SEUIF97

This is the Rust implementation of the high-speed IAPWS-IF97 package SEUIF97 with C, Python and WASM bindings. It is designed for computation-intensive tasks, such as simulating non-stationary processes, on-line process monitoring, and optimization.

SEUIF97 achieves a 5-20x speedup over naive implementations that use the Rust standard library's powi() in for loops for the basic equations of Regions 1, 2, 3, and 5.

This package supports 12 distinct input state pairs for calculating 36 thermodynamic, transport, and derived properties (see Properties), and thermodynamic process functions (see Thermodynamic Process Functions).

What's New in the Rust Version

The Rust version of SEUIF97 is a major upgrade over the original C implementation, delivering significant improvements in performance, functionality, and ecosystem support.

Feature	C Version	Rust Version
Calculation Speed	Baseline	~2× speedup
Supported Properties	30 properties	36 properties (+6 new)
Package Distribution	PyPI only	Crates.io, PyPI, npm
Direct Property Functions	✗	✓ (new)

For detailed comparison and key improvements, see Rust vs C.

Acceleration Algorithms

The acceleration algorithms are detailed in paper: Fast IAPWS-IF97 Evaluation: Profiling-Guided Loop Tiling and Shared-Power Scaling

• Profiling-guided loop tiling: Partitions polynomial summation into cache-efficient tiles with empirically optimized boundaries to boost SIMD vectorization efficiency.
• Shared-power scaling: Leverages the mathematical correlation between Gibbs and Helmholtz free energy polynomials alongside their partial derivatives to evaluate all quantities in a single pass, removing redundant power-term computations.

For code examples, see: Code Snippets for Acceleration Methods

Performance Comparison with CoolProp IF97

SEUIF97 achieves 3-7x speedup over CoolProp IF97. Benchmarking code and data are available in the bench_coolprop_if97 directory.

Property Calculation Functions

The package provides two types of API for property calculation.

Universal Property Functions

The following 12 input pairs are implemented:

  (p,t), (p,h), (p,s), (p,v)
  (h,s)
  (t,h), (t,s), (t,v)
  (h,x), (t,x), (v,x), (s,x)

Each function accepts an input pair, an output property ID (o_id), and an optional region parameter for faster computation. For example: the input pair (p,t): pt(p,t,o_id), pt(p,t,(o_id,region))

Note:

• The region parameter is Rust-only. C, Python and WASM bindings support the o_id form only.
• Only linearly related thermodynamic properties are calculable in the wet steam region.

Direct Property Functions

Function naming convention: {input1}{input2}2{output}.

Input	Outputs	Input	Outputs	Input	Outputs
(p,t)	h,s,v,x	(t,h)	p,s,v,x	(p,x)	t,h,s,v
(p,h)	t,s,v,x	(t,s)	p,h,v,x	(t,x)	p,h,s,v
(p,s)	t,h,v,x	(t,v)	p,h,s,x	(h,x)	p,t,s,v
(p,v)	t,h,s,x	(h,s)	p,t,v,x	(s,x)	p,t,h,v

Total: 48 functions(e.g. pt2h(p,t), ph2t(p,h), hs2p(h,s))

Thermodynamic Process Functions

The following thermodynamic process functions are implemented:

• ishd(pi, ti, pe): isentropic enthalpy drop for steam expansion (kJ/kg)
• ief(pi, ti, pe, te): isentropic efficiency for superheated steam expansion (%)

Install the crate

cargo add seuif97

Usage

use seuif97::*;
fn main() {    
    let p: f64 = 3.0;
    let t: f64 = 300.0-273.15;
    // universal property function with o_id only
    let h = pt(p,t,OH);   
    // the funnction with o_id and region for faster calculation
    let s = pt(p,t,(OS,1)); 
    // direct property function
    let v = pt2v(p,t);

    println!("p={p:.6} t={t:.6} h={h:.6} s={s:.6} v={v:.6}");   

    // thermodynamic process function
    let pi: f64 = 16.0;
    let ti: f64 = 535.1;
    let pe: f64 = 5.0;
    let delta_h = ishd(pi, ti, pe);
    println!("ishd: pi={pi} ti={ti} pe={pe} delta_h={delta_h:.3}");
}

C Shared Library

• SEUIF97_C_TECH

Pre-compiled dynamic link libraries for Windows, Linux and macOS are available in GitHub Releases.

Interfaces and examples are provided in the ./demo_using_lib/ directory, supporting a wide range of languages and environments.

• C/C++, Python, C#, Java, Excel VBA, Rust, Fortran, Golang, JavaScript/TypeScript

#include <stdlib.h>
#include <stdio.h>

#define OH 4

extern double pt(double p,double t,short o_id);
extern double pt2s(double p,double t);

int main(void)
{
    double p = 16.0;
    double t = 530.0;
    // universal property function with o_id only
    double h = pt(p, t, OH);
    // direct property function
    double s = pt2s(p, t);
    printf("p,t %f,%f h= %f s= %f\n", p, t, h, s);
    return EXIT_SUCCESS;
}

Comprehensive Cross-language Examples

• The Rankine Cycle Steady-state Simulator in Python, C++, Rust and Modelica

Python binding

Install

pip install seuif97

from seuif97 import *

OH=4

p=16.0
t=535.1
# universal property function with o_id only
h=pt(p,t,OH)
# direct property function
s=pt2s(p,t)
print(f"p={p}, t={t} h={h:.3f} s={s:.3f}")

Comprehensive Examples in Python

• T-S Diagram
• H-S Diagram
• H-S Diagram of Steam Turbine Expansion
• The Hybrid Steady-state Simulator of Rankine Cycle in Python

WASM binding

• SEUIF97_WASM_TECH

Install

npm install seuif97

import init, { pt, pt2s } from 'seuif97';

await init();

const p = 16.0;  // MPa
const t = 535.1; // °C
// universal property function with o_id only
const h = pt(p, t, 4);     // kJ/kg
// direct property function
const s = pt2s(p, t);      // kJ/(kg·K)

console.log('Properties at p = 16.0 MPa, t = 535.1 °C:');
console.log(`H: ${h.toFixed(3)} kJ/kg`);
console.log(`S: ${s.toFixed(5)} kJ/(kg·K)`);

Properties

Property	Unit	Symbol	o_id	o_id(i32)
Pressure	MPa	p	OP	0
Temperature	°C	t	OT	1
Density	kg/m³	ρ	OD	2
Specific Volume	m³/kg	v	OV	3
Specific enthalpy	kJ/kg	h	OH	4
Specific entropy	kJ/(kg·K)	s	OS	5
Specific exergy	kJ/kg	e	OE	6
Specific internal energy	kJ/kg	u	OU	7
Specific isobaric heat capacity	kJ/(kg·K)	cp	OCP	8
Specific isochoric heat capacity	kJ/(kg·K)	cv	OCV	9
Speed of sound	m/s	w	OW	10
Isentropic exponent	—	k	OKS	11
Specific Helmholtz free energy	kJ/kg	f	OF	12
Specific Gibbs free energy	kJ/kg	g	OG	13
Compressibility factor	—	z	OZ	14
Steam quality	—	x	OX	15
Region	—	r	OR	16
Isobaric cubic expansion coefficient	1/K	ɑv	OEC	17
Isothermal compressibility	1/MPa	kT	OKT	18
Partial derivative (∂v/∂T)p	m³/(kg·K)	(∂v/∂T)p	ODVDT	19
Partial derivative (∂v/∂p)T	m³/(kg·MPa)	(∂v/∂p)T	ODVDP	20
Partial derivative (∂p/∂T)v	MPa/K	(∂p/∂T)v	ODPDT	21
Isothermal throttling coefficient	kJ/(kg·MPa)	δt	OIJTC	22
Joule-Thomson coefficient	K/MPa	μ	OJTC	23
Dynamic viscosity	Pa·s	η	ODV	24
Kinematic viscosity	m²/s	ν	OKV	25
Thermal conductivity	W/(m.K)	λ	OTC	26
Thermal diffusivity	m²/s	a	OTD	27
Prandtl number	—	Pr	OPR	28
Surface tension	N/m	σ	OST	29
Static Dielectric Constant	—	ε	OSDC	30
Isochoric pressure coefficient	1/K	β	OPC	31
Isothermal stress coefficient	kg/m³	βp	OBETAP	32
Fugacity coefficient	—	φ	OFI	33
Fugacity	MPa	f*	OFU	34
Relative pressure coefficient	1/K	αp	OAFLAP	35