def biot(h, r, k):
    """
    Calculate the dimensionless Biot number represented by Bi.

    Parameters
    ----------
    h = heat transfer coefficient, W/m^2K
    r = radius of particle, m
    k = thermal conductivity, W/mK

    Returns
    -------
    Bi = Biot number, -
    """
    Bi = (h*r) / k
    return Bi