Heat transfer characteristics of a novel closed-loop pulsating heat pipe with a check valve

A spring-loaded check valve controlling the one-way circulatory flow of the working fluid was integrated into an initial closed-loop pulsating heat pipe (CLPHP) to improve the thermal performance. The thermal performance of the CLPHP with a spring-loaded check valve (CLPHP/CV) was experimentally investigated and compared to the initial CLPHP. The initial CLPHP was made of a copper capillary tube with an inner diameter of 3 mm and ten spiral loops. The spring-loaded check valve was integrated into two locations in the initial CLPHP: between the two heating (CLPHP/CVh) sections and the two cooling (CLPHP/CVc) sections. Tests were conducted under three orientations: bottom, horizontal, and top heating modes. The CLPHP was charged with deionized water as the working fluid with a filling ratio of 60% by volume. The experimental results show that the check valve creates a one-way circulatory flow of the working fluid and facilitates the start-up of the CLPHP. A 25% decrease in thermal resistance of the CLPHP/CV is achieved compared with the initial CLPHP under top heating mode at a low heating load. Moreover, the check valve decreases the sensitivity of the CLPHP to its orientation, particularly when the check valve is integrated between the two heating sections.