Characterization of microfluidic operations underlying an electrowetting heat pipe

The heat transport capacity of heat pipes is limited by the capillary pressure generated in the wick that pumps the condensate. The current authors recently proposed a novel heat pipe architecture, in which the wick is replaced by electrowetting (EW)-based pumping in the adiabatic section. An electrowetting heat pipe (EHP) overcomes the capillary limit in heat pipes and can enable compact, ultralow power consumption heat pipes, to transport kiloWatt heat loads over long distances. This work studies the microfluidic operations that are the basis of the EHP. Experiments are conducted to estimate the maximum channel gap which sustains reliable EW pumping. This is an important consideration, since the heat transport capacity scales linearly with the channel gap. Experiments are also conducted to estimate the maximum channel gap at which EW voltages can split droplets. This is important to ensure EHP operability in the event of droplet merging. Experiments are also conducted to demonstrate EW-induced droplet generation from an open-air reservoir. This mimics the interface between the condenser and adiabatic sections. All these experiments are conducted on devices manufactured by a novel and scalable manufacturing technique. The results suggest that planar EHPs (water-based) with a 10 cm by 4 mm cross section can transport 1.6 kW over 1 meter long distances, with a thermal resistance of 0.01 K/W.