STP (was atmosphere and compressor maps -read'n 'riting & 'ritmatic)

[Burl Vibert]

Weird, there's a parallel discussion on another German marque
list I'm on.  As I  mentioned there, 1 Bar has nothing to do with
standard atmospheric pressure, it is just coincidentally close at
1 ATM= 1.01325 Bar.  1 bar is based on newtons per square meter,
1 newton per square meter also equals 1 pascal.  1000 pascal, or
1 kilopascal is 1 Bar.

A newton is the force required to accelerate 1 kilogram 1
meter/s2, which is coincidentally almost exactly 1/10th the
acceleration due to gravity, but not quite, it's 1/9.80665 the
acceleration due to gravity, just another
coincidence.
  
A meter is defined as 1/299 792 458 the distance light travels in
a vacuum
in one second. A kilogram is equal to the mass of "The kilogram"
which is a chunk of platinum-iridium alloy kept in a vault
somewhere outside of Paris. One kilometer was originally supposed
to be 1/10,000,000 the distance from the Equator to the North
Pole and one kilogram was the weight of one liter of pure water.
These values were later found to not be quite accurate so instead
of changing the value of the units the definition of the units
was changed.

In US units standard air is defined as air at a temperature of 68
°F, a pressure of 14.70 psia and a relative humidity of 36 per
cent (0.0750 density) as per A.S.M.E.

So, while atmospheric pressure is affected by temperature, 1 ATM
is always 1 ATM regardless of temperature, that's why it's a
standard pressure. 

My mandatory Audi content is that AFAIK the boost guage in my
5000 is an absolute pressure gauge.

Anyone else want some useless facts? 


Burl Vibert
1987 5kcstq
Kingston, Ontario



Dan Masi wrote:

> > > >Standard air temperature is considered 59 Degrees @
> > > >29.235 inches Hg. If my memory serves me correctly.
> > >
> > > That sounds like a strange "standard temperature" to a
> > chemist's ear.
> > > Although standard conditions in use for turbo compressor
> > calculations
> > > might be different, the standard temp that's defined by
> > international
> > > convention for gas-property calculations is 0 degrees C (32 F).
> >
> > STP is 0C and 1 atm. Sources below.
> 
> Apparently, there's confusion about the term "standard".  Different
> industries seem to use different standards when discussing gas properties
> (e.g. the natural gas industry using 1atm/60F as their standard).
> A quick web search shows plenty of counterexamples to the 0C / 1atm usage.
> For just a couple of examples, try this first-year chem text, which uses
> 25C / 1 bar:
> http://www.chem.ualberta.ca/courses/plambeck/p101/p01066.htm
> 
> or look at STP conditions for nitrogen from this online periodic table
> reference,
> which uses 20C / 1 atm:
> 
> http://klbproductions.com/yogi/periodic/N.html
> 
> -dan