calculating flow based on pressure and nozzle size?

Is there a mathematical way... or an online calculator to figure out what kind of flow to expect from a particular nozzle size based on pressure?

I'm running a mechanical preturbo AI system that is used by pressurizing a tank. It's used with boost pressures between 15 - 20 psi. The nozzle is rated at around 380 cc @ 20 psi. I was planning on increasing the nozzle size to somewhere around 0.03125" - 0.4" (1/32" -1/25") to get more flow. I was reading the nozzle size sticky and read that the .9 MM (.0354") equates to the M5 and flows 316 CC/Min at 100 psi. I also found an old post by rotary racing that said he modifies his nozzle tips to about a 1mm opening to give around 700cc of flow @ under 20 psi.

I don't know the exact size of my nozzle but I'm pretty certain its not bigger then 1mm. So something isn't quite adding up. If my nozzle flows 380 cc at 20 psi, and rice racing's is 1mm (.04") (the M7 is .045") flowing 700 cc 20 psi, then why does that chart in the sticky show the same size nozzle (M7) flowing only 442 cc at 100 psi? That's a HUGE difference in flow for the same size orifice, especially considering the nozzles rated at flowing much less, are at a much higher pressure. 20 psi vs 100 psi

the increased flow from going from 20 psi to 100 psi is the square root of 500. so flow at 100 psi should be 22.3% more than at 20.

i suggest you use an air pressure source, a reliable gauge and a pressure regulator and pressurize your tank. measure the amount flowed for a minute and let's see what is really going on.

perhaps due to the suction of the compressor you are getting more flow????

howard

Last edited by howard coleman; 04-13-09 at 08:24 AM.

I doubt the suction would have much if any influence on the flow rate. And in addition to that, my nozzle wasn't designed as a WI nozzle, and it has a flow sheet from Spraying Systems Co that shows the flow at 5, 10, 20, and 40 psi, the ratings would be without any vacuum at the tip. At 20 psi the chart shows 6 GPH or 378cc. I guess I could buy some small drill bits to see what size the orifice is. I'm pretty certain the chart they have is accurate.

__________________ 550+ rwhp thanks to:
Wannaspeed.com's Fast reacting air sensor, Pre turbo water injection, MP t70 @ 25psi, streetport, pfc, twinpower, greddy plugs, ebay intercooler, 3" exhaust, cold air intake,TII LSD, solid mounts, braces, wideband, datalogit, my tune, dual FD fuel pumps, profec b, 550/1680

I already have one for my application, purchased through them. I brought this thread up to discuss the discrepancy between the nozzle size sticky and other information i've found. I was also looking for a formula to figure out orifice size vs pressure and flow because i planned on modifying my nozzle. And wanted to calculate the size i should go with. I ordered some drill bits that go from .4- 1.0 mm so i will be getting to the bottom of this.

__________________ 550+ rwhp thanks to:
Wannaspeed.com's Fast reacting air sensor, Pre turbo water injection, MP t70 @ 25psi, streetport, pfc, twinpower, greddy plugs, ebay intercooler, 3" exhaust, cold air intake,TII LSD, solid mounts, braces, wideband, datalogit, my tune, dual FD fuel pumps, profec b, 550/1680

I bought some tiny drill bits that range from .3mm - 1mm.

I stuck a couple in the nozzle tip to check the size and my nozzle is right between a .65mm -.7 mm (0.026" - 0.028") which would be between an M4 and M5 according to post #23 in the size sticky.

My flow at 20 psi is supposed to be 378cc, an M5 is supposed to flow 379cc at 150 psi.(much much higher pressure)

Within the next couple days I will check the actual flow of my nozzle with a regulator and measuring container.

Howard how do you calculate the flow increase from a pressure increase? Earlier you mentioned the square root of 500 and came up with 22% increase from 20 to 100 psi. Could you show me the formula that allowed you to come to that number? I know the square root of 500 is 22.3 but how did you get the number 500 from 20 and 100? thanks

__________________ 550+ rwhp thanks to:
Wannaspeed.com's Fast reacting air sensor, Pre turbo water injection, MP t70 @ 25psi, streetport, pfc, twinpower, greddy plugs, ebay intercooler, 3" exhaust, cold air intake,TII LSD, solid mounts, braces, wideband, datalogit, my tune, dual FD fuel pumps, profec b, 550/1680

I found this formula for calculating injector flow rate after an increase in fuel pressure. I'm not sure how accurate it is, especially with large pressure increases. the math doesn't add up to the same as what Howard's did. But here it is.
"When you increase or decrease fuel pressure at the injector from its rated flow you change the amount of fuel that is actually forced from the injector (the injectors volume flow).

New Flow = SQRT(New Pressure / Old Pressure) X Old Flow Rate

Here is an example:

New Flow = Square Root of (55psi / 43.5psi) X 30 lbs/hr flow rate
New Flow = 1.124 X 30 lbs/hr
New Flow = 33.73 lb/hr"

Using this formula going from 20 psi to 100 psi with a starting flow rate of 380cc would increase flow to 850cc(much more then a 23% increase.) Here's the math using the formula above: SQRT(100psi/20psi) X 380cc = 849.7cc

I checked the math against the chart in the sticky (post #23) by using the 100 and 150 psi numbers and it checked out to be quite accurate. The smaller nozzles were within 5cc or so of the math's calculations. The largest difference was with the M11 of 17cc. Using the math formula it showed a flow of 850cc vs the charts 833cc. Still very accurate

Since my nozzle is right between an M4 and an M5 in size ill interpolate the flow according to the chart at 280cc (right between 252 & 316cc) @100 psi. Using the new formula and going off that chart would mean that my nozzle is only flowing 125cc @20 psi. I know for a fact its flowing way more then that given how quickly my container empties. Plus my nozzle is rated @ 20 psi to flow 378cc from a quite large and professional company. (though I do plan to check its flow anyway)

My guess is the nozzles either flow a lot more then what they are rated at in that chart.. or the actual size of the nozzles is much smaller. I think this is a very good explanation. The flow numbers in the chart comparing 100 psi and 150 psi seem to add up with the math so I think the sizes are wrong. In any case something isn't adding up and I don't think it's with my nozzle.

__________________ 550+ rwhp thanks to:
Wannaspeed.com's Fast reacting air sensor, Pre turbo water injection, MP t70 @ 25psi, streetport, pfc, twinpower, greddy plugs, ebay intercooler, 3" exhaust, cold air intake,TII LSD, solid mounts, braces, wideband, datalogit, my tune, dual FD fuel pumps, profec b, 550/1680

I dont think you can compare flow based on the size of the opening between different types of nozzles. The typical nozzles used for AI have a groved piece inside to mist the water, without they would spray a jet. Air atomizing nozzles have a clean passage for the water to exit and relys on the air to mist it. So your nozzle has no restriction, thus way higher flow at lower pressure.