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

Heat transfer rates in agitated vessels has been investigated for some Newt onian and non-Newtonian fluids mixed in a flat bottomed vessel equipped wit h a helical ribbon agitator. Heat transfer rates from jacket to bulk liquid were determined for different stirrers, rheological properties and operati ng conditions. The heat transfer coefficient for the liquid inside the vess el is calculated based on the experimental data and an empirical correlatio n is developed to predict the heat transfer coefficient for the specified o perating conditions. The correlation includes the influence of the H/T rati o on the heat transfer coefficient, which has not been studied so far. Inve stigations on the effect of position of impeller in the vessel indicate tha t the heat transfer coefficient is maximum when the impeller is placed slig htly above the centre. Heat transfer rates were also investigated in gassed systems, both in the presence and absence of agitation. The results indica te that the heat transfer coefficient initially increases substantially wit h the superficial velocity of the gas and then increases rather slowly at h igher 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 lo wer gas flow rate as compared to the increase at higher flow rate. (C) 2000 Elsevier Science S.A. All rights reserved.