Pressure Drop

If it was acceptable at commissioning and has climbed since, the selection is not the cause. Rising drop at the same flow means channels are closing up - scale, debris caught at the port entry, or biological growth on an open cooling circuit.

The common field mistake is having nothing to compare against. Without guage points at the inlet and outlet of each side, and a reading taken when the unit was clean, nobody can say whether the pump is short of head or the exchanger is fouled. Fit the gauge points and record the clean figures. They also tell you when a cleaning has actually worked.

No. An allowable drop set far below what the pump can deliver forces the selection toward many plates at low channel velocity. The unit costs more, and slow channels foul faster because nothing scours the plate surface. On a refrigerant evaporator, low velocity also spoils distribution between channels.

State the head that is really available at the exchanger after the piping, valves and strainer have taken their share. A selection that uses most of that allowance runs cleaner and is usually the smaller unit.

Only if the plate type, plate count and pass arrangement all match. Change any one and the drop moves, even where the frame and the connections are identical. An H plate in place of an L plate at the same count will meet the duty with room to spare and may still starve the system of flow, because the existing pump was chosen against the old unit.

When the nameplate is unreadable or the original is another make, send the pump curve or the measured drop on each side along with the duty. We then match the hydraulic behavior as well as the thermal one.

Because part of the drop is in the ports, not the channels. More plates split the flow across more channels, but every bit of it still has to pass through the same four connections and the same port holes down the pack. As flow rises the port loss becomes the larger share, and extra plates do nothing for it.

That is the meaning of the maximum flow on a datasheet: a ceiling set by the ports, not a design flow. A duty running near that ceiling belongs in the next frame up, where the larger ports bring the total back down.