الفهرس 
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Abstract
The author wishes, first of all to express his deepest thanks for Almighty of Allah then he would like to express his gratitude to his supervisors, Prof. Dr. Eed A. Abdel-Hadi, Prof. Dr. Sherif H. Taher, and Prof. Dr. Mohammed M. Elrefaii, for their intensive supervision, fruitful discussion, constant encouragement and continuous guidance during the course of the research work presented in this thesis.
Also the deepest thanks and gratitude are to the Egyptian Company for Refrigeration and Air Conditioning Industries in BAHGAT Group for their kind help during the experimental part of the present investigation.
Last but not least the author wishes to express his sincere appreciation to his parents and his wife whose patience and continuous encouragement constituted a major source of inspiration for him.
ABSTRACT
An experimental apparatus is designed and constructed in the present investigation to study the effect of the lubricating oil on the heat transfer coefficient during forced boiling of refrigerant R-134a inside finned tubes.
The measurements include the effect of heat flux, mass flux and evaporation pressure on the average boiling heat transfer coefficient inside finned tubes of different fin height, at different oil concentrations. The refrigeration cycle used in the experimental work consists of a compressor, condenser, expansion valve, and four test sections of different tube geometry that simulates the evaporator. The test sections are a shell and tube heat exchangers made from copper tubes. Each test section is provided with nine thermocouples distributed along the test section to measure the outside wall temperatures of the refrigerant tube, in addition to two thermocouples used to measure the inlet and the exit temperatures of the hot water passing through the test section.
Experiments were carried out for a range of heat flux of 14 to 100 kW/m2, mass flux ranged from 100 to 265 kg/m2s, oil concentration ranged from 0 to 5 % and for evaporation pressure of 3.2 to 4 bar, using smooth and internally grooved tubes of fin height 0.15, 0.18, and 0.2 mm. respectively.
The measurements show that for the same oil concentration, mass flux, and evaporation pressure, the value of the heat transfer coefficient increases by 2.5 to 13.5 % as the heat flux increases.
Also the measurements indicated that at a certain oil concentration and for constant heat flux and evaporation pressure as the mass flux increases the value of heat transfer coefficient increases by 0.25 to 0.75%.
In addition the measurements indicated that as the evaporation pressure increases the value of heat transfer coefficient increases by 100 to 150%, for constant heat flux, mass flux, and oil concentration, for all tested tubes.
Also the measurements showed that at constant heat flux, mass flux, and evaporation pressure as the oil concentration increases the value of heat transfer coefficient decreases by 14 to 16%.
The measurements shows also that at 2%, 3%, 3.4%, and 3.6% oil concentrations inside smooth and inner grooved tubes of fin height 0.15, 0.18, 0.2 mm, a slight enhancement in the heat transfer coefficient occurs but the values of the heat transfer coefficient is still lower than that of the 0% oil concentration.
The results are compared with the available data in the recent existing literature. The present results showed a good agreement with these data.
A theoretical model is developed here using ANSYS FLUENT 14.0 to predict a wider range of the operating parameters of the refrigerant tubes, such as fin height and oil concentrations under different conditions. The model is verified by comparing its results with the present experimental measurements.
A mathematical correlation equation is deduced to determine the heat transfer coefficient in terms of oil concentration, evaporation pressure, heat and mass fluxes. The deduced equation fits the present experimental measurements with a maximum deviation of ± 10 %.
A computer program written in VISUAL BASIC is used to compute the heat transfer coefficient at different oil concentration, evaporation pressure, heat and mass flux.