Graham Sands and Weizhong Xiang, General Domestic Appliances, Peterborough, Cambridgeshire, England

Mesh scheme of the freezer General Domestic Appliances (GDA) Ltd. is the largest manufacturer of domestic appliances in the UK, with products that include refrigerators, stoves, washing machines, clothes dryers, dishwashers, and more. GDA began using FLUENT in April 2001. The first of their projects to make extensive use of CFD was the development of a new line of frost-free refrigeration appliances.

Mesh scheme of the freezer

One of the main goals of the project was to design the refrigerators with improved energy performance, to cut operating costs. To reduce the energy demands of the units, two aspects of the airflow inside the refrigerators had to be optimized. First, the maximum air flow rate had to be generated using the smallest possible fan. This would not only improve the efficiency, but would also make the unit run more quietly. Second, the fan(s) and other internals needed to be positioned in such a way that the airflow inside both the refrigerator and freezer units was distributed in the most efficient way. Test rigs were constructed so that measurements could be made in parallel with the CFD simulations. The role of these rigs was to validate the results of the CFD simulations and carry out the airflow optimization phase of the project.

The largest freezer studied in this project was 1.8 meters high and had 9 baskets. Because the geometry of the freezer is very complicated, with small gaps between the food packs and baskets, a tetrahedral mesh was used. The results for pressure distribution indicated that the largest pressure losses were occurring below and behind the bottom basket. This result was validated by measurements on the test rig. After increasing the clearance between the baskets and inside walls, the simulation was repeated, and the total airflow rate of the freezer was found to increase considerably.

Pack temperature distribution in the freezer	Pressure distribution in the freezer

The model was also used to study the pack temperature distribution in the freezer. A steady-state simulation was performed for a case where the compressor was running 100% of the time, and a transient simulation was performed when the compressor was cycling on and off. The results for the steady-state case (top left) suggested that the top and bottom basket have the warmest pack temperature if the air is uniformly distributed in the freezer. When the compressor runs intermittently, however, the top basket has the warmest pack temperature. In order to reduce the pack temperature near the top and bottom baskets, the simulations showed that more air should be introduced to these regions.

At GDA, FLUENT has been proven to be a useful tool to assist the development of frost-free refrigerators. It has been used successfully to identify problems before any prototype models were built. Models of other appliances have since been developed and these models have provided further useful information for design decision making, and have assisted in the product development process.

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