On-site O&M personnel often encounter this problem during equipment modification or spare parts replacement: under the same heat load requirement, the heat transfer area estimated by experience deviates from actual operating performance. The model selection verification of the GCH-150 shell-and-tube heat exchanger needs to be implemented one by one from four aspects: design pressure, design temperature, heat transfer area, and nozzle diameter.
Design Pressure and Design Temperature: Define Boundaries First, Then Discuss Area
Design pressure determines the wall thickness grade of the shell, tube bundle, and flanges, while design temperature affects the allowable stress values of materials. The two parameters shall be marked separately according to the extreme working conditions that may occur on the process side, and the same value shall not be used for both the shell side and the tube side. Only after the boundary conditions are clarified can reliable inputs be provided for heat transfer calculation.
Heat Transfer Area Calculation: Back-Calculate Structural Parameters from Heat Transfer Coefficient
The heat transfer area is jointly determined by heat load, logarithmic mean temperature difference, and heat transfer coefficient. The heat transfer coefficient shall be selected in combination with medium physical properties, flow velocity, and fouling thermal resistance; there are differences in the value ranges for working conditions such as steam-water and water-water. After the area calculation is completed, back-calculate the number of tube passes, tube length, and tube bundle arrangement, avoiding determining the structure first and then supplementing the area calculation.
Nozzle Diameter Matching: The Balance Point Between Flow Velocity and Pressure Drop
The nozzle diameter shall match the on-site piping and pump head. If the diameter is too small, it will increase flow velocity and pressure drop; if too large, it will increase investment and may affect flow distribution. O&M personnel can check the nozzle specifications against existing piping dimensions and determine the structural parameters after confirming consistency with on-site working conditions.
Verification Sequence After Parameters Are Complete
Only after the above conditions are complete can the heat transfer area calculation and structural parameter back-calculation be completed. If insufficient heat transfer capacity occurs in on-site O&M, it is advisable to first recheck the values of these four parameters and then determine whether the equipment specifications need to be adjusted.
