4. CFD modeling and simulation in a vertical refrigeration cabinet

Vertical refrigerating cabinets are widely used in supermarkets because the products have good storage conditions and are adequately presented to the consumers.

As mentioned above, the open type refrigerating cabinets use one or more air curtains in order to separate the cold interior from the warm surroundings.

The study of air curtains is necessary because these can be easily disrupted by air circulation in front of the cabinet or by the consumers taking foods from the shelves; the disturbing effect increases with the height of the cabinet. The aerodynamic non-homogeneity of the air curtain increases when the number of "holes" increases, leading to the increase of the temperature inside the display case and of its power consumption; as a result, the products inside the cabinet are stored at temperatures higher that the recommended ones. Moreover, the infiltration of exterior humid air inside the case results in additional ice formation over the evaporator coils, thus reducing the heat transfer and the efficiency of the refrigeration system; therefore, the defrosting cycles become more frequent, further increasing the power consumption.

Some estimations show that 72–75% of the cooling load is used in order to counteract the effect of warm air infiltrations through the air curtain (Figure 18) and can reach even 90% if the operating conditions are not suitable [11]; 50% of the power consumption of a supermarket is due to the refrigeration and freezing cabinets.

CFD simulation was applied to a vertical display cabinet with four shelves, and in order to evaluate the temperature gradient, the following stages were taken into account: preprocessing —geometry set-up and design of the discretization scheme; processing—introduction of the boundary conditions and calculation; post-processing—visualization of the velocity and temperature fields.
