Bronze wool as a porous mixer for air temperature uniformity in energy exchangers

This study investigates the use of bronze wool as a porous air mixer to improve temperature uniformity at the air outlet of a liquid-to-air membrane energy exchanger (LAMEE). Experimental evaluations were conducted using mixers with varying wool mass, porosity, and structure, under both horizontal and vertical duct orientations with laminar flow. Results show that bronze wool mixers significantly reduce temperature gradients, achieving up to 75% statistical effectiveness in horizontal ducts and 54% range effectiveness in vertical ducts. In compact wool structures, thermal conduction within the metal fibers is the primary temperature homogenization mechanism, while physical mixing from advection and dispersion occurs in higher-porosity structures. Among all configurations, the accordion wool structure demonstrated the highest range effectiveness, attributed to enhanced multi-directional conduction. The pressure drop across the mixer was tested for different wool structures over a range of laminar Reynolds numbers (39–586). Pressure drops remained relatively low, confirming the suitability of metal wool air mixers for use in systems where minimizing flow resistance is critical. A dimensionless performance index was developed to compare mixers by balancing thermal mixing effectiveness and pressure drop, which identifies the vertical, high-porosity, basic wool mixer as the best performer. The findings demonstrate that bronze wool offers a lightweight and effective alternative to the traditional mixers for temperature homogenization in air ducts.