The Forward Cycle

The Carnot cycle is a series of four steps that the working substance undergoes in the operation of the engine. At the completion of the four steps, the working substance has been returned to its initial state. In the forward direction, in which the engine transfers a net amount of heat to the working substance and does a net amount of work on the surroundings, the four steps are as follows  

Step I. A reversible isothermal expansion in thermal contact with the high-temperature reservoir at t2- 

Step II. A reversible adiabatic expansion in which the temperature of the working substance decreases to fj. 

Step III. A reversible isothermal compression in thermal contact with the low-temperature reservoir at ti. 

---

In example 2 a simpler approach is used to correctly handle backward cycles (co-products). The difference to the forward cycle is that the co-product quant B created by a quant A cannot be used as predecessor of A, because cycles in the quant network are not allowed (violates the cause effect principle). A model can avoid this cycles using aggregation in such a way that cycles are within these quants A and B (see Figure 4.15). 

Thus, the amount of heat returned to the high-temperature reservoir in the reverse cycle is greater than the amount removed from it in the forward cycle. 

In this case there is a total of four pathways for transition E -> ES -> E. The transition time Te es- e is the forward cycle time multiplied by the probabilities that the transitions E -> ES and ES - E are in the forward (clockwise in Figure 4.2B) direction ... 

After the 20K step increase in feed temperature, not much change could be observed for two minutes. Then the last thermocouple started to increase from 560 to 1200 K level, and the hot zone widened. The forward migration rate of the hot zone was about 5 cm/min. After about six minutes, the oxygen content of the cycle gas became very low and temperature slowly started to decline. With this the experiment terminated. 

As air pollution management moves forward, economics has a major role in reducing pollution. Multimedia considerations are forcing a blend of traditional emission reduction approaches and innovative methods for waste minimization. These efforts are directed toward full cost accounting of the life cycle of products and residuals from the manufacturing, use, and ultimate disposal of materials. 

Cyclic voltammetry is most commonly used to investigate the polymerization of a new monomer. Polymerization and film deposition are characterized by increasing peak currents for oxidation of the monomer on successive cycles, and the development of redox waves for the polymer at potentials below the onset of monomer oxidation. A nucleation loop, in which the current on the reverse scan is higher than on the corresponding forward scan, is commonly observed during the first cycle.56,57 These features are all illustrated in Fig. 3 for the polymerization of a substituted pyrrole.58... 

Figure 12.12 Kinetics of the (2 x 2) —3CO - ( /l9 xvT9)R23.4° — 13CO phase transition on a Pt( 111) electrode in a CO-saturated 0.1M H2SO4 electrolyte, observed via SFG of atop CO. The frequency shift data in (b) and (e) indicate that a new potential is estabhshed on the electrode within 0.2 s. The forward transformation is much slower than the reverse. There are minimal differences between the first and second cycles, indicating minimal change in electrolyte composition during kinetic measurements.

Rapid exchange between Xi and Xi is reported in reference (3). This means that the forward and reverse reaction rates of this step are mnch faster than all others, and hence this particnlar step can be treated as a qnasi-eqnihbrium. The two intermediates in that step are present at all times in concentrations related to one another by a thermodynamic eqnihbrium constant and can be Inmped into one pseudo-intermediate [Xs]. This approach is very useM in reducing the number of terms in the denominator of the rate equation, which is equal to the square of the number of intermediates in the cycle (7). 

Fig. 16. Variation in a stationary cycling state of catalyst temperature, S03, and complex concentrations in the melt phase and the concentration of gas phase species with time in a half cycle in the forward flow portion of a reactor operating under periodic reversal of flow direction with r = 40 min, SV = 900 h (Csodo = 6 vol%, (Co2)o = 15 vol%, Ta = 50°C. Curves 1, just after switching flow direction 2,1 min 3, 6.6 min 4, 13.3 min, and 5, 20 min after a switch in flow direction. (Figure adapted from Bunimovich et at., 1995, with permission, 1995 Elsevier Science Ltd.)...

The hydrolysis of methyl acetate (A) in dilute aqueous solution to form methanol (B) and acetic acid (C) is to take place in a batch reactor operating isothermally. The reaction is reversible, pseudo-first-order with respect to acetate in the forward direction (kf = 1.82 X 10-4 s-1), and first-order with respect to each product species in the reverse direction (kr = 4.49 X10-4 L mol-1 S l). The feed contains only A in water, at a concentration of 0.050 mol L-1. Determine the size of the reactor required, if the rate of product formation is to be 100 mol h-1 on a continuing basis, the down-time per batch is 30 min, and the optimal fractional conversion (i.e., that which maximizes production) is obtained in each cycle. 

Perfume, like other chemical products, follows a life cycle composed of introduction, growth, maturity, and decline. To change the life cycle companies use different strategies to shift products in the maturity phase back or catapult new products forward into growth phase. For instance, a perfume in the maturity phase can be changed to a radically different category to shift the product to a growth phase. The search for the new niche is run by functional decisions. 

---