how do vehicle windscreen demisters work?

Question

please provide the science of how it all works as well as diagrams...

Answer 1

Basically, coolant (water) from the engine is also fed into a small boxed in radiator either on top of the bulkhead under the bonnet, or under the bulkhead inside the car. A motorised fan is then brought into operation to blow air through the radiator, warming the air. A shutter can be used to direct the air to the windscreen, the interior or both.
Simplified, but that's the best description I can give without diagrams.

Answer 2

A demister is a device for clearing condensation from a window, which can also be useful for melting frost, ice, and snow that has collected on the window surface. They commonly exist in automobiles, in two basic varieties. Heating vents can be used to blow warm air over the window surface. Some Ford cars also have very thin wires embedded in the front windscreen (windshield) glass to give rapid demisting before the engine is warm, although these sometimes fail on one side of the screen as the thin elements burn out. Ford call this system "QuickclearTM"

The idea, as far as I remember, is that the warm air raises the temperature of the surface of the glass above the point at which condensation occurs, and any mist already formed evaporates again.

As for the diagrams, you'll have to complete your science homework yourself! Maybe you can crib from an owners's handbook if you can borrow one.

Answer 3

Car Demisters