And, nearly forgot, but optimum cooling *is* desired if weight is to be
optimized. (But cost and other considerations, YMMV, yada, yada...)
David Masten
CTO
Masten Space Systems, Inc.
1570 Sabovich St., Mojave, CA 93501
415.244.9171 (Mobile)
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On 9/18/2015 9:34 AM, Norman Yarvin wrote:
Rockets don't need "optimum cooling", though. They just need enough
cooling to work. One isn't trying to actually maximize heat transfer,
just to have enough of it so that the chamber walls don't fail.
One thing you could do with DMLS is "transpiration cooling", such as
P&W wanted to use for the SSME. Instead of film cooling, where you
have a fuel-rich film flowing down the sides of the chamber, in
transpiration cooling fuel exudes from pores in the chamber walls.
Films can be disrupted by unexpected patterns of flow in the chamber,
such as can occur during combustion instability; transpiration is
harder to disrupt. Transpiration cooling requires a porous surface,
which makes it a good match for laser sintering (where they have to
work to make the material _not_ porous).
Now, it might not work well with hydrocarbons, which could coke and
clog the pores; the SSME proposal was for using it with hydrogen,
which doesn't have that problem. The RL-10, which uses it on the
injector face, is likewise a hydrogen engine. Still, it's not like
it's easy to get methane to coke, or for that matter ethanol, so it
might be worth a try.
On Fri, Sep 18, 2015 at 03:06:36PM +0100, Ian Woollard wrote:
Yes, blood vessels are known to be fractal.
It's the same type of physical process; convecting stuff (in the case of
rockets, heat, in the case of organism, oxygen, food and waste) that
diffuses into or out of the liquid, using the minimum amount of effort (you
want minimum delta-P on your rocket's coolant channels, and organisms want
to have the minimum sized heart that will work.)
Designing fractals isn't necessarily that difficult, for example consider
this diagram:
https://en.wikipedia.org/wiki/File:First_to_third_order_constructs_of_the_constructal_design_of_a_cooling_system.JPEG
It may well be possible to do the maths to design that kind of thing with
just a spreadsheet, or even paper and a pencil and a calculator.
On 18 September 2015 at 08:14, John Dom <johndom@xxxxxxxxx> wrote:
Reminds me to our blood transport system through the body where arteries
get typically smallest close to the skin. Not sure such are fractal though.
jd
*From:* arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx]
*On Behalf Of *Ian Woollard
*Sent:* vrijdag 18 september 2015 0:32
*To:* arocket@xxxxxxxxxxxxx
*Subject:* [AR] Re: DMLS Chambers WAS Re: Rocket Labs
Constructal law theory says that optimum cooling is probably fractal
channels, starting with large channels that divide into multiple smaller
channels and so on until you get down to the boundary layer thickness of
the fluid and then going back again the other way.
Doing that has lower pressure drop, so you can get better flow for any
given surface area; and you want high surface area, and it has *very* high
surface area. Of course you have to have the *right* scaling factor in your
fractal to give good performance.
On 16 September 2015 at 20:23, Dave McMillan <skyefire@xxxxxxxxxxxx>
wrote:
On 9/16/2015 12:36 PM, Ben Brockert wrote:
I'm more curious if they're using standard channels or if they're
using a more modern design appropriate for a printed engine. I'm
always a bit frustrated when I see 3d printed engines with channels
that were designed for a milled chamber. At least spiral them enough
that differences in flow from channel to channel don't cause linear
hot spots and early failures.
That actually reminds me of something I've speculated about in the
past: if one assumes a "perfect" 3D-printing process for creating a regen
engine chamber/throat/nozzle, has anyone ever come up with an optimum
design for the cooling channels layout? While 3DP is hardly perfect, it
certainly does make previously-impossible complex interior geometries
suddenly a lot less impossible.
Hm... and it suddenly occurs to me that 3DP might make it possible to
iterate complex *injector* geometries much more rapidly than was previously
possible. Dunno if injectors might benefit from that as much as regen
channels, but anything that lowers the cost of trying different designs
can't hurt.
Going further afield... watching the various tech journals, it seems
we might not be so far from being able to print sensors, and their
"wiring," directly into the structure of of the engine. I have to imagine
that having a sensor "carpet" every few tens of millimeters throughout the
engine shell would be a boon to engine designers.
--
-Ian Woollard
Sent from my Turing machine
--
-Ian Woollard
Sent from my Turing machine
