Mechanical Engineering - Heat Transfer, Refrigeration and Air Conditioning - Discussion

5. 

Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be

[A]. one
[B]. two
[C]. three
[D]. four

Answer: Option C

Explanation:

No answer description available for this question.

Gaurav said: (Nov 6, 2014)  
Q with shield/Q without shield = 1/n+1.

N = no.of parallel shields.

Arun said: (Jan 11, 2015)  
Little confusion evaporator observe sensible heat or latent heat.

Bharat said: (Mar 8, 2015)  
Emissivity should be given 0.7 to get specified answer and to use Gaurav's formula.

Amal said: (Jan 2, 2016)  
0.25n+0.25 = 1.
0.25n = 0.75.
n = 3.

Heisenberg said: (Aug 14, 2016)  
Thanks a lot @Amal! Your explanation useful to me.

Bavan Bharai said: (Nov 29, 2016)  
Thnks for all your explanation guidance. It is very useful

Emmanuvelbibin said: (Jan 2, 2017)  
Yes, you are correct @Bharat.

Pradeep said: (Oct 8, 2017)  
Emissivity should be same for shield also. Then the given answer is correct.

Dushmant said: (Jan 10, 2019)  
You are Correct @Pradeep.

It is 3 when all emissivity will be same.

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