Exergetic Effectiveness Research Articles

Modeling and analysis of PCM‐encapsulated solar thermal energy storage system for space heating

AbstractIn this study, a phase change material (PCM)‐encapsulated packed‐bed thermal energy storage (PB‐TES) system is intended for Day‐round space heating in the winter. Solar concentric collectors act for day‐time heating and TES charging, while the stored energy can be used at night and intermediate time for space heating. A region‐wise techno‐economic analysis of PCM candidates is made to compare the costs and sizes of solar collectors and PB‐TES. A spherical capsule filled with sodium nitrite (NaNO2) and sodium nitrate (NaNO3) is numerically investigated during the PCM charging at constant thermal input. After complete liquefication, the charging time for NaNO2 and NaNO3 capsules is 3280 and 4300 s, respectively, holding the maximum stored energy of 733.4 KJ/kg at 285°C and 687.27 kJ/kg at 310.12°C, respectively. In addition, the stored exergy is obtained 238.78 and 234.74 kJ/kg for NaNO2 and NaNO3, respectively; however, the average exergetic effectiveness for NaNO2 and NaNO3 are 0.54 and 0.46. Despite the lower energy storage capacity (kJ/kg) of NaNO3, the PB‐TES volume is less with NaNO3 than with NaNO2 due to higher density. However, the average cost ($/tonne) of NaNO3 PCM is 50% higher than NaNO2. Subsequently, the thermal efficiency of the proposed system is estimated at 27.68% and 26.94% during day and night‐time operations.

Simulation and study of the simultaneous use of geothermal energy and flue gas waste energy in an innovative combined framework for power, chilled water, and fresh water generation

The integration of renewable energy sources, such as solar, biomass, and geothermal, with other technologies and energy production cycles holds the potential to significantly enhance power generation processes' efficiency. A novel trigeneration structure is introduced that harnesses geothermal energy and waste energy from flue gases. The proposed system comprises several key components, like combined flash and binary geothermal system, a water desalination unit, a Kalina power and cooling cycle, and organic Rankine cycles. The system is analyzed from various perspectives, encompassing energy, exergy, economic, and environmental viewpoints. This assessment allows for a holistic understanding of the trigeneration structure's performance, considering its energy efficiency, exergetic effectiveness, economic viability, and environmental impact. By combining elements, the trigeneration system aims to optimize the utilization of geothermal energy while efficiently converting waste energy from flue gases into useful power. The implementation and evaluation of this trigeneration structure offer promising prospects for sustainable and more effective power generation, promoting the integration of renewable resources with existing energy production technologies. The potential benefits of this approach could lead to a more environmentally friendly and economically viable solution for meeting our energy demands.

The evaluation of hydrogen production via a geothermal-based multigeneration system with 3E analysis and multi-objective optimization

In this study, a novel geothermal-based multigeneration system is designed and evaluated in energy, exergy and economic (3E) analyses. Besides 3E analyses, multi-objective optimization has been assessed to reach the highest exergetic effectiveness and the lowest total cost rate. To evaluate the designed plant, thermodynamic balance equations are assigned to all sub-systems found in the design. These equations are solved by using Engineering Equation Solver (EES) software. According to the analyses' results, with base parameters, total power production is 1951 kW, the hydrogen generation rate is 0.0015 kg/s, and the whole energy and exergy efficiencies are 59.53% and 53.17%. The economic analysis performed for the multigeneration system indicates that the total cost rate is 186 $/h, and the levelized energy cost is 0.102 $/kWh. These results indicate that the designed geothermal-based multigeneration system performs better than a single-generation plant in terms of efficiency and cost.

Exergetic Effects of Cooled Cooling Air Technology on the Turbofan Engine during a Typical Mission

The cooled cooling air technology (CCA technology) shows expected performance in solving the growing thermal challenge for advanced aero engines by reducing the temperature of cooling air. The effect of CCA technology on the overall propelling performance with or without adjusting cycle parameters is controversial. Based on this, both the energy and exergy methods have been adopted to elaborate the specific mechanisms of the above energy utilization discrepancy. As a result, the scheme of CCA technology without optimizing cycle parameters has lower propelling work and efficiency with the total exergy destruction increasing 0.5~2%. Oppositely, as for the scheme of CCA with meliorated cycle parameters, the propelling efficiency improved by around 2~4% with total exergy destruction reduced by 1~3.5%. By analyzing the distribution of exergy destruction, the avoidable and unavoidable exergy destruction caused by the combustion chamber, compressors, and turbines accounts for the largest proportion, which indicates that more attention needs to be paid in the future. During the whole flight mission, the percentage of exergy destruction is much higher in supersonic, subsonic cruise, combat, and escape conditions. In conclusion, the improvement of cycle parameters to reduce the exergy destruction should be considered when introducing CCA technology.

Heat Transfer and Exergy Analysis of a Shell and Tube Heat Exchanger using PGW based ZnO Nanofluids

In this experimental work, ZnO nanoparticles were synthesized using the chemical precipitation method, and the nanoparticle structure and morphology were characterized through XRD and SEM. Heat transfer and exergetic characteristics were then studied in a shell and tube heat exchanger using PGW-based ZnO nanofluids varying nanoparticle volume concentration and nanofluid (shell side) flow rate at 6, 8, 10 and 12 litres/min. The hot water flow rate was fixed at 12 litres/min. The experimental results show that the heat transfer rate was improved by increasing the nanoparticle concentration and nanofluid flow rate. When the nanoparticle volume concentration was 0.3 per cent, the maximum enhancement of heat transfer rate and average heat transfer coefficient using ZnO nanofluids were 35.9 per cent and 40.2 per cent, respectively, in comparison to the base fluid. Exergy loss and dimensionless exergy loss both increased with nanofluid flow rate and dropped substantially with increased nanoparticle volume concentrations. The average increment of exergetic effectiveness at three different nanoparticle volume concentration (0.1%, 0.2%, and 0.3%) are 10.68%, 23.64%, and 31.23% respectively. The highest exergetic sustainability index (0.41) and lowest environmental impact factor (2.42) were observed when the nanoparticle concentration was 0.3% with the nanofluid flow rate of 6 litres/min.

Energetic and Exergetic performances of a parabolic solar trough collector working with TiO2 & Al2O3 nanofluids for variable temperature applications

ABSTRACT Thermal efficiency of parabolic solar trough collectors (PTCs) can be enhanced by dispersing TiO2 nanoparticles into the conventionally used heat transfer fluids. In the present experimental work, a one-dimensional mathematical model is designed to study the outcome of TiO2 nanoparticles dispersed in the base fluid for variable temperatures PTCs. The major finding of this work is that the TiO2 nanofluid enhances the thermal efficiency of the PTC slightly. Elevated working temperatures are most appropriate for nanofluids using to generate highest gain of energy discharged. It is found that the Exergetic effectiveness enhancement is most important than energetic effectiveness. The maximum exergy efficiency is achieved by TiO2 based nanofluid and is about 8.09%. The highest relative gain of thermal energy discharged is found to be 9.66% higher than the water-based collector by using 0.3% of TiO2 in the base fluid.

Thermodynamic analysis of a new multi-generation plant based on the waste heat from the cement industry for improved energy management

In this paper, the hydrogen production and liquefaction option by utilising the waste heat from the raw material preheating sub-unit of cement facility are investigated thermodynamically. The gas turbine plant and Rankine cycle are chosen to generate power and, also in order to generate hydrogen, a part of the produced power is used for PEM electrolysis. In these conditions, the hydrogen generation from analysed integrated plant is computed as 0.028 kg/s. The energetic and exergetic effectiveness of Brayton and Rankine cycles integrated with the waste heat recovery process in the cement facility are computed as 58.24% and 42.17%, respectively, for the chosen working condition. It is also asserted that increasing the input temperature of gas turbine depended on the cyclone gas temperature, and increases the exergy efficiency of the investigated system.

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.

A novel combined biomass and solar energy conversion-based multigeneration system with hydrogen and ammonia generation

In the present study, an innovative multigeneration plant for hydrogen and ammonia generation based on solar and biomass power sources is suggested. The proposed integrated system is designed with the integration of different subsystems that enable different useful products such as power and hydrogen to be obtained. Performance evaluation of designed plant is carried out using different techniques. The energetic and exergetic analyses are applied to investigate and model the integrated plant. The plant consists of the parabolic dish collector, biomass gasifier, PEM electrolyzer and hydrogen compressor unit, ammonia reactor and ammonia storage tank unit, Rankine cycle, ORC cycle, ejector cooling unit, dryer unit and hot water production unit. The biomass gasifier unit is operated to convert biomass to synthesis gaseous, and the concentrating solar power plant is utilized to harness the free solar power. In the proposed plant, the electricity is obtained by using the gas, Rankine and ORC turbines. Additionally, the plant generates compressed hydrogen, ammonia, cooling effect and hot water with a PEM electrolyzer and compressed plant, ammonia reactor, ejector process and clean-water heater, respectively. The plant total electrical energy output is calculated as 20,125 kW, while the plant energetic and exergetic effectiveness are 58.76% and 55.64%. Furthermore, the hydrogen and ammonia generation are found to be 0.0855 kg/s and 0.3336 kg/s.

Investigation of irreversibilities in a microchannel by differing viscosity, including buoyancy forces and suction/injection

AbstractSingle‐phase Poiseuille flow considering oxides of copper‐water nanoliquid in the upright microchannel with uneven viscosity causes the production of inbuilt irreversibility in the system. This is reported in the present investigation involving the buoyancy force with suction/injection at the walls by taking into account different shapes of nanoparticles. The equations so obtained being highly nonlinear is attempted to solve via Runge–Kutta–Fehlberg shooting scheme. Flow and heat transmission characteristics are explored by considering the nanoparticle's shape. The result exemplifies that the viscosity variation parameter escalates the flow profile as well as temperature profile. The thermal radiation and Biot number boost the let go of thermal energy, which leads to system cooling. The temperature profile for nanoparticle shape factor upholds the fact that temperature is high for lamina‐shaped nanoparticles and least for spherical‐shaped nanoparticles. Also, the Biot number, radiation parameter, and nanoparticle volume fraction serve in lowering the entropy, which augments the exergetic effectiveness of the system.

Mathematical Modeling of Solar Energy based Thermal Energy Storage for House Heating in Winter

A novel solar thermal energy storage (TES) system for house heating purposes is modeled in the present study. The solar parabolic collector acts as a heat source to charge the TES using compressed CO2. The thermal energy in terms of sensible heat is stored in mild steel (MS) block wrapped in the thermal insulation material and buried in the ground at a certain depth. The stored energy will be used for house heating in the winter season. A mathematical model is developed to calculate the quantity of stored energy, consumption, and loss from TES along with the optimal storage volume of the block to fulfill the energy demand for house heating. Computational analysis of the 3D model is executed by adopting stipulated boundary conditions. Quantitative and qualitative studies of numerical results have been investigated for two cases: Initial charging and year-round performance. Numerical results revealed that the initial charging of the block takes in 55.2 days with maximum block temperature and stored energy as 324.2 °C and 2604 MJ, respectively. The average exergy efficiency and exergetic effectiveness of TES are observed as 49.9 % and 0.50, respectively. The partial charging of the block continued to compensate the heat losses after initial charging. The year-round performance of TES exhibits the reduction of stored energy by 71.6% at the end of January due to increased heating demand. Meanwhile, during a cyclic year, the average exergy efficiency and exergetic effectiveness of TES are noticed as 56.12 % and 0.76 respectively. The proposed TES has enough potential for year-round house heating since 28.4 % of net stored energy exists with the least block temperature of 106 °C. The rational economic study endorsed the proposed system 42.5% less expensive than the traditional heating methods for 50 years of utilization in addition to mitigating the average CO2 production of 5.655 Tons/year.

Intrinsic irreversibility of Al2O3–H2O nanofluid Poiseuille flow with variable viscosity and convective cooling

PurposeThis study aims to investigate the flow behavior of aluminum oxide–water nanofluid with variable viscosity flowing through the microchannel parallel with the ground, with low aspect ratio. The study focuses on the first and second law analyses of Poiseuille flow using water as the base fluid with alumina nanoparticles suspended in it. Combined effects of thermal radiation, viscous dissipation, variable viscosity, nanoparticle shape factor and volume fraction on the thermal performance are studied and the in-built irreversibility in the process is examined.Design/methodology/approachThe governing equations with dimensions are reduced to non-dimensional equations by using dimensionless quantities. Then, the Runge–Kutta–Fehlberg shooting scheme tackles the present non-linear equations.FindingsThe outcomes of the present analysis reveal that the activation energy parameter with its increase, depletes the exergetic effectiveness of the system, thus defending the fact to keep the activation energy parameter the lowest as possible for the system efficiency. In addition, thermal radiation and Biot number enhance the release of heat energy, thereby cooling the system. Bejan number graph exhibits the decreasing behavior for the increased nanoparticle shape factor, whereas the temperature enhances with the rise in nanoparticle shape factor.Originality/valueThe effects of nanoparticle shape factor in Poiseuille flow for alumina–water nanoliquid in low aspect ratio microchannel is inspected at the earliest. Exergetic effectiveness of the system is studied and heat transfer characteristics are explored for thermal radiation effect and activation energy parameter. Besides, .

A thermal performance evaluation of a new integrated gas turbine-based multigeneration plant with hydrogen and ammonia production

In this study, a new combined system driving a gas turbine cycle has been proposed for seven useful outputs of power, hydrogen, ammonia, heating-cooling, drying and hot water. The proposed integrated plant mainly consists of the gas turbine cycle, Rankine cycle, two organic Rankine cycles, ejector-based cooling, hydrogen production and liquefaction, ammonia production and storage, drying and hot water generation sub-systems. In order to demonstrate that the designed system is an efficient and environmentally plant, the performance analysis was performed by using a software package. Before performing the performance assessment of the plant, the mathematical model of the integrated plant is prepared in accordance with thermodynamic equations. Basic equilibrium equations are used for the thermodynamic equations used. Obtaining multiple useful outputs from the system also have the positive effect on the system effectiveness. The energetic effectiveness of integrated plant for multigeneration with hydrogen and ammonia production is computed to be 62.18% and exergetic efficiency is 58.37%. In addition, the energetic and exergetic effectiveness of hydrogen production and liquefaction process are 57.92% and 54.23%, respectively.

Performance investigation of a combined biomass gasifier-SOFC plant for compressed hydrogen production

As an alternative, clean and sustainable solution, a biomass-based integrated power plant is designed and studied both thermodynamically and parametrically. Due to the environmental, economic and performance related advantages, the design of multigeneration energy plants is now increasing and becoming widespread technology. Biomass, which is one of the renewable power sources, is selected for the plant to be more sustainable and environmentally friendly. The proposed system using biomass as an energy source consists of several sub-plants integrated to utilize the waste thermal energy and to generate useful products which are electricity, hydrogen, fresh and hot water, heating, and cooling. In this paper, comprehensive work is carried out for plant modeling and simulation. The thermodynamic assessment results reveal that both energetic and exergetic effectiveness of the whole plant are 56.17% and 52.83%, which are affected positively by varying the reference state conditions, combustor temperature, biomass gasifier temperature, SOFC temperature and pressure, and biomass mass flow rate. In addition, the lowest energy and exergy efficiencies occur in the ORC combined ejector refrigeration cycle with 21.87% and 18.26%, respectively.

Thermodynamic performance analysis of a copper–chlorine thermochemical cycle and biomass based combined plant for multigeneration

The primary objective of this work is to investigate a comprehensive thermodynamic assessment of the biomass-assisted multigeneration plant for electrical energy, hydrogen, heating-cooling, drying, and hot water production. The suggested multigeneration plant includes the biomass gasification process, Brayton cycle, Kalina cycle, organic Rankine cycle, and cascade refrigeration plant, which is to produce heating and cooling loads, drying system, hydrogen generation with copper–chlorine thermochemical process, and hydrogen liquefaction process. Based on the thermodynamic laws, the total irreversibility rate and performance assessment of the examined study is conducted. Moreover, the impact of various factors such as reference temperature, biomass gasifier temperature, and mass flow rate of biofuel, on the effectiveness and useful outputs of planned plant are examined. The outcomes of the proposed study show that 18 626, 3948 and 1037 kW electrical energy are generated by using the Brayton, Kalina, and organic Rankine cycle. Furthermore, the total cooling and heating capacities and hydrogen generation rates are 2392, 2864 kW and 0.068 kg s−1. Finally, energetic and exergetic effectiveness of the examined model are calculated as 56.71% and 53.59%.

Development and thermodynamic assessment of a novel solar and biomass energy based integrated plant for liquid hydrogen production

In this paper, a combined power plant based on the dish collector and biomass gasifier has been designed to produce liquefied hydrogen and beneficial outputs. The proposed solar and biomass energy based combined power system consists of seven different subplants, such as solar power process, biomass gasification plant, gas turbine cycle, hydrogen generation and liquefaction system, Kalina cycle, organic Rankine cycle, and single-effect absorption plant with ejector. The main useful outputs from the combined plant include power, liquid hydrogen, heating-cooling, and hot water. To evaluate the efficiency of integrated solar energy plant, energetic and exergetic effectiveness of both the whole plant and the sub-plants are performed. For this solar and biomass gasification based combined plant, the generation rates for useful outputs covering the total electricity, cooling, heating and hydrogen, and hot water are obtained as nearly 3.9 MW, 6584 kW, 4206 kW, and 0.087 kg/s in the base design situations. The energy and exergy performances of the whole system are calculated as 51.93% and 47.14%. Also, the functional exergy of the whole system is calculated as 9.18% for the base working parameters. In addition to calculating thermodynamic efficiencies, a parametric plant is conducted to examine the impacts of reference temperature, solar radiation intensity, gasifier temperature, combustion temperature, compression ratio of Brayton cycle, inlet temperature of separator 2, organic Rankine cycle turbine and pump input temperature, and gas turbine input temperature on the combined plant performance.

Quantifying the effect of nanoparticles addition to a hybrid absorption/recompression refrigeration cycle

Space heating and cooling constitute a major share of electricity consumption in buildings. Nanoparticles provide a powerful solution to improving the efficiency of heating and cooling systems. The effects of nanoparticle addition on the efficiency improvement of a novel absorption-recompression refrigeration system is characterized in the present paper. Three different types of nanoparticles (Fe, Al2O3 and SiO2) are evaluated by varying volume fractions of dissolved nanoparticles in LiBr–H2O solution, flowing in specific parts of the proposed hybrid cycle. The effect of nanoparticle addition on heat exchange rate of absorber, plate heat exchanger and generator is quantified. The pressure drop of heat exchanger, compressor power consumption and overall energetic and exergetic effects are compared and assessed at volume fractions ranging from 0 to 5%. A theoretical analysis indicates market improvement in the coefficient of performance, exergy efficiency and heat exchange properties at the component level in the presence of nanoparticles. The results show the quantitative levels of improved performance and differences among options: addition of Fe nanoparticles is most effective when compared to Al2O3 and SiO2. Adding of Fe nanoparticles (5% by vol) led to the maximum improvement of 7.6% in the effectiveness of heat exchanger, a maximum reduction of 11.8% in compressor power consumption, and a maximum improvement of 14.6% in coefficient of performance.

Second law analysis of a fossil‐geothermal hybrid power plant with thermodynamic optimization of geothermal preheater

AbstractThere is an urgent and compelling need to develop innovative and more effective ways to integrate sustainable renewable energy solutions into the already existing systems or, better yet, create new systems that all together make use of renewable energy. This study aims to establish the optimum working conditions of a geothermal preheater in a power plant that makes use of both renewable and nonrenewable energy resources, where renewable (geothermal) energy is used to boost the power output in an environmentally sustainable way. Hence, two models, one, a simplified model of a Rankine cycle with single reheat and regeneration, and another, with a geothermal preheater substituting the low‐pressure feedwater heater (LPFWH), were compared. The Engineering Equations Solver software was used to perform an analysis of the thermodynamic performance of the two models designed. An analysis was done to evaluate the energetic and exergetic effects of replacing a LPFWH with a geothermal preheater sourcing heat from a low temperature geothermal resource (100°C‐160°C). Results from the thermodynamic analysis reveal that the hybridization boosts the power output by approximately 4% and it is superior in terms of the second law. Entropy generation minimization analysis was then employed to establish optimal working conditions of the hybrid system (ie, the geothermal preheater modeled as a downhole coaxial heat exchanger).

Energy saving in a convective dryer by using novel real-time exergy-based control schemes adjusting exhaust air recirculation

This study was aimed at developing and comparing three different novel real-time exergy-based control schemes for adjusting exhaust air recirculation in a convective dryer for the first time. These control schemes were based on output–input warm exergy ratio of drying cabinet (Scheme I), output–input warm exergy ratio of drying cabinet considering a fixed upper limit for the output wet exergy rate (Scheme II), and output–input warm exergy ratio of drying cabinet considering a varying upper limit for the output wet exergy rate (Scheme III). A continuous time-based control approach (Scheme IV) was also developed for comparison purposes. The exergetic effectiveness improvement and energy saving of the process achieved using the developed control schemes were assessed with respect to the base operation mode (without exhaust air recirculation) in order to make decisions on the most efficient approaches. As a case study, poplar wood chips were dried at two temperatures (55 and 70 °C) and two volumetric flow rates (360 and 450 m3/h) of drying air. The exergetic effectiveness of the drying process varied from 1.4–3.1%. The experimental results showed that the exergetic effectiveness of the drying process could be improved by employing all the developed control schemes. Among the developed control schemes, the control scheme III showed the highest exergetic effectiveness improvement in the range of 46.5–75.9%. This control scheme could also reduce the overall energy consumption of drying system in the range of 30.7–34.5% compared with the base operation mode. The selected control scheme could be implemented on various drying systems in order to improve their efficiency, productivity, and sustainability by recuperating the waste exergy from exhaust air.

Energy and exergy analyses of latent heat storage unit positioned at different orientations – An experimental study

The performance of a latent heat storage unit (LHSU) greatly rely on the melting/solidification rate which in turn affected by the orientation of LHSU. The orientation of the LHSU greatly influences the natural convection phenomenon, thereby affects the melting behavior of PCM. The present study is aimed at investigating the performance of a shell and tube LHSU positioned at various inclinations. Four inclinations are considered from vertical to horizontal position. Lauric acid is chosen as PCM with a melting range of 43.45°C–49.94 °C. Both melting and solidification characteristics are analyzed with the help of energy and exergy analyses (PCM average temperature, melt fraction, energy and exergy efficiency, energetic and exergetic effectiveness). From the experimental results, it is observed that the orientation has a major influence on the melting phenomenon and solidification is unaffected by the orientation of LHSU. Melting rate is observed to be higher for horizontal configuration till the PCM in the upper half portion is melted, however total melting time is observed to be less for vertical configuration. In addition, exergy efficiency is found to be higher for vertical configuration while melting, whereas for discharging process the exergy efficiency is same for all the inclinations.