Normal cubic meter vs. Standard cubic meter ?
Bonehead
Milton R. Beychok
I am quite familiar with the normal cubic meter but I must confess that your query is the first time I have heard of a standard cubic meter. As for the background of why there are two different metric expression for gas volumes, I have no clue.
Milton Beychok
(Visit me at http://www.air-dispersion.com)
__________________________________________________
Bonehead wrote:
Hi experts, A colleague and I are having a slight difference in opinion regarding how an amount of gas can be specified other than by weight, i.e. by "normalised volumes". To the best of my knowledge there are two different "normalised" volumes : the 'standard' cubic meter and the 'normal' cubic meter : a) standard cubic meter : 1Sm³ = amount of gas present in a volume of 1m³ at 15°C & 980.6mbar (1kgf/cm²)b) normal cubic meter : 1Nm³ = amount of gas present in a volume of 1m³ at 0°C & 1013 mbar (atmospheric pressure) For an ideal gas 1Nm³ = 1.09 x 1Sm³, the Sm³ typically used for commercial purposes because one can sell more for the same amount of molecules :). Does anyone know the background / history of why there are two different measures of gas-volume in use and how this came about ? Thanks, Bonehead
Kelvin Hales
> From: "Bonehead" <rep...@news.group>
> Newsgroups: sci.engr.chem,sci.engr,sci.engr.mech
> Subject: Normal cubic meter vs. Standard cubic meter ?
> Date: Wed, 30 Jun 1999 10:21:40 +0200
>
> Hi experts,
>
> A colleague and I are having a slight
> difference in opinion regarding how an amount of gas can be
> specified other than by weight, i.e. by "normalised volumes". To the
> best of my knowledge there are two different "normalised" volumes :
> the 'standard' cubic meter and the 'normal' cubic meter :
I can't find any references here to the history of the two measures;
but you should be aware that both of these are measures are in fact
measures of mass; since they effectively define the density of the gas
at the stated conditions. For example, a gas flow expressed as so many
'standard' or 'normal' cubic meter per unit time is actually an
expression of mass flow, by another name.
I've found from experience that few people remember the definitions,
some use the terms interchangeably and there is always argument about
the precise reference conditions. I've therefore found it safest to
avoid using these terms completely and always state the reference
conditions explicitly and require others to do so as well.
Note also that 'weight' is a measure of the force of attraction of the
earth on a body; hence the weight of a given mass can vary
substantially at different places on the earth (enough to be of
interest in instrument calibration and high-accuracy; e.g. fiscal
metering, applications).
Kelvin B. Hales
Kelvin Hales Associates Limited - Consulting Process Control Engineers
Egham, Surrey, England, TW20 9NB
E-mail: kha...@khales.cix.co.uk
http://www.mathworks.com/connections/khace.shtml
http://www.mathworks.com/connections/mltiflsh.shtml
Bonehead
Ivar Staale Ertesvaag
In article <7lck5k$j...@netnews1.apci.com>, "Bonehead" <rep...@news.group> writes:
|>
|>
|>Hi experts,
|>
|>how an amount of gas can be specified other than by weight, i.e. by =
|>"normalised volumes". To the best of my knowledge there are two =
|>different "normalised" volumes : the 'standard' cubic meter and the =
|>'normal' cubic meter :
|>
|>a) standard cubic meter : 1Sm=B3 =3D amount of gas present in a volume =
|>of 1m=B3 at 15=B0C & 980.6mbar (1kgf/cm=B2)
|>b) normal cubic meter : 1Nm=B3 =3D amount of gas present in a volume of =
|>1m=B3 at 0=B0C & 1013 mbar (atmospheric pressure)
|>
The Standard cubic meter is an international standard:
It is defined at 15 deg.C (288.15 K) and
101325 Pa (1 standard atmosphere, 1 atm).
This is the definition of Standard reference conditions for natural gas
(ISO 13443:1996) and for measuring petroleum gases and liquids
(ISO 5024:1976).
Normal cubic meter is defined at 0 deg.C and 101325 Pa (1 atm).
This definition has a long tradition in Germany and Scandinavia.
I guess it can be found in German standards (DIN) and
textbooks, either present or former issues.
Notice that Thermodynamics textbooks usually refer to
Standard reference conditions at 25 deg.C (298.15 K) and
101325 Pa.
These are convenient conditions for a laboratory.
There are even more definitions, e.g. in English units.
Some of these are described in ISO 13443:1996.
|>For an ideal gas 1Nm=B3 =3D 1.09 x 1Sm=B3, the Sm=B3 typically used for =
|>commercial purposes because one can sell more for the same amount of =
|>molecules :).
The Standard reference conditions is perhaps used because it
is an international standard?
|>
|>Does anyone know the background / history of why there are two different =
|>measures of gas-volume in use and how this came about ?
Different fields of usage, different system of measurements,
etc.
|>
|>Thanks,
|>
|>Bonehead
--
Ivar Ertesvåg
Department of Mechanics, Thermodynamics and Fluid dynamics
Norwegian University of Science and Technology
Trondheim, Norway
email: Ivar.S....@mtf.ntnu.no
Paul D Altpeter
nitrogen, argon, etc) in the US, "standard" temperature is 70°F, about 2%
difference from the petrochemical/refining "standard" of 60°F. It seems
that "standard" is anything but. It pays to be sure this is defined in any
contractual specifications.
Milton R. Beychok wrote in message <3779E072...@home.com>...
You may be interested to know that the petroleum refining industry and
the natural gas industry in the United States almost universally use the
Standard Cubic Foot (SCF) to specifiy volumes, and 1 SCF is defined as the
amount of gas present in a volume of 1 cubic foot at 60 degrees F and 1
atmosphere.
I am quite familiar with the normal cubic meter but I must confess that
your query is the first time I have heard of a standard cubic meter. As for
the background of why there are two different metric expression for gas
volumes, I have no clue.
Milton Beychok
(Visit me at http://www.air-dispersion.com)
__________________________________________________
Bonehead wrote:
Hi experts, A colleague and I are having a slight difference in
opinion regarding how an amount of gas can be specified other than by
weight, i.e. by "normalised volumes". To the best of my knowledge there are
two different "normalised" volumes : the 'standard' cubic meter and the
'normal' cubic meter : a) standard cubic meter : 1Smł = amount of gas
present in a volume of 1mł at 15°C & 980.6mbar (1kgf/cm˛)b) normal cubic
meter : 1Nmł = amount of gas present in a volume of 1mł at 0°C & 1013 mbar
(atmospheric pressure) For an ideal gas 1Nmł = 1.09 x 1Smł, the Smł
typically used for commercial purposes because one can sell more for the
same amount of molecules :). Does anyone know the background / history of
why there are two different measures of gas-volume in use and how this came
about ? Thanks, Bonehead
JDW
control industry that standard was 72F and 1 atm.
Paul D Altpeter <ALTP...@apci.com> wrote in message
news:7lda25$s...@netnews1.apci.com...
rto...@oanet.com
>It is defined at 15 deg.C (288.15 K) and
>101325 Pa (1 standard atmosphere, 1 atm).
>This is the definition of Standard reference conditions for natural gas
>(ISO 13443:1996) and for measuring petroleum gases and liquids
>(ISO 5024:1976).
>
>Normal cubic meter is defined at 0 deg.C and 101325 Pa (1 atm).
>This definition has a long tradition in Germany and Scandinavia.
>I guess it can be found in German standards (DIN) and
>textbooks, either present or former issues.
>
>
>Notice that Thermodynamics textbooks usually refer to
>Standard reference conditions at 25 deg.C (298.15 K) and
>101325 Pa.
>These are convenient conditions for a laboratory.
>
>
>There are even more definitions, e.g. in English units.
>Some of these are described in ISO 13443:1996.
>
>
>|>For an ideal gas 1Nm=B3 =3D 1.09 x 1Sm=B3, the Sm=B3 typically used for =
>|>commercial purposes because one can sell more for the same amount of =
>|>molecules :).
>
>The Standard reference conditions is perhaps used because it
>is an international standard?
>
>
>|>
>|>measures of gas-volume in use and how this came about ?
>
>etc.
>
>
As long as Normal always refers to 0 deg C, as in NTP, etc, and as in
Normalen (as in DIN, meaning a standard), then it really doesn't
matter what STP means to different industries. We should all start to
talk Normal and mean the same thing.
Ivar Staale Ertesvaag
In article <377aee1f...@news.oanet.com>, rto...@oanet.com
comments to:
First, DIN is German, and the same word does not neccessarily
have identical meanings in different languages.
DIN= Deutche Industrie Norm(en) (the -en is plural)
Norm means standard, pattern
normal means more like 'usual'
Do you _know_ that 'Normal always refers to 0 deg C'?
(I do not know about any exceptions, but this does not mean
that there are no).
I agree that we should use the same terminology, and agree upon
it usage.
France, Germany, Norway, etc. have used the international metric
system (today the SI) for more than a century.
Americans are still buying gallons (i.e. american) of gasoline,
driving in miles (i.e. English miles) per hour,
using feet and inches, puonds, BTUs, etc.
--
Ivar Ertesvåg
Trondheim, Noreg/Norway
epost/email: Ivar.S....@mtf.ntnu.no
George Randall
of SI. Your reference to use of SI in Norway must be referring to
scientists, is that correct? Or does the "man on the street" in
Trondheim come outside in January and exclaim, "Oh, it's down to 250
K! I had better button my coat!"
Wolfgang HEES
>
> Being a user of US gallons and pounds, I continue wondering about use
> of SI. Your reference to use of SI in Norway must be referring to
> scientists, is that correct? Or does the "man on the street" in
> Trondheim come outside in January and exclaim, "Oh, it's down to 250
> K! I had better button my coat!"
The men and women on the streets of Trondheim and the rest of
(continental) Europe use a unit for temperature which is called
'degree Celsius'. It relates to the SI unit Kelvin through the
rather simple equation T(K) = T(deg C) - 273.15
(whereas some other people use Fahrenheit (named after a German
scientist G.D. Fahrenheit) which relates to Kelvin through:
T(K) = (5/9 *(T(deg F)-32) - 273.15 ... not pretty !)
What the users of non-SI and non-SI-related units mostly ignore,
is the fact that SI units (and most of the SI-related units) can
be easily calculated with.
You won't get something like 3/16 perches * 7/8 bushels in SI.
By the way, did you know that the US made the SI legal in 1866
(yes, eighteensixtysix) and that they've signed the International
Metric Convention in 1875 ?
It's been a while, since.
Wolfgang
==============================
wolfga...@cern.ch
http://nicewww.cern.ch/~hees
==============================
Milton R. Beychok
Yes, the United States is perhaps being stubborn about not using the metric
system. That being acknowledged, it should be mentioned that there are many
differences between the SI system and the metric system as used in Europe.
As already pointed out, degrees Celsius are commonly used in Europe rather
than using degrees Kelvin. Here are just a *few* other differences:
(1) Heat exchangers and fired heaters in Europe are usually rated in
kilocalories rather than joules or kilojoules.
(2) Heats of vaporization are very often expressed as calories or
kilocalories per kilogram rather than joules or kilojoules per kilogram.
(3) Pressures are usually expressed as atmospheres, bars, or kilograms per
square centimeter rather than Pascals.
(4) Wine and gasoline are sold as litres rather than cubic decimetres.
(5) Land areas are often expressed in hectares rather than square metres
I suspect that the "man/woman in the street" or the "engineer in the
street" would have a very difficult time in using the pure SI system
whether he/she is European or American.
Milton Beychok
(Visit me at http://www.air-dispersion.com>
________________________________________________________
Lance Hill
use of engineers, chemists and physicists. We had an informal design
review that, looking back, was hilarious.
Engineers used deg F, psia & lbm/sec
Chemists used deg C, torr & moles/sec
Physicists used deg K, Pascals & moles/sec
Nobody understood what the hell anybody else was talking about!
Lance
George Randall <gran...@nospam.mediaone.net> wrote...
Ivar Staale Ertesvaag
In article <377BA4A4...@home.com>, "Milton R. Beychok" <mbey...@home.com> writes:
First, I will answer the question directed to me
(moved here from below):
|>> > Being a user of US gallons and pounds, I continue wondering about use
|>> > of SI. Your reference to use of SI in Norway must be referring to
|>> > scientists, is that correct? Or does the "man on the street" in
|>> > Trondheim come outside in January and exclaim, "Oh, it's down to 250
|>> > K! I had better button my coat!"
|>>
The "man in the street" in Trondheim follows the definition in
ISO 31-4 No. 4-2, (cf. IS0 31-0 Sec.2.3.2.2, Table 2) and uses the
SI unit "degree Celcius". (Kelvin is the _basic_ SI unit.)
Furthermore, If you ask him how wide the street is, ho fast his
car runs, and how much gasoline it uses,
he will answer in meters, kilometer per hour and litre per km
(or rather litre per 10 km, which has a numerical value is about 1).
This is in accordance with the SI (hour and liter are "units that can
be used together with the SI"; see ISO 31-0 Sec.2.3.4 Table 5,
and ISO 31-1 No. 1-6.b).
If you ask the gas station about the energy content of gasoline,
diesel oil or fuel oil (yes, I have tried), they will open the big book
of specifications and give you a figure in kilojoule per kilogram. They
will also give you the density in kilogram per liter or kilogram per
cubic meter and the viscosity in Pascal seconds.
|>Dear Wolfgang:
|>
|>Yes, the United States is perhaps being stubborn about not using the metric
|>system. That being acknowledged, it should be mentioned that there are many
|>differences between the SI system and the metric system as used in Europe.
|>As already pointed out, degrees Celsius are commonly used in Europe rather
|>than using degrees Kelvin. Here are just a *few* other differences:
|>
degrees Celsius is a derived SI unit
|>(1) Heat exchangers and fired heaters in Europe are usually rated in
|>kilocalories rather than joules or kilojoules.
|>
Usually? Not in Norway, at least.
I can add that food is sold with energy content in kJ (but often with
kcal in parantheses), but never with mass in "pund" or "mark"
(With exception for imports from certain countries).
Cars are sold with power in kW (but sometimes with horsepowers in
parantheses).
|>(2) Heats of vaporization are very often expressed as calories or
|>kilocalories per kilogram rather than joules or kilojoules per kilogram.
|>
Not that I know about.
|>(3) Pressures are usually expressed as atmospheres, bars, or kilograms per
|>square centimeter rather than Pascals.
|>
1 bar = 10^5 Pa (see ISO 31-3 No. 3-15.a)
This gives you a numerical value of order unity.
1 atm is defined in the standards I referred for the Standard cubic meter
yes, to some extent kilograms per square centimeter is used
|>(4) Wine and gasoline are sold as litres rather than cubic decimetres.
|>
see above
|>(5) Land areas are often expressed in hectares rather than square metres
|>
hectar = hecta-ar = 100 a
hecta = 100 is an SI prefix
1 a = 100 m^2 is defined in ISO 31-1 No. 1-5.a
In Norway dekar = deka-ar = 10 a = 1000 m^2
is more frequently used.
deka (Eng.: deca) = 10 is an SI prefix
hectar and decar are convenient units between the square meter
and the square kilometer.
|>I suspect that the "man/woman in the street" or the "engineer in the
|>street" would have a very difficult time in using the pure SI system
|>whether he/she is European or American.
I think you are confusing the "SI system" to "SI basic units".
In Trondheim (Norway - and I think, most of Europe)
the "man/woman in the street" or the "engineer in the street"
has very few problems with the SI system.
Even the british are learning....
For the american... well. My favourite quotation on units is from
Francis W. Sears and Gerhard L. Salinger:
``Thermodynamics, kinetic theory, and statistical
thermodynamics,'' 3rd ed.,
Addison-Wesley, Reading, Massachusetts, 1975
p.234:
The numerical values of P, T, and s are given, in Fig.8-6, in
the archaic set of units still employed by mechanical engineers
in the United States. The unit of pressure is 1 pound-force per
square inch, the unit of energy is 1 Btu, and the unit of mass is
1 pound-mass. On the temperature axis, temperatures are expressed
in degrees Fahrenheit, but the unit of specific entropy is 1 Btu
per pound-mass, per rankine. It is little wonder that engineering
students in this country lose sight of the principles of
thermodynamics because of the welter of conversion factors involved
in numerical calculations.
|>
|>Milton Beychok
|>(Visit me at http://www.air-dispersion.com>
|>________________________________________________________
|>
|>Wolfgang HEES wrote:
|>
|>> George Randall wrote:
|>> >
|>> > Being a user of US gallons and pounds, I continue wondering about use
|>> > of SI. Your reference to use of SI in Norway must be referring to
|>> > scientists, is that correct? Or does the "man on the street" in
|>> > Trondheim come outside in January and exclaim, "Oh, it's down to 250
|>> > K! I had better button my coat!"
|>>
|>> The men and women on the streets of Trondheim and the rest of
|>> (continental) Europe use a unit for temperature which is called
|>> 'degree Celsius'. It relates to the SI unit Kelvin through the
|>> rather simple equation T(K) = T(deg C) - 273.15
|>> (whereas some other people use Fahrenheit (named after a German
|>> scientist G.D. Fahrenheit) which relates to Kelvin through:
|>> T(K) = (5/9 *(T(deg F)-32) - 273.15 ... not pretty !)
|>>
|>> What the users of non-SI and non-SI-related units mostly ignore,
|>> is the fact that SI units (and most of the SI-related units) can
|>> be easily calculated with.
|>> You won't get something like 3/16 perches * 7/8 bushels in SI.
|>>
|>> By the way, did you know that the US made the SI legal in 1866
|>> (yes, eighteensixtysix) and that they've signed the International
|>> Metric Convention in 1875 ?
|>>
|>> It's been a while, since.
|>>
|>> Wolfgang
|>>
|>> ==============================
|>> wolfga...@cern.ch
|>> http://nicewww.cern.ch/~hees
|>> ==============================
|>
|>
|>
|>
--
Kelvin Hales
forces me to rise to the challenge from this side of the Atlantic! So, here
are some more comments, based on that useful booklet: The International
System of Units, from The National Physical Laboratory, ISBN 0 11 887527.
In article <377BA4A4...@home.com>, Milton R. Beychok wrote:
> From: "Milton R. Beychok" <mbey...@home.com>
> Newsgroups: sci.engr.chem,sci.engr,sci.engr.mech
> Subject: Re: Normal cubic meter vs. Standard cubic meter ?
> Date: Thu, 01 Jul 1999 17:27:18 GMT
>
> Dear Wolfgang:
>
> Yes, the United States is perhaps being stubborn about not using the metric
> system. That being acknowledged, it should be mentioned that there are many
> differences between the SI system and the metric system as used in Europe.
> As already pointed out, degrees Celsius are commonly used in Europe rather
> than using degrees Kelvin. Here are just a *few* other differences:
Since the 13th CGPM (1967), Resolution 3, there has been no such thing as the
'degree Kelvin'; just the kelvin, and it was agreed that a temperature
interval may also be expressed in degree Celsius. The degree Celsius is equal
to the unit 'kelvin', but 'degree Celsius' is a special name in place of
'kelvin' for expressing Celsius temperature. A temperature interval or a
Celsius temperature difference can be expressed in degrees Celisus as well as
in kelvins.
> (1) Heat exchangers and fired heaters in Europe are usually rated in
> kilocalories rather than joules or kilojoules.
That's interesting. In my (albeit limited) experience they are rated in
megawatt (except,of course, when translating for discussion with vendors of
US origin)!
> (2) Heats of vaporization are very often expressed as calories or
> kilocalories per kilogram rather than joules or kilojoules per kilogram.
I don't recall ever having encountered anything other then kJ/kg in the last
20 years, except (again) in discussion with vendors of US origin.
> (3) Pressures are usually expressed as atmospheres, bars, or kilograms per
> square centimeter rather than Pascals.
Yes, the Pascal is indeed a useless unit for everyday use, because it gives
rise to huge numbers. I've just come off a project for Shell in which all
pressures had to be expressed in kPa! I had no 'feel' for any of the pressure
figures. I do, generally, prefer the 'bar', which is allowed under the SI
system. I've only encountered kg/cm^2 in a historical context (before
adoption of the SI system). You sometimes see it on old pressure gauges.
> (4) Wine and gasoline are sold as litres rather than cubic decimetres.
And why not? Resolution 6 of the 12th CGPM declared that the word 'litre' may
be employed as a special name for the cubic decimetre.
> (5) Land areas are often expressed in hectares rather than square metres
You've got me there! I must admit that anyone using the hectare (adopted by
the CIPM in 1879 to express agrarian areas) would have to translate into
square metre for me!
> I suspect that the "man/woman in the street" or the "engineer in the
> street" would have a very difficult time in using the pure SI system
> whether he/she is European or American.
I guess what you mean by 'pure' is the use of 'base' units; but since 1969
the name 'SI units' has been designated to refer to three classes: base
units, derived units and supplementary units (adopted in 1960). The SI system
is often understood (especially by its detractors) to comprise just the base
units, and therefore as not suitable for everyday use. In fact, it is a
system that has grown and adapted through intelligent adoption of derived and
supplementary units to reconcile and encompass both laboratory and everyday
use.
I grew up with imperial units (ft. lb. etc.), switched to the short-lived
metric (cgs) system (cm, gramme, second) in high-school and then moved onto
SI units at University and beyond. The old imperial system was charming and
quaint; but it was a real relief to leave behind all the baggage of
conflicting international definitions of pounds, gallons, etc. Don't forget
the 'international' bit of SI. Before SI there were multiple definitions of
common units between different industries in one country, not to mention
different definitions across international borders.
I'm for the simple life!
George Randall
it makes me wonder about what we were told in the US about 25 years
ago: The SI uses seconds, meters, kilograms, and Kelvins (plus some
electical units). I wonder if that strict version was not true at the
time, or if SI had to be modified to incorporate practical units, like
the degree Celcius, so that people would use it.
A thousand years from now (about 3.2 E+10 seconds), when nation-states
have withered away and 18th & 19th century events are a tiny footnote
in the history books, the French Revolution will live on embodied in
the SI. Wow!
George Randall
By the way, meters, kilograms, kilowatts, and even Kelvins are easy
for US engineers to deal with. But very, very few of us have ever
mastered a heat transfer coefficient in kJ/sec/M^2/K ...
iva...@energy.sintef.no (Ivar Staale Ertesvaag) wrote:
Rich Lemert
> For the american... well. My favourite quotation on units is from
> Francis W. Sears and Gerhard L. Salinger:
> ``Thermodynamics, kinetic theory, and statistical
> thermodynamics,'' 3rd ed.,
> Addison-Wesley, Reading, Massachusetts, 1975
>
> p.234:
>
> The numerical values of P, T, and s are given, in Fig.8-6, in
> the archaic set of units still employed by mechanical engineers
> in the United States. The unit of pressure is 1 pound-force per
> square inch, the unit of energy is 1 Btu, and the unit of mass is
> 1 pound-mass. On the temperature axis, temperatures are expressed
> in degrees Fahrenheit, but the unit of specific entropy is 1 Btu
> per pound-mass, per rankine. It is little wonder that engineering
> students in this country lose sight of the principles of
> thermodynamics because of the welter of conversion factors involved
> in numerical calculations.
>
Chemical engineering students in the US are becoming much more
familiar with SI - too familiar, in many instances. I've often seen
students take forever to understand the whole idea behind converting
units. However, once they've crossed that barrier they want to convert
everything into SI. They'll even go so far in some cases to convert a
problem like the following into SI to work it, then converting the answer
back into English units to report their answer:
"What is the force acting on a door 8 feet high by 3.5 feet wide
that results from a pressure of 1.0 psia?"
As for the remark about "mechanical engineers" in the quote, I
have always found it interesting how their 'R' (the ideal gas constant)
isn't, but instead changes with the gas. Someone explained the rationale
to me once, but it still seems like the hard way of going about things.
Rich Lemert
sterge
George Randall wrote in message <377cbfac....@news.ne.mediaone.net>...
>
>By the way, meters, kilograms, kilowatts, and even Kelvins are easy
>for US engineers to deal with. But very, very few of us have ever
>mastered a heat transfer coefficient in kJ/sec/M^2/K ...
>
Just multiply the Btu/hr/ft^2/F by 5...(5.7 would be better, but by 5 is
usually close enough)
Francisco Adriano Simoes
Jonathan. as wrote
>Trond, And now for a formula you can actually use!
>
>Energy = W x V(2)/451000
>
>Energy of bullet (Foot-Pounds) EQUALS Weight of bullet (in Grains) times
>Velocity Squared (in feet/second) divided by Constant (451000)
... the most hateful thing a professor can do to me is to give me a
formula with a conversion factor in it , that means I have to know the
right units for that precise formula.
I can only speak as a bioprocess engineering student in Portugal
(Europe). The most interesting thing about SI system is that some years
after we use some a formula if we know what we want (the units of the
variable of interest) we can do a kind of reverse engineering an get
back the right formula; and most important of all, we can be pretty sure
we're right.
Cheers,
Adriano Simões
___________________________________________________________________________________
Francisco Adriano Simões, biotechnology engineering student
at the University of Algarve (Portugal) (http://www.ualg.pt)
mailto:adriano...@usa.net
___________________________________________________________________________________
Jan Dirk Arnold
Rich Lemert schrieb:
snip
As for the remark about "mechanical engineers" in the quote, I
have always found it interesting how their 'R' (the ideal gas constant)
isn't, but instead changes with the gas. Someone explained the rationale
to me once, but it still seems like the hard way of going about things.Rich Lemert
snip
The reason of varying R's in thermodynamik calculations is that You divide the universal Gas-Konstant by the molecular mass of the gas You are fooling around with. As only the mass of a batch of substance (i.e. Gas) that You work with will be constant that makes sense... in a very roughshod way. It instantly gives You access to specific heat capacities that are easiser to get by than molar properties.
In the spirit of the discussion I would like to add that this gives
the lie to standardisation efforts. IMHO one could do it in private when
you know what You are doing, but keeping your units clean helps other people
understand what You are saying, so it is efficient to use standardized
units, that are laid down once and universally.
This is also what this discussion might lead to understanding: It's
no use to ask what the "man on the street" thinks, says, accepts and uses
as a unit for a measure. It is important that when people talk about
measures that each partner understands the other. Here standardisation
is important. Wheter the weather is good or bad in pascals or torr, psi
or bananas per flatfeet doesn't matter one whit.
Nevertheless it seems a good idea that increasing measures can be constructed
in a decimal scale, therefore obviating the need of several conversion
factors between measuring units of the same type. (there now, broke my
lance for the metric System, or rather SI)
Oh and by the way, the basic units of the SI are length (m), mass(kg),
Time (s) and....
the Mol (mol) (how do You say Stoffmenge in english ? :-))
Greets
Dirk
Jose E. Calderon,P.E.
Bonehead wrote in message <7lcud4$n...@netnews1.apci.com>...
Hi experts,A colleague and I are having a slight difference in opinion regarding how an amount of gas can be specified other than by weight, i.e. by "normalised volumes". To the best of my knowledge there are two different "normalised" volumes : the 'standard' cubic meter and the 'normal' cubic meter :
a) standard cubic meter : 1Sm³ = amount of gas present in a volume of 1m³ at 15°C & 980.6mbar (1kgf/cm²)b) normal cubic meter : 1Nm³ = amount of gas present in a volume of 1m³ at 0°C & 1013 mbar (atmospheric pressure)
For an ideal gas 1Nm³ = 1.09 x 1Sm³, the Sm³ typically used for commercial purposes because one can sell more for the same amount of molecules :).Does anyone know the background / history of why there are two different measures of gas-volume in use and how this came about ?Thanks,Bonehead
Milton R. Beychok
I believe that your two definitions:
1 Newton (N) = 1 kg m/s/s and 1 Pascal (Pa) = 1 N/m/m
would be better written as:
1 Newton (N) = 1 kg m/s^2 and 1 Pascal (Pa) = 1 N/m^2
Regards,
Milton Beychok
(Visit me at http:www.air-dispersion.com)
_______________________________________
Ivar Staale Ertesvaag wrote:
> In article <377cbfac....@news.ne.mediaone.net>, gran...@nospam.mediaone.net (George Randall) writes:
> |>I do appreciate the lesson about "derived" or non-basic SI units, but
> |>it makes me wonder about what we were told in the US about 25 years
> |>ago: The SI uses seconds, meters, kilograms, and Kelvins (plus some
> |>electical units). I wonder if that strict version was not true at the
> |>time, or if SI had to be modified to incorporate practical units, like
> |>the degree Celcius, so that people would use it.
>
> Most people (and most scientists, engineers, etc.) do not read the
> ISO standard. And also: As a student you were not expected to learn all
> aspects of thermodynamics (or any other subject), either.
>
> The system of basic SI units are extended by derived and
> supplementary units.
> These are combinations or functions of the basic units,
> e.g. 1 Hertz (Hz) = 1/s, 1 Newton (N) = 1 kg m/s/s,
> 1 Pascal (Pa) = 1 N/m/m, 1 Joule = 1 N m, etc.
> This is still SI units but not basic SI units
>
> The Kelvin, the second, and the meter are defined by a difference.
> In thermodynamics, we operate usually with differences.
> If you lock up in a table for properties of steam, the figure of
> internal energy in kJ/kg is not the absolute value, but the
> difference to the reference (usually saturated liquid at the
> triple point, 0.01 deg.C).
> Similarly, temperatures are usually a difference, and then
> 1 degree Celsius is another name of 1 Kelvin. However, they have
> different references. If you heat water by 5 K, you also heat water
> by 5 deg.C. Thus the Celsius degree is a derived SI unit.
>
> Also included in the SI-system is the decimal multipliers,
> like kilo-, mega-, milli-, micro-, etc.
>
> In addition, some units "can be used together with the SI units"
> e.g. liter = 1/1000 m^3, 1 d (= day+night = 24*60*60 s)
> You can say that these are defined for "practical reasons".
>
> Furthermore, the ISO standards defines some units based on the SI units.
> These are some "practical" units that are decimal multiples of the
> basic units, like 1 ar = 100 m^2 and 1 bar = 10^5 Pa;
> and "natural" units, e.g. nautical mile, 1 atm.
>
> |>
> |>A thousand years from now (about 3.2 E+10 seconds), when nation-states
> |>have withered away and 18th & 19th century events are a tiny footnote
> |>in the history books, the French Revolution will live on embodied in
> |>the SI. Wow!
> |>
> |>George Randall
> |>
> |>By the way, meters, kilograms, kilowatts, and even Kelvins are easy
> |>for US engineers to deal with. But very, very few of us have ever
> |>mastered a heat transfer coefficient in kJ/sec/M^2/K ...
> |>
> |>iva...@energy.sintef.no (Ivar Staale Ertesvaag) wrote:
> |>
> |>>The "man in the street" in Trondheim follows the definition in
> |>>ISO 31-4 No. 4-2, (cf. IS0 31-0 Sec.2.3.2.2, Table 2) and uses the
> |>>SI unit "degree Celcius". (Kelvin is the _basic_ SI unit.)
> |>>
> |>>Furthermore, If you ask him how wide the street is, ho fast his
> |>>car runs, and how much gasoline it uses,
> |>>he will answer in meters, kilometer per hour and litre per km
> |>>(or rather litre per 10 km, which has a numerical value is about 1).
> |>>This is in accordance with the SI (hour and liter are "units that can
> |>>be used together with the SI"; see ISO 31-0 Sec.2.3.4 Table 5,
> |>>and ISO 31-1 No. 1-6.b).
> |>>
> |>>If you ask the gas station about the energy content of gasoline,
> |>>diesel oil or fuel oil (yes, I have tried), they will open the big book
> |>>of specifications and give you a figure in kilojoule per kilogram. They
> |>>will also give you the density in kilogram per liter or kilogram per
> |>>cubic meter and the viscosity in Pascal seconds.
> |>>
> |>
> |>
>
Anand Sundararajan
you can be sure that everything (yes: EVERYTHING!) you mentioned is also valid for Germany
and the entire EC (except for - guess whom- the Brits!). I have to collect thermodynamic
data from various data bases, so consequently I am using American literature, as well. Can
anyone explain how to convert the unit "kcal/degF and lbs" found for the specific heat
capacity of a solid in Perry's Handbook for Chemical Engineers into a commonly used SI-Unit
without getting headache???!!!
Anand
George Jefferson
:anyone explain how to convert the unit "kcal/degF and lbs"
if a simple unit conversion gives you a headache maybe you are in the
wrong line of work.
--
george jefferson : geo...@sol1.lrsm.upenn.edu
to reply simply press "r"
-- I hate editing addresses more than I hate the spam!
Anand Sundararajan
> :Can
> :anyone explain how to convert the unit "kcal/degF and lbs"
> :without getting headache???!!!
>
> if a simple unit conversion gives you a headache maybe you are in the
> wrong line of work.
Have you ever tried to collect data and convert every item into SI-Units,
because the software you have to use is based only on SI-Units? No? Then
you do not seem to have worked with literature outside of the U.S.
Gerhild Schinagl
>:Can
>:anyone explain how to convert the unit "kcal/degF and lbs"
>:without getting headache???!!!
>
>if a simple unit conversion gives you a headache maybe you are in the
>wrong line of work.
No, we just don't carry around 100+ pages textbooks with conversion
factors like the average North American science student.
--
oo_oo_oo_oo_oo_oo_oo_oo_o DI Gerhild Schinagl o_oo_oo_oo_oo_oo_oo_oo
|__ Department of Internal Combustion Engines and Thermodynamics __|
|_ Graz University of Technology/ Austria _ Tel. ++43 316 873 7212_|
oo_oo_oo_oo_oo_oo_o http://fvkma.tu-graz.ac.at/ o_oo_oo_oo_oo_oo_oo
Joe
(Gerhild Schinagl) wrote:
> geo...@sol1.lrsm.upenn.edu ( George Jefferson ) wrote:
>
> >:Can
> >:anyone explain how to convert the unit "kcal/degF and lbs"
> >:without getting headache???!!!
> >
> >if a simple unit conversion gives you a headache maybe you are in the
> >wrong line of work.
>
> No, we just don't carry around 100+ pages textbooks with conversion
> factors like the average North American science student.
Carries in his head.
Also, this should read engineering student, unless perhaps we've found the
source of your problem. Scientists never use english units.
--
Joe
Gerhild Schinagl
>> No, we just don't carry around 100+ pages textbooks with conversion
>> factors like the average North American science student.
>
>Carries in his head.
Not those I know ;-)
>Also, this should read engineering student, unless perhaps we've found the
>source of your problem. Scientists never use english units.
Ah, yes, you're right for correcting me. They're engineering students.
(ex- by now).
Chad English
> (Gerhild Schinagl) wrote:
>> No, we just don't carry around 100+ pages textbooks with conversion
>> factors like the average North American science student.
>
> Carries in his head.
>
> source of your problem. Scientists never use english units.
As a Canadian engineering student who has to know both systems (officially
metric, but working with the U.S. so much we have to learn both), for
those I can't remember in my head I keep a CRC book, or use the very handy
OmniCon conversion software (http://www.execulink.com/~pjones).
Conversions are usually quite easy, it's just the conversion factors that
are difficult to remember.
The only hard ones are the unforgivable bastadrizations of correct units,
such as the kg-force (kg is a mass unit) or even the use of cubic meters
in this thread to indicate density (cubic meters is *properly* a volume
that is fixed, not dependent on temperature or substance). If people just
used the proper units all the time, it wouldn't be so hard on everybody.
(Yes, some units become long like kg*m/s/degreeK, or something like that,
but that just means defining a simplified unit name for *that*
combination of units.)
--
Chad English
ceng...@mae.carleton.ca
http://www.mae.carleton.ca/~cenglish
Rich Lemert
> > (Gerhild Schinagl) wrote:
> >> No, we just don't carry around 100+ pages textbooks with conversion
> >> factors like the average North American science student.
> >
> > Carries in his head.
> >
> > Also, this should read engineering student, unless perhaps we've found the
> > source of your problem. Scientists never use english units.
These days you don't carry around the book, you carry around your calculator.
Modern technical calculators like the HP48(?) have conversion factors built in.
Of course, if the students learn this before they learn how to properly convert
units by hand then they never really understand what they're doing and why.
This is not just a problem dealing with English units, either. They won't even
be able to recognize that kg-m/s^2 can be converted to ergs, etc.
Rich Lemert
Material Fellow
This is worth saying again.....
-------------------------------------------------------------------
I am always amazed that there is a massive ignorance of the basics of
units.... be it science or engineering.
Most treat them as some pesky piece of bureaucratic crap that gets in
their way of "Real Engineering" or "Real Science"... In fact the
holders of such opinions are sophisticated knowledge fakes.
------------------------------------------------------------------
Chad English wrote:
>
> In sci.engr Joe <do...@spam.net> wrote:
> > (Gerhild Schinagl) wrote:
> >> No, we just don't carry around 100+ pages textbooks with conversion
> >> factors like the average North American science student.
> >
> > Carries in his head.
> >
> > Also, this should read engineering student, unless perhaps we've found the
> > source of your problem. Scientists never use english units.
>
Chad English
> Hi Chad --
>
> This is worth saying again.....
> -------------------------------------------------------------------
>
> I am always amazed that there is a massive ignorance of the basics of
> units.... be it science or engineering.
>
> Most treat them as some pesky piece of bureaucratic crap that gets in
> their way of "Real Engineering" or "Real Science"... In fact the
> holders of such opinions are sophisticated knowledge fakes.
>
> ------------------------------------------------------------------
Well, I guess that's a good summary, though it seems a little vague. I'd
tend to agree. One's specialized units might be useful to them in that
specific field, but porting information between fields is where the
problem arises. Units are very important and that's why bastardization of
them is counterproductive. It makes it more confusing than less
confusing. But I can certainly understand why one would resist.