Mofid Gorji-Bandpy

*Noshirvani University of Technology Iran* 

## **1. Introduction**

250 Thermodynamics – Interaction Studies – Solids, Liquids and Gases

Scatchard, G. (1976) *Equilibrium in Solutions & Surface and Colloid Chemistry*. Harvard

Zeldowitsch J., Adsorption site energy distribution, Acta Phys. Chim. URSS 1 (1934) 961–

University Press, Cambridge.

973.

The exergy method is an alternative, relatively new technique based on the concept of exergy, loosely defined as a universal measure of the work potential or quality of different forms of energy in relation to a given environment. An exergy balance applied to a process or a whole plant tells us how much of the usable work potential, or exergy, supplied as the input to the system under consideration has been consumed (irretrievably lost) by the process. The loss of exergy, or irreversibility, provides a generally applicable quantitative measure of process inefficiency. Analyzing a multi component plant indicates the total plant irreversibility distribution among the plant components, pinpointing those contributing most to overall plant inefficiency (Gorji-Bandpy&Ebrahimian, 2007; Gorji-Bandpy et al., 2011)

Unlike the traditional criteria of performance, the concept of irreversibility is firmly based on the two main laws of thermodynamics. The exergy balance for a control region, from which the irreversibility rate of a steady flow process can be calculated, can be derived by combining the steady flow energy equation (First Law) with the expression for the entropy production rate (Second Law).

Exergy analysis of the systems, which analyses the processes and functioning of systems, is based on the second law of thermodynamics. In this analysis, the efficiency of the second law which states the exact functionality of a system and depicts the irreversible factors which result in exergy loss and efficiency decrease, is mentioned. Therefore, solutions to reduce exergy loss will be identified for optimization of engineering installations (Ebadi&Gorji-Bandpy, 2005). Considering exergy as the amount of useful work which is brought about, as the system and the environment reach a balance due to irreversible process, we can say that the exergy efficiency is a criterion for the assessment of the systems. Because of the irreversibility of the heating processes, the resulting work is usually less than the maximum amount and by analyzing the work losses of the system, system problems are consequently defined. Grossman diagrams, in which any single flow is defined by its own exergy, are used to determine the flow exergy in the system (Bejan, 1988). The other famous flow exergy diagrams have been published by Keenan (1932), Reisttad (1972) and Thirumaleshwar (1979). The famous diagrams of air exergy were published by Moran (1982) and Brodianskii (1973). Brodianskii (1973), Kotas (1995) and Szargut et al. (1988) have used the exergy method for thermal, chemical and metallurgical analysis of plants. Analysis of the technical chains of processes and the life-cycle of a product were respectively done by Szargut et al. (1988) and Comelissen and Hirs (1999). The thermoeconomy field, or in other words, interference of economical affairs in analyzing exergy, has been studied by Bejan (1982).

Exergy, the Potential Work 253

*w in*

*dV d <sup>T</sup> E W P E PV TS <sup>Q</sup> dt dt <sup>T</sup>*

*in out*

In most of the systems with incoming and outgoing flows which are considered of great

0 0 0

*dV d <sup>T</sup> E WP E PV TS <sup>Q</sup> dt dt <sup>T</sup>*

*in out*

*<sup>w</sup> rev in rev <sup>i</sup> <sup>i</sup>*

The exergy lost, which was previously defined as the difference between the maximum rate of work transfer and rate of the real work transfer, can also be mentioned in another way, namely, the difference between the corresponding parameters and the available work

*lost w w w rev lost*

In equation (6), the exergy transfer caused by heat transfer or simply speaking, the heat

*<sup>Q</sup>* <sup>1</sup> *<sup>T</sup> E Q <sup>T</sup>* 

0

In installation analysis which functions uniformly, the properties do not changes with time

0

(9)

<sup>0</sup> *b h Ts* (10)

0 0 0

importance, there is no atmospheric work, 0 ( ( / )) *P dV dt* and *W* is equal to *Ew*

1988):

(Figure 1):

Fig. 1. Exergy transfer via heat transfer

Using equation (1), the flow availability will be introduces as:

and the stagnation exergy term will be zero, in equation (6):

transfer exergy will be:

*m h Ts m h Ts TS* 

0 0 0 0

0 0 0 0

*m h Ts m h Ts*

1

1 *n*

*i i*

0

1

*W E EE* (8)

1 *n*

*o gen*

0

(6)

(Bejan,

(7)

In this paper, the cycle of a power plant and its details, with two kind fuels, natural gas and diesel, have been analysed at its maximum load and the two factors, losses and exergy efficiency which are the basic factors of systems under study have been analysed.
