Plate Heat Exchangers were first produced in the 1920s and have since been widely used in a great number of sectors.A plate exchanger consists of a series of parallel plates that are placed one above the other so as to allow the formation of a series of channels for fluids to flow between them.  The space between two adjacent plates forms the channel in which the fluid flows.Inlet and outlet holes at the corners of the plates allow hot and cold fluids through alternating channels in the exchanger so that a plate is always in contact on one side with the hot fluid and the other with the cold.The size of a plate can range from a few square centimeters (100 mm x 300 mm side) up to 2 or 3 square meters (1000 mm x 2500 mm side). The number of plates in a single exchanger ranges from just ten to several hundred, so reaching surface exchange areas up to thousands of square meters.Generally, these plates are corrugated in order to increase the turbulence, the thermal exchange surface and to provide mechanical rigidity to the exchanger. Corrugation is achieved by cold forging of sheet metal with thicknesses of 0.3mm to 1 mm.The most frequently used materials for the plates are stainless steel (AISI 304, 316), titanium and aluminium.The corrugation on the plates forces the fluid on a tortuous path, setting a space between two adjacent plates b, from 1 to 5 millimeters.The fluids can cross the channels in series (a less common solution) or in parallel by making counter-current or current configurations.The serial configuration is used when there is a small flow rate for each fluid but high heat jump; the greatest problem is with a high pressure drop and an imperfect counter-current.The parallel configuration with countercurrent channels is used for high flow rates with moderate temperature drops, and is the most widely used.When there is a great difference between the flow rates (or between the maximum permissible pressure drop) of the two fluids, the exchanger can run twice by the fluid with a lower flow (or higher losses) to balance the values of pressure drops or specific flow rates in the channels.One of the most common problems for plate heat exchangers is an irregular supply of the all channels in parallel. In fact, the fluid tends to distribute in greater quantities in the first channels rather than the last ones in order to balance the pressure drop.As the number of plates increases, even distribution declines, resulting in a decrease in the overall performance of the exchanger.

There are two basic types of plate heat exchangers: BPHE-Brazed Plate Heat Exchangers and PHE-Plate Heat Exchangers.