Fire pump bearing box heat transfer calculation and temperature control measures - Database & Sql Blog Articles

In order to find the heating temperature difference of the fire pump bearing box, the Atlantic pump industry calculated the conjugate heat transfer (CHT) value of the heat transfer of the box, which shows that the volume loss is the main factor affecting the heating degree of the pump bearing housing. The structural dimensions of the pump have been improved. The bearing housing often heats up during the operation of a large fire pump, and the temperature can reach above 70oC. Excessive temperatures will affect the performance of the lubricant. Tests have shown that even in the same batch of products, the maximum temperature of the cabinet is high or low. The temperature cannot be controlled by changing the bearing type and adjusting the installation clearance of the radial thrust bearing. It is therefore necessary to find the root cause of temperature uncertainty and to effectively control it. The main reason for the excessive temperature is found by the numerical calculation of the heat transfer conjugate heat transfer (CHT) of the bearing housing. The conjugate heat transfer problem can be divided into two computational regions, a fluid-filled region and a solid region. Energy flow is transferred between the two regions by a diffusion process. In terms of discrete calculation methods, the finite element method (FEM) is very suitable for pure solid heat transfer problems, and it is more effective in the finite element method (FVM) based on finite element method in the conjugate heat transfer problem involving fluids. This article uses the finite volume method. 1. Analysis of heat transfer calculation results ignore the influence of lubricating oil on heat transfer in the tank and the influence of heat transfer on the heat transfer. This problem is an axisymmetric problem, so a sector can be calculated, a and b are bearing installation positions, lines The inside of the frame is water, the rest is the box and the shaft, and the contact between the box and the shaft and the air is the air convection heat transfer boundary. Figure 2 shows the calculation results. The warm color is high temperature and the cool color is low temperature. Although the computer's computational analysis ability is very strong, the actual engineering problems are sometimes complicated, and the relevant calculation parameters have certain approximations. This has an impact on the accuracy of the calculation and should be fully understood in the calculation. When analyzing the calculation results, it is necessary to pay attention to the influence of the uncertainty of the boundary conditions. In the heat transfer calculation of the bearing housing, 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, the dimensional deviation during manufacturing and processing leads 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 specific speed of ns=76, when the volumetric efficiency is 90% to 98%, the heat transfer coefficient equivalent to its flow rate is usually 390W/m2·oC~·1240W. Change in the range of /m2·°C. Air convection heat transfer is a natural convection heat transfer, and its heat transfer coefficient is related to the environment in which the pump is located, so there is also uncertainty. Considering that the fire pump is usually installed indoors, the speed of the air flow does not change much, so the heat transfer coefficient does not change much. If the wind speed varies from 0m/s to 6.4/s, according to the empirical formula, the average air heat transfer coefficient is 5 W/m2. oC varies within the range of 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 heat transfer, and the forced convection heat transfer can be controlled by the designer. Therefore, as shown in Fig. 3, the effects of the two parameters of water convection heat transfer coefficient and average air convection heat transfer coefficient are observed to observe their influence on the calculation results. The temperature shown in Figure 3 is the maximum temperature of the bearing housing, which is usually located near the bearing away from the pump impeller. The single bearing has a heating power of 1000W and an ambient temperature of 20oC. It can be seen that since the variation range of the water convection heat transfer coefficient is much larger than the average air convection heat transfer coefficient, the water convection can more affect the maximum temperature of the bearing housing. 2. Effective temperature control measures In order to control the temperature, the volumetric efficiency can be appropriately reduced. If the maximum temperature is not more than 70oC, the water convection heat transfer coefficient should be no less than 500 w/m2·°C, and the pump volumetric efficiency and corresponding parts should be calculated based on this. size.