[mesa-users] Cp - Cv

[Ehsan Moravveji]

Hi all,
I am preparing some exercises for a MESA lab, and do not get my desired result for the difference of specific heats. Below, I walk you through what I expect, and what I get:

the difference between the specific heats can be written either as 

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or 
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where, chiT = d_lnP_d_lnT_cons_Rho, alpha,  and delta are available as output profile columns. alpha = dlnRho_dlnPgas_const_T, and delta = dlnRho_dlnT_const_Pgas.
Please see the attached plot. I show the left-hand-side (LHS) and right-hand-side (RHS) of both formulae on the top panel, in addition to their relative difference \Delta on the bottom panel:
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The bottom panel says that using either of the two relations for Cp-Cv agree within the same order of magnitude. However, the bottom panel shows that the agreement is not perfect.

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The inlist is attached. I use MESA v.6871.
I would like to know why Delta takes such large values.
I think all quantities on the RHS of both above equations are cell-averages, so I should be fine.
Can anyone shed some light on this?

Best regard
Ehsan.
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