Now thats interesting. Looks like the 1/4J is the one to use, but its going to trend toward slightly small droplets. BUT. They dont say what fluid pressures on those charts? It also looks to me like there is no difference made by changing the air pressure from 10 PSI o 40 PSI? That doesnt seem right to me. If its true, then why not use the lower air pressure?
That chart agrees very well with the one I posted earlier:
So, if we want droplets between 20 micron and 80 micron it works out that 20 micron droplets fall at roughly 25 seconds per foot. Neither chart has 80 micron size listed, and I havent had time to plot a graph, or do the math to interpolate, but Im guessing its going to be around 1.5 - 2 seconds per foot.
So, for my chamber, which is aprox 2 ft tall, I want a maximum hang time of 50 seconds and a minimum of 3 to 4 seconds.
I dont see any way to judge the hang time of the larger droplets visually, so we are stuck just looking at the ones that hang the longest.
Based on those calculations, my hang time is way too long, which means I have a lot of droplets that are way too small. Im guessing down in the 5 to 10 micron range. Some of them hang at least three minutes or more down in the bottom of the chamber.
I agree. The have a note at the bottom: "AA nozzles sizes are generalized ones. Write Wheaton if you need more’.
And the problem is that 1/4J - it the base part of the nozzle, and I believe that different air cap/fluid cap set ups give very different results\droplet sizes.
Yes, quite similar.
And if this is correct - I mean, if 50 micron particles fall down 10 ft in 40 seconds (4 seconds per ft or 30 cm) - I don’t even know if its possible to “fill” a chamber with particles of such size at all - they are going to fall down very quickly and never really “hang”. Probably AA nozzle air turbulence might give it some force but then it will go down very soon. Or it is necessary to start misting much more often to support mist as medium: like every 5-10 seconds with very short cycles (0.2-0.4 seconds depending on required fluid flow rate).
Oh, and another note. These values are VMD, Sauter mean diameter or Volume median diameter. It means that 50% of particles are smaller than given value and 50% are bigger. But this parameter doesn’t give any idea on dispersion: if we have VMD 50 micron it might be that 50% particles have 20 micron diameter and another 50% - 80 micron. And nothing in between. Of course this is a very rough example but dispersion is very important, and we don’t have it.
AFAIK, Exair might have these numbers, but their nozzles are very expensive (actually, about the same price as Spraying Systems ones but there are no ‘used’ or ‘old stock’ options on ebay).
I wonder - looking at the data sheets you posted above - maybe the black dots at th ends of the droplet size bars represent the range of the MVD’s of the different caps? In other words, maybe the smallest flow rate caps give the smallest MVD number and the larger flow rates give the larger MVD number? The lowest MVD being just under 20 and the highest being just under 60 based on the black dots at the ends for the 1/4J?
If I am right about that, then a 1/4J with one of the higher flow rate caps should be a good choice with an MVD just under 60. IF I am right.
BUT - they still dont mention fluid pressure/siphon height - which has to also effect droplet sizes.
I agree. This is one of the things that has been bothering me about Atomizers recommendations. If you look at the video he posted again, he is using very short ON times - maybe 0.3 seconds. BUT relatively long OFF times - 90 seconds. Plus the mist that is left in the chamber towards the end is not really falling at all, so it must be very small droplets.
He, as usual, provides no details, but if you look close, I think you can see a net pot near the top center of the frame, so this video is looking sideways into the chamber. The droplets left at the end are not dropping at all.
Now, part of that is due to the way droplet size and MVD works. If 1/2 the volume is above say 50 microns, and half is below, then there will be many many more small droplets than larger ones. Volume of a sphere varies as the cube of the diameter. I have not done the math, but depending on the size distribution, you will get orders of magnitude more small droplets than large ones.
That still leaves me wondering exactly what he is talking about with the fill the chamber stuff. All we can see are the smallest droplets when it comes to measuring hang time - which seems pretty useless.
This also brings into question his dictate to not spray the roots directly. 50 micron and larger droplets are not going to hang around long enough to hit the roots if you dont spray directly - or very close to it.
Quick note for you. Ive been making changes to my system for the next grow. As part of that, I have been trying out using separate timers on each nozzle with slightly different settings and/or having them staggered so that the nozzles fire at different times.
Too early to tell for sure, but Im liking the effects so far - especially having the times staggered. It looks like doing this allows you to maintain a more uniform mist density without increasing the over all flow rate.
Its too soon to tell how well the roots like having separate timers, but I think its going to work better.
Visually, it sure looks like staggering the firing times does a better job of maintaining a uniform mist density compare to having them all fire at the same time.
Im currently running two nozzles instead of my previous three. I just put two baby plants in the system, so Im running a relatively hi flow rate. The timing is 1.4 sec ON x 31 OFF on one timer and 29 OFF on the other timer. Having the OFF times slightly different means the interval between ON cycles is constantly changing - from zero difference, where they fire at the same time, up to a max of aprox 15 seconds difference.
I am running my nozzles in siphon mode rather than pressure, or gravity feed mode, but I have been playing with slightly different siphon heights. I can adjust the siphon height from zero to several inches, but Im staying near 1". The flow rate drops as the siphon height increases, and with only running two nozzles, I need to keep the flow rate up as high as possible. I could have longer ON times instead, but that increases my compressor run time too much.
I finally got around to doing an Excell plot of the flow rate numbers for my nozzles. The graph helps interpolate the in-between flow rates at different air pressures and siphon heights or pressure/gravity settings. The graph is not perfect, but its reasonably close to my measured values.
I found it interesting that the air consumption was pretty linear as pressure increased, but the liquid flow rates were not. That and the way the siphon and pressure flow rates tend to converge as air pressure increased. I was not expecting to see that convergence where one set of numbers increase while the other decreases with pressure.
Oh - I managed to badger Atomizer into posting some specifics for air atomizing nozzles. He still left out some critical information, but this is the most he has ever posted on AA nozzles - and he included a model number.
Of course, he left out some important details like nozzle placement, and most importantly, timing. He also left quite a wide open range of pressures for the liquid and air, which will mean a large range of flow rates. Flow rates could be anywhere from well under 1 GPH to 8 GPH for liquid and from under 1 scfm to almost 4 scfm for air.
So he still leaves us with a lot of guessing and trial and error to do on our own.
“You will need a 2m x 1m x 0.5m (1000L) chamber and 2x spraying systems SUN23 pressure fed, flat fan AA nozzles. These nozzles require both pressurised air and liquid supplies, air pressure 30- 45psi, liquid 10psi- 30psi. You`ll need a reliable compressor to run them as they can consume over 3scfm. Worst case for your current compressor (set for 90psi-46psi) is it would run for 2 minutes upto twice an hour 24/7. I run 4 of these nozzles comfortably on a 3.3cfm homebrew silent compressor with a 50L tank and 2 external tanks, repurposed 19kg propane cylinders (capacity 43L each).
Attached pics of nozzles and the kind of mist they produce. The rest is upto you. Good luck”
Finally decided to come here and see you just wrote a question
I’ve tried to finish my software at least at some degree. Somewhere in the middle I’ve realized that I set too complex task for the beginning so I decided to start again with a more simple goal and finally made my software work at least at some degree, and now I can use it. It require a lot of work but at least I can start experiments with hardware as well
Big mess, sorry. Its from the last night, now it is afternoon already, and I shot I small messy video about current state.
Now I need to reread my posts and recall last pressure settings. I forgot everything and want to refresh my memory
I’ve got a notification about your last posts but I was very depressed because of the development speed so I dive into it and did nothing aside. Sorry for no reaction. I really hope now I will have slightly more power to visit OG more often.
And an another hanging time test, this time after 0.6 bar air, 0.3 bar water misting:
Now I’ve started an extended flow rate test to fill my table but after that I’m going to try to slightly increase water pressure (to 0.45-0.5 bar). Now hanging time is closer to 100 seconds or even more which is way much higher than required 50 seconds max.
@anon32470837, by the way, did you measure hanging time with your current pressure settings?
An an another “by the way”: with a central air line solenoid now compressor turns on once in every 18-19 minutes which twice less often than before. I open the main valve in 0.5 seconds before the next misting cycle and close it right after it finishes. But I see that the current solenoid can’t hold air pressure, it seems to sip a lot. I’m going to put the same solenoid as I’m using at the nozzles.
And I’ve made a video with 0.6 bar air, 0.45 bar water, 0.5 sec ON, 14.53 sec OFF misting and then somewhere at 6:30 I’ve turned the schedule off to check hanging time. I’m not 100% sure but this looks more like what I need.
Just to be clear: schedules I provided are for the each nozzle: for example, 0.5 sec on left nozzle then 14.53 second off, then 0.5 sec on right nozzle, 14.53 sec off etc.
I’m updating my spreadsheet with flowrate data as well.
I have a lot of comments and questions, but I need to get to bed, so I’ll be quick.
How are you judging the hang time - when to call it done? Im still trying to settle on some sort of “standard” way to judge when the mist is thinned out enough to call it.
Also I have forgotten - how did you come to that 50 second number? Is that based on how fast a certain size droplet will fall to the bottom in your chamber?
This whole process of judging hang times is so imprecise and completely dependent on purely subjective values - none of which I have any idea how to measure with any precision.
I need to go back and look at my last video again. I think the hang time could be around 1 minute - maybe? I still have some mist floating around for more than 3 minutes. Im sure those droplets are under 5 micron size.
I’m afraid I didn’t read our previous conversation carefully: these settings are for your chamber: from 3-4 to 50 seconds max. For my chamber it would be more like from 1-2 to 25-30 seconds max. And if so then it opens even more questions: how could it work with 50-70 seconds off time schedule?
May be I’ll try to use very short cycles - like 0.2 seconds ON and much shorter OFF and set water pressure even higher to get bigger particles. Going home in a couple of hours and will see what could it give. I think I also need to check solenoid open timing: even though my solenoids are pretty strong and fast such short timings might be just too short for mist generation or require much higher pressure settings.
Just visually: trying to figure out when nothing is moving anymore. Of course this method is very subjective. But for something more precise we need to build a lab with very fast cameras, lights and good optics. Pretty expensive as for me.
