Monotube Flash Boiler Design

[Steamchick]

For this specific post, I'm putting our views of what is and is not safe from a physics viewpoint aside, and looking strictly at what is law. Also, I'm not a lawyer and I'm not providing legal advice.

Within the United States, so far as I'm aware, there are no federal laws requiring ASME codes or standards be followed, they are completely voluntary . However, some states have enacted laws requiring ASME and other organizational codes and standards be adhered to, so builders should consult their state laws.

In Thailand, where I live, the governing standards body is TISI (Thai Industrial Standards Institute). I cannot find any standards regarding boilers or even "steam".

OK. It is good to obey the law where there are laws regulating what we do.
But I just follow the Laws of Physics first (So my efforts at making things do not break easily!) and then use anyone's standards and regulations where they have a strong Engineering background (better than my education and ability) as curiously, things like ASME regulations have a lot of simplified Engineering in them. (e.g. it is very difficult to work out appropriate stress concentration factors, so ASME just use "3.3" for simple SCF applied to material stresses of Steam boilers with penetrations). However, I will deviate in special cases where the "global" assumptions are not very appropriate.
There are loads of technical papers - by some very clever and able people - that explain lots of equations to be used in special cases, so I use those as well, if I find something suitable. e.g. I recently found a method of determining the stress in a rectangular tube subjected to internal pressure. This suited a model I was given that used extruded rectangular brass as a boiler tube.... so I did the calculations and they were a better result than my previous "estimations" - but confirmed rather than changed my NWP of that boiler.
I thought your fabricated spiral radiation plate was ingenious, but just needed thick copper sides to withstand your proposed system pressure... Assembly is difficult, as you explain, but that is something within your workshop and skill capabilities - or not - as suits. I would have considered using a paste flux and brazing filler material. Oven Brazing is a process I have worked with in industry - assemblies of steel pipes were made on jigs with Brazing paste, then passed through a long oven by conveyor to heat and cool in a controlled cycle and all the finished parts were pressure tested. Statistically, they had less than 20 pieces per million failed. A very controllable process, not requiring a high skill level.
Enjoy the "hobby", and keep on with your very ambitious designs. I enjoy the discussions and learn a lot from you.
K2

 

[ajoeiam]

For this specific post, I'm putting our views of what is and is not safe from a physics viewpoint aside, and looking strictly at what is law. Also, I'm not a lawyer and I'm not providing legal advice.

Within the United States, so far as I'm aware, there are no federal laws requiring ASME codes or standards be followed, they are completely voluntary . However, some states have enacted laws requiring ASME and other organizational codes and standards be adhered to, so builders should consult their state laws.

In Thailand, where I live, the governing standards body is TISI (Thai Industrial Standards Institute). I cannot find any standards regarding boilers or even "steam".

Well - - - - you may not be finding 'laws' but just go talk to an insurance company.

You will be quite quickly disabused of the idea that there aren't laws.

For most of us if we can't get insurance to cover the place where we live or work will not engage in a behavior that might jeopardize said insurance so even if there are no direct laws - - - in effect - - - there are.

 

[Toymaker]

Well - - - - you may not be finding 'laws' but just go talk to an insurance company.

You will be quite quickly disabused of the idea that there aren't laws.

For most of us if we can't get insurance to cover the place where we live or work will not engage in a behavior that might jeopardize said insurance so even if there are no direct laws - - - in effect - - - there are.

The Insurance contract you must sign before you are issued an insurance policy is a legally binding contract, and, yes, you are legally bound by whatever conditions are spelled out in that contract.

However, I'm at a complete loss to understand what clause in you homeowners insurance policy might be a cause for concern should your hobby steam boiler cause any damage to your home. I've owned homes in both Florida and Arizona in the US and don't recall any policy clause that would have been a cause for concern should any of my jet engine projects gone sideways.

 

[Toymaker]

OK. It is good to obey the law where there are laws regulating what we do.
But I just follow the Laws of Physics first (So my efforts at making things do not break easily!) and then use anyone's standards and regulations where they have a strong Engineering background (better than my education and ability) as curiously, things like ASME regulations have a lot of simplified Engineering in them. (e.g. it is very difficult to work out appropriate stress concentration factors, so ASME just use "3.3" for simple SCF applied to material stresses of Steam boilers with penetrations). However, I will deviate in special cases where the "global" assumptions are not very appropriate.
There are loads of technical papers - by some very clever and able people - that explain lots of equations to be used in special cases, so I use those as well, if I find something suitable. e.g. I recently found a method of determining the stress in a rectangular tube subjected to internal pressure. This suited a model I was given that used extruded rectangular brass as a boiler tube.... so I did the calculations and they were a better result than my previous "estimations" - but confirmed rather than changed my NWP of that boiler.
I thought your fabricated spiral radiation plate was ingenious, but just needed thick copper sides to withstand your proposed system pressure... Assembly is difficult, as you explain, but that is something within your workshop and skill capabilities - or not - as suits. I would have considered using a paste flux and brazing filler material. Oven Brazing is a process I have worked with in industry - assemblies of steel pipes were made on jigs with Brazing paste, then passed through a long oven by conveyor to heat and cool in a controlled cycle and all the finished parts were pressure tested. Statistically, they had less than 20 pieces per million failed. A very controllable process, not requiring a high skill level.
Enjoy the "hobby", and keep on with your very ambitious designs. I enjoy the discussions and learn a lot from you.
K2

I too prefer following the laws of physics when calculating safe limits. My boiler design is a good example; the working pressure for 5/8" diameter copper tube I use in my boiler is listed at 537 psi in this chart: Type L Copper Tube. However, using Barlow's formula and the yield strength of copper results in an allowable pressure of 1198 psi just to reach the yield limit. So, the working pressure value listed in the chart incorporates a safety factor of 2.2 to arrive at their 537 limit. Also, remember that yield strength is defined as the force needed to permanently deform the copper, not break it; in a boiler tube, that means permanently cause it to "balloon" and lengthen, but not burst.

Including the effects of temperature, copper retains 85% of it's yield strength at 200 C. 85% of the listed working pressure of 537 psi results in a 456 psi which is below my boiler design pressure of 500 psi. Using only the working pressure numbers make my boiler design appear unsafe.

However, the laws of physics tell a slightly different story. The yield strength of copper drops from 9366 psi at 66 C down to 7961 psi at 200 C. Using Barlow's equation with the lower yield strength results in an yield pressure limit of 1019 psi, which is a safety factor of just over 2. These numbers look quite safe to me.

The point I'm trying to make is that using working pressure values will certainly keep your design as safe as possible, but not strictly adhering to working pressures doesn't necessarily make a design unsafe. I pay a lot more attention to the ultimate tensile strength and yield strength values.

Finally, my boiler design incorporates two pressure sensors monitored by a computer which limit max pressure to 500 psi, in parallel with a mechanical pop valve also limiting pressure. Certainly failures can always occur, but I believe my design has more than adequate safety measures.

 

[Steamchick]

OK. Your decision. You have knowledge and it's your head nearer to the plant when in service. I am aware that NASA use different standards for their pressure vessels that they launch into the sky... and the Astronauts are happy to rely on the limits they use. (Although there have been a few who sadly didn't survive). Which tells us that sometimes it is another system that fails first and causes the pressure vessel to fail.
But COPPER Steam Boilers have been built with a standard factor of safety of 8 since before 1900... Those are the safe ones that Insurance companies based their premiums on... and the FOS of 8 has been commonplace for COPPER Steam Boilers at boiler temperatures and pressures in Standards since I was a lad (1960s) or earlier.
Hence I only recommend what we do in the UK and other countries this side of the planet.
Cheers,
K2

 

[Toymaker]

OK. Your decision. You have knowledge and it's your head nearer to the plant when in service.
<snip>
But COPPER Steam Boilers have been built with a standard factor of safety of 8 since before 1900... Those are the safe ones that Insurance companies based their premiums on... and the FOS of 8 has been commonplace for COPPER Steam Boilers at boiler temperatures and pressures in Standards since I was a lad (1960s) or earlier.
Hence I only recommend what we do in the UK and other countries this side of the planet.
Cheers,
K2

K2, specifically, what number are you recommending that I multiply by 8?

I used Yield strength values in post #64, so lets now look at Ultimate Tensile values.

Google searches found the copper pipe industry lists current copper alloys used in copper pipe as having an ultimate tensile strength of 35,000 psi. Copper Tube
Barlow's formula (P=2ST/D) shows the actual burst pressure for my 5/8" copper tube as 4,480 psi at room temperature. At my max temperature of 200 C the copper alloy will retain 90% of it's strength, so 0.9 x 4,480 = 4,032

My max design pressure is 500 psi, so my Safety Factor above the actual burst pressure = 4,032/500 = 8.06.

 

[Steamchick]

Hi Toymaker, OK.
I accept you have done the sums... and have a Factor of Safety of >8 at room temperature: I am VERY HAPPY that you understand it so well.
But on what basis did you consider the reduction of UTS at your max working temperature? ("At my max temperature of 200 C the copper alloy will retain 90% of it's strength, so 0.9 x 4,480 = 4,032").
ASME recommend a "Max. permissible stress" limited according to a table of stress versus temperature, so that is what I use. (It is NOT the law as used in the UK, just the best information I have, that I can trust).
Their Temperature adjusting table gives:
Max permissible stress
- at 350deg.F - 3500psi,
- at 400deg.F. - 3000psi
- At room temperature = 6700psi (against the UTS for Copper of 35000psi includes a FOS of 5.22 - which confuses me as it isn't the magic FOS of "8" that I was taught 30+ years ago.. - But I may have used 230MPa, = 33359psi, as the UTS...).

Anyhow, I would extrapolate your 200deg C to 392deg.F. and a Permitted stress of ~3090psi (is this reasonable?), so the hoop stress (Barlow's) would calculate a "Normal working pressure limit" as 395psi. to ASME limits.
= around 80% of your NWP of 500psi.
- so I think it would be 80% of your FOS. = 6.45?
So this is SAFE, just not quite as safe as ASME would recommend, if I have done the sums correctly.

The Boiler inspector at my local club has been teaching me a bit about this and some boilers, to traditional "approved" designs, have a FOS as low as 6.... but a long history of well built boilers being safe. So I am not worried about the intrinsic strength of your designs as per the calculations you have shown. - They are what I use. But I would simply use ASME limits for new designs. I think that is "QED"?
I am just an amateur - learning from your expertise, so I do want you to appreciate that and I am asking the questions so I can learn. I am using you to "reverse engineer" my understanding, as VERY FEW really understand all this, and can tell me if I am right or wrong. I do appreciate your help - as I am a bit naughty in playing "devil's advocate" so I can learn from you. It gives me a lot of confidence in MY calculations as yours are really the same.
THANKYOU for your time and patience discussing this with me. I have learned a lot! (e.g. how you use Yield strength and UTS).
I wish you all success with your design and manufacture of this tremendous project.
K2

 

[Toymaker]

Hi Toymaker, OK.
I accept you have done the sums... and have a Factor of Safety of >8 at room temperature: I am VERY HAPPY that you understand it so well.
But on what basis did you consider the reduction of UTS at your max working temperature? ("At my max temperature of 200 C the copper alloy will retain 90% of it's strength, so 0.9 x 4,480 = 4,032").
ASME recommend a "Max. permissible stress" limited according to a table of stress versus temperature, so that is what I use. (It is NOT the law as used in the UK, just the best information I have, that I can trust).
Their Temperature adjusting table gives:
Max permissible stress
- at 350deg.F - 3500psi,
- at 400deg.F. - 3000psi
- At room temperature = 6700psi (against the UTS for Copper of 35000psi includes a FOS of 5.22 - which confuses me as it isn't the magic FOS of "8" that I was taught 30+ years ago.. - But I may have used 230MPa, = 33359psi, as the UTS...).

I'm not sure I fully understand your question,...I think you're asking me where I found the UTS vs Temperature info.
You can find that info here: UTS vs Temp in the form of graph. I've been using 200 C as my max temperature because it's a nice round number, but the actual number I don't want to exceed is 184 C. I read the graph as showing the UTS for copper at 184 C as somewhere between 85% and 90%, and I chose 90% because I recall reading a web page stating the UTS for CuNi30Mn alloy (alloy used to make tube and pipe) has better strength vs temperature ratings than pure copper. You can see from this graph, Yield vs Temp that different copper alloys have very different mechanical properties. So when ASME states a value for copper, which alloy are they referring to? You can see that it makes a difference.

Anyhow, I would extrapolate your 200deg C to 392deg.F. and a Permitted stress of ~3090psi (is this reasonable?), so the hoop stress (Barlow's) would calculate a "Normal working pressure limit" as 395psi. to ASME limits.
= around 80% of your NWP of 500psi.
- so I think it would be 80% of your FOS. = 6.45?
So this is SAFE, just not quite as safe as ASME would recommend, if I have done the sums correctly.

The Boiler inspector at my local club has been teaching me a bit about this and some boilers, to traditional "approved" designs, have a FOS as low as 6.... but a long history of well built boilers being safe. So I am not worried about the intrinsic strength of your designs as per the calculations you have shown. - They are what I use. But I would simply use ASME limits for new designs. I think that is "QED"?
I am just an amateur - learning from your expertise, so I do want you to appreciate that and I am asking the questions so I can learn. I am using you to "reverse engineer" my understanding, as VERY FEW really understand all this, and can tell me if I am right or wrong. I do appreciate your help - as I am a bit naughty in playing "devil's advocate" so I can learn from you. It gives me a lot of confidence in MY calculations as yours are really the same.
THANKYOU for your time and patience discussing this with me. I have learned a lot! (e.g. how you use Yield strength and UTS).
I wish you all success with your design and manufacture of this tremendous project.
K2

Happy to give whatever help I can, just remember that I too am a student of boilers, learning as I go, and I'm bound to make mistakes along the way

 

[peterl95124]

Toymaker, some of us are viewing this endeavor with skepticism, your machining skills are obviously good, that turbine you made looks B.E.A.Utiful !!!, but boilers are another thing, we're trying to advise you to over-design things because you're going into the unknown. imagine for a moment that the turbine sheds a blade for what ever reason, suppose that blade ends up somewhere downstream and blocks the flow, now you've got a gazillion watts of burner heat going into a boiler with no way out, you've got a time-bomb on your hands.

makers of automotive turbo-chargers destructively test their rotors, IE spin them up until they disintegrate, the containment shield for this is often reinforced concrete a foot or two thick. you are making what they would call a "billet rotor", IE one machined from solid bar stock rather than cast, which is good !, they are the strongest (least likely to contain impurities, voids, cracks, etc), but still you don't have the experience or testing equipment they do.

but the biggest red flag is this, you said "Calculated max power output of the turbine is 144 kW, (193 HP)", this is not a model engine, this is a full size engine, the amount of power and energy is orders of magnitude larger than what our model engines consume and produce. when something goes wrong it will be catastrophic, and its not an "if" its a "when" because this is an experimental design. its not that ORC hasn't been done before and is untested, its that this specific design is untested, you aren't making an exact copy of a proven design.

good engineering is not coming up with a design that *can work*, its coming up with a design that *can't fail*, these are two very different things, that many people don't realize. as I read most of your engineering calculations they come across as "can work" rather than "can't fail", which is just my personal opinion and not necessarily correct, but still over-designing is the best option for an unproven design working with this scale of energy and power. IMHO. YMMV. still wishing you the best of luck.

 

[Toymaker]

Toymaker, some of us are viewing this endeavor with skepticism, your machining skills are obviously good, that turbine you made looks B.E.A.Utiful !!!, but boilers are another thing, we're trying to advise you to over-design things because you're going into the unknown. imagine for a moment that the turbine sheds a blade for what ever reason, suppose that blade ends up somewhere downstream and blocks the flow, now you've got a gazillion watts of burner heat going into a boiler with no way out, you've got a time-bomb on your hands.

When any turbine loses a blade while the rotor is spinning the out-of-balance condition of the rotor caused by the missing blade results in near instantaneous, catastrophic turbine destruction. At that time, the boiler is most likely venting steam into the open air because the turbine is in tiny little pieces.

makers of automotive turbo-chargers destructively test their rotors, IE spin them up until they disintegrate, the containment shield for this is often reinforced concrete a foot or two thick. you are making what they would call a "billet rotor", IE one machined from solid bar stock rather than cast, which is good !, they are the strongest (least likely to contain impurities, voids, cracks, etc), but still you don't have the experience or testing equipment they do.

The gas turbine industry calls my rotor with machined blades a "blisk", for "Bladed Disk". Although a blisk is mechanically stronger than a disk with separately machined blades which are inserted into a disk with machined slots, Blisks are more susceptible to harmonic resonance which can also lead to instantaneous, catastrophic turbine destruction.

but the biggest red flag is this, you said "Calculated max power output of the turbine is 144 kW, (193 HP)", this is not a model engine, this is a full size engine, the amount of power and energy is orders of magnitude larger than what our model engines consume and produce. when something goes wrong it will be catastrophic, and its not an "if" its a "when" because this is an experimental design. its not that ORC hasn't been done before and is untested, its that this specific design is untested, you aren't making an exact copy of a proven design.

I posted two pics in post #27 of experimental monotube boilers built by armature, steam car enthusiasts. You may enjoy reading through some of their posts on boilers: SteamAutomobile Very informative.

Monotube boilers typically fail due to a burst tube, like the one in this pic. It's not a catastrophic failure, just a loud bang or pop, followed by a loss of pressure. Also, as shown by Barlow's formula (P=2ST/D) when both S (Yield or UTS) and wall thickness (T) are equal for different boiler designs, than smaller diameter tubes (D) will always result in higher allowable pressure (P) when compared to a tank style pressure vessel.

good engineering is not coming up with a design that *can work*, its coming up with a design that *can't fail*, these are two very different things, that many people don't realize. as I read most of your engineering calculations they come across as "can work" rather than "can't fail", which is just my personal opinion and not necessarily correct, but still over-designing is the best option for an unproven design working with this scale of energy and power. IMHO. YMMV. still wishing you the best of luck.

Good engineering also implements lots of safety measures, especially on an experimental design, which I have done. First, and most importantly, my monotube boiler is fully controlled by a computer (micro controller) which continuously monitors two steam pressure sensors, one on the input side (feed pump output) with the other sensor on the boiler's output. Steam temperature is also monitored at input and output and one sensor inside the boiler where the burner exhaust directly impacts the boiler tubes, which is most likely the hottest section of the boiler. Finally, a fully mechanical pressure relief valve (pop valve) will be fitted into the boiler's output side.

 

[Steamchick]

Hi Toymaker.
Of course you appreciate the risks you are trying to manage "by computer".
And separately have design skills and knowledge to make things "apparently strong enough".
But I wonder what would happen if a tube burst instantaneously inside the Burner/Boiler chamber? What would the pressurised fluid do? - Of course we know it will rapidly boil, expand and totally fill the burner chamber with some very hot metal that will then potentially overheat the fluid.
If this were water - steam then there would simply be a large steam explosion, which is horrible to contemplate, but not as bad as if the R123 at near limiting temperature suddenly hits metal maybe a few hundred degrees hotter.
I don't know how the gas breaks-down (chemically) when superheated??
Does it produce a hot expanding cloud of inflammable but toxic gas? Or is it combustible?

Here's an analogy. Cars, buses, lorries, etc. carry large tanks of hydrocarbon fuel. They also have other fluids - such as Battery acid (Sulphuric), Liquid Coolant containing typically 50% glycol, Hydraulic fluids for Braking, clutch actuation, power steering, transmissions, etc. and oil for engine and transmission lubrication (and cooling). So what is the most dangerous in a crash when the hot exhaust manifold, catalysts etc. are exposed to a pray of some fluid for some containment that is destructively damaged? - Always the Brake and clutch hydraulic fluid. The temperature of the exhaust manifold when driving is so hot that everything flashes off as gas but the brake and clutch fluids are above their flash-point, so instantaneously ignite. No spark, flame, etc, just a spray of fluid onto pure temperature of hot metal... And the spray ignites.
So Car manufacturers, etc. take great care and crash dozens of cars in various ways to ensure that the brake and clutch fluid can almost never be released onto hot manifolds or exhaust metal. But it still happens in real life.
If you were using a nickel steel or stainless steel tube and components in your boiler tubes, etc. then I would be much happier than the use of Copper, even though you are "in control" via calculation of a reasonable factor of safety for water boilers. Simply because you can have a much larger factor of safety without compromising your design. However the manufacture may be more difficult?
Here is a flash boiler - fed by a multi kW Paraffin oil burner - initially pre-heated by a 5kW Propane burner... see attached file.
https://www.onthewire.co.uk/wwind.htm

He uses a nickel steel tubing as far as I know - I don't know what grade.

My reference for safe stress levels in Copper at temperature come from ASME:
I am not sure if the Moderator will permit this link?
2015 ASME Boiler & Pressure Vessel Code (mass.gov)
PART PMB

REQUIREMENTS FOR MINIATURE BOILERS

GENERAL

PMB-1 GENERAL

The rules in Part PMB are applicable to miniature boilers and parts thereof and shall be used in conjunction with the general requirements in Part PG as well as with the special requirements in the applicable Parts of this Section that apply to the method of fabrication used.

PMB-2 SCOPE

PMB-2.1 The classification miniature boilers applies to boilers that do not exceed the following limits:

(a) 16 in. (400 mm) inside diameter of shell (b) 20 ft2 (1.9 m2) heating surface (not applicable to electric boilers)

(c) 5 ft3 (0.14 m3) gross volume,31 exclusive of casing and insulation

(d) 100 psig (700 kPa) maximum allowable working pressure

PMB-2.2 If a boiler meets the miniature classification, the rules in this Part shall supplement the rules for power boilers and take precedence over them when there is conflict. Where any of the limits in PMB-2.1 are exceeded,

the rules for power boilers shall apply.

MATERIALS

PMB-5 GENERAL

PMB-5.1 Unless specifically permitted elsewhere in this Section, materials used in the construction of pressure parts for miniature boilers shall conform to one of the specifications in Section II and shall be limited to those for which allowable stress values are given in Section II, Part D, Subpart 1, Tables 1A and 1B. Miscellaneous pressure parts shall conform to the requirements of PG-11.

https://fastcdn.pro/filegallery/fou...-II-PART-D-METRIC-2019-www.fouladline.com.pdfTry pages 897, and lots of others ... I am Bamboozled just now!).
I hope some of this helps?
K2

 

[Steamchick]

Hi Toymaker,
I have been trying to find out something about high temperature degradation of R123. But have not really found anything yet - except that it says it breaks down to form large quantities of HF and HCl gases. -Hmm, a bit nasty then! Either of these breathed in is likely to cause severe damage to lungs almost instantly, if not terminally. So do you really want to go there?? I.E. putting this in a boiler just seems to be above the "risk factor" in my Engineering life..
I was taught to use a risk factor chart - very simple:
X-axis: Probability of failure - on a log scale, starting at 10E6: ~10E7 = high risk, 10E7 to 10 E 8 medium risk, 10E8 to 10E9 low risk.
Y-Axis: Result of failure - Low = no harm to humans, or just a scratch or tiny bruise.., Medium = anything that would cause a temporary change of life (can't hold a pen, spoon, wipe your bum, etc.) , High = any longer term or more painful effect. (e.g. death, disability, broken bones, strained muscles, joints, mental anguish, etc.).
Then using this table, I don't go into any Medium "result of failure" if I can help it, and want to stay in low risk.
R123 at elevated temperature in your planned boiler may be low risk, but HIGH "result of failure" - So I would not go there.

Just so you understand where I am coming from...
K2

 

[vk7krj]

I'm enjoying following this discussion, and like K2 am learning lots.

But a small but I hope relevant point- as far as I know a copper boiler doesn't normally fail catastrophically, but relatively gracefully (I do emphasize relatively gracefully- we're talking milliseconds instead of microseconds) with the copper tearing rather than fracturing. This allows the pressure to collapse (again) relatively slowly.
Unlike steels which tend to fracture and drop the pressure almost instantaneously, usually with catastrophic results. IE, the entire body of fluid is suddenly at close to atmospheric pressure and can no longer be a liquid, resulting in a big bang!

 

[Steamchick]

Hmmm .. generating a cloud of gas changing from poisonous (unbreathable and likely to cause nervous poisoning) to toxic (it will burn the lungs and cause lung bleeding, possibly death) in milliseconds instead of microseconds still makes me want to keep away..
But is that better than a scalding cloud of steam that cooks the skin and nerve endings, so hurts like hell for weeks?
Probably the same risk that we take without thinking about the 5 inch loco between our knees and what the boiler contains.
I'll stick to motorcycling. Statistically far more dangerous than being a front-line soldier in war...
To put some perspective on the risk.
Life is not without risk, but as Engineers we are responsible to minimise it by calculation, careful manufacture, sensible material selection and control, and controlled use of the finished thing. Is a knife more deadly than a steam boiler? I do not care, I use both carefully. And I have cut a finger and burned another. Both hurt.
K2

 

[GeoffR]

Attached is a copy of a tensile test report on a piece of 'standard' copper sheet I had carried in 2013.
As vk7krj suggests, graceful is a nice description
Shows the very elastic nature of copper.

 

[Toymaker]

Hi Toymaker,
I have been trying to find out something about high temperature degradation of R123. But have not really found anything yet - except that it says it breaks down to form large quantities of HF and HCl gases. -Hmm, a bit nasty then! Either of these breathed in is likely to cause severe damage to lungs almost instantly, if not terminally. So do you really want to go there?? I.E. putting this in a boiler just seems to be above the "risk factor" in my Engineering life..
I was taught to use a risk factor chart - very simple:
X-axis: Probability of failure - on a log scale, starting at 10E6: ~10E7 = high risk, 10E7 to 10 E 8 medium risk, 10E8 to 10E9 low risk.
Y-Axis: Result of failure - Low = no harm to humans, or just a scratch or tiny bruise.., Medium = anything that would cause a temporary change of life (can't hold a pen, spoon, wipe your bum, etc.) , High = any longer term or more painful effect. (e.g. death, disability, broken bones, strained muscles, joints, mental anguish, etc.).
Then using this table, I don't go into any Medium "result of failure" if I can help it, and want to stay in low risk.
R123 at elevated temperature in your planned boiler may be low risk, but HIGH "result of failure" - So I would not go there.

Just so you understand where I am coming from...
K2

R123 is only one of many Freons and organics such as ammonia, benzene, and toluene which have all been used as a working fluids in place of water. Here's a review of different working fluids: Organic Working Fluids

 

[ajoeiam]

R123 is only one of many Freons and organics such as ammonia, benzene, and toluene which have all been used as a working fluids in place of water. Here's a review of different working fluids: Organic Working Fluids

bummer - - - - its hiding behind another - - - - "log in so we can bomb you" wall.

Do you actually have a copy?

 

[Toymaker]

bummer - - - - its hiding behind another - - - - "log in so we can bomb you" wall.

Do you actually have a copy?

Below is the page I get when I click on the link,...did you try clicking on "See Full PDF" or "Download PDF" buttons?

 

[Toymaker]

Hi Toymaker.
Of course you appreciate the risks you are trying to manage "by computer".

One of my "work life" jobs was to design, build, & test ECU (Engine Control Units) for gas turbine engines (aka jet engines) the small team I was a member of mostly worked on military engines for the F18 and F16 aircraft. So, yes, I'm very comfortable managing engines with a computer.

And separately have design skills and knowledge to make things "apparently strong enough".

That area is still "a work in process". I took a "Statics and Strength of Materials" course in college, but as an electronic engineer, I never used any of what I learned in that class,...so zero real world experience.

But I wonder what would happen if a tube burst instantaneously inside the Burner/Boiler chamber? What would the pressurised fluid do? - Of course we know it will rapidly boil, expand and totally fill the burner chamber with some very hot metal that will then potentially overheat the fluid.
If this were water - steam then there would simply be a large steam explosion,

Look at the photo in post #70. That's all that will happen when a monotube pipe ruptures. There's no large steam explosion.

which is horrible to contemplate, but not as bad as if the R123 at near limiting temperature suddenly hits metal maybe a few hundred degrees hotter.
I don't know how the gas breaks-down (chemically) when superheated??
Does it produce a hot expanding cloud of inflammable but toxic gas? Or is it combustible?

Here's an analogy. Cars, buses, lorries, etc. carry large tanks of hydrocarbon fuel. They also have other fluids - such as Battery acid (Sulphuric), Liquid Coolant containing typically 50% glycol, Hydraulic fluids for Braking, clutch actuation, power steering, transmissions, etc. and oil for engine and transmission lubrication (and cooling). So what is the most dangerous in a crash when the hot exhaust manifold, catalysts etc. are exposed to a pray of some fluid for some containment that is destructively damaged? - Always the Brake and clutch hydraulic fluid. The temperature of the exhaust manifold when driving is so hot that everything flashes off as gas but the brake and clutch fluids are above their flash-point, so instantaneously ignite. No spark, flame, etc, just a spray of fluid onto pure temperature of hot metal... And the spray ignites.
So Car manufacturers, etc. take great care and crash dozens of cars in various ways to ensure that the brake and clutch fluid can almost never be released onto hot manifolds or exhaust metal. But it still happens in real life.
If you were using a nickel steel or stainless steel tube and components in your boiler tubes, etc. then I would be much happier than the use of Copper, even though you are "in control" via calculation of a reasonable factor of safety for water boilers. Simply because you can have a much larger factor of safety without compromising your design. However the manufacture may be more difficult?
Here is a flash boiler - fed by a multi kW Paraffin oil burner - initially pre-heated by a 5kW Propane burner... see attached file.
https://www.onthewire.co.uk/wwind.htm< Big Snip>
I hope some of this helps?
K2

Thanks for you concerns,...I'll manage the risks as best I can.

 

[ajoeiam]

Below is the page I get when I click on the link,...did you try clicking on "See Full PDF" or "Download PDF" buttons?

View attachment 148124

Exactly what I see - - - - when I click on either the 'see full' or 'download' button I am directed to the either 'log in or sign up' page.