Difficulty Finding Hydrogen (H2) Properties for Gas Properties (G) Block

Hi everyone,

I'm having some trouble finding the different properties of Hydrogen (H2) that I need to set in the Gas Properties (G) block in Simscape. I'm hoping someone here can provide me with some guidance on how to approach this.

Can anyone recommend a resource or provide some tips on how to determine these properties for Hydrogen (H2)?

Any help would be greatly appreciated!

Thanks in advance,

Answer 1

[Are Mjaavatten]

The real gas option in Simscape requires tables of properties as functions of temperature and pressure. You will find the data you need in the NIST Chemistry Webbook's Thermophysical Properties of Fluid Systems. You may download 1D tables for constant temperature and varying pressure or vice versa.

My File Exchange contribution nistdata provides a function will read the NIST data and create a struct of 2D tables in temperature and pressure. You may have to convert the units of some variables to agree with Simscape's standards. The units in the tables from nistdata.m are given in the help section of the file.

I also have another File Exchange contribution Thermodynamic models and tools for H2O, H2, CO2 and Air that will give you a flexible tool for solving a range of thermodynamic problems. This uses the same models as NIST. But for your needs, I would recommend nistdata or manually downloading from NIST.

[Luca]

Dear @Are Mjaavatten

Thank you for your contribution, I am using it do define the H2 parameters in simscape gas properties block.

I still have 2 tables of parameters that I have not found in the data:

Isothermal bulk modulus table

Isobaric thermal expansion coefficient table

Do you have any suggestions on where to find them or how to compute them?

BR,

Luca

[Are Mjaavatten]

Dear @Luca

In the GitHub repository https://github.com/are-mj/thermodynamics linked to my thermodynamic models

you will find the document Properties from Helmholtz.pdf which contains a table of molar properties expressed in terms of the partial derivatives of 𝑓(𝑇, 𝑣).

Here you will find expressions for "Coefficient of thermal expansion" and "Isothermal compressibility", which are what you ask for. Once you have a converged th object at the conditions you specify, you can type:

alpha = -th.f_Tv/th.f_vv/th.v;
beta = -1/th.f_vv/th.v;

Note that you must converge the thermodynamic object to the correct phase. Tpcalc(T,p) will give you the vapour phase. The liquid phase is a little more tricky. Here is an example for H2O at 100°C:

th = thermo('H2O');
T = 273.15+100;
[ps,v_liq,v_vap] = th.saturation(T);
th.Tvcalc(T,v_liq);
alpha = -th.f_Tv/th.f_vv/th.v;
beta = -1/th.f_vv/th.v;

Notice that th.p differs by almost 5% from ps. This is an effect of the very low compressibility of the liquid phase. A small change in molar volume results in a large change in pressure. The saturation curve is calculated by a separate function and molar volumes may not agree exactly with the thermodynamic model. Another effect of the low compressibility is that results are pretty much functions of T only, unless your pressure is very much higher than the saturation pressure at the given T.