Monotube Flash Boiler Design

[Toymaker]

Great idea - - - - thanks for confirming your technical terms!!!

Hmmmmm - - - - wonder how that blower would last on a serious furnace boiler?
(I wonder if replacing the bearings and perhaps stabilizing the impellor re: the housing would be enough to transform the blower from an occasion use thing to a serious long term use capable item - - - hmmmmmmmmmmm.)

The impellor is mounted directly onto the motor shaft which means it uses the motor's bearings,... which are now ball bearings with the new, larger motor. Another problem I ran into using this leaf blower was the clearance between impeller and housing was over 5 millimeters. I added plastic sheeting onto the inside surfaces of the housing to reduce the clearance to about 0.5mm,....thereby increasing the volume and pressure of the air output.

 

[ajoeiam]

The impellor is mounted directly onto the motor shaft which means it uses the motor's bearings,... which are now ball bearings with the new, larger motor. Another problem I ran into using this leaf blower was the clearance between impeller and housing was over 5 millimeters. I added plastic sheeting onto the inside surfaces of the housing to reduce the clearance to about 0.5mm,....thereby increasing the volume and pressure of the air output.

Very interesting - - - - what's the operating rpm range on the motor (assuming you have some idea)?

Sounds like you figured out how to make a silk purse out of a sow's ear!!! Good on you!

 

[Toymaker]

Very interesting - - - - what's the operating rpm range on the motor (assuming you have some idea)?

Motor RPM range is 0 to 21,000. RPM is controlled by a 60A motor speed control board that outputs PWM (Pulse Width Modulated) 36 volts to the motor.

The seller spec'd this motor for 18,000 rpm with 36 VDC. However, I was pleasantly surprised when I measured the RPM under load at 21,000 rpm at 36 vdc. I purchased the motor from a Chinese company through AliExpress, and it's been my experience that Chinese companies tend to exaggerate their product's specs, so I was quite surprised when I measured the rpm of the impeller and saw that it was actually out-performing the motor's rpm spec.

I use motor No.2 form this Motor Company.

 

[ajoeiam]

Motor RPM range is 0 to 21,000. RPM is controlled by a 60A motor speed control board that outputs PWM (Pulse Width Modulated) 36 volts to the motor.

The seller spec'd this motor for 18,000 rpm with 36 VDC. However, I was pleasantly surprised when I measured the RPM under load at 21,000 rpm at 36 vdc. I purchased the motor from a Chinese company through AliExpress, and it's been my experience that Chinese companies tend to exaggerate their product's specs, so I was quite surprised when I measured the rpm of the impeller and saw that it was actually out-performing the motor's rpm spec.

I use motor No.2 form this Motor Company.

Thanking you for your assistance - - - sir!!

 

[Toymaker]

I finally took the time to measure the fuel consumption of my little forced air burner; at 95% power setting it's consuming 10 LPH (Liters Per Hour), which equates to 103 KWH or 138 HP-Hours. How much of that power will be transformed into steam output is TBD (To Be Determined), but I'm quite happy with the amount of blue in the exhaust flame.

CAUTION: Adjust your volume down before playing the video,...it's quite loud.

 

[minh-thanh]

Maybe...I'll make money to go to Thailand

 

[Steamchick]

Toymaker, I am impressed by your engineering - again.
Am I right it equates to a 28.6kW burner? In such a small "tin-can" at that! That's similar to the power developed in the fire of the larger 5inch gauge locomotives using coal and forced by the exhaust steam at the chimney. (Someone calculated one of those around 27kW. on a 3in x 5in grate).
Keep it up!
K2

 

[Toymaker]

Toymaker, I am impressed by your engineering - again.
Am I right it equates to a 28.6kW burner? In such a small "tin-can" at that! That's similar to the power developed in the fire of the larger 5inch gauge locomotives using coal and forced by the exhaust steam at the chimney. (Someone calculated one of those around 27kW. on a 3in x 5in grate).
Keep it up!
K2

Allow me to explain my calculations:

When I Googled, "how many kwh in one liter of diesel" I got lots of different answers, from 0.3 kWh to 10.6 kWh. But if I ask, "how many MJ in one liter of diesel" all the answers were the same, 38 MJ per liter.
Therefore:
1 liter of Diesel contains 38 MJ which equates to 10.6 kWh; therefore, 10 liters of Diesel contains 106 kWh.

Since I'm burning 10 liters per hour, I should be releasing 106 kW, yes?

 

[Steamchick]

Yes, sounds about right, but I think that should read 106 kWh. as the chemical energy released in 1 hour. (kWh = Unit of energy, as kW is a unit of POWER, =kJ/second). (Just a typo I guess?). You can calculate kilowatthours from kilowatts and seconds or hours, but you can't convert kilowatthours to kilowatts since kilowatthour and kilowatt units represent different quantities.
So I reckon I should simply divide 380000kJ by 3600 (seconds per hour) to get the 105.6kW... = the Power of your burner. (Energy chemically released per second). Thus makes it comparable to any other heat source.
(I was off my trolley with my previous calculator button pushing! - Sorry for confusion - all mine. I think I have got it right in my head now... Thanks!).
K2

 

[Toymaker]

Yes, sounds about right, but I think that should read 106 kWh. as the chemical energy released in 1 hour. (kWh = Unit of energy, as kW is a unit of POWER, =kJ/second). (Just a typo I guess?). You can calculate kilowatthours from kilowatts and seconds or hours, but you can't convert kilowatthours to kilowatts since kilowatthour and kilowatt units represent different quantities.
So I reckon I should simply divide 380000kJ by 3600 (seconds per hour) to get the 105.6kW... = the Power of your burner. (Energy chemically released per second). Thus makes it comparable to any other heat source.
(I was off my trolley with my previous calculator button pushing! - Sorry for confusion - all mine. I think I have got it right in my head now... Thanks!).
K2

Agreed, I should have stated 106 kWh, and not simply 106 kW.

 

[NapierDeltic]

Hi Toymaker, I think you know old steam locomotives have an overall efficiency of about 10%.
Though I do not put an "=" between a classic steam engine and your turbine, I think you know what you expect from it, more or less.

 

[NapierDeltic]

Just a dumb question. Usually changing plans during the game generates a mess, but have you ever thought at a staged cycle (don't pretend this is the exact technical term) where freon would be the lower stage? This would bring it somehow in the safer area. Off course, I have no ideea what the topping cycle could be...

 

[Toymaker]

Just a dumb question. Usually changing plans during the game generates a mess, but have you ever thought at a staged cycle (don't pretend this is the exact technical term) where freon would be the lower stage? This would bring it somehow in the safer area. Off course, I have no ideea what the topping cycle could be...

Combined cycle systems are essentially two completely separate systems, where the second stage uses the waste heat from the first. Great idea for stationary power plants that have lots of room for a second separate system, and doesn't care about the additional weight of a second system. However, my goal is place this steam engine into a car, with limited engine space and a desire to keep the weight to a minimum.

 

[NapierDeltic]

Tough job! I'm watching closely your progress!

 

[Toymaker]

Pressurized Oil System:

The larger motor which now turns the compressor increased the swash plate compressor RPMs from 700 to 2000, and increased the air pressure through the fuel nozzle up to 20 psi,...which is what I wanted. However, those increases also led to increased heating of the air & compressor frame, and also increased the amount of lubricating oil being blown out of the compressor along with the compressed air. At 700 RPM and below, 3 cc of oil injected into the compressor's center section was plenty of oil to keep the wobble plate and bearings well lubricated.

Photo below shows the new oil recirculating system. The clear plastic bottle acts as both an air and oil accumulator which allows most of the oil mist in the compressed air to quickly fall out of the air into the liquid oil reservoir at the bottom of the bottle.

The metal & white plastic object seen inside the bottle is a motorcycle fuel pump, which pumps 0W-20 motor oil through the 1/8" OD silicone tube. The above photo shows the tube attached to an M4 brass fitting threaded into the compressor housing which feeds oil onto the swash plate, while the below photo shows the silicon tube feeding oil back into the plastic bottle in order to visually check oil flow rate. I was hoping this would be a final solution, but the pressurized air is hot enough that it quickly warms the plastic bottle to a worrisome temperature. I will therefore return to using the stainless steel sphere after I braze in a fill cap large enough to allow the pump to slide inside the sphere.

 

[Steamchick]

I should have directed the incoming air to the reservoir/oil separator to impinge near tangentially on the walls of the cylinder, such that the air/oil mist swirls at high speed around the inside of the pressure vessel. Centrifugal separation of oil droplets and air will then ensue, creating cleaner air at the core of the swirl - like in a tornado or regular centrifugal swirl separators used in vacuum cleaners, etc. The oil on the walls of the chamber will then run down to the collection well for re-cycling.
K2.

 

[Toymaker]

I should have directed the incoming air to the reservoir/oil separator to impinge near tangentially on the walls of the cylinder, such that the air/oil mist swirls at high speed around the inside of the pressure vessel. Centrifugal separation of oil droplets and air will then ensue, creating cleaner air at the core of the swirl - like in a tornado or regular centrifugal swirl separators used in vacuum cleaners, etc. The oil on the walls of the chamber will then run down to the collection well for re-cycling.
K2.

I like your idea K2 I think I can make that happen by putting a 90 degree turn into the air input fitting the hose barb threads into.

 

[Steamchick]

Good luck!

 

[Toymaker]

DIY Air-Oil Separator: I used a stainless steel hollow sphere, sold for use as garden decoration, to separate the atomized oil mixed in with the air from my little wobble plate air compressor. Compressor air is directed into the sphere through a 90 degree nozzle (shown below) such that the air blows parallel to the sphere's wall; air leaves the nozzle just above the oil pool inside the sphere and is forced to circle round & round inside the sphere until it reaches the output port near the top of the sphere; there is very, very little oil left in the output air. The same motorcycle fuel pump partially shown in post #415 is now located inside the hollow sphere and pumps oil into the compressor's center section.

The 2" diameter cap at the top of the sphere (above right photo) is an aluminum gas cap, sold complete with a rubber O-ring inside the cap which makes a good pressure seal. The aluminum cap's stem is attached to the stainless sphere using a liberal amount of steel-filled epoxy, and a 30 degree twist locking mechanism for added strength.

 

[ddmckee54]

If the temperature of the pressurized air was hot enough that you were concerned about your plastic bottle, what about that poor motorcycle fuel pump? Isn't it going to get cooked in there? The temperature's gotta be way above the design rating of the the pump. It would seem to me that pump might last for a little while, then give up the ghost from overheating.