Like Albert, I claim no expertise in thermodynamics as it has been a
few years since I had any training in the area and I may be
completely full of s%^t. However, see my comments below...
--- In coldwarcomms@y..., albertjlafrance@c... wrote:
> In a message dated 12/27/2001 9:47:25 PM Eastern Standard Time,
> wb8foz@n... writes:
> > Err...
> > I can't see the difference will be that big. You take in air at
> > X degrees and dump it at Y. The amount of air you'll need is a
> > function of how many KW of waste heat you have to dump.
> Caution: don't believe any of the following, thermodynamics being
> yet another of my areas of near-total ignorance...
> Also, the heat-transfer path in the turbine is direct from the
> combustion chamber to the discharge air stream, since the
> combustion exhaust *is* the heat-transfer medium. In contrast,
> some of the Diesel's heat has to transfer three times: from the
> cylinders to the water jacket, from the water to the radiator tubes
> and fins, and finally from radiator to the cooling air stream.
And if I remember correctly, in order to get effiecient heat transfer
through water cooling, you have to purposefully reject more heat than
by direct cooling. So not only do you have to remove the heat
generated by the inefficiencies of the generator, you also
must "waste" some additional energy in order to move it through the
cooling water circuit.
> Here, the advantage of the turbine may be that its air intake is a
> rotary compressor which provides higher suction than the cooling
> fan of an engine's radiator, thus moving more air through a given-
> size opening.
It is also interesting to note that if you compare the specs of a 12
kW generator with an air-cooled engine with that of a 12 kW generator
with a water-cooled engine, the water-cooled engine requires a lot
more air-flow. (My Onan catalog say 890 cfm for the air-cooled
engine compared to 2750 cfm for a water-cooled unit.) This tells me
that the water-cooled generator is inherently less efficient in
discharging its waste heat... This isn't quite the same as comparing
a water-cooled diesel to a cumbusion turbine because as Albert
pointed out, the cooling air in the CT is also the heat tranfer
medium. However, this is a much more "apples to apples" comparison
that may indicate where some of the inefficiencies are...
One last thing... About the unit for sale on eBay being a three-phase
unit... Many backup generators can be reconfigured in the field to
have either three- or single-phase outputs. I'm not sure if this is
the case with the one on eBay, but if it has the right number of
windings, it's possible that it could be reconfigured to operate as a