Problem 1: Danfoss  

Modeling thermostatic radiator valves.

The problem is to model the flow through a typical Danfoss thermostatic radiator valve.

Danfoss is able to employ Computational Fluid Dynamics (CFD) in calculations of the capacity of valves, but an experienced engineer can often by rules of thumb "guess" the capacity with a precision similar to the one achieved by the expensive and time consuming CFD calculations. So CFD is only used in case of entirely new designs or where a very detailed knowledge of the flow is required.

Even though rules of thumb are useful for those, who have developed them, Danfoss wants an objective and general method, which can be used to calculate the capacity of valves.

One proposed solution is to identify the significant parts of the interior geometry, quantify the influence and model the valves as a sum of resistors in series. The model should be able to predict the capacity with a precision of 10% in the interesting range of capacities.

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June 4 1999, Marit Hvalsøe Schou, e-mail: