University experiments

[kandnwlr]

Completed the calculations for 4 more of the tests.  for the two remaining running tests that worked properly, I got efficiencies of 60% and 50%.  for two of the stationary tests, I got efficencies of 48% and 52%.  will report back with the final set of results some I've got them calculated.

Have you thought about why that might be? Why would the loco be less - apparently - efficient when stationary. Or is this a measurement thing.

K&NWLR = Andrew (also) from the ETH Zurich

[Matt]

It would be interesting for sure. I wonder if changing the efficiency of the boiler on a Lady Anne or Billy or similar would necessitate a re-design of the fuel tank. Roundhouse like their engines to be set up so the gas normally runs out before the water does. If a better boiler used less gas for a given volume of steam, I suppose you would save gas and if so they might have to make the tank smaller. Of course a smaller tank would look nicer. I'd someday like to make a gas tank for my engine that fits into the dummy side tank so I can have less clutter in the cab.

That's the main idea for doing these tests, to see what the efficiency is, and if there is any meaningful way of improving it. The best way I can think of improving the boiler efficiency would be to increase the number of passes the flue makes through the boiler (being a single flue boiler, the gases just through straight through. doubling the flue back on itself would increase the amount of time the hot gases spend in the boiler, and increase the amount of heat energy transferred to the water) main problem will be that it'll increase the complexity of the boiler design and construction, and reduce the water space in the boiler.

[Matt]

Completed the calculations for 4 more of the tests.  for the two remaining running tests that worked properly, I got efficiencies of 60% and 50%.  for two of the stationary tests, I got efficencies of 48% and 52%.  will report back with the final set of results some I've got them calculated.

Have you thought about why that might be? Why would the loco be less - apparently - efficient when stationary. Or is this a measurement thing.

K&NWLR = Andrew (also) from the ETH Zurich

I'm not too sure. after running the data through the computer, there is still a small decrease in the efficiency when the locomotive is stationary. My supervisor thinks it's probably something to do with the recording of the data rather than an actual trend. again, something to look at if someone does these tests again in the future.

[laalratty]

All very interesting. Roundhouse has used insulation material on at least some locos like the Taliesin, which, admittedly without any quantitative evidence, seems to raise steam faster then my Lady Anne. Lady Anne, and I think all of the others except the Mille has two layers of cladding which would provide some insulation.

[Matt]

ah, I see. Do you know what insulation Roundhouse use? During the tests, the external temperature of the boiler was only 10 degrees lower than the internal boiler temperature. It may be that better insulation material may be required.

[laalratty]

I don't know what material, and as I said, I've only seen it on the Taliesin, my Lady Anne has two layers of boiler cladding, yours being a bit older might only have one?

[Matt]

Yeah, mine is from 2007.

[GTB]

okay, i had to re-do the calculations for the efficiency values on the computer, as I've been using the wrong values for specific enthalpy at working pressure.

Glad I'm not the only one that used the wrong column in the steam table.......

Anyway.....

The only way I can think of to improve boiler efficiency would be to go to a more complex multi-tube boiler design, such as a full loco type boiler, or even a JVR type C, or a Briggs type (dry backhead type).

Insulation will make no measurable difference I think. Kozo Hiraoka has a short discussion on this in his first Shay book. He quotes figures for a 3.5" boiler insulated with 1/8" of asbestos (it's a '70s book....) and if you scale those to a Roundhouse size boiler, it will make maybe 0.5% improvement in efficiency.

I fitted 1/16" of insulation to the boiler on my Argyl Loco Philadelphia and the only difference I see is that the outside of the cleading stays a bit cooler. It doesn't come up to pressure noticeably faster, or give a longer run time.

A Taliesin boiler contains less water than the standard Roundhouse #1 boiler in a Lady Anne, but has the same burner and flue dia. so it will come up to temperature faster anyway. I see the reverse with my Roundhouse SRRL#24. It carries more water and takes a lot longer to come up to pressure, even though there is an air space between the boiler shell and the cleading.

The big railways had accountants who worried about fuel costs (and still do), but any improvement in boiler efficiency in a garden steam dragon is just a drop in the bucket, compared to the inefficiencies in the cylinders and valve gear.

My supervisor is happy with the results I've got, and I'm now ready to starting writing up the final report.

In the final analysis that's the important thing. Good luck with your project report and final exams.

Regards,
Graeme

[Matt]

okay, i had to re-do the calculations for the efficiency values on the computer, as I've been using the wrong values for specific enthalpy at working pressure.

Glad I'm not the only one that used the wrong column in the steam table.......  ;)

Anyway.....

The only way I can think of to improve boiler efficiency would be to go to a more complex multi-tube boiler design, such as a full loco type boiler, or even a JVR type C, or a Briggs type (dry backhead type).

Insulation will make no measurable difference I think. Kozo Hiraoka has a short discussion on this in his first Shay book. He quotes figures for a 3.5" boiler insulated with 1/8" of asbestos (it's a '70s book....) and if you scale those to a Roundhouse size boiler, it will make maybe 0.5% improvement in efficiency.

I fitted 1/16" of insulation to the boiler on my Argyl Loco Philadelphia and the only difference I see is that the outside of the cleading stays a bit cooler. It doesn't come up to pressure noticeably faster, or give a longer run time.

A Taliesin boiler contains less water than the standard Roundhouse #1 boiler in a Lady Anne, but has the same burner and flue dia. so it will come up to temperature faster anyway.  I see the reverse with my Roundhouse SRRL#24. It carries more water and takes a lot longer to come up to pressure, even though there is an air space between the boiler shell and the cleading.

The big railways had accountants who worried about fuel costs (and still do), but any improvement in boiler efficiency in a garden steam dragon is just a drop in the bucket, compared to the inefficiencies in the cylinders and valve gear.

My supervisor is happy with the results I've got, and I'm now ready to starting writing up the final report.

In the final analysis that's the important thing. Good luck with your project report and final exams.

Regards,
Graeme

Thanks for advice Graeme. Would fitting cross tubes into the fire tube make any measurable difference (I head that Cheddar did something along those lines on it's locos)?

[GTB]

Would fitting cross tubes into the fire tube make any measurable difference (I head that Cheddar did something along those lines on it's locos)?

That's basically the Wrightson boiler, which goes way back.....

Cross tubes are also used in single flue vertical boilers. Dave Watkins has them in his Idris boiler design.

Anything that increases the heating area would improve the steam raising ability of a boiler. Cheddar used a blowtorch type burner, which would get the most out of cross tubes I'd imagine.

No idea what improvement it would make with a poker burner, as they are reputed to be touchy about free gas area. Roundhouse do specify a minimum gas flow area for boilers they sell separately.

That would be an interesting project for someone at uni., now that there is software that can simulate gas flows, to work out just what goes on inside a model boiler.

Would also be interesting to see if the inverted burner used by Accucraft makes any difference, if someone is looking for a project.

Graeme

[Matt]

Would fitting cross tubes into the fire tube make any measurable difference (I head that Cheddar did something along those lines on it's locos)?

That's basically the Wrightson boiler, which goes way back.....

Cross tubes are also used in single flue vertical boilers. Dave Watkins has them in his Idris boiler design.

Anything that increases the heating area would improve the steam raising ability of a boiler. Cheddar used a blowtorch type burner, which would get the most out of cross tubes I'd imagine.

No idea what improvement it would make with a poker burner, as they are reputed to be touchy about free gas area. Roundhouse do specify a minimum gas flow area for boilers they sell separately.

That would be an interesting project for someone at uni., now that there is software that can simulate gas flows, to work out just what goes on inside a model boiler.

Would also be interesting to see if the inverted burner used by Accucraft makes any difference, if someone is looking for a project.

Graeme

Thanks. I'll pass that on to my supervisor. maybe they'll give it to one of the students next year as a project.

[11thHour]

[ Would fitting cross tubes into the fire tube make any measurable difference (I head that Cheddar did something along those lines on it's locos)?

I think the theory is not only increased fire tube surface area, but also the more efficient movement of the water currents about the boiler so it heats better .
This reference is not the same as cross tubes, but note in picture 7 the baffles around the fire tube to achieve the same thing.
http://www.susan-parker.co.uk/nwp136-boiler.htm

Tim

[Matt]

Just submitted the final report for the project. Hopefully will get some feedback from my supervisor within the next couple of days.

[kandnwlr]

Just submitted the final report for the project.  Hopefully will get some feedback from my supervisor within the next couple of days.

Good luck - and with the finals.

(Prof.) K&NWLR

[Matt]

Just submitted the final report for the project.  Hopefully will get some feedback from my supervisor within the next couple of days.

Good luck - and with the finals.

(Prof.) K&NWLR

Thank you.