The plate heat exchanger is a new type of high efficiency heat exchanger which is made of a series of metal sheets with a certain corrugated shape. A thin rectangular channel is formed between the heat exchanger plates, and heat is exchanged through the metal sheets. Compared with the conventional shell-and-tube heat exchanger, the heat transfer coefficient is much higher under the same flow resistance and pump power consumption, and there is a tendency to replace the shell-and-tube heat exchanger within the applicable range.The countercurrent of the plate heat exchanger is that the high-temperature steam enters from above and condensed water come out from bottom. The cold water enters and exits from below and comes out from top, Water outlet is the hot water we need in life. The logarithmic mean temperature difference of the countercurrent is larger than the forward flow, the reverse flow heat transfer allows the temperature to cross. In terms of heat transfer, the countercurrent flow is better than the downstream flow, and the heat transfer coefficient is high.