast-wave heating and current drive experiments directly related to ITER
International Nuclear Information System (INIS)
Bhatnagar, V.P.; Eriksson, L.; Gormezano, C.; Jacquinot, J.; Kaye, A.; Start, D.F.H.
1994-01-01
The ITER fast-wave system is required to serve a variety of purposes, in particular, plasma heating to ignition, current profile and burn control and eventually, in conjunction with other schemes, a central non-inductive current drive (CD) for the steady-state operation of ITER. The ICRF heating and current drive data that has been obtained in JET are analyzed in terms of dimensionless parameters, with a view to ascertaining its direct relevance to key ITER requirements. The analysis is then used to identify areas both in physics and technological aspects of ion-cyclotron resonance heating (ICRH) and CD that require further experimentation in ITER-relevant devices such as JET to establish the required data base. (authors). 12 refs., 8 figs
ICRF heating in JET during initial operations with the ITER-like wall
Energy Technology Data Exchange (ETDEWEB)
Jacquet, P.; Brix, M.; Graham, M.; Mayoral, M.-L.; Meigs, A.; Monakhov, I.; Sirinelli, A. [Euratom/CCFE Fusion Association, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Bobkov, V.; Drewelow, P.; Pütterich, T. [Max-Planck-Institut für Plasmaphysik, EURATOM-Assoziation, Garching (Germany); Brezinsek, S. [IEK-4, Forschungszentrum Jülich, Association EURATOM-FZJ (Germany); Campergue, A-L. [Ecole Nationale des Ponts et Chaussées, F77455 Marne-la-Vallée (France); Colas, L. [CEA, IRFM, F-13108 Saint-Paul-Lez-Durance (France); Czarnecka, A. [Association Euratom-IPPLM, Hery 23, 01-497 Warsaw (Poland); Klepper, C. C. [Oak Ridge National Laboratory, Oak Ridge, TN 37831-6169 (United States); Lerche, E.; Van-Eester, D. [Association EURATOM-Belgian State, ERM-KMS, Brussels (Belgium); Milanesio, D. [Politecnico di Torino, Department of Electronics, Torino (Italy); Mlynar, J. [Association EURATOM-IPP.CR, Za Slovankou 3, 182 21 Praha 8 (Czech Republic); Collaboration: JET-EFDA Contributors
2014-02-12
In 2011/12, JET started operation with its new ITER-Like Wall (ILW) made of a tungsten (W) divertor and a beryllium (Be) main chamber wall. The impact of the new wall material on the JET Ion Cyclotron Resonance Frequency (ICRF) operation was assessed and also the properties of JET plasmas heated with ICRF were studied. No substantial change of the antenna coupling resistance was observed with the ILW as compared with the carbon wall. Heat-fluxes on the protecting limiters close the antennas quantified using Infra-Red (IR) thermography (maximum 4.5 MW/m{sup 2} in current drive phasing) are within the wall power load handling capabilities. A simple RF sheath rectification model using the antenna near-fields calculated with the TOPICA code can well reproduce the heat-flux pattern around the antennas. ICRF heating results in larger tungsten and nickel (Ni) contents in the plasma and in a larger core radiation when compared to Neutral Beam Injection (NBI) heating. Some experimental facts indicate that main-chamber W components could be an important impurity source: the divertor W influx deduced from spectroscopy is comparable when using RF or NBI at same power and comparable divertor conditions; the W content is also increased in ICRF-heated limiter plasmas; and Be evaporation in the main chamber results in a strong and long lasting reduction of the impurity level. The ICRF specific high-Z impurity content decreased when operating at higher plasma density and when increasing the hydrogen concentration from 5% to 20%. Despite the higher plasma bulk radiation, ICRF exhibited overall good plasma heating efficiency; The ICRF power can be deposited at plasma centre and the radiation is mainly from the outer part of the plasma. Application of ICRF heating in H-mode plasmas started, and the beneficial effect of ICRF central electron heating to prevent W accumulation in the plasma core could be observed.
Performance of Chilled Beam with Radial Swirl Jet and Diffuse Ceiling Air Supply in Heating Mode
DEFF Research Database (Denmark)
Bertheussen, Bård; Mustakallio, Panu; Melikov, Arsen Krikor
2013-01-01
). The room air temperature was kept at 21 °C. Tracer gas was used to simulate pollution from floor and desk. The experimental conditions comprised: 1) night time without heat sources in the room; the room air conditioning system was used to heat up the room; 2) heat load generated by an occupant (simulated...... by dressed thermal manikin) and a laptop; 3) heating by convectors positioned under the window (convectors used alone and convector used together with CSW supplying isothermal air for ventilation). The heat distribution provided by the systems was not effective compare to the distribution provided......The performance of diffuse ceiling air supply and chilled beam with swirl jet (CSW) in heating mode (winter situation) was studied and compared with regard to the generated indoor environment. An office mock-up with one occupant was simulated in a test room (4.5 x 3.95 x 3.5 m3 (L x W x H...
Alpha heating and isotopic mass effects in JET plasmas with sawteeth
Energy Technology Data Exchange (ETDEWEB)
Budny, R. V. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Team, JET [EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK
2016-02-09
The alpha heating experiment in the Joint European Torus (JET) 1997 DTE1 campaign is re-examined. Several effects correlated with tritium content and thermal hydrogenic isotopic mass < A> weaken the conclusion that alpha heating was clearly observed. These effects delayed the occurrence of significant sawtooth crashes allowing the electron and ion temperatures T e and T i to achieve higher values. Under otherwise equal circumstances T e and T i were typically higher for discharges with higher < A >, and significant scaling of T i, T e, and total stored energy with < A > were observed. The higher T i led to increased ion–electron heating rates with magnitudes comparable to those computed for alpha electron heating. Rates of other heating/loss processes also had comparable magnitudes. Simulations of T e assuming the observed scaling of T i are qualitatively consistent with the measured profiles, without invoking alpha heating
Burnout in a high heat-flux boiling system with an impinging jet
International Nuclear Information System (INIS)
Monde, M.; Katto, Y.
1978-01-01
An experimental study has been made on the fully-developed nucleate boiling at atmospheric pressure in a simple forced-convection boiling system, which consists of a heated flat surface and a small, high-speed jet of water or of freon-113 impinging on the heated surface. A generalized correlation for burnout heat flux data, that is applied to either water or freon-113 is successfully evolved, and it is shown that surface tension has an important role for the onset of burnout phenomenon, not only in the ordinary pool boiling, but also in the present boiling system with a forced flow. (author)
Directory of Open Access Journals (Sweden)
Hussain Alamin
2016-01-01
Full Text Available Due to their ease of manufacture, high heat transfer efficiency and compact design, helically coiled heat exchangers are increasingly being adopted in a number of industries. The higher heat transfer efficiency over straight pipes is due to the secondary flow that develops as a result of the centrifugal force. In spite of the widespread use of helically coiled heat exchangers, and the presence of bubbly two-phase flow in a number of systems, very few studies have investigated the resultant flow characteristics. This paper will therefore present the results of CFD simulations for the two-phase bubbly flow in helically coiled heat exchangers as a function of the volumetric void fraction and the tube cross-section design. The CFD results are compared to the scarce flow visualisation experimental results available in the open literature.
Hussain, Alamin; Fsadni, Andrew M.
2016-03-01
Due to their ease of manufacture, high heat transfer efficiency and compact design, helically coiled heat exchangers are increasingly being adopted in a number of industries. The higher heat transfer efficiency over straight pipes is due to the secondary flow that develops as a result of the centrifugal force. In spite of the widespread use of helically coiled heat exchangers, and the presence of bubbly two-phase flow in a number of systems, very few studies have investigated the resultant flow characteristics. This paper will therefore present the results of CFD simulations for the two-phase bubbly flow in helically coiled heat exchangers as a function of the volumetric void fraction and the tube cross-section design. The CFD results are compared to the scarce flow visualisation experimental results available in the open literature.
International Nuclear Information System (INIS)
Lyczkowski, R.W.; Solbrig, C.W.; Gidaspow, D.
1982-01-01
A numerical solution for laminar flow heat transfer between a flowing gas and its containing rectangular duct has been obtained for many different boundary conditions which may arise in nuclear waste repository ventilation corridors. The problem has been solved for the cases of insulation on no walls, one wall, two walls, and three walls with various finite resistances on the remaining walls. Simplifications are made to decouple the convective heat transfer problem from the far field conduction problem, but peripheral conduction is retained. Results have been obtained for several duct aspect ratios in the thermal entrance and in the fully developed regions, including the constant temperature cases. When one wall is insulated and the other three are at constant temperature, the maximum temperature occurs in the fluid rather than on the insulated wall. This maximum moves toward the insulated wall with increasing axial distance. Nusselt numbers for the same constant flux on all four walls with peripheral conduction lie in a narrow band bounded by zero and infinite peripheral conduction cases. A dimensionsless wall conduction group of four can be considered infinite for the purpose of estimating fully developed Nusselt numbers to within an accuracy of 3%. A decrease in wall and bulk temperatures by finite wall conduction has been demonstrated for the case of a black body radiation boundary condition. Nusselt numbers for the case of constant temperature on the top and bottom walls and constant heat flux on the side walls exhibited unexpected behavior. (orig.)
International Nuclear Information System (INIS)
Lyczkowski, R.W.; Solbrig, C.W.; Gidaspow, D.
1980-01-01
A numerical solution for laminar flow heat transfer between a flowing gas and its containing rectangular duct has been obtained for many different boundary conditions which may arise in nuclear waste repository ventilation corridors. The problem has been solved for the cases of insulation on no walls, one wall, two walls, and three walls with various finite resistances on the remaining walls. Simplifications are made to decouple the convective heat transfer problem for the far field conduction problem, but peripheral conduction is retained. Results have been obtained for several duct aspect ratios in the thermal entrance and in the fully developed regions, including the constant temperature cases. When one wall is insulated and the other three are at constant temperature, the maximum temperature occurs in the fluid rather than on the insulated wall. This maximum moves toward the insulated wall with increasing axial distance. Nusselt numbers for the same constant flux on all four walls with peripheral conduction lie in a narrow band bounded by zero and infinite peripheral conduction cases. A dimensionless wall conduction group of four can be considered infinite for the purpose of estimating fully developed Nusselt numbers to within an accuracy of 3%. A decrease in wall and bulk temperatures by finite wall conduction has been demonstrated for the case of a black body radiation boundary condition. Nusselt numbers for the case of constant temperature on the top and bottom walls and constant heat flux on the side walls exhibited unexpected behavior
Energy Technology Data Exchange (ETDEWEB)
Lyczkowski, R W [Institute of Gas Technology, Chicago, IL (USA); Solbrig, C W [EG and G Idaho, Inc., Idaho Falls (USA); Gidaspow, D [Illinois Inst. of Tech., Chicago (USA). Dept. of Chemical Engineering
1982-02-01
A numerical solution for laminar flow heat transfer between a flowing gas and its containing rectangular duct has been obtained for many different boundary conditions which may arise in nuclear waste repository ventilation corridors. The problem has been solved for the cases of insulation on no walls, one wall, two walls, and three walls with various finite resistances on the remaining walls. Simplifications are made to decouple the convective heat transfer problem from the far field conduction problem, but peripheral conduction is retained. Results have been obtained for several duct aspect ratios in the thermal entrance and in the fully developed regions, including the constant temperature cases. When one wall is insulated and the other three are at constant temperature, the maximum temperature occurs in the fluid rather than on the insulated wall. This maximum moves toward the insulated wall with increasing axial distance. Nusselt numbers for the same constant flux on all four walls with peripheral conduction lie in a narrow band bounded by zero and infinite peripheral conduction cases. A dimensionsless wall conduction group of four can be considered infinite for the purpose of estimating fully developed Nusselt numbers to within an accuracy of 3%. A decrease in wall and bulk temperatures by finite wall conduction has been demonstrated for the case of a black body radiation boundary condition. Nusselt numbers for the case of constant temperature on the top and bottom walls and constant heat flux on the side walls exhibited unexpected behavior.
International Nuclear Information System (INIS)
Ezato, Koichiro; Shimizu, Akihiko; Kunugi, Tomoaki.
1995-01-01
Numerical simulations are presented on the flow and heat transfer characteristics of an impinging round jet of argon plasma with atmospheric pressure. The target slab with finite thickness upon which plasma jet impinges is assumed to be as SiC which is a candidate material for plasma facing material of fusion reactor. The plasma jet is treated by use of a magnetohydrodynamics model that takes its two-temperature non-equilibrium state into account. The rear side of the target slab is assumed to be cooled by a gas-solid suspension impinging round jet. The result shows that the plasma is in non-equilibrium state in which the electron temperature is higher than the heavy particle in the outer region of plasma jet core and that the heat flux to the target slab is over 8 MW/m 2 in the region of the plasma jet core contacts. (author)
Transition to turbulence and noise radiation in heated coaxial jet flows
Energy Technology Data Exchange (ETDEWEB)
Gloor, Michael, E-mail: gloor@ifd.mavt.ethz.ch; Bühler, Stefan; Kleiser, Leonhard [Institute of Fluid Dynamics, ETH Zurich, 8092 Zurich (Switzerland)
2016-04-15
Laminar-turbulent transition and noise radiation of a parametrized set of subsonic coaxial jet flows with a hot primary (core) stream are investigated numerically by Large-Eddy Simulation (LES) and direct noise computation. This study extends our previous research on local linear stability of heated coaxial jet flows by analyzing the nonlinear evolution of initially laminar flows disturbed by a superposition of small-amplitude unstable eigenmodes. First, a baseline configuration is studied to shed light on the flow dynamics of coaxial jet flows. Subsequently, LESs are performed for a range of Mach and Reynolds numbers to systematically analyze the influences of the temperature and the velocity ratios between the primary and the secondary (bypass) stream. The results provide a basis for a detailed analysis of fundamental flow-acoustic phenomena in the considered heated coaxial jet flows. Increasing the primary-jet temperature leads to an increase of fluctuation levels and to an amplification of far-field noise, especially at low frequencies. Strong mixing between the cold bypass stream and the hot primary stream as well as the intermittent character of the flow field at the end of the potential core lead to a pronounced noise radiation at an aft angle of approximately 35{sup ∘}. The velocity ratio strongly affects the shear-layer development and therefore also the noise generation mechanisms. Increasing the secondary-stream velocity amplifies the dominance of outer shear-layer perturbations while the disturbance growth rates in the inner shear layer decrease. Already for r{sub mic} > 40R{sub 1}, where r{sub mic} is the distance from the end of the potential core and R{sub 1} is the core-jet radius, a perfect 1/r{sub mic} decay of the sound pressure amplitudes is observed. The potential-core length increases for higher secondary-stream velocities which leads to a shift of the center of the dominant acoustic radiation in the downstream direction.
Salehin, Musfequs; Ehsan, Mohammad Monjurul; Islam, A. K. M. Sadrul
2017-06-01
Heat transfer enhancement by corrugation in fluid domain is a popular method. The rate of improvement is more when it is used highly thermal conductive fluid as heating or cooling medium. In this present study, heat transfer augmentation was investigated numerically by implementing corrugation in the fluid domain and nanofluid as the base fluid in the turbulent forced convection regime. Finite volume method (FVM) was applied to solve the continuity, momentum and energy equations. All the numerical simulations were considered for single phase flow. A rectangle corrugated pipe with 5000 W/m2 constant heat flux subjected to the corrugated wall was considered as the fluid domain. In the range of Reynolds number 15000 to 40000, thermo-physical and hydrodynamic behavior was investigated by using CuO-water nanofluid from 1% to 5% volume fraction as the base fluid through the corrugated fluid domain. Corrugation justification was performed by changing the amplitude of the corrugation and the corrugation wave length for obtaining the increased heat transfer rate with minimum pumping power. For using CuO-water nanofluid, augmentation was also found more in the rectangle corrugated pipe both in heat transfer and pumping power requirement with the increase of Reynolds number and the volume fraction of nanofluid. For the increased pumping power, optimization of pumping power by using nanofluid was also performed for economic finding.
Effects of Water Jet on Heat-Affected Concretes
Czech Academy of Sciences Publication Activity Database
Sitek, Libor; Bodnárová, L.; Válek, J.; Zeleňák, Michal; Klich, Jiří; Foldyna, Josef; Novotný, M.
2013-01-01
Roč. 57, č. 1 (2013), s. 1036-1044 E-ISSN 1877-7058 R&D Projects: GA MŠk ED2.1.00/03.0082 Grant - others:GA ČR(CZ) GAP104/12/1988; TA ČR(CZ) TA01010948 Program:GA Institutional support: RVO:68145535 Keywords : concrete * heating * repair of structures * fireproof concrete s * surface layers Subject RIV: JN - Civil Engineering http://www.sciencedirect.com/science/article/pii/S1877705813008643
Visualization of the heat release zone of highly turbulent premixed jet flames
Lv, Liang; Tan, Jianguo; Zhu, Jiajian
2017-10-01
Visualization of the heat release zone (HRZ) of highly turbulent flames is significantly important to understand the interaction between turbulence and chemical reactions, which is the foundation to design and optimize engines. Simultaneous measurements of OH and CH2O using planar laser-induced fluorescence (PLIF) were performed to characterize the HRZ. A well-designed piloted premixed jet burner was employed to generate four turbulent premixed CH4/air jet flames, with different jet Reynolds numbers (Rejet) ranging from 4900 to 39200. The HRZ was visualized by both the gradient of OH and the pixel-by-pixel product of OH and CH2O. It is shown that turbulence has an increasing effect on the spatial structure of the flame front with an increasing height above the jet exit for the premixed jet flames, which results in the broadening of the HRZ and the increase of the wrinkling. The HRZ remains thin as the Rejet increases, whereas the preheat zone is significantly broadened and thickened. This indicates that the smallest turbulent eddies can only be able to enter the flame front rather than the HRZ in the present flame conditions. The flame quenching is observed with Rejet = 39200, which may be due to the strong entrainment of the cold air from outside of the burned gas region.
Choi, Byungchul
2012-06-01
The characteristics of autoignited lifted flames in laminar jets of carbon monoxide/hydrogen fuels have been investigated experimentally in heated coflow air. In result, as the jet velocity increased, the blowoff was directly occurred from the nozzle-attached flame without experiencing a stabilized lifted flame, in the non-autoignited regime. In the autoignited regime, the autoignited lifted flame of carbon monoxide diluted by nitrogen was affected by the water vapor content in the compressed air oxidizer, as evidenced by the variation of the ignition delay time estimated by numerical calculation. In particular, in the autoignition regime at low temperatures with added hydrogen, the liftoff height of the autoignited lifted flames decreased and then increased as the jet velocity increased. Based on the mechanism in which the autoignited laminar lifted flame is stabilized by ignition delay time, the liftoff height can be influenced not only by the heat loss, but also by the preferential diffusion between momentum and mass diffusion in fuel jets during the autoignition process. © 2012 The Korean Society of Mechanical Engineers.
Russell, L. D.
1979-01-01
The paper describes expendable, slug-type calorimeter probes developed for measuring high heat-flux levels of 10-30 kW/sq cm in electric-arc jet facilities. The probes are constructed with thin tungsten caps mounted on Teflon bodies; the temperature of the back surface of the tungsten cap is measured, and its rate of change gives the steady-state, absorbed heat flux as the calorimeter probe heats to destruction when inserted into the arc jet. It is concluded that the simple construction of these probes allows them to be expendable and heated to destruction to obtain a measurable temperature slope at high heating rates.
International Nuclear Information System (INIS)
Mirmanto; Kenning, D B R; Lewis, J S; Karayiannis, T G
2012-01-01
Experiments were conducted to investigate the pressure drop and heat transfer characteristics of single-phase flow of de-ionized water in single copper microchannels of hydraulic diameters 0.438 mm, 0.561 mm and 0.635 mm. The channel length was 62 mm. The experimental conditions covered a range of mass flux from 500 to 5000 kg/m 2 s in the laminar, transitional and low Reynolds number turbulent regimes. Pressure drop was measured for adiabatic flows with fluid inlet temperatures of 30°C, 60°C and 90°C. In the heat transfer tests, the heat flux ranged from 256 kW/m 2 to 519 kW/m 2 . Friction factors and Nusselt numbers determined from the measurements were higher than for fully-developed conditions, but in reasonable agreement with predictions made using published solutions for hydrodynamically and thermally developing flow. When entrance effects, experimental uncertainties, heat losses, inlet and exit losses, thermal boundary conditions and departure from laminar flow were considered, the results indicate that equations developed for flow and heat transfer in conventional size channels are applicable for water flows in microchannels of these sizes.
Heat and momentum transfer from an atmospheric argon hydrogen plasma jet to spherical particles
International Nuclear Information System (INIS)
Vaessen, P.H.M.
1984-01-01
In this thesis the author describes the energy and momentum transfer from the plasma jet to the spray particles. This is done both experimentally and theoretically. Also the internal energy process of the recombining plasma is discussed. All elastic and inelastic collisional and radiative processes, as well as transport effects within the plasma are considered. In the next section, the so called passive spectroscopy is treated. It describes the diagnostics of electron density and temperature measurement, as well as the investigation on heat content of the particles. Spatially resolved electron density and temperature profiles are presented. Next, the active spectroscopy, i.e. the laser Doppler anemometer is dealt with. With this diagnostic, axial spray-particle velocities inside the plasma jet were determined. The author also presents heat and momentum transfer modelling of the plasma, related to the plasma particle interaction. Finally, a one dimensional model verification is made, using the experimentally determined particle velocity and plasma temperature profiles. (Auth.)
International Nuclear Information System (INIS)
Koncar, Bostjan; Simonovski, Igor; Norajitra, Prachai
2009-01-01
Numerical analyses of jet impingement cooling presented in this paper were performed as a part of helium-cooled divertor studies for post-ITER generation of fusion reactors. The cooling ability of divertor cooled by multiple helium jets was analysed. Thermal-hydraulic characteristics and temperature distributions in the solid structures were predicted for the reference geometry of one cooling finger. To assess numerical errors, different meshes (hexagonal, tetra, tetra-prism) and discretisation schemes were used. The temperatures in the solid structures decrease with finer mesh and higher order discretisation and converge towards finite values. Numerical simulations were validated against high heat flux experiments, performed at Efremov Institute, St. Petersburg. The predicted design parameters show reasonable agreement with measured data. The calculated maximum thimble temperature was below the tile-thimble brazing temperature, indicating good heat removal capability of reference divertor design. (author)
Directory of Open Access Journals (Sweden)
Mahmood H. Ali
2015-02-01
Full Text Available A numerical study of non-Darcian natural convection heat transfer in a rectangular enclosure filled with porous medium saturated with viscous fluid was carried out. The effects of medium Rayleigh number, porosity, particle to fluid thermal conductivity ratio, Darcy number and enclosure aspect ratio on heat transfer were examined to demonstrate the ability of using this construction in thermal insulation of buildings walls.A modified Brinkman-Forchheimer-extended Darcy flow model was used and no-slip boundary conditions were imposed for velocity at the walls and the governing equations were expressed in dimensionless stream function, vorticity, and temperature formulation. The resulting algebraic equations obtained from finite difference discritization of vorticity and temperature equations are solved using (ADI method which uses Three Diagonal Matrix Algorithm (TDMA in each direction, while that of the stream function equation solved using successive iteration method.The study was done for the range of enclosure aspect ratio ( which is in the tall layers region at medium Rayleigh number ( , Darcy number (Da=10-3, 10-4, 10-5 , porosity (e=0.35, 0.45, 0.55, particle to fluid thermal conductivity (kS/kf=5.77, 38.5, 1385.5.The results showed that the Nusselt number is direct proportional to medium Rayleigh number and porosity and reversely proportional to Darcy number, ratio of particle to fluid thermal conductivity and enclosure aspect ratio. The variables that affect the heat transfer in the above arrangement was correlated in a mathematical equation that account better for their affects on heat transfer which is represented by mean Nusselt number (Nu.
Ion cyclotron resonance frequency heating in JET during initial operations with the ITER-like wall
Czech Academy of Sciences Publication Activity Database
Jacquet, P.; Bobkov, V.; Colas, L.; Czarnecka, A.; Lerche, E.; Mayoral, M.-L.; Monakhov, I.; Van-Eester, D.; Arnoux, G.; Brezinsek, S.; Brix, M.; Campergue, A.-L.; Devaux, S.; Drewelow, P.; Graham, M.; Klepper, C.C.; Meigs, A.; Milanesio, D.; Mlynář, Jan; Pütterich, T.; Sirinelli, A.
2014-01-01
Roč. 21, č. 6 (2014), 061510-061510 ISSN 1070-664X. [Topical conference on radio frequency power in plasmas/20./. Sorrento, 25.06.2013-28.06.2013] Institutional support: RVO:61389021 Keywords : JET * ITER-like wall * ICRF heating * impurities * sawtooth * simulation * transport Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.142, year: 2014 http://scitation.aip.org/content/aip/journal/pop/21/6/10.1063/1.4884354
Directory of Open Access Journals (Sweden)
Foroutani Saeed
2017-01-01
Full Text Available This research investigates the laminar steady-forced convection heat transfer of a Cu-water nanofluid in a 2-D horizontal channel with different block geometries attached to the bottom wall. The block geometries assumed in this research are triangular and curve blocks. The governing equations associated with the required boundary conditions are solved using finite volume method based on the SIMPLE technique and the effects of Reynolds number, nanofluid volume fraction, block geometry, and the numbers of blocks on the local and average Nusselt numbers are explored. The obtained results show that nanoparticles can effectively enhance the heat transfer in a channel. Furthermore, the local and average Nusselt number distribution is strongly dependent on the block geometry. As observed, the heat transfer augments with the increase in the Reynolds number and nanofluid volume fraction for both block geometries. It is also concluded that the average Nusselt number of the curve block is higher than that of the triangular block for different Reynolds numbers which declares the importance of the block geometry in the heat transfer enhancement.
International Nuclear Information System (INIS)
Kinoshita, Hidetaka; Terada, Atsuhiko; Kaminaga, Masanori; Hino, Ryutaro
2001-10-01
In the design of a spallation target system, the water cooling system, for example a proton beam window and a safety hull, is used with narrow channels, in order to remove high heat flux and prevent lowering of system performance by absorption of neutron. And in narrow channel, heat transfer enhancement using 2-D rib is considered for reduction the cost of cooling component and decrease inventory of water in the cooling system, that is, decrease of the amount of irradiated water. But few studies on CHF with rib have been carried out. Experimental and analytical studies with rib-roughened test section, in 10:1 ratio of pitch to height, are being carried out in order to clarify the CHF in rib-roughened channel. This paper presents the review of previous researches on heat transfer in channel with rib roughness, overview of the test facility and the preliminary experimental and analytical results. As a result, wall friction factors were about 3 times as large as that of smooth channel, and heat transfer coefficients are about 2 times as large as that of smooth channel. The obtained CHF was as same as previous mechanistic model by Sudo. (author)
Al-Noman, Saeed M.; Choi, Sang Kyu; Chung, Suk-Ho
2015-01-01
The stabilization characteristics of laminar non-premixed jet flames of pre-vaporized iso-octane, one of the primary reference fuels for octane rating, have been studied experimentally in heated coflow air. Non-autoignited and autoignited lifted
International Nuclear Information System (INIS)
Mobtil, Mohammed; Bougeard, Daniel; Solliec, Camille
2014-01-01
Highlights: • A new method for convective heat flux determination on a moving wall is proposed. • An inverse technique is used for retrieving the heat flux from IR measurements. • Heat flux distribution determination in the slot jet impingement area is performed. • The accuracy of the method is examined using CFD Based simulated experiments. • The inversion quality is tested according to several parameters of the experiments. - Abstract: In this study an inverse method is developed to determine the heat flux distribution on a moving plane wall. The method uses a thin layer of material (the measurement medium) glued on the conveyor belt. The heat flux distribution on the moving wall is then determined by an inverse method based on the temperature measurement by infrared thermography on the upper surface of the measurement medium. A finite element based inverse algorithm of a steady state heat conduction advection in the Eulerian frame is performed. The algorithm entails the use of the Tikhonov regularization method, along with the L-curve method to select an optimal regularization parameter. Both the direct solution of moving boundary problem and the inverse design formulation are presented. The accuracy of the inverse method is examined by simulating the exact and noisy data with four different values of the surface-to-jet velocity ratio, and two different materials (PVC and Aluminum) for the measurement medium. The results show a greater sensitivity to the convective heat flux allowing a better estimation of heat flux distribution for the PVC layer. An alternative underdetermined inverse scheme is also studied. This configuration allows a different extend between the retrieval heat flux surface and the measurement temperature surface
Flow Structure and Heat Transfer of Jet Impingement on a Rib-Roughened Flat Plate
Directory of Open Access Journals (Sweden)
Abdulrahman H. Alenezi
2018-06-01
Full Text Available The jet impingement technique is an effective method to achieve a high heat transfer rate and is widely used in industry. Enhancing the heat transfer rate even minimally will improve the performance of many engineering systems and applications. In this numerical study, the convective heat transfer process between orthogonal air jet impingement on a smooth, horizontal surface and a roughened uniformly heated flat plate is studied. The roughness element takes the form of a circular rib of square cross-section positioned at different radii around the stagnation point. At each location, the effect of the roughness element on heat transfer rate was simulated for six different heights and the optimum rib location and rib dimension determined. The average Nusselt number has been evaluated within and beyond the stagnation region to better quantify the heat transfer advantages of ribbed surfaces over smooth surfaces. The results showed both flow and heat transfer features vary significantly with rib dimension and location on the heated surface. This variation in the streamwise direction included both augmentation and decrease in heat transfer rate when compared to the baseline no-rib case. The enhancement in normalized averaged Nusselt number obtained by placing the rib at the most optimum radial location R/D = 2 was 15.6% compared to the baseline case. It was also found that the maximum average Nusselt number for each location was achieved when the rib height was close to the corresponding boundary layer thickness of the smooth surface at the same rib position.
Dry aerosol jet printing of conductive silver lines on a heated silicon substrate
Efimov, A. A.; Arsenov, P. V.; Protas, N. V.; Minkov, K. N.; Urazov, M. N.; Ivanov, V. V.
2018-02-01
A new method for dry aerosol jet printing conductive lines on a heated substrate is presented. The method is based on the use of a spark discharge generator as a source of dry nanoparticles and a heating plate for their sintering. This method allows creating conductive silver lines on a heated silicon substrate up to 300 °C without an additional sintering step. It was found that for effective sintering lines of silver nanoparticles the temperature of the heated substrate should be about more than 200-250 °C. Average thickness of the sintered silver lines was equal to ∼20 µm. Printed lines showed electrical resistivity equal to 35 μΩ·cm, which is 23 times greater than the resistivity of bulk silver.
The application of complex network time series analysis in turbulent heated jets
International Nuclear Information System (INIS)
Charakopoulos, A. K.; Karakasidis, T. E.; Liakopoulos, A.; Papanicolaou, P. N.
2014-01-01
In the present study, we applied the methodology of the complex network-based time series analysis to experimental temperature time series from a vertical turbulent heated jet. More specifically, we approach the hydrodynamic problem of discriminating time series corresponding to various regions relative to the jet axis, i.e., time series corresponding to regions that are close to the jet axis from time series originating at regions with a different dynamical regime based on the constructed network properties. Applying the transformation phase space method (k nearest neighbors) and also the visibility algorithm, we transformed time series into networks and evaluated the topological properties of the networks such as degree distribution, average path length, diameter, modularity, and clustering coefficient. The results show that the complex network approach allows distinguishing, identifying, and exploring in detail various dynamical regions of the jet flow, and associate it to the corresponding physical behavior. In addition, in order to reject the hypothesis that the studied networks originate from a stochastic process, we generated random network and we compared their statistical properties with that originating from the experimental data. As far as the efficiency of the two methods for network construction is concerned, we conclude that both methodologies lead to network properties that present almost the same qualitative behavior and allow us to reveal the underlying system dynamics
Salama, Amgad; El-Amin, Mohamed; Sun, Shuyu
2014-01-01
Numerical simulation of flow and heat transfer in two adjacent channels is conducted with one of the channels partially blocked. This system simulates typical channels of a material testing reactor. The blockage is assumed due to the buckling of one of the channel plates inward along its width. The blockage ratio considered in this work is defined as the ratio between the cross-sectional area of the blocked and the unblocked channel. In this work, we consider a blockage ratio of approximately 40%. However, the blockage is different along the width of the channel, ranging from 0% at the end of the channel to 90% in the middle. The channel walls are sandwiching volumetric heat sources that vary spatially as chopped cosine functions. Interesting patterns are highlighted and investigated. The reduction in the flow area of one channel results in the flow redistributing among the two channels according to the changes in their hydraulic conductivities. The results of the numerical simulations show that the maximum wall temperature in the blocked channel is well below the boiling temperature at the operating pressure.
Salama, Amgad
2014-08-25
Numerical simulation of flow and heat transfer in two adjacent channels is conducted with one of the channels partially blocked. This system simulates typical channels of a material testing reactor. The blockage is assumed due to the buckling of one of the channel plates inward along its width. The blockage ratio considered in this work is defined as the ratio between the cross-sectional area of the blocked and the unblocked channel. In this work, we consider a blockage ratio of approximately 40%. However, the blockage is different along the width of the channel, ranging from 0% at the end of the channel to 90% in the middle. The channel walls are sandwiching volumetric heat sources that vary spatially as chopped cosine functions. Interesting patterns are highlighted and investigated. The reduction in the flow area of one channel results in the flow redistributing among the two channels according to the changes in their hydraulic conductivities. The results of the numerical simulations show that the maximum wall temperature in the blocked channel is well below the boiling temperature at the operating pressure.
CAUSE AND EFFECT OF FEEDBACK: MULTIPHASE GAS IN CLUSTER CORES HEATED BY AGN JETS
International Nuclear Information System (INIS)
Gaspari, M.; Ruszkowski, M.; Sharma, P.
2012-01-01
Multiwavelength data indicate that the X-ray-emitting plasma in the cores of galaxy clusters is not cooling catastrophically. To a large extent, cooling is offset by heating due to active galactic nuclei (AGNs) via jets. The cool-core clusters, with cooler/denser plasmas, show multiphase gas and signs of some cooling in their cores. These observations suggest that the cool core is locally thermally unstable while maintaining global thermal equilibrium. Using high-resolution, three-dimensional simulations we study the formation of multiphase gas in cluster cores heated by collimated bipolar AGN jets. Our key conclusion is that spatially extended multiphase filaments form only when the instantaneous ratio of the thermal instability and free-fall timescales (t TI /t ff ) falls below a critical threshold of ≈10. When this happens, dense cold gas decouples from the hot intracluster medium (ICM) phase and generates inhomogeneous and spatially extended Hα filaments. These cold gas clumps and filaments 'rain' down onto the central regions of the core, forming a cold rotating torus and in part feeding the supermassive black hole. Consequently, the self-regulated feedback enhances AGN heating and the core returns to a higher entropy level with t TI /t ff > 10. Eventually, the core reaches quasi-stable global thermal equilibrium, and cold filaments condense out of the hot ICM whenever t TI /t ff ∼< 10. This occurs despite the fact that the energy from AGN jets is supplied to the core in a highly anisotropic fashion. The effective spatial redistribution of heat is enabled in part by the turbulent motions in the wake of freely falling cold filaments. Increased AGN activity can locally reverse the cold gas flow, launching cold filamentary gas away from the cluster center. Our criterion for the condensation of spatially extended cold gas is in agreement with observations and previous idealized simulations.
Numerical study of a heated cavity insulated by a horizontal laminar jet
Energy Technology Data Exchange (ETDEWEB)
Besbes, S.; Mhiri, H.; El Golli, S. [Ecole Nationale d' Ingenieurs de Monastir (Tunisia). Lab. de Mecanique des Fluides et Thermique; Le Palec, G.; Bournot, P. [Institut de Mecanique de Marseille (France)
2001-08-01
In this work, we present a numerical study of the thermal insulation of a heated two dimensional cavity limited on its superior part by a horizontal plane air jet. The lower horizontal wall is isothermal, while the two vertical walls are adiabatics. A finite difference method based on the stream function-vorticity formulation is developed to solve the dimensionless Navier-Stokes and energy equations resulting from some assumptions. The results allowed us to point out two flow configurations: if natural convection prevails, the hot jet issuing from the nozzle diffuses upwards, and consequently, the cavity cannot be insulated correctly. However, the use of an aspiration zone can then improve the insulation. When forced convection predominates, the hydrodynamic barrier is conserved, and the enclosure is also thermally well confined. (author)
Non-thermal DT yield with (D)T ICRH heating in JET
International Nuclear Information System (INIS)
Cotrell, G.A.; Bhatnagar, V.B.; Bures, M.; Hellsten, T.; Jacquinot, J.; Start, D.F.H.
1989-01-01
We present projections of the (D)T fusion yield expected during fundamental ICRH heating of D in JET plasmas. To obtain high Q, one needs to use a relatively high plasma density (n e > 5x10 19 m -3 ) and dipole antenna (k≅ 10%-30%), we have used ray-tracing and global wave ICRH codes to estimate cyclotron damping on deuterium (∼80%) and the rf power coupled directly to electrons (∼17%) via TTMP and Landau damping. With launched rf power P rf =12 MW deposited ∼0.3 m off-axis, we predict fusion powers P fus up to ∼8 MW for a range of JET plasmas with achieved plasma pressure n e o T e o = 6x10 20 keV m -3 and Z eff = 2. Projecting to P c = 20 MW, P fus increases to 17 MW with Z eff = 2. (author) 10 refs., 4 figs
Energy Technology Data Exchange (ETDEWEB)
Buschman, Francis X., E-mail: Francis.Buschman@unnpp.gov; Aumiller, David L.
2017-02-15
Highlights: • Direct contact condensation data on liquid jets up to 1.7 MPa in pure steam and in the presence of noncondensable gas. • Identified a pressure effect on the impact of noncondensables to suppress condensation heat transfer not captured in existing data or correlations. • Pure steam data is used to develop a new correlation for condensation heat transfer on subcooled liquid jets. • Noncondensable data used to develop a modification to the renewal time estimate used in the Young and Bajorek correlation for condensation suppression in the presence of noncondensables. • A jet injection boundary condition, using a sub-grid jet condensation model, is developed for COBRA-IE which provides a more detailed estimate of the condensation rate on the liquid jet and allows the use of jet specific closure relationships. - Abstract: Condensation on liquid jets is an important phenomenon for many different facets of nuclear power plant transients and analyses such as containment spray cooling. An experimental facility constructed at the Pennsylvania State University, the High Pressure Liquid Jet Condensation Heat Transfer facility (HPLJCHT), has been used to perform steady-state condensation heat transfer experiments in which the temperature of the liquid jet is measured at different axial locations allowing the condensation rate to be determined over the jet length. Test data have been obtained in a pure steam environment and with varying concentrations of noncondensable gas. This data extends the available jet condensation data from near atmospheric pressure up to a pressure of 1.7 MPa. An empirical correlation for the liquid side condensation heat transfer coefficient has been developed based on the data obtained in pure steam. The data obtained with noncondensable gas were used to develop a correlation for the renewal time as used in the condensation suppression model developed by Young and Bajorek. This paper describes a new sub-grid liquid jet
International Nuclear Information System (INIS)
Buschman, Francis X.; Aumiller, David L.
2017-01-01
Highlights: • Direct contact condensation data on liquid jets up to 1.7 MPa in pure steam and in the presence of noncondensable gas. • Identified a pressure effect on the impact of noncondensables to suppress condensation heat transfer not captured in existing data or correlations. • Pure steam data is used to develop a new correlation for condensation heat transfer on subcooled liquid jets. • Noncondensable data used to develop a modification to the renewal time estimate used in the Young and Bajorek correlation for condensation suppression in the presence of noncondensables. • A jet injection boundary condition, using a sub-grid jet condensation model, is developed for COBRA-IE which provides a more detailed estimate of the condensation rate on the liquid jet and allows the use of jet specific closure relationships. - Abstract: Condensation on liquid jets is an important phenomenon for many different facets of nuclear power plant transients and analyses such as containment spray cooling. An experimental facility constructed at the Pennsylvania State University, the High Pressure Liquid Jet Condensation Heat Transfer facility (HPLJCHT), has been used to perform steady-state condensation heat transfer experiments in which the temperature of the liquid jet is measured at different axial locations allowing the condensation rate to be determined over the jet length. Test data have been obtained in a pure steam environment and with varying concentrations of noncondensable gas. This data extends the available jet condensation data from near atmospheric pressure up to a pressure of 1.7 MPa. An empirical correlation for the liquid side condensation heat transfer coefficient has been developed based on the data obtained in pure steam. The data obtained with noncondensable gas were used to develop a correlation for the renewal time as used in the condensation suppression model developed by Young and Bajorek. This paper describes a new sub-grid liquid jet
Study of mechanism of burnout in a high heat-flux boiling system with an impinging jet
International Nuclear Information System (INIS)
Katto, Y.; Monde, M.
1974-01-01
Nucleate boiling at very high heat fluxes was created on a heated surface covered with a flowing film of saturated water at atmospheric pressure being maintained by a small circular jet of water held at the center of the heated surface. It was found that increasing the heat flux led to a limiting state of flow where the splashing of droplets from the heated surface was no longer increased being kept constant until burnout appeared; and that there was a close relation between the burnout heat flux and the jet velocity. A flow model, which can explain the characteristics of this boiling system, is proposed. It is suggested that the burnout may be connected with the separation of a liquid flow from the heated surface accompanied with the effusion of vapor. (U.S.)
Thielen, L.; Hanjalić, K.; Jonker, H.; Manceau, R.
2005-01-01
We present numerical computations of flow and heat transfer in multiple jets impinging normally on a flat heated surface, obtained with a new second-moment turbulence closure combined with an elliptic blending model of non-viscous wall blocking effect. This model provides the mean velocity and
Guervilly, C.; Cardin, P.
2017-10-01
We study rapidly rotating Boussinesq convection driven by internal heating in a full sphere. We use a numerical model based on the quasi-geostrophic approximation for the velocity field, whereas the temperature field is 3-D. This approximation allows us to perform simulations for Ekman numbers down to 10-8, Prandtl numbers relevant for liquid metals (˜10-1) and Reynolds numbers up to 3 × 104. Persistent zonal flows composed of multiple jets form as a result of the mixing of potential vorticity. For the largest Rayleigh numbers computed, the zonal velocity is larger than the convective velocity despite the presence of boundary friction. The convective structures and the zonal jets widen when the thermal forcing increases. Prograde and retrograde zonal jets are dynamically different: in the prograde jets (which correspond to weak potential vorticity gradients) the convection transports heat efficiently and the mean temperature tends to be homogenized; by contrast, in the cores of the retrograde jets (which correspond to steep gradients of potential vorticity) the dynamics is dominated by the propagation of Rossby waves, resulting in the formation of steep mean temperature gradients and the dominance of conduction in the heat transfer process. Consequently, in quasi-geostrophic systems, the width of the retrograde zonal jets controls the efficiency of the heat transfer.
Hybrid RANS/LES of flow and heat transfer in round impinging jets
International Nuclear Information System (INIS)
Kubacki, Slawomir; Dick, Erik
2011-01-01
Fluid flow and convective heat transfer predictions are presented of round impinging jets for several combinations of nozzle-plate distances H/D = 2, 6 and 13.5 (where D is the nozzle diameter) and Reynolds numbers Re = 5000, 23,000 and 70,000 with the newest version of the k-ω model of and three hybrid RANS/LES models. In the RANS mode of the hybrid RANS/LES models, the k-ω model is recovered. Three formulations are considered to activate the LES mode. The first model is similar to the hybrid models of and . The turbulent length scale is replaced by the grid size in the destruction term of the k-equation and in the definition of the RANS eddy viscosity. As grid size, a maximum measure of the hexahedral grid cell is used. The second model has the same k-equation, but the eddy viscosity is the minimum of the k-ω eddy viscosity and the Smagorinsky eddy viscosity, following a proposal by . The Smagorinsky eddy viscosity is formed with the cube root of the cell volume. The third model has, again, the same k-equation, but has an eddy viscosity which is an intermediate between the eddy viscosities of the first and second models. This is reached by using the cube root of the cell volume in the eddy viscosity formula of the first model. The simulation results are compared with experimental data for the high Reynolds number cases Re = 23,000 and Re = 70,000 and LES data for the low-Reynolds number case Re = 5000. The Reynolds numbers are defined with the nozzle diameter and the bulk velocity at nozzle outlet. At low nozzle-plate distance (the impingement plate is in the core of the jet), turbulent kinetic energy is overpredicted by RANS in the stagnation flow region. This leads to overprediction of the heat transfer rate along the impingement plate in the impact zone. At high nozzle-plate distance (the impingement plate is in the mixed-out region of the jet), the turbulence mixing is underpredicted by RANS in the shear layer of the jet which gives a too high length of
Testa, D.; Albergante, M.
2012-08-01
In the so-called ‘alpha-heating’ experiment performed on the JET tokamak during the deuterium-tritium campaign of 1997, the ion temperature was found to be far exceeding (both in absolute value and in its rise time) the level that could have been expected from direct collisional heating by the fusion-born alpha particles themselves and energy equipartition with the electrons. To date, no explanation has been put forward for this long standing puzzle, despite much work having been performed on this subject in the early 2000s. Two analysis methods that have recently become available have been employed to re-analyse these observations of an anomalous ion heating. First, an algorithm based on the sparse representation of signals has been used to analyse magnetic, reflectometry and electron-cyclotron emission measurements of the turbulence spectra in the drift-wave range of frequencies. This analysis has then been complemented with turbulence simulations performed with the GENE code. We find, both experimentally and in the simulations, that the presence of a minority, but sufficiently large, population of fusion-born alpha particles that have not yet fully thermalized stabilizes the turbulence in the ion-drift direction, but practically does not affect the turbulence in the electron-drift direction. We link such stabilization of the ion-drift-wave turbulence to the increase in the ion temperature above the level achieved in similar discharges that did not have (at all or enough) alpha particles. When the fusion-born alpha particles have fully thermalized, the turbulence spectrum in the ion-drift direction reappears at somewhat larger amplitudes, which we link to the ensuing reduction in the ion temperature. This phenomenological dynamics fully corresponds to the actual experimental observations. By taking into account an effect of the alpha particles that had not been previously considered, our new analysis finally presents a phenomenological explanation for the so
International Nuclear Information System (INIS)
Testa, D.; Albergante, M.
2012-01-01
In the so-called ‘alpha-heating’ experiment performed on the JET tokamak during the deuterium–tritium campaign of 1997, the ion temperature was found to be far exceeding (both in absolute value and in its rise time) the level that could have been expected from direct collisional heating by the fusion-born alpha particles themselves and energy equipartition with the electrons. To date, no explanation has been put forward for this long standing puzzle, despite much work having been performed on this subject in the early 2000s. Two analysis methods that have recently become available have been employed to re-analyse these observations of an anomalous ion heating. First, an algorithm based on the sparse representation of signals has been used to analyse magnetic, reflectometry and electron-cyclotron emission measurements of the turbulence spectra in the drift-wave range of frequencies. This analysis has then been complemented with turbulence simulations performed with the GENE code. We find, both experimentally and in the simulations, that the presence of a minority, but sufficiently large, population of fusion-born alpha particles that have not yet fully thermalized stabilizes the turbulence in the ion-drift direction, but practically does not affect the turbulence in the electron-drift direction. We link such stabilization of the ion-drift-wave turbulence to the increase in the ion temperature above the level achieved in similar discharges that did not have (at all or enough) alpha particles. When the fusion-born alpha particles have fully thermalized, the turbulence spectrum in the ion-drift direction reappears at somewhat larger amplitudes, which we link to the ensuing reduction in the ion temperature. This phenomenological dynamics fully corresponds to the actual experimental observations. By taking into account an effect of the alpha particles that had not been previously considered, our new analysis finally presents a phenomenological explanation for the
Energy Technology Data Exchange (ETDEWEB)
Theron, M.; Bellenoue, M. [Laboratoire de Combustion et de Detonique, CNRS UPR 9028, Poitiers (France)
2006-06-15
In this paper, we explore the effects of heat release on mixing and flow structure in a high-speed subsonic turbulent H{sub 2} jet in an air coflow. Heat release effects are determined from the comparison of nonreacting and reacting jet behavior, boundary conditions being identical in both cases. Experiments are performed in a wind tunnel specifically designed for this purpose. Planar laser induced fluorescence on OH radicals and on acetone (seeded in the hydrogen jet) are used to characterize the cartography of scalars, and laser Doppler velocimetry is used to characterize velocity profiles in the far field of the H{sub 2} jet. Results show significant effects of heat release on mixing and flow structure, indicating an overall reduction of mixing and entrainment in the reacting jet compared to the nonreacting jet. First, a change is observed in the orientation of coherent structures originating from Kelvin-Helmholtz type instabilities, and responsible for air entrainment within the jet, which appear 'flatter' in the jet flame. Then, the flame length is increased over what would be predicted from the intersection of the mean stoichiometric contour with the centerline of the nonreacting jet. And finally, the longitudinal average velocity decrease along the jet axis is quicker in the nonreacting jet, and nondimensional transverse velocity fluctuations are about half as high in the reacting jet as in the nonreacting jet, indicating a reduction of the turbulence intensity of the flow in this direction in the jet flame. (author)
Ongena, Jef; Mailloux, Joelle; Mayoral, Marie-Line
2009-04-01
This special cluster of papers summarizes the work accomplished during the last three years in the framework of the Task Force Heating at JET, whose mission it is to study the optimisation of heating systems for plasma heating and current drive, launching and deposition questions and the physics of plasma rotation. Good progress and new physics insights have been obtained with the three heating systems available at JET: lower hybrid (LH), ion cyclotron resonance heating (ICRH) and neutral beam injection (NBI). Topics covered in the present issue are the use of edge gas puffing to improve the coupling of LH waves at large distances between the plasma separatrix and the LH launcher. Closely linked with this topic are detailed studies of the changes in LH coupling due to modifications in the scrape-off layer during gas puffing and simultaneous application of ICRH. We revisit the fundamental ICRH heating of D plasmas, include new physics results made possible by recently installed new diagnostic capabilities on JET and point out caveats for ITER when NBI is simultaneously applied. Other topics are the study of the anomalous behaviour of fast ions from NBI, and a study of toroidal rotation induced by ICRH, both again with possible implications for ITER. In finalizing this cluster of articles, thanks are due to all colleagues involved in preparing and executing the JET programme under EFDA in recent years. We want to thank the EFDA leadership for the special privilege of appointing us as Leaders or Deputies of Task Force Heating, a wonderful and hardworking group of colleagues. Thanks also to all other European and non-European scientists who contributed to the JET scientific programme, the Operations team of JET and the colleagues of the Close Support Unit (CSU). Thanks are also due to the Editors, Editorial Board and referees of Plasma Physics and Controlled Fusion together with the publishing staff of IOP Publishing who have supported and contributed substantially to
Energy Technology Data Exchange (ETDEWEB)
Wolf, R C [Institut fuer Plasmaphysik, Forschungszentrum Juelich, Association EURATOM/FZJ, Trilateral Euregio Cluster, D-52425 Juelich (Germany); Baranov, Y [UKAEA/EURATOM Fusion Association, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Garbet, X [Association EURATOM-CEA sur la fusion, CEA Cadarache, F-13108 St Paul lez Durance (France); Hawkes, N [UKAEA/EURATOM Fusion Association, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Peeters, A G [Max-Planck-Institut fuer Plasmaphysik, EURATOM-Assoziation, D-85748 Garching (Germany); Challis, C [UKAEA/EURATOM Fusion Association, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Baar, M de [FOM Instituut voor Plasmafyisica Rijnhuizen, Association EURATO-FOM, Trilateral Euregio Cluster, PO Box 1207, 3430 BE Nieuwegein (Netherlands); Giroud, C [FOM Instituut voor Plasmafyisica Rijnhuizen, Association EURATO-FOM, Trilateral Euregio Cluster, PO Box 1207, 3430 BE Nieuwegein (Netherlands); Joffrin, E [Association EURATOM-CEA sur la fusion, CEA Cadarache, F-13108 St Paul lez Durance (France); Mantsinen, M [Helsinki University of Technology, Association-EURATOM Tekes, FIN-02015 HUT (Finland); Mazon, D [Association EURATOM-CEA sur la fusion, CEA Cadarache, F-13108 St Paul lez Durance (France); Meister, H [Max-Planck-Institut fuer Plasmaphysik, EURATOM-Assoziation, D-85748 Garching (Germany); Suttrop, W [Max-Planck-Institut fuer Plasmaphysik, EURATOM-Assoziation, D-85748 Garching (Germany); Zastrow, K-D [UKAEA/EURATOM Fusion Association, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom)
2003-09-01
In ASDEX Upgrade and JET, the ion temperature profiles can be described by R/L{sub Ti} which exhibits only little variations, both locally, when comparing different discharges, and radially over a wide range of the poloidal cross-section. Considering a change of the local ion heat flux of more than a factor of two, this behaviour indicates some degree of profile stiffness. In JET, covering a large ion temperature range from 1 to 25 keV, the normalized ion temperature gradient, R/L{sub Ti}, shows a dependence on the electron to ion temperature ratio or toroidal rotational shear. In particular, in hot ion plasmas, produced predominantly by neutral beam heating at low densities, in which large T{sub i}/T{sub e} is coupled to strong toroidal rotation, the effect of the two quantities cannot be distinguished. Both in ASDEX Upgrade and JET, plasmas with internal transport barriers (ITBs), including the PEP mode in JET, are characterized by a significant increase of R/L{sub Ti} above the value of L- and H-mode plasmas. In agreement with previous ASDEX Upgrade results, no increase of the ion heat transport in reversed magnetic shear ITB plasmas is found in JET when raising the electron heating. Evidence is presented that magnetic shear directly influences R/L{sub Ti}, namely decreasing the ion heat transport when going from weakly positive to negative magnetic shear.
Energy Technology Data Exchange (ETDEWEB)
Dano, B.P.E.; Liburdy, J.A. [Oregon State Univ., Corvallis, OR (United States). Dept. of Mechanical Engineering; Kanokjaruvijit, Koonlaya [Imperial College, London (United Kingdom). Dept. of Mechanical Engineering
2005-02-01
The flow and heat transfer characteristics of confined jet array impingement with crossflow is investigated. Discrete impingement pressure measurements are used to obtain the jet orifice discharge flow coefficient. Digital particle image velocimetry (DPIV) and flow visualization are used to determine the flow characteristics. Two thermal boundary conditions at the impinging surface are presented: an isothermal surface, and a uniform heat flux, where thermocouple and thermochromic liquid crystal methods were used, respectively, to determine the local heat transfer coefficient. Two nozzle geometries are studied, circular and cusped ellipse. Based on the interaction with the jet impingement at the surface, the crossflow is shown to influence the heat transfer results. The two thermal boundary conditions differ in overall heat transfer correlation with the jet Reynolds number. Detailed velocity data show that the flow development from the cusped ellipse nozzle affects the wall region flow more than the circular nozzle, as influenced by the crossflow interactions. The overall heat transfer for the uniform heat flux boundary condition is found to increase for the cusped ellipse orifice. (Author)
Application of a k-epsilon closure to a heated turbulent offset jet
International Nuclear Information System (INIS)
Raghunath, G.; Kumar, R.; Liburdy, J.A.
1986-01-01
The complex flow which occurs when a heated turbulent jet discharges above a cool, isothermal surface was investigated numerically. This flow is influenced by significant flow curvature, buoyancy, impingement, and recirculation. The main features of the flow have been characterized in the literature by the exit Reynolds number and offset ratio. It is the purpose of this study to assess the applicability of a modified k-epsilon closure model to this flow. Comparisons with limited data for the unheated case and flow predictions for the heated case are presented. The impingement distance is determined to within 2 percent of the experimental results. However, detailed velocity profiles are not well predicted near the wall. Curvature modification and the wall boundary condition for epsilon significantly affect the solution. 15 references
Energy Technology Data Exchange (ETDEWEB)
Rahman, M.; Rautaheimo, P.; Siikonen, T.
1997-12-31
A numerical investigation is carried out to predict the turbulent fluid flow and heat transfer characteristics of two-dimensional single and three impinging slot jets. Two low-Reynolds-number {kappa}-{epsilon} models, namely the classical model of Chien and the explicit algebraic stress model of Gatski and Speziale, are considered in the simulation. A cell-centered finite-volume scheme combined with an artificial compressibility approach is employed to solve the flow equations, using a diagonally dominant alternating direction implicit (DDADI) time integration method. A fully upwinded second order spatial differencing is adopted to approximate the convective terms. Roe`s damping term is used to calculate the flux on the cell face. A multigrid method is utilized for the acceleration of convergence. On average, the heat transfer coefficients predicted by both models show good agreement with the experimental results. (orig.) 17 refs.
Cause and Effect of Feedback: Multiphase Gas in Cluster Cores Heated by AGN Jets
Gaspari, M.; Ruszkowski, M.; Sharma, P.
2012-02-01
Multiwavelength data indicate that the X-ray-emitting plasma in the cores of galaxy clusters is not cooling catastrophically. To a large extent, cooling is offset by heating due to active galactic nuclei (AGNs) via jets. The cool-core clusters, with cooler/denser plasmas, show multiphase gas and signs of some cooling in their cores. These observations suggest that the cool core is locally thermally unstable while maintaining global thermal equilibrium. Using high-resolution, three-dimensional simulations we study the formation of multiphase gas in cluster cores heated by collimated bipolar AGN jets. Our key conclusion is that spatially extended multiphase filaments form only when the instantaneous ratio of the thermal instability and free-fall timescales (t TI/t ff) falls below a critical threshold of ≈10. When this happens, dense cold gas decouples from the hot intracluster medium (ICM) phase and generates inhomogeneous and spatially extended Hα filaments. These cold gas clumps and filaments "rain" down onto the central regions of the core, forming a cold rotating torus and in part feeding the supermassive black hole. Consequently, the self-regulated feedback enhances AGN heating and the core returns to a higher entropy level with t TI/t ff > 10. Eventually, the core reaches quasi-stable global thermal equilibrium, and cold filaments condense out of the hot ICM whenever t TI/t ff fashion. The effective spatial redistribution of heat is enabled in part by the turbulent motions in the wake of freely falling cold filaments. Increased AGN activity can locally reverse the cold gas flow, launching cold filamentary gas away from the cluster center. Our criterion for the condensation of spatially extended cold gas is in agreement with observations and previous idealized simulations.
THE JET HEATED X-RAY FILAMENT IN THE CENTAURUS A NORTHERN MIDDLE RADIO LOBE
International Nuclear Information System (INIS)
Kraft, R. P.; Forman, W. R.; Jones, C.; Nulsen, P. E. J.; Murray, S. S.; Hardcastle, M. J.; Croston, J. H.; Birkinshaw, M.; Worrall, D. M.
2009-01-01
We present results from a 40 ks XMM-Newton observation of the X-ray filament coincident with the southeast edge of the Centaurus A Northern Middle Radio Lobe (NML). We find that the X-ray filament consists of five spatially resolved X-ray knots embedded in a continuous diffuse bridge. The spectrum of each knot is well fitted by a thermal model with temperatures ranging from 0.3 to 0.7 keV and subsolar elemental abundances. In four of the five knots, nonthermal models are a poor fit to the spectra, conclusively ruling out synchrotron or IC/CMB mechanisms for their emission. The internal pressures of the knots exceed that of the ambient interstellar medium or the equipartition pressure of the NML by more than an order of magnitude, demonstrating that they must be short lived (∼3 x 10 6 yr). Based on energetic arguments, it is implausible that these knots have been ionized by the beamed flux from the active galactic nucleus of Cen A or that they have been shock heated by supersonic inflation of the NML. In our view, the most viable scenario for the origin of the X-ray knots is that they are the result of cold gas shock heated by a direct interaction with the jet. The most plausible model of the NML is that it is a bubble from a previous nuclear outburst that is being re-energized by the current outburst. The northeast inner lobe and the large-scale jet are lossless channels through which the jet material rapidly travels to the NML in this scenario. We also report the discovery of a large-scale (at least 35 kpc radius) gas halo around Cen A.
Modeling of fuel vapor jet eruption induced by local droplet heating
Sim, Jaeheon
2014-01-10
The evaporation of a droplet by non-uniform heating is numerically investigated in order to understand the mechanism of the fuel-vapor jet eruption observed in the flame spread of a droplet array under microgravity condition. The phenomenon was believed to be mainly responsible for the enhanced flame spread rate through a droplet cloud at microgravity conditions. A modified Eulerian-Lagrangian method with a local phase change model is utilized to describe the interfacial dynamics between liquid droplet and surrounding air. It is found that the localized heating creates a temperature gradient along the droplet surface, induces the corresponding surface tension gradient, and thus develops an inner flow circulation commonly referred to as the Marangoni convection. Furthermore, the effect also produces a strong shear flow around the droplet surface, thereby pushing the fuel vapor toward the wake region of the droplet to form a vapor jet eruption. A parametric study clearly demonstrated that at realistic droplet combustion conditions the Marangoni effect is indeed responsible for the observed phenomena, in contrast to the results based on constant surface tension approximation
International Nuclear Information System (INIS)
Sudo, Y.; Kaminaga, M.
1990-01-01
The effects of channel gap size on mixed forced and free convective heat transfer characteristics were experimentally investigated for water flowing near atmospheric pressure in a 750 mm long and 50 mm wide channel heated from both sides. The channel gap sizes investigated were 2.5, 6, 18 and 50 mm. Experiments were carried out for both aiding and opposing forced convective flows with a Reynolds number Re x of 4x10 to 6x10 6 and a Grashof number Gr x of 2x10 4 to 6x10 11 , where the distance x from the inlet of the channel is adopted as the characteristic length in Re x and Gr x . As for the results, the following were revealed for the parameters ranges investigated in this study. (1) When the dimensionless parameter, Gr x /Re x 21/8 Pr 1/2 is less than 10 -4 , the flow shows the nature of forced convective heat transfer for a channel with any channel gap size in both aiding and opposing flows. (2) When Gr x /Re x 21/8 Pr 1/2 is larger than 10 -2 , the flow shows the nature of free convective heat transfer for a channel with any channel gap size in both aiding and opposing flows. (3) When Gr x /Re x 21/8 Pr 1/2 is between 10 -4 and 10 -2 for the channel with a channel gap size equal to or larger than 6 mm, the heat transfer coefficients in both aiding and opposing flows become, on the average, higher than those predicted by the previous correlations for either the pure turbulent forced convection or the pure free convection, and can be expressed in simple forms with a combination of Gr x /Re x 21/8 Pr 1/2 and the previous correlation for either the pure turbulent forced convection or the free convection along a flat plate. (4) When Gr x /Re x 21/8 Pr 1/2 is between 10 -4 and 10 -2 for the channel with a channel gap size of 2.5 mm, the heat transfer coefficients in both aiding and opposing flows also become, on the average, higher than those predicted by the previous correlations for either the pure turbulent forced convection or the pure free convection. (orig./GL)
Modeling and computation of heat exchanges in the configuration of an impinging jet on a hot plate
International Nuclear Information System (INIS)
Seiler, N.; Mimouni, S.; Simonin, O.; Gardin, P.; Seiler, J.M.
2003-01-01
The knowledge of the metal temperature history is essential, especially when strip leave the rolling mill, to get adequate final mechanical properties of steel. Some experiments have yet been carried out on the heat transfer associated with the impingement of a planar (1*9 mm 2 ) subcooled (5-16 K) water jet on a heated plate. Complete boiling curves were then obtained at different locations from the stagnation point and it was observed a phenomenon of 'shoulder of flux' in the transition boiling region near the impingement point. The aim of this work is to compute the heat flux transferred between a very hot plate and a subcooled liquid under a planar impinging jet to obtain the transient temperature distribution in the plate. To achieve this goal, a physical modelling of the phenomenon of 'shoulder of flux' has been carried out. This modelling is based on the assumption that the apparition of periodic bubble oscillations at the wall surface is due to the hydrodynamic fragmentation by the jet. The relation derived from this modelling is validated against experimental results from the literature obtained for a wide range of jet velocity, subcooling and jet diameter. This model is implemented in the new multiphase flow solver developed by EDF 'SATURNE polyphasique'. Numerical results are then compared to experimental heat fluxes obtained on previous experiments. (authors)
Directory of Open Access Journals (Sweden)
Haritonova Larisa
2017-01-01
Full Text Available The article gives the analytical generalization of the data on the energy efficiency for heat exchangers with the flat heat exchange surface to which systems of impact plane parallel jets are sent. Functional relations of specific power consumption (per unit of area, which were obtained for the first time using the techniques of the similarity law, for moving a heat carrier are shown with regard to design and operation factors. The regression equations representing a mathematical model of the process enable to carry out an analysis of various factors impact on the parameter to be determined. The obtained results can be used to optimize or to create the calculation techniques for new highly-efficient heat exchange devices with jet plane -parallel impingement systems and also to reduce power consumption for moving a heat carrier.
Summary of energy and particle confinement in pellet-fuelled auxiliary-heated discharges on JET
International Nuclear Information System (INIS)
Milora, S.L.; Baylor, L.R.; Bartlett, D.V.
1989-01-01
A transient improvement in plasma performance and central confinement has been observed in auxiliary heated JET limiter plasmas associated with a peaking of the plasma density profile and strong centralized heating. Suitable target plasmas for ICRF and NBI heating experiments are created by deuterium pellet injection with a multi pellet injector system developed jointly by ORNL and JETZ . Two types of discharge conditions have been observed. In the first (type A), the density profiles decay gradually during the first 1.3s of the heating pulse while maintaining an elevated density core plasma inside r/a < 0.6 superimposed on a flat density pedestal. During this phase the central electron and ion temperatures increase rapidly (up to 12 keV and 10 keV respectively in the best discharges). This results in an increase in the central plasma pressure by approximately a factor of three (β(0) 5%) above gas fuelled discharges and gives rise to sharply increased pressure gradients in the plasma. An abrupt collapse of the central electron and ion temperatures terminates the enhanced phase at 1.3 s and leads eventually to a 20% decrease in plasma stored energy. While these discharges are predicted to be stable to kink modes, they approach the first stability boundary for ballooning modes in the region of steepest pressure gradient. The pressure and q profiles inferred from transport analysis are also close to those for which intermediate-n mode instability is predicted. (author) 11 refs., 4 figs
Ion cyclotron heating of JET D-D and D-T optimised shear plasmas
International Nuclear Information System (INIS)
Cottrell, G.; Baranov, Y.; Bartlett, D.
1998-12-01
This paper discusses the unique roles played by Ion Cyclotron Resonance Heating (ICRH) in the preparation, formation and sustainment of internal transport barriers (ITBs) in high fusion performance JET optimised shear experiments using the Mk. H poloidal divertor. Together with Lower Hybrid Current Drive (LHCD), low power ICRH is applied during the early ramp-up phase of the plasma current, 'freezing in' a hollow or flat current density profile with q(0)>1. In combination with up to ∼ 20 MW of Neutral Beam Injection (NBI), the ICRH power is stepped up to ∼ 6 MW during the main low confinement (L-mode) heating phase. An ITB forms promptly after the power step, revealed by a region of reduced central energy transport and peaked profiles, with the ion thermal diffusivity falling to values close to the standard neo-classical level near the centre of both D-D and D-T plasmas. At the critical time of ITB formation, the plasma contains an energetic ICRF hydrogen minority ion population, contributing ∼ 50% to the total plasma pressure and heating mainly electrons. As both the NBI population and the thermal ion pressure develop, a substantial part of the ICRF power is damped resonantly on core ions (ω = 2 ω cD = 3 ω cT ) contributing to the ion heating. In NBI step-down experiments, high performance has been sustained by maintaining central ICRH heating; analysis shows the efficiency of central ICRH ion heating to be comparable with that of NBI. The highest D-D fusion neutron rates (R NT = 5.6 x 10 16 s -1 ) yet achieved in JET plasmas have been produced by combining a low magnetic shear core with a high confinement (H-mode) edge. In D-T, a fusion triple product n i T i τ E = (1.2 ± 0.2) x 10 21 m -3 keVs was achieved with 7.2 MW of fusion power obtained in the L-mode and up to 8.2 MW of fusion power in the H-mode phase. (author)
Mantica, Paola
2016-10-01
Heat transport experiments in JET, based on ICRH heat flux scans and temperature modulation, have confirmed the importance of two transport mechanisms that are often neglected in modeling experimental results, but are crucial to reach agreement between theory and experiment and may be significant in ITER. The first mechanism is the stabilizing effect of the total pressure gradient (including fast ions) on ITG driven ion heat transport. Such stabilization is found in non-linear gyro-kinetic electro-magnetic simulations using GENE and GYRO, and is the explanation for the observed loss of ion stiffness in the core of high NBI-power JET plasmas. The effect was recently observed also in JET plasmas with dominant ICRH heating and small rotation, due to ICRH fast ions, which is promising for ITER. Such mechanism dominates over ExB flow shear in the core and needs to be included in quasi-linear models to increase their ability to capture the relevant physics. The second mechanism is the capability of small- scale ETG instabilities to carry a significant fraction of electron heat. A decrease in Te peaking is observed when decreasing Zeff Te/Ti, which cannot be ascribed to TEMs but is in line with ETGs. Non-linear GENE single-scale simulations of ETGs and ITG/TEMs show that the ITG/TEM electron heat flux is not enough to match experiment. TEM stiffness is also much lower than measured. In the ETG single scale simulations the external flow shear is used to saturate the ETG streamers. Multi-scale simulations are ongoing, in which the ion zonal flows are the main saturating mechanism for ETGs. These costly simulations should provide the final answer on the importance of ETG-driven electron heat flux in JET. with JET contributors [F.Romanelli, Proc.25thIAEA FEC]. Supported by EUROfusion Grant 633053.
International Nuclear Information System (INIS)
Radhouane, Amina; Mahjoub, Nejla; Mhiri, Hatem; Le Palec, George; Bournot, Philippe
2009-01-01
This paper deals with the interaction of twin inclined jets in crossflow. The consideration of this particular configuration is of great interest due to its wide presence in various domains and applications and to its dependence in many parameters. These parameters may be geometric like the jets height, the jet nozzles separating distance, the jet nozzles, exit section, etc... It may also be based upon one of the reigning features like the velocity ratio, the temperature gradient, etc...The gradient between the jets and the crossflow temperatures is precisely the parameter we intend to handle in the present work due to its great relevance in several environmental concerns and in technical constraints as well. The evaluation of this parameter will be carried out numerically on the temperature distribution itself. This evaluation is likely to give a thorough idea about the cooling/heating process resulted from the jets interaction with the oncoming crossflow. Such an understanding is likely to give viable solutions to problems raised by this configuration like the acid rain engendered by too hot fumes or the deterioration of the combustors walls by too high temperature jets, etc...The numerically simulated model is based on the resolution of the Navier-Stokes equations by means of the finite volume method and the RSM second order turbulent model and is validated by confrontation to experimental data depicted on the same geometric replica
Rectangular cartograms: the game
Berg, de M.T.; Nijnatten, van F.S.B.; Speckmann, B.; Verbeek, K.A.B.
2009-01-01
Raisz [3] introduced rectangular cartograms in 1934 as a way of visualizing spatial information, such as population or economic strength, of a set of regions like countries or states. Rectangular cartograms represent geographic regions by rectangles; the positioning and adjacencies of the rectangles
International Nuclear Information System (INIS)
Rylatt, D I; O'Donovan, T S
2014-01-01
Heat transfer to three configurations of ducted jet and un-ducted semiconfined jets is investigated experimentally. The influence of the jet operating parameters, stroke length (L 0 /D) and Reynolds (Re) number on the heat transferred to the jet is of particular interest. Heat transfer distributions to the jet are reported at H/D = 1 for a range of experimental parameters Re (1000 to 4000) and L 0 /D (5 to 20). Secondary and tertiary peaks are discernable in the heat transfer distributions across the range of parameters tested. It is shown that for a fixed Re varying the L 0 /D has little effect on the magnitude of the stagnation region heat transfer but does effect the position and magnitude of the secondary and tertiary peaks in the heat transfer distribution. It is also shown that for a fixed L 0 /D increasing the Re has a significant effect on the magnitude of the stagnation region heat transfer but has little impact on the position of the secondary and tertiary peaks in the heat transfer distributions. Ducting is added to the configuration to improve heat transfer by drawing cold air from a remote location into the jet flow. Ducting is shown to increase stagnation region and area averaged heat transfer across the range of jet parameters tested when compared with an un-ducted jets of equal confinement. Increasing the stroke length from L 0 /D = 5 to 20 for a Reynolds number of 2000 reduces the enhancement in stagnation region heat transfer provided by the ducting from 35% to 10%; the area averaged heat transfer provided by the ducting also changes from a 42% to a 21% enhancement. This is shown to be partly due to relative magnitude of the peaks in heat transfer outwith the stagnation region; at low stroke lengths, the difference in the magnitude of these peaks is large and reduces with increasing L 0 /D. It is also shown that as L 0 /D is increased the stagnation region heat transfer to the un-ducted jets increases while for the ducted jets stagnation region
Non-thermal DT yield with (D)T ICRH heating in JET
International Nuclear Information System (INIS)
Cottrell, G.A.; Bhatnagar, V.P.; Bures, M.; Hellsten, T.; Jacquinot, J.; Start, D.F.H.
1989-01-01
Projections of the (D)T fusion yield expected during fundamental ICRH heating of D in JET tritium plasmas are presented. The highest fusion multiplication factor, Q (≡P fus /P r.f. ), is achieved for a relatively high plasma density (n e0 > 5 x 10 19 m -3 ) and minority concentration ratio n D /n T ≅ 20-40% with dipole antenna (k || ∼ 7 m -1 ). The latter reduces mode conversion and maximizes the r.f. power coupled to the minority ions. We have used ray-tracing and global wave ICRH codes to calculate power deposition profiles; 80% is cyclotron damped by deuterium and 17% is coupled directly to electrons via TTMP and Landau damping. With launched r.f. power P r.f. = 12 MW deposited ∼ 0.3 m off-axis, we predict fusion powers P fus up to ∼ 8 MW for a range of JET plasmas with achieved plasma pressure N e0 T e0 - 6 x 10 20 keV m -3 and Z eff = 2. Projecting to P r.f. = 25 MW, P fus increases to 17 MW with Z eff = 2. (author)
Physics aspects and technical elements of an ICRF heating system for JET
International Nuclear Information System (INIS)
Adam, J.; Jacquinot, J.; Kuus, H.
1980-09-01
We first present an overview of the recent results obtained in existing Tokamaks. These experiments offer a critical test of the basic physics ideas, give an estimate of the overall heating performance and show the degree of development of the RF hardware. A second part is devoted to the basic water-particle physics. JET will have to work in a wide variety of plasma parameters which constitutes an unprecedented constraint. A range of frequency is found which accomodates, within limits, most of the operating scenarios foreseen in JET. Moving from the plasma to the outer world, the wave coupling theory determines the position, the surface and the voltage stand-off of the launching structure which is necessary to transmit the power. Modules capable of transmitting 5 MW per Octant are discussed in the light of the present technology. The most critical parameter influencing the antenna performance appears to be the distance from the antenna to the plasma. Finally we have summarized our experience and our discussions with the industrial firms to outline the components of the RF system: power tubes, power supply requirements, coaxial transmission lines and matching network. A lay out of the power plant is then given
Sim, Jaeheon
2015-05-12
Droplet evaporation by a localized heat source under microgravity conditions was numerically investigated in an attempt to understand the mechanism of the fuel vapor jet ejection, which was observed experimentally during the flame spread through a droplet array. An Eulerian-Lagrangian method was implemented with a temperature-dependent surface tension model and a local phase change model in order to effectively capture the interfacial dynamics between liquid droplet and surrounding air. It was found that the surface tension gradient caused by the temperature variation within the droplet creates a thermo-capillary effect, known as the Marangoni effect, creating an internal flow circulation and outer shear flow which drives the fuel vapor into a tail jet. A parametric study demonstrated that the Marangoni effect is indeed significant at realistic droplet combustion conditions, resulting in a higher evaporation constant. A modified Marangoni number was derived in order to represent the surface force characteristics. The results at different pressure conditions indicated that the nonmonotonic response of the evaporation rate to pressure may also be attributed to the Marangoni effect.
International Nuclear Information System (INIS)
Du, Changhe; Li, Liang; Wu, Xin; Feng, Zhenping
2016-01-01
Highlights: • We establish a suitable vortex chamber model for gas turbine blade leading edge. • Mechanism of vortex cooling is further discussed and presented. • Influences of jet nozzle geometry on vortex cooling characteristics are researched. • This paper focuses on assessment of flow field and thermal performance for different jet nozzle aspect ratio and area. - Abstract: In this paper, 3D viscous steady Reynolds Averaged Navier–Stokes (RANS) equations are utilized to investigate the influence of jet nozzle geometry on flow and thermal behavior of vortex cooling for gas turbine blades. Comparison between calculation with different turbulence models and the experimental data is conducted, and results show that the standard k-ω model provides the best accuracy. The grid independence analysis is performed to obtain the proper mesh number. First, the mechanism of vortex cooling is further discussed, and the pronounced impact of kinetic turbulence intensity, thin thermal boundary layer, violent radial convection and complex vortices on enhanced heat transfer performance is confirmed. Then, seven jet nozzle aspect ratios and seven jet nozzle to chamber cross section area ratios are selected to research the flow field and thermal characteristics of vortex cooling focusing on the streamline, static pressure ratio, total pressure loss ratio and Nusselt number. It is presented that the jet nozzle aspect ratio and jet nozzle to chamber cross section area ratio both impose a significant effect on the flow and thermal parameters. The averaged Nusselt number decreases at first and then increases with the increasing jet nozzle aspect ratio, reaching highest when aspect ratio equals to 1. The effect of area ratio on averaged Nusselt number is complex. Finally, the heat transfer results in this study are compared with other previous works. Results indicate that good agreement with previous data is achieved, and the enhanced thermal behavior may be acquired by
Modelling of combined ICRF and NBI heating in JET hybrid plasmas
Directory of Open Access Journals (Sweden)
Gallart Dani
2017-01-01
Full Text Available During the 2015-2016 JET campaigns many efforts have been devoted to the exploration of high performance plasma scenarios envisaged for ITER operation. In this paper we model the combined ICRF+NBI heating in selected key hybrid discharges using PION. The antenna frequency was tuned to match the cyclotron frequency of minority hydrogen (H at the center of the tokamak coinciding with the second harmonic cyclotron resonance of deuterium. The modelling takes into account the synergy between ICRF and NBI heating through the second harmonic cyclotron resonance of deuterium beam ions which allows us to assess its impact on the neutron rate RNT. We evaluate the influence of H concentration which was varied in different discharges in order to test their role in the heating performance. According to our modelling, the ICRF enhancement of RNT increases by decreasing the H concentration which increases the ICRF power absorbed by deuterons. We find that in the recent hybrid discharges this ICRF enhancement was in the range of 10-25%. Finally, we extrapolate the results to D-T and find that the best performing hybrid discharges correspond to an equivalent fusion power of ∼7.0 MW in D-T.
Steyn, Gideon; Vermeulen, Christiaan
2018-05-01
An experiment was designed to study the effect of the jet direction on convective heat-transfer coefficients in single-jet gas cooling of a small heated surface, such as typically induced by an accelerated ion beam on a thin foil or specimen. The hot spot was provided using a small electrically heated plate. Heat-transfer calculations were performed using simple empirical methods based on dimensional analysis as well as by means of an advanced computational fluid dynamics (CFD) code. The results provide an explanation for the observed turbulent cooling of a double-foil, Havar beam window with fast-flowing helium, located on a target station for radionuclide production with a 66 MeV proton beam at a cyclotron facility.
International Nuclear Information System (INIS)
Sieglin, Bernhard A.
2014-01-01
This work presents divertor heat load studies conducted at two of the largest tokamaks currently in operation, ASDEX Upgrade and the Joint European Torus (JET). A commonly agreed empirical scaling for the power fall-off length in H-mode obtained in carbon devices is validated in JET with the ILW. Bohm and Gyro-Bohm like models are identified as possible candidates describing the divertor broadening. Quantities for the assessment of the thermal load induced by transient heat loads are defined. JET with the ILW exhibits an on average longer ELM duration as compared to the carbon wall. For identical pedestal conditions the ELM durations in both cases are found to be the same within error bars. The energy fluency is found to depend mainly on the pedestal pressure with a weak dependence on the relative loss in stored energy. This is noteworthy since the current extrapolation to ITER assumes a linear dependence on the relative ELM size.
Studies of visible impurity radiation from JET plasmas during heating and fuelling experiments
International Nuclear Information System (INIS)
Morgan, P.D.; Hellermann, M. von; Mandl, W.; Stamp, M.F.; Summers, H.P.; Weisen, H.; Forrest, M.J.; Horton, L.; Zinoviev, A.
1989-01-01
At JET extensive use is made of visible spectroscopy in the study of plasma impurities. Measurements of absolute line intensities from such species as O II, C III and D I are used to deduce the influxes of light impurities as well as deuterium at the plasma periphery. The absolute continuum emission at 523.5 nm, measured using a 15-telescope poloidal array, is used to determine Z eff (r) and its temporal evolution. Charge-exchange recombination spectroscopy (CXRS) has proved to be a powerful technique during NBI to measure, amongst other parameters, the density of C and O at up to 15 separate points on the plasma minor radius. The combination of these diagnostic techniques permits the global impurity behaviour in the plasma to be followed. In this paper, results are reported pertaining to studies of plasmas heated by NBI and ICRF, and fuelled by the injection of D 2 pellets. (author) 5 refs., 4 figs
Transient heat transport studies in JET conventional and advanced tokamak plasmas
International Nuclear Information System (INIS)
Mantica, P.; Coffey, I.; Dux, R.
2003-01-01
Transient transport studies are a valuable complement to steady-state analysis for the understanding of transport mechanisms and the validation of physics-based transport models. This paper presents results from transient heat transport experiments in JET and their modelling. Edge cold pulses and modulation of ICRH (in mode conversion scheme) have been used to provide detectable electron and ion temperature perturbations. The experiments have been performed in conventional L-mode plasmas or in Advanced Tokamak regimes, in the presence of an Internal Transport Barrier (ITB). In conventional plasmas, the issues of stiffness and non-locality have been addressed. Cold pulse propagation in ITB plasmas has provided useful insight into the physics of ITB formation. The use of edge perturbations for ITB triggering has been explored. Modelling of the experimental results has been performed using both empirical models and physics-based models. Results of cold pulse experiments in ITBs have also been compared with turbulence simulations. (author)
Pellet fueling of JET plasmas during ohmic, ICRF and NBI heating
International Nuclear Information System (INIS)
Gondhalekar, A.; Cheetham, A.; Bures, M.
1986-01-01
Pellet fueling experiments have been performed on JET using a single-shot pneumatic injector giving 4.6mm (4.5 x 10 21 D atoms) and 3.6mm (2.2 x 10 21 D atoms) diameter cylindrical deuterium pellets with velocity 0.8 ≤ V(km.s -1 ) ≤ 1.2. Z/sub eff/ 20 m -3 and T/sub e/(0) ≅ 1keV. Separately, high value of n/sub D/(0)tau/sub E/T/sub i/(0) = 1.3 x 10 20 m -3 .s.keV at T/sub i/90) = 6.5keV has been obtained with pellet fueling followed by NBI heating
JET ({sup 3}He)-D scenarios relying on RF heating: survey of selected recent experiments
Energy Technology Data Exchange (ETDEWEB)
Van Eester, D; Lerche, E; Andrew, Y; Biewer, T M; Casati, A; Crombe, K; De la Luna, E; Ericsson, G; Felton, R; Giacomelli, L; Giroud, C; Hawkes, N; Hellesen, C; Hjalmarsson, A; Joffrin, E; Kaellne, J; Kiptily, V; Lomas, P; Mantica, P; Marinoni, A [JET-EFDA Culham Science Centre, Abingdon, OX14 3DB (United Kingdom)] (and others)
2009-04-15
Recent JET experiments have been devoted to the study of ({sup 3}He)-D plasmas involving radio frequency (RF) heating. This paper starts by discussing the RF heating efficiency theoretically expected in such plasmas, covering both relevant aspects of wave and of particle dynamics. Then it gives a concise summary of the main conclusions drawn from recent experiments that were either focusing on studying RF heating physics aspects or that were adopting RF heating as a tool to study plasma behavior. Depending on the minority concentration chosen, different physical phenomena are observed. At very low concentration (X[{sup 3}He] < 1%), energetic tails are formed which trigger MHD activity and result in loss of fast particles. Alfven cascades were observed and gamma ray tomography indirectly shows the impact of sawtooth crashes on the fast particle orbits. Low concentration (X[{sup 3}He] < 10%) favors minority heating while for X[{sup 3}He] >> 10% electron mode conversion damping becomes dominant. Evidence for the Fuchs et al standing wave effect (Fuchs et al 1995 Phys. Plasmas 2 1637-47) on the absorption is presented. RF induced deuterium tails were observed in mode conversion experiments with large X[{sup 3}He] ({approx}18%). As tentative modeling shows, the formation of these tails can be explained as a consequence of wave power absorption by neutral beam particles that efficiently interact with the waves well away from the cold D cyclotron resonance position as a result of their substantial Doppler shift. As both ion and electron RF power deposition profiles in ({sup 3}He)-D plasmas are fairly narrow-giving rise to localized heat sources-the RF heating method is an ideal tool for performing transport studies. Various of the experiments discussed here were done in plasmas with internal transport barriers (ITBs). ITBs are identified as regions with locally reduced diffusivity, where poloidal spinning up of the plasma is observed. The present know-how on the role of
Lerche, E.; Van Eester, D.; Johnson, T. J.; Hellsten, T.; Ongena, J.; Mayoral, M. L.; Frigione, D.; Sozzi, C.; Calabro, G.; Lennholm, M.; Beaumont, P.; Blackman, T.; Brennan, D.; Brett, A.; Cecconello, M.; Coffey, I.; Coyne, A.; Crombe, K.; Czarnecka, A.; Felton, R.; Giroud, C.; Gorini, G.; Hellesen, C.; Jacquet, P.; Kiptily, V.; Knipe, S.; Krasilnikov, A.; Maslov, M.; Monakhov, I.; Noble, C.; Nocente, M.; Pangioni, L.; Proverbio, I.; Sergienko, G.; Stamp, M.; Studholme, W.; Tardocchi, M.; Vdovin, V.; Versloot, T.; Voitsekhovitch, I.; Whitehurst, A.; Wooldridge, E.; Zoita, V.; JET-EFDA Contributors,
2012-01-01
Two ion cyclotron range of frequencies (ICRF) heating schemes proposed for the half-field operation phase of ITER in hydrogen plasmas—fundamental H majority and second harmonic 3 He ICRF heating—were recently investigated in JET. Although the same magnetic field and RF frequencies ( f ≈ 42 MHz and f
Directory of Open Access Journals (Sweden)
Donghwi Lee
2018-06-01
Full Text Available In this study, we investigate the interfacial droplet jetting characteristics and thermal stability of a focused surface acoustic wave device (F-SAW. An F-SAW device capable of generating a 20 MHz surface acoustic wave by applying sufficient radio frequency power (2–19 W on a 128°-rotated YX-cut piezoelectric lithium niobate substrate for interfacial droplet jetting is proposed. The interfacial droplet jetting characteristics were visualized by a shadowgraph method using a high-speed camera, and a heat transfer experiment was conducted using K-type thermocouples. The interfacial droplet jetting characteristics (jet angle and height were analyzed for two different cases by applying a single interdigital transducer and two opposite interdigital transducers. Surface temperature variations were analyzed with radio frequency input power increases to evaluate the thermal stability of the F-SAW device in air and water environments. We demonstrate that the maximum temperature increase of the F-SAW device in the water was 1/20 of that in the air, owing to the very high convective heat transfer coefficient of the water, resulting in prevention of the performance degradation of the focused acoustic wave device.
Fusion performances and alpha heating in future JET D-T plasmas
Energy Technology Data Exchange (ETDEWEB)
Balet, B; Cordey, J G; Gibson, A; Lomas, P; Stubberfield, P M; Thomas, P [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking
1994-07-01
The new pump divertor installed at JET should allow high performance pulses of a few seconds duration by both preventing the impurity influx and controlling the density evolution. The TRANSP code has been used in a predictive mode to assess the possible fusion performance of such plasmas fuelled with a 50:50 mixture of D and T, and the effect of alpha particles heating on Te and Ti. Several cases are considered: 50:50 D-T mix; 50:50 D-T mix, no C bloom; 50:50 D-T mix, VH phase, density control; 50:50 D-T mix, VH phase, density control, 6 Ma. The predictions show that if the the bloom and MHD instabilities can be controlled at higher plasma currents using a higher toroidal field to keep a reasonable beta value, then a higher fusion performance steady state plasma with Q{sub DT} superior to 2.5 should be possible. The alpha heating power of 4.9 MW would lead to a 74% increase in Te. 4 refs., 4 figs., 1 tab.
Ion cyclotron resonance heating for tungsten control in various JET H-mode scenarios
Goniche, M.; Dumont, R. J.; Bobkov, V.; Buratti, P.; Brezinsek, S.; Challis, C.; Colas, L.; Czarnecka, A.; Drewelow, P.; Fedorczak, N.; Garcia, J.; Giroud, C.; Graham, M.; Graves, J. P.; Hobirk, J.; Jacquet, P.; Lerche, E.; Mantica, P.; Monakhov, I.; Monier-Garbet, P.; Nave, M. F. F.; Noble, C.; Nunes, I.; Pütterich, T.; Rimini, F.; Sertoli, M.; Valisa, M.; Van Eester, D.; Contributors, JET
2017-05-01
Ion cyclotron resonance heating (ICRH) in the hydrogen minority scheme provides central ion heating and acts favorably on the core tungsten transport. Full wave modeling shows that, at medium power level (4 MW), after collisional redistribution, the ratio of power transferred to the ions and the electrons vary little with the minority (hydrogen) concentration n H/n e but the high-Z impurity screening provided by the fast ions temperature increases with the concentration. The power radiated by tungsten in the core of the JET discharges has been analyzed on a large database covering the 2013-2014 campaign. In the baseline scenario with moderate plasma current (I p = 2.5 MA) ICRH modifies efficiently tungsten transport to avoid its accumulation in the plasma centre and, when the ICRH power is increased, the tungsten radiation peaking evolves as predicted by the neo-classical theory. At higher current (3-4 MA), tungsten accumulation can be only avoided with 5 MW of ICRH power with high gas injection rate. For discharges in the hybrid scenario, the strong initial peaking of the density leads to strong tungsten accumulation. When this initial density peaking is slightly reduced, with an ICRH power in excess of 4 MW,very low tungsten concentration in the core (˜10-5) is maintained for 3 s. MHD activity plays a key role in tungsten transport and modulation of the tungsten radiation during a sawtooth cycle is correlated to the fishbone activity triggered by the fast ion pressure gradient.
Thermal Response of Tritiated Codeposits from JET and TFTR to Transient Heat Pulses
International Nuclear Information System (INIS)
Skinner, C.H.; Bekrisl, N.; Coad, J.P.; Gentile, C.A.; Hassanein, A.; Reiswig, R.; Willms, S.
2002-01-01
High heat flux interactions with plasma-facing components have been studied at microscopic scales. The beam from a continuous wave neodymium laser was scanned at high speed over the surface of graphite and carbon fiber composite tiles that had been retrieved from TFTR (Tokamak Fusion Test Reactor) and JET (Joint European Torus) after D-T plasma operations. The tiles have a surface layer of amorphous hydrogenated carbon that was co-deposited during plasma operations, and laser scanning has released more than 80% of the co-deposited tritium. The temperature rise of the co-deposit was much higher than that of the manufactured material and showed an extended time history. The peak temperature varied dramatically (e.g., 1,436 C compared to >2,300 C), indicating strong variations in the thermal conductivity to the substrate. A digital microscope imaged the co-deposit before, during, and after the interaction with the laser and revealed 100-micron scale hot spots during the interaction. Heat pulse durations of order 100 ms resulted in brittle destruction and material loss from the surface, whilst a duration of =10 ms showed minimal changes to the co-deposit. These results show that reliable predictions for the response of deposition areas to off-normal events such as ELMs (edge-localized modes) and disruptions in next-step devices need to be based on experiments with tokamak generated co-deposits
Identification of minority ion cyclotron emission during radio frequency heating in the JET tokamak
International Nuclear Information System (INIS)
Cottrell, G.A.
1999-11-01
First measurements and identification of Minority Ion Cyclotron Emission (MICE) during ICRF (H)D minority heating in the JET tokamak are presented. An inner wall radiofrequency (rf) probe shows the new single MICE spectral line, downshifted from the heating, frequency and appearing ∼ 400 ms after the ICRH switch-on. The line is narrow (Δω / ω) ∼ 0.04), characterised by the ion cyclotron frequency of minority protons in the outer edge mid-plane plasma and is observed irrespective of whether single or multi-frequency ICRH is applied. Threshold conditions for MICE are: coupled RF power to the plasma P rf ≥ 4.5 MW; total fast ion energy content W fast ≥ 0.6 MJ. At the time of the rapid switch-on of MICE, the measured power loss from the energetic minority ions is ∼ 0.1 ± 0.1 MW, constituting rf . The observations are consistent with the classical evolution and population of the plasma edge with ∼ 3 MeV ICRH protons on orbits near the outboard limiters. Particle loss and energy filtering contribute to a local non-Maxwellian energetic ion distribution which is susceptible to ion cyclotron instability
Energy Technology Data Exchange (ETDEWEB)
Drobniak, S.; Elsner, J.W. [Tech. Univ. of Czestochowa (Poland). Inst. of Thermal Machinary; El-Kassem, E.S.A. [Cairo University, Faculty of Engineering, Giza (Egypt)
1998-03-19
This paper describes an experimental study of the relationship between coherent vortical structures and the intensity of heat transport in the initial region of a round, free jet. Simultaneous measurements of velocity and temperature were taken with a four-wire combined probe in a jet that was acoustically stimulated with a frequency corresponding to the jet-column mode. The obtained results suggest that the mutual phase relations between oscillatory and random components of velocity and temperature lead to substantial intensification of the radial heat transport. Due to the same reason the longitudinal heat flux does not reveal a significant change in the presence of coherent structures and, as a result, a much wider spread of the temperature field in comparison with velocity may be observed as a characteristic feature of this flow. It was also observed that heat transfer processes are realized in substantial part by random turbulence generated due to the action of coherent motion. (orig.) With 13 figs., 27 refs.
International Nuclear Information System (INIS)
Bhatnagar, V.P.; Taroni, A.; Ellis, J.J.; Jacquinot, J.; Stuart, D.F.
1989-01-01
In this paper, we compare experimental results of electron and ion-heating in discharges that feature monster sawtooth with those in pellet-produced peaked-density profile discharges which were heated with ICRF. Also we carry out a comprehensive analysis of ICRF-heated peaked-density profile discharges by a transport code to simulate the evolution of JET discharges and to provide an insight into the improved heating and confinement found in these discharges. In this analysis, the ICRF power-deposition profile in the minority-heating scenario is computed by the ray-tracing code BRAYCO that self-consistently takes the finite antenna geometry, its radiation spectrum and the hot-plasma damping into account. The power delivered to ions and electrons is calculated based on Stix model. (author) 10 refs., 5 figs
Energy Technology Data Exchange (ETDEWEB)
Bennion, Kevin; Moreno, Gilberto
2015-09-29
Thermal management for electric machines (motors/ generators) is important as the automotive industry continues to transition to more electrically dominant vehicle propulsion systems. Cooling of the electric machine(s) in some electric vehicle traction drive applications is accomplished by impinging automatic transmission fluid (ATF) jets onto the machine's copper windings. In this study, we provide the results of experiments characterizing the thermal performance of ATF jets on surfaces representative of windings, using Ford's Mercon LV ATF. Experiments were carried out at various ATF temperatures and jet velocities to quantify the influence of these parameters on heat transfer coefficients. Fluid temperatures were varied from 50 degrees C to 90 degrees C to encompass potential operating temperatures within an automotive transaxle environment. The jet nozzle velocities were varied from 0.5 to 10 m/s. The experimental ATF heat transfer coefficient results provided in this report are a useful resource for understanding factors that influence the performance of ATF-based cooling systems for electric machines.
Laub, Bernard; Grinstead, Jay; Dyakonov, Artem; Venkatapathy, Ethiraj
2011-01-01
Though arc jet testing has been the proven method employed for development testing and certification of TPS and TPS instrumentation, the operational aspects of arc jets limit testing to selected, but constant, conditions. Flight, on the other hand, produces timevarying entry conditions in which the heat flux increases, peaks, and recedes as a vehicle descends through an atmosphere. As a result, we are unable to "test as we fly." Attempts to replicate the time-dependent aerothermal environment of atmospheric entry by varying the arc jet facility operating conditions during a test have proven to be difficult, expensive, and only partially successful. A promising alternative is to rotate the test model exposed to a constant-condition arc jet flow to yield a time-varying test condition at a point on a test article (Fig. 1). The model shape and rotation rate can be engineered so that the heat flux at a point on the model replicates the predicted profile for a particular point on a flight vehicle. This simple concept will enable, for example, calibration of the TPS sensors on the Mars Science Laboratory (MSL) aeroshell for anticipated flight environments.
Smyth, Trevor; Menary, Gary; Geron, Marco
2018-05-01
Impingement of a liquid jet in a polymer cavity has been modelled numerically in this study. Liquid supported stretch blow moulding is a nascent polymer forming process using liquid as the forming medium to produce plastic bottles. The process derives from the conventional stretch blow moulding process which uses compressed air to deform the preform. Heat transfer away from the preform greatly increases when a liquid instead of a gas is flowing over a solid; in the blow moulding process the temperature of the preform is tightly controlled to achieve optimum forming conditions. A model was developed with Computational Fluid Dynamics code ANSYS Fluent which allows the extent of heat transfer between the incoming liquid and the solid preform to be determined in the initial transient stage, where a liquid jet enters an air filled preform. With this data, an approximation of the extent of cooling through the preform wall can be determined.
Best connected rectangular arrangements
Directory of Open Access Journals (Sweden)
Krishnendra Shekhawat
2016-03-01
Full Text Available It can be found quite often in the literature that many well-known architects have employed either the golden rectangle or the Fibonacci rectangle in their works. On contrary, it is rare to find any specific reason for using them so often. Recently, Shekhawat (2015 proved that the golden rectangle and the Fibonacci rectangle are one of the best connected rectangular arrangements and this may be one of the reasons for their high presence in architectural designs. In this work we present an algorithm that generates n-4 best connected rectangular arrangements so that the proposed solutions can be further used by architects for their designs.
International Nuclear Information System (INIS)
Yu, Shengzhi; Wang, Jianjun; Yan, Ming; Yan, Changqi; Cao, Xiaxin
2017-01-01
Highlights: • The phasic difference between flow rate and frictional pressure drop is negligible. • Effect mechanism of rolling motion on flow behaviors of NC is interpreted. • The startup model is proposed and verified. • Steady-state correlations are feasible to predict transient resistance. • The in-house code can simulate instantaneous flow behaviors of NC correctly. - Abstract: Effects of rolling motion on flow characteristics in a natural circulation system were investigated experimentally and numerically. The numerical results from validated code were mainly used to provide detailed information for the discussion and analysis of experimental results. The results indicate that under rolling motion condition, the phasic difference between flow rate and frictional pressure drop of narrow rectangular channel is negligible. Angular acceleration is the eigenvalue for the effects of rolling motion on flow rate under single-phase natural circulation condition. When angular acceleration is approximately equal, even though either the angle or the period of rolling motion is different, peak, trough and time-averaged values of flow rate are approximately equal. Under rolling motion and single-phase natural circulation conditions, the phenomenon that dimensionless time-averaged mass flow rate is smaller than that under steady state condition is controlled by the nonlinear relationship between mass flow rate and the resistance of loop. The factor also causes the result that the absolute difference of dimensionless flow rate between peak and steady state is smaller than that between trough and steady state. The startup model which is proposed in present paper can be used to predict the flow characteristics of single-phase natural circulation system at startup stage of rolling motion favorably. The self-developed code can simulate instantaneous flow characteristics of single-phase natural circulation system under rolling motion and steady state conditions
International Nuclear Information System (INIS)
Pouransari, Zeinab; Vervisch, Luc; Johansson, Arne V.
2013-01-01
Highlights: ► A non-premixed turbulent flame close to a solid surface is studied using DNS. ► Heat release effects delay transition and enlarge fluctuation of density and pressure. ► The fine-scale structures damped and surface wrinkling diminished due to heat-release. ► Using semilocal scaling improves the collapse of turbulence statistic in inner region. ► There are regions of the flame where considerable (up to 10%) premixed burning occurs. -- Abstract: The present study concerns the role of heat release effects on characteristics mixing scales of turbulence in reacting wall-jet flows. Direct numerical simulations of exothermic reacting turbulent wall-jets are performed and compared to the isothermal reacting case. An evaluation of the heat-release effects on the structure of turbulence is given by examining the mixture fraction surface characteristics, diagnosing vortices and exploring the dissipation rate of the fuel and passive scalar concentrations, and moreover by illustration of probability density functions of reacting species and scatter plots of the local temperature against the mixture fraction. Primarily, heat release effects delay the transition, enlarge the fluctuation intensities of density and pressure and also enhance the fluctuation level of the species concentrations. However, it has a damping effect on all velocity fluctuation intensities and the Reynolds shear stress. A key result is that the fine-scale structures of turbulence are damped, the surface wrinkling is diminished and the vortices become larger due to heat-release effects. Taking into account the varying density by using semi-local scaling improves the collapse of the turbulence statistics in the inner region, but does not eliminate heat release induced differences in the outer region. Examining the two-dimensional premultiplied spanwise spectra of the streamwise velocity fluctuations indicates a shifting in the positions of the outer peaks, associated with large
Effect of guide wall on jet impingement cooling in blade leading edge channel
International Nuclear Information System (INIS)
Zhao, Qing-Yang; Chung, Heeyoon; Choi, Seok Min; Cho, Hyung Hee
2016-01-01
The characteristics of fluid flow and heat transfer, which are affected by the guide wall in a jet impinged leading edge channel, have been investigated numerically using three-dimensional Reynolds-averaged Navier-Stokes analysis via the shear stress transport turbulence model and gamma theta transitional turbulence model. A constant wall heat flux condition has been applied to the leading edge surface. The jet-to-surface distance is constant, which is three times that of the jet diameter. The arrangement of the guide wall near the jet hole is set as a variable. Results presented in this study include the Nusselt number contour, velocity vector, streamline with velocity, and local Nusselt number distribution along the central line on the leading edge surface. The average Nusselt number and average pressure loss between jet nozzle and channel exit are calculated to assess the thermal performance. The application of the guide wall is aimed at improving heat transfer uniformity on the leading edge surface. Results indicated that the streamwise guide wall ensures the vertical jet impingement flow intensity and prevents the flow after impingement to reflux into jet flow. Thus, a combined rectangular guide wall benefits the average heat transfer, thermal performance and heat transfer distribution uniformity
Measurements of time-dependent liquid-metal magnetohydrodynamic flows in a flat rectangular duct
International Nuclear Information System (INIS)
Buehler, L.; Horanyi, S.
2009-01-01
In the helium-cooled lead lithium (HCLL) blanket, which has been chosen as a reference concept for a liquid-metal breeding blanket to be tested in ITER, the heat is removed by helium cooled plates aligned with the strong toroidal magnetic field that confines the fusion plasma. The liquid breeder lead lithium circulates through gaps of rectangular cross-section between the cooling plates to transport the generated tritium towards external extraction facilities. Under the action of the strong magnetic field, liquid metal flows in conducting rectangular ducts exhibit jet-like velocity profiles in the thin boundary layers near the side walls, which are parallel to the magnetic field like the cooling plates in HCLL blankets. The velocity in these side layers may exceed several times the mean velocity in the duct and it is known that these layers become unstable for sufficiently high Reynolds numbers. The present paper summarizes experimental results for such unstable time-dependent flows in strong magnetic fields, which have been obtained in the MEKKA liquid metal laboratory of the Forschungszentrum Karlsruhe. In particular, spatial and temporal scales of perturbation patterns are identified. The results suggest that the flow between cooling plates in a HCLL blanket is laminar and stable. The observed time-dependent flow behavior appears at larger velocities so that the present results are more relevant for applications in dual coolant concepts where high-velocity jets have been predicted along side walls.
International Nuclear Information System (INIS)
Bhatnagar, V.P.; Taroni, A.; Ellis, J.J.; Jacquinot, J.; Start, D.F.H.
1989-01-01
The ion cyclotron resonance heating of monster sawtooth (period greater than the energy confinement time) and pellet-fueled peaked-density profiles in limiter discharges of JET Tokamak are studied. The monster sawtooth is a characteristic JET regime which is related to fast ions generated during the minority ion heating. In the ICRF heating of peaked-density profile discharges, we find typically the T i0 is higher roughly by a factor of 2 and T e0 roughly by 35% at a fixed P TOT /n e0 when compared to non-peaked profile cases. Here, T e0 and T i0 are central electron and ion temperatures, respectively, n e0 is the central electron density and P TOT is the total input power. The ion heating is improved in the pellet case, in part, due to a higher collisionality between the background ions and the energetic minority, but more significantly by a reduction of local ion energy transport in the central region. The transport-code simulation of these discharges reveals that there is a reduction of both χ e and χ i in the central region of the plasma in the ICRF heated peaked-profile discharges where χ e and χ i are the electron and ion heat conductivities, respectively. The improvement of confinement is not explained quantitatively by any of the existing η i -driven turbulence theories as the n i parameter (η i = d ln T i /d ln n i where T i is the ion temperature and n i is the ion density), instead of dropping below the critical value, remains above it for most of the duration of the improved confinement phase. The physical mechanism(s) that plays a role in this improvement is not yet clear. (author)
Experiences with rectangular waveguide
International Nuclear Information System (INIS)
Beltran, J.; Sepulveda, J. J.; Navarro, E. A.
2000-01-01
A simple and didactic experimental arrangement is presented to show wave propagation along a structure with translational symmetry, particularly the rectangular waveguide. Parameters of this waveguide as cutoff frequency, guide wavelength and field distribution of fundamental mode can be measured. For this purpose a large paralelepipedical waveguide structure is designed and built, its dimensions can be varied in order to change its parameters. (Author) 9 refs
Energy Technology Data Exchange (ETDEWEB)
Han, Junkyu; Lee, Yongjae; Kim, Sung Joong [Hanyang Univ., Seoul (Korea, Republic of)
2014-05-15
In operational conditions at Section of Safety of Research Reactor in IAEA Safety Standards, there are five items: Safety limits, Safety system settings, Limiting conditions for safe operation, Surveillance requirements and Administrative requirements. ONB is included in Safety System Settings (SSS). Limiting Safety System Settings (LSSS) are some range parameters in SSS. Major findings from this study can be summarized as followings: The ONB heat flux was predicted using B-R, D-B and P-G correlation. It is observed that the ONB heat flux increases with mass flux. In addition to the prediction, the ONB heat flux was measured experimentally. The experimental results are higher heat flux and temperature compared by two predictions at the bubble departure frequency of 450ms. Visualization of the ONB heat flux suggests that incipience of boiling appears earlier. Need to make sure the visual criteria of determination about ONB. Although the heat flux condition of 900kW/m{sup 2} sec have ONB occurrence, the bubbles are nearly no affect to waterway and blocking.
Energy Technology Data Exchange (ETDEWEB)
Start, D F.H. [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking; Righi, E [Imperial Coll. of Science and Technology, London (United Kingdom); Warrick, C [UKAEA Culham Lab., Abingdon (United Kingdom)
1994-07-01
A model is presented that can simulate the {gamma} emissivity in the poloidal cross-section during ({sup 3}He)D ICRF heated discharges in JET plasmas, by merging information obtained from the fast ion distribution and from nuclear reactions producing the observed {gamma} emissivity (production of {gamma} photons during {sup 3}He-{sup 9}Be reactions). This technique can play an important role in the identification of plasma instabilities that affect the redistribution of the fast ions in the plasma, like the TAE modes and the ripple in the tokamak magnetic field. 9 refs., 4 figs., 1 tab.
Normal Impingement of a Supersonic Jet on a Plane - A Basic Study of Shock-Interference Heating
1975-12-01
George Xaler, Pail Zone Dr. H. Lew 28i0 Mr. J. W. Paust A . Mkrtallucci W. Daskin J. D. Cresaswell J. pvttu" J. Cor%.nto C. l!arri, F. GCOrge1. 4...NSWC/WOL/TR 75195 low zE ~ 1 WHITE OAK LABORATORY SNORMAL IMPINGEMENT OF A SUPERSONIC JET ON A PLANE - A BASIC STUDY OF SHOCK-INTERFERENCE HEATING...OF THIS PAGE ("oin DomejaE’ored) __________________ REPORT DOCUMENTATION PAGE READ INSTRUCTIONS4 2. OV ACE.~ CONTRAT O0GRN NUMBER~ a NS. P ER OR M I
International Nuclear Information System (INIS)
Haines, M.G.; Bond, D.J.; Chuaqui, H.H.
1983-01-01
The paper reports experimental and theoretical contributions to the understanding of non-linear heat flow and the phenomenon of jet-like filamentary structures in inertial-confinement fusion. When lateral heat flow is minimized, through applying more carefully a radially symmetric irradiation at 1.05 and 0.53 μm on a spherical target, it is found that a heat flux in excess of 10% of the free-streaming limit is consistent with simulations and experimental measurements with particle and X-ray diagnostics. A similar result has been found in a scaled experiment in a plasma of electron density 4x10 16 cm - 3 when the condition Tsub(e) approx.=Tsub(i) is satisfied. These results are in marked contrast to earlier assertions, mainly from plane-target measurements, that the flux limiter is 3%, but in agreement with theoretical calculations of steady non-linear heat flow using a discrete-ordinate method. Thus, no anomalous inhibition of heat flow is found, consistent with theoretical predictions that ion-acoustic turbulence is of no importance in dense (n>=10 21 cm - 3 , T approx.= 1 keV) plasmas. However, in the low-density scaled experiment, under conditions where Tsub(e)>>Tsub(i) is found that ion-acoustic turbulence is present, and the flux limiter is 4%. By using shadowgraphic and schlieren techniques with an optical diagnostic probe, fine-scale jet-like structures have been observed on a scale-length of approx. 10 μm on spherical targets. They occur even outside the laser-irradiated region, and are not connected with irregularities in the laser beam; they are more pronounced with higher-Z materials and with shorter-wavelength lasers, and have megagauss magnetic fields associated with them. Electromagnetic instabilities driven by heat flow are the probable cause of the jets, and of the three known modes the thermal instability, enhanced by radiation loss, agrees more closely with the experiments than the Weibel and thermomagnetic modes, since the latter only occur
Alnoman, Saeed
2015-12-01
The stabilization characteristics of laminar non-premixed jet flames of pre-vaporized iso-octane, one of the primary reference fuels for octane rating, have been studied experimentally in heated coflow air. Non-autoignited and autoignited lifted flames were analyzed. With the coflow air at relatively low initial temperatures below 940 K, an external ignition source was required to stabilize the flame. These lifted flames had tribrachial edge structures and their liftoff heights correlated well with the jet velocity scaled by stoichiometric laminar burning velocity, indicating the importance of the edge propagation speed on flame stabilization. At high initial temperatures over 940 K, the autoignited flames were stabilized without requiring an external ignition source. These autoignited lifted flames exhibited either tribrachial edge structures or mild combustion behaviors depending on the level of fuel dilution. Two distinct transition behaviors were observed in the autoignition regime from a nozzle-attached flame to a lifted tribrachial-edge flame and then to lifted mild combustion as the jet velocity increased at a certain fuel dilution level. The liftoff data of the autoignited flames with tribrachial edges were analyzed based on calculated ignition delay times. Analysis of the experimental data suggested that ignition delay time may be much less sensitive to initial temperature under atmospheric pressure conditions as compared with predictions. © 2015 Elsevier Ltd. All rights reserved.
Chikishev, Leonid; Lobasov, Aleksei; Sharaborin, Dmitriy; Markovich, Dmitriy; Dulin, Vladimir; Hanjalic, Kemal
2017-11-01
We investigate flame-flow interactions in an atmospheric turbulent high-swirl methane/air lean jet-flame at Re from 5,000 to 10,000 and equivalence ratio below 0.75 at the conditions of vortex breakdown. The focus is on the spatial correlation between the propagation of large-scale vortex structures, including precessing vortex core, and the variations of the local heat release. The measurements are performed by planar laser-induced fluorescence of hydroxyl and formaldehyde, applied simultaneously with the stereoscopic particle image velocimetry technique. The data are processed by the proper orthogonal decomposition. The swirl rate exceeded critical value for the vortex breakdown resulting in the formation of a processing vortex core and secondary helical vortex filaments that dominate the unsteady flow dynamics both of the non-reacting and reacting jet flows. The flame front is located in the inner mixing layer between the recirculation zone and the annular swirling jet. A pair of helical vortex structures, surrounding the flame, stretch it and cause local flame extinction before the flame is blown away. This work is supported by Russian Science Foundation (Grant No 16-19-10566).
Florschuetz, L. W.; Metzger, D. E.; Su, C. C.; Isoda, Y.; Tseng, H. H.
1982-01-01
Two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate are considered. The jet flow, after impingement, is constrained to exit in a single direction along the channel formed by the jet orifice plate and the heat transfer surface. The configurations considered are intended to model those of interest in current and contemplated gas turbine airfoil midchord cooling applications. The effects of an initial crossflow which approaches the array through an upstream extension of the channel are considered. Flow distributions as well as heat transfer coefficients and adiabatic wall temperatures resolved to one streamwise hole spacing were measured as a function of the initial crossflow rate and temperature relative to the jet flow rate and temperature. Both Nusselt number profiles and dimensionless adiabatic wall temperature (effectiveness) profiles are presented and discussed. Special test results which show a significant reduction of jet orifice discharge coefficients owing to the effect of a confined crossflow are also presented, along with a flow distribution model which incorporates those effects. A nonuniform array flow distribution model is developed and validated.
Turbulent buoyant jets and plumes
Rodi, Wolfgang
The Science & Applications of Heat and Mass Transfer: Reports, Reviews, & Computer Programs, Volume 6: Turbulent Buoyant Jets and Plumes focuses on the formation, properties, characteristics, and reactions of turbulent jets and plumes. The selection first offers information on the mechanics of turbulent buoyant jets and plumes and turbulent buoyant jets in shallow fluid layers. Discussions focus on submerged buoyant jets into shallow fluid, horizontal surface or interface jets into shallow layers, fundamental considerations, and turbulent buoyant jets (forced plumes). The manuscript then exami
Oscillating acoustic streaming jet
International Nuclear Information System (INIS)
Moudjed, Brahim; Botton, Valery; Henry, Daniel; Millet, Severine; Ben Hadid, Hamda; Garandet, Jean-Paul
2014-01-01
The present paper provides the first experimental investigation of an oscillating acoustic streaming jet. The observations are performed in the far field of a 2 MHz circular plane ultrasound transducer introduced in a rectangular cavity filled with water. Measurements are made by Particle Image Velocimetry (PIV) in horizontal and vertical planes near the end of the cavity. Oscillations of the jet appear in this zone, for a sufficiently high Reynolds number, as an intermittent phenomenon on an otherwise straight jet fluctuating in intensity. The observed perturbation pattern is similar to that of former theoretical studies. This intermittently oscillatory behavior is the first step to the transition to turbulence. (authors)
DEFF Research Database (Denmark)
Bertheussen, Bård; Mustakallio, Panu; Kosonen, Risto
2013-01-01
The impact of heat load strength and positioning on the indoor environment generated by diffuse ceiling air supply and chilled beam with radial swirl jet was studied and compared. An office room with two persons and a meeting room with six persons were simulated in a test room (4.5 x 3.95 x 3.5 m3......) and Category B thermal environment in the meeting room at high heat load of 94 W∙m−2. The air distribution pattern was influenced by the convective flows from the heat sources. The maximum local velocity in the occupied zone was 0.23–0.26 m∙s−1. The diffuse ceiling supply did not ensure complete mixing...... temperature was controlled at 24 °C. The quality of the generated indoor environment as defined in ISO standard 7730 (2005) was assessed based on comprehensive physical measurements. The systems created Category A thermal environment in cooling situations at heat load of 50 W∙m−2 and 78 W∙m−2 (office room...
Energy Technology Data Exchange (ETDEWEB)
Vernier, Ph [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires
1962-07-01
The study is experimental and theoretical. The theory is only for fully developed laminar flow. The experimental study is made with water at low temperature. The uniform heat flux varies from 0 to 16 000 BTU/hr ft{sup 2} and the distance between the heated plates from 0.2 to 0.48 inches. The experimental correlations give the mean velocity and the temperature rise of the water, the Nusselt number versus the Rayleigh number. Experience and theory agree well for heat fluxes sufficiently low. Using a special apparatus, one measures the velocity and temperature profiles between the plates and finds interesting results on the flow properties. The profiles show that the flow is not fully developed and not a Poiseuille flow. (author) [French] L'etude est theorique et experimentale. La theorie ne traite que le cas des ecoulements laminaires completement developpes. Pour toute l'etude experimentale le fluide est de l'eau a la temperature ambiante. La densite de flux de chaleur uniforme a varie entre 0 et 5 W/cm{sup 2} tandis que l'espace compris entre les deux parois chauffantes a varie entre 5 et 12 mm. On obtient des correlations empiriques qui permettent de connaitre la vitesse moyenne et rechauffement de l'eau, ainsi que le nombre de Nusselt en fonction du nombre de Rayleigh. La correspondance entre theorie et experience est assez bonne pour des puissances de chauffage suffisamment faibles. La mesure, faite a l'aide d'une sonde speciale, des profils des vitesses et des temperatures a la sortie du canal donne des renseignements interessants sur les proprietes de l'ecoulement. Ces profils montrent notamment que l'ecoulement n'est pas developpe et ne s'effectue pas 'a la Poiseuille'. (auteur)
Heat and mass transfer caused by a laminar channel flow equipped with a synthetic jet array
Czech Academy of Sciences Publication Activity Database
Trávníček, Zdeněk; Dančová, Petra; Kordík, Jozef; Vít, Tomáš; Pavelka, Miroslav
2011-01-01
Roč. 2, č. 4 (2011), 041006-041006 ISSN 1948-5085 R&D Projects: GA AV ČR(CZ) IAA200760801; GA ČR(CZ) GA101/09/1959 Institutional research plan: CEZ:AV0Z20760514 Keywords : synthetic jet * flow control * naphthalene sublimation Subject RIV: BK - Fluid Dynamics http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JTSEBV000002000004041006000001&idtype=cvips&gifs=yes
Rectangular spectral collocation
Driscoll, Tobin A.
2015-02-06
Boundary conditions in spectral collocation methods are typically imposed by removing some rows of the discretized differential operator and replacing them with others that enforce the required conditions at the boundary. A new approach based upon resampling differentiated polynomials into a lower-degree subspace makes differentiation matrices, and operators built from them, rectangular without any row deletions. Then, boundary and interface conditions can be adjoined to yield a square system. The resulting method is both flexible and robust, and avoids ambiguities that arise when applying the classical row deletion method outside of two-point scalar boundary-value problems. The new method is the basis for ordinary differential equation solutions in Chebfun software, and is demonstrated for a variety of boundary-value, eigenvalue and time-dependent problems.
Zhang, Rui-rui; Huang, Wei; Yan, Li; Li, Lang-quan; Li, Shi-bin; Moradi, R.
2018-05-01
To design a kind of aerospace vehicle, the drag and heat flux reduction are the most important factors. In the current study, the counterflowing jet, one of the effective drag and heat flux reduction concepts, is investigated numerically by the two-dimensional axisymmetric Reynolds-averaged Navier-Stokes equations coupled with the SST k-ω turbulence model. An axisymmetric numerical simulation mode of the counterflowing jet on the supersonic vehicle nose-tip is established, and the numerical method employed is validated by the experimental schlieren images and experimental data in the open literature. A pulsed counterflowing jet scheme is proposed, and it uses a sinusoidal function to control the total and static pressures of the counterflowing jet. The obtained results show that the long penetration mode does not exist in the whole turnaround, even in a relatively small range of the jet total and static pressures, and this is different from the phenomenon obtained under the steady condition in the open literature. At the same time, it is observed that the variation of the physical parameters, such as the Stanton number induced by the pulsed jet, has an obvious periodicity and hysteresis phenomenon.
Comparison between dominant NB and dominant IC heated ELMy H-mode discharges in JET
Versloot, T.W.; Sartori, R.; de Vries, P.C.; et al, [No Value
2011-01-01
Abstract The experiment described in this paper is aimed at characterization of ELMy H-mode discharges with varying momentum input, rotation, power deposition profiles and ion to electron heating ratio obtained by varying the proportion between ion cyclotron (IC) and neutral beam (NB) heating. The
Comparison between dominant NB and dominant IC heated ELMy H-mode discharges in JET
Versloot, T. W.; Sartori, R.; Rimini, F.; de Vries, P. C.; Saibene, G.; Parail, V.; Beurskens, M. N. A.; Boboc, A.; Budny, R.; Crombe, K.; de la Luna, E.; Durodie, F.; Eich, T.; Giroud, C.; Kiptily, V.; Johnson, T.; Mantica, P.; Mayoral, M. L.; McDonald, D. C.; Monakhov, I.; Nave, M. F. F.; Voitsekhovitch, I.; Zastrow, K. D.
2011-01-01
The experiment described in this paper is aimed at characterization of ELMy H-mode discharges with varying momentum input, rotation, power deposition profiles and ion to electron heating ratio obtained by varying the proportion between ion cyclotron (IC) and neutral beam (NB) heating. The motivation
International Nuclear Information System (INIS)
Clement, S.; Tagle, J.A.; Bures, M.; Vince, J.; Kock, L. de; Stangeby, P.C.
1989-01-01
The highly anomalous perpendicular transport in the plasma edge of a tokamak is generally attributed to plasma turbulence, primarily to density and electrostatic potential fluctuations. The edge transport could be modified by changing the geometry of objects in contact with the plasma (limiters, radio frequency antennae ...) and during additional heating experiments. Poloidal asymmetries in the scrape-off layer (SOL) in tokamaks using poloidal limiters (eg. ALCATOR-C) have been recently reported, indicating a poloidal asymmetry in cross-field transport. A poloidal ring limiter obstructs communications between different flux tubes in the SOL, thus permitting poloidal asymmetries in n e and T e to develop if D perpendicular is θ-dependent. When JET was operated with discrete limiters, equivalent to a single toroidal limiter at the outside mid-plane, little poloidal variation in the SOL plasma properties was observed. Currently JET is operated with two complete toroidal belt limiters located approximately one meter above and below the outside mid-plane. This configuration breaks the SOL into two regions: the low field side SOL (LFS), between the limiters, and the rest of the SOL on the high field side (HFS). Differences on the scrape-off lengths in the two SOLs are reported here, indicating that cross-field transport is faster on the LFS-SOL, in agreement with observations made on ASDEX and T-10. (author) 8 refs., 6 figs
Energy Technology Data Exchange (ETDEWEB)
Van Eester, D.; Lerche, E.; Crombé, K.; Jachmich, S. [LPP-ERM/KMS, Association Euratom-Belgian State, TEC Partner, Brussels (Belgium); Jacquet, P.; Graham, M.; Kiptily, V.; Matthews, G.; Mayoral, M.-L.; Mc Cormick, K.; Monakhov, I.; Noble, C.; Rimini, F.; Solano, E. R. [Euratom-CCFE Fusion Association, Culham Science Centre (United Kingdom); Bobkov, V.; Maggi, C.; Neu, R.; Pütterich, T. [MPI für Plasmaphysik Euratom Assoziation, Garching (Germany); Czarnecka, A. [Institute of Plasma Physics and Laser Microfusion, Warsaw (Poland); Coenen, J. W. [IEK-4, EURATOM-FZJ, TEC Partner, Jülich (Germany); and others
2014-02-12
The most recent JET campaign has focused on characterizing operation with the 'ITER-like' wall. One of the questions that needed to be answered is whether the auxiliary heating methods do not lead to unacceptably high levels of impurity influx, preventing fusion-relevant operation. In view of its high single pass absorption, hydrogen minority fundamental cyclotron heating in a deuterium plasma was chosen as the reference wave heating scheme in the ion cyclotron domain of frequencies. The present paper discusses the plasma behavior as a function of the minority concentration X[H] in L-mode with up to 4MW of RF power. It was found that the tungsten concentration decreases by a factor of 4 when the minority concentration is increased from X[H] ≈ 5% to X[H] % 20% and that it remains at a similar level when X[H] is further increased to 30%; a monotonic decrease in Beryllium emission is simultaneously observed. The radiated power drops by a factor of 2 and reaches a minimum at X[H] ≈ 20%. It is discussed that poor single pass absorption at too high minority concentrations ultimately tailors the avoidance of the RF induced impurity influx. The edge density being different for different minority concentrations, it is argued that the impact ICRH has on the fate of heavy ions is not only a result of core (wave and transport) physics but also of edge dynamics and fueling.
Spectroscopic analysis of the density and temperature gradients in the laser-heated gas jet
International Nuclear Information System (INIS)
Matthews, D.L.; Lee, R.W.; Auerbach, J.M.
1981-01-01
We have performed an analysis of the x-ray spectra produced by a 1.0TW, lambda/sub L/-0.53μm laser-irradiated gas jet. Plasmas produced by ionization of neon, argon and N 2 + SF 6 gases were included in those measurements. Plasma electron density and temperature gradients were obtained by comparison of measured spectra with those produced by computer modeling. Density gradients were also obtained using laser interferometry. The limitations of this technique for plasma diagnosis will be discussed
Experimental study of subsonic microjet escaping from a rectangular nozzle
Aniskin, V. M.; Maslov, A. A.; Mukhin, K. A.
2016-10-01
The first experiments on the subsonic laminar microjets escaping from the nozzles of rectangular shape are carried out. The nozzle size is 83.3x3823 microns. Reynolds number calculated by the nozzle height and the average flow velocity at the nozzle exit ranged from 58 to 154. The working gas was air at room temperature. The velocity decay and velocity fluctuations along the center line of the jet are determined. The fundamental difference between the laminar microjets characteristics and subsonic turbulent jets of macro size is shown. Based on measurements of velocity fluctuations it is shown the presence of laminar-turbulent transition in microjets and its location is determined.
Study of gas-water flow in horizontal rectangular channels
Chinnov, E. A.; Ron'shin, F. V.; Kabov, O. A.
2015-09-01
The two-phase flow in the narrow short horizontal rectangular channels 1 millimeter in height was studied experimentally. The features of formation of the two-phase flow were studied in detail. It is shown that with an increase in the channel width, the region of the churn and bubble regimes increases, compressing the area of the jet flow. The areas of the annular and stratified flow patterns vary insignificantly.
Two-phase flow patterns in horizontal rectangular minichannel
Directory of Open Access Journals (Sweden)
Ron’shin Fedor
2016-01-01
Full Text Available The two-phase flow in a short horizontal channel of rectangular cross-section of 1 × 19 mm2 has been studied experimentally. Five conventional two-phase flow patterns have been detected (bubble, churn, stratified, annular and jet and transitions between them have been determined. It is shown that a change in the width of the horizontal channels has a substantial effect on the boundaries between the flow regimes.
Ming, Tingzhen; Cai, Cunjin; Yang, Wei; Shen, Wenqing; Gan, Ting
2018-06-01
With increasing heat fluxes caused by electronic components, dimples have attracted wide attention by researchers and have been applied to microchannel heat sink in modern advanced cooling technologies. In this work, the combination of dimples, impinging jets and microchannel heat sink was proposed to improve the heat transfer performance on a cooling surface with a constant heat flux 500 W/cm2. A mathematical model was advanced for numerically analyzing the fluid flow and heat transfer characteristics of a microchannel heat sink with impinging jets and dimples (MHSIJD), and the velocity distribution, pressure drop, and thermal performance of MHSIJD were analyzed by varying the radii of dimples. The results showed that the combination of dimples and MHSIJ can achieve excellent heat transfer performance; for the MHSIJD model in this work, the maximum and average temperatures can be as low as 320 K and 305 K, respectively when mass flow rate is 30 g/s; when dimple radius is larger than 0.195 mm, both the heat transfer coefficient and the overall performance h/ΔP of MHSIJD are higher than those of MHSIJ.
Heat transfer analyses of continuous casting by free jet meltspinning device
Directory of Open Access Journals (Sweden)
B. Karpe
2011-01-01
Full Text Available New method for determining contact resistance through variable heat transfer coefficient is introduced which takes into account physical properties of the casting material, process parameters and contact time/length between molten material (melt puddle and chilling wheel and enables cooling rate prediction before experiment execution. From the results can be concluded, that those process parameters which determine the thickness of the melt puddle in the downstream and consequently the ribbon thickness have major influence on cooling rate of the ribbon. In the case of continuous casting, heat balance of the wheel is calculated and influence of the chill wheel cooling mode on cooling rate of metallic ribbon is analyzed.
A Characterization of Rectangular Distributions
Terrell, George R.
1983-01-01
It is well known that the smaller and the larger of a random sample of size two are positively correlated. The coefficient of correlation is at most one-half, and the upper bound is attained only for rectangular distributions.
Meda, Adimurthy; Katti, Vadiraj V.
2017-08-01
The present work experimentally investigates the local distribution of wall static pressure and the heat transfer coefficient on a rough flat plate impinged by a slot air jet. The experimental parameters include, nozzle-to-plate spacing (Z /D h = 0.5-10.0), axial distance from stagnation point ( x/D h ), size of detached rib ( b = 4-12 mm) and Reynolds number ( Re = 2500-20,000). The wall static pressure on the surface is recorded using a Pitot tube and a differential pressure transmitter. Infrared thermal imaging technique is used to capture the temperature distribution on the target surface. It is observed that, the maximum wall static pressure occurs at the stagnation point ( x/D h = 0) for all nozzle-to-plate spacing ( Z/D h ) and rib dimensions studied. Coefficient of wall static pressure ( C p ) decreases monotonically with x/D h . Sub atmospheric pressure is evident in the detached rib configurations for jet to plate spacing up to 6.0 for all ribs studied. Sub atmospheric region is stronger at Z/D h = 0.5 due to the fluid accelerating under the rib. As nozzle to plate spacing ( Z/D h ) increases, the sub-atmospheric region becomes weak and vanishes gradually. Reasonable enhancement in both C p as well as Nu is observed for the detached rib configuration. Enhancement is found to decrease with the increase in the rib width. The results of the study can be used in optimizing the cooling system design.
Experimental investigation on carbon nano tubes coated brass rectangular extended surfaces
International Nuclear Information System (INIS)
Senthilkumar, Rajendran; Prabhu, Sethuramalingam; Cheralathan, Marimuthu
2013-01-01
Finned surface has been extensively used for free convection cooling of internal combustion engines and several electronic kits etc. Here rectangular brass fin was preferred for analysis. Thermocouples were attached all over the surface of the fin in equal distances. The measurement of surface temperature and calculated convective heat transfer rate were reported for several heat input values. The overall system performance can be improved by enhancing heat transfer rate of extended surfaces. Based on the above requirement, brass surface was coated by carbon nano tubes. The temperature and heat transfer characteristics were investigated using Taguchi method for experimental design. Finally the performances of coated and non-coated rectangular brass fins were compared. The average percentage of increase in heat transfer rate was proved around 12% for carbon nanocoated rectangular brass fins. - Graphical abstract: The designed Natural and Forced convection Heat Transfer Test Rig measures the enhanced rate of heat transfer for nano coated rectangular fins than in non-coated fins. Highlights: ► Rectangular brass fins were preferred for convective heat transfer process. ► The rectangular brass fins are coated with multi wall carbon nano tubes in EBPVD process with nanometer thickness. ► Temperature and heat transfer rate were investigated for nanocoated and non-coated fins by using Taguchi method. ► Multi wall carbon nanotubes act as a pin fin to enhance surface area for effective convective heat transfer rate.
International Nuclear Information System (INIS)
Joshi, Shailesh N.; Dede, Ercan M.
2017-01-01
Highlights: • Jet impingement with phase change on multi-scale porous surfaces is investigated. • Porous coated flat, pin-fin, open tunnel, and closed tunnel structures are studied. • Boiling curve, heat transfer coefficient, and pressure drop metrics are reported. • Flow visualization shows vapor removal from the surface is a key aspect of design. • The porous coated pin-fin surface exhibits superior two-phase cooling performance. - Abstract: In the future, wide band-gap (WBG) devices such as silicon carbide and gallium nitride will be widely used in automotive power electronics due to performance advantages over silicon-based devices. The high heat fluxes dissipated by WBG devices pose extreme cooling challenges that demand the use of advanced thermal management technologies such as two-phase cooling. In this light, we describe the performance of a submerged two-phase jet impingement cooler in combination with porous coated heat spreaders and multi-jet orifices. The cooling performance of four different porous coated structures was evaluated using R-245fa as the coolant at sub-cooling of 5 K. The results show that the boiling performance of a pin-fin heat spreader is the highest followed by that for an open tunnel (OPT), closed tunnel (CLT), and flat heat spreader. Furthermore, the flat heat spreader demonstrated the lowest critical heat flux (CHF), while the pin-fin surface sustained a heat flux of 218 W/cm 2 without reaching CHF. The CHF values of the OPT and CLT surfaces were 202 W/cm 2 and 194 W/cm 2 , respectively. The pin-fin heat spreader has the highest two-phase heat transfer coefficient of 97,800 W/m 2 K, while the CLT surface has the lowest heat transfer coefficient of 69,300 W/m 2 K, both at a heat flux of 165 W/cm 2 . The variation of the pressure drop of all surfaces is similar for the entire range of heat fluxes tested. The flat heat spreader exhibited the least pressure drop, 1.73 kPa, while the CLT surface had the highest, 2.17 kPa at a
International Nuclear Information System (INIS)
Bures, M.; Bhatnagar, V.; Cotrell, G.; Corti, S.; Christiansen, J.P.; Hellsten, T.; Jacquinot, J.; Lallia, P.; Lomas, P.; O'Rourke, J.; Taroni, A.; Tibone, F.; Start, D.F.H.
1989-01-01
The performance of high current discharges can be increased by applying central ICRF heating before or shortly after the onset of sawtooth activity in the plasma current rise phase. Sawtooth-free periods have been obtained resulting in the enhanced discharge performance. High T e (0) 9 - 10.5 keV with peaked profiles T e (0)/ e > = 3 - 4 were obtained giving values of n e (0)T e (0) up to 6x10 20 (keV m -3 ). Improvements in T i (0) and neutron production are observed. A 60 % enhancement in D-D reaction rate from 2nd harmonic deuterium (2ω CD ) heating appears to be present. In all current rise (CR) discharges radiation amounts to 25-50 % of total power. (author) 4 refs., 6 figs
Interpretation of heat and density pulse measurements in JET in terms of coupled transport
International Nuclear Information System (INIS)
Haas, J.C.M. de; O'Rourke, J.; Sips, A.C.C.; Lopes Cardozo, N.J.
1990-01-01
The perturbations of electron density and temperature profiles in a tokamak following a sawtooth collapse are considered. An analytic model for the interpretation of such perturbations is presented. It is shown that the perturbation can be decomposed into two contributions, which are eigenmodes of the linearised coupled diffusion equations for particle and energy. The approximations made in the analytical treatment are checked using computer simulations. Measurements of heat and density pulses in Joint European Torus are used to illustrate the power of the new approach. It is shown that using the coupled equations, an improved description of the heat and density pulses is obtained. The analysis yields the four diffusion coefficients in the linearised transport matrix. The non-zero off-diagonal elements explain certain salient features of the measurements, notably a marked decrease of the local density which occurs during the maximum of the temperature pulse. (author)
International Nuclear Information System (INIS)
Bures, M.; Bhatnagar, V.; Christiansen, J.P.
1989-01-01
The performance of high current discharges can be improved by applying central ICRF heating before or shortly after the onset of sawtooth activity in the plasma current rise phase. Long sawtooth-free periods have been obtained which result in a transiently-enhanced discharge performance. High T c (0) = 9-10.5 keV with peaked profile T e (0)/ e > = 3-4 were obtained giving values of N e (0)T e (0) up to 6 x 10 20 (keV m -3 ). Improvements in T i (0) and neutron production are observed. A best value of n Dd (0)T i (0)τ E = 1.65 x 10 20 (m -3 keV s) was achieved. Local transport simulation shows that the electron and ion thermal diffusivities do not differ substantially in the two cases of current-rise (CR) and flat-top (FT) heating, the performance of the central plasma region being enhanced, in the case of current-rise, entirely by the elimination of the sawtooth instability. The maximum D-D reaction rate is enhanced by a factor of 2 compared to the flat-top value. An appreciable part of the reaction rate is attributed to 2nd harmonic deuterium (2ω CD ) heating. In all current-rise discharges radiation amounts to 25-50% of total power and Ζ eff remains roughly constant. (author)
Utilization of an arc-heated jet for production of supersonic seeded beams of atomic nitrogen
International Nuclear Information System (INIS)
Bickes, R.W. Jr.; Newton, K.R.; Herrmann, J.M.; Bernstein, R.B.
1976-01-01
Intense supersonic beams of atomic nitrogen (>10 17 atoms sr -1 sec -1 ) have been produced from the dissociation of N 2 in an Ar arc (at temperatures in excess of 6000 K) using the arc-heated nozzle beam source of Young, Rodgers, and Knuth. Experiments characterizing the N 2 dissociation and the translational energies of the N, N 2 , and Ar components in the beams are described. Evidence is presented for the formation of atomic C as well as C 2 and CH from the pyrolysis of CH 4 and C 2 H 4 in the Ar arc
Edge localized modes and edge pedestal in NBI and ICRF heated H, D and T-plasmas in JET
International Nuclear Information System (INIS)
Bhatnagar, V.; Lingertat, J.; Barnsley, R.
1998-12-01
Based on experiments carried out in JET in D:T mixtures varying from 100:0 to 5:95 and those carried out in hydrogen plasmas, the isotopic mass dependence of ELM parameters and the edge pedestal pressure in neutral beam (NBI) and ion cyclotron resonance (ICRF) heated H-mode plasmas is presented. The ELM frequency is found to decrease with the atomic mass number both in ICRH and NBI discharges. However, the frequency in the case of ICRH is about 8 - 10 times higher than in the NBI case. Assuming that ELMs occur at a critical edge pressure gradient, limited by the ballooning instability, the scaling of the maximum edge pressure is most consistent with the assumption that the width of the transport barrier scales as the ion poloidal Larmor radius governed by the average energy of fast ions at the edge. The critical edge pressure in NBI heated discharges increases with the isotopic mass which. is consistent with the higher deduced width of the edge transport, barrier in tritium than in deuterium and hydrogen. The critical edge pressure in ICRH discharges is smaller, presumably, due to the smaller fast-ion contribution to the edge region. As a consequence of the edge pressure scaling with isotopic mass, the edge operational space in the n e - T e diagram increases with operation in tritium. If the evidence that the edge pedestal width is governed by the average energy of fast ions in the edge prevails, the pedestal in ITER would be controlled by the slowing down energy spectrum of α-particles in the edge. (author)
International Nuclear Information System (INIS)
Sienicki, J.J.; Spencer, B.W.
1985-01-01
An analysis is presented of the crust stability and heat transfer behavior in the CSTI-1, CSTI-3, and CWTI-11 reactor material experiments in which a jet of molten oxide fuel at approx. 160 0 K above its freezing temperature was impinged normally upon stainless steel plates initially at 300 and 385 K. The major issue is the existence of nonexistence of a stable solidified layer of fuel, or crust, interstitial to the flowing hot fuel and the steel substrate, tending to insulate the steel from the hot molten fuel. A computer model was developed to predict the heatup of thermocouples imbedded immediately beneath the surface of the plate for both of the cases in which a stable crust is assumed to be either present or absent during the impingement phase. Comparison of the model calculations with the measured thermocouple temperatures indicates that a protective crust was present over nearly all of the plate surface area throughout the impingement process precluding major melting of the plate steel. However, the experiments also show evidence for very localized and isolated steel melting as revealed by localized and isolated pitting of the steel surface and the response of thermocouples located within the pitted region
Heating, current drive and confinement regimes with the JET ICRH and LHCD systems
DEFF Research Database (Denmark)
Jacquinot, J.; Adams, J.M.; Altmann, H.
1991-01-01
by pellet injection. A value of n(d) tau-E T(i) = 7.8 x 10(20) m-3 s keV was obtained in this mode with T(e) approximately T(i) approximately 11 keV. In the L-mode regime, a regime, a record (140 kW) D-He-3 fusion power was generated with 10 - 14 MW of ICRH at the He-3 cyclotron frequency. Experiments were....... Paradoxically, LHCD induces central heating particularly in combination with ICRH. Finally we present the first observations of the synergistic acceleration of fast electrons by Transit Time Magnetic Pumping (TTMP) (from ICRH) and Electron Landau Damping (ELD) (from LHCD). The synergism generates TTMP current...
Engineering study of the neutral beam and rf heating systems for DIII-D, MFTF-B, JET, JT-60 and TFTR
International Nuclear Information System (INIS)
Lindquist, W.B.; Staten, S.H.
1987-01-01
An engineering study was performed on the rf and neutral beam heating systems implemented for DIII-D, MFTF-B, JET, JT-60 and TFTR. Areas covered include: methodology used to implement the systems, technology, cost, schedule, performance, problems encountered and lessons learned. Systems are compared and contrasted in the areas studied. Summary statements were made on common problems and lessons learned. 3 refs., 6 tabs
DEFF Research Database (Denmark)
Le Dreau, Jerome; Heiselberg, Per; Jensen, Rasmus Lund
2015-01-01
-state and dynamic conditions. With the air-based cooling system, a dependency of the convective heat transfer on the air jet trajectory has been observed. New correlations have been developed, introducing a modified Archimedes number to account for the air flow pattern. The accuracy of the new correlations has been...... evaluated to±15%. Besides the study with an air-based cooling system, the convective heat transfer with a radiant cooling system has also been investigated. The convective flow at the activated surface is mainly driven by natural convection. For other surfaces, the complexity of the flow and the large......The complexity and diversity of airflow in buildings make the accurate definition of convective heat transfer coefficients (CHTCs) difficult. In a full-scale test facility, the convective heat transfer of two cooling systems (active chilled beam and radiant wall) has been investigated under steady...
On Hubbell's rectangular source integral
International Nuclear Information System (INIS)
Stalker, John
2001-01-01
The integral H(a,b)=∫ 0 b ∫ 0 a dx dy/(1+x 2 +y 2 ) arises naturally in the study of radiation from a rectangular source and has been studied by many authors. This paper introduces a new series expansion which is rapidly convergent for large a and b
Energy Technology Data Exchange (ETDEWEB)
Shakouchih, T. [Mie University, Mie (Japan). Faculty of Engineering; Matsumoto, A.; Watanabe, A.
2000-10-25
It is well known that as decreasing the nozzle to plate spacing considerably the heat transfer coefficient of circular impinging jet, which impinges to the plate normally, increases remarkably. At that time, the flow resistance of nozzle-plate system also increases rapidly. In this study, in order to reduce the flow resistance and to enhance the heat transfer coefficient of the circular impinging jet with a considerably low nozzle to plate spacing, a special nozzle with notches is proposed, and considerable improvement of the flow and heat transfer properties are shown. The mechanism of enhancement of the heat transfer properties is also discussed. (author)
International Nuclear Information System (INIS)
Mostafaei, Amir; Toman, Jakub; Stevens, Erica L.; Hughes, Eamonn T.; Krimer, Yuval L.; Chmielus, Markus
2017-01-01
In this study, we investigate the effect of powders resulting from different atomization methods on properties of binder jet printed and heat-treated samples. Air-melted gas atomized (GA) and water atomized (WA) nickel-based alloy 625 powders were used to binder jet print samples for a detailed comparative study on microstructural evolution and mechanical properties. GA printed samples achieved higher sintering density (99.2%) than WA samples (95.0%) due to differences in powder morphology and chemistry. Grain sizes of GA and WA samples at their highest density were 89 ± 21 μm and 88 ± 26 μm, respectively. Mechanical tests were conducted on optimally sintered samples and sintered plus aged samples; aging further improved microstructure and mechanical properties. This study shows that microstructural evolution (densification, and carbide, oxide and intermetallic phase formation) is very different for GA and WA binder jet printed and heat-treated samples. This difference in microstructural evolution results in different mechanical properties with the superior sintered and aged GA specimen reaching a hardness of 327 ± 7 HV_0_._1, yield strength of 394 ± 15 MPa, and ultimate tensile strength of 718 ± 14 MPa which are higher than cast alloy 625 values.
Sun, Xi-wan; Guo, Zhen-yun; Huang, Wei; Li, Shi-bin; Yan, Li
2017-02-01
The drag reduction and thermal protection system applied to hypersonic re-entry vehicles have attracted an increasing attention, and several novel concepts have been proposed by researchers. In the current study, the influences of performance parameters on drag and heat reduction efficiency of combinational novel cavity and opposing jet concept has been investigated numerically. The Reynolds-average Navier-Stokes (RANS) equations coupled with the SST k-ω turbulence model have been employed to calculate its surrounding flowfields, and the first-order spatially accurate upwind scheme appears to be more suitable for three-dimensional flowfields after grid independent analysis. Different cases of performance parameters, namely jet operating conditions, freestream angle of attack and physical dimensions, are simulated based on the verification of numerical method, and the effects on shock stand-off distance, drag force coefficient, surface pressure and heat flux distributions have been analyzed. This is the basic study for drag reduction and thermal protection by multi-objective optimization of the combinational novel cavity and opposing jet concept in hypersonic flows in the future.
Shuja, S. Z.; Yilbas, B. S.
2013-07-01
Jet impingement onto a two-layer structured hole in relation to laser drilling is investigated. The hole consists of a coating layer and a base material. The variations in the Nusselt number and the skin friction are predicted for various coating materials. The Reynolds stress turbulent model is incorporated to account for the turbulence effect of the jet flow and nitrogen is used as the working fluid. The study is extended to include two jet velocities emanating from the conical nozzle. It is found that coating material has significant effect on the Nusselt number variation along the hole wall. In addition, the skin friction varies considerably along the coating thickness in thehole.
The design of a heat transfer liquid metal MHD experiment for ALEX [Argonne Liquid-Metal Experiment
International Nuclear Information System (INIS)
Picologlou, B.F.; Reed, C.B.; Hua, T.Q.; Lavine, A.S.
1988-01-01
An experiment to study heat transfer in liquid metal MHD flow, under conditions relevant to coolant channels for tokamak first wall and high heat flux devices, is described. The experimental configuration is a rectangular duct in a transverse magnetic field, heated on one wall parallel to the field. The specific objective of the experiment is to resolve important issues related to the presence and heat transfer characteristics of wall jets and flow instabilities in MHD flows in rectangular duct with electrically conducting walls. Available analytical tools for MHD thermal hydraulics have been used in the design of the test article and its instrumentation. Proposed tests will cover a wide range of Peclet and Hartmann numbers and interaction parameters. 14 refs., 3 figs., 1 tab
A systematic study of supersonic jet noise.
Louis, J. F.; Letty, R. P.; Patel, J. R.
1972-01-01
The acoustic fields for a rectangular and for an axisymmetric nozzle configuration are studied. Both nozzles are designed for identical flow parameters. It is tried to identify the dominant noise mechanisms. The other objective of the study is to establish scaling laws of supersonic jet noise. A shock tunnel is used in the investigations. Measured sound directivity, propagation direction of Mach waves obtained by shadowgraphs, and the slight dependence of the acoustic efficiency on the level of expansion indicate that Mach waves contribute significantly to the noise produced by a rectangular jet.
The Role of Combined ICRF and NBI Heating in JET Hybrid Plasmas in Quest for High D-T Fusion Yield
Directory of Open Access Journals (Sweden)
Mantsinen Mervi
2017-01-01
Full Text Available Combined ICRF and NBI heating played a key role in achieving the world-record fusion yield in the first deuterium-tritium campaign at the JET tokamak in 1997. The current plans for JET include new experiments with deuterium-tritium (D-T plasmas with more ITER-like conditions given the recently installed ITER-like wall (ILW. In the 2015-2016 campaigns, significant efforts have been devoted to the development of high-performance plasma scenarios compatible with ILW in preparation of the forthcoming D-T campaign. Good progress was made in both the inductive (baseline and the hybrid scenario: a new record JET ILW fusion yield with a significantly extended duration of the high-performance phase was achieved. This paper reports on the progress with the hybrid scenario which is a candidate for ITER longpulse operation (∼1000 s thanks to its improved normalized confinement, reduced plasma current and higher plasma beta with respect to the ITER reference baseline scenario. The combined NBI+ICRF power in the hybrid scenario was increased to 33 MW and the record fusion yield, averaged over 100 ms, to 2.9x1016 neutrons/s from the 2014 ILW fusion record of 2.3x1016 neutrons/s. Impurity control with ICRF waves was one of the key means for extending the duration of the high-performance phase. The main results are reviewed covering both key core and edge plasma issues.
Time-frequency analysis of submerged synthetic jet
Kumar, Abhay; Saha, Arun K.; Panigrahi, P. K.
2017-12-01
The coherent structures transport the finite body of fluid mass through rolling which plays an important role in heat transfer, boundary layer control, mixing, cooling, propulsion and other engineering applications. A synthetic jet in the form of a train of vortex rings having coherent structures of different length scales is expected to be useful in these applications. The propagation and sustainability of these coherent structures (vortex rings) in downstream direction characterize the performance of synthetic jet. In the present study, the velocity signal acquired using the S-type hot-film probe along the synthetic jet centerline has been taken for the spectral analysis. One circular and three rectangular orifices of aspect ratio 1, 2 and 4 actuating at 1, 6 and 18 Hz frequency have been used for creating different synthetic jets. The laser induced fluorescence images are used to study the flow structures qualitatively and help in explaining the velocity signal for detection of coherent structures. The study depicts four regions as vortex rollup and suction region (X/D h ≤ 3), steadily translating region (X/D h ≤ 3-8), vortex breakup region (X/Dh ≤ 4-8) and dissipation of small-scale vortices (X/D h ≤ 8-15). The presence of coherent structures localized in physical and temporal domain is analyzed for the characterization of synthetic jet. Due to pulsatile nature of synthetic jet, analysis of velocity time trace or signal in time, frequency and combined time-frequency domain assist in characterizing the signatures of coherent structures. It has been observed that the maximum energy is in the first harmonic of actuation frequency, which decreases slowly in downstream direction at 6 Hz compared to 1 and 18 Hz of actuation.
International Nuclear Information System (INIS)
Usui, Tohru; Kaminaga, Masanori; Sudo, Yukio.
1988-07-01
Quantitative understanding of critical heat flux (CHF) in the narrow vertical rectangular channel is required for the thermo-hydroulic design and the safety analysis of research reactors in which flat-plate-type fuel is adopted. Especially, critical heat flux under low downward velocity has a close relation with falling water limitation under counter-current flow. Accordingly, CCFL (Counter-current Flow Limitation) experiments were carried out for both vertical rectangular channels and vertical circular tubes varried in their size and configuration of their cross sections, to make clear CCFL characteristics in the vertical rectangular channels. In the experiments, l/de of the rectangular channel was changed from 3.5 to 180. As the results, it was clear that different equivalent hydraulic diameter de, namely width or water gap of channel, gave different CCFL characteristics of rectangular channel. But the influence of channel length l on CCFL characteristics was not observed. Besides, a dimensionless correlation to estimate a relation between upward air velocity and downward water velocity was proposed based on the present experimental results. The difference of CCFL characteristics between rectangular channels and circular tubes was also investigated. Especially for the rectangular channels, dry-patches appearing condition was made clear as a flow-map. (author)
Motion of rectangular prismatic bodies
International Nuclear Information System (INIS)
Poreh, M.; Wray, R.N.
1979-01-01
Rectangular prismatic bodies can assume either a translatory or an auto-rotating mode of motion during free motion in the atmosphere. The translatory mode is stable only when the dimensionless moment of inertia of the bodies is large, however, large perturbations will always start auto-rotation. The characteristics of the auto-rotational mode are shown to depend primarily on the aspect ratio of the bodies which determines the dimensionless rotational speed and the lift coefficient. Both the average drag and lift-coefficients of auto-rotating bodies are estimated, but it is shown that secondary effects make it impossible to determine their exact trajectories in atmospheric flows
An analytical solution to the heat transfer problem in thick-walled hunt flow
International Nuclear Information System (INIS)
Bluck, Michael J; Wolfendale, Michael J
2017-01-01
Highlights: • Convective heat transfer in Hunt type flow of a liquid metal in a rectangular duct. • Analytical solution to the H1 constant peripheral temperature in a rectangular duct. • New H1 result demonstrating the enhancement of heat transfer due to flow distortion by the applied magnetic field. • Analytical solution to the H2 constant peripheral heat flux in a rectangular duct. • New H2 result demonstrating the reduction of heat transfer due to flow distortion by the applied magnetic field. • Results are important for validation of CFD in magnetohydrodynamics and for implementation of systems code approaches. - Abstract: The flow of a liquid metal in a rectangular duct, subject to a strong transverse magnetic field is of interest in a number of applications. An important application of such flows is in the context of coolants in fusion reactors, where heat is transferred to a lead-lithium eutectic. It is vital, therefore, that the heat transfer mechanisms are understood. Forced convection heat transfer is strongly dependent on the flow profile. In the hydrodynamic case, Nusselt numbers and the like, have long been well characterised in duct geometries. In the case of liquid metals in strong magnetic fields (magnetohydrodynamics), the flow profiles are very different and one can expect a concomitant effect on convective heat transfer. For fully developed laminar flows, the magnetohydrodynamic problem can be characterised in terms of two coupled partial differential equations. The problem of heat transfer for perfectly electrically insulating boundaries (Shercliff case) has been studied previously (Bluck et al., 2015). In this paper, we demonstrate corresponding analytical solutions for the case of conducting hartmann walls of arbitrary thickness. The flow is very different from the Shercliff case, exhibiting jets near the side walls and core flow suppression which have profound effects on heat transfer.
Shuja, S. Z.; Yilbas, B. S.
2013-02-01
Jet emerging from a conical nozzle and impinging onto a tapered hole in relation to laser drilling is investigated and the influence taper location on the heat transfer and skin friction at the hole wall surface is examined. The study is extended to include four different gases as working fluid. The Reynolds stress model is incorporated to account for the turbulence effect in the flow field. The hole wall surface temperature is kept at 1500 K to resemble the laser drilled hole. It is found that the location of tapering in the hole influences the heat transfer rates and skin friction at the hole wall surface. The maximum skin friction coefficient increases for taper location of 0.25 H, where H is the thickness of the workpiece, while Nusselt number is higher in the hole for taper location of 0.75 H.
Czech Academy of Sciences Publication Activity Database
Dejarnac, Renaud; Podolník, Aleš; Komm, Michael; Arnoux, G.; Coenen, J.W.; Devaux, S.; Frassinetti, L.; Gunn, J. P.; Matthews, G. F.; Pitts, R.A.
2014-01-01
Roč. 54, č. 12 (2014), s. 123011-123011 ISSN 0029-5515 Institutional support: RVO:61389021 Keywords : PIC simulations * power flux * plasma–wall interactions * JET * divertor Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 3.062, year: 2014 http://iopscience.iop.org/0029-5515/54/12/123011/pdf/0029-5515_54_12_123011.pdf
Partitioning sparse rectangular matrices for parallel processing
Energy Technology Data Exchange (ETDEWEB)
Kolda, T.G.
1998-05-01
The authors are interested in partitioning sparse rectangular matrices for parallel processing. The partitioning problem has been well-studied in the square symmetric case, but the rectangular problem has received very little attention. They will formalize the rectangular matrix partitioning problem and discuss several methods for solving it. They will extend the spectral partitioning method for symmetric matrices to the rectangular case and compare this method to three new methods -- the alternating partitioning method and two hybrid methods. The hybrid methods will be shown to be best.
Hernandez Perez, Francisco E.; Im, Hong G.; Lee, Bok Jik; Fancello, Alessio; Donini, Andrea; van Oijen, Jeroen A.; de Goey, L. Philip H.
2017-11-01
Large eddy simulations (LES) of a turbulent premixed jet flame in a confined chamber are performed employing the flamelet-generated manifold (FGM) method for tabulation of chemical kinetics and thermochemical properties, as well as the OpenFOAM framework for computational fluid dynamics. The burner has been experimentally studied by Lammel et al. (2011) and features an off-center nozzle, feeding a preheated lean methane-air mixture with an equivalence ratio of 0.71 and mean velocity of 90 m/s, at 573 K and atmospheric pressure. Conductive heat loss is accounted for in the FGM tabulation via burner-stabilized flamelets and the subgrid-scale (SGS) turbulence-chemistry interaction is modeled via presumed filtered density functions. The impact of heat loss inclusion as well as SGS modeling for both the SGS stresses and SGS variance of progress variable on the numerical results is investigated. Comparisons of the LES results against measurements show a significant improvement in the prediction of temperature when heat losses are incorporated into FGM. While further enhancements in the LES results are accomplished by using SGS models based on transported quantities and/or dynamically computed coefficients as compared to the Smagorinsky model, heat loss inclusion is more relevant. This research was sponsored by King Abdullah University of Science and Technology (KAUST) and made use of computational resources at KAUST Supercomputing Laboratory.
Dubois, Yohan; Devriendt, Julien; Slyz, Adrianne; Teyssier, Romain
2012-03-01
We develop a subgrid model for the growth of supermassive black holes (BHs) and their associated active galactic nucleus (AGN) feedback in hydrodynamical cosmological simulations. This model transposes previous attempts to describe BH accretion and AGN feedback with the smoothed particle hydrodynamics (SPH) technique to the adaptive mesh refinement framework. It also furthers their development by implementing a new jet-like outflow treatment of the AGN feedback which we combine with the heating mode traditionally used in the SPH approach. Thus, our approach allows one to test the robustness of the conclusions derived from simulating the impact of self-regulated AGN feedback on galaxy formation vis-à-vis the numerical method. Assuming that BHs are created in the early stages of galaxy formation, they grow by mergers and accretion of gas at a Eddington-limited Bondi accretion rate. However this growth is regulated by AGN feedback which we model using two different modes: a quasar-heating mode when accretion rates on to the BHs are comparable to the Eddington rate, and a radio-jet mode at lower accretion rates which not only deposits energy, but also deposits mass and momentum on the grid. In other words, our feedback model deposits energy as a succession of thermal bursts and jet outflows depending on the properties of the gas surrounding the BHs. We assess the plausibility of such a model by comparing our results to observational measurements of the co-evolution of BHs and their host galaxy properties, and check their robustness with respect to numerical resolution. We show that AGN feedback must be a crucial physical ingredient for the formation of massive galaxies as it appears to be able to efficiently prevent the accumulation of and/or expel cold gas out of haloes/galaxies and significantly suppress star formation. Our model predicts that the relationship between BHs and their host galaxy mass evolves as a function of redshift, because of the vigorous accretion
Directory of Open Access Journals (Sweden)
I. V. Kazachkov
2012-03-01
Full Text Available Important nuclear power safety problem in touch with modeling of melted corium jet spreading inside the coolant pool is considered in the paper. It appears by development of the passive protection systems against se-vere accidents. The non-linear mathematical developed model is presented for the jet under reactor vessel pool for one of the perspective passive protection systems and the results of its analysis and studies are given. The performed analysis and the results of the numerical simulation done on the base of the model have allowed estab-lishing the interesting behaviors of the system, which may be useful for the scientists, as well as the engineers-constructors of the passive protection systems against severe accidents.
International Nuclear Information System (INIS)
Yuhki Takahashi; Yasuo Koizumi; Hiroyasu Ohtake; Tohru Miyashita; Michitsugu Mori
2006-01-01
Characteristics of thermal-hydraulic phenomena in the steam injector were examined. In experiments, a water jet from a nozzle of 5 mm diameter flowed into the condensing test section pipe concentrically. The inner diameter of the condensing section was 7, 10, or 20 mm and the length was 105 mm. Steam flowed into the peripheral space between the water jet and the inner wall of the test section and condensed on the ware jet surface. The radial and the axial distributions of velocity and temperature of the water jet were measured. Analyses by using the STAR-CD code were also performed. The temperature measured in the central portion of the water jet was higher than the predicted assuming the ordinary turbulent flow in a pipe. The temperature measured in the peripheral region was lower than the predicted. The radial temperature distribution measured was flatter than the predicted. When the steam condensation rate was large, the measured radial velocity distribution in the water jet was flatter than the predicted. In the case that the steam velocity was quite high, the velocity measured in the peripheral region was higher than that in the center portion. These results implied that the steam condensing on the water jet brought momentum in the water jet to result in more effective radial transport of heat and momentum. The STAR-CD code analyses to allow the interface between the wall that simulated the steam flow part and the water flow that stood for the water jet to move, i.e. creating momentum in-flux at the water jet interface, provided better results to support the experimental results. To increase the interfacial friction had a minor effect on the radial velocity distribution in the tested range. (authors)
International Nuclear Information System (INIS)
1984-06-01
JET began operations on 25 June 1983. This annual report contains administrative information and a general review of scientific and technical developments. Among them are vacuum systems, toroidal and poloidal field systems, power supplies, neutral beam heating, radiofrequency heating, remote handling, tritium handling, control and data acquisition systems and diagnostic systems
Mapping from rectangular to harmonic representation
International Nuclear Information System (INIS)
Schneider, W.; Bateman, G.
1986-08-01
An algorithm is developed to determine the Fourier harmonics representing the level contours of a scalar function given on a rectangular grid. This method is applied to the problem of computing the flux coordinates and flux surface average needed for 1-1/2-D transport codes and MHD stability codes from an equilibrium flux function given on a rectangular grid
Jet observables without jet algorithms
Energy Technology Data Exchange (ETDEWEB)
Bertolini, Daniele; Chan, Tucker; Thaler, Jesse [Center for Theoretical Physics, Massachusetts Institute of Technology,Cambridge, MA 02139 (United States)
2014-04-02
We introduce a new class of event shapes to characterize the jet-like structure of an event. Like traditional event shapes, our observables are infrared/collinear safe and involve a sum over all hadrons in an event, but like a jet clustering algorithm, they incorporate a jet radius parameter and a transverse momentum cut. Three of the ubiquitous jet-based observables — jet multiplicity, summed scalar transverse momentum, and missing transverse momentum — have event shape counterparts that are closely correlated with their jet-based cousins. Due to their “local” computational structure, these jet-like event shapes could potentially be used for trigger-level event selection at the LHC. Intriguingly, the jet multiplicity event shape typically takes on non-integer values, highlighting the inherent ambiguity in defining jets. By inverting jet multiplicity, we show how to characterize the transverse momentum of the n-th hardest jet without actually finding the constituents of that jet. Since many physics applications do require knowledge about the jet constituents, we also build a hybrid event shape that incorporates (local) jet clustering information. As a straightforward application of our general technique, we derive an event-shape version of jet trimming, allowing event-wide jet grooming without explicit jet identification. Finally, we briefly mention possible applications of our method for jet substructure studies.
Trujillo, Francisco Javier; Knoerzer, Kai
2011-11-01
High power ultrasound reactors have gained a lot of interest in the food industry given the effects that can arise from ultrasonic-induced cavitation in liquid foods. However, most of the new food processing developments have been based on empirical approaches. Thus, there is a need for mathematical models which help to understand, optimize, and scale up ultrasonic reactors. In this work, a computational fluid dynamics (CFD) model was developed to predict the acoustic streaming and induced heat generated by an ultrasonic horn reactor. In the model it is assumed that the horn tip is a fluid inlet, where a turbulent jet flow is injected into the vessel. The hydrodynamic momentum rate of the incoming jet is assumed to be equal to the total acoustic momentum rate emitted by the acoustic power source. CFD velocity predictions show excellent agreement with the experimental data for power densities higher than W(0)/V ≥ 25kWm(-3). This model successfully describes hydrodynamic fields (streaming) generated by low-frequency-high-power ultrasound. Crown Copyright © 2011. Published by Elsevier B.V. All rights reserved.
Preliminary Study of ONB in Narrow-Vertical Rectangular Channel
International Nuclear Information System (INIS)
Omar, S. AL-Yahia; Jo, Daeseong
2015-01-01
The location where the vapor bubble can first exist at the heated surface is called 'onset of nucleate boiling (ONB). The subcooled boiling is highly efficient to remove the heat owing to the high heat transfer coefficient. The heat transfer is affected by the motion of the bulk liquid as well as the latent heat transport of the liquid microlayer between the bubble and the heated wall. However, with increasing in the wall temperature, the bubble growth will increase and may they aggregate at the heated surface forming a vapor film, which will prevent the heat transport from the wall and that leads to highly rise in wall temperature. This phenomenon called departure from nucleate boiling (DNB). Many experimental and numerical CFD methods were carried out to investigate the subcooled boiling because of its importance in the industrial applications. In the present study, vertical narrow rectangular channel heated from both side was simulated by using CFX-14 to investigate the subcooled wall boiling, and identical simulation is done by using TMAP to compare the ONB location between numerical simulation and empirical correlations that implemented in TMAP. The numerical results using CFX-14 are discussed and compared with the results obtained from TMAP. The coolant temperature increases gradually (linearly) in the downward direction owing to the uniform applied heat flux.
Preliminary Study of ONB in Narrow-Vertical Rectangular Channel
Energy Technology Data Exchange (ETDEWEB)
Omar, S. AL-Yahia; Jo, Daeseong [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2015-10-15
The location where the vapor bubble can first exist at the heated surface is called 'onset of nucleate boiling (ONB). The subcooled boiling is highly efficient to remove the heat owing to the high heat transfer coefficient. The heat transfer is affected by the motion of the bulk liquid as well as the latent heat transport of the liquid microlayer between the bubble and the heated wall. However, with increasing in the wall temperature, the bubble growth will increase and may they aggregate at the heated surface forming a vapor film, which will prevent the heat transport from the wall and that leads to highly rise in wall temperature. This phenomenon called departure from nucleate boiling (DNB). Many experimental and numerical CFD methods were carried out to investigate the subcooled boiling because of its importance in the industrial applications. In the present study, vertical narrow rectangular channel heated from both side was simulated by using CFX-14 to investigate the subcooled wall boiling, and identical simulation is done by using TMAP to compare the ONB location between numerical simulation and empirical correlations that implemented in TMAP. The numerical results using CFX-14 are discussed and compared with the results obtained from TMAP. The coolant temperature increases gradually (linearly) in the downward direction owing to the uniform applied heat flux.
Hernandez Perez, Francisco E.; Lee, Bok Jik; Im, Hong G.; Fancello, Alessio; Donini, Andrea; van Oijen, Jeroen A.; de Goey, Philip H.
2017-01-01
Large eddy simulations of a turbulent premixed jet flame in a confined chamber were conducted using the flamelet-generated manifold technique for chemistry tabulation. The configuration is characterized by an off-center nozzle having an inner diameter of 10 mm, supplying a lean methane-air mixture with an equivalence ratio of 0.71 and a mean velocity of 90 m/s, at 573 K and atmospheric pressure. Conductive heat loss is accounted for in the manifold via burner-stabilized flamelets and the subgrid-scale (SGS) turbulencechemistry interaction is modeled via presumed probability density functions. Comparisons between numerical results and measured data show that a considerable improvement in the prediction of temperature is achieved when heat losses are included in the manifold, as compared to the adiabatic one. Additional improvement in the temperature predictions is obtained by incorporating radiative heat losses. Moreover, further enhancements in the LES predictions are achieved by employing SGS models based on transport equations, such as the SGS turbulence kinetic energy equation with dynamic coefficients. While the numerical results display good agreement up to a distance of 4 nozzle diameters downstream of the nozzle exit, the results become less satisfactory along the downstream, suggesting that further improvements in the modeling are required, among which a more accurate model for the SGS variance of progress variable can be relevant.
Directory of Open Access Journals (Sweden)
Jong Won Kim
2017-01-01
Full Text Available Polyethylene is one of the most commonly used polymer materials. Even though linear low density polyethylene (LLDPE has better mechanical properties than other kinds of polyethylene, it is not used as a textile material because of its plastic behavior that is easy to break at the die during melt spinning. In this study, LLDPE fibers were successfully produced with a new approach using a dry-jet wet spinning and a heat drawing process. The fibers were filled with carbon nanotubes (CNTs to improve the strength and reduce plastic deformation. The crystallinity, degree of orientation, mechanical properties (strength to yield, strength to break, elongation at break, and initial modulus, electrical conductivity, and thermal properties of LLDPE fibers were studied. The results show that the addition of CNTs improved the tensile strength and the degree of crystallinity. The heat drawing process resulted in a significant increase in the tensile strength and the orientation of the CNTs and polymer chains. In addition, this study demonstrates that the heat drawing process effectively decreases the plastic deformation of LLDPE.
Hernandez Perez, Francisco E.
2017-01-05
Large eddy simulations of a turbulent premixed jet flame in a confined chamber were conducted using the flamelet-generated manifold technique for chemistry tabulation. The configuration is characterized by an off-center nozzle having an inner diameter of 10 mm, supplying a lean methane-air mixture with an equivalence ratio of 0.71 and a mean velocity of 90 m/s, at 573 K and atmospheric pressure. Conductive heat loss is accounted for in the manifold via burner-stabilized flamelets and the subgrid-scale (SGS) turbulencechemistry interaction is modeled via presumed probability density functions. Comparisons between numerical results and measured data show that a considerable improvement in the prediction of temperature is achieved when heat losses are included in the manifold, as compared to the adiabatic one. Additional improvement in the temperature predictions is obtained by incorporating radiative heat losses. Moreover, further enhancements in the LES predictions are achieved by employing SGS models based on transport equations, such as the SGS turbulence kinetic energy equation with dynamic coefficients. While the numerical results display good agreement up to a distance of 4 nozzle diameters downstream of the nozzle exit, the results become less satisfactory along the downstream, suggesting that further improvements in the modeling are required, among which a more accurate model for the SGS variance of progress variable can be relevant.
Palisoc, Arthur L.; Lee, Chin C.
1988-12-01
Using the method of images and the analytical temperature solution to the multilayer infinite plate structure, the thermal profile over finite rectangular multilayer integrated circuit devices can be calculated exactly. The advantage of using the image method lies in the enhanced capability of arriving at an analytical solution for structures where analytical solutions do not apparently exist, e.g., circular or arbitrarily oriented rectangular sources over multilayered rectangular structures. The new approach results in large savings in computer CPU time especially for small sources over large substrates. The method also finds very important applications to integrated circuit devices with heat dissipating elements close to the edge boundaries. Results from two examples indicate that the edge boundaries of a device may also be utilized to remove heat from it. This additional heat removing capability should have important applications in high power devices.
Energy Technology Data Exchange (ETDEWEB)
Sasaguchi, K [Kumamoto University, Kumamoto (Japan). Faculty of Engineering
1994-12-25
Solid/liquid phase change in porous media has a wide relation with freezing and melting of ground bed, storage of cold heat in soil, and underground heat exchangers. This paper describes an investigation on the effect of density inversion on melting of ice in porous media by using the previously reported numerical analysis method. The high-temperature side temperature and the Darcy number were varied and investigated systematically on the ice in a porous media sealed in a rectangular container of which right hand side is maintained at elevated temperatures and the other three sides are insulated of heat. As a result, a large number of findings were obtained including the following matters: when the Darcy number is fixed at 4.01 {times} 10{sup {minus}5} and the high-temperature side temperature, Tw, is varied, the fluid descends along the high-temperature side because of the density inversion at Tw=4{degree}C, and forms one weak circulation that rotates clockwise; however, when the temperature reaches 16{degree}C, the circulation disappears, and a circulation rotating counterclockwise is observed, becoming identical to the case of a fluid where there is no density inversion; and change in the Nusselt number against the melting ratio, R, is the smallest at Tw=8{degree}C, and decreases monotonously with the R. 15 refs., 12 figs.
International Nuclear Information System (INIS)
Loizides, C.A.
2005-01-01
The ALICE experiment is one of the experiments currently prepared for the Large Hadron Collider (LHC) at CERN, Geneva, starting operation end of 2007. ALICE is dedicated to the research on nucleus-nucleus collisions at ultra-relativistic energies, which addresses the properties of strongly interacting matter under varying conditions of high density and temperature. The conditions provided at the LHC allow significant qualitative improvement with respect to previous studies. In particular, energetic probes, light quarks and gluons, will be abundantly produced. These probes might be identified by their fragmentation into correlated particles, so called jets, of high enough energy to allow full reconstruction of jet properties; even in the underlying heavy-ion environment. Understanding the dependence of high-energy jet production and fragmentation influenced by the dense medium created in the collision region is an open field of active research. Generally, one expects energy loss of the probes due to medium-induced gluon radiation. It is suggested that hadronization products of these, rather soft gluons may be contained within the jet emission cone, resulting in a modification of the characteristic jet fragmentation, as observed via longitudinal and transverse momentum distributions with respect to the direction of the initial parton, as well as of the multiplicity distributions arising from the jet fragmentation. Particle momenta parallel to the jet axis are softened (jet quenching), while transverse to it increased (transverse heating). The present thesis studies the capabilities of the ALICE detectors to measure these jets and quantifies obtainable rates and the quality of jet reconstruction, in both proton-proton and lead-lead collisions at the LHC. In particular, it is addressed whether modification of the jet fragmentation can be detected within the high-particle-multiplicity environment of central lead-lead collisions. (orig.)
Successive Standardization of Rectangular Arrays
Directory of Open Access Journals (Sweden)
Richard A. Olshen
2012-02-01
Full Text Available In this note we illustrate and develop further with mathematics and examples, the work on successive standardization (or normalization that is studied earlier by the same authors in [1] and [2]. Thus, we deal with successive iterations applied to rectangular arrays of numbers, where to avoid technical difficulties an array has at least three rows and at least three columns. Without loss, an iteration begins with operations on columns: first subtract the mean of each column; then divide by its standard deviation. The iteration continues with the same two operations done successively for rows. These four operations applied in sequence completes one iteration. One then iterates again, and again, and again, ... In [1] it was argued that if arrays are made up of real numbers, then the set for which convergence of these successive iterations fails has Lebesgue measure 0. The limiting array has row and column means 0, row and column standard deviations 1. A basic result on convergence given in [1] is true, though the argument in [1] is faulty. The result is stated in the form of a theorem here, and the argument for the theorem is correct. Moreover, many graphics given in [1] suggest that except for a set of entries of any array with Lebesgue measure 0, convergence is very rapid, eventually exponentially fast in the number of iterations. Because we learned this set of rules from Bradley Efron, we call it “Efron’s algorithm”. More importantly, the rapidity of convergence is illustrated by numerical examples.
Numerical investigation of flow past a row of rectangular rods
Directory of Open Access Journals (Sweden)
S.Ul. Islam
2016-09-01
Full Text Available A numerical study of uniform flow past a row of rectangular rods with aspect ratio defined as R = width/height = 0.5 is performed using the Lattice Boltzmann method. For this study the Reynolds number (Re is fixed at 150, while spacings between the rods (g are taken in the range from 1 to 6. Depending on g, the flow is classified into four patterns: flip-flopping, nearly unsteady-inphase, modulated inphase-antiphase non-synchronized and synchronized. Sudden jumps in physical parameters were observed, attaining either maximum or minimum values, with the change in flow patterns. The mean drag coefficient (Cdmean of middle rod is higher than the second and fourth rod for flip-flopping pattern while in case of nearly unsteady-inphase the middle rod attains minimum drag coefficient. It is also found that the Strouhal number (St of first, second and fifth rod decreases as g increases while that of other two have mixed trend. The results further show that there exist secondary interaction frequencies together with primary vortex shedding frequency due to jet in the gap between rods for 1 ⩽ g ⩽ 3. For the average values of Cdmean and St, an empirical relation is also given as a function of gap spacing. This relation shows that the average values of Cdmean and St approach to those of single rectangular rod with increment in g.
Kim, Hyun-Tae; Sips, A. C. C.; Romanelli, M.; Challis, C. D.; Rimini, F.; Garzotti, L.; Lerche, E.; Buchanan, J.; Yuan, X.; Kaye, S.; contributors, JET
2018-03-01
This paper presents the transport analysis of high density baseline discharges in the 2016 experimental campaign of the Joint European Torus with the ITER-Like Wall (JET-ILW), where a significant increase in the deuterium-deuterium (D-D) fusion neutron rate (~2.8 × 1016 s-1) was achieved with stable high neutral beam injection (NBI) powers of up to 28 MW and low gas puffing. Increase in T i exceeding T e were produced for the first time in baseline discharges despite the high electron density; this enabled a significant increase in the thermal fusion reaction rate. As a result, the new achieved record in fusion performance was much higher than the previous record in the same heating power baseline discharges, where T i = T e. In addition to the decreases in collisionality and the increases in ion heating fraction in the discharges with high NBI power, T i > T e can also be attributed to positive feedback between the high T i/T e ratio and stabilisation of the turbulent heat flux resulting from the ion temperature gradient driven mode. The high T i/T e ratio was correlated with high rotation frequency. Among the discharges with identical beam heating power, higher rotation frequencies were observed when particle fuelling was provided by low gas puffing and pellet injection. This reveals that particle fuelling played a key role for achieving high T i/T e, and the improved fusion performance.
Numerical analysis of high-speed Lithium jet flow under vacuum conditions
International Nuclear Information System (INIS)
Gordeev, Sergej; Groeschel, Friedrich; Stieglitz, Robert
2016-01-01
The EVEDA Li test loop (ELTL) [1] is aimed at validating the hydraulic stability of the Lithium (Li) target at a velocity up to 20 m/s at vacuum (≈10 −3 Pa). The ELTL has been designed to demonstrate the feasibility of the major components providing a neutron production liquid Li target for IFMIF. The rectangular shaped Li jet (cross-section 25 mm × 100 mm) necessitates for heat removal flow velocities of 15–20 m/s along a concave shaped back wall (curvature radius 250 mm) towards the outlet pipe, where the Li jet is subjected to vacuum before it finally enters the collecting quench tank. During the validation experiments within the ELTL acoustic waves within the target outlet pipe have been recorded, indicating potential cavitation processes in the jet impinging region, which may cause premature failures. In order to identify potential cavitation phenomena in correlation with the free jet flow in the outlet pipe a numerical study has been performed. The comparison measured and simulated acoustic emissions exhibits that experimentally deduced cavitation area coincides with the location of the jet wall impingement. The simulations further reveal that a part of the fluid after striking the wall even flows opposite to the gravity vector. This reversed flow is inherently unstable and characterized by waves at first growing and then bursting into droplets. The intense generation of small droplets increases significantly the Li free surface area and lead to a production of Li vapour, which is captured by the jet flow and reintroduced in the main flow. As the static pressure is recovered downstream due to jet impact, the vapour bubbles collapse and hence cavitation likely occurs.
Numerical analysis of high-speed Lithium jet flow under vacuum conditions
Energy Technology Data Exchange (ETDEWEB)
Gordeev, Sergej, E-mail: sergej.gordeev@kit.edu; Groeschel, Friedrich; Stieglitz, Robert
2016-11-01
The EVEDA Li test loop (ELTL) [1] is aimed at validating the hydraulic stability of the Lithium (Li) target at a velocity up to 20 m/s at vacuum (≈10{sup −3} Pa). The ELTL has been designed to demonstrate the feasibility of the major components providing a neutron production liquid Li target for IFMIF. The rectangular shaped Li jet (cross-section 25 mm × 100 mm) necessitates for heat removal flow velocities of 15–20 m/s along a concave shaped back wall (curvature radius 250 mm) towards the outlet pipe, where the Li jet is subjected to vacuum before it finally enters the collecting quench tank. During the validation experiments within the ELTL acoustic waves within the target outlet pipe have been recorded, indicating potential cavitation processes in the jet impinging region, which may cause premature failures. In order to identify potential cavitation phenomena in correlation with the free jet flow in the outlet pipe a numerical study has been performed. The comparison measured and simulated acoustic emissions exhibits that experimentally deduced cavitation area coincides with the location of the jet wall impingement. The simulations further reveal that a part of the fluid after striking the wall even flows opposite to the gravity vector. This reversed flow is inherently unstable and characterized by waves at first growing and then bursting into droplets. The intense generation of small droplets increases significantly the Li free surface area and lead to a production of Li vapour, which is captured by the jet flow and reintroduced in the main flow. As the static pressure is recovered downstream due to jet impact, the vapour bubbles collapse and hence cavitation likely occurs.
1975-01-01
A procedure for priming an arterial heat pump is reported; the procedure also has a means for maintaining the pump in a primed state. This concept utilizes a capillary driven jet pump to create the necessary suction to fill the artery. Basically, the jet pump consists of a venturi or nozzle-diffuser type constriction in the vapor passage. The throat of this venturi is connected to the artery. Thus vapor, gas, liquid, or a combination of the above is pumped continuously out of the artery. As a result, the artery is always filled with liquid and an adequate supply of working fluid is provided to the evaporator of the heat pipe.
three dimensional photoelastic investigations on thick rectangular
African Journals Online (AJOL)
user
1983-09-01
Sep 1, 1983 ... Thick rectangular plates are investigated by means of three-dimensional photoelasticity ... a thin plate theory and a higher order thick plate theory. 1. ..... number of fringes lest the accuracy of the results will be considerably.
Experimental study of natural circulation flow instability in rectangular channels
Energy Technology Data Exchange (ETDEWEB)
Zhou, Tao; Qi, Shi; Song, Mingqiang [North China Electric Power Univ., Beijing (China). School of Nuclear Science and Engineering; Passive Nuclear Safety Technology, Beijing (China). Beijing Key Lab.; Xiao, Zejun [Nuclear, Reactor Thermal Hydraulics Technology, Chengdu (China). CNNC Key Lab.
2017-05-15
Experiments of natural circulation flow instability were conducted in rectangular channels with 5 mm and 10 mm wide gaps. Results for different heating powers were obtained. The results showed that the flow will tend to be instable with the growing of heating power. The oscillation period of pressure D-value and volume flow are the same, but their phase positions are opposite. They both can be described by trigonometric functions. The existence of edge position and secondary flow will strengthen the disturbance of fluid flow in rectangle channels, which contributes to heat transfer. The disturbance of bubble and fluid will be strengthened, especially in the saturated boiling section, which make it possible for the mixing flow. The results also showed that the resistance in 5 mm channel is bigger than that in 10 mm channel, it is less likely to form stable natural circulation in the subcooled region.
Rectangular-section mirror light pipes
Energy Technology Data Exchange (ETDEWEB)
Swift, P.D.; Lawlor, R. [School of Physical Sciences, Dublin City University, Dublin 9 (Ireland); Smith, G.B.; Gentle, A. [Department of Applied Physics, University of Technology, Sydney, Broadway, NSW 2007 (Australia)
2008-08-15
Using an integrated-ray approach an expression for the transmission of rectangular section mirror light pipe (MLP) has been derived for the case of collimated light input. The transmittance and the irradiance distribution at the exit aperture of rectangular-section MLPs have been measured experimentally and calculated theoretically for the case of collimated light input. The results presented extend the description of MLPs from the cylindrical case. Measured and calculated transmittances and irradiance distributions are in good agreement. (author)
Random Young diagrams in a Rectangular Box
DEFF Research Database (Denmark)
Beltoft, Dan; Boutillier, Cédric; Enriquez, Nathanaël
We exhibit the limit shape of random Young diagrams having a distribution proportional to the exponential of their area, and confined in a rectangular box. The Ornstein-Uhlenbeck bridge arises from the fluctuations around the limit shape.......We exhibit the limit shape of random Young diagrams having a distribution proportional to the exponential of their area, and confined in a rectangular box. The Ornstein-Uhlenbeck bridge arises from the fluctuations around the limit shape....
Energy Technology Data Exchange (ETDEWEB)
Mhiri, H.; El Golli, S. [Ecole Nationale d`Ingenieurs, Monastir (Tunisia). Lab. d`Energetique; Berthon, A.; Le Palec, G.; Bournot, P. [Technopole de Chateau-Gombert, Marseille (France)
1998-10-01
Because of its numerous industrial applications (air conditioning, thermal insulation, behavior of fires), heat transfer in rectangular cavities has made the subject of many works which concern both theoretical numerical studies and experimental investigations. This work is devoted to a numerical approach of the laminar mixed convection in a cavity which one of the boundaries is materialized by a laminar vertical downstream air jet. The purpose is to analyze the interaction of this flow with the natural movement that grows in the cavity under the combined action of boundary thermal gradients and external medium of the cavity in order to examine thermal insulation qualities of the jet. Calculations have been made with the help of the finite volume method.
Nigodjuk, V. E.; Sulinov, A. V.
2018-01-01
The article presents the results of experimental studies of hydrodynamics and those of loobman single-phase and two-phase flows in capillary nozzle elements propellant thrusters and the proposed method of their calculation. An experimental study was performed in capillaries with a sharp entrance edge of the internal diameter of 0.16 and 0.33 mm and a relative length 188 and 161, respectively, in pouring distilled water and acetone in the following range of parameters Reynolds number Re = (0,3 ... 10) · 103, Prandtl number Pr = (2 ... 10), pressure p = (0,1 ... 0,3) MPa, the heat flux q = (0...2)×106 W/m2, the difference of temperature under-heating of liquid Δtn = (5 ... 80)K. The dependences for calculation of single phase boundaries, the undeveloped and the developed surface of the bubble and film key singing of subcooled liquid. It is shown theoretically and experimentally confirmed the virtual absence of areas of undeveloped nucleate boiling in laminar flow. The dependence for calculation of hydraulic resistance and heat transfer in the investigated areas of current. It is shown that in the region of nucleate boiling surface in the flow in capillary tubes, influence of the formed vapor phase on the hydrodynamics and heat transfer substantially higher than in larger diameter pipes.
International Nuclear Information System (INIS)
Fougairolle, P.
2009-07-01
This work consists in the experimental study of a jet in crossflow in a closed wind tunnel. Depending on the value of the velocity ratio (r U j /U∞), this confined rectangular jet can interact or impact with the opposite wall from the one it issues. The jet is slightly heated (∼10 C) in order to stay in the passive scalar case. An improvement of the experimental facility has been done to obtain thermal boundary conditions compatible with the measurements of slight differences of temperature, imposed by the passive scalar. Concerning the metrology, hot and cold wire anemometry and thermometry are used, and all the anemometric devices are developed and built in the lab. Probes made with Wollaston wire (Pt-Rh) of 0.35μm diameter are coupled with an anemometer and a thermometer optimized to maximize the signal to noise ratio. The results are obtained both thanks to visualizations by fast camera shots for several velocity ratios (r between 3 and 12), and thanks to local hot and cold wire measurements, in the particular case of two velocity ratios (r = 3.3 and 9.4). Mixing properties of the scalar are studied by the plot of statistical values of velocity and temperature in different plans, perpendicularly to the three axis. The analysis of spectral densities of the signals on several typical locations emphasizes some features of the dynamic behaviour of the jet. (author)
Particle image velocimetry measurements of the flow in the converging region of two parallel jets
Energy Technology Data Exchange (ETDEWEB)
Wang, Huhu, E-mail: huhuwang@tamu.edu; Lee, Saya, E-mail: sayalee@tamu.edu; Hassan, Yassin A., E-mail: y-hassan@tamu.edu
2016-09-15
Highlights: • The flow behaviors in the converging region were non-intrusively investigated using PIV. • The PIV results using two measuring scales and LDV data matched very well. • Significant momentum transfer was observed in the merging region right after the merging point. • Instantaneous vector field revealed characteristic interacting patterns of the jets. - Abstract: The interaction between parallel jets plays a critical role in determining the characteristics of the momentum and heat transfer in the flow. Specifically for next generation VHTR, the output temperature will be about 900 °C, and any thermal oscillations will create safety issues. The mixing variations of the coolants in the reactor core may influence these power oscillations. Numerous numerical tools such as computational fluid dynamics (CFD) simulations have been used to support the reactor design. The validation of CFD method is important to ensure the fidelity of the calculations. This requires high-fidelity, qualified benchmark data. Particle image velocimetry (PIV), a non-intrusive measuring technique, was used to provide benchmark data for resolving a simultaneous flow field in the converging region of two submerged parallel jets issued from rectangular channels. The jets studied in this work had an equal discharge velocity at room temperature. The turbulent characteristics including the distributions of mean velocities, turbulence intensities, Reynolds stresses and z-component vorticity were studied. The streamwise mean velocity measured by PIV and LDV were compared, and they agreed very well.
Partial rectangular metric spaces and fixed point theorems.
Shukla, Satish
2014-01-01
The purpose of this paper is to introduce the concept of partial rectangular metric spaces as a generalization of rectangular metric and partial metric spaces. Some properties of partial rectangular metric spaces and some fixed point results for quasitype contraction in partial rectangular metric spaces are proved. Some examples are given to illustrate the observed results.
International Nuclear Information System (INIS)
Tardocchi, M.; Gorini, G.; Andersson Sunden, E.; Conroy, S.; Ericsson, G.; Gatu Johnson, M.; Giacomelli, L.; Hellesen, C.; Hjalmarsson, A.; Kaellne, J.; Ronchi, E.; Sjoestrand, H.; Weiszflog, M.; Johnson, T.; Lamalle, P. U.
2006-01-01
The measurement of fast ion populations is one of the diagnostic capabilities provided by neutron emission spectroscopy (NES). NES measurements were carried out during JET trace tritium campaign with the magnetic proton recoil neutron spectrometer. A favorable plasma scenario is (T)D where the resulting 14 MeV neutron yield is dominated by suprathermal emission from energetic tritons accelerated by radio frequency at their fundamental cyclotron frequency. Information on the triton distribution function has been derived from NES data with a simple model based on two components referred to as bulk (B) and high energy (HE). The HE component is based on strongly anisotropic tritium distribution that can be used for routine best-fit analysis to provide tail temperature values (T HE ). This article addresses to what extent the T HE values are model dependent by comparing the model above with a two-temperature (bi-) Maxwellian model featuring parallel and perpendicular temperatures. The bi-Maxwellian model is strongly anisotropic and frequently used for radio frequency theory
Bivolaru, Daniel; Cutler, Andrew D.; Danehy, Paul M.; Gaffney, Richard L.; Baurle, Robert a.
2009-01-01
This paper presents simultaneous measurements at multiple points of two orthogonal components of flow velocity using a single-shot interferometric Rayleigh scattering (IRS) technique. The measurements are performed on a large-scale Mach 1.6 (Mach 5.5 enthalpy) H2-air combustion jet during the 2007 test campaign in the Direct Connect Supersonic Combustion Test facility at NASA Langley Research Center. The measurements are performed simultaneously with CARS (Coherent Anti-stokes Raman Spectroscopy) using a combined CARS-IRS instrument with a common path 9-nanosecond pulsed, injection-seeded, 532-nm Nd:YAG laser probe pulse. The paper summarizes the measurements of velocities along the core of the vitiated air flow as well as two radial profiles. The average velocity measurement near the centerline at the closest point from the nozzle exit compares favorably with the CFD calculations using the VULCAN code. Further downstream, the measured axial velocity shows overall higher values than predicted with a trend of convergence at further distances. Larger discrepancies are shown in the radial profiles.
International Nuclear Information System (INIS)
Lalizel, Gildas; Sultan, Qaiser; Fénot, Matthieu; Dorignac, Eva
2012-01-01
In actual gas turbine system, unsteadiness of the mainstream flow influences heat transfer and surface pressure distribution on the blade. In order to simulate these conditions, an experimental film cooling study with externally imposed pulsation is performed with purpose of characterizing both effects of turbine unsteadiness on film cooling (with frequency ranges typical to actual turbine), and also to figure out the range of Strouhal number pulsation under various blowing conditions, which could possibly deliver a performance improvement in film cooling. Influence of injection flow pulsation on adiabatic effectiveness and convective heat transfer coefficient are determined from IR-thermography of the wall for distances to the hole exit between 0 and 30 D.
International Nuclear Information System (INIS)
Saxon, D.H.
1985-10-01
The paper reviews studies on jet fragmentation. The subject is discussed under the topic headings: fragmentation models, charged particle multiplicity, bose-einstein correlations, identified hadrons in jets, heavy quark fragmentation, baryon production, gluon and quark jets compared, the string effect, and two successful models. (U.K.)
Directory of Open Access Journals (Sweden)
A. M. El-Jummah
2017-02-01
Full Text Available Numerical calculations relevant to gas turbine internal wall heat transfer cooling were conducted using conjugate heat transfer (CHT computational Fluid Dynamics (CFD commercial codes. The CHT CFD predictions were carried out for impingement heat transfer with different types of obstacle walls (fins on the target surfaces. A 10 × 10 row of impingement air jet holes (or hole density n of 4306 m-2 was used, which gives ten rows of holes in the cross-flow direction and only one heat transfer enhancement obstacle per impingement jet was investigated. Previously, four different shaped obstacles were investigated experimentally and were used to validate the present predictions. The obstacle walls, which were equally spaced on the centreline between each impingement jet are of the co-flow and cross-flow configurations. The impingement jet pitch X to diameter D, X/D and gap Z to diameter, Z/D ratios were kept constant at 4.66 and 3.06 for X, Z and D of 15.24, 10.00 and 3.27 mm, respectively. The obstacles investigated were ribs and rectangular pin-fins shapes, using two obstacles height H to diameter, H/D ratio of 1.38 and 2.45. Computations were carried out for three different mass flux G of 1.08, 1.48 and 1.94 kg/sm2. Relative pressure loss ∆P/P and surface average heat transfer coefficient (HTC h predictions for the range of G, showed good agreement with the experimental results. The prediction also reveals that obstacles not only increases the turbulent flows, but also takes away most of the cooling heat transfer that produces the regions with highest thermal gradients. It also reduces the impingement gap downstream cross-flow.
Active control of continuous air jet with bifurcated synthetic jets
Directory of Open Access Journals (Sweden)
Dančová Petra
2017-01-01
Full Text Available The synthetic jets (SJs have many significant applications and the number of applications is increasing all the time. In this research the main focus is on the primary flow control which can be used effectively for the heat transfer increasing. This paper deals with the experimental research of the effect of two SJs worked in the bifurcated mode used for control of an axisymmetric air jet. First, the control synthetic jets were measured alone. After an adjustment, the primary axisymmetric jet was added in to the system. For comparison, the primary flow without synthetic jets control was also measured. All experiments were performed using PIV method whereby the synchronization between synthetic jets and PIV system was necessary to do.
International Nuclear Information System (INIS)
1989-06-01
The scientific, technical, experimental and theoretical investigations related to JET tokamak are presented. The JET Joint Undertaking, Volume 2, includes papers presented at: the 15th European Conference on controlled fusion and plasma heating, the 15th Symposium on fusion technology, the 12th IAEA Conference on plasma physics and controlled nuclear fusion research, the 8th Topical Meeting on technology of fusion. Moreover, the following topics, concerning JET, are discussed: experience with wall materials, plasma performance, high power ion cyclotron resonance heating, plasma boundary, results and prospects for fusion, preparation for D-T operation, active gas handling system and remote handling equipment
Solving the rectangular assignment problem and applications
Bijsterbosch, J.; Volgenant, A.
2010-01-01
The rectangular assignment problem is a generalization of the linear assignment problem (LAP): one wants to assign a number of persons to a smaller number of jobs, minimizing the total corresponding costs. Applications are, e.g., in the fields of object recognition and scheduling. Further, we show
Steady turbulent flow in curved rectangular channels
De Vriend, H.J.
1979-01-01
After the study of fully developed and developing steady laminar flow in curved channels of shallow rectangular wet cross-section (see earlier reports in this series), steady turbulent flow in such channels is investigated as a next step towards a mathematical model of the flow in shallow river
A solution for the narrow rectangular punch
Panek, C.F.; Kalker, J.J.
1977-01-01
This paper considers the problem of a rectangular flat ended punch acting on an elastic half-space. An approximate solution is generated through application of the elastic line integral equations. The results produced by this method are then compared with another approximate solution already
Applicability of electrical resistance tomography to rectangular vessels
International Nuclear Information System (INIS)
Ichijo, Noriaki; Matsuno, Shinsuke; Tokura, Susumu; Tochigi, Yoshikatsu; Misumi, Ryuta; Nishi, Kazuhiko; Kaminoyama, Meguru
2012-01-01
To ensure a stable operation of Joule-heated glass melters, it is necessary to observe the distribution of platinum group metal particles (noble metals) in molten glass. Electrical resistance tomography (ERT) has a potential to visualize the inside of the melter section because it can be applied at severe conditions such as high temperature and radioactive fields. Due to designing limitations, it is difficult to install electrodes on the wall of the glass melter. In addition, ERT is hardly applied to a rectangular section. To solve these problems, numerical and experimental studies have been implemented. To apply the ERT method, 8 electrodes are inserted from the top of the melter and set near the bottom to visualize the accumulation of noble metals on the bottom area. As a result of the numerical simulation and the experiment, it was clarified that the ERT can be applied to the rectangular vessel by inserting electrodes from the top of the vessel and has a potential to observe the accumulation of noble metals. (author)
Measurements and Predictions of the Noise from Three-Stream Jets
Henderson, Brenda S.; Leib, Stewart J.; Wernet, Mark P.
2015-01-01
An experimental and numerical investigation of the noise produced by high-subsonic and supersonic three-stream jets was conducted. The exhaust system consisted of externally-mixed-convergent nozzles and an external plug. Bypass- and tertiary-to-core area ratios between 1.0 and 2.5, and 0.4 and 1.0, respectively, were studied. Axisymmetric and offset tertiary nozzles were investigated for heated and unheated conditions. For axisymmetric configurations, the addition of the third stream was found to reduce peak- and high-frequency acoustic levels in the peak-jet-noise direction, with greater reductions at the lower bypass-to-core area ratios. For the offset configurations, an offset duct was found to decrease acoustic levels on the thick side of the tertiary nozzle relative to those produced by the simulated two-stream jet with up to 8 dB mid-frequency noise reduction at large angles to the jet inlet axis. Noise reduction in the peak-jet-noise direction was greater for supersonic core speeds than for subsonic core speeds. The addition of a tertiary nozzle insert used to divert the third-stream jet to one side of the nozzle system provided no noise reduction. Noise predictions are presented for selected cases using a method based on an acoustic analogy with mean flow interaction effects accounted for using a Green's function, computed in terms of its coupled azimuthal modes for the offset cases, and a source model previously used for round and rectangular jets. Comparisons of the prediction results with data show that the noise model predicts the observed increase in low-frequency noise with the introduction of a third, axisymmetric stream, but not the high-frequency reduction. For an offset third stream, the model predicts the observed trend of decreased sound levels on the thick side of the jet compared with the thin side, but the predicted azimuthal variations are much less than those seen in the data. Also, the shift of the spectral peak to lower frequencies with
Fluid Flow and Infrared Image Analyses on Endwall Fitted with Short Rectangular Plate Fin
Institute of Scientific and Technical Information of China (English)
Kenyu OYAKAWA; Islam Md. DIDARUL; Minoru YAGA
2006-01-01
An experimental investigation is carried out to study fluid flow and heat transfer characteristics on the endwall fitted with arrays ( 7 × 7 ) of short rectangular plate fins of different pattern (co-angular and zigzag) for different pitch ratio. Experiments were conducted in a rectangular duct of 50 mm height for an air flow of Reynolds number ranged from 18750 to 62500 based on the equivalent diameter and air velocity of the duct. Infrared image analysis technique was employed to make clear the characteristics of local heat transfer coefficients on fin base, endwall and overall surface. Flow pattern around the short rectangular plates were visualized by inducing fluorescent dye in a water channel and longitudinal vortices were observed. Increasing the distance between plates in flow direction causes heat transfer enhancement for co-angular pattern, while decreasing the distance causes heat transfer enhancement for zigzag pattern. Zigzag pattern with pitch ratio 2 is found to be more effective in heat transfer enhancement than any other cases investigated.
Features of two-phase flow patterns in horizontal rectangular microchannels of height 50 μm
Directory of Open Access Journals (Sweden)
Ron’shin Fedor
2016-01-01
Full Text Available The horizontal microchannel with the height of 50 micrometres and width of 40 mm of a rectangular cross-section has been used to study two-phase flow. The classical patterns of two-phase flow in the channel (bubble, stratified, churn, jet, and annular have been detected. Experimental information allows us to define the characteristics of the regimes and to determine precisely the boundaries between the patterns of the two-phase flows.
g-Weak Contraction in Ordered Cone Rectangular Metric Spaces
Directory of Open Access Journals (Sweden)
S. K. Malhotra
2013-01-01
Full Text Available We prove some common fixed-point theorems for the ordered g-weak contractions in cone rectangular metric spaces without assuming the normality of cone. Our results generalize some recent results from cone metric and cone rectangular metric spaces into ordered cone rectangular metric spaces. Examples are provided which illustrate the results.
Irradiated target cooling using circular air jet
International Nuclear Information System (INIS)
Selvaraj, P.; Natesan, K.; Velusamy, K.; Baskaran, V.; Sundararajan, T.
2015-01-01
To study the effect of irradiation on materials, sample coupons are irradiated in cyclotron facilities. During the irradiation process, these samples produce significant heat. This heat needs to be continuously removed from the samples in order to avoid melting of the samples as well as to keep the samples at a particular temperature during irradiation. The area available for heat transfer is limited due to the small size of the samples. To increase the heat transfer rate, jet cooling is used as it provides large heat transfer co-efficient. To understand the heat transfer characteristics of jet cooling under these conditions, experiments have been carried out. Electric Joule heating is adopted to simulate irradiation heat in stainless steel samples. An array of circular nozzles is used to create air jet. From the study the values of the parameters correspond to the maximum heat removal rate are found out. The results are also compared with an empirical correlation from the literature. (author)
Counter-current flow limited CHF in thin rectangular channels
International Nuclear Information System (INIS)
Cheng, L.Y.
1990-01-01
An analytical expression for counter-current-flow-limitation (CCFL) was used to predict critical heat flux (CHF) for downward flow in thin vertical rectangular channels which are prototypes of coolant channels in test and research nuclear reactors. Top flooding is the mechanism for counter-current flow limited CHF. The CCFL correlation also was used to determine the circulation and flooding-limited CHF. Good agreements were observed between the period the model predictions and data on the CHF for downflow. The minimum CHF for downflow is lower than the flooding-limited CHF and it is predicted to occur at a liquid flow rate higher than that at the flooding limit. 17 refs., 7 figs
Metamaterial Embedded Wearable Rectangular Microstrip Patch Antenna
Directory of Open Access Journals (Sweden)
J. G. Joshi
2012-01-01
Full Text Available This paper presents an indigenous low-cost metamaterial embedded wearable rectangular microstrip patch antenna using polyester substrate for IEEE 802.11a WLAN applications. The proposed antenna resonates at 5.10 GHz with a bandwidth and gain of 97 MHz and 4.92 dBi, respectively. The electrical size of this antenna is 0.254λ×0.5λ. The slots are cut in rectangular patch to reduce the bending effect. This leads to mismatch the impedance at WLAN frequency band; hence, a metamaterial square SRR is embedded inside the slot. A prototype antenna has been fabricated and tested, and the measured results are presented in this paper. The simulated and measured results of the proposed antenna are found to be in good agreement. The bending effect on the performance of this antenna is experimentally verified.
Anisotropic rectangular metric for polygonal surface remeshing
Pellenard, Bertrand
2013-06-18
We propose a new method for anisotropic polygonal surface remeshing. Our algorithm takes as input a surface triangle mesh. An anisotropic rectangular metric, defined at each triangle facet of the input mesh, is derived from both a user-specified normal-based tolerance error and the requirement to favor rectangle-shaped polygons. Our algorithm uses a greedy optimization procedure that adds, deletes and relocates generators so as to match two criteria related to partitioning and conformity.
Anisotropic rectangular metric for polygonal surface remeshing
Pellenard, Bertrand; Morvan, Jean-Marie; Alliez, Pierre
2013-01-01
We propose a new method for anisotropic polygonal surface remeshing. Our algorithm takes as input a surface triangle mesh. An anisotropic rectangular metric, defined at each triangle facet of the input mesh, is derived from both a user-specified normal-based tolerance error and the requirement to favor rectangle-shaped polygons. Our algorithm uses a greedy optimization procedure that adds, deletes and relocates generators so as to match two criteria related to partitioning and conformity.
International Nuclear Information System (INIS)
Monde, Masanori; Mitsutake, Yuichi; Ishida, Kenji; Hino, Ryutaro
2003-03-01
An ultra high critical heat flux (CHF) has been challenged with a highly subcooled water jet impinging on a small rectangular heated surface. Major objective of the study is to achieve an ultra high heat flux cooling as large as 100 MW/m 2 and to establish an accurate estimation method of the CHF. The experiments were carried out over the experimental range; a fixed jet diameter of 2 mm, jet velocity of 5 - 35 m/s, degree of subcooling of 80 - 170 K and system pressure of 0.1 - 1.0 MPa. The rectangular heated surface with a thin nickel foil of 0.03 - 0.3 mm in thickness, 5 and 10 mm in length, and 4 mm in width and heated by a direct current. Effects of thickness of heater wall, jet velocity and subcooling on the CHF were experimentally elucidated. The experimental results show that the CHF decreases about 50% as the heater thickness, namely heat capacity of heater decreases. Characteristics of the CHF with heater length of 10 mm are correlated within ±20% by the generalized correlation of subcooled CHF proposed by the authors. However, the CHF with the shorter heater length of 5 mm shows large deviation of -40% especially at lower subcooling and higher velocity. The maximum CHF of 212 MW/m 2 was achieved at the subcooling of 151 K, the jet velocity of 35 m/s and system pressure of 0.5 MPa. The maximum CHF under atmospheric pressure approaches to 48% of the ultimate maximum heat flux given by the assumptions that vapor molecules leave a liquid-vapor interface at the average speed of a Boltzman-Maxwellian gas and any molecules returning to the interface are not permitted. The ratio of the CHF and ultimate maximum heat flux was considerably enhanced from the existing record of 30%. This study can give the feasibility of ultra high heat flux removal facing in a development of components such as a diverter of a fusion reactor. (author)
Numerical study of turbulent flow in a rectangular T-junction
Georgiou, Michail; Papalexandris, Miltiadis V.
2017-06-01
In this paper, we report on a numerical study of the interaction and merging of a turbulent crossflow with an incoming turbulent jet in a T-junction with rectangular cross section. Our study is based on wall-resolved and experimentally validated large eddy simulations. The bulk Reynolds number of the crossflow is 15 000. Further, we consider cases with two different momentum ratios, namely, MR = 2 and MR = 0.5. In the presentation of the results, we elaborate on the main features of the flow, namely, the shear layers that emanate from the corners of the entry of the jet, the large recirculation bubble downstream the incoming jet, and the mixing process beyond the reattachment point. For validation purposes, we compare our simulations with existing experimental data. This comparison shows a good agreement between our numerical predictions and the measurements. First- and second-order statistics of the flow are also presented and analyzed in detail. Our simulations reveal two features of the flow that have not been reported before in studies of T-junctions. The first one is a secondary small-scale recirculation region between the entry of the jet and the large recirculation bubble. The second one is the negative turbulent kinetic energy production that occurs in the recirculation bubble and close to the reattachment of the flow. The analysis of our results further reveals that just across the entry of the jet, the boundary layer in the wall opposite to the jet experiences a favourable pressure gradient due to a Venturi effect induced by the incoming jet. In turn, this favourable pressure gradient contributes to the local relaminarization of the flow. On the other hand, the boundary layer downstream the recirculation bubble experiences an adverse pressure gradient. In both cases, a significant deviation from the universal law of the wall is confirmed.
International Nuclear Information System (INIS)
Juknevich, J.
2014-01-01
We present a study of the substructure of jets high transverse momentum at hadron colliders. A template method is introduced to distinguish heavy jets by comparing their energy distributions to the distributions of a set of templates which describe the kinematical information from signal or background. As an application, a search for a boosted Higgs boson decaying into bottom quarks in association with a leptonically decaying W boson is presented as well. (author)
Schwaller, Pedro; Weiler, Andreas
2015-01-01
In this work, we propose a novel search strategy for new physics at the LHC that utilizes calorimeter jets that (i) are composed dominantly of displaced tracks and (ii) have many different vertices within the jet cone. Such emerging jet signatures are smoking guns for models with a composite dark sector where a parton shower in the dark sector is followed by displaced decays of dark pions back to SM jets. No current LHC searches are sensitive to this type of phenomenology. We perform a detailed simulation for a benchmark signal with two regular and two emerging jets, and present and implement strategies to suppress QCD backgrounds by up to six orders of magnitude. At the 14 TeV LHC, this signature can be probed with mediator masses as large as 1.5 TeV for a range of dark pion lifetimes, and the reach is increased further at the high-luminosity LHC. The emerging jet search is also sensitive to a broad class of long-lived phenomena, and we show this for a supersymmetric model with R-parity violation. Possibilit...
Energy Technology Data Exchange (ETDEWEB)
Schwaller, Pedro; Stolarski, Daniel [European Organization for Nuclear Research (CERN), Geneva (Switzerland). TH-PH Div.; Weiler, Andreas [European Organization for Nuclear Research (CERN), Geneva (Switzerland). TH-PH Div.; Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
2015-02-15
In this work, we propose a novel search strategy for new physics at the LHC that utilizes calorimeter jets that (i) are composed dominantly of displaced tracks and (ii) have many different vertices within the jet cone. Such emerging jet signatures are smoking guns for models with a composite dark sector where a parton shower in the dark sector is followed by displaced decays of dark pions back to SM jets. No current LHC searches are sensitive to this type of phenomenology. We perform a detailed simulation for a benchmark signal with two regular and two emerging jets, and present and implement strategies to suppress QCD backgrounds by up to six orders of magnitude. At the 14 TeV LHC, this signature can be probed with mediator masses as large as 1.5 TeV for a range of dark pion lifetimes, and the reach is increased further at the high-luminosity LHC. The emerging jet search is also sensitive to a broad class of long-lived phenomena, and we show this for a supersymmetric model with R-parity violation. Possibilities for discovery at LHCb are also discussed.
International Nuclear Information System (INIS)
Schwaller, Pedro; Stolarski, Daniel
2015-02-01
In this work, we propose a novel search strategy for new physics at the LHC that utilizes calorimeter jets that (i) are composed dominantly of displaced tracks and (ii) have many different vertices within the jet cone. Such emerging jet signatures are smoking guns for models with a composite dark sector where a parton shower in the dark sector is followed by displaced decays of dark pions back to SM jets. No current LHC searches are sensitive to this type of phenomenology. We perform a detailed simulation for a benchmark signal with two regular and two emerging jets, and present and implement strategies to suppress QCD backgrounds by up to six orders of magnitude. At the 14 TeV LHC, this signature can be probed with mediator masses as large as 1.5 TeV for a range of dark pion lifetimes, and the reach is increased further at the high-luminosity LHC. The emerging jet search is also sensitive to a broad class of long-lived phenomena, and we show this for a supersymmetric model with R-parity violation. Possibilities for discovery at LHCb are also discussed.
Jalinous, Reza; Lisanby, Sarah H.
2013-01-01
A novel transcranial magnetic stimulation (TMS) device with controllable pulse width (PW) and near rectangular pulse shape (cTMS) is described. The cTMS device uses an insulated gate bipolar transistor (IGBT) with appropriate snubbers to switch coil currents up to 7 kA, enabling PW control from 5 μs to over 100 μs. The near-rectangular induced electric field pulses use 22–34% less energy and generate 67–72% less coil heating compared to matched conventional cosine pulses. CTMS is used to stimulate rhesus monkey motor cortex in vivo with PWs of 20 to 100 μs, demonstrating the expected decrease of threshold pulse amplitude with increasing PW. The technological solutions used in the cTMS prototype can expand functionality, and reduce power consumption and coil heating in TMS, enhancing its research and therapeutic applications. PMID:18232369
Recent results on confinement in JET
International Nuclear Information System (INIS)
Campbell, D.J.
1992-01-01
The JET device is the world's largest tokamak and has been utilized in plasma heating experiments at total powers of up to 35MW using both neutral beam injection (NBI) and ion cyclotron resonance heating (ICRH). At the highest performance, JET plasmas have achieved conditions equivalent to energy ''breakeven''. A principal aim of the JET experiment is the investigation of plasma heating and confinement in plasma regimes relevant to thermonuclear ignition. The central issues in confinement physics involved in these advances are briefly reviewed and the most recent investigations of transport in high performance plasmas are summarized. (Author)
Simulation of natural convection in a rectangular loop using finite elements
International Nuclear Information System (INIS)
Pepper, D.W.; Hamm, L.L.; Kehoe, A.B.
1984-01-01
A two-dimensional finite-element analysis of natural convection in a rectangular loop is presented. A psi-omega formulation of the Boussinesque approximation to the Navier-Stokes equation is solved by the false transient technique. Streamlines and isotherms at Ra = 10 4 are shown for three different modes of heating. The results indicate that corner effects should be considered when modeling flow patterns in thermosyphons
Energy Technology Data Exchange (ETDEWEB)
Bunting, P., E-mail: patrick.bunting@ccfe.ac.uk; Thompson, V.; Riccardo, V.
2016-11-15
Highlights: • Experimental work to identify the cause of a bolt seizure inside the JET vessel. • Taguchi method used to reduce tests to 16 while covering 5 parameters. • Experimental work was unable to reproduce bolt seizure. • Thread contamination had little effect on the bolt performance. - Abstract: JET is an experimental fusion reactor consisting of magnetically confined, high temperature plasma inside a large ultra-high vacuum chamber. The inside of the chamber is protected from the hot plasma with tiles made from beryllium, tungsten, carbon composites and other materials bolted to the vessel wall. The study was carried out in response to a JET fastener seizing inside the vacuum vessel. The following study looks at characterising the magnitude of the individual factors affecting the fastener break away torque. This was carried out using a statistical approach, the Taguchi method: isolating the net effect of individual factors present in a series of tests [1](Grove and Davis, 1992). Given the severe environment within the JET vessel due to the combination of heat, ultra-high vacuum and the high contact pressure in bolt threads, the contributions of localised diffusion bonding is assessed in conjunction with various combinations of bolt and insert material.
Conformal boundary state for the rectangular geometry
Energy Technology Data Exchange (ETDEWEB)
Bondesan, R., E-mail: roberto.bondesan@cea.fr [Institute de Physique Theorique, CEA Saclay, F-91191 Gif-sur-Yvette (France); LPTENS, Ecole Normale Superieure, 24 rue Lhomond, 75231 Paris (France); Institut Henri Poincare, 11 rue Pierre et Marie Curie, 75231 Paris (France); Dubail, J. [Department of Physics, Yale University, P.O. Box 208120, New Haven, CT 06520-8120 (United States); Jacobsen, J.L. [LPTENS, Ecole Normale Superieure, 24 rue Lhomond, 75231 Paris (France); Institut Henri Poincare, 11 rue Pierre et Marie Curie, 75231 Paris (France); Universite Pierre et Marie Curie, 4 place Jussieu, 75252 Paris (France); Saleur, H. [Institute de Physique Theorique, CEA Saclay, F-91191 Gif-sur-Yvette (France); Institut Henri Poincare, 11 rue Pierre et Marie Curie, 75231 Paris (France); Physics Department, USC, Los Angeles, CA 90089-0484 (United States)
2012-09-11
We discuss conformal field theories (CFTs) in rectangular geometries, and develop a formalism that involves a conformal boundary state for the 1+1d open system. We focus on the case of homogeneous boundary conditions (no insertion of a boundary condition changing operator), for which we derive an explicit expression of the associated boundary state, valid for any arbitrary CFT. We check the validity of our solution, comparing it with known results for partition functions, numerical simulations of lattice discretizations, and coherent state expressions for free theories.
Numerical study on rectangular microhollow cathode discharge
International Nuclear Information System (INIS)
He Shoujie; Ouyang Jiting; He Feng; Li Shang
2011-01-01
Rectangular microhollow cathode discharge in argon is investigated by using two-dimensional time-dependent self-consistent fluid model. The electric potential, electric field, particle density, and mean electron energy are calculated. The results show that hollow cathode effect can be onset in the present configuration, with strong electric field and high mean electron energy in the cathode fall while high density and quasineutral plasma in the negative glow. The potential well and electric filed reversal are formed in the negative glow region. It is suggested that the presence of large electron diffusion flux necessitates the field reversal and potential well.
Droplet size in a rectangular Venturi scrubber
Costa, M. A. M.; Henrique, P. R.; Gonçalves, J. A. S.; Coury, J.R.
2004-01-01
The Venturi scrubber is a device which uses liquid in the form of droplets to efficiently remove fine particulate matter from gaseous streams. Droplet size is of fundamental importance for the scrubber performance. In the present experimental study, a laser diffraction technique was used in order to measure droplet size in situ in a Venturi scrubber with a rectangular cross section. Droplet size distribution was measured as a function of gas velocity (58.3 to 74.9 m/s), liquid-to-gas ratio (0...
Design of open rectangular and trapezoidal channels
González, C. P.; Vera, P. E.; Carrillo, G.; García, S.
2018-04-01
In this work, the results of designing open channels in rectangular and trapezoidal form are presented. For the development of the same important aspects were taken as determination of flows by means of formula of the rational method, area of the surface for its implementation, optimal form of the flow to meet the needs of that environment. In the design the parameter of the hydraulic radius expressed in terms of the hydraulic area and wet perimeter was determined, considering that the surface on which the fluid flows is the product of the perimeter of the section and the length of the channel and where shear is generated by the condition of no slippage.
Henderson, Brenda
2016-01-01
The presentation highlights NASA's jet noise research for 2016. Jet-noise modeling efforts, jet-surface interactions results, acoustic characteristics of multi-stream jets, and N+2 Supersonic Aircraft system studies are presented.
International Nuclear Information System (INIS)
Vasiliev, N.N.; Sokolov, Yu.A.; Shatalov, G.E.
1995-01-01
One of the problems affiliated to ITER high heat flux elements development is a problem of interface of beryllium protection with heat sink routinely made of copper alloys. To get rid of this problem all beryllium elements could be used as heat receivers in places of enhanced thermal loads. In accordance with this objectives four beryllium test pieces of two types have been manufactured in open-quotes Institute of Berylliumclose quotes for succeeding thermomechanical testing. Two of them were manufactured in accordance with JET team design; they are round open-quotes hypervapotron typeclose quotes test pieces. Another two ones are rectangular test sections with a twisted tape installed inside of the circular channel. Preliminary stress-strain analysis have been performed for both type of the test pieces. Hypervapotrons have been shipped to JET where they were tested on JET test bed. Thermomechanical testing of pieces of the type of open-quotes swirl tape inside of tubeclose quotes have been performed on Kurchatov Institute test bed. Chosen beryllium grade properties, some details of manufacturing, results of preliminary stress-strain analysis and thermomechanical testing of the test pieces open-quotes swirl tape inside of tubeclose quotes type are given in this report
International Nuclear Information System (INIS)
Nur Rahmad Yusuf
2013-01-01
Experimental studies to study the mechanism of boiling heat transfer in narrow rectangular channel under severe accident scenarios of TMI-2 nuclear power plant necessary for the understanding of management-related accidents. The research aims to obtain heat flux values and the critical heat flux (CHF) during the process of boiling heat transfer in narrow rectangular channel. Research methods experimentally using the HEATING-02 test section with cooling fluid is water temperature 98 °C. Experiments performed by varying the hot plate initial temperature of 100 °C, 200 °C and 300 °C with channel size 1 mm. Boiling during the cooling process was recorded by a transient temperature on the hot plate. Temperature data used to calculate the heat flux and wall temperature, the results are represented through the boiling curve. The results show that the higher plate temperature, the narrower width of the curve will be narrower and its mean that the plate surface cooling time will be slower. Results visualization is seen that the CCF occurred at the hot plate initial temperature of 100 °C, 200 °C and 300 °C with channel size 1 mm. (author)
Jet Noise Scaling in Dual Stream Nozzles
Khavaran, Abbas; Bridges, James
2010-01-01
Power spectral laws in dual stream jets are studied by considering such flows a superposition of appropriate single-stream coaxial jets. Noise generation in each mixing region is modeled using spectral power laws developed earlier for single stream jets as a function of jet temperature and observer angle. Similarity arguments indicate that jet noise in dual stream nozzles may be considered as a composite of four single stream jets representing primary/secondary, secondary/ambient, transition, and fully mixed zones. Frequency filter are designed to highlight spectral contribution from each jet. Predictions are provided at an area ratio of 2.0--bypass ratio from 0.80 to 3.40, and are compared with measurements within a wide range of velocity and temperature ratios. These models suggest that the low frequency noise in unheated jets is dominated by the fully mixed region at all velocity ratios, while the high frequency noise is dominated by the secondary when the velocity ratio is larger than 0.80. Transition and fully mixed jets equally dominate the low frequency noise in heated jets. At velocity ratios less than 0.50, the high frequency noise from primary/bypass becomes a significant contributing factor similar to that in the secondary/ambient jet.
Energy Technology Data Exchange (ETDEWEB)
Li, Zi-chao; Qi, Shi; Zhou, Tao; Li, Bing; Shahzad, Muhammad Ali [North China Electric Power Univ., Beijing (China). School of Nuclear Science and Engineering; Beijing Key Laboratory of Passive Safety Technology for Nuclear Energy, Beijing (China); Huang, Yan-ping [Nuclear Reactor Thermal Hydraulics Technology, Chengdu (China). CNNC Key Lab.
2017-12-15
Saturated boiling of two-phase natural circulation has been experimentally investigated based on a natural circulation device with narrow rectangular channels. When heating power reaches a certain range, it is possible to observe the phenomenon of saturated boiling and flow pattern transition in the system. The results show the heat transfer coefficient of saturated boiling decreases with the increasing of pressure, heating power and size of narrow rectangle channels. The buoyancy force causing mixed convection decreases the heat transfer coefficient. Finally, a dimensionless number is introduced, which reflects length to width ratio of rectangular narrow section and Rayleigh number, in order to revise the presented correlation. All errors fall within the range of ±15%.
The design of an ECRH system for JET-EP
DEFF Research Database (Denmark)
Verhoeven, A.G.A.; Bongers, W.A.; Elzendoorn, B.S.Q.
2003-01-01
An electron cyclotron resonance heating (ECRH) system has been designed for JET in the framework of the JET enhanced performance project (JET-EP) under the European fusion development agreement. Due to financial constraints it has been decided not to implement this project. Nevertheless, the design...
The design of an ECRH system for JET-EP
Verhoeven, A. G. A.; Bongers, W. A.; Elzendoorn, B. S. Q.; Graswinckel, M.; Hellingman, P.; Kooijman, W.; Kruijt, O. G.; Maagdenberg, J.; Ronden, D.; Stakenborg, J.; Sterk, A. B.; Tichler, J.; Alberti, S.; Goodman, T.; Henderson, M.; Hoekzema, J. A.; Oosterbeek, J. W.; Fernandez, A.; Likin, K.; Bruschi, A.; Cirant, S.; Novaks, S.; Piosczyk, B.; Thumm, M.; Bindslev, H.; Kaye, A.; Fleming, C.; Zohm, H.
2003-01-01
An electron cyclotron resonance heating (ECRH) system has been designed for JET in the framework of the JET enhanced performance project (JET-EP) under the European fusion development agreement. Due to financial constraints it has been decided not to implement this project. Nevertheless, the design
Directory of Open Access Journals (Sweden)
Youngmin Bae
2016-08-01
Full Text Available In this study, laminar natural circulation and heat transfer in a tall rectangular enclosure with disconnected vertical partitions inside were investigated. Analytical expressions were developed to predict the circulation flow rate and the average Nusselt number in a partially partitioned enclosure with isothermal side walls at different temperatures and insulated top and bottom walls. The proposed formulas are then validated against numerical results for modified Rayleigh numbers of up to 106. The impacts of the governing parameters are also examined along with a discussion of the heat transfer regimes.
The effect of thermal conductance of vertical walls on natural convection in a rectangular enclosure
International Nuclear Information System (INIS)
Kikuchi, Y.; Yoshino, A.; Taii, K.
2004-01-01
This paper deals with the experimental results of natural convective heat transfer in a rectangular water layer bounded by vertical walls of different thermal conductance. The vertical walls were made of copper or stainless steel. A minimum was observed in the horizontal distribution of temperature near the heating wall since a secondary reverse flow occurred outside the boundary layer. For copper case the experimental results of Nusselt number agreed well with calculations under an isothermal wall condition. For stainless steel case, however, the measured values were lower than the calculations since a three-dimensional effect appeared in convection due to non-uniformity in wall temperature. (author)
Energy Technology Data Exchange (ETDEWEB)
Mhiri, H.; Habli, S.; El Golli, S. [Ecole Nationale d' Ingenieurs de Monastir (Tunisia); Le Palec, G.; Bournot, Ph. [Institut de Mecanique de Marseille (France)
1999-11-01
We intend to solve equations governing turbulent plane-vertical isotherm and non isotherm jets by taking into account inflow conditions at the exit of the nozzle. The analysis is focused on the influence of these conditions on this type of flow. Two cases are considered (uniform and parabolic velocity and temperature profiles). A finite difference scheme is developed to solve the governing equations. This numeric model allows us to show that the region of fully developed regime begins much nearer the nozzle for the turbulent case than for the laminar flow case. Indeed, the turbulence increases the mixing between the incoming gas from the nozzle and the ambient fluid, and consequently the size of the potential core zone decreases. The results are compared to other works introducing mathematical variables based on the energy conservation for the case of the mixed convection and the momentum conservation for the forced convection, which allows the validation of our results. (authors)
Rectangular source integral and recurrence relations
International Nuclear Information System (INIS)
Prabha, Hem
2007-01-01
In this paper Hubbell's rectangular source integral H'(a,b), which is a double integral, is expressed as a series of many converging single integrals I n (a,b). Recurrence relations relate these integrals. Once one integral I 1 is computed, recurrence relations are used to compute other integrals. I 1 (a,b) can be computed analytically. H'(a,b) is approximated by considering the first seven terms in the series and the results are found to give good results for various values of a and b. Results are presented for the values of a and b (0.1 to 20 and to 2), respectively. The rate of convergence depends on the values of a and b
Droplet size in a rectangular Venturi scrubber
Directory of Open Access Journals (Sweden)
M. A. M. Costa
2004-06-01
Full Text Available The Venturi scrubber is a device which uses liquid in the form of droplets to efficiently remove fine particulate matter from gaseous streams. Droplet size is of fundamental importance for the scrubber performance. In the present experimental study, a laser diffraction technique was used in order to measure droplet size in situ in a Venturi scrubber with a rectangular cross section. Droplet size distribution was measured as a function of gas velocity (58.3 to 74.9 m/s, liquid-to-gas ratio (0.07 to 0.27 l/m³, and distance from liquid injection point (64 to 173 mm. It was found that all these variables significantly affect droplet size. The results were compared with the predictions from correlations found in the literature.
Large - scale Rectangular Ruler Automated Verification Device
Chen, Hao; Chang, Luping; Xing, Minjian; Xie, Xie
2018-03-01
This paper introduces a large-scale rectangular ruler automated verification device, which consists of photoelectric autocollimator and self-designed mechanical drive car and data automatic acquisition system. The design of mechanical structure part of the device refer to optical axis design, drive part, fixture device and wheel design. The design of control system of the device refer to hardware design and software design, and the hardware mainly uses singlechip system, and the software design is the process of the photoelectric autocollimator and the automatic data acquisition process. This devices can automated achieve vertical measurement data. The reliability of the device is verified by experimental comparison. The conclusion meets the requirement of the right angle test procedure.
The demagnetizing factors for the rectangular samples
International Nuclear Information System (INIS)
Akishin, P.G.; Gaganov, I.A.
1990-01-01
The influence of the demagnetization effect on the distribution of internal magnetic fields for finite samples is considered. The boundary integral method is used to compute the space distribution of the magnetic field in rectangular samples. On the basis of these calculations we compute the distribution of demagnetization factors in the sample for μSR experimental set-up with the real field geometry. The corresponding mathematical expectation and dispersion of this distribution are estimated. The results of the calculation are used in the analysis of the μSR data obtained for high T c superconductors. It is shown for these compounds that the correction to the penetration depth related to the broadening of the field distribution, is not more than 5%. 8 refs.; 2 figs.; 1 tab
Method and structure for cache aware transposition via rectangular subsections
Gustavson, Fred Gehrung; Gunnels, John A
2014-02-04
A method and structure for transposing a rectangular matrix A in a computer includes subdividing the rectangular matrix A into one or more square submatrices and executing an in-place transposition for each of the square submatrices A.sub.ij.
direct method of analysis of an isotropic rectangular plate direct
African Journals Online (AJOL)
eobe
This work evaluates the static analysis of an isotropic rectangular plate with various the static analysis ... method according to Ritz is used to obtain the total potential energy of the plate by employing the used to ..... for rectangular plates analysis, as the behavior of the ... results obtained by previous research work that used.
Towards characterizing graphs with a sliceable rectangular dual
Kusters, V.; Speckmann, B.; Di Giacomo, E.; Lubiw, A.
2015-01-01
Let G be a plane triangulated graph. A rectangular dual of G is a partition of a rectangle R into a set R of interior-disjoint rectangles, one for each vertex, such that two regions are adjacent if and only if the corresponding vertices are connected by an edge. A rectangular dual is sliceable if it
Solar Coronal Jets: Observations, Theory, and Modeling
Raouafi, N. E.; Patsourakos, S.; Pariat, E.; Young, P. R.; Sterling, A.; Savcheva, A.; Shimojo, M.; Moreno-Insertis, F.; Devore, C. R.; Archontis, V.;
2016-01-01
Chromospheric and coronal jets represent important manifestations of ubiquitous solar transients, which may be the source of signicant mass and energy input to the upper solar atmosphere and the solar wind. While the energy involved in a jet-like event is smaller than that of nominal solar ares and Coronal Mass Ejections (CMEs), jets share many common properties with these major phenomena, in particular, the explosive magnetically driven dynamics. Studies of jets could, therefore, provide critical insight for understanding the larger, more complex drivers of the solar activity. On the other side of the size-spectrum, the study of jets could also supply important clues on the physics of transients closeor at the limit of the current spatial resolution such as spicules. Furthermore, jet phenomena may hint to basic process for heating the corona and accelerating the solar wind; consequently their study gives us the opportunity to attack a broadrange of solar-heliospheric problems.
Obtaining S values for rectangular--solid tumors inside rectangular--solid host organs
International Nuclear Information System (INIS)
Stinchcomb, T.G.; Durham, J.S.; Fisher, D.R.
1991-01-01
A method is described for obtaining S values between a tumor and its host organ for use with the MIRD formalism. It applies the point-source specific absorbed fractions for an infinite water medium, tabulated by Berger, to a rectangular solid of arbitrary dimensions which contains a rectangular tumor of arbitrary dimensions. Contributions from pairs of source and target volume elements are summed for the S values between the tumor and itself, between the remaining healthy host organ and itself, and between the tumor and the remaining healthy host organ, with the reciprocity theorem assumed for the last. This method labeled MTUMOR, is interfaced with the widely used MIRDOSE program which incorporates the MIRD formalism. An example is calculated
Directory of Open Access Journals (Sweden)
WANG Minhao
2017-08-01
Full Text Available Plate structures with openings are common in many engineering structures. The study of the vibration characteristics of such structures is directly related to the vibration reduction, noise reduction and stability analysis of an overall structure. This paper conducts research into the free vibration characteristics of a thin elastic plate with a rectangular opening parallel to the plate in an arbitrary position. We use the improved Fourier series to represent the displacement tolerance function of the rectangular plate with an opening. We can divide the plate into an eight zone plate to simplify the calculation. We then use linear springs, which are uniformly distributed along the boundary, to simulate the classical boundary conditions and the boundary conditions of the boundaries between the regions. According to the energy functional and variational method, we can obtain the overall energy functional. We can also obtain the generalized eigenvalue matrix equation by studying the extremum of the unknown improved Fourier series expansion coefficients. We can then obtain the natural frequencies and corresponding vibration modes of the rectangular plate with an opening by solving the equation. We then compare the calculated results with the finite element method to verify the accuracy and effectiveness of the method proposed in this paper. Finally, we research the influence of the boundary condition, opening size and opening position on the vibration characteristics of a plate with an opening. This provides a theoretical reference for practical engineering application.
Supersonic induction plasma jet modeling
International Nuclear Information System (INIS)
Selezneva, S.E.; Boulos, M.I.
2001-01-01
Numerical simulations have been applied to study the argon plasma flow downstream of the induction plasma torch. It is shown that by means of the convergent-divergent nozzle adjustment and chamber pressure reduction, a supersonic plasma jet can be obtained. We investigate the supersonic and a more traditional subsonic plasma jets impinging onto a normal substrate. Comparing to the subsonic jet, the supersonic one is narrower and much faster. Near-substrate velocity and temperature boundary layers are thinner, so the heat flux near the stagnation point is higher in the supersonic jet. The supersonic plasma jet is characterized by the electron overpopulation and the domination of the recombination over the dissociation, resulting into the heating of the electron gas. Because of these processes, the supersonic induction plasma permits to separate spatially different functions (dissociation and ionization, transport and deposition) and to optimize each of them. The considered configuration can be advantageous in some industrial applications, such as plasma-assisted chemical vapor deposition of diamond and polymer-like films and in plasma spraying of nanoscaled powders
International Nuclear Information System (INIS)
Sonnenberg, K.; Deksnis, E.; Shaw, R.; Reiter, D.
1988-01-01
JET plans to install two pump limiter modules which can be used for belt-limiter, inner-wall and X-point discharges and, also, for 1-2s as the main limiter. A design is presented which is compatible with two diagnostic systems, and which allows partial removal of the pump limiter to provide access for remote-handling operations. The high heat-flux components are initially cooled during a pulse. Heat is removed between discharges by radiation and pressure contacts to a water-cooled support structure. The pumping edge will be made of annealed pyrolytic graphite. Exhaust efficiency has been estimated, for a 1-d edge model, using a Monte-Carlo calculation of neutral gas transport. When the pump limiter is operated together with other wall components we expect an efficiency of ≅ 5% (2.5 x 10 21 part/s). As a main limiter the efficiency increases to about 10%. (author)
Two-phase flow in short horizontal rectangular microchannels with a height of 300 μm
Chinnov, E. A.; Ron'shin, F. V.; Kabov, O. A.
2015-09-01
The two-phase flow in a narrow short horizontal channel with a rectangular cross section is studied experimentally. The channel has a width of 10, 20, or 30 mm and a height of 300 μm. The specifics of formation of such two-phase flows are investigated. It is demonstrated that the regions of bubble and churn flow regimes grow and constrain the region of jet flow as the channel gets wider. The boundaries of the regions of annular and stratified flow regimes remain almost unaltered.
Jet Joint Undertaking. Annual report 1990
International Nuclear Information System (INIS)
1991-05-01
The Joint European Torus is the largest project in the coordinated fusion programme of the European Atomic Energy Community (EURATOM). A brief general introduction provides an overview of the planning of the Report. This is followed by a description of JET and the Euratom and International Fusion Programmes, which summarize the main features of the JET apparatus and its experimental programme and explains the position of the Project in the overall Euratom programme. In addition, this relates and compares JET to other large fusion devices throughout the world. The following section reports on the technical status of the machine including: technical changes and achievements during 1989; details of the operational organization of experiments and pulse statistics; and progress on enhancements in machine systems for future operation. This is followed by the results of JET operations in 1990 under various operating conditions, including ohmic heating, radio-frequency (RF) heating, neutral beam (NB) heating and various combined scenarios in different magnetic field configurations; the overall global and local behaviour observed; and the progress towards reactor conditions. In particular, the comparative performance between JET and other tokamaks, in terms of the triple fusion product, shows the substantial achievements made by JET since the start of operations in 1983. The second part of the Report explains the organization and management of the Project and describes the administration of JET. In particular, it sets out the budget situation; contractual arrangements during 1990; and details of the staffing arrangements and complement
Physics from angular projection of rectangular grids
International Nuclear Information System (INIS)
Singh, Ashmeet
2015-01-01
In this paper, we present a mathematical model for the angular projection of a rectangular arrangement of points in a grid. This simple yet interesting, problem has both scholarly value and applications for data extraction techniques to study the physics of various systems. Our work may help undergraduate students to understand subtle points in the angular projection of a grid and describes various quantities of interest in the projection with completeness and sufficient rigour. We show that for certain angular ranges, the projection has non-distinctness, and calculate the details of such angles, and correspondingly, the number of distinct points and the total projected length. We focus on interesting trends obtained for the projected length of the grid elements and present a simple application of the model to determine the geometry of an unknown grid whose spatial extensions are known, using measurement of the grid projection at two angles only. Towards the end, our model is shown to have potential applications in various branches of physical sciences, including crystallography, astrophysics, and bulk properties of materials. (paper)
Federal Laboratory Consortium — Located in Lakehurst, New Jersey, the Jet Car Track Site supports jet cars with J57 engines and has a maximum jet car thrust of 42,000 pounds with a maximum speed of...
Arc Heated Scramjet Test Facility
Federal Laboratory Consortium — The Arc Heated Scramjet Test Facility is an arc heated facility which simulates the true enthalpy of flight over the Mach number range of about 4.7 to 8 for free-jet...
2015-06-23
crackle is correlated to signals with intermittent periods of steepened shock-like waves followed by weaker, longer, rounded rarefaction regions, but to...turbulence is concentrated in a weakly curved (for a typical round jet) shear layer between the high-speed potential core flow and the surrounding co-flow...decreases into the acoustic field. The effect of varying dc between −0.1 and −0.003δm(t)/∆U causes the Nδm/Lx curves to shift downward as fewer waves
Rectangular maximum-volume submatrices and their applications
Mikhalev, Aleksandr; Oseledets, I.V.
2017-01-01
We introduce a definition of the volume of a general rectangular matrix, which is equivalent to an absolute value of the determinant for square matrices. We generalize results of square maximum-volume submatrices to the rectangular case, show a connection of the rectangular volume with an optimal experimental design and provide estimates for a growth of coefficients and an approximation error in spectral and Chebyshev norms. Three promising applications of such submatrices are presented: recommender systems, finding maximal elements in low-rank matrices and preconditioning of overdetermined linear systems. The code is available online.
Rectangular maximum-volume submatrices and their applications
Mikhalev, Aleksandr
2017-10-18
We introduce a definition of the volume of a general rectangular matrix, which is equivalent to an absolute value of the determinant for square matrices. We generalize results of square maximum-volume submatrices to the rectangular case, show a connection of the rectangular volume with an optimal experimental design and provide estimates for a growth of coefficients and an approximation error in spectral and Chebyshev norms. Three promising applications of such submatrices are presented: recommender systems, finding maximal elements in low-rank matrices and preconditioning of overdetermined linear systems. The code is available online.
Rectangular-cladding silicon slot waveguide with improved nonlinear performance
Huang, Zengzhi; Huang, Qingzhong; Wang, Yi; Xia, Jinsong
2018-04-01
Silicon slot waveguides have great potential in hybrid silicon integration to realize nonlinear optical applications. We propose a rectangular-cladding hybrid silicon slot waveguide. Simulation result shows that, with a rectangular-cladding, the slot waveguide can be formed by narrower silicon strips, so the two-photon absorption (TPA) loss in silicon is decreased. When the cladding material is a nonlinear polymer, the calculated TPA figure of merit (FOMTPA) is 4.4, close to the value of bulk nonlinear polymer of 5.0. This value confirms the good nonlinear performance of rectangular-cladding silicon slot waveguides.
Fully developed liquid-metal flow in multiple rectangular ducts in a strong uniform magnetic field
International Nuclear Information System (INIS)
Molokov, S.
1993-01-01
Fully developed liquid-metal flow in a straight rectangular duct with thin conducting walls is investigated. The duct is divided into a number of rectangular channels by electrically conducting dividing walls. A strong uniform magnetic field is applied parallel to the outer side walls and dividing walls and perpendicular to the top and the bottom walls. The analysis of the flow is performed by means of matched asymptotics at large values of the Hartmann number M. The asymptotic solution obtained is valid for arbitrary wall conductance ratio of the side walls and dividing walls, provided the top and bottom walls are much better conductors than the Hartmann layers. The influence of the Hartmann number, wall conductance ratio, number of channels and duct geometry on pressure losses and flow distribution is investigated. If the Hartmann number is high, the volume flux is carried by the core, occupying the bulk of the fluid and by thin layers with thickness of order M -1/2 . In some of the layers, however, the flow is reversed. As the number of channels increases the flow in the channels close to the centre approaches a Hartmann-type flow with no jets at the side walls. Estimation of pressure-drop increase in radial ducts of a self-cooled liquid-metal blanket with respect to flow in a single duct with walls of the same wall conductance ratio gives an upper limit of 30%. (author). 13 refs., 10 figs., 1 tab
Global confinement characteristics of Jet limiter plasmas
International Nuclear Information System (INIS)
Campbell, D.J.; Christiansen, J.P.; Cordey, J.G.; Thomas, P.R.; Thomsen, K.
1989-01-01
Data from a wide variety of plasma pulses on JET (aux. heating, current, field, minority species, plasma shape, etc) are analysed in order to assess the characteristics of global confinement. The scaling of confinement in ohmically and auxiliary heated discharges is examined. The ohmic confinement in the present new JET configuration (Belt Limiter) is essentially the same as previously. Confinement in auxiliary heated discharges shows presently a slight improvement since 1986. Both ohmic and non-ohmic data is used in a set of confinement time regression analyses and certain constraints derived from theory are imposed
Jet joint undertaking. Annual report 1985
International Nuclear Information System (INIS)
1986-06-01
After a presentation of the Jet and nuclear fusion, the results of Jet operations in 1985 are given: energy confinement, MHD activity and disruptive instabilities, impurities and radiation losses, plasma evolution, plasma boundary phenomena, control of plasma current, position and shape, RF heating. Technical achievements in 1985 are summarized: vacuum systems, first wall, multi-pellet injection for fuelling and re-fuelling, containment of forces during vertical instabilities, magnet systems, safety systems, power supplies, neutral beam heating, radio-frequency heating, remote handling, tritium handling, control and data acquisition, diagnostic systems are implied
Energy Technology Data Exchange (ETDEWEB)
Lee, Juh Yung; Chang, Soon Heung; Jeong, Yong [KAIST, Daejeon (Korea, Republic of)
2016-05-15
The onset of flow instability (OFI) is the one of important boiling phenomena since it may induce the premature critical heat flux (CHF) at the lowest heat flux level due to sudden flow excursion in a single channel of multichannel configuration. Especially prediction of OFI for narrow rectangular channel is very crucial in relevant to thermal-hydraulic design and safety analysis of open pool-type research reactors (RRs) using plate-type fuels. Based on high speed video (HSV) technique, the authors observed and determined that OFI and the minimum premature CHF in a narrow rectangular channel are induced by abrupt pressure drop fluctuation due to the mergence of facing bubble boundary layers (BLs) on opposite boiling surfaces. In this study, new mechanistic OFI model for narrow rectangular channel heated on both sides has been derived, which satisfies with the real triggering phenomena. Force balance approach was used for modeling of the maximum BLT since the quantity is comparable to the bubble departure diameter. From the validation with OFI database, it was shown that the new model fairly well predicts OFI heat flux for wide range of conditions.
analytical bending solution of all clamped isotropic rectangular plate
African Journals Online (AJOL)
HP
PLATE ON WINKLER'S FOUNDATION USING CHARACTERISTIC. ORTHOGONAL ... foundations, storage tanks, swimming pools, floor system of buildings, highways ..... “Energy Methods in Theory of Rectangular Plates. (use of Polynomial ...
International Nuclear Information System (INIS)
Xu Jianjun; Chen Bingde; Wang Xiaojun
2011-01-01
The characteristic of the coalesced sliding bubble was visually observed by wide side and narrow side of the narrow rectangular channel using high speed digital camera. The results show that the coalesced time among the sliding bubbles is quick, and the new formation of coalesced bubble is not lift-off, and it continues to slide along the heated surface in low heat flux for the isolated bubble region. The influence region is about 2 times projected area of the sliding bubble when the sliding bubbles begin to interact. The sliding bubble velocities increase duo to the interaction among the bubbles, which contributes to enhance heat transfer of this region. Finally, the effect of coalesced interaction of growing bubble in the nucleation sites on bubble lift-off was discussed and analysed. (authors)
Rectangular waveform linear transformer driver module design
International Nuclear Information System (INIS)
Zhao Yue; Xie Weiping; Zhou Liangji; Chen Lin
2014-01-01
Linear Transformer Driver is a novel pulsed power technology, its main merits include a parallel LC discharge array and Inductive Voltage Adder. The parallel LC discharge array lowers the whole circuit equivalent inductance and the Inductive Voltage Adder unites the modules in series in order to create a high electric field grads, meanwhile, restricts the high voltage in a small space. The lower inductance in favor of LTD output a fast waveform and IVA confine high voltage in secondary cavity. In recently, some LTD-based pulsed power system has been development yet. The usual LTD architecture provides damped sine shaped output pulses that may not be suitable in flash radiography, high power microwave production, z-pinch drivers, and certain other applications. A more suitable driver output pulse would have a flat or inclined top (slightly rising or falling). In this paper, we present the design of an LTD cavity that generates this type of the output pulse by including within its circular array some number of the harmonic bricks in addition to the standard bricks according to Fourier progression theory. The parallel LC discharge array circuit formula is introduced by Kirchhoff Law, and the sum of harmonic is proofed as an analytic result, meanwhile, rationality of design is proved by simulation. Varying gas spark discharge dynamic resistance with harmonic order and switches jitter are analyzed. The results are as following: The more harmonic order is an approach to the ideal rectangular waveform, but lead to more system complexity. The capacity decreases as harmonic order increase, and gas spark discharge dynamic resistance rises with the capacity. The rising time protracts and flat is decay or even vanishes and the shot to shot reproducibility is degenerate as the switches jitter is high. (authors)
Tau method approximation of the Hubbell rectangular source integral
International Nuclear Information System (INIS)
Kalla, S.L.; Khajah, H.G.
2000-01-01
The Tau method is applied to obtain expansions, in terms of Chebyshev polynomials, which approximate the Hubbell rectangular source integral:I(a,b)=∫ b 0 (1/(√(1+x 2 )) arctan(a/(√(1+x 2 )))) This integral corresponds to the response of an omni-directional radiation detector situated over a corner of a plane isotropic rectangular source. A discussion of the error in the Tau method approximation follows
hydrodynamic behavior of particles in a Jet flow of a gas fluidized bed
International Nuclear Information System (INIS)
Mirmomen, L.; Alavi, M.
2005-01-01
Numerous investigations have been devoted towards understanding the hydrodynamics of gas jets in fluidized beds. However, most of them address the problem from macroscopic point of view, which does not reveal the true behavior in the jet region at the single particle level. The present work aims to understand the jet behavior from a more fundamental level, i.e. the individual particle level. A thin rectangular gas fluidized bed, constructed from acrylic glass, with a vertical jet nozzle located at the center of the distributor was used in the work. A high speed camera with a speed up to 10,000 frames per second was used to observe the jet behavior . Analysis of large quantity of images allowed determination of solids flux, solids Velocity and solids concentration in the jet region . The model present in this work has shown better agreement with the experimental data in compare with the previous models presented in the literature
Analysis of flow distribution instability in parallel thin rectangular multi-channel system
Energy Technology Data Exchange (ETDEWEB)
Xia, G.L. [School of Nuclear Science and Technology, Xi’an Jiaotong University, Xi’an City 710049 (China); Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, Harbin Engineering University, Harbin City 150001 (China); Su, G.H., E-mail: ghsu@mail.xjtu.edu.cn [School of Nuclear Science and Technology, Xi’an Jiaotong University, Xi’an City 710049 (China); Peng, M.J. [Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, Harbin Engineering University, Harbin City 150001 (China)
2016-08-15
Highlights: • Flow distribution instability in parallel thin rectangular multi-channel system is studied using RELAP5 codes. • Flow excursion may bring parallel heating channel into the density wave oscillations region. • Flow distribution instability is more likely to happen at low power/flow ratio conditions. • The increase of channel number will not affect the flow distribution instability boundary. • Asymmetry inlet throttling and heating will make system more unstable. - Abstract: The flow distribution instability in parallel thin rectangular multi-channel system has been researched in the present study. The research model of parallel channel system is established by using RELAP5/MOD3.4 codes. The transient process of flow distribution instability is studied at imposed inlet mass flow rate and imposed pressure drop conditions. The influence of heating power, mass flow rate, system pressure and channel number on flow distribution instability are analyzed. Furthermore, the flow distribution instability of parallel two-channel system under asymmetric inlet throttling and heating power is studied. The results show that, if multi-channel system operates at the negative slope region of channel ΔP–G curve, small disturbance in pressure drop will lead to flow redistribution between parallel channels. Flow excursion may bring the operating point of heating channel into the density-wave oscillations region, this will result in out-phase or in-phase flow oscillations. Flow distribution instability is more likely to happen at low power/flow ratio conditions, the stability of parallel channel system increases with system pressure, the channel number has a little effect on system stability, but the asymmetry inlet throttling or heating power will make the system more unstable.
A self-focusing mercury jet target
Johnson, C
2002-01-01
Mercury jet production targets have been studied in relation to antiproton production and, more recently, pion production for a neutrino factory. There has always been a temptation to include some self-focusing of the secondaries by passing a current through the mercury jet analogous to the already proven lithium lens. However, skin heating of the mercury causes fast vaporization leading to the development of a gliding discharge along the surface of the jet. This external discharge can, nevertheless, provide some useful focusing of the secondaries in the case of the neutrino factory. The technical complications must not be underestimated.
International Nuclear Information System (INIS)
Del Duca, V.
1992-11-01
Minijet production in jet inclusive cross sections at hadron colliders, with large rapidity intervals between the tagged jets, is evaluated by using the BFKL pomeron. We describe the jet inclusive cross section for an arbitrary number of tagged jets, and show that it behaves like a system of coupled pomerons
International Nuclear Information System (INIS)
Mishima, K.; Nishihara, H.
1985-01-01
Critical heat flow (CHF) at low flow condition can become important in an MTR-type research reactor under a number of accident conditions. Regardless of the initial stages of these accidents, a condition which is basically the decay heat removal by natural convention boiling can develop. Under such conditions, burnout may occur even at a very low heat flow. In view of this, the CHF at low-flow-rate and low-pressure conditions has been studied for water flowing in thin rectangular channels. Experiments were carried out with two types of rectangular test sections, namely, the one heated from one wide side and the other heated from two opposite sides. In order to observe the effects of gravity, CHF was measured both in upflow and downflow. The CHF at complete bottom blockage was also studied. The results indicate that burnout can occur at a much lower heat flux than pool-boiling CHF or than predicted by the conventional correlations. There was observed a minimum CHF at complete bottom blockage and at very low downflow. The low CHF at very low downflow appears to be due to the stagnation of the bubble in the heated section. This fact indicates that special care should be taken in analyzing the boiling phenomenon which occurs when the coolant flow is very low in a low pressure system. (author)
International Nuclear Information System (INIS)
Mertens, Ph.; Altmann, H.; Chaumet, P.; Joffrin, E.; Knaup, M.; Matthews, G.F.; Neubauer, O.; Nicolai, D.; Riccardo, V.; Tanchuk, V.; Thompson, V.; Uhlemann, R.; Samm, U.
2011-01-01
In the frame of the ITER-like Wall (ILW) for the JET tokamak, a divertor row made of bulk tungsten material has been developed for the position where the outer strike point is located in most of the foreseen plasma configurations. In the absence of active cooling, this represents a formidable challenge when one considers the temperature reached by tungsten (T W,surf > 2000 deg. C) and the vertical gradient ∂T/∂z = 5 x 10 4 K/m. As the development is drawing to an end and most components are in production, actual 1:1 prototypes are exposed to an ion beam with a power density around 7 MW/m 2 on the plasma-facing surface. Advantage is taken of the flexibility of the MARION facility to bombard the tungsten stack under shallow angles of incidence (∼6 o ) with a powerful beam of ions and neutrals (>70 MW/m 2 on axis). The shallow angles are important, with respect to the toroidal wetted surface, for properly simulating the expected performance under actual tokamak conditions. The MARION tests have been used to validate for a few typical cases the thermal calculations that were steadily developed along with the tungsten tile and, at the same time, to gather information on the actual temperatures of individual components. The latter is an important factor to a finer estimation of the power handling capabilities.
Analysis of high aspect ratio jet flap wings of arbitrary geometry.
Lissaman, P. B. S.
1973-01-01
Paper presents a design technique for rapidly computing lift, induced drag, and spanwise loading of unswept jet flap wings of arbitrary thickness, chord, twist, blowing, and jet angle, including discontinuities. Linear theory is used, extending Spence's method for elliptically loaded jet flap wings. Curves for uniformly blown rectangular wings are presented for direct performance estimation. Arbitrary planforms require a simple computer program. Method of reducing wing to equivalent stretched, twisted, unblown planform for hand calculation is also given. Results correlate with limited existing data, and show lifting line theory is reasonable down to aspect ratios of 5.
AGN feedback compared: jets versus radiation
Cielo, Salvatore; Bieri, Rebekka; Volonteri, Marta; Wagner, Alexander Y.; Dubois, Yohan
2018-06-01
Feedback by active galactic nuclei (AGNs) is often divided into quasar and radio mode, powered by radiation or radio jets, respectively. Both are fundamental in galaxy evolution, especially in late-type galaxies, as shown by cosmological simulations and observations of jet-ISM (interstellar medium) interactions in these systems. We compare AGN feedback by radiation and by collimated jets through a suite of simulations, in which a central AGN interacts with a clumpy, fractal galactic disc. We test AGNs of 1043 and 1046 erg s-1, considering jets perpendicular or parallel to the disc. Mechanical jets drive the more powerful outflows, exhibiting stronger mass and momentum coupling with the dense gas, while radiation heats and rarefies the gas more. Radiation and perpendicular jets evolve to be quite similar in outflow properties and effect on the cold ISM, while inclined jets interact more efficiently with all the disc gas, removing the densest 20 {per cent} in 20 Myr, and thereby reducing the amount of cold gas available for star formation. All simulations show small-scale inflows of 0.01-0.1 M⊙ yr-1, which can easily reach down to the Bondi radius of the central supermassive black hole (especially for radiation and perpendicular jets), implying that AGNs modulate their own duty cycle in a feedback/feeding cycle.
AGN Feedback Compared: Jets versus Radiation
Cielo, Salvatore; Bieri, Rebekka; Volonteri, Marta; Wagner, Alexander Y.; Dubois, Yohan
2018-03-01
Feedback by Active Galactic Nuclei is often divided into quasar and radio mode, powered by radiation or radio jets, respectively. Both are fundamental in galaxy evolution, especially in late-type galaxies, as shown by cosmological simulations and observations of jet-ISM interactions in these systems. We compare AGN feedback by radiation and by collimated jets through a suite of simulations, in which a central AGN interacts with a clumpy, fractal galactic disc. We test AGN of 1043 and 1046 erg/s, considering jets perpendicular or parallel to the disc. Mechanical jets drive the more powerful outflows, exhibiting stronger mass and momentum coupling with the dense gas, while radiation heats and rarifies the gas more. Radiation and perpendicular jets evolve to be quite similar in outflow properties and effect on the cold ISM, while inclined jets interact more efficiently with all the disc gas, removing the densest 20% in 20 Myr, and thereby reducing the amount of cold gas available for star formation. All simulations show small-scale inflows of 0.01 - 0.1 M⊙/yr, which can easily reach down to the Bondi radius of the central supermassive black hole (especially for radiation and perpendicular jets), implying that AGN modulate their own duty cycle in a feedback/feeding cycle.
Balboni, John A.; Gokcen, Tahir; Hui, Frank C. L.; Graube, Peter; Morrissey, Patricia; Lewis, Ronald
2015-01-01
The paper describes the consolidation of NASA's high powered arc-jet testing at a single location. The existing plasma arc-jet wind tunnels located at the Johnson Space Center were relocated to Ames Research Center while maintaining NASA's technical capability to ground-test thermal protection system materials under simulated atmospheric entry convective heating. The testing conditions at JSC were reproduced and successfully demonstrated at ARC through close collaboration between the two centers. New equipment was installed at Ames to provide test gases of pure nitrogen mixed with pure oxygen, and for future nitrogen-carbon dioxide mixtures. A new control system was custom designed, installed and tested. Tests demonstrated the capability of the 10 MW constricted-segmented arc heater at Ames meets the requirements of the major customer, NASA's Orion program. Solutions from an advanced computational fluid dynamics code were used to aid in characterizing the properties of the plasma stream and the surface environment on the calorimeters in the supersonic flow stream produced by the arc heater.
International Nuclear Information System (INIS)
Keen, B.E.; O'Hara, G.W.; Pollard, I.E.
1988-07-01
The paper presents the Jet Joint Undertaking annual report 1987. A description is given of the JET and Euratom and International Fusion Programmes. The technical status of JET is outlined, including the development and improvements made to the system in 1987. The results of JET Operation in 1987 are described within the areas of: density effects, temperature improvements, energy confinement studies and other material effects. The contents also contain a summary of the future programme of JET. (U.K.)
International Nuclear Information System (INIS)
Rebut, P.H.; Bartlett, D.V.; Baeumel, G.
1985-01-01
Results obtained from JET since June 1983 are described which show that this large tokamak behaves in a similar manner to smaller tokamaks, but with correspondingly improved plasma parameters. Long-duration hydrogen and deuterium plasmas (>10 s) have been obtained with electron temperatures reaching >4 keV for power dissipations =1.6), loss of vertical stability occurred, as expected from previous calculations. Forces of several hundred tonnes (at Isub(p)=2.7 MA) were transmitted to the vacuum vessel. Measured confinement times are larger than the corresponding INTOR values. The maximum achievable density is limited by disruptions. Impurity levels determine this limiting density, and the paper concludes with proposals to reduce these. In addition, progress in neutral injection and RF heating is described, as well as preparations for D-T operation. (author)
Experimental study of falling film evaporation in large scale rectangular channel
International Nuclear Information System (INIS)
Huang, X.G.; Yang, Y.H.; Hu, P.
2015-01-01
Highlights: • This paper studies the falling film evaporation in large scale rectangular channel experimentally. • The effects of air flow rate, film temperature and film flow rate on falling film evaporation are analyzed. • Increasing the air flow rate is considered as an efficient method to enhance the evaporation rate. • A correlation including the wave effect for falling film evaporation is derived based on heat and mass transfer analogy. - Abstract: The falling film evaporation in a large scale rectangular channel is experimentally studied in this paper for the design and improvement of passive containment cooling system. The evaporation mass transfer coefficient h D is obtained by the evaporation rate and vapor partial pressure difference of film surface and air bulk. The experimental results indicate that increasing of air flow rate appears to enhance h D , while the film temperature and film flow rate have little effect on h D . Since the wave effect on evaporation is noticed in experiment, the evaporation mass transfer correlation including the wave effect is developed on the basis of heat and mass transfer analogy and experimental data
Advanced thermally stable jet fuels
Energy Technology Data Exchange (ETDEWEB)
Schobert, H.H.
1999-01-31
The Pennsylvania State University program in advanced thermally stable coal-based jet fuels has five broad objectives: (1) Development of mechanisms of degradation and solids formation; (2) Quantitative measurement of growth of sub-micrometer and micrometer-sized particles suspended in fuels during thermal stressing; (3) Characterization of carbonaceous deposits by various instrumental and microscopic methods; (4) Elucidation of the role of additives in retarding the formation of carbonaceous solids; (5) Assessment of the potential of production of high yields of cycloalkanes by direct liquefaction of coal. Future high-Mach aircraft will place severe thermal demands on jet fuels, requiring the development of novel, hybrid fuel mixtures capable of withstanding temperatures in the range of 400--500 C. In the new aircraft, jet fuel will serve as both an energy source and a heat sink for cooling the airframe, engine, and system components. The ultimate development of such advanced fuels requires a thorough understanding of the thermal decomposition behavior of jet fuels under supercritical conditions. Considering that jet fuels consist of hundreds of compounds, this task must begin with a study of the thermal degradation behavior of select model compounds under supercritical conditions. The research performed by The Pennsylvania State University was focused on five major tasks that reflect the objectives stated above: Task 1: Investigation of the Quantitative Degradation of Fuels; Task 2: Investigation of Incipient Deposition; Task 3: Characterization of Solid Gums, Sediments, and Carbonaceous Deposits; Task 4: Coal-Based Fuel Stabilization Studies; and Task 5: Exploratory Studies on the Direct Conversion of Coal to High Quality Jet Fuels. The major findings of each of these tasks are presented in this executive summary. A description of the sub-tasks performed under each of these tasks and the findings of those studies are provided in the remainder of this volume
Performance of jet impingement in unglazed air collectors
Energy Technology Data Exchange (ETDEWEB)
Belusko, M.; Saman, W.; Bruno, F. [Institute for Sustainable Systems and Technologies, University of South Australia, Mawson Lakes Boulevard, Mawson Lakes, SA 5095 (Australia)
2008-05-15
Jet impingement is effective at improving the heat transfer between air and a heated surface. Studies have shown that jet impingement can marginally improve the thermal efficiency of a glazed collector. However, little attention has been placed on applying jet impingement to an unglazed solar air collector. This paper presents a theoretical and experimental investigation identifying the performance characteristics of jet impingement. Overall, jet impingement was able to improve the thermal efficiency of the collector by 21%. An increase in the pressure loss was also measured but found to be small. The flow distribution of jets along the collector was the most significant factor in determining the efficiency. Increasing the hole spacing was found to improve the efficiency. (author)
System evaluation of improved thermal stability jet fuels
Energy Technology Data Exchange (ETDEWEB)
Binns, K.E.; Dieterle, G.L.; Williams, T. [Univ. of Dayton Research Institute, OH (United States)
1995-05-01
A single-pass, single-tube heat exchanger device called the Phoenix rig and a single-pass, dual-heat exchanger system called the Extended Duration Thermal Stability Test system are specific devices/systems developed for evaluating jet fuel thermal stability. They have been used extensively in the evaluation of various jet fuels and thermal stability additives. The test results have indicated that additives can substantially improve the thermal stability of conventional jet fuels. Relationships of oxygen consumption, residence time, bulk, and wetted wall temperatures on coking deposits that form in the heated tubes have also been investigated.
Temperature patterns in the gas infrared radiator heating area
Directory of Open Access Journals (Sweden)
Kurilenko N.I.
2015-01-01
Full Text Available The obtained results of experimental studies provide the basis for the heat transfer mechanism specification on the studied conditions that are typical for many practical applications. It was proved appropriateness of the natural convection and heat conduction process simulation while analyzing the heat transfer in rectangular enclosures with the radiant heating sources at the high bound.
High resolution 3D gas-jet characterization
International Nuclear Information System (INIS)
Landgraf, Bjoern; Kaluza, Malte C.; Spielmann, Christian; Schnell, Michael; Saevert, Alexander
2011-01-01
We present a tomographic characterization of gas jets employed for high-intensity laser-plasma interaction experiments where the shape can be non-symmetrically. With a Mach-Zehnder interferometer we measured the phase shift for different directions through the neutral density distribution of the gas jet. From the recorded interferograms it is possible to retrieve 3-dimensional neutral density distributions by tomographic reconstruction based on the filtered back projections. We report on criteria for the smallest number of recorded interferograms as well as a comparison with the widely used phase retrieval based on an Abel inversion. As an example for the performance of our approach, we present the characterization of nozzles with rectangular openings or gas jets with shock waves. With our setup we obtained a spatial resolution of less than 60 μm for an Argon density as low as 2 x 10 17 cm -3 .
Mixed convection flow of nanofluid in a square enclosure with an intruded rectangular fin
International Nuclear Information System (INIS)
Cong, Ran; Zhou, Xuanyu; De Souza Machado, Bruno; Das, Prodip K.
2016-01-01
Mixed convection flow in enclosures has been a subject of interest for many years due to their ever increasing applications in solar collectors, electronic cooling, lubrication technologies, food processing, and nuclear reactors. In comparison, little effort has been given to the problem of mixed convection in enclosures filled with nanofluids, while the addition of nanoparticles in a fluid base to alter specific material properties is considered a feasible solution for many heat transfer problems. Mixed convection of nanofluids is a challenging problem as the addition of nanoparticles changes the fluid’s thermo-physical properties as well as due to the complex interactions among inertia, viscous, and buoyancy forces. In this study, a two-dimensional steady-state numerical model has been developed to investigate mixed convection flow of nanofluids in a square enclosure with an intruded rectangular fin and to optimize the fin geometry for maximizing the heat transfer using the Constructal design. The model has been developed using ANSYS-FLUENT for various fin geometries. Flow fields, temperature fields, and heat transfer rates are examined for different values of Rayleigh and Reynolds numbers for several geometries of the fin with the aim of maximizing the heat transfer from the fin to the surrounding flow. Outcome of this study provides important insight into the heat transfer behavior of nanofluids, which will help in developing novel geometries with enhanced and controlled heat transfer for solar collectors and electronic devices.
Mixed convection flow of nanofluid in a square enclosure with an intruded rectangular fin
Energy Technology Data Exchange (ETDEWEB)
Cong, Ran; Zhou, Xuanyu; De Souza Machado, Bruno; Das, Prodip K., E-mail: prodip.das@ncl.ac.uk [School of Mechanical and Systems Engineering Newcastle University Newcastle upon Tyne, NE1 7RU United Kingdom (United Kingdom)
2016-07-12
Mixed convection flow in enclosures has been a subject of interest for many years due to their ever increasing applications in solar collectors, electronic cooling, lubrication technologies, food processing, and nuclear reactors. In comparison, little effort has been given to the problem of mixed convection in enclosures filled with nanofluids, while the addition of nanoparticles in a fluid base to alter specific material properties is considered a feasible solution for many heat transfer problems. Mixed convection of nanofluids is a challenging problem as the addition of nanoparticles changes the fluid’s thermo-physical properties as well as due to the complex interactions among inertia, viscous, and buoyancy forces. In this study, a two-dimensional steady-state numerical model has been developed to investigate mixed convection flow of nanofluids in a square enclosure with an intruded rectangular fin and to optimize the fin geometry for maximizing the heat transfer using the Constructal design. The model has been developed using ANSYS-FLUENT for various fin geometries. Flow fields, temperature fields, and heat transfer rates are examined for different values of Rayleigh and Reynolds numbers for several geometries of the fin with the aim of maximizing the heat transfer from the fin to the surrounding flow. Outcome of this study provides important insight into the heat transfer behavior of nanofluids, which will help in developing novel geometries with enhanced and controlled heat transfer for solar collectors and electronic devices.
Mixed convection flow of nanofluid in a square enclosure with an intruded rectangular fin
Cong, Ran; Zhou, Xuanyu; De Souza Machado, Bruno; Das, Prodip K.
2016-07-01
Mixed convection flow in enclosures has been a subject of interest for many years due to their ever increasing applications in solar collectors, electronic cooling, lubrication technologies, food processing, and nuclear reactors. In comparison, little effort has been given to the problem of mixed convection in enclosures filled with nanofluids, while the addition of nanoparticles in a fluid base to alter specific material properties is considered a feasible solution for many heat transfer problems. Mixed convection of nanofluids is a challenging problem as the addition of nanoparticles changes the fluid's thermo-physical properties as well as due to the complex interactions among inertia, viscous, and buoyancy forces. In this study, a two-dimensional steady-state numerical model has been developed to investigate mixed convection flow of nanofluids in a square enclosure with an intruded rectangular fin and to optimize the fin geometry for maximizing the heat transfer using the Constructal design. The model has been developed using ANSYS-FLUENT for various fin geometries. Flow fields, temperature fields, and heat transfer rates are examined for different values of Rayleigh and Reynolds numbers for several geometries of the fin with the aim of maximizing the heat transfer from the fin to the surrounding flow. Outcome of this study provides important insight into the heat transfer behavior of nanofluids, which will help in developing novel geometries with enhanced and controlled heat transfer for solar collectors and electronic devices.
Experimental investigation of onset of nucleate boiling in this rectangular channels
International Nuclear Information System (INIS)
Belhadj, M.; Christensen, R.N.; Aldemir, T.
1988-01-01
The 10 kW, HEU fueled Ohio State University Research Reactor (OSURR) will be upgraded to operate with plate type LEU U 3 Si 2 , fuel elements in the power range 250-500 kW. The core will be cooled by natural convection and an onset of nucleate boiling (ONB) margin of 1.2 will be maintained in the hot channel under steady-state operation. The validity of the correlations used for predicting ONB in plate type research reactors is not known for low heat flux-low velocity flows. An experiment has been set up at The Ohio State University to investigate ONB for laminar flow in this rectangular channels. The results show that: The Bergles-Rohsenow correlation and the correlation proposed by Ricque and Siboul predict higher and lower ONB fluxes than actual, respectively. The ONB heat flux is flow velocity dependent
Does Thermal Granulation Drive Tephra Jets?
White, J. D.; Zimanowski, B.; Buettner, R.; Sonder, I.; Dellino, P.
2011-12-01
Surtseyan tephra jets, also called cypressoid or cock's tail plumes, comprise a characteristic mixture of ash with bombs travelling roughly ballistic paths that tip the individual fingers of the projecting jet. Jets of similar form but smaller scale are generated by littoral magma-water interactions, confirming the general inference that surtseyan tephra jets are a characteristic product of explosive magma-water interaction, and suggesting that magmatic volatiles play a subsidiary role, if any, in their formation. Surtseyan jets have been inferred to result from both intense fuel-coolant interactions, and from simple boiling of water entrained into rising magma, and little new information has become available to test these two positions since they were clearly developed in the 1980s. Recent experiments in which magma is poured into standing water have produced vigorous jetting of hot water as melt solidifies and undergoes extensive thermal granulation. We present high-resolution hi-speed video of these jets, which we see as having the following origin. As thermal granulation takes place, a fracture network advances into the melt/glass body, and water invading the cracks at the rate of propagation is heated nearly instantaneously. Vapor produced at the contact expands and drives outward through cooled cracks, condensing as it moves to the exterior of the magma body where it is emitted as a jet of hot water. In ocean ridge hydrothermal systems a diffuse crack network inducts cold water, which is heated and expelled in focused jets. Focusing of hot outflow in experiments is inferred to result, as suggested for ridge hydrothermal systems, from thermoelastic closure of cracks near the one(s) feeding the jet. From the cooled products of our experimental runs, we know that thermal contraction produces a network of curved cracks with modal spacing of 1-2 mm, which separate domains of unbroken glass. It is during growth of this crack network that cold water enters, is
Elliptic nozzle aspect ratio effect on controlled jet propagation
Energy Technology Data Exchange (ETDEWEB)
Kumar, S M Aravindh; Rathakrishnan, Ethirajan, E-mail: aravinds@iitk.ac.in, E-mail: erath@iitk.ac.in [Department of Aerospace Engineering, Indian Institute of Technology, Kanpur (India)
2017-04-15
The present study deals with the control of a Mach 2 elliptic jet from a convergent–divergent elliptic nozzle of aspect ratio 4 using tabs at the nozzle exit. The experiments were carried out for rectangular and triangular tabs of the same blockage, placed along the major and minor axes of the nozzle exit, at different levels of nozzle expansion. The triangular tabs along the minor axis promoted superior mixing compared to the other controlled jets and caused substantial core length reduction at all the nozzle pressure ratios studied. The rectangular tabs along the minor axis caused core length reduction at all pressure ratios, but the values were minimal compared to that of triangular tabs along the minor axis. For all the test conditions, the mixing promotion caused by tabs along the major axis was inferior to that of tabs along the minor axis. The waves present in the core of controlled jets were visualized using a shadowgraph. Comparison of the present results with the results of a controlled Mach 2 elliptic jet of aspect ratio 2 (Aravindh Kumar and Sathakrishnan 2016 J. Propulsion Power 32 121–33, Aravindh Kumar and Rathakrishnan 2016 J. Aerospace Eng. at press (doi:10.1177/0954410016652921)) show that for all levels of expansion, the mixing effectiveness of triangular tabs along the minor axis of an aspect ratio 4 nozzle is better than rectangular or triangular tabs along the minor axis of an aspect ratio 2 nozzle. (paper)
Elliptic nozzle aspect ratio effect on controlled jet propagation
International Nuclear Information System (INIS)
Kumar, S M Aravindh; Rathakrishnan, Ethirajan
2017-01-01
The present study deals with the control of a Mach 2 elliptic jet from a convergent–divergent elliptic nozzle of aspect ratio 4 using tabs at the nozzle exit. The experiments were carried out for rectangular and triangular tabs of the same blockage, placed along the major and minor axes of the nozzle exit, at different levels of nozzle expansion. The triangular tabs along the minor axis promoted superior mixing compared to the other controlled jets and caused substantial core length reduction at all the nozzle pressure ratios studied. The rectangular tabs along the minor axis caused core length reduction at all pressure ratios, but the values were minimal compared to that of triangular tabs along the minor axis. For all the test conditions, the mixing promotion caused by tabs along the major axis was inferior to that of tabs along the minor axis. The waves present in the core of controlled jets were visualized using a shadowgraph. Comparison of the present results with the results of a controlled Mach 2 elliptic jet of aspect ratio 2 (Aravindh Kumar and Sathakrishnan 2016 J. Propulsion Power 32 121–33, Aravindh Kumar and Rathakrishnan 2016 J. Aerospace Eng. at press (doi:10.1177/0954410016652921)) show that for all levels of expansion, the mixing effectiveness of triangular tabs along the minor axis of an aspect ratio 4 nozzle is better than rectangular or triangular tabs along the minor axis of an aspect ratio 2 nozzle. (paper)
Numerical and experimental study of two turbulent opposed plane jets
Energy Technology Data Exchange (ETDEWEB)
Besbes, Sonia; Mhiri, Hatem [Laboratoire de Mecanique des Fluides et Thermique, Ecole Nationale d' Ingenieurs de Monastir, Route de Ouardanine, Monastir (Tunisia); Le Palec, Georges; Bournot, Philippe [Institut de Mecanique de Marseille, UNIMECA, Technopole de Chateau-Gombert, 60 rue Joliot-Curie, 13453 Marseille (France)
2003-09-01
The turbulent interaction between two opposed plane jets separated by a distance H is experimentally studied by using a PIV (Particle Image Velocimetry) method and numerically investigated by means of a finite volume code. Two turbulence models have been tested: the standard k-{epsilon} model and a second-order model. The validation of the numerical study was performed by comparing the results with experimental data obtained for the case of two interacting opposed jets at ambient temperature (isothermal case). The effect of the angle of inclination of the jets is studied. Conclusions of the validation are then used to study the interaction between two jets, one being maintained at ambient temperature whereas the other is heated. Results show that the stagnation point moves towards the heated jet. It is shown that the heating induces a stabilizing effect on the flow. (orig.)
International Nuclear Information System (INIS)
Madarame, Haruki; Iida, Masao
1998-01-01
An upward plane jet impinging on the free surface of a shallow rectangular tank oscillates without any external periodic force. The movement of the impinging point leaves additional fluid mass on the surface behind the point, which does not balance the momentum supplied by the jet. The imbalance generates propagating waves, and a surface level gap appears there. The level gap is flattened not by the waves but by the vertical motion of water columns. The imbalance causes lateral displacement of jet, which in turn causes the imbalance, forming a positive feedback loop. The above model explains well why the frequency corresponds to that of water column oscillation in a partitioned tank with the same water depth, and the oscillation region has a wide range above a certain velocity limit determined by the water depth. (author)
Joining of Aluminium Alloy Sheets by Rectangular Mechanical Clinching
International Nuclear Information System (INIS)
Abe, Y.; Mori, K.; Kato, T.
2011-01-01
A mechanical clinching has the advantage of low running costs. However, the joint strength is not high. To improve the maximum load of the joined sheets by a mechanical clinching, square and rectangular mechanical clinching were introduced. In the mechanical clinching, the two sheets are mechanically joined by forming an interlock between the lower and upper sheets by the punch and die. The joined length with the interlock was increased by the rectangular punch and die. The deforming behaviours of the sheets in the mechanical clinching were investigated, and then the interlock in the sheets had distribution in the circumference of the projection. Although the interlocks were formed in both projection side and diagonal, the interlock in the diagonal was smaller because of the long contact length between the lower sheet and the die cavity surface. The maximum load of the joined sheets by the rectangular mechanical clinching was two times larger than the load by the round mechanical clinching.
A two-component NZRI metamaterial based rectangular cloak
Directory of Open Access Journals (Sweden)
Sikder Sunbeam Islam
2015-10-01
Full Text Available A new two-component, near zero refractive index (NZRI metamaterial is presented for electromagnetic rectangular cloaking operation in the microwave range. In the basic design a pi-shaped, metamaterial was developed and its characteristics were investigated for the two major axes (x and z-axis wave propagation through the material. For the z-axis wave propagation, it shows more than 2 GHz bandwidth and for the x-axis wave propagation; it exhibits more than 1 GHz bandwidth of NZRI property. The metamaterial was then utilized in designing a rectangular cloak where a metal cylinder was cloaked perfectly in the C-band area of microwave regime. The experimental result was provided for the metamaterial and the cloak and these results were compared with the simulated results. This is a novel and promising design for its two-component NZRI characteristics and rectangular cloaking operation in the electromagnetic paradigm.
Errors generated with the use of rectangular collimation
International Nuclear Information System (INIS)
Parks, E.T.
1991-01-01
This study was designed to determine whether various techniques for achieving rectangular collimation generate different numbers and types of errors and remakes and to determine whether operator skill level influences errors and remakes. Eighteen students exposed full-mouth series of radiographs on manikins with the use of six techniques. The students were grouped according to skill level. The radiographs were evaluated for errors and remakes resulting from errors in the following categories: cone cutting, vertical angulation, and film placement. Significant differences were found among the techniques in cone cutting errors and remakes, vertical angulation errors and remakes, and total errors and remakes. Operator skill did not appear to influence the number or types of errors or remakes generated. Rectangular collimation techniques produced more errors than did the round collimation techniques. However, only one rectangular collimation technique generated significantly more remakes than the other techniques
Vector boson tagged jets and jet substructure
Directory of Open Access Journals (Sweden)
Vitev Ivan
2018-01-01
Full Text Available In these proceedings, we report on recent results related to vector boson-tagged jet production in heavy ion collisions and the related modification of jet substructure, such as jet shapes and jet momentum sharing distributions. Z0-tagging and γ-tagging of jets provides new opportunities to study parton shower formation and propagation in the quark-gluon plasma and has been argued to provide tight constrains on the energy loss of reconstructed jets. We present theoretical predictions for isolated photon-tagged and electroweak boson-tagged jet production in Pb+Pb collisions at √sNN = 5.02 TeV at the LHC, addressing the modification of their transverse momentum and transverse momentum imbalance distributions. Comparison to recent ATLAS and CMS experimental measurements is performed that can shed light on the medium-induced radiative corrections and energy dissipation due to collisional processes of predominantly quark-initiated jets. The modification of parton splitting functions in the QGP further implies that the substructure of jets in heavy ion collisions may differ significantly from the corresponding substructure in proton-proton collisions. Two such observables and the implication of tagging on their evaluation is also discussed.
International Nuclear Information System (INIS)
Keilhacker, M.; Gibson, A.; Gormezano, C.; Rebut, P.H.
2001-01-01
The paper highlights the JET work in physics and technology during the period of the JET Joint Undertaking (1978-1999), with special emphasis on what has been learned for extrapolation to a NEXT STEP device. - Global confinement scaling has been extended to high currents and heating powers. Dimensionless scaling experiments of ELMy H mode plasmas suggest that bulk plasma transport is gyro-Bohm and predict ignition for a device with ITER-FDR parameters. Experiments in which the plasma elongation and triangularity were varied independently show a strong increase of confinement time with elongation (τ E ∼κ α 0.8±0.3 ), thus supporting a basic design principle of ITER-FEAT. With the Pellet Enhanced Performance (PEP) mode, JET has discovered the beneficial effect of reversed magnetic shear on confinement, opening the possibility of advanced tokamak scenarios. - With a three stage programme of progressively more closed divertors, JET has demonstrated the benefits of divertor closure, in particular, of high divertor neutral pressure which facilitates helium removal. It has also shown that in detached (or semidetached) radiative divertor plasmas the average power load on the target plates of a NEXT STEP device should be tolerable but, in addition, that the transient power loads during ELMs could cause problems. - In 1991 JET has demonstrated the first ever controlled production of a megawatt of fusion power. More extensive D-T experiments in 1997 (DTE1) have established new records in fusion performance: 16 MW transient fusion power with Q in =0.62 (i.e. close to breakeven, Q in =1) and 4 MW steady state fusion power with Q in =0.18 for 4 s. DTE1 has also allowed a successful test of various reactor ICRF heating schemes and a clear demonstration of alpha particle heating, consistent with classical expectations. - JET has developed and tested some of the most important technologies for a NEXT STEP and a reactor, in particular the safe handling of tritium and the
Karabasov, S A
2010-08-13
Jets are one of the most fascinating topics in fluid mechanics. For aeronautics, turbulent jet-noise modelling is particularly challenging, not only because of the poor understanding of high Reynolds number turbulence, but also because of the extremely low acoustic efficiency of high-speed jets. Turbulent jet-noise models starting from the classical Lighthill acoustic analogy to state-of-the art models were considered. No attempt was made to present any complete overview of jet-noise theories. Instead, the aim was to emphasize the importance of sound generation and mean-flow propagation effects, as well as their interference, for the understanding and prediction of jet noise.
Very forward jet, Mueller Navelet jets and jet gap jet measurements in CMS
Cerci, Salim
2018-01-01
The measurements of very forward jet, Mueller-Navelet jets and jet-gap-jet events are presented for different collision energies. The analyses are based on data collected with the CMS detector at the LHC. Jets are defined through the anti-$k_\\mathrm{t}$ clustering algorithm for different cone sizes. Jet production studies provide stringent tests of quantum chromodynamics (QCD) and contribute to tune Monte Carlo (MC) simulations and phenomenological models. The measurements are compared to predictions from various Monte Carlo event generators.
Natural Vibration Analysis of Clamped Rectangular Orthotropic Plates
dalaei, m.; kerr, a. d.
The natural vibrations of clamped rectangular orthotropic plates are analyzed using the extended Kantorovich method. The developed iterative scheme converges very rapidly to the final result. The obtained natural frequencies are evaluated for a square plate made of Kevlar 49 Epoxy and the obtained results are compared with those published by Kanazawa and Kawai, and by Leissa. The agreement was found to be very close. As there are no exact analytical solutions for clamped rectangular plates, the generated closed form expression for the natural modes, and the corresponding natural frequencies, are very suitable for use in engineering analyses.
Perron-Frobenius Theorem for Rectangular Tensors and Directed Hypergraphs
Lu, Linyuan; Yang, Arthur L. B.; Zhao, James J. Y.
2018-01-01
For any positive integers $r$, $s$, $m$, $n$, an $(r,s)$-order $(n,m)$-dimensional rectangular tensor ${\\cal A}=(a_{i_1\\cdots i_r}^{j_1\\cdots j_s}) \\in ({\\mathbb R}^n)^r\\times ({\\mathbb R}^m)^s$ is called partially symmetric if it is invariant under any permutation on the lower $r$ indexes and any permutation on the upper $s$ indexes. Such partially symmetric rectangular tensor arises naturally in studying directed hypergraphs. Ling and Qi [Front. Math. China, 2013] first studied the $(p,q)$-...
A new metamaterial-based wideband rectangular invisibility cloak
Islam, S. S.; Hasan, M. M.; Faruque, M. R. I.
2018-02-01
A new metamaterial-based wideband electromagnetic rectangular cloak is being introduced in this study. The metamaterial unit cell shows sharp transmittances in the C- and X-bands and displays wideband negative effective permittivity region there. The metamaterial unit cell was then applied in designing a rectangular-shaped electromagnetic cloak. The scattering reduction technique was adopted for the cloaking operation. The cloak operates in the certain portion of C-and X-bands that covers more than 4 GHz bandwidth region. The experimental results were provided as well for the metamaterial and the cloak.
Heat transfer problems in ductus of retangular cross section
International Nuclear Information System (INIS)
Cintra Filho, J. de S.
1976-01-01
The finite difference method is used to resolve the problem of heat transfer in the rectangular ducts in turbulent conditions. Velocities, temperatures and diffusivity distributions are determined. A computer programme is also developed for such calculations [pt
Study of two-phase underexpanded jets by gas jet
International Nuclear Information System (INIS)
Uchida, Mitsunori; Someya, Satoshi; Okamoto, Koji
2008-01-01
When a heat exchange in a Fast Breeder Reactor cracks, a sodium-water reaction occurs. When a tube cracks, highly pressurized water or steam escapes into the surrounding liquid sodium and a sodium-water reaction occurs forming the disodium oxide. The disodium oxide caught in the steam jet strikes other tubes in the reactor. The struck disodium oxide can then cause these tubes to crack. The release of steam into the liquid sodium media is a two-phase flow involving underexpansion. In this paper qualitative measurement of the underexpanded gas jet which injected into water was carried our for the purpose of analyzing the behavior of the two-phase flow. (author)
Directory of Open Access Journals (Sweden)
Abderraouf Messai
2013-01-01
Full Text Available A rigorous full-wave analysis of high Tc superconducting rectangular microstrip patch over ground plane with rectangular aperture in the case where the patch is printed on a uniaxially anisotropic substrate material is presented. The dyadic Green’s functions of the considered structure are efficiently determined in the vector Fourier transform domain. The effect of the superconductivity of the patch is taken into account using the concept of the complex resistive boundary condition. The accuracy of the analysis is tested by comparing the computed results with measurements and previously published data for several anisotropic substrate materials. Numerical results showing variation of the resonant frequency and the quality factor of the superconducting antenna with regard to operating temperature are given. Finally, the effects of uniaxial anisotropy in the substrate on the resonant frequencies of different TM modes of the superconducting microstrip antenna with rectangular aperture in the ground plane are presented.
Jet Vertex Charge Reconstruction
Nektarijevic, Snezana; The ATLAS collaboration
2015-01-01
A newly developed algorithm called the jet vertex charge tagger, aimed at identifying the sign of the charge of jets containing $b$-hadrons, referred to as $b$-jets, is presented. In addition to the well established track-based jet charge determination, this algorithm introduces the so-called \\emph{jet vertex charge} reconstruction, which exploits the charge information associated to the displaced vertices within the jet. Furthermore, the charge of a soft muon contained in the jet is taken into account when available. All available information is combined into a multivariate discriminator. The algorithm has been developed on jets matched to generator level $b$-hadrons provided by $t\\bar{t}$ events simulated at $\\sqrt{s}$=13~TeV using the full ATLAS detector simulation and reconstruction.
Analysis of jet flames and unignited jets from unintended releases of hydrogen
Energy Technology Data Exchange (ETDEWEB)
Houf, W.G.; Evans, G.H.; Schefer, R.W. [Sandia National Laboratories, Livermore, CA 94551-0969 (United States)
2009-07-15
A combined experimental and modeling program is being carried out at Sandia National Laboratories to characterize and predict the behavior of unintended hydrogen releases. In the case where the hydrogen leak remains unignited, knowledge of the concentration field and flammability envelope is an issue of importance in determining consequence distances for the safe use of hydrogen. In the case where a high-pressure leak of hydrogen is ignited, a classic turbulent jet flame forms. Knowledge of the flame length and thermal radiation heat flux distribution is important to safety. Depending on the effective diameter of the leak and the tank source pressure, free jet flames can be extensive in length and pose significant radiation and impingement hazard, resulting in consequence distances that are unacceptably large. One possible mitigation strategy to potentially reduce the exposure to jet flames is to incorporate barriers around hydrogen storage equipment. The reasoning is that walls will reduce the extent of unacceptable consequences due to jet releases resulting from accidents involving high-pressure equipment. While reducing the jet extent, the walls may introduce other hazards if not configured properly. The goal of this work is to provide guidance on configuration and placement of these walls to minimize overall hazards using a quantitative risk assessment approach. The program includes detailed CFD calculations of jet flames and unignited jets to predict how hydrogen leaks and jet flames interact with barriers, complemented by an experimental validation program that considers the interaction of jet flames and unignited jets with barriers. As a first step in this work on barrier release interaction the Sandia CFD model has been validated by computing the concentration decay of unignited turbulent free jets and comparing the results with the classic concentration decay laws for turbulent free jets taken from experimental data. Computations for turbulent hydrogen
Predictions of laminar natural convection in heated cavities
International Nuclear Information System (INIS)
Winters, K.H.
1982-06-01
Several examples of laminar, natural convection in heated cavities are discussed with illustrative calculations. These include convection in a square cavity at high Rayleigh number; in a narrow cavity at moderate aspect ratio; in a rectangular cavity heated from below; in a trapezoidal cavity, and in a rectangular cavity containing a conducting obstruction. The steady equations for the velocity, pressure and temperature are solved in the Boussinesq approximation, using a standard Galerkin formulation of the finite-element method. (author)
Start-up of the ohmic phase in JET
International Nuclear Information System (INIS)
Tanga, A.; Christiansen, J.P.; Cordey, J.G.; Ejima, S.; Kellman, A.; Lazzaro, E.; Lomas, P.J.; Thomas, P.R.
1985-01-01
JET has been designed to permit the study of plasmas in which alphaparticle heating is a significant part of the power balance. In order to have a sufficient thermonuclear yield and to trap the resulting alphaparticles, JET is similar in its dimensions and plasma current to the next generation of reactor-like devices such as NET, FER and INTOR. For this reason, the authors see the results from the study of the start-up of ohmically heated plasmas in JET as highly relevant. Discussed is the range that has been achieved in all major parameters with ohmic heating. Experiences with the wall conditioning technique and the results of ion cyclotron heating experiments in JET are outlined. This paper also describes the stages of plasma formation, current rise and ohmic flat-top
International Nuclear Information System (INIS)
Konishi, K.
1980-01-01
The author discusses, in an introductory fashion, the latest developments in the study of hadronic jets produced in hard processes, based on perturbative QCD. Emphasis is on jet calculus (and its applications and generalizations), and on the appearance of a parton-like consistent, over-all picture of jet evolution in momentum, colour, and real space-time. (Auth.)
Analysis of Rectangular Microstrip Antennas with Air Substrates ...
African Journals Online (AJOL)
This paper presents an analysis of rectangular microstrip antennas with air substrates. The effect of the substrate thickness on the bandwidth and the efficiency are examined. An additional thin layer supporting the dielectric material is added to the air substrate in order to make the antenna mechanically rigid and easy to ...
Graphene-based tunable terahertz filter with rectangular ring ...
Indian Academy of Sciences (India)
A plasmonic band-pass filter based on graphene rectangular ring resonator with double narrow gaps is proposed and numerically investigated by finite-difference time-domain (FDTD) simulations. For the filter with or without gaps, the resonant frequencies can be effectively adjusted by changing the width of the graphene ...
Plasma-ﬁlled rippled wall rectangular backward wave oscillator
Indian Academy of Sciences (India)
Performance of the backward wave oscillator (BWO) is greatly enhanced with the introduction of plasma. Linear theory of the dispersion relation and the growth rate have been derived and analysed numerically for plasma-ﬁlled rippled wall rectangular waveguide driven by sheet electron beam. To see the effect of plasma ...
Internal flow characteristics of a rectangular ramjet air intake
Moerel, J.-L.; Veraar, R.G.; Halswijk, W.H.C.; Pimentel, R.; Corriveau, D.; Hamel, N.; Lesage, F.; Vos, J.B.
2009-01-01
Two research institutes TNO Defence, Security and Safety and DRDC-Valcartier have worked together on the improvement of modeling and simulation tools for the functioning of supersonic air intakes for realistic ramjet engines of tactical missiles. The emphasis laid on complex rectangular intake
The problem of isotropic rectangular plate with four clamped edges
Indian Academy of Sciences (India)
of rectangular plates has been a subject of study in solid mechanics for more than a cen- .... loading is solved first, giving the deflection function for the strip case and .... The authors gratefully acknowledge the advice and encouragement of ...
FDTD Analysis of U-Slot Rectangular Patch Antenna
Luk, K. M.; Tong, K. F.; Shum, S. M.; Lee, K. F.; Lee, R. Q.
1997-01-01
The U-slot rectangular patch antenna (Figure I) has been found experimentally to provide impedance and gain bandwidths of about 300 without the need of stacked or coplanar parasitic elements [1,2]. In this paper, simulation results of the U-slot patch using FDTD analysis are presented. Comparison with measured results are given.
Graphene-based tunable terahertz filter with rectangular ring ...
Indian Academy of Sciences (India)
WEI SU
2017-08-16
Aug 16, 2017 ... Abstract. A plasmonic band-pass filter based on graphene rectangular ring resonator with double narrow gaps is proposed and numerically investigated by finite-difference time-domain (FDTD) simulations. For the filter with or without gaps, the resonant frequencies can be effectively adjusted by changing ...
Optical vortex propagation in few-mode rectangular polymer waveguides
DEFF Research Database (Denmark)
Lyubopytov, Vladimir S.; Chipouline, Arkadi; Zywietz, Urs
2017-01-01
We demonstrate that rectangular few-mode dielectric waveguides, fabricated with standard lithographic technique, can support on-chip propagation of optical vortices. We show that specific superpositions of waveguide eigenmodes form quasi-degenerate modes carrying light with high purity states...
Shielding calculations for changing from circular to a Rectangular ...
African Journals Online (AJOL)
The Radiation Technology Centre (RTC) of the Ghana Atomic Energy Commission operates a 1.85 PBq Co-60 gamma irradiator for research, food preservation and medical sterilization. It has become necessary to improve the do-se rate delivered by changing the circular arrangement of sources to a rectangular one.
A study of the condensation of a high-velocity vapor jet on a coflowing turbulent liquid jet
Ovsiannikov, V. A.; Levin, A. A.
A method for the experimental determination of the local value of the heat transfer coefficient under conditions of jet condensation is proposed which employs a heat balance expression in differential form. The method is used in an experimental study of the heat transfer characteristics of the condensation of a high-velocity coaxial jet of a slightly superheated (3 percent) steam on a coflowing cylindrical turbulent water jet. In the experiment, the relative velocities reach hundreds of m/s; the temperature nonequilibrium of the phases is high, as is the steam flow mass density during the initial contact; heat transfer between the phases is significant. The results can be used as the basis for determining experimental criterial dependences for jet condensation.
International Nuclear Information System (INIS)
Mital, Manu
2013-01-01
Thermal management issues are limiting barriers to high density electronics packaging and miniaturization. Liquid cooling using microchannels is an attractive alternative to bulky aluminum heat sinks. The channels can be integrated directly into a chip, and cooling can be further enhanced using nanofluids. The goals of this study are to evaluate heat transfer improvement of a rectangular channel nanofluid heat sink with developing laminar flow, taking into account the pumping power penalty. The proposed model uses semi-empirical correlations to calculate effective nanofluid thermophysical properties, which are then incorporated into heat transfer and friction factor correlations in literature for single-phase flows. The predictions of the model are found to be in good agreement with experimental studies. The validated model is used to predict the thermal resistance and pumping power as a function of four design variables that include the channel width, the wall width, the flow velocity and the particle volume fraction. The parameters are optimized using a Genetic Algorithm (GA) with minimum thermal resistance as the objective function, and fixed specified value of pumping power as the constraint. For a given value of pumping power, the benefit of nanoparticle addition is evaluated by independently optimizing the heat sink, first with nanofluid, and then with base fluid. Comparing the minimized thermal resistances revealed only a small benefit since the nanoparticles increase the pumping power which can alternately be diverted toward an increased velocity in a pure fluid heat sink. The benefit further diminishes with increase in available pumping power. -- Highlights: ► Validated model used to predict heat transfer and pumping power (p.p.) in nanofluids. ► Genetic algorithm used to minimize thermal resistance with p.p. constraint. ► Heat sink design independently optimized with nanofluid and base fluid coolant. ► No significant benefit through particle
International Nuclear Information System (INIS)
Nave, M.F.F.; Campbell, D.; Joffrin, E.; Pegoraro, F.; Porcelli, F.; Smeulders, P.; Thomsen, K.
1989-01-01
A variety of MHD activity has been observed in JET during auxiliary heating experiments. In particular, periodic bursts of oscillations detected in several diagnostics show signatures similar to that of the 'fishbone' instabilities. Here we describe the characteristics of these instabilities, discuss the operating conditions under which they are observed, and compare these with the predictions of theory. (author) 7 refs., 6 figs
Connections between turbulence and jet morphology
International Nuclear Information System (INIS)
Benford, G.
1982-01-01
The author discusses the crucial problem of how to generate large scale turbulence and convey the stored energy to reaccelerated particles, without simultaneously heating the jet so that it expands drastically. He assumes that the cascade process is efficient enough, and allows estimations of the time scale for energy transfer. (Auth.)
International Nuclear Information System (INIS)
Keen, B.E.; Lallia, P.; O'Hara, G.W.; Pollard, I.E.
1987-06-01
The paper presents the annual report of the Joint European Torus (JET) Joint Undertaking, 1986. The report is divided into two parts: a part on the scientific and technical programme of the project, and a part setting out the administration and organisation of the Project. The first part includes: a summary of the main features of the JET apparatus, the JET experimental programme, the position of the Project in the overall Euratom programme, and how JET relates to other large fusion devices throughout the world. In addition, the technical status of JET is described, as well as the results of the JET operations in 1986. The final section of the first part outlines the proposed future programme of JET. (U.K.)
Miller, David W
2011-01-01
Measurements are presented of the jet invariant mass and substructure in proton-proton collisions at $\\sqrt{s} = 7$ TeV with the ATLAS detector using an integrated luminosity of 37 pb$^{-1}$. These results exercise the tools for distinguishing the signatures of new boosted massive particles in the hadronic final state. Two "fat" jet algorithms are used, along with the filtering jet grooming technique that was pioneered in ATLAS. New jet substructure observables are compared for the first time to data at the LHC. Finally, a sample of candidate boosted top quark events collected in the 2010 data is analyzed in detail for the jet substructure properties of hadronic "top-jets" in the final state. These measurements demonstrate not only our excellent understanding of QCD in a new energy regime but open the path to using complex jet substructure observables in the search for new physics.
Runaway beam studies during disruptions at JET-ILW
International Nuclear Information System (INIS)
Reux, C.; Plyusnin, V.; Alper, B.; Alves, D.; Bazylev, B.; Belonohy, E.; Brezinsek, S.; Decker, J.; Devaux, S.; Vries, P. de; Fil, A.
2015-01-01
Highlights: • Runaway electrons (RE) have been obtained at JET-ILW using massive argon injection. • The runaway electron domain entry points are similar between JET-C and JET-ILW. • Inside the runaway electron domain, higher RE currents are observed with JET-ILW. • RE impact has been observed without material melting up to 100 kA RE current. • Heat deposition of 2 ± 1 mm is confirmed by measurements and simulations. - Abstract: Runaway electrons (RE) during disruptions are a concern for future tokamaks including ITER with its metallic wall. Although RE are rare in spontaneous disruptions with the JET ITER-like Wall (JET-ILW), RE beams up to 380 kA were obtained using massive injection (MGI) of argon in JET-ILW divertor discharges. Entry points into the RE domain defined by operational parameters (toroidal field, argon fraction in MGI) are unchanged but higher RE currents have been obtained inside the JET-ILW MGI-generated RE domain when compared to JET-C. This might be due to the influence of the metallic wall on the current quench plasma. Temperatures of 900 °C have been observed following RE impacts on beryllium tiles. Heat deposition depth of ∼2 mm has to be assumed to match the tile cooling time. 3D simulations of the RE energy deposition using the ENDEP/MEMOS codes show that material melting is unlikely with 100 kA RE beams
Runaway beam studies during disruptions at JET-ILW
Energy Technology Data Exchange (ETDEWEB)
Reux, C., E-mail: cedric.reux@cea.fr [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France); Plyusnin, V. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Instituto de Plasmas e Fuso Nuclear, Instituto Superior Tcnico, Universidade de Lisboa, Lisboa (Portugal); Alper, B. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); CCFE, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Alves, D. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Instituto de Plasmas e Fuso Nuclear, Instituto Superior Tcnico, Universidade de Lisboa, Lisboa (Portugal); Bazylev, B. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Institut für Hochleistungsimpuls und Mikrowellentechnik, Karlsruhe Institute of Technology, Campus Nord, 76021 Karlsruhe (Germany); Belonohy, E. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); EFDA-CSU, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Brezinsek, S. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Forschungszentrum Jülich GmbH, Institut für Energie-und Klimaforschung-Plasmaphysik, 52425 Jülich (Germany); Decker, J. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France); Devaux, S. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); CCFE, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Vries, P. de [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); ITER Organization, Route de Vinon sur Verdon, 13115 St Paul Lez Durance (France); Fil, A. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France); and others
2015-08-15
Highlights: • Runaway electrons (RE) have been obtained at JET-ILW using massive argon injection. • The runaway electron domain entry points are similar between JET-C and JET-ILW. • Inside the runaway electron domain, higher RE currents are observed with JET-ILW. • RE impact has been observed without material melting up to 100 kA RE current. • Heat deposition of 2 ± 1 mm is confirmed by measurements and simulations. - Abstract: Runaway electrons (RE) during disruptions are a concern for future tokamaks including ITER with its metallic wall. Although RE are rare in spontaneous disruptions with the JET ITER-like Wall (JET-ILW), RE beams up to 380 kA were obtained using massive injection (MGI) of argon in JET-ILW divertor discharges. Entry points into the RE domain defined by operational parameters (toroidal field, argon fraction in MGI) are unchanged but higher RE currents have been obtained inside the JET-ILW MGI-generated RE domain when compared to JET-C. This might be due to the influence of the metallic wall on the current quench plasma. Temperatures of 900 °C have been observed following RE impacts on beryllium tiles. Heat deposition depth of ∼2 mm has to be assumed to match the tile cooling time. 3D simulations of the RE energy deposition using the ENDEP/MEMOS codes show that material melting is unlikely with 100 kA RE beams.
1993-01-01
maximum jet velocity (6.36 m/s), and maximum number of jets (nine). Wadsworth and Mudawar [49] describe the use of a single slotted nozzle to provide...H00503 (ASME), pp. 121-128, 1989. 40 49. D. C. Wadsworth and I. Mudawar , "Cooling of a Multichip Electronic Module by Means of Confined Two-Dimensional...Jets of Dielectric Liquid," HTD-Vol. 111, Heat Transfer in Electrglif, Book No. H00503 (ASME), pp. 79-87, 1989. 50. D.C. Wadsworth and I. Mudawar
Experimental investigation of submerged single jet impingement using Cu–water nanofluid
International Nuclear Information System (INIS)
Li Qiang; Xuan Yimin; Yu Feng
2012-01-01
Jet impingement cooling is a vital technique for thermal management of electronic devices of high-heat-flux by impinging fluid on a heater surface due to its high local heat transfer rates. In this paper, two types of Cu–water nanofluids (Cu particles with 25 nm diameter or 100 nm) are introduced into submerged single jet impingement cooling system as the working fluid. The heat transfer features of the nanofluids were experimentally investigated. The effects of the nanoparticle concentration, Reynolds number, nozzle-to-plate distance, fluid temperature, and nanoparticle diameter on the heat transfer performances of the jet impingement of nanofluids are discussed. The experimental results show that the suspended nanoparticles remarkably increase the convective heat transfer coefficient of the base fluid. The convective heat transfer coefficient of Cu–water nanofluid with the volume fraction of 3.0% has 52% higher than the pure water. The experiments also revealed that the suspended nanoparticles brought almost no extra addition of pressure drop in both submerged single jet impingement. In addition, by considering the effects of the suspended nanoparticles as well as the condition of impinging jet, a new heat transfer correlation of nanofluids for the submerged single jet impingement has been proposed. - Highlights: ► Cu–water nanofluids are introduced into submerged single jet impingement. ► The affecting parameters on the heat transfer performances of nanofluids are discussed. ► New heat transfer correlation of nanofluid for single jet impingement is proposed.
Heat disposal in water environment
International Nuclear Information System (INIS)
Harleman, D.R.F.
1975-01-01
The need for continuing development of techniques for predicting temperature distributions due to waste heat discharges into lakes, rivers, estuaries, and the oceans is presented. Diffusion of buoyant jets is examined, including heated surface jets and multiple jets issuing from a submerged multiport diffuser. In the near-field analysis of surface jets the important problems are related to the lateral spreading caused by buoyancy. Comparison of theoretical predictions with laboratory and field observations is given. The mechanics of multiport diffusers for heated discharges in shallow receiving waters are explained in contrast to sewage diffusers. The important problem is the degree to which stratification can be maintained in order to minimize local reintrainment and reduction of dilution capacity. Criteria for stable and unstable flow regimes are provided. A mathematical model for temperature distribution, with or without waste heat addition, in unsteady flows under time-varying meteorological conditions is given. (auth)
On jet substructure methods for signal jets
Energy Technology Data Exchange (ETDEWEB)
Dasgupta, Mrinal [Consortium for Fundamental Physics, School of Physics & Astronomy, University of Manchester,Oxford Road, Manchester M13 9PL (United Kingdom); Powling, Alexander [School of Physics & Astronomy, University of Manchester,Oxford Road, Manchester M13 9PL (United Kingdom); Siodmok, Andrzej [Institute of Nuclear Physics, Polish Academy of Sciences,ul. Radzikowskiego 152, 31-342 Kraków (Poland); CERN, PH-TH,CH-1211 Geneva 23 (Switzerland)
2015-08-17
We carry out simple analytical calculations and Monte Carlo studies to better understand the impact of QCD radiation on some well-known jet substructure methods for jets arising from the decay of boosted Higgs bosons. Understanding differences between taggers for these signal jets assumes particular significance in situations where they perform similarly on QCD background jets. As an explicit example of this we compare the Y-splitter method to the more recently proposed Y-pruning technique. We demonstrate how the insight we gain can be used to significantly improve the performance of Y-splitter by combining it with trimming and show that this combination outperforms the other taggers studied here, at high p{sub T}. We also make analytical estimates for optimal parameter values, for a range of methods and compare to results from Monte Carlo studies.
Energy Technology Data Exchange (ETDEWEB)
Kim, Dong Eok; Myung, Byung-Soo [Kyungpook Nat’l Univ., Daegu (Korea, Republic of); Park, Su Cheong; Yu, Dong In [POSTECH, Pohang (Korea, Republic of); Kim, Moo Hwan [Korea Institute of Nuclear Safety (KINS), Daejeon (Korea, Republic of); Ahn, Ho Seon [Incheon Nat’l Univ., Incheon (Korea, Republic of)
2016-06-15
Based on a surface design with rectangular cavities and channels, we investigated the effects of gravity and capillary pressure on pool-boiling Critical Heat Flux (CHF). The microcavity structures could prevent liquid flow by the capillary pressure effect. In addition, the microchannel structures contributed to induce one-dimensional liquid flow on the boiling surface. The relationship between the CHF and capillary flow was clearly established. The driving potentials for the liquid supply into a boiling surface can be generated by the gravitational head and capillary pressure. Through an analysis of pool boiling and visualization data, we reveal that the liquid supplement to maintain the nucleate boiling condition on a boiling surface is closely related to the gravitational pressure head and capillary pressure effect.
Vacuum stress tensor of a scalar field in a rectangular waveguide
International Nuclear Information System (INIS)
Rodrigues, R.B.; Svaiter, N.F.; Paola, R.D.M. de
2001-11-01
Using the heat Kernel method and the analytical continuation of the zeta function, we calculate the canonical and improved vacuum stress tensors, {T μν (vector x)} and {Θ μν (vector x)}, associated with a massless scalar field confined in the interior of an infinity long rectangular waveguide. The local depence of the renormalized energy for two special configurations when the total energy is positive and negative are presented using {T 00 (vector x)} and {Θ 00 (vector x)}. From the stress tensors we obtain the local casimir forces in all walls by introducing a particular external configuration. It is hown that this external configuration cannot give account of the edge divergences of the local forces. The local form of the forces is obtained for three special configurations. (author)
Energy Technology Data Exchange (ETDEWEB)
Kurpiers, Philipp; Walter, Theodore; Magnard, Paul; Salathe, Yves; Wallraff, Andreas [ETH Zuerich, Department of Physics, Zuerich (Switzerland)
2017-12-15
Low-loss waveguides are required for quantum communication at distances beyond the chip-scale for any low-temperature solid-state implementation of quantum information processors. We measure and analyze the attenuation constant of commercially available microwave-frequency waveguides down to millikelvin temperatures and single photon levels. More specifically, we characterize the frequency-dependent loss of a range of coaxial and rectangular microwave waveguides down to 0.005 dB/m using a resonant-cavity technique. We study the loss tangent and relative permittivity of commonly used dielectric waveguide materials by measurements of the internal quality factors and their comparison with established loss models. The results of our characterization are relevant for accurately predicting the signal levels at the input of cryogenic devices, for reducing the loss in any detection chain, and for estimating the heat load induced by signal dissipation in cryogenic systems. (orig.)