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Different between Nm3/h = m3/h ?

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  • 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
    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 C or 20 C.

    In the case of air compressors, I do not think it will matter much. Just use m/hr instead of Nm/hr. You can convert to liter/minute on the flow rate conversion page.

    Comment


    • #3
      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

      Comment


      • #4
        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 0C or 20C, 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

        Comment


        • #5
          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 20C), where the density of the air is 1.2060 kg/m3. m3/h usually correspond to the flow at pressure conditions (7 bar and 60C), 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)

          Comment


          • #6
            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

            Comment


            • #7
              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.

              Comment


              • #8
                Re: Different between Nm3/h

                What is the conversion factor between Nm3/h and KW/h

                Comment


                • #9
                  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.

                  But I will try to answer your question anyway :
                  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

                  Comment


                  • #10
                    Re: Different between Nm3/h = m3/h ?

                    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

                    adnan_hanif@ffc.com.pk

                    Regards,

                    Muhammad Adnan Hanif
                    Process Engineer

                    Comment


                    • #11
                      Re: Different between Nm3/h = m3/h ?

                      very simple:
                      If u want to convert from Nm3/hr to Sm3/hr: Multiply nm3/hr*1.091584.

                      If u want to convert from Sm3/hr to Nm3/hr: Multiply nm3/hr*0.9161.

                      regards

                      Syed Khaleelullah

                      Comment


                      • #12
                        Re: Different between Nm3/h = m3/h ?

                        Hello,

                        can someone please check my problem?

                        I have a flow rate of 708.4 Nm/hr of nitrogen at a temperature
                        of -39C and a pressure of 0.48MPa(g). It's molecular weight is
                        defined as 28.01 kg/kmol and it's density as 8.418 kg/m.

                        What I need is the calculation of 708.4 Nm/hr into kg/hr.

                        My equation was: 708.4Nm/h * 1/22.414 *28.01kg/kmol=885.26 kg/hr

                        Is that correct?

                        Comment


                        • #13
                          Re: Different between Nm3/h = m3/h ?

                          Originally posted by Lampost22 View Post
                          Hello,

                          can someone please check my problem?

                          I have a flow rate of 708.4 Nm/hr of nitrogen at a temperature
                          of -39C and a pressure of 0.48MPa(g). It's molecular weight is
                          defined as 28.01 kg/kmol and it's density as 8.418 kg/m.

                          What I need is the calculation of 708.4 Nm/hr into kg/hr.

                          My equation was: 708.4Nm/h * 1/22.414 *28.01kg/kmol=885.26 kg/hr

                          Is that correct?
                          It is correct provided that the volume has already been "adjusted" to volume at normal conditions, 0 C, 101.325 kPa.

                          If the volume were stated at measured (actual) temperature and pressure, the answer would be quite different. The density appears to be density at actual temperature and pressure.

                          Comment


                          • #14
                            Re: Different between Nm3/h = m3/h ?

                            Please explain how did you get the density of 8.3934 kg/m3 at 7 bar and 60 deg C.

                            Regards,

                            Charlie

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

                            Comment


                            • #15
                              compressor size

                              Dear Friends,

                              Could you please help me sizing the compressor needed if this data below are given.

                              Total air consumption : 500 Nm3/h
                              Site condition : 40 deg C , 500 Meter elevation and 45 % RH
                              Compressed air pressure needed : 8 bar

                              What is the volume flow rate needed in terms of actual m3/H , Nm3/H , standard m3/H, FAD
                              of the air compressor?

                              Regards,

                              Charlie

                              Comment

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