Performance comparison of electrowetting heat pipe for extended distance heat transport

Abstract

Heat pipes are effective heat transport devices, due to their low thermal resistance, passive nature and high reliability. However, the heat transport capacity of conventional heat pipes over extended distances is limited by the maximum condensate flow that their wicks can sustain. The capillary pressure induced by small wick pores drives fluid flow, but viscous losses dominate at long distances and prevent the expected heat pipe operation. We propose a novel planar heat pipe technology that replaces the adiabatic wick section of a conventional heat pipe with electrowetting-based pumping, enabling ultra high heat dissipation (> 1 kW) over extended distances (> 1 meter). Electrowetting is a well-developed fluid handling technique based on electrical modulation of surface tension. The concept of an electrowetting heat pipe (EHP) uses electrowetting pumping of condensate to the evaporator in the form of discrete droplets. This pumping force does not lessen with distance; therefore, EHPs are not subjected to the capillary limit at extended lengths. First-order models predict that EHPs 10 cm wide by 4 mm thick can transport 1.5 kW over 1 meter. In a previous study, it was shown that the EHP can transport more than twice the heat capacity of either a loop heat pipe or a thermosyphon of similar dimensions while still offering a low thermal resistance of 0.01 K/W. In this work, we compare the EHP with actively pumped single-phase and two-phase microchannel systems of equivalent cooling capacity. We show that the EHP requires less pumping power than a single-phase system by two orders of magnitude. Furthermore the EHP offers half the thermal resistance of a two-phase system at a lower pumping power.