Help me dial in the droplet size in my HPA/TAG system

Hello,

i need help to dial in my new HPA/TAG system. Some aero wizard please put me on the fast lane.



Given is the following scenario:

Pump: M.R.S. Whisper PowerPump Ultimate 320 PSI (22 bar) (It appears that with the 4 large nozzles i can go up 290 PSI (20 bar))
Nozzle type: M.R.S. Micro Fog Nozzle Stainless Steel (0.4 mm or 0.5 mm)
Number of nozzles: 4
Pressure tank/solenoid: No, i spray directly from the pump
Aero chamber size: 23.7 Gal (90 L)
Number of plants: 2
Distance of nozzles to plants: 0.4 inch (22 cm)
Shortest possible spray interval: 1 second (I can go below but as of now iam not keeping the pressure on the tubes during pause, hoping for a bit cooler water)

Available are two nozzles:

Smaller Nozzle
Nozzle Diameter: 0.015748 inch (0.4mm)
Spray angle: 90°
Droplet size: 11 micron at 1015.26 PSI (70 bar)
Flow: 1.19gph (4.5 L/h) at 217.557 - 290 PSI (15-20 bar)

Larger Nozzle
Nozzle Diameter 0.019685 inch (0.5mm)
Spray angle: 95°
Droplet size: 13 micron at 1015.26 PSI (70 bar)
Flow: 2.85gph (10.8 L/h) at 217.557 - 290 PSI (15-20 bar)
Flow? (Its possible that the 2.85gph is wrong info on the manufacturer site): 1.58gph (6 L/h) at (15-20 bar)


To achieve the disired average micron size, at what pressure do i have to run the pump?
Which of the two nozzles is a better fit? And what spray interval to use?

A mathematical explanation is highly appreciated.

Currently iam running at 260 PSI (18 bar) with the larger Nozzle and spray interval 10s on/ 3min off.

According to this article where my nozzle size is between the two mentioned, i think it should be not more than 90 PSI? Taking into accound that ideal droplet sizes are larger, the pressure has to be even lower?

https://www.tandfonline.com/doi/full/10.1080/17429145.2018.1472308
"The jet spray nozzles with 0.000635 m (0.025-inch) and 0.0004064 m (0.016-inch) orifice under the operating pressure pump at 551580.5832 and 689475.729 Pa (80 to 100 psi) deliver the drop size of 5–50 microns and 5–25 microns respectively. However, in the aeroponics system, the ideal droplet size range for most of the plant species is in-between 30 and 100 microns."

I tried to calculate the required pressure using this formula with the 13 micron at 1015.26 PSI (70 bar) and target micron size of 55 but so far the results seem off.



https://www.wolframalpha.com/input?i=solve+[//math:d1/d2=(p1/p2)^-0.3//]+for+[//math2//]

p2=(d1^(10/3)*p1)/d2^(10/3)

Realizing that my current pressure might be way too high, i have cranked the pump down to 170 PSI (11.7 bar) with the larger nozzle and an interval of 2s on, 60s off.

Are you gonna do a journal when it's up and running? I was interested in this a few years back, equipment failure would be to costly for my liking, I ran into a site that had all the info I believe you need, I'll look to see if I can find it. Been a while

Thanks for joining my thread. That will depend on if we can get the system dailed in soon.

The vehicle is ready, passengers are seated, we just need a TAG fligh officer here to give us directions for takeoff.

Any other experience? or just jumping straight in the deep end? I rarely see these things take off, most people give up pretty easily, sadly. Id suggest running coco plants as well so you know you'll have at least them if something fails. It is very discouraging when you lose a whole crop, but you can only get better.

Iam an engineer playing around with hydroponics for some years. For me, aeroponics is the next logical step. Problems, challanges, yes, but there are also solutions. Iam willing to find and apply them.

Everyone has to choose a way that works for him. For me its recirculating hydro. If not a lot of tech would be involved here i wouldnt be playing. Coco is too much dirt in recirculating hydro for my likes. Rockwool is too much of an health issue (dry). Also these two i would use only in drip systems. Hydrocorrels leave too little space for roots. Iam fed up of adjusting the acidity of substrates, cleaning pots, dealing with mold and algae. Fed up of dealing with DO, high PH drift in DWC. Fed up with too little height of the root zones in NFT and Ebb-And-Flow. Id say i have reasons and a good starting point.

I can manage a rez, now its just another delivery system attached.



While we are waiting, still hoping for some old aeroheads to arrive, feel free to challange my system and proccesses. Do you have a specific risk in mind?

For me it's always been power outages that scare me the most. I've lived in this house 6 years and we have had so many, like at least 4 that were more than a couple days. And I am in Oklahoma City, it's ridiculous. And I live less than a quarter mile from a power grid, but still the ghetto lol. Do you have a generator? I've also considered buying lithium cells I've found a company that sells lightly used ones for under $70 per kilowatt hour. They build em outta used apc computer backups it's all 18650 cells. Then there is pump failure, nozzles clogging, and the fact that your environment needs to be perfectly dialed in, you need consistency for it to work properly. When I used the fog machines you would get these hairy looking roots that grew fast, The advantages of hpa and most hydroponics really show in veg, it's very fast growth most people don't believe it till they see for them selves. Being an engineer I can see that all sounding fun for you. My grows are all for fun as well and I diy almost everything.

Power outages:

Where i operate, luckily power outages are very rare. We had one like 2-3 years ago that lastet a couple of hours. As of now that is not a problem iam adressing at all. I was eyeballing with this device https://us.ecoflow.com/products/delta-pro-portable-power-station?variant=40516140138569.
It has the LFP batteries that i consider way safer than Li-Ion. Actually for other reasons i had ordered one of theese, but when it arrived i realized alone the battery weights 92 pounds. I felt crazy and sent it back

Pump Failure:

Preventative:
[x] Use a filter before the pump of 150um or smaller
[x] Use the best hardware available
[x] Replace the pump within its lifetime
[x] Regular cleaning (after each cycle) of the whole system using TA Flash Clean

Backup/Disaster Recovery:
[ ] Rule of thumb in HPA/TAG, have a backup pump. Iam close to ordering one but need to confirm the correct PSI first, currently it looks like i have to step down to the next smaller pump.

Unattended:
[ ] Have a pressure sensor on the tube that alerts once pressure drops. So far i have only the analog display of the pressure.

Nozzle clogging:

Preventative:
[x] Use a filter before the pump of 150um or smaller
[x] Ensure that your water is overall clean/ free from (larger) particles. Have a good filtering.
[x] Use high pressure instead of low pressure as clogs are much more likely to occur with low pressure.
[x] Never stop spraying. When system is idle still keep the spray running, maybe at bigger intervals. The system should not come to rest to recude sedimentation. If stopped always replace nozzles with clean ones.
[x] Nozzle coverage. I have 2 nozzles per plant, so there is always a second nozzle to keep the plant alife in case one nozzle should fail. On the other side i keep the numer of nozzles to the absolute minimum to reduce maintenance and system complexity. Also i do not use multi-headed-nozzles since to get a good coverage in the chamber (for a very small setup) it was important to allow as much individual nozzle positions as possible and also not use multiple nozzle types as they would behave slightly different (e.g. single-headed on the edges and dual-headed in the middle).
[x] Do not run at maximum pressure of your components. If a nozzle clogs and the pressure rises, the system should allow for a little more pressure before a leak occurs. Running at a bit higher pressure until the next maintenance should not be a big problem.
[x] Use stainless steel nozzles and a cleaning process with an ultrasonic cleaner: I have a second set of nozzles for quick replacement. Ultrasonic cleaning takes like 30-60 minutes. I use intensive cleaner solution and also heat in the ultrasonic cleaner. That should make the nozzles perfectly clean everytime. The process is so simple i can apply it every two weeks.
[x] Premix the nutes outside of the system to ensure its mixed well before it enters. I have a premix tank and a circulation pump in it. Also fill and drain pumps on the rez. That makes mixing a new rez and refilling the system quite handy. After adding the nutes i just leave the circulation pump on for another 30-60 minutes to have it mixed very well. Also without this process i could not replace the water fast enough for aero. My RO water takes like 4 hours to get ready.

Backup/Disaster Recovery:
[x] Have the second set of nozzles always clean and ready

Unattended:
[ ] Have a pressure sensor on the tube that alerts once pressure rises.


(Haha, yes, sorry this thing is currently located on a toilet as i have limited space)

Conclusion:
Technically a second pump, tubing, set of nozzles could be installed on a backup power supply. Triggered by sensors for the pressure and the power outage, the secondary spray system could be activated.

However, i think that with good preventative measures and processes the problems can already be reduced into a range that is fully acceptable.