HOW DOES A FOG MACHINE WORK?
Updated: Jul 24, 2022
Fog machines, sometimes called smoke machines, are devices that produce a vapor that is very similar to dense natural fog. They are often used in the entertainment industry to create special effects. Since the technology of these machines is very simple, it is possible to acquire them for a low price, and they are available to ordinary consumers. Although this machine is often referred to as a smoke machine, it does not actually produce smoke but vapor.
A fog machine uses a special liquid to create fog. This liquid is usually a mixture of water and glycerin. The fog machine heats the mixture to the required temperature, and the vapor escapes into the atmosphere through the nozzle. When the hot vapor mixes with cooler air, it condenses and forms fog.
All fog machines can be divided into three major groups: regular fog machines, haze machines, and low-lying fog machines. Although they are all designed to produce fog, the fog produced can vary in density or how long it stays in the air. Let's explore how they work and what their main differences are.
How does a regular fog machine work?
The picture below shows the main parts of a typical fog machine. The liquid fog mixture is poured into a tank, from where it is pumped into the heat exchanger by a small pump. In the heat exchanger, the temperature of the mixture rises rapidly and the mixture starts to evaporate. The hot vapor escapes into the atmosphere through the nozzle.
On the right side of the picture, you can see the heat exchanger, which is the most important part of the fog machine. The heat exchanger temperature switches control the temperature of the heat exchanger, switching the contacts on or off at the right moment. The temperature in the heat exchanger must be just right for the mixture to evaporate. If the temperature is too low, the mixture will not be pumped into the heat exchanger. Similarly, the heat exchanger must also not overheat. However, if it should ever fail it's a fairly easily replaceable part.
The wattage of the heat exchanger also determines how much vapor it can generate. Fog machines have different wattages, but they usually range from 400 watts to 1000 watts. Machines with higher wattages can also produce significantly more vapor. The amount of fog produced is measured in cubic feet per minute (CFM) or cubic meters per minute (CMM). By definition, it should show fog output in cubic feet per minute. If we have a 500-watt fog machine rated at 2000 CFM 2-3 meters from the machine, it should theoretically produce a maximum of 2000 cubic feet of fog per minute at that distance.
However, since there is no standard for fog density, the CFM number is not always unambiguous. For example, one and the same machine can produce 500 cubic feet of dense fog per minute and 1,000 cubic feet of thin fog per minute. But you can always be sure that a machine with a higher wattage will always produce more fog than a machine with a lower wattage.
What is the difference between a fog machine and a haze machine?
A haze machine, in the same way as a fog machine, produces fog, but the vapor droplets produced by a fog machine are large compared to the particles produced by the haze machine. The haze machine produces fine vapor particles about a micrometer in diameter, creating a haze that disperses well and stays in the air for a long time. Since the haze particles are very small, they are difficult to notice under normal lighting conditions. It gives the best effect with light beams because the light is reflected back from the tiny fog particles and makes the path of the light beam visible.
While some haze machines use heat exchangers like fog machines, many do not include a heating element. Haze machines with a heat exchanger are simply fogging machines with a fan added, to thin the vapor and disperse it more. Haze machines without a heating element don't need a warm-up time and can create fine vapor right away. Instead of a heating element, this machine uses an air compressor to atomize the liquid and create very small vapor particles. When the liquid comes into contact with air moving at a high speed, it breaks up into small particles due to friction with the air particles.
How does a low-lying fog machine work?
Low-lying fog machines produce dense fog that floats low on the ground. It creates the effect of walking on clouds. This fog does not rise and does not disperse easily, because its temperature is lower than the ambient room temperature. Vapor is cooled before exiting the machine, usually using ice. As you can see in the picture below, this machine is very similar to a regular fog machine with the addition of a vapor cooling chamber.
One of the most classic low fog machines uses carbon dioxide (dry ice) to produce fog. Since dry ice changes directly from a solid to a gas, it is said to sublimate, as it exists in a gaseous state at normal pressure and room temperature. This machine has a dry ice basket located above the hot water reservoir. The air above the hot water is saturated with water vapor, and when it mixes with carbon dioxide, it condenses and forms a dense and heavy white fog.
It is also possible to create low-lying dense fog without carbon dioxide or ice. Fog machines that use high-frequency waves to atomize water do not even need ice to cool the vapor, because it is not hot. These machines have piezoelectric discs in the water tank. When the piezoelectric discs oscillate at a high frequency, the water above the discs is turned into tiny droplets. This method is called ultrasonic atomization. But of course, fogging without ice and carbon dioxide is significantly more convenient, and these machines come with a higher price tag for that.