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| flash steam - a long slog to a whizzy boat |
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| flashtwo:
Hi Steve, This is my first post on this forum and its good to see others interested in flash steam. Last May my experimental model boat "Vital Byte" had its maiden voyage after two and a half years of flash steam boiler development. I started off, like yourself, with only the knowledge that flash steam boilers existed. I was aiming to develop an alternative to the conventional boiler to power an ordinary model boat and not the straight runners or the ultra high speed tethered variety. The project has been very successful with the boat steaming in excess of forty minutes with the extremely rare capability for a flash steam vessel of variable speed and forward/reverse motion. I have gradually increased the length of the copper pipe from 5 metres of 1/4inch to 15 metres of 3/8inch with corresponding increase in performance. The boiler supplies steam to a very hungry Stuart D10 engine. The only downside, for the purists amoungst us, is the use of electric feed water pumps and a computer control system! I'm using gas firing with a consumption of 4grams/minute. Like in your diagram, I have used a preheater (economiser) in the boiler outlet, which preheats the water to around 70degC. If I can be of any help let me know Ian. |
| sbwhart:
Hi Ian First welcome aboard the cube :borg: That look a very interesting project, have you tried any other materials for your tubeing. (stainless steel) Thanks for showing Stew |
| flashtwo:
Hi Stew, No, I've not tried stainless. I've been hand winding soft coiled copper tube onto various sizes of plastic pipe formers from 33mm diameter upwards, which for the 15 metre coil, took under two hours to wind including a silver soldered joint and end fittings. How tough would the stainless be to bend and is it cheaper than copper? The pressures and temperatures that the boiler is running at are those of a conventional model boiler, i.e. 60psi (normally 30psi) and 150degC (including superheat). I have heard of those engines that run at an unbelievable 1500degC! You can appreciate the advantages of a flash boiler construction wise - low skill, very fast construction, low cost of materials. I can get the engine running within a couple of minutes of fuel ignition, unlike some silmilar sized conventional plant which require a cylinder of gas just to get up to pressure and takes 30minutes. At other model clubs, I do sometimes have a few minutes discussion convincing them that I have no need for insurance or test certificates and, to that end always carry a copy of the MPBA steam rules which always helps. I've got to the point now where I consider my boiler is normal and the conventional boilers - well, boring. I forgot to say that the boat has a displacement of 72lbs, has a 5inch prop and the hull dynamics of a brick! Ian. |
| sbwhart:
Hi Ian The reason I asked about the stainless steel is that when I eventualy get round to making my loco boiler I intend fitting stainless steel supperheating coils to it, but I understand that it can be a bit of a bitch to bend, and was after some tips. Stainless would be able to withstand a higher operating temperature than copper and is less suseptable to errosion. Thanks Stew |
| NickG:
Stew, I know somebody who has built a flash steam boiler as you describe. They bent the stainless tubing around some sort of mandrel in the lathe on slowest back gear I think. Will find out more next time I go down. Nick |
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