Abstract
Many fast-moving consumer goods such as foods and pharmaceutical products exhibit yield stress behavior, which favors adhesion to the internal walls of processing tanks and vessels. This can lead to cross-contamination between batches, so effective cleaning is essential to ensure product quality and for hygiene control. Impinging liquid jets are widely used in cleaning-in-place (CIP) operations, as they usually clean faster and require smaller volumes of liquids when compared to traditional fill and soak methods. In this talk, I will present experimental observations of the cleaning of insoluble petroleum jelly layers coated on transparent flat surfaces by coherent liquid jets and discuss different approaches to model these flows. The rheological characterization of the jelly indicated that yielding is a gradual transition, with significant creep below the critical shear stress above which catastrophic collapse takes place. Removal by a perpendicular jet normal to the surface involves the growth of a circular cleaned region bounded by a berm of displaced material, reaching an asymptotic maximum cleaned radius at long times. The shape of the berm was measured and found to depend on the ratio of the height of the liquid film and the initial thickness of the soil layer.
The models presented consider the case when the liquid film is thin when compared to the soil. In the first model [1], a semi-empirical term was incorporated into the adhesive removal model proposed by Glover et al. [2] to describe the transition from fast, momentum-driven cleaning near the impinging point to slow, creep-dominated cleaning far from it. In the second model [3], the semi-empirical parameters employed in previous models are linked to the rheology of the layer through an argument based on the rate of viscous dissipation within a shallow wedge at the cleaning front. This yields a result of the form of the model in [2], with expressions linking the kinetic parameters to measurable quantities including the rheology of the soil. Other cases, such as the removal of soil layers by thick liquid films and the cleaning of reactive soils will also be introduced, and future challenges will be discussed.
About the speaker
Rubens is a final-year PhD student in Chemical Engineering at the University of Cambridge (UK) and is supervised by Prof. Ian Wilson. He graduated in Mechanical Engineering at the Federal University of Technology - Parana (Curitiba - Brazil, 2014), and holds a master's degree in Mechanical Engineering from the same university (2016). His research experiences lie in the rheology of yield stress materials and in non-Newtonian fluid mechanics, particularly in cleaning viscoplastic soils from surfaces via the hydrodynamic interactions with Newtonian fluid flows. He is also interested in the rheology of foods and thixotropic multiphase systems such as drilling fluids.
Host: Professor Randy Ewoldt
