1, the heat transfer calculation results Analysis of the bearing housing of the oil on the heat transfer and air density difference caused by heat transfer, the problem is axisymmetric problem, so you can calculate a fan-shaped area, a, b is the bearing installation position, the line Box for the water, the rest for the box and shaft, box, shaft and air contact part of the air convection heat transfer boundary. Figure 2 is the calculation results, warm color is high temperature, cold color is low temperature. Although computers have strong computational and analytical abilities, the actual engineering problems are sometimes complicated and the relevant computational parameters have some similarities. This has implications for the accuracy of the calculations and should be fully understood in the calculation. When analyzing the results of calculations, take note of the effects of the uncertainty of the boundary conditions. In the calculation of bearing box heat transfer, water convection heat transfer is the forced convection heat transfer caused by the volume loss of the pump. Its heat transfer coefficient is related to the volume loss of the pump and should be controlled by the design. However, dimensional variations in manufacturing process lead to the uncertainty of volume loss, which leads to the uncertainty of water convection heat transfer coefficient. The calculation shows that the heat transfer coefficient has a wide variation range. For a fire pump with a rotation speed of ns = 76, the heat transfer coefficient equivalent to the flow rate when the volumetric efficiency is between 90% and 98% is usually 390W / m2 · oC ~ 1240W / M2 · ℃ range of change. Air convection heat transfer is a natural convection heat transfer, its heat transfer coefficient and pump environment, and therefore there are uncertainties. Consider fire pumps are usually installed indoors, the speed of air flow changes will not be large, so the heat transfer coefficient will not change much. If the wind speed varies from 0m / s to 6.4 / s, the average heat transfer coefficient of air varies from 5W / m2.oC to 25W / m2 · ℃ according to empirical formula. The water convection heat transfer coefficient is much larger than the air convection heat transfer coefficient, which is the dominant factor affecting the heat transfer, meanwhile the forced convection heat transfer can be controlled by the designer. Therefore, as shown in Figure 3, the effects of water convection heat transfer coefficient and mean air convection heat transfer coefficient on these two parameters were observed. The temperature shown in Figure 3 is the maximum temperature of the bearing housing, which is usually located near the bearings away from the pump impeller. A single bearing heating power 1000W, the ambient temperature is 20oC. It can be seen that due to the water convection heat transfer coefficient of variation range than the average air convection heat transfer coefficient range is much larger, so water convection can affect the bearing box maximum temperature. 2, the effective temperature control measures In order to control the temperature can be appropriately reduced volumetric efficiency, if the maximum temperature is not greater than 70oC, the water convection heat transfer coefficient should be not less than 500w / m2 · ℃, and based on this calculate the pump volumetric efficiency and the corresponding part size .
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