Reduced Pressure of Real Gas using Wohl Equation given Critical and Actual Parameters Calculator

Reduced Pressure Formula (Wohl Equation):

\[ P_r = \frac{\left(\frac{[R]T}{V_m'-b} - \frac{a}{TV_m'(V_m'-b)} + \frac{c}{T^2V_m'^3}\right)}{P_c} \]

Temperature of Real Gas (K):

Molar Volume of Real Gas (m³):

Wohl Parameter b:

Wohl Parameter a:

Wohl Parameter c:

Critical Pressure (Pa):

Reduced Pressure (dimensionless):

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1. What is Reduced Pressure in Wohl Equation?

Definition: Reduced pressure is the ratio of the actual pressure of a fluid to its critical pressure. It's a dimensionless quantity used in corresponding states theory.

Purpose: The Wohl equation provides a method to calculate reduced pressure for real gases by accounting for molecular interactions through empirical parameters.

2. How Does the Calculator Work?

The calculator uses the Wohl equation:

\[ P_r = \frac{\left(\frac{[R]T}{V_m'-b} - \frac{a}{TV_m'(V_m'-b)} + \frac{c}{T^2V_m'^3}\right)}{P_c} \]

Where:

\( P_r \) — Reduced pressure (dimensionless)
\( [R] \) — Universal gas constant (8.314 J/mol·K)
\( T \) — Temperature of real gas (K)
\( V_m' \) — Molar volume of real gas (m³)
\( a, b, c \) — Wohl parameters (empirical constants)
\( P_c \) — Critical pressure (Pa)

3. Importance of Reduced Pressure Calculation

Details: Reduced properties are crucial for thermodynamic calculations and help predict gas behavior under different conditions using corresponding states principle.

4. Using the Calculator

Tips: Enter all required parameters: temperature, molar volume, Wohl parameters (a, b, c), and critical pressure. All values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: What are typical values for Wohl parameters?
A: Parameters vary by substance. For example, for CO₂: a ≈ 3.59, b ≈ 0.0427, c ≈ 2.30×10⁵ (units depend on equation form).

Q2: Why use reduced pressure instead of actual pressure?
A: Reduced properties allow comparison of different substances at equivalent states and simplify equations of state.

Q3: What's the range for reduced pressure?
A: Typically 0 < Pᵣ < 1 for subcritical conditions, but can exceed 1 for supercritical fluids.

Q4: How accurate is the Wohl equation?
A: It's reasonably accurate for many real gases but less accurate near critical points compared to modern equations.

Q5: Where can I find Wohl parameters for specific gases?
A: Consult thermodynamic databases or research literature for specific substances.