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This study presents a comprehensive system-level analysis model for evaluating performance characteristics of a hundred-kilowatt proton exchange membrane fuel cell (PEMFC) test system. Unlike conventional power-focused systems, the test system has a more complex architecture and numerous balance of plants (BOPs). The developed model integrates detailed input-output traits of each system component. The energy efficiency ratio (EER) and energy conversion efficiency (η) are introduced as metrics for assessing net power consumption and conversion capability of the test system. By simulating various operational scenarios (considering temperature, load current, cathode pressure, humidity, and PEMFC power), the model predicts the behaviors of BOPs and energy flow relations. The changing rules of the EER and η are also investigated. An increase in temperature, current, and cathode pressure leads to an improvement in EER. Increasing operating temperature, cathode pressure, and humidity can enhance η. Key findings suggest optimal conditions for system self-sufficiency include an operating temperature below 90 °C, load current over 1200 mA cm−2, and air humidity under 90%. Furthermore, the PEMFC power is advisable to configure between 50% and 100% of the test system's maximum power. These insights are pivotal for improving the design and functionality of PEMFC testing equipment, further contributing significant advancements to fuel cell technology. • A system-level analysis model for a hundred-kilowatt PEMFC test system is developed. • The system model contributes to predict operating and energy flow parameters. • Two system indicators are proposed to assess the test system operating performance. • The necessary conditions for the test system to achieve self-sufficiency is determined. [ABSTRACT FROM AUTHOR]

• Similarity principle analysis on nanochannel-based i-TE system is constructed. • Fifteen dimensionless variables are derived to reflect dimension unification. • Performance optimization and sample expansion are realized for applications. • Parameters dominating the nanochannel-based i-TE performance are presented. Ionic thermoelectric (i-TE) systems convert low-grade heat into electricity based on ion migration driven by the Soret effect under a temperature gradient. Current research conducts tentative experiments for superior i-TE materials and performance, whereas universal physical quantities reflecting the unified essence are still needed to guide experiments. In this study, the unified mechanism of i-TE energy conversion is analyzed using similarity principle by establishing nanochannel-based i-TE models, considering the Soret effect and heat transfer. Fifteen dimensionless variables are derived to represent the i-TE energy conversion process. Dimension unification is achieved by normalizing various dimensional phenomena with the deviation of 48.3% into one dimensionless situation with the deviation of 0.011%. These dimensionless variables can be further utilized to practical applications. Specifically, upon equal dimensionless variables, sample expansion is achieved with relative errors within 0.018% and the total time acceleration ratio of 7.33, alleviating experimental burden. Besides, the i-TE output power can be improved by 100% upon higher characteristic output power and equal dimensionless variables. Orthogonal tests are further implemented to clarify the parameter dominance, showing that the cationic reduced Soret coefficient is dominant on performance with contribution rates more than 25%. This work provides unified insight into coupling relations of multi-physical parameters in i-TE energy conversion to guide experimental designs. [ABSTRACT FROM AUTHOR]

Energy efficiency evaluation of natural draft wet cooling towers (NDWCTs) is essential to the energy saving process. There is a lack of comprehensive methods that can evaluate and grade the NDWCTs energy efficiency quantitatively. In this study, a comprehensive energy efficiency assessment indicator (CEEAI) including thermal performance, water conservation, and electric saving aspects is proposed. The CEEAI is based on the analysis of NDWCTs mass and heat transfer mechanism. Total 48 actual test reports of the NDWCTs whose water flow rate changes from thousands to hundred thousand tons per hour for test period spans of 16 years, are collected as the database. The CEEAI is validated through statistical analysis and thermodynamics law. Based on the CEEAI and database, an energy-efficiency grading criteria is proposed, the NDWCTs are graded into high, middle and low energy efficiency. Therefore, the energy efficiency of one NDWCT can be clearly observed, which is beneficial for the common researchers to understand the energy efficiency level among all the NDWCTs. In addition, through comparing the CEEAI of different NDWCTs, the energy efficiency gap can be obtained, which provides the optimization guidelines and theoretical support for the improvement of the overall energy efficiency level for the NDWCTs. • A comprehensive energy evaluation assessment indicator for NDWCT was developed. • 48 NDWCTs actual test reports with various size and years was collected as database. • The proposed indicator was verified by statistical and thermodynamic analysis. • An energy-efficiency grading criteria was proposed based on indicator and database. [ABSTRACT FROM AUTHOR]

• Osmotic power is improved by non-symmetrically heating the low concentration solution. • Ion conductance and selectivity are enhanced by downstream heating on the nanochannel exit. • A matching principle by heating thicker electric double layer region is verified. • Osmotic system for sustainable electricity output is designed. Salinity gradient power generation is largely elevated through ubiquitous solar energy by promoting ion mobility or ion selectivity. In this paper, a universal energy utilization approach is presented to improve osmotic power with saved energy consumption by photothermal effects. The salinity gradient energy is combined with nonsymmetric photothermal heating, which is exerted at the solution with the low concentration side. The coordination between thermal regulation and salt difference regulation is then achieved. The ion conductance near the nanochannel exit is enhanced, and the cation selectivity transport is correspondingly accelerated. Compared with symmetric heating both at high and low concentration solutions, the power density of nonsymmetric heating against the concentration gradient increases by 141%. A salinity-gradient osmotic model coupled with a temperature gradient is developed to understand the mechanism of ion selective transport under different photothermal heating patterns. An electric double layer (EDL) matching principle by improving the temperature in the location of the thicker EDL region is verified. In addition, the enhancement effect becomes less evident when the solution concentration level is increased at a fixed concentration ratio. Furthermore, a two-phase change material (PCM)-supported thermo-osmotic system is designed for sustainable electricity output, and the total electricity energy is 7.4% higher than that of the system without PCM in a light–dark cycle. This nonsymmetric sunlight-produced thermo-osmotic energy conversion provides an alternative method for solar energy cascade utilization. [ABSTRACT FROM AUTHOR]

The overheated photovoltaic (PV) panels during the late experimental period and severe temperature stratification of the phase change materials (PCMs) are critical factors influencing the photovoltaic/thermal-PCM system efficiency. In this work, an outdoor experimental switchable PV/T-PCM system coupled with copper fins and flexible thermal regulation strategies was investigated to maximize the energy conversion efficiency. The effect of different fin heights on the efficiency of the PV-PCM system without water flow was firstly investigated. Second, five cases under various thermal regulation strategies utilizing water flow were comprehensively investigated by the energy and exergy analysis. For the full-time regulation, both thermal energy and exergy efficiencies (η th and E x _th) increased when the water flow rate grew from 0.11 L/min (Case 2) to 2.92 L/min (Case 5). Case 5 presented the highest η th and E x_th of 86.49% and 2.06%, respectively, and increments of 4.40% and 4.35% in the electrical energy and exergy efficiencies, respectively, with the addition of PCMs. At the same water flow rate of 0.11 L/min, the electrical energy and exergy efficiencies in Case 6 increased by 11.46% and 11.35%, compared with Case 2, indicating that the intermittent regulation is more beneficial for improving the photoelectric efficiency of the PV/T-PCM system. [ABSTRACT FROM AUTHOR]

Abstract An ionic wind pump is an energy-saving device that can produce a volume flow when electrodes are applied with high voltage. Compared to the traditional methods, ionic wind pumps possess the advantages of low energy consumption, no moving parts, compact structure and flexible design. In this study, a large-size ionic wind pump, consisting of many single regular hexagonal needle-ring ionic wind generators, was developed as the preliminary model. However, its experimental performance was not as good as our expectations. In order to improve this preliminary model, a simulation method was used to investigate the configuration factors of the single ionic wind pump. In the optimized model, mesh gap is 6 mm, eccentricity is 0.26, section area is 238.44 mm2 and needle electrode number is 3. In subsequent experiments, the final optimized large-size ionic wind pump showed a great promotion in velocity, and the maximum average velocity of the optimized pump was higher than the preliminary model by 13.3%. Our numerical simulation and experiment results have practical significance in designing ionic wind pumps. Highlights • A 3D numerical model is established for large size ionic wind pump. • Influences of multi-parameter on the performance of ionic wind pump are investigated by numerical and experimental method. • Optimized large-size ionic wind pump showed a great promotion in velocity. [ABSTRACT FROM AUTHOR]

• APF maximum solution with multi constraints is established. • Mathematical solution of APF functions without any simplification are programed. • Multi constraints are obtained from simple energy performance tests. • Max APF of a prototype unit is increased by 7.71% using the proposed method. • The proposed method greatly simplifies the R&D procedure for HPs. Air conditioners is expected to be the second largest source of growth in global electricity demand. To promote electrification, heat pump air conditioner is encouraged to replace natural gas furnace. Improving heat pump's energy efficiency can help reduce global energy consumption and greenhouse gas emissions. Annual performance factor is one of the key metrics to evaluate heat pump systems' energy performance. Seeking annual performance factor maximum belongs to an optimization problem with multi constraints. However, due to the nested variables, continuous non-differentiable and piecewise form of annual performance factor definition functions, the optimized objective function is usually based on the simplification with large errors. Meanwhile, the multi constraint boundaries are either ignored or considered but through complicated and high-cost tests. In this research, the variable iteration logic of the annual performance factor definition functions is sorted firstly. Then the above exact mathematical definitions are programmed as the objective functions without any simplification. Enumeration method is used to establish the annual performance factor maximum solution algorithm. More importantly, taking a 3.5 kW cooling capacity mini-split heat pump prototype as an example, energy performance tests are conducted to fit the multi constraints, namely using less global parameters to cover more local parameters, which greatly simplifies the test procedures and cost. Then, using our proposed method, the maximum annual performance factor is predicted and validated by experiments. The prediction accuracy is 99.6%, with a 38.4% improvement compared to the best reported value from literature. Based on the recommended variable values, the prototype's annual performance factor achieves the maximum with a 7.71% improvement from the baseline. The proposed method can save time and experimental resources in the product development stage compared with the traditional trial and error method. [ABSTRACT FROM AUTHOR]

• The PV/T-PCM system with a novel latent heat solar collector was proposed in Shanghai. • The energy and exergy efficiencies were comprehensively compared among five cases. • The thermal regulation strategy played a key role for the energy conversion improvement. • The 45 ℃ intermittent thermal regulation performed best for the PV/T-PCM system. The photoelectric conversion efficiency generally decreases with increasing temperature of a photovoltaic (PV) panel; therefore, temperature control is the key issue in the photovoltaic/thermal (PV/T) system. We experimentally analyzed the energy conversion performance of a PV/T system combined with a latent heat solar collector under the real outdoor climate of Shanghai. The solar collector was filled with the phase change material (PCM) of fatty acid for cooling the PV panel. Five cases under different thermal regulation strategies for the PV/T-PCM system were comprehensively analyzed to optimize the system performance. The results indicated that the temperature stratification of PCM was still significant in the solar collector even when metal fins were employed. The temperature fluctuation of the PV panel can be well alleviated by PCM; however, the PCM was easily overheated under long-term operation of the PV/T-PCM system. Among the five cases, the overall energy efficiency of the PV/T-PCM system with full-time thermal regulation was 5.4% and 22.2% higher than the two systems without thermal regulation, respectively. The relatively low temperature setting of the thermal regulation strategy facilitated the heat transfer from the PCM. In comparison with the full-time thermal regulation strategy, the 45 °C intermittent thermal regulation strategy (Case 4) demonstrated the best performance. The total energy and exergy efficiencies of Case 4 were 86.3% and 15.5%. The exergy efficiency of thermal energy varied slightly in the range of 1.1%–1.4% for the five cases. It was concluded that the energy conversion performance of the PV/T-PCM system could be significantly improved by a suitable intermittent thermal regulation strategy. [ABSTRACT FROM AUTHOR]