8 replies to this topic

[starter_2011]

Dear all,

We all express liquid flow rate in kg/h or m3/h.
If it is a gas we express in Nm3/h.

Why we are expressing steam in kg/cm2 i.e in terms of pressure not in terms of flowrate.
I understand that based on pressure its boiling point and enthalphy changes.I agree with that.

But my doubt is why we are expressing steam flow in pipes in kg.cm2 i.e in terms of pressure instead of flowrate.

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Thanks in advance.

[S.AHMAD]

1. We measure steam flowrate in kg/h for small flowrate of tph for bigger flowrate. The kg/cm² is the steam pressure, not the flowrate.
2. However, pressure can indirectly measure flowrate, depending on piping configuration of system
3. For example, you have fixed orifice plate downstream

Edited by S.AHMAD, 24 October 2011 - 02:43 AM.

[kkala]

As clarified by S.AHMAD, we measure mass flow rate in kg/h (or even kg/s). If you could bring the specific example, a better explanation might be given.
By the way, two clarifications related to kg/cm2 could be useful.
1. kg/cm2 does not precisely mean pressure. The former means mass per unit area, pressure is force per unit area. In the old technical (European) system of units, force was expressed in kilograms of force (not in Nt) written as kgr*, or kp (kilopond), of kgf, or even kg. That kg has so far survived, actually meaning weight of a mass of 1 kg. Hence 1 kg/cm2 pressure means 1 kgf/cm2.
2. Velocity in pipes = volumetric flow / pipe cross section, expressed as m3/s/m2 =m/s. Mass velocity is mass flow rate / pipe cross section, expressed as kg/s/m2, or even kg/cm2/s. The kg/cm2/s indicates mass flowrate per unit area of pipe cross section.

Edited by kkala, 24 October 2011 - 05:03 AM.

[starter_2011]

Dear Ahmed ,

Thank you for your response.

As you told pressure can indirectly measure flowrate,then pls tell me what will be the flowrate of 5kg/cm2 steam that is flowing through 1 inch pipe of 20 m long.

[starter_2011]

Dear kkala
thank you

[starter_2011]

dear all

Kindly share the complete details for designing a condenser.

[S.AHMAD]

1. As I have mentioned earlier, pressure can indirectly measure flowrate depending on the piping configuration
2. We need to know the downstream pressure (P₂)
3. If P₂ is less than about P₁/2, then use choke flow equation, otherwise use sub-critical flow equation
4. For example if the downstream unit is a steam stripper operated at 1 kg/cm², (upstream 5 kg/cm^₂) then use choke flow equation.
5. Deaerator operated below 1 barG, use sub-critical flow equation to estimate the venting steam

Edited by S.AHMAD, 24 October 2011 - 07:20 PM.

[nikhil.sharma]

Dear S Ahmad & KKala,

Thanks a lot. Your reply really cleared my doubt.

Thanks & Regards
Nikhil Sharma

[breizh]

This resource should support your query :


http://www.spiraxsar...sting-pipes.asp

note : select sizing on pressure drop

Breizh

Edited by breizh, 15 November 2011 - 01:29 AM.