def biot(h, d, k):
    """
    Calculate the dimensionless Biot number.

    .. math:: Bi = \\frac{h\\, d}{k}

    Parameters
    ----------
    h : float
        Convective heat transfer coefficient [W/(m²⋅K)]
    d : float
        Characteristic length or dimension [m]
    k : float
        Thermal conductivity [W/(m⋅K)]

    Returns
    -------
    bi : float
        Biot number [-]

    Example
    -------
    >>> biot(4.63, 0.001, 3.84)
    0.0012057

    References
    ----------
    Daizo Kunii and Octave Levenspiel. Fluidization Engineering.
    Butterworth-Heinemann, 2nd edition, 1991.
    """
    bi = (h * d) / k
    return bi