Characterization of centrifugal pumps used for professional equipment, development of control strategies to prevent cavitation

The field of household appliances, especially professional equipment used in the catering sector, must always present new developments and controls to improve their operating cycles and life cycles. The work refers to an industrial research aimed to investigate the effect of cavitation on centrifugal pumps. The need to undertake this study arises from the demand to solve a problem related to a machine used for catering. It is therefore understandable the interest shown by Electrolux Professional Spa for the development of new solutions and control strategies. Therefore the purpose of this research is the study of cavitation on centrifugal pumps. Cavitation is a well-known phenomenon that may occur, among other turbo-machines, in centrifugal pumps and can result in severe damage of both the pump and the whole hydraulic system. In this research a characterization of the cavitation phenomenon in centrifugal pumps was carried out. In particular, in chapter 1 it was carried out a study on washing machines used in the domestic and professional fields. Furthermore, the main detergent factors are described, represented by the Sinner circle. Chapter 2 describes the two test benches designed and built to perform characterization and cavitation tests in centrifugal pumps. Moreover it is made an overview of the mechanical and electrical layout, on the acquisition system used and on the instruments and sensors used to characterize the cavitation. Chapter 3 describes the effects of washing in centrifugal pumps. Centrifugal pumps have been characterized by studying the behavior under different operating conditions, varying the temperature and concentration of the detergent. The results obtained from experimental tests were compared. The effects of temperature and detergent were then compared through experimental tests. Subsequently, a study on cavitation conditions was carried out. In chapter 4 different methods for the detection of cavitation are presented: from the most common, studying the hydraulic quantities, to the most innovative, studying the vibrations of the pump. Furthermore, a characterization of the cavitation phenomenon was carried out by varying the operating flow of the centrifugal pump. In chapter 5, a procedure for preventing cavitation formation is described . In fact, by reducing the number of revolutions of the pump it is possible to change the working point of the pump and exit the cavitation. In chapter 6 and 7, instead, the two controls developed to prevent the phenomenon of cavitation, and the results obtained, are described. In chapter 6 a PI control is presented, while in chapter 7 a non-linear control is exposed. Finally, in chapter 8, conclusions are given with possible future applications. In particular, this research allows to obtain improvements in the operation of centrifugal pumps used in professional catering machines.