Seems to me that a tempering valve (mixes cold & hot water to lower the temperature for things like showers) would be an easy way to implement a bypass to control coolant temperature entering the engine.

The WAI debate is a little off topic, but it's interesting.

Wait a sec, shouldn't the thermostat valve be able to control the temp? Is it that the valve opens at a suboptimal temp? Or has a slow response time or too much hysteresis or isn't accurate or something?

Viscosity of the fluid does not mean the example is flawed. Air and milkshake are both fluids, so the same principles apply. In fact, he is correct- by creating a lower pressure in his mouth (i.e. a slight vacuum), the fluid is pushed *by the atmosphere* up through the straw. If you simultaneously sucked through the straw, and created a vacuum above the milkshake in the glass, no milkshake would go through the straw because the atmosphere is no longer "pushing".

In reality, the words pushing and pulling are interchangeable (although technically you are correct in the sense that fluids can only be pushed, not pulled). A fluid will move whenever there is a pressure difference- whether it is cause by one side being above atmospheric pressure, or the other side being below atmospheric pressure, (or both), is irrelevant. The higher the pressure difference the higher the flow rate. (Obviously a higher viscosity fluid like milkshake will flow more slowly than a lower viscosity fluid like air with the same pressure difference). In other words if you have a pipe, and you have 200 PSI at one end and 100 PSI at the other end, you'll have the exact same flow (given the same viscosity, pipe diameter, pipe length, etc.) if you have 100 PSI at one end and 0 PSI at the other end.

And as mentioned previously, the ONLY time you want cold air is for maximum HP (trying to cram as much air/fuel in the cylinder as possible). For all other driving conditions, hotter air (and fuel) will combust more completely and efficiently. That's true with pretty much any chemical reaction. More combustion =more power from the same amount of fuel and fewer unburnt HCs.

There are plenty of users on this forum who have proven that warm-air intakes (WAIs) have helped them.

You are right that you could reach a point of diminishing returns if you encounter knock retard. But for "economical" driving you'll never see KR. KR is typically only encountered during transitional situations (i.e. upshift / heavy throttle) and quick throttle position changes.

-BC

While strictly true, the practical effects can vary a lot with the properties of the fluid. Exaggerating a particular effect by reference to a more viscous fluid can be very useful for illustration purposes, which I'm pretty sure was the intention.

Same with thinking in terms of cold or heat transfer, in most circumstances (HVAC engineering uses the term "coolth" sometimes as an analog to heat). Or positive charge carriers or negative ones for that matter.

Your example is still flawed. A brisk run is akin to driving 100+ mph. I highly doubt the group here is interested in high speed, they are interested in cruising along in the right lane while fuel guzzling drivers zip by.

How about breathing through the same coffee stirrer while walking down the street?

See, the problem is a coffee stirrer will never be able to provide enough volume of a runner however. In the same way an engine at 1/4 open throttle can supply the volume of air for 100+ mph. However, it's more than enough for cruising.


Viscosity makes all the difference. If it didn't, why do people swith to a thinner motor oil like 0W20 from a thicker oil like say 10W40?

I wouldn't go from 10w40 to 0w20, but I have switched cars from 10w40 to 5w30.

-Jay

While having some insomnia last night I dug out my college fluid dynamics textbook and looked at the reduced air resistance theory for a WAI performance increase. Unfortunately, I'd need to know the exact geometry to be able to do anything detailed (assuming flow in a duct is not going to cut it). Then I'd probably need to computer model it (yeah, right - be easier for me to do empirical tests). While the valve will be open more, more air is required, so you have two competing effects. If the transition were quite sharp with a very nearly closed valve (so driving at low power levels), I would think the the change in resistance could be very significant. The difference between pretty far open (higher power levels) and slightly more than pretty far open would be much less.

So basically I didn't learn squat that helps settle anything. Helped me back to sleep though.

Well, if you can't do the theory research, might as well do applied research...right? :)

That reminds me of something from college. One of our class mates (an engineer) had his girlfriend leave him. He joked that at least she didn't dump him for a physicist. We replied that maybe she wanted more theory and less "hands on". :P

So are you saying that the laws of fluid dynamics apply only to fluids of certain viscosities?

-BC