# Is there an equation for convection?

1. Jan 28, 2005

### bross7

I know that there is an equation for conduction, and radiation, but is there an equation for convection?

Last edited by a moderator: Mar 7, 2013
2. Jan 29, 2005

### maverick280857

3. Jan 29, 2005

### dextercioby

Yes,free convection can be modelled by nonequilibrium statistical mechanics (Boltzmann equation "momenta").But you need to know a great deal of physics to understand that...

Daniel.

4. Jan 29, 2005

### bross7

A little addendum to my initial question. But does this equation actually exist? We were told this is an equation for convection but nothing else was said about it. There is nothing about it in the textbook, mind you it is calculus based and the prof is not teaching any calculus.
We were given the equation with absolutely no explanation whatsoever, and a few students are having some doubts about it's use as we have found not secondary source to back it up.

$$H = qA \Delta T$$

It is the absolute lack of information given that makes us question the equation because it seems odd that nothing was described regarding it, and we received no derivation of the equation to understand where it came from that brings up question marks.

Last edited: Jan 29, 2005
5. Jan 29, 2005

### maverick280857

It is actually a onedimensional version of Fourier's Heat equation (which involves partial differential equations and advanced mathematics)...

$$\frac{dQ}{dt}=-kA\frac{dT}{dx}$$

In steady state (when temperatures are not changing with time),

$$H = \frac{\Delta T}{R}$$

(where R = thermal resistance = L/kA, H = dQ/dt ).

As far as I know the setup is based on emperical observations that the heat flow per unit time is proportional to the area of crosssection and to the temperature gradient. The constant k is the thermal conductivity of the material (which is strictly a function of temperature but can be assumed to be a constant for a small range of temperatures).

I am surprised why you didn't encounter this in full steam in your general physics course. (Maybe it was supposed to be an assignment for you folks to read and understand, which is equivalent.) Which textbook do you use?

Cheers
Vivek