-=> Quoting Alec Cameron to Gregory Procter <=-
 AC> Hi Gregory
 AC> Unsolved problem- would the steam evaporate the water and the bucket
 AC> become empty......... or would the steam condense to water so's the
 AC> bucket overflowed?
 AC> I never did find out, there was always a queue of washer- men waiting
 AC> turn!
Another of life's little conundrums!!
 GP>       If in a steam loco, you try to recover the exhaust heat energy by
 GP>       directing it to the cold water supply (the tender) you end up with 
a
 GP> hot
 GP>       water supply and boiler feed problems.
 AC> Comparable problems in stationary boilers. If you use the exhaust to
 AC> preheat something, then this must impede the exhaust flow and increase
 AC> the back pressure.
 AC> Consequently the engine delivers less HP, because it is not the stop
 AC> valve pressure but the difference between SV pressure and exhaust
 AC> pressure, that defines the work done by the pistons.
We're back to the same problem you had with your washing!
The energy savings can be appreciable in recovering the waste heat, and it
is relatively simple to provide a flap to exhaust to the open air when full
power is needed.
The potential big saving with condensing on a steam loco is to not need such
a big water cart, which needs hauling around.
 AC> Hence racing cars may have "open exhausts" ie no muffler, hence little
 AC> or no back pressure to subtract from the pistons' output. Noisy!
Not quite! The open exhausts are very carefully designed to provide
back-pressure at operating speeds. Because the inlet and exhaust valves are 
open
at the same time, the design trick is to get all the burnt gasses out, but 
ot
to loose too much intake air and unburnt fuel.
The "open" exhausts only provide the required back pressure over a very small
rev range, hence the funny sounds from a racing engine at idle.
(todays lecture completed)
Greg.P.
Chch. NZ.
  
... Catch the Blue Wave!
--- FMail 1.02
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