Monotube Flash Boiler Design

[Steamchick]

Another one I saw was a copper pipe.. the key is a heated wire mesh screen about 1/5th to 1/4 of the way up the pipe. The note is a resonance of the column of air in the pipe length.
The "thermodynamics" are as follows:
Warmth in the pipe expands the air and it rises - convection currents then draw air through the pipe. As the air transitions through the wire mesh screen, it is heated, expands rapidly, and causes a tiny reverse shock wave to pass back through the screen. So some of the hot air is then cooled when it gets to the cold side of the screen, contracting, and causing a low pressure zone, but this is immediately forced back through the screen by the convection current and heated again, so the high pressure shock wave passes back through the screen, cools, etc.
Note how a pipe held horizontally does not resonate? = no flow by convection. Like a flute when no-one is blowing. but - like a flute - when the air flow is above a threshold value, the oscillations begin and the pipe resonates at the natural frequency of the quarter-length of the wave being the distance from the hot mesh to the "long" end.... - I think?
The wire mesh needs to be a substantial wire thickness to hold the heat for the time he uses the Rijke's tube. Possibly his pipe is plastic - ABS, or something? - as it is cold enough to hold. Copper, steel, etc. gets hot.
Note: There is a very small amount of heat powering the tube when removed from the flame. Mostly creating the convection current, but a small proportion making the sound. Yet is is VERY LOUD, and Health and Safety recommend less than 1 minute exposure to such loud sounds before ear damage can occur! (I once had a table of something like 85dBA limit for a week's average industrial exposure, 90dBA continuous sound for hearing protection to be required, or max 10 mins exposure, 100 dBA for max 1 minute exposure, 110dBA for 0.1 minute exposure (6 seconds!), and a whole concert for Megadeath music!!).
I was testing a large air motor (single 10in dia piston powered by 28Bar air and when the valve opened to release the air the meter recorded 137 DB at 1 metre - with me holding the meter...). The "bang" (single pulse) caused permanent damage to me. (max 10 in a week) - It left my head ringing for hours, I have permanent tinnitus now. NOT NICE. So PLEASE wear ear defenders when playing with a Rijke's tube. (Over 100dBA!).
K2

 

[NapierDeltic]

Thank you very much for details!
Cheers!

 

[Steamchick]

Hi Toymaker,
A BIG SORRY - for the distraction about Rijke's tube resonance. - Something that happens with other boilers but I am pretty sure cannot happen with yours.
After hijacking your thread for a few days, How are you progressing?
K2

 

[Toymaker]

Hi Toymaker,
A BIG SORRY - for the distraction about Rijke's tube resonance. - Something that happens with other boilers but I am pretty sure cannot happen with yours.
After hijacking your thread for a few days, How are you progressing?
K2

I do find Rijke's tube fascinating, it reminds me of all the designing that goes into jet engines to avoid all possible resonances; at a very basic level, jet engines consist of a tube having very high flow rates of hot gases under differing pressures, and with spinning metal parts inside....so lots of opportunity for destructive resonance. But I agree with you that Rijke resonance is not very likely to occur in my burner or boiler assembly.

Now that my boiler is finally finished and passed the initial 100 psi leak test, I've been looking into other methods of high pressure testing the boiler other than using a scuba tank. I can buy a new hand hydraulic pump here in Thailand, rated at 700Kg/sqr cm (10,000 psi) for $120 US. If I tried to build one from scratch, I would need to buy almost all the various parts and stock metals, which would likely cost me more. (link: Hydraulic Pump) This pump was made to use oil, not water, so I would need to dry it out and thoroughly oil it after use with water, but that's easy enough to do.

BTW, This is what it will look like when it's ready to fire up,...still need to make a few more bits and pieces, like a latch for the "V" clamp.

 

[Steamchick]

Why not just test using hydraulic oil? The copper doesn't care if the pressure is in water or oil. You could even use diesel fuel. Just carefully fill and eliminate (bleed) all air before starting to raise pressure. Do it slowly, in maybe 10% steps, relieving to zero between each step. Watch out for leaks. A fine spray of oil can atomiser and be flammable (and smelly) or a high pressure jet can cut through flesh! Very painful, and toxic when your fluid is injected into the body by accident!
Take care however to do the test.
K2

 

[Toymaker]

Why not just test using hydraulic oil? The copper doesn't care if the pressure is in water or oil. You could even use diesel fuel. Just carefully fill and eliminate (bleed) all air before starting to raise pressure. Do it slowly, in maybe 10% steps, relieving to zero between each step. Watch out for leaks. A fine spray of oil can atomiser and be flammable (and smelly) or a high pressure jet can cut through flesh! Very painful, and toxic when your fluid is injected into the body by accident!
Take care however to do the test.
K2

Tube volume is just over 1 gallon, so if I do get a leak, or worse, a rupture, either hydraulic oil or Diesel will make quite a mess. If I use water and get a leak, than my wife thanks me for watering her plants and lawn.

If all goes well and there are no leaks, the first few times I boiled any water in the coils after the hydrostatic test, the residual hydraulic oil or Diesel would again make for quite a smelly, toxic mess.

It will be much easier to dry the water out of the inside of the hand pump.

 

[HMEL]

Hi Steamchick, I do not have any reason to deny what you are saying, but this means Carnot approach - taken as master when comes to evaluate IC engines efficiency - is wrong. Because Carnot is a pure thermal cycle conserving mass and state of fluid (gas) in cycle; not to mention chemical reactions with different phase for reaction products. But how much is the difference?

The Carnot cycle can be constructed for many different arrangements and fluids. Including an IC engine. The calculated engine efficiency will give you the maximum efficiency of a theoretically reversible engine. This is what the Carnot cycle answers what is the best efficiency you can get. However it is impossible to construct that engine and it will have irreversible properties. This implies the actual efficiency will be a lot lower then a reversible engine.
And it is then necessary to use the amount of work (expressed in heat units) divided by the amount of energy in heat units put into the cycle. So Carnot is not wrong just have to consider the assumptions being made.

 

[TimTaylor]

Why? Be specific.

Temperature/pressure limits for soldered joints, insufficient safety factor temp vs pressure of copper tubing

 

[NapierDeltic]

The Carnot cycle can be constructed for many different arrangements and fluids. Including an IC engine. The calculated engine efficiency will give you the maximum efficiency of a theoretically reversible engine. This is what the Carnot cycle answers what is the best efficiency you can get. However it is impossible to construct that engine and it will have irreversible properties. This implies the actual efficiency will be a lot lower then a reversible engine.
And it is then necessary to use the amount of work (expressed in heat units) divided by the amount of energy in heat units put into the cycle. So Carnot is not wrong just have to consider the assumptions being made.

Hi HMEL . I don't deny the main nature of IC engines as thermal engines. What I'm saying is there is a fraction of engine's output which is not due to thermal cycle but to phase transition solely (and I have illustrated it in nitroglycerin's case).
While it might not be important and is lost among various irreversibility in real engines, it looks to me unprofessional from scholar physics to ignore it.

 

[Steamchick]

Hi Toymaker, I understand why you will hydraulic test with water. Add some automotive long life coolant just to let the glycol lubricate the pump, otherwise the low lubricity of the water in the pump may damage the close fit/seals in the pump cylinder.
On Car engines - in the factory - the first pump and engine tests and the first tank of fuel in the car MUST have diesel fuel with a high lubricity when the system is First filled, to avoid any initial scuffing before the pump and seals settle. It is a part of the controlled assembly from NEW that enables the car to achieve very high mileages. Cheaper fuel without the low lubricity additives will reduce the pump life by a factor of ten or more. I guess your hydraulic pump is intended for use with oils, so will be to a very fine tolerance and finish requiring the lubricity of the oils, etc.
K2

 

[HMEL]

Hi HMEL . I don't deny the main nature of IC engines as thermal engines. What I'm saying is there is a fraction of engine's output which is not due to thermal cycle but to phase transition solely (and I have illustrated it in nitroglycerin's case).
While it might not be important and is lost among various irreversibility in real engines, it looks to me unprofessional from scholar physics to ignore it.

Based on the laws of thermodynamics particularly the first law . The change in Heat = The change in Work done across a cycle is the scientific rule. So now matter how you cut it for every cycle this law holds. And its useful in predicting how the engine will perform.

The carnot engine answers the question what is the best that can be done. Because it is a reversible engine which is impossible to make. But there are many different ways to visualize a Carnot cycle if you follow the four basic rules of building it.

A chemical reaction is not a complete cycle. It does have thermodynamic properties but because we know the bond energies in Nitro reaction we could calculate the heat released and the resultant pressures and temperatures. We can also predict if a reaction will proceed. But few reactions work in a cycle. Biological ones for instance form cycles and they absorb and release heat.

So we are not violating scholarly laws of physics.

 

[NapierDeltic]

We are too much used to consider heat the only output of a chemical reaction.
But - for one instance - in batteries (rechargeable type) the output of chemical reactions is electric energy which at it's turn can generate mechanical output; while heat generation during charging-discharging is a waste. And here you have also a cycle; yes, very different from thermodynamic one ... it is not my point to discuss differences.

 

[peterl95124]

Hi HMEL . I don't deny the main nature of IC engines as thermal engines. What I'm saying is there is a fraction of engine's output which is not due to thermal cycle but to phase transition solely (and I have illustrated it in nitroglycerin's case).
While it might not be important and is lost among various irreversibility in real engines, it looks to me unprofessional from scholar physics to ignore it.

there's no "phase transition" in nitro-glycerin, its a chemical reaction, you start with atoms in one configuration (chemical) and you end up with atoms in different configurations (chemicals) of lower internal energy hence the release of external energy, exactly the same with fuel/air mixture except there's no mixture in nitro its just one chemical.

 

[Toymaker]

Temperature/pressure limits for soldered joints, insufficient safety factor temp vs pressure of copper tubing

Thanks for getting back with me with your friend's specific concerns; I'll address both of them.

1) There are no soldered joints anywhere in the boiler, all joints and splices are brazed using BCuP-2 which melts at 1460 F. Information from web searches stated BCuP-2 joints have greater strength than the base copper.

2) Using the yield strength of annealed copper, 11,000 psi, plugged into Barlow's equation for determining max pressure limits of pipes, and using 0.042" wall thickness for Type L copper tube with 0.625" diameter, results in 1,478 psi at room temp. Copper retains 85% strength at 365 F, which drops the max yield limit to 1,256 psi. My boiler's max pressure is limited to 500 psi, making my boiler's YIELD pressure 2.5 times below the max yield limit.
Doing the math for Ultimate Tensile strength results in a max pressure limit at 365 F of 3,484 psi for a safety factor of 7.

 

[NapierDeltic]

Sorry, my mistake. I wanted to underline that before reaction we have liquid and after, gases which occupy a much larger space (or raise the pressure accordingly) . But I think this discussion tends to cover the real subject of this thread so I'll stay low. Everybody is free to see things as he wants.
Sorry Toymaker! I am really watching your progress with much interest!

 

[TimTaylor]

Thanks for getting back with me with your friend's specific concerns; I'll address both of them.

1) There are no soldered joints anywhere in the boiler, all joints and splices are brazed using BCuP-2 which melts at 1460 F. Information from web searches stated BCuP-2 joints have greater strength than the base copper.

2) Using the yield strength of annealed copper, 11,000 psi, plugged into Barlow's equation for determining max pressure limits of pipes, and using 0.042" wall thickness for Type L copper tube with 0.625" diameter, results in 1,478 psi at room temp. Copper retains 85% strength at 365 F, which drops the max yield limit to 1,256 psi. My boiler's max pressure is limited to 500 psi, making my boiler's YIELD pressure 2.5 times below the max yield limit.
Doing the math for Ultimate Tensile strength results in a max pressure limit at 365 F of 3,484 psi for a safety factor of 7.

Thanks for getting back with me with your friend's specific concerns; I'll address both of them.

1) There are no soldered joints anywhere in the boiler, all joints and splices are brazed using BCuP-2 which melts at 1460 F. Information from web searches stated BCuP-2 joints have greater strength than the base copper.

2) Using the yield strength of annealed copper, 11,000 psi, plugged into Barlow's equation for determining max pressure limits of pipes, and using 0.042" wall thickness for Type L copper tube with 0.625" diameter, results in 1,478 psi at room temp. Copper retains 85% strength at 365 F, which drops the max yield limit to 1,256 psi. My boiler's max pressure is limited to 500 psi, making my boiler's YIELD pressure 2.5 times below the max yield limit.
Doing the math for Ultimate Tensile strength results in a max pressure limit at 365 F of 3,484 psi for a safety factor of 7.

We have standards and codes (ASME) that all pressure vessels above 15psig must comply with. These are based on engineering practice as well as almost 150 years of actual practice, field experience and analysis of in field failures.
Your design operating pressure/temperature do not fall within the AMSE code specifications for the materials you are using.

• ASME-BPVC - the following sections would apply to your project:
• ASME BPVC Section II - Materials - parts B,C,D
• ASME BPVC Section I - Rules for Construction of Power Boilers
• ASME BPVC Section IV - Rules for Construction of Heating Boilers
• ASME BPVC Section V - Nondestructive Examination
• ASME BPVC Section VI - Recommended Rules for the Care and Operation of Heating Boilers
• ASME BPVC Section VII - Recommended Guidelines for the Care of Power Boilers
• ASME BPVC Section VIII - Rules for Construction of Pressure Vessels
• ASME BPVC Section IX - Qualification Standard for Welding, Brazing, and Fusing Procedures; Welders; Brazers; and Welding, Brazing, and Fusing Operators
• ASME BPVC Section XIII - Rules for Overpressure Protection
• ASME BPVC Code Cases - Boilers and Pressure Vessels

 

[Toymaker]

We have standards and codes (ASME) that all pressure vessels above 15psig must comply with. These are based on engineering practice as well as almost 150 years of actual practice, field experience and analysis of in field failures.
Your design operating pressure/temperature do not fall within the AMSE code specifications for the materials you are using.

• ASME-BPVC - the following sections would apply to your project:
• ASME BPVC Section II - Materials - parts B,C,D
• ASME BPVC Section I - Rules for Construction of Power Boilers
• ASME BPVC Section IV - Rules for Construction of Heating Boilers
• ASME BPVC Section V - Nondestructive Examination
• ASME BPVC Section VI - Recommended Rules for the Care and Operation of Heating Boilers
• ASME BPVC Section VII - Recommended Guidelines for the Care of Power Boilers
• ASME BPVC Section VIII - Rules for Construction of Pressure Vessels
• ASME BPVC Section IX - Qualification Standard for Welding, Brazing, and Fusing Procedures; Welders; Brazers; and Welding, Brazing, and Fusing Operators
• ASME BPVC Section XIII - Rules for Overpressure Protection
• ASME BPVC Code Cases - Boilers and Pressure Vessels

In my search for the above ASME-BPVC codes I found the ASME web page where they can be ordered,....in round numbers, your above list would cost me in excess of $10,000 !!! Sure seems like ASME is out to make as much money as they can.

I'm not a boiler company making a profit from sales and repairs of commercial boilers, I'm just a simple retired hobbyist building a boiler for his own enjoyment and satisfaction, so unless ASME has a FREE searchable web site open to non-ASME member-hobbyists like me, I simply cannot afford to learn what their codes and best practices might be...., they're waaaayyy out of my price range.

Guess I'll just have to continue following the laws of physics ,....they're readily available on the internet for free.

 

[Toymaker]

Below is an excerpt from ASME's order form for BPVC Pressure Vessel code for 2021. This is only a partial list of what ASME wants boiler builders to spend so they can follow their codes. I don't know a single hobbyist that could, or would, afford to spend nearly $1000 USD for a single book or pdf file.

Rules for Construction of Power Boilers $540.00
Materials II.A, Ferrous Material Specifications $820.00
Nonferrous Material Specifications $820.00
Specifications for Welding Rods, Electrodes, and Filler Metals $940.00
Properties (Customary) $820.00
Properties (Metric) $820.00

 

[ajoeiam]

In my search for the above ASME-BPVC codes I found the ASME web page where they can be ordered,....in round numbers, your above list would cost me in excess of $10,000 !!! Sure seems like ASME is out to make as much money as they can.

I'm not a boiler company making a profit from sales and repairs of commercial boilers, I'm just a simple retired hobbyist building a boiler for his own enjoyment and satisfaction, so unless ASME has a FREE searchable web site open to non-ASME member-hobbyists like me, I simply cannot afford to learn what their codes and best practices might be...., they're waaaayyy out of my price range.

Guess I'll just have to continue following the laws of physics ,....they're readily available on the internet for free.

I remember looking at the pricing for the ASME boiler code and it was some $7k but that's some 20 years ago.

Standards pricing isn't about affordability - - - - its to promote obfuscation!

I wonder if part of the logic isn't - - - - obscure the crap out of something, standardize the snot out of it, inspect the profit out of it all in the name of 'keep everyone safe'. (I don't think this works but then I don't have the money to challenge any of this mountain of info!!)

 

[Toymaker]

I remember looking at the pricing for the ASME boiler code and it was some $7k but that's some 20 years ago.

Standards pricing isn't about affordability - - - - its to promote obfuscation!

I wonder if part of the logic isn't - - - - obscure the crap out of something, standardize the snot out of it, inspect the profit out of it all in the name of 'keep everyone safe'. (I don't think this works but then I don't have the money to challenge any of this mountain of info!!)

Perhaps when ASME was first founded it was meant to help boiler makers, whom had great fabrication skills but were light on metallurgy, math and physics, make safe boilers that didn't go boom. And to ensure those old boilers never went boom, even when the welds aren't quite as good as they should be, and quality of the steel wasn't as good as it was sold to be, they made the safety factors ridiculously high. Fast forward to today; If NASA followed ASME rules for pressure vessels for their LOX and fuel tanks, none of their rockets would ever lift off the pad,...they would be far too heavy. This should be proof enough that safe, reliable pressure vessels can be made with much smaller safety factors than those listed by ASME.

I believe somewhere on ASME's time-line they became more interested in profit than in good engineering. Perhaps after a few states passed laws mandating ASME codes be followed or you couldn't get certified and sell your boilers, ASME realized they could charge as much as they wanted for copies of their standards. Following codes and standards with built-in safety factors of 8 will certainly ensure a boiler wont explode, but IMHO, just blindly following codes and standards isn't good engineering; the engineers at NASA, Space X, etc prove this with ever launch.