Plate heat exchanger is a new type of high efficiency heat exchanger which is composed of a series of corrugated metal sheets.In a pasteurizer for dairy processing, in order to increase the residence time of the dairy at the sterilization temperature, it is usually necessary to mount the retardation plate at a specific position of the sterilizer. In order to save floor space, some companies will adopt a double-frame structure. The structure has two forms. The first one is to share a maintenance space. One fixed compression plate is arranged on the left and right, and two movable compression plates are arranged in the middle. The second type is a common intermediate compression plate, and a movable pressing plate is arranged on each of the left and right sides. The structure of the double frame can be seen as two plate heat exchangers mounted together.