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

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Process Equipment and Plant Design
A stuffing box is used for

Absorbing the contraction/expansion of pipeline due to temperature changes
Prevention of fluid leakage around moving parts
Reducing the resistance of fluid flow
Facilitating smooth opening and closing of a valve

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Process Equipment and Plant Design
High pressure fluid in a shell and tube heat exchanger should preferably be routed through the

Shell side for large overall heat transfer co-efficient
Shell side, if the flow is counter-current and tube side if the flow is co-current
Shell side for smaller total pressure drop
Tubes to avoid the expansion of high pressure shell construction

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