Use of sound to dry clothes

By Eli Rejwan

April 25, 2001

Very short sound waves are likely to prove effective in removing the residual moisture left after washing and spin drying clothes in the familiar washing machine. The moisture is in the form of droplets clinging to the fibers of the clothes and the sound is expected to dislodge them, particularly when resonance is achieved.

Use of sound to dry clothes.

Washing machines are designed to get rid of most of the water by spinning the clothes at the end of the wash cycle. Hardly any of the remaining water is absorbed by the fiber: it hangs in there in the form of tiny droplets hugging the fibers. The centrifugal pull is not enough to dislodge the smaller droplets.

Adding high frequency sound should do the trick.

The sound can be produced within the washing machine at the second half of the spinning cycle, its frequency to vary continuously within such a range as is expected to result in resonance with the droplet of water or with the fiber on which it is hanging. The violent shaking dislodges the water droplets, and spinning directs them towards the walls of the spinning cylinder. On the way some of these will reattach to other fibers, but many more will drag other water droplets and grow in size, like the growth of rain drops on their way down. Once they become large they are driven out by the mere centrifugal force.

Two forces act on the droplet of water: the centrifugal force and the water-to-fiber inter-molecular attraction. In larger droplets the centrifugal force prevails and the water moves out. The sound energy needed is just enough to cause a perturbance in the water and change the balance between the two forces.

The sound frequency is not intended to cause molecular resonance. Its wave length relates to the diameter of a water droplet or its multiples (effects of the harmonics of the sound wave).

There are important advantages in doing this. The energy required to produce sound is negligible when compared with evaporation by heat. Time saving, and possibly doing away with the drying machine altogether.

Another important advantage is ridding the clothes of the harmful salts and other compounds that are left on the fiber when water is removed by evaporation.

Industrial applications are not difficult to find. In the textile industry yarn has to be dried more than once (particularly wool) in the process of production.

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