Heat and Momentum Transfers: Multiple-Disc Rotor Units

An investigation has been carried out to determine the performance characteristics of a multiple-disc rotor device used as a combined fan/heat exchanger. The advantages of such a system, when applied for example to an air-conditioning system, stem primarily from the simplicity of design and compact nature of the equipment. The assessment of the particular test unit as a fan was done under normal atmospheric conditions using air as the working fluid. A speed range from 550 to 1290 rpm was used in these tests. The maximum efficiency of the momentum transfer from the rotor to the fluid was about 14 percent. The unit capability as a heat exchanger using air flow under normal atmospheric conditions may be judged by the maximum heat transfer effectiveness of about 40 percent. Rotor speeds were varied in the range 700 to 1600 rpm, and at each rotational speed the ratio of the mass flow in the cool stream to that in the hot stream was varied from 0.48 to 1.30. Two different techniques were used in an endeavor to predict the performance of the experimental unit. Of these, the more successful was that based on the assumption that a turbulent boundary layer covered the rotating disc. However, the simpler approach, using calculated friction factors, may well prove acceptable for some engineering applications. The results from each of the prediction techniques are given for comparison with the test results.