Critical heat flux: Performance of R1234yf, R1234ze and R134a in an aluminum multi-minichannel heat sink at high saturation temperatures

In this paper, new saturated critical heat flux (CHF) values at medium-to-high saturation temperatures are presented for an aluminum multi-minichannel test section. Among the possible working fluids, R134a and the low GWP refrigerants R1234yf and R1234ze have been selected. The aluminum heat sink used as test section is made up of seven minichannels, each of them 2 mm wide, 1 mm high and 35 mm long, thus resulting in an internal equivalent diameter of 1.33 mm. All tests were carried-out by taking into account the influence of the mass flux and the saturation temperature. The first was set from 150 up to 350 kg/m2 s, while the latter was varied from 25 °C up to 75 °C. The results in the form of diagrams and boiling curves show that the experimental CHF significantly increases with mass velocity, whereas a general CHF drop with the saturation temperature is detected, especially for lower mass fluxes. Finally, the agreement of the present database with some well-known CHF correlations is also tested. In order to perform valuable comparisons, the experimental points in which the uncertainty in the operative parameters was superior to a chosen threshold have been excluded from the statistics. The results show that the equations of Anwar et al. [28] and Callizo et al. [25] best predict the experimental values.