Nucleate boiling in a flat grooved heat pipe

The present paper is devoted to an experimental study aiming at determining the thermal behavior of a flat plate heat pipe (FPHP) with micro grooves and at focusing especially on the effect of boiling in the grooves. The FPHP is hermetically sealed on its upper face with a transparent plate for observations. Experimental results obtained with methanol are presented. Nucleate boiling in the grooves is observed for relatively small heat fluxes (3 W cm−2). The presence of nucleate boiling in the grooves improves the thermal performance of the flat heat pipe, and it must be emphasized that it does not constitute an operation limit as it is generally stated. The dry out of the evaporator is observed for heat fluxes much higher than the heat flux of onset of nucleate boiling. The results obtained for different filling ratios show the influence of this parameter that has to be optimized to improve the performance of the device.