Hello,
I have the following two questions about flash.
FIRST question. I use flash for MHD:
#Modules file for rosetta generated by setup -auto
INCLUDE database/amr/paramesh2.0
INCLUDE driver/time_dep
INCLUDE hydro/mhd/divb_diffuse
INCLUDE io/amr/hdf5_serial
INCLUDE materials/eos/gamma
INCLUDE materials/magnetic_resistivity/const
INCLUDE materials/viscosity/constant
INCLUDE mesh/amr/paramesh2.0/second_order_old
INCLUDE util/tools
INCLUDE util/wrapping
My hydro initial conditions are ideal gas with pressure, density,
and gamma index all constant in space. I check the initial conditions
with the initial .chk point file, rosetta_hdf5_chk_0000, and find the
following:
density rho = 1.00000 g/cm^3
pressure P = 6.00000e-4 erg/cm^3
temperature T = 7.21630e-12 K
specific internal energy eint = 9.00000e-4 erg/g
gamma index gamma = 5/3
Next, I check equation of state for my ideal gas:
P = rho*k_B*T/(rho/n) = rho*k_B*T/m,
where k_B is the Boltzmann constant, n is concentration (particles
per cm^3), and by definition
m = rho/n
is the averaged pass of the particles of the ideal gas.
Using data for P, rho and T, one finds
m = rho*k_B*T/P = 1.00000*1.38062e-16*7.21630e-12/6.00000e-4
m = 1.66049e-24 gramm
This is a very very strange result, because
the proton mass is 1.67261e-24 gramm, it's larger by 1% !!!
the average of proton and electron masses (assuming fully
ionized proton plasma) is 0.5*(m_p+m_e)=0.83676e-24 gramm
Does flash have the proton mass and Boltzmann constant right?
--------------------------------------------------------
SECOND question.
In the flash guide, page 92, section 9.1.3.1, "Thermal diffusion", one
can read in the line just before the line previous to equation (9.13)
that the thermal diffusivity is \lambda = \sigma/(\rho*c_p), where
\sigma is the thermal conductivity, and \rho is density. This looks
extremely misleading, because c_p is not defined there, and one naturally
assumes that c_p is the specific heat capacity at constant pressure. I
believe this may be wrong because is may should have been c_v, which is
the specific heat capacity at constant volume. Note that c_p/c_v=gamma.
The reason i ask this question is not that i want to point out a minor
misprint in the guide, but because I may be wrong and c_p may be the
right heat capacity to use, in case the heat conduction equations in
flash are written in some unconventional way. So, what should really be
there, c_p or c_v?
Thank you very much,
Leonid
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