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Science Forum Index » Space Forum » Answer to a critic's question about MEMs...
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 Posted: Sat May 10, 2008 1:17 pm |
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| Posted: Sat May 10, 2008 1:20 pm |
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I have attempted to respond to a person's objections related to MEMs
and Google will not take my post. |
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| Posted: Sat May 10, 2008 1:56 pm |
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On May 10, 7:20 pm, Willie.Moo... at (no spam) gmail.com wrote:
Quote: I have attempted to respond to a person's objections related to MEMs
and Google will not take my post.
I've attempted to respond to a critic's response to my MEMs articles
several times. While Google will gladly post test statements, I
don't
seem to be capable of posting my lengthy reply with references and
whatnot. Now when I started by Word program to transfer my clipboard
there, I lost what I had copied to the clipboard. So, I must retype
everything... hopefully it will take this time.
JS said that the rotor would fail, that's not the case;
High Rotor Speeds
http://www.
greencarcongress
.com/2006/09/
memsbased_turbi_1.html
Okay - so it posted up to this point, so I've got to believe it has
something to do with the URL? and maybe JS name?
So, I've broken up the URL - just reassemble it to read it. Rotor
speeds are really high and they don't melt down as JS asserts.
JS said that the combustion wouldn't be efficient, again not the case
Microcombustion
http://
ronney.usc.edu/
publications/ISC31
SwissRollModel.pdf
JS said that thrust would be inadequate, not the case
MEMs rockets
http://www.me.berkeley.edu/
mrcl/rockets.html
JS said that viscous effects would degrade performance - while it is
an important design factor, it can be mitigated in careful design.
For example, increasing chamber pressure, or careful control of
surface chemistry
Heat Transfer and Viscous Effects
http://www.uvm.edu/
~vacc/pdf/AIAA%202007
-3987.pdf
Viscous Effects
http://www.engin.brown.edu/
Faculty/breuer/KSB%20
Papers/ASME98_Nozzles.pdf
Scaling of Viscous Effects
http://raphael.mit.edu/
Technical_Reports/
Bayt_Thesis.pdf
Surface chemistry and viscous effects
http://ame-www.usc.edu/
afrlmicrofluidics/Oral%20
Breuer.pdf
JS misquoted Dr. K stating that he said there would be a 50% specific
impulse drop in micro-thrusters. Dr. K actually said that careful
attention must be paid to details of microthruster design or one
might
suffer such large losses.
JS said that rockets are only useful for rockets and spacecraft. He
did not say why. Perhaps it is their high cost. Perhaps it is their
inherent risk. Perhaps it is their complexity. i showed that a
320,000 to 1 thrust to weight ratio would produce propulsive devices
of immense capability at trivial costs which clearly have huge
potential effects. I also did an analysis of a spacecraft
application
- to the lunar module. So, I am talking spacecraft as well as other
potential applications.
It should be up to the market to decide what use this technology has
once its further along. While 320,000 to 1 and 100% large engine
performance is agressive, its a reasonable target. Yet even at
2,000
to 1 and 50% engine performance might prove useful.
Consider a 1 kg lifting surface made of a microengine array that has
a
2,000 to 1 thrust to weight. The surface itself masses 500
milligrams. At $5,300 per kg - typical of aerospace equipment - this
costs $2.65 - with a specific impulse of say 200 seconds - a
propellant fraction of 20% achieves 446 m/sec. Enough to toss 1 kg
across Manhattan. It costs $20 to $50 to have a package delivered
same day in Manhattan. One can imagine office supply stores selling
half pound packages with propulsive surfaces at office supply stores
10 for $100 - and them being used to send packages cross-town in
seconds.
So, even accepting all of JS' conclusions - of modest thrust to
weight
and modest performance, we still have the potential of interesting
commercial uses.
This doesn't say that such uses are certain. This does say that its
premature to prejudge things based on faulty reasoning. |
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