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

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Process Equipment and Plant Design
In a vertical short tube evaporator (Calendria type), the

All of these
Tube dia of 2.5-7.5 cms, tube length of 75-200 cms and cylinderical drum dia of 1-6 metres are normally used
Area of central downtake is equal to 40 to 100% of total cross-sectional area of the surrounding tube
Liquor is inside the tube while the steam is outside the tube

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Process Equipment and Plant Design
A stuffing box is used for

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

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