Chemical Engineering MCQs

Page No. 442

Harmonic mean temperature difference is given by_________________?


a√(ΔT1 . ΔT2)


b2 (ΔT1 . ΔT2)/(ΔT1 + ΔT2)


c2 (ΔT1 . ΔT2)/(ΔT1 – ΔT2)


d(ΔT1 – ΔT2)/(ΔT1 . ΔT2)



If average heat transfer co-efficient is ha and the local coefficient at the end of the plate is hl then in case of heat transfer to a fluid flowing over a flat plate, heated over its entire length________________?


aha = hl


bha = 2hl


cha = 0.5 hl


dha = 0.75 hl


View Answer ha = 2hl

The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as______________?


a(ΔT)1/4


b(ΔT)1/2


c(ΔT)5/4


d(ΔT)3/4


View Answer (ΔT)3/4

Heat transfer occurs by natural convection because change in temperature causes difference in__________________?


aViscosity


bDensity


cThermal conductivity


dHeat capacity


View Answer Density

A metal ball of radius 0.1 m at a uniform temperature of 90°C is left in air at 30°C. The density and the specific heat of the metal are 3000 kg/m3 and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m2.K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60°C is_________________?


a555


b55.5


c0.55


d0.15


View Answer 0.15

The ratio of momentum diffusivity to thermal diffusivity is the ______________ number?


aPrandtl


bNusselt


cStanton


dGrashoff


View Answer Prandtl

What is the thermal conductivity of a perfect heat insulator ?


aZero


bOne


c


dBetween 0 and ∞


View Answer Zero

The value of Stefan-Boltzmann constant in SI unit is_________________?


a5.6697 × 10-8W/m2.°K4


b0.1714 × 10-8W/m2.°K4


c5.6697 × 10-8kcal/m2. °K4


d0.1714 × 10-8kcal/m2. °K4



A metal wire of 0.01 m dia and thermal conductivity 200 W/m.K is exposed to a fluid stream with a convective heat transfer coefficient of 100 W/m2.K. The Biot number is ______________?


a5.6


b0.025


c3.5


d0.0035


View Answer 0.025

Air is best heated with steam in a heat exchanger of__________________?


aPlate type


bDouble pipe type with fin on steam side


cDouble pipe type with fin on air side


dShell and tube type



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