Comparison between a heat pipe and a thermosyphon performance with variable evaporator length

Abstract EN

Heat pipes and two phase thermosyphons are heat transfer devices whose operating principles are based on the evaporation/condensation of a working fluid using the capillary pumping forces (in the case of heat pipe) and gravity forces (in the case of two phase thermosyphons) to ensure the fluid circulation.

The two systems were designed and constructed to investigate the performance and the affecting parameters, using ethanol as a working fluid.

The affecting parameters which were studied are power input (200≤Q≤700) W, working fluid filling ratios (35% and 85%) and aspect ratio, the ratio of evaporator length to inner diameter, (4.0, 7.8 and11.5) .

The experimental results showed that the best performance of heat pipe obtained at aspect ratio (7.8) and (85%) filling ratio at (500) W where the maximum heat transfer coefficient was (9950) W/m2.oC, while for the two phase thermosyphon the best performance was obtained at aspect ratio (4.0) for (35%) filling ratio and power input (600) W with maximum heat transfer coefficient equals to(4590) W/m2.oC.

The overall comparison between the two systems showed that the performance of the heat pipe is better than that of the two phase thermosyphon.

The experimental results of heat pipe was compared with theoretical and empirical correlations showing reasonable agreement especially with immura with percent 70%.