Finite element simulation of a long narrow workload immersed in an ultrasonic cleaning bath - practical comparisons and implications for cleaning efficacy

Abstract

Ultrasonic vessels are widely utilised in medical and industrial settings for cleaning a wide variety of soiled objects and as a crucial part of sterilization cycles. A paper is presented in which the role of boundary reflections on cavitation in an ultrasonic vessel is discussed. A two-dimensional finite element model of such a bath containing a long flat workload is developed and simulated with and without reflection of the radiated sound wave from the tank boundaries by using a time harmonic Helmholtz solution to the wave equation. This specific problem relates to the positioning of items on trays within ultrasonic baths and is part of a wider project on the generic 3D modelling for ultrasonic bath design. Unlike many previous studies this paper concentrates on the steady state standing wave field caused by the continuous time harmonic variation in pressure amplitude and reflections. Reflections from the vessel geometry are found to have a positive impact on the pressure profile presented to the upper side of the work piece and hence the cavitation of the vessel. Practical validation of the model is conducted via the foil ablation test and data from a commercially available cavitation probe. Practical results are found to be in reasonable agreement with the simulation output with the location of standing waves within the vessel giving rise to areas of higher cavitational density. Limitations of the current model are discussed along with directions for future development. Nomenclature