Comparative investigation on the droplet evaporation characteristics of hydrochlorofluorocarbon, hydrofluoroolefin, and hydrofluoroether under complex environments

As a premier thermal management solution for high-heat-flux and low-temperature applications, the performance of spray cooling is profoundly influenced by the evaporation characteristics of the liquid droplet. The choice of working fluids (refrigerant) also plays a fundamental role in enhancing overall performance. Motivated by the above, the evaporation characteristics of 1,1-dichloro-1-fluoroethane (R141b), cis-1,1,1,4,4,4-hexafluoro-2-butene [R1336mzz(Z)], and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HFE-347pcf2) droplets are compared across varied temperatures (50–250 °C) and pressures (1–20 bars) using the droplet suspension method. The results reveal the inconsistency between the evaporation rate and saturation temperature (Tsat) sequence. R1336mzz(Z) demonstrates the highest droplet evaporation rate across all tested conditions, attributable to its synergistic combination of lower Tsat and minimal latent heat of vaporization (Lv). The highest Lv of R141b inhibits its evaporation rate, whereas HFE-347pcf2 has moderate Lv but the highest Tsat, which suppresses its droplet evaporation. Ambient temperature and pressure synergistically regulate droplet evaporation. Quantitative analysis reveals that at fixed ambient pressure, as ambient temperature increases, the average evaporation rate (Kave) increases almost linearly, while the normalized lifetime (tL) decreases exponentially. Elevated pressure enhances the temperature sensitivity of Kave and tL by (1) suppressing gas-phase diffusion, (2) enhancing nonlinear vapor pressure gradients, and (3) promoting droplet heating. These synergistic effects drive a transition from vapor-diffusion-dominated to heat-transfer-dominated evaporation in high-pressure environments. Eventually, the quantitative correlation between Kave and tL and varying ambient temperature under different ambient pressures are proposed.