Numerical Study on Start-up Characteristics of Oscillating Heat Pipes with Check Valves

An oscillating heat pipe (OHP) is a two-phase heat transfer device using self-existed oscillation. An OHP consists of a bended capillary tube with a heating section at one side and a cooling section at the other. Because of the capillary force, the working fluid is distributed as vapor plugs and liquid slugs in the tube. As heat is applied to the heating section, the working fluid is driven by the pressure difference between each channel. In the OHP, heat is transported by the oscillation and/or circulation of liquid slugs and vapor plugs which go back and forward between the heating section and cooling section by a combination of sensible and latent heat transfer. Experimental studies have shown that the OHP has a higher thermal performance than conventional heat pipes. It has also shown that oscillating heat pipe with check valves (CVOHP) has much higher heat transfer capability than OHP without check valves. In the CVOHP, check valves regulate the flow direction, and the oscillatory amplitude of the waves is increased. For that reason, the local dry-out phenomenon is prevented in CVOHPs, and heat transfer efficiency becomes higher than the OHP. Because of its high performance and simple structure, CVOHP is attractive for a thermal control system for spacecraft. However, the experimental study shows that there is a considerable difference in the resistance between individual check valves, and estimating the value of resistance is difficult because the configuration of check valves is complicated. Furthermore, it is suggested that the start-up characteristics of the OHP changes by the different configuration/flow resistance of the check valve. This paper describes the start-up characteristics of CVOHPs using numerical simulation.