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Mechanical Engineering Exam  >  Mechanical Engineering Tests  >  Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Mechanical Engineering MCQ

Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Mechanical Engineering MCQ


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15 Questions MCQ Test - Past Year Questions: Heat Transfer In Flow Over Plates And Pipes

Past Year Questions: Heat Transfer In Flow Over Plates And Pipes for Mechanical Engineering 2024 is part of Mechanical Engineering preparation. The Past Year Questions: Heat Transfer In Flow Over Plates And Pipes questions and answers have been prepared according to the Mechanical Engineering exam syllabus.The Past Year Questions: Heat Transfer In Flow Over Plates And Pipes MCQs are made for Mechanical Engineering 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Past Year Questions: Heat Transfer In Flow Over Plates And Pipes below.
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Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 1
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For the fluid flowing over a flat plate with Prandtl number greater than unity, the thermal boundary layer for laminar forced convection.

[1988]

Detailed Solution for Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 1

Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 2
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A fluid flowing over a flat plate has the following properties: dynamic viscosity = 25 × 10–6 kg/ ms, specific heat = 2.0 kJ/kgK, thermal conductivity 0.05 W/mK. The hydrodynamic boundary layer thickness is measured to be 0.5 mm. The thickness of the thermal boundary layer would be

[1992]

Detailed Solution for Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 2


Now, δ = 0.5 mm
∴ δ = δt = 0.5mm

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Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 3
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Water (Prandtl number = 6) flows over a flat plate which is heated over the entire length. Which one of the following relationship between the hydrodynamic boundary layer thickness (δ) and thermal boundary layer thickness (δt) is true

[2001]

Detailed Solution for Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 3


Here, Pr = 6 > 1
or 
∴ δ > δt

Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 4
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Consider a laminar boundary layer over a heated flat plate. The free stream velocity is U∝. At some distance x from the leading edge the velocity boundary layer thickness is δv and the thermal boundary layer thickness is δT. If the Prandtl number is greater than 1, then

[2003]
Detailed Solution for Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 4

Prandtl number

From question, since prandtl number > 1
∴ Velocity boundry thickness (δv) > thermal boundary thickness (δt)

Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 5
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An un-insulated air conditioning duct of rectangular cross section 1 m × 0.5 m, carrying air at 20°C with a velocity of 10 m/s, is exposed to an ambient of 30°C. Neglect the effect of duct construction material. For air in the range of 20 – 30°C, data is as follows: thermal conductivity = 0.025 W/mK; viscosity = 18 μPa.s; Prandtl number = 0.73; density =1.2 kg/m3. For laminar flow Nusselt number is 3.4 for constant wall temperature conditions and , for turbulent flow, Nu = 0.023 Re0.8Pr0.33.The Reynolds number for the flow is

[2005]
Detailed Solution for Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 5


Reynolds number,

Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 6
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An un-insulated air conditioning duct of rectangular cross section 1 m × 0.5 m, carrying air at 20°C with a velocity of 10 m/s, is exposed to an ambient of 30°C. Neglect the effect of duct construction material. For air in the range of 20 – 30°C, data is as follows: thermal conductivity = 0.025 W/mK; viscosity = 18 μPa.s; Prandtl number = 0.73; density =1.2 kg/m3. For laminar flow Nusselt number is 3.4 for constant wall temperature conditions and , for turbulent flow, Nu = 0.023 Re0.8Pr0.33.

The heat transfer per meter length of the duct, in watts, is

[2005]
Detailed Solution for Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 6

As Re > 4000, the flow is turbulent

Surface area of duct
A = 2 × al + 2 × bl
where, l = length of duct
∴ A = 3l
Heat transfer rate, Q = h A(T0 – T)
Q = 25.60 × 3l × (30 – 20)
Q/I = 769W

Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 7
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The temperature distribution with in the thermal boundary layer over a heated isothermal flat plate is given by  where TW and T∝ are the temperatures of plate and free stream respectively, and y is the normal distance measured from the plate. The local Nusselt number based on the thermal boundary layer thickness δt is given by

[2007]
Detailed Solution for Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 7

Only (b) satisfies the conditions

Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 8
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For flow of fluid over a heated plate , the following fluid properties are known: viscosity = 0.001 Pa.s; specific heat at constant pressure = 1 kJ/kgK; thermal conductivity = 1 W/mK.
The hydrodynamic boundary layer thickness at a specified location on the plate is 1 mm. The thermal boundary layer thickness at the same location is

[2008]

 
Detailed Solution for Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 8

Given:

 (Fluid thermal conductivity)
Hydrodynamic boundary layer thickness, δ = 1 mm

Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 9
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A pipe of 25 mm outer diameter carries steam. The heat transfer coefficient between the cylinder and surroundings is 5 W/m2K. It is proposed to reduce the heat loss from the pipe by adding insulation having a thermal conductivity of 0.05 W/mK. Which one of the following statements is TRUE?

[2011]
Detailed Solution for Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 9

Critical radius of insulation = (k/h)
 = 10mm
(router) > rcritical
Thus, adding insulation shall decrease H.T. Rate.

Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 10
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The ratios of the laminar hydrodynamic boundary layer thickness to thermal boundary layer thickness of flows of two fluids P and Q on a flat plate are 1/2 and 2 respectively. The Reynolds number based on the plate length for both the flows is 104. The Prandtl and Nusselt numbers for P are 1/8 and 35 respectively. The Prandlt and Nusselt numbers for Q are respectively

[2011]
Detailed Solution for Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 10


For fluid Q : 
⇒ Pr = 8
For fluid P :  Laminar flow over flat plate

Similarly for fluid Q:

Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 11
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Consider a two-dimensional laminar flow over a long cylinder as shown in the figure below.

The free stream velocity is U∝ and the freestream temperature T∝ is lower than the cylinder surface temperature T∝. The local heat transfer coefficient is minimum at point

[2014]
Detailed Solution for Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 11

For laminar flow, the heat transfer coefficient is minimum where the boundary layer thickness is maximum and vice versa. For turbulentregion boundary layer thickness is maximum at 3 but for laminar boundary layer thickness is maximum at 2 so minimum heat transfer coefficient.

Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 12
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The non-dimensional fluid temperature profile near the surface of a convectively cooled flat plate is given by   where y is measured perpendicular to the plate, L is the plate length, and a, b and c are arbitrary constants. TW and T∝ are wall and ambient temperatures, respectively. If the thermal conductivity of the fluid is k and the wall heat flux is q', the Nusselt number Nu  is equal to

[2014]
Detailed Solution for Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 12


at y = 0

∴ Nu = b.

Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 13
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For flow of viscous fluid over a flat plate, if the fluid temperature is the same as the plate temperature, the thermal boundary layer is

[2015]
Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 14
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The Blausius equation related to boundary layer theory is a

[2015]
Detailed Solution for Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 14

Blausius equation :

This order non-linear D.E.

Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 15
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For flow through a pipe of radius R, the velocity and temperature distribution are as follows:  where C1 and C2 are constants. The bulk temperature is given by  with Um being the mean velocity of flow. The value of Tm is

[2015]
Detailed Solution for Past Year Questions: Heat Transfer In Flow Over Plates And Pipes - Question 15


Since u(r, x) is constant, um = C1
∴ tm = 0.6C2

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