Ceramic Canisters for Lithium Fluoride Thermal Storage Integrated with Solar Dynamic Space Power Systems.

Abstract

LIF is one of the most suitable thermal energy storage (TES) materials for space applications because of its high heat of fusion of approx. 1044 kJ/kg at a melting temperature of 848 degrees centigrade. The high corrosivity and the large volume change during melting/freezing of approx. 22 % cause problems with metallic canisters. Enforcement of the canisters leads to a disadvantageous phase change material/containment (PCM/CTM) ratio besides the high costs of machining. A containment made of graphite was developed which cannot suffer from corrosion because it is not wetted by molten LIF. In order to match the forces caused by the volume change, a dV mechanism was integrated into the wall through which heat transfer takes place. The volume compensation is based on the capillary depression which experiences LiF due to the nonwettability of graphite by the liquid in a channel-like structure. Tests of the volume compensation which was developed exclusively for space application, showed promising results under gravity conditions. A problem of graphite is its open porosity through which gaseous LiF can permeate, leading to a significant loss of PCM with time. Preliminary tests with coatings on the outer walls of the containers have been carried out with encourageing results.