Plate heat exchanger is a new type of high efficiency heat exchanger which is made of a series of metal sheets piled up having a certain ripple shape. A thin rectangular channel is formed between the plates, and the heat exchanging is carried through the plate. The plate heat exchanger is an ideal for liquid - liquid, liquid – vapor heat exchanging. It has the characteristics of high heat transfer efficiency, small heat loss, compact structure, small land coverage, convenient installation and cleaning, wide application and long service life, etc. Under the same situation of pressure loss, its heat transfer coefficient is 3-5 times higher than that of the tube type heat exchanger. It covers an area of 1/3 of the tube type heat exchanger, and its heat recovery rate can be as high as 90%.