orifice plate theory
orifice plate theory
(OP)
I have a submersible body that's about 3m tall and that takes in water from the bottom through three 120mm holes and allows the air to escape at the top through three 50mm holes. I am trying to work out the pressure inside the body, using standard orifice plate theory as described in BS EN ISO 5167 and just wanted to see if anyone has suggestions on how applicable this method is and if there other techniques that might be better suited?





RE: orifice plate theory
RE: orifice plate theory
Jimbo
EngCo Solutions Ltd
www.engcosolutions.com
RE: orifice plate theory
RE: orifice plate theory
Jimbo
EngCo Solutions Ltd
www.engcosolutions.com
RE: orifice plate theory
Ain't no way to ever get a pressure build up between flowing water and air caused by the orifice size stated above.
At 74th year working on IR-One2 - - UHK PhD - - -
RE: orifice plate theory
Jimbo
EngCo Solutions Ltd
www.engcosolutions.com
RE: orifice plate theory
Does the air going thru the 50mm orifices enter a closed chamber or does it vent to atmosphere?
At 74th year working on IR-One2 - - UHK PhD - - -
RE: orifice plate theory
Jimbo
EngCo Solutions Ltd
www.engcosolutions.com
RE: orifice plate theory
To get a pressure differential across the air holes, determining how small the air holes have to be to restrict the volume of flow of air to be less than the existing volume of water entering thru the 120 mm holes during a specific time period?
At 74th year working on IR-One2 - - UHK PhD - - -
RE: orifice plate theory
If it sinks by itself... The speed it moves will be partially determined by the rate air escapes (plug the holes, and it will reach some equilibrium depth unless it hits the floor first.)
Hard to imagine much of a pressure buildup in that scenario.
RE: orifice plate theory
Jimbo
EngCo Solutions Ltd
www.engcosolutions.com
RE: orifice plate theory
Then, you have a flowrate.
Do the orifice calc of the air out, using that same flowrate and ignoring any compression of the air.
The pressure drop across the orifice should equal the pressure that could be retained in the vessel... Right?
RE: orifice plate theory
RE: orifice plate theory
I'm trying to calculate the failure mode for the vessel. This could come in the form failure through collapse due to external pressure or maybe pressure build up within the vessel. Either way you need to know what the internal pressure is correct? Yes both holes are open but the inlet is of greater size then the outlet.
Jimbo
EngCo Solutions Ltd
www.engcosolutions.com
RE: orifice plate theory
If the vessel is sinking 4m/s, the pressure increases 0.4bar/s. In a worst case scenario you can calculate
Say your vessel can withstand an external pressure of 2 barg and have a volume V.
If we would forget to open all holes and drag the vessel down 20m we would reach its pressure limit. We now open the bottom holes and simulate 1 second, the external pressure would now be 2.4 barg.
In order to hold, the internal pressure would have to reach 0.4 barg in that same second. This equals a compression of the air according to p*V=p_2*V_2, or 1bara*V=1.4bara*V_2. V_2 = 0.71 V. Thus 0.29 V would have to be filled with water in one second or Vs = 0.29V/s (29% of the volume per second)
If you are able to get a flow of 29% of the vessel volume through the bottom holes with a differential pressure 2 bar (or whatever the vessel can withstand) you are ok with margin as the top holes would further help stabilize the pressure.
Unfortunately i realize at this point that this will not be the case and you will have to make a simulation or similar..
The simulation will be difficult as modeling the top hole will be complicated. You will have an underpressure in the vessel and water will try to get in and air bubbles out.
RE: orifice plate theory
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: orifice plate theory
Any idea or estimate of the vessels dry weight?
At 74th year working on IR-One2 - - UHK PhD - - -
RE: orifice plate theory
Jimbo
EngCo Solutions Ltd
www.engcosolutions.com
RE: orifice plate theory
Seems to me that part of the solution to the issue involves buoyancy.
Without any air vent holes, the device will float at some level in the water with water inside covered with a calculable volume of compressed air at a calculable pressure.
Now You will have a known gas pressure to start working on an orifice size for controlled sinking of the vessel.
At 74th year working on IR-One2 - - UHK PhD - - -