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A novel coaxial mixer was proposed,which had an outer wall-scrapingframe and a combined inner impeller consisting of a four-pitched-bladeturbine paddle (PBT-4) and a Rushton turbine paddle (RT-6). Its heattransfer performance in Newtonian fluid under different operatingmodes (single rotation of inner impeller, corotation and counter-rotation)was experimentally investigated in a stainless steel agitated vesselwith semicircle spiral jacket and ellipsoidal head by measuring theaverage heat transfer coefficient of the inner wall. Meanwhile, thewall temperature, the heat flow rate and the local heat transfer coefficientin the coaxial agitated vessel were determined with the help of numericalsimulation. The results show that the heat transfer coefficient nearthe inner wall surface of the agitated vessel will increase with theincreasing speed of the inner or outer impeller whether under single-shaftagitation or under coaxial agitation mode, whereas the effect of speedof the inner impeller on heat transfer is more obvious and efficient.Under the same conditions, the heat transfer of coaxial agitationis more efficient than that of single-shaft agitation, especiallythe local heat transfer coefficient on the upper and lower part ofthe agitated vessel, which is increased greatly. In addition, thelocal heat transfer coefficient varies with the axial position ofthe agitated vessel, and the heat transfer coefficient in zones betweenthe upper and lower impeller is relatively high. The effect of thecorotation mode and counter-rotation mode on heat transfer is of littledifference, but the corotation mode is recommended owing to its advantageof low power consumption and good mixing performance. [ABSTRACT FROM AUTHOR]

The power consumption of a coaxialmixer consisting of an outer anchor and different inner impellerswas experimentally characterized in an agitating vessel full of Newtonianfluids (highly viscous malt syrup). Meanwhile, taking the rotationmode, speed ratio, and diameter ratio between the inner and outerimpellers into consideration, a novel correlation for the calculationof the total power consumption of the coaxial mixer was introducedby defining a new characteristic diameter and a new characteristicspeed. The results show that the inner impeller has an obvious effecton the power consumption of the outer impeller: the power consumptionof the outer impeller will decrease under co-rotation mode and increaseunder counter-rotation mode. The power consumption of the high-speedinner impeller accounts for a large percentage of the total powerconsumption and the outer impeller has little effect on it. Comparedwith other existing correlations, the Reynolds number calculated fromthe novel correlation is greater and the power number is smaller,which can better reflect the high efficiency and low power consumptionof the coaxial mixer. [ABSTRACT FROM AUTHOR]