Thermal mixing of hot and cold fluids is an important phenomenon in domestic water systems, process equipment, heat-transfer systems and other engineering applications. The quality of mixing is influenced by inlet temperature difference, flow rate, velocity ratio, Reynolds number, junction geometry, branch angle, inlet flow profile and downstream mixing distance. The present article reviews published research on thermal mixing in T-junctions, mixing tees and mixing valves. Experimental investigations and numerical approaches including computational fluid dynamics, large-eddy simulation and improved delayed detached-eddy simulation have been considered. The reviewed studies report that strong temperature gradients and fluctuations occur near the mixing region, while temperature uniformity generally increases downstream. Flow structures such as shear layers, recirculation zones and vortices play an important role in transporting hot and cold fluid across the mixing interface. The literature also indicates that changes in branch angle, inlet flow profile, flow-rate ratio and internal valve geometry can significantly alter the thermal mixing behavior. Recent studies have extended the investigation from simple T-junctions to practical mixing-valve configurations. The review identifies the major parameters affecting thermal mixing and summarizes the development of research in this field.

Keywords

Thermal mixing; hot and cold fluid; T-junction; mixing valve; computational fluid dynamics.