redeng50
Mechanical
- Jun 11, 2017
- 4
I'm trying to calculate the flow of nitrogen through an orifice and wanted to check to see if my method is correct. The inlet of the orifice is at 1.38 Barg and the outlet is unrestricted flow to atmospheric conditions at 21 C. The cross sectional area of the pipe is 1.78x10^-5 m^2. I have been using Crane 410 equation 2-24, q=Y*C*A*(2*delta_p/rho)^0.5. Here's what I got:
rho=349p'Sg/T=349*2.39*0.967/(21+273)=2.746
d1/d2=0.2
Crane said that for orifices discharging compressible fluids to atmosphere, use the flow coefficient C in the Reynolds number range where C is constant for the given diameter ratio. To me this seemed like the Re>10000 range and C=0.6 in the page A-20 chart.
Pressure ratio delta_p/p'1=1.38/(1.38+1.013)=0.577, so I found the expansion factor Y to be 0.84 with the chart on A-21
q=0.84*0.6*1.78*10^-5*(2*1.38/2.746)^0.5=8.99x10^-6 m^3/s
One strange thing that I noticed was that when I calculated the Re I got a value in the laminar range rather than something in the range I close C from.
Re=d*v*rho/mu=4.7625*(8.99x10^-6/1.78x10^-5)*2.746/0.018=367
Does this seem correct or should I be doing this differently?
rho=349p'Sg/T=349*2.39*0.967/(21+273)=2.746
d1/d2=0.2
Crane said that for orifices discharging compressible fluids to atmosphere, use the flow coefficient C in the Reynolds number range where C is constant for the given diameter ratio. To me this seemed like the Re>10000 range and C=0.6 in the page A-20 chart.
Pressure ratio delta_p/p'1=1.38/(1.38+1.013)=0.577, so I found the expansion factor Y to be 0.84 with the chart on A-21
q=0.84*0.6*1.78*10^-5*(2*1.38/2.746)^0.5=8.99x10^-6 m^3/s
One strange thing that I noticed was that when I calculated the Re I got a value in the laminar range rather than something in the range I close C from.
Re=d*v*rho/mu=4.7625*(8.99x10^-6/1.78x10^-5)*2.746/0.018=367
Does this seem correct or should I be doing this differently?