def sigma_thermpollution(pollution_1, pollution_2, sigma, lyambda_wall):
    """
    Calculates the sum of thermal pollutions.
    Parameters
    ----------
    pollution_1 : float
        The thermal pollution of the first coolant, [m**2 * degrees celcium / W]
    pollution_2 : float
        The thermal pollution of the second coolant, [m**2 * degrees celcium / W]
    sigma : float
        The thickness of pipe wall, [m]
    lyambda_wall : float
        The thermal conducivity of wall, [W / (m * degrees celcium)]  
    Returns
    -------
    sigma_thermpollution : float
        The the sum of thermal pollutions, [m**2 * degrees celcium / W]
    References
    ----------
    &&&&&
    """                  
    return (sigma / lyambda_wall) + (1 / pollution_1) + (1 / pollution_2)