الفهرس 
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Abstract
The present thesis is an experimental study of the nucleate pool boiling heat transfer of horizontal copper tubes, submerged in saturated R-134a and distilled water. for the aspect, a pool boiling test rig is designed and constructed to perform heat transfer experiments using two sets of test tubes with R-134a and distilled water as working fluids.
The first set of test tubes consists of five copper tubes having the same external dimensions. One of them is the bare tube, while the remaining four tubes are provided with copper porous layer lined internally just below the external tube surface. The thickness of the porous layer is varied significantly from one tube to the other. Experiments were carried out on this set using saturated distilled water and asturated R-134A.
The second set of test tubes are those remaining four tubes of the first set provided with a defined number of drilled holes to flood the porous layer with the liquid pool. Experiments were conducted on this set using saturated distilled water at the same tested pressures of the first set.
Effects of heatflux, saturation pressure of both R-134a and distilled water, condition of porous layer dry or wet and porous layer thickness on the nucleation characteristics and boiling heat transfer coefficient are thw major studied parameters.
A detailed analysis of the experimental results showed two different trends for the effect of the porous layer thickness on the boiling process, nucleation characteristics and accordingly the heat transfer coefficient. for the first set of test tubes; increasing porous layer thickness deteriorated the thermal performance. while the second set of test tubes show a significant enhancement of thermal performance with increasing porous layer thickness.
The three parametric distribution function N for the size of the stable vapor bubbles in active nucleation sites were deduced for all tubes using saturated distilled water and R-134a A trail eas made to find the relationship between the size distribution function`s constants and the porous layer thickness.
More attention is directed to correlate the experimental data of heat transfer coefficient, heat flux, excess temperature and nucleation site density; to get a helpful tool for predicting the thermal performanceof this mode of heat transfer. Good agreement was obtained between the present experimental data and the available published data.