Effect of particle size on superheated steam generation in a zeolite-water adsorption heat transformer

An adsorption heat transformer system based on a direct-contact heat exchange method to elevate the hot water temperature level has been proposed. Superheated steam over 150°C was directly generated from hot water. A mathematical model is developed to investigate the effect of zeolite particle size on the transient mass and heat transfer during the generation process. This model features a three-phase calculation and a moving water-gas interface. The calculations are conducted in the zeolite-water and zeolite-gas regions. The numerical results show the maximum temperature in both zeolite and the generated steam gradually decreases as the zeolite particle size increases.Meanwhile, the adsorption rate becomes slower, which takes longer for the packed bed to achieve adsorption equilibrium. The steam generation time is the same for different particle sizes, while the average steam generation temperature declines with the increase in particle sizes. After the preheating process, the maximum temperature in steam slightly decreases for small particle size but obviously increases for large particle size. The gross temperature lifts are the same regardless of the changes in particle size. The steam generation time remarkably expands to almost the whole range of the process. The average temperature for steam generation is dramatically upgraded for large sized particles with the preheating process. Future work will focus on experiments for different sizes of zeolite and packing density to enhance the steam generation process.