Re: PBS Series: "The Carrier"

On Sun, 04 May 2008 12:56:11 GMT, Vince Brannigan
<firelaw@xxxxxxxxxxx> wrote:

Peter Skelton wrote:
On Sat, 3 May 2008 19:29:15 -0700 (PDT), mike
<marathag@xxxxxxxxx> wrote:


On May 3, 10:23 am, "Jeff Crowell" <jeffDOTcrow...@xxxxxx> wrote:


Subjectively, it feels like the acceleration is pretty constant.
If you guesstimate track length as 300 feet (by eye, the flight deck
of the Nimitz class is about 3.5 'cat tracks' long) and endspeed of
145 knots, stroke time of 2 seconds, that comes out to 10.8Gs.
It does cage your eyeballs pretty well!

Given the volume of steam that's passing through one or two valves,
I suspect acceleration may drop off with distance traveled. Only
way I can see to avoid that would be to have more valves open
along the track as the piston proceeds on its merry way, that
way you could hold pressure nearly constant..

Thats one of the neat things about high pressure steam.

It keeps expanding-- something that multi-stage turbines
(and old compound cylinder engines) take well advantage of.

Its also why its so dangerous when its vented. A 60psi boiler
popping is far,far worse than a same size airtank pressurized
to 250psi. Even a home waterheater with a bad relief valve
can do amazing amounts of damage


A 60 psi boiler generally contains more water by mass than steam.
The water is heated above its boiling point at standard pressure,
so much of it flashes to steam greatly increasing the volume of
gas if the boiler ruptures.

Don't think so

There is not enough energy to vaporize much of it

Nonsense, see below


Energy Requirements

The energy required to heat water is significantly lower than that
needed to vaporize it, for example for steam distillation^[10]
<http://en.wikipedia.org/wiki/Superheated_water#cite_note-9> and the
energy is easier to recycle using heat exchangers. The energy
requirements can be calculated from steam tables. For example, to heat
water from 25°C to steam at 250°C at 1 atm requires 2869 kJ / kg. To
heat water at 25°C to liquid water at 250°C at 5 MPa requires only 976
kJ / kg.

For every six kilos of water in the boiler, you get a kilo of
steam. (This is consistent with your arithmetic and a heat loss
of 50% rounded). So for a boiler with twelve kilos of water for
every kilo of steam (an absurdly low amount of water) there is
twice as much energy in the flashed steam as in the original
steam.

Water flashing is a very widely recognized hazard in steam
operations. It scares me that somebody might read some of your
material and believe it.

Peter Skelton
.

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