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#1
05-14-2006, 10:56 PM
 Liow Guest Posts: n/a
Different between Nm3/h = m3/h ?

Hi,I'm newbie here,
need some help from all bros here, Thank you very much.

Can anybody explain to me different between Nm3/h and m3/h ?
This is for air compressor capacity requirement and how about
convert to litre/min ?

Thank You.
#2
05-15-2006, 04:34 AM
 Robert Fogt Administrator Join Date: Dec 2005 Location: Seattle, WA Posts: 3,449 Rep Power: 13
Re: Different between Nm3/h = m3/h ?

The N stands for Normal. It means it was measured at standard temperature and pressure.

Because the volume of gasses change with temperature or pressure, it is necessary to specify the temperature and pressure the flow rate was measured at.

Standard pressure is 1 atmosphere. Standard temperature varies between industries, usually 0 ºC or 20 ºC.

In the case of air compressors, I do not think it will matter much. Just use m³/hr instead of Nm³/hr. You can convert to liter/minute on the flow rate conversion page.
#3
07-31-2006, 01:31 AM
 Unregistered Guest Posts: n/a
Re: Different between Nm3/h = m3/h ?

Hi
can you please give me the mathematical relation between Nm3/mn and Sm3/mn for compressed
thanks
my email is
cghediri@yahoo.com
#4
07-31-2006, 10:33 AM
 Robert Fogt Administrator Join Date: Dec 2005 Location: Seattle, WA Posts: 3,449 Rep Power: 13
Re: Different between Nm3/h = m3/h ?

N is metric normal temperature and pressure
S is standard temperature and pressure

I do not know if they differ at all. The standard temperature and pressure differs between industries, and it may be that Normal and Standard use the same temperature for your industry. Standard temperature is usually either 0ºC or 20ºC, and standard pressure is usually 1 atmosphere.

If standard and normal do use different temperatures, then the relationship would be according to the ideal gas law. PV = nRT
#5
02-09-2007, 02:21 AM
 Unregistered Guest Posts: n/a
Re: Different between Nm3/h = m3/h ?

The difference between Nm3/h and m3/h for compressor is very important because the first one correspond to standard conditions (1 bar and 20°C), where the density of the air is 1.2060 kg/m3. m3/h usually correspond to the flow at pressure conditions (7 bar and 60°C), where the density of the air is 8.3934 kg/m3.

As the characteristics of the compressor correspond to standard conditions, you have to take care that X flow at pressure conditions correspond to Y flow at normal conditions. It means:
Y (m3/s) = X (m/s)*(8.3934/1.2060) = X*6.9597.

regards

Carlos Fuenzalida
(Chile)
#6
12-13-2007, 02:03 AM
 Vacuum Engineer Guest Posts: n/a
Re: Different between Nm3/h = m3/h ?

Nm3/hr - Normal Metres Cubed per Hour
This is at a Temp of 0 deg C and 1013mbarA

Sm3/hr - Standard Metres cubed per hour
This is an old throw back from SCFM and based on 60 Deg F and Atmospheric pressure..............i.e. 1013 mbarA and 15.6 Deg C

Am3/hr - Actual Metres cubed per hour
As it says "Actual" at the temperature and pressure conditions stated.

To convert Nm3/hr to Sm3/hr it's a ratio of the absolute temperatures -
(The difference between 0 and 15.5 deg C)

10 Nm3/hr *(15.6+273)/ (0+273) = 10.57 Sm3/hr

Where -273 is absolute zero on the temperature scale.

To convert either of the above to Am3/hr or m3/hr (as normally written)
you need to convert both the temperature and pressure ratios

10 Nm3/hr ..... To Am3/hr at 20 deg C and +2 bar G (Two bar above atmospheric)

10 Nm3/hr *(20+273)/ (0+273)*(1013/1013+2000) = 3.6 Am3/hr

A way to think of the above is:
You heated the volume to start with to 20 degC .... It therefore it got bigger.....Then you squeezed it at a higher pressure...It shrank

Just remember to convert using the absolute Temperatures and Pressures and you can't go wrong
#7
02-01-2008, 11:18 PM
 Unregistered Guest Posts: n/a
Re: Different between Nm3/h = m3/h ?

Nm3/h is a mass unit.m3/h is a volume unit. With Nm3/h you will always be able to relate to a beginning ie 0C.
#8
04-11-2008, 05:01 AM
 Unregistered Guest Posts: n/a
Re: Different between Nm3/h

What is the conversion factor between Nm3/h and KW/h
#9
08-16-2008, 09:55 PM
 Unregistered Guest Posts: n/a
Re: Different between Nm3/h = m3/h ?

I think that difference between Nm3/h and kW/h is another question. "N" in the initial question of this topic means "Normal" for "Normal conditions". But I guess in your question "N" means Newton.

To understand why your question has not the same meaning you can wonder about the meaning of the unit : here Nm3/h and m3/h are both to count the flow. (a certain volume by a certain time). But kW is a power and kW/h is a power consumption. A power consumption has generally not the same meaning than a flow.

The first thing you have to do to convert an unit into another is to mind in international unit.

SI base units[9] Name Symbol Quantity
metre m length
kilogram kg mass
second s time
ampere A electric current
kelvin K thermodynamic temperature
mole mol amount of substance
candela cd luminous intensity

Candela is less used, but the other are very important.
You can convert any unit to a certain relation binding these base units.
To do this, you have to use the physical relations.

In your question you have first to detect what is not base units and to v=convert them
Newton (N) is a quantity of strengh, so you know the base physical relation that P=mg (here m means mass!)
P is expressed in N, m in kilogram, g in m.s-2 (acceleration)
So you can convert N in kg.m/s2 base units

W is Watt, it is a power. A power is the work during a certain time and the work is strengh needed to act on a certain distance.
Work is logically expressed in N.m.
So W is equivalent to N.m/s
As seen previously N is equivalent to kg.m/s2
So W is equivalent to kg.m2/s3 in base units of international system

you know 1k= 1000
and 1h= 3600s

So kW/h <=> (1000/3600) * kg.m2/s4 (A)

Then you can convert the other unit :

Nm3/h <=> (1/3600) * kg.m4/s3 (B)

So you can see that (A) and (B) have not common base units. That means their is no relation to convert Nm3/h to kW/h in the classical physic.

If you have written a phycial equation where on term is express in (A) unit and the other in (B) unit, we call this unhomogeneous relation it says false in term of classical physic. You can understand intuitively that it is very hard here to convert /s into m2

Moreover, one thing very important : when you use the method of conversion I have given you, pay attention that the physic equations you use to convert are applicable in the case you are studying. For example if you are not in an inertial reference frame, the expression of weight would change.

If you have any question about these explanations : derbouc@yahoo.fr

Lionel
#10
08-29-2008, 11:10 AM
Re: Different between Nm3/h = m3/h ?

Quote:
 Originally Posted by Unregistered Hi can you please give me the mathematical relation between Nm3/mn and Sm3/mn for compressed thanks my email is cghediri@yahoo.com
Dear friend,
Nm3/Min is "Volumetric flow at normal temperature & pressure conditions". Normal temperature & pressure differ for company to company. Most used values are 1atm for pressure and 15.5 C or 288.5K for temperature.
Sdm3/min is "Volumetric flow at standard temperature & pressure conditions"
Standard temperature pressure conditions are standard valve and used same all over the world. For temperaure= 0 C or 273K and for pressure = 1atm.

Why we use them instead of simple m3/min?

The simple answer is to make calculations easy. e.g. we are compressing 100 Nm3/min air from 1atm to 50 atm pressure then the volumetric flow through the compressor will remains same in Nm3/min as we have clearly defined its temp and pressure conditions for volume calculations.

Simple relations b/w Sm3/min and Nm3/min:

Use modified form of ideal gas equation as given below,

(P1V1)/(T1) = (P2V2)/(T2)

Here,

P1 = Pressure at normal conditions i.e. 1atm
T1 = Temperature at normal conditions i.e. 288.5K
V1 = volume at normal conditions in m3/min
P2 = Pressure at standard conditions i.e. 1atm
T2 = Temperature at standard conditions i.e. 273K
V2 = volume at Standard conditions in m3/min

OR

For more accurate calculations use following relations,

(P1V1)/(T1Z1) = (P2V2)/(T2Z2)

Here Z is compressibility factor at operating temperature and pressure conditions. Available in literature for most of gases at different temperature and pressures.

I hope it may resolve your most of issues regarding Standard and normal volumetric flows. If you have any quarry you may mail me at

Regards,

Process Engineer

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