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Dusty's Experimental Boiler

Posted by Dusty 
Re: Dusty's Experimental Boiler
November 05, 2023 03:41PM
Dusty, while I'm looking at around 800 to 1000 psi
I am not planning on using what you are. I can see that what you plan may work
For your application. For my feedwater pump it shouldn't see temperatures
Reaching 212 F. The circulation pump will but its will be designed
For high temperatures.
The engine itself is radically different and can use very high expansion.
Or I should say is expected to use high expansion.
But this thread is your system and I'm interested
In how it comes out.
SteveW
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


Re: Dusty's Experimental Boiler
November 15, 2023 05:03AM
First, thanks for the graphs and especially for the "rules of thumb" sizing info on monotube boilers; they're great to use as a starting point and also to cross-check one's design to see if it's at least in the ball park.

Years ago, I started my boiler design by first examining lots of other successful designs trying to find something close to the power output I wanted; I settled on the 1970's SES boiler as what I wanted to come close to. Then I tried to learn as much as I could about heat transfer by listening to a few on-line courses on the subject. In this Heat Transfer Course the instructor states that tube walls can be ignored in transfer equations when using a relatively thin wall; so it's not just an assumption, it's what's actually being taught.
Re: Dusty's Experimental Boiler
November 15, 2023 05:49AM
SteveW, I look forward to reviewing posts of your radically different expander. smiling smiley

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.
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.


Re: Dusty's Experimental Boiler
November 16, 2023 12:49PM
Dusty,
Have you considered using some sort of finned tubing inside instead of wires? There are a lot of designs that might work well for you. Of course wire should be much less expensive.
Just a thought.
SteveW
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 smiling smiley



Edited 1 time(s). Last edit at 11/16/2023 08:09PM by Dusty.
Re: Dusty's Experimental Boiler
November 18, 2023 11:44AM
Dusty, thanks for the correction on the wires. I understand about winding finned tubing
If I find an easy way way to do so I'll let you know.
As for the compression to increase heat density I am looking into the sam thing however I'm looking at trying to do so where the gasses have cooled enough to keep from producing Nox.
All the best on your project.
SteveW
Re: Dusty's Experimental Boiler
December 12, 2023 07:20AM
Just an update for those following this thread. The Osias High Pressure fuel pump I was hoping to use as a feed pump arrived in the mail this past week and I had a chance to test it. I'm rather disappointed with the results; the pump could only manage to push a trickle of water through the copper coil,...not even close to the 3 liters per minuet I was hoping for. Also, the pump is a "wet" design, meaning the pumped liquid flows through the windings of the motor, including the brushes, keeping the internal parts cool. Not a problem with fuel, but pumping water will cause everything to rust, and electrolysis will occur at the brushes, adding dissolved oxygen into the feed water.

I reluctantly decided these fuel pumps would not make very reliable feed pumps.

I'm now looking at using an RO Pump (Reverse Osmosis). The Silvertec ST-650G advertises a working pressure of 70 psi at a working flow of 5.3 Liters per min. Initial test results with this pump are encouraging, as the flow through the coil was impressive. I'm now waiting for a handful of AN-10 fittings, including a manual ball valve, to arrive from Hong Kong so I can restrict the pump's flow on the output side of the boiler coil, to see what pressure RO Pump can actually produce. Hopefully the pump will deliver the rated 70 psi, which should be enough to run the steam driven Tesla turbine powered feed pump.
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.
Re: Dusty's Experimental Boiler
December 30, 2023 08:23AM
Feed Pumps: Hydraulic Power Equation

Wish I had found this equation months ago, but, better late than never.

The Power required to drive a feed pump, or any hydraulic pump, is determined by the following equation:

Power = (P x Q)/600

where: Power is kW
P = Pressure in Bar
Q = Flow in liters/minute

Max requirements for my boiler are 800 psi (55 Bar) input from the pump, at a flow rate of 8 liters/minute.

Therefore: (55 Bar x 8 LPM)/600 = 0.73 kW

So, if I want to power the feed pump with an electric motor, I should use a 1kW motor. Clearly, hand held cordless pressure washers will not work.
Re: Dusty's Experimental Boiler
December 30, 2023 10:06AM
The small electric motors we use in RC boat racing develop well over 2 KW. They are 3 phase and need a dedicated speed control. We use lithium ion batteries and only need a few minutes of run time. Any 12 to 24 volt DC supply will work. Very high quality motors are available from Neu. The best speed controls are available from Castle. Some are water cooled, but if you only need 1 KW, air cooled ones should work. If the pressure washer pumps can stand the higher power, a better motor is out there. Let me know if you are interested in detail information. For reference I was involved in the design of this electric hydroplane.

Lohring Miller
Re: Dusty's Experimental Boiler
December 30, 2023 09:16PM
Very impressive hydroplane boat,...sounds like a jet flying by.

Thanks for the motor and controller links, I will definitely keep them in mind for future revisions; BLDC motor and controller is indeed the best solution,...but for now, I already have an older brushed 36 VDC motor (MY1020), originally sold to power electric scooters & quads, I will use for initial testing.

The only cordless (Battery powered) pressure washers I've found through Google searches are far too small to deliver the pressure and flow I need for my boiler, so I will use the hydraulic pump section from an easily obtained, AC motor powered, pressure washer, and connect the pump section to a 1kW DC motor, which is easily controlled with a PWM speed controller. If this pump conversion works as well as I hope, I will be looking for a smaller, lighter motor to replace the rather heavy brushed motor.



Edited 1 time(s). Last edit at 12/30/2023 09:20PM by Dusty.
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. smiling smiley


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 senor 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.

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Untitled.png 16 KB open | download Dusty 07/01/2023 Read message
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WIN_20220812_12_15_06_Pro.jpg 283.7 KB open | download Dusty 07/01/2023 Read message
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