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D4650-19 – Standard Test Method Technical Guide
🧪 Scope and Data Source
ASTM D4650-19 provides standard thermophysical property tables for normal butane (n-C₄H₁₀), developed using the National Institute of Standards and Technology Standard Reference Database product REFPROP, version 10.0. These tables are intended for use in calculating pressure-volume-temperature (PVT), thermodynamic, and transport properties for process design and operations involving normal butane.
The specification provides two tables covering the saturated liquid and saturated vapor phases at vapor-liquid equilibrium from 135 K up to the critical point of normal butane at 425.13 K. A third table provides properties along isobars for the equilibrium phase at temperatures between 140 K and 570 K at pressures reaching 20 MPa.
📊 Table Definitions and Molar Properties
The standard organizes the thermophysical data into three distinct tables, all employing SI units:
- Table 1: Thermophysical Properties of Normal Butane Liquid at Vapor-Liquid Equilibrium
- Table 2: Thermophysical Properties of Normal Butane Vapor at Vapor-Liquid Equilibrium
- Table 3: Thermophysical Properties of Normal Butane Along Isobars
Each table provides a consistent set of molar properties defined by the following symbols and units:
| 🟦 Property | 📏 Symbol | ⚡ Unit |
|---|---|---|
| Temperature | T | K |
| Molar Density | ρ | mol·L⁻¹ |
| Molar Enthalpy | H | J·mol⁻¹ |
| Molar Entropy | S | J·K⁻¹·mol⁻¹ |
| Constant Volume Heat Capacity | Cv | J·K⁻¹·mol⁻¹ |
| Constant Pressure Heat Capacity | Cp | J·K⁻¹·mol⁻¹ |
| Speed of Sound | c | m·s⁻¹ |
| Viscosity | η | µPa·s |
| Thermal Conductivity | λ | mW·m⁻¹·K⁻¹ |
⚙️ Reference State and Key Constants
For consistent thermodynamic property calculation, the standard adopts the reference state specified by the International Institute of Refrigeration (IIR). This defines the enthalpy and entropy of the saturated liquid at 273.15 K (0 °C) as 200 J/g and 1 J/(g·K), respectively.
⚡ Implementation Note: The IIR reference state is a critical detail for process simulation. Default reference conditions in standard equation-of-state packages may differ from the IIR standard. Engineers must verify their thermodynamic models use H = 200 J/g and S = 1 J/(g·K) at 273.15 K for the saturated liquid to ensure data consistency with these tables.
The following table summarizes the key technical parameters specified in ASTM D4650-19:
| 📐 Parameter | 🎯 Specification |
|---|---|
| Chemical Identity | Normal Butane (n-C₄H₁₀) |
| Molar Mass | 58.122 g·mol⁻¹ |
| Critical Temperature | 425.13 K |
| Saturation Temperature Range | 135 K to 425.13 K |
| Isobar Temperature Range | 140 K to 570 K |
| Maximum Pressure | 20 MPa |
| Data Source Software | NIST REFPROP, Version 10.0 |
💡 Applicability Note: While these tables directly characterize pure normal butane, Section 2.1 of the standard explicitly states they may be used in mathematical models and tables for predicting the thermophysical properties of mixtures containing normal butane. This makes the standard a foundational reference for natural gas and hydrocarbon processing calculations.
❓ Frequently Asked Questions
🔍 What is the temperature range of the thermophysical property tables?
The saturation property tables (liquid and vapor) provide data from 135 K up to the critical point of normal butane at 425.13 K. The isobaric table extends the temperature range from 140 K to 570 K at pressures up to 20 MPa.
💡 What reference state is used for enthalpy and entropy calculations?
The standard strictly adopts the International Institute of Refrigeration (IIR) reference state. The molar enthalpy (H) is defined as 200 J/g and the molar entropy (S) as 1 J/(g·K) for the saturated liquid state at 273.15 K (0 °C).
📌 What is the molar mass of normal butane used in these tables?
All specific molar quantities in the tables are calculated using a molar mass of 58.122 g/mol for normal butane, as defined in Section 4.2 of the standard.
⚡ Can these tables be applied to mixtures containing normal butane?
Yes. Section 2.1 of the standard explicitly states that while the tables apply directly only to pure normal butane, they may also be used in mathematical models and tables for the thermophysical properties of mixtures containing normal butane. Appropriate mixing rules apply.