Kelvin water dropper

The Kelvin water drop generator or Kelvinsche generator is a Wimshurst machine that wins the power to the structure of the electric power from the kinetic energy of falling water droplets, which are decelerated in the electrostatic field. The device was described by William Thomson, who called himself from the 1892 Lord Kelvin of Largs, in 1867.

General

Kelvin generator continuously

Kelvin generator with fluttering leaf electroscope

Kelvin generator, discontinuous

The electrostatic induction by the electric charges of the upper, smaller cylinder causes the ends of the water column is still closed, the ungleichnamigen to the charges of the charges are attracted to the cylinder which are then transported by the drops falling down. These charged droplets fall from the upper, smaller, not equally charged cylinders in the lower, larger, same name loaded cylinders containing in its interior conical funnel, the drops are decelerated by the electrostatic field. In the funnels of the lower cylinder, the drops give their charge, because distribute the mutually repulsive charges on the outside of the metallic conductive cylinder.

On which side of the Kelvin - generator, the positive and the negative voltage builds up depends either on chance or from a previously discontinued electrostatic charge. So long as one does not completely discharge the Kelvin - generator, it increases its voltage due to the positive feedback of the cross-connected upper and lower cylinders until a spark-over occurs, or until the water droplets are repelled by the electrostatic field of the lower cylinders and radiate in all directions.

With smaller devices, with for example 60 mm in height and by measuring the lower cylinders, as they are shown in the images, one can achieve approximately 3000 volts, which corresponds to a spark gap of about 3 mm. To view the discharges better, you still a 220 volt neon lamp can install before the spark gap in series.

Energy balance

The electric power of the Kelvin generator derived from the potential energy of the dripping of water at the top. Falling is braked by electrostatic repulsion from the bottom as well as by electrostatic attraction from above, so that a part of the kinetic energy is converted into electrical energy in the field cases. At high loads, the proportion may be so high that the droplets do not reach up to the hoppers because they are previously decelerated to zero velocity case, and now in the inhomogeneous field dodge to the side. For example, through a flutter leaf electroscope can be partially " recover " the mechanical energy of water drops.

The discontinuous device

Is structured yet simple discontinuous unit (in the right picture in the series of images ), but which has the disadvantage that one must empty his cup from time to time. On glass as an insulator should be abandoned generally in electrostatic machines because it possesses by the formation of a thin water film an appreciable surface conductivity. Insulators therefore water-repellent plastics are much better suited.

Other liquids

Kelvin of the generator can also be operated with distilled water ( deionized water). The autoionization of water represents the required (low ) conductivity safe. The conductive mercury would be due to its high density, particularly suitable, but it has a toxic vapor. The liquids used must have a certain conductivity to ensure potential equalization between the two Abtropfpunkten and also within the funnel.