Multipass heat exchanger is a particular type of ‘shell and tube’ heat exchanger. Here, the fluid flowing through tubes is made to flow multiple number of times in the path of another fluid flowing through shell. Generally, the second fluid is made to flow through a shell for once. In most of the commercial applications, Multi-pass heat exchanger is used to increase heat transfer rate by increasing the heat transfer surface area per unit volume. Thus, without any increase in size and space required for accommodation, the Multipass heat exchanger has high heat transfer capacity as compared to other heat exchangers of same size.
Construction of Multipass Heat Exchanger
Fig. 1: Multipass (Double pass) heat exchanger
Multipass heat exchanger consists of large number of tubes, arranged parallel to each other. The ends of tubes are mounted in a plate known as ‘tube sheet’. This assembly is called as ‘tube bundle’. Tube bundle is housed in a cylindrical vessel known as ‘shell’. The shell is closed on both sides using dish ends.
Working of Multipass Heat Exchanger
Fig. 1 shows cross-section of a heat exchanger with two tube-pass and one shell-pass. One of the fluids (water) enters the dish located at left side and flow through the tubes. The other fluid (steam) enters the shell and flows over the tubes. The transfer of heat takes place across the walls of tubes. Now, the water is made to change its direction. In the figure 1, it can observed that, water enters at the bottom end, moves from left to right. Now, the flow of water is reversed, i.e. water moves from right to left and exit from the top end. As the water passes two times in the path of steam, this heat exchanger is called as Two pass or Double pass heat exchanger. This is achieved by providing a baffle plate in the shell or partition in the dish ends. Therefore, number of times the changes ¡n the direction of fluid are termed as number of passes made by the fluid. Figure 2 shows four pass heat exchanger.
Fig. 2: Multipass (Four pass) heat exchanger
Applications of Multipass Heat Exchanger
- Thermal power plants,
- Refrigeration plants.
