| Recycling the large amount of waste heat generated by industrial processes is important for improving energy efficiency and reducing carbon emissions to achieve carbon neutrality.As an energy-saving and environmentally friendly technology,the adsorption heat pump can recover industrial waste heat without damage to the environment.The open-loop adsorption heat pump utilizes zeolite 13X-water as the adsorption working pair and can recover low-grade waste heat to generate high-temperature steam based on the direct contact heat exchange method.However,the strong hydrophilicity of zeolite makes the performance of the adsorption heat pump system lower.In this study,surface superhydrophobic modification of zeolite13 X was performed to regulate the migration of non-adsorbed liquid water in the adsorption heat pump,enhance the steam generation performance and reduce the regeneration energy to improve the overall performance of the open-loop adsorption heat pump system.(1)The surface hydrophobicity of zeolite 13 X was modified by using vinyltrimethoxysilane,and the modified zeolites were prepared with different degrees of hydrophobicity by controlling the temperature of the modification process,and the modified zeolites were measured and characterized for various properties.The water contact angle measurements showed that the modified zeolite reached 152° and had a superhydrophobic surface.The water adsorption capacity of the modified zeolite decreased slightly,but the integral adsorption heat remained at the same level.Infrared spectroscopic analysis display that the modification process did not destroy the original structure of the zeolite and the addition of organic functional groups was found in the modified zeolite.The thermogravimetric analysis showed that the modified hydrophobic zeolites had good thermal stability within 400℃.(2)The modified zeolite 13 X was used in an open-loop adsorption heat pump system to explore the effect of different hydrophobicity degrees of the modified zeolite on the system performance improvement.As the hydrophobicity of the filled zeolite increased,the temperature rise time at the temperature measurement point in the bed was correspondingly earlier,and the overall steam generation process time was also reduced.Compared with zeolite 13 X,the mass and temperature of the steam generated from the hydrophobically modified zeolite were also improved.At the end of the steam generation process,the free water content in the superhydrophobic zeolite bed was reduced by 37.6% compared to zeolite 13 X.During the regeneration process,the thermal response time of the hydrophobic zeolite bed was variously advanced compared to that of zeolite 13 X,and the energy consumption used to remove free water from the bed was reduced.(3)The performance of the adsorption heat pump system was evaluated in various aspects by experimental data.The performance of the system was improved differently with the increase of zeolite hydrophobicity.Compared to zeolite 13 X,the superhydrophobic modified zeolite for open-loop adsorption heat pump improved the system coefficient of performance for heating and specific heating power by 38.1%and 22.1%,respectively,and the gross temperature lift rise by 13℃.The superhydrophobic modified zeolite changed the migration pattern of liquid water in the bed and improved the overall performance of the adsorption heat pump system.(4)The effect of the superhydrophobic modified zeolite on the performance of the open-loop adsorption heat pump system was further investigated at different regeneration temperatures.As the regeneration temperature increased,the initial state of the zeolite samples differed,as did the time to start heating up and the peak temperature reached at the temperature measurement point within the bed,and the duration of the overall steam generation process was slightly extended.The mass and temperature of the steam generated from the zeolites regenerated at higher temperatures also increased significantly.The coefficient of performance for heating and specific heating power was increased by a factor of 1.4 and 1.15,respectively,and the gross temperature lift was increased by 20℃. |
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