Nonlinear observer design and experimental verification for heat exchangers during the start-up process

In this paper, a nonlinear observer design is proposed to estimate the two-phase section length in the evaporator during the start-up process for the use of oil monitoring of air conditioning systems. The dynamic system is non-autonomous due to the time-varying parameters such as heat transfer coefficients. The convergence of the observer is proved using contraction theory which is applicable to non-autonomous systems and the experiment testing demonstrates the accuracy and convergence of the nonlinear observer.