Investigation of heat transfer characteristics of rotational jets.

摘要

Electric motors and generators are used for many applications in industry. Efficiencies drop in electric generators and motors as stator temperatures increase. To improve efficiencies, the stators can be cooled. One cooling method is by impinging rotating spray jets on the inside surface of the windings on the stator. The objective of this research is to determine the heat transfer characteristics of this impinging rotating spray jets with varying number of geometrical and flow parameters such as RPM, fluid flow rate, number of jets, diameter of jets, and the distance from the jet to the impingement surface using experimental test facility. An experimental test rig has been fabricated. The experimental setup is equipped with simplified stator, housing, rotor system, heaters for simulated heating conditions, numerous temperature sensors, RPM sensors, volume flow meter, and NI-DAQ-LabVIEW computer data acquisition system. Tests were performed to estimate heat transfer coefficients with varying system parameters. The flow rate was found to be the most influential variable in the heat transfer performance. The heat transfer coefficient increased as the flow rate increased. The rotation rate, number of nozzles, and nozzle diameter, given a constant flow rate, had a very small influence on the performance of the system. Most of the variation found was well within the repeatability and uncertainty of the system. The jet impingement distance had a slightly larger effect but was still small compared to the flow rate. Correlations were found for heat transfer performance. The results of visualization implied that the jet was not broken up. The jet was not captured but the impingement zone and surrounding oil film were discussed. The results of the testing provide background for effectively cooling electric motors and generators.