Thermophysical characterization of magnesium chloride and its application in open sorption thermal energy storage system

Sorption thermal energy storage is considered as a promising method to reduce energy consumption of building heating. MgCl2 center dot 6H(2)O could be a good candidate due to its high energy storage density. This paper first summarizes phase equilibrium lines of four MgCl2 hydration/dehydration processes to evaluate reaction enthalpy and entropy variation. Thermal diffusivities and specific heat of MgCl2, MgCl2 center dot 6H(2)O and MgCl2-ENG composite are determined which are compared with common counterparts of MgSO4 center dot 7H(2)O and MgSO4-ENG. Then the performance of open sorption thermal energy storage system is assessed in terms of various sorbents. Results show that the obtained thermal conductivities of MgCl2 center dot 6H(2)O range from 0.15 W m(-1) K-1 to 0.96 W m(-1) K-1 at the temperature range of 15-70 degrees C while thermal conductivities of MgSO4 center dot 7H(2)O range between 0.29 W m(-1) K-1 and 0.68 W m(-1) K-1 at 20-45 degrees C. At 20 degrees C testing temperature, thermal conductivities of composite MgCl2 are improved which range between 0.97 W m(-1) K-1 and 2.92 W m(-1) K-1 under the condition of 500-900 kg m(-3) density and 67-80% mass ratio of salt. Besides, MgCl2 composite is preferable for open sorption thermal energy storage which could achieve stable heat output for more than 4 h under the conditions of 15.4 degrees C inlet temperature, 40% relative humidity and 0.26 m s(-1) air velocity.