Results 1 - 10 of 5076
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[en] Modeling studies are preformed to investigate the plasma and heat transfer characteristics of a low power argon arcjet thruster. Computed temperature, velocity, static pressure, and Mach number distribution in arcjet thruster under typical operating condition are presented in this paper. It shows that the performance data from numerical modeling results are basically consistent with the experimental measured values.
[en] DOWTHERM A oil is being considered for use as a heat transfer fluid in experiments to help in the design of heat transfer components for the Next Generation Nuclear Plant (NGNP). In conjection with the experiments RELAP5-3D/ATHENA will be used to help design and analyzed the data generated by the experiments. Inorder to use RELAP5-3D the thermophysical properties of DOWTHERM A were implemented into the fluids package of the RELAP5-3D/ATHENA computer propgram. DOWTHERM A properties were implemented in RELAP5-3D/ATHENA using thermophysical property data obtain from a Dow Chemical Company brochure. The data were curve fit and the polynomial equations developed for each required property were input into a fluid property generator. The generated data was then compared to the orginal DOWTHERM A data to verify that the fluid property data generated by the RELAP5-3D/ATHENA code was representitive of the original input data to the generator.
[en] A numerical study has been performed to analyze the combined temperature and special gradients induced buoyancy-driven natural convection flow of cold water, near its density extremum, contained in a rectangular partitioned enclosure with isothermal side walls and insulated top and bottom. A highly conductive thin baffle is attached to the hot wall. The flow is assumed to be two-dimensional. Numerical solutions of the governing equations are obtained using the two-step ADI method coupled with the SOR technique. The results of investigation are presented in the form of steady state streamlines, isotherms and isoconcentration lines. The results are discussed for different positions and lengths of the baffle and different values of Schmidt number and hot-wall temperature. The heat and mass transfer rates calculated are found to behave nonlinearly. The average heat transfer rate is enhanced when the position of the baffle is raised. The heat and mass transfer are increased with increasing enclosure size. It is also found that the convective heat transfer is greatly influenced by the presence of a density maximum in the convective fluid. (author)
[en] The conductive radiative transfer problem in homogeneous plane parallel medium of anisotropic scattering with specularly reflecting boundaries has been considered. The angular dependent reflectivity of the boundary is considered as Fresnel reflection probability function. A Galerkin-iterative technique is used to solve the coupled conductive radiative heat equations in integral forms. Numerical results are obtained for the temperature, the conductive, radiative and the total heat fluxes for homogeneous upon the reflective index of the medium with isotropic or anisotropic scattering. Results obtained for homogeneous medium with isotropic or anisotropic scattering are compared with the published calculations.
[en] This paper covers a verification plan of the results of heat transfer analysis in the MACSTOR/KN-400 on a transient state basis. The transient state reflects several natural environment parameters such as solar loads and daily temperature variations. These factors seriously affect analysis results in terms of concrete temperature and temperature gradients. There are two objectives to verifying the heat analysis results under transient state. First, there is the need to meet the request of the regular body to confirm that concrete temperature stays below the level of the design criteria. Second, it is necessary to recognize how much conservative the analysis is. In actual operating conditions, concrete temperature would be reduced by less conservative conditions
[en] The analysis under the second law of thermodynamics is the gateway for optimisation in thermal equipments and systems. Through entropy minimisation techniques it is possible to increase the efficiency and overall performance of all kinds of thermal systems. Radiation, being the dominant mechanism of heat transfer in high-temperature systems, plays a determinant role in entropy generation within such equipments. Turbulence is also known to be a major player in the phenomenon of entropy generation. Therefore, turbulence-radiation interaction is expected to have a determinant effect on entropy generation. However, this is a subject that has not been dealt with so far, at least to the extent of the authors' knowledge. The present work attempts to fill that void, by studying the effect of turbulence-radiation interaction on entropy generation. All calculations are approached in such a way as to make them totally compatible with standard engineering methods for radiative heat transfer, namely the discrete ordinates method. It was found that turbulence-radiation interaction does not significantly change the spatial pattern of entropy generation, or heat transfer, but does change significantly their magnitude, in a way approximately proportional to the square of the intensity of turbulence
[en] We investigated the nonlinear behavior of a microbubble under ultrasound, taking into account the heat transfer inside the bubble and through the bubble wall. The polytropic relation, which has been used for the process of pressure change depending on the volume variation of ideal gases, cannot properly treat heat transfer involving the oscillating bubble under ultrasound. In this study, a set of solutions of the Navier-Stokes equations for the gas inside the bubble along with an analytical treatment of the Navier-Stokes equations for the liquid adjacent to the bubble wall was used to treat properly the heat transfer process for the oscillating bubble under ultrasound. Entropy generation due to finite heat transfer, which induces the lost work during bubble evolution, reduces the collapsing process and considerably affects the nonlinear behavior of the bubble
[en] 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/m2, 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 quinconcerectangular mini-channel heat exchanger, with a hydraulic diameter Dh = 2mm. NOMENCLATURE h D Hydraulic diameter (mm). int
[en] The papers deals with a numerical 3D study of natural convection in a finned Rayleigh-Be nard (RB) cubical enclosure. A single fin with a thickness of 10 pour cent of the cavity side (and a height of 50 pour cent ) is placed vertically on the bottom hot wall at TH. The working fluid is air with Prandtl number Pr = 0.71 and the Rayleigh number (Ra) varies from 103 to 105. The solid-to-fluid thermal conductivity ratio (kR) was fixed at RK = 7000, corresponding to a metal of high conductivity. The top wall is at the temperature TC < TH and the remaining four surfaces are insulated. Inside the RB enclosure, the flow structure and the temperature distribution are presented in terms of mean velocity vector plots and isotherm plots. The effects of the Rayleigh number on the mean heat transfer rate through the cold wall are presented and discussed. A correlation between the averaged Nusselt number through the top wall and Ra is proposed
[en] The effect of a dielectric coating on the near-field radiative heat transfer between two plane surfaces is numerically studied in the framework of the fluctuational electrodynamics. The dielectric coating is assumed to be a SiC or SiO2 film, which is on top of the emitter. The results show that the near-field radiative flux between the plane surfaces can be either diminished or enhanced by the dielectric coating, depending on the thermal radiative properties of the emitter and the receiver. Furthermore, the dielectric coating effect on the near-field radiative flux can be very different from that on the far-field radiative flux. Detailed analysis on the variations of the TE- and TM-wave components of the radiative flux by adding the dielectric coating is provided, along with the physical mechanisms that account for these changes. Dielectric coatings such as SiC and SiO2 films are widely seen in microelectronic structures and nanofabrication devices. The results obtained in this work should be valuable for further study and nanotechnological applications of near-field radiative heat transfer.