Category: vacuum cleaners

Why does dust settle on the moving blades of a fan?

Lou Bloomfield Leave a comment

Why does dust settle on the moving blades of a fan?

As the air flows across the blades of a fan, the dust particles in it occasionally pierce through the airflow and hit the blades. The same sort of process occurs when a bug hits the windshield of a car; the bug would normally follow the airflow but its inertia prevents it from moving out of the way quickly enough and it hit. Once a dust particle hits the fan blades, there isn’t much to remove it. The air moves remarkably slowly right at the surface of the fan because that surface layer of air experiences lots of viscous drag. Even though the air is moving swiftly only a few millimeters away, the air right on the fan blade is almost stationary. Thus the dust can cling to the blade indefinitely.

For aerosol sprays such as Lysol, are they essentially creating “dustlike” par…

Lou Bloomfield Leave a comment

For aerosol sprays such as Lysol, are they essentially creating “dustlike” particles that float in the air?

Yes, except that the word “float” isn’t what you really mean. An aerosol is a suspension of fine solid or liquid particles in a gas. What holds those particles up against their downward weights isn’t the buoyant force—these particles are much more dense than the gas that surrounds them. Instead, it’s viscous drag. When the particles begin to fall downward through the gas, they experience such large upward viscous drag forces that they reach terminal velocity at only about 1 millimeter-per-second. The slightest breeze carries the particles with it so that they rarely have a chance to settle to the floor because of gravity. In an aerosol spray, the particles are carried forward by the gas emerging from the bottle and they hit the surfaces in front of the bottle.

How does a water aspirator pump work?

Lou Bloomfield Leave a comment

How does a water aspirator pump work?

The water aspirator pump is essentially a pipe with a narrowing in it. As water flows through that narrowing, it speeds up and its pressure drops—it’s exchanging its pressure energy for kinetic energy. A tiny opening in the side of the narrowing allows water or air to enter the high-speed flow. Since the pressure in that high-speed flow is very low, atmospheric pressure pushes fluids through the tiny opening and into the flow. The flow pumps fluids through the opening and into the water stream. If you connect a hose to the tiny opening, you can suck chemicals up the hose and into the water stream.