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Author Topic: Steam dryers - superheaters?  (Read 1622 times)

DBS88

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Steam dryers - superheaters?
« on: May 11, 2020, 07:34:35 pm »

Please feel free to add further detailed comments. I have been reading through previous posts to learn morn about dryers/superheaters before buying a boiler for my current build, so thought it might be useful to take a straw poll to find out from experienced steamers whether or not they are worth it. Thank you for taking the time to do this it is appreciated.
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rhavrane

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Re: Steam dryers - superheaters?
« Reply #1 on: May 11, 2020, 09:20:51 pm »

Bonjour,
On almost all my steam machines, I try to apply a working pressure of about 2 bar (30 PSI) to save autonomy and let the steam keep its role of lubricant in complement of the oil lubricators sometimes empty before the end of my navigations.


To my opinion, and I am not a specialist at all, with a pressure 30-45 PSI and a few centimeters of heated pipe cooling again after from the boiler to the machine, it does nothing in the end apart from complications of pipe joints.


[/size]I was even told that some model makers had not oil lubricators and addes just a drop of oil (how ?) at the beginning of their navigations.


I will read with a great interest other and possible different opinions.
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Raphaël
Raphaëlopoulos Steam Lines UnLimited
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tghsmith

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Re: Steam dryers - superheaters?
« Reply #2 on: May 12, 2020, 01:41:31 pm »

I've been working on using a stuart turner compound twin block to build a 1890's US navy launch engine, during this build a full scale steamboat expert has been providing support,advice, documents and casting assistance,, we got to talking about dry steam,wet steam and oil,, his advice wet steam without an oiler,, some oil in cylinders at start and after for storage,, rings to be installed with a high temp moly paste.. work on the project has stopped due to my metal shop tools are at my shop at work..
https://www.rcgroups.com/forums/showthread.php?3018430-US-navy-28ft-steam-cutter
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steamboatmodel

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Re: Steam dryers - superheaters?
« Reply #3 on: May 12, 2020, 03:32:24 pm »


Once your boiler pressure starts to get above 50psi the steam tends to dry out a bit and losses its lubrication effect. It also seams to lose its ability to pick up oil, but if you dry it out a bit (we can not superheat at the scale we are working at) it seams to condense better in the lubricator. These are just my thoughts on the subject I can not prove any of it scientifically, just my experiences.
Gerald. 
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DBS88

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Re: Steam dryers - superheaters?
« Reply #4 on: May 17, 2020, 08:44:31 am »

Just wondering if it’s ok to use steam drying/superheating with brass engines?

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rhavrane

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Re: Steam dryers - superheaters?
« Reply #5 on: May 17, 2020, 11:45:51 am »

Bonjour,
Our models are never correctly insulated (ends of pipes with nuts, oil lubricator, RC valve...) and heat our machines level is never a prpblem to my opinion, but lubrication would be.
I think our major problem is not super heating or not but the ablilty to adapt the bolier to its steam machine(s) to get the best quantity of steam, possibly managed with a gas regulator to prevent any over pressure (we do not navigate full ahead all the time) and loss of steam / autonom through the safety valve.
Please, listen to what I consider as the "perfect" adequation Boiler / steam machine : [font=var(--ytcp-font-subheading_-_font-family)][/size][size=var(--ytcp-font-subheading_-_font-size)]https://youtu.be/qk74P2k8W2o[/size][/font]
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Raphaël
Raphaëlopoulos Steam Lines UnLimited
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KBIO

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Re: Steam dryers - superheaters?
« Reply #6 on: May 17, 2020, 11:49:23 am »

Hello!
If I can help.
Talking about "super heat" , "dryer" or  others means nothing if here is no figure. What we want to achieve is having a satured steam 100% with no water inside at all to enter the engine.


A 3b gauge (4 b abs) steam pressure is +/- 143 °C.
Whatever the pressure is , those figures are given for 100% saturated steam.
As KNO3 said , all depends of the engine seals and segmentation.
But overheating the steam outlet by 20°C gives an equivalent steam of 6 b - 160°C = same pressure but 20°c more.
If you let the steam outlet coiling inside the burner flare, you are ahead of big problems = TOO hot . If you are away from it, you may be too hot still. Leading to soldering issues. The temperature of a boiler tube with water inside is slightly above of the steam temp. With no water , the temp is +/- equivalent of the flare. This si why it is not recommended to flare a dry burner. A Wilesco boiler work with 1 b pres = +/- 120°
So no worry for the welding as long as there is water inside.
The best way to find out is to install a gauge just before the engine inlet. If you know the pressure, you know the temp, then.
And you can tell if you are too hot or not.
I would say that overheating by 10c is more than enough to be well above the saturated point (where start the condensation) .
It means that your steam can lose 10 °c before to start to start to get back to the liquid phase.
Train operators do know very well how to get the benefit of the steam by just cracking up the supply valve .
Hoping not to be too boring.
Cheers.
A good instrument  to find out what you are doing:



DBS88

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Re: Steam dryers - superheaters?
« Reply #7 on: May 17, 2020, 07:51:51 pm »

Thank you for taking the time to make such an informative reply, thats really helpful.
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DBS88

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Re: Steam dryers - superheaters?
« Reply #8 on: May 18, 2020, 07:41:16 pm »

Thank you for voting and your feedback comments, I have been trying to find out about steam drying because I have found differing views.  The results of the Poll were 2 to 1 in favour of steam drying. To sum up the comments received. Mild Steam Drying – to raise the wet steam by between 10 and 15 degrees. Having spoken with experienced steamers and people who have made and used boilers. The consensus is that steam drying is both good and bad, however done in a mild form is beneficial. Those against say that wet steam acts as a lubricant so no worries about running out of steam oil, no risk of damaging engines with excessive heat. Those for, claim reduced condensate and better engine running, with the aim to get the steam to the engine at the temp it left the boiler by raising its temp a few degrees.
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KBIO

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Re: Steam dryers - superheaters?
« Reply #9 on: May 20, 2020, 08:37:39 am »

Hello!
For a better understanding, I kindly recommend the video of Keith : a great man who explains very well in proper English (not like mine! %) ) how to overheat the steam out of the boiler. (I recommend his videos , we learn a lot and it is clear) :-))
Taking into account that the wet steam coming out of the boiler is always charged with droplets of water = sucking effects added to washing machine turbulences inside. And depending of the (too) high level inside, it is suitable to overheat .... a bit
The goal is to have a steam with a temperature slightly above the saturated one to allow an expansion with no condensation.
[size=78%]https://youtu.be/WzK0PJ6soxs[/size]


20°C above is plenty enough . It does not superheat and allows the oil condenser do its job.
Note also , as Steamboatmodel says, that the higher the steam pressure is , the higher is the temperature ,so this keeps the machine hot and helps limiting the condensates.
Thinking that the steam lubricates is like  walking bare feet on the gravel. You walk but you'll go further and smoother with a pair of shoes! O0 :}
Sorry to appear as a "Know all", this is not the case but I learn everyday and if I can share to avoid falses ideas, I'll be glad to contribute at my modest level. This is why I am often on this forum to benefit of the experiences of some great "STEAMERs"
Thanks for share your experience.
Best regards.







DBS88

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Re: Steam dryers - superheaters?
« Reply #10 on: May 28, 2020, 08:43:06 am »

KBIO thank you for taking the time to share your experience, the replies have been most helpful
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KNO3

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Re: Steam dryers - superheaters?
« Reply #11 on: June 01, 2020, 12:48:01 pm »

Hello!
If I can help.
Talking about "super heat" , "dryer" or  others means nothing if here is no figure. What we want to achieve is having a satured steam 100% with no water inside at all to enter the engine.


A 3b gauge (4 b abs) steam pressure is +/- 143 °C.
Whatever the pressure is , those figures are given for 100% saturated steam.
As KNO3 said , all depends of the engine seals and segmentation.
But overheating the steam outlet by 20°C gives an equivalent steam of 6 b - 160°C = same pressure but 20°c more.
If you let the steam outlet coiling inside the burner flare, you are ahead of big problems = TOO hot . If you are away from it, you may be too hot still. Leading to soldering issues. The temperature of a boiler tube with water inside is slightly above of the steam temp. With no water , the temp is +/- equivalent of the flare. This si why it is not recommended to flare a dry burner. A Wilesco boiler work with 1 b pres = +/- 120°
So no worry for the welding as long as there is water inside.
The best way to find out is to install a gauge just before the engine inlet. If you know the pressure, you know the temp, then.
And you can tell if you are too hot or not.
I would say that overheating by 10c is more than enough to be well above the saturated point (where start the condensation) .
It means that your steam can lose 10 °c before to start to start to get back to the liquid phase.
Train operators do know very well how to get the benefit of the steam by just cracking up the supply valve .
Hoping not to be too boring.
Cheers.
A good instrument  to find out what you are doing:


Hello, could you please explain how the device in your drawing is used? Especially what the reading of the two manometers tells you about the steam temperature.
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KBIO

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Re: Steam dryers - superheaters?
« Reply #12 on: June 01, 2020, 07:20:22 pm »

Hello KNO !
Nice to hear from you !
To answer to the question ( I must admit that I haven't been clear enough in the first time %) ) I don't know if  I will this time thou ! {:-{

[/size]The principle is quite simple.
[/size]For each steam pressure, there is a correspondant température. Roughly : 10/12 °c per bar of pressure in our working range.We know that if we heat water in a closed volume, it will evaporate until it reaches  an equilibrium between the liquid and gaz phases. The pressure of this saturated steam is directly linked to the temperature. At each temperature corresponds a given pressure and vice-versa. That correspondance can be found using classic steam charts or Mollier diagram.[/font][/size]It is difficult to measure accurately temperature with our usual modelist tools. Fortunately with our standard gauge  we can read pressures.
The over heated steam comes from the coiled pipe at the back of the boiler through the measuring device toward the engine.So  is the principle of this little device: 1- We have an internal sealed chamber 3/4 filled with water,  on top of which we have fitted a manometer.2- This sealed cell is introduced (and welded) in a by-pass chamber through which  circulates the superheated steam. Around the sealed cell.  See schem & picture)- With a good insulation around the whole device, the inner chamber will quickly heat up to the temperature of the circulating steam and part of the enclosed water will be vaporized.We just then need to read the pressure on top of the device and use the tables to find the corresponding temperature.-Let’s say that the boiler gauge reads  3b  on « A », ( 4b abs) . At this pressure the temperature is 143,62°C according the chart.  -On the manometer « B » on our  little device we can read 5b, ( 6b abs). The table gives a temperature of 158,84°C.Hence we can deduct that the steam circulating is super heated by: 158,84 - 143,62 = 15,22°C
So, you can see that a 3 b pressure on the boiler has the same temperature as 5 b  pressure after heating up. Same pressure, higher temp ! :-))
It means that you can afford to lose 15°c before to Start to get back to water phase (condensing)
Your steam will be hot & dry. No need to burn the installation . 20°c is good enough and more that we need. If you read 20 bar , you have to work out the length of the heating coil , then ! {-) {-)
That measure of the temperature will be as accurate as the pressure gauge is… Use copper for the sealed cell, it has a much better heat transfer coefficient than brass.
Don't be afraid to burn your gauge as the temperature on it will be a lot lower than the one inside the cell as there is no circulation in the Bourbon tube.
I hope that it will answer your question.
Thanks for your interest.
Regards.

note: also be aware that there is a pressure drop of 1 b or more between the boiler and the engine. Depending of the installation.
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