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Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2


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25 Questions MCQ Test GATE Mechanical (ME) 2023 Mock Test Series | Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2

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Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 1

Which one of the following statements is correct?  
The curve for unsteady state cooling or heating of bodies 

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 1

Ans. (b)

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 2

Heisler charts are used to determine transient heat flow rate and temperature distribution when: 

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 2

Ans. (d)

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 3

The properties of mercury at 300 K are: density = 13529 kg/m3, specific heat at constant pressure = 0.1393 kJ/kg-K, dynamic viscosity = 0.1523 ×10-2 N.s/m2 and thermal conductivity = 8.540 W/mK. The Prandtl numberof the mercury at 300 K is:  

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 3

Ans. (a)



= 0.0248

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 4

Free convection flow depends on all of the following EXCEPT  [ 

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 4

Ans. (d)

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 5

A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficient of h1, h2 and h3 respectively. The average heat transfer coefficient for the cube is: 

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 5

Ans. (d)



Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 6

(a) (b)
(c)  (d)

Match the velocity profiles labelled A, B, C and D with the following situations:  
1. Natural convection
2. Condensation
3. Forced convection
4. Bulk viscosity ≠ wall viscosity
5. Flow in pipe entrance

Select the correct answer using the codes given below:
Codes: A B C D                A B C D
        (a) 3 2 1 5             (b) 1 4 2 3
        (c) 3 2 1 4             (d) 2 1 5 3

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 6

Ans. (a) It provides right matching

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 7

Match List-I (Dimensionless quantity) with List-II (Application) andselect the correct answer using the codes given below the lists:

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 7

Ans. (b) The correct matching for various dimensionless quantities is provided by
code (b)

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 8

When there is a flow of fluid over a flat plate of length 'L', the average heat transfer coefficient is given by (Nux = Local Nusselt number; other symbols have the usual meaning) 

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 8

Ans. (c)

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 9

For steady, uniform flow through pipes with constant heat flux supplied to the wall, what is the value of Nusselt number?  

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 9

Ans. (a)

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 10

For steady, uniform flow through pipes with constant heat fluxsupplied to the wall, what is the value of Nusselt number? 

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 10

Ans. (a)

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 11

A fluid of thermal conductivity 1.0 W/m-K flows in fully developed flow with Reynolds number of 1500 through a pipe of diameter 10 cm. The heat transfer coefficient for uniform heat flux and uniform wall
temperature boundary conditions are, respectively.

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 11

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 12

A 320 cm high vertical pipe at 150°C wall temperature is in a room withstill air at 10°C. This pipe supplies heat at the rate of 8 kW into theroom air by natural convection. Assuming laminar flow, the height ofthe pipe needed to supply 1 kW only is 

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 12

Ans. (b) For vertical pipe characteristic dimension is the length of the pipe.
For laminar flow Nu = (Gr.Pr)1/4

h become independent of length

L2 = 40cm

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 13

The average Nusselt number in laminar natural convection from avertical wall at 180°C with still air at 20°C is found to be 48. If the wall temperature becomes 30°C, all other parameters remaining same, the average Nusselt number will be: 

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 13

Correct Answer :- c

Explanation : Nu2/Nu1 = Δt2/Δt1

= 60/160

Nu2 = 24

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 14

Nusselt number for a pipe flow heat transfer coefficient is given by the equation NuD = 4.36. Which one of the following combinations ofconditions does exactly apply for use of this equation? 

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 14

Ans. (d)

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 15

Nusselt number for fully developed turbulent flow in a pipe is given by  The values of a and b are: 

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 15

Ans. (c) Fully developed turbulent flow inside tubes (internal diameter D):
Dittus-Boelter Equation:
Nusselt number, NuD = 0.023

where, n = 0.4 for heati=g (Tw > Tf) and n = 0.3 for cooling (Tw < Tf)

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 16

Which one of the following numbers represents the ratio of kinematic viscosity to the thermal diffusivity? 

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 16

Ans. (b)

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 17

In free convection heat transfer transition from laminar to turbulentflow is governed by the critical value of the  

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 17

Ans. (d)

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 18

Which one of the following non-dimensional numbers is used fortransition from laminar to turbulent flow in free convection? 

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 18

Ans. (d) Laminar to Turbulent Transition: Just as for forced convection, a boundary layer will form for free convection.
The insulating film will be relatively thin toward the leading edge of the surface
resulting in a relatively high convection coefficient. At a Rayleigh number of about 10the flow over a flat plate will transition to a turbulent pattern. The increased
turbulence inside the boundary layer will enhance heat transfer leading to relative high convection coefficients, much like forced convection.


Ra < 109Laminar flow [Vertical flat plate]
Ra > 109 Turbulent flow [Vertical flat plate]

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 19

In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the 

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 19

Ans. (d)

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 20

Match List-I (Type of heat transfer) with List-II (Governing dimensionless parameter) and select the correct answer:  
List-I                                                              List-II
A. Forced convection                                1. Reynolds, Grashof and Prandtl number
B. Natural convection                                2. Reynolds and Prandtl number
C. Combined free and forced convection  3. Fourier modulus and Biot number
D. Unsteady conduction with                     4. Prandtl number and Grash of convection at surface number
Codes: A B C D             A B C D
       (a) 2 1 4 3         (b) 3 4 1 2
       (c) 2 4 1 3         (d) 3 1 4 2

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 20

Ans. (c)

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 21

Match List-I (Process) with List-II (Predominant parameter associated with the process) and select the correct answer using the codes given below the lists:  
List-I                                                     List-II
A. Mass transfer                          1. Reynolds Number
B. Forced convection                   2. Sherwood Number
C. Free convection                      3. Mach Number
D. Transient conduction              4. Biot Number
                                                    5. Grashoff Number
Codes: A B C D                            A B C D
       (a) 5 1 2 3                         (b) 2 1 5 4
       (c) 4 2 1 3                         (d) 2 3 5 4

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 21

Ans. (b)

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 22

Data are given below. Solve the problems and choose correct answers.
Heat is being transferred by convection from water at 48°C to a glass plate whose surface that is exposed to the water is at 40°C. The thermal conductivity of water is 0.6 W/mK and the thermal conductivity of
glass is 1.2 W/mK. The spatial Water gradient of temperature in the water at the water-glass interface is dT/dy =1 × 104 K/m.

Q. The value of the temperature gradient in the glass at the water-glass interface in k/m is:

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 22

Ans. (c) Kw = 0.6W/mK; KG =1.2 W/mK 

 
The spatial gradient of temperature in water at the water-glass interface

At Water glass interface,


or 

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 23

Data are given below. Solve the problems and choose correct answers.
Heat is being transferred by convection from water at 48°C to a glass plate whose surface that is exposed to the water is at 40°C. The thermal conductivity of water is 0.6 W/mK and the thermal conductivity of
glass is 1.2 W/mK. The spatial Water gradient of temperature in the water at the water-glass interface is dT/dy =1 × 104 K/m.

Q. The heat transfer coefficient h in W/m2K is:

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 23

Ans. (d) Heat transfer per unit area q = h ( Tf – Ti)

or 

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 24

Match List-I (Phenomenon) with List-II (Associated dimensionless parameter) and select the correct answer using the code given below the lists: 


Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 24

Ans. (c)

Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 25

For natural convective flow over a vertical flat plate as shown in the given figure, the governing differential
equation for momentum is:

If equation is non-dimensionalized by

then the term gβ (T -  T) , is equal to:

Detailed Solution for Test: One Dimensional Unsteady Conduction & Free & Forced Convection - 2 - Question 25

Ans. (d)

gives dimensionless number which signifies whether flow is forced or free connection.
 Forced convection
 Natural convection

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