Insights Into Pool Boiling Heat Transfer on Minichannel Surfaces Through Point and Field Measurements

Abstract

In this study, saturated pool boiling experiments were conducted on copper minichannel and flat surfaces at atmospheric pressure using water as the working fluid. The heat transfer performance was assessed through point measurements with a heater block, cartridge heaters, and thermocouples, as well as field measurements using a thin-foil heater and infrared thermography. Two copper minichannel surfaces with square cross sections of 1 mm (minichannel-1) and 2 mm (minichannel-2) side lengths were tested and compared to a flat surface. Minichannel-1 and minichannel-2 enhanced the critical heat flux (CHF) by 17% and 45%, respectively, and improved the heat transfer coefficient by 24–40% and 51–75%, respectively, compared to the flat surface. Minichannel-2 exhibited the lowest and most uniform boiling surface temperature, making it the best performer among the three. There was no significant change in departure frequency among the surfaces, and no significant change in departure diameter for the flat surface and minichannel-1. However, minichannel-2 had lower departure diameters due to its deeper channels, which prevented bubble coalescence and maintained low departure diameters. Additionally, minichannel-2 delayed vapor film formation by breaking it with its deeper fins, thereby improving CHF and slightly enhancing bubble dynamics. The enhancement in boiling heat transfer is primarily attributed to the increased surface area provided by the minichannels, with a minor contribution from improved bubble dynamics. However, the dominant factor in enhancing pool boiling heat transfer on minichannel surfaces is the increase in surface area.