Performance prediction of a compact sorption heat storage prototype using LiCl/H2O as working pair.

Thermal energy storage systems based on the sorption technology are attracting the attention of many researchers, mainly owing to the benefits of high storage density, no significant heat loss and combing cold storage and heat storage functions in one system. Among different working pairs, LiCl/H2O shows a great potential for thermal energy storage with its large water sorption capacity. A new type of consolidated composite matrix is developed, by using activated carbon (AC) as a porous host matrix to carry LiCl, mixing with expanded natural graphite treated with sulfuric acid (ENG-TSA) to increase heat transfer and adding silica solution (SS) as a binder to enhance mechanical strength. Related characteristics of the sorbents including thermal conductivity and permeability were experimentally investigated. Based on the obtained properties of the sorbent, a compact sorption prototype with designed 1 kWh storage capacity was designed for thermal energy storage. The sorption reactor consists of three identical plate-fin heat exchangers, for which the fins are removed previously to fill consolidated composite sorbent blocks into the space between adjacent plates. A 2-D numerical simulation model was built to predict the discharging performance of the sorption reactor under different discharging temperatures. It is found that the total output heat capacities are 1.19 kWh, 1.01 kWh, 0.87 kWh and 0.76 kWh when inlet fluid temperatures are 30°C, 35°C, 40°C and 45°C.