Artificial clouds

Artificial Cloud/Smoke Ring/Bubble/Cannon/Cannon Smoke Ring - Science Museum Exhibits Solution

Science Behind It

Gas vortex

Vortices are sometimes referred to as whirlpools. It refers to a flow phenomenon in which a cylinder with a very small radius rotates in a stationary fluid, causing the surrounding fluid to make circular motion. Generally speaking, there is a dense vortex region inside the vortex, called the vortex core, whose motion is similar to rigid body rotation. Outside it, the circumferential velocity of the fluid is proportional to its radius; Inside it, it is proportional to half of its diameter, and the circumferential velocity at the center of the vortex is zero. Vortex is a form of eddy current that refers to uneven and irregular vortices of various sizes in turbulent motion. Its size is the same as the size of the widespread diffusion of the entire turbulence, for example, in the turbulent boundary layer, the maximum vortex is the same as the thickness of the boundary layer; The smaller, the lower the molecular viscosity of momentum exchange. In turbulent motion, due to the mutual stretching mechanism of eddies, eddies change from large to slightly smaller and smaller eddies of various sizes. The rotational energy of the vortex is then transferred from the large vortex to the small vortex, and then to the small vortex, until the viscous stress on the minimum vortex directly converts the rotational kinetic energy into thermal energy and dissipates it.

Exhibition items description

The exhibition items are designed as a booth type device with a circular air outlet in the center, surrounded by a compressible elastic tabletop with touch buttons and a smoke machine hidden underneath.

During operation, multiple participants can simultaneously press the elastic tabletop with force, triggering the smoke machine to start. Smoke gas is suddenly sprayed out from the narrow space under the tabletop, forming a gas vortex with a fast internal airflow rotation speed, thereby ejecting mushroom shaped smoke clouds from the jet nozzle.

form of expression

Mechanical interaction

How to Operate

1. Participants tap the tabletop;

2. Observe the smoke clouds produced by the jet nozzle;

3. Repeat tapping on the tabletop and compare the impact of different force levels on the formation of smoke clouds; End the experience and leave the exhibits.

Knowledge Expansion

Although people say smoking is harmful to health, children are still excited to beat the beautiful smoke rings that adults exhale when smoking, just like they beat the soap bubbles blown out in Western circles.

How are these beautiful smoke rings formed? You can press the start button on the exhibits. When there is moisture, you can press the sign with your hand and see the beautiful smoke ring rotate upwards. What the hell is going on here?

The essence of smoke ring formation is that the circular vortex of air restricts smoke particles (solid particles of cigarettes or small beads of dry ice, etc.) within a circular area.

When smoke particles and air quickly pass through a circular hole, the air particle mixture flowing out of the hole will pull the surrounding stationary air, forming a vortex that rotates outward and inward from the edge of the hole, as the air around the hole outlet is stationary. This can also be understood as Bernoulli's principle - that is, the pressure of fluid flow decreases, and static air with high peripheral pressure is added to the area with low pressure, thereby forming vortices. This vortex is distributed around the circular hole, forming a ring and moving upwards.

This circular vortex prevents the smoke particles from diffusing into the surrounding air at the same speed, meaning they are bound by the vortex and form the smoke ring we see.

Under the push of airflow, the smoke ring will slowly rise, and the velocity of particles in the smoke ring will also decrease. The binding ability of vortices will also decrease. Therefore, as the smoke ring rises, the smoke will gradually spread until it disappears.

video demonstration