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In this paper, a numerical model describing the heat transfer and air flow inside and outside the casing of the permanent magnet brushless direct current (PM BLDC) motor is presented. In the model, a conjugate heat transfer including the heat conduction with heat sources in windings, magnets, bearings, natural and forced convection and radiation phenomena within internal and external air domain were analysed. The complex geometrical model included windings, a magnet circuit, a rotor with neodymium magnets, a PCB electronic plate, plastic covers, internal air between solid parts as well as a portion of the external air. The validation process of the developed model was realised on the basis of the velocity and temperature fields. The experimental data were recorded by 7 constant temperature anemometers at 4 levels above the motor housing, Laser Doppler Anemometry sensors in two axes inside the rear portion of the motor and 25 thermocouples fixed inside and outside the motor. The experimental and numerical tests were performed for 4 motor loadings and 3 rotational speeds. The average temperature error for the internal point was of 9 K, while that of the external points was of 2 K. The velocity field was very well predicted close to the housing wall in terms of horizontal and vertical components. A slightly worse agreement was found for the vertical component, especially in the vicinity of the shaft. The results were consistent for all the considered motor loadings and rotational speeds. [ABSTRACT FROM AUTHOR]

Abstract: The wave-finned flat tube heat exchangers are widely used in air-cooled condensers of a power plant. Due to the oblique arrangement of the wavy fins on the A-frame tube bundles of the air-cooled condenser, the finned tube is prone to fouling thus the thermo-flow performances of air-cooled condensers are likely to become deteriorated. A new configuration of wave-finned flat tube, in which the fin surface rotates to be perpendicular, is proposed in this paper to prevent the fouling from gathering on the finned tube. The physical and mathematical models for the fluid and heat flows of the cooling air through the present and proposed wave-finned flat tube bundles are setup, and the thermo-flow characteristics are compared. For the proposed finned tube, the influences of the fin pitch, height and the Reynolds number on the flow and heat transfer performances are investigated, and the correlations of the friction factor and Nusselt number are recommended. The results show that the buoyancy effect should be taken into account for the correlation of the friction factor at low Reynolds numbers, but this buoyancy force can be ignored for the Nusselt number. [Copyright &y& Elsevier]