The aim of the research presented in this paper was determination of power consumption and gas hold-up in mechanically agitated aerated aqueous low concentration sucrose solutions. Experimental studies were conducted in a vessel of diameter 0.634 m equipped with high-speed impellers (Rushton turbine, Smith turbine or A 315). The following operating parameters were changed: volumetric gas flow rate (expressed by superficial gas velocity), impeller speed, sucrose concentration and type of impeller. Based on the experiments results, impellers with a modified shape of blades, e.g. CD 6 or A 315, could be recommended for such gas-liquid systems. Power consumption was measured using strain gauge method. The results of gas holdup measurements have been approximated by an empirical relationship containing dimensionless numbers (Eq. (2)).
The results of the experimental studies
of local heat process for
a gas–liquid system in the region of the cylindrical wall of
an agitated vessel equipped with the system of CD 6–RT impellers
are presented. A lower CD 6 impeller (Smith turbine) and upper RT
impeller (Rushton turbine) were located on the common shaft in a baffled
agitated vessel of inner diameter equal to 0.3 m. Liquid height in
the agitated vessel was equal to 0.6 m. Newtonian liquids of different
physical properties were used as a continuous phase. Air was dispersed
in the liquid. Local heat transfer coefficients were measured using
both thermal and electrochemical methods. In total, 2280 experimental
points were obtained. Distributions of the heat transfer coefficients
were described by means of eqs 12–17 and 18–23 as a
function of the Re and Pr numbers,
dimensionless axial coordinate z/H, and modified Fr
g number, separately, for turbulent and transitional
ranges of the fluid flow in the agitated vessel. Equations 12–17
and 18–23, concerning both coalescing and noncoalescing gas–liquid
systems, have no equivalent in the open literature.
Experimentally found local heat transfer coefficients are analyzed as a function of the measuring point on the heat transfer surface area of the agitated vessel wall and of the impeller eccentricity. Eccentric Rushton turbine and A 315 impeller are considered. Local heat transfer coefficients were measured by means of the computer-aided electrochemical method. The measurements were performed in an agitated vessel with inner diameter 0.3 m, filled with liquid up to the height equal to the vessel diameter. The experiments were carried out within the turbulent regime of the Newtonian liquid flow in the agitated vessel. The results were compared with the data obtained for the agitated vessel equipped with an eccentrically located axial flow propeller or an HE 3 impeller. Experimental studies show that the distributions of the heat transfer coefficient values depend on the impeller eccentricity, impeller type and the direction of the liquid circulation in the agitated vessel.
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