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Good day, forum
Sorry for english - I have rare practice.
A flow orifice is the cheapest and simplest (and therefore reliable) means to control gas flowrate. I have some particular questions concerning flow orifice calculation. There is a lot of information about critical flow and flow orifice calculation. So, if you have a worth link, source or file - you are welcomed. If you have some general information - please do not flood. And I know that wikipedia is not a worth engineering source but it is the most convenient when you work on internet.
All sources I have found talk about critical (sonic, choked) flow of ideal gas through ideal orifice. E.g. Perry's Chemical Engineers' Handbook 8th ed. provides with calculation for ideal gas and ideal orifice. But one deals with a real gase, a real piece of metal and a real turners. How a real gas affects gas flowrate through a real orifice? Some sources talk about more problems with a real gas. E.g. Wikipedia talks:
The technical literature can be very confusing because many authors fail to explain whether they are using the universal gas law constant R which applies to any ideal gas or whether they are using the gas law constant Rs which only applies to a specific individual gas.
So my questions are:
Q1a: How compessibility shall be taken into account?
Q1b: Does isentropic index shall be used instead of adiabatic index? How I can easy and fast evaluate isentropic index for real gas mixture?
Q1c: Does temperature and density drop in orifice bore shall be taken into account? When?
Some sources talk about thick and thin plates. E.g. Wikipedia talks:
"The flow of real gases through thin-plate orifices never becomes fully choked. The mass flow rate through the orifice continues to increase as the downstream pressure is lowered to a perfect vacuum, though the mass flow rate increases slowly as the downstream pressure is reduced below the critical pressure."
When sources talk about a real orifice some correction factor (discharge coefficient) appears. E.g Wikipedia talks:
The value of Cd can be calculated using the below expression:
So my questions are:
Q2a: When a plate is thin or thick?
Q2b: What is the min thickness of plate to guarantee critical flow?
Q2c: How to calculate the correction factor? How it depends on shape and dimensions of bore, e.g cant.
Q2d: How flow fluctuations affect calculation accuracy? Does upstream and downstream pipe require straight run as those for flow restriction devices? How straight run requirements can be estimated?
One deals with not only gases. A wet gas contains a small portion of liquid upstream of orifice which flashes when pressure drops. Some gases do not contain liquid but produces liquid when pressure drops. Liquid can condense into orifice bore and flashes downstream. Liquid can condense into orifice bore and partially flashes downstream. Liquid can condense downstream of orifice. So my questions are:
Q3a: How liquid flash/condensation affects critical flow?
Q3b: How liquid affects metal? When erosion shall be considered? How metal can be protected from erosion (process means, manufacturing means)?
Q3c: A small drain bore can be provided to prevent liquid accumulation ustream of flow orifice. How this drain bore affects total gas flow through flow orifice? Can e.g. cemicircle bore be provided in case wet gas? How to calculate e.g. cemicircle bore?
Flow orifice can be purchased in professional company or manufactured in situ by a local turner or even by personnel using hand drill. So my questions are:
Q4a: Please share your positive/negative experience with flow orifice procurement? When it can/should/shall be purchased/manufactured and how?
Edited by shvet1, 24 October 2018 - 02:15 AM.
