Discontinuous modes of operation

When the eore s flux is eompletely emptied prior to the next cyele, it is referred to as the discontinuous-mode of operation. This is seen in the induetor eurrent and voltage waveforms in Figure 3-4. When the eore does not eompletely empty itself, a residual amount of energy remains in the eore. This is ealled the continuous mode of operation and ean be seen in Figure 3-5. The majority of boost-mode eonverters operate in the diseontinuous mode sinee there are some intrinsie instability problems when operating in the eontinuous mode. 

For a discontinuous mode of operation (batch reactors), these parameters are defined based on the initial number of moles i 0 and wj. 0, and the stoichiometric coefficients v (< 0 for reactants, > 0 for products) ... 

Fig. 16 Experimental setup of the miniplant in a discontinuous mode of operation (a) as well as in continuous circulation of both phases (b), and an illustration of the processes occurring during the particle extraction process (c) (schematics were created by Leistner, 1)...

Therefore, the analysis of the main object of this book, namely, the batch chemical reactor, can start by considering the different ideal chemical reactors. In fact, ideal reactors are strongly simplified models of real chemical reactors [10], which however capture the two major features mentioned above. These models can be classified according to the mode of operation (i.e., discontinuous vs. continuous) and to the quality of mixing (i.e., perfect mixing vs. no mixing). The three resulting ideal reactors are sketched in Fig. 2.1. 

Constant current ECD is the most common mode of operation but fixed frequency is gaining acceptance. The thermal electron concentration in the detector cell is measured discontinuously by a pulsed voltage. A pulsed discharge ECD a nonradioactive source is more sensitive than the radioactive source for most compounds, covers a wide dynamic response range similar to the radioactive source. Cell volumes are typically 480 jA to 1.5 ml with 150 /tl for the micro ECD at a data acquisition frequency of 50 Hz. 

Extruders can have different designs and modes of operation, e.g., single or multi-screw, continuous or discontinuous. The basic operation of the most widely used extruder for forming thermoplastics into finished products, the single screw extruder, will be reviewed in the next section. This provides the concepts that can be extended to other, more complex machines, viz. the multiscrew and specialty extruders discussed briefly in... 

In the subsequent steps the procedures to answer the two questions differ. In the first case, the assessment of a newly designed plant, usually the desired conversion, the optimal process temperature and the required production rate are fixed. Also the mode of operation, such as continuous or discontinuous, is predetermined by demands on selectivity and 3deld. The safety evaluation now has to assess, whether or not the parameter combination selected fi om the multi-dimensional space defined by reactor size, initial concentrations, characteristic reaction time as well as coolant and feed temperature can ensure safe operation under normal conditions. 

Two quite frequently occurring questions regarding the safety technical assessment of chemical reactions cannot be placed directly into the order presented here so far. The first case is the evaluation of reactions performed imder reflux conditions. The safety assessment of such processes does not depend primarily on the general mode of operation, which in most cases is either discontinuous or semi-continuous, but on the peripheral installations to the reactor itself. In industrial practice, numerous designs can be found. Consequently the discussion here has to focus on two examples to outline the general assessment procedure. If these examples demonstrating the fimdamental approach to the assessment of processes under reflux are combined with the assessment criteria presented so far, the basis is provided to perform the safety evaluation for any other unique design as required. 

Diaiiltration The convective elimination of permeable solutes by the addition of fresh solvent (water) to the retentate. Two modes of operation may be used in diafiltration continuous or discontinuous. 

Application of New Types of Process Techniques. As will be further explored in Chap. 3, a great number of mixing and aeration systems have been developed that could be of industrial interest. All of these reactors can be operated in discontinuous, semicontinuous, or fully continuous modes. The semi-continuous mode of operation offers some advantages (Pickett, Topiwala, and Bazin, 1979). However, a fully continuous operation seems to be limited (infections, strain stability, continuous flow). 

The mode of operation of the reactor—discontinuous, completely continuous, semicontinuous, or semidiscontinuous—including transient or steady-state operation techniques. 

Reactor operation includes discontinuous and continuous operations, steady-state and transient-state modes, and a group of intermediate modes that can be referred to collectively as semicontinuous operation. The modes of operation are compared in Fig. 3.30. 

Extruders in the polymer industry come in many different designs. The main distinction between the various extruders is their mode of operation continuous or discontinuous. The latter type extruder delivers polymer in an intermittent fashion and, therefore, is ideally suited for hatch type processes, such as injection molding and blow molding. As mentioned earlier, continuous extruders have a rotating member, whereas batch extruders have a reciprocating member. A classification of the various extruders is shown in Table 2.1. 

Ram or plunger extruders are simple in design, rugged, and discontinuous in their mode of operation. Ram extruders are essentially positive displacement devices and are able to generate very high pressures. Because of the intermittent operation of... 

FIGURE 10.64 Operating waveforms for the discontinuous current mode of operation. 

In order to determine precisely the latent-heat values, the calorimeter has to be operated in the relaxation mode. In the most recent version of this mode, the bath is accurately stabilized and then a linearly ramped power is applied to the sample [31], This mode of operation is sensitive not only to the continuous but also to the discontinuous part of the enthalpy change, i.e. the latent heat L. Hence, L can be quantitatively determined by subtracting the integrals of the resulting Cp and Cp ff anomalies of the ac and relaxation modes, respectively ... 

Discontinuous and Semicontinuous Mode of Operation (Batch Type Reactor) In... 

The operation of a discontinuous-mode, flyback converter is quite different from that of a forward-mode converter, and likewise their control-to-output characteristics are very different. The topologies that fall into this category of control-to-output characteristics are the boost, buck/boost, and the flyback. The forward and flyback-mode converters operating under current-mode control also fall into this category. Only their dc value is determined differently. Their representative circuit diagram is given in Figure B-12. 

The use of stirred fermenters with automatic control of the culture environment is the most suitable technique to evaluate bacterial or fungal kinetics. Cultures can be operated in discontinuous mode (batch cultures). 

The traditional operation mode of synchrotron light sources is a discontinuous one particles are injected in the storage ring, the beam current is decaying exponentially, and after several hours the synchrotron radiation run is stopped for a new injection. 

Bioreactors are operated in discontinuous mode, with a sequential or continuous feed of the substrate (fed-batch operation) or in continuous mode. The choice of the operating mode depends mainly on the reaction characteristics ... 

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