Added test for mixture and pseudo mixture (pure substance as mixture) for viscosity

Rolf Stierle · Rolf Stierle · commit be1f67c59be2 · 2025-12-04T13:45:22.000+01:00
diff --git a/crates/feos/src/pcsaft/eos/mod.rs b/crates/feos/src/pcsaft/eos/mod.rs
@@ -386,7 +386,8 @@ impl EntropyScaling for PcSaft {
 mod tests {
     use super::*;
     use crate::pcsaft::parameters::utils::{
-        butane_parameters, propane_butane_parameters, propane_parameters,
+        butane_parameters, nonane_heptane_parameters, nonane_parameters, propane_butane_parameters,
+        propane_parameters,
     };
     use approx::assert_relative_eq;
     use feos_core::*;
@@ -547,23 +548,23 @@ mod tests {
 
     #[test]
     fn viscosity_mix() -> FeosResult<()> {
-        let e = &propane_butane_parameters();
-        let t = 300.0 * KELVIN;
-        let p = 2.0 * BAR;
-        let n = dvector![1.0, 0.0] * MOL;
-        let s = State::new_npt(&e, t, p, &n, None)?;
-        assert_relative_eq!(
-            s.viscosity(),
-            0.00797 * MILLI * PASCAL * SECOND,
-            epsilon = 1e-5
-        );
-        assert_relative_eq!(
-            s.ln_viscosity_reduced(),
-            (s.viscosity() / e.viscosity_reference(s.temperature, s.volume, &s.moles))
-                .into_value()
-                .ln(),
-            epsilon = 1e-15
-        );
+        // Test case: compare fig 15 of Lötgering-Lin 2018 (https://doi.org/10.1021/acs.iecr.7b04871)
+        let e = &nonane_heptane_parameters();
+        let nonane = &nonane_parameters();
+
+        let t = 303.15 * KELVIN;
+        let p = 500.0 * BAR;
+        let n = dvector![0.25, 0.75] * MOL;
+        let viscosity_mix = State::new_npt(&e, t, p, &n, None)?.viscosity();
+        let viscosity_paper = 0.68298 * MILLI * PASCAL * SECOND;
+        assert_relative_eq!(viscosity_paper, viscosity_mix, epsilon = 1e-8);
+
+        // Make sure pure substance case is recovered
+        let n_pseudo_mix = dvector![1.0, 0.0] * MOL;
+        let viscosity_pseudo_mix = State::new_npt(&e, t, p, &n_pseudo_mix, None)?.viscosity();
+        let n_nonane = dvector![1.0] * MOL;
+        let viscosity_nonane = State::new_npt(&nonane, t, p, &n_nonane, None)?.viscosity();
+        assert_relative_eq!(viscosity_pseudo_mix, viscosity_nonane, epsilon = 1e-15);
         Ok(())
     }
 
diff --git a/crates/feos/src/pcsaft/parameters.rs b/crates/feos/src/pcsaft/parameters.rs
@@ -391,6 +391,33 @@ pub mod utils {
         PcSaft::new(PcSaftParameters::new_pure(butane_record).unwrap())
     }
 
+    pub fn nonane_parameters() -> PcSaft {
+        let nonane_json = r#"
+            {
+                "identifier": {
+                    "cas": "111-84-2",
+                    "name": "nonane",
+                    "iupac_name": "nonane",
+                    "smiles": "CCCCCCCCC",
+                    "inchi": "InChI=1S/C9H20/c1-3-5-7-9-8-6-4-2/h3-9H2,1-2H3",
+                    "formula": "C9H20"
+                },
+                "molarweight": 128.258,
+                "m": 4.2079,
+                "sigma": 3.8448,
+                "epsilon_k": 244.51,
+                "viscosity": [
+                    -1.4629,
+                    -3.0058,
+                    -0.5842,
+                    -0.1222
+                ]
+            }"#;
+        let nonane_record: PureRecord<PcSaftRecord, PcSaftAssociationRecord> =
+            serde_json::from_str(nonane_json).expect("Unable to parse json.");
+        PcSaft::new(PcSaftParameters::new_pure(nonane_record).unwrap())
+    }
+
     pub fn dme_parameters() -> PcSaftPars {
         let dme_json = r#"
             {
@@ -522,6 +549,54 @@ pub mod utils {
         PcSaft::new(PcSaftParameters::new_binary(binary_record, None, vec![]).unwrap())
     }
 
+    pub fn nonane_heptane_parameters() -> PcSaft {
+        let binary_json = r#"[
+            {
+                "identifier": {
+                    "cas": "111-84-2",
+                    "name": "nonane",
+                    "iupac_name": "nonane",
+                    "smiles": "CCCCCCCCC",
+                    "inchi": "InChI=1S/C9H20/c1-3-5-7-9-8-6-4-2/h3-9H2,1-2H3",
+                    "formula": "C9H20"
+                },
+                "molarweight": 128.258,
+                "m": 4.2079,
+                "sigma": 3.8448,
+                "epsilon_k": 244.51,
+                "viscosity": [
+                    -1.4629,
+                    -3.0058,
+                    -0.5842,
+                    -0.1222
+                ]
+            },
+            {
+                "identifier": {
+                    "cas": "142-82-5",
+                    "name": "heptane",
+                    "iupac_name": "heptane",
+                    "smiles": "CCCCCCC",
+                    "inchi": "InChI=1S/C7H16/c1-3-5-7-6-4-2/h3-7H2,1-2H3",
+                    "formula": "C7H16"
+                },
+                "molarweight": 100.204,
+                "m": 3.4831,
+                "sigma": 3.8049,
+                "epsilon_k": 238.4,
+                "viscosity": [
+                    -1.2979,
+                    -2.6936,
+                    -0.4951,
+                    -0.0988
+                ]
+            }
+        ]"#;
+        let binary_record: [PureRecord<PcSaftRecord, PcSaftAssociationRecord>; 2] =
+            serde_json::from_str(binary_json).expect("Unable to parse json.");
+        PcSaft::new(PcSaftParameters::new_binary(binary_record, None, vec![]).unwrap())
+    }
+
     #[test]
     pub fn test_kij() -> FeosResult<()> {
         let ch3: String = "CH3".into();
