Twin attack on moisture build-up
Two non-competing technologies use a small amount of electricity to remove moisture continuously from inside a closed volume. Tom Shelley reports
A family of Japanese solid-state devices removes moisture from inside enclosures electrolytically, while a rather larger British-made device continuously eliminates moisture from power transformers and tanks of chemical by utilising absorbent, a heater and natural changes in atmospheric pressure.
Both devices are ‘fit and forget’. However, while the Japanese device is ideal for maintaining the functioning of electronic products in a damp climate, the British device is equally adept in its application areas.
The solid-state devices were originally invented in one of Mitsubishi Electric’s R&D laboratories for use in preventing condensation in cameras and laser-type applications. Now made by Rosahl, which is also a Japanese company, they are marketed in the UK by Westside International of Chinnor, Oxfordshire. They work by absorbing moisture in a porous anode electrode (positive) on the inside of the enclosure, where the water molecules are split up into oxygen and hydrogen ions. These ions then pass through a polymer electrolytic membrane in the centre and recombine with oxygen in the air at the porous cathode electrode (negative) on the outside. They come in sizes that range from a 2W unit measuring 31 x 26 x 6mm and can remove 0.2g of moisture per day from an enclosure of about 0.2 cubic metres, to a 58W model measuring 195 x 370 x 70mm that can remove 58g of moisture per day from an enclosure of about 8 cubic metres. List prices are from 55-65 euros, to 1,400 euros each. Suggested applications include: traffic control cabinets, outdoor multimedia screens and displays, mobile phone outstations, storage cabinets, museum displays and semiconductor manufacturing.
The British device is called Re-Actrans and is made by Brownell in Park Royal, which describes it as a “self-reactivating transformer breather”. It is designed specifically to be fitted to transformers and large tanks that have to avoid possible pressure differentials relative to the ambient environment, but are liable to take in moisture as air flows in when the ambient atmospheric pressure is greater than that inside. A desiccant container then has to be fitted to prevent moisture getting in with the air.
A regeneration cycle where the desiccant is heated to 70-80oC is initiated when what Brownell director Martin Partridge describes as an ultra sensitive pressure switch detects that the pressure inside the tank is greater than that outside, so air must be flowing out. This outflowing air can then be used to carry away moisture that has been released by heating the desiccant. “The diaphragm pressure switch is one we did ourselves, which is sensitive to pressure differentials down to 0.1psi”, Partridge explains.
The device uses 280W of power and is suitable for transformers containing up to 25,000 litres of oil. The pressure switch setting is adjustable from 10 to 50 millibars (0.15 to 0.72psi). The device measures 355mm high, is 200mm in diameter and environmentally protected to IP65. It is also deployed on large tanks of concentrated sulphuric acid and hydraulic oil.
* The solid-state devices use an electrolytic process to transform hydrogen in the moisture from the inside of enclosures, releasing oxygen, and recombine the hydrogen ions with oxygen in the air on the outside
* The Brownell devices remove moisture from air entering large transformers and tanks using desiccant and regenerate it when the internal pressure is greater than ambient, so that air is known to be moving outside
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