Superhydrophobic Surface-modified zeolite to regulate the migration of nonadsorbed liquid water in an Open-loop adsorption heat pump

Abstract

Superhydrophobic surface-modified zeolite 13X has been utilized to regulate nonadsorbed liquid water in an open-loop adsorption heat pump system for steam generation. The zeolite is modified by vinyltrimethoxysilane to achieve a superhydrophobic surface effect. The measured static water contact angles of the modified zeolite reached 152°. Thermogravimetric analysis results show good thermal stability at temperatures less than 400 °C. The measured adsorption capacity and adsorption heat slightly decrease for the modified zeolite. During the regeneration process dry air at 140 °C drives wet zeolite to remove adsorbed and free water. Then generation process proceeds for steam generation at a maximum of 220 °C from water at 72 °C. The mass and temperature of the steam generated from the modified zeolite bed increase compared with those of unmodified zeolite 13X. This is because of the apparent decrease in the total amount of free water, which allows the released adsorption heat to be transferred to passing water quickly for steam generation. Energy consumption during regeneration simultaneously reduces. System indicators such as the coefficient of performance for heating (COPh), specific heating power (SHP), gross temperature lift (GTL) and exergy efficiency (ηe) increase with increasing hydrophobicity of zeolite particles. The surface hydrophobicity decreases the affinity of zeolite for useless free water which cannot contribute to increasing the overall adsorption heat.