Performances of MOF vs. zeolite coatings in adsorption cooling applications

The performances of zeolite and metal-organic framework (MOF) coatings on metal heat exchanger surfaces were determined for various operating conditions of adsorption cooling systems. A mathematical model was used to calculate the optimum coating thicknesses of the adsorbents, maximizing the power of the system. The highest optimum coating thickness and power values were generally obtained for the hydrophilic triazolyl phosphonate MOF, which seemed to be superior to the different types of zeolites investigated. The power provided by zeolite LiX coatings was about 10-20% higher than that obtained for zeolite NaX coatings. Although zeolite X has quite high water adsorption capacity similar to that of triazolyl phosphonate MOF, its coatings did not perform so well. This seemed to originate mainly from the relatively slow diffusion in zeolite X, especially at the lower temperatures. The coating texture should also be taken into account in the selection of suitable materials for adsorption heat pumps/cooling systems since open coatings may lead to significant improvements in the performances of these devices.