Effect of wick oxidation on the thermal performance of a copper-acetone loop heat pipe. (5th January 2022)

• Record Type: Journal Article
• Authors: Kumar, Prem; Gachake, Mayur; Khandekar, Sameer
• Is Part Of: Applied thermal engineering. Volume 200(2022)
• Publication Date: 2022-01-05
• Subjects: Loop heat pipe -- Thermal performance -- Heat pipe wick -- Wick oxidation -- Heat leak; Heat engineering -- Periodicals; Heating -- Equipment and supplies -- Periodicals; Periodicals; 621.40205
• DOI: 10.1016/j.applthermaleng.2021.117627
• Languages: English
• ISSNs: 1359-4311

Abstract

Highlights: High heat leak from evaporator to compensation chamber adversely affects LHP performance. High thermal conductivity of pure copper wicks leads to high heat leak. Oxidation of pure copper wick is used as a new approach to reduce the heat leak. Effect of fluid (acetone) charging ratio and wick oxidation on LHP performance is investigated. Wick oxidation reduces thermal conductivity and doubles the heat transporting capacity of LHP. Abstract: Loop Heat Pipe (LHP) is a passive phase-change heat transfer device. Among other factors, its performance largely depends on the heat leak from the evaporator to the compensation chamber (CC). For copper wick LHP, a high heat leak creates a problem in successful LHP start-up and can adversely affect its operation. The present study focuses on reducing the heat leak through manipulation of the copper wick properties. The effect of fluid charging, overall pressure drop, and wick oxidation on thermal performance is investigated. A cylindrical copper-acetone LHP is tested in favorable orientation for two cases with (1) oxygen-free, or pure copper wick and (2) oxidized copper wick in its evaporator. For Case #1, LHP is filled with acetone at different Charging Ratios (CR) of 50%, 60%, and 70%. For Case #2, the charging ratio is kept constant at 50%. For the pure copper wick, a charging ratio of 50% provides the best thermal performance, and it decreases with an increase in charging ratios. At CR = 50%, LHP can transfer a heat load of 90 W ( h Evp = ∼900 W/m 2 K) and 180 W ( h Evp = ∼2500 W/m 2 K) at the evaporator temperature below 100 °C for the pure copper and oxidized wick, respectively. The significant improvement in LHP thermal performance of the latter is attributed to a decrease in heat leak because of the low thermal conductivity of the oxidized porous wick. The heat leak for pure and oxidized wick is found ∼18% and ∼7% of input heat loads, respectively. This can be an effective methodology to pave the way for the usage of commercial copper-based LHPs for the thermal management of terrestrial devices.