In a message dated 5/9/00 10:17:26 AM Eastern Daylight Time,
rpalmer@ames.ucsd.edu writes:
<< Optimum with respect to what? With respect to heat dissipation by the
radiator to the ambient, a delta T of zero degrees is best, but the
difference between zero and ten degrees is negligible (ca. 5%) and the
extra energy consumed by the water pump to reduce the delta T below ten
degrees would begin to eat up the gain in heat dissipation. If Chris
improves the air flow and that produces a twenty degree temperature drop,
the heat dissipation will be doubled. If the temperature difference between
the radiator and ambient is 100 degrees, then a ten degree drop in
temperature (average of five degrees across the radiator) will decrease the
efficiency by only 5%; not a big deal, but if it's too much (I would say
30 or 40 degrees is probably too much), then a better water pump or less
restrictive radiator is needed. If Chris puts on a better fan, then maybe
he can increase the delta T at idle to fifteen degrees, which would solve
his problem and be considered "ideal" in this case.
>>
Hi Bob,
Ten degrees delta T across the radiator is optimum in respect to a properly
balanced total cooling system on the road at a steady state. If you are
having cooling problems and getting a delta T of fifteen degrees then your
problem is low water flow rate through the radiator. This could be the pump
or restrictions in the system. If you are getting five degrees under the same
conditions and having cooling problems then your problem is heat transfer to
the air. This could be caused by low cool air flow through the radiator, a
heat transfer problem through the radiator such as loose fins, internal and
external dirt or insufficient fin area or just not enough radiator frontal
area which isn't easy to correct in a Tiger.
These are just rules of thumb that give you a clue to where to look for the
problem. Idle will follow the same rules but you can't optimize both
conditions with the same hardware so you end up over designing something to
solve both problems.
If you are designing a race car then conditions are not steady state and
different rules apply.
If you are designing a car from scratch and you want to optimize the system,
these rules of thumb help you decide if you have too much or too little
radiator, the frontal area is too large or too small, or you are using too
much or to little water pump HP.
John Logan
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