Experimental investigation of condensation heat transfer of zeotropic refrigerant/oil mixtures in plate heat exchanger

Abstract

Plate heat exchanger (PHE) has been wildly used as the condenser of the organic Rankine cycle (ORC). As a potential zeotropic working fluid of ORC system, it is of great significance to study the condensation heat transfer of the mixture of R245fa/R141b and lubricating oil in PHE for the development of ORC system. In this paper, an experimental study on the condensation heat transfer coefficient (HTC) of a mixture of R245fa/R141b (0.5/0.5 by mass) and polyester oil (POE) in a plate heat exchanger (PHE) has been carried out. In addition, the results were compared with those of R245fa and R141b. The parameters in the experiment range from 0 to 0.9 for vapor quality, 0%–4% for oil concentration and 20 to 60 (kg·m−2·s−1) for mass flux. The results showed a 20% reduction in HTC for R245fa/R141b with 4% oil concentration compared to oil-free refrigerant. In addition, the HTC of R245fa/R141b-POE mixture was between that of R245fa/POE and R141b/POE. The oil enhancement factor of different refrigerant/POE mixtures was less than 1.0, which could be well predicted by the Eckels correlation with a maximum mean absolute deviation (MAD) of 13.4%. The product of the predicted enhance factor and HTC predicted by the Jung et al. correlation agreed well with the tested HTC of different refrigerant/POE mixtures in the PHE. The maximum MAD of different refrigerant/POE mixtures was 20.6%, and 96.3% of predicted results were within ±30% deviation. A new correlation with a maximum MAD of 15% was proposed, which predicted the condensed HTC of refrigerant/POE mixture by using its physical properties.