Increase In Exergy Efficiency Research Articles

Modelling and optimization of combined supercritical carbon dioxide Brayton cycle and organic Rankine cycle for electricity and hydrogen production

Hydrogen as a clean fuel, is key energy carrier for sustainable development, and its production via water electrolysis is most desirable for its carbon free nature. Nuclear power provides good opportunity to satisfy the huge energy demand associated with the process, in addition to electrical power generation. Modelling an efficient and cost effective nuclear based power and Hydrogen cogeneration system and optimizing it to enhance its performance is the core academic problem addressed in the present study. It proposes a power plant cycle aided by a nuclear reactor, providing 300 MW thermal power input. Supercritical CO2 Brayton cycle is used as the main cycle, instead of traditional Helium Brayton cycle or steam Rankine cycle. To increase the cycle efficiency, by reducing the compression work and by reducing the cold source loss, main compression intercooling and waste heat recovery by an Organic Rankine Cycle (ORC) is introduced together with recompression Brayton cycle arrangement. The power coming from recovered waste heat goes to a Proton Exchange Membrane Electrolyzer (PEME), which facilitates the production of Hydrogen by splitting water via electrolysis. Additional attention is given to ORC fluid selection by employing and comparing the performance of widely acknowledged R245fa together with its more eco friendly replacements, R1233Zd(E) and R1234Ze(Z). The evaluation of the system performance is conducted through the lenses of Energy, Exergy, and Economics. Essential parameters are scrutinized to gauge their impact on two pivotal objectives. Overall Exergy Efficiency(ηex) takes care of the thermodynamic performance and the economic aspect is scrutinized by Levelized Cost of Energy (LCOEn). Notably, by employing R245fa as the ORC working fluid, the system attains peak Energy efficiency of 42.13% and Exergy efficiency of 58.32%, and a minimum LCOEn of 0.063 USD/kWh. Of all the components associated with the system nuclear reactor tops the chart for maximum exergy destroyed(40.8% of total) as well as maximum investment cost(65.7% of total). Pump contributes least to exergy destruction(0.03% of the total) and heat exchangers hold least share(1.1% of total) for investment cost. Furthermore, a multiobjective optimization exercise is executed to fine-tune the system’s operational parameters. This optimization results in a 3.12% increase in Overall Exergy Efficiency and a 9.79% decrease in LCOEn compared to the base operating condition with R245fa used as the ORC fluid. The ηex & LCOEn in best possible operating condition are 58.25% & 0.0645 USD/kWh using R245fa as ORC fluid, 58.23% & 0.0645 USD/kWh using R1233Zd(E) as ORC fluid and 58.22% & 0.0644 USD/kWh using R1234Ze(Z) as ORC fluid. If same amount of electrical Power is supplied to PEME for both with and without ORC configuration, having an ORC is advantageous both in terms of superior Exergy Efficiency and lower LCOEn. The proposed configuration is also economically more lucrative with higher Net Present Value(NPV) and Benefit to Cost Ratio(BCR). For example, when PEME power input for both the cases is 10 MW, proposed system has NPV = 201.79 Million USD & BCR = 1.70 compared to NPV = 164.03 Million USD & BCR = 1.58 for without ORC configuration. Even if in without ORC configuration, no electrical power is supplied to the electrolyzer, adding an ORC to produce Hydrogen will still achieve maximum 1.57% Exergy Efficiency increment, compared to only electrical power production by sCO2 Brayton cycle. It is seen that in base condition, the NPV is still superior for the proposed configuration (203.03 to 189.32 Million USD), and the BCR dips only slightly from 1.72 to 1.71.

ENERGY AND EXERGY ANALYSIS OF A TWO-STAGE CASCADE VAPOR COMPRESSION REFRIGERATION SYSTEM WITH MODIFIED SYSTEM CONFIGURATION

This study proposes a modification to the two-stage cascade vapor compression refrigeration system by adding internal heat exchangers that function as subcoolers and desuperheater. The influence of each internal heat exchanger proposed on the exergy destruction rate, exergy efficiency, compressor power consumption, ECOP, and COP of the system was investigated. Additionally, various refrigerant combinations were considered as working fluids to evaluate which combination is the most suitable for the proposed system. Mathematical models based on the principles of thermodynamics were established in Engineering Equation Solver (EES), a software used for energy and exergy analysis. The results reveal that the addition of specific internal heat exchangers causes either an increase or decrease in overall system performance, depending on the type of refrigerant combination used. Consequently, there exists an optimal system configuration for each refrigerant combination. Compared with the conventional two-stage cascade refrigeration system, the optimal system configurations in the present study exhibited higher overall system performance. A maximum increase in exergy efficiency, ECOP, and COP of 7.31%, 9.8%, and 7.3%, respectively, can be observed with the refrigerant combination R450A/R404A. Additionally, the results of the exergy analysis identify that the HTC compressor, condenser, LTC compressor, and cascade condenser are the primary contributors to the exergy destruction rate within the system.

Thermodynamic analysis and multi-objective optimization of different gas turbine configuration strategies for an atmospheric SOFC system

Solid oxide fuel cells (SOFCs) play a critical role as a key technological component in the utilization of hydrogen energy. Extensive research has been conducted on pressurized SOFC hybrid systems, focusing on performance enhancement and novel system configurations, etc. However, the planar SOFC suitable for commercial application exists limitations that confine its operation solely to atmospheric pressure. Moreover, SOFC exhaust contained considerable potential for energy recovery. In light of these limitations, two hybrid power generation systems of SOFC and GT have been proposed: direct and indirect utilization of SOFC cycle exhaust. Parameter and exergy analysis has been conducted to investigate the characteristic of SOFC-GT system. Multi-objective optimization is performed by setting exergy efficiency and output power as objective. The results reveal that the combustion process contributes significantly to system losses, with exergy efficiency reaching a maximum of 49.48% and 41.61%, respectively. Additionally, the system's maximum output power reaches 92 kW. Notably, the indirect SOFC-GT system demonstrates an 8% increase in exergy efficiency compared to the direct SOFC-GT system at the same output power. To improve the overall system fire efficiency, it is recommended to develop planar SOFCs suitable for high pressure and slow down the reaction process inside the combustion chamber.

Integration of the single-effect mixed refrigerant cycle with liquified air energy storage and cold energy of LNG regasification: Energy, exergy, and efficiency prospectives

The escalating global energy demand has prompted increased focus on the industry of liquefied natural gas (LNG), emphasizing the need for optimizing liquefaction processes to minimize capital costs. Thus, the integration between liquified natural gas LNG regasification and liquid air energy storage (LAES) to produce electricity and utilize the cold energy of LNG regasification has several interests to maximize the benefits of the process to generate power and face the challenges such as energy saving and reducing the total operations costs … etc. Fortunately, this study introduces a novel approach that combines a single-effect mixed refrigerant (SMR) cycle with air liquefaction, incorporating regenerative Rankine cycles for enhanced efficiency. The effectiveness of the LNG-SMR-LAES process was evaluated using comprehensive energy, exergy, and economic analyses to ascertain its viability. The results showed a notable improvement in the overall net power energy by 6 % and an increase in exergy efficiency by 11.7 % compared to the base case. Energy savings of 31.6 % (470.10 kW) contributed to the process's environmental and economic feasibility. The net present value was estimated at 11,230.4 US dollars, affirming the industrial-feasible design and economic viability of the LNG-SMR-LAES process.

Energy, exergy, exergoeconomic, economic, and environmental analyses and multi-objective optimization of a novel combined cooling and power system with dual-pressure Kalina cycle-absorption refrigeration

A novel combined cooling and power system, the dual-pressure Kalina cycle-absorption refrigeration (DPKC-AR-CCP), is proposed for the cascade utilization of waste heat from high-temperature flue gas and jacket water from internal combustion engines. A pneumatic booster pump unit is employed to increase the inlet pressure of the low-pressure expander, with heat generated during the compression process utilized for preheating the ammonia/water mixture, and exhaust gas from the low-pressure expander is combined with driving gas for absorption refrigeration. By integrating the first and second laws of thermodynamics with the SPECO Methodology, models for energy, exergy, exergoeconomy, economy, and environment of the DPKC-AR-CCP system are developed. A multi-objective optimization model is formulated with maximum exergy efficiency, minimum total exergy cost rate, and maximum annual equivalent carbon dioxide (CO2) emission reduction as objective functions. MATLAB software (combined with REFPROP software) is utilized for simulation and multi-objective optimization. The performance of each component under specific conditions is assessed, and a comparison with the simple absorption refrigeration/Kalina cogeneration system (AR/KC) highlights the advantages of the DPKC-AR-CCP system; an investigation into the effects of different operating parameters on performance is conducted. The results indicate that, under identical operational parameters, the DPKC-AR-CCP system exhibits a substantial increase in net output power (230.2 %), cooling capacity (98.7 %), and exergy efficiency (148.8 %) compared to the simple AR/KC system; payback period is reduced by 64.8 %; and annual equivalent CO2 emissions are decreased by 202.2 %. However, there is an increase in the total exergy cost rate by 90.5 %. The optimal concentration of ammonia/water is determined to be 0.816/0.184, with a heat exchanger outlet temperature of 341.07 K, driving pressure of 0.654 MPa, and low-pressure expander inlet pressure of 5.064 MPa. Correspondingly, the optimal exergy efficiency is 87.2 %, the annual reduction in CO2 emissions is 5.53 × 107 kg, and the total exergy cost rate is 288.48$/h.

Augmentation of the tubular distiller performance via hot air injection from a parabolic trough collector, nanocoating, and nanofluid

Nowadays, due to freshwater scarcity intensifying, researchers are actively seeking to improve solar desalination, a technology with immense potential, but there are still limitations in production capacity. This study investigated the integration of various additives in tubular solar still (TSS) at three configurations. In Case I, a V-corrugated basin and an air parabolic trough collector (PTC) equipped with evacuated tubes were integrated. Then, with the same attachments, CuO nanocoating was applied to the basin surface in Case II, aiming to enhance heat absorption. Finally, in Case III, CuO nanofluid was used in the presence of all previous enhancers. The system was studied during summer days with weather parameters having average ranges (minimum – peak) of 32.5–37.5 °C (ambient temperature), 318.5–1000 W/m2 (solar radiation), and 1.1–2.3 m/s (wind speed). The results were very acceptable and competitive. All modified configurations of the advanced TSS (ATSS) significantly increased distillate production compared to the classic TSS (CTSS), with a range of 49.84–79.88 %. Case III stood out as the most successful configuration, achieving outstanding gains in both energy and exergy efficiencies. Compared to the CTSS, Case III boasted an impressive 83.69 % improvement in energy efficiency and a staggering 242.45 % increase in exergy efficiency. This refers to a system that not only produces more desalinated water but also does so with significantly less wasted energy, making it a more environmentally sustainable solution. Case III also offered a good economic advantage with a 13.51 % cost reduction compared to CTSS.

Techno-economic optimization and working fluid selection of a biogas-based dual-loop bi-evaporator ejector cooling cycle involving power-to-hydrogen and water facilities

Biogas-fueled decentralized energy systems featuring gas turbines emerge as pivotal players in the quest for more adaptable and eco-friendly energy solutions. This study presents the design of a cutting-edge multigeneration system that harnesses the potential of a gas turbine coupled with ejector-driven dual-loop bi-evaporator technology, reverse osmosis desalination, proton exchange membrane electrolysis, and an organic Rankine cycle. The research encompasses an extensive sensitivity analysis and deploys a genetic algorithm-based optimization technique. Through meticulous Optimization, the system achieves remarkable outcomes, including electricity generation, cooling capacity, heating capacity, desalinated water production, and hydrogen yield, measured at 957.3 kW, 231.4 kW, 272.3 kW, 7.336 kg/s, and 0.99 kg/h, respectively. Notably, this performance surpasses the base case by 2% and 8.9%, yielding exergy efficiency and total unit cost improvements of 33.3% and 16.4 $/GJ. Among the critical decisions made was selecting an organic working fluid for the organic Rankine cycle. Through rigorous evaluation, isobutene emerged as the optimal choice, demonstrating significantly improved output power compared to alternatives. Isobutane as the working fluid led to a substantial increase in overall exergy efficiency and a resultant total unit cost of 18.06 $/GJ, accompanied by an impressive 23.48% exergy efficiency.

Identifying enhancement of double slope solar still performance by adding water cooling to walls

The object of this research is a double-slope solar still with the addition of water cooling on the wall (DSSS.WCW). The issue with solar stills is that the temperature of the cover glass is quite high, which consequently reduces the rate of evaporation. Methods to reduce the cover glass temperature involve water cooling, by flowing water and spraying it onto the cover glass. Both of these methods have been shown to reduce the temperature of the cover glass, but they still require additional energy and can decrease the solar radiation energy received by the absorber plate. This research proposes using a water cooling method on the wall that does not require additional energy and can prevent a reduction in the solar radiation energy received by the absorber plate. Experimental and theoretical research was conducted to study the effect of using DSSS.WCW. The results showed a 13.48 % reduction in the cover glass temperature, consequently increasing the temperature difference between the fins and the cover glass by 9.82 °C. The increase in temperature difference resulted in a 13.82 % increase in freshwater productivity theoretically by 2.80 kg/hour and a 13.10 % increase experimentally for the DSSS.WCW by 2.58 kg/hour. In addition, there was a theoretical increase in energy efficiency of 22.29 % and an experimental increase of 22.82 %, along with an increase in exergy efficiency of 15.71 %. The implementation of water cooling on the wall has been shown to enhance the efficiency of the double-slope solar still. In addition, the water cooling method on the wall does not reduce the solar radiation energy that can be received by the absorber plate and does not require additional energy. The results of this research can be applied in remote islands in Indonesia, particularly during the dry season

Experimental study of solid particles in thermal energy storage systems for shell and tube heat exchanger: Effect of particle size and flow direction

The solid particle thermal energy storage method offers cost-effective, simple, and high-temperature suitable solutions. It effectively resolves chemical compatibility and thermal stress issues in shell-and-tube heat exchangers. This work studies the quartz sands' particle sizes and flow direction's impact on heat exchanger performance. The results show that heat conduction and natural convection heat transfer mechanisms exist on the particle side. Flow direction minimally affects charge/discharge time and stored energy but significantly impacts delivered/recovered energy and exergy and energy and exergy efficiencies. Optimal performance is achieved when HTO enters from the top during charging and from the bottom during discharging, creating a transparent thermal gradient of “Top Temperature High, Bottom Temperature Low”. This distribution minimizes natural convection losses, resulting in a 15–17 % increase in energy efficiency and an 11–13 % increase in exergy efficiency compared to reverse flow. Smaller particles show slightly faster temperature rise due to lower energy storage density. Large and medium particles perform well, achieving energy efficiencies of 81.5 % and 81.0 % and exergy efficiencies of 62.1 % and 61.8 %, respectively. Small particles have an energy efficiency of 79.0 % and an exergy efficiency of 60.4 %, possibly due to higher porosity and increased heat losses.

Thermoradiative coupling graphene-based thermionic solar conversion

Thermionic conversion, due to its simple solid-state structure capable of converting heat to electricity directly, is promising for concentrated solar power. However, because of the extremely high cathode temperature, a large portion of the heat is lost to the environment. The paper introduces a novel concept of selective thermoradiative-graphene thermionic conversion (STR-GTI) that involving a combined control of photon and electron emission to modify the radiation dissipation. A detailed thermodynamic model is developed to evaluate the energy transfer irreversibility of STR-GTI solar conversion. The results demonstrate that the selective themoradiative photon emission and graphene thermionic electron emission effects synergistically reduce internal irreversible losses in the STR-GTI system, leading to a maximum energy efficiency of 34.34 % at a concentration ratio of 425, cathode work function of 1.8 eV and thermoradiative bandgap of 0.2 eV. The STR-GTI system outperforms both individual GTI and STR converters in terms of exergy efficiency and entropy production minimization. It exhibits a remarkable 102.03 % increase in exergy efficiency compared to the STR & GTI system at a thermoradiative voltage of −0.14 eV, accompanied by a 28.56 % reduction in exergy loss and a 37.83 % decrease in entropy production. The combination of narrowing the spectral radiation bandwidth and significant electron emission capabilities of graphene contribute to the system’s resilience against solar radiation fluctuations.

Exergy and energy investigations of ET-150 PTSC with non-Newtonian nanofluid

This paper investigates the performance of the EuroTrogh-150 solar collector. The analyzes of energy, exergy, environmental, enviroeconomic, exergoenvironmental and exergoenviroeconomic are considered. For the first time, this study examines these analyzes in several absorber tubes of EuroTrough-150 collector (absorber tubes are installed in series) and for non-Newtonian nanofluid (water-CMC/TiO2). According to the results, energy efficiency, Nusselt number and Thermal Hydrodynamic Efficiency for the first absorber tube have the highest values, and are equal to 0.8, 161.88, and 2.47, respectively. The exergy efficiency has a maximum value for the last absorber tube, and is equal to 0.216. At Re = 5000, increasing the wind speed from 1 m/s to 21 m/s decrease the energy and exergy efficiencies by 8.8 % and 18.3 %, respectively. At Re = 17500 (compared to Re = 5000), the exergy efficiency increase is equal to 50 % and 32 % in the last and first absorber tubes, respectively. In addition, the sixth absorber tube is more affected by the wind speed than the first absorber tube. According to enviroeconomic and exergoenviroeconomic analyses, the price of CO2 emission for nanofluid decreases by 10.28 % and 9.09 %, respectively. Moreover, based on the environmental and exergoenvironmental analyses, the base fluid emits more CO2 than the nanofluid.

Integration of proton exchange membrane fuel cell with air gap membrane distillation for sustainable electricity and freshwater cogeneration: Performance, influential mechanism, multi-objective optimization and future perspective

Proton exchange membrane fuel cell (PEMFC) converts vast majority of hydrogen energy into waste heat, resulting in energy wasting, membrane drying and even lifetime shortening. Herein, air gap membrane distillation is proposed to immediately remove and harness the waste heat from PEMFC for additional freshwater production. By quantifying the irreversible thermodynamic and electrochemical losses, mathematical formulas for the water production, power generation and overall efficiency are derived to evaluate the system performance. After a rigorous model validation, the performance feature, feasibility and competitiveness of the proposed system are examined. The integration system achieves a peak power density 23.69 % higher than that of a single PEMFC at 353 K, with a corresponding increase in exergy efficiency by 3.61 %. In addition, the influential mechanisms of the PEMFC operating conditions, air gap thickness, coolant temperature, and properties of the proton exchange membrane and hydrophobic porous membrane are investigated to discern potential avenues for further performance improvement. The gradient-based local sensitivity analyses further determine the optimal parameter regulation strategies for different output targets. The economic study indicates that the levelized costs of water and electricity over the total lifecycle are 21.53 $ m−3 and 0.061 $ kWh−1, respectively. The multi-objective optimization, integrating genetic algorithm and the technique for order preference by similarity to an ideal solution, maximizes the exergy efficiency and output power density while minimizing the initial investment cost per unit area, with values of 42.84 %, 0.975 W cm−2, and 27.33 $ cm−2, respectively.

Study on a novel hydrogen liquification process applying mixed-refrigerant for pre-cooling and cryogenics

Reducing the energy consumption of hydrogen liquefaction process is an urgent issue to improve the economy of liquid hydrogen transportation. A novel large-scale hydrogen liquefaction system, with a capacity of 100 TPD, is proposed in this paper. The pre-cooling system is composed of a mixed-refrigerant (MR) refrigeration cycle and a CO2–NH3 cascade refrigeration cycle. Due to the auxiliary pre-cooling effect of the CO2–NH3 cascade cycle, temperature of the pre-cooled hydrogen can be as low as −200.9 °C. A modified MR Joule Brayton cycle with an additional compressor is used as the cryogenic system to cool the hydrogen from −200.9 °C to −252.2 °C. Besides, a four-stage ortho-to-para conversion (OPC) process is utilized. Performance of the novel system is investigated and optimized using the Aspen HYSYS software. According to the results, the lowest specific energy consumption (SEC) of the proposed process is 6.15 kWh/kgLH2 and the exergy efficiency is as high as 67.4%. Based on the energy analysis, the best system coefficient of performance is 0.1751 with a 96.3% of p-H2 in the liquid hydrogen. In addition, compared to the initial conceptual system, the proposed system exhibits significant performance enhancements, a 20% reduction in SEC and a 27.9% increase in exergy efficiency. A sensitivity analysis is conducted to assess the impact of refrigerant composition and hydrogen pressure on the system, resulting in the determination of the optimal proportions of refrigerant components and the optimal inlet pressure. Results of the study can provide theoretical reference for the further development of large-scale hydrogen liquefaction technology.

Numerical investigation on mixed convection for laminar molten salt in horizontal square tubes

Molten salts are the key working media in nuclear and new energy fields. However, the mixed convection of molten salt is rarely investigated. The mixed convection of laminar flow in horizontal square tubes with constant heat flux is analyzed using Fluent software for the first time. The effects of heat flux, inlet temperature and Reynolds number on the flow and heat transfer performances are evaluated. It is found that as the buoyancy force increases, the friction factor, flow entropy generation rate, Nusselt number, and exergy efficiency increase, while the heat transfer entropy generation rate and exergy loss decrease. Compared to the forced convection, the maximum local friction factor, flow entropy generation rate, mean Nusselt number and mean exergy efficiency for mixed convection increase by 25.8%, 50.5%, 109.0% and 7.6%, respectively. Moreover, the maximum mean heat transfer entropy generation rate and exergy loss decrease by 56.1% and 57.3%, respectively. In addition, approximately 42% of the friction factor predicted by Fluent and 30% of the heat transfer predicted by Fluent exceed 20.0% uncertainties of conventional correlations. Therefore, an accurate friction factor correlation with 12.9% uncertainty and an accurate heat transfer correlation with 9.1% uncertainty are proposed.

Analysis of cascade vapor compression refrigeration system using nanorefrigerants: Energy, exergy, and environmental (3E)

Nanorefrigerants are considered the most efficient heat transfer fluids for improving heat transfer properties in the refrigeration and air conditioning equipment. For the first time in this study, energy, exergy, and environmental evaluation (3E) analyses were performed by the addition of different nanoparticles to a low GWP refrigerant pair such as R290/R1233ZDE in a cascade refrigeration system. CNT, CuO, and, TiO2 nanoparticles were added to the refrigerant. The effect of nanoparticles on the cascade refrigeration system was analyzed using a model based on density changes. A detailed thermodynamic analysis was performed of the cascade refrigeration system at different evaporator temperatures and mass ratios. The power consumption of the compressor decreases as the evaporator temperature increases for all types of nanoparticles, resulting in an increase in COP values. The analyses showed that CuO nanoparticles had the highest performance. It has been observed that the energy and exergy efficiency increase as compressor work decreases with increasing mass ratios in all nanorefrigerants. In addition, the results indicated that all nanorefrigerants emit lower monthly CO2 emissions compared to the pure refrigerants. The nanorefrigerants play a crucial role in reducing energy consumption and promoting environmental protection compared to traditional refrigerants.

Thermodynamic investigation of a Carnot battery based multi-energy system with cascaded latent thermal (heat and cold) energy stores

Carnot batteries store electricity in thermal form, allowing for power balancing and also multi-vector energy management as a unique asset. Cascaded thermal energy storage therefore has a vital role in Carnot battery, particularly multi-energy systems delivering electricity and thermal energy at various temperatures. Here, we propose a Carnot battery multi-energy system with cascaded latent thermal energy stores. The effects of compressor pressure ratio, total stage number, stage area and fluid velocity in tubes, on system-level coefficient of performance and total exergy efficiency are investigated. The results show that both the coefficient of performance and exergy efficiency increase significantly and then level off with the total stage number and stage area increasing, while they only increase slightly before a significant decrease with the increase of fluid velocity in tubes. The selection of compressor pressure ratios relates to the demands of cold, heat and electricity. The multi-energy system achieves a maximum coefficient of performance of 95.0% in combined cooling, heating and power mode. Although the thermodynamic performance yileds comparable with Carnot battery systems integrated with packed-bed or liquid-based sensible heat stores, the Carnot battery multi-energy system can deliver electricity and multi-grade heat and cold simultaneously, thus increasing flexibility in future energy systems.

Advanced Cascaded Recompression Absorption System Equipped with Ejector and Vapor-Injection Enhanced Vapor Compression Refrigeration System: ANN based Multi-Objective Optimization

Although traditional compression absorption refrigeration cycle (CARC) addresses the respective limitations of the Absorption Refrigeration Cycle (ARC) and Vapor Compression Refrigeration (VCR) systems while harnessing their individual strengths. But this arrangement faces challenges related to power wastage, insufficient thermal energy absorption, and high compressor power requirements. To address these issues, in this study, an advanced RAC (Recompression Absorption System) is integrated with enhanced VCR incorporated with ejector to develop advanced proposed Ejector-Compression Recompression Absorption cycle (E-CRAC) and Ejector enhanced Vapor-Injection Compression Recompression Absorption Cycle (EI-CRAC). A computational model is developed in the Engineering Equation Solver (EES) employing energy, mass, and exergy conservation principles to conduct a thorough 1st and 2nd law analysis. An Artificial Neural Network (ANN) model, combined with a Genetic algorithm, enabled multi-objective optimization to pinpoint optimal operational conditions. The COP of the proposed systems is nearly three times higher than the traditional CARC system, showing an improved efficiency in cooling operations. Additionally, EI-CRAC and E-CRAC demonstrate near 10% and 20% COP enhancement, as well as 15% and 25% increase of Exergy efficiency over benchmark basic CRAC respectively. Furthermore, the research highlights the sensitivity of these systems to various operating conditions, such as pressure drop across ejector nozzle, evaporator temperature, condenser pressure, absorber temperature etc., emphasizing the need for precise control to maximize efficiency. The results of this detailed theoretical thermodynamic analysis with optimization provide a comprehensive understanding of the proposed systems while offering valuable insights for further scope of improvements.

Experimental investigation on the performance of a Solar-Ocean Thermal Energy Conversion system based on the Organic Rankine Cycle

To improve the performance of the Ocean Thermal Energy Conversion (OTEC) system based on the Organic Rankine Cycle (ORC), a solar-assisted cycle is added, and the power generation experimental setup for the Solar-Ocean Thermal Energy Conversion (S-OTEC) system has been constructed. Through energy and exergy analysis, the effects of solar hot water temperature and working fluid flow rate on the components and system performance are investigated, and the performance differences between S-OTEC and OTEC at the same seawater temperature and working fluid flow rate are compared. The results show that: in the S-OTEC system, as the solar hot water temperature is increased from 54 °C to 72 °C, the isentropic efficiency of the working fluid pump and expander is improved, but the heat transfer coefficient of the heat exchanger is decreased. Futhermore, the thermal efficiency, power generation efficiency, and exergy efficiency increase in the ranges of 2.02–3.26 %, 2.93–3.15 %, and 37.93–41.01 %, respectively. When the working fluid flow rate is increased from 124.33 kg/h to 216.73 kg/h, the isentropic efficiency of the working fluid pump and expander as well as the heat transfer coefficient of the heat exchanger are improved. Additional, the thermal efficiency, power generation efficiency and exergy efficiency increase in the ranges of 2.05–2.75 %, 2.46–2.97 % and 38.01–48.13 %, respectively. What's more, the thermal efficiency, power generation efficiency and exergy efficiency of the S-OTEC system can be increased by 154.32 %, 39.33 % and 27.87 % respectively compared to the OTEC system.

Mathematical model of the solar combined cycle power plant using phase change materials in thermal energy storage system (Thermodynamic analysis)

This research presents a novel mathematical framework for optimizing solar combined cycle power plants, with a particular emphasis on the exergy analysis of various superheating heat exchanger configurations used in thermal energy storage. The importance of phase change materials (PCMs) in improving the thermodynamic efficiency of solar combined cycle power plants is emphasized in this study. The investigation includes three configurations, two with a single PCM and one with two PCMs. The use of PCMs is intended to increase storage density, reduce volume, and maintain consistent temperatures, thereby favoring latent energy storage. The model developed evaluates exergy efficiency and output temperature profiles during the charging and discharging processes. The results show that the single PCM configuration has an impressive charging efficiency of 93.12 %, reaching an output temperature of 371 °C in 8 h. The two PCM configurations, on the other hand, achieve even higher efficiency at 94.89 % during charging, with an output temperature of 367 °C over a slightly longer 10-hour period. This comparison emphasizes the benefits of using two PCMs, demonstrating increased exergy efficiency and a marginal increase in output temperature over a single PCM setup. Furthermore, a comparison of the outcomes resulting from the use of a single type of PCM in exchangers reveals that the disparity in PCM melting temperatures causes only minor variations in the system's efficiency. The findings emphasize the significance of optimal PCM utilization for efficient solar energy retention, particularly during periods of low radiation.

Numerical Study on Peak Shaving Performance of Combined Heat and Power Unit Assisted by Heating Storage in Long-Distance Pipelines Scheduled by Particle Swarm Optimization Method

Thermal energy storage in long-distance heating supply pipelines can improve the peak shaving and frequency regulation capabilities of combined heat and power (CHP) units participating in the power grid. In this study, a one-dimensional numerical model was established to predict the thermal lag in long-distance pipelines at different scale levels. The dynamic response of the temperature at the end of the heating pipeline was considered. For the one-way pipe lengths of 10 km, 15 km and 20 km, the response times of the temperature at the distal end were 2.33 h, 2.94 h and 3.54 h, respectively. The longer the flow period, the further the warming-up time is delayed. An optimization scheduling approach was also created to illustrate the peak shaving capabilities of a CHP unit combined with a long-distance pipeline thermal energy storage component. It was demonstrated that the maximum heating load of the unit increased up to 503.08 MW, and the heating load could be expanded in the range of 17.88 MW to 203.76 MW at the minimum electric load of the unit of 104.08 MW. Finally, the particle swarm optimization method was adopted to guide the operating strategy through a whole day to meet both the electric power and heating power requirements. For the optimized case, the comprehensive energy utilization efficiency and the exergy efficiency increase to 64.4% and 56.73%. The thermal energy storage applications based on long-distance pipelines were simulated quantitively and proved to be effective in promoting the operational flexibility of the CHP unit.