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Old 11-15-13, 09:01 PM   #41
jeff5may
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This story just keeps getting more interesting the deeper I look. It seems that AIL Research and the DOE/NREL/ORNL did a few proof of concept studies over the last couple of years.

First, AILR worked with Kathabar, Inc. as a subcontractor / consultant to build a large-scale prototype. It worked, but not real well for long.

Then, they built and beat the peewaddin out of a solar thermal powered system at Tyndall AFB in Florida. During this study, the original design had to be modified. The solar collector had been built with flow-through collectors (instead of heat pipes) using glycol water as the heat-transfer fluid, with no thermal dump. It was not a drainback system, so the unit had to be able to withstand freezing and stagnation. During stagnation, the collector developed 450+degF temps, generating glycol acid steam that they had not properly prepared for. It took 6 months to refine operation of the solar thermal unit. The resulting kludge that worked meh could not supply all the solar btu's to the regenerator it was originally designed for. It was redesigned to use straight water, so it had to be drained and winterized during the cold season, during which time it could not operate.

The LDAC achieved all its design criteria except one: target EER was 40, it could only muster between 15 and 25. Nevertheless, the system was deemed a proof of concept, with valuable lessons learned.

Meanwhile, Dr. Lowenstein, Andrew, the driving L in AIL Research, built a few of his own systems with the help of venture capital. Patents were awarded and rights licensed to third parties everywhere. Big ticket buyers are hospitals, hockey rinks, supermarkets, and indoor swimming facilities. He has licensed this LDAC technology to the Munters Corp., a commercial HVAC manufacturer, to bring this technology to the industrial world.

The research paper with glorious technical details and secrets is here:
http://www.nrel.gov/docs/fy13osti/56437-2.pdf

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Old 11-15-13, 09:07 PM   #42
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it seems with CaCl2, the magic number is 43%. Above 43% CaCl2, below 57% H2O, crystals appear in the solution. Above 57% H2O, the salt is fully dissolved. At room temperature.

Calcium chloride has five hydrate states:
772 °C (anhydrous)
260 °C (monohydrate)
176 °C (dihydrate)
45.5 °C (tetrahydrate)
30 °C (hexahydrate)
At atmospheric pressure.

So, at 45.5 degC it naturally dehydrates to dihydrate. Which is well in the range of solar thermal.

Aha! found another chart! Relative humidity vs Temperature
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Old 11-16-13, 12:23 PM   #43
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Quote:
Originally Posted by jeff5may View Post
...
Calcium chloride has five hydrate states:
772 °C (anhydrous)
260 °C (monohydrate)
176 °C (dihydrate)
45.5 °C (tetrahydrate)
30 °C (hexahydrate)
At atmospheric pressure.
So, at 45.5 degC it naturally dehydrates to dihydrate. Which is well in the range of solar thermal.
This may or may not be germane to your research, but when I was focusing on CaCl2 as a phase change material, it seems that the big problem with CaCl2 salt solution is that every time the hexahydrate form of CaCl2 went from a solid phase to a liquid phase at 86F (30C) it would remain in the hexahydrate mostly... but for some reason, some small percentage would go to the tetrahydrate state, and since the phase change material was being used in the temperature range from maybe 10 to 20 degrees F above and below the 86F temperature, the useful hexahydrate percentage became less and less available for thermal storage and recovery. George Lane's work focused on additions to the solution to prevent the CaCl2 hexahydrate from going into the CaCl2 tetrahydrate state.

Again, may be useful, maybe not.

-AC
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Old 11-16-13, 02:16 PM   #44
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This is what the dehumidifier takes advantage of! The affinity for water is greatest near room temps (below 86F, 30C). This is illustrated in the graph above as segments BC and B'C'. Between about 20C and 45C, the solution actually is a mixture of hexa- and two orientations of tetra- hydrate. Hexahydrate is the dilute form, which rises to the top of the stratification tank as "weak" solution. Tetra is more dense, and fills the middle layer. When heated above 45C, the hexa- and tetra- hydrates cannot exist, so they decompose and lose the water to form dihydrate. This dihydrate sinks to the bottom of the tank as "strong" solution.

More to come...
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Old 11-17-13, 11:22 AM   #45
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Check out these two charts:

http://www.magnumsolvent.com/product...20Chloride.pdf

As AC has described, when the brine solution cools (in a regenerator or a heat store), especially when cooled from above 45 degC (around 115 degF), the calcium chloride has an inconsistent behavior as to when and how the dissolved, melted salts refreeze. Mainly, different crystals form at random.

To further complicate matters, the fractions which freeze first are less soluble in water. It works against someone using a sealed container for a heat store, because the dihydrate and tetrahydrate give up water molecules to solution as they freeze, effectively diluting the solution. The heat store engineers are all about the hexahydrate since its heat of fusion is the highest. More heat of fusion = more heat storage per unit of measure.

In a dehumidifier, this effect doesn't really affect much UNLESS the salt concentration gets upwards of 45% or so. As long as there is enough water in the solution, all the salt will remain dissolved in it. At sky high temperatures (above 250 degF at 40% concentration), the water will eventually boil out of the mixture due to vapor pressure. Due to this boiling, solutions of more than 69% cannot be achieved at atmospheric pressure. At around 320 degF, solid dihydrate separates from solution as a solid. The solution can never reach 70%.

If I were trying to make some sort of solar distiller/reformer outdoors, I could set up a still that would heat the pot or column to near 300 degF, evaporating and/or boiling the water out of solution. At or near 300 degF, the vessel could be drained into a cooler place (think ice trays) where the highly concentrated solution would refreeze, giving up gobs and gobs of heat in the process. This solid could then be used many ways. It could be recycled as desiccant. It could be used to heat water (just toss it in a container of pure water and it naturally warms the container as it dissolves). However, this is not a highly efficient process used just to dehumidify the air.

Last edited by jeff5may; 11-19-13 at 11:48 AM.. Reason: grammar
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Old 11-17-13, 12:46 PM   #46
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Quote:
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Check out these two charts...
I see that this stuff would make a great dryer for improving the quality of hardware store propane, and make it better suited for HVAC.

What are you seeing that is interesting you?

-AC
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Old 11-17-13, 04:10 PM   #47
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For a more effective liquid dehumidifier, we want to move the most water per btu or watt used to regenerate the dessicant. This means the regenerator should only be heated enough to drive the water from the solution to a concentration where solid salt would not form. Raising the brine temp to above 115 degF would make the hexahydrate want to give up water to form tetrahydrate, so if you had a regenerator with a large enough surface area, you could evaporate the brine out to around 50% strength effectively at or above that temperature. Higher regenerator temperatures equate to smaller surface areas with the same evaporation rate. Most commercial units shoot for around 180 degF to make the evaporation highly effective.

Indoors, the solution must have a certain strength to effectively pull water from the air. At normal room temps, this equates to somewhere above 40% minimum concentration. At 40%, the solution will dry the air down close to 40% relative humidity. More CaCl2 in the water equates to more dehumidifying power per liter.

Above 45% strength, the solution will tend to form crystals in the dehumidifier (which would tend to warm the liquid as they re-dissolved into the water) as the solution cools below 105 degF. So there is a sweet spot (between 40 and 45 percent concentration) that the solution should stay to avoid all manner of phase-change mayhem, assuming that solid crystal formation is unwanted.

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Old 11-17-13, 04:57 PM   #48
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AC,

The petroleum industry actually uses CaCl2 to dry their wet streams of gas, most probably because it is much cheaper and abundant than zeolite. It would be dead simple to rig up an inexpensive filter-drier.

I am intentionally leaving a lot out of my posts as to the many applications of this material. The phase change theory fit into the overall process for explanation's sake, but the omitted possibilities should provoke the imagination, to say the least.
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Old 11-19-13, 01:55 PM   #49
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Quote:
Originally Posted by jeff5may View Post
A retail, residential, affordable dessicant wheel dehumidifier:

SD-014V: Desiccant Dehumidifier


I looked at the manual for this unit, see below...


I have no idea if this represents typical effficiency, but a vapor compression unit that draws 650 W would be able to remove about three times the amount of humidity.

So for this scheme to be competitive, some kind of "free" power like either solar thermal or solar PV might be required.

-AC
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Old 11-20-13, 02:19 PM   #50
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The above example is a plug-and-play, off-the shelf example of a dessicant-wheel-powered dehumidifier. From the specs, it is said that the heater used to regenerate the wheel uses 200W, 400W, 600W on lo, med, hi settings respectively. So the vast majority of energy this unit consumes is used to recharge the wheel. Of the 615 rated Watts on Hi, only 15 or so Watts is used by the blower.

What I found VERY interesting about the unit is the relatively low discharge temperatures cited. The manual says 105 to 120 degF discharge temps are typical with 83 to 86 degF ambient. This is well within the range of even "crude" solar collectors. So with a 30-ish degree delta T on the supply air side, a hacked unit such as this could be made to use only fan power to do its job with not that much additional thermal sun power. It could easily be made to slow down or stop as sun exposure faded in and out.


Last edited by jeff5may; 11-20-13 at 03:44 PM.. Reason: info
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