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Heat pump accounting and temperature control method for fire pump bearing housing
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In the process of large fire pump operation, the bearing box often heats up; the temperature can reach 70oC or above. The temperature will affect the function of the lubricant. The experiment indicates that even the same batch of products; the maximum temperature of the box is high or low; after replacement bearing varieties, adjustment The radial thrust bearing device gap can not handle the temperature. Therefore, it is necessary to find the root cause of the temperature uncertainty; and it can be manipulated. Through the bearing box heat transfer conjugate heat transfer (CHT: conjugate heat transfer) numerical calculation finds the temperature is too high. The main reason is that the conjugate heat transfer problem can divide the two accounting areas; the area filled with fluid and the solid area. The energy activity is transferred between the two areas through the dispersion process. In the discrete accounting method; the finite element method (FEM) is very suitable. In the simple solid heat transfer problem; it is more useful according to the finite element method of finite element method (FVM) in the conjugate heat transfer problem of touching fluid. This paper chooses the finite volume method.
1. Analysis of heat transfer accounting results Figure 1 is an accounting grid model; neglecting the influence of lubricating oil on heat transfer and the effect of air density difference on heat transfer; the problem is axisymmetric problem; thus, it can calculate a sector area; b is the bearing device orientation; the inside of the wire frame is water; the other is the box and the shaft; the box, the shaft and the air touch part are the air convection heat transfer gap. Figure 2 is the calculation result; the warm color is high temperature; the cool color is low temperature. The accounting analysis of the computer can be very strong; but the practical engineering problems are sometimes very messy; the relevant accounting parameters have a certain approximation. This has an impact on the accuracy of accounting; in the accounting, there is a good understanding of this point. When analyzing the accounting results It is necessary to pay attention to the influence of the uncertainty of the chasm condition. In the heat transfer accounting of the bearing box; water convection heat transfer is the forced convective heat transfer of the volume loss of the pump; its heat transfer coefficient is associated with the volume loss of the pump. It should be able to be manipulated by the depiction. However, the scale error in the manufacturing process leads to the uncertainty of volume loss; it also leads to the uncertainty of the water convection heat transfer coefficient. The thermal coefficient changes greatly; the fire pump with specific speed ns=76; when the volume power is 90% to 98%; the heat transfer coefficient equivalent to its flow rate is generally 390W/m20?ordm; C~0?240W /m20?å©€å©ºD scheme? Air convection heat transfer is natural convection heat transfer; its heat transfer coefficient is related to the environment where the pump is located; therefore, there is also uncertainty. Consider the general installation of fire pump indoors; the speed of air activity changes. It will not be very large; therefore, the change of heat transfer coefficient will not be very large. If the wind speed is changed within the range of 0m/s~6. 4/s; according to the empirical formula; the uniform heat transfer coefficient of air is 5 W/m2. oC to 25 W/m20?
The water convection heat transfer coefficient is much larger than the air convection heat transfer coefficient; it is the dominant factor affecting heat transfer; together with the forced convection heat transfer can be manipulated by the painter. Thus, as shown in Figure 3, the water convection heat transfer coefficient, uniform air pair The two parameters of the flow heat transfer coefficient are investigated to investigate their influence on the accounting results. The temperature shown in Figure 3 is the highest temperature of the bearing housing; this point is generally located adjacent to the bearing of the pump impeller. The heating power of a single bearing is 1000W; The temperature is 20oC. It can be seen; because the change of water convection heat transfer coefficient is much larger than the uniform air convection heat transfer coefficient; therefore, water convection can affect the maximum temperature of the bearing housing.
2, useful temperature control method in order to control the temperature can properly reduce the volume power; if the maximum temperature is not greater than 70oC; then the water convection heat transfer coefficient should be not less than 500 w / m20? å¦«å¾Š (14) source Song?? èŽºæ€‚é—¼?è·‹å˜¤èµ·è·‹å˜¤Î±æ…µ?å¨?
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