Fellow sheet metal enthusiasts,
Before I spend lots of time and money trying to figure this out alone I want to toss this out to the sheet metal community for advice. If you have a better way to do this, I need to know.
My project involves making a vacuum tight container about a meter square of corrugated steel roofing material. I'm happy to go into the nature of this project with those interested in another post.
I'm going to be using two sheets of 29 to 24 gauge corrugated galvanized steel laid on top of each other. This will create crude tubes that I'm going to stuff full with pellets of a reasonably strong material that will hold the shape of the corrugations when under vacuum. The container needs to hold vacuum down to about 25" hg, 3000 Pa, 25 torr, .5 psi (pick your favorite measurement system).
My thoughts were to weld, solder, braze or epoxy bond the two sheets together, with or without a rolled seam. There will be regularly cycled thermal shock from 100 o C to about 20 o C two or more times per day, so the seams are going to have a bit of contraction/expansion abuse of 1/32" to 1/64" per cycle. This container needs to hold vacuum for 20-50 years, so I want to build it right the first time.
This container will also need two or three penetrations for a vacuum gauge and an input and output line, so your advice on how to reinforce these penetrations will also be greatly appreciated.
Adam Beslove
beslove@mris.com
Vacuum tight container of corrugated steel roofing
Re: Vacuum tight container of corrugated steel roo
A vacuum can be very difficult to contain, and trying to contain one for 20 - 50 years is going to be a real challenge. Since you're not trying to contain a "high" vacuum your task will be easier.
Soldered, welded or brazed joints will be a must; any of them should work. (I don't have enough experience with epoxies with respect to sealing a vacuum to say whether or not they might work.) Since the quality of the joints is very critical use whatever process you're most skillful doing.
I wouldn't expect the temperature fluctuations to be a problem unless there are restraints which cause high local stresses. Leak testing your container will be difficult because without special equipment locating vacuum leaks is tough. The design you describe would not withstand any significant internal pressure, and even if it did that would not be an effective means to leak test for vacuum. It is not uncommon for vessels and systems to hold pressure, but not hold vacuum.
When designing this container keep in mind that the atmosphere will impose an external pressure of more than 14 psi on it. (That's about 21,700 lbs. on a square meter.)
This sounds like an interesting project. Tell us more.
Good Luck,
Bill
Soldered, welded or brazed joints will be a must; any of them should work. (I don't have enough experience with epoxies with respect to sealing a vacuum to say whether or not they might work.) Since the quality of the joints is very critical use whatever process you're most skillful doing.
I wouldn't expect the temperature fluctuations to be a problem unless there are restraints which cause high local stresses. Leak testing your container will be difficult because without special equipment locating vacuum leaks is tough. The design you describe would not withstand any significant internal pressure, and even if it did that would not be an effective means to leak test for vacuum. It is not uncommon for vessels and systems to hold pressure, but not hold vacuum.
When designing this container keep in mind that the atmosphere will impose an external pressure of more than 14 psi on it. (That's about 21,700 lbs. on a square meter.)
This sounds like an interesting project. Tell us more.
Good Luck,
Bill
Re: Vacuum tight container of corrugated steel roo
Bill,
Thank you for your response.
I'm not seriously skilled in bonding sheet metal with anything but rivets, screws and bolts, so I'll use up a bunch of corrutaged practicing. The only things I've soldered have been electrionics, and that's a whole different technique. I'm leaning toward brazing because of the metalurgical properties of a brazed bond. Then again, radiators and air conditioning heat exchangers are soldered, but they are under pressure except for the times when they are occasionally evacuated to approximately the same vacuum pressure I'm using.
It may be wise to wrap the material in a plastic bag, then seal it in the corrugated so there will be two layers of vacuum, but that would decrease the thermal transparency I chose the corrigated for in the first place.
*deep breath*
This project is about building solar powered ice makers. This is a charity project designed for third world, out in the boondocks users. It is going to be my contribution to humanity. If I can work out the kinks and make it bullet proof and easy to build with materials common in the third world (such as corrugated steel roofing), lots of these things can get built and lots of people will be able to keep medicine cool and food preserved instead of having it spoil before it can be consumed or get to market.
Yes, it can be done, has been done, and it doesn't use photovoltaics, just direct solar captured heat. It uses a chemical process called adsorption (not absorbtion). In its most basic form, it's a day/night cycle. Heat up the adsorbant and the refrigerant evaporates. Cool it off at night and it readsorbs the refrigerant, sucking heat along with the refrigerant vapor. If the refrigerant resevoir happens to be, say, a car radiator laying in a styrofoam ice chest with bags of water, that water will become ice by morning. There are various efficiency enhancing techniques, but this is the basic cycle.
The average performance of academically built basic cycle prototypes is about 4-5 kilos of ice per day with a square metre flat collector. I'm reading all of the scientific papers I can find and they have plenty of great information, but they're using lab-grade parts and materials. My goal is a unit that's down and dirty and frontier maintainable.
The corrugated is going to be filled with adsorbant and will be immersed in a hot water bath with said hot water solar heated. The water bath will prevent it from going over 100 o C. Yeah, I know galvinized will eventually rust if exposed to water, so it will have to be coated with tar or paint and regularly monitored. Aluminum would definitely be better.
As for testing the vacuum, one of the penetrations will be for a vacuum gauge. Vacuum sealant in aerosol cans is available, but it's expensive and can't be purchased at Home Depot or 7-11. I imagine any leaks will whistle. Fixing the system in the field will be a pain. I'll have to separate the water from the refrigerant and evaporate any remaining water vapor in the adsorbant. I'm also working on a 3d world bicycle chain and crank driven vacuum pump.
Again, any and all suggestions are welcome. I can't do this alone.
Adam
beslove@mris.com
Thank you for your response.
I'm not seriously skilled in bonding sheet metal with anything but rivets, screws and bolts, so I'll use up a bunch of corrutaged practicing. The only things I've soldered have been electrionics, and that's a whole different technique. I'm leaning toward brazing because of the metalurgical properties of a brazed bond. Then again, radiators and air conditioning heat exchangers are soldered, but they are under pressure except for the times when they are occasionally evacuated to approximately the same vacuum pressure I'm using.
It may be wise to wrap the material in a plastic bag, then seal it in the corrugated so there will be two layers of vacuum, but that would decrease the thermal transparency I chose the corrigated for in the first place.
*deep breath*
This project is about building solar powered ice makers. This is a charity project designed for third world, out in the boondocks users. It is going to be my contribution to humanity. If I can work out the kinks and make it bullet proof and easy to build with materials common in the third world (such as corrugated steel roofing), lots of these things can get built and lots of people will be able to keep medicine cool and food preserved instead of having it spoil before it can be consumed or get to market.
Yes, it can be done, has been done, and it doesn't use photovoltaics, just direct solar captured heat. It uses a chemical process called adsorption (not absorbtion). In its most basic form, it's a day/night cycle. Heat up the adsorbant and the refrigerant evaporates. Cool it off at night and it readsorbs the refrigerant, sucking heat along with the refrigerant vapor. If the refrigerant resevoir happens to be, say, a car radiator laying in a styrofoam ice chest with bags of water, that water will become ice by morning. There are various efficiency enhancing techniques, but this is the basic cycle.
The average performance of academically built basic cycle prototypes is about 4-5 kilos of ice per day with a square metre flat collector. I'm reading all of the scientific papers I can find and they have plenty of great information, but they're using lab-grade parts and materials. My goal is a unit that's down and dirty and frontier maintainable.
The corrugated is going to be filled with adsorbant and will be immersed in a hot water bath with said hot water solar heated. The water bath will prevent it from going over 100 o C. Yeah, I know galvinized will eventually rust if exposed to water, so it will have to be coated with tar or paint and regularly monitored. Aluminum would definitely be better.
As for testing the vacuum, one of the penetrations will be for a vacuum gauge. Vacuum sealant in aerosol cans is available, but it's expensive and can't be purchased at Home Depot or 7-11. I imagine any leaks will whistle. Fixing the system in the field will be a pain. I'll have to separate the water from the refrigerant and evaporate any remaining water vapor in the adsorbant. I'm also working on a 3d world bicycle chain and crank driven vacuum pump.
Again, any and all suggestions are welcome. I can't do this alone.
Adam
beslove@mris.com
Re: Vacuum tight container of corrugated steel roo
I'm familiar with adsorption refrigeration systems. There is a lot of information about them available on the Internet. The experts say combining the ice maker with a solar water heater greatly improves the efficiency of the system which is pretty low.
I admire you for wanting to help humanity, but I don't believe that such a system could ever be put together in the manner you suggest. The manufacture of the components for these systems requires hi-tech equipment and a skilled work force.
Bill
I admire you for wanting to help humanity, but I don't believe that such a system could ever be put together in the manner you suggest. The manufacture of the components for these systems requires hi-tech equipment and a skilled work force.
Bill
Re: Vacuum tight container of corrugated steel roo
Bill,
All I can say is "watch me." [img]/ubb/images/graemlins/smile.gif"%20alt="[/img] I don't want to start a dust-up here, let alone a flame war. Whether a sheet metal working forum is the right place to discuss the feasibility of this project is appropriate, I'm happy to do so.
Maybe I overstated where these things might be built. Most countries, even in the 3d world, have urban centers with machine tools, skilled people that know how to use them and people that know how to build and fix things. Air conditioners, mostly Korean, are ubiquitous in 3d world cities, as are AC repairmen. What I'm getting at is that hi-tech is a relative term.
Regarding materials: If the adsorber can't hold vacuum for 20 years, it will just need replacement or repair, but the less the better. Rapid globalization is getting materials everywhere on the planet, so whether it works specifically with corrugated or not is okay. Regular plumbing pipe and sheet metal will work, too.
Certain parts will no doubt have to be imported, like vacuum gauges (US $10 each mail order or about US $20 at an auto parts store) and plumbing valves (globally available). Finished steel is mostly imported, but small foundries recycling scrap abound in the 3d world. The materials of the adsorber pair, activated charcoal-methanol can either be made locally or imported. Methanol is a byproduct of charcoal making, which is a pretty ancient art; just add a condenser and separate the methanol. Plumbing pipe is available everywhere. A simple plastic Chinese-made US $30 hand vacuum pump on ebay will pull the required pressure. Anyone with hands can operate one of those. [img]/ubb/images/graemlins/smile.gif"%20alt="[/img] A modified 2 cycle motorbike engine, turned with a modified bicycle, can pull vacuum, too.
Regarding skilled labor: A recent training program in India that teaches women of the "untouchable" caste to repair hand operated water pumps has been very successful. There is a scarcity of pump repair techs in most rural regions of India. So the government advertised a parttime class that lasted a month. Most Indian villages have a common well and a hand pump to operate it, so these women have become pretty important. Even those of higher castes that ordinarily wouldn't touch anything that's been touched by an "untouchable" (hence the name) are giving up on that taboo, especially when it comes to being thirsty, when there's nobody else around that can fix their pumps.
Making these ice makers will require no more skill than it takes to fix a hand operated water pump. It's basically just plumbing. Teaching these skills for this application isn't rocket science. I've known a few real rocket scientists and most of them have to wear velcro sneakers because they can't tie their shoes. [img]/ubb/images/graemlins/smile.gif"%20alt="[/img]
Regarding efficiency and cost: Whether I get absolute top efficiency, even if thermal fluid or matter transfer techniques are employed, isn't the point. The system is scalable. Low efficiency units still add up to lots of ice. What's an extra square meter or two of solar panel cost? Not much, especially when my cost projections show a nice size unit outputting 20-50 pounds of ice per day costing less than a 100cc motorbike -- and those motorbikes abound in the 3d world.
Adam
All I can say is "watch me." [img]/ubb/images/graemlins/smile.gif"%20alt="[/img] I don't want to start a dust-up here, let alone a flame war. Whether a sheet metal working forum is the right place to discuss the feasibility of this project is appropriate, I'm happy to do so.
Maybe I overstated where these things might be built. Most countries, even in the 3d world, have urban centers with machine tools, skilled people that know how to use them and people that know how to build and fix things. Air conditioners, mostly Korean, are ubiquitous in 3d world cities, as are AC repairmen. What I'm getting at is that hi-tech is a relative term.
Regarding materials: If the adsorber can't hold vacuum for 20 years, it will just need replacement or repair, but the less the better. Rapid globalization is getting materials everywhere on the planet, so whether it works specifically with corrugated or not is okay. Regular plumbing pipe and sheet metal will work, too.
Certain parts will no doubt have to be imported, like vacuum gauges (US $10 each mail order or about US $20 at an auto parts store) and plumbing valves (globally available). Finished steel is mostly imported, but small foundries recycling scrap abound in the 3d world. The materials of the adsorber pair, activated charcoal-methanol can either be made locally or imported. Methanol is a byproduct of charcoal making, which is a pretty ancient art; just add a condenser and separate the methanol. Plumbing pipe is available everywhere. A simple plastic Chinese-made US $30 hand vacuum pump on ebay will pull the required pressure. Anyone with hands can operate one of those. [img]/ubb/images/graemlins/smile.gif"%20alt="[/img] A modified 2 cycle motorbike engine, turned with a modified bicycle, can pull vacuum, too.
Regarding skilled labor: A recent training program in India that teaches women of the "untouchable" caste to repair hand operated water pumps has been very successful. There is a scarcity of pump repair techs in most rural regions of India. So the government advertised a parttime class that lasted a month. Most Indian villages have a common well and a hand pump to operate it, so these women have become pretty important. Even those of higher castes that ordinarily wouldn't touch anything that's been touched by an "untouchable" (hence the name) are giving up on that taboo, especially when it comes to being thirsty, when there's nobody else around that can fix their pumps.
Making these ice makers will require no more skill than it takes to fix a hand operated water pump. It's basically just plumbing. Teaching these skills for this application isn't rocket science. I've known a few real rocket scientists and most of them have to wear velcro sneakers because they can't tie their shoes. [img]/ubb/images/graemlins/smile.gif"%20alt="[/img]
Regarding efficiency and cost: Whether I get absolute top efficiency, even if thermal fluid or matter transfer techniques are employed, isn't the point. The system is scalable. Low efficiency units still add up to lots of ice. What's an extra square meter or two of solar panel cost? Not much, especially when my cost projections show a nice size unit outputting 20-50 pounds of ice per day costing less than a 100cc motorbike -- and those motorbikes abound in the 3d world.
Adam
Re: Vacuum tight container of corrugated steel roofing
Well I'm certainly not an expert on this subject, but would tend to think that gluing the sheets together is your best option. I can't visualize how the sheets could be welded (other than a rolled seam weld that would require equipment that is out of the question). Brazing (or even soldering) would require a large furnace in order to get the entire panel up to temperature at once. Epoxy requires no special equipment and could be used by anyone at any location. I also think that there is an epoxy that would have the required vacuum tightness and allow for thermal expansion without failing. I would think that if you approach the major manufacturers you might be able to get free technical assistance and maybe even some financial help if the company thought that the marketing and goodwill would be benifical to them. Making a fixture out of wood dowels, plywood, and sandbags would seem to be easy to hold the panels together while bonding. I don't know if that style of panel is available in aluminum, but if so, it would be a much better choice for heat transfer. If I understand the concept, the tubes that will be formed will be under partial vacuum, not that one side of a one meter square panel will be exposed to ambient pressure and the other side of the panel to the vacuum. In the latter case, as someone else pointed out, the panel will not have nearly the required strength (without reinforcements) to withstand the resulting force due to the differential pressure. I am familiar with ammonia adsorption chillers, but not with the chemistry of methanol and charcol. Can you explain that a bit? Bill
Re: Vacuum tight container of corrugated steel roo
Bill,
Given what you said about heating the panels for brazing, epoxy does make much more sense. What little experience I've had in epoxying aluminum it should work. As you suggest, contacting various manufacturers to find the right one, that has the strenght, chemical resistance and elasticity for this application is key. There's some interesting web articles on vacuum bagging composite glider wings to suck air bubbles out of resins, that support your suggestion. I found lots of interesting stuff through click-throughs on the excellent amateur site http://www.belljar.net/.
Your recommendation for making a fixture to hold the panels during bonding is great!
Aluminum panels are available for around the same price as galvanized. Al is definitely a better bet for thermal transparency. It's easier for me to work, too. A few years ago I built one of Gingery's blast furnaces, a project I can heartily recommend to anyone with an understanding spouse. [img]/ubb/images/graemlins/smile.gif"%20alt="[/img] For melting and casting more than a litre of Al at a time it's not really practical, but for scaring the bejezus out of pets, turning a 3 metre radius of snow and mud into hard-packed dirt, and shooting a 4' column of fire, it's unparalleld.
You understand the panel configuration correctly. The idea I proposed was two panels 180 o out of phase, creating the tubes, and will have partial vacuum on one side and ambient on the other. If the tubes were empty, they would crush like the famous high school boiled water/sealed/crushed can experiment, but they are going to be densly stuffed with the activated carbon pellets. These pellets are pretty hard and I need pliers to crush them individually. The skin strength of the sheet metal should hold up, but that will be part of the experiment. Another idea just occured to just keep the panels in phase.
From your handle, I'll guess you're either an HVAC or a refrigeration guy. I'm a real estate agent and not a chemist, so if there are any of you out there please pipe up. The way I understand it, a.c. has an internal surface area of something like 100 square meters per gram comprised of small tunnels. Something has to fill up this space and a.c. is great at sucking up certain types of molecules. The Van der Waal's(sp?) forces grab onto the molecules, up to 36% of the a.c.'s weight depending upon the type of a.c. and molecule.
Add energy in the form of heat to the a.c. until the methanol vaporizes (squeezing the chemical sponge) and condense that vapor and collect it in an evaporator. Next, stop adding energy to the a.c. and let it cool. Now you have a dry chemical sponge. The cooling "dry" a.c. "sponge" lowers the system's pressure enough to vaporize some of the liquid methanol.
As the a.c. cools, it radiates heat and readsorbs methanol vapor. That vapor has a certain amount of energy. As the a.c. sponges up the vapor, the vapor and that vapor's energy, are lost by the liquid methanol in the evaporator -- enough to lower the liquid methanol remaining in the evaporator to 0 to -10 o C.
I probably butchered that, but it's the best I can do.
Adam
Given what you said about heating the panels for brazing, epoxy does make much more sense. What little experience I've had in epoxying aluminum it should work. As you suggest, contacting various manufacturers to find the right one, that has the strenght, chemical resistance and elasticity for this application is key. There's some interesting web articles on vacuum bagging composite glider wings to suck air bubbles out of resins, that support your suggestion. I found lots of interesting stuff through click-throughs on the excellent amateur site http://www.belljar.net/.
Your recommendation for making a fixture to hold the panels during bonding is great!
Aluminum panels are available for around the same price as galvanized. Al is definitely a better bet for thermal transparency. It's easier for me to work, too. A few years ago I built one of Gingery's blast furnaces, a project I can heartily recommend to anyone with an understanding spouse. [img]/ubb/images/graemlins/smile.gif"%20alt="[/img] For melting and casting more than a litre of Al at a time it's not really practical, but for scaring the bejezus out of pets, turning a 3 metre radius of snow and mud into hard-packed dirt, and shooting a 4' column of fire, it's unparalleld.
You understand the panel configuration correctly. The idea I proposed was two panels 180 o out of phase, creating the tubes, and will have partial vacuum on one side and ambient on the other. If the tubes were empty, they would crush like the famous high school boiled water/sealed/crushed can experiment, but they are going to be densly stuffed with the activated carbon pellets. These pellets are pretty hard and I need pliers to crush them individually. The skin strength of the sheet metal should hold up, but that will be part of the experiment. Another idea just occured to just keep the panels in phase.
From your handle, I'll guess you're either an HVAC or a refrigeration guy. I'm a real estate agent and not a chemist, so if there are any of you out there please pipe up. The way I understand it, a.c. has an internal surface area of something like 100 square meters per gram comprised of small tunnels. Something has to fill up this space and a.c. is great at sucking up certain types of molecules. The Van der Waal's(sp?) forces grab onto the molecules, up to 36% of the a.c.'s weight depending upon the type of a.c. and molecule.
Add energy in the form of heat to the a.c. until the methanol vaporizes (squeezing the chemical sponge) and condense that vapor and collect it in an evaporator. Next, stop adding energy to the a.c. and let it cool. Now you have a dry chemical sponge. The cooling "dry" a.c. "sponge" lowers the system's pressure enough to vaporize some of the liquid methanol.
As the a.c. cools, it radiates heat and readsorbs methanol vapor. That vapor has a certain amount of energy. As the a.c. sponges up the vapor, the vapor and that vapor's energy, are lost by the liquid methanol in the evaporator -- enough to lower the liquid methanol remaining in the evaporator to 0 to -10 o C.
I probably butchered that, but it's the best I can do.
Adam
Re: Vacuum tight container of corrugated steel roo
Adam,
The handle may be a bit misleading. I have been a racing fan all of my life and have done some amateur motorcycle and SCCA racing and used to do a bit of drag racing. My favorite part of racing has always been engine building and lately a new hobby has been building minature scale engines, hence internal combustion engine maker (icemaker) struck my fancy when I needed to pick a handle. So I don't really do a lot of HVAC work, I am an electrical engineer by training. Years ago I worked for Air Liquide as a start-up engineer (control systems) at a few air separation plants (they make liquid oxygen, liquid nitrogen, and liquid argon) and learned a bit about cryogenic processing and the refigeration processes they utilize. Do you have a process diagram for this cycle? Are there any other components involved, pumps, heat exchangers, evaporators, tanks, piping, etc.? A bit more information on the overall process would be useful.
I am aware of the vacuum bagging process and have used it to make small parts for the race bikes and cars out of fiberglass and carbon fiber in the past. As you have noted, the home built aircraft guys use this process a lot since there are a lot of composite construction aircraft these days. The race car guys use it extensively also. Bill
The handle may be a bit misleading. I have been a racing fan all of my life and have done some amateur motorcycle and SCCA racing and used to do a bit of drag racing. My favorite part of racing has always been engine building and lately a new hobby has been building minature scale engines, hence internal combustion engine maker (icemaker) struck my fancy when I needed to pick a handle. So I don't really do a lot of HVAC work, I am an electrical engineer by training. Years ago I worked for Air Liquide as a start-up engineer (control systems) at a few air separation plants (they make liquid oxygen, liquid nitrogen, and liquid argon) and learned a bit about cryogenic processing and the refigeration processes they utilize. Do you have a process diagram for this cycle? Are there any other components involved, pumps, heat exchangers, evaporators, tanks, piping, etc.? A bit more information on the overall process would be useful.
I am aware of the vacuum bagging process and have used it to make small parts for the race bikes and cars out of fiberglass and carbon fiber in the past. As you have noted, the home built aircraft guys use this process a lot since there are a lot of composite construction aircraft these days. The race car guys use it extensively also. Bill
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Henriksen
Re: Vacuum tight container of corrugated steel roo
Sounds like a godd idea. I would be concerned with the effects of UV light on epoxies over a long period. The sun and heat in sub saharan africa has quite an effect on even car paints. I think I would look more at welds or solders.
Re: Vacuum tight container of corrugated steel roo
If I understand the method of construction properly, the epoxy joints would be between the sheets and therefore shielded from sunlight. For any exposed joints, black paint can be very effective for UV protection (may require periodic reapplication). I don't think any kind of welding or brazing other than roll seam welding or furnace brazing could join the sheets together. Both of these methods would not be practical for field fabrication in an underdeveloped country. Bill
Re: Vacuum tight container of corrugated steel roo
Somehow I don't quite follow this discussion. If all the formed tubes between two sheets are under vacuum, why is sealing between the tubes necessary? How will the open ends of the tubes be connected and sealed to the other parts? Folding and soldering should take care of the closed sides. Also, any galvanized steel roofing is strong enough to withstand 14.7 psi over the width of the corrugations without worry about collapsing the tubes. The materials will definitely not hold a long term vacuum; you better plan on including a simple vacuum pump for maintaining it.
Best Regards, Don Young
Best Regards, Don Young
Don Young
Re: Vacuum tight container of corrugated steel roo
Bill,
Again, thank you for your salient comments. You convinced me that epoxy is a good place to start experimenting. Never even heard of roll seam welding or furnace brazing. And aluminum is definitely the way to go instead of galvanized. It will have to be non-anodized though, because of outgassing.
Called 3M, as they seem to have innovative solutions for so many weird problems. Oddly, they don't have any structural adhesives that won't break down under methanol exposure. Even when folks that were using their epoxies to mend pinholed gas tanks started having adhesive failure, after methanol was introduced into auto fuels, they didn't reformulate or offer another product to meet that need. The tech directed me toward GE's silicones division, but they were closed today for the long weekend.
So I made my ritual journey to the sacred house of holy material and inspiration (Home Depot). Fortunately, there was a little old man there, not an employee, and he pointed out the epoxies. He's tried them all. The epoxies Home Depot stocks have high temperature limits below 200 o F, except for J-B Weld. Fortunately, it was early enough, so I called their tech support line. She said it would do everything we need. Every question, from thermal shock to methanol bath was met wtih an almost bored "yes", like she gets asked these BS questions all the time. And she probably does. Unbelievable! People must regularly use this stuff to glue on accidentially amputated limbs. Ho hum. Their website offers some interesting information. 1. They distribute internationally. 2. They're a family company and essentially a matriarchy since papa died in '89. 3. They very proudly list their charitable contributions and community involement. http://jbweld.net/index.php I'll buy what we need for testing, and if it works out, I'll have to ask for some material, after there's something to show them.
The best technical paper I've found on the asdorption ice-making process is: http://fsec.ucf.edu/ed/iasee/isree/s22236.pdf. My goal is to replicate her work. My process is: 1. Find what works. 2. Immitate. 3. Assimilate. 4. Innovate.
Being an EE you might also know some tricks on how to cheaply electronically measure temperature inside the vacuum with minimum penetration and no outgassing from the wires or sensors. I've been putting off this problem. All I can think of are are bad rectal thermometer jokes.
Henriksen,
Your concerns are valid regarding UV and heat. The panel will be submerged in a water bath, so it won't be heated over 212 o F, and the water box/collector will be painted black with no glass, so no internal UV exposure. But the paint on the submerged panel and the water box/collector will have to be maintained. Any suggestions? I hadn't even thought about UV paint damage, and you're right. Most of the 3d world car bodies I've seen have badly needed a paint job.
Don,
Good distinction. Having a vacuum seal between the tubes shouldn't be necessary unless something really weird and unforseen happens (Hello, Dr. Murphy!). They just need to be sealed from each other for structural stability and to keep the a.c. from moving around too much when the panel is moved. Even though the tubes are going to be densely packed with a.c., there will be settlement, and the whole process is pretty dynamic pressure-wise. Thoughts?
The plan for connecting the tubes is to place a manifold (a 1/2" copper tube perforated with 1/8" or 1/16" drilled holes) at one end of the tubes, seal it's penetration through one side of the panel, and tap a vacuum gauge and the plumbing from it.
You're right. Field units ought to include one of those little plastic hand vacuum pumps with a vacuum gauge. Having a regular vacuum check schedule will also eliminate the need to include an expensive installed vacuum gauge, too.
Adam
Again, thank you for your salient comments. You convinced me that epoxy is a good place to start experimenting. Never even heard of roll seam welding or furnace brazing. And aluminum is definitely the way to go instead of galvanized. It will have to be non-anodized though, because of outgassing.
Called 3M, as they seem to have innovative solutions for so many weird problems. Oddly, they don't have any structural adhesives that won't break down under methanol exposure. Even when folks that were using their epoxies to mend pinholed gas tanks started having adhesive failure, after methanol was introduced into auto fuels, they didn't reformulate or offer another product to meet that need. The tech directed me toward GE's silicones division, but they were closed today for the long weekend.
So I made my ritual journey to the sacred house of holy material and inspiration (Home Depot). Fortunately, there was a little old man there, not an employee, and he pointed out the epoxies. He's tried them all. The epoxies Home Depot stocks have high temperature limits below 200 o F, except for J-B Weld. Fortunately, it was early enough, so I called their tech support line. She said it would do everything we need. Every question, from thermal shock to methanol bath was met wtih an almost bored "yes", like she gets asked these BS questions all the time. And she probably does. Unbelievable! People must regularly use this stuff to glue on accidentially amputated limbs. Ho hum. Their website offers some interesting information. 1. They distribute internationally. 2. They're a family company and essentially a matriarchy since papa died in '89. 3. They very proudly list their charitable contributions and community involement. http://jbweld.net/index.php I'll buy what we need for testing, and if it works out, I'll have to ask for some material, after there's something to show them.
The best technical paper I've found on the asdorption ice-making process is: http://fsec.ucf.edu/ed/iasee/isree/s22236.pdf. My goal is to replicate her work. My process is: 1. Find what works. 2. Immitate. 3. Assimilate. 4. Innovate.
Being an EE you might also know some tricks on how to cheaply electronically measure temperature inside the vacuum with minimum penetration and no outgassing from the wires or sensors. I've been putting off this problem. All I can think of are are bad rectal thermometer jokes.
Henriksen,
Your concerns are valid regarding UV and heat. The panel will be submerged in a water bath, so it won't be heated over 212 o F, and the water box/collector will be painted black with no glass, so no internal UV exposure. But the paint on the submerged panel and the water box/collector will have to be maintained. Any suggestions? I hadn't even thought about UV paint damage, and you're right. Most of the 3d world car bodies I've seen have badly needed a paint job.
Don,
Good distinction. Having a vacuum seal between the tubes shouldn't be necessary unless something really weird and unforseen happens (Hello, Dr. Murphy!). They just need to be sealed from each other for structural stability and to keep the a.c. from moving around too much when the panel is moved. Even though the tubes are going to be densely packed with a.c., there will be settlement, and the whole process is pretty dynamic pressure-wise. Thoughts?
The plan for connecting the tubes is to place a manifold (a 1/2" copper tube perforated with 1/8" or 1/16" drilled holes) at one end of the tubes, seal it's penetration through one side of the panel, and tap a vacuum gauge and the plumbing from it.
You're right. Field units ought to include one of those little plastic hand vacuum pumps with a vacuum gauge. Having a regular vacuum check schedule will also eliminate the need to include an expensive installed vacuum gauge, too.
Adam