How Does a Plate Heat Exchanger Work?

A plate heat exchanger consists of a stack of pressed metal plates clamped between two frame plates. Gaskets around the edge of each plate direct the hot fluid into the odd-numbered channels and the cold fluid into the even-numbered channels, so every hot channel is sandwiched between two cold channels (and vice versa) for highly efficient heat transfer.

Each plate is pressed with a herringbone or chevron pattern. When stacked, adjacent plates form a network of contact points and narrow channels that force the fluid into turbulent flow at very low velocities. This turbulence dramatically raises the heat-transfer coefficient and reduces fouling compared with smooth tubes.

Most plate heat exchangers are arranged in counter-flow: hot fluid enters at the top of one side and exits at the bottom; cold fluid enters at the bottom of the other side and exits at the top. This gives the highest possible log-mean temperature difference and supports close temperature approaches down to 1–2 °C.

Elastomeric gaskets seal the channels and keep the two fluids apart. In gasketed plate-and-frame units the gaskets are replaceable, so plates can be removed, inspected, cleaned and re-assembled in the field. Brazed and welded plate constructions eliminate gaskets at the cost of serviceability.

Standard gasketed plate units handle up to ~25 bar and ~180 °C. Above those limits, semi-welded, fully welded or plate-and-shell constructions extend the operating window. The right plate count, pattern and material are matched to the duty by the manufacturer's selection software.