Efficiency and Energy Consumption

If the mixing time obtained experimentally in all micromixers is related to the specific power dissipation, the empirical relation given in Equation 4.27 is found. 

By comparing it with the theoretical mixing time, the energetic efficiency of mixing 1 ) can be defined as the ratio between shear rate effectively used for mixing and total shear rate used for the flow  

It is impossible to determine theoretically the value of the energetic efficiency of mixing and, therefore, the comparison of the experimental correlation (Equation 4.27) with the theoretical relation (Equation 4.26) can be used for its evaluation  

It is observedthat the mixing efficiency in microchannels is about 3-4%. The efficiency is even lower in conventional reactors, for example, 1% in twin-screw extruders [72]. As the mixing time is inversely proportional to the efficiency, an increase of the energetic mixing efficiency, say by a factor 3 (from 3-10%), has the same influence on the mixing time as an increase of 1 order of magnitude (10 times) power dissipation. 

The reason behind such a low energetic efficiency is the mismatch of flow fields and concentration fields. The mechanical energy provided to the mixer is used to achieve the flow in device, but in zones of pure component with no interface with another component, this energy does not contribute in mixing. In the case of micromixers, multilamination improves mixing by reducing the striation thickness, but it requires additional mechanical power to create fine multilamellae before contacting. 

---

As anodes age their performance gradually deteriorates, and thus small changes in electrolyte composition must be made to maintain current efficiency and energy consumption. The EMOS system has been used by some operators to determine the optimum composition of the electrolyte in these circumstances and in some cases to control the composition selectively for each cell line. 

Efficient use of electrical energy was achieved in the HDH reactor. Figure 13.12 shows current efficiency and energy consumption for the electrochemical HDH of DCP in paraffin oil. Here the unit for energy consumption is defined as kWh (kg DCP)-1. 

Energy Guide Labels - The labeis piaced on appiiances to enable consumers to compare appliance energy efficiency and energy consumption under specified test conditions as required by the Federal Trade Commission. 

Figure 3 - Voltage, Current Efficiency and Energy Consumption for a Representative Experiment. Oxygen Evolving DSA. 38°C. Catholyte 30 g/l Zn (as ZnCb), 7 g/1 HCl and 50 g/1...

Figure 6 - Cell Voltage, Current Efficiency and Energy Consumptions at Different Current Densities for 10 ppm TBACL (1461, 2190, 2920, 3651 and 4381 A/m ) Old 22 mm Cell, A1 Current Feeder, DSA (O2) Anode, 0.6 mm Daramic [30 g/1 Zn, 7 g/1 HCL and 50 g/1 NaCl...

Kashid, M., Renken, A., and Kiwi-Minsker, L. (2011) Mixing efficiency and energy consumption for five generic microchannel designs. Chem. 

Electrolyzer refurbishment is the largest item in plant maintenance cost. The mean time between refurbishments should be optimized. The need for membrane replacement is the most frequent determinant of electrolyzer operating life. Maintenance of stable current efficiency and energy consumption and avoidance of membrane damage are keys to economic cell lifetimes. 

The current efficiency of an actual HaU-Heroult (HH) ceU depends on internal interactions in the magnetohydrodynamic (MHD) flow, reactions in different zones of the cell, electrical contact system, operating parameters, and anode-to-cathode distance, hi principle, Haupin and Frank [65] developed a model of relevant zones within the HHceR. This model is shown in Figure 7.12 and it suggests that the possible interactions that are related to current efficiency and energy consumption may be attributable to diverse potentials in the these zones... 

An application is then presented to show the efficiency of electrocoagulation/ electroflotation in removing colour from synthetic and real textile wastewater by using aluminum and iron electrodes in an external-loop airlift reactor. The defluoridation is also showed. The time, pH, conductivity and current density are the most parameters for the removal efficiency and energy consumption. 

---