The exergy-topological method also called exergy graph method is a new approach in exergy studies based on the arrangement or mapping of elements (links and nodes) of a network. In this method, the components: turbines, pumps, heat exchangers, etc linked by the pipes, valves and other devices are the major elements. Different steps involved in the application of the topological methodology are summarized below:

■ Step 1: drawing of the flow sheet of the system,

■ Step 2: establishment of the exergy flow graph,

■ Step 3: determination of the matrix of incidence,

■ Step 4: determination of the flow parameters,

■ Step 5: determination of the thermodynamic characteristics and

■ Step 6: analysis of the results.

The useful parameters for the analysis of the system are as follows:

V = E°ut / E” (Degree of thermodynamic perfection of i th-element) (1)

l = Ei” — E°ut (Exergy loss of i th-element) (2)

rfx = Ei /Ea (Exergy efficiency of i th-element) (3)

в = Ef / El (Coefficient of influence of i th-element) (4)

Vj, = ElU / El” (Degree of thermodynamic perfection of the system) (5)

n

= ^ili (Total exergy loss of the system) (6)

i=1

Пі = Ej / Ej (Overall exergy efficiency of the system) (7)

Where, E“ and E°ut are the sum of exergy flows at the inlet and outlet of the element i; Eut and Ef are the sum of useful and available exergy of i th-element and the subscript E refers to the system. The exergy rate of a j-flow is given by

Ej = mej (8)

ej is the specific exergy flow and m represents the mass flow rate. Specific exergy can be calculated by the following equation for any flow [8]:

ej = (hj — h0) -T0(Sj — s0) + ef (9)

Where hj and sj are specific enthalpy and specific entropy at the point under consideration. T0, h0 and s0 are the temperature, specific enthalpy and entropy at the restricted dead conditions. ef is the chemical exergy.

The specific exergy transfers by heat and by work are respectively given by Eqs. 10 and 11.

ej = q} (1 — TJ Tj) (10)

ej = Wj (11)

Where qj is the specific amount of heat, Tj is the average thermodynamic temperature of the

working body at which heat is added or removed, w3 is the specific work.

The methodology of calculation of useful and available exergy rates is described in Ref.[8]. A description and exemplification of this approach can be found in Mago et al. [4] and Nikulshin et al. [5-7].