Question 31 : In an interphase heat transfer process, the equilibrium state corresponds to equality of temperature in the two phases, while the condition for equilibrium in an interphase mass transfer process is equality of
1. concentrations
2. chemical potentials
3. mass transfer co-efficients
4. activity co-efficients
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Question 32 : Low thermal conductivity of heat insulating materials is due to its
1. dense structure
2. high proportion of air space.
3. high specific heat
4. none of these.
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Question 33 : The most conducive surface for dropwise condensation to occur is the __________ surface.
1. coated
2. smooth
3. oily
4. glazed & polished
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Question 34 : Value of Nusselt number [Nu = (hD/k)] for the heat transfer by conduction from a droplet or a spherical particle to a surrounding stagnant film is
1. 0.5
2. 10
3. 100
4. 2
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Question 35 : In pipe flow, heat is transferred from hot wall to the liquid by
1. forced convection only.
2. conduction only
3. free and forced convection.
4. forced convection and conduction.
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Question 36 : For turbulent flow in a tube, the heat transfer co-efficient is obtained from the Dittus-Boelter correlation. If the tube diameter is halved and the flow rate is doubled, then the heat transfer co-efficient will change by a factor of
1. 6.1
2. 1.74
3. 1.63
4. 1
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Question 37 : Radiator of an automobile engine is a __________ type of heat exchanger.
1. counter-current
2. co-current
3. cross-current
4. direct contact
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Question 38 : Sensible heat of hot industrial flue gases can not be recovered by a/an
1. economiser
2. regenerator
3. ceramic recuperator
4. none of these
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Question 39 : The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe whose surface temperature remains constant is
1. 1.66
2. 88.66
3. 3.66
4. 5.66
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Question 40 : Heat transfer by conduction in the turbulent core of a fluid flowing through a heated pipe is negligible, if the value of Prandtl number is
1. 0.8
2. 0.2
3. 0.4
4. 0.6
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