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Participant

Join Date: Jun 2011
Posts: 2

Convert Nm^3 to kg/hr

06/26/2011 2:44 PM

I have Air flow in Nm^3/hr and oil flow in Kg/hr.

so as to compare them i need to convert them to same units for Furnace application.

I want to convert Nm^3/hr to kg/hr.

Nm^3.here "N" mean at normal conditions at 0 degre temp and at 1 atm pressure.

How do i convert the same and do i NEED TO TAKE ANY TEMPERATURE AND PRESSURE into consideration.

For example:

i want to conver the air flow =115 Nm^3/hr into Kg/Hr ?

kindly provide me the steps/formula for conversion.Reply as soon as possible.

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#1

Re: Convert Nm^3 to kg/hr

06/26/2011 2:46 PM
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#2

Re: Convert Nm^3 to kg/hr

06/26/2011 9:11 PM

I do not know why you want to do this, but the difference lies in the density of the air.

If you want to compare mass flow rates of the oil and the air, you must convert the volumetric flow rate of the air to a mass flow rate. First year engineering stuff.

The density of air at normal conditions is 1.204 kg/m3. Multiply the volumetric flow rate (Nm3/hr) by the normal air density (1.204 kg/m3), and you have your answer:

115 Nm3/hr x 1.204 kg/m3 = 138.46 kg/hr.

Could you be so kind as to tell us why such a simple calculation is so urgent that you could not do it yourself?

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#4
In reply to #2

Re: Convert Nm^3 to kg/hr

06/26/2011 10:31 PM

Perhaps it's due in tomorrow and "Sir" wont give an extension.

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#8
In reply to #4

Re: Convert Nm^3 to kg/hr

06/27/2011 12:05 AM

I hate homework questions as much as anyone. However, this did not seem as such.

In light of the question and my answer, kindly vote me a Good Answer!

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#9
In reply to #8

Re: Convert Nm^3 to kg/hr

06/27/2011 5:41 AM

No Sir, I can't give you GA, because it seem you answered in hurry and anger with OP and made it wrong. Density of air at NTP (at 0 deg C and 1 atm pressure) is 1.293 kg/Nm3. So, the right answer is

115 Nm3/hr x 1.293 kg/m3 = 148.7 kg/hr.

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#3

Re: Convert Nm^3 to kg/hr

06/26/2011 10:31 PM

It is a straight conversion, you do not need any pressure or temperature into consideration.

The calculation is:

115 Nm3/hr x 28.95 (MW of air) / 22.414 Nm3 = 148.5 kg/hr

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#11
In reply to #3

Re: Convert Nm^3 to kg/hr

06/27/2011 5:09 PM

Thanks alot for the reply.

You have cleared my confusion for the Temperature and pressure consideraations.

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#5

Re: Convert Nm^3 to kg/hr

06/26/2011 10:44 PM

In my official capacity as district pedant I'd like to point out that some of the symbols people are using are confusing (and wrong).

N means Newton (there's probably another symbol used to specify the particular temperature and pressure you mean), it's kg not Kg and I don't know what the MW stands for but it's not MegaWatt.

This is not being fussy, you're trying to clearly and unambiguously explain your thinking so you need to get the details right. Correct use of units, spelling and grammar says something about you as a person and people, perhaps unconsciously, do notice. (And yes, I've probably made a grammatical error in this post)

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#6
In reply to #5

Re: Convert Nm^3 to kg/hr

06/26/2011 11:15 PM

Science is in the details, good answer!

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#10
In reply to #5

Re: Convert Nm^3 to kg/hr

06/27/2011 9:30 AM

I agree that the symbols used can be confusing to those not familiar.

N is the common designation for "normal", which in this case stands for "standard temperature and pressure" or STP. Unfortunately, STP itself has various definitions.

MW stands for molecular weight, as any high school chemistry student can tell you.

Both of these symbols are very commonly used, and were used correctly in this case.

Saying that N "means" Newton is just as wrong as not defining N to begin with. Correcting Kg with kg is just being fussy.

I do agree that symbols should be defined, as they can mean many different things depending on the field, language and culture. However, in this case, the symbols used are very common when dealing with gases, and should be very familiar to anyone who could answer this question.

So the OP has asked a question using widely accepted symbols, which was clearly understood and has been answered. It probably is not important to him that you did not understand.

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#12
In reply to #10

Re: Convert Nm^3 to kg/hr

06/27/2011 5:21 PM

Assumptions in science are just plain wrong, unless you are an evil scientist!

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#7

Re: Convert Nm^3 to kg/hr

06/26/2011 11:53 PM

Multiply the volume flow rate ( m3/hr) by density( kg/m3) you will get mass flow rate.(kg/hr).

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#13

Re: Convert Nm^3 to kg/hr

06/27/2011 9:24 PM

We shouldn't prolong the continuation of misinterpretation of the definitions of STP and NTP condition, and the value of density at each of the different conditions.

NTP, Normal Temperature and Pressure is air at 20oC (293.15 K and 1 atm (101.325 kN / m2, 101.325 kPa, 30 inches Hg, 760 torr)
NTP dry air has a density of 1.204 kg / m3.

STP, Standard Temperature and Pressure is air at 0oC (273.15 K, and 1 atm (101.325 kN / m2, 101.325 kPa, 30 inches Hg, 760 torr)
STP dry air has a density of 1.292 kg / m3.

Standard sea level atmospheric pressure = 101 325 Pa
Air density, Kg / m3 = [1.2929 X 273.13 X (AP - ( SVP x RH ) / ( T + 273.13)] X 760
Where:
T = oC
AP = Absolute Pressure, mm of Hg

SVP = Saturation Vapour Pressure of air over water at temp T

RH = Relative Humidity (decimal)

and Mikerho, a GA

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#14
In reply to #13

Re: Convert Nm^3 to kg/hr

06/27/2011 10:46 PM

Isn't RH expressed in %? Great disambiguation btw.

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#15
In reply to #13

Re: Convert Nm^3 to kg/hr

06/28/2011 9:37 AM

Ahh, it would be simple if this were true. I have never heard NTP used here in the states, but Nm^3 is common.

STP is "defined" here in many different ways different ways: STP

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Users who posted comments:

AussieBob (1); ffej (2); gigaconcept.com (3); lyn (1); Mikerho (2); mrswamy (1); pritam (1); sv13 (1); Tad (2); thakkarmayank24 (1)

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