Updated the HTP BOTE.
1) 85% HTP means each 240 g of solution has 15% - 15 * 240/ 100 = 36 g
- of H2O and
85% - 85 * 240 / 100 = 204 g - of H2O2.
2) 36 g of H2O is 2 mols, 18 g each, and 204 g of H2O2 is 6 mols, 34 g each.
3) After decomposing, 240 g of 85% HTP becomes 8 mols H2O and 3 mols O2. Total
11 mols.
4) Avogadro law - at 100 kPa pressure and 273 K temperature 1 mol of
gas is 22.7 l, so
1 kg of 85% HTP which is 1000 / 240 * 11 mols becomes
22.7 * 11 * 1000 / 240 = 1040 l.
5) Approximating for 50 atm pressure and 905 K temperature, just
linearly scaling, have
(1/50) * 905 * 1040 / 273 = 68 l
6) 1 l 85% HTP is ~1325 g, so 1 kg 85% HTP is 0.755 l . We have that
0.755 l of liquid 85%
HTP pushes 68 l at pressure of 50 atm, the ratio is 68 / 0.755 = 90 .
This is just a slightly less crude BOTE calculation, of course. It
could be hard to keep decomposed peroxide to work under 905 K, it may
cool and lose some efficiency. To compare with electric variant, motor
and centrifugal pump efficiency need to be taken into account.
Dropping batteries could be tricky, but hardware itself could be way
simpler for electric variant. Naturally everybody and their particular
case have their own decisions applied.
On 4/7/23, Alexander Mikhailov <alexander.mikhailov@xxxxxxxxx> wrote:
Awesome, thanks!
On 4/7/23, Robert Steinke <robert.steinke@xxxxxxxxx> wrote:
On Thu, Apr 6, 2023 at 10:54 AM Alexander Mikhailov <
alexander.mikhailov@xxxxxxxxx> wrote:
When you run the numbers the energy density of modern batteriesquite well to the kinetic energy extractable from decomposed peroxide
compares
monoprop in a practical steam engine. I did a presentation about this
maybe
10 years ago at space access because when I looked at the numbers I was
floored by how good batteries are nowadays.
I'd definitely be very interested to look at that presentation.
My BOTE calculations for peroxide go like that: at ~50 atm liquid
output pressure amount of input peroxide to drive pumps is ~1/20 of
the total amount of peroxide, mass of pump hardware is negligible,
nothing to drop as too heavy.
What would be approximate numbers for electrical pumping system?
Alex
1 cubic meter of 85% H2O2 (1350 kg) pumped uphill against a dP of 5MPa
takes 5MJ of work. Here's a hobby battery with a "nominal" capacity of
1.8MJ
https://hobbyking.com/en_us/turnigy-high-capacity-battery-20000mah-6s-12c-drone-lipo-pack-xt90.html
Three of them weigh 7.9kg, 1/170 the mass of the peroxide.
Now, this is a back of the envelope assuming 100% efficiency and the
battery actually delivers its nominal capacity at a high discharge rate,
and not accounting for electric motor and pump hardware mass. But it's
still surprising that batteries are competitive with an H2O2 monoprop
steam
engine.