The effect of a boiling additive on R123 condensation on a vertical integral-fin surface

This paper examines the effect of the addition of 0.5% mass isopentane to R123 on the vapor-space condensation heat transfer of R123. In a previous study, the pool boiling performance of R123 was improved by adding 0.5% mass isopentane. Consequently, the impetus of the present study was a desire to quantify the consequence of the boiling additive on the condensation heat transfer performance of pure R123. In this way, the net effect of the additive on the cycle performance of pure R123 can be estimated. The data consisted of the heat flux and the wall temperature difference measurements for pure R123 and R123/isopentane (99.5/0.5) on an integral-trapezoidal-fin surface. The temperature of the saturated vapor was held constant at 313.15 K for all of the tests. On average, the R123/isopentane mixture exhibited a 4% smaller heat flux than that of pure R123. Presumably, the degradation was caused by the zeotropic behavior of the mixture, which led to a loss of available driving temperature difference for heat transfer across the liquid film. Considering that the boiling performance was enhanced on average by 10% with the addition of 0.5% mass isopentane, isopentane may still be a viable means of improving the cycle performance of R123 despite the 4% condensation heat transfer degradation.