Planning simple basin still prototype 2

I posted a test of the simple basin prototype #1 yesterday:

https://bkhome.org/news/201911/first-test-basin-type-proto-1.html

The result was promising, so decided to go ahead and design prototype #2. A major requirement is that it be as flat as possible, so as to take up little space when slid into the back of a hatchback car or 4wd vehicle. In fact, that was one of the main reasons, that and promised improved efficiency, that I went for the tilted wicking-cloth type of still. However, I have now learnt that the glass can be very close to the water, water depth can be mere millimetres, and the glass angle can be as little a 5 degrees, maybe even lower.

It may be possible to design the still to be only about 100mm (4 inches) thick at the widest end, which would be great. However, might not quite get that thin. This reference recommends a minimum glass angle of 10 degrees (scroll to page 445):

https://books.google.com.au/books?id=H8aJC5BWCSEC&pg=PA445#v=onepage&q&f=false

...it is unclear whether that 10 degrees figure is for plastic panes. Water droplets stick to glass better, and perhaps it would still work for angles less than 10 degrees.

The above reference also recommends water depth of 20-30mm and side and bottom insulation thickness of 20-30mm.

In all of my reading, I keep coming back to silicone as the superior product. Inert, extreme resistance to corrosion and UV light, and retaining its flexibility for 10-20 years.

Rather than build the still out of wood, as I have done so far, I am thinking of using aluminium insect screen mesh, coated with silicone sealant. This would give me a flat surface that I can bend into shape, to form the basin and support for the glass. There could be an outer frame, into which insulation is poured -- maybe polyurethane expanded foam -- or even silicone mixed with foam bubbles.

Thinking along these lines, I have started testing coating of insect screen mesh. I bought a roll of aluminium mesh, 1220x2050mm, AU$23:

https://www.bunnings.com.au/cyclone-1220mm-x-2-05m-aluminium-insect-screen_p4110400

Also some cheap Parfix brand acetic-cure white silicone sealant, AU$6.68:

https://www.bunnings.com.au/parfix-300g-white-bathroom-and-kitchen-silicone_p1232690

I have a plastic spreader, that was used for the early wicking-cloth type prototypes:

https://www.bunnings.com.au/uni-pro-wallpaper-smoother-and-straight-edge_p1661659

I tested spreading on a mesh offcut, with newspaper backing, plastic backing, and hanging vertically in the air:

I then pulled the backings off and hung it up to set.

From this initial test, it looks like two or three coats will be required. For the final construction, I will probably do two coats of cheap white silicone, then one coat of black Silastic 732 silicone.  In earlier experiments I found that silicone-on-silicone adheres extremely well, so there will be no adverse issues with doing multiple coats. 

Tags: nomad

First test basin type proto 1

Yesterday I posted some design notes, and construction details of a first prototype of a simple basin-type solar water distiller, using parts found in my garage:

https://bkhome.org/news/201911/simple-basin-solar-distiller-design-notes.html

After knocking it up, further reading revealed some design shortcomings. However, this first prototype will probably be useful for "ball park" measurements, to see if this type has potential. As already stated, I was very surprised at the claimed output of the Rainmaker 550, and if I can also achieve this level of efficiency, then this simple design looks like the best way for me to go.

Here in Perth, Western Australia, we are having our first summer heatwave. Prediction today was 40 degC (104 Fahrenheit), superb day for testing!

I set it up early in the morning. The previous evening, I had stuck some cardboard on the sides, a rather feeble attempt to improve the insulation, don't know if it will make much difference. Here it is, photo taken at 8.20am, the sun has just hit the top corner:

...I only put in 3 litres of water, as efficiency is said to be improved with less water depth. Glass is 600x900, as is outside dimensions of the base, so water depth is only a few millimetres.

Oriented the panel for peak output at about 11am, and waited for the sun to march across the panel. About 9.00am had sun on all of the panel, and a tiny bit of distilled water appeared, so started measuring from 9.00am.

9.00am. Some gusty wind. Sunny sky with some fluffy clouds.

10.30am. Sun: 870 W/m2, ambient: 31 degC, temperature about 3/4 up the panel, IR sensor about 2 inches away from glass: 53 degC, 1/4 up: 52 degC, back side of distiller, about 2 inches away: 39 degC

12.00 noon. Only very slight breeze. Fluffy clouds mostly gone. Sun: 890 W/m2, ambient: 34 degC, 3/4: 64 degC, 1/4: 63 degC, back: 45 degC

1.30pm. Sun: 960 W/m2, ambient: 38 degC, 3/4: 64.7 degC, 1/4: 64 degC, back: 48 degC

3.15pm. Stop.

Collected distilled water: 1.525 litres

Collection duration was 6 hours and 15 minutes, so collected 244 millilitres/hour. Collection area is 0.568x0.868 metres2 which is 0.493 m2.

Now for the exciting part, to compare with the F-Cubed panel. Different weather conditions of course, so this comparison is a very rough guide only. Refer to prototype #4 results:

https://bkhome.org/news/201911/solar-distiller-prototype-4-first-test.html

Quoting, result for prototype #4:

the collection: 1.1 litres, in 7 hours. That is 157 millilitres/hour. The cloth has a surface area of 0.3327 m2, so to compare efficiency with the F-Cubed panel which is 1 m2, need to scale up: 157*(1/0.3327) which is 471.9 ml/hr. The F-Cubed panel gave 563.6 ml/hr, so the test has a comparable efficiency of 83.7%.

Today's test (simple basin type, prototype 1) also needs scaling: 244*(1/0.493) which is 495 ml/hr. Efficiency relative to the F-Cubed panel is 87.8%

Wow! And that's with a design that probably has room for improvement.

I must re-state that these comparison percentages may be way off. The F-Cubed was tested mid-winter, full sun but much lower ambient temperature. I really do need to set up my panels alongside each other for a proper comparison test.

The most obvious improvement that can be done, as seen from today's test, is to improve thermal insulation on sides and bottom. At 1.30pm, the back side of the panel measured 48 degC, 10 degC above ambient.

Another area of improvement will be to decrease glass angle, and bring glass very close to the water surface. There is however, a tradeoff, as if sun angle to the glass is more than about 70 degrees off perpendicular then it just reflects off the glass. A balance needs to be found, to suit summer and winter sun angles.  

Tags: nomad

Simple basin solar distiller design notes

A few days ago, I posted about the Rainmaker 550 single-slope simple-basin type of solar water distiller:

https://bkhome.org/news/201911/rainmaker-550-solar-water-distiller.html

...for which the manufacturer claimed remarkably high distilled water output. I want to find out for myself, so decided to build one, no, at least two.

I re-purposed prototype #2, which was the trickle-down type, just one sheet of glass, and the frame was MDF. The interior was coated with silicone sealant. That was built back in June:

https://bkhome.org/news/201906/diy-solar-water-distiller.html

...took those legs off, and it then became the water basin. Cut some more pieces of MDF, and coated the inside with black silicone sealant, then a bit more patching with some leftover grey sealant:

...also stuck some foam silicone strips on top, and the glass (600x900mm) will just sit on top. Used a length of 10x10mm aluminium channel as the distilled water runoff.

I used cheap Parfix brand black sealant, two 310 gram tubes, used it all, hence resorted to the grey sealant for final patching.

For the record, black silicone sealant rated as "food grade" and "potable water" safe, is Silastic 732, available at a very reasonable price from Autobarn (Australia), AU$18.99:

https://www.autobarn.com.au/silastic-732-black-cartridge-310g

The build so far is good enough for basic ball-park testing I suppose, however, there are two things "wrong" with this design -- let's call it prototype #1 of the simple-basin design.

Firstly, there is going to be too much heat loss. This design needs insulation, and I might just stick cardboard onto the sides and bottom of the MDF.

Secondly, the glass angle is 35 degrees, however, after some more reading, I found a recommendation that the optimum angle is 15 degrees. This information comes from here:

https://www.appropedia.org/Improving_Basin_Solar_Stills

...which has a link to this PDF which is where the 15 degrees figure came from:

https://www.ircwash.org/resources/solar-powered-desalination-case-study-botswana

Another recommendation is that the water depth in the basin be kept low, like about 10mm. Can do.

I could cut a slice out of it to lower the angle, but might just leave it as-is, the after some testing, move onto prototype-2.

For basin-prototype-2, might investigate a better insulating material. I am thinking of black corflute, such as Tunnelcore, from Bunnings:

https://www.bunnings.com.au/tunnelcore-2250-x-1220-x-2-5mm-black-double-walled-plastic-board_p0390221

...corflute is made with polypropylene, and Tunnelcore has UV resistance. Polypropylene is one of those slippery kind of plastics that is very difficult to glue. I am planning to experiment with heat-gluing. 

Tags: nomad

Prototype 4 warped wood has unwarped

Fascinating! I posted about first test of solar water distiller protototype #4 two days ago:

https://bkhome.org/news/201911/solar-distiller-prototype-4-first-test.html

And the wood warped and split:

Most curiously, there was no noticeable warping or splitting when testing prototype #3, which was essentially the same design. I think what happened in the last test, it was longer duration, higher ambient temperature, and when the wood started to split, that allowed water ingress which accelerated the warping.

It was the top piece of wood that had warped the worst. This would be the hottest part of the distiller.

After the test, I pulled it apart to dry out, and the big surprise this morning:

...the wood has returned to normal shape, and the crack closed.

I received some advise from David ('wdt' in the forum), on a method to preserve wood:

Wood that is well impregnated with wax, is waterproof,
will last almost forever, very stable
Melt wax, no water in bottom (normal for protection,<100)
Wax to 115-125C, do not leave unattended with heat on
Wood in for at least 10 min or longer
Problem is pot, something large enough
Large truck exhaust pipe? up to 3.5", flatten slightly
Sand or file one end 1/4", flatten, crimp in vise, solder with acid flux
OR split with slitting cut-off wheel, solder ends on both
Will not be able to glue ever
More convenient if you can do 2 pieces at once
Careful not to burn, maybe small nail 1/2way in, string

Obviously as you add wood it will cool wax as it boils water out of wood, will also carry the air entrained in wood.
For best impregnation, let it cool in wax until start of solidification, then heat for adequate drainage
Let drip over WET newspaper for easiest clean-up

...looks like an excellent method! However, I have already painted the wood with mineral oil. Mineral oil is food-safe, can be ingested as a laxative, or used as a skin softener. It is describe in Wikipedia:

https://en.wikipedia.org/wiki/Mineral_oil

The problem is to find it without additives. Pharmacies in Australia sell it as liquid paraffin, though one has to be careful about that word "paraffin" -- there may be other products in hardware stores with that name, that are not mineral oil.

I bought a bottle of Gold Cross liquid paraffin from a local pharmacy. This is 100% pure mineral oil. The 200ml bottle cost AU$6.95. I am sure that it could be obtained cheaper, but was not sure about the products on offer at Bunnings. Anyway, don't need much.

Unlike wdt's solution, I think that the mineral oil is not a permanent fix. The wood will need periodic recoating.

There is also the problem of the cracks in the wood. After two coats of mineral oil, I might smear the surface where the cracks are, with silicone sealant.

Another thing to bare in mind when considering how to treat the wood, is that the internal temperature of the distiller can get up to about 65 degC (149 degF). This can melt and leach out some treatments. I have read this 65 degC figure in online reports, for inclined wicking-type distillers, but maybe could get even higher -- I have yet to test in ambient 40+ degC heatwave!

Changing the subject, I have started to build a basic basin-type distiller, using parts from prototype #2. It is going to be extremely interesting to setup three distillers alongside each other, the prototype #4, F-Cubed Carocell 1000, and the simple basin-type. 

Tags: nomad

Rainmaker 550 solar water distiller

Taking some time out to think about the design, after yesterday's test of prototype #4:

https://bkhome.org/news/201911/solar-distiller-prototype-4-first-test.html

I got to thinking that I should build a simple basin type of solar water distiller, for comparison. It could be run alongside my own design, and could also run the F-Cubed panel alongside, to get a true comparison. I did this awhile back with photovoltaic solar panels, and it was very meaningful to see one particular photovoltaic was shown to definitely have overstated its claimed power output.

While browsing on the Internet last night, I looked up a commercially available simple basin type distiller, the Rainmaker 550, just wanted to see it's specs. The simple basin type is supposed to be the least efficient, I say "least" because that is what I have read, however the published figures for the Rainmaker have taken me by surprise.

Here is a photo:

Here is a webpage with specs:

http://www.solaqua.com/solstils1.html

They are claiming:

In temperate climates, the Rainmaker 550 produces up to 1.5 gallons (six liters) per day in the summer, and approximately half that in the winter months. Thermal efficiency (60%) is equivalent to about 550 Watts when operated in full sunlight. Production is about 0.8 liters per sun hour (kWh/m2).

The surface area is given as 0.93 m2. So, 800 millilitres/hour, and adjust to compare with the F-Cubed panel, 800*(1/0.93) which is 860 ml/hr -- surely not, that is far higher output than I got with the F-Cubed Carocell 1000 panel!

Are the Solaqua people telling porkies?

I only got 564 litres/hour when testing the F-Cubed panel, but that was mid-winter, though a sunny day (ambient was about 17 degC). So, to be fair here, need to compare with the claimed output. See here, for the Carocell 1000 (the model I own):

http://fcubedmalaysia.my/carocell-solar/

...they claim 7 litres/day in summer with ambient temperature 30 degC. OK, a tad better than the 6 litres claimed for the Rainmaker 550, but gosh, the Rainmaker is a far simpler design, easier to setup and use in the field also.

Hmmm, I have to find out for myself. I can easily knock one up from bits and pieces lying around in the garage, will hardly cost anything. Already have glass from the earlier prototypes. I could even build it with cardboard, as the inside will be lined with black silicone sealant and should be able to prevent any moisture to reach the cardboard -- good enough for doing the comparison testing anyway. 

Just one extra note: one reason that I went for the sloping wick-type distiller, is want something fairly flat that will slide into the back of a car and take up minimal space. That, and improved efficiency. So if I do decide to go for a simple basin type, it will have to be a collapsible design. 

Tags: nomad

Solar distiller prototype 4 first test

Today, November 7, 2019, in Perth, Western Australia, a sunny day, mildly warm with prediction of 30 degC, slight breeze in the morning, wispy clouds, a good day to test the solar water distiller prototype #4. Previous blog posts have been construction details, last post:

https://bkhome.org/news/201911/water-distiller-prototype-4-leg-assembly.html

I set it up at 7.35am. It is summer here in the Southern Hemisphere, and the sun is already quite high in the sky. Some wispy clouds:

As the day progressed, the wispiness became less pronounced, but there was a slight haze, so the sky was not quite the brilliant blue that is typical of Aussie summers. Sun intensity quite high though. Here is the setup:

Despite high hopes for the design of the distilled water runoff, the runoff slope still is not right and the water didn't want to go into the outlet tube. That needs more thought, but anyway, did manage to get the distilled water to come out in one place. There was quite a long time before any distilled water came out though...

Here is the report on test of prototype #3:

https://bkhome.org/news/201910/first-test-of-water-distiller-prototype-3.html

...which is essentially the same design, just some detail differences. In that test, it took about 50 minutes for the inlet water to trickle down the cloth to the bottom. However, in today's test, the inlet water was connected at 7.35am, and it did not reach the bottom of the cloth until 8.50am, a duration of 1 hour and 15 minutes. Waste water started to come out of the outlet pipe at 9.00am.

Why did it take so much longer today, an extra 25 minutes. I think that is because of lower water head. Although the water tank is the same height as the previous test, it might seem as though the water head is the same, however, it isn't. This might seem counter-intuitive, but the water head depends on how much air is in the pipe from the container tap down to the trickle flow reducers.

I discovered this problem back when I was designing the flow rate reducers:

https://bkhome.org/news/201906/testing-pope-4-litre-per-hour-dripper.html

For today's test, I didn't bother about getting the air out of the pipe, and ended up with a slower flow rate. Which has turned out to be a good thing. Today a very high distiller efficiency was achieved, which may be due to the water flowing more slowly down the cloth, or maybe part of the reason.

At 9.08am distilled water started to come out, and I started the measurements from that time.

At 9.30am, sun intensity was 830 W/m2, ambient was 24 degC, temperature measured with an IR reader, held about three inches away from the panel, about 3/4 from the top, was 44 degC front and 40 degC back.

At 10.15, sun 930 W/m2, ambient 24 degC, front 52 degC, back 47 degC. Note, the panel was oriented at a fixed position right from the start, estimated to be facing the sun most directly at about 11am.

Ha ha, I have done it again! I went into the city by train, didn't get back until 1.40pm, and the 450g pickle jar that was left to catch distilled water had overflowed. Quite a bit, from the puddle. I had only left a small jar there, as there wasn't much height. Besides, from previous tests I only expected the jar to be approaching full in that time duration.

1.40pm, sun 930 W/m2, ambient 27 degC, front 52 degC, back 50 degC. Note, measuring the IR temperature at the top of the panel, about 2 inches away from the glass, measured 57.6 degC, and right at the bottom, front, measured 42.7 degC. So, a good differential, ensuring the circulating airflow.
Moved the panel to better face the sun -- this would probably not happen in practice, but wanted to make up for the previous unknown water loss.

4.08pm, finished, as shade from patio had just reached the panel. Sun 870 W/m2, ambient 27 degC, front 48 degC, back 44 degC.

By this time, the panel is probably becoming less efficient, due to loss of air sealing from the outside, as the wood has warped. More about that below.

Anyway, the collection: 1.1 litres, in 7 hours. That is 157 millilitres/hour. The cloth has a surface area of 0.3327 m2, so to compare efficiency with the F-Cubed panel which is 1 m2, need to scale up: 157*(1/0.3327) which is 471.9 ml/hr. The F-Cubed panel gave 563.6 ml/hr, so today's test has a comparable efficiency of 83.7%.

It would actually be higher than that, due to the unknown amount lost. And the problem of the wood warping. Very good, well on the way to my survival goal of 1.5 litres per day.

Now the warping problem...

My lack of experience with the properties of wood has caught me out here. I did think that the wood might swell slightly with the moisture, but didn't expect that much, and so quickly. I had planned to treat the wood with mineral oil, however, had not yet done so. I think though, the oil would probably not have prevented the warping, just slowed it down. So it was probably a good thing that I have seen the problem so soon.

Here is a photo, taken after 4pm:

Even worse, it has split:

Right, lesson learned. The design is good, excellent efficiency, with further improvements in efficiency likely by tweaking type of cloth, panel angle, type of glass, etc. Note, the glass is cheap "window glass", which has a slight green tinge, that can be seen when looking at the edge of the glass. This is due to iron in the glass. There is low-iron glass available, more expensive. I don't know if it will make an appreciable difference, but might test replacing the front panel with low-iron glass.

Anyway, before trying those variations, the frame needs to be constructed with some other material, perhaps polycarbonate.  The saga continues... 

Tags: nomad

Water distiller prototype 4 leg assembly

Sunny today and mildly warm, slight breeze, excellent day to test the solar water distiller prototype #4. Which I have done, and got an excellent result, but also discovered a fatal flaw in the design. But firstly, the legs. This is a continuation from this post:

https://bkhome.org/news/201911/distiller-prototype-4-assembly.html

As mentioned, I have some 6mm thick marine plywood, and wanted to use that rather than make yet another trip to Bunnings. I cut out two end pieces, and two bracing pieces, that simply slot together:

I have some 10x10mm aluminium channel that was put to good use, stuck on the bottom of the ply, where it sits on the ground, to give it some durability. The assembly is rigid, and the panel angle is 30.5 degrees. A practical note: those bracing pieces can pack between the two legs and the glass, so the whole thing becomes one piece for transport.

I am really not so sure about the long-term durability of 6mm ply though. And then there is the above-mentioned "fatal flaw", which is going to require a rebuild with different materials -- see the next post.

So, prototype #5 is already being planned. For the record though, here is one of my construction planning sketches. This was not intended to be published, and is very rough, however, if someone comes along reading this post one day and wants to experiment with something similar, these measurements might be useful:

...ha ha, yes, I am using old "tractor feed" paper. Shows my vintage! 

The above sketch shows the top and bottom slots for the glass panes as 3mm, but actually I used a Diablo 1/8 inch router bit, which is 3.2mm. Also, the sketch shows the slots as 6mm in from the wood edges, but when I cut it, it was 5mm. 

EDIT 2019-11-15:
Might as well throw in this sketch of the folding legs. This also is a very rough sketch, was not intended for publishing:

...I used 6mm marine ply. The two vertical pieces had slots cut in them, and the bracing pieces slotted into them. 

Tags: nomad

Distiller prototype 4 assembly

I posted yesterday, construction notes for solar water distiller prototype #4:

https://bkhome.org/news/201911/distiller-prototype-3-morphs-into-4.html

Today I assembled it, which required construction of items to hold everything together. Well, this part was constructed yesterday, the bracing bars:

...these bars attach underneath the distiller, and serve two purposes: they hold the wood frame sides together, and they are mounting points for the leg hinges.

The bars are aluminium rectangular extrusion 20x10mm and wall thickness 2mm. I bought two 1m lengths from Bunnings, at AU$6.20 each:

https://www.bunnings.com.au/metal-mate-20-x-10-x-2mm-x-1m-aluminium-rectangular-tube_p1130559

I could have just screwed them as-is (cut to 600mm) underneath the wood frame, however decided to cut indents. This only reduces the width of the solar panel by 3-4mm, but went for it anyway. The above photo shows the ends cut-out and holes drilled. The pieces of wood were epoxied in to give a flush surface.

Today I started to assemble the distiller. This photo shows the bracing bars screwed underneath, to the side wood frame pieces, the bottom piece of the wood frame screwed onto the side pieces, and the bottom glass pane has been slid in:

Next, the middle glass pane was slid in, the cloth laid on it, and the inlet pipe assembly inserted. Then the top glass pane was slid in:

The inlet assembly is two silicone tubes, 6mm OD. Each end of the assembly has a brass rod sticking out, that is latched in place -- see earlier posts. Here is a picture showing the inlet-end:

Almost finished! The top piece of the wood frame has to be pushed on, and this must have quick-release latches, so that it can be taken off. Removal of the top piece will allow the inside to dry out, which is vital if the distiller is to be taken out of service for long periods. Removal will also allow the glass panes to slide out so as to access all parts of the interior.

The quick-release latches for the top wood frame are made from 12x3mm aluminium bar, attached with screws. The bar and screws were in the garage, so didn't have to buy anything. Photo of one of the latches:

Another detail of the construction: the following photo shows the two outlet pipes, waste water and distilled water. The waste water comes out of the 16mm OD aluminium pipe, and notice the screw on top:

...that screw is 6g 30mm countersunk-head wood screw, with a 2mm hole drilled through the wood and the pipe. The screw is just long enough to reach the pipe and lock it in place, to prevent it from turning.

The final step of assembly will be the legs. I have some 6mm marine plywood that I want to use, rather than making yet another purchase at Bunnings. This will probably happen tomorrow afternoon, as a family engagement in the morning. 

Tags: nomad