الفهرس 
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Abstract
The present study investigates experimentally the pool boiling characteristics of nanofluids during nucleate stage over a stainless steel heater at different heat flux and different pressure. The nanofluid has been prepared by the suspension of Aluminum oxide with diameter of 40 nm (according to the manufacturer, M K Impex Corp. - CANADA) in a base fluid R134a with concentrations of 0.01, 0.05, 0.1, 0.25 and 0.5 % by volume. An experimental test rig has been designed and manufactured for this purpose. The results showed that the nucleate pool boiling heat transfer coefficient increases with increasing both applied heat flux and operating pressure. The heat transfer coefficient also increases with the increase of the nanoparticles concentration in the range from 0.01 to 0.25% by volume, but it decreases with more concentration. The effect of surface roughness of the heating surface was studied and the results showed that the heat transfer coefficient increases with the increase of surface roughness. In general, an enhancement up to 167% is observed during the investigation of present study. An empirical correlation was deduced to generalize the experimental data as dimensionless groups within uncertainty of ±9 %. The present results based on the experimental measurements were compared with the corresponding available published data showing favorable agreement between the present results and published ones.