On-line fouling detection of aircraft environmental control system cross flow heat exchanger

A Diagnostics, Prognostics and Health Management (DPHM) solution is proposed for the aircraft environmental control system (ECS) cross flow heat exchanger. In particular, a dynamic model is derived and applied to on-line detection of fouling in the aircraft ECS crossflow plate-and-fin heat exchanger. Predictive maintenance actions can be scheduled as per the on-line detected fouling status of the specific component, supporting condition based maintenance. The heat exchanger model is of the lumped state space form where the state is represented by the core and fin temperatures. The ratios of the thermal capacities of the masses of the two air streams to the thermal capacity of the core itself are negligibly small, and hence can be equated to zero. The model parameters' functional dependency of mass flow rate and inclusion of secondary surfaces (fins) accurately describes the dynamic behavior of the heat exchanger. Since the parameters are functions of mass flow rate as are the core and fin temperatures, and the model is nonlinear in the state variables, the extended Kalman filtering (EKF) algorithm is applied to estimate the state dependent parameters. The model's formulation is justified by the quality of the predicted results, as validated via experimental tests.