Experimental investigation of the effects of inclinations and wicks on the thermal behavior of heat pipes for improved thermal applications

Abstract

Given the highly complex thermo-hydrodynamic features in heat pipes (HPs) but the inevitable need for efficient thermal solutions, this study investigated the effects of various wick types on the time-dependent thermal behavior of HPs. The results revealed that varying the cooling conditions and wick types in parallel is necessary for peak performance. Appropriate cooling lengths and temperatures improve the thermal limits of HPs with low-performing wicks. The composite wicks prompted faster steady performance, smooth startup, and low instabilities. Heat increment from 25 to 200 W decreased the thermal resistance from 1.75 to 0.05 °C/W. The HPs with homogeneous wicks have higher thermal resistance than those with composite wicks. Increased cooling lengths improve the performance of the former HPs. Inclining the HPs at angles relative to the horizontal position improves the HPs' thermal limits. The composite wicks minimized the effects of inclinations on the HPs’ performance. The HPs with composite multi-layered wicks presented transient profiles typical of first-order systems, whereas homogenous multi-layered wicks have complex responses upon step heat input. The transient profiles offer great insight into the instability inside the HPs. This study may guide future optimization analysis in selecting the best HPs and wicks for improved thermal management.

Keywords

• Heat pipes performance
• Homogenous wicks
• Composite wicks
• Heat pipes inclination
• Phase change heat transfer
• Heating and cooling length