Suitability of plate versus cylinder surface for the development of low flow falling film liquid desiccant dehumidifiers

Abstract

Liquid desiccant systems (LDS) are promising as they can be driven by renewable energy. Presently, plastic falling film towers are gaining more attention than metallic columns in LDS due to their excellent anti-corrosive characteristics. However, plastics suffer from penurious performance due to their hydrophobic nature. Apart from solid surface wettability, its geometry also plays a vital role in the formation of the continuous thin film over it. In the current experimental work, the dehumidification performance of adiabatic vertical polypropylene (PP) solid circular cylinders is investigated as an alternative to vertical PP plates. Modified circular cylinder surface is prepared following surface modification to overcome hydrophobic nature of the plastic surface. The performance of the circular cylinder surface is compared with the plate surface. It was found that the Plain PP circular cylinder offered 21–200% improvement in dehumidification rate as compared to the Plain PP plate with an average improvement of 55.9%. Similarly, the Modified PP circular cylinder enhanced the dehumidification rate of the Plain PP circular cylinder by 18.2–61% with an average improvement of 31.3%. A new generalized correlation is proposed to predict the effectiveness of adiabatic and non-adiabatic falling film towers by incorporating shear force, enthalpy difference, and moisture transfer potential between liquid desiccant and air along with wetness behavior parameters. The mean effective error of the current correlation is 11.7% for eight datasets. The findings of this study could be useful for designing small capacity low flow falling film tower-based solar hybrid liquid desiccant systems for residential and commercial applications.