def helix(Di, rs, pitch, N, fd):
    r'''Returns loss coefficient for any size constant-pitch helix
    as shown in [1]_. Has applications in immersed coils in tanks.

    .. math::
        K = N \left[f\frac{\sqrt{(2\pi r)^2 + p^2}}{d} + 0.20 + 4.8 f\right]

    Parameters
    ----------
    Di : float
        Inside diameter of pipe, [m]
    rs : float
        Radius of spiral, [m]
    pitch : float
        Distance between two subsequent coil centers, [m]
    N : float
        Number of coils in the helix [-]
    fd : float
        Darcy friction factor [-]


    Returns
    -------
    K : float
        Loss coefficient [-]

    Notes
    -----
    Formulation based on peak secondary flow as in two 180 degree bends per
    coil. Flow separation ignored. No f, Re, geometry limitations.
    Source not compared against others.

    Examples
    --------
    >>> helix(Di=0.01, rs=0.1, pitch=.03, N=10, fd=.0185)
    14.525134924495514

    References
    ----------
    .. [1] Rennels, Donald C., and Hobart M. Hudson. Pipe Flow: A Practical
       and Comprehensive Guide. 1st edition. Hoboken, N.J: Wiley, 2012.
    '''
    return N*(fd*((2*pi*rs)**2 + pitch**2)**0.5/Di + 0.20 + 4.8*fd)
def helix ( Di , rs , pitch , N , fd ) : return N * ( fd * ( ( 2 * pi * rs ) ** 2 + pitch ** 2 ) ** 0.5 / Di + 0.20 + 4.8 * fd )
r'''Returns loss coefficient for any size constant-pitch helix
    as shown in [1]_. Has applications in immersed coils in tanks.

    .. math::
        K = N \left[f\frac{\sqrt{(2\pi r)^2 + p^2}}{d} + 0.20 + 4.8 f\right]

    Parameters
    ----------
    Di : float
        Inside diameter of pipe, [m]
    rs : float
        Radius of spiral, [m]
    pitch : float
        Distance between two subsequent coil centers, [m]
    N : float
        Number of coils in the helix [-]
    fd : float
        Darcy friction factor [-]


    Returns
    -------
    K : float
        Loss coefficient [-]

    Notes
    -----
    Formulation based on peak secondary flow as in two 180 degree bends per
    coil. Flow separation ignored. No f, Re, geometry limitations.
    Source not compared against others.

    Examples
    --------
    >>> helix(Di=0.01, rs=0.1, pitch=.03, N=10, fd=.0185)
    14.525134924495514

    References
    ----------
    .. [1] Rennels, Donald C., and Hobart M. Hudson. Pipe Flow: A Practical
       and Comprehensive Guide. 1st edition. Hoboken, N.J: Wiley, 2012.