Do We Radiate Heat in Closed Rooms?

[stochastic]

When you are in a closed room with other people is the heat produced simply from the the CO2 we exhale or do we radiate something from our skin?

 

[ranger]

Radiating heat from the human body is normal. Refer to this for more details:

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

 

[stochastic]

ok but what is it that we radiate specifically? I've already read about radiation and it was stated that its the emmision of electromagnetic waves... so what is happening, we have excess energy and so the electromagnetic waves become more intense?

 

[ranger]

The radiation can be said to be of specific frequencies. When you look at the human body through an infrared camera, what do yo see? Don't you see all sorts of cool color distortions? This is radiated energy in the form of infrared.

The human body needs to be in temperature equilibrium (steady state); therefore, when the usual ways of getting rid of excess energy (radiation and convection) are not sufficient, we rely on perspiration . If you are interested in finding the net power, you'll have to apply Stefan-Boltzmann law.

 

[oedipa maas]

I'd figure that most of the heat removed from your body leaves by convection or through the latent heat needed to vaporize water.

If you treat a human body as a blackbody you'll emit in the infrared. The sun emits quite a bit in the visible, which is why wearing a black shirt on a sunny day is warmer than wearing a white shirt on a sunny day. But if you're indoors then the colour of your shirt doesn't make a difference to how hot or cold you are - your body emits radiation in the infrared (which your shirt doesn't absorb) and fluorescent lights emit more in the high-end of the visible (which doesn't help to warm you up).

So if you have a choice between a black shirt and a white shirt in a cold room, you're probably better off just wearing BOTH shirts because your body is mostly losing heat through convection rather than radiation.

 

[stochastic]

So help me understand this then.. I agree the heat moving around the room is do to convection but when the air molecules touch the skin and absorb the heat is that conduction?

 

[Integral]

So help me understand this then.. I agree the heat moving around the room is do to convection but when the air molecules touch the skin and absorb the heat is that conduction?

No, it is convection.

 

[stochastic]

oky doky :) danke

 

[oedipa maas]

So help me understand this then.. I agree the heat moving around the room is do to convection but when the air molecules touch the skin and absorb the heat is that conduction?

The air next to your skin is heated through conduction - but then that air moves away from your skin and cooler air replaces it. That's convection.

 

[xez]

Yes, the radiation of heat from the body is from
conduction, convection, heat of vaporization,
wien law blackbody radiation of electromagnetic waves
with high power concentration being around 10um
wavelength corresponding to a temperature of ~ 300K.

People radiate especially strongly on hot humid days
when they've not bathed recently, though that's another
sort of radiation...

 

[russ_watters]

You guys are mixing words together that don't belong together.

First, Integral was correct and the reason is that there is no coherent layer of air next to your skin to say there is conduction going on: individual molecules in constant near-random motion bounce off your skin and that is convection.

Second, radiation is radiation is radiation. Radiation is not conduction and radiation is not convection.

 

[rasensuriken]

May i know why do we radiate? As in what mechanism actually happening that caused us to radiate em wave?

 

[Dale]

Here is the HyperPhysics link to http://hyperphysics.phy-astr.gsu.edu/hbase/bbcon.html#c1".

 

[stochastic]

people give that link often on this forum. i don't see how it answers his question though. i think he wants to know if a bio-chemical reaction is causing us to radiate em waves and if not, what is? if that's not his question, i would like to know ;)

im sure this is more of a chemistry/biology topic but hopefully someone can tell us here.

 

[russ_watters]

people give that link often on this forum. i don't see how it answers his question though. i think he wants to know if a bio-chemical reaction is causing us to radiate em waves and if not, what is? if that's not his question, i would like to know ;)

It does answer the question. For your question: no, there is no biochemical reaction causing us to radiate. We radiate (as the link describes) via the same mechanism all black bodies do.

 

[DaveC426913]

The biochemical reaction that contributes to heat loss is perspiration. We perspire even when we're not actually "sweating". Live at a comfy room temperature for a whole day and you will still lose a fair amouint of moisture from your skin. Evaporation is an endothermic reaction - it takes away heat from the body.

(On an anecdotal note: once, when I was bored waiting in the car in winter, I was touching the window with my finger. A halo of condensing dew danced around on the window next to the tip of my finger, out to about a half inch. I was astonished to realize the implication: at all times, I am surrounded by a thin layer of off-gassing water vapour continually evaporating from my body. I'd always known it, but I'd never seen it so graphically portrayed. After 24 hours, over the entire surface of my vbody, I must lose some fraction of a litre of water.)

And the tie-in here is that all this water vapour has absorbed heat from my body to evaporate, and is taking it with it as it off-gasses.

 

[Dale]

The biochemical reaction that contributes to heat loss is perspiration.

Yes, that is true, but that is evaporation, not radiation. I am sure you already know, but just so that the OP is aware there are three primary mechanisms of heat transfer: conduction, convection, and radiation. Conduction is when two (usually solid) objects of different temperatures are touching and exchange heat through that contact. Convection is when heat is transferred through contact between an object and a flowing fluid. Radiation is when heat is transferred through EM radiation without any contact.

In addition to those three mechanisms of pure heat transfer there are also mechanisms where both heat and mass are transfered, specifically evaporation and condensation. In evaporation some of the liquid phase converts to gas phase which results in heat and mass being transferred to the gas phase. Condensation is the reverse. I am sure there are other heat and mass transfer mechanisms, but evaporation is the most important biologically.

 

[russ_watters]

Well I would say that perspiration is not a biochemical reaction and the question was about radiation, not evaporation...

 

[HallsofIvy]

Yes, the radiation of heat from the body is from
conduction, convection, heat of vaporization,
wien law blackbody radiation of electromagnetic waves
with high power concentration being around 10um
wavelength corresponding to a temperature of ~ 300K.

loss of heat is from conduction, convection and vaporization, not "radiation". That word only applies to black body radiation.

[/quote]People radiate especially strongly on hot humid days
when they've not bathed recently, though that's another
sort of radiation...[/QUOTE]

 

[Dale]

loss of heat is from conduction, convection and vaporization, not "radiation". That word only applies to black body radiation.

I point you to http://hyperphysics.phy-astr.gsu.edu/Hbase/thermo/bodrad.html#c1 and http://en.wikipedia.org/wiki/Black_body#Radiation_emitted_by_a_human_body and you can Google many other references. Radiation is an important mechanism for heat loss from the human body.

 

[stochastic]

now my question has been misunderstood. i actually read both of those last night dalespam as well as that original blackbody link you gave. that first link, to be honest, was way past my self education on physics, making it complete nonsense.

im pretty sure none of those answer my question anyhow, i understand that we radiate to maintain homeostasis. my question was, what is it that produces/generates the em waves. is it the break down of ATP in cells? i have also heard the heart produces a strong field.

 

[Dale]

now my question has been misunderstood. i actually read both of those last night dalespam as well as that original blackbody link you gave. that first link, to be honest, was way past my self education on physics, making it complete nonsense.

im pretty sure none of those answer my question anyhow, i understand that we radiate to maintain homeostasis. my question was, what is it that produces/generates the em waves. is it the break down of ATP in cells? i have also heard the heart produces a strong field.

The mechanism of radiation is called "blackbody radiation". It has nothing to do with anything physiological like the breakdown of ATP or the electrical excitation of cardiac cells. It is purely physical, due to the thermal oscillations of charges on the molecular level. Essentially, due to thermal energy molecules are always shaking around, shaking is acceleration, molecules have charges, when charges accelerate they radiate. Try this link http://galileo.phys.virginia.edu/classes/252/black_body_radiation.html

 

[mikelepore]

what is it that produces/generates the em waves

The classical explanation is: Everything is made of atoms ... atoms are made of charged particles ... everything has a temperature above absolute zero, therefore we have charged particles that are continuously in motion ... these motions are not simply constant velocities, therefore we have charged particles being continuously accelerated ... the acceleration of any charged particle radiates an electromagnetic wave ... therefore every object radiates electromagnetic waves ...

The higher its temperature, the more it radiates .. that radiation rises sharply with temperature, according to the Kelvin temerature raised to the 4th power.

 

[stochastic]

ahh there we go :)

your explanation was apt. also the link seems more up my ally. thanks dale

 

[Dale]

You're welcome. Sometimes it just takes a few tries to figure out the right "flavor" of explanation!

 

[dantose]

And here I was assuming you were talking about things like beta decay and positron emmission.

Major cause of that is naturally occurring ⁴⁰K by the way.