Alistair Warburton

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since Jun 29, 2013
A long and sad tail ... I will spare you detail.
Did the whole chasing the dream via money for a long while, struggled with lack of qualifications but made it eventually.
Then it all fell apart, as did I ...
Very ill for so long ... Got help eventually ...
Work just enough to afford to play now and loving it.
I am now 50, have a long suffering wife Val, 3 kids and 2 grand kids.
Work is split between industrial programming, that's the bit that pays the bills, and commissioning and maintaining micro hydro sites. Just about to start renovating an old stone build.
Wales, UK
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Recent posts by Alistair Warburton

concave and convex surface ....
Interesting I hadn't thought of that, although now I am I wonder if the whole thing might not be prone to bending like a giant spine.
It defiantly sounds like it is worth some thought though.

As I said earlier "I know nothing" but I think the benefits of this approach would be:-

Faster drying as sections will have a big surface area in comparison to their volume, much greater than a single massive part.
Less massive parts are likely to suffer less slump during casting so forms can be lighter and simpler, also filler and air pockets will not get compressed so the density of the casting should be similar for all parts.
(Don't actually know if this would be a problem in the first place)
Individual form cores can be slightly tapered so that taking them out is possible, again I doubt you could do this with a tube although I appreciate a tube could be burned out.
A poor casting is not a total loss.
Sections damaged during construction or even use can easily be replaced.
Riser height is adjustable during development.
Different section parts could be substituted, all be it with a new form, but still changing the dimensions of the burn tube during development would not require the whole casting to be scrapped.

Disadvantages:- (It seems only fair)
More complex and time consuming to build, cant do one big mix without multiple forms.
Might leak and need grouting.
Parts could crack into relatively small chunks and become unusable.

I expect I will not know if this is even viable, let alone worth while, until I try it.

We will see ... I am currently researching cast-able insulating refractory.

5 years ago
Hay Al, I was thinking a similar thing, well the casting bit at least.

Shortly after I posted the sketch I realised that the bottom section would have been better if it was square, at least one side, so that either other cast sections, or bricks could but up against it.
I hadn't thought about using similar bits to build up the burn tube but it would probably make sense if the casting is hardy enough.

I would want to keep the concept similar though, basic bits in multiples I mean.
The sketch is what I think you meant, it would only take a single adaptable form with removable cores, to produce the parts.
It also occurs to me that mould making would be simplified by making the exterior hexagonal as opposed to round,
I have done a quick sketch of a form, with three removable cores, capable of making all four sections.

What is this "expansion strip" you refer to, it sounds like something I should know about?

I would be very interested in comments about suitable materials, commercial, home grown or a mix.

5 years ago
That is far more longevity than I imagined and is good to know, thanks Al
5 years ago
Hi Al thanks,
I haven't read the whole shippable core thread, perhaps I should, it didnt immidiatly seem relavent to my research but now I think about discussions about manufacturing ma well be interesting and enlightening.

Dragon Heaters I was on top of but thanks anyway.
They look nice and have clearly had some considerable research done on them but cost !! WOW

Let me make a promise ...
If I get this stuff to work as well as I suspect it might I will publish all plans and experimental date free along with credits for all contributors.
It's all about the planet not me and I earn enough to be comfortable.

I find it most interesting that the burn tunnel in the Dragon is cast and they have still retained a brick, well board, riser.
I cant help thinking that there must be a very good reason for that as the attention to detail is clearly very high, heading such exemplar warnings would be wise me thinks.

Insulating the top?
Actually it is all insulation but I anticipate needing something extra right above the riser to 'spread the heat out'.
OK I know, actually I will be dropping the pressure, cooling and slowing the gas a little, before it hits the heat exchangers but still I think the top will be vulnerable to erosion.

Anyway that's me for today, unfortunately I have to work, real work. I promised myself I would start at 10 and I am now late which is a neat trick when working from home.
laters folks ...
5 years ago
Thanks for all the links Al, you are right it will keep me busy for a while.

Alas my experience with water is not at the expert level, mostly I do the control system design. Obviously I need to know how it all hangs together and works but I rely on the mechanical guys for the raw calcs.
That said I am a good all rounder, sorry if that sound a little immodest but it is why I have a job playing with systems I love to work on.

I haven't heard of the trip wire but then the last thing I would want to do with a hydraulic flow would be to break it up. You are correct that the boundary layer will move slower than the main body of the fluid but the beast way to minimise pressure drop is to keep all direction changes slow so that the boundary layer inst disrupted. laminar flow is just that, laminar, not all the fluid is moving at the same speed but critically very little of it is changing speed.
Once you mix things up pockets of fluid have to change velocity which requires some energy that will end up being dissipated as heat or sound.
In laminar flow conditions it is not unreasonable to think of the boundary layers as if it were a lubricant protecting the majority of the flow from the frictional losses associated with the pipe wall.
We typically recommend pigging a pipe at least once every two years, scouring it out with a sort of bobbin thing that the water pushes through.
This is done because even small irregularities, algae or general detritus, is sufficient to destabilise the flow and significantly increase the pressure drop. The actual change in size plays a small part but it is by far the smallest contributory factor.

"Use smooth pipe for your RMH bench ducting" .... its the same thing. ( I have seen this said several times )
Technically, the duct would perform better with long sweeping corners and bungs in the clean-out ports so that the 'T' leg was filled with something that matched the ducts inner wall.
Fluids simply don't like changing direction a 90 degree elbow will typically have 5 times the pressure drop that a pipe of the same length would exhibit.

I'v been thinking about your comments and reading associated posts and now have concept 2 in mind ... It may be no better than concept 1 but stagnant isn't an option.

The sketch is not to scale, mainly because I don't know what size things will need to be either in finite units or in relation to each-other.
I suspect that it will need to be tall and relatively skinny in comparison which should maximise draft in both the up-flow and down-flow sections.

I have modified the heat exchangers to be two large tubes for want of a better description, think barrel in barrel with the top and bottom cut off and a narrow flange joining the inn and outer skin. There are two of these inside an insulated outer skin.
I know a guy who can spool stainless up to 2m X 2m in material up to 8mm thick so a couple of spools from 1mm with nominal diameters of 450mm and 500mm respectively shouldn't be a problem whatever height they need to be.
Pipe fittings will be welded bosses. There will be a small vapour lock at the top which will partially bubble out when it expands but it will be no more dangerous than an air locked radiator in a vented system.
I may have a word wit Pete, my spool guy, it might be possible to slit a tube and weld it over a slot in the shell to give a vertical connection which would get rid of all the air.
I might even look at getting the case done that way, spooled I mean, if it isn't too expensive.

I have already found "Existing Chimney", it was interesting and provoked me into looking at the subject in general.
I have to say though, if I was facing a similar problem I would be looking at ways to put warm gas into the flue, either permanently with just enough heat to drive, it or possibly using a damper to feed it directly whilst starting.
It will be interesting to measure the relative pressures, I haven't seen that anywhere yet, but I suspect that the top of the barrel will be significantly above atmospheric and full of very hot gas, bleeding a little of that into an existing flue would defiantly create draft in a conventional way. The point is that peeping over the box lid as opposed to jumping out might work in those situations, sacrifice a little heat to mitigate the cold existing flue and keep everything else the same.

I used to work on naturally aspirated boilers back in the day and many of those, particularly the industrial ones in tall buildings had balanced flue dampers. Just a counterbalanced swinging plate really, that would open when the flue was too hot and drawing too much. The idea was that the flue was always going to draw enough even with the boiler very cool on a low flame but when the burner was turned up and the flue got hotter room air was sucked in through the damper protecting the boiler from excessive pressure differential.
If you were to turn that on its head you could have a mechanical mechanism that varied the hot gas to the flue based on the current draw, more draw less hot gas.
That way you would naturally start on bypass, for want of a better phrase, and progress to maximum flow through the mass as things warmed up and the flue started working.

I have listened to some of Paul's stuff, it seems very informative but there is a great deal of it and the format makes cherry picking difficult.
E & E's Vid, the hour long talk, was worth the effort though so I will persuasive with the pod-casts I think.

My last thought for the day is possibly a little contravention, Gasp !!
I was pondering long burn solutions and thinking about my log grate idea. Reading suggests that this sort of thing hasn't been that successful in the past and I found myself thinking about gasifying wood burners again.
And then ...
Well what if I were to build a fire box with a sloping floor, front to back and a rear grate leading to the burn tube. Primary air would go in through the box and round the fuel creating a pyrolysis zone at the rear and discharging gas and smoke into the burn chamber. Secondary air would then be introduced to complete the combustion.
Well so far that needs a fan and would actually be a pretty standard arrangement if it had one.
Now scrap the fan and use the thermal drive characteristics of the RMH in its place.
Basically what I am suggesting is putting downdraught gasifying fire box, all be it with a 45 degree burn as opposed to a vertical one, in place of the feed tube and part of the burn tube.
Now I appreciate that starting would need a bypass of some sort but that could be done and once the flue was pre warmed the system could switch to downdraught and heat the riser would quickly take over the job of creating draft so that heat could be extracted and the flue allowed to cool.

Is a gasifying / Rocket Hybrid possible? Has anyone tried this?

5 years ago
Disclaimer ...
I am new to this and the suggestion might be entirely bonkers, if nothing else have a good chuckle on me!

Thinking about design options, for me, I hit on the idea of casting rings that could be grouted together but may also work with dry joints, furnace rope in a rebate.
That would be shippable and modular so different height cores could be built from the same Segments, granted you would still need a burn tube.

The taper is exaggerated in the section and would be necessary to remove the centre core, mould core that is, the outer circumference could either be contained in a spring form or also slightly tapered to ease the release process.

Just a thought ! Am I bonkers or might this fly?


5 years ago
Oops, that should have been 'Segment' I don't want anyone thinking I meant 'Cement', that would be a bad thing

Hay just had a thought, with all this talk about shippable cores, what about segmented shippable core blocks, easier to pack, stackable to different heights, even replaceable as individual segments if damage occurs or the hottest bits degrade.

I don't know that much about gas but I would imagine that they would be gas tight, at least tight enough for a core with a furnace rope seated in matching groves between them, they certainly wouldn't be moving about.

Just a passing thought!

5 years ago
Thanks Al,
I look forward to your comments when you have the time, I hate it when that happens, so much so that I usually coppy and past to text doc before pressing 'post' I have been caught out too many times in the past.

The more I read the less I seem to know, go figure, I am hoping that the equation will turn round at some point so that I start going forwards.
That said I would rather find out here how wrong I am than when I am looking at an expensive pile of rubble!

I have been looking at cast-able refractory, commercial stuff it isn't as expensive as I thought, has anyone played with it?

it seems to fall into two basic categories, dense strong stuff and light insulating stuff which I expect is just the dense stuff with a filler. What I am finding suggests that one can be used as a backer, or face depending on your view point, for the other.

I find myself wondering about casting, well donuts, flat top and bottom faces of course, but with a rebate, circular trough, to enclose furnace rope as a seal between sections.
Spring form cake tin springs to mind, pun intended ...
The centre could be slightly tapered which would make it easier to remove from the mould and in service would create little ridges that might actually promote ambulance. ( The section is extremely exaggerated )

Anyone with casting experience? I would welcome a critique ...

Still thinking, feel free to chime in!
5 years ago
Thanks so much for your time Allen,
I know that my post may look as if it came form someone self obsessed and not prepared to listen to reason or experience but that couldn't be further from the truth.
In fact it exists because I know I cant possibly have got this right with my first conceptualisation, what I don't know is how wrong I am yet.

This is one of those times when feeling a little deflated is actually refreshing ... All be it humbling at the same time.

Mass ...
It isn't about space, it is about hot water. We will be off grid with very limited power and being in the UK very limited sunshine for the most part.
I absolutely could have a stone / cob mass vertically or horizontally in the immediate vicinity of the core in fact that was my first thought.
However once I started thinking about how to add in a heat exchanger it occurred to me that, provided I could get it to work safely, placing thermal storage tanks in the same space that the stone mass and ducts would need to occupy would actually store more heat. E & E say in one of their vids or pod casts that water is the best heat store, just before going on to say you shouldn't mess with it unless you are aware of the risks and can design them out.

"Understand just applying high temperature ....... "
Alas no, I fear that enthusiasm got the better of me there.
I appreciate the need for the insulated riser but hadn't given much thought to how that was working as a 'pump' - my assumption not a fact.
I looked at the stove concept and simply saw a thermal pump but when I looked at the RMH concept I failed to appreciate that the very same pump was being augmented with a second stage, the cooling gasses moving downwards.

My conceptual sketch shows clearly that I failed to consider the system as a whole when thinking about the mechanism for driving the air flow. I am suggesting cooling gasses that are moving upwards which is not going to work unless the riser is capable of creating a great deal of pressure differential.
Is that something that has been measured or calculated ? How much differential is created in the riser and how much in the barrel in a conventional system?

I am not too discouraged as placing the heat exchangers in a section of downdraught is actually a far better plan and will produce the counter flow I need without reversing the water flow through multiple exchangers.

Air ...
A point well made but also one I have considered extensively. Since I want, in fact need, to ventilate when the heater is not running an HRV is almost a given.
The house is an old stone build and moisture would quickly make the space uninhabitable without significant ventilation.
The HRV will work with forced extract as opposed to forced supply so that the space is negative as this will give the best results as far as I understand it and it appears that you agree.
The problem that I envisaged is that the very negative pressure that keeps the space healthy would negatively impact the gas flow in the heater which is why I envisage using what will effectively be a room sealed unit.
Of course I may have overlooked something fundamental but provided that the ducts are big enough I don't at this point see why it wouldn't work.
However I am now aware that E & E abandoned an air supply below the feed tube as it was causing smoke back and I can see how that might be an issue which leads me to think that ducting the air would probably work OK but that I will need to have at least some primary air going in at the top of the feed tube.
I am also aware that the co-axial flue may be a poor plan as it directly works against the flow by cooling the exhaust and heating the incoming air which will/would reduce the flow of both!

"6-8 hrs of close attention ....."
Isn't that a function of the size of the heater. I get that a few sticks, however well they are burned, isn't going to heat much mass but then I wasn't thinking of sticks ....
There go's that box again, I just don't seem to be able to stay in it! Perhaps actually knowing where the sides are would be a good start

Anyway ... Part of the reason for thinking water mass is the ability to move it away from the heat source when it is hot and replace it with new cold mass. I reasoned that this approach would allow me to extract heat more quickly and therefore utilise a bigger fire. The second thought was to use more massive fuel in much the same way as a bale burner consumes the end of a bale that is fed in as it is consumed.
I am not suggesting that I will be burning bales but I hope to be burning the end off logs that are sitting on a 'grate' for want of a better analogy. (Concept sketch attached)
Primary air is drawn under the fuel, and probably a little from the feed tube to combat smoking, whilst secondary air flows under the grate support plate directly to the burn chamber.
The grates will be 3mm stainless, welded and will need toi be sacrificial I suspect.
I expect I will have to play with this in a mock-up to have any chance of getting it to work.

Water, thermo-syphon and Un-vented System ...
IT will not be sealed, that is just asking for an explosion, my reference to sealed was on the DHW side and even that is more risky than a vented system which is my preference.
You may be correct about the coil arrangement shown, although the flow in all the elements exposed to a temperature gradient is the right way.
Given that I now think the coil would be best placed in the down draft chamber, barrel in conventional terms, I dont think it will be an issue but there is a little trick that can be employed if I need more flow.
Ironically it works the same way a RMH does. You create a long vertical loop with its feed leg, upward insulated and the return leg uninsulated. The water cooling in the down leg gets more dense and drives the system.
Obviously you loose some heat in the process, you have to or no work is done but since the loop could be a nice polished pipe in the living space that isn't much of an issue.
This type of thermal pump was employed in large bore single pipe heating systems, mostly commercial, for years to drive water round horizontal pipes supplying heat to floors.

Calculations ... Well I suspect it will be more trial and error, OK probably mostly error, rather than calculation. I suspect that the thermodynamics and flow calculations required for such a complex space will be way beyond me even if I could find the information I doubt I would recognise it.
It is interesting that you say use a tall riser, that seems to me to be intuitively correct, but I suspect it will need to be a larger CSA to counteract the pressure drop.
My original thought process was to use a square riser, as I expect to be using kiln brick, but the cast solution is very appealing, either way I will offset the burn tube so that a turbulent, hopefully a vortex, is created.

I have already looked at Web4deb Channel and you are correct It was very interesting although I would not be keen on using aluminium fins in a potentially corrosive hot environment.
There is another design I like the look of but I will need to do some calculations on exchanger area as it may noy have enough without being stupidly big.
Heat exchanger on rocket heater - Apostol Engineering

I would be most interested to hear what everyone else thinks.

Pleas keep the questions and challenges coming, the more I have to consider and explain my thoughts in context's I haven't thought about the closer I will get to actually being able to build a test rig.
Or perhaps just starting again because I was way of base in the first place

There are some deal breakers here that may turn out to be insurmountable problems.
Fuel feed and long burn time being the one I am currently most worried about. I cant believe that feeding logs hasn't been tried and yet it I haven't seen a single example of this being done, that is worrying.

Looking forward to your thoughts, collectively
5 years ago
Thanks for the link I am off there now ...
I am an engineer, although I mostly work on micro hydro schemes and program PLC's, but still I am well aware of the dangers of heating water in anything potentially sealed and not controllable.

That said I also don't know, well anything, about the burn characteristics of this type of heater.

BoomSquash ... Mmmm I can see the requirement to learn, that said any other heater would / could explode if not properly managed and I expect that the systems used as safety systems, the low tech ones, could probably be employed to make a rocket based system safe.

Anyway, the link looks likely to be a good place to start, I may even learn some of the terminology so I can ask better questions.

5 years ago