cubiceos

cubiceos

Solvers and tools for cubic Equations of State (EOS) in Go.

Supported EOS:

• Van der Waals (vdW)
• Redlich–Kwong (RK)
• Soave–Redlich–Kwong (SRK)
• Peng–Robinson (PR)

This repository contains three parts:

1. Library: github.com/rickykimani/cubiceos — reusable Go package for EOS calculations
2. TUI: an interactive terminal app to explore EOS results quickly
3. Web UI: a simple browser app for solving and visualizing results

Table of Contents

• Part I — Library (github.com/rickykimani/cubiceos)
  • General cubic EOS
  • Requirements
  • Install
  • Usage
  • API overview
  • Interpreting results
  • Example program
• Part II — Terminal UI (TUI)
  • Install
  • Run
  • Controls & input
  • Results view
  • Demo
• Part III — Web UI
  • Features
  • Run
  • Screenshots
• Project layout
• License

Part I — Library (github.com/rickykimani/cubiceos)

What is a cubic EOS?

• Polynomial equations that are cubic in molar volume are the simplest equations capable of representing the 𝑃𝑉𝑇 behaviour of both liquids and vapours for a wide range of temperatures, pressures, and molar volumes.

\begin{align*}
P &= \frac{RT}{V-b} - \frac{a(T)}{(V + \varepsilon b)(V + \sigma b)}\\
b &= \Omega\frac{R T_c}{P_c}\\
a(T) &= \Psi\frac{\alpha(T_r, \omega) R^2 {T_c}^2}{P_c}
\end{align*}

and the corresponding cubic in V:

\begin{align*}
0 &= V^{3} 
+ \left[\;(\varepsilon + \sigma - 1)b - \frac{RT}{P}\;\right]V^{2} \\[6pt]
&\quad + \left\{\,b\left[(\varepsilon\sigma - \varepsilon - \sigma)b - (\varepsilon + \sigma)\frac{RT}{P}\right] + \frac{a(T)}{P}\,\right\}V \\[6pt]
&\quad -\,\varepsilon\sigma\, b^{2}\left(b + \frac{RT}{P}\right) - \frac{a(T)\,b}{P}.
\end{align*}

this describes

Requirements

• Go 1.22+

Install

go get github.com/rickykimani/cubiceos

Usage

package main

import (
	"log"

	"github.com/rickykimani/cubiceos"
)

func main() {
    //n-butane example
	eq := cubiceos.NewRKCfg(
		350,    // T (K)
		9.4573, // P (bar)
		425.1,  // Tc (K)
		37.96,  // Pc (bar)
		83.14,  // R (bar•cm^3/(mol•K))
	)
	res, err := cubiceos.CubicEOS(eq)
	if err != nil {
		log.Fatal(err)
	}
	cubiceos.ResultPrinter(res)
}

API overview

• Builders:
  • NewvdWCfg(T, P, Tc, Pc, R)
  • NewRKCfg(T, P, Tc, Pc, R)
  • NewSRKCfg(T, P, Tc, Pc, W, R)
  • NewPRCfg(T, P, Tc, Pc, W, R)
• Call CubicEOS(cfg) to solve and return three roots (possibly complex).
• Print ResultPrinter(roots)

Interpreting results

CubicEOS returns three roots. Physical molar volumes are the real, positive roots:

• One positive root → single phase.
• Two positive roots (with one unstable in-between) → phase split (liquid/vapor).
• At critical conditions, the three real roots can coalesce.

For examples, see example/main.go:

go run ./example

Part II — Terminal UI (TUI)

Install

go install github.com/rickykimani/cubiceos/cmd/eos-cli@latest

Run

eos-cli

Controls & input

• Navigate: ↑/↓ or j/k
• Select: Enter
• Back: Esc
• Quit: q or Ctrl+C
• Inputs: numeric values for T, P, Tc, Pc, R, and omega (for SRK/PR).

Results view

• Displays which EOS was used and the computed roots.

Demo

Part III — Web UI

Features

• Per-field unit selectors (T, P, Tc, Pc) with correct SI conversion internally
• Volume display units (e.g., m³/mol, cm³/mol) applied to results
• a(T) and b displayed with unit labels (a(T) in Punit·(Vunit)², b in Vunit)
• Clean results view with phase classification badges and error messages
• Dark mode with a top-right toggle; GitHub link in the header
• Embedded static assets (works when installed via go install, no external files required)

Run

Quick start (opens browser on a local port):

eos-cli --http

Screenshots

Project layout

• cubiceos.go — core types and CubicEOS
• solve.go — general cubic polynomial solver and helpers
• vdw.go, rk.go, srk.go, pr.go — EOS implementations and config builders
• cmd/ — interactive terminal UI and web UI
• example/ — minimal library usage example

License

This project is licensed under the MIT License.