Abstract
The performance of a dual helical ribbon impeller in a gassed stirred tank reactor filled with a shear-thinning polymer has been investigated experimentally in this study. Sodium carboxymethyl cellulose with different concentrations were applied to change the viscosity and rheological behaviour of working fluid. Titration reaction between HCl and NaOH then took place inside the reactor under controlled pH, evaluating the influence of a dual helical ribbon impeller on the performance of a two-phase agitated reactor. The impact of impeller rotational speed, gas flow rate, viscosity, and clearance to the bottom on power uptake and mixing time are explored. The results thus reveal that the presence of bubbles reduces both required power uptake and mixing time to reach an endpoint reaction. Contrary to expectations, this study indicates that increasing the impeller's speed beyond a certain level, not only fails to further reduction in mixing time, whilst the power uptake increases exponentially.Furthermore, for the first time, this study suggest that power number is inversely proportional to the square root of Reynolds number when systems are equipped with a dual helical ribbon impeller. The response surface method and quadratic numerical models are applied to suggest models in order to calculate the mixing time and power consumption.
Highlights
Stirred tank reactors (STRs1) are one of the most widely used pieces of equipment in process industries
The influence of gas flow rates of 0.5–2.2 liquid pumping upwards by rising bubbles (Lpm) is examined when the system is agitated by a dual helical ribbon impeller between 50–100 rpm under transient flow regime
This work provides a conceptual understanding of the flow pattern inside a gassed reactor equipped with a dual helical ribbon impeller and filled with a shear thinning fluid
Summary
Stirred tank reactors (STRs1) are one of the most widely used pieces of equipment in process industries. The efficient and cost-effective heat and mass transfer and homogeneity of dispersed phase and nutrients are the main objectives of these multiphase mixing processes [7]. Various methods have been developed and introduced to enhance the mixing performance of gas-liquid reactors that contain shear-thinning fluids [8,9,10,11,12,13]. Using a high rotational speed in some cases might reduce mixing times, it reduces the productivity of microorganisms in biological units, and the performance of final products, where it increases the operational costs of chemical processes. In cases where the shear sensitivity of substrate is an issue for reactor performance, using low rotational speed impellers has been suggested within the literature [14,15]
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