[tintivilus]

Yes, sure we're digressing, but it's fun

Originally Posted by ilia@industry

It's simply the inverse of the same equation. Take a gas like air, and assume it's sitting in a jar.

I think we might be suffering from differing assumptions about the experimental apparatus... the issue I took was with this statement in particular:

Originally Posted by ilia@industry

Raising flow velocity increases temperature and pressure.

Are you talking about reducing the delta-V between the intake and output of the IC? The more I read this, the more it sounds like blowing air faster through an IC makes it hotter, which I just can't fathom based on ideal gas law.

If your IC is cooling the charge air (as it should be) the volume entering the IC should be greater than the volume leaving the IC (since reduction of temp yields reduction of volume). This is plain enough. If you increase the velocity of air at the intake (pushing greater volume in a given period of time) then the air at the output will probably be warmer and therefore at higher pressure than before due to transferring less of its energy to the IC... and is this the point you were trying to make that I just misunderstood?

I really don't recall enough of my thermodynamics to judge whether the increase in delta-T will speed up heat transfer enough to cancel out the reduced transfer time due to increased velocity through the cooler. Could any ME's out there chime in on that?

[Dascamel]

haha, back to high school chemistry: PV=nRT, don't remember it, google for some fun.

edit

[IND-Distribution]

Yep, you've got me now.

Say you're pushing 30CFM through an intercooler and the temp is 20 degrees Celsius. When you go to run 60CFM through the same intercooler setup the temp will be 20+x degrees Celsius.

More than anything, I was explaining the ideal gas law, and how all the variables affect each other. Temperature affects pressure, pressure affects volume, etc...

[stressdoc]

I hope that the younger set here is getting enthused about thermodynamics and the importance of Physics courses...

The basic idea is that the explosions that take place inside the cylinders of your engine generate heat. Heat is basically a measure of the speed at which molecules are moving around. The faster they are moving, the more energy, the more "push" from expansion that moves the pistons. The explosions are the release of energy from the breaking down of complex hydrocarbon molecules in gasoline/petrol into smaller molecules. There is energy stored in the chemical bonds, and when they are broken, the energy is released. This chemical reaction needs Oxygen molecules, and that is where the function of the IC comes in. Colder air is more dense, it has more O2 molecules in it per unit of volume, because the molecules are not moving as fast. During an intake cycle of your engine, a set volume of air is allowed into the cylinder, along with a set amount of fuel, which the spark ignites and sets off the chemical reaction. The colder the air, the more O2. This can produce more power: if there is more O2, then engine management systems can adjust the amount of fuel accordingly. More fuel, more O2, more chemical reaction, more energy. More O2 may also increase the efficiency of the chemical reaction, resulting in less unburned fuel entering the exhaust. Because fuel entering into the exhaust does not contribute usable power (it's not moving the pistons), but still may generate heat energy if it continues to burn (which it does), then the power / heat ratio diminishes. Hence an IC may decrease engine temperatures if the cooled air results in a more efficient burn (lower EGTs).

An additional factor involves the potential interference of the IC with other cooling systems (water radiator, oil cooler). This depends on the shared airflow. If the IC is placed where the air that it uses to transfer heat (from the intake air compressed by the spinning turbos) via its cooling fins will also flow over the radiators of the other systems, then that raises the heat of the air passing over those other radiators and diminishes their cooling abililty. Hence the concern with placement of the IC so that it does not interfere with the air flow over other cooling systems, and does not 'pre-heat' the air that will flow over them either.

On a related point, all things being equal (that is, the efficiency of the chemical reaction), when you mod your engine to produce more power, that entails more heat production. A piggybacked engine is capable of producing more power, with associated higher levels of heat that need to be dissipated. Similarly, an engine with an IC that enables higher horsepower will have higher cooling demands, but only when the higher power is realized.

[IND-Distribution]

Originally Posted by stressdoc

On a related point, all things being equal (that is, the efficiency of the chemical reaction), when you mod your engine to produce more power, that entails more heat production. A piggybacked engine is capable of producing more power, with associated higher levels of heat that need to be dissipated. Similarly, an engine with an IC that enables higher horsepower will have higher cooling demands, but only when the higher power is realized.

Exactly! Well said. I think that's what I said before we got sidetracked from our original topic, and then got sidetracked from the second topic...

[Orb]

Originally Posted by tintivilus

Yes, sure we're digressing, but it's fun



I think we might be suffering from differing assumptions about the experimental apparatus... the issue I took was with this statement in particular:



Are you talking about reducing the delta-V between the intake and output of the IC? The more I read this, the more it sounds like blowing air faster through an IC makes it hotter, which I just can't fathom based on ideal gas law.

If your IC is cooling the charge air (as it should be) the volume entering the IC should be greater than the volume leaving the IC (since reduction of temp yields reduction of volume). This is plain enough. If you increase the velocity of air at the intake (pushing greater volume in a given period of time) then the air at the output will probably be warmer and therefore at higher pressure than before due to transferring less of its energy to the IC... and is this the point you were trying to make that I just misunderstood?

I really don't recall enough of my thermodynamics to judge whether the increase in delta-T will speed up heat transfer enough to cancel out the reduced transfer time due to increased velocity through the cooler. Could any ME's out there chime in on that?

You gut feeling is right. So much physics have been missed here that it is not worth getting into this. ilia comments seem to on the right track but increasing velocity will not increase pressure. I will use his example. I heat a can and the pressure increases. I vent the heated can and velocity increase while pressure decrease…makes sense I hope.

If anyone is taking this discussion further then start by looking at ALL the properties of this two phase gas.

Orb