Abstract
Air curtain performance is a function of the source angle (θ), deflection modulus (DM) and the neutral height (hn). For given values of hn and θ there is a critical DM.C above which the air curtain will reach the floor. However, the air curtain alters the location of the neutral height. Herein the simultaneous solution of the integral forms of the momentum and angular momentum equations leads to a prediction of the change in the neutral height due to the presence of the air curtain. For a vertical two-dimensional air curtain the predicted value is hn/H=1/3 and leads to DM.C=0.167. Experimental and computational studies show that above this DM.C the curtain effectiveness increases to a peak at DM.max and then decreases. The peak effectiveness being above the critical DM is typically attributed to installation issues. However, it is shown that the application of an entrainment model for modeling the air curtain volume flux leads to a prediction of the peak effectiveness occurring at DM.max=1.26DM.C even for an idealized two-dimensional flow. This is almost identical to the minimum air curtain safety factor of 1.3 found in the literature. The model shows that the reduction in effectiveness as DM decreases from DM.max to DM.C is not due to three-dimensional effects but is due to the increased path length of the air curtain as DM approaches DM.C.
Published Version
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