I'm assuming that he has a fan mounted to the radiator, and that it is running at a constant speed. Not perfect, I know. If this is the case, the airflow should be a relatively consistent turbulent flow, which is what you want. Besides, the point was that the whole equation is restricted by the temperature difference, and that doesn't change no matter the type of air flow over the radiator.
Energy transfer is more efficient with a
turbulent airflow, as it exposes more air molecules to the radiator surface. Same goes for the fluid. If the flow is
laminar (lacking turbulence) the same air molecules, or water molecules, flow over the radiator surface the entire time, and thus the heat must be transferred through them into the neighboring molecules. The nature of the flow is dependent on the geometry of the object it is flowing through or around, and the velocity of the flow.
The equations that govern the nature of the airflow are very tricky, but one can determine whether the flow is laminar or turbulent using the
Reynolds Number. Here is the equation for the Reynolds # in a pipe:
R=pVL/u
p = density
V = fluid velocity
L = length of pipe
u = dynamic viscosity
This gives you the Reynolds Number for the flow through the pipe, which you then compare to a chart to determine whether the flow is laminar or turbulent. I would be willing to bet that the flow over the radiator fins is turbulent just based on the geometry of the device and the velocity of the air moving over it. Unfortunately, there is no easy equation to determine that.
I have cut this thermo- and fluid-dynamics lesson short but please keep the discussion going.
Ethan