Design, Manufacturing, and Characterization of Copper Capillary Structures for Loop Heat Pipes

Abstract

Mono and bi-layer capillary structures are designed by means of a thermo-hydraulic model of a loop heat pipe in order to optimize the performance of the system. The model tends to show that bi-layer wicks with a thermally conducting bottom layer and an insulating top layer are the most efficient in loop heat pipes. An experimental study is then led to manufacture and characterize the bottom layer. Eight samples made of copper powder are manufactured following a twolevel fractional factorial design. The top layer is not manufactured in this study. The sintering parameters are adjusted to provide porous samples with sufficient mechanical resistance. The porous structure permeability and its capacity to provide a sufficient capillary pressure are evaluated using a specific test bench dedicated to this study, as well as with microstructural observations (tomography, microscopy). The experimental characterization of the samples enables to determine the influence of each sintering parameter as well as the interactions between them. The characteristics of the porous samples are found to be mainly affected by the sintering time and the pressure. High values of these parameters decrease the permeability and the porosity but increase the maximum capillary pressure due to a smaller effective pore radius. A set of optimum sintering parameters is found in order to manufacture the bottom layer. The best porous structure is supposed to enhance the latent heat transfer in a LHP.