Study of a new heat pipe utilizing electrowetting technique

Abstract

Heat pipe consists of a sealed container, a working fluid, and a wick, and is divided into three parts: an evaporating section, an insulating section, and a condensing section. It is a heat transport device used to dissipate and cool heat by utilizing latent heat during evaporation and condensation of the working fluid enclosed in the sealed container. However, large increase in heat input causes dryout near the evaporation zone of the heat pipe, which results in that the heat transport ability is lost due to the stagnation of the fluid inside because it does not return to the evaporation zone by capillary force of the wick. The authors are developing a new heat pipe using electrowetting(EW) technique to suppress dryout. EW is a process in which a droplet of liquid is placed on an electrode and the associated dielectric layer, and an electric voltage is applied to the electrode. The contact angle between the droplet and the dielectric layer is changed by applying a voltage. This technique promotes the flow of the working fluid and suppresses dryout by changing the contact angle of the fluid. However, the authors have not found a clear condition under which dryout surely occurs. Therefore, they attempted to investigate the conditions under which dryout occurs and the suppressing effect of EW on dryout by examining the internal pressure and temperature of a newly developed heat pipe. Therefore, by examining the internal pressure and temperature of the newly developed heat pipe, we sought conditions under which dryout occurs and confirmed that EW can improve the cooling capacity of the heat pipe.