Evaporation-Induced Shear Stress-Driven Heat Pipes.
- Heat pipes are used extensively in the thermal management of electronics, due to their ability to transport large amounts of heat efficiently over long distances. However, heat pipe performance is limited by the rate at which its wick can return liquid to the evaporator and by the thermal conductivity of its wick. Our proposed silicon heat pipe design utilizes a super-hydrophobic nanosurface (SNS)... read morein the evaporator which takes advantage of surface tension forces in order to suspend water on micron scale ridges, creating vapor microchannels beneath the liquid. Thus heat input beneath the SNS conducts through the heat pipe base, into the SNS ridges, and drives evaporation at the liquid-vapor interface. A pressure gradient develops as vapor evaporates, forcing the vapor to flow through the microchannels. This flow of vapor is directed in order to exert a driving shear stress on the liquid above it. Thus, an evaporation-induced shear stress replaces the capillary pressure generated by a wick in a typical heat pipe for the purpose of pumping liquid. Thus, the device is named an evaporation-induced shear stress-driven heat pipe, or ESHP. This shear stress scales with the heat flux, virtually eliminating the dependence of the capillary limit on heat flux. Moreover, the sub-millimeter thick evaporator and condenser lead to small thermal resistances, and gravity has a negligible affect on performance on ESHP performance do a bidirectional fluid flow. In this thesis, an evaporation induced shear stress heat pipe design is proposed, a first order model is used to illustrate the benefits, and analytical and numerical methods are used to investigate fluid flow and heat transfer in the evaporator.read less