Influence of system pressure on the boiling heat transfer coefficient in a closed two-phase thermosyphon loop

Abstract

In recent years heat generation from electronic components has been rapidly increasing. Natural and forced convection air-cooled heat sinks are not well suited for cooling the components generating the highest heat fluxes. Other methods are therefore sought. Recently the use of thermosyphons has attracted attention as a simple and effective cooling system for high heat flux components. In a thermosyphon system the heat is absorbed during boiling and transferred as heat of vaporization from the hot part to the cold part of the system, with relatively small temperature differences. The setup used in this study consists of a thermosyphon loop, including evaporator, condenser, downcomer and riser. The loop has three evaporators, connected in parallel, made from small blocks of copper (10×20×15) mm in which five vertical channels with diameters 1.5 mm and length 15 mm were drilled. Experimental results in terms of heat transfer coefficients at different system pressures and heat inputs are presented and compared to predictions of correlations from the literature. In all tests Isobutane is used as working fluid.