Numerical investigation of air mixer for HVAC testing applications (ASHRAE RP-1733)

摘要

Accurate performance measurements of equipment in the laboratory requires air mixing to reduce temperature and humidity measurement error. The National Bureau of Standards (NBS), now known as National Institute of Standards and Technology (NIST)conducted in-depth experimental research on the static air mixing devices in the late 1960s, which remains the most comprehensive work in this area. Today, very limited guidelines are available for air mixers, with ASHRAE RP-1733 addressing this gap. In this paper, computational fluid dynamics (CFD) analyses are presented to quantify the performance of candidate air mixers for RP-1733. It was found that the proposed static air mixing models, consisting of louvers with and without baffles as well as orifice and orifice-target combinations, add turbulence to the airstream, enhancing the mixing process. It was observed that the louver-baffle, orifice, and orifice-target mixer have greater pressure drop than louver mixers with only a negligible increase in mixing effectiveness. Therefore, the louver mixers provide a better tradeoff between mixing effectiveness and pressure drop.