Heat Transfer
The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U0 = 400 W/m².K. The fouling factor after one year of operation is found to be hd0 = 2000 W/m².K. The overall heat transfer co-efficient at this time is

1200W/m².K
894W/m².K
333W/m².K
287 W/m².K

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Heat Transfer
A dilute aqueous solution is to be concentrated in an evaporator system. High pressure steam is available. Multiple effect evaporator system is employed, because

Total heat transfer area of all the effects is -less than that in a single effect evaporator system
Heat transfer co-efficient in a single effect is much lower than that in any effect in a multieffect system
Total amount of vapor produced per Kg of feed steam in a multiple effect system is much higher than in a single effect
Boiling point elevation in a single effect system is much higher than that in any effect in a multieffect system

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