الفهرس 
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Abstract
The present study aims to investigate experimentally the effect of the concentration of the lubricating oil on the condensing heat transfer coefficient during condensation process of referigerant R-134a.
The experimental runs include the variation of the heat flux, mass flux and condensation pressure and indicating their effect on the condensing heat transfer coefficient for different oil concentrations. The refrigeration cycle used in the present investigation consists of a compressor, evaporator, expansion valve, and water cooled condenser. The test section is a tube in tube heat exchanger made of copper tubes. the test section is provided with forty-eight thermaocouples distributed along the test section to measure the outside wall temperatures of the refrigerant tube. Two thermocouples are used to measure the inlet and outlet temperatures of the refrigerant in addition to two digital thermometers used to measure the inlet and outlet temperatures of the cold water in the annular part of the test section.
Experiments were carried out for heat fluxes ranged from20.49 to 45kw/m; mass fluxes ranged from 80 to 400 kg/m oil concentrations ranged from 0 to 10% and condensation pressures ranged from 7.35-12.37 bar.
The measurements indicated that for a certain oil concentration as heat flux and condensation pressure increase, the condensing heat transfer coefficient increases. The measurements indicated also that condensing heat transfer coefficient increases for an oil concertration ranged from 0 to 1% then decreases for higher values of concentration.
Experimental measurements indicate that as the condensation pressure decreases the condensing heat transfer coefficient decreases, for all values of heat transfer flux, mass flux and oil concentration.
The results of the present experimental measurements are compared with the available data in the recent existing literature. The results showed good agreement with the previous published data. A general empirical correlationn equation is deduced to estimate the condensing heat transfer coefficient in terms of the heat flux, mass flux, oil concentration and condensation pressure. the deduced correlation equation obtainedhere fits the present measurement with a maximum deviation of 10%.