LAUSR

Abstract A guidance structure mounted above a heating surface is proposed to enhance pool boiling heat transfer in this paper. The basic idea is to form separated vapor-liquid pathways with a rising slug flow and a replenishing liquid impingement vertically onto the heating surface through an integrated bubble pump. Visualization and heat transfer experiments of pool boiling of water on a copper surface are conducted under saturation temperatures of 50 °C, 70 °C and 100 °C for 3 test sections without a guidance tube, with a straight guidance tube and with a trumpet guidance tube. It is found with increasing heat flux, the unidirectional fluid circulation becomes steadier, and the bubble pumping velocity and liquid impingement velocity increase. The trumpet guidance tube is more favorable to achieve unidirectional fluid circulation than the straight guidance tube due to the bubble collection effect of the trumpet, which has larger liquid impingement velocity due to its narrower annulus for the returning liquid. Both guidance tubes can enhance the critical heat flux (CHF) and the heat transfer coefficient (HTC) drastically, especially at lower saturation temperatures where bubble pump is more efficient because of lower vapor density. At a saturation temperature of 50 °C, the CHF and the maximum HTC of trumpet guidance tube are 109.0 W/cm2 and 38.8 kW/m2 °C, respectively, which are 4.1 and 2.8 times of the test section without a guidance tube. In general, the trumpet guidance tube has better performance than the straight guidance tube with respect to CHF and the maximum HTC. However, at a saturation temperature of 100 °C, HTC of the trumpet guidance tube at relatively low heat fluxes is lower because of the suppression of nucleate boiling by the larger liquid impingement velocity.