> So the amount of heat dissipated by the radiator is a function of
> both the temperature differential AND the flow through the radiator.
I disagree. The thermodynamic equation for the heat dissipated by the surface
of the radiator cares nothing for how fast the water is moving inside, only what
the temperature at the surface is.
Let's say you have a radiator dissipating 100,000 Btu/hr and 180F water is
moving through it at 100,000 lbs/hr (about 185 gpm). That means the outlet
temperature is 1 degree F lower than the inlet temperature, or 179F, giving an
average water temp of 179.5F.
Now what happens if we lower the water flow by 10% ? As a first approximation,
if the heat output stays the same, we can work out that the outlet water
temperature will fall by 0.11 degree. (100,000 / 90,000 = 1.11...) So, to keep
the exact same heat output, all we have to do is raise the inlet temperature by
.055F . Which IMO is not enough to be relevant, certainly far less than you can
see on a standard temperature gauge.
> This works just fine until the condition is met where the thermostat is full
> open and yet there is inadequate cooling because a portion of the coolant is
> bypassing the radiator
So the question becomes, is this ever the case ? The answer depends on how high
the relative flow is and the temperature drop across the radiator. If the water
temperature drop across the radiator is large, then yes, a small change in flow
will have a small effect on heat dissipation. But if the water temperature drop
across the radiator is small, then a small change in flow will have an
infinitesimal effect on heat dissipation.
Randall
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