Dynamics and optimal control of flexible heat-exchanger networks

A distributed-parameter model of multi-tube, single-pass heat exchangers are used to construct the dynamic model of a heat-exchanger network (HEN). Based on the control-vector parameterization technique, open-loop (time-dependent bypass manipulation) and closed-loop (target-temperature dependent bypass manipulation) centralized optimal-control schemes are developed and tested. The parameterizations are done in such a way that the manipulated variables approach and eventually match the values obtained from static optimization which refers to an algebraic model of the HEN. Manipulation of the bypasses linearly in time up to their optimal values results in a quite satisfactory dynamic response of the HEN and eliminates temporary violations of the target-temperature control-precision constraints.