The potential use of metal-organic framework/ammonia working pairs in adsorption chillers

Adsorption chillers (ACs) powered by low-grade solar or waste heat energy have attracted increasing research interest due to their low electricity consumption and carbon emission. Ammonia working fluid with a high enthalpy of evaporation and large vapor pressure that is favorable for heat and mass transfer has been commonly used in ACs. Currently, promoting the cooling performance of ACs greatly relies on the exploration of high-performance adsorbent/ammonia working pairs. Metal-organic frameworks (MOFs) have been demonstrated as promising adsorbents for ACs using water or alcohol working fluids. However, the use of ammonia and MOF adsorbents in ACs is extremely challenging due to the difficulties in achieving ammonia adsorption performance and ammonia stability of MOFs. In this study, we evaluated the cooling performance of nine MOF/ammonia working pairs based on the ammonia adsorption data from grand canonical Monte Carlo (GCMC) simulations, from which it was found that NU-1000/ammonia exhibited the highest coefficient of performance for cooling (COPC) of 0.58 and specific cooling effect (SCE) of 560 kJ kg(-1), while MIL-101/ammonia showed the highest SCE of 924 kJ kg(-1) and COPC of 0.50. Such a trend was further proved by experimental measurements. However, ammonia cycling measurements demonstrated that NU-1000 suffered from a severe reduction in adsorption capacity due to its ammonia instability. In contrast, MIL-101 displayed excellent recyclability in ammonia as well as outstanding cooling performance, suggesting its great potential in AC applications.

Automated summary

This study evaluated the cooling performance of nine MOF/ammonia working pairs, with NU-1000/ammonia and MIL-101/ammonia showing the highest COPC and SCE values. However, NU-1000 suffered from a severe reduction in adsorption capacity due to ammonia instability, while MIL-101 exhibited excellent recyclability in ammonia and outstanding cooling performance.