SIZE_CV_GAS

This function computes the required metric valve coefficient K_v for gas flow using the IEC 60534 gas sizing model. The calculation uses inlet thermodynamic properties, pressure drop, and standard-reference volumetric flow to estimate the valve capacity needed to deliver the specified duty.

In sizing form, the relation is commonly expressed as:

K_v = f\left(T, MW, \mu, \gamma, Z, P_1, P_2, Q\right)

where f(\cdot) denotes the IEC-compliant nonlinear model accounting for gas expansion behavior under the stated process conditions.

Excel Usage

=SIZE_CV_GAS(t, mw, mu, gamma, z, p_in, p_out, q)
  • t (float, required): Temperature of the gas at the inlet [K]
  • mw (float, required): Molecular weight of the gas [g/mol]
  • mu (float, required): Viscosity of the fluid at inlet conditions [Pa*s]
  • gamma (float, required): Specific heat capacity ratio [-]
  • z (float, required): Compressibility factor at inlet conditions [-]
  • p_in (float, required): Inlet pressure of the gas before valves and reducers [Pa]
  • p_out (float, required): Outlet pressure of the gas after valves and reducers [Pa]
  • q (float, required): Volumetric flow rate of the gas at STP [m^3/s]

Returns (float): Kv - Metric Kv valve flow coefficient [m^3/hr], or error message (str) if input is invalid.

Example 1: Baseline gas valve sizing case

Inputs:

t mw mu gamma z p_in p_out q
433 44.01 0.00014665 1.3 0.988 680000 310000 1.0555555555555556

Excel formula:

=SIZE_CV_GAS(433, 44.01, 0.00014665, 1.3, 0.988, 680000, 310000, 1.0555555555555556)

Expected output:

58.6107

Example 2: Very small-flow gas sizing case

Inputs:

t mw mu gamma z p_in p_out q
320 39.95 0.00005625 1.67 1 280000 130000 0.0001277777777777778

Excel formula:

=SIZE_CV_GAS(320, 39.95, 0.00005625, 1.67, 1, 280000, 130000, 0.0001277777777777778)

Expected output:

0.0131229

Example 3: High-pressure-drop gas sizing case

Inputs:

t mw mu gamma z p_in p_out q
300 28.97 0.000018 1.4 1 500000 200000 0.1

Excel formula:

=SIZE_CV_GAS(300, 28.97, 0.000018, 1.4, 1, 500000, 200000, 0.1)

Expected output:

4.93156

Example 4: Low-temperature gas sizing case

Inputs:

t mw mu gamma z p_in p_out q
250 16.04 0.00001 1.3 0.95 400000 300000 0.05

Excel formula:

=SIZE_CV_GAS(250, 16.04, 0.00001, 1.3, 0.95, 400000, 300000, 0.05)

Expected output:

2.59016

Python Code

Show Code 
from math import isfinite

from fluids.control_valve import size_control_valve_g as fluids_size_control_valve_g

def size_cv_gas(t, mw, mu, gamma, z, p_in, p_out, q):
    """
    Calculates flow coefficient of a control valve passing a gas according to IEC 60534 using fluids.control_valve.size_control_valve_g.

    See: https://fluids.readthedocs.io/fluids.control_valve.html#fluids.control_valve.size_control_valve_g

    This example function is provided as-is without any representation of accuracy.

    Args:
        t (float): Temperature of the gas at the inlet [K]
        mw (float): Molecular weight of the gas [g/mol]
        mu (float): Viscosity of the fluid at inlet conditions [Pa*s]
        gamma (float): Specific heat capacity ratio [-]
        z (float): Compressibility factor at inlet conditions [-]
        p_in (float): Inlet pressure of the gas before valves and reducers [Pa]
        p_out (float): Outlet pressure of the gas after valves and reducers [Pa]
        q (float): Volumetric flow rate of the gas at STP [m^3/s]

    Returns:
        float: Kv - Metric Kv valve flow coefficient [m^3/hr], or error message (str) if input is invalid.
    """
    try:
      # Validate input parameters
      try:
        t = float(t)
        mw = float(mw)
        mu = float(mu)
        gamma = float(gamma)
        z = float(z)
        p_in = float(p_in)
        p_out = float(p_out)
        q = float(q)
      except (TypeError, ValueError):
        return "Error: All parameters must be numeric values."

      # Check for non-finite values
      if not all(isfinite(val) for val in [t, mw, mu, gamma, z, p_in, p_out, q]):
        return "Error: All parameters must be finite numbers."

      # Check for invalid values
      if t <= 0:
        return "Error: Temperature (t) must be positive."
      if mw <= 0:
        return "Error: Molecular weight (mw) must be positive."
      if mu < 0:
        return "Error: Viscosity (mu) must be non-negative."
      if gamma <= 0:
        return "Error: Specific heat capacity ratio (gamma) must be positive."
      if z <= 0:
        return "Error: Compressibility factor (z) must be positive."
      if p_in <= 0:
        return "Error: Inlet pressure (p_in) must be positive."
      if p_out < 0:
        return "Error: Outlet pressure (p_out) must be non-negative."
      if q < 0:
        return "Error: Volumetric flow rate (q) must be non-negative."
      if p_in == p_out:
        return "Error: Inlet pressure (p_in) and outlet pressure (p_out) cannot be equal."

      try:
        result = fluids_size_control_valve_g(T=t, MW=mw, mu=mu, gamma=gamma, Z=z, P1=p_in, P2=p_out, Q=q)

        if isinstance(result, dict):
          result = result.get('Kv')

        if result is None or not isinstance(result, (int, float)):
          return f"Error: Fluids library returned invalid result: {result}"

        if not isfinite(result):
          return "Error: Calculated flow coefficient is not finite."

        return float(result)
      except Exception as e:
        return f"Error: Failed to compute gas valve sizing: {str(e)}"
    except Exception as e:
      return f"Error: {str(e)}"

Online Calculator

Temperature of the gas at the inlet [K]
Molecular weight of the gas [g/mol]
Viscosity of the fluid at inlet conditions [Pa*s]
Specific heat capacity ratio [-]
Compressibility factor at inlet conditions [-]
Inlet pressure of the gas before valves and reducers [Pa]
Outlet pressure of the gas after valves and reducers [Pa]
Volumetric flow rate of the gas at STP [m^3/s]