Keith Henson wrote:
[...]

Assuming the radiator and collector mass per square meter is about the
same, then you can see from the graph that the minimum occurs a bit
above 100 deg C, which is far below the 370-650 deg C quoted in an old
paper he

http://contrails.iit.edu/DigitalColl...2article42.pdf


I'd use something like 1,000 K as Tl. High efficiency and high rate heat
radiation in space is problematic unless the temp is high. Radiative
heat dispersal is about 100 kW/m^2 for the low temp radiator.

Incident radiation on the collector is 1.1 MW/m^2, the mirror (which
weighs 0.005 kg/m^2 excluding support) concentrates sunlight from 1.33
kW/m^2 to 1.1 MW/m^2, approximately 820 times at 80% efficiency.


Th is 1800 K, Carnot efficiency is 44%, assumed overall efficiency to
local electricity is 29%.


I can't say for sure what the mass per unit area of radiation or
collection are. I need to analyze a canvas tube (like an air
mattress) radiator filled with low pressure gas and air float
charcoal, Buckey balls or BeO. Assuming they are both around a
kg/m^2, a kW should come in around 3.2 kg.


I do not understand that. Ignoring the mirror, which I think - actually,
I don't know what you are doing -

In my example design the single sided collector has a mass of 5 kg/m^2,
the double sided radiator 1 kg/m^2.

The gas contact areas are 15 times the collecting or radiating areas.
The coefficients of convective heat transfer are 800 and 80 W/m^2 K (the
gas in the high temperature one is at twelve times the pressure of the
low temperature one). The temperature difference across each is 100 K -
the collector surface is at 1900K, the radiator surface at 900 K.

One m^2 of collector produces 400 kWe at the station, and needs 8 or 10
square meters of radiator, so 15 kg of collectors and radiators are
needed to produce 400 kWe, or 0.0375 kg/kW.

My numbers might be a little hard to achieve, though they are meant to
be only medium-tech at best, so let's be very generous and say 150 grams
per kW. That's still 20 times less.


Turbines and generators
are around 0.1 kg/kW based on Boeing 777 engines. Transmitters have
been analyzed at less than a kg/kW. So giving room for such parts as
power conductors and the joint to the transmitter, it *might* come in
at 5kg/kW.

If anyone has some spare web space to hang a small xls file, I can
send it to you.


Yes please. I seem to be missing something in your argument. Will put it
up too.

-- Peter Fairbrother



Keith

-- Peter Fairbrother