Thermally-Induced Oscillatory Flow and Heat Transfer in a U-Shaped Minichannel

Abstract

Thermally-induced oscillatory flow and heat transfer in a U-shaped minichannel – a building block of an Oscillating Heat Pipe (OHP) – is modeled by analyzing evaporation and condensation in the heating and cooling sections, effect of axial variation of surface temperature on sensible heat transfer between the liquid slug and the minichannel wall, as well as pressure loss at the bend. The oscillatory flow of the liquid slug is driven by variations of pressures of the vapor plug due to evaporation and condensation. The sensible heat transfer coefficient between the liquid slug and the minichannel wall are obtained by analytical solution for laminar liquid flow and by empirical correlations for turbulent liquid flow. The effects of the initial temperature and pressure loss at bend on the heat transfer performance are thoroughly investigated. Nomenclature 2 m p c = specific heat at constant pressure, J/kg-K v c = specific heat at constant volume, J/kg-K d = diameter of the miniature channel, m n G = constant lv h = Latent heat of vaporization, J/kg e h = evaporation heat transfer coefficient, 2 W/m -K c h = condensation heat transfer coefficient, 2 W/m -K k = thermal conductivity, W/m-K K = loss coefficient L = length, m m = mass of vapor plugs, kg m� = mass flow rate, kg/s Nu = Nusselt number p = vapor pressure, Pa R = gas constant, J/kg-K t = time, s T = temperature, K p v = velocity of the liquid plug, m/s p x = displacement of the liquid plug, m