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Fix calculation of phase equilibria if one or more component has 0 composition #331

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Fix calculation of phase equilibria if one or more component has 0 composition #331

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9 changes: 8 additions & 1 deletion crates/feos-core/src/state/critical_point.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@ use num_dual::{
implicit_derivative_binary, implicit_derivative_vec, jacobian, partial, partial2,
third_derivative,
};
use num_traits::Zero;
use quantity::{Density, Pressure, Temperature};

const MAX_ITER_CRIT_POINT: usize = 50;
Expand Down Expand Up @@ -537,7 +538,13 @@ where
let n = n + sqrt_z.component_mul(&u).map(Dual3::from_re) * s;
let t = Dual3::from_re(temperature);
let v = Dual3::from_re(molar_volume);
let ig = n.dot(&n.map(|n| (n / v).ln() - 1.0));
let ig = n.dot(&n.map(|n| {
if n.is_zero() {
Dual3::zero()
} else {
(n / v).ln() - 1.0
}
}));
eos.lift().residual_helmholtz_energy(t, v, &n) / t + ig
},
D::from(0.0),
Expand Down
31 changes: 30 additions & 1 deletion crates/feos/tests/pcsaft/critical_point.rs
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Original file line number Diff line number Diff line change
@@ -1,10 +1,11 @@
use approx::assert_relative_eq;
use feos::pcsaft::{PcSaft, PcSaftParameters};
use feos_core::State;
use feos_core::parameter::IdentifierOption;
use feos_core::{SolverOptions, State};
use nalgebra::dvector;
use quantity::*;
use std::error::Error;
use std::sync::Arc;
use typenum::P3;

#[test]
Expand Down Expand Up @@ -47,3 +48,31 @@ fn test_critical_point_mix() -> Result<(), Box<dyn Error>> {
);
Ok(())
}

#[test]
fn test_critical_point_limits() -> Result<(), Box<dyn Error>> {
let params = PcSaftParameters::from_json(
vec!["propane", "butane"],
"tests/pcsaft/test_parameters.json",
None,
IdentifierOption::Name,
)?;
let options = SolverOptions {
verbosity: feos_core::Verbosity::Iter,
..Default::default()
};
let saft = Arc::new(PcSaft::new(params));
let cp_pure = State::critical_point_pure(&saft, None, None, options)?;
println!("{} {}", cp_pure[0], cp_pure[1]);
let molefracs = dvector![0.0, 1.0];
let cp_2 = State::critical_point(&saft, Some(&molefracs), None, None, options)?;
println!("{}", cp_2);
let molefracs = dvector![1.0, 0.0];
let cp_1 = State::critical_point(&saft, Some(&molefracs), None, None, options)?;
println!("{}", cp_1);
assert_eq!(cp_pure[0].temperature, cp_1.temperature);
assert_eq!(cp_pure[0].density, cp_1.density);
assert_eq!(cp_pure[1].temperature, cp_2.temperature);
assert_eq!(cp_pure[1].density, cp_2.density);
Ok(())
}
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