RE: Another Firebox Question
Tony, Thank you for the offer to measure the fireboxes on your coal-fired locos. I will do that. And I'd very much like to take a look at that G1MRA article about firebox arches. Today I sent off for a copy of Alec Farmer's book on boilers. Keith Taylor encouraged me to read it. Steve
Re: Another Firebox Question
The spring 2002 issue of the G1MRA Newsletter has an article by Peter McCabe about incorporating an arch into the design of a G1 boiler. When he cut the boiler out of the copper pipe he left a tongue at the bottom of the boiler which he subsequently bent up into the firebox becoming the arch. Seemed pretty clever. Jim
RE: Another Firebox Question
Jim, Regarding Peter McCabe's addition of a tongue at the bottom of the boiler which was bent up into the firebox: it seems like this would have increased the heating area of the boiler as well, because the tongue, being part of the boiler shell, would conduct heat directly to the boiler contents. Steve
Re: Another Firebox Question
I know this started off as a coal-fired boiler question, but I have significantly improved the performance of spirit fired boilers by adding a brick arch made of thin brass. Its function is twofold:- a) it prevents cold air going straight up the tubes and b) it increases the distance the alcohol fumes have to travel and, by promoting turbulence, greatly improves combustion. Mike
RE: Another Firebox Question
Hi Steve and list. I'd agree with that - it would be a long conduction path in the copper tongue, but as the end of the tongue would get very hot a large temperature gradient would help the rate of conduction mightily. Another potential virtue of this would be that as the tongue / arch is running much hotter than the water cooled boiler surfaces the flame will not be cooled below combustion temperature so quickly there, as well as the longer flame path doing the same thing. This will both reduce the incidence of vile smells from unburnt hydrocarbons, and also gain more available heat from the fuel through-put, and that means better steaming, which is where we came in! Both LBSC and Henry Greenly made the point about lots of flame headroom in meths (alcohol) fired locos being a great virtue for these reasons back in the 20s and 30s. Jim Gregg. .At 10:35 AM 10/16/02 -0700, you wrote: Jim, Regarding Peter McCabe's addition of a tongue at the bottom of the boiler which was bent up into the firebox: it seems like this would have increased the heating area of the boiler as well, because the tongue, being part of the boiler shell, would conduct heat directly to the boiler contents. Steve
Re: Another Firebox Question
Convect = heat transfer between solid and fluid (gas or liquid). A very complex process that is dependent upon viscosity, turbulence, gravity vector, temperature difference between hot side and cold side, condition of solid surface, geometry, etc etc. Highly non-linear and difficult to predict precisely. Conduct = heat transfer through homogeneous, immobile media: A relatively simple (read predictable) process governed by thermal conductivity, cross sectional area, temperature difference between hot side and cold side, length of conduction path. Since sucessful model boilers are made from both copper (high conductivity) and steel (low conductivity), one can surmise that conduction isn't the big issue - it's convection and radiation (which is dependent upon temperature difference between hot side and cold side, geometry/view factor, surface condition - emissivity) that counts. James Curry wrote: Steve: Decoder ring says: convect=conduct Jim
Re: Another Firebox Question
Hi Steve. Something similar using a stainless steel Brick Arch has been done quite successfully. I know also of some experiments with a Nichrome or similar mesh equivalent. By the way I go along with bronze or copper for stays, I have used Monel, but that is overkill, far more hassle (and cost) than it is worth, and if you overheat the joints when silver brazing the Monel may go Hot Short ie brittle, and be weaker than copper. Jim Gregg.At 06:30 AM 10/15/02 -0700, you wrote: Harry, Keith, Jeff, and Mike, Your information is great. Now I have another question for the list about gauge 1 coal-fired fireboxes. Has a brick arch, or its equivalent, ever been used in a gauge 1 coal-fired firebox? Or is it irrelevant because the combustion path is so short in gauge 1 size? I understand that the alcohol-fired C-type boiler configuration accomplishes a similar effect by lengthening the combustion path, but I have almost zero experience with gauge 1 coal-fired firebox designs. Steve
RE: Another Firebox Question
Jim, Thank you for the feedback about the use of stainless and nichrome for brick arches. Can I assume the nichrome was wire mesh? If sufficiently hot it might make a good radiant heat source nearer to the crown sheet than the bed of coals on the grate. thank you also for the tip about overheating Monel. Steve
RE: Another Firebox Question
Yes Steve. The various Nichrome /Inconel / stainless meshes were trieed with the intent of producing a radiant source as you surmise. This is less necessary with a coal fire obviously, but part of the aims of this bit of experimentation was to make a multi - fuel boiler, which could use Meths, gas or coal, or even a vapourising or atomising paraffin (Kerosine) burner. Work proceeds! Jim Gregg. At 04:43 PM 10/15/02 -0700, you wrote: Jim, Thank you for the feedback about the use of stainless and nichrome for brick arches. Can I assume the nichrome was wire mesh? If sufficiently hot it might make a good radiant heat source nearer to the crown sheet than the bed of coals on the grate. thank you also for the tip about overheating Monel. Steve
Re: Another Firebox Question
Hi Steve, G1 Firebox Arches. You can come over and measure the fireboxe's on my three coal fired engines anytime. None have arches, although there was a very interesting article in the G1MRA approx. one year ago (I will pull out the article for you). This illustrated how to calculate arch size and shape for a G1 engine and install. As I recall the arch was added as an after market loose feature to allow firing studies and adjustments. Apparently it made a significant difference to the running and steaming capabilities of the particular engine discussed. I cannot remember if the arch was copper or stainless. I am tempted to try it to define cause and affect. Apparently the arch makes for a more efficient fire, and prevents coals/ash being drawn into the lower boiler tubes. Will keep you posted, Regards, Tony D. At 06:30 AM 10/15/02 -0700, Shyvers, Steve wrote: Harry, Keith, Jeff, and Mike, Your information is great. Now I have another question for the list about gauge 1 coal-fired fireboxes. Has a brick arch, or its equivalent, ever been used in a gauge 1 coal-fired firebox? Or is it irrelevant because the combustion path is so short in gauge 1 size? I understand that the alcohol-fired C-type boiler configuration accomplishes a similar effect by lengthening the combustion path, but I have almost zero experience with gauge 1 coal-fired firebox designs. Steve
