Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: uanna2341 on 03/03/2013 08:29:04

Title: Which form of heat transfer is the dominant one?
Post by: uanna2341 on 03/03/2013 08:29:04

For each of the following situations, indicate which method of heat transfer is the dominant one.
a)  Clothes being dried by hanging well above a campfire.
b)  A piece of chocolate melting in your mouth.
c)  The loss of heat during the lunar night on the moon.

Title: Re: heat transfer is the dominant one
Post by: graham.d on 03/03/2013 10:57:19

a) evaporation, b)conduction, c)radiation

Title: Re: heat transfer is the dominant one
Post by: CliffordK on 04/03/2013 20:13:07

I'm not sure that evaporation is correct.  Evaporation does occur in the shirt.

However, the heat transfer to the shirt would be a combination of radiation and convection.

Keep in mind that hanging your shirt above the campfire will give you very smoky smelling clothes.

Title: Re: heat transfer is the dominant one
Post by: graham.d on 04/03/2013 22:44:45

Oh yes, quite right. The question is heat transfer. Ha ha, I failed that one.

Title: Re: What is the dominant mode of heat transfer?
Post by: lightarrow on 05/03/2013 17:53:07

Quote from: CliffordK on 04/03/2013 20:13:07

I'm not sure that evaporation is correct.  Evaporation does occur in the shirt.

However, the heat transfer to the shirt would be a combination of radiation and convection.

I'm not sure graham.d's answer is wrong  [:)]
Even if the surrounding doesn't heat the shirt, the water's shirt can evaporate the same, taking the vaporization enthalpy from the liquid water itself in the shirt, which cools; the water molecules in the vapour state have higher energy and they heat the surrounding mixing with the air around. So the dominant mechanism of heat transfer could really be evaporation, in this case.

Title: Re: What is the dominant mode of heat transfer?
Post by: CliffordK on 05/03/2013 18:28:59

Evaporation cools the shirt, rather than warming the shirt.

However, it is a component of Latent Heat Flux (http://disc.gsfc.nasa.gov/hydrology/data-holdings/parameters/latent_heat_flux.shtml), or the transfer of heat from the surface of Earth to the upper troposphere.

So, Graham was just answering the wrong question as evaporation is merely transferring the heat from the fire to the upper troposphere.

Title: Re: What is the dominant mode of heat transfer?
Post by: lightarrow on 06/03/2013 15:40:11

Quote from: CliffordK on 05/03/2013 18:28:59

Evaporation cools the shirt, rather than warming the shirt.

I misinterpreted "campfire"   [xx(]...
You're right.

--
lightarrow

Title: Re: What
Post by: shagydeep on 14/03/2013 10:00:41

I don't understand what is your exact question is?...

Title: Re: Which form of heat transfer is the dominant one?
Post by: CliffordK on 15/03/2013 06:24:23

Quote from: shagydeep on 14/03/2013 10:00:41

I don't understand what is your exact question is?...

Clarified.