Thermohydraulic Modeling of Capillary Pumped Loop and Loop Heat Pipe

Abstract

Capillary pumped loop (CPL) and loop heat pipe (LHP) are passive heat transport devices that are gaining importance as a part of the thermal control system of modern high power spacecraft. A mathematical model to simulate the thermohydraulic performance of CPLs and LHPs is required for the design of such a thermal control system. In this study a unified mathematical model to estimate thermal and hydraulic performance of a CPL and an LHP with a two-phase or a hard-filled reservoir is presented. The steady-state model is based on conservation of energy and mass in the system. Heat exchange between the loop and the surroundings and pressure drops in the loop are calculated. This study presents the results of numerical studies on a CPL and an LHP. The constant conductance regime in a CPL or an LHP occurs when the reservoir is hard-filled. It also occurs in an LHP if the condenser is fully used. The heat leak across the wick becomes significant in a hard-filled LHP because the core is no longer saturated and hence the mass flow rate must be calculated using an energy balance on the outer surface of the wick. Nomenclatureenergy imbalance in the evaporator core and CC, W f = Darcy friction factor G = mass velocity, kg m 2 s 1 H = heat transfer coefficient, W m 2 K 1 h = enthalpy, J kg 1 K = wick permeability, m 2 k = thermal conductivity, W m 1 K 1 L = length, m L cond = length of condenser, m L condensation = length of condensation, m L evap-rt = distance between points 7 and 4, m L rt-hydr = vertical distance between loop and the reservoir, m L step = refers to step size in RKM, m M = mass of working fluid, kg _ m = mass flow rate, kg s 1 P = pressure, Pa Q = heat, W Q deprime = heat load at which CPL deprimes for limited condenser length, W Q hf = heat load at which reservoir is hard-filled, W Q open = heat load at which condenser fully opens, W r = radius, m T = temperature, K t = thickness, m U = overall heat transfer coefficient, W m 2 K 1 u = velocity, m s 1 V = volume, m 3 x = dryness fraction of vapor z = length, m v = void fraction, A v =A = volume fraction of liquid in the reservoir = perimeter, m = porosity " = numerical error (convergence criterion) # = normalized energy imbalance = conductance, W K 1 = density, kg m 3 = surface tension, N m 1 = two-phase friction multiplier Subscripts acc = acceleration c = core cond = condenser cond 0 = refers to region where condensation is occurring e = effective evap = evaporator ex = exchange f = friction fg = difference in thermodynamic property in liquid and vapor phase g = groove i = inner part of tube ins = insulation L = leak l = liquid ll = liquid line lo = liquid only load = refers to heat load applied externally loop = part of the system excluding the reservoir o = outer part of tube P = pressure r = reservoir/radial res = reservoir sc = subcooler sink = sink of condenser t = tube/evaporator teeth tp = two-phase v = vapor/(volume in case of specific heat) vl = vapor line vo = vapor only w = wick wp = wick pore ws = particle diameter in sintering z = length dir...

Investigation of power battery thermal management by using mini-channel cold plate

“…Based on the large amount of liquid latent heat of vaporization, the use of heat pipes for BTM allows for a significant reduction in battery operating temperature [9,[20][21][22]. Greco et al [23] proposed a simplified thermal network based on the heat transfer principle associated with the use of heat pipes, with which a one-dimensional computational model was developed.…”

Design optimization of a loop heat pipe to cool a lithium ion battery onboard a military aircraft

“…vg H is the forced convection heat transfer coefficient. The present studies are compared with the previous results of Adoni et al [12], Chung [16] and Kaya [3]. The prediction for Adoni's result is computed by Thome's correlation [14].…”

“…as shown in Fig.1. Assumptions and mathematical models refer to Adoni [12]. For energy balance, the energy relation is expressed as Eq.…”

“…First, to verify usefulness of the optimization process, Adoni's LHP [12] is optimized with respect to 4 design variables as shown in Table 2.…”

Effect of Heat Pipe Figure of Merit on an Evaporating Thin Film

“…The evaporative heat transfer coefficient is influenced by the following factors [1]: 1) the thermal resistance from the evaporator wall to the liquid-vapor interface, 2) the wick structure characteristics (geometry, thermal conductivity, and permeability), 3) the working fluid transport properties, 4) the location of meniscus in the wick at various imposed heat fluxes, and 5) the inlet temperature to the evaporator. The heat transfer and fluid flow in these devices are analyzed at different scales: 1) the microscale, which encompasses the extended evaporating meniscus thin-film region [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]; 2) the pore scale, which encompasses the bulk meniscus region with a comprehensive model of the evaporating thin film and intrinsic bulk meniscus [17][18][19][20][21]; 3) the wick scale, which encompasses the entire porous medium [1,[22][23][24][25][26][27][28][29][30][31][32][33][34]; and 4) the system scale, which encompasses the whole loop [35][36][37][38]. In this paper, the effect of working fluid properties on evaporative heat transfer at the microscale is examined.…”