Radiant Cooling with Liquid Nitrogen

[Green Xenon]

Hi:

 

I thinking of a radiant cooling device for houses and buildings in which the cooling -- in the direct sense -- involves only radiation. Sort of like a glass-ceramic radiant-stove-top in reverse. Indirectly, however, some amount of convection and conduction will be needed [liquid nitrogen, cold metals]. The cooling panel is the ceiling and cools objects below it.

 

Quote from http://en.wikipedia.org/wiki/Glass-ceramic :

 

"A glass-ceramic stove uses radiant heating coils as the heating elements. The surface of the glass-ceramic cooktop above the burner heats up, but the adjacent surface remains cool because of the low heat conduction coefficient of the material."

 

Here is an example of a radiant stovetop switched on:

http://www.istockphoto.com/file_thumbview_approve/4799702/2/istockphoto_4799702-glowing-ceramic-stove-top.jpg

 

My theoretical glass-ceramic radiant cooler is similar to the infrared radiant stovetop described in the wikipedia link, except:

 

1. It faces downward

2. The coils are hollow [as opposed to being solid all the way through], this hollow within the coils allows liquid nitrogen to flow through them can cool them down to near absolute zero

3. Liquid nitrogen -- not electricity -- flows through the coils.

4. Obviously, the coils get cold instead of hot.

 

The radiant cooling panel is on the ceiling of the room it is supposed to cool. Those standing under it will feel cold.

 

Yes, heat absorbed into the radiant cooling panels is carried off using convection and conduction -- but this is not what the subject inside the room feels. The direct cooling effect on anything/anyone inside the room is radiant.

 

By direct radiant cooling, I mean that if you place your body at a noticeable distance from panel, you'll feel cold because the extreme cold of the coil will draw IR radiation away from your body.

 

I’m thinking of more intense versions of this hypothetical glass ceramic radiant infrared cooler to be used in refrigerators and freezers.

 

This radiant cooling is something that I am deeply interested in. I don't know why.

 

Radiant cooling will feel to the object like "cold rays" just like radiant heating feels like "heat rays".

 

I know there is no such thing as "cold rays", it's simply heat radiating from my body to a colder object. My body is giving of heat rays causing it's temperature to lower, thereby giving me a perception of coldness.

 

To prevent water from condensing on the panel, a separate air-dehumidifier is used.

 

 

Thanks a bunch,

 

Green Xenon

Edited December 22, 2010 by Green Xenon

[Mr Skeptic]

A continuation of your unnatural and inefficient ideas? By using very cold temperatures as required for radiant heat to be effective cooling, you have to remove heat against a huge temperature differential, which will cost you a lot more energy per unit of cooling than conventional air conditioners.

[John Cuthber]

Apart from anything else the cold ceiling would cool the air near it which would become denser and fall. This would set up a convection current which would do a much better job of taking heat from the person than radiation will. People are just not hot enough to radiate much.

[Green Xenon]

A continuation of your unnatural and inefficient ideas? By using very cold temperatures as required for radiant heat to be effective cooling, you have to remove heat against a huge temperature differential, which will cost you a lot more energy per unit of cooling than conventional air conditioners.

 

What if, hypothetically-speaking, the temperature of the coils were somehow dropped to the astronomically-low temperature of the following degree Kelvin:

 

a decimal followed by a Graham's-number of zeros followed by one 1

 

http://en.wikipedia.org/wiki/Graham's_number

 

Now that is an one *extremely* low temperature!

 

Would this result in significant radiant cooling of objects in the room?

[CaptainPanic]

What if, hypothetically-speaking, the temperature of the coils were somehow dropped to the astronomically-low temperature of the following degree Kelvin:

 

a decimal followed by a Graham's-number of zeros followed by one 1

 

http://en.wikipedia.org/wiki/Graham's_number

 

Now that is an one *extremely* low temperature!

 

Would this result in significant radiant cooling of objects in the room?

I'm sorry if this sounds rude, but I am afraid you just don't understand heat transfer...

 

The amount of energy (heat) transferred equals:

 

[math]E=U\cdot{A\cdot{\Delta{T}}}[/math]

in which:

[math]E[/math] = energy (Joule)

[math]U[/math] = overall heat transfer coefficient(depends on a lot of things) in (J/m2K)

[math]A[/math] = surface area (m2)

[math]\Delta{T}[/math] = temperature difference (K)

 

Notice that the formula contains "[math]\Delta{T}[/math]". So, we take the difference between room temperature (probably about 295 K) and the coolant.

 

If we have 1 coolant at 1 Kelvin

And another coolant at a gazillion decimal zero's and then a one Kelvin

 

Then the temperature difference for our formula is in one case 295-1 = 294

And in the other case it's 295-0.0000000000000000000000000000001 = 295

 

That's a whopping 0.3% increase in cooling! And a whopping 100000000% increase in power consumption (or more - I'm just guessing). So, that's a bad idea.

 

Ok. So we have established that going near the absolute zero is completely and utterly pointless if your only goal is to absorb heat from the surroundings.

 

That leaves us with just 1 question: what is the cheapest "coolant"? And your answer is: cooling water. Just plain cold water.

 

You only use fancier coolants, such as glycol mixtures, liquid nitrogen or even liquid helium if you actually want to make something really frickin' cold. But unless you want to simulate the arctic in your room, I would just use water.

[Mr Skeptic]

What if, hypothetically-speaking, the temperature of the coils were somehow dropped to the astronomically-low temperature of the following degree Kelvin:

 

a decimal followed by a Graham's-number of zeros followed by one 1

 

http://en.wikipedia.org/wiki/Graham's_number

 

Now that is an one *extremely* low temperature!

 

Would this result in significant radiant cooling of objects in the room?

 

I doubt you'd notice it being any quicker than at 1 K, although it would be by a little. It won't speed up the rate at which warm bodies emit radiation though, it would just mean that the cold body radiates less.

 

Incidentally, the night sky is very cold, just a few degrees K.

[swansont]

By direct radiant cooling, I mean that if you place your body at a noticeable distance from panel, you'll feel cold because the extreme cold of the coil will draw IR radiation away from your body.

 

That's not how it works. A body that is radiating does not "know" what the radiation will hit. To the extent that this works it will be because the panel does not radiate very much, while the person standing near it radiates normally.

 

In reality what you'll get is a block of ice on your panel.

[John Cuthber]

Once you chill the ceiling below about 80K it will start to rain liquid air.

That will cool you in a hurry.

GX seems to have missed my point. People are not hot enough to radiate much.

[swansont]

Apart from anything else the cold ceiling would cool the air near it which would become denser and fall. This would set up a convection current which would do a much better job of taking heat from the person than radiation will. People are just not hot enough to radiate much.

 

Actually, the bulk of our heat loss is via radiation. Around 500 Watts/m^2 for an average person, but under average ambient conditions we absorb almost as much from our surroundings, so our net loss is about 100 Watts or so.

 

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/coobod.html

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/bodrad.html