Measurement of power consumption in stirred vessels - A review

Mixing is a very common operation in the process industries, usually performed by mechanical agitation. Accurate methods are necessary for the estimation of the net power draw to the fluid (the only relevant for process results). This paper reviews the literature of the last 35 years on the methods for measuring power draw in stirred tanks and fermentors (during actual cultures) of sizes ranging from laboratory to industrial scale. Overall, very few papers report details on the techniques. The majority of the information comes from reports in which power consumption measurements were only a technique and where this specific methodology is in general poorly described. Depending upon the principle of measurement, four main techniques have been reported: electric, calorimetric, reaction torque and strain. The advantages and disadvantages of the methods are discussed, some new data from the authors' laboratory are provided and the potential of new techniques is outlined.