Computer modeling of the vapour vortex orientation changes in the short low- temperature heat pipes

Abstract

The results of computer studies of the vortex formation and orientation changes inside short heat pipes (HP’s) with profiled vapour channel in the Laval–liked nozzle form are presented. For the first time it was found that the vapour vortex of moist compressible vapour flow in the cooled part of vapour channel changes its rotational motion direction. The rotation direction of the toroidal vapour vortex is dependent on the heat power value, entering to the HP’s evaporator. With low heat power loads (a small temperature head) the rotational direction of the circular toroidal vapour vortex due to the Coanda effect and sticking moving vapour jets to the channel’s walls occurs from the periphery to the longitudinal axis of the vapour channel. While the heat power loads increasing, the direction of the toroidal vapour vortex ring rotation changes to the opposite, from the longitudinal axis to the periphery of the vapour channel. The thickness of the formed working fluid condensate film located under the toroidal vapour vortex also related to the evaporator heat power load and vapour vortex rotation direction. With weak temperature head, the vapour vortex rotates from the walls to the channel center and slow down the movement condensate film on the HP’s top cover surface to the capillary-porous insert, thereby increasing the effective film thickness. As the heat head increases, the vapour vortex rotation direction changes to the opposite one and direction of vapour flow and the liquid condensate film becomes the same, which leads to decrease in the effective film thickness. Experimental results of the condensate film thickness measurements, obtained with capacitive sensors show a sharp decrease in thickness with a temperature head increasing, what could be an indirect confirmation of the vapour vortex rotation direction changes. Numerical method for vapour turbulent flows based on Navier-Stokes (Reynolds) full equation system was used to calculate the moist vapour vortex flow in low-temperature HP’s.