الفهرس 
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Abstract
In this work the effect of the wick configuration and the thermo-physical properties of the compatible working fluids on the performance of the gravity assisted heat pipe are investigated.
A test apparatus was designed and constructed to achieve heat transfer measurements from five heat pipes having different wick structures. Aluminum pipes each of 250mm long and 25mm outside diameter were used.
The internal surfaces of these pipes were fabricated to have different configurations. These configurations were squared grooves, triangular grooves, two different mechanically roughened surfaces and a smooth surface.
Acetone, R-11,R-12,R-22, and R-134a were tested as heat pipe working fluids.
The tests were spotted on the boundary conditions at the evaporator constant heat flux to investigate the heat transfer coefficient and the overall thermal conductance.
Comparison of booth the heat transfer coefficient and the overall thermal conductance of the five tested heat pipes should a similar trend at the same operating pressure. It should be noted that the heat pipe overall thermal conductance is affected alternately by both the wick shape and the working fluid in conjunction with the operating pressure.
The experimental results should that:
1.The heat transfer coefficient at both evaporator and condenser sections is very sensitive to the operating pressure and rapidly increases with it.
2.The overall thermal conductance is affected by the operating pressure and increases with the increase of it.
3.Modification of the wick configuration can significantly change the heat transfer performance. In case of Acetone and R-11, the squared grooves improve the evaporating coefficient. In the case of R-22, a smooth surface gives poor evaporating heat transfer coefficient and the results for roughened and squared groove surfaces are much higher. In the case of R-12, a roughened surface gives the best evaporating coefficient. In the case of all the tested fluids, a triangular grooved surface gives poor evaporating coefficient.
When choosing a fluid, both the evaporating coefficient and the overall thermal conductance must be considered. In this case, when using a squared groove or a roughened surface, R-22 will give better overall heat transfer coefficient at high operating pressures while Acetone and R-11 will be superior at low pressures.
4.The comparison of the experimental data with the equation of Cosarosa et al. {41}, showed that wick configuration and the thermophysical properties of the heat pipes working fluid are highly pertinent to the performance of the gravity-assisted heat pipes.