The occurrence and characterization of fouling during membrane evaporative cooling

Evaporative cooling provides a low-cost and energy efficient method of cooling air. Most conventional evaporative cooling methods involve collection and re-circulation of water to keep the wetting media or misting region saturated. There exists an environment of nearly stagnant water in direct contact with outside air, which aids in the spread of many liquid phaseborn bacterial diseases, most notably Legionnaire's Disease.;This study focuses on utilizing hollow fiber membranes as wetting media in evaporative cooling applications. Unlike conventional wetting media, hollow fiber membranes do not allow direct contact between water and air. Water-air interaction instead occurs through membrane pores of a size too small (<0.1 mum) to allow the passage of microbes yet still allowing for water vapor transfer. Previous studies have demonstrated the efficacy of this approach but used distilled water within the membranes which eliminated fouling, but current evaporative cooling systems generally use water which may contain scale forming minerals. Further research is needed to quantify potential fouling that can occur.;In this research, a duct-mountable, hollow fiber membrane array is fed tap water or water with a known concentration of calcium sulfate or calcium carbonate to simulate evaporative cooling with scale forming waters. Mass transfer coefficients are experimentally derived from collected data, and concentration polarization effects and fouling mechanisms are quantified from changes in the measured mass and heat transfer coefficients along with visual verification from SEM imaging. Results indicate that membrane fouling can be characterized by a decrease in the effective porosity of the membrane due to crystal growth from the supersaturated mineral solution within the membrane fibers.