CD_GRAF

Overview

Calculate drag coefficient of a sphere using the Graf correlation.

Excel Usage

=CD_GRAF(Re)

• Re (float, required): Particle Reynolds number [-]

Returns (float): Drag coefficient [-], or error message (str) if input is invalid.

Examples

Example 1: Reynolds number of 200

Inputs:

Re
200

Excel formula:

=CD_GRAF(200)

Expected output:

Result
0.8521

Example 2: Reynolds number of 1000

Inputs:

Re
1000

Excel formula:

=CD_GRAF(1000)

Expected output:

Result
0.4978

Example 3: Reynolds number of 10000

Inputs:

Re
10000

Excel formula:

=CD_GRAF(10000)

Expected output:

Result
0.3247

Example 4: Reynolds number of 100

Inputs:

Re
100

Excel formula:

=CD_GRAF(100)

Expected output:

Result
1.1536

Python Code

import micropip
await micropip.install(["fluids"])
from fluids.drag import Graf as fluids_Graf

def cd_graf(Re):
    """
    Calculate drag coefficient of a sphere using the Graf correlation.

    See: https://fluids.readthedocs.io/fluids.drag.html#fluids.drag.Graf

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

    Args:
        Re (float): Particle Reynolds number [-]

    Returns:
        float: Drag coefficient [-], or error message (str) if input is invalid.
    """
    # Validate Reynolds number
    try:
        Re = float(Re)
    except (ValueError, TypeError):
        return "Error: Re must be a number."

    if Re <= 0:
        return "Error: Re must be positive."

    try:
        result = fluids_Graf(Re=Re)
        if result != result:  # NaN check
            return "Calculation resulted in NaN."
        return float(result)
    except Exception as e:
        return f"Error: {str(e)}"

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