Stirring power

Mechanically stirred gas-liquid reactor performances are affected by the degree of mixing, apparatus geometry, stirring power, flow rate, discharge and feed locations for the gas and liquid. For a correct design, the following requirements must be satisfied ... 

Finally, one can easily obtain the properties of the stirring system (rotational speed and torque) and compute the stirring power from their product, but these variables are only indirectly linked to the reactor status through the system density. 

For the sake of completeness, two different scale-up rules are briefly considered here, and their different results are shown. First, let us define the stirring power P as... 

Stirring vessels. Upon the examination of different stirring operations it was indeed found that the intensively formulated process parameter P/V represented the pertinent scale-up criterion only if the stirring power has to be dissipated in the volume as evenly as possible (micro-mixing, isotropic turbulence). Examples of this are the dispersion of a gas in a liquid or the dispersion of immiscible liquids s. [22]. 

In this regime, baffles are fully effective and they can increase the required stirring power by a factor as great as 10. This is illustrated in Fig. 24 for a vessel containing the blade stirrer with (curve cs) and without (curve c) baffles. 

Stirring power - 1 w m volume fraction of solids- in the slurry... 

Submerged fermentations are mostly operated in batch processes but can also be run continuously in certain cases (continuous fermentation). Batch fermentations may last up to 10 days. Following the fermentation the flavour raw material is extracted from the fermentation broth. In industrial fermentations typically cell counts of 10-30 g/1 are obtained. For a profitable cost/efficiency relation a product yield of 20-30 g/1 has to be achieved. Aerobe fermentations require oxygen transfer rates to the fermentation broth of about 100 mmol/1 per hour. Depending on the viscosity of the media 0.75-2.5 KW stirring power has to be applied for each m of fermentation broth. 

In this connection it is important to be able to ascertain the smallest material ball attainable and to estimate the homogenization time, which is thereby required. Mixing or stirring power has to be expended to decrease the diffusion length or decrease the size of the segregated liquid balls. According to the statistical theory of turbulence due to Kolmogorov [143, 289], see Section 1.4.2, the size of the liquid balls can be estimated ... 

For Fr 10, F eFrlQ = const applies, i.e. P/q oc d. In this range P/q increases directly proportionally with scale P/q cc d. (In case of a scale-up of n = 1 10, the full-scale device required a ten-fold stirring power for the same gas throughput )... 

The Difasol reaction involves a mechanically stirred reactor and settlers. An injection of fresh catalyst components is defined to compensate the detrimental effects of accidental impurities present in the feed and slight carryover of the catalyst. Mixing of the solvent phase with the organic phase ensures advantageous butene conversion. However, importantly, the stirring power combined with a high... 

The power required to operate a stirred tank is mostly the mechanical power required to rotate the stirrer. Naturally, the stirring power varies with the stirrer type. In general, the power requirement will increase in line with the size and/or rotating speed, and will also vary according to the properties of the liquid. The stirrer power requirement for a gassed (aerated) liquid is less than for an ungassed liquid,... 

The power abstracted from the liquid in the CSTR consists of two items the rate, Pq, at which work is done against the cover-gas pressure and the net stirring power, P experienced by the liquid in the reactor. The power expended in increasing the liquid volume against the cover-gas pressure, Pq, is found using equation (3.47) of Section 3.6 ... 

Ne, the so-called Newton number, is tabulated in the standard literature for numerous types of agitators [58,59]. The revolution rate of the stirrer determines to the first power the conductive heat removal rate and to the third power the dissipated stirring power, respectively. 

Heat transfer is proportional to stirring speed to the power 5/3 and also changes on scale-up. For example, for a tenfold increase in size of the crystallizer, the introduced stirring power must be increased by a factor of 10 (risk of crystal abrasion) to remove the heat of crystallization at the same driving force AT for heat exchange. 

Increasing the stirring power, optimizing the geometry, and introducing an external forced circulation led to further advantages and the development of the attritor... 

The stirring/mixing continues until the emulsion breaks. An emulsion breaking is considered to occur when the bituminous emulsion and filler mixture becomes pasty and forms lumps, which do not adhere to the walls of the pan. This, combined with a noticeable increase in stirring power, indicates the end of mixability. 

The stirring power developed in the tanks is around 40 W-m of tank for MWW, but can often reach or exceed 60 W for IWW (high sludge concentrations). 

With Cj = 10 and = 1.5, Tj = 0.76 at 15 to 20 C. Disregarding the two other parameters, the corrected amount of oxygen becomes 2 358 kg day b. Correction factor F related to the shape of the aeration tank and to hydraulic conditions. Depending on the type of surface aerator and the shape of the tank, the second F fector 12 = Fi can be calculated (shape of the tank) x F2 (ratio between width and depth) x F3 (specific stirring power) char can be 0.9 for example. A nominal net specific aerator input measured at the shaft of 2 kg kWh of O2 becomes a real input of 1.8. Four aerators, with 20 kW of absorbed power, therefore supply 4 x 20 x 1.8= 144 leg of O2 per hour for a total of 74 that are required on the average. They can be run intermittently and still ensure a maximum stirring power of 37 W m of tank. 

Stirring speed circulation number concentration distribution parameter of a flow model stirring power Peclet number... 

The effect of activation energy on yield is clearly shown by Figure 13-40, where yield is plotted as a function of stirring power per unit volume for the various determining variables. Power per unit volume and tank size have a much stronger effect for the exothermic reactions than for the isothermal reactions, as shown. In both cases direct comparison of results in the 0.785 L tank with the 3785 L tank indicates a yield difference of about 25%. Figures 13-41 and 13-42 show how concentration and temperature change with time as the semibatch... 

By 1917, Hesse s data-driven, precise, and concrete analyses were overshadowed by more passionate arguments. The war stirred powerful emotions, and... 

The motor torque is transferred unchanged to the stirrer shaft, and the relation between the stirring power psa. and the total motor power pm2 reads... 

The change in stirring power 5r2 corresponds to the change in the total motor power 5m2 when the lost power remains constant. 

The enlargement of the stirring power pst2 l>y Psa and unchanged (k F)2 would cause an increase in the present difference in temperature AT2. 

In the second case is decreased by the amount of the increased stirring power... 

The heat-transfer coefficient (k-F)i and the effective heat capacity Ci of the filling in the intermediate thermostat are constant during the reaction. k F)i, C and C2 can be found using an analogous procedure to that just illustrated. The stirring powers pst2 and psti must be measured (Sect. 6.3). 

The heat-transfer coefficient (k F)i and the stirring power psti of the intermediate thermostat are not influenced by the reaction within the measiuing kettle they are to a certain extent apparatus constants. ATi remains constant because pi changes, regulated by a control procedure, opposite and equal to the change in the heat flow (k F)2 AT2 from the measuring kettle into the intermediate thermostat. 

---