Validation of a CFD model simulating charge and discharge of a small heat storage test module based on a sodium acetate water mixture

AbstractExperimental and theoretical investigations are carried out to study the heating of a 302 x 302 x 55mm test box of steel containing a sodium acetate water mixture. A thermostatic bath has been set up to control the charging and discharging of the steel box. The charging and discharging has been investigated experimentally by measuring surface temperatures of the box as well as the internal temperature of the sodium acetate water mixture through a probe located in the center of the steel box. The temperature developments on the outer surfaces of the steel box are used as input parameters for a Computational Fluid Dynamics (CFD) model. The CFD calculated temperatures are compared to measured temperatures internally in the box to validate the CFD model. Four cases are investigated; heating the test module with the sodium acetate water mixture in solid phase from ambient temperature to 52oC; heating the module starting with the salt water mixture in liquid phase from 72oC to 95oC; heating up the module from ambient temperature with the salt water mixture in solid phase, going through melting, ending in liquid phase at 78oC/82oC; and discharging the test module from liquid phase at 82oC, going through the crystallization, ending at ambient temperature with the sodium acetate water mixture in solid phase. Comparisons have shown reasonable good agreement between experimental measurements and theoretical simulation results for the investigated scenarios

Laboratory Test of a Cylindrical Heat Storage Module with Water and Sodium Acetate Trihydrate

AbstractCylindrical heat storage modules with internal heat exchangers have been tested in a laboratory. The modules were filled with water and sodium acetate trihydrate with additives. The testing focused on the heat content of the storage material and the heat exchange capacity rate during charge of the module. For the tests with the phase change materials, the focus was furthermore on the stability of supercooling and cycling stability. Testing the module with sodium acetate trihydrate and 6.4% extra water showed that phase separation increased and the heat released after solidification of supercooled phase change material was reduced over 17 test cycles. The heat released after solidification of the supercooled sodium acetate trihydrate with thickening agent and graphite was stable over the test cycles. Stable supercooling was obtained in 7 out of 17 test cycles with the module with sodium acetate trihydrate with extra water and in 6 out of 35 test cycles for the module with thickening agent

Laboratory test of a prototype heat storage module based on stable supercooling of sodium acetate trihydrate

AbstractLaboratory test of a long term heat storage module utilizing the principle of stable supercooling of 199.5kg of sodium acetate water mixture has been carried out. Avoiding phase separation of the incongruently melting salt hydrate by using the extra water principleincreased the heat storage capacity. An external expansion vessel minimized the pressure built up in the module while heating and reduced the risk of instable supercooling. The module was stable supercooled at indoor ambient temperature for up to two months after which it was discharged. The energy discharged after activating the supercooled sodium acetate water mixture was 194kJ/kg of sodium acetate water mixture in the first test cycles dropping to 179kJ/kg in the later test cycles. Instability of the supercooling occurred when the charging periods were short and in the last test cycles where the tube connecting the module to the expansion vessel had been blocked by the salt hydrate