From b6a18df17bfcd4efc4128fbc07e986a034c66b54 Mon Sep 17 00:00:00 2001
From: Alex Selimov <alex@alexselimov.com>
Date: Wed, 1 Apr 2026 23:33:24 -0400
Subject: [PATCH] Add consts and gas_mixtures with initial calculations

---
 src/consts.rs               |  2 +
 src/lib.rs                  | 13 +++++-
 src/mixtures/gas_mixture.rs | 79 +++++++++++++++++++++++++++++++++++++
 src/mixtures/mod.rs         |  1 +
 src/properties/mod.rs       |  4 +-
 5 files changed, 95 insertions(+), 4 deletions(-)
 create mode 100644 src/consts.rs
 create mode 100644 src/mixtures/gas_mixture.rs
 create mode 100644 src/mixtures/mod.rs

diff --git a/src/consts.rs b/src/consts.rs
new file mode 100644
index 0000000..1cc9a2b
--- /dev/null
+++ b/src/consts.rs
@@ -0,0 +1,2 @@
+// 1 bar ref pressure in Pa
+pub const P_REF:f64 = 1e5;
diff --git a/src/lib.rs b/src/lib.rs
index c92486b..eee60c5 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,3 +1,5 @@
+pub mod consts;
+pub mod mixtures;
 pub mod properties;
 
 #[macro_export]
@@ -7,7 +9,10 @@ macro_rules! assert_delta {
         assert!(
             diff <= $delta,
             "|{} - {}| = {} > {}",
-            $left, $right, diff, $delta
+            $left,
+            $right,
+            diff,
+            $delta
         );
     }};
 }
@@ -29,7 +34,11 @@ macro_rules! assert_vec_delta {
             assert!(
                 diff <= $delta,
                 "element {} not within delta: |{} - {}| = {} > {}",
-                i, l, r, diff, $delta
+                i,
+                l,
+                r,
+                diff,
+                $delta
             );
         }
     }};
diff --git a/src/mixtures/gas_mixture.rs b/src/mixtures/gas_mixture.rs
new file mode 100644
index 0000000..cc09169
--- /dev/null
+++ b/src/mixtures/gas_mixture.rs
@@ -0,0 +1,79 @@
+use crate::{
+    consts::P_REF,
+    properties::{
+        thermo_fit::{Phase, SpeciesThermoData},
+        transport_fit::SpeciesTransportData,
+    },
+};
+
+pub struct GasMixture {
+    pub(crate) ns: Vec<f64>,
+    pub(crate) nsum: f64
+    pub(crate) species: Vec<SpeciesThermoData>,
+    pub(crate) transport_data: Vec<SpeciesTransportData>,
+}
+
+impl GasMixture {
+    // Calculate the normalized chemical potential (μ/RT) for each component in the mixture.
+    //
+    // Equations 2.11 from reference paper
+    pub fn gas_chem_potentials_over_rt(&self, temp: f64, pressure: f64) -> Vec<f64> {
+        self.ns
+            .iter()
+            .zip(self.species.iter())
+            .map(|(n, s)| -> f64 {
+                match s.phase {
+                    Phase::Gas => {
+                        let p = s
+                            .polynomial_at(temp)
+                            .expect("Gas doesn't have a polynomial");
+                        p.h_over_rt(temp) - p.s_over_r(temp) + (pressure / P_REF).ln() + (n/self.nsum).ln()
+                    }
+                    Phase::Condensed => todo!(),
+                }
+            })
+            .collect()
+    }
+    
+    // Calculate the normalized entropy (S/R) for each mixture component
+    //
+    // Equations 2.17 from reference paper
+    pub fn gas_entropies_over_rt(&self, temp: f64, pressure: f64) -> Vec<f64> {
+        self.ns
+            .iter()
+            .zip(self.species.iter())
+            .map(|(n, s)| -> f64 {
+                match s.phase {
+                    Phase::Gas => {
+                        let p = s
+                            .polynomial_at(temp)
+                            .expect("Gas doesn't have a polynomial");
+                        p.s_over_r(temp) - (n/self.nsum).ln() - (pressure/P_REF).ln()
+                    }
+                    Phase::Condensed => todo!(),
+                }
+            })
+            .collect()
+    }
+    
+    // Calculate the normalized mixture enthalpy (H/RT)
+    // Note that the enthalpy doesn't have a dependence on the pressure.
+    // Equation 2.14 from the paper
+    pub fn mixture_h_over_rt(&self, temp: f64) -> Vec<f64>{
+         self.ns
+            .iter()
+            .zip(self.species.iter())
+            .map(|(n, s)| -> f64 {
+                match s.phase {
+                    Phase::Gas => {
+                        let p = s
+                            .polynomial_at(temp)
+                            .expect("Gas doesn't have a polynomial");
+                        n*p.h_over_rt(temp)
+                    }
+                    Phase::Condensed => todo!(),
+                }
+            })
+            .collect()       
+    }
+}
diff --git a/src/mixtures/mod.rs b/src/mixtures/mod.rs
new file mode 100644
index 0000000..2e98a6c
--- /dev/null
+++ b/src/mixtures/mod.rs
@@ -0,0 +1 @@
+pub mod gas_mixture;
diff --git a/src/properties/mod.rs b/src/properties/mod.rs
index 4d0a782..f160f70 100644
--- a/src/properties/mod.rs
+++ b/src/properties/mod.rs
@@ -1,9 +1,9 @@
 mod data;
 mod error;
 pub mod thermo_db;
-mod thermo_fit;
+pub mod thermo_fit;
 pub mod transport_db;
-mod transport_fit;
+pub mod transport_fit;
 mod utils;
 
 pub use error::PropertiesError;