Chemical Engineering MCQs

Page No. 458

What is the logarithmic mean of r1 and r2 ?


a(r1 – r2)/ln(r1/r2)


b(r1 – r2)/ln(r2/r1)


c(r2 – r1)/ln(r1/r2)


d(r1 – r2)/-ln(r1/r2)


View Answer (r1 – r2)/ln(r1/r2)

The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe, where the wall heat flux is constant, is__________________?


a2.36


b4.36


c120.36


dDependent on NRe only


View Answer 4.36

The overall resistance for heat transfer through a series of flat resistance, is the _____________ of the resistances?


aAverage


bGeometric mean


cProduct


dSum


View Answer Sum

Heat transfer co-efficient equation for forced convection, Nu = 0.023 Re 0.8. Pr n, is not valid, if the value of __________________?


an = 0.4 is used for heating


bn = 0.3 is used for cooling


cReynolds number for the flow involved is > 10000


dReynolds number for the flow involved is < 2100



An ejector is used to__________________?


aIncrease pressure


bIncrease temperature


cRemove condensate


dNone of these


View Answer None of these

In a laboratory test run, the rate of drying was found to be 0.5 x 10-3 kg/m2.s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m2/kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is______________________?


a2000


b4000


c5000


d6000


View Answer 5000

Peclet number (Pe) is given by____________________?


aPe = Re.Pr


bPe = Re/Pr


cPe = Pr/Re


dPe = Nu.Re


View Answer Pe = Re.Pr

In Fourier’s law, the proportionality constant is called the______________________?


aHeat transfer co-efficient


bThermal diffusivity


cThermal conductivity


dStefan-Boltzmann constant


View Answer Thermal conductivity

When the ratio of the Grashoff number and to the square of Reynolds number is one, the dominant mechanism of heat transfer is _______________?


aFree convection


bEntry length problem in laminar forced conduction (developing thermal boundary layer)


cMixed convection (both free and forced)


dForced convection



The units of resistance to heat transfer is _____________________?


aJ.m-2.K-1


bJ.m-1.K-1


cW.m-2.K-1


dW-1m2K


View Answer W-1m2K

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