Heat- conductivity, fluid properties, hot-wire method, oil-refrigerant-mixture
The Montreal Protocol and especially the European F-Gas-regulation proclaim the reduction of refrigerants with high global warming potential (GWP). Over the next decades, the phase-down of the production and the use of high GWP hydrofluorocarbons (HFCs) is declared. One viable alternative for HFCs are natural refrigerants and their blends. The modification, optimization as well as the simulation of refrigerant cycles for new refrigerants requires knowledge of the thermophysical properties of the alternative refrigerants and their mixtures with the refrigeration oil. While pure refrigerants are well explored, there is a lack of information about the properties of their blends as well as of the refrigerant lubricant mixtures. Among other properties, this includes the heat conductivity of the pure lubricant as well as the heat-conductivity of refrigerant lubricant mixtures. The experimental setup and the results of the heat conductivity measurements of different lubricants such as polyol ester oils (POE) and mineral oils (MO) as well as of refrigerant–lubricant-mixtures with natural refrigerants and their blends are presented. The test cell according to the hot-wire method with platinum wires was specially developed for the measurement of refrigerant–lubricant-mixtures at different compositions. The measurements are performed at temperatures of up to 80 °C and pressures of up to 40 bar.