buoyancy hot air flow rate question 1

[mielke]

Can anyone refer me to how to determine the flow rate of hot air caused by buoyancy.

For example assume no air flow and constant conditions. If there is a hot plate on the table it will heat up the air directly above it and due to buoyancy the hot air will rise up drawing the cold air to the place above the hot plate and then that will heat up etc. Thus creating a flow rate of air going up directly above the hot plate.

I can figure out the acceleration due to the buoyant force but that doesn't seem applicable to me and am wondering if there is an empiracle formula.

Thanks

 

[25362]

There is one formula expressing the velocity of thermally buoyant air, to be taken with a pinch of salt due to other side effects, and it is:

u_b = (g[β]H[Δ]T)^0.5​

u_b = buoyant air speed, m/s
g = acceleration of gravity, 9.8 m/s²
[β] = volume expansivity, for deal gases = 1/T
[Δ]T = temperature diference, hot air to ambient
H = height, m

It is generally recommended to use empirical results for each particular case.

 

[IRstuff]

You might also look at the derivation of convective heat transfer equations, as it is the buoyancy of air that is the mechanism by which heat is removed from an object.

TTFN

FAQ731-376