def calculate_Re_bounds(asm_obj):
    """Calculate the Reynolds numbers for the boundaries of the
    laminar, transition, and turbulent flow regimes

    Parameters
    ----------
    asm_obj : DASSH assembly object
        Required attributes: pin diameter (m) and pin pitch (m)

    Returns
    -------
    tuple
        Reynolds numbers (float) for the boundaries between the
        laminar-transition and transition-turbulent flow regimes

    """
    re_bt = 1e4 * 10**(0.7 * (asm_obj.pin_pitch
                              / asm_obj.pin_diameter - 1.0))
    re_bl = 320.0 * 10**(asm_obj.pin_pitch
                         / asm_obj.pin_diameter - 1.0)
    return (re_bl, re_bt)