Fractal Loop Heat Pipe Performance Comparisons of a Soda Lime Glass and Compressed Carbon Foam Wick

Abstract

This study compares heat flux performance of a Loop Heat Pipe (LHP) wick structure fabricated from compressed carbon foam with that of a wick structure fabricated from sintered soda lime glass. Each wick was used in an LHP containing a fractal based evaporator. The Fractal Loop Heat Pipe (FLHP) was designed and manufactured by Mikros Manufacturing Inc. The compressed carbon foam wick structure was manufactured by ERG Aerospace Inc., and machined to specifications comparable to that of the initial soda lime glass wick structure. Machining of the compressed foam as well as performance testing was conducted at the United States Naval Academy. Performance testing with the sintered soda lime glass wick structures was conducted at NASA Goddard Space Flight Center. Heat input for both wick structures was supplied via cartridge heaters mounted in a copper block. The copper heater block was placed in contact with the FLHP evaporator which had a circular cross-sectional area of 0.88 cm 2 . Twice distilled, deionized water was used as the working fluid in both sets of experiments. Thermal performance data was obtained for three different Condenser/Subcooler temperatures under degassed conditions. Both wicks demonstrated comparable heat flux performance with a maximum of 76 W/cm 2 observed for the soda lime glass wick and 75 W/cm 2 for the compressed Carbon foam wick. Nomenclature Area= area (cm 2 ) P = pressure (kPa) T = temperature (°C) TC = thermocouple TM = thermistor δ = error ∆ = difference k = thermal conductivity (W/m-K) h fg = enthalpy of vaporization (kJ/kg) q ɺ ′ ′ = heat flux per unit area(W/cm 2 ) q ɺ ′ ′ δ = uncertainty (W/cm 2 ) ܴ" = Thermal resistance (°C/W/cm 2 ) x = thermocouple distance (mm) Subscripts cond,avg = condenser average int = heat flux probe/evaporator interface k = conductivity sat = saturation surf = surface 1 Senior Principle Engineer/Scientist, KDM Systems Inc., AIAA Senior Member 2 Branch Head, Cryogenics and Fluids, Code 552.0, AIAA Member Downloaded by CORNELL UNIVERSITY on July 31, 2015 | http://arc.aiaa.org |