Evaporation Heat Transfer Coefficient in a Capillary Pumped Loop and Loop Heat Pipe for Different Working Fluids

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

“…Because the heat transfer in the pore of the wick structure will depend on Q mic , it is expected that the evaporative heat transfer coefficient in an LHP evaporator will also depend on the working fluid heat pipe figure of merit. This appears to justify the assertion in [1] that the heat transfer coefficient of an LHP depends on the working fluid figure of merit. The left-hand side of Eq.…”

“…The evaporative heat transfer coefficient between the casing and wick is the primary parameter that dictates the size of the evaporator. 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].…”

“…The heat transfer coefficient of ammonia is an order of magnitude higher than for R-11. Adoni et al [1,23] obtain experimental heat transfer coefficients from a CPL and an LHP for various working fluids, namely, ammonia, R-134A, and acetone. From a qualitative analysis of the data, they infer that a working fluids' heat transfer coefficient appears to be related to the CPL figure of merit (ρ v σh 1.75 fg ∕μ 0.25 v ) [35].…”

Comparative study of two loop heat pipes using R134a as the working fluid

“…[ [29][30] experimentally investigated a LHP using R134a as the working fluid. The evaporator wick was made of ultra-high molecular weight (UHMW) polyethylene.…”