Analysis of the thermal cooling capacity of heat pipes under a low Reynolds number flow

A detailed investigation into determining the optimum working fluid for providing passive airside cooling in ventilation airstreams was carried out. The effectiveness of water, ethanol and R134a as heat pipe fluids was systematically compared by analysing their thermal cooling capacity under a low Reynolds number airstream, typically found under natural ventilation. The internal multiphase flow profiles and the subsequent external air temperatures were numerically predicted using Computational Fluid Dynamics (CFD), the findings of which were quantitatively validated using wind tunnel experimentation. Using a source temperature of 314 K or 41 °C and an inlet velocity of 2.3 m/s, the emergent thermal profiles were established to comprehend the optimum working fluid. The results showed that the highest heat transfer due to convection was obtained using water as the working fluid, determined at 977 W. The corresponding effectiveness of the heat pipe heat exchanger was found to be 6.5% for water, 4.9% for R134a and 3.7% for ethanol. The findings determined that water incorporated the greatest capability of efficiently reducing air temperatures by approximately 24% higher than the refrigerant R134a and 42% higher than ethanol which was found to be the least effective working fluid under the range of investigated temperatures. Good correlation was obtained between the numerical and experimental findings with a maximum error variation of approximately 3%. The present work successfully classified the sustainable operation of replacing synthetic refrigerants with a natural fluid such as water in delivering energy-free cooling under ventilation airstreams.