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Fire pump bearing box heat transfer calculation and temperature control measures
Abstract: To investigate the reasons behind the varying temperatures in fire pump bearing housings, this study focuses on volumetric losses as a key factor influencing heat generation within the bearing box. Through numerical heat transfer analysis, it was found that pump design and performance significantly affect thermal behavior. During operation, large fire pumps often experience bearing housing temperatures exceeding 70°C, which can degrade lubricant performance. Even with identical products, temperature variations are observed, and adjusting bearing type or radial clearance has limited effectiveness. Therefore, identifying and controlling the root cause of these temperature fluctuations is essential.
The primary cause of overheating was identified through conjugate heat transfer (CHT) simulations. CHT problems involve both fluid and solid regions, with energy transfer occurring through conduction and convection. The finite volume method (FVM) is particularly effective for such coupled problems. This paper presents a detailed analysis of heat transfer mechanisms, focusing on water and air convection effects.
Figure 1 shows a computational mesh model that simplifies the heat transfer process by ignoring oil effects and air density differences. As an axisymmetric problem, only a sector needs to be analyzed. Bearings are located at points a and b, while the rest represents the housing and shaft. Air convection is considered at the interface between the housing, shaft, and surrounding air. Figure 2 illustrates the temperature distribution, with warm colors indicating high temperatures and cool colors showing low temperatures.
Despite the power of computational tools, real-world engineering problems often involve uncertainties. Parameters like boundary conditions and material properties must be carefully considered. In the case of bearing housing heat transfer, water convection—driven by pump volumetric loss—is a major factor. Its heat transfer coefficient depends on the pump’s efficiency and can vary due to manufacturing tolerances. For a fire pump operating at speeds above 76 rpm, the heat transfer coefficient ranges from 390 to 1240 W/m²·°C when volumetric efficiency is between 90% and 98%.
Air convection, on the other hand, is natural and influenced by environmental factors. Fire pumps are typically installed indoors, where airflow changes are minimal, leading to relatively stable heat transfer coefficients. Empirical data suggests that air convection coefficients range from 5 to 25 W/m²·°C, depending on wind speed.
Since water convection has a much higher heat transfer coefficient than air, it plays a dominant role in temperature distribution. As shown in Figure 3, variations in the water convection coefficient have a more significant impact on maximum bearing housing temperature than air convection. With a single bearing generating 1000W of heat and an ambient temperature of 20°C, it’s clear that controlling water convection is critical.
To effectively manage temperatures, reducing volumetric efficiency slightly may help. If the maximum temperature is to stay below 70°C, the water convection coefficient should not drop below 500 W/m²·°C. Based on this, pump design and component dimensions should be optimized accordingly. This approach ensures better thermal management and improved operational reliability.