Stu,
I ain't an auto expert, but I am a mechanical engineer, and you are
absolutely correct that slowing down the coolant flow won't help, but
it doesn't hurt that much, either. The key is the air flow through the
radiator, and the efficience of heat transfer to that air.
The combustion chamber produces heat, and it has to be carrried away as
fast as it is produced, or the engine will continue to heat up until it
reaches the combustion temperature of the fuel. In a properly operating
cooling system the system reaches equilibrium (heat produced in the
combustion chamber equals heat lost at the radiator) at a temperature
that is below the boiling point of water for the ressure within the
cooling system.
Heat transfer by convection (which, despite the name, is a how a
radiator works) is a function of the flow of coolant through the
radiator tubes, the air flow around the tubes, and the heat transfer
between them. The thermostat cuts the radiator out of the circuit when
the engine is cold, so the only heat transfer is between the engine and
the air that flows around it, which results in rapid heating of the
water that is just circulating in the engine block. When the thermostat
opens, the water goes throguh the radiator, where efficient heat
transfer takes place and equilibrium is reached.
So, in actuality, the rate of water flow through the radiator is not,
in itself, that important, so long as there is a steady flow. The keys
are the size of surface area where the heat transfer takes place and
the rate of air flow over that surface. So, the reason my tiger
overheats in traffic is purely and simply a result of the fact that the
fan alone doesn't force enough cool air through the radiator to take
care of the heat produced in the combustion chamber. I could double the
water flow rate through the radiator, or cut it in half, and it
wouldn't solve the problem. The heat transfer surfaces in the radiator
have to be enlarged, or the cool air flow through the radiator has to
be increased, or the efficiency of heat transfer in the radiator has to
be increased.
Joe
|