Add support for mass flow rate in control valve sizing

[Unmask06]

Summary

Added the parameter m (mass flow rate) to size_control_valve_g. If m is provided, the function automatically calculates the required standard volumetric flow Q based on the gas molecular weight and standard conditions (, ).

Changes

• New Parameter: m (mass flow rate in ).
• Logic: If m is specified and Q is None, is derived using the Ideal Gas Law at standard conditions.

Technical Implementation

The conversion follows this simple logic:

1. Standard Density:
2. Conversion:

Example Usage

from fluids.control_valve import size_control_valve_g

# Old way (Manual conversion to standard m^3/s)
# Q_std = 0.5 
# Kv = size_control_valve_g(..., Q=Q_std)

# New way (Directly using mass flow)
Kv = size_control_valve_g(T1=300, MW=28.97, mu=1.8e-5, gamma=1.4, Z=0.99, 
                           P1=1e6, P2=8e5, m=2.5) # m in kg/s

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Why this is better

• Reduced Error: Users often confuse "Standard" () and "Normal" ( or ) conditions. Handling this internally ensures the math matches the ISA-75.01.01 standard used by the library.
• Cleaner Code: Removes the need for the user to import constants () and perform density calculations before calling the function.

[Unmask06]

@CalebBell We can also have a single common function to calculate Flow rate through valve by proving Cv, fluid properties

Reference ISA S75.01

[CalebBell]

Hello Prasanna,
I am also the author of thermo, which provides rigorous thermodynamic properties. Fluids , ht, chemicals, and thermo all operate at their own level of abstraction. You can make the proposed function and use it yourself; however, it doesn't belong in any of these libraries because it mixes abstractions by using the ideal gas law inside it. You could also ask - why doesn't the function support molar flow rates? Or why won't it automatically calculate properties with Peng Robinson for me? Why can't I just tell it the name of my chemical and the temperature and it looks up information for me? The answer is that you can build your own functions, that do those things, as an application. Fluids is a library though, it contains core calculations.