Substitution of flow test fluid
Substitution of flow test fluid
(OP)
I have a nozzle with complex geometry that has a specified flow condition that must be met. The specification gives a flow rate (lb/hr) at a given test stand pressure (psig) using MIL C7024 type 2 fluid (commonly sold as stoddard solvent or white spirit).
I would like to be able to flow test the nozzle using water in our test stand, rather than the solvent. I was hoping to find an accurate way to correlate the flow rates of water and oil through the nozzle. Ideally I would like to be able to run the test at a different test pressure to compensate for the fluid's density and viscosity change, and be able to get the same flow rate, and therefor be able to verify the nozzle's geometry in this way.
I have experimented with similitude, but am not that familiar with this method. Using similitude it seemes that I must match both the Re and Cp values given the variables. Using the equations for both, I get an equation dP*rho/mu^2=constant between the flows. This equation makes no sense physically as it suggests that the more viscous fluid requires less total pressure drop to result in a matched flow rate.
I know some companies use different test media, so this should be possible.
I would like to be able to flow test the nozzle using water in our test stand, rather than the solvent. I was hoping to find an accurate way to correlate the flow rates of water and oil through the nozzle. Ideally I would like to be able to run the test at a different test pressure to compensate for the fluid's density and viscosity change, and be able to get the same flow rate, and therefor be able to verify the nozzle's geometry in this way.
I have experimented with similitude, but am not that familiar with this method. Using similitude it seemes that I must match both the Re and Cp values given the variables. Using the equations for both, I get an equation dP*rho/mu^2=constant between the flows. This equation makes no sense physically as it suggests that the more viscous fluid requires less total pressure drop to result in a matched flow rate.
I know some companies use different test media, so this should be possible.





RE: Substitution of flow test fluid
There are a lot of representations of Reynolds Number, for a similitude evaluation I use
Re=rho*v*D/mu but you can just as easily use
Re=rho*q*(pi/4)D^3/mu
The "D" value can be selected at any point, I like to use the diameter and velocity at a point where I have a constant diameter for a ways (not just after the convergent section of a nozzle for example). For water you want to look at changes in density and viscosity with changes in pressure and temperature to see if those changes are material (they may be, you have to check).
"Cp" has at least 4 definitions that I know of (so there are probably more than 20 definitions). I'm not going to guess which one you are referring to.
David
RE: Substitution of flow test fluid
RE: Substitution of flow test fluid
Do you match the Reynolds number and run the new fluid with the same Reynolds number, expirementally determining what the new flow rate acceptance will be? How do I verify the accuracy of this method, other than just repeating it?
or..
Would I be calculating the exit Re for the specified conditions, and then keeping the inlet conditions the same with the new fluid and the exit Re should end up still matching? This does not seem like it would be the case.
Thanks
RE: Substitution of flow test fluid
Better get approval first before modifying the test procedures. The owner may not accept the product due to specfication deviation.
RE: Substitution of flow test fluid
RE: Substitution of flow test fluid
RE: Substitution of flow test fluid
Our vendors are quite good, and have been able to meet our needs and specifications. In transfering products from one vendor who was unreliable to this vendor, they are having dificulties purchasing the specified test fluid due to their location in the world. They are a machine shop and not a dedicated testing facility, and they have done a good job so far with quality testing of our other parts.
eadwine, do you have any help or are you just going to point out flaws in our engineering department and our vendors?
RE: Substitution of flow test fluid