Theoretical study of thermo-hydrodynamic performances inside an agitated tank equipped with modified two-blade design

Abstract

The process of heating and cooling in jacketed stirred tanks holds significant importance, particularly in applications involving chemical and food mixing. Due to the various types of complex fluids present in the industrial field, especially those with high viscosity, agitators primarily generate tangential flow. However, controlling convective thermal process through purely tangential flow remains challenging, particularly when the free surface plays a role in thermal operations. Hence, the purpose of the present study is to provide a numerical investigation into the kinetic and thermal performance of a new type of two-blade designed to improve axial velocities inside a cylindrical tank equipped with a heated lateral sidewall jacket. The new type impeller is based on two juxtaposed sub-two-blades of different diameters. The impeller rotation speed (Reynolds number = 0.1–30), the height of the lower two-blade (agitator Length ratio = 1–0) as well as the thermal fluid nature (Prandtl number = 1––1000) represent the parameters guiding the present study in terms of hydrodynamics, thermal aspects, and even energetics. The laminar flow induced by the agitator, resulting in forced convection, is governed by the Navier-Stokes and heat equations, which are solved using the finite element method. The results have shown that the adoption of the modified two-blade configuration not only enhances axial velocity and reduces energy consumption but also improves heat transfer with a slight modification compared to the standard two-blade configurations. Moreover, as the Reynolds number increases, the Nusselt number also rises. It should be noted that the agitated system tends to become more thermally insulated as a thicker standard configuration is employed. This study on modified impellers enhances mixing and heat transfer efficiency in agitated tanks, making it valuable for industries, especially in applications like improved temperature control in food and beverage production.