Dusty's Experimental Boiler
Posted by Dusty
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Re: Dusty's Experimental Boiler November 14, 2023 05:53AM |
Dusty,
I wanted to explain my comment pertaining to analysis paralysis. Attached is a graph of the thermal conductivity of water. As you can see, no straight lines and variation is considerably high as a function of temperature and pressure. The calculation to predict boiler output in a tube boiler is difficult and can take several days. The thermal conductivity of water sucks.
A gentleman I'll call George did a calculation like this for a forced circulation boiler. It took him days to perform this calculation. This boiler was never built. I have great respect for George in his ability to put the differential equations together and perform the calculation. Boundary layer fluid dynamics is not a walk in the park.
However, there is many ways to skin a cat. From experience or values that people have observed from their boilers is another way to approach boiler calculations. Here are some values for your next steps.
Fire tube boiler 5 sq ft/BoHP
Ofeldt boiler 3 sq ft/BoHP
Mono-tube 2 sq ft/BoHP (economizer)
Mono-tube 1 sq ft/BoHP (generator coil & super heat)
There is an engineering assumption that the thermal conductivity of the metal used in the boiler design is super conductive of heat. Therefore consider the temperature say within a fire tube is the temperature in effect on the water on the outside of the fire tube. Therefore, the calculation for square feet per boiler horsepower is perform on the OD of the tube. Opposite for a tube boiler in that you use the sq ft (area) of the inside of the tube in your calculation.
So here is your development process. You might build a tube boiler either with pancakes and or coils for trial. Measure the results of the steam generation and compare to the values presented. Once through you'll have a good idea of the steam production of your boiler. A key part is to measure your water rate.
Good luck and hope this helps. All fun right...
Rick
I wanted to explain my comment pertaining to analysis paralysis. Attached is a graph of the thermal conductivity of water. As you can see, no straight lines and variation is considerably high as a function of temperature and pressure. The calculation to predict boiler output in a tube boiler is difficult and can take several days. The thermal conductivity of water sucks.
A gentleman I'll call George did a calculation like this for a forced circulation boiler. It took him days to perform this calculation. This boiler was never built. I have great respect for George in his ability to put the differential equations together and perform the calculation. Boundary layer fluid dynamics is not a walk in the park.
However, there is many ways to skin a cat. From experience or values that people have observed from their boilers is another way to approach boiler calculations. Here are some values for your next steps.
Fire tube boiler 5 sq ft/BoHP
Ofeldt boiler 3 sq ft/BoHP
Mono-tube 2 sq ft/BoHP (economizer)
Mono-tube 1 sq ft/BoHP (generator coil & super heat)
There is an engineering assumption that the thermal conductivity of the metal used in the boiler design is super conductive of heat. Therefore consider the temperature say within a fire tube is the temperature in effect on the water on the outside of the fire tube. Therefore, the calculation for square feet per boiler horsepower is perform on the OD of the tube. Opposite for a tube boiler in that you use the sq ft (area) of the inside of the tube in your calculation.
So here is your development process. You might build a tube boiler either with pancakes and or coils for trial. Measure the results of the steam generation and compare to the values presented. Once through you'll have a good idea of the steam production of your boiler. A key part is to measure your water rate.
Good luck and hope this helps. All fun right...
Rick
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Re: Dusty's Experimental Boiler November 15, 2023 05:49AM |
SteveW, I look forward to reviewing posts of your radically different expander. 
I contacted the fuel pump manufacturer and they cautioned me that I should not go over 60oC fuel temperature and told me their pumps weren't designed to pump water. Looking at the design drawings, the pump looks like a "wet pump" meaning the water would be in contact with all the internal parts, including those made of soft iron and thus prone to rust. The other potential issue is electrolysis at the brushes, which would produce free oxygen and hydrogen gases that would dissolve into the water. I'm hopeful that I will be able to mitigate both these potential problems by using distilled water in a closed circulation system. Distilled water is actually a very good insulator, which should prevent any electrolysis from taking place, thereby keeping dissolved free oxygen atoms to a minimum, which will limit rust formation. As for the 60oC temp limit,...I'm not totally buying such a low limit. I will need to do a bit testing for my self to find out.
I contacted the fuel pump manufacturer and they cautioned me that I should not go over 60oC fuel temperature and told me their pumps weren't designed to pump water. Looking at the design drawings, the pump looks like a "wet pump" meaning the water would be in contact with all the internal parts, including those made of soft iron and thus prone to rust. The other potential issue is electrolysis at the brushes, which would produce free oxygen and hydrogen gases that would dissolve into the water. I'm hopeful that I will be able to mitigate both these potential problems by using distilled water in a closed circulation system. Distilled water is actually a very good insulator, which should prevent any electrolysis from taking place, thereby keeping dissolved free oxygen atoms to a minimum, which will limit rust formation. As for the 60oC temp limit,...I'm not totally buying such a low limit. I will need to do a bit testing for my self to find out.
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Re: Dusty's Experimental Boiler November 15, 2023 06:31AM |
Some other sources of mono-tube boilers are:
Doble, found in Jim Crank's book
Chuk Williams, reference in threads here in this forum
White, the famous steam car
Jerry Oliver, he built a successful mono-tube based on Richard Smith design
Inspiration, British LSR boiler
Last but not least is to think about these little Hydrofoil boats that use flash boilers. This is in line with Serpollet and his flash boiler.
Attached are concept(s) I'm toying with...also something to think about.
Doble, found in Jim Crank's book
Chuk Williams, reference in threads here in this forum
White, the famous steam car
Jerry Oliver, he built a successful mono-tube based on Richard Smith design
Inspiration, British LSR boiler
Last but not least is to think about these little Hydrofoil boats that use flash boilers. This is in line with Serpollet and his flash boiler.
Attached are concept(s) I'm toying with...also something to think about.
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Re: Dusty's Experimental Boiler November 16, 2023 08:06PM |
SteveW, I'm not using the wire technique posted by Rick.H.
I did look into using finned tubing, and I would love to use them in the economizer section of the boiler, but bending finned tubes into coils requires tools I don't have. If my overall steam engine works as well as I hope it will, I'll likely build a new boiler using finned tubes, but that's likely quite some time away.
Also, before I use finned tubes, I plan to improve the burner's blower by adding a small steam driven turbine to power the blower. At this time in my build, the small electric motor driving the blower cannot provide the power needed to further increase air flow into the burner. The SES burner used a hydraulic motor to dive their fan,...I plan to use a small steam turbine. Then, I will restrict the exhaust gas flow exiting the boiler thereby allowing a small pressure increase inside the boiler container, which in theory will increase BTU density of the hot combustion gases circulating around the tubes.
I still have much work to do
Edited 1 time(s). Last edit at 11/16/2023 08:09PM by Dusty.
I did look into using finned tubing, and I would love to use them in the economizer section of the boiler, but bending finned tubes into coils requires tools I don't have. If my overall steam engine works as well as I hope it will, I'll likely build a new boiler using finned tubes, but that's likely quite some time away.
Also, before I use finned tubes, I plan to improve the burner's blower by adding a small steam driven turbine to power the blower. At this time in my build, the small electric motor driving the blower cannot provide the power needed to further increase air flow into the burner. The SES burner used a hydraulic motor to dive their fan,...I plan to use a small steam turbine. Then, I will restrict the exhaust gas flow exiting the boiler thereby allowing a small pressure increase inside the boiler container, which in theory will increase BTU density of the hot combustion gases circulating around the tubes.
I still have much work to do
Edited 1 time(s). Last edit at 11/16/2023 08:09PM by Dusty.
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Re: Dusty's Experimental Boiler December 17, 2023 08:11PM |
Feed Pump DO NOT USE THIS ONE
The cordless washer shown in the picture is advertised to deliver 60 Bar with a flow rate of 10 liters/min.; in my tests it delivered only 2 liters of pressurized flow and only 4 liters/min open flow with no pressure. I found this one advertised on both AliExpress and eBay:
I didn't bother to measure the pressure but I suspect it's no more than a few hundred PSI,...if that.
Edited 2 time(s). Last edit at 12/30/2023 07:33AM by Dusty.
The cordless washer shown in the picture is advertised to deliver 60 Bar with a flow rate of 10 liters/min.; in my tests it delivered only 2 liters of pressurized flow and only 4 liters/min open flow with no pressure. I found this one advertised on both AliExpress and eBay:
Edited 2 time(s). Last edit at 12/30/2023 07:33AM by Dusty.
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Re: Dusty's Experimental Boiler January 06, 2024 02:04AM |
Modified Pressure Washer Feed Pump.
I replaced the 220 VAC motor in the Toma pressure washer with a 1 kW, 36 VDC motor to make an easily controlled feed pump. By using a PWM motor speed controller, I'm able to control the pressure output from zero to over 3000 psi. I used this modified pump to pressure-wash my concrete patio with 20 MPa (2900 psi) indicated pressure. Since the max pressure on my boiler is only 1000 psi, and working pressure no more than 600 to 700 psi, I will need to careful not to over-pressure the boiler.
I replaced the 220 VAC motor in the Toma pressure washer with a 1 kW, 36 VDC motor to make an easily controlled feed pump. By using a PWM motor speed controller, I'm able to control the pressure output from zero to over 3000 psi. I used this modified pump to pressure-wash my concrete patio with 20 MPa (2900 psi) indicated pressure. Since the max pressure on my boiler is only 1000 psi, and working pressure no more than 600 to 700 psi, I will need to careful not to over-pressure the boiler.
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Re: Dusty's Experimental Boiler January 31, 2024 09:08PM |
Sensors & Pressure Connectors:
I machined two simple manifolds for the boiler's input and output connections. These manifolds hold the pressure and temperature sensors which allow the computer the read feedwater temperature and pressure, and steam temperature and pressure output. Both manifolds were pressure tested to 1000 psi using the feed pump to supply the pressure.
Below pic shows the feedwater input manifold connected to the boiler. To give an idea of scale, the blue nut is for an AN-10 flare connector, but the flare connection has been replaced with a different type pressure connector which works much, much better than a flare.
Below pic shows the same input manifold removed from the boiler exposing the pressure connector with two green FKM O-rings. I didn't need two O-rings, but there was plenty of room, so I machined a second groove into the nipple, which slides into the center hole in the male AN-10 flare connector. This connection needs only "finger tightening" of the nut to form the 1000 psi seal.
The steam output manifold is nearly identical to the input side, except the nipple with the O-ring has a larger diameter and only one O-ring, also, a third port, currently plugged, allows for a future poppet safety valve connection.
This final pic shows the sensor manifold disassembled. This is an earlier pic taken before I replaced the black rubber O-rings with Red Silicone O-rings which have temperature ratings up to 250 C.
Edited 1 time(s). Last edit at 03/02/2024 02:14AM by Dusty.
I machined two simple manifolds for the boiler's input and output connections. These manifolds hold the pressure and temperature sensors which allow the computer the read feedwater temperature and pressure, and steam temperature and pressure output. Both manifolds were pressure tested to 1000 psi using the feed pump to supply the pressure.
Below pic shows the feedwater input manifold connected to the boiler. To give an idea of scale, the blue nut is for an AN-10 flare connector, but the flare connection has been replaced with a different type pressure connector which works much, much better than a flare.
Below pic shows the same input manifold removed from the boiler exposing the pressure connector with two green FKM O-rings. I didn't need two O-rings, but there was plenty of room, so I machined a second groove into the nipple, which slides into the center hole in the male AN-10 flare connector. This connection needs only "finger tightening" of the nut to form the 1000 psi seal.
The steam output manifold is nearly identical to the input side, except the nipple with the O-ring has a larger diameter and only one O-ring, also, a third port, currently plugged, allows for a future poppet safety valve connection.
This final pic shows the sensor manifold disassembled. This is an earlier pic taken before I replaced the black rubber O-rings with Red Silicone O-rings which have temperature ratings up to 250 C.
Edited 1 time(s). Last edit at 03/02/2024 02:14AM by Dusty.
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Re: Dusty's Experimental Boiler April 08, 2024 09:13AM |
I ran into a few air compressor problems I needed to fix before I move forward. I started out driving my little wobble plate compressor with what turned out to be an underpowered 150W DC motor; at full power, the poor little thing was almost smoking hot. The replacement motor is rated at 350 W and has enough torque to drive the compressor directly, more than doubling the RPM.
Edit: I don't know why this photo isn't displaying. If you click on the "open image URL" the photo can be seen.
With higher RPMs came the need for a continuous oiling system, and the oiling system then required a air-oil separator to remove the increased oil being blown out with the compressed air. The shiny stainless steel sphere is sold as a yard & garden decoration, but makes a pretty good combination air-oil separator & oil reservoir. A small motorcycle fuel pump is located inside the metal sphere and pumps oil into the center section of the compressor through a 1/8" silicone rubber tube. The oil-laden compressed air is shot into the sphere at a 90 degree angle such that it flows along the inside walls of the sphere before making it's way out of the sphere near the top. It works quite well allowing almost no oil to escape the sphere.
Max pressure with the smaller motor was about 14 psi, while max pressure with this larger motor is 25 psi through the 2mm fuel nozzle. Fuel consumption is now 10 L/Hr.
Edited 3 time(s). Last edit at 04/11/2024 08:17PM by Dusty.
Edit: I don't know why this photo isn't displaying. If you click on the "open image URL" the photo can be seen.
With higher RPMs came the need for a continuous oiling system, and the oiling system then required a air-oil separator to remove the increased oil being blown out with the compressed air. The shiny stainless steel sphere is sold as a yard & garden decoration, but makes a pretty good combination air-oil separator & oil reservoir. A small motorcycle fuel pump is located inside the metal sphere and pumps oil into the center section of the compressor through a 1/8" silicone rubber tube. The oil-laden compressed air is shot into the sphere at a 90 degree angle such that it flows along the inside walls of the sphere before making it's way out of the sphere near the top. It works quite well allowing almost no oil to escape the sphere.
Max pressure with the smaller motor was about 14 psi, while max pressure with this larger motor is 25 psi through the 2mm fuel nozzle. Fuel consumption is now 10 L/Hr.
Edited 3 time(s). Last edit at 04/11/2024 08:17PM by Dusty.
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Re: Dusty's Experimental Boiler April 25, 2024 08:01PM |
Making Steam Again: I paced the burner assembly inside the boiler coils and made a little steam today. Below is a photo of my outdoor test stand; Lowest shelf shows the feed pump just to the left of the bright red Diesel fuel container. On the middle shelf, from left to right, is the air compressor assembly, center is the ECU (Engine Control Unit), far right is a power strip, 36 vdc power supply, and 1 liter fuel container. Top shelf, center is the boiler/burner assembly and the display screen. (continued below photo)
I performed this test mostly to determine what numbers were needed for the feed pump at the burner's idle power setting, (with no pressure) so that I could plug that value into the ECU software, as this is how I want the boiler to start up. I initially set the feed pump for what I knew would be too much flow, and once wet steam began to exit, I slowly decreased the feed pump's RPM until I determined only dry steam was exiting the boiler tube. Once I had the feed pump RPM number, I turned the burner off and allowed the feed pump to continue pumping without changing the setting. After a few seconds of cooling down, the water from the boiler's steam outlet was flowing smoothly; placing a measuring cup to catch the water from the boiler, I timed the flow rate at 425 ml/minute. Since 1 ml of water = 1 gram, that meant my boiler was producing 425 grams of steam per minute, at it's lowest power setting. Converting to pounds; 425 grams/min = 0.937 lbs/min,...or 56.2 lbs/Hr.
I'm aware that some folks consider Boiler Horse Power (BHP) to be obsolete, but I've also noticed that many text still use it, and since I'm only looking for a ball-park value, seems appropriate to use here.
1 BHP = 34.5 lbs steam per Hr at atmosphere pressure.
Therefore, my boiler's output of 56.2 lbs/Hr divided by 34.5 = 1.63 BHP.
Since 1 BHP = 13.15 HP than 1.63 BHP x 13.15 HP/BHP = 21.4 HP,....at idle
I performed this test mostly to determine what numbers were needed for the feed pump at the burner's idle power setting, (with no pressure) so that I could plug that value into the ECU software, as this is how I want the boiler to start up. I initially set the feed pump for what I knew would be too much flow, and once wet steam began to exit, I slowly decreased the feed pump's RPM until I determined only dry steam was exiting the boiler tube. Once I had the feed pump RPM number, I turned the burner off and allowed the feed pump to continue pumping without changing the setting. After a few seconds of cooling down, the water from the boiler's steam outlet was flowing smoothly; placing a measuring cup to catch the water from the boiler, I timed the flow rate at 425 ml/minute. Since 1 ml of water = 1 gram, that meant my boiler was producing 425 grams of steam per minute, at it's lowest power setting. Converting to pounds; 425 grams/min = 0.937 lbs/min,...or 56.2 lbs/Hr.
I'm aware that some folks consider Boiler Horse Power (BHP) to be obsolete, but I've also noticed that many text still use it, and since I'm only looking for a ball-park value, seems appropriate to use here.
1 BHP = 34.5 lbs steam per Hr at atmosphere pressure.
Therefore, my boiler's output of 56.2 lbs/Hr divided by 34.5 = 1.63 BHP.
Since 1 BHP = 13.15 HP than 1.63 BHP x 13.15 HP/BHP = 21.4 HP,....at idle
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