The convective heat transfer from the open surface of the rotating shaft in a high-temperature furnace fan to the surroundings is studied experimentally at different fan speeds. In comparable conditions, the mean heat-transfer coefficient from the open shaft surface is 40-60% greater than the heat-transfer coefficient from a single immobile cylinder in a transverse air flux. A method is proposed for calculating the shaft cooling, and a formula is derived for estimating its temperature in the bearing region as a function of the fan parameters and the furnace's operating conditions. Calculations show that, with increase in shaft speed, the bearing temperature falls rapidly in the range 100-600 rpm. At higher speeds, the bearing temperature practically stabilizes. Analysis of the formula indicates that, with fixed shaft speed and diameter, the heating of the bearings may be reduced by increasing the length of the open shaft surface or employing less conductive materials. The results may be used in the design of high-temperature furnace fans.
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