Exergetic Aspects Research Articles

Investigating the economic, energetic and exergetic aspects of semi-cylindrical solar still integrated with stepped-basins and phase change material

This study aims at improving the thermal analysis of a semi-cylindrical, stepped-basins solar still (SCSBSS) that incorporated with (PCM-Paraffin-wax) phase change material. The SCSBSS was evaluated and compared with the semi-cylindrical solar still (SCSS) as a conventional one under various water depths for Egyptian climate conditions for different salt water quantities. Furthermore, the economic analysis, energy and exergy efficiencies for various modifications were discussed. The results show that the best performance belongs to the SCSBSS with PCM which produced 3889mL/m2.day with an increase of the daily productivity of 44.52% compared with SCSS without using PCM at salt water quantity of 20L. The CPL of potable water and payback period for a SCSBSS with PCM were approximately 0.0157US$/L and 123 days with a considered lifespan of 10 years at salt water quantity of 20L. In addition, the results indicated that the thermal and exergy efficiencies of SCSBSS with PCM were 36.86% and 3.27% respectively.

Methods of Thermal Energy Storage by Using Smart Heat Pumps

Abstract To address energy problems in thermodynamic installations, the authors of the paper propose a working methodology in which the determining role of the exergetic aspects of the processes is especially emphasized. One of these energy problems, addressed in many papers in recent years, is of particular importance in the fight to reduce chemical and thermal pollution of the environment: the problem of storing excess energy and energy from renewable or residual sources. Approaching this issue as well from this point of view, the authors propose a series of solutions by which they seek to use the most of the exergy extracted from the available energy sources. The solutions proposed here are based on the use of an own invention, the isothermalizer, a particularly powerful tool, able to bring highly effective solutions to many of the problems that concern researchers determined to create a cleaner planet. Designers and users of thermodynamic systems now have the possibility of an initial choice and subsequent changes (with the change of external conditions), of their energy and exergetic efficiency, as well as the possibility of calculating the material and energy costs necessary to achieve the proposed objective. In any gas compression/expansion problem, the energy efficiency is established precisely, by choosing the isothermal speed of the process (so of the isothermal temperature), and the power density, by choosing the total surface of the thermal sponge, the flow rate and the mode of distribution of the cooling agent. As the isothermalizer is equipped with a processor that controls and modifies the isothermal speed in such a way that the exergy consumption is optimized, the energy storage processes become processes of extracting thermal energy from a tank and transferring it to another tank, a process accompanied by consumption/supply of mechanical energy.

Design and performance study of a double-acting collector-assisted absorption cooling system in a hot region

The solar cooling system results in a variety of technologies. It is an alternative and economical technology to conventional cooling systems and is environmentally friendly. In this work, a design of a H2O-LiBr absorption chiller driven by a double-acting collector was proposed and studied under thermo-economic, energetic, and exergetic aspects according to Bamako climatic conditions. Higher performance was reached when the generator was operated at 85 °C, a condensing temperature of 40 °C with 8 °C as the evaporation temperature of the working fluid. The annual cooling production of the system was 52.272 MWh and the annual solar energy received on the area of the double-acting collector was 138.778 MWh. The annual energy and exergy efficiencies of the system were 0.39 and 0.025, respectively. The investment cost of the system was 36.9 k€ and the cooling cost was 0.08 €/kWh. Additionally, the simple payback period is approximately 10.4 years.

Exergoeconomic and Environmental Evaluation of a Ground Source Heat Pump System for Reducing the Fossil Fuel Dependence: A Case Study in Rome

By 2050, the European Commission aims to achieve a 90% reduction in greenhouse gas emissions within the construction sector due to new targets set for greenhouse gases by the Commission. One of the most effective solutions for mitigating the environmental impact of buildings is to integrate renewable-energy systems such as air-to-water heat pumps or geothermal heat pumps. Several works in the literature investigated the advantages of heat pumps, particularly ground source heat pumps, for specific contexts. Furthermore, the evaluation can encompass not only energy considerations but also exergetic aspects, and this paper makes a significant contribution to the latter. The study presented here applies exergy analysis to a geothermal heat pump system that is interconnected with photo-voltaic and solar collector systems in a building located in Rome. Feasibility and environmental assessments were also conducted. It is evident that the exergy efficiency obtained is much lower than the energy efficiency. The heat pump demonstrates higher exergy efficiency by producing high-temperature thermal power compared to a constant dead state at relatively low temperatures. Following the heat pump, the adiabatic mixer exhibits the second highest exergy efficiency, trailed by two heat exchangers. Compared to a conventional plant case, the money saved is EUR 16,772 per year, translating to a Payback Period of 23 years. Furthermore, the average annual reduction in fossil fuel emissions is estimated at 26.2 metric tons of CO2.

Experimental Investigation on Heat Transfer Enhancement with Passive Inserts in Flat Tubes in due Consideration of an Efficiency Assessment

This paper presents results of an experimental investigation on pressure drop and heat transfer for a wide range of Reynolds and Prandtl numbers ranging from 8 < Pr < 60 and 40 < Re < 3500, for flat tubes without and with passive inserts. For three different kinds of passive insert designs, the impact on heat and momentum transfer due to coaction of the total set of passive inserts with different shape and amount was investigated. Experimental results were analyzed regarding two main aspects: Heat transfer mechanisms and pressure drop induced by friction and form drag forces due to the presence of different shapes. After heat and momentum transfer mechanisms for each passive insert design were analyzed, heat transfer and pressure drop enhancement were compared to each other, leading to an efficiency discussion. Different concepts for efficiency evaluation, which are cited in literature, were applied to the presented experimental data. Pros and cons of the different concepts are discussed. Finally, we propose an equation for evaluation of total performance, which fully respects the energetic and exergetic aspects of heat transfer and pressure drop enhancement.

Energy and exergy analysis of two novel hybrid solar photovoltaic geothermal energy systems incorporating a building integrated photovoltaic thermal system and an earth air heat exchanger system

In this paper, two novel configurations of the building integrated photovoltaic thermal (BIPVT)-compound earth-air heat exchanger (EAHE) system are proposed. Both the configurations operate in two modes, namely heating and cooling modes. In the heating mode of the configuration A, the cold outdoor air is twice preheated by passing through the EAHE and BIPVT systems. In the cooling mode of the configuration A, the hot outdoor air is precooled by flowing inside the EAHE system and the PV modules are cooled using the building exhaust air. The cooling mode of the configuration B is similar to the configuration A, while in the heating mode of the configuration B, the outdoor air first enters the BIPVT collector and then passes through the EAHE system. The energetic and exergetic performances of the configurations are investigated for climatic conditions of Kermanshah, Iran. In addition, the impacts of length, width, and depth of air duct located underneath the PV panels, air mass flow rate, length and inner diameter of the pipe of EAHE system on the annual average energetic and exergetic aspects of the best configuration of the BIPVT-EAHE system are evaluated. The outcomes revealed that the annual rate of thermal energy, electrical energy, and thermal exergy captured from the configuration A are respectively 3499.59, 5908.19, and 55.59 kWh, while these values for the configuration B are respectively 3468.16, 5969.87, and 51.76 kWh. In addition, it was found that the configuration A has superior energetic performance than the configuration B, while the overall exergetic performance of the configuration B is higher than the configuration A. Furthermore, it was depicted that both the energetic and exergetic performances of the suggested configurations intensify by augmenting the duct length, duct width, and tube diameter whereas they decline with an increase in the air mass flow rate and duct depth.

Thermo-economic optimization of solar air heaters with arcuate-shaped obstacles

In this study, thermo-economic optimization of single-pass SAHs (solar air heaters) with obstacles of arcuate shape has been carried out. The research is conducted in order to compare the exergy efficiency of three different types of flat plate SAHs. Also, using NSGA-II (non-dominated sorting genetic algorithm) influencing factors were optimized. The SAHs were two different arcuate obstacles (type II and type III), and the other one had no obstacles (type I). All heater types with single and double glass cover were evaluated. The results showed that the heater with double glass cover and the obstacles (type III) had the highest function in both economic and exergetic aspects. Based on the NSGA-II results, collector with flow rate, area and the outlet temperature of 0.017 kg s−1, 2.6 m2 and 78 °C, respectively, had the best performance.

Exergy Analysis and Optimization of a Combined Heat and Power Geothermal Plant

This paper presents the optimization of parallel distribution between electricity and heat production for a geothermal plant. The geothermal fluid is split into two streams, one used for an Organic Rankine Cycle (ORC) system, and the other for a District Heating Network (DHN). The superstructure to be used for the optimization problem includes the ORC components and the DHN topology constituted by a definite consumer and optional consumers. A Mixed Integer Non-Linear Programming (MINLP) optimization problem is formulated and solved using the GAMS software. This paper is focused on exergetic aspect. The main lines for formulation of the problem are reminded, yet the exergetic model is fully described. Exergy analysis is performed for two optimal solutions (economic and exergetic objective functions). Results for both optimizations are first compared. The analysis of exergetic efficiency of the ORC and the DHN may suggest that exergetic optimization privileges the system with the highest efficiency: the ORC. The DHN configuration is then the smallest as possible. Finally, a sensitive analysis is performed for the exergetic optimization. This analysis reveals our previous conclusion is not necessarily true. Taller configuration can exist even if ORC efficiency is higher than DHN efficiency. These results highlight the relevance of using an optimization approach for a Combined Heat and Power (CHP) plant.

Vapor absorption system powered by different solar collectors types: Cooling performance, optimization, and economic comparison

The current article presents the comprehensive thermodynamic modeling to compare the performance and optimization of single-stage LiCl-H2O and LiBr-H2O type absorption cooling system integrated with different solar collector types for the Gujarat, India. A 10 kW system at 7°C is analyzed which includes four different solar collectors (flat-plate collectors, parabolic-trough collectors, flat plate with compound parabolic collector reflectors, and evacuated-tube collectors) attached with insulated thermal storage tank to power the LiCl-H2O and LiBr-H2O vapor absorption system. The study investigated the effect of heat source temperature on performance aspects of systems. Optimum heat source temperature corresponding to energetic and exergetic aspects for LiCl-H2O pair is found to be lower in comparison to LiBr-H2O pair for all collectors type system. The examined performance parameters are exergetic efficiency, coefficient of performance, and area of collector. Exergetic optimization of each system estimated the required optimum collecting area for cooling. At optimum collector areas, capital cost is evaluated. Differentiation between optimized systems determined that evacuated-tube collectors-based technology is most economic and from exergetic point-of-view, parabolic-trough collectors is recommended. For effective comparison and conclusion, key performance indicator is evaluated to select optimum collector and working fluid pair from both thermodynamic and economic criteria.

Optimum Heat Source Temperature and Performance Comparison of LiCl–H2O and LiBr–H2O Type Solar Cooling System

This comprehensive investigation has been executed to compare the thermodynamic performance and optimization of LiCl–H2O and LiBr–H2O type absorption system integrated with flat-plate collectors (FPC), parabolic-trough collectors (PTC), evacuated-tube collectors (ETC), and compound parabolic collectors (CPC). A model of 10 kW is analyzed in engineering equation solver (ees) from thermodynamic perspectives. Solar collectors are integrated with a storage tank which fueled the LiCl–H2O and LiBr–H2O vapor absorption system to produce refrigeration at 7 °C in evaporator for Gujarat Region of India. The main objective includes the evaluation and optimization of critical performance and design parameters to exhibit the best working fluid pair and collector type. Optimum heat source temperature corresponding to energetic and exergetic aspects for LiCl–H2O pair is lower than that of LiBr–H2O pair for all collectors. Simulation shows that FPC has lowest capital cost, exergetic performance wise PTC is optimum, and ETC requires lowest collector area. On the basis of overall evaluation, solar absorption cooling systems are better to be powered by ETC with LiCl–H2O working fluid pair.

Exergetic Aspects of Hydrogen Energy Systems—The Case Study of a Fuel Cell Bus

Electrifying transportation is a promising approach to alleviate climate change issues arising from increased emissions. This study examines a system for the production of hydrogen using renewable energy sources as well as its use in buses. The electricity requirements for the production of hydrogen through the electrolysis of water, are covered by renewable energy sources. Fuel cells are being used to utilize hydrogen to power the bus. Exergy analysis for the system is carried out. Based on a steady-state model of the processes, exergy efficiencies are calculated for all subsystems. The subsystems with the highest proportion of irreversibility are identified and compared. It is shown that PV panel has exergetic efficiency of 12.74%, wind turbine of 45%, electrolysis of 67%, and fuel cells of 40%.

Three‐dimensional energetic and exergetic analysis of the injection orientation of DI diesel engine under different engine speeds

AbstractThree‐dimensional (3‐D) computational code was implemented to solve conservation equations based on finite volume method as to simulate 1.8 L Ford diesel engine. Velocity and pressure of each computational cell is achieved by SIMPLE (semi‐implicit method for pressure‐linked equations) algorithm. For the exergetic aspect, the initial condition is set at 0.1 MPa and 300 K. The engine modeling is performed with 130 °, 140 °, and 150 ° with respect to x‐axis under 1500 and 2500 rpm engine speeds. The results, however, indicate better air/fuel mixture (near stoichiometric equivalence ratio) for 130 ° of injection angle, albeit smaller spray droplets (lower sauter mean diameter) were introduced with 140 °. It is seen that higher soot and NOx mass fraction is attributed to 1500 rpm engine speed. The highest NOx and soot are exhausted at 130 ° and 150 ° of injection, respectively. Second law efficiency was calculated for different spray angle and engine speed schemes such that 36.62%, 30.2%, and 32.07% are associated with 130 °, 140 °, and 150 ° of injection angle under 1500 rpm, respectively. In terms of engine performance, that is, indicated mean effective pressure, indicated specific fuel consumption, and temperature, the best performance metrics are of 130 ° equal to 15.4 bar, 0.3856 kg/kW‐h, and 2074.97 K under 1500 rpm, respectively. Instant irreversibility rate is the highest amount with peak value of 17.48 J/deg for 130 deg‐1500 rpm, while 140 ° shows higher mean irreversibility rate over crank angle (CA) period.

Comparing advanced exergetic assessments of two geothermal district heating systems for residential buildings

Advanced exergy analysis method has been increasingly utilized in analyzing and assessing the performance of energy-related systems in recent years due to more deeply investigating the exergy destructions. In this study, two various geothermal district heating systems (GDHSs), the Afyon and Bigadiç GDHSs, which have been operated in Turkey, were considered to perform their advanced exergy analyses and assessments. The GDHSs studied were also compared with each other for the first time in terms of advanced exergetic aspects. In the analyses and calculations of the GDHS, the actual operational data obtained from the measurements and technical staff were utilized.The overall conventional and advanced exergetic efficiency values for the Afyon GDHS are determined to be 27.53% and 34.72% while those for the Bigadiç GDHS are obtained to be 21.03% and 32.52%, respectively. Considering both the interactions among components and the potential for improving components, more effective and efficient improvement priorities were proposed.

Hydrogen generation from biomass materials: challenges and opportunities

In this review, various processes for conversion of ligno(hemi)cellulosic biomass into hydrogen gas are comprehensively reviewed in terms of two main groups, namely (1) thermochemical processes [pyrolysis, catalytic pyrolysis, different gasification, co‐gasification, supercritical water gasification (SCWG)] and (2) biochemical‐cum‐biological conversions, along with electrolytic and photolytic processes. This review depicts much about the thermochemical processes for hydrogen production and its utilization via pyrolysis of biomass, gasification, gasification combined with pyrolysis, supercritical water (fluid‐gas) extraction, steam reforming (SR), auto thermal reforming (ATR), dry reforming (DR), liquid phase reforming (LPR), aqueous‐phase reforming (APR), and partial oxidation (POX) of renewable carboxylates such as bioethanol, acetic acid, phenol, glycerol, carbohydrates, different water‐soluble sugars, and bio‐oil, which are some of the areas to be explored for widespread awareness of hydrogen usage. Biomass‐based hydrogen production systems are emphasized and discussed in terms of their energetic and exergetic aspects with the help of reaction mechanisms. Different oxygenate compounds as derived from biomass with their potential catalyst tested by several literature studies and potential methods are then summarized. WIREs Energy Environ 2015, 4:139–155. doi: 10.1002/wene.111This article is categorized under: Bioenergy > Science and Materials Fuel Cells and Hydrogen > Science and Materials Fuel Cells and Hydrogen > Systems and Infrastructure Energy and Development > Science and Materials

Investigation of Hydrodynamics, Kinetics, Energetic and Exergetic Aspects of Fluidized Bed Drying of Rough Rice

Abstract The hydrodynamics, kinetics as well as energy and exergy analyses of fluidized bed drying of rough rice under various experimental conditions were investigated. Drying experiments were conducted at drying air temperatures of 55, 60, and 70°C, superficial fluidization velocities of 2.3, 2.5, and 2.8 m/s, solid holdups of 0.66 and 1.32 kg, and rough rice initial moisture content of 0.25 d.b. Various popular drying models were used to fit the drying data. It was found that the fluidized bed hydrodynamics of the rough rice was uniform and stable. The drying rate was found to increase with increase in drying air temperature and superficial fluidization velocity, while decreased with increase in solid holdup. Statistical analyses showed that the Midilli et al. model was the best model in describing fluidized bed drying characteristics of the rough rice. The results showed that the values of energy efficiency were higher than the corresponding values of exergy efficiency during the entire drying process. Furthermore, at initial stage of drying, the energy and exergy efficiencies were higher than those at the end of drying. It was also found that both the energy and the exergy efficiencies increased with increasing drying air temperature and solid holdup, whereas decreased with the increase in superficial fluidization velocity.

Comparative analysis between a PEM fuel cell and an internal combustion engine driving an electricity generator: Technical, economical and ecological aspects

In the recent years the fuel cells have received much attention. Among various technologies, the Proton Exchange Membrane Fuel Cell (PEMFC) is currently the most appropriate and is used in several vehicles prototype. A comparative technical, economical and ecological analysis between an Internal Combustion Engine fueled with Diesel driving an electricity Generator (ICE-G) and a PEMFC fed by hydrogen produced by ethanol steam reforming was performed. The technical analysis showed the advantages of the PEMFC in comparison to the ICE-G based in energetic and exergetic aspects. The economic analysis shows that fuel cells are not economic competitive when compared to internal combustion engine driving an electricity generator with the same generation capacity; it will only be economically feasible in a long term; due to the large investments required. The environmental analysis was based on concepts of CO2 equivalent, pollution indicator and ecological efficiency. Different to the ICE-G system, the Fuel Cell does not emit pollutants directly and the emission related to this technology is linked mainly with hydrogen production. The ecological efficiency of PEMFC was 96% considering the carbon dioxide cycle, for ICE-G system this parameter reach 51%.

Future Aspects of Geothermal Energy in Saudi Arabia

Geothermal energy seems to be a clean, proven, and reliable resource for supplying the needs of a sustainable society and helping to improve the global environment. Although the studies on geothermal resources exploration in Saudi Arabia were started in 1980, since then any serious geothermal projects have not been undertaken, excepting to the availability of some potentially resources-rich geothermal locations. The first in situ determination of the thermal properties of the underground soil required for the design of borehole heat exchangers was reported in 2009 for the first time. In this study, future aspects of geothermal energy were treated first. The exergetic aspects of some geothermal resources available were then explained using a specific exergy index. Finally, the results obtained were given and discussed. It is expected that some barriers hindering the utilization of geothermal resources in Saudi Arabia will be overcome and geothermal energy utilization will become a viable option in the near future.

Exergetic and sustainability performance assessment of geothermal (ground source) ejector heat pumps

Although ejectors have been used in cooling/refrigeration and Heat Pumps (HP) applications for a long time, utilisation of Geothermal Ejector Heat Pump (GEHP) with Ground–Heat Exchanger (GHE) is a new idea, which has recently appeared in the literature. In this study, we model a GEHP system with a GHE in terms of exergetic aspects and apply our model to this system in the heating mode. The system consists of mainly three parts, namely a GEHP unit, a GHE, and a heat distribution system. We determine the exergy transports between the components and the consumptions in each of the components of the whole system and we also calculate exergy efficiency and Sustainability Index (SI) values for the system components to evaluate its performance. In this regard, exergy efficiency values for the GEHP unit and whole system are calculated to be 85.3% and 84.6% on the product/fuel basis at dead (reference) state values for 19°C and 101.325 kPa, respectively. An improvement of about 16.17% in the energetic and exergetic coefficient of performance value of the GEHP unit is obtained by adding an ejector to the HP system. SI values for some system components such as ejector, compressor, condenser and evaporator are also obtained to be 1.82, 2.79, 3.22 and 3.94, respectively.

Visual and thermal comfort and its relations to exergy consumption in a classroom with daylighting

This paper discusses the exergetic aspect of daylighting together with luminous and thermal comfort aspect. We calculated the exergy consumption for lighting and cooling in a classroom for the cases with and without electric lighting. The full use of daylighting decreases chemical exergy input to the power plant by 89%. According to a questionnaire survey asking the students' perception of sensations and comfort in the classroom, while daylighting was being used, the cut–off of fluorescent tubes did not cause any luminous discomfort and it made their thermal comfort even better.

Exergetic performance analysis of a recirculating aquaculture system

This paper examines exergetic aspects of a Recirculation Aquaculture System (RAS) for Black Sea trout (Salmo trutta labrax) fingerling rearing at the Trabzon Central Fisheries Research Institute, Turkey. In its thermodynamic analysis, each component of the RAS is treated as a steady-state steady flow system and its exergetic efficiencies are studied. In addition, the following parameters are measured and recorded in experiments: the mass flow rates, inlet and outlet temperatures and of the system components, surrounding temperatures, and electrical work utilized by the components in the RAS. Based on these experimental data, inlet and outlet exergy values, exergy losses, and exergetic efficiencies of each component in the system are determined to assess their performance. Moreover, the overall system exergy efficiency is determined. The results show that exergy efficiencies of the system components are highly affected by varying input exergy flows as a function of the surrounding temperature and chiller’s operating period.