The Plate Heat Exchanger consists of a stack of cold pressed, corrugated metal plates clamped together in a frame. The fluids are spread out over the plates and thus exposed to a much larger surface area. This makes plate heat exchanger more advantageous compared to the conventional heat exchanger. The gap between two plates varies from 2 - 5 mm. Each plate has four corner ports which, in pairs, provide access to the flow passages on either side of the plate. The frame consists of an upper and lower carrying bar that supports and aligns the plates and two covers (pressure plates- one fixed and the other movable) that compress the corrugated plates. All wetted parts are accessible for inspection by removing the clamping bolts and rolling back the movable cover. Sealing of the gap between two plates is accomplished by means of elastomeric gaskets (made of Nitrile rubber, EPDM, butyl rubber, PTFE etc.) which direct the two streams exchanging heat into their proper flow paths. The gaskets are usually designed with a double seal to prevent intermixing of fluids. The fluid flow between the successive pairs of plates in countercurrent/co-current mode. Successive plates are assembled with their patterns pointing in opposite directions, thereby producing a complex three dimensional flow passage of almost constant cross-sectional flow area. The corrugations increase the plate rigidity, increase the effective surface area and promote turbulence. The smaller hydraulic diameter of the flow path provides efficiencies of up to five times those achieved in a shell and tube version for a similar application.

Advantages:

1. PHE offers a high heat transfer coefficient on both sides of the plates.
2. It is a cheaper alternative if exotic materials are required due to the corrosive nature of the fluid.
3. It is more suitable for viscous fluid.
4. It is easy to clean and maintain.
5. It is easy to increase the heat transfer area because all connections are on one side (plate can be added from the other side).

Disadvantages:

1. It is of proprietary design from a limited number of suppliers.
2. High pressure drop and not suitable for application involving pressure greater than 30 bar.
3. Plugging in the case of services involving slurries.
4. Temperature is limited to about 2500C due to performance of available gasket materials.

The corrugations on the plates will increase the projected plate area, and reduce the effective gap between the plates. For rough sizing, where the actual plate design is not known, this increase can be neglected. The channel width equals the plate pitch minus the plate thickness.

There is no heat transfer across the end plates, so the number of effective plates will be the total number of plates less two.

Conclusion: This manual provides insights into how flow rate and temperature affect the heat transfer coefficient in plate heat exchangers. By understanding these effects, you can optimize heat exchanger performance, improve energy efficiency, and make informed design decisions.