Question

Two parallel thin sheets are placed 2 cm apart. The sheets are squares of sides 5 m. Temperature of both sheets are constant with one at ?! = 15 °? and the other at ?! = -120 °?.

The emissivity of surfaces can be assumed to be 1.

Determine the rate of heat transfer between the plates assuming the gap between the plates is:

a. Vacuum

b. Filled with air at atmospheric pressure (air is not moving)

c. Please state any assumptions you make in your calculations

Thermal conductivity of air at 1 atm is 0.0223 W/m · °C Thermal conductivity of superinsulation is 0.00015 W/m · °C

Answer 1

The answers are in the red boxes. Also, I am not sure why there is thermal conductivity of superinsulation at the end. It is not even used anywhere in the question.

Now the solution of

Part c

The assumptions

Literrally speaking is there is no any assumption.

But, By assumption you mean. Treating stationary air like a solid body.

We used conduction formula to calculate heat transfer through air.

Why?

Because, air is stationary.

So, we know from the defination of conduction that, conduction is a heat transfer between solids and stationary fluid. This is its defination not an assumption. But its upto you, how to think about it.

Also stefan boltzman Constant 5.67 x 10^-8 is also not assumption. Its a standard value.

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