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Discussion Starter · #42 ·
yes u r right.

is it possible to get accurate reynolds number for this device?
Not easily, I'm afraid. There are online calculators out there, http://airfoiltools.com/calculator/reynoldsnumber for instance but you would have to do some research for some of the input data.

There are plenty of things you can do to lower the reynolds number, even if you don't know what the reynolds number is. Some of the suggestions I made before should help. Keeping your airways close together will help a lot. The larger the diameter of each cell also negatively affects laminar quality. Smaller, more numerous cells will help immensely. My first iteration was using straws with a 6mm diameter. My second iteration is using a honeycomb with a cell diameter of 9mm. I had better laminar results using 6mm cells but the water condensation kept clogging the straws. The 9mm cells didn't cause condensation problems but the reynolds number was higher and therefor, the laminar flow was harder to tame. Your cell diameters look rather large and that can be another issue.
 

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Discussion Starter · #45 ·
another problem!

the water drop...

how can I prevent it?
The water drip is really difficult to to deal with. When more fog is pushed through, the drip gets worse. I am still trying to figure out a good way to combat that. Adding a drip channel helped a lot. So, what I have going on is; in the fog chamber, where the fog gets funneled down to the straws, there is a small aluminum channel that works like a drip tray. It's mounted at an incline so gravity moves the water to a drain hose. This channel is mounted on the side of the chamber where the fog enters. You can see the drip channel in one of my previous pictures.
 

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Discussion Starter · #46 ·
After getting a few inquiries about set-up, I decided to put up a new video showing out I set this thing up.

Enjoy!

 

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Discussion Starter · #48 ·
Basically yes. Everything on this fogscreen is controlled via DMX. I may do another video showing the control of the fogscreen.

The fog density adjustment is pretty basic. All I do is adjust the speed of the fans at the top, the ones that push the fog through. The speed at which the fog exits the fogscreen doesn't affect the laminar flow hardly at all. Having the density of the fog variable also helps with condensation and drip. If I were to turn the top fog fans all the way up, the condensation becomes a problem and water starts to drip quite a bit. I mean, it doesn't pour out but within five minutes or so, I will have a 5" puddle on the ground. I run the fans at about 20% to produce the density of fog that I like. At 20%, there is little to no drip. Maybe a few drops every five minutes or so. Totally manageable and acceptable.
 

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about laminar flow... does it depend on honeycomb, air flow and the straws only? no other element?

the 2nd question; could you say how many mist maker we need for making a 30*30cm screen of fog? (i wanna make a small one first)

and finally the 3rd question ;)
where can i buy a honeycomb? do you have any links?

tnx
 

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716586
,

Hi Absolom7691,

I saw a fog curtain machine in the India Pavilion at the Venice Biennale (world art show) in Italy. It was showing a letter from Mahatma Ghandi (see pic). I was so inspired by the immersive quality and viewer interaction of the work that I want to use a fog curtain for an art project. After doing some research I found out that these machines are way too expensive to buy!! So I looked for ways to make one myself and then discovered your project! Really amazing what you did!!! I'm gobsmacked!

I would like to build a scale model first and if that works I can build a big one. So I’ve been looking at how you have constructed your machine and I pretty much understand how it works except for the top part of the machine that contains the water with ultrasonic foggers and the ventilation.

I apologise for taking up your time but would you please be so friendly to answer some questions I have? I will sum up my questions so it doesn’t become confusing.
  1. What I don’t understand is the route of the airflow of the fog?
  2. How does the fog get pushed from the water container into the straws?
  3. And what are the ventilators on the top for? Do blow the air inside and then push the fog towards the straws?
  4. And why you have these little aluminum Plates above the foggers? Are they for condensation?
  5. You posted some documents (air flow drawing) but unfortunately these pages don't open.

I really hope you can help me out and answer my question. If I manage to pull it off I will credit you in my work if you like. I will have an art show showing the work.

Greetings from Amsterdam!
?
 

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Let's start with the honeycomb. So, after procuring aluminum honeycomb (not as easy a task as it sounds) It needed to be cut, expanded and trimmed to size. Of course, going into this, I didn't know how to do any of it! Cutting was the most physically demanding part but didn't taking much figuring to do it. Expanding it was a pretty daunting task. After trying to look up the procedure for expanding honeycomb, I became a little despondent. Commercially expanded honeycomb required a special expander to do the job right. I finally had to look up one of these devices to see how they worked. Now, I could have ordered the honeycomb expanded and cut to size but due to the fragility of aluminum honeycomb, the shipping costs (which were already high for the unexpanded) would have been astronomical. It probably would have added another $200~$300 to the shipping. Well, after learning how the honeycomb expanders worked, I figured out how to make my own "expander" :D

So, there it is... 120lbs worth of unexpanded aluminum honeycomb. Solid as a brick!
View attachment 517010 View attachment 517018

After several hours of cutting with a hack saw, I sliced off the piece I needed.
View attachment 517026 View attachment 517034

...And now for the expansion!
View attachment 517042 View attachment 517050 View attachment 517058 View attachment 517066

After expanding, cleaving was easy. Just a sharp kitchen knife and some patience
View attachment 517074 View attachment 517082

Stay tuned for more!
where did u buy it? any links?
 

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It seems as you started with an UP flow version first and then went to an above mounted DOWN flow version. I was wondering if you had any specific issue with the UP flow version? I understand that the DOWN flow version probably works better, but would you recommend building one if up flow is the only realistic option.
Thanks,
JD
 

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Discussion Starter · #54 ·
It seems as you started with an UP flow version first and then went to an above mounted DOWN flow version. I was wondering if you had any specific issue with the UP flow version? I understand that the DOWN flow version probably works better, but would you recommend building one if up flow is the only realistic option.
Thanks,
JD
Not really. I just wanted kids to be able to walk through it and the only way that would be possible is down flow from above.
 

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I am not sure how he did it, but I have used the below item in the past and 12VDC computer fans. You should be able to put multiple fans on one channel, just make sure the fans can be controlled by varying the voltage (most DC fans are like this) and don't exceed the current capacity of that channel. I personally keep it to 80% of the total ampacity. Motors you would have to decrease that percentage dramatically due to start up ampacity, but with fans you should be okay.

 

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I am not sure how he did it, but I have used the below item in the past and 12VDC computer fans. You should be able to put multiple fans on one channel, just make sure the fans can be controlled by varying the voltage (most DC fans are like this) and don't exceed the current capacity of that channel. I personally keep it to 80% of the total ampacity. Motors you would have to decrease that percentage dramatically due to start up ampacity, but with fans you should be okay.

Thanks!
 

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Discussion Starter · #59 ·
Hey guys! Sorry I have been absent from this forum for so long. Quarantine has, no doubt, affected everyone, myself included! To answer the question about speed controlling the fans via DMX, I am using a PWM generator that has a 5V output. 4 wire computer fans have a speed controller already built in. They just need a PWM signal to vary the speed. So, I run 12VDC to the fans at full voltage and the fans derive the speed from the PWM signal on the blue wire that runs from my DMX board. I have a schmitt trigger in line with the PWM signal though because fans actually pull a slight current on the signal wire and combined, it's more than my little DMX board can source.

I would recommend not using a DMX LED dimmer for PC fans. They are not a typical brushed DC motor. They are brushless. This means they are a multi poled motor that normally self regulates its speed via PWM. They don't deal well with modulated power, which is what LED dimmers do. LED dimmers don't actually vary the voltage. Instead, they pulse current at a set frequency and vary the "on" time of each pulse. This works fine for regular DC motors but your milage will vary a lot with brushless computer fans and they can potentially fry.
 

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After getting a few inquiries about set-up, I decided to put up a new video showing out I set this thing up.

Enjoy!

Dear absolom7691,

THANK YOU for taking the time to inspire and inform us about your amazing fog screen creation! VERY COOL!! If this forum offered an "Evil Genius" award, you'd certainly be one of many forum contributors worthy of nomination. :)

Along with reading your responses to questions and examining your posted photos, your "Setup" video answered several of my remaining questions. It helped me understand the concept of an air shield to maintain the fog screen in laminar flow as well as understand the size and scope of your system. If you've time, I do have a few more questions:

Q1. Why is it necessary to expand the honeycomb material (apparently only along the length)? Was it difficult/critical to realize uniform expansion across the matrix?

Q2. Judging by your video, fan noise doesn't appear to be distracting (especially when the projections - accompanied by sound - are so mesmerizing). 'Safe to assume that operating noise was an important criteria for fan selection? Do you have any other recommendations for minimizing fan noise (e.g. acoustically isolating the fans using foam gasket/mounting material)?

Q3. To what extent can your air shield adjustments insulate the fog screen from breezes?

Q4. What if any changes would you make to further refine your fog screen?

Thanks again!
 
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