Steady State Model of a Loop Heat Pipe (LHP) With Coherent Porous Silicon (CPS) Wick in the Evaporator

A theoretical study is conducted to explore the effect of different parameters on the performance of a Loop Heat Pipe (LHP). These parameters are evaporator temperature, condenser temperature, total mass charge, the tube size of piping system, and pumping distance between evaporator and condenser. This paper pres ents a steady state model that describes the thermodynamics, heat transfer, and fluid mechanics inside an LHP. A LHP is a two-phase device with extremely high effective thermal conductivity that utilizes the thermodynamic pressure difference that developed between the evaporator and condenser to circulate a working fluid through a closed loop. The loop heat pipe efficiently transports the heat generated by a highly localized concentrated heat source and discharges this heat to a convenient sink. The steady state LHP model is described by the conservation equations, thermodynamic relations, and capillary and nucleate boiling limits. The loop heat pipe cycle is presented on a temperature-entropy diagram. A relationship is developed to predict the ratio of the heat of evaporation to the heat leaked to the compensation chamber. This work predicts the size of a LHP, the pumping distance, and the maximum power that can be dissipated for a fixed source temperature. Nomenclature A Wick cross sectional area, m Cp Thermal capacity of the liquid CPL Capillary pumped loop CPS Coherent Porous Silicon h Enthalpy, KJ/kg cc h Compensation chamber convection coefficient k Thermal conductivity, W/m.K l Tube length L Wick thickness, m LHP Loop heat pipe m& Mass flow rate, kg/s M Total mass charge P Pressure, Pa Q Heat load, W R Tube radius, m r Pore radius, m T Temperature, K v Specific volume, m/kg V Volume, m Greek symbols ε Porosity θ Vapor-liquid interface contact angle β Volumetric ration,