Design of Shell and Tube Heat Exchanger

The design of a shell-and-tube heat exchanger is an iterative process because heat transfer coefficients and pressure drop depend on many geometric factors, including shell and tube diameters, tube length, tube layout, baffle type and spacing, and the munbers of tube and shell passes, all of which are initially unknown and are determined as part of the design process. 

The previous procedure is tedious if done by hand calculations. Therefore, it is more convenient to conduct the design with available computer programs. For example, the HE ATX subroutine of the ASPEN PLUS simulator computes heat transfer coefficients, pressure drops, and outlet conditions for a shell-and-tube heat exchanger of known geometry, as illustrated in Example 13.7. It can be used by trial-and-error with the iterative procedure to design an exchanger. 

The HEATX subroutine (block) of the ASPEN PLUS simulator is used to make the calculations. It has built-in correlations of the type described above for estimating shell-side and tube-side heat transfer coefficients and pressure drops. The following results are obtained (both streams are liquid)  

Toluene exit temperature = 257.4°F Styrene exit temperature = 175.9°F Tube-side tube pressure drop = 3.59 psi Tube-side nozzle pressure drop = 0.56 psi Toluene exit pressure = 85.85 psia Shell-side baffled pressure drop = 4.57 psia Shell-side nozzle pressure drop = 4.92 psia Styrene exit pressure = 40.52 psia Heat transfer area (tube outside) = 3,217 ft  

Estimated overall heat-transfer coefficient, U , clean = 101.6 Btu/(hr-fF-°R) 

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For fixed tubesheet design of shell and tube heat exchangers don t allow too high a temperature difference between tubeside and shellside without providing a shellside expansion joint. The author has seen 70 F (one company) and 100°F (another company) used as this limit. An easy way to calculate the maximum stress is as follows ... 

Konings, A. M., Guide Values for the Pouling Resistance of Gooling Water with Different Types of Treatment for Design of Shell and Tube Heat Exchangers, Heat Transfer Eng, V. 10, No. 4.,p. 54 (1989). 

Butterworth, D. (1973) Conference on Advances in Thermal and Mechanical Design of Shell and Tube Heat Exchangers, NEL Report No. 590. (National Engineering Laboratory, East Kilbride, Glasgow, UK). A calculation method for shell and tube heat exchangers in which the overall coefficient varies along the length. 

A.C. Mueller, Thermal design of shell-and-tube heat exchangers for liquid-to-liquid heat transfer," Eng. Bull, Res. Ser., 121, Purdue University Eng. Exp. Sta., 1954. 

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