I have found Forbes magazine, perhaps surprisingly, a good source for interesting articles about inventions.
Recently I read in it an interesting article about Leif Hauge of Norway and his research into using pressure exchangers in the desalinization of sea water. Using sea water as a source of potable water has long been desirable, but the problem is the amount of power involved.
The sea water is subjected to great pressure so that the water is forced through a membrane which enables the small water molecules to pass through but not the larger salt molecules. Traditionally, the story says, that pressure was allowed to go to waste. Hauge wanted to utilise it in a pressure exchanger where the pressure was used again.
Pressure exchangers do exist but Hauge's worked on a new principle. The exiting water enters chambers in a cylinder and, as water can't compress, transfers nearly all its momentum to water entering the chambers at the other end before exiting. The cylinder spins 1000 times a minute, and is the only part that moves.
The article says that the PX-300 pressure exchanger is 4 feet long and weighs 180 pounds. 13,000 gallons of water is handled an hour. The device costs $25,000 and has 70% of the market for desalination energy-recovery devices. It needs no maintenance and pays for itself in electricity savings in about six years.
Hauge eventually lost control of the company, Energy Recovery Inc. I can trace two relevant patents, the second being his Pressure exchanger patent application.
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