reflection and absorption

[elmitodeherta]

 

Hello,

I would like to calculate the difference between a white surface wall surface and the same kind of wall but with brown outer surface. I would like to know the reflection and absorption indices and then calculate the surface temperature of the wall in the two solutions at the same temperature as the outside air temperature. How could I proceed?

Thank you in advance.

[studiot]

You need to distinguish between emissivity and reflectivity to start with.

 

First the energy naturally emitted.

First calcualte the energy emitted by a perfect emitter ( a black body) then multiply it by experimentally determined emissivity (engineering tables are available) to obtain the emission from your wall.

As to reflectivity, this coefficient is also available from engineering tables, and will tell you how mauch irradiated energy is reflected.

So for instance a polished metal has low emissivity bu high reflectivity.

 

Does this help?

[elmitodeherta]

35 minutes ago, studiot said:

First the energy naturally emitted.

Quote

yes it is

 

First calcualte the energy emitted by a perfect emitter ( a black body) then multiply it by experimentally determined emissivity (engineering tables are available) to obtain the emission from your wall.

As to reflectivity, this coefficient is also available from engineering tables, and will tell you how mauch irradiated energy is reflected.

Quote

I already have it that values

So for instance a polished metal has low emissivity bu high reflectivity.

Quote

of course it is

 

Does this help?

Quote

I got that values, so I'd like to know how can I go forward in order to see the different surface temperature

 

 

[studiot]

Why would there be a different surface temperature?

A wall in contact with an atmosphere and nothing else in the system, will be at the same temperature.

This is often known as the zeroth law of thermodynamics.

[elmitodeherta]

2 minutes ago, studiot said:

Why would there be a different surface temperature?

A wall in contact with an atmosphere and nothing else in the system, will be at the same temperature.

This is often known as the zeroth law of thermodynamics.

I don't think so, because there is both different emissivity and reflection, should be different temperature