Backward calculation of orifice plates
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What is the air flow rate when using a orifice plate with a pore diameter of 3 mm and a thickness of 8 mm, using compressed air at room temperature, with an upstream pressure of 0.1 MPa (gauge) and a downstream pressure of 0 (gauge)? If all other conditions remain unchanged, what is the air flow rate when the upstream pressure is 1 MPa (gauge pressure)? If all other conditions remain unchanged, what is the air flow rate when the upstream pressure is 10 MPa (gauge pressure)? If all other conditions remain unchanged and only the upstream pressure is increased, will there be a limit to the air flow rate? That is, at a certain pressure level, the flow rate will no longer increase as pressure rises.
The flow rate is 0; there’s no pressure downstream, which indicates that the flow hasn’t reached there. Go ahead and mess around; we’re not going to waste our brain cells thinking about it.
Have you ever thought about installing a orifice plate on the vent pipe, with an infinite space downstream? Stop thinking about it – it’s a shame to waste so many brain cells on it.
1. Pressure ratio = 1/2 = 0.5, establishing the choked flow condition. 2. t/d=8/3=2.6. 3. For 1+2, it can be assumed that the discharge coefficient remains constant at 0.839, and the mass flow rate is proportional to the upstream absolute pressure.
Under the original conditions, assuming a upstream pressure of 0.1 MPa (gauge pressure) results in a flow rate of 10 Nm3/h, then when the upstream pressure increases to 1.0 MPa (gauge pressure), the flow rate will increase proportionally. By how much will it increase?
The pressure at the downstream end can’t be 0 either; it’s around 7 or 8. Do you have any common sense? If the pipe isn’t full, it can’t be measured.
Once those parameters are determined, the flow rate of air exiting through the small hole is a fixed value that can definitely be calculated. It’s just that not many people know how to calculate it. If you can’t do it, then you can’t; it’s not embarrassing at all. What’s the point of saying it can’t be measured?
The value can be calculated; it’s 0 both behind the orifice plate and at the vent point. How can there be flow without any pressure difference? It’s around seven or eight – not even basic common sense. Still calling it an orifice plate? Do you know how to calculate the values for an orifice plate? Create a software and call it a hole plate calculator.
The upstream pressure is 0.1 MPa (gauge pressure), and the downstream pressure is 0 (gauge pressure). So the differential pressure is 0.1 MPa. Can’t even understand the question? Have all the brain cells died?
It’s not that I’m criticizing you, but you don’t seem like someone who knows how to exercise self-control. For orifice plates with a 3mm aperture, based on the aperture ratio, the pipe diameter is at most 10mm; with such a small pipe, who would choose an orifice plate to measure flow rate?
The last edit to this post was made by XZGSW1 on 2021-3-25 at 09:12. The issue is that once those parameters are determined, the flow rate of air exiting through the small hole is a fixed value that can definitely be calculated. It’s just that not many people know how to calculate it. If you can’t do it, then you can’t; it’s not embarrassing at all. What’s the point of saying it can’t be measured? No one uses it anyway.