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

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

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Process Equipment and Plant Design
In a double pipe (concentric) heat exchanger, the hydraulic radius for heat transfer (for a fluid flowing through the annulus) would be

Less than that for fluid flow
D₂ - D₁ (D₁ and D₂ are I.D. of inner and outer pipes respectively)
More than that for fluid flow
Same as that for fluid flow

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Process Equipment and Plant Design
Pick out the wrong statement pertaining to the design of a horizontal tube evaporator.

Liquor flows inside the tube, while the steam is outside submerging the tube
Its usual dimensions are: tube dia = 2-3 cms; evaporator body dia = 1-4 metres and evaporator height = 2.5-4 metres
It is suitable for process, in which the final product is a liquor instead of solid
It is unsuitable for concentrating those liquids, which form a scale or deposit salt

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