On Feb 26, 11:42 am, IsaacKuo <mech...@[EMAIL PROTECTED]
> wrote:
> On Feb 26, 9:55 am, CharlesRCap...@[EMAIL PROTECTED]
wrote:
> > On Feb 25, 4:29 pm, IsaacKuo <mech...@[EMAIL PROTECTED]
> wrote:
> > > On Feb 25, 2:14 pm, CharlesRCap...@[EMAIL PROTECTED]
wrote:
> > > Where is "the heat" coming from? A fission reactor, perhaps?
> > > In principle, you can make a very efficient reactor that converts
> > > almost all of its heat energy into electricity. Conveniently,
> > > a heat engine is most efficient when the radiator temperature
> > > is a small fraction of the reactor's temperature. For stealth,
> > > this seems like a win-win situation. Your radiator is a lower
> > > temperature, and you have less waste heat to worry about!
> > I am assuming the use of a MITEE nuclear thermal rocket which can
> > produce very little waste heat for its output. Further, I am assuming
> > that the efficiency of that reactor can be adjusted downward so that
> > more waste heat is radiated into the heat engine system if needed.
>
> Oh, well then forget about any sort of stealth. The reason a
> nuclear thermal rocket "produces little waste heat" is
> because it actually produces lots of waste heat but most
> of it is conveniently dumped into the exhaust. The rocket
> exhaust is going to be rather visible; a Space Shuttle launch
> is stealthy in comparison.
Indeed? Well it gets back to the question that I had asked in that
other thread which was how detectible is the trail from an Ion drive
or a VASIMR's hydrogen trail? Is it even worth trying to stealth your
craft if your exhaust is going to give you away no matter what? If the
exhaust from an ion drive or VASIMR (or a MITEE) is going to be very
detectible then there is no reason to ever worry about the temperature
of your craft's hull. How different is the exhaust from a MITEE than
from a VASIMR? They both heat and spew out hydrogen. In any case you
can replace stage 0 with just a plain old fission plant if you like
and then I need to make sure I have enough electricity left over to
run a drive of some sort that isn't as 'noisy' as a MITEE. What I'm
working on now is not about the propulsion system, rather it is about
the heat rejection system.
***
To preface this: Obviously something in the math is off. Probably
several things and very badly off. If everyone says it can't be done,
then if I have something that says it can, I have a problem somewhere.
I'm feeling really troubled about the values I came up with to
describe the compression stages, I feel that they are probably more
than an order of magnitude or more off. I'm also unhappy with the
values I got for the Electrothermal devices as well.
***
I'm pretty sure my calculations are flawed in a serious manner, but
I'm not sure how exactly. I am proceeding on the assumption that they
are within an order of magnitude in accuracy. I'm expecting to refine
them as I get a better understanding of the math involved with the
various stages. It's my hope that the end result will be within an
order of magnitude, but who knows if that'll be the case.
Main Cycle:
Stage 0: Reactor - MITEE Nuclear Thermal Rocket
Capacity: 20mw thermal @[EMAIL PROTECTED]
3000K
Efficiency: 75% (adjustable)
Waste: 5mw thermal @[EMAIL PROTECTED]
3000K
Stage 1: Helium Coolant Reservoir + Intercooler at 3000-1123K
Input: 5mw thermal at 3000K
Output: 5mw thermal at 1123K (K^4 = 1,590,446,354,641)
Stage 2: Brayton Cycle Helium Turbine
Input: 5mw thermal at 1123K
Efficiency: 50.11%
Generation: 2.5055mw electrical
Waste: 2.4945mw thermal at 378.7K
Stage 3: Helium Coolant Reservoir at 378.7K
Input: 2.4945mw thermal at 378.7K
Output: 2.4945mw thermal at 378.7K
Stage 4: Multi-Stage Silicon Electrothermal Nano-Devices (#1) ****
Input: 2.4945mw thermal at 378.7K (K^4 = 20,567,486,479)
Efficiency: 60%
Generation: 1.4967mw electrical
Waste: 0.9978mw thermal at 301.2K (K^4 = 8,226,994,544)
Stage 5: Helium Coolant Reservoir at 301.2K
Input: 0.9978mw thermal at 301.2K
Output: 0.9978mw thermal at 301.2K
Stage 6: Multi-Stage Silicon Electrothermal Nano-Devices (#2) ****
Input: 0.9978mw thermal at 301.2K (K^4 = 8,226,994,544)
Efficiency: 60%
Generation: 0.5987mw electrical
Waste: 0.3991mw thermal at 239.5K (K^4 = 3,290,797,817)
Stage 7: Helium Coolant Reservoir at 301.2K
Input: 0.3991mw thermal at 239.5K
Output: 0.3991mw thermal at 239.5K
Stage 8: Multi-Stage Silicon Electrothermal Nano-Devices (#3) ****
Input: 0.3991mw thermal at 239.5K (K^4 = 3,290,797,817)
Efficiency: 60%
Generation: 0.2395mw electrical
Waste: 0.1596mw thermal at 190.5K (K^4 = 1,316,319,127)
Stage 9: Helium Coolant Reservoir at 190.5K
Input: 0.1596mw thermal at 190.5K
Output: 0.1596mw thermal at 190.5K
Stage 10: Multi-Stage Silicon Electrothermal Nano-Devices (#4) ****
Input: 0.1596mw thermal at 190.5K (K^4 = 1,316,319,127)
Efficiency: 60%
Generation: 0.0958mw electrical
Waste: 0.0638mw thermal at 151.5K (K^4 = 526,527,651)
Stage 11: Helium Coolant Reservoir at 151.5K
Input: 0.0638mw thermal at 151.5K
Output: 0.0638mw thermal at 151.5K
Stage 12: Helium Compressor/Intercooler (#1)
Input: 0.0638mw thermal at 151.5K (K^4 = 526,527,651)
Draw: 0.0089mw electrical**
Waste: 0.0009mw thermal***
Output: 0.0647mw thermal at 174.1K* (K^4 = 917,737,696)
Stage 13: Helium Coolant Reservoir at 174.1K
Input: 0.0647mw thermal at 174.1K
Output: 0.0647mw thermal at 174.1K
.
. (Jumping ahead a bit, some 21 cycles of compression are assumed
here.)
.
Stage 55: Helium Compressor/Intercooler (#22)
Input: 0.0855mw thermal at 2800.1K (K^4 = 61,474,381,270,411)
Draw: 0.0120mw electrical**
Waste: 0.0012mw thermal***
Output: 0.0866mw thermal at 3217.3K* (K^4 = 107,143,600,341,952)
Stage 56: Helium Coolant Reservoir at 3217.3K
Input: 0.0866mw thermal at 3217.3K
Output: 0.0866mw thermal at 3217.3K
Total Electricity for Compression: 0.2285mw
Stage 57: Radiator and Reflector
Input: 0.0866mw thermal at 3217.3K
Reflection Efficiency: 98%
Rejected: 0.0849mw thermal
Reabsorbed: 0.0017mw thermal at 3217.3K
Stage 58: Reflector Active Cooling to 50K or less
Input: 0.0017mw thermal at 3217.3K
Output: 0.0017mw thermal at 50K or less
Stage 59: Outer Hull Helium Reservoir at 50K or less
Input: 1700w thermal at 50K
Radiation: 0.3542 watts per m^2 at 0.9994 Emissivity
Hull Area: 4800 m^2 to Eliminate 1700w at 50K
* I'm assuming a factor of 1.743 on the energy for each compression
stage, this is derived from the values listed in the Brayton cycle
simulation software. I feel that I am making bad assumptions on this
though.
** I'm assuming a factor of 0.1401 on the energy (per thermal unit)
needed to compress per stage. Which is also derived from the values
listed in the Brayton cycle simulation software. I feel that I am
making bad assumptions on this though.
*** I'm assuming 10% waste heat on the electricity drawn is added to
the heat moved. This is a wild guess.
**** I assume that if the devices work at 60% efficiency that they
take out 60% of the energy in the heated medium, the energy is
equivalent to T(K)^4 and they leave 40% of that to pass through as
waste. Thus the output temperature is sqrt(sqrt(((T^4)*0.4))) which
could be wildly incorrect and I have the feeling that it is, I think
the output temperature is much lower than that equation represents,
but I don't have another equation to work with.
All of these values could be off by huge amounts.
Also this does not take into account the heat that is returned from
using the electrical generation that's left over. I assume that one
would tune the output of the reactor so that no unused electricity
would be generated.
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