Maximum Exergy Efficiency Research Articles

Performance Optimization and Techno-Economic Analysis of an Organic Rankine Cycle Powered by Solar Energy

Abstract To improve the performance of traditional solar power generation systems, a new solar organic Rankine cycle system that can generate electricity and heat is proposed. The system incorporates the separation-flash process, regenerator, and ejector to enhance its efficiency. The optimization of the working fluid, pinch point temperature difference, evaporator outlet dryness, flash dryness, and entrainment ratio is conducted to achieve optimal performance. Aiming at maximum exergy efficiency and minimum levelized energy cost, the operating parameters are further optimized using a multi-objective optimization algorithm. R245fa is the optimal working fluid for the system, offering maximum net output power and thermal efficiency. The optimal performance can be achieved when the pinch point temperature difference is 1 K, evaporator outlet dryness is 0.6, flash dryness is 0.44, and entrainment ratio is 0.29. Moreover, the photovoltaic subsystem can further increase the net output power and thermal efficiency by 15.52% and 15.45%, achieving a maximum net output power and thermal efficiency of 33.95 kW and 10.61%. Additionally, when the solar hot water temperature is 100 °C, pinch point temperature difference is 1.8 K, evaporator outlet dryness is 0.6, flash dryness is 0.65, and entrainment ratio is 0.16, the system can achieve the optimal state of both performance and economy, exhibiting an optimal exergy efficiency and levelized energy cost of 64.1% and 0.294 $/kWh, respectively. Finally, the payback period of system is 3.43 years, indicating the potential for significant economic benefits.

Exergo-economic approach for comprehensive evaluation of the performance of industrial-scale milk and coffee beverage process lines

This study aimed to perform comprehensive analyses of the performance of the industrial-scale production of three different beverages (whole milk, black coffee, and milk coffee) in carton aseptic and glass bottle packaging process lines from raw material to the secondary packed final product by using innovative exergo-economic approach to promote a detailed data for a sustainable, performance-efficient production and economy in beverage industry. System performance efficiencies (energy and exergy) for the whole of production lines and individual processing steps were determined, and the exergo-economic performance of the industrial productions of three different beverages was compared. The maximum overall exergy efficiencies for glass bottle and carton aseptic packaging lines were as 52.57 % and 55.90 %, respectively, in whole milk production whereas the minimum overall exergy efficiencies were for these lines were 47.39 % and 48.67 %, respectively, for milk coffee production. For whole milk, the process steps having the minimum exergy efficiency were the filling step in carton aseptic (23.14 %±1.25) and the seperation step (26.90 %±1.09) in glass bottle packaging lines. For black coffee and milk coffee productions, the process step with the highest improvement potential was the homogenization/deaeration step for both carton aseptic and glass bottle packaging lines. The highest exergy destruction costs were obtained for the milk coffee; 72.52±0.03$/MJ for carton aseptic package and 63.82±1.85$/MJ for glass bottle. The most cost-efficient process was determined to be the black coffee in the carton aseptic packaging line due to the minimum product cost rate (89.71±2.39 $/MJ). It is thought that this study contributes valuable information on the approach of the comparing the performance of different production lines using exergo-economic evaluation.

Solar FPC performance enrichment with Al2O3 / SiO2 nanofluids and hybrid nanofluid

Sustainable energy harvesting plays a crucial role in advancing the goals outlined in the United Nations Sustainable Development Goals (SDGs). Solar flat plate collectors (FPC) are integral to sustainable energy harvesting, aligning closely with several Sustainable Development Goals (SDGs) particularly goals 7, 8, 9, 13 and 17. The heat transfer fluid is one of the most important inputs in the solar flat plate collector system. The improvement in the properties of heat transfer fluid significantly improves the collector efficiency. Though Nanofluid is one of the solutions, this investigation is motivated by the use of Al2O3 and SiO2 along Syltherm 800 in the form of nanofluids and hybrid nanofluid to improve the efficiency of FPC. The Syltherm 800 fluid (BF), Syltherm 800/Al2O3 nanofluid (ANF), Syltherm 800/SiO2 nanofluid (SNF), and Syltherm 800/Al2O3/SiO2 hybrid nanofluid (HNF) were tested and analysed to improve FPC performance. The results exemplified that using HNF improved the outlet temperature to the high of 126.9 °C, the average heat absorption of 4734.5 W, and the heat transfer coefficient (HTCO) of 166.3 W/m2K. The maximum average thermal efficiency and exergy efficiency of about 76.3%, and 49.8% respectively. Based on the experimental outcomes of the Syltherm 800/Al2O3/SiO2 hybrid nanofluid is recommended to improve the FPC thermal performances.

Influence of geometric design variables on the performance of a novel V-shaped cavity receiver

This study presents a novel cavity receiver for parabolic trough concentrators, incorporating a triangular envelope, a trapezoidal cavity, and a semi-circular flow channel. A total of 5120 designs were examined by tuning the rim angle of parabolic mirrors, the width and angle of the receiver's opening, and the depth of the absorber for different operating flow rates and temperatures. Batch simulations of these designs were automated by coupling newly developed and validated models of Monte Carlo ray tracing and semi-analytical 1-D energy balances in SOLTRACE® and MATLAB® to determine the heat fluxes and surface temperatures of the receiver, respectively. The results show that the rim angle must be reduced to maximize sun rays' interception, and the opening angle has the largest impact on performance. All dimensions must be decreased when operating at low flow rates and high temperatures to avoid excessive thermal losses. This results in maximum energy and exergy efficiencies of 74.7 % and 40.7 %, respectively. When operating at low temperatures and large flow rates, the largest energy and exergy efficiencies increase and decrease to 80.5 % and 27 %, corresponding to optimal rim angle, absorber depth, opening width, and opening angle of 60°, 85 mm, 200 mm, and 100°, respectively.

Numerical and Thermodynamic Analysis of the Effect of Operating Temperature in Methane-Fueled SOFC

This study examines the thermodynamic and numerical analyses of a methane-fed solid oxide fuel cell (SOFC) over a temperature range varying between 873 K and 1273 K. These analyses were conducted to investigate and compare the performance of the SOFC under various operating conditions in detail. As part of the thermodynamic analysis, important parameters such as cell voltage, power density, exergy destruction, entropy generation, thermal efficiency, and exergy efficiency were calculated. These calculations were used to conduct energy and exergy analyses of the cell. According to the findings, an increase in operating temperature led to a significant improvement in performance. At the initial conditions where the SOFC operated at a temperature of 1073 K and a current density of 9000 A/m2, it was observed that when the temperature increased by 200 K while keeping the current density constant, the power density increased by a factor of 1.90 compared to the initial state, and the thermal efficiency increased by a factor of 1.45. Under a constant current density, the voltage and power density values were 1.0081 V, 1.0543 V, 2337.13 W/m2, and 2554.72 W/m2 at operating temperatures of 1073 K and 1273 K, respectively. Under a current density of 4500 A/m2, the entropy generation in the cell was determined to be 29.48 kW/K at 973 K and 23.68 kW/K at 1173 K operating temperatures. The maximum exergy efficiency of the SOFC was calculated to be 41.67% at a working temperature of 1273 K and a current density of 1500 A/m2. This study is anticipated to be highly significant, as it examines the impact of temperature variation on exergy analysis in SOFC, validating both numerical and theoretical results, thus providing a crucial roadmap for determining optimized operating conditions.

Triple effect absorption refrigeration systems for the deep recovery of low grade waste heat

With regard to energy conservation, low grade waste heat recovery technology is attracting significant interest. The absorption refrigeration can significantly utilize waste heat. The current researches have devoted little attention to the recovery of waste heat at lower temperature. This paper presents three triple effect absorption refrigeration systems for the deep recovery of low grade waste heat, which can make use of more waste heat as low as 60 °C. The involvement of absorption heat transformer cycle enables the proposed systems to exploit waste heat at lower temperature. The models of three systems are established using EES software. Energy, exergy and economic analysis of three systems are conducted. The results indicate that the best of three systems can achieve a coefficiency of performance of 0.178 and the maximum exergy efficiency is 0.190. The triple effect absorption refrigeration systems not only generate more cold energy, but also demonstrate better economic performance than the previous cascade absorption refrigeration system. Except for the first system, the other two systems achieve reductions of 8.7% and 15.2% in the cost of unit cold energy respectively. This paper provides three novel approaches for producing high grade cool energy from lower temperature of waste heat.

A full solid-state conceptual magnetocaloric refrigerator based on hybrid regeneration

The environmental friendliness and high efficiency of magnetocaloric refrigeration make it a promising substitute for vapor compression refrigeration. However, the common use of heat transfer fluid in conventional passive magnetic regenerators (PMRs) and active magnetic regenerators (AMRs) makes only partial materials contribute to the regeneration process, which produces large regeneration loss and greatly limits the regeneration efficiency and refrigeration performance at high frequency. Herein, we propose a new conceptual hybrid magnetic regenerator (HMR) composed of multiple solid-state high thermal conductivity materials (HTCMs) and magnetocaloric materials (MCMs), in which both HTCM and MCM elements participate in the regeneration process. This novel working mode could greatly reduce regeneration losses caused by dead volume, pressure losses, and temperature nonuniformity in heat transfer substances to markedly improve regeneration efficiency at high working frequencies. Using the experimentally obtained adiabatic temperature change and magnetic work and with the help of finite element simulation, a maximum temperature of 26 K, a dramatically large cooling power of 8.3kW/kg, and a maximum ideal exergy efficiency of 54.2% are achieved at the working frequency of 10Hz for an ideal prototype device of a rotary HMR magnetocaloric refrigerator, which shows potential for achieving an integrative, advanced performance against current AMR/PMR systems.

Experimental and numerical investigation on latent heat/cold stores for advanced pumped-thermal energy storage

Pumped-thermal energy storage plays a pivotal role in large-scale harvesting and utilization for renewable resource endowments with intrinsic properties such as intermittency and instability. Here, we conducted detailed experimental and numerical studies on latent heat/cold stores of Brayton-like pumped-thermal energy storage. A demonstration thermal energy storage system with rated power of 20 kW including phase change materials (PCMs) preparation and structural design of energy storage units is synergistically designed and built. In this paper, the operating mechanism behind the theoretical experiment and control groups that raises the intake temperature through an air heater is uncovered and compared. Moreover, an auxiliary numerical model for further energy and exergy analyses is established to perfect the system-wide assessment. In terms of the first law of thermodynamics, the speed of energy storage and efficiency increase with higher operational pressures. For instance, system properties like roundtrip efficiency can reach up to 0.37 at an operating pressure of 0.7 MPa. As for systematic exergy despite the total destruction of thermal energy storage units amounts to 12.25 kWh the maximum exergy efficiency could reach 0.61 simultaneously.

The influence of using MWCNT/ZnO-Water hybrid nanofluid on the thermal and electrical performance of a Photovoltaic/Thermal system

Rising photovoltaic panel temperatures significantly compromise their performance and lifespan, leading to lower power output and conversion efficiency. Consequently, research on PV panel cooling strategies has gained momentum to address these challenges. This study presents an experimental investigation of a photovoltaic/thermal system's performance using a cooling fluid – a multi-walled carbon nanotube/zinc oxide nanofluid. A comparative analysis is conducted on three PV panels: uncooled, water-cooled, and nanofluid-cooled. Notably, our experiment employed a low mass flow rate (0.156 kg/min), significantly lower than typical values reported in prior literature, and a 0.1 wt% nanofluid concentration. Our primary objective was to evaluate the efficacy of MWCNT/ZnO nanofluid in enhancing the thermal management and overall efficiency of a PVT system. This study focused on the impact of nanofluid on electrical efficiency, thermal efficiency, and exergy performance of the system. The results demonstrate significant improvements. The key findings of this investigation reveal that MWCNT/ZnO nanofluid effectively improves the base fluid's thermal properties, leading to substantial enhancements in both electrical and thermal efficiencies of the PVT system. Compared to the uncooled panel, the nanofluid achieved a maximum temperature reduction of 14.9 °C on the panel surface, a 16.8 % increase in average electrical efficiency, and a maximum thermal efficiency of 51.3 % compared to 45.5 % for water cooling. Moreover, the average overall efficiency of the system with nanofluid cooling reached 58.7 %. Furthermore, the implementation of MWCNT/ZnO nanofluid cooling resulted in a significant boost in maximum overall exergy efficiency, surpassing water cooling and conventional systems by 7 % and 27 %, respectively. Additionally, a 3.5 % reduction in entropy generation and exergy destruction was observed compared to the conventional system.

Energy and exergy analysis for advanced air-conditioning: Comparative evaluation of electrodialysis and aerodynamic thermal methods in liquid-desiccant reconcentration

A comprehensive exploration into the efficiency thresholds of electrodialysis (ED) and conventional aerodynamic thermal (AT) methods for reconcentrating high-concentration solutions is absent in current discourse. To address the gap, this study undertakes explicit derivations and experimental investigations to discern the divergences in energy and exergy performances between these two methods. The experimental results reveal that the ED method exhibits 6.9 times higher energy output/input ratio than the AT method, yet its exergy efficiency is 2.1 times lower in the baseline scenario due to the oversight of spent solution restoration costs. Moreover, the exergy loss of each component is identified by comparing the maximum exergy efficiency with the experimental exergy efficiency. These results help pinpoint measures to address significant exergy loss in key components, thereby boosting system performance. For the ED method, innovation and advancement in membrane technology and materials should be prioritized due to the significant limitations imposed by imperfect membranes. While for the AT method, utilizing renewable energy sources like solar energy to power the heater can greatly enhance system efficiency, considering that exergy loss within the heater is the primary limiting factor.

Thermodynamic analysis of power generation thermal management system for heat and cold exergy utilization from liquid hydrogen-fueled turbojet engine

Hydrogen propulsion is generally treated as the ultimate net zero-emission option for aviation, therein liquid hydrogen storage appears to provide the only feasible solution for aircraft with the constraints imposed by aircraft weight and volume. Hydrogen liquefaction consumes a great amount of energy, which significantly boosts the cost of hydrogen as an aviation fuel. Besides the H2 chemical exergy for combustion to provide thrust, the H2 physical exergy in the form of cold energy is also a kind of high-quality clean energy to produce power output, which offers great opportunities to achieve cost-effective use of hydrogen fuel. Thus, this paper presents a Rankine cycle and H2 direct expansion cycle (RC-DEC) combined power generation thermal management system for the simultaneous utilization of exhaust gas heat exergy and hydrogen fuel cold exergy from the liquid hydrogen-fueled turbojet engine. In the Rankine cycle, the transcritical mode is applied on the hot side while the liquid separation condensation concept is adopted on the cold side to achieve better thermal matchings with heat and cold sources. The hydrocarbon/inert gas binary mixture is proposed as the working fluid of the Rankine cycle. The effects of key thermodynamic parameters and the influence of Para-Ortho hydrogen conversion on system performance are discussed, then a comparison of the mixture working fluid is conducted. Results show that there exists an optimal separation temperature ratio and condensation pressure of RC to obtain maximum total net power output. As the DEC expander inlet pressure increases, the total net power output first increases and then levels off. The introduction of the Para-Ortho hydrogen conversion has a negligible impact on net power output but leads to a significant reduction in the exergy efficiency, which is attributed to the cold energy release nature of Para-Ortho hydrogen conversion. The results of the working fluid comparison indicate that the optimal inert gas retardant for CH4 is Kr, while those for C2H6 and C3H8 are Xe to achieve the maximum net power output and exergy efficiency of the proposed power generation system. Among them, C2H6/Xe(0.6/0.4) obtains the maximum net power output of 2717.9 kW and maximum exergy efficiency of 33.1%, which suggests an opportunity to provide megawatts of electrical power for the aircraft in place of the APU.

Analysis of the exergy performances of a glazed and unglazed PV/T collector under different conditions

The exergy performances of the hybrid PV/T solar collector using different heat transfer fluids was numerically investigated. The mathematical model is based on the energy balance equations applied to each collector element as well as exergy balance founded on the second law of thermodynamics. The governing equations are discretized and solved using Finite difference method based on alternating directions implicit scheme. A comparative study of the exergy performances of the hybrid collector with and without glass cover using nanofluid Cu−water, distilled water and water-EG mixture as transfer fluids is conducted. The results showed that Cu−water nanofluid enhances the total exergy of the collector by 1.6% and 2.7% highest than water and water-EG respectively. However, regarding the thermal exergy, water-EG mixture is the best fluid which allows to improve the collector production by 17% and 28.5% than water and Cu−water respectively. The maximum energy and exergy efficiencies reached over the day are around 70% and 15% respectively. In addition, it is found that the overall exergy produced by the unglazed system is 6.45% higher than the collector with glass cover. While, the total energy yield of this latter is 26% higher than the system without cover. The effect of operating parameters on the collector exergy effectiveness is analyzed and discussed in this work.

Investigation of the performance of cathode supported solid oxide fuel cell with energy and exergy analysis at different operating temperatures

In this research, the performance analysis of a cathode-supported solid oxide fuel cell (SOFC) with an active cell area of 0.0834 m2 and a cathode thickness of 750 µm was carried out under three different operating temperatures (973 K, 1073 K and 1173 K). The power density and cell potential were calculated by determining the losses in the cell at 8 different current densities (1500 A/m2 - 5000 A/m2) for each operating temperature. It was observed that ohmic losses in SOFC have a lower effect on the cell potential compared to other losses. An increase of the operating temperature by 100 K resulted in a decrease in ohmic losses of 3.36×10-8 V under constant current density (CD). In addition, the rise in CD negatively affected all the losses in the cell and decreased the cell voltage. The exergy and energy analysis of SOFC was carried out by calculating the thermal efficiency, exergy destruction, entropy production and exergy efficiency for various operating parameters. An increment of 200 K in the operating temperature increased the thermal efficiency by approximately 2 times at a CD of 5000 A/m2. Also, the minimum entropy production was obtained at an operating temperature of 1173 K and a CD of 1500 A/m2. In this case, the entropy production was calculated as 2.63 kW/K, resulting in a maximum exergy efficiency of 66.93%.

Influence of solar insolation on energy and exergy efficiency of a rectangular duct solar air heater with various types of V rib roughness: An analytical approach

In the current work, the energy and exergy evaluations for several V ribs in a rectangular duct SAH are evaluated and compared with smooth SAH for a heat flux range of 800 to 1200 W/m2. The analysis uses correlations for the friction factor and Nusselt number for different V ribs that have been developed by various researchers. The investigators' recommended optimum design parameters are employed to analyse the specific rib. The thermohydraulic and exergy efficiency of various V ribs are evaluated using the MATLAB code and comparisons of the findings are provided. The staggered discrete multi-V-shape rib configurations achieves the maximum thermal efficiency of 76.63% for Reynolds number of 21,000 and solar radiation heat flux of 800 W/m2. Corresponding to a Reynolds number of 21,000 and solar radiation heat flux of 1200 W/m2, the perforated multi-V-shaped rib gives a maximum thermohydraulic efficiency of 74.82%. At 800 W/m2 of heat flux, a maximum exergy efficiency of 5.17% is obtained for the staggered discrete multi-V-shape rib configuration at lower Reynolds number. Whereas, corresponding to higher Reynolds number, the maximum exergy efficiency is 4.18% for perforated multi-V rib.

Cost and thermodynamic analysis of wind-hydrogen production via multi-energy systems

With rising temperatures, extreme weather events, and environmental challenges, there is a strong push towards decarbonization and an emphasis on renewable energy, with wind energy emerging as a key player. The concept of multi-energy systems offers an innovative approach to decarbonization, with the potential to produce hydrogen as one of the output streams, creating another avenue for clean energy production. Hydrogen has significant potential for decarbonizing multiple sectors across buildings, transport, and industries. This paper explores the integration of wind energy and hydrogen production, particularly in areas where clean energy solutions are crucial, such as impoverished villages in Africa. It models three systems: distinct configurations of micro-multi-energy systems that generate electricity, space cooling, hot water, and hydrogen using the thermodynamics and cost approach. System 1 combines a wind turbine, a hydrogen-producing electrolyzer, and a heat pump for cooling and hot water. System 2 integrates this with a biomass-fired reheat-regenerative power cycle to balance out the intermittency of wind power. System 3 incorporates hydrogen production, a solid oxide fuel cell for continuous electricity production, an absorption cooling system for refrigeration, and a heat exchanger for hot water production. These systems are modeled with Engineering Equation Solver, and analyzed based on energy and exergy efficiencies, and on economic metrics like levelized cost of electricity (LCOE), cooling (LCOC), refrigeration (LCOR), and hydrogen (LCOH) under steady-state conditions. A sensitivity analysis of various parameters is presented to assess the change in performance. Systems were optimized using a multi-objective method, with maximizing exergy efficiency and minimizing total product unit cost used as objective functions. The results show that System 1 achieves 79.78 % energy efficiency and 53.94 % exergy efficiency. System 2 achieves efficiencies of 55.26 % and 27.05 % respectively, while System 3 attains 78.73 % and 58.51 % respectively. The levelized costs for micro-multi-energy System 1 are LCOE = 0.04993 $/kWh, LCOC = 0.004722 $/kWh, and LCOH = 0.03328 $/kWh. For System 2, these values are 0.03653 $/kWh, 0.003743 $/kWh, and 0.03328 $/kWh. In the case of System 3, they are 0.03736 $/kWh, 0.004726 $/kWh, and 0.03335 $/kWh, and LCOR = 0.03309 $/kWh. The results show that the systems modeled here have competitive performance with existing multi-energy systems, powered by other renewables. Integrating these systems will further the sustainable and net zero energy system transition, especially in rural communities.

Experimental performance investigation of a novel movable greenhouse solar dryer for drying potato slices in the arid climate of India

In the present study, the drying of 5 kg potato slices in a small-size movable greenhouse solar dryer is performed experimentally to determine its performance. The study was carried out at Ajmer, India, in May 2022, and the results demonstrated that the dryer could heat the air to a maximum temperature of 59.5°C with a daily average air temperature of 56.2°C under the no-load test for an average ambient temperature and a solar intensity of 39.8°C and 676 W/m2. Under load, the moisture content of potato slices was reduced to 6.3%, 21.1% and 55.9% from an initial moisture content of 85% (w.b.) in the greenhouse solar dryer, open sun and under shade, respectively, in 5 h. However, for complete drying up to 6.3% moisture content, open sun drying and shade drying took 6 and 9.5 h, respectively. Maximum exergy inflow and outflow of 13.2 W and 9.2 W and maximum exergy efficiency of 69.6% were attained during the drying. The payback period for the developed greenhouse solar dryer was 0.35 years for an expected life of 10 years. Also, the efficiency of the developed greenhouse dryer under load was 26.9%.

Thermo-economics, emissions, and sustainability comparison of a novel hybrid evaporative cooled solid oxide fuel cell-recuperated gas turbine with conventional system

A novel integration of a solid-oxide fuel cell to an evaporative intercooled recuperated gas turbine (SOFC-EIc-RGT) is presented. The goal of this integrated system is to reduce power consumption associated with the work of compression and hence augment power plant performance. The proposed system is compared with a conventional evaporative intercooled recuperated gas turbine (EIc-RGT). Both energetic and exergetic performance of the systems were carried out. A range of sustainability indexes were evaluated for each component of both configurations. The sustainability index helps to identify the impact on the environment. A novel entropy generation number, a dimensionless number, was proposed to identify “the ratio of component’s irreversibility to the heat supplied.” The maximum energy and exergy efficiencies for SOFC-EIc-RGT were nearly double that of the EIc-RGT. A novel performance map and emission map were plotted for power plant design engineers and researchers to analyse CO and NOx emissions with various operating parameters for EIc-RGT and SOFC-EIc-RGT. This economic analysis makes the system more reliable, which includes environmental and fuel cost rates.

A novel data center free radiating system driven by waste heat and wind energy system (DCFRWWs) and its operation performance analysis

Refrigeration equipment for data centers consumes a significant portion of global electricity, resulting in high Power Usage Effectiveness (PUE) values and increased entropy of the data center. To address these challenges, this study proposes a novel data center free radiating system driven by waste heat and wind energy (DCFRWWs). This approach recovers low-grade heat energy from the hot air heated by the central processing units (CPUs) and transform it into work. Unlike conventional cooling systems, the DCFRWWs do not require additional energy to meet CPU cooling demands and can effectively suppress the entropy increase of the data center. The Bernoulli equation was used to establish the mathematical model for DCFRWWs, which explained the underlying mechanisms of pipeline wind speed and the influence of ambient wind speed and pipeline inlet temperature on system operating characteristics. In addition, this study employed pipeline height and diameter as decision variables, while maximizing exergy efficiency served as the optimization objective. To obtain the optimal pipeline size (height and diameter) that is effective under real-world experimental conditions, the optimization calculations were conducted using weather data from Qinhuangdao. To verify the reliability and accuracy of the model, an experimental system was constructed, and the simulation results indicated that the relative error rates for the three key parameters are as follows: pipeline wind speed (33.09%), pipeline inlet temperature (0.59%), and CPU temperature (3.85%). A single factor analysis was performed on 14 different operating conditions to analyze the operating characteristics of the DCFRWWs. Moreover, the applicability verification conducted in three distinct cities across different regions suggest that the system is indeed suitable for diverse settings. The DCFRWW system, utilizing the dual forces of the chimney effect of waste hot air in pipelines and the extraction force generated by unpowered roof ventilator, achieves the objective of free heat dissipation. Furthermore, the DCFRWWs can not only be applied in the field of data center cooling but also serves as a thermodynamic reference for low-grade waste heat recovery in other sectors, thereby further expanding the scope of direct utilization of wind energy.

Transcritical [formula omitted] precooled single mixed refrigerant natural gas liquefaction process: Exergy and Exergoeconomic optimization

This study proposes a two-stage transcritical CO2 pre-cooled single mixed refrigerant process to investigate the potential improvement in exergy efficiency and exergoeconomic performance. Two different objective functions, namely maximizing exergy efficiency and minimizing the unit cost exergy of LNG, were optimized using the particle swarm optimization algorithm to compare the performance of the CO2 pre-cooled single mixed refrigerant process with single mixed refrigerant process. The results of the first objective function indicate a higher exergy efficiency of the CO2 pre-cooled single mixed refrigerant process, with an increment of 7.56%. This improvement can be attributed to not only the lower total power consumption but also the better matching of the temperature-difference composite curve, particularly the location of the pinch temperature at the warm end of the heat exchanger. Additionally, the exergy destruction of the CO2 pre-cooled single mixed refrigerant process was 30.12% lower than that of the single mixed refrigerant process. The second objective function demonstrated that the CO2 pre-cooled single mixed refrigerant process had a unit exergy cost value of 7.46 $/GJ, which was 11.98% lower than the single mixed refrigerant process. In conclusion, the proposed process contributes to energy saving throughout the LNG chain. Previous studies on the transcritical CO2 precooling cycle were limited to only one-stage configuration paving the way for thermodynamic efficiency enhancement by modifying the design of the process. This study also considers the effects of two objective functions maximizing exergy efficiency and minimizing the unit exergy cost of LNG on the optimization of decision variables which has not been discussed yet in the literature. Moreover, innovative exergoeconomic analysis presents a comprehensive criterion for evaluating economic performance, providing guidance for the initial construction and sustainable development of LNG plants.

Performance enhancement of the solar still using textiles and polyurethane rollers

The acquisition of clean drinking water in regions with limited power sources has been a challenge of paramount concern. Solar stills have emerged as a popular and sustainable option for obtaining clean water in such regions. This process involves employing solar radiation to heat up water, which is then condensed to obtain potable water. The present study introduces a solar still system that is both cost-effective and energy-efficient, while simultaneously ensuring sustainability. Fabric-coated polyurethane rollers with capillary action enhance evaporation area, leading to notable performance improvements. Water vapour condensed on the cooling chamber's inclined aluminium plate and collected in the distillate chamber within the solar still. The thermal, energetic, and economic performance and productivity of the proposed model were evaluated. The fabricated solar still boasted maximum instantaneous system efficiency and exergy efficiency of approximately 62.16% and 7.67%, respectively. This system's cost-effectiveness and performance improvements are particularly noteworthy. The daily average distillate productivity of the proposed still was estimated at 1.14 L/m2, resulting in an annual production rate of 416.54 L/year. The estimated cost of producing 1 L of distillate was 0.023 $.