A New Theory of Heat Transmission

[Nicholas Kang]

Problem Statement:

 

Recently, I ran SETI@home on my computer. I placed a white and shiny Aluminium plate underneath the heat exhaust fan lobe/openings of my CPU-something looks like the car radiator model but I don`t know the appropriate word. The exhaust lobe became hot after the PC was on for a while. And of course the aluminuim plate became hot after a while. But when I removed the plate, it became cool within not more than 30 seconds.

 

We know that white and shiny surface is a good heat reflector and black and dull surface is a good heat radiator/absorber. My question is how is it possible that the white and shiny surface aluminium plate could turn out to be a good heat radiator in this condition.

 

Hypothesis and Inference: My speculations based on my current knowledge-15 years old is as follows:

 

I think we should take the surrounding darkness as consideration too when dealing with heat transmission. For instance, in my case, my computer is black including the heat exhaust area. if I placed a WHITE AND SHINY Al plate underneath there, the plate would become a temporary heat absorber/radiator due to the surrounding temperature which is black because my computer isn`t transparent, so light cannot penetrate through the PC. the area which my Aluminium plate was placed became dark. So, heat was absorbed due to thermal equilibrium. When the plate was taken out, it was exposed to light source (in this case-sunlight because it was daytime). The shiny and white surface Aluminium plate retains its original properties, the temporary "BLACK AND DULL" surface then became a normal plate again, being a good heat reflector and a poor heat radiator/absorber.

 

Thus, the plate absorbs heat well when underneath my PC because it was temporary dark and reflects heat away during exposure towards sunlight/light source.

 

Conclusion: Heat transmission may take the surrounding light intensity into consideration upon considering whether which materials is a good heat radiator/heat absorber/heat reflector.

 

Speculation complete.

 

Speculation report done by

 

Nicholas Kang Zheng Tien

 

Student,

 

SMJK Chung Ling Butterworth

 

Penang, Malaysia

Edited July 15, 2014 by Nicholas Kang

[studiot]

 

I placed a white and shiny Aluminium plate underneath the heat exhaust fan lobe/openings of my CPU-something looks like the car radiator model but I don`t know the appropriate word.

 

Good morning Nicholas.

 

The holes are called vents and the lumps are called (cooling) fins.

Yes some computers, particularly laptops have a radiator, similar to car radiators but smaller.

They serve the same function.

They are also similar to the cooling radiator on the back of fridges and freezers and inside airconditioning units.

 

Unfortunately calling these radiators is inappropriate since they do not transfer much heat by radiation.

The correct term is convection.

If there is also a fan it is called forced convection.

If there is no fan it is called free convection.

 

So think carefully about what comes out of your vents.

 

 

 

 

 

So, heat was absorbed due to thermal equilibrium.

 

The whole point if equilibrium is that nothing happens in equilibrium. That is no heat is transferred, buildings do not fall down and so on during equilibrium.

 

 

 

 

The shiny and white surface Aluminium plate retains its original properties

 

Thinking about the properties of your aluminium plate, what can you say about its surface area, compared to a cube of the same amount of metal?

 

 

 

Conclusion: Heat transmission may take the surrounding light intensity into consideration upon considering whether which materials is a good heat radiator/heat absorber/heat reflector.

 

 

Can you test this in a dark room using, say, a hair drier?

Edited July 15, 2014 by studiot

[Strange]

 

Thinking about the properties of your aluminium plate, what can you say about its surface area, compared to a cube of the same amount of metal?

 

Ah yes, a very good point.

 

Nicholas, you might also want to think about the weight (mass) of the aluminium plate compared to, say, a piece of steel of the same size. And what this might mean for the amount of heat stored in the plate. (Keyword to look up: specific heat.)

[Nicholas Kang]

Once again I am checkmated.

 

So think carefully about what comes out of your vents.

 

You mean heat and hot air. I can feel the hot air now by touching, not even touching and just by placing my hand near the vents.

Ok, Strange

 

You mean specific heat capacity? that is in my 16 years old science syllabus. I haven`t learn it. But I do have some brief understanding

You mean aluminium can store more heat than other materials?

[studiot]

Glad to be of service.

 

 

I see there are plenty of others willing to discuss this in as much detail as you like, so I will leave it to their capable hands now I've pushed the boat in the right direction.

Edited July 15, 2014 by studiot

[Nicholas Kang]

What do you mean, studiot?

You are going to leave this topic now?

Ok, leave. Bye. Studiot.

 

Good morning Nicholas.

 

The holes are called vents and the lumps are called (cooling) fins.

Yes some computers, particularly laptops have a radiator, similar to car radiators but smaller.

They serve the same function.

They are also similar to the cooling radiator on the back of fridges and freezers and inside airconditioning units.

 

Unfortunately calling these radiators is inappropriate since they do not transfer much heat by radiation.

The correct term is convection.

If there is also a fan it is called forced convection.

If there is no fan it is called free convection.

 

So think carefully about what comes out of your vents.

 

The whole point if equilibrium is that nothing happens in equilibrium. That is no heat is transferred, buildings do not fall down and so on during equilibrium.

 

Thinking about the properties of your aluminium plate, what can you say about its surface area, compared to a cube of the same amount of metal?

 

Can you test this in a dark room using, say, a hair drier?

 

it is 5:11 p.m. now. Remember, Malaysia is 8 hours ahead of GMT.

 

Thanks for teaching me about thermal equilibrium. So, thermal equilibrium is a condition, not a process. Am I right?

 

Now I know why Malaysia is back of time. I only learned convection in my school, without any classification of it, like forced convection and free convection. I learnt about them now. thanks again.

 

Test in dark room? How? And maybe there is a figurative meaning behind this sentence. What is it?

I am going to reply to Essay now. Wait for a while.

Back now.

[Strange]

You mean specific heat capacity? that is in my 16 years old science syllabus. I haven`t learn it. But I do have some brief understanding

 

You mean aluminium can store more heat than other materials?

You can learn the details later but, intuitively, something that is more massive (has a greater mass) can store more heat than something with less mass (at a given temperature). So a small piece of metal can store less heat than a larger piece. I would expect an aluminium sheet to be lighter, and therefore store less heat than a steel sheet of the same size (which is heavier). And so it might cool quicker than a piece of steel.

 

But as you say: specific heat - this is the amount of heat per unit mass that different materials can store. This complicates the simple intuitive idea above.

 

However, I think studiot's point about the surface area of a flat sheet (compared to a cube or sphere of the same amount of metal) is probably more significant.

 

The colour of the surface will also have an effect. But I don't think the "apparent colour" (i.e. it appearing darker because it is in the shade of the computer) is important. But a (matt) black surface is more effective at absorbing heat and (perhaps surprisingly) also more effective at radiating heat than a light colour.

 

 

Once again I am checkmated.

 

Not at all. You have noticed something. You have come up with some ideas about what factors might be involved. You have learnt about some of the other factors that might be relevant.

 

Maybe you could think of some experiments you could do that might help you identify which effects are real or important, and which have little or no effect. (That is the beginnings of a scientific enquiry. Then you could start to think about what might cause those experiments to give wrong or confusing results, and how you would change them to eliminate other effects. And so on ....)

 

This might encourage you to keep looking and thinking about why things happen: http://en.wikipedia.org/wiki/Mpemba_effect

[Nicholas Kang]

Shall we continue?

You can learn the details later but, intuitively, something that is more massive (has a greater mass) can store more heat than something with less mass (at a given temperature). So a small piece of metal can store less heat than a larger piece. I would expect an aluminium sheet to be lighter, and therefore store less heat than a steel sheet of the same size (which is heavier). And so it might cool quicker than a piece of steel.

But as you say: specific heat - this is the amount of heat per unit mass that different materials can store. This complicates the simple intuitive idea above.

However, I think studiot's point about the surface area of a flat sheet (compared to a cube or sphere of the same amount of metal) is probably more significant.

The colour of the surface will also have an effect. But I don't think the "apparent colour" (i.e. it appearing darker because it is in the shade of the computer) is important. But a (matt) black surface is more effective at absorbing heat and (perhaps surprisingly) also more effective at radiating heat than a light colour.

 

A small piece of metal can store heat less heat than a larger one? Not so. In my opinion, that might be just simply the volume is large but not the mass is larger.

 

So, would the apparent colour have an effect or totally no/zero. yes, of course, the colour of the surface has an effect but my new question is

 

When dealing with heat transmission including conduction,convection and radiation, the heat capacity and the surface colour, which has more significant impact on the result?

thanks for your website too.

[Janus]

The colour of the surface will also have an effect. But I don't think the "apparent colour" (i.e. it appearing darker because it is in the shade of the computer) is important. But a (matt) black surface is more effective at absorbing heat and (perhaps surprisingly) also more effective at radiating heat than a light colour.

 

Sometimes visible color can be misleading. There once was a time when they used White lead-based paint for radiators because it was actually a strong absorber/radiator in the infrared spectrum.

[Sensei]

We know that white and shiny surface is a good heat reflector and black and dull surface is a good heat radiator/absorber. My question is how is it possible that the white and shiny surface aluminium plate could turn out to be a good heat radiator in this condition.

I think so you're misunderstanding this a bit.

 

White color surface is good at reflecting photons at VISIBLE spectrum (approximately 400 nm-700 nm wavelengths).

Black color surface is good at absorbing photons at visible spectrum.

 

But it doesn't tell how good or bad they are at reflecting or absorbing photons at frequencies that are below or above visible spectrum.

 

Hot black color surfaces usually are emitting light at infrared range. And are visible by IR cameras.

f.e. hot carbon might still be black to us, but emitting a lot of IR photons.

 

They need to lost energy that they absorbed from visible range photons (or other sources of energy), otherwise energy would go to infinity.

If energy increases faster than material is able to emit it, it's starting changing state (solid -> liquid, liquid-> gas)

 

 

 

Carbon dioxide gas emitting IR photons video:

 

 

 

 

Metals are good at conducting heat, because (but not only) they are made of uniform atoms, which have average very short distance to each other.

 

1 m^3 of Aluminum has approximately 6.022141e+28 atoms

1 m^3 of Oxygen has approximately 2.69e+25 molecules.

[Nicholas Kang]

 

I think so you're misunderstanding this a bit.

 

White color surface is good at reflecting photons at VISIBLE spectrum (approximately 400 nm-700 nm wavelengths).

Black color surface is good at absorbing photons at visible spectrum.

 

But it doesn't tell how good or bad they are at reflecting or absorbing photons at frequencies that are below or above visible spectrum.

 

Hot black color surfaces usually are emitting light at infrared range. And are visible by IR cameras.

f.e. hot carbon might still be black to us, but emitting a lot of IR photons.

 

They need to lost energy that they absorbed from visible range photons (or other sources of energy), otherwise energy would go to infinity.

If energy increases faster than material is able to emit it, it's starting changing state (solid -> liquid, liquid-> gas)

 

You mean my Al plate absorbs heat from other EM wave as well? And then how do you simplify the fact that one silver shiny surface absorbs different rates of EM wave heat. If say Visible +1 unit, IR +2 units, UV -5 units, etc. then what is the final resultant heat absorption and radiation. The system seems complex to me.