Venturi flow calculations
Venturi flow calculations
(OP)
I am trying to do some energy calculations for an aquaculture project that is trying to calculate different methods of creating flow in a channel and injecting air into water. So I am electrical engineer in background, but have some basic fluid knowledge. They currently want me to evaluate a 2 HP pump with a 2" PVC pipe going in to multiple 2" venturi with a 1"x 60" pipe at the throat of the venturi. My job is to determine how much air is being injected and then the total flow. So assuming the entry is P1*A1 and the throat is P2*A2 and the water going into the venturi is at 30 psi at a velocity of 8.17 f/s in a 2" pipe I solved for P2. I came up with P2=P1 + C*(SW*V1^2(1-1/B^2)/(2*g)) where B=A2/A1 and SW=Specific weight and g=gravity rate and C=discharge coefficient. Is that correct? Step 2) Assuming the 1" throat injector pipe is supplied from sea level atmosphere at 14.7 psi, is it true that I have to get P2 below 14.7 to start sucking air in? by playing with the B I can get the pressure down to minus 45 psi which is impossible so there must be a theoretical limit on P2 (Choke flow)? Suppose P2 is at 7 psi from the water flow and I used Poisevilles Equation to determine R of .667, does that mean the air intake is (14.7-7)/.667 (I have some conversion in so that I come up with 298 CFH. The problem is Mazzei Injectors show a much different number. I have enclosed a spread sheet to show my calcs.





RE: Venturi flow calculations
RE: Venturi flow calculations
RE: Venturi flow calculations
There will be suction of air at the throat or even past the throat where you still have high velocities. A simple experiment would be to expose one end of a plastic tube perpendicular to the water jet from a nozzle supplying recirculated water to a pool and the other end to atmosphere. Air will be aspirated which is what you want,a two phase flow. Another example would be the old snow gun technology used in ski area where water and air are combined in a ventury and released to atmosphere as a fine spray turned to ice.