iT's FREE!

Psee said:A retired chemist that lives down the street says the secret to his great looking lawn is nitrogen. Is this same thing and how do you get it into the grass?

fertilizer provides nitrogen for the plants to grow on.

BWAHAHAH!

i knew this would get plopped here!

gobbers!

On the topic of inflating your tires. If you buy non-factory tires for your car, do you still go by the tire pressure recommended in the manual for the car? I inflated mine to what Toyota recommended, about 27 PSI, but when I press the sidewall there seems to be too much give, and they look a bit flat.
Als, do you need different pressure depending on the amount of weight you normally carry? Should the PSI of the front and rear tires be different due to the engine side being heavier?

frugalmcdoogle said:While MIT's statement:

'This shows that when you eliminate water, or in fact ANY other compound with a higher density (mole for mole, gaseous nitrogen has a lower density than water and even oxygen), you will get a lower coefficient in front of the temperature in the equation, thus you end up with a lower fluctuation in pressure.'

is technically accurate, his formula grossly exaggerates the effect of 'the water in tire effect' because it does not account for the physical limitation of mixing vapor water in nitrogen or air. Even at 120 F (hot tire!), having 100% humidity in the tire only amounts to having a saturation pressure (maximum partial pressure) of 1.69 psi, or about 5% of the total pressure of a 32 psi tire and about 3.5% of the mass of gas in the tire. This physical constraint is not reflected in is calculation and thus the contribution of the vapor is overstated.

His 'formula':
P=(p1)287T + (p2)455T ; Where (p1) is the density of the "dry" gas and (p2) is the density of water vapor.

He should have used some reasonable mass multipler (like for the conditions above):
PV= mgas287T+mvapor455T
=0.965mtotal*287+0.035*mtotal455T

P=0.965(p1)287T+0.035(p2)455T

Just keeping MIT honest...

There were no exaggerations, overstatements, or unreflected physical constraints. I would rightly assume that only the people who can recognize this "exaggeration" that you are talking about can also recognize the boundary limitations that the two variables p1 and p2 have. The limitations introduced by the saturation of water vapor are inherent these boundary limitations.

Your equation, although flawed because you should have either changed the labeling or factored something out because p1=p2 in your last form, can be somewhat of an acceptable form but severly limited to FLUID STATICS, moreover, fluid statics only with uniform distributions.

OTOH, my "exaggerated" form happens to be one of the STANDARD FORMS used in DIFFERENTIAL AND COMPUTATIONAL FLUID DYNAMICS. The numbers and equations are referenced and standard. Try using your form when the tire has rotational and translational motion with radially distributed density and temperatures.

In laymans terms, his equation can analize the "performance" benefits of a tire that is not moving, or rotating, without gravity, using GenChem concepts which work great for beakers that dont move, but makes no sense in a tire that does move ... while the one I mentioned is used for a moving, rotating tire, with non uniform density and temperature WHICH IS WHAT ACTUALLY HAPPENS WHEN YOU MOVE/ROTATE A TIRE. I do these computations for a living and the effects are compounded by movement and differential density and pressure variables.

If you think you are going to ::::w/ sarcasm:::: "foil my master plan to trick the masses of FW users" think again. I have better things to do. The only reason I brought up equations and numbers is because people dont like to listen to "because i said so" types of answers. But for the people that say I am exaggerating trying to trick people with numbers, heres my answer:

If its free, then it is to your benefit to use dry nitrogen to inflate yor tires. Why? BECAUSE I SAID SO!!

I guess my input is unappreciated here, so next time something comes up about a subject that I have studied and applied for many years, I'll remember to shut up so that the skeptics, psuedo-scientists, overconfident college GenChem slackers, and self-proclaimed Google.com doctorates can have the floor.

uh-oh - upgraded to wanker!

(a wanker with a degree is still just a wanker)

You don't need CFD to resonably calculate the gas temperature effects of a tire (rolling or not) at a given mean temperature, pressure, and gaseous composition.

Hi.

larrymoencurly said:More importantly, do you remember the episode of Alias where Sidney Bristow escapes by driving a car off a dock and crashing it in the ocean? She was able to evade capture by staying underwater and breathing air from the car's tires, something that would not have been possible if the tires had been installed by Costco.


totally!

whew - thank goodness sidney is ok.

sidney is really, really smart.
she has social skilly too!!!