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Heat Transfer
Quiz 1
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Q.1
Steam trap is used to
Condense the steam flowing in the pipeline
Remove water resulting from partial condensation of steam
Stop the supply of steam
None of these
Q.2
Pick out the wrong statement:
The capacity of an evaporator is reduced by the boiling point elevation
Corrosive liquid is normally passed through the tubes in a shell and tube heat exchanger
Steam jet ejector is used for vapor compression in a thermal recompression evaporator
Heat sensitive materials should be concentrated in high pressure evaporators
Q.3
The Graetz number is concerned with the
Mass transfer between a gas and a liquid
Absorption with chemical reaction
Heat transfer in turbulent flow
Heat transfer in laminar flow
Q.4
Vibrations in the tubes of a shell and tube heat exchanger is induced due to the
Flow of fluid on the tube and shell sides
Oscillations in the flow of shell/tube sides fluid
Vibrations transmitted through piping and/or supports due to external reasons
All of the above
Q.5
Radiation heat losses from satisfactorily insulated high pressure boilar may be about __________ percent.
1
7
18
26
Q.6
Which of the following forced convection heat transfer equation accounts for the liquid viscosity effect for viscous liquids?
Dittus-Boeltier equation
Sieder-Tate equation
Nusselt equation
None of these
Q.7
Which of the following situations can be approximated to a steady state heat transfer system?
A red hot steel slab (having outside surface temperature as 1300°C) exposed to the atmosheric air at 35°C
10 kg of dry saturated steam at 8 kgf/cm² flowing through a short length of stainless steel pipe exposed to atmospheric air at 35°C
Boiling brine kept in open vessel when the bottom surface temperature of the vessel is maintained constant at 180°C
A sub-cooled refrigerant liquid at 8°C flowing at the rate of 6 Kg/minute through a copper pipe exposed to atmospheric air at 35°C
Q.8
While the total emissivity of a perfect black body is unity, the same for a real body is
0
1
> 1
Between 0 and 1
Q.9
The ratio of momentum diffusivity to thermal diffusivity is the __________ number.
Prandtl
Nusselt
Stanton
Grashoff
Q.10
The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe, where the wall heat flux is constant, is
2.36
4.36
120.36
Dependent on N
Re
only
Q.11
Water always boils when its
Temperature reaches 100° C
Vapour pressure equals 76 cm of Hg
Saturated vapour pressure equals the external pressure on its surface
Saturated vapour pressure is less than the atmospheric pressure
Q.12
Which one gives the monochromatic emissive power for black body radiation?
Planck's law
Kirchhoffs law
Wien's law
Stefan-Boltzman law
Q.13
If heat transfer rate varies with the time, it is termed as
Forced convection
Steady state conduction
Monochromatic radiation
None of these
Q.14
A sphere of radius 'R₁' is enclosed in a sphere of radius 'R₂'. The view (or shape) factor for radiative heat transfer of the outer sphere with respect to the inner sphere is
0
R₂/(R₁+R₂)
1
(R₁/R₂)2
Q.15
For hot feed, forward feeding as compared to backward feeding results in __________ economy.
Increased
Decreased
No effect on
None of these
Q.16
Reynold's analogy states that
N
st
α f
N
st
α N
Re
N
Nu
α f
N
Re
α f
Q.17
A perfect black body is a perfect __________ of radiation.
Absorber
Emitter
Both A & B
Neither A nor B
Q.18
Tubes are held between top and bottom tube sheets in Calenderia type evaporator by keeping
Both the tube sheets fixed
Both the tube sheets floating
The top tube sheet floating and bottom tube sheet fixed
The top tube sheet fixed and the bottom tube-sheet floating
Q.19
Heat flux is the time rate of heat transfer per unit
Length
Area
Volume
None of these
Q.20
Radiation heat transfer rates does not depend upon the
Type of absorbing surface
Distance between the heat source and the object receiving the heat
Surface area and temperature of the heat source
None of these
Q.21
A multiple effect evaporator as compared to a single effect evaporator of the same capacity has
Lower heat transfer area
Lower steam economy
Higher steam economy
Higher solute concentration in the product
Q.22
If the thermal conductivity of a wall material is independent of temperature, the steady state temperature distribution in the very large thin plane wall having steady, uniform surface temperature follows __________ law.
Hyperbolic
Parabolic
Linear
Logarithmic
Q.23
Nusselt number is the ratio of the temperature gradient at the wall to
Temperature difference
Heat flux
That across the entire pipe
None of these
Q.24
With the increase of temperature, the Col-burn jH factor
Increases
Decreases
Remains unchanged
May increase or decrease ; depending on temperature
Q.25
For a liquid in laminar flow through a very long tube, when the exit fluid temperature approaches the wall temperature, the equation to be used is
Nu = 0.023 Re0.8 . Pr0.4
Nu = Gz
Nu = Gz
Nu = 2Gz0.5
Q.26
In case of a vertical tube evaporator, with increase in the liquor level, the
Capacity of the evaporator is decreased
Capacity of the evaporator is increased
True temperature drop increases
Both B and C
Q.27
For a perfectly transparent surface (like gases), the
Absorptivity = 0
Transmissivity = 1
Reflectivity = 0
All of the above
Q.28
The inside heat transfer co-efficient in case of turbulent flow of liquid in the tube side in a 1-2 shell and tube heat exchanger is increased by __________ times, when the number of tube passes is increased to 8.
2
0.8
4
0.8
4
0.4
2
0.4
Q.29
The units of resistance to heat transfer is
J.m⁻².K⁻¹
J.m⁻¹.K⁻¹
W.m⁻².K⁻¹
W⁻¹m²K
Q.30
Electromagnetic radiations propagate in vacuum with a velocity of __________ metre/second.
3 x l0
5
3 x l0
8
3 x l0
10
3 x l0
12
Q.31
Which of the following is generally considered as opaque surface towards radiations?
Gases
Solids
Liquids
Both B and C
Q.32
The characteristic dimensionless groups for heat transfer to a fluid flowing through a pipe in laminar flow are
Re.Gz
Nu, Pr
Nu, Pr, Re
Nu, Gz
Q.33
Heat transfer by __________ may not necessarily require the presence of a medium.
Conduction
Natural convection
Forced convection
Radiation
Q.34
Electro-magnetic spectrum range, which is important for radiation varies from __________ microns.
1 to 100
0.5 to 50
10 to 100
100 to 1000
Q.35
Which of the following has the lowest Prandtl number?
Molten sodium (a coolant used in fast breeder reactor)
Water
Transformer oil
Dilute H₂SO₄
Q.36
Which has the lowest Prandtl number?
Liquid metal
Aqueous solution
Water
Lube oil
Q.37
In a heat exchanger, one transfer unit means
A section of the exchanger in which change in temperature of one stream equals the average driving force in the section
The size of the exchanger in which heat transfer rate is 1 kcal/hr
Both A and B
None of these
Q.38
When does the heat generated by fluid friction becomes appreciable compared to the heat transferred between the fluids?
At high fluid velocity
At low velocity
When fluid flows past a smooth surface
None of these
Q.39
The absorptivity of a grey body at a given temperature __________ with increasing wavelength of radiation.
Increases
Decreases
Remains constant
May increase or decrease ; depends on the material
Q.40
For a given ambient air temperature with increase in the thickness of insulation of a hot cylinderical pipe, the rate of heat loss from the surface would
Decrease
Increase
First decrease and then increase
First increase and then decrease
Q.41
__________ chart is known as transient heat conduction chart.
Dirhing's
Heisler's
Mollier's
Cox
Q.42
It is not preferable to use superheated steam in evaporators, because of its very
High temperature
High pressure
Low film co-efficient
None of these
Q.43
Vent pipes are provided in a condenser to
Remove non-condensable gases
Purge the condenser
Facilitate easy cleaning of tubes
None of these
Q.44
Economy of a multiple effect evaporator is not influenced much by the
Boiling point elevations
Temperature of the feed
Rate of heat transfer
Ratio of the weight of the thin liquor to thick liquor
Q.45
The heat transfer co-efficient in film type condensation is __________ that for dropwise condensation.
Greater than
Lower than
Is same as
Half
Q.46
The driving potential for the crystal growth during crystallisation is the __________ of the solution.
Concentration
Viscosity
Super-saturation
Density
Q.47
The thermal boundary layer at N
Pr
> 1
Is thicker than hydrodynamic boundary layer
Is thinner than hydrodynamic boundary layer
And the hydrodynamic boundary layer are identical
Disappears
Q.48
In a heat exchanger, the rate of heat transfer from the hot fluid to the cold fluid
Varies directly as the area and the LMTD
Directly proportional to LMTD and inversely proportional to the area
Varies as square of the area
None of these
Q.49
Latent heat absorbed by 1 lb of water at 212°F, when it is changed to steam at 212°F, may be around __________ BTU.
180
970
3.97
None of these
Q.50
h.D/K is called the __________ number.
Nusselt
Peclet
Rayleigh
Grashoff
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