Heat transfer to viscous Newtonian and non-Newtonian fluids using helical ribbon agitator

Abstract

Heat transfer rates in agitated vessels has been investigated for some Newtonian and non-Newtonian fluids mixed in a flat bottomed vessel equipped with a helical ribbon agitator. Heat transfer rates from jacket to bulk liquid were determined for different stirrers, rheological properties and operating conditions. The heat transfer coefficient for the liquid inside the vessel is calculated based on the experimental data and an empirical correlation is developed to predict the heat transfer coefficient for the specified operating conditions. The correlation includes the influence of the H/ T ratio on the heat transfer coefficient, which has not been studied so far. Investigations on the effect of position of impeller in the vessel indicate that the heat transfer coefficient is maximum when the impeller is placed slightly above the centre. Heat transfer rates were also investigated in gassed systems, both in the presence and absence of agitation. The results indicate that the heat transfer coefficient initially increases substantially with the superficial velocity of the gas and then increases rather slowly at higher gas flow rates. It also indicates that the heat transfer coefficient does not increase substantially when aeration is coupled with agitation as compared to only aeration. The marginal increase is relatively higher at lower gas flow rate as compared to the increase at higher flow rate.