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Porta wrote an introductory note which carries caveats:-
Introductory Note (added February 1999)
This theory refers to the fundamentals defining the main dimensions of the ejector. It requires the calculation (or the obtention by experimental procedures) of the boiler characteristics, a serious matter in itself. It also presupposes that a large number of details coming from a long experience are to be respected. It does not include the swirl of both of the steam jet and the gas intake. Finally, a still pending serious problem is that it assumes that the flow is steady, non-pulsating, a field open to future investigation. It is not a “kitchen recipe” guaranteeing good results without a good tuning up with measurements. However, the reader may try, provided that if success crowns his trial and error, the merit is to be credited to the theory. If not, the Author expects that the failure is not to be credited to the theory, but to the user.
Hi Martin – in earlier you post you wrote:-
‘John – If you look at the sidebar item “Lempor CFD?” on the page I gava shortcut to, you wil see that both CFD models are of a Lempor style arrangement, the only difference being the first example (2 plots on of pressure, one of velocity) has the blast nozzle level with the intake bellmouth, while the second (2 plots again) has it below the intake bellmouth. I cannot see how the statement by JK squares with the results the CFD plots are showing.’
I can’t tell anything about the positioning of the nozzles from the images or am I missing something blindingly obvious.
Hi Martin – have you a copy of Jos Koopman’s book ‘The fire burns much better….’?
The book is useful in that lists and critiques the history of exhaust system development over the last 200 years. It also includes the various formula derived over the years for describing mathematically the workings of exhausts systems. It also includes the formulae derived by his PhD Supervisor – Dr Robin Saunders.
In the book he praises the Lempor Exhaust but like yourself is sceptical aboout the formula and points out a transcription error on the versions available on the web – if my memory is right a plus should be a minus or vice versa in one of the terms. He also reverse engineers the equation and concludes that it is the same as one developed by Zeuner in the 1850’s.
I used the equation, but put in realistic values for inlet loss and for diffuser performance taking into account diffuser geometry and correcting the transcription error. I developed a spreadsheet using the corrected equation and then developed graphs of draught for different steam rates. The graphs showed decreasing vaccuum for increasing steam and gas flow rates which is contrary to what is seen in real life. So I am sceptical of the equation and given time would like to use the same input data into other equations and see what the results are.
Others have used the equation and developed succesful exhausts, see this website
There is a link in it to a Excel based calculator developed from the Porta Equation.
Despite our scepticism about the equation others have developed succesful Lempor exhausts. The Lempor we fitted to S160 has achieved its objectives of turning a poorly steaming engine in a better steaming one, which uses less coal than it did before. We had a one off chance to measure vacuum on it back in early 2017. We are in the course of doing similar measurements on a similar engine of the same class on another railway. To do these tests we are in the hands of the railway so progress is slow depending on locomotive availability and access to run trains.
The experience we have had with Lempor Exhausts is simlar to others who have fitted Lempor Exhausts, so despite the equation the Lempor Exhaust does work.
Currently, I am reading his book but not completed it. I think JK’s initial comment applies to a ‘coventional exhaust’ ie single blastpipe and chimney which may or may not be taper (diffuser).
The CFD is for a Lempor Exhaust, which uses 4 convergent/divergent nozzles which discharge into a mixing chamber and then into a diffuser.
In a conventional exhaust if the blastpipe is too close to the chimney, the exhaust can be ineffective as the jet from the blastpipe does not fill the chimney and you get a backflow into the smokebox. I am currently dealing with a locomotive which has been modified by others and I have been told that this happens (I have not seen it as I have not had a chance to ride the engine) but I have seen evidence in the chimney that it is happening.
We are doing some more drawings to check whether the jet of steam from the blastcap actually fills the chimney as it expands and entrains the flue gasses as they flow from the smokebox up into the chimney.
If the steam and the flue gasses do not fill the chimney then you get back flow into the smokebox.
In the 1930’s rules of thumbs were established for the spreads of the steam jets as they emerged from the blast cap and in the chimney. The spread of the jet in the chimney is less than the spread of a jet coming out of the blast pipe. I am over-checking these rules of thumb against current research in other fields.
For a Lempor, Porta’s recommendation was that the nozzle exhaust is at the bottom of the mixing chamber. We followed this recommendation on the Lempor we fitted to S160 No 5820. The nozzles are angled so that steam jets impinge the mixing chamber walls so that there is thorough mixing before the entrance to the diffuser, so that there is a ‘flat velocity’ profile and turbulent flow which diffusers need to work effectively. If the exit from the nozzles is too far away from the mixing chamber then the jets may not even enter the mixing chamber. This is the opposite of a conventional exhaust.
Regarding the CFD examples I cannot really comment on the results as I do not know enough about the configuration and the flows he was testing.
I do not believe you compare how you configure a Lempor with a conventional exhaust.
Over the next couple of weeks I will be tabulating steam and gas flows for typical locomotive exhausts (using Rugby Test Data) in the hope that we can persuade someone to do some free CFD studies for us, then we will be able to evaluate the CFD against actual test result and have a useful tool.
JK has done a service by compiling the history of exhaust system development and offering some ideas of his own guided by his tutors, however, he is handicapped by having to communicate with the rest of the world in his second language. Heseems to have overlooked research in other fields that could help us to understand one of the great unsolved mysteries in Fluid Dynamics – what is the optimum steam locomotive exhaust!!!
Chapter 12.1 of Applied Gas Dynamics by Ethirajan Rathakrishnan and published in 2010. Gives an explanation.
There has been lots of work on understanding the physics of jets because of their applicability in a number of fields.
The chapter goes onto explain why ‘Goodfellow Tips’ work.
Through practical experience steam locomotive engineers developed solutions that worked and it is only now through research in other fields that we are starting to understand how they work.
Hi Guys – pleased to see that this has started a bit of a debate. During my lunchtimes, (when I get them), I trawl the internet for recent research articles. The video was the result of one of these searches.
As we cannot fund research ourselves I look to see what others are doing and whether it has relevance to our interests. Over the weekend I will I post more.
Hi Chris – CFD has been used for pulsing flows – see this paper from 2009.
Numerical simulation of transient flows
in a vacuum ejector-diffuser system
V Lijo1,HDKim1∗,G Rajesh2, and T Setoguchi3
1School ofMechanical Engineering, Andong National University, Andong, Republic of Korea
2Indian Institute of Space Science and Technology, Kerala, India
3Saga University, Saga, Japan
Abstract: The objective of the present study is to analyse the transient flow through the vacuum
ejector system with the help of a computational fluid dynamics method. An attempt is made
to investigate the interesting and conflicting phenomenon of the continuous entrainment into
the primary stream with limited mass supply from the secondary chamber. The results obtained
show that the one and only condition in which a continuous mass entrainment can be possible
in such types of ejectors is the generation of a recirculation zone near the primary nozzle exit. The
flow in the secondary chamber attains a state of dynamic equilibrium of pressure at the onset of
the recirculation zone. A steady flow assumption in such ejector systems is valid only after the
dynamic equilibrium state.
Keywords: compressible flow, ejector, internal
Proc. IMechE Vol. 224 Part G: J. Aerospace Engineering
There were applications of Pulverised Fuel/Micronised Fuel firing in Germany and Australia. There are a couple of ILocE papers from the late 1920’s describing the applications. If you are an I MechE member you can get electronic copies from the archive.
If anyone who is not am IMechE member is interested in them, PM me.