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.

 

1. Hydrodynamic layer is a thin layer of fluid

   1. Close to the outside solid surface

   2. Close to the inside solid surface

   3. Both close to inside & outside solid surface

   4. None

ANS: (a)

2. In a hydrodynamic boundary layer

   1. Tensile stresses influence the velocity distribution

   2. Compressive stresses influence the velocity distribution

   3. Shear stresses influence the velocity distribution

   4. None

ANS: (c )

3. Velocity varies in the hydrodynamic layer from

   1. Firstly    Zero to 0.9 times of free velocity

   2. Secondly    Zero to 2 times the free velocity

   3. Thirdly    Zero to 0.99 times the free velocity

   4. None

ANS: (C )

4. Hydrodynamic boundary layer is invented by

   1. Newton

   2. Nusselt

   3. Prandtl

   4. None

ANS: (c )

5. Leading edge in a boundary layer is

   1. Firstly    Edge facing the incoming fluid

   2. Secondly    Edge facing the outgoing fluid

   3. Thirdly    Edge facing incoming & outgoing fluid

   4. None

ANS: (a)

6. Trailing edge in a boundary layer is

   1. Firstly    Edge facing the incoming fluid

   2. Secondly    Edge facing the outgoing fluid

               © Thirdly    Edge facing incoming & outgoing fluid

               (d)None

ANS: (b)

7. Velocity of the fluid at the solid surface is

   1. > 0

   2. < 0

   3. = 0

   4. None

ANS: (C )

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

   1. Increasing

   2. Decreasing

   3. Increasing & decreasing

   4. None

ANS: (a)

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

   1. Solid surface

   2. Free liquid surface

   3. In-between solid and free liquid surface

   4. None

ANS: (b)

10. The thickness of boundary layer is

    1. Constant

    2. Variable

    3. Constant & variable

    4. None

ANS: (b)

11. Thickness of boundary layer is

    1. Zero at leading edge and maximum at trailing edge

    2. Zero at trailing edge and maximum at leading edge

    3. Maximum at the leading edge

    4. None

ANS: (a)

12. Fluid velocity outside hydrodynamic layer is

    1. Variable

    2. Constant

    3. Variable & constant

    4. None

ANS: (b)

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

    1. More

    2. Less

    3. Can’t say

    4. None

ANS: (b)

14. In the flow direction, boundary layer is

(a) Laminar first & turbulent later

(b) Turbulent first & laminar later

© Transition layer first

(d) None

ANS: (a)

15. In the transition zone, the flow is

    1. Unstable

    2. Stable

    3. Unstable & stable

    4. None

ANS: (a)

16. The flow pattern in boundary is judged by

    1. Prandtl number

    2. Reynolds Number

    3. Prandtl & Reynolds numbers

    4. None

ANS: (b)

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

    1. 3 lacs

    2. 7 lacs

    3. 5 lacs

    4. None

ANS: (c )

18. Reynolds number at the end of laminar flow is

    1. Laminar

    2. Critical

    3. Laminar & critical

    4. None

ANS: (b)

19. The value of Reynolds number where turbulent flow starts is

    1. 3 lacs

    2. 5 lacs

    3. 7 lacs

    4. None

ANS: (c )

20. Shear stress is maximum at the

    1. Solid surface

    2. Free liquid surface

    3. Solid & free liquid surface

    4. None

ANS: (a)

21. Velocity variation in a hydrodynamic layer is

    1. Curvilinear

    2. Parabolic

    3. Linear

    4. None

ANS: (b)

22. The equation for entrance length L_e in a pipe laminar flow is

    1. Firstly    L_e/D= 0.08R_e

    2. Secondly    L_e/D= 0.04R_e

    3. Thirdly    L_e/D= 0.06R_e

    4. None

ANS: (c )

23. The equation for entrance length L_e in a pipe turbulent  flow is

    4. Firstly    L_e/D= 4.4 R_e^1/4

    5. Secondly     L_e/D= 0.04R_e^1/3

    6. Thirdly    L_e/D= 0.06R_e^1/6

    7. None

ANS: (c )

24. Value of Reynolds number in a pipe laminar flow is

    1.  < 500
    2.  < 2100
    3.  > 4000
    4. None

ANS: (b)

25. Value of Reynolds number in a pipe turbulent flow is

    1. > 500
    2. < 2100
    3. > 4000
    4. None

ANS: (c)

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

    1. Less

    2. Greater

    3. Equal

    4. None

ANS: (b)

27. Shear stress equation is

    1. τ=µ∂u/∂y

    2. τ =µ²∂u/∂y

    3. τ =5 ∂u/∂y

    4. None

ANS: (a)

28. Momentum equation for hydrodynamic layer is

    1. Firstly    u ∂u/∂x + v ∂u/∂y =ν ∂²u/∂x²

    2. Secondly    u ∂u/∂x + v ∂u/∂y =ν ∂²u/∂y²

    3. Thirdly    u ∂u/∂x + v ∂u/∂y =ν ∂²u/∂x ∂y

    4. None

ANS: ( b)

29. Based on Blasius equation, hydrodynamic boundary layer thickness

    at distance ‘x’ from the leading edge is

    4. Firstly    δ/x = 4.64/Re_x⁵

    5. Secondly    δ/x = 5.64/Re_x⁵

    6. Thirdly    δ/x = 5.00/Re_x⁵

    7. None

ANS: (c )

30. Based on Von-Karman Integral Momentum equation, hydrodynamic

    boundary layer thickness at distance ‘x’ from the leading edge is

    4. Firstly    δ/x = 4.64/Re_x⁵

    5. Secondly    δ/x = 5.64/Re_x⁵

    6. Thirdly    δ/x = 5.00/Re_x⁵

    7. None

ANS: (a )

31. Local friction coefficient based on Blasius equation

    1. Firstly    C_fx = 0.699/Re_x⁵

    2. Secondly    C_fx = 0.664/Re_x⁵

    3. Thirdly    C_fx = 0.646/Re_x⁵

    4. None

ANS: (b)

32. Local friction coefficient based on Von-Karman equation

    1. Firstly    C_fx = 0.699/Re_x⁵

    2. Secondly    C_fx = 0.664/Re_x⁵

    3. Thirdly    C_fx = 0.646/Re_x⁵

    4. None

ANS: (c)

33. Average friction coefficient based on Blasius equation

    1. Firstly    C_fx = 1.118/Re_x⁵

    2. Secondly    C_fx = 1.228/Re_x⁵

    3. Thirdly    C_fx = 1.328/Re_x⁵

    4. None

ANS: (c)

34. Average friction coefficient based on Von-Karman equation

    1. Firstly    C_fx = 1.192/Re_x⁵

    2. Secondly    C_fx = 1.292/Re_x⁵

    3. Thirdly    C_fx = 1.492/Re_x⁵

    4. None

ANS: (b)

35. Velocity distribution in turbulent flow hydrodynamic boundary layer is

1. Firstly    u/U = (y/δ)^1/5

2. Secondly    u/U = (y/δ) ^1/9

3. Thirdly    u/U = (y/δ)^1/7

4. None

ANS: (c )

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

1. Firstly    δ/x = 0.317(R_e)^1/5

2. Secondly    δ/x = 0.337(R_e)^–1/5

3. Thirdly    δ/x = 0.371(R_e)^–1/5

4. None

ANS: (c )

 

     37. Thermal boundary layer is a thin space of temperature variation

1. Firstly Close to outside solid surface

2. Close to inside solid surface

3. Both close to inside & outside solid surface

4. None

ANS: (a)

     38. In a thermal boundary layer

1. 1. Tensile stresses influence the velocity distribution

   2. Compressive stresses influence the velocity distribution

   3. Shear stresses influence the velocity distribution

   4. None

ANS: (d)

     39. Temperature varies in the thermal boundary layer from

1. Firstly Zero to 0.9 times of free flow layer temperature

2. 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

1. Newton

2. André Lévêque

3. Prandtl

4. None

ANS: (b)

     41. Leading edge in a thermal boundary layer is

1. 1. Firstly Edge facing the incoming fluid

   2. Secondly Edge facing the outgoing fluid

   3. Thirdly Edge facing incoming & outgoing fluid

   4. None

ANS: (a)

      42. Trailing edge in a thermal boundary layer is

1. 1. Firstly  Edge facing the incoming fluid

   2. 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

1. > 0

2. < 0

3. =0

4. None

ANS: (a)

      44. Within the thermal boundary layer, the temperature variation ∂t/∂y from solid surface to free fluid surface is

1. 1. Increasing

   2. Decreasing

   3. Increasing & decreasing

   4. None

ANS: (b)

     45. Temperature of fluid ‘t’ is equal to t _solid at the

1. 1. Solid surface

   2. Free liquid surface

   3. In-between solid and free liquid surface

   4. None

ANS: (a)

      46. The thickness of thermal boundary layer is

1. 1. Constant

   2. Variable

   3. Constant & variable

   4. None

ANS: (b)

     47. Thickness of thermal boundary layer is

1. 1.  Firstly  Zero at leading edge and maximum at trailing edge

   2. 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

1. 1. Variable

   2. Constant

   3. Variable & constant

   4. None

ANS: (b)

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

1. 1. More

   2. Less

   3. Can’t say

   4. 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

• 1. Prandtl number

  2. Reynolds Number

  3. Prandtl & Reynolds numbers

  4. None

ANS: (a)

       52. Thermal boundary layer thickness is greater than the thickness of hydrodynamic boundary layer thickness when

1. 1. Firstly    Pr > 1

   2. Secondly    Pr < 1

   3. Thirdly    Pr = 1

   4. None

ANS: (b)

     53. Thermal boundary layer thickness is less than the thickness of hydrodynamic boundary layer thickness when

1. Firstly    Pr > 1

2. Secondly    Pr < 1

3. Thirdly    Pr = 1

4. None

ANS: (a)

      54. Thermal boundary layer thickness is equal than the thickness of hydrodynamic boundary layer thickness when

1. Firstly    Pr > 1

2. Secondly    Pr < 1

3. Thirdly    Pr = 1

4. None

ANS: (c )

      55. Temperature variation in the thermal boundary layer is

1. Linear

2. Parabolic

3. Curvilinear

4. None

ANS: (b)

      56. Energy equation for thermal boundary layer is

1. Firstly    u ∂t/∂x + v ∂t/∂y =ν ∂²t/∂y²

2. Secondly    u ∂t/∂x + v ∂t/∂y =β ∂²t/∂y²

3. Thirdly    u ∂t/∂x + v ∂t/∂y =α ∂²t/∂y²

4. None

ANS: ©

     57. The relation between δ_t and δ is

1. Firstly    δ_t = δ Pr ^1/3

2. Secondly    δ_t = δ Pr ^–1/3

3. Thirdly    δ_t = δ Pr ^2/3

4. None

ANS: (b)

     58. Local heat transfer coefficient in the thermal boundary layer is

1. Firstly    h_x = 0.664 (k/x) (R_e)⁵ (Pr)^0.33

2. Secondly    h_x = 0.996 (k/x) (R_e)⁵ (Pr)^0.33

3. Thirdly    h_x = 0.332 (k/x) (R_e)⁵ (Pr)^0.33

4. None

ANS: (c )

     59. Average heat transfer coefficient in the thermal boundary layer is

1. 1. Firstly    h_x = 0.664 (k/x) (R_e)⁵ (Pr)^0.33

   2. Secondly    h_x = 0.996 (k/x) (R_e)⁵ (Pr)^0.33

   3. Thirdly    h_x = 0.332 (k/x) (R_e)⁵ (Pr)^0.33

   4. None

ANS: (a )

     60. Ratio of Average to local heat transfer coefficient is

1. Three

2. Two

3. One

4. None

ANS: (b)

     61. Local Nusselt number in thermal boundary layer is

1. 1. Firstly    Nu_x = 0.664 (R_e)⁵ (Pr)^0.33

   2. Secondly    Nu_x = 0.996 (R_e)⁵ (Pr)^0.33

   3. Thirdly    Nu_x = 0.332 (R_e)⁵ (Pr)^0.33

   4. 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

1. ANS: (a )
   

        63. In the transition zone, the temperature variation is

   1. Unstable

   2. Stable

   3. Unstable & stable

   4. None

             ANS: (a)

64. Local skin friction coefficient in turbulent thermal boundary layer is

1. Firstly    C_fx = 0.5760 (R_e)^–1/5

2. Secondly    C_fx = 0.0576(R_e)^–1/5

3. Thirdly    C_fx = 0.0675(R_e)^–1/5

4. None

ANS: (b)

     65. Name the fluids for which Prandtl number is less than one

1. 1. Water

   2. Liquid metals

   3. Oils

   4. None

      ANS: (b )

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

   1. Air

   2. Liquid metals

   3. Oils

   4. None

      ANS: (c )

      67. Name the fluids for which Prandtl number is equal to one

      1. Water

      2. Gases

      3. Liquid metals

      4. None

      ANS: (b) 

       

      https://mesubjects.net/wp-admin/post.php?post=14112&action=edit                MCQ HYDRODYNAMIC LAYER

      https://www.mesubjects.net/wp-admin/post.php?post=630&action=edit               CONVECTION HEAT TRANSFER

      https://mesubjects.net/wp-admin/post.php?post=14077&action=edit                    MCQ CONVECTION