Process Equipment and Plant Design
In the case of a shell and tube heat exchanger, the logarithmic mean temperature difference

May be either more or less than geometric mean and arithmetic mean value depending upon whether the flow of stream is co-current or counter-current
Is always less than arithmetic average value
Is always more than arithmetic mean value and the geometric mean value
Is always less than arithmetic mean value, but more than geometric mean value

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Process Equipment and Plant Design
Triangular pitch tube layout as compared to square pitch in a shell and tube heat exchanger

Facilitates comparatively easier external cleaning because of large clearance
Permits the use of more tubes in a given shell diameter
Permits the use of less tubes in a given shell diameter
Both B and C

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Process Equipment and Plant Design
Pick out the wrong statement pertaining to a shell and tube heat exchanger.

The minimum value of baffle spacing is 50 mm
The maximum value of baffle spacing is equal to the I.D. of the shell
Disk and doughnut baffle is the most commonly used baffle
The maximum unsupported tube span is generally about 75 times tube diameter, but is reduced to about 60 times for aluminium, copper & alloys of these

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Process Equipment and Plant Design
In a shell and tube heat exchanger, triangular pitch arrangement as compared to square pitch arrangement

Can accomodate less number of tubes for a given shell diameter
Results in higher shell side pressure drop
Creates relatively lower turbulence on the shell side resulting in lower shell side heat transfer co-efficient
Facilitates easier shell side cleaning; hence is more suitable for handling high dirt factor shell side fluid

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