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DIY Fog Screen
If you’ve ever ridden latest iteration of the Pirates of the Caribbean ride at Disneyland, you will remember how, right before you hit the first drop, you are greeted with the ghostly image of the tentacle-faced Davey Jones creature warning you that “dead men tell no tales”. I certainly did.
The effect uses rear-projection video, shined onto a screen of water vapor created by ultasonic atomization, that is sandwiched between 2 laminar airflows, which keep the sheet of fog contained. The commercial Fog Screen that spits out this screen costs tens of thousands of dollars for the small one.
I attempted to create my own cheap version of this system using a wooden box, a window fan, some drinking straws, and a cheap fog machine. I almost succeeded.
The original idea was to mimic the commercial unit, and sandwich the fog between 2 sheets of air. Unfortunately, I had problems delivering the fog to the center chamber of the box. As I was building this rig as an effect for a haunted house, Halloween crept up on me and I ran out of tinkering time, so I just decided to block off one side of the box and pump the fog and the air together into the chamber, letting it exit together out of just one of the vents. This actually worked out fairly well, but I do plan to work out the bugs for a future version. I think that if the fog and “plain” air are sandwiched, the screen will remain coherent for quite a bit longer, and make for a much nicer screen effect.
I have no idea how the commercial fog screen makes those glass-smooth sheets of air, but all I could think of was to shoot the air through some drinking straws. I made a little box-jig and hot-glued up some bricks of 2 inch straw sections. I then chained those bricks together into long vents. It does straighten out the airflow quite a bit, but certainly does not produce a laminar flow. Oh well.
One thing to consider whenever you are using a glycol fogger, as this design does, is that these units use a heating element and a high-pressure pump to create the fog, which comes out hot and therefore rises, filling the room, or drifting away into the night. In order to keep the fog dense, and clinging eerily to the ground, you will want to employ a fog chiller.
I made my fog chiller with a 25 foot length of dryer duct coiled inside a garbage can. The garbage can is filled with ice, and the fog chills out while making its way through the pipe. The fogger sits on top of the garbage can lid and enters the chiller through the curved upper pipe.
The biggest hangup with this rig, was the intermittent nature of the fog. Cheap glycol foggers will only spit out fog for about 20 seconds at a time before pausing to reaheat before the next burst. Mine is off more than it is on.
Thoughts on further development:
If I can gather up enough muffin fans and ultrasonic misters, look for a much improved fog screen next Halloween.
This year, I showed Mark Gervais’s “The Eye” animation on the fog. Next Halloween I think that I will show a live feed of my green-lit self on a black background, that way I can talk to the trick-or-treaters from the fog.
Here are some more build photos.
Awesome! I have been looking for a DIY version of this for a while now. This would be great to do with the kids for next Halloween. Thank you and please give us updates on any changes.
Brian.
Your straw method is very similar to the way they achieve air flow at the Wind Tunnel, the one in San Diego uses a large honeycomb to clean up the air currents just before it arrives at the testing platform.
If you are interested I have pictures that I took inside the wind tunnel it might help you to figure out the dynamics of moving air by looking at their setup.
If you want to create laminar flow you need to make sure that the Reynolds Number of the air flowing is less than 2100.
Reynolds number is a unit-less number found by the formula
((Vx bar)(D)(rho))/(eta) = Re
rho is the density of the flowing gas/fluid
for air at room temp: rho = 1.177 kg/cubic meter
eta is the viscosity of the flowing gas/fluid
for air at room temp: eta = 1.85 * 10^-5 Pa*s
D is the diameter of the pipe
(Vx bar) is the average velocity of the gas/fluid
thus if you measure the diameter of the straws you used and you set Re = 2100 and solve for Vx you can find the absolute maximum velocity your gas can flow at before becoming turbulent.
I’ll bet if you scaled down the speed of the flow or increased the diameter of the straws you would be able to create your fog screen better.
The density and viscosity of the fog will be different than that of air but the values I have given you will be a good place to start.
Im sure you could find recorded values for glycol based fog somewhere.
Happy Making
I love this project, I wonder if going up would be better than down. The commercial version uses water; it has to drop to work. However unchilled fog rises I wonder if working with its natural tendencies might give you better results.
You are such a genius. I am in awe. I salute you.
Thanks Goat!
But I’m no genius, just stubborn - err, persistent.
Would love to see video of this in action. It’s a really cool project.
One small nit - the fog effect in the Pirates ride at Disneyland is a fairly recent addition, so to say that anyone who has “ever ridden” the ride knows the effect is not really the case.
Just saw the video at the top of the page. I feel like an idiot. But it looks great.
“One small nit - the fog effect in the Pirates ride at Disneyland is a fairly recent addition, so to say that anyone who has “ever ridden” the ride knows the effect is not really the case.” plus, the effect is not right before the first drop, it is right before the pirate ship harbor scene, so I guess that is two nits… Ed
Ed -
Right you are! I have edited the copy to read ” As anyone who has ridden the latest iteration of…”
-s
Awesome. I tried building one for Halloween this year too but ran out of time. Please keep us posted with updates. I will to at http://www.thehauntedshack.com
I keep staring at this. I feel like I am in the Gadget Louvre. I wonder if it could be adapted to make a cold smoker for my cheese? Must chill woodsmoke or it melts cheese.
this is a great job for a DIY project, well done!
I second the anon post above re: making use of the reynold’s number approach, that is the same method which is utilized for rough-draft designing and sizing of wind-tunnels, it can prove suitable to helping guide future revisions of this project.