Question:

home made pool solar water heater  I am building a small evacuated tube collector system.  I am using the tubes from flourescent lights (each end cut off, and the phosphor cleaned out).  Each end then has a cap turned from aluminum, bored to 1/2 inch to allow a thin-walled Aluminum tube to pass through, and the assembly then is epoxied together. I have a valve on one end where I evacuate the inside air .  The overall assembly is three feet, with approx 4 inches of the tube extending from each end.  The inside tubes will be “daisy-chained” to  whatever number of tubes I can make.  An anti-freeze solution will circulate through the Aluminum tubes using a small pump, and then go through something like a car heater with a blower  to transfer the heat.   My first prototype tube is done, but I have not collected any data on the amount of heat that it will collect yet. I have the following questions: The prototype has the Aluminum tube painted flat black – would a black Anodized tube be more efficient? What would be a way to construct a small parabolic reflector behind each tube (or would it be worth doing? I am concerned about the co-efficient of expansion of the glass and Aluminum ; hopefully they are not too different which could cause the glass tube to crack. Is there something better than epoxy to use as a sealer?  I thought about silicone, since it would tolerate some expansion/contraction, but it might not cure properly inside the evacuated glass tube. Will a tracking mechanism be worth it?  (I would think so) This is a long-winded post – hopefully some of you experts out there can provide some guidance, which will probably generate more questions. home made pool solar water heater

Response:

what happened to the mercury? most places require a permit to dispose of these tubes in quantities of 15 or greater because of the mercury risk. home made pool solar water heater  I am building a small evacuated tube collector system.  I am using the tubes from flourescent lights (each end cut off, and the phosphor cleaned out). Each end then has a cap turned from aluminum, bored to 1/2 inch to allow a thin-walled Aluminum tube to pass through, and the assembly then is epoxied together. I have a valve on one end where I evacuate the inside air .  The overall assembly is three feet, with approx 4 inches of the tube extending from each end.  The inside tubes will be “daisy-chained” to  whatever number of tubes I can make.  An anti-freeze solution will circulate through the Aluminum tubes using a small pump, and then go through something like a car heater with a blower  to transfer the heat. My first prototype tube is done, but I have not collected any data on the amount of heat that it will collect yet. I have the following questions: The prototype has the Aluminum tube painted flat black – would a black Anodized tube be more efficient? What would be a way to construct a small parabolic reflector behind each tube (or would it be worth doing? I am concerned about the co-efficient of expansion of the glass and Aluminum ; hopefully they are not too different which could cause the glass tube to crack. Is there something better than epoxy to use as a sealer?  I thought about silicone, since it would tolerate some expansion/contraction, but it might not cure properly inside the evacuated glass tube. Will a tracking mechanism be worth it?  (I would think so) This is a long-winded post – hopefully some of you experts out there can provide some guidance, which will probably generate more questionshome made pool solar water heater.

Response:

home made pool solar water heater, I am building a small evacuated tube collector system.  I am using the tubes from flourescent lights (each end cut off, and the phosphor cleaned out). Each end then has a cap turned from aluminum, bored to 1/2 inch to allow a thin-walled Aluminum tube to pass through, and the assembly then is epoxied together. I have a valve on one end where I evacuate the inside air…

Sunmaster tubes… They are about 3.5′ long, with a 1/4″(?) glass return tube inside a 1.5″ glass tube with a selective surface inside a 2″ outer glass tube. The prototype has the Aluminum tube painted flat black – would a black Anodized tube be more efficient?

Maybe, if it’s a selective surface. What would be a way to construct a small parabolic reflector behind each tube (or would it be worth doing? home made pool solar water heater

Seems worth doing. Jim’s tubes have a 6″ wide cusped reflector behind them, made from aluminum, with a reflective film (mostly peeled now) as a part of the mounting structure. I am concerned about the co-efficient of expansion of the glass and Aluminum; hopefully they are not too different which could cause the glass tube to crack.

You could figure that out, with elasticities, yield strengths and temperature differences… Is there something better than epoxy to use as a sealer?

Silicone sounds better than epoxy, but not as long lasting as glass.home made pool solar water heater  Will a tracking mechanism be worth it?  (I would think so)

Tracking may not improve performance much, given a large inner tube and low concentrtation.home made pool solar water heater

Response:

Thanks Nick I will email jim & see if any are for sale.home made pool solar water heater

Response:

Nice Idea making your own evacuated collector from flourescent tubes. A few comments: 1)   Be careful about breathing the mercury vapour and phospours in the tubes.  Sulphur dust or other specific mercury binders will help “get” the mercury in the tube.  I don’t think that there is much, but I think mercury is especially bad for kids. 2)   You could try to make the connection between the glass and the aluminum plug at a thin turned down lip or extension to the plug itself which would flex somewhat and thus compensate for the expansion. 3)  In scientific glassblowing, soft metals such as indium are used as glass-metal seals but they are quite tricky to make – you can buy ready made glass-metal connections which you can fuse onto your tubes.  (Glass blowing 101 next!) 4) Epoxy will work ok, Silicone not. Epoxy sticks better if you roughen up the glass with some abrasive grit (valve grinding compound or fine abrasive paper) and then clean the mating surfaces well with alcohol etc.  Allow sufficent joint area. 5) Anodizing aluminum is quite easy to do with a battery charger (make it the anode) and some sulphuric acid and then a lead sulphate or other compound for the black coating.  (Kind of nasty chemicals though)   Better to get some selective coating paint. Let us know how it goes. Graham Parkinson

- home made pool solar water heater  I am building a small evacuated tube collector system.  I am using the tubes from flourescent lights (each end cut off, and the phosphor cleaned out). Each end then has a cap turned from aluminum, bored to 1/2 inch to allow a thin-walled Aluminum tube to pass through, and the assembly then is epoxied together. I have a valve on one end where I evacuate the inside air .  The overall assembly is three feet, with approx 4 inches of the tube extending from each end.  The inside tubes will be “daisy-chained” to  whatever number of tubes I can make.  An anti-freeze solution will circulate through the Aluminum tubes using a small pump, and then go through something like a car heater with a blower  to transfer the heat. My first prototype tube is done, but I have not collected any data on the amount of heat that it will collect yet. I have the following questions: The prototype has the Aluminum tube painted flat black – would a black Anodized tube be more efficient? What would be a way to construct a small parabolic reflector behind each tube (or would it be worth doing? I am concerned about the co-efficient of expansion of the glass and Aluminum ; hopefully they are not too different which could cause the glass tube to crack. Is there something better than epoxy to use as a sealer?  I thought about silicone, since it would tolerate some expansion/contraction, but it might not cure properly inside the evacuated glass tube. Will a tracking mechanism be worth it?  (I would think so) This is a long-winded post – hopefully some of you experts out there can provide some guidance, which will probably generate more questions.home made pool solar water heater

Response:

home made pool solar water heater  Thanks for the feedback.  I am aware of the Hg problem, even though it is a extremly small amount.  I am using a special container for the dust, end caps, and everything else that comes out of the tubes. I have completed a “first prototype:, using epoxy as a sealer, and it is holding up well. I am trying some high temp automotive gasket sealer, silicone based, on the second prototype.    I tested the tube by simply leaning it against the wall of my shop, outside temp was around 10 ; the liquid  heated to over 90 degrees in a very short while.  When properly mounted, with the ends insulated etc, , overall efficiency will greatly improve.   I am not confident that I have sufficient vacuum yet, so have made a better valve which will assure a better seal. There are some excellent websites on anodizing.  They do not mention the need for lead sufphate, since after anodizing the piece is placed in a hot solution of Rit dye, of all things!   All I will have to construct is a long container to hold a 3″ tube. I am still searching for equations or other data to calculate the radius of the parabolic reflectors that will be placed behind the tubes.  Also a source for reflective Mylar or some such to face the reflectors with. A tracking mechanism will also be added in the final version. I can keep you posted of my progress.home made pool solar water heater

Response:

home made pool solar water heater  The catenary curve of a suspended chain is almost the same as a parabola. Use a fine-linked chain to trace a pattern for the width and depth of your reflector. The NREL site has solar trough information, most of the reflectors are rather shallow. home made pool solar water heater   I am aware of the Hg problem, even though it is a extremly small amount.  I am using a special container for the dust, end caps, and everything else that comes out of the tubes. I have completed a “first prototype:, using epoxy as a sealer, and it is holding up well. I am trying some high temp automotive gasket sealer, silicone based, on the second prototype.    I tested the tube by simply leaning it against the wall of my shop, outside temp was around 10 ; the liquid  heated to over 90 degrees in a very short while.  When properly mounted, with the ends insulated etc, , overall efficiency will greatly improve. I am not confident that I have sufficient vacuum yet, so have made a better valve which will assure a better seal. There are some excellent websites on anodizing.  They do not mention the need for lead sufphate, since after anodizing the piece is placed in a hot solution of Rit dye, of all things!   All I will have to construct is a long container to hold a 3″ tube. I am still searching for equations or other data to calculate the radius of the parabolic reflectors that will be placed behind the tubes.  Also a source for reflective Mylar or some such to face the reflectors with. A tracking mechanism will also be added in the final version. I can keep you posted of my progress. home made pool solar water heater.  I also see that anodized black seems to be very much in the same boat.  Cruise the list to find easily accessible materials which have good a/e ratios.  I’m assuming it would defeat the home-made nature of the project to go out and buy Black Crystal or something like that.  Are you capable of plating the aluminum?  Black sulfide plating seems to be attractive.  I know nothing about that, though.  ”Dull aluminum” alone apparently has a ratio of 2.10, which seems pretty good.  I’m assuming you’d have to rough up all your tubes to acheive this ‘dull’ characteristic. Note that i’m making a big assumption when reading this table — the text above it seems to imply that the absorptivity ratings are for the visible wavelengths (ie. ’solar absorptivity’), and the emissivities are for thermal (IR) wavelengths.  If this is not the case, my above info may be erroneous. Hope i helped.  Any and all input welcomed.  Corrections encouraged.home made pool solar water heater

Response:

For a circular cross section mirror the quasi focal point is at half the radius. For a parabolic mirror the focal point is exact (for points on the mirror axis) and the equation of the surface is Y^2=4fx  where f=focal length. This becomes  the same as the circle equation if the circle is inscribed to fit inside the parabola. The principle of anodizing is that the current “raises the grain” of the aluminum and produces a porous surface that can hold a coloured agent.  We used nasties like lead sulphate for black colour and chromium for yellow.  Glad to hear that Rit also works. I once wanted to build an aluminum sailboat and then anodize the whole thing by sinking it in a plastic bag with a little of the reagents hooked up to a welder for current.

home made pool solar water heater The catenary curve of a suspended chain is almost the same as a parabola. Use a fine-linked chain to trace a pattern for the width and depth of your reflector. The NREL site has solar trough information, most of the reflectors are rather shallow. Jim Graham: Thanks for the feedback.  I am aware of the Hg problem, even though it is a extremly small amount.  I am using a special container for the dust, end caps, and everything else that comes out of the tubes. I have completed a “first prototype:, using epoxy as a sealer, and it is holding up well. I am trying some high temp automotive gasket sealer, silicone based, on the second prototype.    I tested the tube by simply leaning it against the wall of my shop, outside temp was around 10 ; the liquid  heated to over 90 degrees in a very short while.  When properly mounted, with the ends insulated etc, , overall efficiency will greatly improve. I am not confident that I have sufficient vacuum yet, so have made a better valve which will assure a better seal. There are some excellent websites on anodizing.  They do not mention the need for lead sufphate, since after anodizing the piece is placed in a hot solution of Rit dye, of all things!   All I will have to construct is a long container to hold a 3″ tube. I am still searching for equations or other data to calculate the radius of the parabolic reflectors that will be placed behind the tubes.  Also a source for reflective Mylar or some such to face the reflectors with. A tracking mechanism will also be added in the final version. I can keep you posted of my progreshome made pool solar water heaters.

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