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The flow field is a crucial factor affecting the performance of proton exchange membrane fuel cells (PEMFCs). To enhance cell performance, this paper proposes a radial serpentine flow field. Using COMSOL software, a three-dimensional steady-state model is established for numerical simulation, focusing on the number of channels and inlet flow rate. The study analyzed cell output performance, velocity distribution, water-oxygen distribution, and pressure drop. Results indicate that increasing the number of channels can achieve two improvements: firstly, the channel length becomes shorter, improving gas supply capacity and gas uniformity; secondly, increasing the number of channels creates a shunt effect on the gas, significantly reducing the pressure drop. Optimal cell performance is observed when the number of channels is six and the inlet flow rate is 0.4 m/s. Compared to the traditional serpentine flow field (SFF), the radial serpentine flow field exhibited substantial advantages. Notably, it showed significant improvements in oxygen distribution uniformity and reduced pressure loss. At maximum power density, the oxygen distribution uniformity in Case 5 increased by 48.8% compared to SFF. Additionally, due to overcoming the significant pressure drop issue in the SFF, the radial serpentine flow field notably improved net power output, showing a 6% increase compared to the SFF. [ABSTRACT FROM AUTHOR]

In order to boost the cycles' thermal efficiency, their power generations and reduce industrial equipment costs the growing need to develop and improve the performance of power generation cycles has provided the basis for research. Currently, there are quite a few investigations aiming to consider Kalina cycles as a power generation system using low-grade heat sources. In this research, firstly KCS-11 (Kalina Cycle System11) as well as Ekalina cycle (enhanced KCS-11 with ejector) has been studied. The SEKalina cycle, which is a modification of Ekalina cycle, is introduced, examined, and simulated by EES software. In the structure of the EKalina, the throttle valve and absorber are removed and the ejector is used instead. The use of the ejector reduces pressure at the turbine's outlet and augments the difference between the enthalpy of two turbine ends, leading to enhancement of the thermal proficiency and net power output. Including an ejector and benefited from a split configuration, SEKalina cycle proposes a potential for efficiency improvement. Examining the results of the cycles, it is found that by employing the SEKalina cycle, compare to the two previously introduced cycles (EKalina and KCS-11), the thermal efficiency and net power output rise significantly. Moreover, as a result, the net power output in SEKalina cycle is 2% higher than that of EKalina cycle. [ABSTRACT FROM AUTHOR]

Copyright of Natural Gas & Oil is the property of Editorial Department of Natural Gas & Oil and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The critical temperature (Tcr) is one of the important thermophysical properties of the working fluid, and it has a crucial effect on the output parameters of thermodynamic cycles used for power generation. This study aims to show the effect of the working fluids Tcr on the cycle thermal performance (thermal efficiency (ηth) and net-work output (Wnet) at the same heat source/heat sink temperature. For this purpose, 13 alkanes and 10 halogenated alkanes working fluids were investigated. Two different kinds of subcritical cycles, namely the Organic Rankine Cycle (ORC) and Trilateral Flash Cycle (TFC), were investigated. Pure and mixed (with various compositions) working fluids were used. Finally, it has been shown that although the critical temperature is an important factor, it can be correlated with output parameters only by using chemically similar working fluids.

To meet the continuous demand for energy of industrial as well as commercial sectors, researchers focus on increasing the power generating capacity of gas turbine power plants. In this regard, the combined cycle is a better solution in terms of environmental aspects and power generation as compared to a simple gas turbine power plant. The present study is the thermodynamic investigation of five possible air bottoming combined cycles in which the topping cycle is a simple gas turbine cycle, regenerative gas turbine cycle, inter-cool gas turbine cycle, reheat gas turbine cycle, and intercool-reheat gas turbine cycle. The effect of pressure ratio of the topping cycle, the turbine inlet temperature of topping cycle, and ambient temperature on net power output, thermal efficiency, total exergy destruction, and exergetic efficiency of the combined cycle have been analyzed. The ratio of the net power output of the combined cycle to that of the topping cycle is maximal in the case when the topping cycle is a simple gas turbine cycle. The ratio of net power output and the total exergy destruction of the combined cycle to those of the topping cycle decrease with pressure ratio for all the combinations under study except for the case when the topping cycle is the regenerative gas turbine cycle.

This study presents the energy and exergy analysis for unit three of the Al-Mosyab thermal power plant, which has a capacity of 225 MW. The energy losses, exergy destruction and second law efficiency, are computed. The objective is to obtain a comprehensive prediction of improvement that will happen in the performance. Results showed that the second law efficiency of the cycle is 34.91%, and the maximum exergy destruction was at the boiler by 86%. The plant's second law efficiency improves successfully to 37.65%, and 0.67 kg/s of the fuel mass flow rate can be saved. As well as, the total exergy destruction decreased by 10.8% at increasing the feedwater temperature to 230 °C. The second law efficiency has enhanced to 35.74% and 1.32% of the exergy destruction drops when reducing the mass flow rate of the desuperheater spray water of the main steam. The second law efficiency increased by 2.27%, and 1.25% of the total exergy destruction was reduced when the hot reheat pressure increased. Moreover, the analysis reveals that the plant's second law efficiency has grown by 6.45% and that the total exergy destruction has fallen by 3.31% when cold reheat steam temperature is reduced. [ABSTRACT FROM AUTHOR]

Kalina cycle and organic Rankine cycle have different optimal heat source temperatures. To realize cascade utilization of low-temperature waste heat, a model of novel Kalina-organic Rankine combined cycle is established by using a dual-pressure Kalina cycle as top cycle and a dual-pressure organic Rankine cycle as bottom cycle, and constructal thermodynamic optimization is carried out by uniting constructal theory and finite-time thermodynamics. With the total turbine volume and total heat exchanger area being fixed, the optimal tube external diameters of the evaporators in the dual-pressure Kalina cycle and dual-pressure organic Rankine cycle are obtained by maximizing the net power output of the Kalina-organic Rankine combined cycle system. The results prove that the net power outputs of the Kalina-organic Rankine combined cycle system after four progressive optimizations are increased by 2.62%, 5.41%, 15.05% and 16.17%, respectively, compared to the initial one. In the quartic constructal thermodynamic optimization, the optimal tube external diameters of the high- and low-temperature evaporators in the DPKC are 0.024mand 0.023m, respectively, and the those in the DPORC are 0.020mand 0.024m, respectively. The results obtained will improve the performance of the KORCC and promote the efficient utilization of waste heat.

A new methodology for the systematic study of thermoelectric generator (TEG) design and economic analysis is presented, with the objective of assessing the performance and financial feasibility of small-scale TEG installations, for 4 leading candidate thermoelectric materials. Temperature of a steam trap pipe surface were measured at the University of California Davis Pilot Brewery, and device performance was modeled using the finite-element modeling software ANSYS. The model integrated temperature-dependent material properties from leading candidate thermoelectric materials and experimental time-variant temperature data. Calculated power outputs were utilized in a net present value (NPV) framework to assess the financial feasibility and economic implications of small scale TEG installations, as well as to address the aspects of TEG research, design and implementation which have potential for rapid and substantive improvement. This model, along with case study results, provides a powerful platform for analyzing the performance of real-world systems and can be used to predict where further technological development on TEG materials and devices would be most effective. It is found that a BiSbTe based TEG generated the highest power output at the measured temperatures and consequently resulted in the highest NPV at the end of 25 years. Sensitivity analysis of the NPV revealed a strong dependence on the heat-exchanger cost, highlighting the importance of efficient heat transfer design. The zT necessary for a 7-year payback period as a function of the capital cost and hot-side temperature was also calculated for a SiGe based TEG.

To meet the continuous demand for energy of industrial as well as commercial sectors, researchers focus on increasing the power generating capacity of gas turbine power plants. In this regard, the combined cycle is a better solution in terms of environmental aspects and power generation as compared to a simple gas turbine power plant. The present study is the thermodynamic investigation of five possible air bottoming combined cycles in which the topping cycle is a simple gas turbine cycle, regenerative gas turbine cycle, inter-cool gas turbine cycle, reheat gas turbine cycle, and intercool-reheat gas turbine cycle. The effect of pressure ratio of the topping cycle, the turbine inlet temperature of topping cycle, and ambient temperature on net power output, thermal efficiency, total exergy destruction, and exergetic efficiency of the combined cycle have been analyzed. The ratio of the net power output of the combined cycle to that of the topping cycle is maximal in the case when the topping cycle is a simple gas turbine cycle. The ratio of net power output and the total exergy destruction of the combined cycle to those of the topping cycle decrease with pressure ratio for all the combinations under study except for the case when the topping cycle is the regenerative gas turbine cycle. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The paper presents a new numerical solution as a method for the thermodynamic cycle of a thermoacoustic engine estimation. A mathematical solution for calculating the gas averaged velocity was developed. The proposed method uses acoustic impedance of the engine's thermal core and the dynamic pressure distribution and enables to calculate gas averaged velocity and prower output. The results of power output and thermal efficiency obtained from the numerical solution and experiments performed for the tested traveling-wave engine and presented in this paper. Relative deviation between theoretical and experimental values of thermal efficiency was 10.7%. This study provides a useful approach for the calculation of the produced power of thermoacoustic engines and can be useful in designing of cycle where the power maximization is crucial.

A new, experimental method based on air flow rate rather than current is presented to optimize operating parameters for the stacks and systems of proton exchange membrane fuel cells (PEMFCs) for maximizing their net power. This approach is illustrated for a commercial 18 kW PEMFC module. The impact of contamination pressure drop across the cathode air filter is also investigated on the compressor behavior. It is further shown that a 4V reduction in the compressor voltage reduces its power consumption by 9.1%. Using the 3D graphs of the power-pressure-flow data, it is found that the stack pressure of 180 kPaa is superior to the higher tested pressures as it enhances the net power by 7.0 and 13.7% at different conditions. Application of the present study will lead to the development of PEMFCs with higher power output by optimizing stack pressure, stoichiometry and air flow to properly deliver the system design specifications. [Display omitted] • A new method based on air flow, rather than current, to maximize PEMFCs power. • A low stack pressure of 180 kPaa enhances the PEMFC power output by 13.7%. • A 4V difference in the compressor voltage reduces its power consumption by 9.1%. • Stack power increases/reduces with air stoichiometry at constant currents/flows. • Compressors behave unstably for contaminated filters showing a high pressure drop. [ABSTRACT FROM AUTHOR]

• A single-well enhanced geothermal combined organic Rankine cycle system is proposed. • Detailed thermodynamic model that couples the wellbore, reservoir, and organic Rankine cycle is built. • The effect of various parameters on the ORC system performance is probed. • The optimal operation parameters of SEGS ORC are obtained. This study proposes a single-well enhanced geothermal system (SEGS) to mitigate the high-risk of traditional Enhanced Geothermal Systems (ESGs) with two or more wells and enhance the general applicability. A detailed thermodynamic model that couples the wellbore, reservoir, and organic Rankine cycle is built. For the reservoir, a three-dimensional flow and heat transfer model featuring a discrete fracture network is employed. The effects of injection flow rate, injection temperature, branch well length, and branch well spacing on net output work, pump power consumption, thermal efficiency, and exergy efficiency have been investigated. The results indicate that an increase in the injection flow rate improves the shaft power of the expander and the power consumption of the injection pump. An optimal flow rate of 30 kg/s is identified, which maximizes the annual net power output to 1221.2 kW. Additionally, an increase in the injection temperature is found to enhance the buoyancy effect, thereby improving both thermal and exergy efficiency, and reducing the power consumption of the injection pump. The maximum net output power is achieved at an injection temperature of 60 °C. The study also notes that the branch well length has a negligible effect on thermal and exergy efficiency and expander shaft work. However, a longer branch well length contributes to a decrease in the power consumption of the injection pump and an increase in the net power output. Finally, it is observed that increasing the lateral well spacing slows the rate decay of the production temperature. A spacing of 360 m is found to yield a maximum annual net output power of 1259.4 kW. In conclusion, this study offers significant insights and practical guidance for the development and utilization of SEGS, demonstrating its potential as an effective alternative to conventional EGS methodologies. [ABSTRACT FROM AUTHOR]

In this study, an electro-thermo-structural coupled numerical analysis is conducted to evaluate the thermal, electrical, and structural performances of a thermoelectric generator system. The hot heat exchangers with six different internal fin structures are compared in terms of temperature distribution, pressure drop, net power output, overall efficiency, and stress using the coupled numerical approach. Experiments are conducted on the heat exchanger with straight fins to validate the accuracy and reliability of the proposed coupled analysis. The hot gas outlet temperature, coolant outlet temperature, power output, and stress predicted using the coupled approach are validated within errors of 1.5, 6, 3, and 5.45%, respectively. Among the proposed heat exchanger designs, the heat exchanger with inclined fins and that with the combination of inclined and perpendicular fins exhibit higher net power outputs and overall efficiencies. The heat exchanger with the inclined fins and that with the combined fins exhibit overall efficiencies of 1.81 and 1.88% and net power outputs higher by 29 and 35%, respectively, than those of the heat exchanger with straight fins at the hot gas temperature of 600 °C. At the hot gas temperature 600 °C, the maximum stresses induced in the heat exchanger with the inclined fins and that with the combined fins are approximately 25.87 and 26.53 MPa, respectively, which are lower than the maximum allowable stress of 70 MPa. [ABSTRACT FROM AUTHOR]

The purpose of this research is the calculation of the exergy destruction of the single-flash and double-flash cycles of a geothermal power plant located on the ladder of the 233 m Cerro Prieto volcano, on the alluvial plain of the Mexicali Valley, Mexico. The methodology developed in this research presents thermodynamic models for energy and exergy flows, which allows determining the contribution of each component to the total exergy destruction of the system. For the case-base, the results indicate that for the single-flash configuration the efficiency of the first and second law of thermodynamics are 0.1888 and 0.3072, as well as the highest contribution to the total exergy destruction is provided by the condenser. For the double-flash configuration, the efficiency of the first and second law of thermodynamics are 0.3643 and 0.4983. The highest contribution to the total exergy destruction is provided by the condenser and followed by the low-pressure turbine.

Thermoelectric waste heat recovery can improve the thermal efficiency of internal combustion engines and reduce CO2 emissions. In this study, a mathematical optimization using a genetic algorithm method is applied to obtain the optimal fin parameters of a rectangular offset-strip fin heat exchanger, used with an automotive thermoelectric generator (TEG) system. Three fin parameters are considered (fin spacing, fin thickness and fin height). Their effect on the exhaust pumping power, the exhaust heat transfer coefficient and the system performance is explored. The main goal is to maximize the net power output of the system. Results show that fin spacing has the most significant effect on the system performance. Moreover, when fin spacing is reduced below 0.5 mm, a negative net power output is obtained. By comparing the performance of stainless-steel (SS) and copper heat exchangers, it was found that the SS heat exchanger requires smaller fin spacing and fin height, which induces a higher pressure drop. TEGs with higher maximum operating temperature will allow further utilization of the exhaust heat, without a decline in performance due to overheating. Finally, a maximum net power output of 553.3 W is achieved using the copper heat exchanger and commercial bismuth-telluride (Bi2Te3) thermoelectric modules. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is experimentally comparing of organic Rankine cycle (ORC) system, by using R245fa, R123 and their mixtures to generate maximum net power on simulated low-temperature industrial waste heat. Four mass fractions of R245fa:R123 have been injected into the system with the ratios of 1:0, 2:1, 1:2 and 0:1 to test the system performance separately. To imitate industrial low-temperature waste heat, the heat source temperature is fixed at 110 °C and 120 °C with specified mass flow rate of heat source. Focusing on the change of mass flow rate of working fluid and expander inlet superheating, experiment results show that the system heat input increases when mass flow rate of working fluid increases. All four mass fractions of working fluids generate maximum net power when the system mass flow rate is around 0.15 kg/s. The case of pure R245fa generates a maximum net power 1.56 kW with an electrical efficiency of about 3.9% when heat source temperature is fixed at 110 °C. While, the case of mixture R245fa:R123 = 2:1 generates a maximum net power 1.66 kW with an electrical efficiency of about 4.4% when heat source temperature input is fixed at 120 °C. [ABSTRACT FROM AUTHOR]

This paper presents the performance evaluation of several combinations of working fluids for a new heat recovery cogeneration system which combines an Organic Rankine Cycle (ORC), a Vapor Absorption Cycle (VAC) and a Vapor Compression Cycle (VCC). NH 3 –NaSCN is chosen as the working fluid in the VAC. Seven different refrigerants in the ORC-VCC were studied to identify the fluid that would allow the overall system to achieve a high efficiency in the tropical region. These fluids were chosen because of their low Global Warming Potential and Ozone Depletion Potential. A thermodynamic simulation allowed to set the appropriate operating conditions of the VAC. Subsequently, energy and exergy analyses showed that R717 is the appropriate working fluid for system operation in the tropical region. For this fluid, the highest values of cooling capacity, net power output, thermal efficiency, exergy efficiency and exergy destruction of the system were respectively 1205 kW, 158.3 kW, 64.32%, 39.39% and 690.4 kW for VCC evaporation temperature of 15 °C, for ORC-VCC condensation temperature of 40 °C and for ORC steam generator outlet temperature of 219.7 °C. The most exergy-destroying components are the steam generator and the ORC/VCC condenser with 57.29% and 22.58%, respectively. • Vapor recovery at the turbine outlet improves overall system performance. • Electricity produced is not influenced by the operation of the VAC cycle. • For R717, cold production slightly increases with ORC/VCC condensation temperature. • Cold is produced by the VAC by recovering the waste heat at the turbine outlet. [ABSTRACT FROM AUTHOR]

The performance analysis of a supercritical organic Rankine cycle system driven by exhaust heat using 18 organic working fluids is presented. Several parameters, such as the net power output, exergy efficiency, expander size parameter (SP), and heat exchanger requirement of evaporator and the condenser, were used to evaluate the performance of this recovery cycle and screen the working fluids. The results reveal that in most cases, raising the expander inlet temperature is helpful to improve the net power output and the exergy efficiency. However, the effect of the expander inlet pressure on those parameters is related to the expander inlet temperature and working fluid used. Either lower expander inlet temperature and pressure, or higher expander inlet temperature and pressure, generally makes the net power output more. Lower expander inlet temperature results in larger total heat transfer requirement and expander size. According to the screening criteria of both the higher output and the lower investment, the following working fluids for the supercritical ORC system are recommended: R152a and R143a.

Efficient electrode materials are essential to convert salinity gradient energy into oxidative degradation energy and electrical energy by reverse electrodialysis reactor (REDR). In this context, comparative experiments of REDR using different anodes (Ti/IrO 2 –RuO 2 , Ti/PbO 2 and Ti/Ti 4 O 7) were conducted. The effects of output current and electrode rinse solution (ERS) flowrate on mineralization efficiency and energy output were discussed. Results demonstrated that the COD removal rate(η COD) rose almost linearly with output current and ERS flowrate when using Ti/Ti 4 O 7 anode, but excessive operating conditions caused a slow increase or even decrease of η COD when using Ti/IrO 2 –RuO 2 or Ti/PbO 2 anodes. The order of electrode system potential loss (E ele) for the three anodes was Ti/Ti 4 O 7 > Ti/PbO 2 > Ti/IrO 2 –RuO 2. High E ele was beneficial to η COD but had a negative effect on the net output power (P net) of REDR. Regardless of the applied anodes, increasing the current and decreasing the ERS flowrate was detrimental to P net due to higher E ele. Based on these findings, four energy efficiency parameters were defined to evaluate energy recovery from multiple perspectives by linking energy output with mineralization capacity. They were electrode efficiency (η ele), energy efficiency (EE), general current efficiency (GCE) and energy consumption (EC), respectively. Results showed that REDR with Ti/Ti 4 O 7 anodes and suitable operating conditions achieved the optimal energy indicators and mineralization efficiency, which provided an efficient and economical option for wastewater treatment and energy recovery. [Display omitted] • Developed efficient and suitable anode materials for REDR water treatment system. • Four energy indices(η ele , EE , GCE and EC) were used to assess performance of REDR. • Oxidative degradation energy was ranked as Ti/Ti 4 O 7 > Ti/PbO 2 > Ti/IrO 2 –RuO 2. • The anode with high oxidation potential had high removal rate but low output power. • REDR using Ti/Ti 4 O 7 obtained the maximum energy recovery and removal rate. [ABSTRACT FROM AUTHOR]

This article demonstrates a study on finite-time thermodynamic assessment and analysis of a Stirling heat engine. Finite-time thermodynamics is performed to specify the net thermal efficiency and power output of the Stirling system with finite-rate heat transfer, regenerative heat loss, conductive thermal bridging loss and finite regeneration process time. The model investigates effects of the inlet temperature of the heat source, the volumetric ratio of the engine, effectiveness of heat exchangers and heat capacitance rates on the net power output and thermal efficiency of the engine. Output power of the Stirling engine is maximized under two optimization scenarios. In the first scenario, the higher working temperature of the Stirling engine is considered as a decision design parameter (decision variable) while in the second scenario, in addition to the higher working temperature, the temperature ratio of the engine is also considered as a design parameter. Furthermore, the thermal efficiency of the cycle corresponding to the magnitude of the maximized power of the engine is evaluated. Finally, sensitivities of results towards shift in the thermal parameters of the engine are studied. [ABSTRACT FROM AUTHOR]

Compared with the ORC (organic Rankine cycle) and the steam Rankine cycle, the CDTPC (CO 2 (carbon dioxide) transcritical power cycle) shows a higher potential in converting middle-grade waste heat into useful work. In this paper, we propose a novel type of single-pressure, multi-stage CDTPC to overcome the shortcomings of the CDTPC in utilizing waste heat of exhaust gas from gas turbines or internal combustion engines. System parameter optimization is carried out in various CDTPC to achieve the maximum net power output of cycle by using the genetic algorithm(GA). A comparative study between the existing CDTPC and the proposed novel type of CDTPC with the same exhaust gas temperature T gi (250–500 °C) at the inlet of the gas heater shows that the novel type of CDTPC can increase the net power output by 3.9–26.3% and decrease the optimum working pressure by 13.2–31.0%. If exhaust gas is non-corrosive, waste heat can be utilized more effectively by the double-stage CDTPC when 250 °C ≤ T gi ≤ 412 °C and by the three-stage CDTPC when 412 °C < T gi ≤ 500 °C. However, if the exhaust gas is corrosive, waste heat is utilized more effectively by the single-stage CDTPC when 250 °C ≤ T gi ≤ 338 °C and by the double-stage CDTPC when 338 °C < T gi ≤ 500 °C. In addition, the effect of the regenerator on the thermal performance of various CDTPC is studied. [ABSTRACT FROM AUTHOR]

A modified recompression S–CO 2 Brayton cycle (RCSCBC) that combines advantages of the preheated S–CO 2 Brayton cycle (PSCBC) is proposed to recovery the gas turbine waste heat. The modified RCSCBC cycle model considers finite temperature difference heat transfer between heat reservoir and working fluid, irreversible compression, irreversible expansion and other irreversibility losses. It is established by using finite time thermodynamics. Influences of various parameters on net power output (NPO) and thermal efficiency (TEF) of the cycle are analyzed. Performances of the modified RCSCBC are compared with those of the unmodified RCSCBC and the PSCBC. Performance optimizations are performed by optimizing diversion coefficients and heat conductance distributions among heat exchanges. The results show that the first diversion coefficient is the main factor affecting TEF, and there are optimal first diversion coefficient and pressure ratio to maximize the cycle TEF; the second diversion coefficient is the main factor affecting the NPO, and there is an optimal second diversion coefficient to maximize the NPO. Compared with unmodified RCSCBC, NPO of the modified RCSCBC can be increased by 14.34%, and TEF can be increased by 10.89%. Compared with PSCBC, NPO can be increased by 14.20%, and TEF can be increased by 16.60%. [Display omitted] • A modified recompression S–CO 2 Brayton cycle is proposed. • Finite time thermodynamics is applied to analyze and optimize cycle's performance. • Net power output and thermal efficiency are analyzed and optimized. • Thermodynamic performances are compared with those of other S–CO 2 Brayton cycles. • Power and efficiency increase by 14.34% and 10.89% compared with unmodified cycle. [ABSTRACT FROM AUTHOR]

Highlights: [•] WFs in small hills can be more productive compared to strictly mountainous terrain. [•] Limited space for WFs in mountains “squeezes” WTs, increasing losses 2–4.5%. [•] WFs installed near dust dispersion sites is effective only with repeated cleaning. [ABSTRACT FROM AUTHOR]

Abstract: The low-grade heat sources coupled by ORC (organic Rankine cycle) are categorized into two groups. For the first one, the inlet temperature and the mass flow rate are known, and the working mass of the heat source is directly discharged after being used. For the second, the heat release is specific and the working mass of the heat source is usually recycled after releasing heat. The theoretical formulas of net power output and thermal efficiency for subcritical ORC coupling with the two kinds of heat source are proposed to elucidate the selection criteria of working fluids. The new mathematical relation of working fluid selection is given out. The selection of working fluids for subcritical ORC should couple with the types of low-grade heat sources. For the first heat source, both the theoretical analysis and numerical simulation results show that the working fluids with high liquid specific heat and low latent heat of evaporation should be selected as the working fluids. In contrast, the working fluids with low liquid specific heat and the high latent heat of evaporation are better for the second heat source. [Copyright &y& Elsevier]

The performance analysis of a supercritical organic Rankine cycle system driven by exhaust heat using 18 organic working fluids is presented. Several parameters, such as the net power output, exergy efficiency, expander size parameter (SP), and heat exchanger requirement of evaporator and the condenser, were used to evaluate the performance of this recovery cycle and screen the working fluids. The results reveal that in most cases, raising the expander inlet temperature is helpful to improve the net power output and the exergy efficiency. However, the effect of the expander inlet pressure on those parameters is related to the expander inlet temperature and working fluid used. Either lower expander inlet temperature and pressure, or higher expander inlet temperature and pressure, generally makes the net power output more. Lower expander inlet temperature results in larger total heat transfer requirement and expander size. According to the screening criteria of both the higher output and the lower investment, the following working fluids for the supercritical ORC system are recommended: R152a and R143a. [ABSTRACT FROM AUTHOR]

High-temperature proton exchange membrane fuel cells have garnered huge attention in the recent past because of faster electrode kinetics, high CO tolerance, and possible waste heat recovery. The flow channel is a crucial component of the fuel cell, which helps to improve its performance by facilitating uniform distribution of the reactant species, current density, and temperature. Conversely, the pressure drop imposed by various flow channel configurations increases the auxiliary power requirement of the fuel cell, which is a critical issue. Here, the main objectives are to enhance the electrochemical performance and reduce the auxiliary power loss of the high-temperature proton exchange membrane fuel cell by selecting a proper flow configuration. This work compares the parallel, serpentine, and hybrid flow configurations using a physics-based fuel cell model. It involves the mass, momentum, energy, species, and current conservation equations. The simulation results show that the shape and size of the common channel width in the parallel flow configuration have a noticeable influence on the cell performance. The thermal analysis demonstrates that the temperature gradients of the serpentine and hybrid configurations are two times lower than the parallel configuration due to uniform current density distribution and heat dissipation. This study illustrates that the hybrid configuration with the net power output of 0.383 W/cm2 provides the best performance with an auxiliary power loss of 3.6% compared to the serpentine configuration with an 11% loss. The net power output of the hybrid configuration remains superior under various stoichiometric conditions, including cell starvation. The outcome of this work provides a helpful insight into the flow configuration design for maximizing the net available power from the cell. [ABSTRACT FROM AUTHOR]

The purpose of this research is the calculation of the exergy destruction of the single-flash and double-flash cycles of a geothermal power plant located on the ladder of the 233 m Cerro Prieto volcano, on the alluvial plain of the Mexicali Valley, Mexico. The methodology developed in this research presents thermodynamic models for energy and exergy flows, which allows determining the contribution of each component to the total exergy destruction of the system. For the case-base, the results indicate that for the single-flash configuration the efficiency of the first and second law of thermodynamics are 0.1888 and 0.3072, as well as the highest contribution to the total exergy destruction is provided by the condenser. For the double-flash configuration, the efficiency of the first and second law of thermodynamics are 0.3643 and 0.4983. The highest contribution to the total exergy destruction is provided by the condenser and followed by the low-pressure turbine. [ABSTRACT FROM AUTHOR]

Phase change materials used for the storage of thermal energy can play a critical role in the efficient use and conservation of solar energy. The effect of the different types of phase change materials on the thermodynamic performance of a direct vapor generation solar organic Rankine cycle system is evaluated in this study. The system consists of an array of evacuated flat plate collectors, phase change material based thermal storage, expander, condenser, and organic fluid pump. The thermodynamic cycle model of the ORC system is integrated with phase change material heat storage tank that is modeled using the finite difference method in MATLAB. The thermodynamic performance of the system is analyzed by using 12 different phase change materials. Effect of phase change materials on the thermodynamic performance of organic Rankine cycle including the net power output, rise and fall in the working fluid temperature, and on the amount of energy stored and released are evaluated and compared for charging and discharging mode. The results indicate that MgCl 2 ·6H 2 O has shown the highest overall system's efficiency. However, KNO 2 –NaNO 3 and Acetamide have resulted in maximum ORC and collector efficiency, respectively. Moreover, Acetamide, KNO 2 –NaNO 3 and Mg(NO 3) 2 ·6H 2 O have shown maximum rise and fall in organic fluid temperature, maximum net power and maximum amount of energy stored and released during charging and discharging mode. Salt hydrates have shown overall better performance among the selected PCMs in terms of overall system efficiencies and the amount of energy stored and released. • Impact of 12 different Phase Change Materials solar organic Rankine cycle system. • Modelling and validation of Phase Change Material storage tank. • Impact of evaporation temperature and mass flow rate on system's performance during charging and discharging mode. • Salt hydrates have shown best performance among the selected Phase Change Materials. • Mg(NO3)2·6H2O is found to be most suitable candidate because of its all-round better performance. [ABSTRACT FROM AUTHOR]

• A novel parallel dual-pressure Kalina cycle system is proposed. • Working fluid concentration and evaporating pressure are optimized. • The sliding pressure regulation is applied to response the heat source parameters. • The cost of electricity is considered as the economic evaluation criterion. In this paper, a novel parallel dual-pressure Kalina cycle system is presented to utilize the low-grade geothermal energy. In order to highlight the performance of the proposed cycle, the comparison of parallel dual-pressure Kalina cycle system and the basic Kalina cycle system is conducted and set at the same boundary conditions. The maximal net power output of cycle is considered as the single-objective function based on particle swarm optimization algorithm. The exergy analysis and economic cost for both cycles are investigated at design conditions. Furthermore, as operating at off-design conditions, the variation ranges of geothermal energy mass flux and inlet temperature are 7.5–14 kg/s and 136–150 °C, respectively. The sliding pressure regulation strategy is applied to response to the variations of geothermal energy parameters. The two-levels evaporation pressures in the parallel dual-pressure Kalina cycle are adjusted to remain the invariable temperature difference between geothermal energy inlet temperature of evaporators and the corresponding turbine inlet temperature. The results show that, at design conditions, the maximal net power output of parallel dual-pressure Kalina cycle and basic Kalina cycle is 329.62KW and 274.94KW, the corresponding exergy efficiency is 44.52% and 33.39%. Besides, the condenser contributes to the largest exergy destruction ratio in parallel dual-pressure Kalina cycle and basic Kalina cycle, which are 33.96% and 44.94% of overall exergy destruction, respectively. According to the off-design performance investigation, it is shown that the higher geothermal energy mass flux and inlet temperature are in favor of the larger net power output for both cycles. The thermodynamic evaluation shows that the proposed parallel dual-pressure Kalina cycle exhibits a more excellent performance in terms of net power output and exergy efficiency than basic Kalina cycle. [ABSTRACT FROM AUTHOR]

• Thermo-economical optimization of a Supercritical-Subcritical organic Rankine cycle. • The lower U A sys UA sys does not mean the higher net power output or exergy efficiency. • A higher condensation temperature can benefit improving system economic performance. • The Pareto-optimal solutions for exergy efficiency and U A sys UA sys are 61.25% and 20.08 kW/K, respectively. The Supercritical-Subcritical organic Rankine cycle could combine the superiorities of supercritical ORC and dual-pressure organic Rankine cycle to recover more heat and improve the system performance. The parametric analysis and thermo-economical optimization of a Supercritical-Subcritical organic Rankine cycle using R1234ze has been investigated in this study. The effects of five key operation parameters on the thermodynamic performance and economical factor are examined. A single-objective optimization for maximizing net work output, maximizing exergy efficiency and minimizing UA sys (heat transfer requirement) is examined and compared. The bi-objective optimization for maximizing exergy efficiency and minimizing UA sys simultaneously is also addressed. Research demonstrates that the net output power increases first and then decreases as supercritical stage temperature and supercritical stage pressure. UA sys decreases first and then increases with the supercritical stage temperature. The lower UA sys does not mean the higher net power output or exergy efficiency. A higher supercritical stage pressure and temperature are detrimental to system economic performance, while a higher condensation temperature can benefit improving system economic performance. The Pareto-optimal solutions for exergy efficiency and UA sys are 61.25% and 20.08 kW/K, respectively. [ABSTRACT FROM AUTHOR]

• A constructal thermodynamic optimization model for OTEC system is established. • OTEC system includes a dual-pressure organic Rankine cycle. • Combination of constructal theory with finite time thermodynamics is applied. • Net power output of OTEC system is chosen as the optimization objective. • Net power output after optimization is improved by 14.95%. A constructal thermodynamic optimization model for ocean thermal energy conversion system (OTECS) with a dual-pressure organic Rankine cycle (DPORC) to make better use of the ocean thermal energy is established in this paper. It is performed by combing constructal theory with finite time thermodynamics. Optimal design of the OTECS is conducted under the conditions of the fixed total heat transfer area of the heat exchangers and the total volume of the dual-pressure turbines. The net power output of the OTECS is chosen as the optimization objective, and six parameters, that is, the heat transfer plate effective lengths of the high-temperature evaporator, low-temperature evaporator, and condenser, volume fraction of the high-pressure turbine as well as heat transfer area fractions of the condenser and high-temperature evaporator, are employed as the optimization variables. The optimal performance and optimal construct of the OTECS are obtained. The influences of total mass flow rate and mass flow rate ratio of the working fluid, inlet temperatures of the warm and cold seawaters, and wheel diameter ratio of the turbine on the optimization results are analyzed. Moreover, the optimal performances of the OTECS with the DPORC and single-pressure organic Rankine cycle (SPORC) are compared. The results show that the net power outputs after the primary, twice, triple, and sextuple constructal thermodynamic optimizations are improved by 2.80%, 4.66%, 9.95%, and 14.95%, respectively, compared with the initial net power output. The net power output can be further improved by increasing the total mass flow rate of the working fluid, warm-seawater inlet temperature, and wheel diameter ratio of the turbine in reasonable ranges. Compared with the SPORC, the DPORC has advantages in both the net power output and net thermal efficiency. The obtained results can provide theoretical guidelines for the optimal designs of the OTECS. [ABSTRACT FROM AUTHOR]