enyawix
Quote:
Originally Posted by Wallzy
Why are you putting a restrictor in the thermostat??? You think the hole is too large allowing the water to move thru the radiator too fast??? Where do you think the rest of the water resides? The engine temperature gradient is way steeper than the ambient/radiator temperature gradient, you want to get the heat out of the engine, not keep it in. Take it out; regulate the water pump speed to the temperature.
You just do not have enough information to make that statement.
1.
You have a restrictor in your car, it is called a thermostat. Your thermostat is a flow restriction, and it limits how fast coolant can flow through your radiator .
2.
Engine temperature gradient is way steeper than the ambient/radiator temperature gradient, but this is only because engine coolant has a high thermal capacity. This means engine coolant can absorb a good amount of heat energy, before dissipating it. This is why "engine temperature gradient is way steeper than the ambient/radiator temperature gradient"
3.
This is where you missed the boat
The radiator can only exchange so much heat energy, for a given surface area and rate of air flow. Temperature gradient and rate of heat exchange do not directly coincide. If the engine releases a spike of thermal energy, It is absorbed into the thermal capacity of the engine coolant. You must thermally saturate the engine coolant, before you see a chance in temperature.
Bottom line: You do not want a coolant to flow at a rate that exceeds the rate of heat exchange of your radiator.
Actually, I can make that statement.
1) A thermostat is used to keep the engine at a constant temperature (within a certain design range) by opening when the temperature gets too hot, and closing when it cools. You are correct that a thermostat will restrict the flow, but it's primary function is to maintain constant temperature in the system under a variety of "driving styles" and wether conditions.
2) The temperature gradient between the engine vs. the coolant inside the engine (block/heads) and the coolant in the radiator vs. the ambient air has nothing to do with the engine coolants thermal capacity. Its thermal capacity is dependant on the additives to the coolant and the pressure at what the system operates. These things are what prevent regular water at atmospheric pressure from boiling inside the engine. Point is, when you look at a heat transfer curve, for delta temperature over time (assuming heat loss to a stable heat sink, such as the outside weather conditions of a particular time and day), it is a parabolic curve with your highest amount of heat loss to ward the beginning of the curve, thus by keeping the water inside the radiator (in a free flowing system, not a thermostat controlled system) you are not rejecting heat to the atmosphere as fast as you can.
3) Missed the boat...hmmm - "A radiator can only exchange so much heat energy,"
--Yes, but it is also dependant upon what is going on in the flowing system, not only what happens outside of the system.
"Temperature gradient and rate of heat exchange do not directly coincide"
-- This statement is completely incorrect, the temperature gradient between the radiator and the air around it most definitely does...this is why cars have a greater tendency to overheat in the summer than in the winter.
"If the engine releases a spike of thermal energy, it is absorbed into the thermal capacity of the engine coolant"
--This is correct.
"You must thermally saturate the engine coolant before you see a change in temperature."
--This is not correct either, saturating means that the coolant can not hold any more energy in it, by thermally saturating the coolant you are creating a state change within the system, aka nucleic boiling. Ultimately changes in temperature are caused by differences in temperature gradients.
Bottom Line: Your rate of heat exchange is determined based on a set flow rate, but changing the flow inside the system - while holding everything else constant- one can increase or decrease the rate at which heat can be extracted from an engine.
Here is the real problem, and it is hard to see unless you look at the entire system:
A radiator exchanges heat, BTUs, and the faster they can be extracted from a system, the cooler the overall system becomes. You can't look at only what is going on in the radiator. By slowing down the flow into the radiator, you are rejecting more heat from the radiator per given time, but your heat rejection rate is actually lower because of the dependant factors heat transfer. At the same time that you are absorbing way-way-way more heat from the engine per given time. This becomes a circular problem. By capturing the heat, and getting rid of it as fast as you can, you can reach a steady state that is lower than if you slow your flow down.
I have a few thermodynamic books I can recommend to you if you want to check them out.
Walz