Steady State Heat Transfer Characteristics in He I with Different Surface Area
Accuracy of stability analyses for pool boiling superconductors depends on heat transfer from the conductor surface to liquid helium. Previously, many heat transfer measurements from copper plates have been reported.1–4 These heat transfer surfaces were different in size and in condition. At the same heat flux, as surface area increases, the quantity of bubbles is also increasing. Free convection in the liquid helium around the surface is considered to be influenced by bubbles. It is assumed that various surface areas take different heat transfer characteristics. In this paper, the heat transfer of copper plates has been measured as a function of heat transfer surface area. We studied four types of heat transfer surface areas including : a) 10 × 18 mm, b) 18 × 18 mm, c) 40 × 18 mm, and d) 76 × 18 mm. The surface roughness is less than 10 μm. It is well-known that the heat transfer characteristics depend on surface orientation. To estimate the dependence for these samples in this study, the surface orientation was changed from 0°(horizontal, heat transfer surface upward), through 90°(vertical), to 180°(horizontal, downward) at the interval of 15°. The dependence of the heat transfer characteristics on the surface areas is discussed.
KeywordsHeat Transfer Heat Flux Heat Transfer Coefficient Free Convection Liquid Helium
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