Monotube Flash Boiler Design

[Steamchick]

Toymaker, Just a comment on "Horrible design" in my previous post. It is not just the array of tubes with fabricated corners that troubles me a bit, but as I learned lessons in industry, and "why" industrial standards are what they are, I feel I should remind you of some of the facts about copper, steam, etc.
ASME (The American Society of Mechanical Engineers) are an erstwhile body of that nation's top - and possibly most sensible - engineers. SO if they tell me that they do not condone braze fabricated copper assemblies over 400degrees F. (about 200deg.C). = steam at 100psi - then I take that as a sensible limit. It can (is) argued that their factors of safety are "too high", but the facts are that copper loses strength very rapidly with temperature. They set a permissible stress limit for copper at 6700psi at below 100 degrees F, yet - because the copper is so weak at elevated temperature - the permissible stress limit at 400 deg. F is only 3000psi. - The tube you are using is probably supplied for system pressure of 6 bar at "room" temperature, - which would relate to a Normal working pressure of 2.68bar (39psi) at 400deg. F. (<45% of the room temperature stress - because it is copper). Yet you are talking of operating at 34 bar. = 500psi. I.E. 5 times the permissible room temperature stress. Or 12.7 times the elevated temperature permissible stress for 200deg.C. - or 168 times the ASME permissible stress limit?
This just sounds crazy to me, so I am not trying to scare you at all. Simply remind you that your expedient copper tube solution to making a boiler, may be expecting a bit too much? - Please re-check your calculations of all this.
Incidentally, NASA ignore ASME design limits - because they can calculate everything to the extremity of man's capability, then manufacture with the utmost care, with the best materials and processes, and they can afford the failures that occur. - But I work to ASME limits because I am not NASA.
K2

 

[Toymaker]

Custom Pressure Connectors:

As a way to make my experimental boiler project easier to move around and make changes to for testing, I made a few custom pressure fittings for both boiler input and output. Two new fittings (connectors) are essentially M22 pressure washer fittings made to different sizes. The other change was made to the AN-10 flare fitting's beveled face and I posted a separate thread on that topic here: Sealing AN flare Fittings

Below is a pic of the feedwater input connections; what looks like an AN fitting on the left, with the blue nut is actually a quick disconnect fitting which slides into the inside of the AN-10 male fitting, as shown in the next photo. The aluminum block labeled "IN" also has the pressure sensor and temperature sensor.

The Blue nut needs to be only finger-tight to get a good seal for at least 1000 psi.

Both input and output connections are shown below. The steam output connection design is the same as the input, except the output diameter is larger.

This final photo below shows the output quick connector disassembled. The black rubber O-rings seen below have already been replaced with high temperature red silicone O-rings.

 

[Steamchick]

Hi Toymaker,
I was getting crossed-wires a bit...
Your original premise was to use R123 at 500psi. And constrain the temperature to below 183C - or something.... (hidden in earlier posts).
Of course this is within the "operating temperature limit" of copper tube (200C), but still means the "tensile strength limit" - according to ASME - has been reduced from 6700psi at room temperature (as domestic water piping) to around or below 3000psi for the metal temperature (perhaps 30~35 deg.C hotter than the fluid being heated?) that you'll have for a fluid at around 180deg.C....
But if you try and simulate this with a steam test, to achieve 500barg you will be up over 260C (Steam temp) and may have a metal temp as high as 300C... which I think is over the annealing temperature of copper (500deg.F?), so you cannot consider the tube to be as strong with steam at 500psi as with R123 at 500psi.
But I'm still worried that you want to operate what looks like "6 bar domestic copper tube" at around 34 bar with elevated temperature so the tensile strength is reduced below 45% of "normal use"...
N.B. I figure that you are trying to work at more than 11 times the "manufacturer's rating" for the tube. From this I expect it to fail when very hot and at high pressure. What is the highest hydraulic pressure you have reached at room temperature? Multiply that by 0.45 and you have simulated the pressure you have proven at the elevated temperature stress condition.
I am curious to fully understand this engineering. You did state initially that "I’m a retired electronics engineer with almost no formal education in thermodynamics. All the meager knowledge I have on boiler design comes entirely through self-learning. So don’t take anything I state as being 100% accurate. Which means I’m open to advice, critique and suggestions,... which I may, or may not take", but I suggest you take heed of this matter about the strength of COPPER for the tubes you are using. I have not even considered stress concentrations and how they affect the design...
Please take care. I do not want you to have a failure...
K2

 

[Toymaker]

Hi Toymaker,
I was getting crossed-wires a bit...
Your original premise was to use R123 at 500psi. And constrain the temperature to below 183C - or something.... (hidden in earlier posts).
Of course this is within the "operating temperature limit" of copper tube (200C), but still means the "tensile strength limit" - according to ASME - has been reduced from 6700psi at room temperature (as domestic water piping) to around or below 3000psi for the metal temperature (perhaps 30~35 deg.C hotter than the fluid being heated?) that you'll have for a fluid at around 180deg.C....
But if you try and simulate this with a steam test, to achieve 500barg you will be up over 260C (Steam temp) and may have a metal temp as high as 300C... which I think is over the annealing temperature of copper (500deg.F?), so you cannot consider the tube to be as strong with steam at 500psi as with R123 at 500psi.
But I'm still worried that you want to operate what looks like "6 bar domestic copper tube" at around 34 bar with elevated temperature so the tensile strength is reduced below 45% of "normal use"...
N.B. I figure that you are trying to work at more than 11 times the "manufacturer's rating" for the tube. From this I expect it to fail when very hot and at high pressure. What is the highest hydraulic pressure you have reached at room temperature? Multiply that by 0.45 and you have simulated the pressure you have proven at the elevated temperature stress condition.
I am curious to fully understand this engineering. You did state initially that "I’m a retired electronics engineer with almost no formal education in thermodynamics. All the meager knowledge I have on boiler design comes entirely through self-learning. So don’t take anything I state as being 100% accurate. Which means I’m open to advice, critique and suggestions,... which I may, or may not take", but I suggest you take heed of this matter about the strength of COPPER for the tubes you are using. I have not even considered stress concentrations and how they affect the design...
Please take care. I do not want you to have a failure...
K2

K2, you're over-thinking the use of water as a test fluid. I'm very aware that water doesn't have the same thermal properties as R123, if it did, I wouldn't need to use R123. The purpose of using water as a test fluid is NOT to test the boiler to it's maximum limits, but rather to ensure that it's not leaking anywhere and to test the ECU and it's software to ensure the computer is controlling everything as planned. Testing will proceed in steps, starting with low pressures, then gradually increasing the pressures while insuring max temperatures are not exceeded.

What do you mean by "domestic copper tube"? My understanding is that copper tube is specified as either Type K, M, or L, and all three can be considered "domestic".

 

[HMEL]

K2, you're over-thinking the use of water as a test fluid. I'm very aware that water doesn't have the same thermal properties as R123, if it did, I wouldn't need to use R123. The purpose of using water as a test fluid is NOT to test the boiler to it's maximum limits, but rather to ensure that it's not leaking anywhere and to test the ECU and it's software to ensure the computer is controlling everything as planned. Testing will proceed in steps, starting with low pressures, then gradually increasing the pressures while insuring max temperatures are not exceeded.

What do you mean by "domestic copper tube"? My understanding is that copper tube is specified as either Type K, M, or L, and all three can be considered "domestic".

K2 is absolutely correct. R123 heat of vaporization is about 70 btu/lb while that of water is 800 btu/lb give depending of course on incoming temperature and pressure. You are getting lots of cooling using water which you will not get with R123. Wall temperatures will sky rocket when you switch to R123 and the tubes will fail due to overheating. Does not matter what grade of copper you have at that point. Using water tells you only its not leaking with water. I also expect that the R123 will break down into chlorine gas or acids at the proposed operating temperatures. That is my opinion after looking at the chemistry ant operating temperatures proposed.

 

[Toymaker]

K2 is absolutely correct. R123 heat of vaporization is about 70 btu/lb while that of water is 800 btu/lb give depending of course on incoming temperature and pressure. You are getting lots of cooling using water which you will not get with R123. Wall temperatures will sky rocket when you switch to R123 and the tubes will fail due to overheating. Does not matter what grade of copper you have at that point. Using water tells you only its not leaking with water. I also expect that the R123 will break down into chlorine gas or acids at the proposed operating temperatures. That is my opinion after looking at the chemistry ant operating temperatures proposed.

I explained the differences you're pointing out in the first post in this thread. Your above comparison assumes the same flow rate for water and R123, which it wont be. I will need to have a bit over 10 times the flow rate for R123 as would be needed for water. The 10x increased flow of R123 will provide the same cooling capacity of water with a much slower flow. BTW, the need for much higher flow with R123 is the reason I built the steam driven centrifugal feed pump, as centrifugal pumps are known for their high flow rates.

 

[Toymaker]

The ugly copper strip shown in the photo was added to the copper tube maze-like structure for additional strength.
I'm a bit reluctant to post this photo because it's sooooo bloody ugly,....but it does show that even ugly brazing jobs can still be strong enough to hold 1000 psi, which I tested it to.

 

[Steamchick]

Hi Toymaker,
As I (we on this site?) only have what you explain on the various posts, and don't have all the information, then we can only comment on what we read and see in photos.
My mis-understanding was first in thinking you were going to include a test at 500psi with the burner making steam, at some point in the procedure. Then I figured you were only hydraulically testing at 500psi / 1000psi with cold water to "simulate" the stresses of the R123 at 500psi (a lower temperature).
Therefore I was correcting my analysis - and (I thought - maybe wrongly?) that putting the stresses that the copper can manage as "relative pressures" would make the understanding easier. - I got that bit wrong.
But the principle I was presenting is irrefutable. Copper at 180deg.C is only 44% of the strength of copper at 20deg.C. from all the data I have seen on the web. e.g.

So IF (You can clarify this) you are using "Domestic" copper tube, - I.E. wall thickness - that is RATED for 6 bar max, then at 180deg.C it is ONLY rated at 2.64bar (37psi) working pressure. But you want to run at 34bar (500psi) working pressure = 13 times the Manufacturer's rating.
To put it another way, the "Test pressure" at 20deg. C needs to be 2.3 times the working pressure to simulate the stresses at the elevated temperature. I.E. 2.3 x 500 = 1150psi. So well done on testing at 100psi, but please consider testing at an hydraulic test pressure representing "Twice" the stress level of NWP at elevated temperature - as is common practice - I.E 2 x 1150 = 2300psi.
I am sorry if you do not like the advice, but for me, the job is NOT yet proven to be safe.
But if you tell me the wall thickness is much thicker than "domestic" copper piping then that changes the equation. - Or if the tube is a nickel alloy, - or something.... But it LOOKS like domestic copper tubing. I am guessing, because I cannot see the wall thickness, but am assuming that it is about 1/2inch bore domestic pipe, based on the original drawing dimensions for the burner and heat exchanger coils. - the photo shows something like a 5" wide array for 8 tubes + 1/8" gaps?
0.5% Yield stress (COLD) is shown here as 20,000psi:
https://www.copper.org/applications.../technical-discussion/fundamentals/intro.htmlThat would mean a max permissible stress at your working temperature of 180deg.C of 8800psi. (Extrapolating from some ASME data).
Also: Not necessarily a "game stopper", but another factor that increases stress in the assembly. - whatever the material: The stress concentration in the inside corner of Mitred bends is somewhere between 2.5 and 5. I.E. there is at least 2.5 times the stress in the corner of the mitre that there is in the nearby straight pipe.
https://www.researchgate.net/public...ssurized_Multiple_90_Degree_Mitred_Pipe_BendsSo supposing the limiting stress at elevated temperature is 8800psi for straight tube, for the mitred bends you are further limited to dividing this by at least 2.5 => a Max. Permissible Stress in the copper/joint of 3520psi.
This should be further reduced to provide some factor of safety. - What have you used in your calculations?
And as the stress concentration factor analysis is not an exact science, you should consider if the assembly will fail with the Higher SCF of 5 (for corners unsupported by the tie - Can you tie the other end of the array?). The ties I suggested for BOTH ends should mitigate this to some degree, but I cannot assess the effect.
Notwithstanding, the major issue I have - in calling it an "horrible" design - is that the copper is likely to fail at 500 psi and elevated temperature, if you are using "domestic" copper pipe. Hence I advise you to re-asses the design to make it safer for you. Perhaps a stainless steel assembly? or other material? Or much thicker-walled copper tube?
I can only advise my opinion, as you asked for our opinions in your original post.
Cheers,
K2

 

[Toymaker]

Hi Toymaker,
<snip>
So IF (You can clarify this) you are using "Domestic" copper tube, - I.E. wall thickness - that is RATED for 6 bar max, <snip>

Cheers,
K2

I have no idea where you're able to find copper tube rated at only 6 bar,...it must be paper thin. Even Type M copper tube, which has the thinnest wall available for purchase, is rated at above 27 bar at 100F. Keep in mind that down here in the tropics of Thailand, 100F is very nearly room temperature,....it's currently 90F today,...and this winter. So, the temperature I've been most recently testing at is only 10 degrees F lower than 100F,....keep that in mind when you look at this chart: Pressure for Type M
All my tubing is 5/8" (16mm) OD, which is the one size not listed on the chart, so we'll need to approximate the psi value between 1/2" and 3/4" which should be close to 450 psi for annealed. So, this chart is telling me that the NWP of the 5/8" copper tube I'm using is only 450 psi for annealed and 725 psi for drawn at 100F. Something is clearly wrong, as I've already shown that the 5/8" copper tube I'm using easily holds 1000 psi at nearly 100F.
I believe the most likely reason for the discrepancy is that the copper tube I'm using isn't pure copper, but rather a copper alloy, and one which I do not have any data for.

Bottom line; I'm most likely using a copper alloy of unknown temperature-pressure characteristics.

 

[Steamchick]

There is another perspective. The Manufacturer's rating is based on National Regulations (somewhere) so he quotes that for all his sales. Any National Regulations will incorporate some safety margin built-in. But the technicalities are determined by experts in metallurgy and Engineering, so maybe they have a view (expressed in Regulations) worthy of consideration? Do you know any better? - I do not.
Copper tubing in the UK for domestic use has always been considered "6 bar" tubing, as that is the supposed max. mains pressure.
https://www.engineeringtoolbox.com/copper-tube-working-pressure-d_20.htmlManufacturers always supply the minimum metal they can achieve to get the certificate, then charge as much as the market will pay. - That's life.
For "sound engineering" you should work on "Annealed" values of the table, as you do not know the state of hardening you have, or will have when in the working boiler... The hardening you will be getting by pumping and relaxing the tube as you pressurise it will certainly help your factor of safety...
But all the guys I have met (and books I have read) AVOID copper tube for flash boilers, because they KNOW to do so. I have no experience, but can only advise based on material properties, etc. - Which you don't seem to know...? "one for which I do not have any data - either"!! (In that case, assume Annealed Copper and accept the benefit of any additional strength?). It says so in the table:
"When brazing or welding is used to join drawn tube, the corresponding annealed rating must be used."
You used: "to approximate the psi value between 1/2" and 3/4" which should be close to 450 psi for annealed."
But I am a different Engineer, and my experience tells me to use the value AT YOUR WORKING TEMPERATURE. Nearest is 350deg.F. in the table, but I think you are nearer to 365F, so should be further de-rated...
I.E. the mean of the values is ~300psi... - And you are happy to consider contain R123 (at close to degradation temperature) at 500psi...
Boiler work (calculations by others, on other copper boilers) suggests the metal temperature in working boilers at around the same temperature as yours, will be between 20deg.C and 40deg.C higher than the fluid temperature. So it is not unreasonable for you to design your boiler for limiting stress for "copper at 450F". But the table ends at 400deg.F... possibly because they do not want their products used above 400deg.F? (Or any liability for failures, so safer not to mention it at all!). - 400deg.F. would rate your tube for 225psi internal pressure.... NOT 450psi. (I.E. rated for less than half your working pressure).
I have previously explained a test pressure of 2400psi... based on my Boiler design information. Can you do it? I think your boiler will burst. - And that is not a factor of safety of 8, or 6, but 2.
Some people tune cars for racing, and when the cars break and they get hurt - or killed - people have blamed "engineers" for making things un-safe. Too late. The hurt has happened. Good Engineers predict and design to avoid failure. So I cannot condone your design as I know it.

K2

 

[Toymaker]

<snip>
But all the guys I have met (and books I have read) AVOID copper tube for flash boilers, because they KNOW to do so.
<snip>

K2

I posted these two photos back in post #27, showing two different monotube boilers, both using copper tubes and both operating at around 450F at 400psi. I also noted that quite a few steam auto DIY builders construct what they call 400 x 400 monotube boilers using copper tube; i.e. 400 psi at 450F. At least one builder I read about in the SteamAutomobile forums, used 3/8" copper tube with a 0.020" wall thickness. Many of these builders have been running their boilers for years without problems. This SteamAutomobile hot link will take you to a thread titled, "How would I build my boiler" and discusses Flash Boilers. If you really want to learn about monotube boilers, read through their thread, and learn from their experience.

You see, I know my design will work, with copper,... because others have already proven that it will.

 

[HMEL]

I explained the differences you're pointing out in the first post in this thread. Your above comparison assumes the same flow rate for water and R123, which it wont be. I will need to have a bit over 10 times the flow rate for R123 as would be needed for water. The 10x increased flow of R123 will provide the same cooling capacity of water with a much slower flow. BTW, the need for much higher flow with R123 is the reason I built the steam driven centrifugal feed pump, as centrifugal pumps are known for their high flow rates.

You will be dealing with gas flow. The probability is high because of the sharp turns in the assembly choke flow will occur and flow will be limiting. And velocity is part of the heat transfer calculations. Because it works on water does not mean its going to work with R123. You will have a higher velocity, lower contact times, hotter internal wall temperatures with a material that will not stand elevated temperatures and pressures. Yes you can test for leaks for water but that is about all. Its either built for water or its built for R123 two different design points. Very different design points!

 

[user 52078]

I think we might have a problem with units or trailing zeros on the strength of copper tube. I am working from the UK BSS catalogue which gives 6mm BS2871 Table X tube a max working pressure of 133 BAR which would agree with the link in K2's post 370. So we are a long way from 6 Bar.
Discuss.

Martin

 

[Toymaker]

You will be dealing with gas flow. The probability is high because of the sharp turns in the assembly choke flow will occur and flow will be limiting. And velocity is part of the heat transfer calculations. Because it works on water does not mean its going to work with R123. You will have a higher velocity, lower contact times, hotter internal wall temperatures with a material that will not stand elevated temperatures and pressures. Yes you can test for leaks for water but that is about all. Its either built for water or its built for R123 two different design points. Very different design points!

Higher fluid flow velocity does mean lower contact time, but that condition does not produce hotter internal wall temperatures, in fact, just the opposite.

Let's do a little thought experiment: lets direct a blow torch to heat a metal pipe. Water is flowing though the pipe at a rate of one gallon per minute, and the pipe is dimly glowing red hot from the torch. Now, increase the water flow rate through the pipe up to 10 gallons per minute; the water inside the pipe is now moving 10 times faster then it was at one gallon per minute, leading to the water now having a much shorter contact time with the pipe walls. Your assertion that fluids having higher flow velocity, shorter contact time, will lead to the pipe actually getting hotter, and glowing an even brighter red, with the higher flow rate just doesn't make a lot of sense. Higher flow rates result in greater cooling, not less.

 

[Toymaker]

I think we might have a problem with units or trailing zeros on the strength of copper tube. I am working from the UK BSS catalogue which gives 6mm BS2871 Table X tube a max working pressure of 133 BAR which would agree with the link in K2's post 370. So we are a long way from 6 Bar.
Discuss.

Martin

I THINK, K2's use of the term "6 Bar" is simply a label used by plumbing suppliers in the UK, and actually refers to the max pressure used by city water pumping stations to supply water to homes and businesses. So, K2's use of 6 Bar has nothing to do with the pipes actual max or nominal pressure rating, at least, that's my best guess. Hopefully K2 will give you a better answer.

 

[HMEL]

Higher fluid flow velocity does mean lower contact time, but that condition does not produce hotter internal wall temperatures, in fact, just the opposite.

Let's do a little thought experiment: lets direct a blow torch to heat a metal pipe. Water is flowing though the pipe at a rate of one gallon per minute, and the pipe is dimly glowing red hot from the torch. Now, increase the water flow rate through the pipe up to 10 gallons per minute; the water inside the pipe is now moving 10 times faster then it was at one gallon per minute, leading to the water now having a much shorter contact time with the pipe walls. Your assertion that fluids having higher flow velocity, shorter contact time, will lead to the pipe actually getting hotter, and glowing an even brighter red, with the higher flow rate just doesn't make a lot of sense. Higher flow rates result in greater cooling, not less.

Except water will remain a liquid and the R123 will be a gas. But a more common example is the heat transfer difference between water and oil. Additional the velocity depends on the tube diameter not the mass flow rate.
On average water will keep the tube temperature at about 70 degrees above the fluid temperature. Water is one of those sort of miraculous fluids. R123 does not have anywhere near those properties. So lets take your thought experiment one bit further. Remove the water and replace it with air.(a gas)

The proper engineering way is to consider the properties of R123 and design accordingly. Boiling point of water at one atmosphere is 212 and R123 80 deg f. Just for starters. And with respect to velocity it is fundamental in calculations of viscosity and can drastically effect heat transfer coefficients. Here is a classic heat transfer book
Process Heat Transfer by Kerns Mcgaw Hill Book Company 1950

 

[Toymaker]

Except water will remain a liquid and the R123 will be a gas.

NO!!! Go back to the first post in this thread and study the P-h diagram for R123. Due to the 500 psi pressure supplied by the feed pump, R123 will remain a liquid for almost the entire length of the boiler tubes, and will only turn into a saturated vapor towards the very end of the boiler. There will never be a length of boiler tube where the R123 is a dry, unsaturated gas. BTW, this process is typical of monotube boilers (aka Flash Boiler). No matter what working fluid you're using, the pressure exerted by the feed pump keeps the fluid in the liquid state as temperature increases throughout most of the length of the boiler tube. Only a very short length of boiler tube sees the liquid change state into a vapor (gas), and even then, it's a saturated vapor, not a dry gas.

But a more common example is the heat transfer difference between water and oil. Additional the velocity depends on the tube diameter not the mass flow rate.

Fluid velocity through a tube depends on both tube diameter and mass flow rate.

On average water will keep the tube temperature at about 70 degrees above the fluid temperature. Water is one of those sort of miraculous fluids. R123 does not have anywhere near those properties. So lets take your thought experiment one bit further. Remove the water and replace it with air.(a gas)

Comparing the heat capacity of a fluid vs a gas doesn't demonstrate that your assertion that shorter contact time results in higher wall temperatures, is, how shall I put it,... wrong.

The proper engineering way is to consider the properties of R123 and design accordingly. Boiling point of water at one atmosphere is 212 and R123 80 deg f. Just for starters. And with respect to velocity it is fundamental in calculations of viscosity and can drastically effect heat transfer coefficients. Here is a classic heat transfer book
Process Heat Transfer by Kerns Mcgaw Hill Book Company 1950

Here's a link to a much more recent online course explaining heat transfer, it's 54 lessons in length, starting out with the basics and getting progressively harder and deeper into the math. I don't recall which lessons, but the instructor covers viscosity and thin wall tubes. I found the course well worth the time investment,...hopefully you will too.
Heat Transfer Course

 

[HMEL]

NO!!! Go back to the first post in this thread and study the P-h diagram for R123. Due to the 500 psi pressure supplied by the feed pump, R123 will remain a liquid for almost the entire length of the boiler tubes, and will only turn into a saturated vapor towards the very end of the boiler. There will never be a length of boiler tube where the R123 is a dry, unsaturated gas. BTW, this process is typical of monotube boilers (aka Flash Boiler). No matter what working fluid you're using, the pressure exerted by the feed pump keeps the fluid in the liquid state as temperature increases throughout most of the length of the boiler tube. Only a very short length of boiler tube sees the liquid change state into a vapor (gas), and even then, it's a saturated vapor, not a dry gas.


Fluid velocity through a tube depends on both tube diameter and mass flow rate.


Comparing the heat capacity of a fluid vs a gas doesn't demonstrate that your assertion that shorter contact time results in higher wall temperatures, is, how shall I put it,... wrong.



Here's a link to a much more recent online course explaining heat transfer, it's 54 lessons in length, starting out with the basics and getting progressively harder and deeper into the math. I don't recall which lessons, but the instructor covers viscosity and thin wall tubes. I found the course well worth the time investment,...hopefully you will too.
Heat Transfer Course

All that taken into consideration, fluids transferring heat just consider the maximum temperature R123 can stand. Nucleate boiling will not occur and flashing will occur and the tube wall will be uncovered. However this fluid is usually reserved for low temperature recovery. But prove me wrong build it put it under the heat and pressures proposed. But what water will do is not what R123. will do. And given when I look at the state properties of temperature and pressure I find its actually in the super heated gas state above 180 deg and 300 psi. This makes it a gas.

Thanks for the course reference but I have no interest in taking more heat transfer courses.

 

[Toymaker]

All that taken into consideration, fluids transferring heat just consider the maximum temperature R123 can stand. Nucleate boiling will not occur and flashing will occur and the tube wall will be uncovered.

As long as the feed pump keeps pressure inside the boiler tube at, or above, 500 psi (3.5 megapascal), the R123 cannot flash into a vapor.

And given when I look at the state properties of temperature and pressure I find its actually in the super heated gas state above 180 deg and 300 psi. This makes it a gas.

I believe you miss-read the P-h diagram,... the pressure scale is in megapascal, not psi. At 180C, which is below the critical temperature of 184C, the pressure reading from the diagram is just over 3.2 megapascal (464 psi), which is below the critical pressure of 533 psi for R123 which all means its not in a super heated state, and the R123 is still in the liquid state.

 

[HMEL]

As long as the feed pump keeps pressure inside the boiler tube at, or above, 500 psi (3.5 megapascal), the R123 cannot flash into a vapor.


I believe you miss-read the P-h diagram,... the pressure scale is in megapascal, not psi. At 180C, which is below the critical temperature of 184C, the pressure reading from the diagram is just over 3.2 megapascal (464 psi), which is below the critical pressure of 533 psi for R123 which all means its not in a super heated state, and the R123 is still in the liquid state.

The ph diagram in english units shows critical temperature at 532 abs lbs/ f in2 and temperature of 382 F. Given the high heat flux doubt you can keep it from flashing.