Surface tension of low GWP refrigerants R1234ze(Z) and R1233zd(E).

R1234ze(Z) and R1233zd(E) are very recently under consideration as a potential candidate to replace R245fa that is widely used in organic Rankine cycles and high-temperature industrial heat pumps. The capillary constant and surface tension of saturated R1234ze(Z) and R1233zd(E) were measured across the temperature range from 274 K to 350 K using a measuring apparatus based on the differential capillary rise method. The measurement uncertainty in the surface tension was typically 0.3 mN m-1. The experimental surface tension was well represented by a van der Waals type equation expressing the temperature dependence as, σ = 59.90 (1 - Tr) 1.237 for R245fa , σ = 56.57 (1 - Tr) 1.220 for R1234ze(Z), and σ = 61.95 (1 - Tr) 1.277 for R1233zd(E), where, σ and Tr are the surface tension in mNm-1 and the reduced temperature, Tr = T /Tcrit. The critical temperatures Tcrit are given as 427.01 K for R245fa, 423.27 K for R1234ze(Z) by Higashi et al. (2015), and 438.75 K for R1233zd(E) by Hulse et al. (2012). The constants and exponents are empirically determined by the least square mean method. The above correlations represent the experimental surface tension within ± 0.13, ± 0.21 mN m-1, and ± 0.05 mN m-1 for R245fa, R1234ze(Z), and R1233zd(E), respectively.