Performance evaluation of absorption thermal energy storage/transmission using ionic liquid absorbents

Efficient thermal energy storage and transmission are considered as two of the most significant challenges for decarbonisation in thermal energy utilization.The liquid-gas absorption thermal energy storage/transmission sys-tem is promising approach to tackle these challenges,owing to the long-term stability,flexibility in heat/cooling output,and liquid medium.At present,the shortcomings of conventional absorption working fluids have trig-gered considerable interest in searching for novel working pairs,such as ionic liquids(ILs).However,it is still unknown whether ILs can work effectively in thermal energy transmission with long distance.In this study,the absorption thermal energy storage/transmission systems using IL absorbents are theoretically investigated.mod-eling frameworks for working pairs screening and performance evaluation are proposed.Results show that the IL-based working pairs present better or comparable performance than conventional working pairs(including H_(2) O/Salts and NH 3/Salts).Among the investigated IL-based working pairs,H_(2) O/[EMIM][EtSO 4]presents high-est COP(around 0.62)and exergy efficiency(around 0.32),and is relatively close to H_(2) O/LiBr.As for energy storage density,H_(2) O/[EMIM][Ac]performs better than H_(2) O/LiBr,presenting 137.4 kWh/m 3 with a desorption temperature of 115°C.The present work provides a straightforward screening of IL absorbents for thermal energy storage and transmission purposes.

Heat Recovery for Adsorption Refrigeration System via Pinch Technology

An adsorption refrigeration system can be driven by low grade heat and uses natural refrigerant with the advantage of reducing the greenhouse gases emission.However,one of the weaknesses is its low efficiency and more importantly its high cost.The recovery of internal waste heat becomes therefore very important in order to improve the coefficient of performance(COP).Analysis based on pinch technology can be helpful to optimal heat recovery operation.In this paper,temperature-heat diagrams and problem tables for adsorption refrigeration systems are proposed and analyzed using Pinch Technology.The results show that pinch point is located between beds and the main waste heat needs to be recovered between beds.Dynamic characteristic(time factor)of adsorption refrigeration system is the main resistance for heat recovery.The effect of pinch point temperature difference on the system COP is not distinct.Furthermore,when the driving temperature is 90°C,the COP of adsorption refrigeration via optimization of pinch analysis is 0.73 which is fairly comparable to Li Br-water absorption refrigeration system.Pinch Technology can be adopted in different types of adsorption refrigeration systems(two-bed,four-bed,mass recovery,et al.).