HYDRODYNAMIC & THERMAL BOUNDARY LAYERS MULTIPLE CHOICE QUESTIONS (MCQ) WITH ANSWERS
HYDRODYNAMIC & THERMAL
BOUNDARY LAYERS
MULTIPLE CHOICE QUESTIONS
(MCQ) WITH ANSWERS
MCQ increases the knowledge and
understanding. It also improves the
clarity. This helps in the proper analysis
and design of practical applications.
Hydrodynamic and thermal boundary
layers are spaces over the flat plate or
inside a pipe. Hydrodynamic boundary
layer shows the velocity variation. It
depends on Reynolds number. Thermal
boundary layer shows the temperature
variation in a laminar and turbulent
flows. Thermal boundary layer depends
upon the thermal conductivity of the fluid.
Larger is the conductivity, larger is the
space within the thermal boundary layer.

Hydrodynamic layer is a thin layer of fluid

Close to the outside solid surface

Close to the inside solid surface

Both close to inside & outside solid surface

None

ANS: (a)

In a hydrodynamic boundary layer

Tensile stresses influence the velocity distribution

Compressive stresses influence the velocity distribution

Shear stresses influence the velocity distribution

None

ANS: (c )

Velocity varies in the hydrodynamic layer from

Firstly Zero to 0.9 times of free velocity

Secondly Zero to 2 times the free velocity

Thirdly Zero to 0.99 times the free velocity

None

ANS: (C )

Hydrodynamic boundary layer is invented by

Newton

Nusselt

Prandtl

None

ANS: (c )

Leading edge in a boundary layer is

Firstly Edge facing the incoming fluid

Secondly Edge facing the outgoing fluid

Thirdly Edge facing incoming & outgoing fluid

None

ANS: (a)

Trailing edge in a boundary layer is

Firstly Edge facing the incoming fluid

Secondly Edge facing the outgoing fluid

© Thirdly Edge facing incoming & outgoing fluid
(d)None
ANS: (b)

Velocity of the fluid at the solid surface is

> 0

< 0

= 0

None

ANS: (C )

Within the hydrodynamic boundary layer, the velocity variation ∂u/∂y from solid surface to free fluid surface is

Increasing

Decreasing

Increasing & decreasing

None

ANS: (a)

Velocity of fluid ‘u’ is equal to U at the

Solid surface

Free liquid surface

Inbetween solid and free liquid surface

None

ANS: (b)

The thickness of boundary layer is

Constant

Variable

Constant & variable

None

ANS: (b)

Thickness of boundary layer is

Zero at leading edge and maximum at trailing edge

Zero at trailing edge and maximum at leading edge

Maximum at the leading edge

None

ANS: (a)

Fluid velocity outside hydrodynamic layer is

Variable

Constant

Variable & constant

None

ANS: (b)

If the incoming velocity is high, thickness of boundary layer will be

More

Less

Can’t say

None

ANS: (b)

In the flow direction, boundary layer is
(a) Laminar first & turbulent later
(b) Turbulent first & laminar later
© Transition layer first
(d) None
ANS: (a)

In the transition zone, the flow is

Unstable

Stable

Unstable & stable

None

ANS: (a)

The flow pattern in boundary is judged by

Prandtl number

Reynolds Number

Prandtl & Reynolds numbers

None

ANS: (b)

The value of Reynolds number at the end of laminar flow is

3 lacs

7 lacs

5 lacs

None

ANS: (c )

Reynolds number at the end of laminar flow is

Laminar

Critical

Laminar & critical

None

ANS: (b)

The value of Reynolds number where turbulent flow starts is

3 lacs

5 lacs

7 lacs

None

ANS: (c )

Shear stress is maximum at the

Solid surface

Free liquid surface

Solid & free liquid surface

None

ANS: (a)

Velocity variation in a hydrodynamic layer is

Curvilinear

Parabolic

Linear

None

ANS: (b)

The equation for entrance length L_{e} in a pipe laminar flow is

Firstly L_{e}/D= 0.08R_{e}

Secondly L_{e}/D= 0.04R_{e}

Thirdly L_{e}/D= 0.06R_{e}

None

ANS: (c )

The equation for entrance length L_{e} in a pipe turbulent flow is

Firstly L_{e}/D= 4.4 R_{e}^{1/4}

Secondly L_{e}/D= 0.04R_{e}^{1/3}

Thirdly L_{e}/D= 0.06R_{e}^{1/6}

None

ANS: (c )

Value of Reynolds number in a pipe laminar flow is
 < 500
 < 2100
 > 4000
 None
ANS: (b)

Value of Reynolds number in a pipe turbulent flow is
 > 500
 < 2100
 > 4000
 None
ANS: (c)

Entrance length of laminar flow vs turbulent flow in a pipe flow is

Less

Greater

Equal

None

ANS: (b)

Shear stress equation is

τ=µ∂u/∂y

τ =µ^{2}∂u/∂y

τ =5 ∂u/∂y

None

ANS: (a)

Momentum equation for hydrodynamic layer is

Firstly u ∂u/∂x + v ∂u/∂y =ν ∂^{2}u/∂x^{2}

Secondly u ∂u/∂x + v ∂u/∂y =ν ∂^{2}u/∂y^{2}

Thirdly u ∂u/∂x + v ∂u/∂y =ν ∂^{2}u/∂x ∂y

None

ANS: ( b)

Based on Blasius equation, hydrodynamic boundary layer thickness
at distance ‘x’ from the leading edge is

Firstly δ/x = 4.64/Re_{x}^{5}

Secondly δ/x = 5.64/Re_{x}^{5}

Thirdly δ/x = 5.00/Re_{x}^{5}

None

ANS: (c )

Based on VonKarman Integral Momentum equation, hydrodynamic
boundary layer thickness at distance ‘x’ from the leading edge is

Firstly δ/x = 4.64/Re_{x}^{5}

Secondly δ/x = 5.64/Re_{x}^{5}

Thirdly δ/x = 5.00/Re_{x}^{5}

None

ANS: (a )

Local friction coefficient based on Blasius equation

Firstly C_{fx} = 0.699/Re_{x}^{5}

Secondly C_{fx} = 0.664/Re_{x}^{5}

Thirdly C_{fx} = 0.646/Re_{x}^{5}

None

ANS: (b)

Local friction coefficient based on VonKarman equation

Firstly C_{fx} = 0.699/Re_{x}^{5}

Secondly C_{fx} = 0.664/Re_{x}^{5}

Thirdly C_{fx} = 0.646/Re_{x}^{5}

None

ANS: (c)

Average friction coefficient based on Blasius equation

Firstly C_{fx} = 1.118/Re_{x}^{5}

Secondly C_{fx} = 1.228/Re_{x}^{5}

Thirdly C_{fx} = 1.328/Re_{x}^{5}

None

ANS: (c)

Average friction coefficient based on VonKarman equation

Firstly C_{fx} = 1.192/Re_{x}^{5}

Secondly C_{fx} = 1.292/Re_{x}^{5}

Thirdly C_{fx} = 1.492/Re_{x}^{5}

None

ANS: (b)

Velocity distribution in turbulent flow hydrodynamic boundary layer is

Firstly u/U = (y/δ)^{1/5}

Secondly u/U = (y/δ) ^{1/9}

Thirdly u/U = (y/δ)^{1/7}

None
ANS: (c )

Boundary layer thickness at distance x from the start of turbulent layer is

Firstly δ/x = 0.317(R_{e})^{1/5}

Secondly δ/x = 0.337(R_{e})^{–1/5}

Thirdly δ/x = 0.371(R_{e})^{–1/5}

None
ANS: (c )
37. Thermal boundary layer is a thin space of temperature variation

Firstly Close to outside solid surface

Close to inside solid surface

Both close to inside & outside solid surface

None
ANS: (a)
38. In a thermal boundary layer


Tensile stresses influence the velocity distribution

Compressive stresses influence the velocity distribution

Shear stresses influence the velocity distribution

None

ANS: (d)
39. Temperature varies in the thermal boundary layer from

Firstly Zero to 0.9 times of free flow layer temperature

Secondly Zero to 2 times the free flow layer temperature
(c ) Thirdly Zero to 0.99 times the free flow layer temperature
(d ) None
ANS: (c)
40. Thermal boundary layer is invented by

Newton

André Lévêque

Prandtl

None
ANS: (b)
41. Leading edge in a thermal boundary layer is


Firstly Edge facing the incoming fluid

Secondly Edge facing the outgoing fluid

Thirdly Edge facing incoming & outgoing fluid

None

ANS: (a)
42. Trailing edge in a thermal boundary layer is


Firstly Edge facing the incoming fluid

Secondly Edge facing the outgoing fluid

© Thirdly Edge facing incoming & outgoing fluid
(d)None
ANS: (b)
43. Temperature of the fluid at the hot solid surface

> 0

< 0

=0

None
ANS: (a)
44. Within the thermal boundary layer, the temperature variation ∂t/∂y from solid surface to free fluid surface is


Increasing

Decreasing

Increasing & decreasing

None

ANS: (b)
45. Temperature of fluid ‘t’ is equal to t_{ solid }at the


Solid surface

Free liquid surface

Inbetween solid and free liquid surface

None

ANS: (a)
46. The thickness of thermal boundary layer is


Constant

Variable

Constant & variable

None

ANS: (b)
47. Thickness of thermal boundary layer is


Firstly Zero at leading edge and maximum at trailing edge

Zero at trailing edge and maximum at leading edge

c. Maximum at the leading edge
d. None
ANS: (a)
48. Temperature outside thermal boundary layer is


Variable

Constant

Variable & constant

None

ANS: (b)
49. If the incoming velocity is high, thickness of thermal boundary layer will be


More

Less

Can’t say

None

ANS: (b)
50. In the flow direction, thermal boundary layer has
(a) Laminar first & turbulent later
(b) Turbulent first & laminar later
© Transition layer first
(d) None
ANS: (a)
51. The thermal boundary is effected by


Prandtl number

Reynolds Number

Prandtl & Reynolds numbers

None

ANS: (a)
52. Thermal boundary layer thickness is greater than the thickness of hydrodynamic boundary layer thickness when


Firstly Pr > 1

Secondly Pr < 1

Thirdly Pr = 1

None

ANS: (b)
53. Thermal boundary layer thickness is less than the thickness of hydrodynamic boundary layer thickness when

Firstly Pr > 1

Secondly Pr < 1

Thirdly Pr = 1

None
ANS: (a)
54. Thermal boundary layer thickness is equal than the thickness of hydrodynamic boundary layer thickness when

Firstly Pr > 1

Secondly Pr < 1

Thirdly Pr = 1

None
ANS: (c )
55. Temperature variation in the thermal boundary layer is

Linear

Parabolic

Curvilinear

None
ANS: (b)
56. Energy equation for thermal boundary layer is

Firstly u ∂t/∂x + v ∂t/∂y =ν ∂^{2}t/∂y^{2}

Secondly u ∂t/∂x + v ∂t/∂y =β ∂^{2}t/∂y^{2}

Thirdly u ∂t/∂x + v ∂t/∂y =α ∂^{2}t/∂y^{2}

None
ANS: ©
57. The relation between δ_{t} and δ is

Firstly δ_{t} = δ Pr ^{1/3}

Secondly δ_{t} = δ Pr ^{–1/3}

Thirdly δ_{t} = δ Pr ^{2/3}

None
ANS: (b)
58. Local heat transfer coefficient in the thermal boundary layer is

Firstly h_{x} = 0.664 (k/x) (R_{e})^{5} (Pr)^{0.33}

Secondly h_{x} = 0.996 (k/x) (R_{e})^{5} (Pr)^{0.33}

Thirdly h_{x} = 0.332 (k/x) (R_{e})^{5} (Pr)^{0.33}

None
ANS: (c )
59. Average heat transfer coefficient in the thermal boundary layer is


Firstly h_{x} = 0.664 (k/x) (R_{e})^{5} (Pr)^{0.33}

Secondly h_{x} = 0.996 (k/x) (R_{e})^{5} (Pr)^{0.33}

Thirdly h_{x} = 0.332 (k/x) (R_{e})^{5} (Pr)^{0.33}

None

ANS: (a )
60. Ratio of Average to local heat transfer coefficient is

Three

Two

One

None
ANS: (b)
61. Local Nusselt number in thermal boundary layer is


Firstly Nu_{x} = 0.664 (R_{e})^{5} (Pr)^{0.33}

Secondly Nu_{x} = 0.996 (R_{e})^{5} (Pr)^{0.33}

Thirdly Nu_{x} = 0.332 (R_{e})^{5} (Pr)^{0.33}

None

ANS: (c )
62. Average Nusselt number in the thermal boundary layer is
a. Firstly Nu^{–} = 0.664 (R_{e})^{0.5} (Pr)^{0.33}
b. Secondly Nu^{–} = 0.996 (R_{e})^{5} (Pr)^{0.33}
c. Thirdly Nu^{–} = 0.332 (R_{e})^{5} (Pr)^{0.33}
d. None
 ANS: (a )
63. In the transition zone, the temperature variation is

Unstable

Stable

Unstable & stable

None

ANS: (a)
64. Local skin friction coefficient in turbulent thermal boundary layer is

Firstly C_{fx} = 0.5760 (R_{e})^{–1/5}

Secondly C_{fx} = 0.0576(R_{e})^{–1/5}

Thirdly C_{fx} = 0.0675(R_{e})^{–1/5}

None
ANS: (b)
65. Name the fluids for which Prandtl number is less than one


Water

Liquid metals

Oils

None
ANS: (b )


66. Name the fluids for which Prandtl number is greater than one

Air

Liquid metals

Oils

None
ANS: (c )
67. Name the fluids for which Prandtl number is equal to one

Water

Gases

Liquid metals

None
ANS: (b)
https://mesubjects.net/wpadmin/post.php?post=14112&action=edit MCQ HYDRODYNAMIC LAYER
https://www.mesubjects.net/wpadmin/post.php?post=630&action=edit CONVECTION HEAT TRANSFER
https://mesubjects.net/wpadmin/post.php?post=14077&action=edit MCQ CONVECTION

