The shell and tube heat exchanger is made up of a bundle of parallel heat exchanger tubes held in place with tube sheets and placed into a shell. Fluid flows through the tubes and exchanges heat with fluid that is external to the tubes. There are quite a variety of flow options for shell and tube heat exchangers, as discussed in the following sections. In all of the configurations for shell and tube heat exchangers, one fluid passes through the tubes, the tube side fluid, and the other passes through the shell, the shell side fluid. The type of designed that is employed determines the rate at which heat exchange occurs. We will attempt to give you a brief overview of how shell and tube heat exchanger systems work and which type might best suit your needs.
Heat is exchanged between to fluids, these fluids are called the shell side fluid and the tube side fluid.
Additional important components of these systems include the tube sheet, baffles, and channels for the tube side fluid, and inlet and outlet nozzles for both tube and shell fluid. The purpose of the tube sheets is to keep the tubes in place and increase the efficiency of heat exchange by creating turbulence. The end channels are used to channel the fluid to either the outlet nozzle, or direct the fluid back to the other end of the heat exchanger for another flow through the system.
There are two general classifications for this type of heat exchange system, namely straight tube and U-tube designs. Usually, tube sheets are in place to secure the position of the tubes and to baffle the flow of shell fluid. When an U-tube design is used, the fluid enters and exits the exchanger at the same end. This should serve as a guide to the primary difference in designs of shell & tube heat exchangers.
The other type of design is the straight tube exchanger. For fluids that tend to foul the tubes, a straight tube heat exchanger is used, due to its relative ease of cleaning. The U-tube heat exchanger works well if the two fluids have greatly different thermal expansion characteristics, because it can allow the tube and the shell to expand or contract independently.
In reference to the tube side fluid, the number of passes refers to the number of times the tube side fluid is redirected within the system prior to leaving via the exit nozzle. The most common designs of shell and tube heat exchangers utilize one, two, or four passes, however other designs can be custom made. The U-tube exchanger has an inherent two pass system in place. For a straight tube, two pass heat exchanger, instead of an U-tube bundle, the end channel and an internal horizontal baffle, are used to cause the two passes.
The choice of configuration for a shell and tube heat exchanger affects the overall heat transfer coefficient and thus affects the heat exchanger tube surface area needed. The fluid flow in the heat exchange system is commonly a combinations of cross flow, counter flow and parallel flow. But, counter flow is the most efficient type of flow for minimizing the amount of surface area required to obtain effective heat exchange.
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A very common heat exchange design is called a shell and tube heat exchanger. The heat transfer coefficient affects the heat transfer rate and the total heat exchanger tube area needed. Several different options are available depending upon the specifics of your particular application.
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