Reduced Pressure Formula (Wohl Equation):
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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.
The calculator uses the Wohl equation:
Where:
Details: Reduced properties are crucial for thermodynamic calculations and help predict gas behavior under different conditions using corresponding states principle.
Tips: Enter all required parameters: temperature, molar volume, Wohl parameters (a, b, c), and critical pressure. All values must be positive.
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.