Comparison of Exergy and Advanced Exergy Analysis in Three Different Organic Rankine Cycles

Advanced Exergy Analysis of an Absorption Chiller/Kalina Cycle Integrated System for Low-Grade Waste Heat Recovery

Exergy analysis and advanced exergy analysis of an absorption chiller/Kalina cycle integrated system are conducted in this research. The exergy destruction of each component and overall exergy efficiency of the cascade process have been obtained. Advanced exergy analysis investigates the interactions among different components and the actual improvement potential. Results show that among all the equipment, the largest exergy destruction is in the generators and absorber. System exergy efficiency is obtained as 35.52%. Advanced analysis results show that the endogenous exergy destruction is dominant in each component. Interconnections among different components are not significant but very complicated. It is suggested that the improvement priority should be given to the turbine. Performance improvement of this low-grade waste heat recovery process is still necessary because around 1/4 of the total exergy destruction can be avoided. Exergy and advanced exergy analysis in this work locates the position of exergy destruction, quantifies the process irreversibility, presents the component interactions and finds out the system improvement potential. This research provides detailed and useful information about this absorption chiller/Kalina cycle integrated system.

Computational fluid dynamic simulations to improve heat transfer in shell tube heat exchangers

Improving the thermal efficiency of shell-tube heat exchangers is essential in industries related to these heat exchangers. Installing heat transfer boosters on the side of the converter tube is one of the most appropriate ways to enhance heat transfer and increase the efficiency of this equipment. In this article, spring turbulence is studied using the computational fluid dynamics tool. The displacement heat transfer coefficient and the friction coefficient were selected as the primary target parameters, and the effect of using spring tabulators on them was investigated. The ratio of torsion step length to turbulence pipe length, wire diameter to pipe diameter ratio, and flow regime was studied as the main simulation variables, and the simulation results were compared with a simple pipe. The effect of water-acting fluid, R22, and copper Nanofluid on tubes containing turbidity was compared and investigated. This study showed that due to the pressure drop, the pipe with a torsional pitch to pipe length ratio of 0.17, a turbulent diameter to pipe diameter ratio of 0.15, and a Reynolds number of 50,000 with fluid R22 has the best performance for heat transfer.

A New Hybrid Algorithm for Multi-Objective Reactive Power Planning via FACTS Devices and Renewable Wind Resources

The power system planning problem considering system loss function, voltage profile function, the cost function of FACTS (flexible alternating current transmission system) devices, and stability function are investigated in this paper. With the growth of electronic technologies, FACTS devices have improved stability and more reliable planning in reactive power (RP) planning. In addition, in modern power systems, renewable resources have an inevitable effect on power system planning. Therefore, wind resources make a complicated problem of planning due to conflicting functions and non-linear constraints. This confliction is the stochastic nature of the cost, loss, and voltage functions that cannot be summarized in function. A multi-objective hybrid algorithm is proposed to solve this problem by considering the linear and non-linear constraints that combine particle swarm optimization (PSO) and the virus colony search (VCS). VCS is a new optimization method based on viruses' search function to destroy host cells and cause the penetration of the best virus into a cell for reproduction. In the proposed model, the PSO is used to enhance local and global search. In addition, the non-dominated sort of the Pareto criterion is used to sort the data. The optimization results on different scenarios reveal that the combined method of the proposed hybrid algorithm can improve the parameters such as convergence time, index of voltage stability, and absolute magnitude of voltage deviation, and this method can reduce the total transmission line losses. In addition, the presence of wind resources has a positive effect on the mentioned issue.

CFD-based simulation to reduce greenhouse gas emissions from industrial plants

Greenhouse gas (GHG) pollution is considered one of the challenging concerns in industrial plants, and to emit the appropriate designation in nitrogen oxide reduction, it is required to implement proper numerical simulation procedures. In this study, ANSYS Fluent® software is used as dynamic software to solve heat and mass flow transfer numerically by considering non-structured networks for complex geometries. Dry nitrogen oxide burners have an additional thermocouple to provide an extra fuel pathway to combine with air. Then, standard K-ε is used in the numerical simulations to calculate thermal efficiency in combustion processes for turbulent flow regimes. It can cause the removal of 50% of nitrogen oxide into the atmosphere. Furthermore, by the increase of temperature, nitrogen oxide concentration has been increased in the system. After 1975 K, Fuel has been changed to dry fuel, and therefore nitrogen oxide concentration increased because the steam can provide a relatively non-combustible compound increase than fuel. On the other hand, regarding the water volume increase at inlet steam, nitrogen oxide volume percentage has been decreased dramatically, especially in the first periods of water volume increase. Consequently, when the steam percentage is increased instead of water, nitrogen oxide reduction is increased. Moreover, our simulation results have a proper match with Gibbs energy equilibrium.

Techno-Economic Planning and Operation of the Microgrid Considering Real-Time Pricing Demand Response Program

The optimal planning of grid-connected microgrids (MGs) has been extensively studied in recent years. While most of the previous studies have used fixed or time-of-use (TOU) prices for the optimal sizing of MGs, this work introduces real-time pricing (RTP) for implementing a demand response (DR) program according to the national grid prices of Iran. In addition to the long-term planning of MG, the day-ahead operation of MG is also analyzed to get a better understanding of the DR program for daily electricity dispatch. For this purpose, four different days corresponding to the four seasons are selected for further analysis. In addition, various impacts of the proposed DR program on the MG planning results, including sizing and best configuration, net present cost (NPC) and cost of energy (COE), and emission generation by the utility grid, are investigated. The optimization results show that the implementation of the DR program has a positive impact on the technical, economic, and environmental aspects of MG. The NPC and COE are reduced by about USD 3700 and USD 0.0025/kWh, respectively. The component size is also reduced, resulting in a reduction in the initial cost. Carbon emissions are also reduced by 185 kg/year.

Flow Characteristics and Energy Loss within the Static Impeller of Multiphase Pump

The internal flow is very complex in the multiphase pump, especially in the static impeller, where the flow is more disorganized than that in the impeller wheel, and it will cause greater hydraulic losses. In order to investigate deeply the flow rules within the static impeller, all kinds of the flow losses are analyzed quantificationally in the multiphase pump. Based on the standard SST k-ω turbulence model, selected the helical axial flow multiphase pump as the research object, used the three-dimensional modeling software for the three-dimensional modeling of the flow through parts of the multiphase pump, such as impeller wheel, the static impeller, the suction chamber, and the extrusion chamber. The ANSYS software is used to simulate the three-dimensional flow in static impeller, and the ICEM software was used to divide the mesh of suction chamber, press outlet chamber, moving impeller and static impeller respectively. The results show that the flow within the impeller wheel is more uniform than the static impeller, and larger axial vortexes appear in the static impeller. Compared with the impeller wheel, the effect of the flow rate on the flow within the first static impeller is greater. The friction loss is the largest among all kinds of losses in the static impeller, followed by the turbulence dissipation loss. What’s more, the shock loss and the contraction loss are the smallest, they are all less than 20%, and the main loss within the static impeller are the turbulent dissipation loss and friction loss. The proportion of energy losses in the first and second static impeller is almost the same, which is around 50%, respectively. The results can be used as a reference for the improvement of the hydraulic performance of the multiphase pump.

CFD Modelling of a Hydrogen/Air PEM Fuel Cell with a Serpentine Gas Distributor

Hydrogen-fueled fuel cells are considered one of the key strategies to tackle the achievement of fully-sustainable mobility. The transportation sector is paying significant attention to the development and industrialization of proton exchange membrane fuel cells (PEMFC) to be introduced alongside batteries, reaching the goal of complete de-carbonization. In this paper a multi-phase, multi-component, and non-isothermal 3D-CFD model is presented to simulate the fluid, heat, and charge transport processes developing inside a hydrogen/air PEMFC with a serpentine-type gas distributor. Model results are compared against experimental data in terms of polarization and power density curves, including an improved formulation of exchange current density at the cathode catalyst layer, improving the simulation results’ accuracy in the activation-dominated region. Then, 3D-CFD fields of reactants’ delivery to the active electrochemical surface, reaction rates, temperature distributions, and liquid water formation are analyzed, and critical aspects of the current design are commented, i.e., the inhomogeneous use of the active surface for reactions, limiting the produced current and inducing gradients in thermal and reaction rate distribution. The study shows how a complete multi-dimensional framework for physical and chemical processes of PEMFC can be used to understand limiting processes and to guide future development.

Analysis of the Inner Fluid-Dynamics of Scroll Compressors and Comparison between CFD Numerical and Modelling Approaches

Scroll compressors are widely adopted machines in both refrigeration systems and heat pumps. However, their efficiency is basically poor and constitutes the main bottleneck for improving the overall system performance. In fact, due to the complex machine fluid dynamics, scroll design is mainly based on theoretical and/or semi-empirical approaches. Designs strategies that do not guarantee an in-depth analysis of the machine behavior can be supplemented with a Computation Fluid Dynamics (CFD) approach. To this purpose, in the present work, the scroll compressor inner fluid dynamics is numerically analyzed in detail using two CFD software and two different modelling strategies for the axial gap. The analysis of the fluid evolution within the scroll wraps reveals unsteady phenomena developing during the suction and discharge phases, amplified by the axial clearance with negative impact on the main fluid flow (e.g., −13% of average mass flow rate for an axial gap of 30 μ) and on the scroll performance (e.g., +26% of average absorbed power for an axial gap of 30 μ). In terms of accuracy, the k-ε offers good performance on the estimation of average quantities but proves to be inadequate for capturing the complexity of the unsteady phenomena caused by the axial gap (e.g., −19% of the absorbed power in case of perfect tip seal). The need for considering specific geometric details in design procedures is highlighted, and guidelines on the choice of the most suitable numerical model are provided depending on the analysis needs.

Overview of the Development and Application of the Twin Screw Expander

With the development of society, the energy crisis has become increasingly prominent, which greatly affects the sustainable development of the economy of various countries. Industrial energy consumption accounts for more than 70% of China’s total energy consumption, of which more than 50% is converted to industrial waste heat, and recyclable waste heat resources account for about 60% of the total waste heat resources, while China’s current utilization rate of industrial waste heat only reaches about 30%. The development of renewable energy and recovery of low-grade waste heat in industry is the key to solve the problem. As a type of volumetric expander with full flow expansion, the screw expander is extensively applied in the industrial waste heat recovery and geothermal energy generation industry because of its effective utilization of low enthalpy energy. Improving the performance of the screw expander as the core, the paper concludes and summarizes the research status of the leakage, rotor geometry, sealing and lubrication, processing and manufacturing, which can affect the performance of the screw expander. In addition, it also introduces the application status and potential utilization of screw expander.

Energy, Exergy, Economic, and Exergoenvironmental Analyses of a Novel Hybrid System to Produce Electricity, Cooling, and Syngas

Efficient solar and wind energy to electricity conversion technologies are the best alternatives to reduce the use of fossil fuels and to evolve towards a green and decarbonized world. As the conventional photovoltaic systems use only the 600–1100 nm wavelength range of the solar radiation spectrum for electricity production, hybrid systems taking advantage of the overall solar radiation spectrum are gaining increasing interest. Moreover, such hybrid systems can produce, in an integrated and combined way, electricity, heating, cooling, and syngas through thermochemical processes. They have thus the huge potential for use in residential applications. The present work proposes a novel combined and integrated system for residential applications including wind turbines and a solar dish collector for renewables energy harvesting, an organic Rankine cycle for power production, an absorption chiller for cold production, and a methanation plant for CH4 production from captured CO2. This study deals with the energy, exergy, economic, and exergoenvironmental analyses of the proposed hybrid combined system, to assess its performance, viability, and environmental impact when operating in Tehran. Additionally, it gives a clear picture of how the production pattern of each useful product depends on the patterns of the collection of available renewable energies. Results show that the rate of methane production of this hybrid system changes from 42 up to 140 Nm3/month, due to CO2 consumption from 44 to 144 Nm3/month during a year. Moreover, the energy and exergy efficiencies of this hybrid system vary from 24.7% and 23% to 9.1% and 8%, respectively. The simple payback period of this hybrid system is 15.6 and the payback period of the system is 21.4 years.

Special Issue on “Chemical Process Design, Simulation and Optimization”

Since humanity has been able to transform materials, such as raw minerals, and produce food or beverages, a central question was the type of operation and how and where it should be performed [...]

Conventional and Advanced Exergy-Based Analysis of Hybrid Geothermal–Solar Power Plant Based on ORC Cycle

Today, as fossil fuels are depleted, renewable energy must be used to meet the needs of human beings. One of the renewable energy sources is undoubtedly the solar–geothermal power plant. In this paper, the conventional and advanced, exergo-environmental and exergo-economic analysis of a geothermal–solar hybrid power plant (SGHPP) based on an organic Rankin cycle (ORC) cycle is investigated. In this regard, at first, a conventional analysis was conducted on a standalone geothermal cycle (first mode), as well as a hybrid solar–geothermal cycle (second mode). The results of exergy destruction for simulating the standalone geothermal cycle showed that the ORC turbine with 1050 kW had the highest exergy destruction that was 38% of the total share of destruction. Then, the ORC condenser with 26% of the total share of exergy destruction was in second place. In the hybrid geothermal–solar cycle, the solar panel had the highest environmental impact and about 56% of the total share of exergy destruction. The ORC turbine had about 9% of all exergy destruction. The results of the advanced analysis of exergy in the standalone geothermal cycle showed that the avoidable exergy destruction of the condenser was the highest. In the hybrid geothermal–solar cycle, the solar panel, steam economizer and steam evaporator were ranked first to third from an avoidable exergy destruction perspective. The avoidable exergo-economic destruction of the evaporator and pump were higher than the other components. The hybrid geothermal–solar cycle, steam economizer, solar pane and steam evaporator were ranked first to third, respectively, and they could be modified. The avoidable exergo-environmental destruction of the ORC turbine and the ORC pump were the highest, respectively. In the hybrid geothermal–solar cycle, steam economizers, solar panel and steam evaporators had the highest avoidable exergy destruction, respectively. For the standalone geothermal cycle, the total endogenous exergy destruction and exogenous exergy destruction was 83.61% and 16.39%. Moreover, from an exergo-economic perspective, 89% of the total destruction rate was endogenous and 11% was exogenous. From an exergo-environmental perspective, 88.73% of the destruction rate was endogenous and 11.27% was exogenous. For the hybrid geothermal–solar cycle, the total endogenous and exogenous exergy destruction was 75.08% and 24.92%, respectively. Moreover, 81.82% of the exergo-economic destruction rate was endogenous and 18.82% was exogenous. From an exergo-environmental perspective, 81.19% of the exergy destruction was endogenous and 18.81% was exogenous.