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Shell and tube heat exchanger design
Design & Technology
Pages 7 (1757 words)
Heat exchangers operations are guided by the fact that heat transfer is a product of temperature variation between cold process stream and hot process stream. A thin solid layer is used in separation of the two streams. …
The wall has to be conducive to allow heat exchange and still be sufficiently strong to withstand fluid/gas pressures. In shell and tube heat exchangers, two closed process streams move across the unit; one move inside the tube and the other moves on the shell side. Convection and conduction allows heat to pass from hot stream to cold stream from the side of the tube side or from shell side.
As temperature variation between the process streams rise, heat exchange rate for every surface area unit also rises. Conversely, heat exchangers per surface are unit drops non-linearly as temperature difference between the two process streams drops. Increasing the effective surface area of the entire system helps in maintenance of the total transfer of heat between two streams although eventually the system reaches a point where extra surface area has no effect on extra heat transfer.
The other variable which affects heat exchange in shell and tube exchanger is each process stream’s velocity. This velocity directly contributes to a rise in convection cold process and hot process streams. Raising the velocity also raises heat exchange, more especially, in countercurrent design. Finally, velocity increments are limited by maximum permitted for a specific metallurgy constituting shell or tube. For carbon steel, for instance, velocity cannot exceed 6 ft. /sec. whilst for the case of stainless and high-alloy steel; rate is 12 ft. /sec. for liquids. ...
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