Experimental analysis of high heat-flux microchannel condensation

The present study explores condensation of FC-72 through a microchannel heat sink cooled by a counterflow of water in tubes that are soldered to the underside of the heat sink. The microchannels were formed by machining 10 of 1 mm square grooves across the 20.1 mm width of a 300.0 mm long copper plate, which was topped with a transparent plastic plate. Experiments were performed with the FC-72 spanning the following conditions: inlet pressure of 104.0 - 133.0 kPa (15.09 - 19.29 psi), flow rate of 0.682 - 3.665 g/s, inlet quality of 1.0 - 1.1, and with water flow rates of 2.97 - 5.95 g/s. Both pressure drop and temperature drop were measured in the FC-72 across the heat sink. In addition, temperatures were measured at many locations within the copper plate. These measurements were used to explore trends in both the pressure drop and condensation heat transfer coefficient. Measured pressure drop and condensation heat transfer coefficient values ranged from 0.547 to 24.832 kPa (0.08 to 3.60 psi) and 176.08 to 11,448 W/m2-K, respectively. Pressure drop was found to increase with increasing flow rate of FC-72. The condensation heat transfer coefficient was highest at the channel inlet and increased with increasing flow rate of FC-72 and/or deceasing flow rate of water. In addition to the measurements, high-speed and close-up photographic techniques were used to map dominant two-phase flow regimes and determine operating conditions that yield the annular flow regime responsible for netting the highest heat transfer coefficients. A new turbulent annular film model recently developed at the Boiling and Two-Phase Flow Laboratory (BTPFL) is shown to predict both the pressure drop and the condensation heat transfer coefficient for the annular regime with high degrees of accuracy