DA-2396 -- Influence of Initial Turbulence Intensity on the Development of Plane Air-Curtain Jets PDF

In recent years, there has been an increasing trend of replacing solid doors of many kinds ofbuildings with air curtain doors. In addition to these applications, air curtains are widelyused on refrigerated display as well as protective entrances to refrigerated storage spaces.

An air curtain door is a stream or a combination of streams of air blowing across an openingat a specified velocity and angle such that it greatly reduces natural circulation of the airbetween the inside of the structure and the outside of the structure. A schematic diagram ofa recirculated air curtain is shown in Fig. 1. Many air curtains are also designed so as torestrict the penetration of insects, dirt, and cross winds. The number of jets, thickness,width, height, velocity, as well as the pressure and temperature differences across the jetplay important roles in air curtain performance. A heretofore uncertain variable in air curtainperformance has been the initial turbulence level of the air jets. It is the intent hereto establish the importance of the initial turbulence intensity in determining the developmentof the velocity and temperature profiles of the jet. Knowledge of how the jet develops allowsthe determination of the heat and moisture transfer through the air curtain.

Energy conservation considerations require the minimization of airflow between the controlledenvironment and the surroundings. When compared to an open doorway, the air curtaindoor provides the necessary restriction to airflow while maintaining optimum traffic flow.However, optimum design values may be desirable in order to improve the sealing power of theair curtain while minimizing the transfer of heat, moisture, and contaminants.