Experimental investigations of the flow boiling characteristics of green refrigerants in a novel petaloid micropin-fin heat sink

Abstract

Although micropin-fin heat sinks (MPFHSs) are widely regarded as an effective way to dissipate heat in microelectronic equipment, the pin fin structure has not changed much over the years. Inspired by the flower of Clematis montana, a novel petaloid structure was designed. The flow boiling characteristics of green refrigerants, including R1234ze(E) and R1234yf, in the petaloid MPFHS were investigated under mass fluxes of 100–200 kg/m2 s, heat fluxes of 20–40 kW/m2 and saturation pressures of 0.4–0.6 MPa and compared with those of R134a. In the nucleate boiling zone, the heat transfer coefficient (HTC) rises with saturation pressure, vapor quality, and heat flux; in the convective boiling region, it rises with mass flux. With mass flux and vapor quality, the frictional pressure drop (FPD) rises; with saturation pressure, it falls; with heat flux, it keeps constant. R1234ze(E) shows the largest HTC and the smallest FPD, and R1234yf and R134a have similar HTC and FPD. Specific bubbles, slugs, confined slugs and liquid films yielded by the petaloid micropin fins are identified, and the flow behaviors, including coalescence and separation of bubbles/slugs, are described. Comparing the existing empirical correlations for flow boiling HTC and FPD in plain and micropin-fin channels with the experimental data yields unsatisfactory mean absolute deviations (MADs). Hence, new correlations for petaloid MPFHS are developed, which yield satisfactory MADs of 12.6% and 9.9% for HTC and FPD, respectively.