Steady state heat transfer through a rarefied gas confined between two parallel plates or two coaxial cylinders maintained at different temperatures is investigated using the nonlinear S-model kinetic equation and the DSMC technique for a large range of gas rarefaction. The profiles of heat flux, density and temperature are reported for different values of gas rarefaction parameter and given values of temperature and aspect ratios. In the slip regime the results of the S-model and DSMC technique are compared to the simulations performed using the Lin and Willis temperature jump boundary conditions at the at the solid surface implemented in ANSYS/Fluent CFD simulations. The analytical expressions for density number, temperature and heat flux in the free molecular regimes are obtained for both parallel plates and coaxial cylinders geometries with hot and cold surfaces having different values of the thermal accommodation coefficient. The solutions of these analytical expressions are compared to the S-model kinetic equation and DSMC technique results in the free molecular regime.

This version is available at https://strathprints.strath.ac.uk/60004/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Strathprints administrator: strathprints@strath.ac.ukThe Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output. Continuum and kinetic simulations of Heat Transfer trough Rarefied Gas in Annular and Miles GreinerProfessor, ASME Fellow Mechanical Engineering Department University of Nevada, Reno Reno, Nevada, 89557 Email: greiner@unr.edu ABSTRACT Steady-state heat transfer through a rarefied gas confined between parallel plates or coaxial cylinders, whose surfaces are maintained at different temperatures is investigated using the non-linear Shakhov (S) model kinetic equation and DSMC technique in the slip regime. The profiles of heat flux and temperature are reported for different values of gas rarefaction parameter δ, ratios of hotter to cooler surface temperatures T , and inner to outer radii ratio R . The results of S-model kinetic equation and DSMC technique are compared to the numerical and analytical solutions of the Fourier equation subjected to the Lin & Willis temperature-jump boundary condition. The analytical expressions are derived for temperature and heat flux for both geometries with hotter and colder surfaces having different values of the thermal accommodation coefficient. The results of the comparison between the kinetic and continuum approaches showed that the Lin & Willis temperature-jump model accurately predicts heat flux and temperature profiles for small temperature ratio T = 1.1 and large radius ratios R ≥ 0.5, however, for large temperature ratio, a pronounced disagreement is observed.

Measurements of heat transfer from an array of vertical heater rods to the walls of a square, helium-filled enclosure are performed for a range of enclosure temperatures, helium pressures, and rod heat generation rates. This configuration is relevant to a used nuclear fuel assembly within a dry storage canister. The measurements are used to assess the accuracy of computational fluid dynamics (CFD)/radiation simulations in the same configuration. The simulations employ the measured enclosure temperatures as boundary conditions and predict the temperature difference between the rods and enclosure. These temperature differences are as large as 72 °C for some experiments. The measured temperature of rods near the periphery of the array is sensitive to small, uncontrolled variations in their location. As a result, those temperatures are not as useful for validating the simulations as measurements from rods near the array center. The simulated rod temperatures exhibit random differences from the measurements that are as large as 5.7 °C, but the systematic (average) error is 1 °C or less. The random difference between the simulated and measured maximum array temperature is 2.1 °C, which is less than 3% of the maximum rod-to-wall temperature difference.

During vacuum drying of used nuclear fuel canister, helium pressure is decreased to as low as 67 Pa to promote evaporation and removal of water remaining in the canister following draining operation. At low pressures associated with vacuum drying, there is a temperature jump (thermal resistance) between the solid surfaces and helium in contact with them. This temperature jump increases as the pressure decreases (rarefied condition), which contributes to the fuel assembly’s temperature increase. It is important to keep the temperature of the fuel assemblies below 400°C during vacuum drying to ensure their safety for transport and storage. In this work, an experimental apparatus consisting of a 7×7 array of electrically heated rods maintained between two spacer plates and enclosed inside a square cross-section stainless steel pressure vessel is constructed to evaluate the temperature of the heater rods at different pressures. This geometry is relevant to a BWR fuel assembly between two consecutive spacer plates. Thermocouples are installed in each of the 49 heater rods, spacer plates and enclosure walls. They provide a complete temperature profile of the experiment. Different pressures and heat generation relevant to vacuum drying conditions are tested. The results showed that the maximum temperature of the heater rods increases as the pressure decreases. The results from these experiments will be compared to computational fluid dynamics simulations in a separate work.

No abstract