Cooling performance of metal organic framework-water pairs in cascaded adsorption chillers

Adsorption chillers powered by the low-grade thermal energy or renewable solar energy for cooling have gained growing research interests due to their environmental friendliness and low electricity consumption. The cascaded adsorption chillers consisting of the high-temperature stage and low-temperature stage exhibit a higher coefficient of performance for cooling than the single-stage adsorption chillers. Searching for high-performing working pairs in advanced cascaded adsorption chillers is essential to improve their cooling performance. In this work, three water-stable metal organic frameworks including UiO-66, DUT-67 and NU-1000 were chosen as adsorbents with water as working fluid. Their cooling performance of the four-bed cascaded adsorption chillers was tested by a dynamic adsorption cooling model under different desorption temperatures. It was demonstrated that DUT67-water working pair for the low-temperature stage and DUT-67-water working pair for the high-temperature stage in cascaded adsorption chillers can achieve the highest coefficient of performance for cooling of 1.43 and a circulating cooling capacity of 2.6 x 10(4) kJ. Moreover, the operation conditions of the cascaded adsorption chiller based on DUT-67 (high-temperature stage)/DUT-67 (low-temperature stage) have been optimized. It was revealed that the hot water inlet temperature of 373 K, the hot and heat recovery water mass flow rate of 0.5 kg/s, the chilled water mass flow rate of 1 kg/s, the adsorbent for the low-temperature stage and the high-temperature stage mass ratio of 1, and the cycle time of 1600 s were beneficial for the coefficient of performance for cooling and circulating cooling capacity of the cascaded adsorption chiller based on DUT-67/DUT-67.

Automated summary

Cascaded adsorption chillers with DUT-67-water working pair for both low-temperature and high-temperature stage achieve the highest coefficient of performance for cooling and circulating cooling capacity. The optimized operation conditions include a hot water inlet temperature of 373 K, hot and heat recovery water mass flow rate of 0.5 kg/s, chilled water mass flow rate of 1 kg/s, adsorbent mass ratio of 1 for the low-temperature and high-temperature stage, and a cycle time of 1600 s.