Will someone kindly do the math that shows the energy needed to raise the temperature of water to steam vs the energy needed to lower the pressure on water to near vacume state so that it flashes to steam. Email the formula to me at cakilmer at yahoo.com and I’ll post it.

(See below for updated formula.)


Well it would be helpful to verify the claim that its more energy efficient to lower the pressure around water so as to flash it to steam than to raise the temperature of water to boil it to steam.

I first heard about this from one of the tenor guys in my community chorus last fall. He was doing consulting work for some outfit or other. I never got the details. They were looking into temperature differentials between say water at the surface and water +1000 feet down to power their vacume pumps. But the whole thing worked out to be too expensive. Recently, a report was published in New Scientist about some UK researchers who are working on a device which will use wave action to power a pump which will lower pressure and thus the temperature needed to evaporate (and then distill) water.

I mention this by way of introducing some Florida Atlantic University Grad Students who claim they can reduce the cost of water desalination by a factor of ten by using waste heat as an energy source to lower the pressure on water so that it will flash to steam. ( The key concept here is using heat to lower pressure on water to flash it to steam — rather than using the heat to raise the temperature of water to boil it.)

“I’ve been able to build this incredibly eccentric machine, spill gallons of water everywhere, and generally act like the mad scientist I always wanted to be as a kid,” said Eiki Martinson, one of the students involved. “Best of all, we solved one of the biggest problems of today — with an invention that can save millions of lives around the world.”

Martinson and Brandon Moore developed a process estimated to be 10 times more efficient than existing desalination technologies.

Sounds like these guys are having fun.

Moore and Martinson have been working in conjunction with their advisor, Dr. Daniel Raviv, an electrical engineering professor, to create a process that depends on recycling waste energy to distill water at a near vacuum and at room temperature. The project was initiated and sponsored by inventor Michael R. Levine, who currently holds 76 patents.

Levine said he came up with the first version of the distillation process on paper, and the FAU team took it to another level, augmenting the inventor’s idea — and creating the working apparatus.

The FAU team and Levine are working with power and water agencies to scale up the project so it can provide a million gallons of fresh water per day.

The students entered the project in the 2006 Collegiate Inventors Competition, a program of the National Inventors Hall of Fame Foundation. They were among the top seven finalists in the United States/Canada competition. This honor recognizes the innovations, discoveries and research by college and university students and their advisors for projects leading to inventions that can be patented.

How might this be incorporated into current tech.

Well– as I mentioned in Greenhouses For Desalinised Water and OilAquasonics technology is currently using waste heat to power a special nozzle that breaks water into a very fine mist. This mist is then hit with hot air. Instead of using waste heat to hit the mist — maybe the waste heat could be used to create a vacume. The question is–is the energy used to create the vacume orders of magnitude lower than the energy used to heat the water. And is the equipment needed to create the vacume relatively simple/inexpensive.


P=Pressure V=Volume T=Temperature



P1V1/T1 = P2V2/T2=P3V3/T3

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  1. The point of using low pressure to be able to flash evaporate water centers on using sea surface water in the tropics as the heat source – about 80 deg F. To generate water vapor at 80 deg F, it must be at low pressure. The water vapor is then condensed by cold water pumped up from depths – about 40 deg F.

    All the effort is in between the latent heat of vaporization to vaporize and then removing that heat. It takes 2260 kJ/kg to vaporize water at 100 deg C.

    The idea works if one could pull a vacuum to get the process going. The vacuum would be maintained by condensing the water vapor. (That’s how hurricanes work, and why they are low pressure – all that water vapor condensing due to altitude cooling; the vapor the warm ocean is generating.)

    The problem is due to the dissolved gases in the ocean surface water. Once sprayed into the vacuum chamber, CO2, O2, etc., get released, and removing these gases makes the process not economical.

    Comment by Ed McMahon — February 12, 2007 @ 9:27 pm

  2. Combine deep water oilwell support tubes with temperatre diference technology
    and wave action pumps to send oil and water to the coast.

    Comment by mike payne — July 4, 2007 @ 2:50 pm

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