BSP is the Greek branch of BOSCH-SIEMENS Household Appliances, which is a major manufacturer of domestic appliances in Europe. In association with Enervac-Flutec Ltd., distributor of FLUENT in Southeastern Europe, they have used FLUENT to simulate and optimize the novel No-Frost range of refrigerators and freezers.

No-Frost technology is based on the circulation of air inside the freezer and refrigerator compartments to maintain required temperature distribution and prevent ice formation in the evaporator area. Cold air is fed into the freezer and refrigerator compartments through slots situated at the back panels. The task faced by BSP engineers was to optimize the size, shape, and positioning of the air inlets in order to achieve the design specifications of velocity and temperature distribution, while at the same time maintaining the low cold-air flow rate requirements, to maximize energy savings. In the refrigerator industry, extremely tight deadlines must be met during product development, as the market is seasonal to a large extent and new product lines are usually launched every spring. BSP engineers had previous knowledge of CFD techniques and had long anticipated integrating a CFD software package into the product design procedure.

Surface-heat-flux plots of the No-Frost refrigerator and freezer compartments helped BOSCH-SIEMENS engineers to optimize the location of air inlets.

The refrigerator geometry is characterized by large open spaces coexisting with small gaps, which calls for the application of unstructured grid technology, complemented with advanced turbulence models. FLUENT simulations were performed for both the refrigerator and freezer compartments. The geometry was imported from a CAD package and full three-dimensional grids were built. The simulations were performed with the RNG turbulence model. Several configurations of the air inlet area were studied and the most appropriate design was selected.

When the prototype was constructed, the FLUENT results were validated against experimental measurements taken at 300 positions inside the refrigerator and freezer compartments. The agreement between experimental and calculated temperatures was very good.

BSP has recently been awarded a Greek government grant to partially fund the development of user-defined functions for modeling moisture formation on the lining of the refrigerator compartment.

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