On Feb 25, 5:53 pm, Luke Campbell <lwc...@[EMAIL PROTECTED]
> wrote:
> On Feb 25, 1:14 pm, CharlesRCap...@[EMAIL PROTECTED]
wrote:
> > On Feb 23, 11:16 pm, IsaacKuo <mech...@[EMAIL PROTECTED]
> wrote:
> I am not sure I understand the basic setup - my guess is you have a
> helium turbine as a primary heat engine, then run the thermoelectrics
> off the exhaust heat of the turbine? Then you place the
> thermoelectric coated heat sink inside of a gold mirror with a window
> to let the heat out?
Yes:
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 at 3000K-1123K
(Cycles helium through reactor to the Brayton Cycle Helium Turbine
and back.)
Input: 5mw thermal at 3000K
Output: 5mw thermal at 1123K (K^4 = 1,590,446,354,641)
Stage 2: Brayton Cycle Helium Turbine
(Device using extensive regeneration and consisting of multiple
compressors and intercoolers feeding a hydrogen 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)
(Scavenges waste heat from the Brayton Cycle Helium Turbine)
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
I'm considering putting another Multi-Stage Silicon Electrothermal
Nano-Device stage in there and then just having more compression
cycles to further reduce the amount of heat that needs to be moved to
the radiator.
My assumptions about how temperature differential for electrothermal
devices is calculated is probably flawed though.
I assume that the Helium Turbine would be more efficient if the input
temperature was closer to the 3000K that the engine operates at, but I
don't have numbers for that, and so I stick with what I do have a
model for which has an input temperature of 1123K.
In regards to your suggestion to place the thermoelectrics on the
radiator directly:
That's an interesting idea about mounting the thermoelectrics on the
radiator directly. I might use that if the operating temperature
wouldn't be too high to melt them or worse, reduce their efficiency.
What I am thinking is a radiator with a gold (or some unobtanium
alloy) reflector set up to direct the radiation in a small cone. The
actual cone itself does not really matter because I'm assuming that
all of the energy is hitting the reflector and not radiating directly
to space. So the narrowness of the cone is only important for
determining the size of the reflector which I have not gotten to
calculating yet. The reflector will be actively cooled at to about
133K (see below for details) and the coolant pumped to the interior of
the ship for compression back to operating temperatures. (On the way
it passes through some thermoelectric that radiate directly to space.)
The hull at 50K with an emissivity of around 0.99 is roughly 0.35w per
square meter radiated. The reflector at 133K with 0.02 emissivity is
roughly the same. So if we actively cool the reflector to 133K and
pump the coolant through the electrothermal devices radiating directly
to the 3K background (does not need to be on the back side of the
reflector since we would need to actively cool it anyway and can pump
the helium somewhere else) then we might not get 60% efficiency but
it's still something... 130K differential is what kind of efficiency,
50% maybe? I don't know the math, I've been making it up for now.
So then we need to calculate the heat lost from the reflector directly
(0.35w m^2), the heat reflected to space (98%), and the heat absorbed
back into the system from the reflector (2% of the radiator output,
minus 0.35w m^2 that the reflector is emitting directly) and then how
much heat the electrothermal devices take out of it (50%?), which
leaves some amount to be recycled through the system. We also need to
know what temperature the helium is at when it is cycled back from the
electrothemal devices so we know how much we need to compress it to
get it back to operating temps.
Let's see. The energy of 133K is 312900721 (T^4 if I am making a
correct assumption) so if we take 50% out of it we are left with
111.8K (sqrt(sqrt(312900721))/2 or the fourth root of 50% of the
energy we started with.) in the system. So we then need to compress
that back up to whatever temp I run the radiator at.
What I'm doing basically is reducing the amount of heat that needs to
be compressed and radiated as much as possible (and consequently
generating electricity from it) and then taking the remainder and
getting rid of enough that I can pump the rest to the hull at about
50K. I can create internal reservoirs down to 50K or less inside the
ship if that is needed to operate the thermoelectrics. This however
will cost more (on a percentage base) to compress back up to radiator
temps, but since I'll be working with a smaller about of thermal
energy the relative costs can be manageable. (maybe)
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