Calculation of fire pump bearing box heat transfer and take the temperature control measures (with photos)

During the operation of the fire pump bearing box often heat up to temperatures above 65 º C. High temperature will affect the lubricant performance. Tests showed that even with the same batch of products, the highest box temperature is high and low, by changing the type of bearing, adjust the radial thrust bearing installation gap can not control the temperature. Therefore, we need to find the root cause of temperature uncertainty and effectively control it. The calculation of the heat transfer conjugation heat transfer through the bearing housing found the main reason for the high temperature. The problem of conjugate heat transfer can be divided into two computational regions, fluid-filled regions and solid regions. Energy flow through the diffusion process in the transfer between the two regions. Finite element method is very suitable for purely solid heat transfer problem in discrete calculation method. Finite element-based finite volume method is more effective in conjugate heat transfer problems involving fluid. In this paper, the finite volume method. Calculation of Heat Transfer Results As shown in Fig. 1, the grid model is calculated and the influence of the oil in the tank on the heat transfer and the influence of air density difference on the heat transfer are neglected. This problem is an axisymmetric problem, so a fan-shaped area can be calculated, a, b Is the bearing installation position, the wire frame is water, and the rest is the box body and the shaft. The contact part of the box body and the shaft with the air is 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, when the volumetric efficiency is between 90% and 98%, the heat transfer coefficient equivalent to the flow rate is usually 390W / m 2 · 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 the air is 5 W / m2 according to empirical formula. ºC to 25 W / m2 · ° C. 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 convection heat transfer coefficient and the convection heat transfer coefficient of the air convection were used to observe the influence of these two parameters on the calculation results. 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 of 1000W, the ambient temperature is 20 º C. 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 the water convection can affect the bearing box maximum temperature. In order to control the temperature, the volumetric efficiency can be properly reduced. If the maximum temperature is not more than 70ºC, the water convection heat transfer coefficient should not be less than 500 w / m 2 · ° C. Based on this, the pump volumetric efficiency and corresponding part size should be calculated.

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