Exergy destruction number

The use of an augmentation device results in an improved heat transfer coefficient, thus reducing exergy destruction due to convective heat transfer however, exergy destruction due to frictional effects may increase. The exergy destruction number Nx is the ratio of the nondimensional exergy destruction number of the augmented system to that of the... 

Here, exm is the flow-exergy destruction, or irreversibility, and T0 the reference temperature. The system will be thermodynamically advantageous only if the Nx is less than unity. The exergy destruction number is widely used in second-law-based thermoeconomic analysis of thermal processes such as heat exchangers. 

Then the exergy destruction for any process system may be obtained as the shaded area on the energy - direction factor diagram shown in Fig. A2. When the number of subprocesses is increased, the width of each AHha is decreased, resulting in continuous change in Dha 1" and Dhd ", Of course the exergy destruction obtained in this method is the same as that in the text (jL), hut Eq. (29) becomes now the sufficient condition for a process system to hold. 

Let us now explore in more detail the factors that determine the number of steady-state solutions. First, we notice from Eq. (5.11) that the slope of the line is steep for small heat exchangers (e<heat exchanger at all (e = 0). This is completely opposite to what we observed for a jacketed CSTR in Chap. 4. In a jacketed CSTR the slope of the heat removal line increases with the size of the heat transfer area. The difference is that, in the case of a CSTR, a large heat transfer area increases the rate of heat removal (exergy destruction), driving the system toward stable operation at a single steady state, whereas in the case of an FEHE system,... 

---