Thixotropy of sweetened condensed milk applied to flow fluid dynamics analysis of cylindrical pipes

Abstract

Understanding the rheological behavior of fluids and the parameters related to flow fluid dynamics is important for better designing equipment and enhancing processes in the food industry. Thus, the objective of this study was to characterize the rheological behavior of sweetened condensed milk (SCM) in the temperature range of 278.15 to 343.15 K, investigate the friction factor in laminar flow for this fluid, and evaluate the correlation between the rheological behavior obtained from fluid dynamics data and that obtained from rheological assays. The rheological properties of the SCM were determined in triplicate using an AR 2000 controlled tension rotational rheometer with a parallel-plate and cone-and-plate geometry and the pressure drop measurement system consisting of stainless steel pipes connected to a 0.1 m3 stainless steel cylindrical tank. Pseudoplastic behavior with thixotropy was observed, and the friction factor in laminar flow diverged from the theoretical value, with a maximum relative deviation of 42.4% for the data in the descending curve. The maximum relative deviation between the calculated pressure drop and the experimental values was 36.8%. A satisfactory correlation was obtained between the SCM rheological behaviors obtained using rheometer data and pressure drop assays. Practical Applications: Sweetened condensed milk is one of the main products used in the production of sweets and desserts. Its production involves unity operations, for example, pumping and heat treatments. Correctly designing the equipment used in these operations, as well as enhancing the processing parameters, requires the understanding of fluid rheological behavior, specifically the changes induced when shear rates are applied to the fluid. In the present study, the correlation between the rheology of SCM indicated by fluid dynamics data obtained using a pipe and pumping system and the rheological parameters obtained via rheological tests using a rheometer was investigated to evaluate the behavior of this fluid during its flowing.