The plate heat exchanger is a new type of high efficiency heat exchanger which is assembled by a series of metal plates with a certain corrugated shape. A thin rectangular channel is formed between the various phe plates, and heat is exchanged through the metal sheets. The plate heat exchanger is ideal for heat exchange between liquid-liquid and liquid-vapor. The solderless structure of the plate heat exchanger makes it easy to disassemble cleaning or replacement, increase or decrease the plate. Therefore it has high flexibility. The smooth surface of the metal plates and the high turbulence of the fluid in the channel will result in a thinner scale, and the thermal resistance coefficient is only 1/5 of that of the tubular heat exchanger. When the fluid leaks from the gasket, it can only flow out of the drain without mixing. The high heat transfer efficiency of the countercurrent mode makes the temperature difference at the end only 1℃, and the heat recovery rate is as high as 95%.