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Post by thumpersdad on Mar 3, 2019 8:26:27 GMT
Do you know how much steam you need?
With latent heat of vapourisation somewhere north of 2x10^6 J/kg (I think) you will get less than 0.5g/s from 1kW.
Eric
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Post by Roger on Mar 3, 2019 9:35:48 GMT
Hi Rodger, Um the pipe is either 6” or 7”.......he’s not sure were he got it from....7” is an odd ball size except in the oil & gas industry were they use some very strange sizes! Yep the heater is a standard house hold element, would think 3 kw would be more than enuff! Yep a pressure switch would be a great addition, tweak the switch so that it cuts out say 5 psi below the safety lift point, means one less thing to remember to keep an eye on! The other option could be use 2 elements, you would need a controller, were you could have it switch both on / off or just one to help controll the steam generation, maybe of 2 different wattages. Cheers Kerrin Hi Kerrin, Sorry, I did a quick conversion of the diameter in my head an somehow made it 4". Yes, I think 6" is sensible, although I did briefly toy with 8" since there's a piece on eBay at the moment. It's just too big though. I've just had a good look for pressure switches, and found that they are very expensive. I'll probably make one, it's only a plunger with a spring, seal and microswitch after all. How hard can it be? It would certainly be useful to maintain the pressure automatically.
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Post by Roger on Mar 3, 2019 9:37:31 GMT
Do you know how much steam you need? With latent heat of vapourisation somewhere north of 2x10^6 J/kg (I think) you will get less than 0.5g/s from 1kW. Eric Hi Eric, Good question, I was thinking of using a 3Kw heater. That ought to be enough for a short test of an injector.
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JonL
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Post by JonL on Mar 6, 2019 21:11:47 GMT
Following with interest.
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Post by Roger on Mar 6, 2019 22:12:50 GMT
I've received the new/old stock 3KW 11"" immersion heater I won on eBay for £8.98 and I've ordered the Seamless Steel pipe and end plated from the Steel Stockholder for £66.12 inc VAT so those are the main parts I need to make a start on the detail design once the Steel is in my hands. I asked for 6" pipe with 1/4" wall but in the end it was way cheaper to just buy the 3/8" wall material they had in stock which was £30 less! I guess they had some left over from another order and wanted to get rid of it. It's a bit chunky, but I can always turn it down a bit if I feel so inclined. The main thing is to get it here and see what the bore really ends up being and then modelling it around that. The same goes for the Immersion heater, you need these things in your hand to measure else the 3D model isn't of much value. Once I've got those details nailed, I can really get down to business.
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JonL
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Post by JonL on Mar 7, 2019 7:08:33 GMT
I don't think more meat to the walls is a bad thing if only for peace of mind. Does a thicker wall mean it would retain heat better? Thermodynamics isn't my strong point.
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Post by Roger on Mar 7, 2019 8:05:36 GMT
I don't think more meat to the walls is a bad thing if only for peace of mind. Does a thicker wall mean it would retain heat better? Thermodynamics isn't my strong point. Agreed, it's not a bad thing, but it makes it a lot heavier. Yes it will retain heat, but will also take longer to heat up. It does mean the weld joint will be bigger, so that makes the end attachment stronger.
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Post by andyhigham on Mar 7, 2019 8:41:39 GMT
3/8" wall is also plenty thick enough to tap for fittings instead of using bushes
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Post by Roger on Mar 7, 2019 20:55:35 GMT
These are the parts I've got so far for the test boiler. They cut two short lengths of bar for the ends, and that's not really what I wanted because I don't think that's going to be suitable for a welded end. I'll order a couple of square pieces of 10mm rolled plate instead and make them from that. Better safe than sorry. You can see there's going to be plenty of room for the immersion heater. The tube is 30mm longer than it needs to be. 20190307_203601 by Anne Froud, on Flickr
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JonL
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Post by JonL on Mar 8, 2019 9:02:25 GMT
Will you be using a steam collection dome? I'm guessing you will be mounting the element as low as you can.
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Post by Roger on Mar 8, 2019 10:21:44 GMT
Will you be using a steam collection dome? I'm guessing you will be mounting the element as low as you can. I wasn't planning a dome, but there will probably be a turret. Yes, the element will be very close to the bottom. I've just ordered the 10mm plate to make the ends from. I'll turn those so they fit inside the ends and have a huge chamfer on both parts so the weld can be built up through the full thickness of the material.
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jem
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Post by jem on Mar 8, 2019 18:18:47 GMT
I have an old diving air cylinder,cut in half, it used to have 2000 psi air pressure, and its 1/4 inch wall thickness. so the wall thickness is no problem. a bit late now, but perhaps you should have bought an old air cylinder, and used that. since it all ready has one end on it. Pity you dont live out here, I could give you several. Hydraulic rams also would perhaps be a way forward!
best wishes
Jem
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Post by steamer5 on Mar 11, 2019 4:30:33 GMT
Hi Rodger, We found the article! So for those interested it’s in July 2014 Engineering in Miniature. Robert talks about the elements used ( not jug elements but a cartridge heater) & shows the circuit diagram he’s friend came up with to control the boiler. It includes a potentiometer to control the heat input, a cut out for pressure & a low level probe for a cut out on....you guessed it low water level! If I read it right the heater input is 1000 w max. I’m sure someone on here could up rate the curcuit for a larger heater.
Cheers Kerrin
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Post by Roger on Mar 11, 2019 8:07:47 GMT
Hi Rodger, We found the article! So for those interested it’s in July 2014 Engineering in Miniature. Robert talks about the elements used ( not jug elements but a cartridge heater) & shows the circuit diagram he’s friend came up with to control the boiler. It includes a potentiometer to control the heat input, a cut out for pressure & a low level probe for a cut out on....you guessed it low water level! If I read it right the heater input is 1000 w max. I’m sure someone on here could up rate the curcuit for a larger heater. Cheers Kerrin Hi Kerrin, That's interesting, I'd like to see what they did. I think a pressure switch is a useful addition. Whether a low water level one is worth doing it debatable if this isn't something that's going to be used infrequently. Mine has a 3Kw heater, but controlling that with a solid state relay is probably favourite since I've got those for machine spares anyway.
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Post by steamer5 on Mar 11, 2019 8:17:58 GMT
Hi Rodger, Email coming your way shortly!
Cheers Kerrin
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Post by Roger on Mar 11, 2019 22:37:39 GMT
Thanks for taking the trouble to do that Kerrin, it's very kind of you.
Looking at the construction of the immersion heater, it turns out that it's Soft Soldered, so that's not going to be any good as it is. I'm just cutting it up to see if the element can be salvaged and Silver Soldered instead. We'll see.
The article kindly sent to me explains that Cartridge heaters were used on the second version of the test boiler in question, and that's another possibility, although so far the ones I've looked at have been pretty expensive and more than one would probably be needed.
It's a pity that electric shower elements are too high power, they would be an ideal size.
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JonL
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Post by JonL on Mar 11, 2019 22:50:07 GMT
Why isn't soft solder going to be good enough? Also the shower element is whatever power you dictate if you regulate the current.
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Post by Roger on Mar 11, 2019 23:02:38 GMT
Why isn't soft solder going to be good enough? Also the shower element is whatever power you dictate if you regulate the current. It's the melting point that's of concern, because you have to bear in mind that steam at 90PSI is at 160C not 100C. That starts to edge too close to the melting point of Soft Solder for my liking, the mechanical strength isn't great to start with. Yes, you can regulate the power to a shower element, but bear in mind that 3KW is the absolute maximum you'll want to take from a domestic 13A plug. Showers take typically twice that as a minimum, so at best you're going to be using half the waveform with about twice the peak current acceptable and then nothing for the other half. The average may be less, but the peak current still has to be supplied by the outlet. I really wouldn't want to connect an element that could draw more than 13A from a domestic socket, even if it was set to draw less, just from a safety point of view. I know it's fused, but to my mind it's dangerous.
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Post by steamer5 on Mar 12, 2019 2:29:37 GMT
Hi Rodger, Only to happy to help out if it means advancing injector design, out of the black arts...practiced by a few under clouds of secret incantations!!
Cheers Kerrin
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JonL
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Post by JonL on Mar 12, 2019 7:15:00 GMT
Why isn't soft solder going to be good enough? Also the shower element is whatever power you dictate if you regulate the current. It's the melting point that's of concern, because you have to bear in mind that steam at 90PSI is at 160C not 100C. That starts to edge too close to the melting point of Soft Solder for my liking, the mechanical strength isn't great to start with. Yes, you can regulate the power to a shower element, but bear in mind that 3KW is the absolute maximum you'll want to take from a domestic 13A plug. Showers take typically twice that as a minimum, so at best you're going to be using half the waveform with about twice the peak current acceptable and then nothing for the other half. The average may be less, but the peak current still has to be supplied by the outlet. I really wouldn't want to connect an element that could draw more than 13A from a domestic socket, even if it was set to draw less, just from a safety point of view. I know it's fused, but to my mind it's dangerous.
Fair enough. I only ever ask to enable me to understand, not to criticise!
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