Mixing characteristics

The heat integration characteristics of reactors depend both on the decisions made for the removal or addition of heat and the reactor mixing characteristics. In the first instance, adiabatic operation is considered, since this gives the simplest design. 

Ethane. Ethane VPO occurs at lower temperatures than methane oxidation but requires higher temperatures than the higher hydrocarbons (121). This is a transition case with mixed characteristics. Low temperature VPO, cool flames, oscillations, and a NTC region do occur. At low temperatures and pressures, the main products are formaldehyde, acetaldehyde (HCHOiCH CHO ca 5) (121—123), and carbon monoxide. These products arise mainly through ethylperoxy and ethoxy radicals (see eqs. 2 and 12—16 and Fig. 1). 

The polysulfide impression materials can be formulated to have a wide range of physical and chemical characteristics by modifying the base (polysulfide portion), and/or the initiator system. Further changes may be obtained by varying the proportion of the base to the catalyst in the final mix. Characteristics varied by these mechanisms include viscosity control from thin fluid mixes to heavy thixotropic mixes, setting-time control, and control of the set-mbber hardness from a Shore A Durometer scale of 20 to 60. Variations in strength, toughness, and elasticity can also be achieved. 

Ventilation efficiency Indices that provide a method of assessing the mixing characteristics of incoming air with the room air. It presents a means of determining the pollutant distribution within the space. 

Houcine, L, Plasari, E., David, R. and Villermaux, J., 1997. Influence of mixing characteristics on the quality and size of precipitated calcium oxalate in a pilot scale reactor. Transactions of the Institution of Chemical Engineers, 75, 252-256. 

Figure 19.2 shows how the production of CO can vary with excess air for two typical burners. It is seen that to limit CO to, say, 50 ppm with burner B, 3 per cent oxygen in the flue is needed, and with burner A, which exhibits better mixing characteristics, only 0.75 per cent excess oxygen is required. It is also seen that the heel in the curve is more pronounced with burner A such that... 

A-l,3-dimethylbutyl-A -phenyl quinone diimine (6QD1) has been introduced as a multifunctional additive for diene rubbers and provides an advantage in mixing characteristics (functions as peptizer and improves scorch safety) as well as improved performance (better antioxidant activity than paraphenylenediamine antidegradants) of the end products [36]. 

Fig. 3. Mixing characteristics with variation of fluidizing velocities and of discharging rate...

The early zinc polycarboxylate cement did not possess the ease of mixing characteristic of the zinc phosphate and zinc eugenolate cements. It suffered because it was expected to mix exactly as a traditional zinc... 

Cobby, D., Angeli, P., Gaveiilidis, A., Mixing characteristics of T-type microfluidic mixers, J. Micromech. Microeng. 11 (2001) 126-132. 

The gas-liquid flow characteristics of stirred vessels depend both on the level of agitation and the rate of gas flow and can vary from the case of bubble column type operation to that of a full circulating tank, as shown in Fig. 5.123. The mixing characteristics and gas distribution obtained, obviously exert a considerable influence on the rate of mass transfer obtained (Harnby et al., 1985). 

The hydrodynamic data will depend on the mixing characteristics of the reactor. In terms of the modeling of the reactor, the hydrodynamic data will depend on the mixing characteristics of each phase and the combinations of mixing characteristics for the phases. Table 7.3 gives typical data for various combinations of mixing characteristics for gas-liquid reactors16. 

Mixing characteristics of phase Practical device Gas hold-up (%) kL A (s )... 

When reacting two phases that are not very soluble in each other, for example when carrying out nucleophilic substitution reactions, phase transfer catalysts should be considered when scaling down from equipment with poor mixing characteristic, rather than buying new equipment. 

Lee, K. C., An experimental investigation of the trailing vortex structure and mixing characteristics of mixing vessels , Ph.D. Thesis, King s College, London, (UK) (1995). 

From the slope of the straight line, the effective mixing cell volume was calculated to be 30.1 cm, with a 50% relaxation time of about 0.08 s. Similar mixing characteristics were observed following a step decrease (i.e., CO + N ), giving an effective mixing cell volume of 31.8 cm and a 50% relaxation time of 0.09 s. Since these response times of the reactor are not much faster than the time scale of the adsorption process (a halfscale relaxation time of about 0.2 s), the transients of the reactor cell were included in our analysis. For our simulations, the mixing cell volume was taken to be 31 cm. ... 

The microreactor shown in Fig. 1 can be regarded as a continuous-flow reactor equivalent to the common batch reactor flask. The microreactor has a mixer section that provides more precise mixing characteristics than those typically achievable in a stirred vessel. For example, in the... 

A PFR is similar to a CSTR in being a flow reactor, but is different in its mixing characteristics. It is different from a BR in being a flow reactor, but is similar in the progressive change of properties, with position replacing time. These features are explored further in this section, but first we elaborate the characteristics of a PFR, as follows ... 

As discussed in Section 17.2.3.1, reactor performance in general depends on (1) the kinetics of reaction, (2) the flow pattern as represented by the RTD, and (3) mixing characteristics within the vessel. The performance predicted by ideal reactor models (CSTR, PFR, and LFR) is determined entirely by (1) and (2), and they do not take (3)... 

Reactive Tracer. If the tracer is reactive, the measured concentrations reflect both mixing characteristics and decay of the tracer. Therefore, the data must be adjusted, such that the residence time distribution within the reactor can be obtained. Example 19-3 illustrates how to adjust the data following a step input of a reactive tracer. 

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