FWIW the difference here may be between thermodynamic predictions, which are
modeled by Propep and the like and use Gibbs free energy and other parameters
to perform calculations, and kinetic predictions---rates of reactions---which
aren't very predictable, and mostly require that you go into the lab (or in
this case, the testing range) and actually measure the rate and output of a
particular reaction.
Thermodynamically there is no difference between, for example, an 80/20 alloy
of Li/Al and an 80% coating of Li on 20% Al (or 20% Al coated on 80% Li). There
can be an enormous difference kinetically, such that a properly designed
mixture will more closely approach the theoretical thermodynamic limits of the
chemical reaction.
Someone once said that thermodynamics tells us what is possible---a particular
value of Isp, for example. Kinetics tells us what is practical---whether we can
actually obtain that value in practice.
Best -- Terry
________________________________
From: arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> on behalf of
Barry Jolly <1bcjolly@xxxxxxxxxxxxx>
Sent: Tuesday, May 3, 2022 1:01 PM
To: arocket@xxxxxxxxxxxxx <arocket@xxxxxxxxxxxxx>
Subject: [AR] Re: Regarding alitec propellants
I don’t know how to deal with your questions. Not enough education I guess.
My thinking is that the chemical equilibrium programs are based on minimization
of Gibbs free energy. How does one derive a heat of formation value for an
alloy of a small amount of lithium mixed with a large amount of aluminum?
Furthermore, how does one anticipate the mechanisms involved in combustion of
that alloy? I guess what I am trying to figure out is how a program based on
chemical oxidation/reduction reactions can predict a performance increase
caused by the method an intimate mixture of two metals reacts. I read what I
could find on the research of Alitec and they used a chemical equilibrium
program in their research. I find it amazing that a program can predict a
performance increase caused by different boiling points of two metals. I am
doing a poor job of communicating my thoughts so will quit here. I need a face
to face with a professor who can answer my questions.
Sent from my iPhone
On May 3, 2022, at 13:11, Ben Brockert <wikkit@xxxxxxxxx> wrote:
Wouldn't that show up as variation of c* efficiency? The models assume the
chemicals are fully involved, if a significant amount of propellants are going
out the nozzle unreacted then there would be a performance shortfall between
the real motor and the model.
Does non-lithiated HTPB run at 85% c* typical?
Do lithiated rocket programs take into account that lithiated propulsion
engineers will be less worried about performance numbers?
On Tue, May 3, 2022 at 6:28 PM Barry Jolly
<1bcjolly@xxxxxxxxxxxxx<mailto:1bcjolly@xxxxxxxxxxxxx>> wrote:
Question: Do computer programs such as Micropep and NASA’s CET85 have the
ability to predict improvements in parameters, such as Isp, due to changes in
combustion phenomena? From my understanding of Alitec’s explanation, their
propellants increased performance is due to a difference in boiling temperature
of lithium as compared to aluminum in alloy form causing an explosion of the
alloy into nano-type particles which burn very close to the surface of the
propellant. Such explanation appears to me to be based on burning
characteristics of the propellant rather than differences between enthalpies of
propellant reactants and exhaust products.
Sent from my iPhone
