**2.1 Design of plate heat exchangers**

The heat exchangers are mainly regarded as pressure vessels. For this reason, the choice of design pressure, design temperature and appropriate material is crucial in the design of PHEXs. Once these criteria are established, the necessary calculations are made for the design. In the design of a PHEX, the surface A for heat transfer, the logarithmic mean temperature difference (ΔTm) and the total heat transfer coefficient (K), pressure drop, physical size and economics are significant factors.
