Evaluation Of Exergy Efficiency Research Articles

Incorporating artificial intelligence-powered prediction models for exergy efficiency evaluation in parabolic trough collectors

Exergy analysis is essential for evaluating the second law of thermodynamics efficiency in solar thermal applications such as parabolic trough collectors (PTCs). This study creates ML models to tackle complex challenges in renewable energy systems and components. Six prediction models were developed such as Adaptive Boosting (AdaBoost), Multivariate adaptive regression splines (MARS), Stochastic Gradient Descent (SGD), Tweedie Regressor, voting, and stacking ensemble learning, were developed to predict the exergy efficiency of PTCs. The base fluids were three molten salts (Solar Salt, Hitec, and Hitec XL). Three nanoparticle types (Al2O3, CuO, and SiO2) were mixed homogeneously in a single-phase approach to prepare nine nanofluids. The output was predicted based on different input parameters such as molten salts, nanoparticle types, input temperature, volume fraction, Reynolds number (Re), Nusselt number (Nu), and friction factor (f). The results indicated that the stacking regressor efficiently predicted the exergy efficiency using (3-5) input parameters with a coefficient of determination (R2 = 0.963), followed by the AdaBoost algorithm with R2 = 0.947 using the fifth input combination over the testing phase. Further, AdaBoost and Stacking Regressors models were compared with the previously published study and showed an overall accuracy of R2 = 0.9472 and R2 = 0.9634, respectively.

Multi-objective optimization of regional integrated energy system matrix modeling considering exergy analysis and user satisfaction

Integrated energy system achieves the collaborative optimization of different energy forms such as electricity/gas/heat/cold, and it is an important strategic development direction in the international energy field in the future. However, with the development of smart grid technology and the increase of renewable energy penetration, it needs more flexible load to adapt to the changing energy supply–demand relationship. Considering the impact of user-side load fluctuations on the system, this paper establishes a two-tier closed-loop system model formed by users and the market. The upper-layer is based on the user’s perspective. A comprehensive user satisfaction model is established by the radar chart area method and consumer preference theory. The lower-layer is based on the market perspective. It proposes an improved layering matrix Energy Hub model and conducts the regional integrated energy system exergy efficiency evaluation study. Then, taking economy, carbon emission and exergy efficiency as objective functions, a multi-objective optimization model is constructed. Non-dominated Sorting Genetic Algorithms-II is applied to solve the model, and the output parameters is a Pareto front surface. A combination weighting TOPSIS method is used to select a compromise solution of multi-objective optimization from the optimal solution set. Compared with the primary energy utilization efficiency as the objective function, the exergy efficiency reduces the system cost by 8.64%. Finally, the multi-objective optimization solution based on different user satisfaction is obtained. Through the analysis of the examples, compared with the original load, the introduction of the upper-layer user satisfaction model reduces the system cost by 2.8%. The reasonable setting of user satisfaction and load adjustment amount can improve the economy of system, which verifies the effectiveness of the two-tier closed-loop system based on user satisfaction model.

Experimental investigation of solar‐powered food steamer based on parabolic dish concentrator for domestic applications

AbstractSteam cooking is beneficial over other cooking techniques like boiling since it preserves more vitamins lost during other methods. In this study, a novel solar food steamer (SFS) based on a parabolic dish concentrator (PDC) is designed and constructed for domestic food preparation. A straightforward fabrication process of a 2.626 m2 PDC with design calculations is also presented. The system's instantaneous energy and exergy efficiency evaluation has been examined from different tests over three consecutive days. The system's high energetic and exergetic efficiency was achieved in the case of sweet potato, that is, 72.83% and 15.14%, respectively. In the case of dried chickpeas, the maximum steaming duration of 70 min was attained, along with an energy efficiency of 47.74% and an exergy efficiency of 10.07%. In addition, an economic analysis was performed to determine the payback time in terms of cost and utility. The payback time for the proposed method is 2.4 years. The SFS may save 43 kg/month of carbon dioxide from escaping into the atmosphere; it can be considered an environmentally valuable device.

Numerical evaluation of exergy efficiency of innovative turbulators in solar collector filled with hybrid nanofluid

In the current study, the impact of two-phase water-Al2O3-MWCNT hybrid nanofluid in turbulent flow on exergy efficiency in a solar collector equipped with innovative turbulators is investigated numerically. To simulate two-phase nanofluid, the mixture model was employed, and to simulate radiation and turbulent flow, the surface-to-surface (S2S) method and standard k-e model were utilized. The study is performed for two-phase water-Al2O3-MWCNT hybrid nanofluid in Reynolds numbers (Re) of 5000–20,000, volume fraction (φ) of 1–3%, torsion ratios of 0.05, 0.15 and 0.25 at heights of 5, 10, 15 and 20 mm made of innovative turbulator. According to the results, exergy efficiency decreases with increasing torsion and height ratio in innovative turbulators. The highest exergy efficiency occurs at the Re = 20,000 and φ = 0.03 at a torsion ratio of 0.05 and a turbulator height of 5 mm. Also, the lowest extrusion efficiency occurs in Re = 5000 and φ = 0.01 in torsion ratio of 0.25 and turbulator height of 19 mm. This is while the exergy efficiency in the solar collector with turbulator with a height of 5 mm and a torsion ratio of 0.25 in Re = 20,000 and φ = 0.03 by 6.04% compared to the solar collector with the same characteristics in the ratio the torsion decreases by 0.05.

Exergy analysis of the regulating measures of operational flexibility in supercritical coal-fired power plants during transient processes

Operational flexibility improvement of coal-fired power plants has become a priority objective with the high penetration of renewable energy sources. The regulating measures applied frequently in improving the operational flexibility indeed affect the exergy efficiency of coal-fired power units during transient processes. In this study, the exergy efficiency evaluation of operational flexibility measures during primary frequency control processes was focused on, and the exergy analysis methods of the thermal system were used on the basis of the second law of thermodynamics to analyze the mechanisms for improving the flexibility at four regulation measures, and the exergy storage conversion efficiency and exergy destruction accumulation were quantitatively compared. It turns out that: among the throttling extraction steam of high-pressure heaters, feedwater bypass of high-pressure heaters, and condensate water decrease of low-pressure heaters measures, the exergy storage conversion efficiency and the exergy destruction accumulation increase with the regulating time of primary frequency control. The measure of throttling extraction steam of high-pressure heaters is the most potential option for improving operational flexibility, with maximum value of the maximal output power increment and maximal exergy storage change rate of 71.11 MW and −89.84 MW, respectively. With respect to the economy, the measure of throttling extraction steam of low-pressure heaters is the best option due to its smallest exergy destruction accumulation among all the measures. This study provides a detailed guidance for the selection of the optimal regulating measures when considering the enhancement of exergy efficiency and flexibility comprehensively under different conditions and periods.

Exergy Evaluation of a Heat Supply System with Vapor Compression Heat Pumps

The vapor compression heat pumps are very popular solutions regarding heat supply systems of modern, low energy buildings. It is partly due to the fact that they are treated as a sustainable heat supply. The question arises: Can a vapor compression heat pump be treated as a sustainable heat supply? To answer this question; the exergy model of a heat pump system operation has been proposed. The proposed model has been employed for evaluation of exergy efficiency of an existing heat supply system equipped with two heat pumps installed in an educational building located on the campus of Poznan University of Technology, Poznan, Poland. The analysis shows that the system exergy efficiency decreases with an increase in outdoor temperature and its values are in the range of 10.9% to 42.0%. The primary exergy efficiency, which considers the conversion of fossil fuel into electricity, is on average 3.2 times lower than the system exergy efficiency for the outdoor temperature range of −9 °C to 11 °C. The performed analysis allowed for the identification of a set of solutions that may increase the exergy and primary exergy efficiency of the system. The first solution is to cover a part of the electricity demand by a renewable energy source. The second proposition is to apply a low-temperature emission system for heating. The third idea is to apply a district heating network as the heat supply instead of the heat pump. The conclusion is that the exergy performance of systems with heat pumps is rather poor because they generate low-quality heat from high-quality electricity. The best way to improve the primary exergy efficiency of a heat pump system is to power the system by electricity generated from a renewable energy source.

Effects of paralleled magnetic field on thermo-hydraulic performances of Fe3O4-water nanofluids in a circular tube

Stable Fe3O4-water nanofluids are prepared and sedimentation observation is used to investigate its stability. A convection heat transfer experiment is set up to investigate the thermo-hydraulic performances of Fe3O4-H2O nanofluids in a circular tube considering the effects of different nanoparticle mass fractions (ω = 1.0%, 3.0% and 5.0%), Reynolds Numbers (Re = 600–11000) and paralleled magnetic induction intensities (B = 0G, 100G, 200G and 300G). The result is that Nusselt number is proportional to nanoparticle mass fraction but opposite trend is found with the increasing paralleled magnetic induction intensity. Nanofluids with ω = 5.0% show the best performance of heat transfer. The resistance coefficient increases with mass fraction and can be enhanced by magnetic field further. Nanofluids with ω = 5.0% under magnetic induction intensity B = 300G show the largest resistance coefficient. A comprehensive evaluation index and an exergy efficiency evaluation plot are developed to discuss the thermo-hydraulic performances of nanofluids from quantity and quality. The thermo-hydraulic performance increases with nanoparticle mass fraction but decreases with paralleled magnetic induction intensity.

Experimental study on thermo-hydraulic performance of nanofluids in CPU heat sink with rectangular grooves and cylindrical bugles based on exergy efficiency

An experiment system for CPU cooling based on nanofluids is set up. The flow and heat transfer characteristics of TiO2-water nanofluids in CPU heat sink are experimentally investigated. The influences of rectangular groove depths (1 mm, 2 mm) and cylindrical bulge arrangement modes (aligned and staggered arrangements) on thermo-hydraulic performances of CPU cooled by TiO2-water nanofluids are analyzed. In addition, the influences of nanoparticle mass fractions (0.0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%) and Reynolds numbers (472-1198) are studied. The thermal efficiency and exergy efficiency evaluation plots are developed and are applied to evaluate the thermo-hydraulic performance of nanofluids. It is found that large depth rectangular groove and staggered arrangement cylindrical bulges are beneficial to heat transfer enhancement. Nanofluids with mass fraction of 0.3% and 0.4% show the best cooling performance for rectangular grooves structure and cylindrical bulges structure respectively. CPU with rectangular grooves and cylindrical bugles shows higher exergy efficiency than that with smooth surfaces under the same pump power. The exergy efficiency is sensitive to deep grooves, aligned arrangement bulges, small Reynolds number. Nanofluids with low mass fraction (0.1%) show the highest exergy efficiency.

Mathematical modeling of a split-conditioner operation for evaluation of exergy efficiency of the R600A refrigerant application

Mathematical modeling of a split-conditioner operation for evaluation of exergy efficiency of the R600A refrigerant application

Effect of rotating twisted tape on thermo-hydraulic performances of nanofluids in heat-exchanger systems

Stable TiO2-H2O nanofluids are prepared and their stabilities are studied. An experimental set for studying the heat transfer and flow characteristics of nanofluids is established. Heat transfer and flow characteristics of TiO2-H2O nanofluids in a circular tube with rotating and static built-in twisted tapes are experimentally investigated and compared. An innovative performance evaluation plot of exergy efficiency is developed and the exergy efficiency of tube with rotating and static built-in twisted tapes filled with nanofluids is analyzed in this paper. The results indicate that the combination of rotating built-in twisted tape and TiO2-H2O nanofluids shows an excellent enhancement in heat transfer, which can increase the heat transfer by 101.6% compared with that of in a circular tube. The effects of nanoparticle mass fractions (ω= 0.1%, 0.3% and 0.5%) and Reynolds numbers (Re = 600–7000) on the heat transfer and flow characteristics of TiO2-H2O nanofluids are discussed. It is found that there is a critical Reynolds number (Re = 4500) for the maximum value of relative heat transfer enhancement ratio. The comprehensive performance of the experimental system is analyzed. It can be found that the comprehensive performance index of the experimental system firstly increases and then reduces with Reynolds number, and it can reach 1.519 at best. However, for the performance evaluation of exergy efficiency, the coupling of rotating twisted tape and nanofluids deteriorates the exergy efficiency. Also, it can be found that the exergy efficiency of the circular tube with twisted tape is greater than that of circular tube under the same pumping power and pressure drop, but it shows deterioration under the same mass flow rate.

Energy and exergy balance methodology. Wood chip dryer

Drying is widely used in a variety of thermal energy applications ranging from food drying to wood drying. Utilization of high amount of energy in the drying industry makes drying one of the most energy-intensive operations in pellet production. Thermodynamic analysis has appeared to be an essential tool for system design, analysis and optimization of thermal systems. The aim of current paper is to make an algorithm to evaluate wood chip drying process energy and exergy efficiency. Energy and exergy efficiency evaluation consist of the drying process energy and exergy balance analysis.On the basis of the results of the study it can be concluded that under the given assumptions drying process energy efficiency varies between 22.69 % and 10.25 % but the exergy efficiency varies between 16.47 % to 0.7 %. Decrease of drying air mass flow increases the energy and exergy efficiency. This is because less heat is required to heat drying smaller air mass flow. Decreasing drying air humidity ratio of air before dryer, increases energy and exergy efficiency. This is because the drying air with smaller humidity ratio content are able to attract more moisture from the drying product.

Concerning exergy efficiency evaluation of heat recovery exchangers for air handling units

The energy chain of building energy services begins with primary energy resources and ends with building services systems (BSS). The analysis for such chain and its' elements should rely on fundamentals of thermodynamics. This paper pays attention to one of them that exergy efficiency is in the range of 0-1. In this study, exergy analysis of heat recovery exchangers for air handling units is carried out. Special attention is paid to the direction of thermal exergy flow when temperatures inducing heat transfer are close to a near-environmental temperature. On the basis of the proposed methodology, the dependency of exergy efficiency on dimensionless temperature and thermal recuperator efficiency is discussed. It is important to take the dimensionless temperature interval 0-1 into account. Here the exergy efficiency values are the lowest. Design and management measures should be used to avoid operating a heat exchanger there.

Exergy analysis in ProSimPlus® simulation software: A focus on exergy efficiency evaluation

On industrial sites, the promotion of best practices to enable an efficient utilization of energy has emerged as one of the major point of focus. Among the different approaches existing to improve industrial processes, the exergy analysis, although limited to the academic world, has been shown to be a powerful tool for improving energy efficiency of thermal and chemical systems. The purpose of this paper is then to present the use of the ProSimPlus® modelling and simulation environment as an exergy analysis computer-aided tool. Expressions implemented in the simulator for computing exergies in its various forms are presented. The adopted approach for calculating exergy efficiency in a systematic way is also exposed; it combines the fuel-product concepts to the transit exergy concept. ProsimPlus® exergy module's capabilities are illustrated through the example of an ammonia production plant.

Exergy efficiency evaluation of the production of sulfuric acid from liquid sulfur

Sulfuric acid is one of the most important products in inorganic synthesis. Half of the manufactured amount of sulfuric acid is used for the production of mineral fertilizers. In this paper, a technological scheme for the manufacture of sulfuric acid from liquid sulfur using double contacting with intermediate absorption is studied. The production method allows the increase of the degree of oxidation of sulfur dioxide up to 99.5%, and the decrease of its content in the waste gas. For evaluation of the exergy efficiency of the technological scheme investigated, one of the modern methods of thermodynamic analysis-exergy method is used. Exergy balance of the whole manufacture and its individual steps is done. Internal and external exergy losses, exergy efficiency are calculated. The overall exergy efficiency is 55.15%. The main sources for losses are determined, and the methods for minimizing losses are described.