Design and optimization of falling film absorbers by air flow modification for cold store dehumidification using a newly developed open-source OpenFOAM-based CFD solver

Abstract

This study investigates the design and optimization of falling film absorbers with vertical plates by air flow modification for dehumidification in cold store applications. Two novel absorber designs – the wire geometry and the stacked arrangement – were developed and analyzed using a newly created open-source computational fluid dynamics (CFD) solver based on OpenFOAM. The study addresses the limited vapor diffusion from the humid air core to the desiccant film surface, a critical constraint in falling film absorbers. The wire geometry, incorporating wires into the air channel, significantly enhances mixing of the air flow through induced vortex shedding. A single 1.5 mm wire increased the absorbed mass flow rate by up to 28%, allowing for a 35% shorter absorber but raising the pressure drop by 60%. The stacked arrangement, featuring offset absorber steps to ensure contact between the humid air core and the desiccant surface, demonstrated superior performance. With three absorber steps, the design reduced the absorber length by 25% while limiting the increase in pressure drop to 25%. Thus, the stacked arrangement achieved similar absorption improvements as the wire geometry with significantly lower pressure drop, making it the more suitable for practical use. The open-source solver developed in this study facilitates reproducibility and provides a platform for further research in open absorption systems. These findings highlight the potential of falling film absorbers to enhance energy efficiency in cold store by preventing frost formation and utilizing low-grade waste heat for desiccant regeneration. The results pave the way for industrial implementation of these optimized designs, with the stacked arrangement offering the most compelling balance of performance and efficiency.