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Re: Lamont boiler January 22, 2012 01:41AM |
Caleb Ramsby Wrote:
> What, uhh, what type of noise was the pump making?
> By light do you mean low speed, low pressure or
> low fire?
It was a sort of rattling, random sound.
The Procon was basically running w/o any head, since input pressure was only slightly less than output pressure. This might let the vanes rattle around - I don't know. The Procon on the expresso machine at work doesn't make that much noise.
The problem George was describing was:
But the value of Hfg drops only by 8 percent or so from 250 psi to 500 psi, so that hardly seems that big a deal... and a natural circulation boiler capable of 20 hp peak output is a pretty large thing to put in a boat you're also trying to fit a galley, head, shower, and friends into as well. The weight difference can also be quite large, which affects boat performance as well. A downdraft gasifier-style burner combined with a Lamont coil and a suction draft system, with a big (5.75" x 5.75"
single cylinder poppet valve zero clearance uniflow would make a nice power plant for our big boat. 750 F steam temp, and 5% or less cutoff.... Need to keep things quiet, since I'm next to the plant and I don't want to listen to a lot of high frequency stuff.
I've been experimenting with the freesteam software table software; if I can sort out the calculations required for the Lamont I'll try coding them up in Python (a handy programming language for things like this) so that I can crunch the numbers iteratively. I guess some sort of assumptions regarding tube heat flux are required, hmmm. Been a while since the thermo and heat transfer classes, and we never covered much of multi-phase heat transfer even in graduate school.
- Bart
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Bart Smaalders [smaalders.net]
> What, uhh, what type of noise was the pump making?
> By light do you mean low speed, low pressure or
> low fire?
It was a sort of rattling, random sound.
The Procon was basically running w/o any head, since input pressure was only slightly less than output pressure. This might let the vanes rattle around - I don't know. The Procon on the expresso machine at work doesn't make that much noise.
The problem George was describing was:
Quote
I would not use or design a Lamont boiler for low pressures as the lower the pressure the longer the Lamont coil has to be as its required heat input is dependent upon Hfg. The longer the coil the more back pressure on the pump and the lower the pressure the higher the specific volume of the ever changing saturated water to steam is and that increases flow resistance in that circuit as well.
This increases the required circulating pump horsepower.
From my experiences with their designs I would suggest not going to the bother to design one under a pressure of 400psi. In a steamboat you have all the room for a larger natural circulation boiler which is not a luxury of room for an auto boiler. Hope that helps.
But the value of Hfg drops only by 8 percent or so from 250 psi to 500 psi, so that hardly seems that big a deal... and a natural circulation boiler capable of 20 hp peak output is a pretty large thing to put in a boat you're also trying to fit a galley, head, shower, and friends into as well. The weight difference can also be quite large, which affects boat performance as well. A downdraft gasifier-style burner combined with a Lamont coil and a suction draft system, with a big (5.75" x 5.75"
single cylinder poppet valve zero clearance uniflow would make a nice power plant for our big boat. 750 F steam temp, and 5% or less cutoff.... Need to keep things quiet, since I'm next to the plant and I don't want to listen to a lot of high frequency stuff.
I've been experimenting with the freesteam software table software; if I can sort out the calculations required for the Lamont I'll try coding them up in Python (a handy programming language for things like this) so that I can crunch the numbers iteratively. I guess some sort of assumptions regarding tube heat flux are required, hmmm. Been a while since the thermo and heat transfer classes, and we never covered much of multi-phase heat transfer even in graduate school.
- Bart
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Bart Smaalders [smaalders.net]
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Re: Lamont boiler January 22, 2012 05:33PM |
Quote
Actually steam should not be generated in the Lamont coil, only hot water. The steam is what gets separated in the drum or outside coil, then passed to the buried superheater. The whole idea as I understand it is for the coils that see the greatest heat transfer into them should only be full of nothing but water. So much greater heat transfer rate that way over steam.
This is correct - but as George points out, the problem is that if the coils are at the same pressure as the drum, there will likely be some steam formation in the coils at higher firing rates. This results in a large increase in volume, and greatly increases water velocity and thus pressure drop. The trick is to drive the circulation rate high enough so that the amount of heat being added to the water on each pass is small; this will reduce the formation of steam.
If we could, we'd put the drum 10 feet above the heating coil and pump; this would mean that the coil was running 5 psi or so over the drum pressure, which would reduce steam formation in the coils and prevent cavitatation in the pump.
For my boat, I'm considering various options - increasing the height of the drum is one of them.
The idea of copying the car water pumps is a good one... given the low power levels and lack of belt drive, I'm inclined to use something a lot smaller than the 5/8" diameter drive shaft, though. I need to do some experiments. I wish centrifugal pumps were as easy to design as displacement piston pumps
.
- Bart
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Bart Smaalders [smaalders.net]
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Re: Lamont boiler January 22, 2012 08:35PM |
To me the process looks something like this:
1. The pump forces saturated --- steam-free --- water out of the drum, and into the coil.
2. The coil adds BTU to the circulating fluid. Being saturated, a portion (10 or 20%, maybe) of the water picks up enough BTU to overcome the latent heat of vaporization and changes phase into steam.
3. The steam/water mix leaves the coil and re-enters the drum, the steam is separated from the flow and directed to the superheater while the remaining saturated water is routed back to the coil...along with whatever makeup feed is supplied.
The reason for all this effort is that excess water in the tube delays onset of a DNB (Departure from Nucleate boiling) condition...a congregation of large bubbles or stable steam films on the tube walls. These steam formations insulate the tube walls from the cooling effects of the water in the coil and lead to rapid burnout. The excess of water that comes from the higher circulation ratio delays DNB because water has something like 60 times the thermal conductivity and will suck the heat out of the tube faster than the steam AND because the much higher water density bulldozes incipient steam films off the tube wall. Add to the equation the fact that you now have 5 or more times as much material both cooling and bulldozing and it becomes obvious that you can delay (but not prevent) DNB at much higher firing rates....making for a more compact and energy dense boiler.
OK, OK, everyone has already said this stuff....but I wanted my chance to reword things and submit them as well.....
Ken
1. The pump forces saturated --- steam-free --- water out of the drum, and into the coil.
2. The coil adds BTU to the circulating fluid. Being saturated, a portion (10 or 20%, maybe) of the water picks up enough BTU to overcome the latent heat of vaporization and changes phase into steam.
3. The steam/water mix leaves the coil and re-enters the drum, the steam is separated from the flow and directed to the superheater while the remaining saturated water is routed back to the coil...along with whatever makeup feed is supplied.
The reason for all this effort is that excess water in the tube delays onset of a DNB (Departure from Nucleate boiling) condition...a congregation of large bubbles or stable steam films on the tube walls. These steam formations insulate the tube walls from the cooling effects of the water in the coil and lead to rapid burnout. The excess of water that comes from the higher circulation ratio delays DNB because water has something like 60 times the thermal conductivity and will suck the heat out of the tube faster than the steam AND because the much higher water density bulldozes incipient steam films off the tube wall. Add to the equation the fact that you now have 5 or more times as much material both cooling and bulldozing and it becomes obvious that you can delay (but not prevent) DNB at much higher firing rates....making for a more compact and energy dense boiler.
OK, OK, everyone has already said this stuff....but I wanted my chance to reword things and submit them as well.....
Ken
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Re: Lamont boiler January 22, 2012 09:26PM |
Hmmmmmmmm.....
"We turned off the Lamont pump on occassion and gradually you could hear the steam explosions going on in that coil as it would blow the water out of both ends of the Lamont coil."
So maybe we could add a check valve to one or both ends, turn it into a hydraulic "pulse jet", and really shoot the water through the tubes? Add the cool feed intermittently to quench the vapor in the tube and create a new suction wave to bring in the next round of water for vaporization?
>Ducking now...<
That lil 'ol troublemaker....
Ken
Edited 1 time(s). Last edit at 01/22/2012 09:29PM by frustrated.
"We turned off the Lamont pump on occassion and gradually you could hear the steam explosions going on in that coil as it would blow the water out of both ends of the Lamont coil."
So maybe we could add a check valve to one or both ends, turn it into a hydraulic "pulse jet", and really shoot the water through the tubes? Add the cool feed intermittently to quench the vapor in the tube and create a new suction wave to bring in the next round of water for vaporization?
>Ducking now...<
That lil 'ol troublemaker....
Ken
Edited 1 time(s). Last edit at 01/22/2012 09:29PM by frustrated.
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Re: Lamont boiler January 22, 2012 09:31PM |
To which I would add that some steam will be generated in the drum, when first opening the throttle causes the drum pressure to drop a bit.
Note that it is the rapid recirculation which allows generating more steam from a given area of tube surface. Not the use of a pump to circulate the water, per se. In theory, an eductor or other device could be used to achieve the same recirculation rate. I have a theory that water recirculation at a rate 5x or more the steam generating rate can be achieved with natural circulation in a car-sized boiler if the cross-sectional area of the flowpaths is large enough, and if the effective length of flowpaths is short enough. IE, if the steam/water flow resistance is low enough. In practice, this looks like it means a lot of parallel tubes.
I am brainstorming an experimental mini-boiler to empirically test this theory. If it works, its tube elements could be multiplied and assembled into a single boiler suitable for a powerful and roadworthy steam car. Hopefully I can avoid 2 other "DNB" conditions: Does Not Boil, and Disturbingly Nervewracking Blowout.
Peter
Note that it is the rapid recirculation which allows generating more steam from a given area of tube surface. Not the use of a pump to circulate the water, per se. In theory, an eductor or other device could be used to achieve the same recirculation rate. I have a theory that water recirculation at a rate 5x or more the steam generating rate can be achieved with natural circulation in a car-sized boiler if the cross-sectional area of the flowpaths is large enough, and if the effective length of flowpaths is short enough. IE, if the steam/water flow resistance is low enough. In practice, this looks like it means a lot of parallel tubes.
I am brainstorming an experimental mini-boiler to empirically test this theory. If it works, its tube elements could be multiplied and assembled into a single boiler suitable for a powerful and roadworthy steam car. Hopefully I can avoid 2 other "DNB" conditions: Does Not Boil, and Disturbingly Nervewracking Blowout.
Peter
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Re: Lamont boiler January 22, 2012 10:09PM |
frustrated Wrote:
-------------------------------------------------------
> To me the process looks something like this:
>
> 1. The pump forces saturated --- steam-free ---
> water out of the drum, and into the coil.
> 2. The coil adds BTU to the circulating fluid.
> Being saturated, a portion (10 or 20%, maybe) of
> the water picks up enough BTU to overcome the
> latent heat of vaporization and changes phase into
> steam.
> 3. The steam/water mix leaves the coil and
> re-enters the drum, the steam is separated from
> the flow and directed to the superheater while the
> remaining saturated water is routed back to the
> coil...along with whatever makeup feed is
> supplied.
>
> The reason for all this effort is that excess
> water in the tube delays onset of a DNB (Departure
> from Nucleate boiling) condition...a congregation
> of large bubbles or stable steam films on the tube
> walls. These steam formations insulate the tube
> walls from the cooling effects of the water in the
> coil and lead to rapid burnout. The excess of
> water that comes from the higher circulation ratio
> delays DNB because water has something like 60
> times the thermal conductivity and will suck the
> heat out of the tube faster than the steam AND
> because the much higher water density bulldozes
> incipient steam films off the tube wall. Add to
> the equation the fact that you now have 5 or more
> times as much material both cooling and bulldozing
> and it becomes obvious that you can delay (but not
> prevent) DNB at much higher firing rates....making
> for a more compact and energy dense boiler.
>
> OK, OK, everyone has already said this
> stuff....but I wanted my chance to reword things
> and submit them as well.....
>
Ken:
Yep--that's a nice summation of the process IMO.
I think the Lamont has advantages even for systems operating on lower pressures. These would be: 1) The operation of a water-level type of boiler with its attendant simplicity and thermal inertia, and 2) The additional heating efficiency offered by the water (instead of steam) contact with the tube walls.
>So maybe we could add a check valve to one or both ends, turn it into a hydraulic "pulse jet", and really shoot the water >through the tubes? Add the cool feed intermittently to quench the vapor in the tube and create a new suction wave to bring >in the next round of water for vaporization?
Y, I was gonna mention the addition of a check valve, at the inlet end; it's stoopid-simple and won't solve all the problems but it could certainly solve some of them with a minimum of effort. Also, the check valve seating spring would establish a pressure rise on its own as recently discussed.
I still think there are real-world parameters to discuss in establishing the diameter of the vertical standpipe. These would describe the minimum allowable diameter to promote separation of the steam and water due to velocity reductions. Also, the addition of baffles to promote further separation. I also liked the mention of an internal "stay" between the vertical caps of the standpipe in the G. Nutz papers--a nice detail. All in all, there's lots of minutia to consider.
Bill
-------------------------------------------------------
> To me the process looks something like this:
>
> 1. The pump forces saturated --- steam-free ---
> water out of the drum, and into the coil.
> 2. The coil adds BTU to the circulating fluid.
> Being saturated, a portion (10 or 20%, maybe) of
> the water picks up enough BTU to overcome the
> latent heat of vaporization and changes phase into
> steam.
> 3. The steam/water mix leaves the coil and
> re-enters the drum, the steam is separated from
> the flow and directed to the superheater while the
> remaining saturated water is routed back to the
> coil...along with whatever makeup feed is
> supplied.
>
> The reason for all this effort is that excess
> water in the tube delays onset of a DNB (Departure
> from Nucleate boiling) condition...a congregation
> of large bubbles or stable steam films on the tube
> walls. These steam formations insulate the tube
> walls from the cooling effects of the water in the
> coil and lead to rapid burnout. The excess of
> water that comes from the higher circulation ratio
> delays DNB because water has something like 60
> times the thermal conductivity and will suck the
> heat out of the tube faster than the steam AND
> because the much higher water density bulldozes
> incipient steam films off the tube wall. Add to
> the equation the fact that you now have 5 or more
> times as much material both cooling and bulldozing
> and it becomes obvious that you can delay (but not
> prevent) DNB at much higher firing rates....making
> for a more compact and energy dense boiler.
>
> OK, OK, everyone has already said this
> stuff....but I wanted my chance to reword things
> and submit them as well.....
>
Ken:
Yep--that's a nice summation of the process IMO.
I think the Lamont has advantages even for systems operating on lower pressures. These would be: 1) The operation of a water-level type of boiler with its attendant simplicity and thermal inertia, and 2) The additional heating efficiency offered by the water (instead of steam) contact with the tube walls.
>So maybe we could add a check valve to one or both ends, turn it into a hydraulic "pulse jet", and really shoot the water >through the tubes? Add the cool feed intermittently to quench the vapor in the tube and create a new suction wave to bring >in the next round of water for vaporization?
Y, I was gonna mention the addition of a check valve, at the inlet end; it's stoopid-simple and won't solve all the problems but it could certainly solve some of them with a minimum of effort. Also, the check valve seating spring would establish a pressure rise on its own as recently discussed.
I still think there are real-world parameters to discuss in establishing the diameter of the vertical standpipe. These would describe the minimum allowable diameter to promote separation of the steam and water due to velocity reductions. Also, the addition of baffles to promote further separation. I also liked the mention of an internal "stay" between the vertical caps of the standpipe in the G. Nutz papers--a nice detail. All in all, there's lots of minutia to consider.
Bill
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Re: Lamont boiler January 23, 2012 12:47AM |
The AC drive water pump through a non magnetic housing (sometimes referred to as a "canned pump" may be more workable than a magnetic drive via permanent magnets.
Magnetic materials have a "Curie temperature" above which they lose magnetic susceptibility. High performance permanent magnets are quickly destroyed by moderately high temperatures.
may be more workable than a magnetic drive via permanent magnets.
Magnetic materials have a "Curie temperature" above which they lose magnetic susceptibility. High performance permanent magnets are quickly destroyed by moderately high temperatures.
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