[modeleng] Re: Smokebox Innards
- From: "Phill Smith" <steam@xxxxxxxxxxxxxx>
- To: <modeleng@xxxxxxxxxxxxx>
- Date: Sat, 13 Nov 2004 00:27:46 +0800
Sorry mate.
For some completely stupid reason, unexplainable, I didn't read you whole
email.
Can I blame tiredness?????
Cheers,
Phill.
----- Original Message -----
From: "alanjstepney" <alan@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
To: <modeleng@xxxxxxxxxxxxx>
Sent: Friday, November 12, 2004 11:58 PM
Subject: [modeleng] Re: Smokebox Innards
> Phil,
> I DO have a copy.
> However, it is old information and even Steels re-write didn't update much
> of it.
>
> The work that Clif mentioned by the GWR, was by Sam Ell, and was based
upon
> work by Prof Goss of Pardua University.
> That resulted in many improvements to UK loco's, and also showed that the
> one big problem was that our loading gauge was too small, thus restricting
> the area of chimney to below the ideal size. The answer as, of course,
dual
> or multiple chimneys-blastpipes.
>
> Since GWR times others have also worked on draughting, including Port, and
> Wardale and, Jos Koopmans, among many others.
> Prof Bill Hall did some work on it, and showed that provided the area of
the
> entry to the petticoat pipe is twice that of the chimney, a straight
chimney
> only loses some 15% of efficiency compared to a properly constructed
> venturi. The entry acts as the convergent part, thus increasing the gas
> velocity, and creating a partial vacuum..
> Of course, 15% can make the difference between a good and a mediocre
> performance.
>
> Rather than calculate the size of the blast pipe orifice it is probably
> easier to sue the software he designed and try out different sizes, whilst
> checking the vacuum produced.
>
> As you say, the 1:3 and 1:6 angels are important, and I did mention this
on
> my previous email.
>
> alan@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
> www.alanstepney.info
> Model Engineering, Steam Engine, and Railway technical pages.
>
>
> ----- Original Message -----
> From: "Phill Smith" <steam@xxxxxxxxxxxxxx>
> To: <modeleng@xxxxxxxxxxxxx>
> Sent: Friday, November 12, 2004 3:55 PM
> Subject: [modeleng] Re: Smokebox Innards
>
>
> Alan,
>
> The petty coat is the convergent section of the nozzle (which is what you
> were decribing as a venturi), and the chimney should always get larger in
> diameter as you progress up (along) the chimney. This alows for the
decrease
> in velosity of the gas stream moves up the chimney. A straight chimney
will
> work (by all appearances quite nicely) but it will not work as well as a
> expanding taper one, and hence cannot move as much air without the use of
a
> smaller nozzle (and hence higher back pressures).
> Also, the steam, as it exits the nozzle, has 2 expansion cones. The first
is
> a cone of 1 in 6 (diameter to height), which must touch the sides of the
> chimney (preferably an inch or 2 before the top, or longer) to create the
> main "pull" up the chimney. The second is a cone of 1 in 3, which should
> just touch the throat of the peticoat (smallest diameter section). The
> second cone is mostly caused by the interaction with the surrounding
gasses
> (on the external surface of the first cone), which slows down the jet
stream
> and causes the increase in the jet streams area, and hence the second
cone.
>
> I really recommend that you read Henry Greenly's book "Model Steam
> Locomotives". (edited by E.A. Steel in later editions) E.A. Steel was his
> son inlaw.
>
> Actually, I am surprised that you don't own a copy. He was a brilliant
> engineer, and model engineer to boot.
> He was also a POM, so you POM's should all have copies of his books.
<GRIN>
>
> If you want to know more about the workings of blast nozzles and chimneys
> (including single, and double, and tripple pettycoat pipes) you know where
> to find me.
>
>
> Cheers,
>
> Phill.
>
>
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