Analytical Model for Characterization of Loop Heat Pipes

Abstract

The present paper proposes general equations for predicting the steady-state behavior of a loop heat pipe, linking its operating temperature to various fluidic and geometrical parameters. The closed-form solutions determined for various loop-heat-pipe operatingmodes are deduced from the equations of a previously developed numerical model. This new approach of the loop-heat-pipe modeling facilitates the identification of the physical mechanisms that influence its operating behavior. In addition, the transition heat flux between variable and fixed conductance modes can also be estimated. This simplified model has been validated for each loop-heat-pipe operating mode for various geometries and operating conditions. The present model could be a useful tool for the design of loop heat pipes. Nomenclature A = cross-sectional area cp = specific heat D = diameter e = thickness f = friction factor g = gravitational acceleration h = convective heat transfer coefficient hC = condensation heat transfer coefficient K = overall heat transfer coefficient or permeability k = thermal conductivity L = length lv = latent heat of vaporization _m = mass flow rate P = pressure Q = heat transfer rate R = thermal resistance Rp = pore radius Re = Reynolds number S = heat exchange surface area T = temperature!H = relative elevation! = wetting angle " = dynamic viscosity # = density $ = surface tension Subscripts A = ambient C = condenser or condensation E = evaporator eff = effective exp = experimental i = input or inlet or inner L = liquid line l = liquid max = maximum model = simulated by the model o = output or outlet or outer R = reservoir sink = heat sink sat = saturation sub = subcooled zone t = total trans = transition V = vapor line v = vapor w = wick wall = wall 2 ’ = two phase I.