def R_total(deltaT_sub, Q_drop):
    """ total thermal resistance of a single drop
    
    Parameters
    ----------
    deltaT_sub: float
                temperature difference to the cooled wall in K
    Q_drop:     float
                rate of heat flow through drop in W
    
    Returns
    ----------
    R_total:    float
                total thermal resistance of drop in K/W
    """
    R_total = deltaT_sub / Q_drop
    return R_total