Heat transfer and pressure drop in narrow rectangular channels

Abstract

Recently, with the advent of more powerful electronic chips and the miniaturization of electronic circuits and other compact systems, a great demand exists for developing efficient heat removal techniques to accommodate these high heat fluxes. With this objective in mind, both single-phase forced convection and subcooled and saturated nucleate boiling experiments have been performed in small rectangular channels using FC-84 as test fluid. The test section used in these experiments consisted of five parallel channels with each channel having the following dimensions: hydraulic diameter ( D h)=0.75 mm and length to diameter ratio ( L/ D h)=409.8. The experiments were performed with the channels oriented horizontally and uniform heat fluxes applied at the top and bottom surfaces. The parameters that were varied during the experiments included the mass flow rate, inlet liquid subcooling, and heat flux. In each of the experiments conducted, the temperature of both the liquid and the wall were measured at various locations along the flow direction. Based on the measured temperatures, pressure drops, and the overall energy balance across the test section, the heat transfer coefficients for both single-phase forced convection and flow boiling has been calculated. Additionally, in these experiments, the single- and two-phase pressure drop across the channels was also measured. A correlation has been developed for two-phase flow pressure drop under subcooled and saturated nucleate boiling conditions. Furthermore, two new correlations are proposed – one for subcooled flow boiling heat transfer and the other for saturated flow boiling heat transfer.