IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Tuesday Sessions
       Session SS3-TuP

Paper SS3-TuP21
Thermal Accommodation Coefficients Measurement of Inert Gas on Surface of Stainless Steel Sphere

Tuesday, October 30, 2001, 5:30 pm, Room 134/135

Session: Adsorption/Desorption Poster Session
Presenter: B.S. Jun, University of Missouri-Columbia
Authors: B.S. Jun, University of Missouri-Columbia
T.K Ghosh, University of Missouri-Columbia
R.V. Tompson, University of Missouri-Columbia
S.K Loyalka, University of Missouri-Columbia
Correspondent: Click to Email
Heat transfer in the fuel-clad gap in a nuclear reactor impacts the overall temperature distribution, stored energy and the mechanical properties of a nuclear fuel rod. Therefore, an accurate estimation of the gap conductance between the UO2 fuel and the clad is critically important for reactor design and operations. To obtain the requisite accuracy in the gap conductance estimation, it is necessary to take into account the thermal accommodation coefficients of the various gases that are involved. This paper summarizes some recent efforts to obtain stainless steel accommodation coefficients experimentally. To get these values, a high-vacuum system was constructed incorporated in tandem a mechanical vacuum pump and a turbo molecular pump. Thermal accommodation coefficients for helium on stainless steel have been obtained by measuring the cooling rates of a stainless steel sphere suspended in the vacuum chamber. The cooling rate in vacuum is measured and subtracted from the cooling rate in helium at various pressures to yield the approximate net cooling rate of the sphere due to molecular impacts. Knowing the heat capacity of the sphere, its net cooling rate, the temperature difference between the sphere and the ambient gas far from the sphere, the pressure, and the rate of impingement of the gas molecules on the surface of the sphere, one can calculate the efficiency of the energy transfer to the impinging molecules. These measurements have been made on so-called engineering surfaces where no special attempt other than standard baking under high vacuum to remove volatile surface contaminants was used to clean the surfaces. It has been found for helium and argon gas that the thermal accommodation coefficient values with stainless steel are quite constant over the range of pressures studied.