Dual-cycle process

The Dual cycle as shown in Fig. 3.20 is composed of the following five processes ... 

What five processes make up the dual cycle ... 

The combustion process in internal combustion engines as an isobaric or isometric heat-addition process is oversimplistic and not realistic. A real cycle p-v diagram of the Otto or Diesel cycle looks like a curve (combination of isobaric and isometric) rather than a linear line. Are the combustion processes in the dual cycle more realistic ... 

The dual cycle involves two heat-addition processes, one at constant volume and one at constant pressure. It behaves more like an actual cycle than either the Otto or Diesel cycles. 

The dual-cycle system is favored over the single cycle system if the cleaning process requires the use of cosolvent. Although the cosolvent reclaim system adds to initial capital costs, it yields a net gain by lowering material costs and improving consistency and operating efficiency. 

The second process investigated was an alternative for a xylene cleaning process. The dual-cycle (two step) process, as described previously in this chapter, is used due to the nature of the contaminant being removed. Figure 7 shows a bar chart of the annual costs (normalized) for the two processes. Once again the key differences are in the equipment and consumables. 

Process and equipment developments continue to make supercritical carbon dioxide cleaning a more competitive option and to expand the applications for this process. These developments are primarily aimed at reducing the requirements for continuous carbon dioxide flow, producing effective cleaning at lower temperatures and pressures, and the construction of equipment with less expensive materials. These objectives are being reached primarily because of improved understanding of the effectiveness of carbon dioxide as a solvent and the required performance of the equipment. It appears that the dual-cycle (two step) process will continue to receive primary attention as the most effective supercritical carbon dioxide alternative to conventional cleaning methods. 

To reduce the work of compression in this cycle a two-stage or dualpressure process may be used whereby the pressure is reduced by two successive isenthalpic expansions. Since the isothermal work of compression is approximately proportional to the logarithm of the pressure ratio, and the Joule-Thomson coohng is roughly proportional to the pressure difference, there is a greater reduction in compressor work than in refrigerating performance for this dual-pressure process. 

This reaction demonstrated broad scope and good functional group tolerance. These authors presented the following mechanism for the catalytic cycle, which reputedly involved a dual catalytic process (Scheme 4.3). 

Figure 4-9. Ammonia combustion at air compressor discharge pressure of 2-5 bar, absorption at nitrous gas compressor discharge pressure of 7-15 bar (Process 3, dual-pressure cycle).

In-well aeration is the process of injecting air into the lower portion of a dual-screened well with perforations at the bottom and above the water table. As the bubbles rise, they expand, which causes the mixed mass of air and water to have less density. The result is an air-lift pump effect. When the water rises and exits the upper perforations, replacement water enters the bottom of the well. The result is a circulation cycle. Free air does not enter the aquifer, but dissolved air (and oxygen) travels with the circulating water. Figure 9.4 is a schematic diagram of in-well aeration. 

FIGURE 19-55 Dual roles of cytochrome b6f and cytochrome c6 in cyanobacteria. Cyanobacteria use cytochrome bsf, cytochrome c6, and plastoquinone for both oxidative phosphorylation and photophosphorylation. (a) In photophosphorylation, electrons flow (top to bottom) from water to NADP+. (b) In oxidative phosphorylation, electrons flow from NADH to 02. Both processes are accompanied by proton movement across the membrane, accomplished by a Q cycle. 

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