Heat Transfer Calculation and Temperature Control Measures for Fire Pump Bearing Housing

To identify the cause of inconsistent temperature variations in the heating response of fire pump bearing housings, conjugate heat transfer (CHT) numerical analysis was conducted on the housing's heat transfer. This revealed that effective volume loss is the primary economic factor influencing the severity of heating in pump bearing housings, leading to research and improvements in the pump's structural design dimensions. Diesel-powered fire pumps are categorized into different types based on various classification methods. With their fully sealed, leak-free, and corrosion-resistant characteristics, they are widely used in environmental protection, water treatment, and firefighting sectors for pumping various liquids. They are ideal pumps for creating leak-free, pollution-free workshops and factories. The pump types used in firefighting systems are similar, differing only in head and flow rate. During maintenance of vertical fire pumps, fault diagnosis is critical. Below are common issues and corrective measures for targeted troubleshooting. For automatic inspection cabinets of fire pumps, the centerline of the impeller outlet (i.e., the midline of the outlet width) must align with the centerline of the volute inlet. If misalignment occurs, adjust by adding shims between the impeller hub and shaft shoulder. Maintain both centerlines within 0.5 mm tolerance. For high specific speed pumps, slight deviations have minimal impact. However, for medium-to-low specific speed pumps with narrow impeller outlets (e.g., 10 mm width), a 1 mm deviation from the volute centerline significantly affects pump performance. It is recommended that after adjustment, the deviation between the two centerlines (impeller and volute) be controlled within 5% of the impeller outlet width.

During operation of large fire pumps, the bearing housing often overheats, with temperatures reaching above 70°C. High temperatures degrade lubricant performance. Tests indicate that even within the same batch, the maximum housing temperature cannot be controlled by altering bearing types or adjusting the installation clearance of radial thrust bearings. Therefore, it is essential to identify the root cause of temperature uncertainty and implement effective control measures. Numerical calculations of conjugate heat transfer (CHT) revealed the primary cause of elevated temperatures. The conjugate heat transfer problem can be divided into two regions: the fluid-filled zone and the solid zone. Energy flows between these two regions through diffusion processes. Finite Element Analysis (FEM-RRB) is highly suitable for pure solid heat transfer problems, while the Finite Volume Method (fVM) based on finite elements is more appropriate for conjugate heat transfer problems involving fluids. This article employs the finite volume method.

Analysis of Heat Transfer Computation Results

The mesh model calculation disregards the influence of lubricating oil within the housing and the impact of air density differences on heat transfer. This problem exhibits axisymmetry, allowing calculation of a sector area. Points A and B represent bearing mounting positions, with water contained within the frame. The remaining areas constitute the housing and shaft, where air-contact surfaces define convective heat transfer boundaries. Calculation Results: Warm colors indicate high temperatures, cool colors indicate low temperatures. Although computers possess strong computational analysis capabilities, real-world engineering problems can be complex, and relevant calculation parameters are approximate to some extent. This affects computational accuracy, and we must fully understand this when performing calculations. When analyzing results, note the impact of boundary condition uncertainties. In bearing housing heat transfer calculations, water convective heat transfer involves forced convection caused by pump volumetric losses. Its heat transfer coefficient relates to pump volumetric losses, which should be controlled during design. However, dimensional deviations during manufacturing introduce uncertainties in volumetric losses, leading to uncertainties in the water convective heat transfer coefficient. Calculations indicate significant variations in the heat transfer coefficient. For fire pumps with a specific speed ns=76, when volumetric efficiency ranges from 90% to 98%, the heat transfer coefficient corresponding to the same flow rate typically varies between 390 W/m²·°C and 1240 W/m²·°C. Air convective heat transfer falls under natural convection, where the heat transfer coefficient depends on the pump's environment, introducing additional uncertainty. Considering fire pumps are typically installed indoors with minimal airflow velocity variation, the heat transfer coefficient remains relatively stable. If wind speed varies between 0 m/s and 6.4 m/s, empirical formulas indicate the average air heat transfer coefficient ranges from 5 W/(m²·°C) to 25 W/(m²·°C).

The convective heat transfer coefficient for water is significantly greater than that for air, making it the primary factor influencing heat transfer. Forced convective heat transfer can be controlled by designers.