The fluid mechanics of two-phase solid-liquid food flows: A review

Continuous processing of food products is being increasingly advocated as a substitute for traditional heat sterilization in containers. Although the technology has been successfully applied to single phase Liquid foods, its widespread application to food products containing both liquid and solid constituents is being severely limited by the lack of understanding of the principles that govern the flow of such foods through the processing equipment. Even without heat transfer, the design of equipment to transport food mixtures is still empirical. The often complicated rheology of the foods which usually consist of a highly viscous non-Newtonian liquid carrying almost neutrally-buoyant solid food pieces, causes the flow through process equipment to be non-uniform and often unpredictable. The process may thus be subjected to a wide distribution of particle concentration; velocities, residence times, and temperatures, thereby causing a wide and still largely unpredictable distribution of those quality changes that are imparted to the food by the heat treatment. This paper presents a comprehensive review of the-existing knowledge on the fluid mechanics of two phase solid-liquid flows which largely emanates from the process engineering literature, and discusses its exploitation in continuous food processing.