Variation of Transfer Function for Dynamic Behavior of a Vegetable Oil Refrigeration Unit

Cíntia C.M de Oliveira, Maíra de P. Gonçalves, José L. P. Brittes, and Vivaldo Silveira Junior

Keywords

system identification, nonlinear, heat exchanger, transfer function

Abstract

The knowledge of the dynamic behavior of a process variable is essential for characterizing the process and defining the control logic configuration to be implemented in automated plants. This work aims to characterize the dynamic behavior of a cooling process of vegetable oil under different perturbation, starting from the same initial steady state conditions. The experimental unit is consists of two sectors: 1) modular heating and 2) cooling of the vegetable oil. In the second section there are three cooling modules: 2a) set of serial finned heat exchangers with forced-air; 2b) nebulization system and 2c) plate heat exchanger with chilled water as cold fluid. Both heat exchangers showed a good adjustment to a linear second-order function for each perturbation applied. The processes, however, showed low level nonlinear behavior. In regard to these nonlinearities, the process curves were adjusted to a nonlinear second-order function with parameters – proportional gain, perturbation intensity and time constant – varying with the manipulated variable. It was verified that the proposed model is suitable for the process in the considered operating range of the manipulated variable.

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