These are indirect heat exchangers where the heat transfer surface is formed by plates. They are compact in structure and have a large heat transfer area per unit volume. The main types include:
① Spiral Plate Heat Exchanger: Consists of two parallel metal plates rolled together at a certain distance. Cold and hot fluids flow in spiral channels on either side of the metal plates. This type of heat exchanger has a high heat transfer coefficient (approximately 1-4 times higher than shell-and-tube heat exchangers), a large average temperature difference (due to the complete counter-current flow of cold and hot fluids), low flow resistance, and is less prone to scaling; however, maintenance is difficult. The operating pressure should not exceed 2 MPa.
② Flat Plate Heat Exchanger: Consists of corrugated thin plates of a certain shape and gaskets stacked alternately and assembled using a frame. Cold and hot fluids flow through channels on either side of the corrugated plates, exchanging heat through the plates. The corrugated plates are typically made of thin plates of stainless steel, aluminum, titanium, molybdenum, etc., with a thickness of 0.5-3 mm. The advantages of flat-plate heat exchangers are their high heat transfer coefficient (approximately 2-4 times higher than shell-and-tube heat exchangers), ease of disassembly and cleaning, and the ability to adjust the heat transfer area by increasing or decreasing the number of plates. Operating pressure typically does not exceed 2 MPa, and operating temperature does not exceed 250℃.
③ Plate-fin heat exchangers consist of heat exchange plate bundles enclosed in a manifold with inlets and outlets for cold and hot fluids. The plate bundles are constructed by alternating layers of flat plates and corrugated fins, brazed together. Cold and hot fluids exchange heat on both sides of the flat plates. The fins increase the heat transfer area, promote fluid turbulence, and enhance the performance of the equipment. Plate-fin heat exchangers have a very compact structure (heat transfer area up to 4400 m²/m³), good heat transfer performance, and can operate at pressures up to 15 MPa. However, their manufacturing process is complex, the flow channels are small, and internal leaks are difficult to repair. Therefore, they are limited to use with clean, non-corrosive fluids, such as heat exchangers used for air separation.
