Units of property functions

[larschrj]

It would be nice if the documentation explicitly stated that properties are per unit mol when dealing with a single fluid (for the functions that are not already explicitly intensive such as density). That might be the assumption for some people but certainly not all 😉.

Also, there seems to be a copy-paste error in the docstring for mass_density. It states that it calculates the molar density, not mass density.

[longemen3000]

hi!,
on documenting that, do you mean as a preface? all functions that are volume derivatives tend to be intensive (pressure does not depend on the amount of matter), but temperature derivative functions (like Cp and Cv) are extensive. each function has their units documented, but adding additional information never hurts.

on the doc error, i'm fixing that right away

[larschrj]

Some comment in the preface would be helpful at least to me but I take your point that the information is there in the documentation 🙂.

As a tangent to this, it would be nice if mass could passed as an argument to f.ex. volume when dealing with single fluids like IAPWS95 (which is what I have been using so far). I noticed in the docs that this is an option when dealing with mixtures. It would save some tedious calculations for me, but perhaps it is not a good idea for some reason.

[longemen3000]

single fluids are mixtures! (of only one component), you can pass a mass argument in the following way:

julia> using Clapeyron, Unitful

julia> model = IAPWS95()
MultiParameter Equation of state for water:
 Polynomial power terms: 7
 Exponential terms: 44
 Gaussian bell-shaped terms: 3
 Non Analytic terms: 2

julia> volume(model,1u"atm",30u"°C",1u"kg",phase = :l, output = u"L")
1.0043695560170631 L

In this particular example, i pass 1u"kg as a number, i technically abuse one of julia quirks that a number is considered a vector of length 1 in some cases. the correct way would be to pass a [1u"kg"] instead, but that would cause some slowdowns

[larschrj]

My mistake. I must have made an error when trying this previously. That's great 🙂 Thanks 👍

[longemen3000]

I will keep this open in the meantime. The typo in mass_density was corrected. There is a docs PR that should fix this, but it isn't merged yet.

[larschrj]

Although if I pass the vector argument for the mass I get a no method matching error for a_res. But in any case your solution was what I was looking for.

[longemen3000]

Yeah, a_res is more of an internal function 😅, but there should be an api to access those (something like helmholtz_free_energy_res that I thought we had)

[larschrj]

Ooops, missed your comment about keeping this open. Reopened with this.

[ianhbell]

Aside: it should be helmholtz_energy_res rather than helmholtz_free_energy_res according to IUPAC