A plate heat exchanger passes two fluids through alternating gaps between thin plates. Use the view to look inside and follow both streams, then see how heat crosses the plate from hot to cold.
A plate heat exchanger transfers heat between two fluids that never mix. It is built from a stack of thin, slightly corrugated plates clamped together in a frame. One fluid runs through every second gap, the other through the gaps in between, and heat passes through the plates from the hotter stream to the cooler one.
Outside it is just a rectangular frame with four pipe connections. The whole duty is done by what happens in the narrow channels between the plates, so a cutaway is the only way to see how the two streams are kept apart while heat is handed from one to the other.
Warm fluid is fed in through the hot inlet and distributed into every second channel in the stack. Gaskets keep it from spilling into the channels next door.
Cool fluid enters through the cold inlet and takes the alternating channels. A hot channel and a cold channel therefore sit side by side, with a single plate between them.
Because only a thin metal wall separates the streams, heat flows straight across it from the hot side to the cold side. The corrugations stir the fluid so the heat reaches the plate all along the channel.
The hot fluid exits at the far corner, having given up heat, and the cold fluid exits warmer on the other side. The two streams stay separate the whole way through.
They never mix. Each fluid stays in its own set of channels, and every hot channel is separated from the next cold channel only by a thin metal plate. Gaskets around the plate edges seal the two streams from each other and from the outside.
Heat always flows from the hotter side to the cooler side. Because only a thin metal plate sits between the streams, heat crosses it quickly, cooling the hot fluid and warming the cold one.
Counter-flow keeps a large temperature difference between the two streams along the whole stack. That lets the exchanger recover more heat than if both fluids ran the same way.
Narrow gaps put the fluid close to the plate and speed it up, so heat does not have to travel far. That is why a plate exchanger can be far smaller than a shell-and-tube unit for the same duty.
The frame. Thick end plates and long tie bolts press the plate pack tightly so the gaskets seal and no fluid leaks between channels.