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

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

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

Is always less than arithmetic mean value, but more than geometric mean value
Is always more than arithmetic mean value and the geometric mean value
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

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