def order_streams(in_a, in_b, out_a, out_b):
    """
    Return cold and hot inlet and outlet streams.
    
    Parameters
    ----------
    in_a : Stream
        Inlet a.
    in_b : Stream
        Inlet b.
    out_a : Stream
        Outlet a.
    out_b : Stream
        Outlet b.
    
    Returns
    -------
    ci : Stream
        Cold inlet.
    hi : Stream
        Hot inlet.
    co : Stream
        Cold outlet.
    ho : Stream
        Hot outlet.
    
    """
    if in_a.T < in_b.T:
        return in_a, in_b, out_a, out_b
    else:
        return in_b, in_a, out_b, out_a