Proceedings of I-Therm VI, pp. 349-355, Seattle, WA, 1998

Combined Effects of Sub-Cooling and Operating Pressure on the Performance of a Two-Chamber Thermosyphon

C. Ramaswamy, Y. Joshi, W. Nakayama and W. Johnson
CALCE Electronic Products and Systems Consortium
University of Maryland, College Park, MD 20742


This study investigates the combined effect of sub-cooling and pressure on the performance of an enhanced microstructure based thermosyphon, which has shown very high heat transfer rates (up to 100 W/cm2 with a wall superheat of 27.8oC). The pressure levels tested were partial vacuum (40-101.3 kPa), atmospheric pressure (101.3 kPa) and high pressure (101.3-370 kPa). The experiments were initiated at room temperature, and hence the sub-cooling corresponded to the difference in the liquid saturation temperature at the starting system pressure and room temperature. The results show a reduction in wall superheat values at higher pressures, at a given heat flux. The performance of the system was evaluated by defining a surface-to-ambient resistance. Results show that a partial vacuum at all heat fluxes results in better performance compared to higher pressures. The combined effect of pressure and sub-cooling was also tested for a compact evaporator and the results obtained were similar to the baseline case (larger evaporator).

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