Plate heat exchanger

A plate heat exchanger is a type of heat exchanger that uses metal plates to transfer heat between two fluids. This has a major advantage over a conventional heat exchanger in that the fluids are exposed to a much larger surface area because the fluids spread out over the plates. This facilitates the transfer of heat, and greatly increases the speed of the temperature change. It is not as common to see plate heat exchangers due to the fact that they need well-sealed gaskets to prevent the fluids from escaping, although modern manufacturing processes have made them feasible.

The concept behind a heat exchanger is the use of pipes or other containment vessels to heat or cool one fluid by transferring heat between it and another fluid. In most cases, the exchanger consists of a coiled pipe containing one fluid that passes through a chamber containing another fluid. The walls of the pipe are usually made of metal, or another substance with a high thermal conductivity, to facilitate the interchange, whereas the outer casing of the larger chamber is made of a plastic or coated with thermal insulation, to discourage heat from escaping from the exchanger.

The plate heat exchanger (PHE) was invented by Dr Richard Seligman in 1923 and revolutionised methods of indirect heating and cooling of fluids.

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Design of plate and frame heat exchangers

    The plate heat exchanger is a specialized design well suited to transferring heat between medium- and low-pressure liquids. Welded, semi-welded and brazed heat exchangers are used for heat exchange between high-pressure fluids or where a more compact product is required. In place of a pipe passing through a chamber, there are instead two alternating chambers, usually thin in depth, separated at their largest surface by a corrugated metal plate. The plate produces an extremely large surface area, which allows for the fastest possible transfer. Making each chamber thin ensures that the majority of the volume of the liquid contacts the plate, again aiding exchange. The plate design ensures that turbulent flow is maintained within the heat exchanger.

Basically, a plate heat exchanger consists of a series of thin, corrugated plates that are gasketed, welded together or brazed together depending on the application. The plates are compressed in a rigid frame to create an arrangement of parallel flow channels with alternating hot and cold fluids.

Due to corrugations in the plate, highly turbulent flow increases the heat transfer rate. As compared to shell and tube heat exchangers, the temperature approach in a plate heat echangers may be as low as 1 °C whereas shell and tube heat exchangers require an approach of gives 5°C or more. For the same amount of heat exchanged, the size of the plate heat exchanger is smaller, because of the large heat transfer area afforded by the plates (the large area through which heat can travel). Expansion and reduction of the heat transfer area is possible in a plate heat exchanger.

Evaluating plate heat exchangers

All plate heat exchangers look similar on the outside. The difference lies on the inside, in the details of the plate design and the sealing technologies used. Hence, when evaluating a plate heat exchanger, it is very important not only to explore the details of the product being supplied, but also to analyse the level of reasearch and development carried out by the manufacturer and the post-commissioning service and spare parts availability.

For the above reasons, plate heat exchangers are used for better and more controlled heat transfer.

See also

• Plate fin heat exchanger
• Heat transfer
• LMTD

Bibliography

• Sadik Kakac and Hongtan Liu (March 2002). Heat Exchangers: Selection, Rating and Thermal Design, 2nd Edition, CRC Press. ISBN 0-8493-0902-6. 
• T. Kuppan (February 2000). Heat Exchanger Design Handbook, 1st Edition, CRC Press. ISBN 0-8247-9787-6. 

• Update on compact composite plate heat exchangers by Per F. Peterson and Haihua Zhao, University of California, Berkeley.

• A screening method for the optimal selection of plate heat exchanger configurations by J.M.Pinto and J.A.W.Gut, University of São Paulo, Brazil.

• Designing novel compact heat exchangers for improved efficiency using a CFD code by Athanasios G. Kanaris, Katerina A. Mouza and Spiros V. Paras, Aristotle University of Thessaloniki.