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Past Year Questions: Free And Forced Convection


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13 Questions MCQ Test | Past Year Questions: Free And Forced Convection

Past Year Questions: Free And Forced Convection for Mechanical Engineering 2022 is part of Mechanical Engineering preparation. The Past Year Questions: Free And Forced Convection questions and answers have been prepared according to the Mechanical Engineering exam syllabus.The Past Year Questions: Free And Forced Convection MCQs are made for Mechanical Engineering 2022 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Past Year Questions: Free And Forced Convection below.
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Past Year Questions: Free And Forced Convection - Question 1

Match List-I with List-ll and select the correct answer using the code given below the lists:
List-I
A. Grashof number
B. Schmidt number
C. Weber number
D. Fourier number

List-II
1. Mass diffusion
2. Transient heat conduction
3. Free convection
4. Forced convection
5. Surface tension
6. Radiation

[1996]

Past Year Questions: Free And Forced Convection - Question 2

The ratio of momentum diffusivity (v) to thermal diffusivity (α), is called

[2015]

Detailed Solution for Past Year Questions: Free And Forced Convection - Question 2

Past Year Questions: Free And Forced Convection - Question 3

Grashof number signifies the ratio of

[2016]

Detailed Solution for Past Year Questions: Free And Forced Convection - Question 3

Grash of number = inertia force x 

Past Year Questions: Free And Forced Convection - Question 4

In pool boiling the highest HTC occurs in

[1990]

Past Year Questions: Free And Forced Convection - Question 5

Heat transfer coefficients for free convection in gases, forced convection in gases and vapours, and for boiling water lie, respectively, in the range of

[1998]

Past Year Questions: Free And Forced Convection - Question 6

For the three-dimensional object shown in the figure below, five faces are insulated. The sixth face (PQRS), which is not insulated, interacts thermally with the ambient, with a convective heat transfer coefficient of 10W/m2K. The ambient temperature is 30°C. Heat is uniformly generated inside the object at the rate of 100 W/m3. Assuming the face PQRS to be at uniform temperature, its steady state temperature is

[2000]

Detailed Solution for Past Year Questions: Free And Forced Convection - Question 6

Given data;


Volume,
V = 2×1×2=4 m3
Heat generated,
Q = qG × V = 100 × 4 = 400 W
Convection heat transfer from face PQRS,

Past Year Questions: Free And Forced Convection - Question 7

Water (specifie heat, c = 4.18 kJ/kgK) enters a pipe at a rate 0.01 kg/s and a temperature of 20°C. The pipe, of diameter 50 mm and length 3 m, is subjected to a wall heat flux q"w in W/m2.

If q"w = 2500x, where x is in m and in the direction of flow (x = 0 at the inlet), the bulk means temperature of the water leaving the pipe in °C is

[2013]

Detailed Solution for Past Year Questions: Free And Forced Convection - Question 7

At the inlet of pipe
x = O
q "wi = 2500 x 0 = 0
At the exit of pipe,
x = 1

Average heat transfer,

Net heat transfer

By solving above equation, we get
To = 62° C

Past Year Questions: Free And Forced Convection - Question 8

Water (specifie heat, c = 4.18 kJ/kgK) enters a pipe at a rate 0.01 kg/s and a temperature of 20°C. The pipe, of diameter 50 mm and length 3 m, is subjected to a wall heat flux q"w in W/m2.

If q"w = 5000 and the convection heat transfer coefficient at the pipe outlet is 1000 W/m2K, the temperature in °C at the inner surface of the pipe at the outlet is

[2013]

Detailed Solution for Past Year Questions: Free And Forced Convection - Question 8


Heat transfer through pipe wall,

Q = mCP(T0–Ti), amount of heat gained by the water
2355 = 0.01 × 4180 (T0 – 20)
T0 = 76.33°C

5000 = 1000 (Tso – 76.33)
Tso = 81°C

Past Year Questions: Free And Forced Convection - Question 9

For laminar forced convection over a flat plate, if the free stream velocity increases by a factor of 2, the average heat transfer coefficient​

[2014]

Detailed Solution for Past Year Questions: Free And Forced Convection - Question 9

Forlaminar flow, Nu = 0.664 (Re)0.5 (Pr)0.33

So when free stream velocity increases by a factor of 2, then the average heat transfer coefficient rises by a factor of √2.

Past Year Questions: Free And Forced Convection - Question 10

The properties of mercury at 300 K are: Density = 13529 kg/m3, cp = 0.1393 kJ/kgK, dynamic viscosity = 0.1523 × 10–2 Ns/m2 and thermal conductivity = 8.540 W/mK. The Prandtl number of the mercury at 300 K is

[2002]

Detailed Solution for Past Year Questions: Free And Forced Convection - Question 10

Prandtl number = 

Past Year Questions: Free And Forced Convection - Question 11

In the laminar flow of air (Pr = 0.7) over a heated plate, if δ and δT denote, respectively, the hydrodynamic and thermal boundary layer thicknesses, then

[2015]

Detailed Solution for Past Year Questions: Free And Forced Convection - Question 11

When

Past Year Questions: Free And Forced Convection - Question 12

For a hydrodynamically and thermally fully developed laminar flow through a circular pipe of constant cross-section. The Nusselt number at constant wall heat flux (Nuq) and that at constant wall temperature (NuT) are related as

[2019]

Detailed Solution for Past Year Questions: Free And Forced Convection - Question 12

(Nu)q for constant wall heat flux and (Nu)T at constant wall temperature for a hydrodynamically and thermally fully developed laminar flow through a circular pipe of constant cross-section is 4.36 and 3.66 respectively.

Past Year Questions: Free And Forced Convection - Question 13

The wall of a constant diameter pipe of length 1 m is heated uniformly with flux q” by wrapping a heater coil around it. The flow at the inlet to the pipe is hydrodynamically fully developed. The fluid is incompressible and the flow is assumed to be laminar and steady all through the pipe.
The bulk temperature of the fluid is equal to 0°C at the in let and 50°C at the exit. The wal l temperatures are measured at three locations, P, Q an d R as shown in the figure. The flow thermally develops after some distance from the inlet. The following measurements are made :

Among the locations P, Q and R, the flow is thermally at :

[2019]

Detailed Solution for Past Year Questions: Free And Forced Convection - Question 13

In case of uniform heat flux, bulk mean temperature varies linearly. The difference between bulk mean temperature and wall temperature is constant in thermally developed region so bulk tempeature,

Here,

So, Q and R in thermally developed region.

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