Chemical Engineering MCQs

Page No. 457

Nusselt number is the ratio of the ____________________?


aTemperature gradient of the wall to that across the entire pipe

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bTemperature difference to the temperature gradient at the wall

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cHeat flux at the wall to that across the entire pipe

✓


dNone of these

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Prandtl number is the reciprocal of____________________?


aThermal diffusivity/Momentum diffusivity

✓


bThermal diffusivity × Momentum

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cThermal diffusivity × Mass diffusivity

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dMass diffusivity × Momentum diffusivity

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For a multipass shell and tube heat exchanger, the LMTD correction factor is always________________?


a1

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b> 1

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c< 1

✓


dBetween 1 & 2

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View Answer < 1

Thermal conductivity of a gas at low density, ___________ with increase in temperature ?


aDecreases

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bIncreases

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cRemains unchanged

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dMay increase or decrease; depends on the gas

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View Answer Increases

The interchange factor for radiation heat transfer from surface ‘x’ to surface ‘y’ in case of an infinite parallel planes with emissivities εx & εy is given by_______________?


aεx + εy

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bεx . εy

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c1/εx + 1/εy

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d(εx + εy)/( εx + εy – εx . εy)

✓



With increase in temperature, the thermal conductivity of a gas ___________________?


aIncreases

✓


bDecreases

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cRemain same

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dMay increase or decrease depending on the type of gas

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View Answer Increases

Which area is used in case of heat flow by conduction through a cylinder ?


aLogarithmic mean area

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bArithmetic mean area

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cGeometric mean area

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dNone of these

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View Answer Logarithmic mean area

The rate of emission of radiation by a body does not depend upon the__________________?


aWavelength of radiation

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bSurface temperature of the body

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cNature of the surface

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dShape and porosity of the body

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In a cooling tower, water becomes cool by________________?


aLoosing sensible heat

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bHeat transfer to surroundings

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cVaporisation due to heat loss to air

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dLoosing latent heat

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View Answer Loosing sensible heat

Out of the following four assumptions used in the derivation of the equation for LMTD [LMTD = (Δt1 – Δt2)/ln(Δt1/Δt2)], which one is subject to the largest deviation in practice ?


aConstant overall heat transfer co-efficient.

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bConstant rate of fluid flow

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cConstant specific heat

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dNo partial phase change in the system

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