Plate heat exchangers are devices used to transfer heat from one fluid to another. The fluids do not come into direct contact - they are kept separate by metal transfer plates laid parallel to each other. In other words, these devices work via the principle of indirect heat exchange, in which heat is transferred via an intervening medium.
Plate heat exchangers are used with water, oil, refrigerant and other fluids. In larger commercial models, the plates responsible for the transfer of heat are bolted together with supporting bars and sealed by rubber gaskets. In smaller models, by contrast, the plates are normally joined directly to each other.
Hot and cold liquid flows in opposing currents - typically parallel to each other - through separate channels or tubes in the spaces between each plate, from the inlet tubes to the outlets. A lengthy, irregular channel for hot fluid runs alongside one side of each plate, and a channel for cold fluids alongside the other. Each channel creates a large surface area for the fluid to emit or absorb heat. The amount of heat transferred over an area is referred to as the heat transfer coefficient. An additional fixed plate secures the device and a flexible plate responds to pressure.
The transfer plates are typically made from stainless steel, which is noted for its strength, corrosion resistance, and ability to withstand high temperatures and pressures. It is also food-safe, so can be used with food, drink and pharmaceutical products. However, some models feature non-ferrous metals such as aluminium, copper and titanium.
Plate heat exchangers are also known as plate and frame heat exchangers.
