Heat storage performance analysis of ZMS-Porous media/CaCl2/MgSO4 composite thermochemical heat storage materials

Abstract

A new composite thermochemical heat storage (TcHS) material was proposed herein with good heat storage performance and desirable stability, which was prepared by using solid-state cold pressing with a zeolite molecular sieve (ZMS) and two salts (CaCl2 and MgSO4). First, the optimized mass content (CaCl2:MgSO4 = 6:4) denoted Smix was obtained, which represents an equilibrium between the adsorption capacity and deliquescence. Then, two types of ZMS porous media: 13X and NaY were added to Smix to further prevent deliquescence and improve stability, respectively. An orthogonal experiment with four factors (mass fraction, pressure, temperature, and humidity) and three levels was used to test the optimal preparation conditions, and the optimal configurations were obtained for Xopt (13X-ZMS: CaCl2: MgSO4 = 10: 54: 36) and Yopt (NaY-ZMS: CaCl2: MgSO4 = 20: 48: 32). The optimized samples were measured by SEM, XRD and thermal conductivity tests, and the adsorption capacities for Smix, Xopt, and Yopt were found to follow the order of Xopt (0.449 g/g) > Smix (0.374 g/g) > Yopt (0.335 g/g). The accumulated void formation for the porous media can promote heat and mass transfer and can significantly improve the adsorption capacity and avoid deliquescence. Differential scanning calorimetry (DSC) results showed that the heat storage density (HSD) for Xopt (1414.49 J/g) is higher than that for Yopt (1097.02 J/g). Finally, 20 cycles showed that Xopt has good cycle stability based on the normalized ad/desorption mass (>1) and normalized desorption heat (>0.8). The results showed that Xopt shows application potential as a TcHS composite material in medium- and low-temperature thermochemical adsorption heat storage systems.