ht1
Short Description
MCQ...
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Question In the equation Q = UAΔt; Δt is A
geometric mean temperature difference.
B
arithmetic mean temperature difference.
C
logarithmic mean temperature difference.
D
difference of average bulk temperatures of hot and cold fluids.
Answer
C
Marks
1
Question The Convective heat transfer coefficient in case of fluid flowing in the tubes is not affected by the tube length/diameter ratio, if the flow is in the __________ zone. A
Laminar
B
transition
C
both 'a' & 'b'
D
highly turbulent
Answer
D
Marks
1
Question The unit of heat transfer co-efficient in SI unit is A
J/m2°K
B
W/m2°K
C
W/m°K
D
J/m°K
Answer
B
Marks
1
Question Controlling heat transfer film co-efficient is the one, which offers __________ resistance to the heat transfer. A
No
B
The least
C
The largest
D
lower
Answer
C
Marks
1
Question Bulk of the convective heat transfer resistance from a hot tube surface to the fluid flowing in it, is A
in the central core of the fluid.
B
uniformly distributed throughout the fluid.
C
mainly confined to a thin film of fluid near the surface
D
none of these
Answer
C
Marks
1
Question The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe, where the wall heat flux is constant, is A
2.36
B
4.36
C
120.36
D
Depends on Reynolds number only
Answer
B
Marks
1
Question For flow over a flat plate, the ratio of thermal boundary layer thickness, δt' to hydrodynamic boundary layer thickness 'δ' is proportional to (where, NPr = Prandtl number) A
NPr
B
NPr1/3
C
NPr-1
D
NPr-1/3
Answer
D
Marks
1
Question A
In forced convection, the heat transfer depends on Re, Pr
B
Re, Gr
C
mainly Gr
D
Re only
Answer
A
Marks
1
Question 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 A
ha= hl
B
ha= 2hl
C
ha= 0.5hl
D
ha= 0.75hl
Answer
B
Marks
1
Question Value of Prandtl number for water ranges from A
l to 2
B
5 to 10
C
100 to 500
D
1000 to 2000
Answer
B
Marks
1
Question Heat transfer in the laminar sublayer in case of a liquid flowing through a pipe, is mostly by A
eddies current
B
conduction
C
Convection
D
none of these
Answer
B
Marks
1
Question Heat transfer co-efficient (h1) for liquids increases with A
increasing temperature.
B
decreasing temperature
C
decreasing Reynolds number
D
none of these
Answer
A
Marks
1
Question Heat transfer occurs by natural convection because change in temperature causes difference in A
viscosity
B
density
C
thermal conductivity
D
heat capacity
Answer
B
Marks
1
Question The ratio of kinematic viscosity to thermal diffusivity is called the __________ number. A
Peclet
B
Prandtl
C
Stanton
D
Nusselt
Answer
B
Marks
1
Question What is Nusselt number? A
Cp µ /k
B
hD/k
C
K /Cp µ
D
None of these
Answer
B
Marks
1
Question Convective heat transfer, in which heat is transferred by movement of warmed matter is described by A
Fourier's law
B
Newton's law of cooling
C
Fick's law
D
none of these
Answer
B
Marks
1
Question The Grashof number is defined as the ratio of the A
buoyancy to inertial forces
B
buoyancy to viscous forces
C
inertial to viscous forces
D
buoyancy to surface tension forces
Answer
B
Marks
1
Question When warm and cold liquids are mixed, the heat transfer is mainly by A
Conduction
B
convection
C
Radiation
D
both(a) & (c)
Answer
B
Marks
1
Question Heat transfer by natural convection is enhanced in system with A
high viscosity
B
high co-efficient of thermal expansion
C
low temperature gradients
D
low density change with temperature
Answer
B
Marks
1
Question In forced convection, the Nusselt number is a function of A
Re and Pr
B
Re and Gr
C
Pr and Gr
D
Re and Sc
Answer
A
Marks
1
Question Prandtl number is the ratio of A
momentum diffusivity to mass diffusivity.
B
momentum diffusivity to thermal diffusivity.
C
thermal diffusivity to mass diffusivity.
D
thermal diffusivity to momentum diffusivity.
Answer
B
Marks
1
Question Thermal Diffusivity is given by A
K / (Cp.ρ )
B
Cp./ k ρ
C
µ ρ / Cp
D
µ.Cp / k
Answer
A
Marks
1
Question At what value of Prandtl number, the hydrodynamic and thermal boundary layers are identical ? A
0.5
B
1
C
1.5
D
10
Answer
B
Marks
1
Question Natural convection is characterised by A
Grashof number
B
Peclet number
C
Reynolds number
D
Stanton number
Answer
A
Marks
1
Question Nusselt number for full developed, laminar, constant property flow in a pipe at uniform heat flux is A
0.72
B
4.36
C
18
D
83
Answer
B
Marks
1
Question Thickness of thermal boundary layer is more compared to that of hydrodynamic boundary layer, when the value of Prandtl number is A
1
B
1
D
>5
Answer
B
Marks
1
Question Overall heat transfer co-efficient of a particular tube is U1. If the same tube with some dirt deposited on either side has coefficient U2, then A
U1 = U2
B
U2 >U1
C
U1 > U2
D
U1 = dirt factor - U2
Answer
C
Marks
1
Question Which of the following has the lowest Prandtl number? A
Molten sodium (a coolant used in fast breeder reactor)
B
Water
C
Transformer oil
D
Dilute H2SO4
Answer
A
Marks
1
Question In SI units, fouling factor is expressed in A
m2°K/W
B
W/m2°K
C
m2°K/W
D
m°K/W
Answer
A
Marks
1
Question Nusselt number is the ratio of the A
temperature gradient of the wall to that across the entire pipe
B
temperature difference to the temperature gradient at the wall
C
heat flux at the wall to that across the entire pipe
D
none of these
Answer
C
Marks
1
Question Fouling factor A
is a dimensionless quantity.
B
does not provide a safety factor for design.
C
accounts for additional resistances to heat flow.
D
none of these.
Answer
C
Marks
1
Question With the increase of temperature, the Col-burn jH factor A
increases.
B
decreases.
C
remains unchanged
D
may increase or decrease; depending on temperature
Answer
A
Marks
1
Question Dietus-Boelter equation used for the determination of heat transfer co-efficient is valid A
for fluids in laminar flow.
B
for fluids in tubulent flow.
C
when Grashof number is very important
D
for liquid metals.
Answer
B
Marks
1
Question Which of the following forced convection heat transfer equation accounts for the liquid viscosity effect for viscous liquids? A
Dittus-Boelter equation
B
Sieder-Tate equation
C
Nusselt equation
D
None of these
Answer
B
Marks
1
Question A fluid is flowing inside the inner tube of a double pipe heat exchanger with diameter 'd'. For a fixed mass flow rate, the tube side heat transfer co-efficient for turbulent flow conditions is proportional to A
d0.8
B
d-0.2
C
d-1
D
d-1.8
Answer
B
Marks
1
Question The Dietus-Boelter equation for convective heat transfer can not be used for, A
low Reynold's number
B
very low Grashoff number
C
molten metals
D
all (a), (b) and (c)
Answer
D
Marks
1
Question Dietus-Boelter equation cannot be used for molten metals mainly due to its very low A
Prandtl number
B
Grashoff number
C
thermal conductivity
D
viscosity
Answer
A
Marks
1
Question Heat transfer by natural convection is enhanced in system with A
high viscosity.
B
high co-efficient of thermal expansion.
C
low temperature gradients
D
low density change with temperature.
Answer
B
Marks
1
Question For a laminar flow of fluid in a circular tube, 'h1' is the convective heat transfer coefficient at velocity 'V1'. If the velocity is reduced by half and assuming the fluid properties are constant, the new convective heat transfer co-efficient is A
1.26 h1
B
0.794 h1
C
0.574 h1
D
1.741 h1
Answer
B
Marks
1
Question Peclet number (Pe) is given by A
Pe = Re.Pr
B
Pe = Re/Pr
C
Pe = Pr/Re
D
Pe = Nu.Re
Answer
A
Marks
1
Question (NGr x NPr) is called the __________ number. A
Graetz
B
Rayleigh
C
Nusselt
D
Stanton
Answer
B
Marks
1
Question (Re.Pr) .(D/L) is called ---------------- Number. A
Peclet
B
Stanton
C
Graetz
D
None of these
Answer
C
Marks
1
Question The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe whose surface temperature remains constant is A
1.66
B
5
C
3.66
D
dependent on NRe only
Answer
C
Marks
1
Question Prandtl number for most of dry gases is about A
0.001
B
0.72
C
70
D
150
Answer
B
Marks
1
Question
Which has the lowest Prandtl number ?
A
Liquid metal
B
Aqueous solution
C
Water
D
Lube oil
Answer
A
Marks
1
Question
Heat transfer co-efficient equation for forced convection, Nu = 0.023 Re0.8 . Prn, is not valid, if the value of
A
n = 0.4 is used for heating.
B
n = 0.3 is used for cooling.
C
Reynolds number for the flow involved is > 10000.
D
Reynolds number for the flow involved is < 2100.
Answer
D
Marks
1
Question
A graph between __________ is called Wilson plot.
A
B C
V0.8 Vs . U
D Answer
A
Marks
1
Question
The Grashof Number is defined as
A
Product of Buoyancy and Inertia forces to (Viscous force)2
B
Product of Buoyancy and viscous forces to (inertial force) 2
C
Inertial to viscous forces
D
Buoyancy to surface tension forces
Answer
A
Marks
1
Question
In natural convection heat transfer the correlating parameter is
A
Reynold number
B
Bond Number
C
Grashof Number
D
Eckert number
Answer
C
Marks
1
Question
Match the Overall heat transfer coefficient for given fluids on vessel and jacket side. Jacket side Vessel side Overall heat transfer coefficient (W/m2K) I Steam I Water a. 30 – 75, b. 5000 – 6000, II Water II Polymer monomer c. 285 - 800 d. 850 - 1700
A
(I) – (d), (II) – (c)
B
(I) – (c), (II) – (d)
C
(I) – (a), (II) – (b)
D
(I) – (b), (II) – (a)
Answer
A
Marks
1
Question
Match the Dimension numbers with terms, I Graetz Number a. Heat transfer in creeping flow, II Rayleigh number b. thermally developed flow c. Product of Grashof and Prandtl no. d. Product of Reynold and Prandtl number
A
(I) – (a), (II) – (d)
B
(I) – (b), (II) – (d)
C
(I) – (b), (II) – (c)
D
(I) – (d), (II) – (c)
Answer
C
Marks
1
Question
When a vertical plate is heated in an infinite air environment under natural convection conditions, the velocity profile in air, normal to the plate,
A
is linear
B
is parabolic
C
exhibits minimum
D
exhibits maximum
Answer
D
Marks
1
Question
When the ratio of Grashof number to the square root of the Reynolds number is one, the dominant mechanism of heat transfer is
A
free convection
B
forced convection
C
mixed convection (both free and forced)
D
None of these
Answer
C
Marks
1
Question
The Hydrodynamic and Boundary layers will merge when
A
Prandtl Number is one
B
Schmidt Number tends to infinity
C
Nusselt Number tends to infinity
D
None of these.
Answer
A
Marks
1
Question
Rayleigh Number is associated
A
Buoyancy effects
B
free convection
C
forced convection
D
Heat Conduction
Answer
B
Marks
1
Question
Gibbs phase Rule finds application when heat transfer occurs by
A
Conduction
B
Convection
C
Radiation
D
Condensation
Answer
B
Marks
1
Question
When the ratio of Grashof number to the square root of the Reynold number is Ten, the dominant mechanism of heat transfer is
A
free convection
B
forced convection
C
mixed convection (both free and forced)
D
None of these
Answer
A
Marks
1
Question
Heat Transfer by Natural Convection is enhanced by the system with
A
high viscosity
B
high coefficient of thermal expansion
C
low temperature gradient
D
none of these
Answer
B
Marks
1
Question
Prandtl Number of Liquid Metal is of the order of
A
1
B
0.01
C
10
D
100
Answer
B
Marks
1
Question
Heat Transfer occurs by Natural convection because change in temperature causes difference in
A
Density
B
Thermal Conductivity
C
Heat Capacity
D
none of these
Answer
A
Marks
1
Question
In pipe flow, heat is transferred from one fluid through the hot wall to the other fluid by
A
free and forced convection
B
forced convection only
C
forced convection and conduction
D
conduction only
Answer
C
Marks
1
Question
The Graetz number is concerned with the
A
mass transfer between a gas and a liquid.
B
absorption with chemical reaction
C
heat transfer in turbulent flow
D
heat transfer in laminar flow.
Answer
D
Marks
1
Question
Log mean temperature difference (LMTD) cannot be used, if
A
heat transfer co-efficient over the entire heat exchanger is not constant.
B
there exists an unsteady state.
C
the heat capacity is not constant and there is a phase change.
D
none of these.
Answer
D
Marks
1
Question
The Sieder-Tate correlation for heat transfer in laminar flow in pipe gives, where, Nu is the Nusselt number and Re is the Reynolds number for the flow. Assuming that this relation is valid, the heat transfer co-efficient varies with the pipe diameter (D) as
A
(D)-1.8
B
(D)-0.2
C
(D)0.2
D
(D) -0.33
Answer
D
Marks
1
Question
The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe whose surface temperature remains constant is
A
1.66
B
88.66
C
3.66
D
dependent on NRe only
Answer
C
Marks
1
Question
Match the Dimensionless number with their Expressions I Stanton Number (a) hD/k (b) h / CpρV II Prandtl Number (c) µ / Cpk (d) Cpµ / k
A
(I) – (a), (II) – (b)
B
(I) – (a), (II) – (d)
C
(I) – (b), (II) – (c)
D
(I) – (b), (II) – (d)
Answer
D
Marks
1
Question
Match the Dimensionless number with the ratio of resistances I Nusselt Number (a) Convective Resistance / fluid conduction Resistance II Prandtl Number (b) fluid conduction Resistance / Convective Resistance (c) Momentum Diffusivity / Thermal Diffusivity (d) Thermal Diffusivity / Kinematic Diffusivity
A
(I) – (a), (II) – (c)
B
(I) – (b), (II) – (c)
C
(I) – (b), (II) – (d)
D
(I) – (a), (II) – (d)
Answer
B
Marks
1
Question
A high value of thermal Diffusivity of material results from a ....(a)…. Value of thermal conductivity and a ….(b)…. Value of thermal heat capacity.
A
(a) high (b) high
B
(a) low (b) high
C
(a) high (b) low
D
(a) low (b) low
Answer
C
Marks
1
Question
Thermal Diffusivity has Unit of
A
m2 /s
B
W / m.k
C
W
D
None of these
Answer
A
Marks
1
Question
Liquid Metals are used as heat transfer fluid in a nuclear reactor due to …. (a) … heat transfer coefficient and …(b)… heat capacity.
A
(a) high (b) high
B
(a) low (b) high
C
(a) high (b) low
D
(a) low (b) low
Answer
A
Marks
1
Question
Heat transfer coefficients for liquid metals are high due to their high
A
viscosity
B
density
C
thermal conductivity
D
none of these
Answer
C
Marks
1
Question
The Prandtl Number for liquid metals are low due to
A
high thermal conductivity
B
high Thermal diffusivity
C
Both A and B
D
none of these
Answer
C
Marks
1
Question
At the entrance of the pipe in which the fluid is being heated, the heat transfer
coefficient is A
zero due to absence of temp gradient
B
equal to heat transfer coefficient for fully developed turbulent flow
C
Infinite due to absence of temp gradient
D
zero due to zero thickness of boundary layer
Answer
C
Marks
1
Question
Near the entrance of the pipe in which the fluid is being heated, the temp profile is not fully developed then the local heat transfer coefficient is
A
zero
B
smaller than the heat transfer coefficient for fully developed turbulent flow
C
Infinite
D
greater than the heat transfer coefficient for fully developed turbulent flow
Answer
D
Marks
1
Question
The thickness of thermal boundary layer in heat transfer to liquid metals is
A
more than thickness of hydrodynamic boundary layer
B
less than thickness of hydrodynamic boundary layer
C
equal to thickness of hydrodynamic boundary layer
D
zero
Answer
A
Marks
1
Question
Which of the dimesionless group is used to compare thermal boundary layer and hydrodynamic boundary layer formed in heat transfer and fluid flow.
A
Fourier Number
B
Biot Number
C
Prandtl Number
D
Nusselt Number
Answer
C
Marks
1
Question
Within the thermal boundary layer,
A
temperature is uniform
B
temperature gradient exists
C
temperature gradient does not exist
D
heat flux is zero
Answer
B
Marks
1
Question
Peclet Number is defined as
A
Ratio of Reynold Number to Prandtl Number
B
Product of Reynold Number and Prandtl Number
C
Product of Nusselt Number and Prandtl Number
D
Ratio of Nusselt Number to Prandtl Number
Answer
B
Marks
1
Question
In Natural Convection heat transfer, the Nusselt Number is a function of
A
Reynold Number and Prandtl Number
B
Grashof Number and Prandtl Number
C
Schmidt Number and Prandtl Number
D
None of these
Answer
B
Marks
1
Question
The log mean Temperature difference of two temperature differences θ1 and θ2 is defined as,
A
(θ1 - θ2) / loge (θ1 / θ2)
B
(θ1 / θ2) / loge(θ1 - θ2)
C
(lnθ1 - lnθ2) / ln (θ1 / θ2)
D
(θ1 + θ2) / 2
Answer
A
Marks
1
Question
Newton’s Law cooling is a special case of
A
Planck’ Law
B
Kirchoff’ Law
C
Wein’s Displacement Law
D
Stefan’s- Boltzmann’s Law
Answer
D
Marks
1
Question
Why is superheated steam not preferred as a heating medium in evaporators
A
metal tubes cannot withstand high temperature
B
superheated steam has very low film coefficient
C
metal tubes cannot withstand high pressure
D
because of all above three factors
Answer
B
Marks
1
Question
Natural Convection is characterized by
A
Grashof Number and Prandtl Number
B
Peclet Number
C
Reynolds Number and Prandtl Number
D
none of these
Answer
A
Marks
1
Question
Colburn Analogy is valid when
A
0.1< Pr < 10
B
0.6 < Pr < 1
C
1 < Pr < 100
D
1 < Pr < 10
Answer
C
Marks
1
Question
What is the value of Reynold number at which transition of the laminar to turbulent flow occurs for fluid flows over a flat horizontal plate?
A
5 x 105
B
2100
C
4000
D
1
Answer
A
Marks
1
Question
The hot radiator used for heating a room is a device which transfers the heat by
A
forced convection
B
free convection
C
conduction
D
all of the above
Answer
B
Marks Question
For a practical situation, Gr / Re2 > 10,
A
forced convection effects dominates
B
free convection effects dominates
C
Neither free nor forced convection effects dominates
D
None of above
Answer
B
Marks
1
Question
What is the accepted range of Reynold number for transition region between laminar and turbulent regions occurs when fluid flows through the tube?
A
1000 < Re < 5 x 105
B
2000 < Re < 4000
C
100 < Re < 1000
D
0.1 < Re < 50
Answer
B
Marks
1
Question
Free convection depends up on all of the following EXCEPT
A
Density
B
Coefficient of thermal Expansion
C
Gravitational force
D
Velocity
Answer
D
Marks
1
Question
The Ratio of fluid Convective Heat flux to the fluid Conductive Heat Flux is called
A
Grashof Number
B
Nusselt Number
C
Prandtl Number
D
Peclet Number
Answer
B
Marks
1
Question
In free Convection, Transition from Laminar to Turbulent region is distinguished by
a critical value of A
Product of Reynolds Number and Prandtl Number
B
Product of Grashof Number and Prandtl Number
C
Product of Nusselt Number and Prandtl Number
D
None of these
Answer
B
Marks
1
Question
For a practical situation, Gr / Re2 > 10,
A
forced convection effects dominates
B
free convection effects dominates
C
Neither free nor forced convection effects dominates
D
None of above
Answer
B
Marks
1
Question
In heat exchangers, the values of log mean temperature difference should be
A
minimum possible
B
maximum possible
C
zero
D
any of above
Answer
B
Marks
1
Question In Natural Convection, The characteristic dimension of vertical pipe used in the dimensionless numbers is, A
Diameter of pipe
B
Vertical Length of pipe
C
Perimeter
D
Area
Answer
B
Marks
1
Question Coefficient of thermal Expansion of the fluid in natural convection is related with A
Absolute Temperature of the fluid
B
Velocity of the fluid
C
Both of above
D
None of A & B
Answer
A
Marks
1
Question Higher value of Prandtl Number shows, A
Rapid heat transfer by forced convection to mutual convection
B
Rapid diffusion of momentum by viscous force as compared to diffusion of energy
C
both A & B
D
Neither A & B
Answer
B
Marks
1
Question Product of Reynolds Number and Prandtl Number is, A
Stanton Number
B
Peclet Number
C
Grashof Number
D
Biot Number
Answer
B
Marks
1
Question Stanton Number is the Ratio of Nusselt Number to , A
Prandtl Number
B
Product of Reynolds Number and Prandtl Number
C
Product of Grashof Number and Prandtl Number
D
Biot Number
Answer
B
Marks
1
Question Thermal Diffusivity of the substance is proportional A
directly to thermal conductivity
B
Inversely to Density
C
Inversely to specific heat
D
All of above
Answer
D
Marks
1
Question Minimum Thermal Diffusivity is of the substance A
Aluminium
B
Rubber
C
Iron
D
Lead
Answer
B
Marks
1
Question Unit of overall heat transfer coefficient is A
Kcal/ hr. m2
B
Kcal/ hr. m2. 0C
C
Kcal/hr
D
None of these
Answer
B
Marks
1
Question The value log mean Temperature difference(LMTD) for counter flow heat exchanger as compared to the parallel flow heat exchanger is A
more
B
less
C
same
D
none of these
Answer
A
Marks
1
Question Rayleigh Number in Natural convection is the product of A
Reynolds Number and Prandtl Number
B
Peclet Number and Grashof Number
C
Grashof Number and Prandtl Number
D
Nusselt Number and Prandtl Number
Answer
C
Marks
1
Question The Transition from laminar to turbulent regime for heat transfer by Natural convection in flow of fluid is distinguished by the Number A
Stanton Number
B
Rayleigh Number
C
Prandtl Number
D
Biot Number
Answer
B
Marks
1
Question Unit of thermal Diffusivity is A
m /hr K
B
W /mK
C
m /hr
D
m2 /hr
Answer
D
Marks
1
Question Ratio of Kinematic viscosity to Thermal Diffusivity is called A
Nusselt Number
B
Grashof Number
C
Prandtl Number
D
Reynolds Number
Answer
C
Marks
1
Question In the development of Laminar boundary layer and heat transfer over a flat plate of length L, The average value of heat transfer coefficient can be obtained from the local heat transfer coefficient hx at the trailing edge in the direction of flow by the factor, ∫L hxdx
A
0
B
d/dx(hx)
C
L 0∫L hxdx
D
none of the above
Answer
C
Marks
1
Question In the development of Laminar boundary layer and heat transfer over a flat plate, The average value of heat transfer coefficient can be obtained by multiplying the local heat transfer coefficient at the trailing edge in the direction of flow by the factor, A
1.5
B
2
C
1
D
0.75
Answer
B
Marks
1
Question The ratio of thickness of thermal boundary layer and hydrodynamic boundary layer is proportional to (Prandtl Number)n, where n is, A
1
B
-1/3
C
-2/3
D
-1
Answer
B
Marks
1
Question Grashof Number is defined by A
(gβΔTL3) /µ2
B
(gβΔTρ2L3) /µ2
C
(gβΔTµ2L3 )/ρ2
D
(gβΔTρ3L3) /µ3
Answer
B
Marks
1
Question A very low value of Nusselt Number means that A
Fluid conduction resistance is negligible as compared to surface convective resistance
B
surface convective resistance is negligible as compared to fluid conduction resistance
C
fluid conduction resistance is almost equal to surface convective resistance
D
none of these
Answer
A
Marks
1
Question A water Droplet at 25 0C is suddenly introduced into an infinite gas medium at 100 0 C saturated with water vapor. At steady state, A
Drop attains WBT and vanishes
B
drops remains unchanged and attains temperature of 100 0C
C
drop increases in size and it attains temperature of 100 0C
D
none of these.
Answer
C
Marks
1
Question The overall resistance for heat transfer between the two fluids through barrier of surface, is the __________ of the resistances to convection and conduction. A
Average
B
geometric mean
C
Product
D
Sum
Answer
D
Marks
1
Question The overall heat transfer coefficient for the heat transfer between the two fluids through barrier of surface, is__________ to/of the sum of all resistances to convection and conduction. A
Equal
B
Inverse
C
More than
D
Less than
Answer
B
Marks
1
Question Mode of heat transfer in which the flu moves under the influence of changes in flu pressure produced by external work is called A
Radiation
B
natural convection
C
forced convection
D
Conduction
Answer
C
Marks
1
Question Mode of heat transfer involved in the cooling of air cooled internal combustion engine is
A
Conduction
B
natural convection
C
forced convection
D
none of these
Answer
B
Marks
1
Question Which of the following has the lowest overall heat transfer co-efficient? A
Dowtherm
B
Molten sodium
C
Water
D
Air
Answer
D
Marks
1
Question Convection heat transfer takes place between a steel plate with surface temperature (Ts) of 100°C and the surrounding air (Ta) at 25°C. If the surface area (A) of the plate is 1 m2 and the convection heat transfer coefficient (h) is 25 W/m2K find the heat transfer rate to the air. A
1775W
B
1875W
C
1475W
D
1375W
Answer
B
Marks
1
Question Find the heat transfer rate by forced convection between a surface of area (A) 15m × 1.5 m and air, if the surface temperature (Ts) is 30°C and the air temperature (Ta) is 45°C. Assume the average convective heat transfer coefficient (h) to be 8 W/m2K. A
2.7kW
B
270kW
C
2700kW
D
27kW
Answer
A
Marks
1
Question Minimum value of Prandtl Number is of the substance A
Water
B
Air
C
Liquid Metal
D
Petroleum
Answer
C
Marks
1
Question Convective heat transfer co-efficient in case of fluid flowing in tubes is not affected
by the tube length/diameter ratio, if the flow is in the __________ zone. A
laminar
B
transition
C
highly turbulent
D
None of the above
Answer
C
Marks
1
Question The unit of resistance to heat transfer is A
J/(m2K)
B
(m2-K)/W
C
W/(m2-K)
D
J/sm2K
Answer
B
Marks
1
Question Which one of the following statements about baffles in shell and tube heat exchanger is false? Baffles A
acts as support to the tube bundle
B
reduce the pressure drop on shell side
C
alter the shell side flow pattern
D
help in increasing the heat transfer coefficient on shell side
Answer
B
Marks
1
Question Sieder Tate correction Factor takes into account the variation in A
Pressure
B
Viscosity
C
specific heat
D
velocity
Answer
B
Marks
1
Question
Which of the following statements about the Dittus- Boelter equation is/are not true
A
It is applicable for turbulent flow in pipe
B
Nusselt number is a function of Reynolds number and Prandtl number
C
Neither A nor B
D
Both A & B
Answer
C
Marks
1
Question
Hydraulic or equivalent diameter of non circular conduit can be determined by
A
(4 x Wetted perimeter)/ cross sectional area
B
(4 x cross sectional area)/ Wetted perimeter
C
(cross sectional area)/ Wetted perimeter
D
none of these
Answer
B
Marks
1
Question
Hydraulic or equivalent diameter of annulus of two concentric pipe can be determined, if Do = OD of inner pipe Di = ID of outer pipe
A
( D02- Di2) / Di
B
Di / ( D02- Di2)
C
( D0- Di)/ Di
D
None of these
Answer
A
Marks
1
Question
If Overall heat transfer coefficient for the convective heat transfer without phase change is U1 and Overall heat transfer coefficient for the convective heat transfer with phase change is U2 with keeping other parameters same for same system, then
A
U1 = U2
B
U2 > U1
C
U1 > U2
D
U1 = dirt factor - U2
Answer
B
Marks
1
Question
Inside Convective Heat transfer coefficient h1 for the fluid flows through straight tube as compared to Inside Convective Heat transfer coefficient h2 for the same fluid through the helical tube of same dimensions, under the same condition is
A
h1 > h2
B
h1 < h2
C
h1 = h2
D
None of these
Answer
B
Marks
1
Question
Inside Convective Heat transfer coefficient for fully developed flow of fluid in smooth tubes can be determined by
A
Sieder – Tate Correlation
B
Dittus – Boelter correlation
C
Nusselt Equation
D
Prandtl Equation
Answer
B
Marks
1
Question
In Dietus-Boelter equation used for the turbulent flow through the pipe, heat transfer co-efficient is proportional to
A
(Reynolds Number)0.2
B
(Reynolds Number)0.8
C
(Reynolds Number)0.33
D
(Reynolds Number)0.5
Answer
B
Marks
1
Question
In Dietus-Boelter equation used for the heating of turbulent flow through the pipe, heat transfer co-efficient is proportional to
A
(Prandtl Number)0.3
B
(Prandtl Number)0.4
C
(Prandtl Number)0.8
D
(Prandtl Number)0.5
Answer
B
Marks
1
Question
In Dietus-Boelter equation used for the cooling of turbulent flow through the pipe, heat transfer co-efficient is proportional to
A
(Prandtl Number)0.3
B
(Prandtl Number)0.4
C
(Prandtl Number)0.8
D
(Prandtl Number)0.5
Answer
A
Marks
1
Question
For a turbulent flow of fluid in a circular tube, h1 is convective heat transfer coefficient at velocity v1. If the velocity is reduced to half and assuming that fluid properties are constant the new convective heat transfer coefficient is
A
1.26 h1
B
0.794h1
C
0.574 h1
D
1.741h1
Answer
C
Marks
1
Question
For a turbulent flow of fluid in a circular tube, h1 is convective heat transfer coefficient at velocity v1. If the velocity is doubled and assuming that fluid properties are constant the new convective heat transfer coefficient is
A
1.26 h1
B
0.794h1
C
0.574 h1
D
1.741h1
Answer
D
Marks
1
Question
For a laminar flow of fluid in a circular tube, 'h1' is the convective heat transfer coefficient at velocity 'V1'. If the velocity is reduced by half and assuming the fluid properties are constant, the new convective heat transfer co-efficient is
A
1.26 h1
B
0.794h1
C
0.574 h1
D
1.741h1
Answer
B
Marks
1
Question
For turbulent flow in a tube, the heat transfer co-efficient is obtained from the Dittus-Boelter correlation. If the tube diameter is doubled and the flow rate is halved, then the heat transfer co-efficient will change by a factor of approximately,
A
1
B
2
C
0.5
D
5
Answer
C
Marks
1
Question
For laminar flow in tube, the heat transfer coefficient is obtained from Sieder Tate equation. If the tube diameter is halved and the flow rate is doubled, then the heat
transfer coefficient will change by factor, A
1
B
3.2
C
1.6
D
8.2
Answer
C
Marks
1
Question
In heat exchangers with steam outside the tubes, a liquid gets heated to 45 0C when its velocity in the tubes is 2 m/s. If the velocity is reduced to 1 m/s, other things remaining the same, the temperature of the exit liquid will be
A
less than 45 0C
B
equal to 45 0C
C
greater than 45 0C
D
initially decreases and remains constant
Answer
A
Marks
1
Question
If the baffle spacing in a shell and tube heat exchanger increases, then the Reynolds number of the shell side fluid
A
remains unchanged
B
increases
C
increases or decreases depends on no. of shell passe4s
D
decreases
Answer
D
Marks
1
Question
If the baffle spacing in a shell and tube heat exchanger decreases, then the Reynolds number of the shell side fluid
A
remains unchanged
B
increases
C
increases or decreases depends on no. of shell passe4s
D
decreases
Answer
B
Marks
1
Question
If the diameter of the tubes in shell and tube heat exchanger decreases, then the Reynolds number on the tube side fluid
A
remains unchanged
B
increases
C
increases or decreases depends on no. of shell passe4s
D
decreases
Answer
B
Marks
1
Question
If the diameter of the tubes in shell and tube heat exchanger increases, then the Reynolds number on the tube side fluid
A
remains unchanged
B
increases
C
increases or decreases depends on no. of shell passe4s
D
decreases
Answer
D
Marks
1
Question
For a laminar flow of fluid in a circular tube, h1 is convective heat transfer coefficient at velocity v1. If the velocity is reduced to half and assuming that fluid properties are constant the new convective heat transfer coefficient is
A
1.26 h1
B
0.794h1
C
0.574 h1
D
1.741h1
Answer
B
Marks
1
Question
For Turbulent flow in tube, the heat transfer coefficient is obtained from DittusBoelter equation. If the tube diameter is halved and the mass flow rate is halved, then the heat transfer coefficient will change by factor,
A
1
B
0.5
C
6.6
D
0.66
Answer
D
Marks
1
Question
In heat exchanger, floating head is provided to
A
facilitate cleaning of heat exchanger
B
increase the heat transfer area
C
relieves the stresses by thermal expansion
D
increase log mean temperature gradient
Answer
C
Marks
1
Question
Why is superheated steam not preferred as a heating medium in evaporators
A
metal tubes cannot withstand high temperature
B
superheated steam has very low film coefficient
C
metal tubes cannot withstand high pressure
D
because of all above three factors
Answer
B
Marks
1
Question
Which one of the following tube configurations in heat exchangers results in the
maximum heat transfer rate? A
Triangular Pitch
B
Square Pitch
C
Rectangular Pitch
D
Rhombus pitch
Answer
A
Marks
1
Question
In shell and tube heat exchanger, baffles are provided on the shell side due to
A
prevent the stagnation of fluid
B
improve Heat Transfer
C
Provide the support for tubes
D
All of these
Answer
D
Marks
1
Question
In Sieder- Tate equation used in laminar flow through the pipe, heat transfer coefficient is proportional to
A
(Prandtl Number)1/3
B
(Prandtl Number)0.4
C
(Prandtl Number)0.8
D
(Prandtl Number)0.5
Answer
A
Marks
1
Question
In Sieder- Tate equation used in laminar flow through the pipe, heat transfer coefficient is proportional to
A
(Reynolds Number)0.5
B
(Reynolds Number)0.8
C
(Reynolds Number)2
D
(Reynolds Number)1/3
Answer
D
Marks
1
Question
Film Condensation occurs when
A
Condensate liquid does not wet the surface
B
Using surface coatings and vapour additives
C
Oil and greasy surface
D
Condensate liquid wets the surface
Answer
D
Marks
1
Question
The average heat transfer co-efficient for laminar film condensation on vertical surface is inversely proportional to (where, ΔT = Temperature drop across condensate film
A
(ΔT)2
B
ΔT
C
(ΔT)1/4
D
(ΔT)3/2
Answer
C
Marks
1
Question
Film condensation is promoted on a/an __________ surface.
A
Oily
B
coated
C
clean & smooth
D
dirty
Answer
C
Marks
1
Question
The thickness of condensate layer in filmwise condensation depends on the
A
condensation rate
B
surface configuration
C
liquid flow rate from the surface
D
all (a), (b) and (c)
Answer
D
Marks
1
Question
For condensation of pure vapors, if the heat transfer co-efficients in filmwise and drop-wise condensation are respectively hf and hd, then
A
hf = hd
B
hf >hd
C
hf< hd
D
hf could be greater or smaller than hd
Answer
C
Marks
1
Question
Dropwise condensation is promoted on a/an __________ surface.
A
glazed
B
oily
C
coated
D
smooth
Answer
B
Marks
1
Question
For condensation of pure vapors, if the heat transfer coefficients in filmwise and dropwise condensation are respectively hf and hd
A
hf = hd
B
hf > hd
C
hf < hd
D
hf is smaller or greater than hd
Answer
C
Marks
1
Question
A water Droplet at 25 0C is suddenly introduced into an infinite gas medium at 100 0 C saturated with water vapor. At steady state,
A
Drop attains WBT and vanishes
B
drops remains unchanged and attains temperature of 100 0C
C
drop increases in size and it attains temperature of 100 0C
D
none of these
Answer
C
Marks
1
Question
Match each of the processes with Heat Transfer coefficient Process Heat transfer coefficient (W / m2 0C) I Dropwise condensation of steam (a) 1700 - 50000 II Boiling Water (b) 50 - 1500 (c) 1 - 5 (d) 30000 - 100000
A
(I) – (b), (II) – (c)
B
(I) – (a), (II) – (b)
C
(I) – (d), (II) – (a)
D
(I) – (a), (II) – (c)
Answer
C
Marks
1
Question
The condensation of binary mixture of vapors at a constant pressure occurs
A
at constant temperature and yield a condensate of constant composition
B
over a temperature range and yield a condensate of constant composition
C
over a temperature range and yield a condensate of variable composition
D
At a temperature higher than the dew point temperature of vapors mixture
Answer
C
Marks
1
Question
Consider the following statements in condensation:
I. Presence of non condensable gases causes vapor molecules to reach condensate – vapor interface by diffusion through vap-gas mixture II. Presence of non condensable gases creates a mass transfer or diffusional resistance besides heat transfer resistance for condensation. Which of the statements given above is/ are correct? A
I only
B
II only
C
Both I & II
D
Neither I or II
Answer
C
Marks Question
Dropwise Condensation usually occurs on
A
Glazed surface
B
Smooth Surface
C
Oily Surface
D
Coated Surface
Answer
C
Marks
1
Question
Filmwise Condensation does not occur when
A
Condensate wets the surface
B
Smooth Surface
C
Oily Surface
D
Polished Surface
Answer
C
Marks
1
Question
Dropwise Condensation does not take place, if
A
Condensate liquid does not wet the surface
B
Using surface coatings and vapour additives
C
Oil and greasy surface
D
Condensate liquid wets the surface
Answer
D
Marks
1
Question
Heat transfer Rate in Dropwise Condensation may be 10 times greater than that in film condensation because,
A
film formed offers thermal Resistance to heat flow in film condensation
B
Surface is continuously exposed to vapors in dropwise condensation
C
Both A & B
D
Neither A nor B
Answer
C
Marks
1
Question
Dropwise Condensation occurs when
A
Condensate liquid does not wet the surface
B
Using surface coatings and vapour additives
C
Oil and greasy surface
D
All of the above
Answer
D
Marks
1
Question Drowise condensation is not promoted on a/an __________ surface. A
Oily
B
coated
C
clean & smooth
D
dirty
Answer
C
Marks
1
Question Consider the following statements in condensation:
I. Presence of non condensable gases causes vapor molecules to reach condensate – vapor interface by diffusion through vap-gas mixture II. Presence of non condensable gases does not create a mass transfer or diffusional resistance besides heat transfer resistance for condensation. Which of the statements given above is/ are correct? A
I only
B
II only
C
Both I & II
D
Neither I or II
Answer
A
Marks
1
Question Consider the following statements in condensation: I. Presence of non condensable gases does not cause vapor molecules to reach condensate – vapor interface by diffusion through vap-gas mixture II. Presence of non condensable gases does not create a mass transfer or diffusional resistance besides heat transfer resistance for condensation. Which of the statements given above is/ are correct? A
I only
B
II only
C
Both I & II
D
Neither I or II
Answer
D
Marks
1
Question Dropwise condensation is not promoted on a/an __________ surface. A
Oily
B
coated
C
clean & smooth
D
dirty
Answer
C
Marks
1
Question
Dropwise condensation is promoted on a/an __________ surface.
A
Oily
B
coated
C
dirty
D
All of the above
Answer
D
Marks
1
Question
In the processe of Boiling of water, the Heat Transfer coefficient (W / m2 0C) is in the range of
A
1700 - 50000
B
50 - 1500
C
1-5
D
30000 - 100000
Answer
A
Marks
1
Question
In the processe of Dropwise condensation of steam,the Heat Transfer coefficient (W / m2 0C) is in the range of
A
1700 - 50000
B
50 - 1500
C
1-5
D
30000 - 100000
Answer
D
Marks
1
Question Consider the following statements in condensation: I. Heat transfer coefficient in filmwise condensation is always less than Dropwise condensation. II. Presence of non condensable gases does not create a mass transfer or diffusional resistance besides heat transfer resistance for condensation. Which of the statements given above is/ are correct?
A
I only
B
II only
C
Both I & II
D
Neither I or II
Answer
A
Marks
1
Question Consider the following statements in condensation: I. filmwise condensation is always preferred over Dropwise condensation. II. filmwise condensation occurs on the oily/ coated surface. Which of the statements given above is/ are correct? A
I only
B
II only
C
Both I & II
D
Neither I or II
Answer
D
Marks
1
Question Average heat transfer coefficient for condensation of vapors is directly proportional to __________ power of Thermal conductivity of the film of the fluid. A
1/4
B
3/4
C
2
D
1/2
Answer
B
Marks
1
Question Average heat transfer coefficient for condensation of vapors over a vertical plate is ________ times the local heat transfer coefficient. A
2
B
1/2
C
3/4
D
4/3
Answer
D
Marks
1
Question Various surface coatings and vapor additive have been used in in attempts to maintain A
Filmwise condensation
B
Dropwise condensation
C
Both A & B
D
Neither A& B
Answer
B
Marks
1
Question If the condensation of vapors occurs on the horizontal tube, the heat transfer coefficient is proportional to ( D is diameter of tube) A
D1/4
B
D3/4
C
D-1/4
D
D-3/4
Answer
C
Marks
1
Question The average heat transfer co-efficient for laminar film condensation on vertical surface is inversely proportional to (where, ΔT = Temperature drop across condensate film A
(ΔT)2
B
ΔT
C
(ΔT)1/4
D
(ΔT)3/2
Answer
C
Marks
1
Question Leidenfrost point is a term concerned with the
A
condensation of the saturated vapor on a cold surface.
B
concentration of a corrosive solution by evaporation.
C
heat transfer between two highly viscous liquids.
D
boiling of a liquid on a hot surface.
Answer
D
Marks
1
Question
'Burnout heat flux' is a term concerned with the
A
condensation of the saturated vapor on a cold surface.
B
concentration of a corrosive solution by evaporation.
C
heat transfer between two highly viscous liquids.
D
boiling of a liquid on a hot surface.
Answer
D
Marks
1
Question
Heat flux increases with temperature drop beyond the Leiden frost point in the plot of heat flux vs. temperature excess for a boiling liquid, because
A
convection becomes important
B
conduction becomes important
C
radiation becomes important
D
sub-cooled boiling occurs
Answer
C
Marks
1
Question
Boiling point of a solution according to Duhring's rule is a linear function of the __________ of water.
A
boiling point (at the same pressure)
B
viscosity
C
density
D
thermal conductivity
Answer
A
Marks
1
Question
In a boiling curve, the peak heat flux is called the __________ point.
A
Nusselt
B
Leidenfrost
C
boiling
D
burnout
Answer
D
Marks
1
Question
As the difference between the wall temperature and the bulk temperature increases, the boiling heat transfer coefficient
A
continues to increase
B
continues to decrease
C
goes through minimum
D
goes through a maximum
Answer
D
Marks
1
Question
When Bubbles begins to form on the surface, the region of pool Boiling is called as,
A
Film Boiling
B
Nucleate boiling
C
Interface Evaporation
D
None of these
Answer
B
Marks
1
Question
Pool Boiling Curve is the log Graph of
A
Boiling point versus Heat flux
B
Heat flux versus Temperature Excess
C
Heat flux versus Boiling Time
D
Temperature Excess Versus Time
Answer
B
Marks
1
Question
Burnout Flux is a term associated with the
A
condensation of the saturated vapor on a cold surface.
B
concentration of a corrosive solution by evaporation
C
heat transfer between two highly viscous liquids.
D
boiling of a saturated liquid on a hot surface.
Answer
D
Marks
1
Question
If the temperature of the liquid in the boiling is ------------------ the saturation temperature, the process is called subcooled boiling.
A
Equal to
B
More than
C
Less than
D
Can not be predicted
Answer
C
Marks
1
Question
If the temperature of the liquid in the boiling is ------------------ the saturation temperature, the process is called saturated or bulk boiling.
A
Equal to
B
More than
C
Less than
D
Can not be predicted
Answer
A
Marks
1
Question
In subcooled or local boiling phenomenon, the liquid is maintained at a temperature
A
Below the saturation temperature
B
Above the saturation temperature
C
Equal to the saturation temperature
D
Can not be predicted
Answer
A
Marks
1
Question
In saturated or bulk boiling phenomenon, the liquid is maintained at a temperature
A
Below the saturation temperature
B
Above the saturation temperature
C
Equal to the saturation temperature
D
Can not be predicted
Answer
C
Marks
1
Question
In boiling the convection currents are responsible for the motion of the fluid near the surface , the regime is called as,
A
Interface Evaporation
B
Bubbling regime
C
Film boiling
D
None of the above
Answer
A
Marks
1
Question
Bubbles begin to form on the heated surface and dissipated in the liquid after breaking away from the surface during the boiling, the said regime is
A
Interface Evaporation regime
B
Nucleate boiling regime
C
Film boiling regime
D
None of the above
Answer
B
Marks
1
Question
In the pool boiling, the maximum heat flux at which the temperature usually exceeds the melting point of the wire, is referred to as
A
Leidenfrost point
B
Burnout flux
C
Boiling limit
D
None of these
Answer
B
Marks
1
Question
I. Pool Boiling Curve is the plot of heat flux data against temperature excess. II. If the temperature of the liquid is below the saturation temperature of the, the process is called as subcooled or local boiling. Which sentence/s is/are correct?
A
I only
B
II only
C
Both I & II
D
Neither I nor II
Answer
C
Marks
1
Question
I. In the saturated boiling the bubbles may break away from the surface because of the buoyancy action and move into the bulk of liquid II. In the saturated boiling, the heat transfer rate is not influenced by the agitation caused by the bubbles and vapor transport of energy into the bulk of liquid.
Which sentence/s is/ are correct? A
I only
B
II only
C
Both I & II
D
Neither I & II
Answer
A
Marks
1
Question
I. In the saturated boiling the bubbles may break away from the surface because of the buoyancy action and move into the bulk of liquid II. In the saturated boiling, the heat transfer rate is influenced by both the agitation caused by the bubbles and vapor transport of energy into the bulk of liquid. Which sentence/s is/ are correct?
A
I only
B
II only
C
Both I & II
D
Neither I & II
Answer
C
Marks
1
Question
Boiling of milk in an open vessel is an example of __________ boiling.
A
film
B
sub-cooled
C
saturated nucleate
D
none of these
Answer
A
Marks
1
Question
Boiling point elevation of an ideal solution
A
increases rapidly with temperature rise
B
in independent of pressure
C
decreases rapidly with temperature rise
D
None of these
Answer
A
Marks
1
Question
According to Duhring's rule, Boiling point of a solution is a linear function of the __________ of pure water.
A
boiling point (at the same pressure)
B
viscosity
C
density
D
thermal conductivity
Answer
A
Marks
1
Question
The regime of pool boiling in which Leidenfrost point exists, is referred to as
A
Interface evaporation
B
Nucleate boiling
C
Film boiling
D
None of the above
Answer
C
Marks
1
Question
I. Free convection currents are responsible for the motion of the fluid near the surface in the regime of interface evaporation. II. Bubbles are formed so rapidly as they blanket the heating surface to provide the thermal resistance in the film boiling. Which sentence/s is/ are correct?
A
I only
B
II only
C
Both I & II
D
Neither I & II
Answer
C
Marks
1
Question
I. Free convection currents are responsible for the motion of the fluid near the surface in the regime of interface evaporation. II. Bubbles are formed so rapidly as they blanket the heating surface to provide the thermal resistance in the film boiling. Which sentence/s is/ are false?
A
I only
B
II only
C
Both I & II
D
Neither I & II
Answer
D
Marks
1
Question
Heat flux increases with temperature drop beyond the Leiden frost point in the plot of heat flux vs. temperature excess for a boiling liquid, because
A
convection becomes important
B
conduction becomes important
C
radiation becomes important
D
sub-cooled boiling occurs
Answer
C
Marks
1
Question
I. Free convection currents are not responsible for the motion of the fluid near the surface in the regime of interface evaporation. II. Bubbles are formed so rapidly as they blanket the heating surface to provide the thermal resistance in the film boiling. Which sentence/s is/ are correct?
A
I only
B
II only
C
Both I & II
D
Neither I & II
Answer
B
Marks
1
Question
I. Free convection currents are responsible for the motion of the fluid near the surface in the regime of interface evaporation. II. Bubbles are formed so rapidly as they blanket the heating surface to provide the thermal resistance in the film boiling. Which sentence/s is/ are False?
A
I only
B
II only
C
Both I & II
D
Neither I & II
Answer
D
Marks
1
Question
I. In the saturated boiling the bubbles may break away from the surface because of the buoyancy action and move into the bulk of liquid II. In the saturated boiling, the heat transfer rate is influenced by both the agitation caused by the bubbles and vapor transport of energy into the bulk of liquid. Which sentence/s is/ are False?
A
I only
B
II only
C
Both I & II
D
Neither I & II
Answer
D
Marks
1
Question
Burnout Flux is a term associated with the
A
condensation of the saturated vapor on a cold surface.
B
concentration of a corrosive solution by evaporation
C
heat transfer between two highly viscous liquids.
D
boiling of a saturated liquid on a hot surface.
Answer
D
Marks
1
Question
In film type condensation over a vertical plate, local heat transfer coefficient is
A
Inversely proportional to the local film thickness
B
Directly proportional to the local film thickness
C
equal to the local film thickness
D
independent of the local film thickness
Answer
A
Marks
1
Question
In sub-cooled boiling,
A
temperature of the heating surface is less than the boiling point of the liquid.
B
temperature of the heating surface is more than the boiling point of the liquid.
C
bubbles from heating surface are absorbed by the mass of the liquid.
D
very large vapour space is necessary.
Answer
B
Marks
1
Question
Nucleate boiling is promoted
A
on polished surfaces
B
on rough surfaces
C
in the absence of agitation
D
none of these
Answer
B
Marks
1
Question
When vaporisation takes place through a blanketing film of gas, the phenomenon is termed as __________ boiling.
A
Pool
B
Nucleate
C
Transition
D
Film
Answer
D
Marks
1
Question
When vaporisation takes place directly at the heating surface, it is called
A
film boiling
B
nucleate boiling
C
vapour boiling
D
none of these
Answer
B
Marks
1
Question
The bubbles grow to the certain size on the heated surface during boiling, is not dependent on
A
Surface tension at vap-liq interface
B
Temperature
C
pressure
D
None of the above
Answer
D
Marks
1
Question
The bubbles grow to the certain size on the heated surface during boiling, is dependent on
A
Surface tension at vap-liq interface
B
Temperature
C
pressure
D
All of the above
Answer
D
Marks
1
Question
Bubbles are created by the expansion of the entrapped gas at a small cavity in the surface during the pool boiling, the boiling regime is said to be,
A
Interface evaporation
B
Nucleate boiling
C
Film boiling
D
None of the above
Answer
B
Marks
1
Question
During the pool boiling, Radiation is coming into play
A
Just after the burnout heat flux
B
Just before the burnout heat flux
C
Just before the leidenfrost point
D
Just after the Leidenfrost point
Answer
D
Marks
1
Question
The thickness of the film of the condensate formed over a vertical cold plate in condensation depends up on
A
Thermal conductivity of the film only
B
Viscosity of the fluid only
C
Temperature difference between gas and plate only
D
All of the above
Answer
D
Marks
1
Question
The thickness of the film of the condensate formed over a vertical cold plate in condensation is proportional to, (λfg is latent heat of condensation)
A
(λfg)1/2
B
(λfg)1/4
C
( λfg)-1/2
D
(λfg)-1/4
Answer
D
Marks
1
Question
The thickness of the film of the condensate formed over a vertical cold plate in condensation is proportional to, (k is thermal conductivity of condensate)
A
(k)1/2
B
(k)1/4
C
(k)-1/2
D
(k)-1/4
Answer
B
Marks
1
Question
The heat transfer coefficient for the condensation over a vertical cold plate is proportional to, (k is thermal conductivity of condensate)
A
(k)1/2
B
(k)3/4
C
(k)-1/2
D
(k)-1/4
Answer
B
Marks
1
Question
In saturated boiling,
A
temperature of the liquid is at its saturation temperature only
B
temperature of the heating surface is more than the boiling point of the liquid only.
C
Both A & B
D
Neither A & B
Answer
C
Marks
1
Question
The point at which it may be possible to observe the partial nucleate boiling and unstable film boiling region is referred to as
A
Leidenfrost point
B
Burnout heat flux
C
Interface evaporation
D
None of the above
Answer
B
Marks
1
Question
For laminar film condensation on horizontal tubes, heat transfer coefficient is proportional to the following
A
Density, viscosity of condensate and thermal conductivity of condensate only
B
Latent heat of condensation and Temperature excess only
C
Diameter of the tube only
D
All of the above
Answer
D
Marks
1
Question
On condensation, Mixed vapors yield the condensate as
A
Liquid of variable composition
B
Liquid of constant composition
C
Mixture of vapor and liquid
D
None of these
Answer
A
Marks
1
Question
Design of any heat exchange equipment used for condensation of vapors is done on the following type of condensation to occur on the surface
A
Dropwise condensation only
B
Filmwise condensation only
C
Both A & B
D
Neither A nor B
Answer
B
Marks
1
Question
Which of the following type of condensation to occur on the surface, is difficult to achieve and maintain, needs oily and greasy surface,
A
Dropwise condensation only
B
Filmwise condensation only
C
Both A & B
D
Neither A nor B
Answer
A
Marks
1
Question
Which of the following type of condensation to occur on the surface is well determined and needs clean, smooth surface,
A
Dropwise condensation only
B
Filmwise condensation only
C
Both A & B
D
Neither A nor B
Answer
B
Marks
1
Question
The presence of non condensable gas in the vapors during condensation
A
Offers the resistance to heat flow
B
Decreases the rate of condensation
C
Reduces the heat transfer coefficient
D
All of the above
Answer
D
Marks
1
Question
The bubbles grow to the certain size on the heated surface during boiling, is not dependent on
A
Surface tension at vap-liq interface
B
Temperature
C
pressure
D
None of the above
Answer
D
Marks
1
Question
The average heat transfer coefficient for the condensation over a vertical cold plate is proportional to, (λfg is latent heat of condensation)
A
(λfg)1/2
B
(λfg)1/4
C
( λfg)-1/2
D
(λfg)-1/4
Answer
B
Marks
1
Question
The thickness of the film of the condensate formed over a vertical cold plate in condensation is proportional to, where, ( Tg - Tw) is temperature difference between cold surface and vapors)
A
(Tg - Tw)1/2
B
(Tg - Tw)1/4
C
(Tg - Tw)-1/2
D
(Tg - Tw)-1/4
Answer
B
Marks
1
Question
The average heat transfer coefficient for the condensation over a vertical cold plate is proportional to, where, ( Tg - Tw) is temperature difference between cold surface and vapors)
A
(Tg - Tw)1/2
B
(Tg - Tw)1/4
C
(Tg - Tw)-1/2
D
(Tg - Tw)-1/4
Answer
D
Marks
1
Question
For the film condensation over a vertical cold plate, the critical value of Reynold number is,
A
3200
B
1800
C
10000
D
1000
Answer
B
Marks
1
Question
For the film condensation over a vertical cold plate, ripples will develop in the film at the value of Reynold number as low as is,
A
100-120
B
3-4
C
30-40
D
150-190
Answer
C
Marks
1
Question
The transition Reynolds Number for flow over a flat plate is 5 x 105. What is the distance from the leading edge at which transition will occur for flow of water with uniform velocity of 1 m/s and the kinematic viscosity of 0.858 x 10-6 m2/s?
A
1m
B
0.43m
C
43 m
D
103 m
Answer
B
Marks
2
Question
A fluid flows over a flat plate has the following properties: Dynamic viscosity : 25 x 10-6 kg /ms, Specific heat : 2.0 kJ /Kg K Thermal Conductivity: 0.05 W /mK The hydrodynamic boundary layer thickness is measured to be 0.5 mm. The thickness of thermal boundary layer would be,
A
1.3 mm
B
0.023 mm
C
0.079 mm
D
0.5 mm
Answer
D
Marks
2
Question
Air at 293K is flowing over a flat plate at 373 K at a velocity of 3 m/s. The plate is 2m long and 1m wide. if the Prandtl number is 0.69, kinematic viscosity 15 x 10-6 m2/s, then The thickness of thermal boundary layer at a distance 0.4 m from the leading edge of the plate is,
A
6.56 mm
B
7.2 mm
C
3.6 mm
D
3.28 mm
Answer
B
Marks
2
Question
Hydraulic or Equivalent Diameter(De) of annulus of two concentric pipes with inner diameter of outer pipe 8cm and outer diameter of inner pipe 4 cm, determined is,
A
10cm
B
12cm
C
14cm
D
16cm
Answer
B
Marks
2
Question
In double pipe heat exchanger, the ID and OD of the pipe are 4 cm and 5 cm respectively. The ID of the outer pipe is 10 cm with wall thickness of 1 cm. Then the equivalent diameter of the annulus for the heat transfer is
A
4.5cm
B
7.8cm
C
10cm
D
15 cm
Answer
D
Marks
2
Question
Air at 300K is flowing over a flat plate at 333 K at a velocity of 2 m/s. The plate is 2m long and 1m wide. The average heat transfer coefficient is 12.3 W/m2K. The heat transferred from the plate is,
A
81.18 W
B
811.8W
C
78.28 W
D
18.18 W
Answer
B
Marks
2
Question
Water at 20 oC and µ = 1.002 x 10-3 kg/m.s, k= 0.603W/mK, Cp= 4.183 KJ/kgK, The Prandtl Number for this case would be,
A
0.695
B
0.75
C
6.95
D
69.5
Answer
C
Marks
2
Question
Mercury at 20 oC and µ = 1520 x 10-6 kg/m.s, k= 0.0081 kW/mK, Cp= 0.139 kJ/kgK, The Prandtl Number of mercury would be,
A
2.61
B
0.0261
C
26.1
D
261
Answer
B
Marks
2
Question
Air at 27oC and 1 atm flows over a flat plate at speed of 2 m/s. Viscosity = 1.85 x 10-5 kg/m.s, Density = 1.177kg/m3. Boundary layer thickness at a distance of 20 cm from the leading edge of the plate is,
A
55.9 mm
B
5.59 mm
C
0.0559 mm
D
0.559 mm
Answer
B
Marks
2
Question
Air at 27oC and 1 atm flows over a flat plate at speed of 2 m/s. Boundary layer thickness at a distance of 20 cm from the leading edge of the plate is 5.59 mm and Prandtl Number of air is 0.70. Then Thermal boundary layer thickness is,
A
6.13mm
B
4.2 mm
C
6.9 mm
D
5.9 mm
Answer
A
Marks
2
Question
Air at 27oC and 1 atm flows over a flat plate at speed of 2 m/s. Boundary layer thickness at a distance of 40 cm from the leading edge of the plate is 7.9 mm and Prandtl Number of air is 0.70. Then Thermal boundary layer thickness is,
A
6.66 mm
B
6.86 mm
C
8.66 mm
D
7.86 mm
Answer
C
Marks
2
Question
A fluid flowing with Reynolds No. 26.26 through the tube 20 mm ID and 5 cm length. Prandtl No. is 2625, viscosity in the bulk is 0.8 Ns/m2and that at the wall(µw) is 1 Ns/m2, thermal conductivity = 0.384W/m.K. Using Sieder-Tate equation, the inside heat transfer coefficient is,
A
520 W/m2K
B
225 W/m2K
C
425 W/m2K
D
825 W/m2K
Answer
B
Marks
2
Question
A fluid flowing with Reynolds Number 12198 through the tube 40 mm ID. Prandtl
Number is 42.5 and thermal conductivity = 0.256 W/m.K. If the fluid is being heated, using Dittus-Boelter equation, the inside heat transfer coefficient would be, A
1225 W/m2K
B
1525 W/m2K
C
825 W/m2K
D
425 W/m2K
Answer
A
Marks
2
Question
Water at 353K entering and leaves at 309K with a velocity of 3 m/s through the tube of 16 mm diameter. The tube temperature is 297K. Prandtl No. is 3.09, viscosity = 485 x 10-6 kg/m.s, thermal conductivity = 0.657 W/m.K and density = 984.1 kg/m3, using Dittus-Boelter equation, the inside heat transfer coefficient would be,
A
9970 W/m2K
B
10970 W/m2K
C
11970 W/m2K
D
12970 W/m2K
Answer
D
Marks
2
Question
Hot water enters the tube side of a counter current shell and tube heat exchanger at 80°C and leaves at 50°C. Cold oil enters at 20°C and leaves at 45oC. The log mean temperature difference in °C is approximately
A
32
B
37
C
45
D
50
Answer
A
Marks
2
Question
Hot oil at 150 oC is used to preheat a cold fluid at 30 oC in a shell and tube heat exchanger. The exit temperature of the hot oil is 110 oC. Product of Heat capacity and mass flow rate of each of the streams is same. The heat duty is 2 KW. Under concurrent flow conditions, the log mean temperature difference is
A
82.2 oC
B
72.8 oC
C
68.32 oC
D
120.2 oC
Answer
B
Marks
2
Question
In counter current Heat Exchanger, cold fluid enters at 30 0C and leaves at 60 0C, whereas the hot fluid enters at 150 0C and leaves at 110 0C, The log mean temperature difference for this case is,
A
100 0C
B
85 0C
C
107 0C
D
35 0C
Answer
B
Marks
2
Question
Air at 27oC and 1 atm flows over a flat plate at speed of 2 m/s. Boundary layer thickness at a distance of 40 cm from the leading edge of the plate is 6.5 mm and Prandtl Number of air is 0.70. Then Thermal boundary layer thickness is,
A
6.66 mm
B
6.86 mm
C
8.66 mm
D
7.13 mm
Answer
D
Marks
2
Question
Water at 27oC and 1 atm flows over a flat plate at speed of 2 m/s and Boundary layer thickness at a distance of 30 cm from the leading edge of the plate is 9 mm and Prandtl Number of air is 6.5. Then Thermal boundary layer thickness is,
A
4.7 mm
B
7.4 mm
C
10 mm
D
7.9 mm
Answer
A
Marks
2
Question
Oil at 20oC and 1 atm flows over a flat plate at speed of 1.2 m/s with properties density 876kg/m3, kinematic viscosity 0.00024 m2/s and thermal conductivity as 0.144 W/moC, Cp specific heat is 1965.75 J/kgoC, Then Prandtl Number is
A
2910
B
2870
C
2120
D
2139
Answer
B
Marks
2
Question
Oil having flow rate 2000 kg/hr at 107 0C is cooled to 30 0C by water which enters at 15 0C and leaves at 80 0C in counter flow heat exchanger. What is its LMTD?
A
12.4 0C
B
20.4 0C
C
24.4 0C
D
16.4 0C
Answer
B
Marks
2
Question
Air at 500 K has kinematic viscosity of 37.9 x 10-6 m2/s and thermal diffusivity of 0.5564x 10-4 m2/s, then Prandtl number is
A
0.702
B
0.680
C
0.860
D
0.720
Answer
B
Marks
2
Question
Air at 293 K is flowing at velocity 2m/s over heated rectangular plate of length 2 m at 407K , Prandtl number 0.7 and thermal conductivity of air is 0.03W/mK, kinematic viscosity 20.76 x 10-6m2/s, the average heat transfer coefficient would be,
A
3.9 W/m2K
B
4.9 W/m2K
C
5.9 W/m2K
D
6.9 W/m2K
Answer
A
Marks
2
Question
Air at 293 K is flowing at velocity 2m/s over heated rectangular plate of length 2 m at 407K, the average heat transfer coefficient is 3.9 W/m2K, the heat lost from the plate is 1500W, the width of the plate is
A
4.69 m
B
3.69 m
C
2.69 m
D
1.69 m
Answer
D
Marks
2
Question
Air at 293 K is flowing at velocity 2m/s over heated rectangular plate of length 2 m and unit width at 407K, the average heat transfer coefficient is 3.9 W/m2K, the heat lost from the plate is,
A
1200W
B
1300W
C
1400W
D
1500W
Answer
D
Marks
2
Question
Air at 300K blows at a free stream velocity of 4 m/s across a 12 mm diameter sphere maintained at 350 K , the heat transfer coefficient is 97.85 W/m2K, the heat lost from the sphere is,
A
1.21 W
B
2.21 W
C
3.21 W
D
4.21 W
Answer
B
Marks
2
Question
Air at 293 K is flowing at velocity 2m/s over heated rectangular plate of length 2 m and unit width at 407K with kinematic viscosity 20.76 x 10-6 m2/s, the said fluid is flowing in
A
Laminar region
B
Transition Region
C
Turbulent region
D
Fully turbulent
Answer
A
Marks
2
Question
Air at 293 K is flowing at velocity 35 m/s over heated rectangular plate of length 75 cm at 333K , Prandtl number 0.7 and thermal conductivity of air is 0.03W/mK, kinematic viscosity 20.76 x 10-6m2/s, the average heat transfer coefficient would be,
A
79 W/m2K
B
89 W/m2K
C
99 W/m2K
D
109 W/m2K
Answer
C
Marks
2
Question
Air at 293 K is flowing at velocity 35 m/s over heated rectangular plate of length 75 cm at 333K , Prandtl number 0.7 and thermal conductivity of air is 0.03W/mK, kinematic viscosity 20.76 x 10-6m2/s, the said fluid is flowing in
A
Laminar region
B
Transition Region
C
Turbulent region
D
None of these
Answer
C
Marks
2
Question
Air at 293 K is flowing at velocity 35 m/s over heated rectangular plate of 75 cm x 75cm in dimension maintained at 333K, the average heat transfer coefficient 99 W/m2K, the heat lost from only one side of the plate is,
A
2227.5 W
B
1227.5 W
C
4455 W
D
3227.5 W
Answer
D
Marks
2
Question
Saturated steam at 353 K condenses on outside of horizontal tube of 100 mm O. D. and length L. The tube wall is maintained at 343 K. When the tube wall is vertical, it was observed that the rate of condensation was same as the horizontal, then the tube length required is
A
2.9 m
B
29 m
C
0.29 m
D
0.029 m
Answer
C
Marks
2
Question
In heat exchangers with steam outside the tubes, a liquid gets heated to 45 0C when its velocity in the tubes is 2 m/s. If the velocity is reduced to 1 m/s, other things remaining the same, the temperature of the exit liquid will be
A
less than 45 0C
B
equal to 45 0C
C
greater than 45 0C
D
initially decreases and remains constant
Answer
A
Marks
2
Question
1000 kg of liquid at 30 0C in a well stirred vessel has to be heated to 120 0C, using immersed coils carrying condensing steam at 1500C. the area of the steam coils is 1.2 m2 and overall heat transfer coefficient to the liquid is 1500 W/m2 0C. Assuming negligible heat loss to the surroundings and specific heat capacity of liquid to be 4 kJ / kg 0C, the time taken for the liquid to reach desired temperature will be
A
15 min
B
22 min
C
44 min
D
51 min
Answer
D
Marks
2
Question
The Overall heat transfer coefficient for shell and tube heat exchanger for clean surface is Uc = 400 W /m2 K. The fouling factor after one year of operation is found to be hdo = 2000 W /m2 K . the overall heat transfer coefficient at this time is
A
1200 W /m2 K
B
894 W /m2 K
C
333 W /m2 K
D
287 W /m2 K
Answer
C
Marks
2
Question
A horizontal pipe 1ft. (0.3048 m) in diameter is maintained at temperature of 250oC in a room where ambient air is at 15oC. Product of Grashof Number and Prandtl Number is 1.571 x 108, thermal conductivity = 0.03406 W/m.K. Convective heat transfer coefficient is,
A
3.66 W/m2K
B
66.36 W/m2K
C
6.63 W/m2K
D
36.6 W/m2K
Answer
C
Marks
2
Question
Steam at 373 K is condensed over a vertical plate 0.3 x 0.3 m2 maintained at 371 K. The heat transferv coefficient is 13150 W/m2K, the latent heat of condensation is 2225kJ/kg, The rate of condensation is,
A
38 kg/hr
B
3.8 kg/hr
C
0.38 kg/hr
D
380 kg/hr
Answer
B
Marks
2
Question
A horizontal pipe 1ft. (0.3048 m) in diameter is maintained at temperature of 250oC in a room where ambient air is at 15oC. Properties are evaluated at mean film temperature of 405.5K. thermal conductivity = 0.03406 W/m.K, Kinematic viscosity = 26.54 x 10-6 m2/s, Grashof Number calculated is,
A
1.571 x 108
B
2.29 x 108
C
15.71 x 108
D
22.9 x 108
Answer
B
Marks
2
Question
Oil having flow rate 2000 kg/hr at 107 0C is cooled to 30 0C by water which enters at 15 0C and leaves at 80 0C in counter flow heat exchanger. The specific heat of oil is 2.51 kJ/kg K. The overall heat transfer coefficient is 1500 W/m2K. What is the heat transfer area required?
A
25 m2
B
3.5 m2
C
4.5 m2
D
3 m2
Answer
B
Marks
2
Question
Steam is condensed with heat lost 5 kW on the cold surface. If the latent heat of condensation is 2225 kJ/kg, the mass flow rate of the condensate is,
A
8 kg/hr
B
9 kg/hr
C
10 kg/hr
D
11.2 kg/hr
Answer
A
Marks
2
Question
A straight tube having a diameter of 40 mm carries fluid with velocity of 10 m/s. the temperature of tube surface is 50 oC and flowing fluid is heated from temp 15 oC to 25 oC. The physical properties of fluid at mean temp Pr. = 0.702, µ/ρ = 1.006 x 10-6 m2/s, k = 0.599 W/mK The heat transfer coefficient would be approximately,
A
9020 W/m2oC
B
8359 W/m2 oC
C
3258 W/m2 oC
D
7680 W/m2 oC
Answer
A
Marks
2
Question
Water flowing in a steel pipe of diameter 0.02 m is to be cooled from 40 oC to 30 oC. The velocity of water in the steel pipe 1.5m/s. The inside surface temp is maintained at 25 oC. Viscosity is 7.65 x 10-4, Thermal conductivity = 0.623 W/mK, Density = 995 Kg/m3 and Pr = 5.3 The convective heat transfer coefficient for water is,
A
6240 W/m2K
B
5565 W/m2K
C
3250 W/m2K
D
7680 W/m2K
Answer
B
Marks
2
Question
Saturated vapors at 323 K condensed on the cold surface maintained at 313 K , heat transfer coefficient is 1000 W/m2K, the heat transfer area is 1m2,and the latent heat of condensation is 132kJ/kg, the rate of condensation is,
A
723.7kg/hr
B
272.7 kg/hr
C
327.3 kg.hr
D
100 kg/hr
Answer
B
Marks
2
Question
Hot oil at 150 oC is used to preheat a cold fluid from 30 oC to 70 oC in a shell and tube heat exchanger. The exit temperature of the hot oil is 110 oC. The heat duty is 2 KW. Under counter current flow conditions, overall heat transfer resistance (1/UA) is,
A
0.04 oC/W
B
0.4oC/W
C
0.36 oC/W
D
0.036 oC/W
Answer
A
Marks
2
Question
Hot oil at 150 oC is used to preheat a cold fluid from 30 oC to 70 oC in a shell and tube heat exchanger. The exit temperature of the hot oil is 110 oC. The heat duty is 2 KW. Under concurrent flow conditions, overall heat transfer resistance (1/UA) is,
A
0.04 oC/W
B
0.4oC/W
C
0.36 oC/W
D
0.036 oC/W
Answer
D
Marks
2
Question
Hot liquid is flowing with the velocity of 2 m/s through a metallic pipe having inner diameter of 3.5 cm and length of 20 m. The temperature at the inlet of the pipe is 90 o C. Data: Density = 950 kg/m3, viscosity = 2.55 x 10-4 kg/ms, thermal conductivity = 0.685 W/moC
Prandtl Number = 1.57, then the convective heat transfer coefficient in KW/m2 oC would be, A
11.2 KW/m2 oC
B
111.2 KW/m2 oC
C
22.2 KW/m2 oC
D
221.2 KW/m2 oC
Answer
A
Marks
2
Question
Air at temperature 523 K flows over a flat plate 0.3 m wide and 1m long at velocity of 8 m/s, if the plate is maintained at 351 K, The average convective heat transfer coefficient is 3.06W/m2K. The rate of heat flow from one side of the plate only is,
A
158W
B
258W
C
358W
D
316W
Answer
A
Marks
2
Question
Air at temperature 523 K flows over a flat plate 0.3 m wide and 1m long at velocity of 8 m/s, if the plate is maintained at 351 K, thermal conductivity = 36.4 x 10-3 W/m.K, Kinematic viscosity = 3.9 x 10-4 m2/s, Prandtl number is 0.69, The average convective heat transfer coefficient would be,
A
9.06 W/m2K
B
6.06 W/m2K
C
3.06 W/m2K
D
5.06 W/m2K
Answer
C
Marks
2
Question
Air at 8 kPa and 523 K flows over a flat plate 0.3 m wide and 1.5 m long at velocity of 8 m/s, if the plate is maintained at 253 K, thermal conductivity = 36.4 x 10-3 W/m.K, Kinematic viscosity = 3.9 x 10-4 m2/s, Prandtl number is 0.69. The average convective heat transfer coefficient is,
A
1.5 W/m2K
B
2.5 W/m2K
C
3.5 W/m2K
D
4.5 W/m2K
Answer
B
Marks
2
Question
Air at 333K is flowing at a velocity of 15 m/s parallel on both sides of the flat square plate having sides each of 20cm, maintained at 293 K. if the Prandtl number is 0.699, kinematic viscosity 16.96 x 10-6 m2/s, thermal conductivity of air is 0.0276W/mK. Then the average heat transfer coefficient is
A
17.1 W/m2 oC
B
43.2 W/m2 oC
C
22.2 W/m2 oC
D
34.2 W/m2 oC
Answer
D
Marks
2
Question
A fluid flowing with velocity 1.14 m/s is heated through the hot tube of 40mm diameter. Data: Prandtl number = 42.5, Density = 1070 kg/m3, viscosity= 0.004 Ns/m2 and thermal conductivity = 0.256 W/mK. Inside heat transfer coefficient for this case is,
A
122.5 W/m2 K
B
1225.5 W/m2 K
C
2250.5 W/m2 K
D
212.5 W/m2 K
Answer
B
Marks
2
Question
Air at 2 atm and 200oC is heated as it flows at velocity of 10 m/s through a tube with diameter of 2.54 cm. Prandtl no.= 0.681, µ = 2.57 x 10-5 kg/m.s, k= 0.0386W/mK, Cp= 1.025 KJ/kgK, ρ = 1.493kg/m3 . The heat transfer coefficient would be
A
32.65 W/m2K
B
64.85 W/m2K
C
46.65 W/m2K
D
16.35 W/m2K
Answer
B
Marks
2
Question
Air at 2 atm and 200oC is heated as it flows at velocity of 10 m/s through a tube with diameter of 5 cm and 1m length. The tube wall is maintained at a temperature 20oC above the air temperature. The heat transfer coefficient is 70 W/m2K. Then The heat flow would be,
A
22 W
B
220 W
C
2220 W
D
22.5 W
Answer
B
Marks
2
Question
A large vertical plate 4 m high and 10 m wide maintained at 60 oC and exposed to atmospheric air at 10 oC. If the product of Grashof No. and Prandtl No. is 2.62 x 1011, The Nusselt Number will be,
A
640
B
460
C
560
D
450
Answer
A
Marks
2
Question
A large vertical plate 4 m high and 10 m wide maintained at 60 oC and exposed to
atmospheric air at 10 oC. Air properties evaluated at mean film temperature 308 K are, k = 0.02685 W/mK, Kinematic viscosity = 16.5 x 10-6 m2/s, β = 3.25 x 10-3 K-1, the Grashof Number calculated for this case is, A
2.74 x 1011
B
3.74 x 1011
C
4.74 x 1011
D
1.74 x 1011
Answer
B
Marks
2
Question
2 cm diameter horizontal heater is maintained at surface temperature of 38 oC and submerged in water at 27oC, the product of Grashof and Prandtl Number is 2.18 x 106, thermal conductivity = 0.630W/m.K. Convective heat transfer coefficient is,
A
462 W/m2K
B
642 W/m2K
C
264 W/m2K
D
426 W/m2K
Answer
B
Marks
2
Question
Air at temperature 523 K flows over a flat plate 0.3 m wide and 1m long at velocity of 8 m/s, if the plate is maintained at 351 K, The average convective heat transfer coefficient is 3.06W/m2K. The rate of heat flow from both sides of the plate is,
A
158W
B
258W
C
358W
D
316W
Answer
D
Marks
2
Question
Steam at 373K is condensed over a cylindrical surface of diameter 25 mm maintained at 357 K, heat transfer coefficient is 10864 W/m2K, the rate of heat transfer per unit length of cylinder is
A
16.35kW/m
B
13.65kW/m
C
12.56kW/m
D
15.36kW/m
Answer
B
Marks
2
Question
Water at 5 atm flows inside the tube of 0.0254 m and 1 m length under the local boiling conditions where the tube wall temperature maintained is 10oC above the saturation temperature, the heat transfer coefficient is 3521 W/m2 K. then the heat transfer is
A
2180 W
B
2810 W
C
1280 W
D
2018 W
Answer
B
Marks
2
Question
A fluid flowing with velocity 1.14 m/s is heated through the hot tube of 40mm diameter. Data: Prandtl number = 42.5, Density = 1070 kg/m3, viscosity= 0.004 Ns/m2 and thermal conductivity = 0.256 W/mK. Inside heat transfer coefficient for this case is,
A
122.5 W/m2 K
B
1225.5 W/m2 K
C
2250.5 W/m2 K
D
212.5 W/m2 K
Answer
B
Marks
2
Question
Steam is condensed with heat lost 10 kW on the cold surface. If the latent heat of condensation is 2225 kJ/kg, the mass flow rate of the condensate is,
A
8 kg/hr
B
9 kg/hr
C
16 kg/hr
D
11.2 kg/hr
Answer
C
Marks
2
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