الفهرس 
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Abstract
In the present study, the thermal performance of conventional two-phase closed thermosyphon (CT) and modified thermosyphon (MT) with a separator in the evaporator section is investigated in case of using distilled water and nanofluid (Al2O3/water) as working fluids. The effect of input heat flux, filling ratio (40%, 50%, 55%, 60%, 75%, and 90%), inclination angle (90°, 60°, 45° and 40°), separator diameter (25mm, 32mm and 40mm), working fluid (pure water and Al2O3/water nanofluid), nanoparticles volume concentration (0.5%, 1.0%, 1.5% and 2.0%) on heat transfer coefficient, thermal resistance and Nusselt number are experimentally investigated.
The results showed that, an average increase of 6.5 % up to 17 % in heat transfer coefficient can be achieved when using a separator in the evaporator section with distilled water as a working fluid. Also an average increase of 26.5 % up to 200% in heat transfer coefficient can be achieved when using Al2O3/water nanofluid as a working fluid instead of distilled water for conventional thermosyphon. In case of using Al2O3/water nanofluid as a working fluid in the presence of a separator in the evaporator section, an average increase of 80 % up to 236% in heat transfer coefficient can be achieved.
An empirical correlation is developed for the prediction of Nusselt number taking into consideration the effect of varying the diameter of the separator used in the evaporator section. The maximum error in calculated Nusselt number (Nu) by the suggested correlation is found to be nearly 6.5 %. The experimental data are compared with the available literature and fairly good agreement was found.