Assessment of the effect of dual impeller alignment on the heat transfer coefficient in stirred tanks

Chemical processes usually rely on mechanically stirred tanks to perform several operations in sequential or simultaneous manner. Existing correlations for local heat transfer coefficient estimation are valid only for specific geometrical configurations and most academic works regard the so-called standard geometry using only one impeller. However, many industrial tanks operate with two or more impellers whose alignment has been rarely studied previously. In this work, we study the effect of impeller alignment (phase angle) in the local heat transfer coefficient (h_i) for lab-scale heating experiments in a stirred cylindrical tank (turning anti clockwise) equipped with two high-efficiency impellers (HE3) and two pitched blade impellers (PB4). It was found that a 0° phase angle yields higher values of h_i for the HE3 impellers, i.e., this configuration is more efficient for heat transfer purposes than its counterpart with a 60° phase angle. No significant effect was observed by varying the aligned between impellers for the case of pitched blade impellers. In addition, Computational Fluid Dynamics (CFD) analysis was used to evaluate the hydrodynamic inside the tank for the four different impeller configurations. It was observed a more efficient synchronization of the pumping loops generated by both impellers with 0° phase angle between impellers.