An Experimental Attempt to Improve Start-up Characteristics of Oscillating Heat Pipe with Check Valves

An oscillating heat pipe consists of a meandering capillary tube and working fluid in it. It has high heat transport capability due to the use of both sensible and latent heat and has an advantage of simple structure. Moreover, it enables heat transfer from narrow space, compared to the conventional heat pipes with wicks or grooves. Therefore, an OHP is one of the desired thermal control devices for future space spacecraft with larger heat dissipation. We have developed an OHP with check valves (CVOHP) for space application. The check valves make the fluid flow one-directional rather than oscillatory, resulting in the enhancement of the effective thermal conductivity and operational limit of the CVOHP. The on-orbit experiment of the CVOHP was conducted from 2012 to 2016 as one of the missions of Small Demonstration Satellite-4 (SDS-4) by JAXA. The CVOHP had successfully operated on orbit for four years without any degradation of heat transfer performance, however, the start-up difficulty was observed under the certain initial conditions. The most severe initial condition for start-up is the liquid-vapor distribution where most of the liquid localizes in the cooling section of the CVOHP. There are two approaches to improve the start-up characteristics; one is to prevent the liquid localization, the other is to make the CVOHP start up at any initial liquid-vapor distributions. This paper describes the experimental attempt to improve of the start-up characteristics.