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Thread: air flow rate measurements

  1. #1
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    air flow rate measurements

    ipt>
    how can i find the flow rate by calculations for a compressed air at 4 bar in a tank and its connected to a cylinder with half inch pipe, the air finally escape through the holes of dia 5 mm in ten in numbers on the cylinder. would you please help me to find , its urgent. please

  2. #2
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    What is the length of the half inch diameter pipe and are there any pipe fittings along its route?

    Additionally, what is the thickness of the cylinder wall in which the holes are located?
    Last edited by JAlberts; 01-03-2014 at 06:56 PM. Reason: Added cylinder wall question

  3. #3
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    the length of the between the cylinder and the compressor is 20 m. i will connect a air heater in between the cylinder and compressor to heat up the air to 80 degree celsius. the thickness of the cylinder is 5mm

  4. #4
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    Assuming you are using 20 m (787 in.) of 1/2" schedule 40 pipe with an inside diameter of .622 in. and a compressor discharge temperature of 15 degrees C (60 degrees F) then a proprietary conduit flow loss program I can access indicates that your maximum flow rate is going to be restricted strictly by the piping to a maximum of 76 scfm with a piping discharge pressure of 1.65 Bar (24 psig) to your cylinder.

    As a result, even with your 80 degree C cylinder air temperature and a sharp edge entry orifice efficiency coefficient of .80 for your 5 mm holes, assuming your holes are discharging to atmosphere, my orifice flow program indicates that a minimum of 5 holes in your cylinder would allow this maximum piping limited flow.

    I apologize for the English system scfm (i.e. standard equivalent cubic feet/minute air flow at 14.7 psi and 60 degrees F) flow volume values given but that is the standard for the USA based programs I use.
    Last edited by JAlberts; 01-05-2014 at 07:04 PM. Reason: added hole discharge pressure assumption

  5. #5
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    than you JAlbert for the great reply. can you please tell me the method for to find discharge such conditions?. and the factors which depends the flow rate...

  6. #6
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    First, all of the analyses were performed using programs based upon the classical piping flow loss analysis method and equations, and orifice flow equations that can found in a number of engineering reference books on gas flow analysis.

    This being said, for your problem I used an iterative process whereby:

    I first determined the maximum flow rate for one of your holes using a 4 Bar inlet pressure and an atmospheric discharge pressure and then multiplied that by 10 to determine the absolute maximum total flow capacity of the holes.

    Next, I used the piping program with your 4 bar inlet pressure and multiple flow rate trials to determine the pressure loss and maximum flow for the 20 m of piping.

    Next, I analyzed the holes' maximum flow capacity again using the reduced piping discharge pressure of 1.65 bar at 80 degrees C which informed me that the combined maximum flow volume for the holes with those inlet conditions exceeded the maximum calculated flow rate for the piping.

    Finally, I divided the maximum piping flow rate by the maximum rate for one hole to determine the minimum number of holes that would flow the maximum piping capacity without imposing any further back pressure at the piping discharge.

    NOTE: If the maximum capacity of the hole had been less than that of the piping, then a series of iterations of the piping flow and holes' flow would have been required to establish the correct piping discharge pressure at which the piping capacity and the holes' capacity matched.

    As you can see the analysis is a very straight forward process but one that is made much faster and expedient by having access to the required computer programs for each stage of the analysis process. The equation for the orifice flow is very straight forward to manually calculate; but, unfortunately, the piping flow determination by manual calculation is a very slow and tedious iterative process.

    I hope I have given you the information you desired; but, if you need more information just ask.

  7. #7
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    thank you. if i regulate the outlet valve of the compressor to make the inlet pressure to be 2 bar at the inlet of cylinder, is it effect the current mass flow rate of the pipe?

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