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

To identify the cause of varying bearing housing temperatures in fire pumps, numerical calculations of conjugate heat transfer (CHT) through the housing revealed that volumetric loss is the primary factor influencing bearing housing heating. This insight led to improvements in the pump's structural dimensions. In the volute pump of the fire pump automatic inspection cabinet, the centerline of the impeller outlet—defined as the centerline of the impeller outlet width—should align with the centerline of the volute inlet. If misalignment occurs, adjust by inserting shims between the impeller hub and shaft shoulder. Maintain both centerlines within a 0.5 mm tolerance range. For pumps with high specific speed, minor deviations have negligible performance impact. However, for medium-to-low specific speed pumps with narrow impeller outlets (e.g., 10 mm outlet width), a 1 mm deviation from the volute centerline significantly affects fire pump performance. After adjustment, it is recommended to control the deviation between the two centerlines (impeller and volute) within 5% of the impeller outlet width. Inspect and adjust the packing in the fire pump control cabinet, replacing it as required. Adjust the mechanical seal (refer to the manufacturer's instructions provided with the pump or consult the manufacturer). During maintenance of horizontal fire pumps, fault diagnosis is a critical step. Below are several common faults and their remedies to facilitate targeted troubleshooting. Air-lift equipment features advanced multi-functional programmable control, displays operational status on screen, accepts various fire signals, and can interface with fire control centers. The fire pump automatic inspection cabinet allows increasing or decreasing pump stages without altering installation footprint, achieving required impeller outer diameter by trimming. This capability is unique among pumps. Horizontal fire pumps feature compact structure, small footprint, and aesthetically pleasing design. Their vertical configuration minimizes installation space, with the center of gravity positioned at the pump base center, enhancing operational stability and service life.

Bearing housings in large fire pumps frequently overheat during operation, reaching temperatures exceeding 70°C. Excessive heat degrades lubricant performance. Test results indicate significant variation in maximum operating temperatures even within the same product batch. Adjusting bearing types or radial thrust bearing clearances fails to control ambient temperatures. Therefore, identifying the root cause of temperature fluctuations and implementing effective control measures is essential. Numerical simulations of conjugate heat transfer (CHT) in bearing housings revealed excessive temperatures as the primary cause. Conjugate heat transfer problems can be divided into two computational domains: the fluid-filled region and the solid region. Energy flows between these two domains through diffusion processes. Regarding computational methods, the Finite Element Method (FEM) is highly suitable for pure solid heat transfer problems. For conjugate heat transfer problems involving fluids, the Finite Volume Method (FVM) based on FEM proves more effective. This study employs the Time-Dependent Finite Volume Method.

1. Analysis of Heat Transfer Computation Results

The influence of oil on heat transfer and the effect of air density on heat transfer were neglected. This problem exhibits axisymmetry. Consequently, areas A and B can be calculated as fan surfaces, where A and B denote bearing mounting locations, the wireframe represents water, and the remainder constitutes the housing. Heat transfer boundaries include the contact regions between the body and shaft/housing, as well as between the shaft and air. Figure 2 displays the computational results, where warm colors indicate high temperatures and cool colors denote low temperatures. Although computers possess robust computational analysis capabilities, real-world engineering problems can be complex, and relevant computational parameters exhibit certain similarities. This affects calculation accuracy and must be fully understood during computations. When analyzing results, note the impact of boundary condition uncertainties. In calculating heat transfer within the bearing housing, water convective heat transfer refers to forced convection caused by pump volumetric losses. The heat transfer coefficient correlates with pump volumetric losses and should be controlled through design. However, dimensional deviations during manufacturing introduce uncertainties in volumetric losses, leading to uncertainties in the water heat transfer coefficient. Results indicate significant variations in heat transfer coefficients. For fire pumps with a specific speed NS = 76, corresponding flow heat transfer coefficients typically range from 390 W/m²·°C to 1240 W/m²·°C when volumetric efficiency falls between 90% and 98%. Air convective heat transfer constitutes natural convection heat transfer. Its heat transfer coefficient depends on the pump's ambient environment, introducing inherent uncertainty.