VARIATION OF TRANSFER FUNCTION FOR DYNAMIC BEHAVIOR OF A VEGETABLE OIL REFRIGERATION UNIT

摘要

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.