A typical plate and frame heat exchanger is composed of gasketed pressed metal plates attached to carrying bars and secured between two covers that are fastened with compression bolts. Hot and cool process fluids run through the device at the corners. A dual-gasket seal prevents leakage into the environment or the fluids coming in contact with the plates, and the plates are compressed so that they retain pressure. Spacing in plate and heat exchangers varies with particle size and according to a formula.
The unit works by causing turbulence between the plates, an effect achieved through the design, which incorporates narrow gaps with a high number of contact points with high-heat-transfer coefficients (up to 14,200 W/m2 °C). This also can crease very high pressure drops per length, but this is mitigated by keeping the channel plate lengths fairly short, under three meters.
There are numerous plate designs and sizes, as well as two different styles of channel plates — chevron type channel plate being used by oil & gas and washboard type used by food processor. The plates are thin, which enhances heat transfer, although this can be somewhat reduced if alloy materials are required.
It’s easy to expand the unit in the field, as the original frame is typically designed to fit 15-20 percent more channel plates above the original design. To expand a unit, you only have to unscrew the carrying bolts and remove the frame plate, add the new channel plates, and close the unit.
One drawback to these otherwise quite useful devices is a short gasket life due to high operating temperatures and pressure, and it’s best to ask suppliers to offer a guaranteed lifetime.
Plate and heat exchangers are typically used in liquid-liquid services, but as they have a long history in the food industry, they are also commonly used with steam heaters and evaporators.
These devices make it possible to carefully control temperature and have a heat transfer surface that can be easily cleaned; these two aspects were a boon to the food industry.