Investigations on Transient and Steady-State Performance of a Micro Heat Pipe

Abstract

A numerical study is presented of the vapor and liquid e ow in a micro heat pipe with triangular channels, utilizing water as the working medium. The governing equations are derived taking into account the variation in the e ow cross-sectional areas of the vapor and liquid phases and incorporating the phase change during the process. The velocity, pressure, and temperature distributions in the vapor and liquid, in the transient and steady states, are obtained from the analysis. The effective thermal conductivity of the micro heat pipe is calculated, and its dependence on the heat input and the heat transfer coefe cient at the condenser section is investigated. The results of the analysis are compared with those available in literature and discussed in the light of the assumptions made and the extensions incorporated in the present model. Nomenclature Ac = area of cross section of the heat-pipe channel, m 2 Cl = specie c heat of the liquid, J/kg K Cv = specie c heat at constant volume of the vapor, J/kg K DH = hydraulic mean diameter of the channel, m d = one side of the triangular channel, m El = total energy of the liquid per unit volume, q l(ClT + 1 u 2 ), J/m 3 Ev = total energy of the vapor per unit volume, q v(CvT + 1 u 2), J/m 3 f = friction coefe cient h fg = latent heat of vaporization, J/kg h0 = heat transfer coefe cient at the condenser, W/m 2 K k