Energy required to heat up a 4000 cm^3 of air to 1500 Celsius

[Panthera Leo]

Hello,

I have been struggling to calculate the joules required to heat a sealed chamber (cuboid shape 20x20x10cm=4000cm^3) filled with Air from room temperature to 1500 Celsius and couldn't get any straight answers from my calculations...!

Considering this chamber (which is actually an electric furnace) has to reach 1500C from room temperature in 1 hour how many watts would you guess?

Highly appreciate any contributions.

 

[mfb]

Do you know the concept of heat capacity? Did you find values for air?
Even if this is not homework, I think you should calculate it yourself.

Within 1 hour, I would expect that heat losses and the heating of the walls would be significant. Did you consider this?

 

[Panthera Leo]

Yes I did... & this is what I got which makes no sense from my point of view:

The specific heat capacity of air 1.012 joules per gram per kelvin
The mass of air in 4000cm^3 chamber is nearly 5 gram (1.22 kg/m^3)

Therefore, Total Joules=1.012*5*1500 = 7590 joules

W=J/t hence heating in 3600s = 2W which is ridiculous...!

I have had some experience with nichrome heating elements and nothing less than 1500W would work...

I am missing something here...

 

[Borek]

I am missing something here...

ROFL.

You are missing heat that is missed.

 

[mfb]

W=J/t hence heating in 3600s = 2W which is ridiculous...!

I have had some experience with nichrome heating elements and nothing less than 1500W would work...

I am missing something here...

That is what I expected. You are heating the walls and the environment. Just a very small fraction of the heat goes into the air in your chamber.

 

[Panthera Leo]

So 2W is actually true for the energy required for 4000cm^3 of air to be heated from RTP to 1500C ?!

& all the rest of energy is used for the walls... !

 

[voko]

Forget heating. Just think what it would take to insulate a 1500 C object from losing most of its temperature within one hour.

 

[Panthera Leo]

Alumina based insulation bricks are very good at high temp applications. I had a furnace made of such insulation bricks and it was 7cm thick, once the interior was about 1200C the exterior part of the brick never surpasses 100C ...