Effect of small inclination angle on heat transfer performance of Ω-grooved bending heat pipe

Abstract

Grooved bending heat pipe may operate at small inclination angle caused by practical installation errors. Previous researches mainly focused on large inclination angles of straight heat pipes, but fewer experiments were conducted at small inclination angle of bending heat pipe where liquid accumulation and gravity effect on liquid-vapor transport varies along the pipe. This paper experimentally studied the effect of small inclination angle (±3°) on heat transfer of aluminum-ammonia Ω-grooved bending heat pipe with total length of 650mm, vapor chamber diameter of 4mm and grooved wick diameter of 1.24mm. The results showed that small inclination angle significantly affect the heat transfer performance of bending heat pipe with heat transfer limit changed by 9 times form 20W to 180W and thermal resistance changed by 8 times from 0.04 K/W to 0.32 K/W. Effect of negative and positive angles in bending heat pipe is complex than that in straight heat pipe. Positive condensation end inclination enhances heat transfer due to gravity-driven liquid reflux. Negative condensation end inclination inhibits heat transfer due to anti-gravity reflux and liquid accumulation suppressing gas condensation. Positive evaporation end inclination weakens heat transfer due to anti-gravity reflux. Negative evaporation end inclination also weakens heat transfer due to thick liquid film, increasing thermal resistance and potentially blocking vapor channels. Attributed to coupling effect of liquid accumulation at bending section and capillary force dominant at tiny incline, maximum heat transfer limit of 180 W is achieved at both end inclination of -0.5°.