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Forum Index : Solar : Deciding if I should build this solar heater
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| Warpspeed Guru  Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Ah ! I did not know that. Have never personally handled these tubes, only ever seen pictures of them in which they appear to be just plain glass. So that changes quite a few things. I bet it is, and now I can understand why. Cheers, Tony. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Time for an update. I've been experimenting with various setups and plan for more tomorrow. The following picture is a bit messy but is actually two separate experiments. The one on the right has 6 tubes venting into the bottom of the box and with the cold air inlet on the bottom left. Warm air is meant to rise to the top and be pushed out on the top right hand side. The inlet tube goes all the way across and has holes in the side facing downwards. The idea was to try and limit the colder air from mixing immediately with the warmer air ... and hopefully flow into the tubes as the warm air flows out. Doesn't really seem likely to work ... but I've based it on the fact that many of the cheaper, more basic water heating systems have the pipes directly into the tank ... and as the water is warmed in the tubes, it rises into the tank ... being replaced by cooler water at the bottom. From some of the literature I've read ... the water heating systems that use heatpipes are between 15-20% more efficient than this basic system ... so this should work at least to a degree. The fan is a 2 speed inline exhaust fan that draws 30 watts on low at 467 cubic meters/hr ... and 60 watts on high at 552 cubic meters/hr. I had just got home from Bunnings last weekend where I looked at various fans etc ... sat down with a cup of coffee and was checking out FB Marketplace ... and in the top row were three of these fans ... for $50 the lot. Two 6 inch and one 8 inch. Needless to say I jumped on them quick smart.  This next photo shows the view from through the warm air outlet. You can see the tops of the evacuated tubes ... and the cold air inlet tube, though of course you can't see the holes in the bottom of the tube that spread the cooler air across the bottom.  Cheers, Roger |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
I have been wondering how you were going with this and keeping an eye out for updates. Those inline fans were a steal. They are worth hundreds of Dollars each. They are meant to last a lifetime literally in AC applications and built and priced accordingly. I look forward to seeing how this goes. How is the weather where you are? It's been so warm and sunny here it's scary. I'm sure that winter is going to hit like a freight train when it does arrive. Actually into winter now and still wearing T shirts and sweating while doing things in the yard. been very little acclimatization for the cold so when it does come, Really going to feel it. I went another way for my home heating and bought one of those Chinese Diesel heaters. Completely against my usual luck, Few days before it arrives Brother in law shows up and says I have some old diesel Fuel out of the new boat I bought I want to get rid of, do you want any? Ummm, yes please! Went down to his marina on Thursday and loaded up 500L. I was dreaming he might have 200L but that was a score I wasn't planning on but am very happy for. That will probably be a life time supply for the little heater. Have been testing some old waste oil burners but being designed for high output, > 200Kw, They don't do well at 10-20. Built a new one yesterday which shows some promise. Bit of tweaking and I might have the first part of the puzzle. Keep us up to date with your testing. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
I missed a few posts apparently I just saw while re reading this interesting discussion. That's pretty much what I though and espoused some pages back. Once the heat is in there, it has to go somewhere and can't just keep getting hotter ad infinitum. It's wither going to have to seek the cooler air as is the way heat travels by convection/ thermosyphoning or conduction, passing the heat onto cooler air. I can't see it being stagnant when one end of the tube is oppen and there is a large temp differential with the cooler air passing the open end. I think there would be a combination of both heat transfer actions as the surface will only be heated on one side no matter where the suns position, there will be a hot and cold side in the tube which will allow for air circulation in and out. I do see mikes point about having the internal tube disturb and break up the boundary layer of gasses. That is air sticks to a surface in a fairly constant depth despite scale. It's a thing with designing Model Jet engines, you get the same size layer of air sticking to the blades of a 20mm fan on a model as you do a 2 meter one on an airliner but Obviously the inefficiency is a lot greater the smaller you go as a proportion. If said air is hot or cold similar to the surface doing the heat transfer, it tends to insulate the layer of gasses next to it so heat transfer is greatly reduced. In this case in my minds eye, I don't see a completely laminar flow going on despite the smooth glass tubes. I think there could be almost a pulsing effect where the heated air expands in the tube and overcomes the pressure of the colder falling air and then " Burps" all the hot air up and then there is an inrush of cold air. It may also be there are just eddy currents created which cause disturbance and interrupt the laminar flow of the boundary layer gasses on the hot side of the tube. When the tube is being hit from the sides by the sun, the heated air will want to also rise from the side to the top of the tube which may cause some disturbance in the gas flow. You can see this layered effect in swimming pools and even the ocean. The warmer water sits on top of the cooler water but in a vessel heated from one side, the thermosyphon currents would keep the flows moving and they would not be completely smooth. If there was a boundary layer that insulated heat transfer, The solution would be very cheap and easy. Like gas hot water heaters have a disruptor in the flue to break up the boundary layer of gas that has given up it's energy, a similar mechanism could be simply dropped in the tubes. It would only have to be a thin strip of metal that had cuts so small sections could be folded out. I have no Drawing ability but very roughly something akin to the old Fuzz stick used in lighting camp fires. Just a metal strip with wings folded out one way and the opposite so air passing by it would be disturbed. I made one for a gas heater that I was blasting with a burner and the original burned and rusted away. Just clipped the sides of a strip of metal one way and the other. Had more " Roughness" than the original and worked perfect although was a little more restrictive. The second one I did I just got some gal ( !!!) sheetmetal strips and twisted it. That worked fine too and had a bit less restriction. In this case I would strongly suggest a side by side test. One lot of tubes with a disruptor and one without. I see the possibility that the disruptor could in fact do just that and disturb the natural flow pattern of the air currents within the tube and confuse it all. That said, once again, if you have 200o air at the bottom of the tube it's probably not going to be happy sitting there and want a way out and find it somehow. Testing would show If there was a benefit or loss with these or if there was insufficient difference to justify the things at all. Does also bring me back to the idea of just the Beveled tubes. They may assist in the air flow. Again a Side by side test would tell if they had any value or not. With only a 5% margin to play with positive pressure to the bottom of the tubes Vs. Nothing at all, I'd tending to think the lower cost and infinitely greater simplicity of the tubes on their own could not be worth it. I also don't see the air acting any different to the water setup that was tested. Looks like we might all be on the hunt for cheap tubes if setting them up is this easy. I was wondering why they put ends on them though instead of just having them as straight through Tubes? Manifold on the bottom, manifold on the top, done. Surely the manufacturing cost to do that would not be greater than adding in the heat Pipes? Would require an extra set of seals and doubling the leak points but I can't see that being a big problem as they seem to seal well anyway. Could still easily be made with the internal vac and just bevel the ends so they could be positively located and sealed in the manifolds. Just off for a quick Browse of Dumbtree and marketwaste. :0) PS, The Disruptors are called Baffles in the water heaters.  Seems some are just Twisted sections. Got it right without knowing it!! :0)  |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
That is a rather thought provoking observation Dave. What if you place a mirror behind the tubes ? You can buy mirrored tiles suitable for bathrooms, that are impervious to water/heat/steam which should stand up pretty well to outdoor use. A mirror behind, might significantly increase the output ?? Cheers, Tony. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Yeah, if I hadn't been researching fans and known what the prices were, I might have looked straight past them. The seller, lovely guy, told me he could have sold them 1000 times. I was just lucky to spot them early enough and jump in. 250km rouind trip to pick them up but definitely still worth it. I have one of those jumping castle type fans ... which is far too powerful for this size experiment ... but it draws 440 watts ... literally 10 times as much, though it throttles back well plugged into a variac. Sounds the same here ... been warm all week and going for 29 today!! Then a forecast for low 20's all next week. Though it's getting a little chilly in the evenings, had to break out my beanie a few times. Great gift there and a good encouragement for your experimenting. Always easier if you can experiment cheaply. Doesn't feel so bad then when you have to spend a bit to complete it. So do they use the same system as the Chinese Diesel heaters? I did read up on oil burners a few years ago but the guy I was following was talking big power levels coz he's in the snow and ice in the US. Trouble was he was a miserable so and so to everyone he interacted with and finally got kicked out of the forum so I didn't learn much more. Wife just got home from night shift and is keen to go collect more firewood ... so my experimenting might get held off till later today.  Cheers, Roger |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
I thought about that Tony. My idea was it may help early and late in the day. The mirror will bounce the light off at the angle of incidence it hit at. It would depend on where the sun was and spacing of the tubes. I don't know if there is a standard for that? I would guess it would be something between 150 -200% Tube width as a rule of thumb. No Idea, would just seem to be the ideal so as not to shade each other and not to waste too much space in layout. Probably also varies with latitude and sun angle. I can see where a lot of the time a tube would shade the mirror behind it so there would be no direct light at least to reflect. At other times the light may be bounced back into space without doing anything useful. If the tubes were in an encapsulation with something like the mentioned suntuff or other covering, it may hit that on the return and help offset any insulation losses at least. I'm sure the smart people could work it all out with simple mathematics which is certainly not my strong Suit. I'd probably get a torch or set square and work out the sun angles and do it by brute force. :0) The other thing I thought of as an alternative to mirrors was just a black background. Again if the tubes were enclosed, heating up the air space around them might be effective but given they are vac tubes and the losses I expect would be low, the transmission back into them from a warm environment may be minimal as well. The 3rd thought, again in a brute force method may be Double stacking the Tubes. Put another one behind and below the primary collectors. If Rodger has an excess of tubes and a limited area where he can locate them, This would give a 100% area coverage. I perceive it would be of limited usefulness, mainly at peak sun when the light was hitting direct but that is also when the most if short lived gains are to be made. I spose if one could double the collection area for an hour or 4, that may be very worth while especially if there is a surplus of tubes already paid for and a limited area to put them. There may also be a small reflection advantage where any light bouncing off the lower tubes would be likely to hit the upper tubes so that would increase efficiency and decrease losses there. I surmise these tubes are not anti reflection coated, couldn't see it standing up to the sun and potential heat and in any case, that's not 100% effective so there would have to be some gains, from marginal on up. In any case the peak sun gain in doubling the collector area would be worth the exercise alone to me If I had spare tubes. Maybe the lower set could be set up for water to offset the domestic water use? Would only take a small circ pump and as I read that these tubes often boil the water quite early in the day, having a limited heating time may well be all that is needed anyway? Any heat they could generate would be a saving on the power or gas even if they didn't carry the full load. Either that or get an old water heater and use that for thermal storage for night heating use. Been getting on the AC fairly early here of late as the nights are getting chilly to heat sink the place but I do notice the temp drop inside once the sun goes down. Having a heat reserve would be handy I think. I have also notice even though I have been putting a powerful fan blowing the warm day air in the house, the furniture etc is very slow to gain much temperature. Mrs has been wondering why I have been walking round the house shooting things with a Temp gun. I tell her I'm checking for Chinnnaahh Flu. 400L tank taken even up to a 40C temp increase would have 18Kwh of heat energy which wouldn't be bad. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Yes, I use them for my Oil Burners. Brilliant things, they do volume AND pressure and can be bought for $20 If you are prepared to negotiate the often laughable prices people ask. Once they have been offering them for a month with no takers, they get the clue that maybe they weren't worth following what everyone else was asking after all. They will support up to 1200Kw of combustion with oil which is something to behold. Been there a couple of times and 2L of oil a minute is substantial heat output! The average heater size for an Olympic outdoor pool is only 2-400KW. :0) I use mine with an AC PWM controller to throttle them back, marvellous things, you just have to watch you don't go too far down and click them into the start windings although some seem to have them and some are universal motors or whatever they call them that don't have start caps. The PWM can make them Groan a bit but does not seem to hurt them. [QUOTE Sounds the same here ... been warm all week and going for 29 today!! Then a forecast for low 20's all next week. Though it's getting a little chilly in the evenings, had to break out my beanie a few times. The daytime heat is what I have been trying to pump into the house to heat soak it. Not as easy as I would have wished for. 5 or so degrees above the temp you are at seems difficult to get much energy out of. I'm thinking that Double input temp is more where one wants to be or above. We are predicted to have some rain next week which is good but temps down to a low of 10 or 11 which is good for here. Still mid to low 20 Tops again, not going to complain about that! Yes, I am prepared to throw a bit of money at this home heater and do it to the reasonable best of my ability because it is an investment and an important one being comfort and self sufficiency. The Mrs is complaining of being too hot if over about 20, the daughter literally has a jumper on under 30 and I'm smack in the middle with 25 being a good temp for winter. The packaging will I perceive, be more difficult than the technicals. I'll start basic and then look at adding automation once I better understand what is needed and learn more about how to implement it. A big reason I bought the China heater is it has press button control and automation so the Mrs and Daughter can use it with no problems. Long as the thing has fuel and power, it's good to go and is safe and reliable. No, mine all work on retained heat in the burner itself to vaporise the oil. There is a preheat with Gas, diesel or even wood and I use forced air generally in a swirling motion to run the burn chamber red or near it hot. The big advantage with my designs which are all on the same principal although applied differently, is they will run on any old waste oil ( unlike the Chinnah heaters ) and don't need cleaning like about every other design I see. The combination of heat, an over oxygen rich air fuel ratio and the turbulence means you can burn them all day or week and when shut down, there is barely a wiff of fine dust like ash in the bottom. Used engine Oil will leave about 5% residue but mine will self clean through complete combustion through all the burning phases and run with no smoke at all and leave no residue in the burner itself. they also used blown air rather than a lot using fine nozzles that need an air compressor. My burners are very simple ( like their inventor)and I find that's often the most difficult thing for people to comprehend. You show them the whole thing in a vid and show the setup and how you light them up and explain it all but people are still looking for the catch and the complexity. Some people just HAVE to have things involved, expensive and energy intensive before they will believe it will work. I made a burner out of a bent bit of exhaust tube and a gazunder ( chamber pot ) and did vids on that and people still were looking for the catch. There are 2 parts to it plus a $20 Bilge blower and a bit of hose dripping oil in which I clearly showed and explained. What the hell is the confusion ??? Well I have mainly done the high power stuff as well. People asked for more practical burners for heating sheds and homes but when I did them the views were low. Do a vid on something pumping out 600Kw which is a Piece of cake compared to low output burners and you get loads of views. I think the real smart cookies in this game are the Russkies. They all seem to be born with a stick welder in their hands and they seem to think nothing of stitching something up that must take a 100M of weld bead but some of their concepts and Ideas are absolutely brilliant and no one in the west seems to use their principals. They too inherently understand the principals and apply them in extremely clever ways. You can see many of these people are poor and have limited resources But by geez they are bloody clever in what they come up with making very effective devices out of nothing! I can't understand what they are saying in the vids but generally easy enough to get the concept and they are brilliant in their design and application. Things I wanted to do in principal but wasn't clever enough to work out in practice. I am planning on stealing some of their ideas and modifying them a bit. I am really big on using forced air over draft for the cleaning side especially and I think a bit of very low level supercharging even with just a low ( 17W) power bilge blower could make a big difference. They always pretty much use Draft and do well with it but I think a bit of forced air would improve things. We'll see! Pffft! I have been kicked off more forums than I can count. The Yanks especially don't seem to be able to handle straight forward language that we here take for granted. I'm feeling a bit motivated to get back into Vids, it's been a long time. Mrs has been at me to go back to making some of my aluminium cast art Pieces. She loves them, not sure if anyone else does but she did give a few away and the recipients gave the impression they genuinely liked them. She wants me to make a heap and set up a stall at the local markets. Spose it will give me something to do, not going to cost a lot to make and if they don't sell I can always just get some return on them at the scrap yard. If they do Fly then might amount to something... Till someone else starts making them.... :0) |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
I hadn't thought about that. Certainly the inside layer at the top does get hotter than at the bottom. Something else I noticed was with 6 tubes open to the air on a hot day ... I could see in the shadow on the ground, what looked like smoke coming out the top ... all wispy and floating around. Could not see it directly out of the tubes. I actually took a video of the effect. It was like a heat haze ... so obviously heat does pour out of the tubes and cooler air must flow down in to take its place. Yes, agreed ... that was the way I had originally planned to do it ... I couldn't see any other way of getting all the heat out. A guy I have seen on youtube has done some similar experiments and he fitted a spiral around the outside of his central tube by soldering a copper wire in a spiral up the tube ... then fitting a further two (on top of each other) to create a barrier to the air and force it to spend more time in the tube ... and gather more heat. He had to reduce the number of turns around the tube though, because it slowed the airflow too much. Yeah, and that was the reason I set up my stand with two lots of 6 tubes ... so I could compare different configurations. With sun and clouds and temperature changing all the time it is impossible to make comparisons without doing them concurrently. I've realised I need more and better thermometers to be able to make sense of my experiments though. It's too easy otherwise to come to false conclusions. Yes, that makes sense. I have seen a paper on some tubes that were as you described ... open at both ends ... and they did feed the cold air in the bottom and harvested the hot air from a maniflod at the top. But I haven't seen any for sale, so don't know where they sourced them. It seems that sealing is not really that difficult ... especially with air, not difficult at all ... but even with water in the tubes I haven't read of any problems with constant leaks ... though I suspect they all need to be low pressure systems with a vented expansion tank. Systems with heatpipes or heattubes can get away with mains pressure because the water is contained within the manifold. Maybe we'll have to load our respective trailers with evacuated tubes and solar panels and meet half way to do a trade. Cheers, Roger |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
There are quite a few people who have experimented with parabolic trough reflectors and they certainly do get higher efficiency ... but all the papers I have seen on them, they are only using one tube with a very wide trough ... maybe 12 inches or so. That makes it hard to put a decent number together because it becomes far too unwieldy. It still would be worthwhile to try for sure ... but because the tubes are generally spaced with only 22mm between them ... the value would only occur with the sun pretty much overhead. The rest of the time, the mirrors could only reflect light that gets bounced onto them off the tubes ... so not sure how much value that would be. I suppose you could space all the tubes out to 6 inches or so ... but then my 2.5 meter 36 tube array is going to end up 5.5 meters wide.  Cheers, Roger |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
I know exactly what you are talking about and have seen it many times myself. I just call it heat haze but it's very definate if only a shadow of what can't be seen otherwise. Good to get a confirmation of the heat flowing out the tubes though. The temp must be pretty high to see it like that. I can see how that would be the tricky part. Really have to measure the air volume and average temp I'd imagine to get a specific BTU number to compare each setup. Maybe if you had an anemometer and set both fans up to give the same airflow you could then measure the temp out of each test batch. Might just want to use the one thermometer or make sure if you used 2 they were very closely calibrated. I was playing with a couple of those laser temp Guns I have today. I found they were half a degree out. Also found that turning off the laser pointer brought them back to equal or .1 of a degree difference. I know how I'll be using them from now on. Hard to find to thermos that will read alike to a 10th of a degree but then again, for this test you may want several degrees for the difference to be worth anything in practicality. Well the Mrs has been saying she wants to go away somewhere when she is on holidays in a few weeks time. Not sure how keen either of us would be On Vic or SA ATm though. Could get stuck there for months if a couple of people sneeze and they lock the places down. :0) |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Closer than I would have thought. Yeah, that's what I was thinking when I suggested double stacking the tubes. If you had 100% area coverage, wouldn't need reflectors as the secondary tubes would bounce anything they didn't absorb. I can see an over 100% efficency with this because of the reflected light having a chance to be put to work instead of bounced back to nothing and wasted. Would be interesting to again see where the best performance was.... at 22MM spacing with the tubes behind in the gaps or open the primary tube spacing out to maybe 80-100% the tube width. As the secondary back layer would all be bonus heat gain in effect, maybe the 22% would be all that was needed. Might mean more tubes in a given area which would have to be a good thing because it simply gives more surface area to harvest the solar radiation. More I think about it, the better I can see that Idea working and in a single manifold layout, would be easy and practical to set up as well. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
I should probably give some figures so you can see what sort of results I've seen so far. In the photo above with the cardboard box ... I was replicating an air version of the water-in-tube heater. I blocked off the vents and after about half an hour had 62 degrees at the top of the box ... ambient was about 25 degrees. Later I fitted the fan in place ... ambient 25.5 degrees ... This time, with the inlet and outlet both open ... the temp in the top of the box got to 42 (after half an hour or so). I was using a dial thermometer with its stem just poked through into the box. 12.40 pm Turned on the fan ... 2 mins and temp inside top of box down to 35 4 mins down to 30 17 mins still on 30 ... ambient still 25.5 So, 4.5 degree gain. Later I started using an IR thermometer facing into the outlet ... and that seemed a couple degrees higher than the dial gauge stuffed through the side of the box ... but I have no idea of the accuracy of them all. 1.10pm 26 into fan inlet (IR thermometer) 32 coming out 2.00pm 26 into fan 31.5 out Bear in mind, this was a nice warm day with reasonable sun ... 25-26 degrees I could probably try a dozen different things around this setup ... but my plan is to build a setup with tubes going down into the glass tubes to blow the hot air out ... I should be able to run both systems at the same time to compare the different methods ... that way it will be easier to see which is the better process. I'm kinda leaning towards the central tube idea being more efficient ... but only one way to find out. If it is markedly better, I will then start playing around with different versions of that. Once I have something that seems reasonable ... I will put all 18 tubes into the stand and place it at the side of the house facing north ... and just pipe the air out of a temporary vent in one sliding window and back into the next. Don't sweat, I have approval ... but I couldn't get an ok on blowing the air under a mat ... not sure why that's an issue ... but she's not home 24/7 ... so I'll still have a shot at it. It seems reasonable to expect that 18 tubes should be able to collect 3 x the heat of just 6. If I feel that it is worthwhile ... my idea is to join two frames together and have 36 tubes laying on the roof. Perhaps draw the air out of the passage ... and pipe the return into a colder area of the house. In fact, I can't see why I couldn't join 3 lots together for a total of 54 tubes though that may be overdoing it. Just needs a longer manifold. Obviously going to need some smarts to control it as well. No point getting ahead of myself. Cheers, Roger |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Yeah, they don't have to be ... it's just that the frames have pre-cut holes for the plastic tube locators. Maybe other brands are different. I have plenty of tubes, so that's not an issue ... just adds a little more work in building the manifolds perhaps. If I can narrow down the best output system ... then I could try this as well. Just to throw out some more info that I keep coming across. Some of the papers on these things have added in PCM ... phase change material ... So instead of just heating the air (or water) and using that to warm a home ... they use it to warm some PCM ... which then can release its thermal energy when the temperature drops. Like a battery in a solar system stores energy for night time when the sun is gone. The thing that got my attention though was that ... if you warmed up a pile of rocks ... you could get that heat energy out again as things cooled down ... ... but with a good quality PCM, you can get 10-12 times the energy back out. Of course there's no such thing as a free lunch ... PCM is expensive. There are various proprietary materials that are used, different salt concoctions and even things like coconut oil ... but of course even that is expensive in the quantities needed to have an effect. At the same time ... those sort of gains could easily turn a system from a fizzer to a boomer ... just gotta work out where to get some of the stuff ... or how to afford it!!! Cheers, Roger |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Sorry, I missed this reply Dave. Yeah, it looks effective and certainly shows heat moving out of the pipes These sort of measurements are all foreign to me and I need to gain an understanding of the best way to measure results ... and also what new gear I might need to buy to help in the process. So far, out near the shed and when it's breezy, I can tell the readings go all over the place, so I have to work out how to get around that. Haha, yeah that's going to affect us all for a long time yet, though SA has been pretty good so far. Hopefully it stays that way. If you decide to check out SA, you're welcome to stay here for a few days. Would be good to meet you. Cheers, Roger |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Okay ... so I have to admit I've been more than a little underwhelmed with my results so far. Anyway, my next experiment is with tubes down the centre of the evacuated tubes and push the cooler air down through them to push the warm air out of the tubes. Pictures are easier than explaining ... I must also say I love my new holesaw set.  Here's a view in the cold inlet manifold ... the other end is now closed so the air must go down the tubes.  Here's a view of this setup with the 6 tubes on the left.  I only started this at 4.00pm this arvo and the sun was already way off to the side. This photo was taken at 4:15pm.  Okay, the tubes had been in the frame and in the sun all day so had gained a lot of heat inside ... all between 165-170 degrees. I assembled my manifolds and tubes and inserted them into the evac tubes. The tubes are all probably a foot too short ... but they only cost me $2 each ... so I wasn't going to complain. While I was fitting the fan, one of the tubes fell through to the bottom of the glass tube. Lucky it didn't break. So all these figures are with only 5 tubes not 6. Ambient was 21 degrees Turned on the fan at 4:08pm and outlet temp went steadily up to 71.4 degrees C. 4:10 ... 80.4 ... ambient 21 4:15 ... 70.6 4:27 ... 52.8 4:32 ... 44.6 4:50 ... 28.7 ... ambient now 18.7 5:05 ... 22.4 (Had visitors so a little hard to stay on track!!!) I have to admit, this has me a lot more excited than all my previous experiments. Considering the sun was already low in the sky and way off to the side, I'm amazed at the heat that was pumping out ... and for how long it pumped before it dropped right down Am really keen to see what it's like in the middle of the day when the sun is at right angles to the array ... and just how well the sun recharges the tubes ... and how long the array can maintain a useful output. Again, the fan was on low speed ... 30 watts and 467 cubic meters/hr ... though it is a 6 inch fan pumping into a 4 in manifold in this case. I think it's safe to dismantle the previous array, these new results feel a lot more worthwhile pursuing. Video of Heat Haze Edited 2021-05-02 20:54 by rogerdw Cheers, Roger |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
The smart and knowledgeable people here that probably know better might like to chime in and point out the flaws in the idea but I would be basicly just trying to standardise airflow and measure the temp output. You need to get the same airflow going through so you are measuring the heat imparted to it. The right way I believe would be to measure the density but I think for this purpose, having a fixed apeture ( the Pipe being same size) and measuring the air speed out to make sure it's the same and then measure the temp would be close enough. Heating the air will reduce it's density so won't be perfect but again, I think would be close enough. No need to measure fractions of degree here. You would want to see several degrees to make the extra work worth while... Maybe. Going back to the water heating test which was 5% difference, I'd expect the air to be similar. Play devils advocate, if it makes 10% Difference, Is it worth it? How much extra heat in real terms would that bring you and what is the amount of heat in real terms and what is it going to cost in time and money to get it? My Suspicion ( completely clueless, totally inexperienced, pitifully uneducated Guess) is that being solar, My rule based on solar PV will apply. The most efficient thing with solar is inefficiency. In other words, Trying to make things more efficient is always more costly, time consuming and only partially effective than Just adding more ( panels). In this case Tubes. I understand you may have limited area to put these but maybe, making a temporary ground mount you put away when the weather warms up or mount it on the roof or do a westerly facing set of tubes with the air just blowing across may in fact be cheaper and easier than doing the centre input tubes? Just thinking, If you have an air compressor you may be able to do as I think you did initially and just set up one tube for each test. As a suggestion, Put a vent in one and manifold it and manifold the other without and have the same ( maybe 1" )outlets on both. Set the air compressor to do a low output, maybe 10 PSI through an air duster or something so the actually airflow is fairly small and measure the output of both setups. Long as you don't touch the pressure setting on the compressor and use the same air duster as you would, the flow will be the same and then measure the temp of the outlet. Tape off the end of the inlet and poke the duster through so you don't get variation with different positions of the duster inducing greater or lesser airflow. This will limit your expense in building a test setup and as long as the same thermo is used and the tests done in quick succession, should tell you if there is any difference. I Imagine you'll be looking for 10ths of a degree But if you see a couple of degrees difference, You can multiply that by 30 and divide by the airflow increase but it sure would be worth while. If you see a tenth difference, then again you multiple that by 30 which will be 3o and divide that by airflow and you have nothing worth while worrying about. You might have to have a standardised outlet as well and say 300MM Long. Put the thermocouple the same distance in the outlet when you measure. If you have the same airflow for both, that should get you close enough as long as the measuring position is the same. Like any test, it's simply eliminating the variable so and difference in measurement is caused by what you are testing not outside influences. Thank you! Very generous and kind offer. I don't think the Mrs wants to drive that far this time and I think she was more intent on going North a bit. I haven't been to SA since I was a small girl travelling with my grandparents. My father particularly didn't like me taking time off school going with my grandparents around the country. Time I got to high school, I realised having been there, seen it and collected the Souvenirs from sheep stations, Mines and wheat farms etc was the best education I could have possibly had and put me ahead of most of the rest of the kids just though having seen it first hand and learning things that were not in the books. You might change your mind if you did but it would certainly be interesting to see your Tubes and potentially do some testing with you on them. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Why? Forget all of what I wrote above, you are way ahead of it all already with your test setup. As you said, You were testing pretty late when anything solar would be in it's dying stages of limited production. The fact you got any measurable improvement at all at 5 PM with an air flow of 4" with 5 tubes I'd say is a win . |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Yeah sorry, that probably came out wrong ... up to that point I had been a little disappointed ... but those latest figures with the new setup have been a real encouragement. That makes sense. With some reasonable length inlet and outlet pipes it should be more consistant, though I'd be very happy for some guidance on measuring heat output level. I realise that temperature is only part of the story. That's sorta what I was hoping too ... but this latest setup is so far beyond what I was getting from my first experiments that I need to use this as my base and try variations of this. And because I have a large number of tubes I can still add as many as I need to scale it up if needed. You're very welcome. I have the same view with our youngest. I've been exposing him to all sorts of activities and fields with the view to education. From dragging him out to help pull down a motor, wreck electronic gear, printers, photocopiers, TVs ... build circuit boards ... ... check out farming activities, tractors, gokarts etc He still wants to spend all his time on screens like most kids but he's not going to get away with that all the time. Having said that, he's learned an amazing amount from some of the kids educational programs ... and regularly schools us on various topics. It wasn't until recently that I came to really appreciate growing up on the farm and all that I learned there. Mechanical skills, work ethic etc. Haha, I might do, but I reckon we'd have enough to chat about for quite a while in the meantime ... and as far as experimenting, they say that two heads are better than one. Cheers, Roger |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
That's a really impressive piece of hardware you have built there Roger, very nice  I have been thinking about how to take some measurements from it. One instrument you might find useful would be a low cost digital anemometer, I bought one many years ago from Dick Smith electronics, but they are also available from e-bay and Ali. The one I bought measures in several different units, but feet per minute, is very useful for calculating flow in any given pipe diameter. I used it to measure airflow from one of those 100mm diameter 12v bilge blowers, and surprisingly the figure agreed exactly with the bilge blower specification, so it is useful information to have. The one I have also displays air temperature, which they probably all do. https://www.ebay.com.au/sch/i.html?_from=R40&_trksid=p2380057.m570.l1311&_nkw=digital+anemometer&_sacat=0 The other idea is a way to measuring the actual heat output. If you could fit an electric heating element to the hot air outlet, and adjust the electrical power so that the final total temperature rise was exactly doubled, the electrical power input should then be equal to the solar power input. Again a cheapy e-bay plug in ac wattmeter might be the easy way to do that, along with a variac which I believe you already have. Just subtract the no load idling power of the variac from the final power reading, should be simple enough. The bare heating element from a fan heater might be pretty ideal. Should be able to buy a dead one from the local rubbish tip for a couple of dollars. With fairly simple basic equipment it should be possible to record some rather useful numbers. Edited 2021-05-03 09:33 by Warpspeed Cheers, Tony. |
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