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D4651-14 – Standard Test Method Technical Guide
📜 Standard Overview and Scope
ASTM D4651-14 (Reapproved 2020) provides standardized thermophysical property tables for pure isobutane, generated using the NIST REFPROP Version 9.1 database. These tables facilitate the calculation of pressure-volume-temperature (PVT), thermodynamic, and transport properties critical for process design and operations. All values are expressed in strict SI units, covering temperatures from 120 K up to 570 K and pressures up to 20 MPa.
⚙️ Key Properties and Table Structures
The standard defines three distinct tables: saturated liquid properties (Table 1), saturated vapor properties (Table 2) spanning from 120 K to the critical point of 407.81 K, and properties along isobars (Table 3) at selected T, p points. The following properties are systematically tabulated across all tables.
| 🟦 Property | 📏 Symbol | 🎯 SI Unit |
|---|---|---|
| Temperature | T | K |
| Molar Density | ρ | mol·L⁻¹ |
| Molar Enthalpy | H | J·mol⁻¹ |
| Molar Entropy | S | J·K⁻¹·mol⁻¹ |
| Heat Capacity (Const. Vol.) | Cv | J·K⁻¹·mol⁻¹ |
| Heat Capacity (Const. Press.) | 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 |
🔍 Technical Note: While the printed tables cover specific state points, the underlying REFPROP v9.1 software (NIST Standard Reference Database 23) allows users to retrieve data in a wide selection of units (engineering, chemical) and access additional thermophysical properties.
📊 Reference State Specifications
The calculation of enthalpy and entropy from an equation of state requires a defined reference state. This standard adopts the specifications provided by the International Institute of Refrigeration (IIR).
| ⚡ Specification | 📌 Defined Value |
|---|---|
| Molar Mass of Isobutane | 58.122 g·mol⁻¹ |
| Reference State Condition | Saturated Liquid at 273.15 K (0 °C) |
| Reference Enthalpy (H) | 200 J·g⁻¹ |
| Reference Entropy (S) | 1 J·K⁻¹·g⁻¹ |
⚠️ Important User Advisory: Per Section 1.3 of the standard, this specification does not address all safety concerns associated with its use. Users must establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to using isobutane in any process.
❓ Frequently Asked Questions
🔍 What temperature range is covered by the saturation property tables?
The saturation property tables for both the liquid and vapor phases provide data at temperatures between 120 K and the critical point of isobutane, which is 407.81 K.
💡 Which software was used to develop the thermophysical property tables?
The tables were developed using the National Institute of Standards and Technology (NIST) Standard Reference Database 23, titled “Reference Fluid Thermodynamic and Transport Properties Database (REFPROP): Version 9.1.”
📌 Are these tables applicable only to pure isobutane?
Section 2 of the standard states that the tables apply directly only to pure isobutane. However, they may also be utilized in mathematical models and tables for calculating the thermophysical properties of mixtures containing isobutane.
📐 What are the reference state values for saturated liquid isobutane?
Following the International Institute of Refrigeration (IIR) standard, the reference state for saturated liquid isobutane at 273.15 K (0 °C) is defined as an enthalpy (H) of 200 J·g⁻¹ and an entropy (S) of 1 J·K⁻¹·g⁻¹.