Exergy Sustainability Index Research Articles

Mass Transfer, Energy-Exergy Analysis, and Mathematical Modeling of Chili Pepper during Drying

There are no literature data on the effects of air velocity and relative humidity on moisture diffusivity, mass transfer coefficient, and energy-exergy analysis of chili pepper during cabinet-tray hot-air drying. This study tends to address this gap by presenting comprehensive drying kinetic, energy, and exergy analyses of a cabinet-tray hot-air drying for red chili pepper. Drying was conducted at varying levels of air temperature (40-70 oC), air velocity (0.5-2.0 m/s), and relative humidity (60-75%). The effect of drying conditions on drying time, drying coefficient, lag factor, drying efficiency, moisture ratio, effective moisture diffusivity, mass transfer coefficient, total energy consumption (TEC), specific energy consumption (SEC), energy utilization ratio (EUR), heat loss, energy efficiency, exergy loss, exergy efficiency, exergetic improvement potential (EIP), and exergy sustainability index (ESI)) was evaluated. Five different mass transfer models (Dincer-Dost, Bi-Di, Bi-S, Bi-G, and Bi-Re) were applied to determine the mass transfer parameters. A new drying mathematical model was developed for the prediction of drying kinetic, energy, and exergy parameters. Effective moisture diffusivity values of 1.58×10–8 - 5.10×10–8 m2/s and mass transfer coefficient values of 0.053×10–6 - 8.79×10–6 m/s over the drying conditions range were respectively obtained. The TEC, SEC, and EUR achieved over the range of drying conditions in the course of drying were in the range of 43.56-77.36 MJ, 49.0-87.02 MJ/kg, and 0.035-0.325, respectively. Heat loss and exergy loss varied from 0.16 to 2.39 MJ and from 0.026 to 0.622 kW, respectively. Drying, energy, and exergetic efficiency values obtained varied in the range of 2.80-8.25%, 2.69-7.91%, and 73-94.5%, respectively. EIP and the ESI values varied from 0.0068-0.114 kW and 3.70-18.18, respectively. The developed multivariate linear regression model provided an innovative model to predict drying kinetic, energy, and exergy parameters.

Exergy based evaluation of power plants for sustainability and economic performance identification

Enhanced sustainability and efficiency are among the prime indicators to achieve in the power generation sector of any country. The decline in efficiency might be caused by improper utilization of fuels and increasing entropy in outdated generation units. Reduced efficiency in power generation is particularly detrimental for the sustainability in developing countries, as resources are limited and need to be carefully allocated and maintained. Exergy analysis based on the laws of thermodynamics are currently gaining traction among researchers to study the overall performances of power generation units. Taking Bangladesh as a case study, this work investigates the power generation data for the country since 2009 till 2019 to study the internal energy losses of natural gas, oil, high-speed diesel, coal, and hydro based plants and provides a baseline for investment policy formulation. Our study found that, due to lack of maintenance and proper planning during the initial phases, the overall energy efficiencies among these sectors are relatively low, staying in the range of 34.55%–36.1% while the exergy efficiencies are 35.07%–36.59%. Corresponding exergetic parameters as depletion number, exergy sustainability index, relative irreversibility, lack of production, cumulative exergy loss, waste exergy ratio, and environmental effect factor pointed to similar findings in terms of sustainability as well. Comparing these parameters, it is observed that hydroelectric plants are more sustainable and efficient compared to fossil fuel-based generation units. Cost estimation of fuels and financial losses in the power generation sector are also explored for a better understanding of the return on investment.

Thermodynamic analysis of a novel integrated system operating with gas turbine, s-CO2 and t-CO2 power systems for hydrogen production and storage

In this paper, a proposal for a novel integrated Brayton cycle, supercritical plant, trans critical plant and organic Rankine cycle-based power systems for multi-generation applications are presented and analyzed thermodynamically. The plant can generate power, heating-cooling for residential applications, and hydrogen simultaneously from a single energy source. Both energetic and exergetic analyses are conducted on this multi-generation plant and its subsystems in order to evaluate and compare them thermodynamically, in terms of their useful product capabilities. The energetic and exergetic effectiveness of the multi-generation system are computed as 44.69% and 42.03%, respectively. After that, a parametric study on each of the subsystems of the proposed combined system is given in order to provide a deeper understanding of the working of these subsystems under different states. Lastly, environmental impact assessments are provided to raise environmental concerns for several operating conditions. For the base working condition, the results illustrate that the proposed plant has 0.5961, 0.0442, 0.6265 and 1.678 of exergo-environmental impact factor, exergy sustainability index, exergy stability factor and sustainability index, respectively.

ECOLOGIC PERFORMANCE AND SUSTAINABILITY EVALUATION OF A TURBOJET ENGINE UNDER ON-DESIGN CONDITIONS

Interest in air transportation in the last decade has seen aviation fleet growth and a rise in the energy consumption of aircraft. In accordance with the latest data, the air transportation sector consumes 7.5% of total oil consumption worldwide. This high share by air transportation forces designers and researchers to develop more efficient propulsion systems by considering the constant rise in energy costs. In the current paper, an exergy based sustainability assessment of a turbojet engine under design point conditions is presented while two novel ecological performance indicators, namely the ecological objective function and ecological coefficient of performance, are introduced for the turbojet engine. These ecological performance indicators can be considered useful for improving the efficiency of any turbojet engine. As a result of an exemplifying analysis, the exergy efficiency, exergy sustainability index, ecological objective function and ecological coefficient of performance have been calculated to be 50.13%, 0.503, 68.294 kW and 1.005, respectively. In the light of the results, the author concludes that the exergy destruction rate of the turbojet engine should be minimized to improve the sustainability index and ecological coefficient of performance, while increasing or maintaining a constant thrust of the examined turbojet engine.