Reply To: Porta's Derivation of Lempor Theory

[Chris Corney]

Hi Martin,

In reply to your points above:-
There was a paper recently which Jos Koopmans mentioned on the National Preservation forum (I’ll try to find it later). From this I drew the conclusions that a convergent mixing chamber could be shorter than a parallel type, with similar performance. This would be useful for railway applications.
I’m just trying to interpret your second point with respect to the principle of de Laval nozzles, which have been around for eons. I’m thinking that if transonic flow occurred in a de Laval nozzle it would probably just create shocks.
For transonic flow in diffusers, Prof. Eames at Nottingham University has done some work on CRMC theory (constant rate of momentum change), with one or two papers availableon the internet; you may find these interesting.
While various arrangements of ejectors using conical and parallel sections are proposed, I’m wondering if a smooth curve would be better. Hence my suggestion of a hyperboloid. CRMC theory also proposes a curve, although it is a different curve and potentially more difficult to manufacture than a hyperboloid.
For chimney machining we are thinking of miniature up to standard gauges, although I’m thinking that a de Laval nozzle with a CRMC divergent section could theoretically have some advantages with pulsating flows.
We discussed castings with complex curves in the group a while ago, and someone asked how you would go about improving the surface finish of a casting.
There are a number of miniature locomotives running with saturated boilers and exhausts with de Laval nozzles, and I can’t help wondering how these would operate with wet steam. If there is a sharp drop in pressure in the nozzle, does this just cause an appreciable amount of condensation?
Chris