We've all seen those halloween lawn displays, with halloween props and jumping spiders, but have you noticed some of them have a misty cloud of fog near your feet? Or wedding dance floors, with fog seemingly errupting out of the ground. That's low lying fog, and traditionally it's done with strapping a A/C unit to a regular fog machine and using some special fog liquid. But these can cost hundreds, maybe thosuands, of dollars, and A/C units are loud & heavy, and eww I don't want that!
What if there was a way to get a very similar effect, but on a budget? It's crucial to understand what makes fog look like fog. In physics class we were taught that higher density gasses/liquids like to stay low, and lower density object like to be at the top. It's like when you mix water & oil, the water stays at the bottom, and the oil floats to the top. Water has a higher density than oil; and this is the same for gases.
Taking this logic, we need the fog to be "heavier" (a higher density) than the surronding air. But it isn't just the weight alone - it's the opacity. while simultaniously retaining it's opacity. We can each optimize both
Other than increasing the concentration of Vegetable Glycerin in the fog liquid, there are several ways we can add mass by cooling the fog or decreasing the temperature directly.
- Cooling the fog
- Adding a A/C unit
- Using something already cold like Ice or dry ice
- Evaporating water
- Peltier cooling modules
Indirectly by cooling the fog, we're increasing the relative humdity but not the absolute humidity. If there's no water in the air there's no fog to be seen. There's only one way to increase the absolute humidity of air: encoruging evaporation.
Evaporating water is by far the best method to both cool the fog and raise it's absolute humidity, but this isn't always enough. The Wet Bulb Temperature dictates how cold the fog can get by way of evaporation, and if it's very humid outside, you won't get much cooling effect. Evaporative cooling works best in a dessert, but if your say, in a jungle, you'll have to rely on the other methods.
Air can be very cold and humid, but as soon as it touches the outside and warms up, it'll vanish. This is what the fog machine helps with, creating a everlasting thick smoke. Besides a 100% relative humidity creating natural fog, evaporating a liquid such as propelene glycol will create this smoke effect.
This leaves a few options, I'm going to eliminate adding a A/C unit, and reframe from using something cold like Ice or Dry ice, since they're consumables. Great! Now I have a list!
We ways we want to accomplish it, now we need to actually apply it and figure out the specifics. Fortunately, there are many videos on this on Youtube, with most of them using a Ultrasonic Mister / Atomizer / Nebulizer in order to accomplish both cooling and to increase the humidity of the fog. I feel there are ways to improve upon this design though.
Most basic designs have a fog machine on top of a large plastic box, with a angled piece of PVC piping extending from the box to the nozzle of the fog machine, spaced about a few centimeters away to allow for outside air to be pulled in as well. The box is filled with water with the ultrasonic mister sitting near the water's surface to generate water vapor, the pressure forces the fog & water droplets to mix and eventually exit through an opening on the side.
I am terrible with CAD software and I hate TinkerCad, so I made a model in what I know best, Roblox Studio. I created a rough deisgn as a 3D model showing a bit what it would look like.
Check out the 3D Model here at Poly.cam. Unfortunately the water didn't render correctly when exporting from roblox - so just imagine there's water at the bottom and at the far back where theres the piping.
Master plan for ultimate cooling potential.
Throughout the stages a thermometer would be strategically placed to allow for a MCU to adjust various stages power limits to get to the optimium temperature.
However there is only so much speculation and prepartion you can do, and for something like this you really need to go and try it and then see what you can improve.
Directing the newly created fog through underwater piping before landing at the ultrasonic mister will allow for,
- Increased reservoir water capacity
- Inital cooling through water as heat sink
- Efficent ultrasonic mister water regultion through the use of 'water level control valve'
A thermometer and humidity sensor will be put into the exit of the pipe to allow for a wet bulb temperature and dew point calculation. A fan will also be placed exiting the pipe to allow f0r adjustable flow to speed up or down the fog entering.
These ultrasonic misters will increase the humidity of the fog and evaporate water in the process thereby cooling the fog, a fan may be placed directed at the water to increase water evaporation.
Peliter cooling elements may be used to further cool the fog, meant to use sparingly and only as a miniscule cooling source as their very inefficent.