An outer wall of a furnace is it at Tw kelvins and it faces an environment at Te. The wall’s-average convective connective heat transfer coefficient h is 4 W/m2 K. For radioactive heat transfer the wall’s emissivity e equals its absorptive α and equals 0.8. The ratio of net heat loss by radiation to heat loss by convection from the wall is closest to

1.  

2.  

3.  

4.  

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4
Correct Answer :


Explanation :
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A block of metal is heated well above the room temperature and then left to cool in the room. Which of the graphs shown in figure below correctly represents the rate of cooling

1.  

2.  

3.  

4.  

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4
Correct Answer :


Explanation :
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The ratio of energy transferred by convection to that by conduction is called

1.  Station number

2.  Nusselt number

3.  Biot number

4.  Preclet number

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4
Correct Answer :

Biot number


Explanation :
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Free convection flow depends on all of the following EXCEPT

1.  Density

2.  Coefficient of viscosity

3.  Gravitational force

4.  Velocity

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4
Correct Answer :

Density


Explanation :
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The ratio surface convection resistance/internal conduction resistance is known as

1.  Grashoff number

2.  Biot number

3.  Stanton number

4.  Prandtl number

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4
Correct Answer :

Biot number


Explanation :
No Explanation available for this question

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

1.  Reynold’s number

2.  Grashoff’s number

3.  Reynold’s number, Grashoff number

4.  Prandtl number, Grashoff number

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4
Correct Answer :

Prandtl number, Grashoff number


Explanation :
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Match List-I wish List-II and select the correct answer using the codes given below the lists List-I (Dimensionless quantity) (A) Stanton number (B) Grashoff number (C) Peclet number (D) Schmidt number List-II (Application) 1. Natural convection for ideal gases 2. Mass transfer 3. Forced convection 4. Forced convection for small Prandlt number

1.  A-2,B-4,C-3,D-1

2.  A-3,B-1,C-4,D-2

3.  A-3,B-4,C-1,D-2

4.  A-2,B-1,C-3,D-4

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4
Correct Answer :

A-3,B-1,C-4,D-2


Explanation :
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A designer chooses the value of fluid flow rates and specific heats in such a manner that the heat capacities of the two fluids are equal. A hot fluid enters the counter flow heat exchanger at 1000 C and leaves at 600 C. The cold fluid enters the heat exchanger at 400 C. The mean temperature difference between the two fluids is

1.  (100 +60 + 40)/30 C

2.  600 C

3.  450 C

4.  200 C

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4
Correct Answer :

200 C


Explanation :
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A thin flat plate 2 m * 2 m is hanging freely in air. The temperature of the surroundings is 250 C. solar radiation is falling on one side of three plates at the rate of 500 W/m2. The temperature of the plates will remain constant at 300 C, if the convective heat transfer coefficient (in W/m2 0C) is

1.  25

2.  50

3.  100

4.  200

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4
Correct Answer :

25


Explanation :
No Explanation available for this question

Given the following data: Inside heat transfer coefficient = 25 W/m2 0C Outside heat transfer coefficient = 25 W/m2 0C Thermal conductivity of bricks (15 cm thick) = 0.15 W/mK The overall het transfer coefficient (in W/m2 K) will be closer to the

1.  Inverse of heat transfer coefficient

2.  Heat transfer coefficient

3.  Thermal conductivity of bricks

4.  Heat transfer coefficient based on the thermal conductivity of the bricks alone

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4
Correct Answer :

Heat transfer coefficient based on the thermal conductivity of the bricks alone


Explanation :
No Explanation available for this question
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