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

In summary, the conversation discusses the struggle of calculating the joules required to heat a sealed chamber filled with air from room temperature to 1500 Celsius in 1 hour. The person also mentions the concept of heat capacity and the importance of considering heat losses and heating of the walls. They also mention their experience with nichrome heating elements and the use of alumina-based insulation bricks. However, there seems to be a misunderstanding in terms of the amount of energy needed for the heating process.
  • #1
Panthera Leo
109
0
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.
 
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  • #2
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?
 
  • #3
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...
 
  • #4
Panthera Leo said:
I am missing something here...

ROFL.

You are missing heat that is missed.
 
  • #5
Panthera Leo said:
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.
 
  • #6
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... !
 
  • #7
Forget heating. Just think what it would take to insulate a 1500 C object from losing most of its temperature within one hour.
 
  • #8
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 ...
 

1. What is the formula for calculating the energy required to heat up a given volume of air to a specific temperature?

The formula for calculating the energy required to heat up a given volume of air to a specific temperature is Q = m x c x ΔT, where Q is the energy in joules, m is the mass of the air in kilograms, c is the specific heat capacity of air (1.005 J/g·K), and ΔT is the change in temperature in Kelvin.

2. How do I convert the given volume of air from cm^3 to kg?

To convert from cm^3 to kg, you will need to know the density of air, which is approximately 1.225 kg/m^3. You can then use the formula V = m/ρ, where V is the volume in m^3, m is the mass in kg, and ρ is the density in kg/m^3. Simply rearrange the formula to solve for m and then convert the volume from cm^3 to m^3.

3. How do I convert the given temperature from Celsius to Kelvin?

To convert from Celsius to Kelvin, simply add 273.15 to the given temperature. Kelvin is an absolute temperature scale, meaning that 0 K is equivalent to -273.15 Celsius. So to get the temperature in Kelvin, you need to add 273.15 to the temperature in Celsius.

4. Can I use a different specific heat capacity for air in the calculation?

While the specific heat capacity for air is generally accepted to be 1.005 J/g·K, this value can vary depending on factors such as temperature and pressure. If you have a more precise value for the specific heat capacity of air at the given temperature and pressure, you can use that in the calculation for a more accurate result.

5. How does the energy required to heat up air vary with changes in volume and temperature?

The energy required to heat up air is directly proportional to both the volume and the change in temperature. This means that as the volume of air increases, the energy required to heat it up also increases. Similarly, as the temperature that the air needs to be heated to increases, the energy required also increases. This relationship is described by the formula Q = m x c x ΔT.

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