Korey King
05-11-2009, 03:49 PM
This is one of the cooler technologies coming into the mainstream, whether or not it's viable as a DC3D I'm not sure but it's definitely worth a mention here.
Sciperio has an excellent overview (http://www.sciperio.com/watertech/water-from-air.asp) of how the modern process works:
For purposes of water harvesting, we are using liquid desiccants to absorb water vapor from the air. Liquid desiccants have at least two major advantages over conventional solid desiccants:
1. Liquid desiccants have significantly smaller absorption-evaporation cycle hysteresis characteristics than the adsorption-desorption cycle of conventional solid desiccants. This means that the energy losses per hydration-dehydration process cycle are smaller for liquid desiccants than they are for typical solid desiccants. A water-from-air system based on the application of liquid desiccants is inherently more energy efficient than a system based on conventional solid desiccant surfaces.
2. Liquid desiccants have a much higher relative water mass uptake capacity than conventional solid desiccants. Upon dissolution, for example, a LiCl ion pair generates two hydration shells comprised of a total of 26 water molecules (e.g., 26 moles of water per molar equivalent of dissolved solute). Only a few water molecules may be condensed and held within a traditional solid desiccant crystallite. As a result, liquid desiccants exhibit a 15-100 fold mass uptake advantage over traditional solid desiccants as shown in the figure below. This means that liquid desiccant-based water-from-air systems, in principle, will be lighter and more compact than comparable systems based on traditional solid state adsorbents.
http://www.sciperio.com/images/graphc_solidstate_adsorbents.gif
Hygroscopic salts, like LiCl, make excellent liquid desiccants. The free energy of hydration, ∆G hyd, is so large for such salts that, upon exposure to typical ambient room air, they dissolve in their own waters of hydration. Figure 5 represents a timed-sequence series of photographs, shot at Sciperio, showing the dissolution of solid LiCl crystals and the formation of a desiccant solution due to water vapor extraction from a flowing air stream (70 oF / 50% RH, 0.5 standard L/min flow rate):
http://www.sciperio.com/images/solid_licl_crystals_small.jpg
Below is an example of the water collection in our liquid desiccant solutions as a function of time at 50% relative humidity.
http://www.sciperio.com/images/graph_water_collected.gif
Simply put, the key advantage of a liquid desiccant cooling system (versus a pure refrigeration-type) lies in the fact that water vapor may be extracted from the process air stream without first removing the sensible heat.
Sciperio, LexCarb and others have some working models of the technology but AFAIK Aqua Sciences (http://www.aquasciences.com/) has the best implementation so far:
"People have been trying to figure out how to do this for years, and we just came out of left field in response to Darpa," said Abe Sher, chief executive officer of Aqua Sciences. "The atmosphere is a river full of water, even in the desert. It won't work absolutely everywhere, but it works virtually everywhere."
"I was pretty blown away by the things it's able to do," Rowe said. "The fact that this technology is not tied to high humidity like others are makes it an attractive alternative for military bases in the Mideast where humidity is not really an option.
Several systems on the market can create water through condensation, but the process requires a high level of humidity. Aqua Sciences' machines only require 14 percent humidity, Roy said.
The 20-foot machine can churn out 600 gallons of water a day without using or producing toxic materials and byproducts.
The cost to transport water by C-17 cargo planes, then truck it to the troops, runs $30 a gallon. The cost, including the machines from Aqua Sciences, will be reduced to 30 cents a gallon, Roy said.
"This is our secret sauce," Sher said. "Like
Kentucky Fried Chicken, it tastes good, but we won't tell you what's in it."
He did, however, provide a hint: Think of rice used in saltshakers that acts as a magnet to extract water and keeps salt from clumping.
"We figured out how to tap it in a very unique and proprietary way," Sher said. "We figured out how to mimic nature, using natural salt to extract water and act as a natural decontamination.
"Think of the Dead Sea, where nothing grows around it because the salt dehydrates everything. It's kind of like that."
Unfortunately it's not hard to see that their interests are aligned to pure profit potential courtesy of the military, which is a damn shame because this is a truly revolutionary way to provide clean water, for everyone, literally anywhere.
Sciperio has an excellent overview (http://www.sciperio.com/watertech/water-from-air.asp) of how the modern process works:
For purposes of water harvesting, we are using liquid desiccants to absorb water vapor from the air. Liquid desiccants have at least two major advantages over conventional solid desiccants:
1. Liquid desiccants have significantly smaller absorption-evaporation cycle hysteresis characteristics than the adsorption-desorption cycle of conventional solid desiccants. This means that the energy losses per hydration-dehydration process cycle are smaller for liquid desiccants than they are for typical solid desiccants. A water-from-air system based on the application of liquid desiccants is inherently more energy efficient than a system based on conventional solid desiccant surfaces.
2. Liquid desiccants have a much higher relative water mass uptake capacity than conventional solid desiccants. Upon dissolution, for example, a LiCl ion pair generates two hydration shells comprised of a total of 26 water molecules (e.g., 26 moles of water per molar equivalent of dissolved solute). Only a few water molecules may be condensed and held within a traditional solid desiccant crystallite. As a result, liquid desiccants exhibit a 15-100 fold mass uptake advantage over traditional solid desiccants as shown in the figure below. This means that liquid desiccant-based water-from-air systems, in principle, will be lighter and more compact than comparable systems based on traditional solid state adsorbents.
http://www.sciperio.com/images/graphc_solidstate_adsorbents.gif
Hygroscopic salts, like LiCl, make excellent liquid desiccants. The free energy of hydration, ∆G hyd, is so large for such salts that, upon exposure to typical ambient room air, they dissolve in their own waters of hydration. Figure 5 represents a timed-sequence series of photographs, shot at Sciperio, showing the dissolution of solid LiCl crystals and the formation of a desiccant solution due to water vapor extraction from a flowing air stream (70 oF / 50% RH, 0.5 standard L/min flow rate):
http://www.sciperio.com/images/solid_licl_crystals_small.jpg
Below is an example of the water collection in our liquid desiccant solutions as a function of time at 50% relative humidity.
http://www.sciperio.com/images/graph_water_collected.gif
Simply put, the key advantage of a liquid desiccant cooling system (versus a pure refrigeration-type) lies in the fact that water vapor may be extracted from the process air stream without first removing the sensible heat.
Sciperio, LexCarb and others have some working models of the technology but AFAIK Aqua Sciences (http://www.aquasciences.com/) has the best implementation so far:
"People have been trying to figure out how to do this for years, and we just came out of left field in response to Darpa," said Abe Sher, chief executive officer of Aqua Sciences. "The atmosphere is a river full of water, even in the desert. It won't work absolutely everywhere, but it works virtually everywhere."
"I was pretty blown away by the things it's able to do," Rowe said. "The fact that this technology is not tied to high humidity like others are makes it an attractive alternative for military bases in the Mideast where humidity is not really an option.
Several systems on the market can create water through condensation, but the process requires a high level of humidity. Aqua Sciences' machines only require 14 percent humidity, Roy said.
The 20-foot machine can churn out 600 gallons of water a day without using or producing toxic materials and byproducts.
The cost to transport water by C-17 cargo planes, then truck it to the troops, runs $30 a gallon. The cost, including the machines from Aqua Sciences, will be reduced to 30 cents a gallon, Roy said.
"This is our secret sauce," Sher said. "Like
Kentucky Fried Chicken, it tastes good, but we won't tell you what's in it."
He did, however, provide a hint: Think of rice used in saltshakers that acts as a magnet to extract water and keeps salt from clumping.
"We figured out how to tap it in a very unique and proprietary way," Sher said. "We figured out how to mimic nature, using natural salt to extract water and act as a natural decontamination.
"Think of the Dead Sea, where nothing grows around it because the salt dehydrates everything. It's kind of like that."
Unfortunately it's not hard to see that their interests are aligned to pure profit potential courtesy of the military, which is a damn shame because this is a truly revolutionary way to provide clean water, for everyone, literally anywhere.