What is the difference between gas and vapour?

[BadBrain]

Androgogue:

I sort of an aficionado of the so-called "New Steam", and one little trick is to use supercritical steam, but in such small amounts that safety hazards are reduced to a near nullity. I'm also much more interested in reciprocating plants than in turbines, as my primary interest is in railroad locomotives.

Seeing as this is getting a little off-topic, I'll start a new thread under "Mechanical Engineering". If you wish to continue this discussion, meet me there.

 

[BadBrain]

Saturated steam is the steam taken directly off the top of the steam drum. It is at its boiling/condensing temperature at the given pressure. (You might even call it a dewpoint vapor.)

Superheated steam is defined simply as steam heated above its boiling/condensing temperature at a given pressure. To make it, you take the saturated steam and put in through additional tubes in the firebox to add the superheat. The steam's temperature and its enthalpy are both increased.

I'm kinda sort of aware of that. In fact, your description of a water-tube boiler fails to account for the fire-tube superheater boilers of the American-type locomotive:

You can get useful power out of saturated steam. But you will obviously get more power out of an equal mass of superheated steam due to its higher enthalpy. Studying a steam table makes this apparent.

I know that. My question concerns the weight of any kind of condensing engine versus the power which can be extracted from LP exhaust, as my primary interest involves engines other than stationary.

However, if you remember the difference between sensible heat (the heat energy that would be extracted through dropping the temperature of superheated steam) and latent heat (the heat energy that would be extracted by condensing saturated steam), in other words, about 0.5 btu/lb-deg F vs. 970 btu/lb at one atmosphere, you get potentially MORE heat energy out of steam if you condense it as you use it. (Of course, the actual amounts vary with system pressure.)

I totally get that. But, when you're drawing that last possible energy from saturated steam, don't you begin to need pumps to get the exhaust to the condenser, and, from there, to the water reservoir? What is the weight of those pumps, and the expenditure of energy needed to operate them, compared to the horsepower extracted from limp steam? (Once again, my primary interest is in non-stationary engines.)

I've operated both kinds of systems in industrial plants. New power plants operate with supercritical steam; which in this case is superheated steam raised to very high pressure. The benefit, beyond the higher enthalpy of the working fluid, is that as long as supercritical pressure is maintained as the steam expands in the turbine, you need not worry about a phase change (i.e., liquids condensing.)

No problem there, as that sounds like the recipe for New Steam (as long as you limit the live steam in your system, no matter how high the pressure, to an amount easily containable by means of light-weight containment vessels).

As to the comment about calling things by whatever names you want to use, I thought that was the whole point of this exercise... ? It does make a difference, my friend.

What this thread has demonstrated to me is the extent to which nomenclatural confusion is blocking access to conceptual reality.

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I've now launched my new thread entitled: "Welcome to the "New Steam"" in the Mechanical Engineering category, and I think it's best that, if you wish to continue this discussion, you post any response you may have there.