International Journal of Exergy

Clay, Joshua; Mathias, James

doi: 10.1504/IJEX.2018.096000pmid: N/A

This paper reports the results of an energy and exergy audit of a 173 MW pulverised coal fired, subcritical steam power plant unit in the Midwestern USA. Energy and exergy analysis determined the thermal efficiency and identified the greatest sources of irreversibilities and also mapped the flow of energy and exergy throughout the plant. The overall plant energetic and exergetic efficiencies were found to be 32.8% and 33.7%, respectively. The largest source of exergy destruction in the cycle was found to be within the steam generator. Options explored to increase the exergetic efficiency were to improve the steam turbines to operate with higher temperature steam, to bring water into the condenser from the lake that is closer to the ambient temperature, and to replace a valve after the boiler feedwater pump with a hydro-turbine to produce some power.

Khanjari, Ali; Mahmoodi, Esmail; Sarreshtehdari, Ali; Chahartaghi, Mahmood

doi: 10.1504/IJEX.2018.096002pmid: N/A

In this study, energy and exergy analyses of a horizontal axis wind turbine are presented based on blade element momentum theory (BEM) under different yaw angles. Velocity, temperature, pressure and specific humidity are considered as metrological parameters. The wind flow is assumed steady, and exergy destruction are taken to account for wind blades. Results show that the BEM can predict he axial and tangential forces in different spans satisfactory. It is interesting to note that by increasing of yaw angle from 0° to 15° at wind speeds from 10 to 24 m/s, the energy and exergy efficiencies see a slight decrease in comparison with yaw angle of 0°. At wind speeds from 18 to 24 m/s, under yaw angle of 30°, by rising the wind speed, energy and exergy efficiencies increase due to reduction of the axial force on the wind turbine rotor.

Khasawneh, Khaleel Al; Kharouf, Duaa M.

doi: 10.1504/IJEX.2018.096012pmid: N/A

In this study, the entropy generation for steady, compressible gas flow inside two-dimensional rectangular microchannel at slip flow regime with constant walls temperature under the influence of magnetic field was analytically investigated. The obtained velocity and temperature distributions were used in this study. The influences of changing several parameters, such as, Knudsen number, Brinkman number, Hartmann number, aspect ratio, electric field to magnetic field ratio and pressure ratio were investigated. A finite volume method was used for numerical validation. The obtained results showed that the total entropy generation decreases in the direction toward the wall of the microchannel and increases along the flow direction. The total entropy generation increases as Knudsen number, aspect ratio, electric to magnetic field ratio, pressure ratio and Brinkman number increases. Entropy generation due to the magnetic field effect had the maximum value except the region near the walls of the microchannel. Entropy generation due to the friction effect was low along the centreline and increase toward the walls, while entropy generation due to the heat transfer effect was very low as compared to the friction effect and magnetic effect.

Saloux, Etienne; Sorin, Mikhail; Teyssedou, Alberto

doi: 10.1504/IJEX.2018.096013pmid: N/A

This paper tackles the development of an exergy diagram, adapted from the heat (Q)-Carnot factor (θ) one, where energy quality factors are given in the ordinate axis while energy terms constitute the abscise axis. Energy and exergy balances are then shown and the nature of irreversibility sources (energy loss, energy potential degradation) is revealed, contrary to traditional Grassman diagrams. In this paper, the graphical construction is extended to integrated energy systems where energy paths are differentiated according to renewable and non-renewable sources. Thus, it permits the electricity use, which is really paid, to be emphasised, and the overall behaviour to be better understood. As well, the diagram is developed to illustrate the results of dynamic analyses by considering environment reference state variations. To this aim, the graphical construction has been applied to individual units and then, step by step, to a solar assisted heat pump using ice storage.

Khaliq, Abdul; Mokheimer, Esmail M.A.; Kumar, Rajesh

doi: 10.1504/IJEX.2018.096015pmid: N/A

This study aims to assess the thermodynamic performance of a novel solar powered multi-effect cooling cycle through the cascaded utilisation of energy and exergy. The effects of parameters such as: direct normal irradiation (DNI), turbine inlet temperature, turbine back pressure, and evaporator temperature of ERC were ascertained on the energetic and exergetic performance of the cycle. Exergy destruction occurs throughout the plant components is quantified and illustrated using an exergy flow diagram, and compared to the corresponding energy flow diagram. The exergy efficiency of the cycle was significantly less than its corresponding energy efficiency. Computational analysis further revealed that the maximum exergy losses of more than 34% occur in the solar field followed by 7.25% and 6.75% in the components of ARC and CRC, respectively. Percentage of these exergy losses indicates the sites where the efforts should be made to improve the real performance of proposed cooling cycle.

Abid, Muhammad; Khan, Muhammad Sajid; Ratlamwala, Tahir A.H.

doi: 10.1504/IJEX.2018.096014pmid: N/A

This comparative research concentrates on the parabolic dish system with two types of supercritical CO2 Brayton cycles, (a recompression with reheat and without reheat) solar assisted Brayton cycles. The performance of both systems has been numerically analysed by comparing their net power output, overall energetic and exergetic efficiencies, exergo-environmental analysis and individual components exergy destruction rates by varying several input parameters. Super critical CO2 has been circulated into the Brayton cycle loop, whereas, fresh water is used as a heat transfer fluid in solar collector. The simulations has been performed for Pakistan (Southern Punjab, latitude for the location is 29° 25/5.0448 N while longitude is 71° 40/14.4660 E), where, DNI is higher and almost equal to 1,000 W/m2. The simulation results show that the overall energy and exergy efficiencies of recompression with reheat system are considerably higher (almost 11.50%) than the recompression without reheat system.