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Author Topic: Pressure loss?  (Read 4077 times)

tonyH

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Pressure loss?
« on: June 22, 2016, 09:40:07 pm »

Hi All,

New project lends itself to steam BUT to keep the scale dimensions the steam pipe from boiler to engine is about 40cm. I will insulate the pipe with string and probably foil but is there likely to be a significant pressure loss over that length. The nominal running pressure is 40-45psi and the pipe is 4mm. Since I'm having the boiler made, is it worth specifying a working pressure higher than the 45 or am I thinking too much? The hull is an open launch type.

Thanks

Tony
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derekwarner

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Re: Pressure loss?
« Reply #1 on: June 23, 2016, 12:12:50 am »

Tony...these ready reckoners are OK to use even for model steam guestimations  :embarrassed:

http://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0ahUKEwitpbyu2bzNAhUI4WMKHYxtAYcQFggpMAM&url=http%3A%2F%2Fwww.pressure-drop.com%2FOnline-Calculator%2F&usg=AFQjCNG6HYEQEZVNhN2A8_2zdUU61BAJ9w

The values I have used are arbitrary [3 Bar, 400mm tube length and 3mm ID tube] but ball park for model steam ...with the resulting a mighty huge PD of 0.01 Bar  O0 in this setup

The interesting point is that the decrease in pressure drop by increasing the pressure from 3 Bar to 5 Bar is minimal

The calculations do not really consider temperature drop which is far more important to us in these applications....as you have said you will insulate the 400 mm long tube spool...... I found using a $20.00 cheap digital pyrometer invaluable in understanding heat loss

Stick you finger on the boiler steam discharge valve & it feels 'blinking!' hot......stick your finger on the steam tube near the engine & it feels 'blinking!' hot, and yet in my case [the pyrometer confirmed] there was a 15 degree temperature loss in 300 mm of uninsulated tube which prompted me to insulate the hot steam tubes...the temperature loss was reduced to 11 degree at the engine or a 4 degree net gain

So if you are serious about understanding you steam plant, why not also invest in a digital tachometer ...again about $20.00 ..I find them invaluable and great value :-))

Derek

PS.....the work ''blinkin' is not in my vocab.........the moderators auto corrector substituted it  {-)
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ooyah/2

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Re: Pressure loss?
« Reply #2 on: June 23, 2016, 02:19:26 pm »

Hi All,

New project lends itself to steam BUT to keep the scale dimensions the steam pipe from boiler to engine is about 40cm. I will insulate the pipe with string and probably foil but is there likely to be a significant pressure loss over that length. The nominal running pressure is 40-45psi and the pipe is 4mm. Since I'm having the boiler made, is it worth specifying a working pressure higher than the 45 or am I thinking too much? The hull is an open launch type.

Thanks

Tony

Tony,
If it was me that was having a boiler made I would specify that the max W.P. had to be 60 p.s.i as you don't know what you may want in later years and a W.P. of 45 p.s.i. may not be enough.
Your boiler maker will be able to keep the dimensions the same as for 60 p.s.i. and all you will have to do is have the Safety Valve set at 45 p.s.i.
Yes there will be a pressure drop at the engine but not enough to worry about and yes lag the steam pipe from the boiler to the engine.

Don't get hung up on technicalities and unless you want to know these figures don't spend extra cash on measuring gear that you won't need.

Put your steam plant into your launch hull and fit as large a prop that you can get on and go and enjoy sailing under steam.

George.
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tonyH

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Re: Pressure loss?
« Reply #3 on: June 23, 2016, 08:49:56 pm »

Thanks for the input chaps. The implication seems to be that even with a fairly extended steam pipe the actual losses are manageable. All I was concerned about was the heat/pressure available to do work at the engine end of the pipe and whether to increase the heat (with a pipe run back through the flue) or the pressure available at the boiler in the spec for the builder.
Project S will proceed!

Tony :-))
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derekwarner

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Re: Pressure loss?
« Reply #4 on: June 23, 2016, 11:33:32 pm »

Hi Tony............. thank goodness I didn't mention my set of digital scales 0gm to 7000gm [yes another $20.00]......invaluable for understanding gas consumption.......it was not the cost of gas, but an understanding of ...is the tank full?....the last time I filled the tank on a cold day...it only ran for XX minutes, however ......etc etc

Or the digital strain gauge....[yes another $20.00]......certainly not necessary but has proved useful in checking the weight of my air flight case so as not to exceed the 23kg domestic Australian limit....[exceed this by 2kg & pay $40.00!!!!!!!!!!]

I also use this digital strain gauge to help 5" Gauge steam engine owners understand the tractive pulling force from rest of their respective engines. The digital pyrometer has helped me to identify a partially seized bush in another 5" Gauge engine......all of the push rod components were boarding on too hot to touch, however one singular bush was 18 degrees hotter than the rest of the components

All absolutely unnecessary granted <*<......but useful.......... Derek 
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tonyH

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Re: Pressure loss?
« Reply #5 on: June 24, 2016, 10:06:24 am »

Definitely 'Thank Goodness' %) Derek,
All I remembered was Boyles Law and temperature gradients etc. hence the original question.

Unfortunately my son is a hydraulics engineer, so when he added in pressure gradients and velocity gradients as soon as you open the valve my brain started hurting and I needed the combined wisdom of you and George :-))
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ooyah/2

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Re: Pressure loss?
« Reply #6 on: June 24, 2016, 07:46:28 pm »


[ my brain started hurting and I needed the combined wisdom of you and George :-)) ]


Thanks Tony for the kind words, I can't offer you the knowledge that Derek has of the instruments he mentioned or info on Boiler level controls and gas regulator devices as due to my age these modern tools were not available when I worked in industry and to Derek's credit he will gladly keep you posted on them.

What I can give that Derek can't is 25 years of practical experience building boilers and machining steam engines and running them in a model under steam.
I make no appologies on past comments that all these Gizmo's are not required in a steam boat as you don't get the practical knowledge in running a steam boat and the extra cost of them is inclined to put some members off getting into steam, if however after running a steam boat you wish to fit electronic boiler level control and a gas burner regulator that's up to the builder.

There are so many members on this forum that have great technical and practical knowledge and all are only too willing to pass on any help that they can, so go to it and keep us informed of your progress.

What you havn't said is the type of boiler you are having built, the type of engine that will power your launch so how about letting us know.

Welcome to the burny finger brigade.

George.


 
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frazer heslop

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Re: Pressure loss?
« Reply #7 on: June 24, 2016, 10:23:13 pm »

Hi Tony, very much in the George camp of the old suck it and see engineering although Iv built boiler level control systems and gas regulators but ended up stripping them out and going back to the Keep It Simple brigade.
So Iv ended back where I started building the simplest plant possible to do the job required and my feet dont get wet as often
I dont do much steam now been afflicted with the Stirling engine disease
As George mentioned you dont say what type of engine you a running if its an oscillator a wee bit of wet steam wont be a problem and from a personel point of view I find the oscillators to be very good for the smaller boats as they are just more reliable and only need one channel for for/reverse.
Just my personnel findings from building toy steam boats for nigh on 40 years .
Welcome to the burnt fingers brigade
cheers
frazer   
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derekwarner

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Re: Pressure loss?
« Reply #8 on: June 24, 2016, 11:29:37 pm »

Morning Tony......

George is certainly correct and is aware that I have never built a boiler nor a boiler feed pump. I also acknowledge the similar number of years that he has spent actually building and getting these model components & systems to work without attachments or test equipment %)...Over the years George has also shown examples of his work and kindly offered sound engineering advice to many [including myself]

In my defence, I do have a lifetime's experience in the real world of hydraulic fluid systems in merchant marine, Naval an lastly for 18 years prior to retirement as a self employed consultant to our Australian steel industry engaged specifically in the fluid power arena............. from this, I have no intention or need in boring this thread in espousing the benefits of [inexpensive but accurate] technology

From my humble experience, a burnt thumb would have little perception of an 18 degree variance in temperature ......

Derek

PS....for any one interested ...some really good reading on the subject
_____________________________________________________________

http://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwjC6MGu3cHNAhXKnpQKHSv0AqsQFggkMAE&url=http%3A%2F%2Fwww.scholarpedia.org%2Farticle%2FThermal_touch&usg=AFQjCNFHXd9whwy7zs2rAYcWYWPG9KpTjg
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Derek Warner

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ooyah/2

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Re: Pressure loss?
« Reply #9 on: June 25, 2016, 10:43:34 am »

Derek,
I apologise if what I have written makes you need to defend yourself as it wasn't my intention to make you do so. I am glad to hear that you have retired and now you can get started on building P.S. Decoy which will be another challenge and then I can't rib you about never having built anything !!!!!!!

Apologies to Tony for highjacking your thread, it will not happen again.

George.
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tonyH

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Re: Pressure loss?
« Reply #10 on: June 25, 2016, 05:05:55 pm »

Gentlemen, gentlemen, please accept my sincere apologies if I've unintentionally opened a rift between the two schools of engineering.
My experience of steam is limited to a couple of builds, one of which was incredibly underpowered due to limited airflow, although Mr Bishop was kind enough to put a pic in Model Boats. The other was a large model of a WW1 Saint class rescue tug which looked superb and sailed wonderfully using an old York oscillator and a huge Cheddar boiler. I wish I still had that one because it was bl***y lovely!
The new one is a variation on an open launch. It's about 1m long with a relatively narrow beam and comes in at about 4.5kg. The engine is an 11mmx11mm twin, in-line oscillator driving a 75mm prop. The original vessel in 1886 used a forced air system which I could reproduce should the need arise.
The reason for the original question was that I've always believed that the steam pipe should be as short as possible to minimise, or so I thought, power loss. Since, in this vessel, the steam pipe was extended, I wanted to know what, if any, the actual losses would be and, if necessary, incorporate changes.
My knowledge of the physics is based on information from Mr Nelkon and his textbooks of the 1960's plus some formulae, sorry algorithms, from my son and a home lesson on computational fluid dynamics %% so each and every snippet of information that stops me from making a complete 'horlicks' of the build is much appreciated.
 {:-{
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frazer heslop

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Re: Pressure loss?
« Reply #11 on: June 25, 2016, 10:36:02 pm »

Derek, I also wish to express my apologise it was not my intention to cause offence.
Tony , dont know if youve ever come across these formula. Not perfect but give some idea
The size of engine for a hull
L X B X D divided by a =cubic contents of cylinder/s
L= length of hull on water line
B=beam
D=average draught
a= upto 2ft6inch 3000
              3ft         2800
              3ft6       2700
              4ft         2500
Personally for a wobbler 45 psi should be more than enough and as Derek's link shows the pressure drop is not a problem
These rough and ready formula  and more canbe found in the old Machinery for Model Steamers by Percival Marshel and reprinted by Tee publications as Iv said not perfect but still relevant and Iv not had a problem with my steam plants using them although I tend to go that wee bit bigger
cheers
frazer
 
 
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derekwarner

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Re: Pressure loss?
« Reply #12 on: June 25, 2016, 10:54:57 pm »

Gents...certainly no offence was taken...we have tough skins out here

Tony asked a question, I responded with the experience I have from the full sized world of engineering, but have no examples of self built model engines or boilers

George offered an alternate view of the world and speaks from well documented experience in both those areas.....[although I do wonder how he calibrates his burnt thumb for heat checks]

So now Tony has offered the engine as an 11mmx11mm twin, in-line oscillator driving a 75mm prop, we could consider the matter of lubrication....

I have a distinct preference for the design which provides a visual confirmation of the oil/condensate ratio ..... I would also rather use too much oil than not enough

George is well known for his abhorrence in wasting steam oil

Both lubricator designs [fixed or variable] to a certain extent extract a thermal gradient [and hence pressure loss] from our precious steam supply so is in line with the original question

Derek

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Derek Warner

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frazer heslop

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Re: Pressure loss?
« Reply #13 on: June 25, 2016, 11:21:00 pm »

Derek, as Im firmly in the KISS camp for me it would be a simple displacement lubricator as per the Stuart Turner style and to be honest Iv never been worried about the pressure loss it will create just more concerned its delivering some oil.
This would not be the case for a high performance plant as George likes to play with. I simply prefer to putter round the pond at a rather pedestrian pace and although of the same /similar heritage to George I dont mind a wee bit of extra oil although Iv a 5 gallon drum of the stuff to get through :} .
i  gave up on flash steam a long time ago but do remember the hotter the steam the more expletives hence Georges non deplume .
This plant has a simple displacement lubricator fitted and at one time electronic boiler level control that used a Schmitt trigger hence the dummy safety valve
Sorry for the poor pic I v cleared out my photo bucket account

cheers
frazer
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