r'''Calculates Nusselt number for single-phase flow in a 
    Chevron-style plate heat exchanger according to [1]_.
    
    .. math::
        Nu = \left(0.0161\frac{\beta}{\beta_{max}} + 0.1298\right)
        Re^{\left(0.198 \frac{\beta}{\beta_{max}} + 0.6398\right)} 
        Pr^{0.35} 
                
    Parameters
    ----------
    Re : float
        Reynolds number with respect to the hydraulic diameter of the channels,
        [-]
    Pr : float
        Prandtl number calculated with bulk fluid properties, [-]
    chevron_angle : float
        Angle of the plate corrugations with respect to the vertical axis
        (the direction of flow if the plates were straight), between 0 and
        90. Many plate exchangers use two alternating patterns; use their
        average angle for that situation [degrees]

    Returns
    -------
    Nu : float
        Nusselt number with respect to `Dh`, [-]

    Notes
    -----
    The viscosity correction power is recommended to be the blanket
    Sieder and Tate (1936) value of 0.14.
    
    The correlation is recommended in the range of Reynolds numbers from
    500 to 2500, chevron angles between 30 and 60 degrees, and Prandtl
    numbers between 3.5 and 6.

    Examples
    --------
    >>> Nu_plate_Khan_Khan(Re=1000, Pr=4.5, chevron_angle=30)
    38.40883639103741
    
    References
    ----------
    .. [1] Khan, T. S., M. S. Khan, Ming-C. Chyu, and Z. H. Ayub. "Experimental
       Investigation of Single Phase Convective Heat Transfer Coefficient in a 
       Corrugated Plate Heat Exchanger for Multiple Plate Configurations." 
       Applied Thermal Engineering 30, no. 8 (June 1, 2010): 1058-65.
       https://doi.org/10.1016/j.applthermaleng.2010.01.021.

def Nu_plate_Khan_Khan(Re, Pr, chevron_angle):
    r'''Calculates Nusselt number for single-phase flow in a 
    Chevron-style plate heat exchanger according to [1]_.
    
    .. math::
        Nu = \left(0.0161\frac{\beta}{\beta_{max}} + 0.1298\right)
        Re^{\left(0.198 \frac{\beta}{\beta_{max}} + 0.6398\right)} 
        Pr^{0.35} 
                
    Parameters
    ----------
    Re : float
        Reynolds number with respect to the hydraulic diameter of the channels,
        [-]
    Pr : float
        Prandtl number calculated with bulk fluid properties, [-]
    chevron_angle : float
        Angle of the plate corrugations with respect to the vertical axis
        (the direction of flow if the plates were straight), between 0 and
        90. Many plate exchangers use two alternating patterns; use their
        average angle for that situation [degrees]

    Returns
    -------
    Nu : float
        Nusselt number with respect to `Dh`, [-]

    Notes
    -----
    The viscosity correction power is recommended to be the blanket
    Sieder and Tate (1936) value of 0.14.
    
    The correlation is recommended in the range of Reynolds numbers from
    500 to 2500, chevron angles between 30 and 60 degrees, and Prandtl
    numbers between 3.5 and 6.

    Examples
    --------
    >>> Nu_plate_Khan_Khan(Re=1000, Pr=4.5, chevron_angle=30)
    38.40883639103741
    
    References
    ----------
    .. [1] Khan, T. S., M. S. Khan, Ming-C. Chyu, and Z. H. Ayub. "Experimental
       Investigation of Single Phase Convective Heat Transfer Coefficient in a 
       Corrugated Plate Heat Exchanger for Multiple Plate Configurations." 
       Applied Thermal Engineering 30, no. 8 (June 1, 2010): 1058-65.
       https://doi.org/10.1016/j.applthermaleng.2010.01.021. 
    '''
    beta_max = 60.
    beta_ratio = chevron_angle/beta_max
    Nu = (0.0161*beta_ratio + 0.1298)*Re**(0.198*beta_ratio + 0.6398)*Pr**0.35
    return Nu