Experimental investigation of heat transfer and pressure drop during condensation of R134a-lubricant-mixtures in a multi-port flat tube.

The contribution presents an experimental setup for the investigation of the condensation of R134a-lubricant-mixtures in a multi-port flat tube as used in compact flat tube condensers of AC systems. New correlations for heat transfer and pressure drop for this application are needed, as previous investigations on the condensation of refrigerant-lubricant-mixtures (e.g. Bassi and Bansal (2003), Eckels et al. (1994), Shao and Granryd (1995)) have revealed a significant influence of the lubricant and poor agreement with correlations for pure refrigerants. Therefore, an experimental facility has been set up to measure both the heat transfer coefficients and the pressure drop values in the two-phase flow regime with refrigerant-lubricant-mixture. The test section is an extruded aluminum multi-port tube with a length of 800mm containing 18 parallel channels with square-shaped cross section and a hydraulic diameter of 0.91 mm. In order to provide an even distribution of the refrigerant-lubricant-mixture in the multi-port flat tube, a special transition section including a sight glass for observation purposes has been designed. For the experiments, the nominal concentration of the fully miscible lubrication oil (0-10 wt%), saturation pressure (10-20 bar), mass flux (50-1000 kg m-2 s-1) and inlet vapour quality (0.1-0.9) are varied. A PAG-oil is used as lubricant. The experimental results will be compared with different promising heat transfer and pressure drop correlations from literature.