Optimization of the sintering parameters of a biporous copper-nickel composite wick for loop heat pipes

Abstract

This work deals with a multi-faceted objective of decreasing the heat leak to the compensation chamber (CC)/ reservoir of a Loop Heat Pipe (LHP) and simultaneously to utilize this heat to vaporize the liquid in contact with the evaporator by optimizing the fabricating parameters of the wick. In this study, the wick consists of three layers of equal thickness with different compositions of Nickel and Copper with naphthalene added as pore former (30% volume). The various parameters studied are sintering temperature (range of 700–800 °C), and composition gradient across different layers. The effect of these parameters on the wick properties – thermal diffusivity, porosity, permeability, pore radius and evaporation rate were studied. Five wicks with different composition gradient were cold-press sintered at 700 °C, 750 °C and 800 °C for 90 min in an inert atmosphere. The permeability of the wicks were determined using falling head permeater and an optimum value of permeability of 1.305 × 10-12 m2 was obtained for a sample of 36.4% mass of Cu. The porosity of the wicks were measured using the Archimede’s principle and the aforementioned wick has a porosity of 44.7% which was found to possess the lowest thermal diffusivity and subsequently highest evaporation rate.