Abstract: In order to find out the causes of the different heating temperature of the bearing box of fire pump, the volumetric loss is the main factor that affects the degree of heat generation in the pump bearing box through the numerical calculation of the heat transfer through the heat transfer of the box body. Pump size has been improved. Aluminium Tripods,Triangle Tripods,Ellipse Tripods Jiangsu Laiao Material Technology Co., Ltd. , https://www.jiangsulaiao.com
In large fire pump operation, bearing housing often heat up to temperatures above 70ºC. 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, the root cause of temperature uncertainty needs to be found and effectively controlled. The main reason for overheating was found by numerical calculation of the heat transfer conjugate heat transfer (CHT) in the bearing housing. 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 (FEM) is very suitable for purely solid heat transfer problem in discrete calculation method. Finite element based finite volume method (FVM) is more effective in conjugate heat transfer problem involving fluid. In this paper, the finite volume method.
1, heat transfer calculation results
Figure 1 is a computational mesh model that ignores the effects of oil in the tank on the heat transfer and the effect of heat transfer on air density differences. This problem is an axisymmetric problem, so a sector can be calculated, where a and b are the bearing mounting locations, Wire frame 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 varies widely. For a fire pump with a speed of more than 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 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 effects of water convection heat transfer coefficient and mean air convection heat transfer coefficient on these two parameters were observed to see their effects 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 water convection can affect the bearing box maximum temperature.
2, effective temperature control measures
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.