The Heat Exchange Always Takes Place Between Two Fluids Through Heat Exchanger Tube Wall

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. The heat exchange always takes place between two fluids through the heat exchanger tube wall. There are numerous design variations that are utilized to accomplish heat transfer within heat exchangers. In all these type of heat exchangers the mechanism of heat transfer is the same, one fluid flowing through the tubes exchanges heat with another fluid that flows through the shell. The particular design that is utilized determines the heat transfer coefficient and the rate at which heat exchange occurs. We will attempt to give you a brief synopsis of typical shell and tube heat exchangers that are commonly utilized. Heat is exchanged between to fluids, these fluids are called the shell side fluid and the tube side fluid. Other components that are important in this type of heat exchange system are the inlet and outlet nozzles for the tube and shell fluid, as well as tube sheets and baffles that are used to accelerate the heat exchange process. The purpose of the tube sheets is to keep the tubes in place and increase the efficiency of heat exchange by creating turbulence. End channels are designed to either direct the fluid back to the opposite end of the heat exchanger or funnel it to the outlet nozzle. One way of classifying shell and tube heat exchangers is U-tube or straight tube. Most often there are tube sheets which baffle the fluid flow and hold tubes in place. When a U-tube design is used, the fluid enters and exits the exchanger at the same end. This should serve to give you a general idea regarding the basic differences in shell & tube heat exchanger. Another design the is frequently used is the straight tube exchanger. A straight tube heat exchanger is easier to clean than a U-tube heat exchanger, so it is better for a tube side fluid that tends to foul the tube, causing a need for regular cleaning. For fluids that have far different thermal expansion properties a U-tube design is used since it allows for independent expansion of the tube and shell. 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. With straight tube designs and internal baffle is used to redirect the fluid for a second pass. The type of design that is utilized determines the coefficient of heat transfer and thus has an affect upon the surface are needed to obtain the desired level of heat exchange. The flow pattern through most shell and tube heat exchangers is a combination of counter flow, cross 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. Source: w3devil.com