致冷空气幕墙的雾沫夹带现象研究
Refrigerated air curtains are used in supermarket display cases to keep warm ambient air from entering therefrigerator case. Entrainment of ambient air into the curtain by shear layer mixing contributes to both the sensibleand the latent heat load on the cases. In order to reduce this entrainment, a closer look at the air curtain is undertakenhere. Particle Image Velocimetry was used to examine idealized air curtains of various Reynolds and Richardsonnumbers. The air curtain entrainment was seen to be dominated by eddies that engulfed ambient air into the aircurtain. For the isothermal (Ri=0) curtains, it was observed that the air curtain dynamics and entrainment were notsensitive to Reynolds number variation between Re=3800 and Re=8500. At low air velocities (Re=1500), the curtainwas found to detach, leading to extremely high entrainment rates. Variations in Richardson number of the curtainaffected the flow at the curtain inlet most dramatically, where the acceleration of gravity caused the curtain to neckinwards. The overall thermal entrainment was shown to reduce with reducing Reynolds number, implying that areduction in air curtain entrainment could be achieved by reducing the air velocity of the curtain, as long as aircurtain integrity is maintained.