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, ω= 59.90 (1 - T_r)^1.237 for R245fa, ω= 56.57 (1 - T_r) ^1.220 for R1234ze(Z), and ω= 61.95 (1 - T_r) ^1.277 for R1233zd(E), where, ω and T_r are the surface tension in mNm^-1 and the reduced temperature, T_r = T/T_crit. The critical temperatures T_crit 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 m¹, and ±0.05 mN m^-1 for R245fa, R1234ze(Z), and R1233zd(E), respectively.