Effect of zeolite A coating thickness on adsorption kinetics for heat pump applications

Zeolite A coatings of various thicknesses were directly crystallized on stainless steel plates by using the substrate heating method. The coatings prepared were characterized by X-ray diffraction (XRD), laser microscopy and thermogravimetry (TG). Kinetic measurements were performed to determine the rates of adsorption of these materials, which exhibited rough corrugated surfaces with accessible nature. It was observed that the overall adsorption kinetics slowed down to some extent with the increasing thickness of the coatings. Regarding the power estimated for their use in adsorption heat pumps, the higher mass of the thicker samples could compensate for this limiting effect up to some point. An optimum zeolite A coating thickness, maximizing the power, was determined to exist between 58 mm and 176 mm, representing the thinnest and thickest coatings investigated in this study. For the operating conditions used, the optimum thickness value was around 130-140 mm, which varied to some extent with the amount of normalized loading.