Atmospheric air freshwater using TPMS compact heat exchangers

Abstract

The technology of extracting freshwater from atmospheric air is currently accessible in tropical regions and is experiencing substantial growth in areas where freshwater scarcity is prevalent. Moreover, the water-cooling towers in power plants and district cooling chillers produce saturated air, which serves as a significant supply of humid air and consequently freshwater. Dehumidification is the necessary procedure for extracting water vapor from moist and saturated air in order to generate water. An efficient heat exchanger with a high ratio of surface area to volume is necessary to enhance the production of freshwater by condensing the water vapor present in the air. Triply periodic minimum surface (TPMS) structures possess intricate geometries, resulting in a high ratio of surface area to volume and intense turbulence. Consequently, these structures have exceptional heat transmission capabilities. The internal network structure of the TPMS enables the formation of a consistent layer of freshwater by direct interaction with humid airflow, resulting in a continuous flow. The objective of this study was to examine the structural architectures of TMPS that maximize the generation of freshwater from moist air under various humidity and flow conditions. This was achieved by employing accurate 3D computational fluid dynamics (CFD) models. The purpose of developing these models is to analyze the performance of the Gyroid-Solid TPMS structure and compare it to a vertical flat plate with the same surface area. Furthermore, the study examines the freshwater production efficiency of various TPMS designs (Gyroid-Solid, Gyroid-Sheet, and Diamond-Solid) with same porosity but varying levels of humidity in the air. The findings indicate that the Gyroid-Solid structure enhances the condensation flow rate by a threefold factor in comparison to the flat plate across different levels of humidity in the air. Furthermore, the findings indicated that Diamond-Solid exhibited superior performance when subjected to low airflow Reynolds numbers, whereas at high Reynolds numbers The Gyroid-Sheet exhibits the highest level of condensation among the three solid structures, surpassing the Diamond-Solid by 25% and the Gyroid-Solid by 65 %. The findings demonstrated a notable increase in the production of freshwater through the utilization of TPMS structures, thereby deepening our understanding of the crucial influence of geometry on the condensation process. Empirical formulae have been formulated to calculate the Nusselt number of atmospheric air for TPMS heat exchangers, taking into account various design and operational factors.