Electrowetting Heat Pipes for Heat Transport Over Extended Distances

Abstract

The heat transport capacity of the conventional heat pipes over extended distances is limited by the maximum condensate flow that their wicks can sustain. This paper introduces and analyzes a new planar heat pipe technology, which can transport ultrahigh heat loads (>1 kW) over extended distances (>1 m). The concept of an electrowetting heat pipe (EHP) is based on replacing the adiabatic wick section of a conventional heat pipe with EW-based pumping. EW is a well-developed fluid handling technique to carry out various microfluidic operations, such as droplet pumping, and is based on the electrical modulation of surface tension. The EHP relies on EW pumping of the condensate to the evaporator in the form of discrete droplets. EHPs are not subject to the capillary limit on heat transport capacity. The first-order models predict that EHPs with a cross section footprint of 10 cm $\times 4$ mm (width $\times $ thickness) can transport 1.5 kW over extended distances (>1 m) using water as the working fluid. Other benefits include ultralow power consumption (microwatts), opportunities for active control of heat pipes, selection of a wide range of working fluids, and the absence of moving parts. The heat transport capacity and the thermal resistance of an EHP are compared with four other devices of similar dimensions: 1) a sintered powder heat pipe; 2) an axial groove heat pipe; 3) a loop heat pipe; and 4) a thermosyphon. The EHP can transport more than twice the maximum heat capacity of other devices while offering a low thermal resistance of 0.01 K/W. Thus, EW is an enabling technology for the development of long, high-capacity heat pipes.