Measurement of vapour pressure, miscibility and thermal conductivity for binary and ternary refrigerant lubricant mixtures in the context of heat pump tumble dryers

Abstract

Household appliances need to be both efficient and cost-effective. As a result, electrically driven tumble dryers were converted to heat pump driven ones several years ago in order to comply with energy directives, in this case in Germany. In order to increase the efficiency of heat pumps of different performance classes, the use of zeotropic refrigerant mixtures can be useful, since the temperature glide during the phase change of the refrigerant mixture can be adapted to the temperature gradients of the secondary fluids. In order to take advantage of this unique property, a refrigerant mixture selection was carried out by a screening procedure using REFPROP. Within the investigation presented here, two different zeotropic refrigerant blends, propane (R290)/dimethyl ether (DME or RE170) (30 wt.%/70 wt.%) and R152a/carbon dioxide (R744) (90 wt.%/10 wt.%) are focused on as substitutes with low global warming potential (GWP) for R134a in heat pump tumble dryers. The focus is on the interaction between the refrigerant mixtures and the respective lubricant to ensure usability in the heat pump tumble dryer. A specialised polyolefin-based (POE) lubricant was chosen for each refrigerant blend. Because the numerous combinations of possible refrigerant mixtures can lead to unanticipated challenges with oil mixtures, additional experimental investigations are necessary to ensure the compatibility of the lubricant and refrigerant mixture combination in the temperature ranges associated with the investigated application. Therefore, measurements of the vapor pressure, miscibility gaps and thermal conductivity of the refrigerant-lubricant mixture have been carried out and are the focus of this paper.