def Le_water(t, sal):
    """
    computes latent heat of vaporization for pure water and seawater
    reference:  M. H. Sharqawy, J. H. Lienhard V, and S. M. Zubair, Desalination
                and Water Treatment, 16, 354-380, 2010. (http://web.mit.edu/seawater/)
    validity: 0 < t < 200 C;   0 <sal <240 g/kg

    usage: Le_w, Le_sw = Le_water(t, sal)

    inputs: T in deg C
            sal in ppt

    output: Le_w, Le_sw in J/g (kJ/kg)

    """

    # polynomial constants
    a = [2.5008991412E+06, -2.3691806479E+03, 2.6776439436E-01,
        -8.1027544602E-03, -2.0799346624E-05]

    Le_w = a[0] + a[1]*t + a[2]*t**2 + a[3]*t**3 + a[4]*t**4
    Le_sw = Le_w*(1 - 0.001*sal)
    return (Le_w/1000.0, Le_sw/1000.0)