[FLASH-BUGS] is the proton mass right in flash?

[Paul Ricker]

I can answer the first question.

The physical constants in FLASH are set in physical_constants.F90.
The gamma-law EOS uses the ideal gas constant (8.3145119843E7 erg/mol/K)
to relate the density, temperature, and pressure.  This is just equal
to Boltzmann's constant times Avogadro's constant.  The effective
atomic weight used in this calculation is (one over) the
abundance-weighted sum of the (inverses of the) atomic weights of the
constituents, set in init_mat.F90.  By default I believe you get one
fluid with an atomic weight of 1.

The proton mass is separately listed in the physical constants
database with a value of 1.672623110E-24 g, though it is not used
by the gamma-law EOS.

So the constants have the correct values, but the effective atomic
mass seems to assume mass units of 1/N_A g.  In these units the
effective atomic weight of pure neutral hydrogen is 1.0078251,
and for fully ionized hydrogen it is 0.503913.  You should create
a special version of init_mat.F90 that sets "A" for the fluid equal
to one of these values rather than 1.

Add this to the "improve documentation" to-do list...

Best,
Paul


On Tue, 2003-04-15 at 12:12, Leonid Malyshkin wrote:
> 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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Paul M. Ricker                                Department of Astronomy
Assistant Professor   National Center for Supercomputing Applications
pmricker at uiuc.edu          University of Illinois at Urbana-Champaign
http://www.astro.uiuc.edu/~pmricker              Urbana IL 61801-3074
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