Bolsover boiler?

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Mike Rometer
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Re: Bolsover boiler?

Post by Mike Rometer » Sun Oct 01, 2017 8:33 am

A sudden minor bout of confusion here. Where would you expect the water level to be, above or below the re-entry of the coils (steam manifold)? If below, how far?
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Re: Bolsover boiler?

Post by DetroiTug » Sun Oct 01, 2017 2:28 pm

Mike,

On boilers of these types, the water level is a bit erratic, higher heat, higher internal circulation, the water level can drop in the drum, but level is maintained somewhere near and below the upper tube exits. Much of that up and down reading is a simple result of low internal reserve, frequent water tending. My Loco uses about a gallon of water per mile, an average speed of 20 miles per hour, results in consumption in the neighborhood of one gallon every three minutes. The boiler only holds around 2 gallons. So, the driver/engineer has to stay on that bypass valve. Most driving is stop and go and creeping around car shows, so it isn't that bad, but it illustrates how quickly the level in the glass can change by water consumption alone.

Fred, Thanks for that info. I did some calculations this morning and the results are somewhat disappointing. The average rise in the tubes works out to be around 5°. Also based on the Bolsover 3D model as drawn, there is only around 15 sq/ft of heating surface which is only around three theoretic horsepower - not good, for the application anyway.

The model as drawn is 23" in diameter and 24" tall, coils are 20" tall. Reducing the number of turns would increase the angle, but would lower the square feet of heating surface, and we're already in trouble there. The coil spacing could be tightened up on the manifold to allow for more coils, but I think it would be very difficult to assemble especially with arc welding and too it would be near impossible to replace a tube if needed.

Back to the Ofledt. The 16 coil Ofeldt in the Loco measures 14" tall and 18" OA in diameter, the 4.2" pitch circle coils are 12" tall with 1" spacing in between and 1.54 on center. This works out to 7.2° rise in the coils after calculating the circumference. And too it has around 25 sq/ft of heating surface making 5 theoretic horsepower - in a much smaller package. And the Ofledt can be repaired without too much trouble, long drill bit could drill out an old coil if necessary, the Bolsover on the other hand would not allow room for this type of repair. An Ofledt with 22 coils with above dimensions and the same OA diamter of the Bolsover as drawn and could be much shorter would have around 37 sq ft of heating surface - over twice as much boiler and theoretic horsepower on the same footprint.

So, it was a short romance with the Bolsover :lol:

-Ron
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Re: Bolsover boiler?

Post by Mike Rometer » Sun Oct 01, 2017 6:14 pm

So you just fit it with a long gauge glass, and keep an eye on it. :o
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Re: Bolsover boiler?

Post by fredrosse » Mon Oct 02, 2017 3:51 am

If the sight glass comes off one of the horizontal headers,the level readings would tend to be erratic, with the two phase mixture while steaming. One way around this is to have the lower gauge glass connection to one of the lower horizontal headers, with an internal pipe that leads to the center of the main drum. Same thing could be done for the upper gauge connection if the operating water level is below the upper horizontal headers.

Having an independent lower gauge glass connection is somewhat difficult, as the most intense fire is in this vicinity. That tapping would have to be insulated from fire heat, a complication that is unnecessary if the gauge pipe leads to the drum by running inside a horizontal header pipe.

The upper gauge connection can be directly to the drum, and run horizontal to the outside of the boiler casing, placed well above the upper horizontal headers. That pipe would see lower gas temperature so it would not be overheated, and since only steam is in the high gauge connection, no boiling concerns.
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Re: Bolsover boiler?

Post by fredrosse » Mon Oct 02, 2017 4:27 am

Ron, have you examined larger tube size? I would think maybe 1 inch boiler tubes could be put into the Bolsover, possibly getting more surface area. Say an 8.625 inch main drum, horizontal headers 6 inches (inside the furnace), for a net 20.625 furnace inside diameter. This arrangement allows 16 watertubes, 4 off each horizontal header.

I am guessing about 40 square feet heat transfer surface, with horizontal headers (2.375 inch dia) about 24 inches change in elevation. All tubes about 10 feet long. 3 turns on innermost tubes, RH, 2.5 on next,LH , 2.25 on next, RH, and 2 turns on outermost tubes LH.

What might I be missing here, its late, I have been working 12 hrs already today, so don't trust my numbers without a thorough check.
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Re: Bolsover boiler?

Post by DetroiTug » Tue Oct 03, 2017 2:54 am

Fred,

I'm not sure how 1" tubes would work out in regard to heating surface. One of my guru friends says that large water tubes have an issue with large volume and not being as effective. They use straight tubes for fuel vaporizers and slide a piece of round steel rod inside to decrease the volume and increase the reaction time to heat. A side note, once the rod heats up it helps to vaporize also.

Anyways, I redrew the boiler with as many tubes as I could virtually jam in there. 52 tubes instead of 24, I calculated the other one at 15 sq/ft in the tubes alone, this one should have around 35 square feet and about 40 all surfaces tolled. I snapped a few screenshots starting out to show how the coils lay on to the center drum. I'm pretty confident this would be a good steam maker.

Over on the SACA forum they mentioned "thermal shorting" in regard to circulation, whereby the shorter tubes would take most of the circulation, and some other longer tubes could become stagnant and boil dry. Goes along with your 100:1 rule on water tube circulation.
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Re: Bolsover boiler?

Post by DetroiTug » Tue Oct 03, 2017 2:55 am

more pics
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Re: Bolsover boiler?

Post by fredrosse » Tue Oct 03, 2017 8:28 am

".....One of my guru friends says that large water tubes have an issue with large volume and not being as effective."

In general that is true, the smaller tubes have greater heat transfer surface area per unit gross volume, and less water volume. However that statement has a requirement that tube pitch spacing is porportional to the tube diameter. Using small diameter tubes, with large spacing between them negates much of the small tube advantage.

This is especially applicable to the Bolsover design, where the required tube slope tends to fix the distance between coil passes, be they 1/2 inch tubes or 1 inch tubes. From the looks of your sketches it appears that the tube slopes are relativly small, and the tubing L/d ratios are far greater than 100:1 I believe this would result in slow, or worse yet, cyclic reverse circulation issues.

The 1 inch tube design I was thinking of has about equal slope on every tube, and equal L/d on every tube, so circulation within each tube should be about the same in each tube. I will try to make a sketch, too late for that now tho.
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