How to properly install multi-pass plate heat exchangers

This week, let’s talk about mono pass and multi pass plate heat exchangers. Despite we’re used to see images of heat exchangers with the traditional four attachments on a single side, the front, there are also exchangers with attachments of two sides, both the front and the rear. These multi-pass heat exchangers have inside usually a particular scheme of the plates, called multi-pass design which involves a multi-pass flow control.

This multi-step diagram is employed in case we need very long thermal lenghts and very high temperature crossings, usually required in heat recovery applications. This sort of a ‘trick’ allows to stretch the plates, obtaining a thermal length of the plates a lot higher, in fact twice high compared to the height of the exchanger. This solution allows to push the recovery, that is the intersection of temperatures, up to very high limits.


On the other side, this solution brings some inconvenience, such as the pressure drops that will tend to increase. But it’s also true that those can be managed while designing the exchanger, by inserting them into the engineering software in order to compensate pressure drops by increasing the number of plates, i.e. the number of channels in parallel.

Another possible issue in case of a multi pass exchanger installation is the fact that it has connections on both the front and the rear, and it can bring some inconvenience. Having valves directly mounted on the rear side of the exchanger, when doing maintenance of the heat exchanger the pipes will make it difficult to access the rear stem to dismantle the plates, washing them, replacing the gaskets and so on. That’s why in case of multi-pass heat exchangers is suitable to install 90° curves on the rear connections, moving the valves outside the shape of the exchanger, so that during maintenance valves can be intercepted and the curves can easily be disassembled, gaining easy access to the rear stem.

One last issue that occurs with multi-pass exchangers is the fact that they cannot be boosted and upgraded without connection pipes adjustments.

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