Method for determining the maximum permissible rotor speed of rotary lobe pumps when pumping fish mince based on its rheological properties

The relevance of the study is determined by the need to preserve the structure and quality of fish mince systems during their inter-operational transportation by rotary lobe pumps in food production lines. Existing manufacturers' recommendations on limiting rotor speed are primarily applicable to Newtonian fluids and do not account for the complex rheological behaviour of fish minces, which is characterized by yield stress, pseudoplasticity, and thixotropic destruction of the fibrous structure under shear deformation. The aim of this work is to improve the method for determining the maximum permissible rotor speed of rotary lobe pumps when pumping pollock mince with various fillers (millet, buckwheat, oat flakes, rye flour). Based on a rheological model describing shear stress as a sum of instantaneous-elastic deformation, plastic shear, and viscoelastic flow components, an analytical dependence of effective dynamic viscosity on rotor speed has been derived. For JRZL-series pumps, a generalized formula relating permissible speed to pump working volume and dimensionless viscosity of the pumped medium has been obtained, with the exponent β = 0.181 remaining constant across the entire pump line. An algorithm for solving the nonlinear equation to calculate limiting pump operating modes has been developed. It has been found that for the RZL-120 pump, transitioning from mince without additives to mince with rye flour reduces the permissible rotor speed from 232 to 68.7 rpm. The proposed methodology enables a scientific election of pump type and operating mode, ensuring product quality preservation and optimization of energy efficiency indicators in food processing technologies.

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