Temperature Differences in Shell-and-Tube Heat Exchangers

3 TEMPERATURE DIFFERENCES IN SHELL-AND-TUBE HEAT EXCHANGERS 

If both fluids had been isothermal, then the logarithmic and average temperature differences would be equal and ATh = ATc = AT. It should also be noted that  

The Ft correction factor is usually correlated in terms of two dimensionless ratios, the ratio of the two heat capacity 

Note therefore that Fr depends only on the inlet and outlet temperatures of the streams in a 1-2 heat exchanger. An expression can be developed for the FT in a 1-2 heat exchanger. The proof is lengthy and can be found elsewhere1,6. 

Consequently, to be confident in a design, those parts of the I r chart where slopes are steep should be avoided, irrespective of FT 0.757. A simple method to achieve this is based upon the fact that for any value of R there is a maximum asymptotic value for P, say Pmax, which is given as I f tends to — oo, and is given by7  

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