The margin of heat exchanger is generally divided into fouling margin and corrosion margin. Generally, the corrosion margin of plate heat exchanger is not considered, so the corrosion margin of plate material is 0. Unless otherwise specified, only the corrosion margin of unlined nozzle is considered. The scaling margin is calculated as follows:
Kclean: clean heat transfer coefficient, heat transfer coefficient before scaling
Kservice: operating heat transfer coefficient, heat transfer coefficient after scaling
The conventional fouling resistance of shell and tube heat exchanger is not suitable for the thermal calculation of plate heat exchanger. The fouling resistance of plate heat exchanger should not be greater than 1 / 5 of the published fouling resistance of shell and tube heat exchanger. If the actual fouling resistance is known, it should be clearly pointed out. In the absence of a suitable or reference fouling thermal resistance, at least 10% fouling margin should be retained. For crude oil medium or other easy scaling medium, the margin can be increased to 25%. The wall shear stress of plate in plate heat exchanger is an index to measure the scaling tendency. Generally, the minimum wall shear stress should be greater than 50pA. If there are particles in the medium and the particle size is greater than 50% of the plate spacing, a filter shall be provided.