Experimental study of flow boiling of FC-72 in parallel minichannels under sub-atmospheric pressure

Using FC-72 as the coolant, a closed-loop two-phase minichannel heat sink driven by a micro-gear pump was developed in this work. The cooling system was made of oxygen-free copper containing 14 parallel channels of the dimension of 0.8 mm (W) × 2 mm(D) × 20 mm(L). The cooling performance of the heat sink was evaluated by the heat transfer coefficient and pressure drop under different conditions. Experiments were performed under the conditions of initial pressure of P_in = 73 and 101 kPa, mass velocity of G = 71-250 kg/m² s, outlet quality of x_e,out = 0-0.9 and heat flux of q″ = 25-140 W/cm². The experiments show that a maximum heat dissipation rate of 96 W/cm² can be achieved while keeping the heating surface temperature below 85 °C within the experimental range. A strong dependence of the average heat transfer coefficients (HTC) on both mass flux and heat flux was observed, and the data of atmospheric pressure followed the same trend qualitatively with that of sub-atmospheric pressure. Further discussion of the boiling mechanism shows some distinctive features of FC-72 in multiple minichannels.