Current methods can be classified into gravity separation, centrifugation, chemical separation, and acoustic separation. This section introduces various separation techniques employed in the food industry and discusses investigations into the influential parameters for each according to the available literature. Accordingly, the future trend for the development of potential transducers will be presented which can be more cost-effective and require lower initial and maintenance costs.

Conventional industrial techniques and newer approaches at research stage will be discussed and compared to elucidate advantages and disadvantages. The aim of this review is to elaborate on various techniques with a focus on acoustic separation in the dairy sector. However, more research is required to develop suitable transducers for each application. The geometry of a hollow cylindrical transducer makes it an attractive alternative for dynamic applications where a flowing fluid is required to pass through the transducer, and it can be fit in-line with the incoming flow. To the best of the authors’ knowledge, application of these cylindrical transducers has been limited to very few studies on ultrasonic drying of foodstuff, water particle disintegration for airway humidification and separation of suspended microparticles in a fluid simulating blood conditions at a laboratory scale. Also, piezoelectric cylindrical transducers with geometrical variations in the form of stepped-thickness have shown much stronger acoustic fields at the same input power compared to identical non-stepped-thickness transducers. The use of cylindrical transducers has been associated with the increase of the strength of the acoustic field due to better focus and interference of the radiated waves as a result of a suitable vibration mode shape. The use of different transducer shapes such as square or rectangular plates, circular plates, horn transducers and cylindrical shells for separation and its respective configurations such as parallel square plates, perpendicular plates, and interaction between plates and horn transducers, have been investigated. In order to generate acoustic waves, one or multiple piezoelectric transducers are needed depending on the nature of the application. It also has a low machinery and maintenance cost.Ĭonsidering all the potential, research has been concentrating more on acoustic separation to further develop and establish suitable transducers for various applications. An advantage to this technique is that the particle size distribution in the fluids treated with acoustic waves is adjustable with the frequency and acoustic strength and is scalable and modular.

Compared to previous techniques, this process decreases the processing time and the power consumption. A relatively newer technique has also been studied called acoustic separation, which involves the use of acoustic waves to accelerate the process of coalescence and agglomeration of suspended particles in a stationary fluid. These will be separately reviewed in the following sections with examples of their specific application areas, advantages, and disadvantages which cause some limitations in their use. Currently, there are many techniques available in the literature and industry for separation of two mixed liquids or particles in liquids such as gravity separation, chemical separation and centrifugation. A wide range of applications necessitates ongoing research into the development of more efficient, cost-effective, and low-maintenance separation techniques. The process of separation is widely used both at laboratory and industrial scales for many different applications ranging from food industry including various edible oil extraction and milk creaming, to crude oil recovery from water in oil industry and to biological cell separation applications in biomedical industry.

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