Small boilers

[jason udallParticipant @jasonudall57142]

Cross linked boilers

[jason udallParticipant @jasonudall57142]

Ok for reasons of fit. I have reason to consider a pair of small boiler for a launch..in side by side configuration. .so should I cross link them water to water and common the steam or what. ..
Boilers planed as simple tubes about 50mm dia by 200 mm long..consumption about 3cc/rev@5rps at 2bar..by my calcs. 30 cc /second thus a touch over 25 mg of water per second….

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Jason ,

No problem using side by side boilers but how to connect them depends on what you actually want to achieve .

(1)Simplest arrangement is two independent boilers – each with its own water feed , heat source and fittings and stop valves on each connected to one common steam outlet .

Can then run boilers as one in steam – either boiler – or both in steam .

This is actually a common arrangement on large full size steam plant and can be extended to multiple boilers . Allows very good economy with varying demands and also loss of one boiler due to mishap or for maintenance does not affect overall steam supply very much .

(2) In specific case of just two boilers they can be connected together in a more complex manner and run as one boiler in several ways .

Simplest is connect water spaces together at lowest level and steam spaces together at highest level – effectively making one boiler . Needs largish pipes but easy to do .

More difficult but sometimes worthwhile is to use auxilliary drums and water tubes so as to make an approximation to a Yarrow boiler .

(3) Whatever you decide upon think about circulation patterns in the water and pipes – avoid any places where drum / pipes are heated but where there is no certainty of water circulation .

In simplest arrangement it probably doesn't matter too much but in principle introduce some slopes and bends in the water space connecting pipes so as to get just a little circulation . An example would be water pipes lowest point on one drum but just a little higher on other drum then next pipe the other way around etc .

Ask any questions you like .

Regards ,

MikeW

[jason udallParticipant @jasonudall57142]

Thanks MikeW will hack up some diagrammes later. .plan to couple water spaces via tube rising from near bottom through top of boiler to same in other.. thus expecting water levels to equalise . Tapping steam from one only..safety valve each though

[Sub MandrelParticipant @submandrel]

If you only take steam from one boiler, make sure steam from the other can pass easily into the other – if not the steam will blow all the water out of that side into the other, and it could boil dry. I suggest linking both steam and water spaces.

neil

[jason udallParticipant @jasonudall57142]

Neil…that was the plan …until I started putting it down in writing. ..more the writing than plan. .if you get what I mean….I am thinking that this best wait for the sketch…

[nigel jones 5Participant @nigeljones5]

I built something similar once. I has separate water clacks on each, seperate sight glasses and a joined out feed with a single pressure gauge and relief valve – worked well.

[jason udallParticipant @jasonudall57142]

Thanks guys…my original thoughts are developing along a different path..I mean 60cc will last about forty minutes which I think will long out last the fuel…so a single 100cc boiler would suffice. ..thinking along the kettle-flash evaporator route ..now…

[jason udallParticipant @jasonudall57142]

More random ramblings may follow…thanks again

[nigel jones 5Participant @nigeljones5]

Now your into technical musings…flash boilers…outside my scope!

[jason udallParticipant @jasonudall57142]

My problem is . If I build it and it doesn’t match theory ..is that down to theory or execution. ..my skill does not meet my demands…so sometimes I need to find a smarter solution

[nigel jones 5Participant @nigeljones5]

A difficult one…I designed my last 5" myself and am doing again in 71/4, but theyre built on proven designs. Is there one someone else has built and proved? Ive got all the equipment if you want help on that front, im interested in this one

[jason udallParticipant @jasonudall57142]

the idea kicking round.[ and delaying work on the steam launch]..i to generate steam on demand..stroke by stroke , cylinder by cylinder ..

each cylinder drives a feed pump "timed" to inject water into a flash "boiler"..th pump delivering just enough water for the steam requirement of that stroke..eg. 18g of water produces 22.4 L of steam at 1 bar and room temperture..[ok steam at room temp.]..or say 1g 1L..or at 3 bar 3g 1 L

so for a 1000 cc engin you need to vapourise say 3 g of water per stroke

take a mass of copper …heat ..inject water…if copper mass holds enough heat then water flashes to steam…steam exits to cylinder[water injection timed to coincide with inlet open]..does work and exits…

now just like diesel this uses a high [ well a couple of bar] pressure pump and correct timing…but no stored steam..no boiler..the thermal store is a lump of copper not boiling water…..

[Les Jones 1Participant @lesjones1]

Hi Jason,
The specific heat of copper is less than a tenth of the specific heat of water so you would need quite a high mass of copper (Or raise the copper to a very high temperature.) to to store enough heat to raise the water temperature from say 20 Deg. C. to 100 Deg. C and also to provide the latent heat of vaporisation of water. I think it would be worth doing some calculations before going to far with the design.

Les.

[jason udallParticipant @jasonudall57142]

Hi Les.
Yes I was aware of the s h c water
vs copper..and the latent heat of vaporisation plus the heat input for rising the steam to the required pressure…
This is as yet in the thought experiment stage..
Futher thoughts to a closed cycle motor. .start to look like a compressor fridge..or I think there is a design for a closed cycle steam engine name eludes me at moment…any way just kicking ideas at moment

[Clive HartlandParticipant @clivehartland94829]

I think you are describing a Nuclear reactor jason ! How small can they go?

A closed circuit needs a condenser which will add more wieght to shift unless you go for Alu.

One I saw years ago used the piston coming up to open a steam valve in the head by direct contact, very high revving if i remember. That also had a flash boiler.

Clive

[Gordon WassParticipant @gordonwass]

If it helps at all, I remember reading an article on steam generation using chemical reaction to produce the heat, the engine seemed to be along the lines you are thinking about. sorry can't remember any more, but might be worth googling.

[Ian S CParticipant @iansc]

Gordon, are you perhaps thinking of torpedoes, the name Whitehead seems to come to mind, Tjhere was an article in ME maybe somewhere in the 1990s. Ian S C

[jason udallParticipant @jasonudall57142]

Some VERY esoteric heat/work motors have been trialed in torpedoes…

[simondavies3Participant @simondavies3]

Posted by jason udall on 06/08/2013 23:35:08:

take a mass of copper …heat ..inject water…if copper mass holds enough heat then water flashes to steam…steam exits to cylinder[water injection timed to coincide with inlet open]..does work and exits…

I built a flash steam boiler many years ago to match the ST D10 that I had just built. It used 2 pumps, a hand pump to get everything going and an engine driven one that had an adjustable output flow.

In practise the biggest problem was the lag between the water going in and appearing as steam at the other end. So the cycle went something along the lines of:

burner on

allow tubes to heat

pump hand pump

water flashes to steam and after a short delay, D10 springs into life and starts pumping water

influx of water momentarily cools coils so sudden reduction in steam flow

D10 pump slows

water now boils to temperature

D10 slowly recovers being now driven on wet but rapidly drying steam and spins to speed

Influx of water momentarily cools coils so sudden reduction in steam flow

D10 pump slows

etc…etc…

You are trying to control a closed loop feedback system with an inherent delay in the system caused by t he steam generation so your water flow will have to take this into account.

I did eventually make the system work but it was very sensitive to burner temperature and the exact setting of the pump overflow valve. I also incidentally did it all in my father's workshop and caused many if his tools to collect a fine layer of rust, something that he still reminds me about from time to time!

Simon

[jason udallParticipant @jasonudall57142]

That is the sort of aim
In effect a boilerless system
..or at least little or no storef steam.
.yes thermal lag would be a challenge but my current approach would be to use a copper lined block of cast iron for the boiler. Good conductivity , specific heat cap. .

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Jason ,

(1) You don't need a boiler at all – just inject metered amounts of water direct into hot cylinder head or ( better ) into a little heat exchanger attached directly to cylinder head . Quite a catalogue of problems to solve but entirely feasible .

(2) Been done before – sort of / not very well – look up Hall engine in 1960's ME and related patent (expired) . Lots of scope for designing a more practical engine which could actually be used to deliver useful power .

Would benefit greatly in performance by preheating the water under pressure before injecting into cylinder .

(3) Lots of scope also for hybrid IC + steam cycle engines if you want a new new direction of thought . Can be very efficient at cost of added complexity .

(4) Perfectly possible to make a close cycle steam engine but as Clive says condenser is usually going to be big and need a heat sink .

Best heat sink arrangement is to use waste heat for another process rather than throw it away .

(5) There is a possible way of making a closed cycle steam engine using abnormally high temperatures and pressures and the film heating / cooling effect . Needs gas turbine materials and thinking . At least one experimental engine got built a few years ago but nothing more heard of it .

(6) There are many more possibilities for building advanced steam engines if you start thinking about turbines rather than reciprocating engines .

(7) Just for general background look up the Kitson-Still engine .

Regards ,

MikeW

[jason udallParticipant @jasonudall57142]

Btw…the name I was looking for …the Rankin cycle
.. Rankin the other Kelvin
…

[Author]

Posts