Air curtains

Air Curtains: an overview

Fig. 1: Experimental setup for air curtains characterization acording to the AMCA-220/05.

An air curtain is basically a device which acts as an ambient separator producing a plane air jet.

Therefore, the study of air curtains is mainly based in the fundamental understanding of plane air jets physics.

In the CTTC the know-how acquired is the product of several years of a collaborative effort with manufacturers in the characterization and modification of air curtain units.

Prediction of the efficency

In order to achieve an accurate description of the air curtain flow three different approaches are employed: the experimental characterization, the semi-analytical approach and the CFD simulations.

The experimental characterization is carried out in the laboratory by means of hot wire anemometry (see Fig. 1) and the international standard stated by the ANSI/AMCA-220 is taken into account in the characterization of the devices. In this way it is ensured both a high reliability of the measurements and the possibility of comparison with the existing data from other studies.

The semi-analytical approach is based on a simplified momentum balance in the jet direction, allowing the possibility of fast calculations with an online interface developed at the CTTC. The results obtained  with this interface has been employed in the industry and compared with the other approaches, being this type of description adjusted with the CFD and experimental measurements.

The CFD simulations are carried out employing the high performance parallel numerical code TermoFluids, developed at the CTTC. The simulations allow the prediction of the efficiency of different air curtain prototypes in order to determine the optimum geometries before manufacturing. Once determined the efficiency obtained with each different prototype, the optimum one can be constructed with a high degree of confidence in the efficiency predicted by the simulations (see Fig. 2).

Fig. 2: Large Eddy Simulation of  the plane air jet produced by an air curtain.

Video 1: Large Eddy Simulation of a refrigerated chamber protected by an air curtain.

Plenum Optimization

 

The plenum is the inner chamber of an air curtain responsible of producing an unidirectional and low turbulence level plane air jet.
By employing fully 3D simulations it can be determined the plenum geometries that produce the better levels of uni-directionality and the lower quantity of turbulence.
The proposition of different air curtain geometries is also a task carried out in the CTTC.

Refrigerating Chambers

One of the most interesting applications of air curtains is within the field of refrigeration. By means of advanced CFD simulations it can be described the flow produced  in the whole inner protected space (see Fig. 3). Once the entrainment of heat and/or moisture produced with some particular installation is predicted the required adjustments can be carried out. The adjustments can be the air curtain placement (vertical or horizontal), the air jet orientation (upwards or downwards), the jet discharge velocity or thickness and other different parameters.
 
Fig. 3: Temperature distribution in a chamber protected by an air curtain.