In this case study, EXERGY analysis is applied to a mini two-shaft gas turbine which is located in Islamic Azad University Khomeini Shahr Branch`s Thermodynamics laboratory and a proposal presented to make EXERGY destruction less using a Heat Recovery Water Heater (HRWH). Calculations were done for N2=20000 (rpm) constant and various N1 and after that for N1=60000 (rpm) constant and various N2. Results revealed that the highest EXERGY destruction rate occurs in combustion chamber in all conditions and a huge part of EXERGY destruction through the turbine exhaust. Increase in N1 leads to increases in all component EXERGY destruction rates. On the other hand, power turbine is the only component which is affected by changes in N2 and the EXERGY destruction rate increases with increase in N2. Moreover, EXERGY gained rate within HRWH increased with increase in N1 and is almost constant with changes in N2. In the same vein, exergetic efficiency of HRWH and EXERGY gained rate within HRWH are increased with decrease in water outlet temperature of HRWH.

The mechanical aspect of entropy-EXERGY relationship, together with the thermal aspect usually considered, leads to an extended formulation of physical EXERGY based on both maximum useful work and maximum useful heat that are the outcome of available energy of a thermodynamic system.This approach suggests that a mechanical entropy can be studied, in addition to the already used thermal entropy, with respect to work interaction due to volume variation. The mechanical entropy is related to energy transfer by means of work and it is complementary to the thermal entropy that accounts energy transfer by means of heat. Furthermore, the paper proposes a definition of EXERGY based on Carnot cycle that is reconsidered in the case the inverse cycle is adopted and, as a consequence, the concept that work depends on pressure similarly as heat depends on temperature, is pointed out. Then, the logical sequence to get mechanical EXERGY expression to evaluate work withdrawn from available energy is demonstrated. On the basis of the mechanical EXERGY, the mechanical entropy set forth is deduced in a general form valid for any process.Finally, the extended formulation of physical EXERGY is proposed, that summarizes the contribution of either heat and work interactions and related thermal EXERGY as well as mechanical EXERGY that both result as the outcome from the available energy of the system interacting with an external reference environment (reservoir). The extended formulation contains an additional term that takes into account the volume, and consequently the pressure, that allows to evaluate EXERGY with respect to the reservoir characterized by constant pressure other than constant temperature. The conclusion is that the extended physical EXERGY takes into account the equality of pressure, other than equality of temperature, as a further condition of mutual stable equilibrium state between system and reservoir.

EXERGY analysis and response surface methodology (RSM) is applied to reduce the EXERGY loss and improve energy and EXERGY efficiency of acetic acid production plant. EXERGY analysis is run as a thermodynamic tool to assess EXERGY loss in reactor and towers of acetic acid production process. The process is simulated in Aspen Plus (v.8.4) simulator and the necessary thermodynamics data for calculating EXERGY of the streams is extracted from the simulation. By applying EXERGY balance on each one of the equipment, EXERGY losses are calculated. Response Surface Methodology (RSM) is a well-known statistical optimization method adopted in optimizing and modeling chemical processes, and operational parameters in reactor and towers. In this optimization framework the objective is to minimize EXERGY loss as objective function, subject to engineering and operational constraints. One of the modifications made on the reaction section is consumption of hot effluent stream from the reactor to produce steam. This modification prevents wasting the generated heat in the reactor and leads to improving EXERGY efficiency in reactor. All tunable operation parameters regarding reactor and towers and their upper and lower limits are specified and optimized through the RSM method. As a result, by optimization, EXERGY loss is reduced by 11365.8 Mj/hr and 2496.1Mj/hr in reactor and towers, respectively.

In this research, using Harris Hawks optimization method, the gasket- plate heat exchangers is studied with an EXERGY- economic approach. Six parameters of hot fluid inlet temperature, cold fluid inlet temperature, hot fluid mass flow rate, cold fluid mass flow rate, port diameter and the number of plates were selected as design variables. The ratio of hot fluid mass flow rate to cold fluid mass flow rate, λ, is introduced to the analysis of EXERGY loss. The results showed that using Harris Hawks optimization method, EXERGY loss and total cost can be reduced by 70% and 81%, respectively. The optimization results showed that minimizing the EXERGY loss, the efficiency of the gasket- plate heat exchanger increases by 30%. It is also found that for λ>1, with the increase of cold fluid mass flow rate, the EXERGY loss number decreases and for λ<1, with the increase of cold fluid mass flow rate, the EXERGY loss number increases.

The EXERGY analysis is a proper method for performance evaluation of industrial systems. A generic and detailed analysis of the GPCSs on the second gas pipeline of Iran is made by the means of EXERGY. The two main improvement measures of fuel pre-heating and steam injection technologies are presented for the current conventional stations. Steady state equations regarding the second law of thermodynamics and the chemical and physical EXERGY analysis are presented as well. The results indicate that the improved cycle is a more energy saving one, with an overall efficiency and net output power. The exegetic efficiency of every gas turbine of the improved station is increased by 31% in average and their EXERGY destruction is decreased by 84%. The amount of total EXERGY saving for the case study would be 552 MW. A higher overall efficiency can be achieved by an increase in both the turbine inlet temperature (TIT) and steam mass flow (SMF).

The mechanical aspect of entropy-EXERGY relationship, together with the thermal aspect usually considered, leads to a formulation of physical EXERGY based on both useful work and useful heat that are the outcomes of available energy of a thermodynamic system with respect to a reservoir. This approach suggests that a mechanical entropy contribution can be defined, in addition to the already used thermal entropy contribution, with respect to work interaction due to pressure and volume variations. The mechanical entropy is related to energy transfer by means of work interaction and it is complementary to the thermal entropy that accounts energy transfer by means of heat interaction. Furthermore, the study proposes a definition of EXERGY based on Carnot cycle that is reconsidered in the case the inverse cycle is adopted and, as a consequence, the concept that work depends on pressure similarly as heat depends on temperature, is pointed out. Then, the logical sequence to get mechanical EXERGY expression to evaluate useful work withdrawn from available energy is demonstrated. Based on mechanical EXERGY expression, the mechanical entropy set forth is deduced in a general form valid for any process. Finally, the formulation of physical EXERGY is proposed that summarizes the contribution of either heat or work interactions and related thermal EXERGY as well as mechanical EXERGY that both result as the outcome from the available energy of the composite of the system interacting with a reservoir. This formulation contains an additional term that takes into account the volume and, consequently, the pressure that allow to evaluate EXERGY with respect to the reservoir characterized by constant pressure other than constant temperature. The basis and related conclusions of this paper are not in contrast with principles and theoretical framework of thermodynamics and highlight a more extended approach to EXERGY definitions already reported in literature that remain the reference ground of present analysis.