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To meet the demands for high power density, enhancing the water discharge capacity of proton exchange membrane fuel cells (PEMFCs) is imperative. The microporous layer (MPL), placed between a catalyst layer and gas diffusion layer, plays a crucial role in water management for PEMFCs. In this study, we fabricated electrospun MPLs of different pore sizes and characterized their morphology and pore structures. The mercury intrusion test showed that the mean pore sizes of electrospun MPLs are about 1.2–2.3 μm, much larger than commercial MPL's (about 70 nm). The electrospun MPLs were assembled in single PEMFCs to test their performance and Electrochemical Impedance Spectroscopy (EIS). The results demonstrate that the electrospun MPLs with a pore size exceeding 1.9 μm significantly enhance water discharge and oxygen transport at the cathode relative humidity (RH) of 50 % and 100 %. Moreover, the EIS testing and fitting outcomes indicate that when the PEMFC performance is dominated by mass transport under high current density and 100 % cathode RH, the electrospun MPLs with a pore size exceeding 1.9 μm exhibit a better water discharge capacity and lower mass transport resistance. • Electrospun MPLs have larger pore sizes (>1 μm) than commercial ones (∼100 nm). • Electrospun MPLs of a pore size exceeding 1.9 μm enhance water discharge. • Fuel cell performance was improved at cathode relative humidity >50 %. [ABSTRACT FROM AUTHOR]

The gas diffusion layer (GDL) plays a vital role in water management of proton exchange membrane fuel cells. In this study, GDLs with nanoscale gradient pore sizes (nano-GDLs) are fabricated using electrospinning to explore the influence of the gradient layer number and degree of the pore size gradient on the water transport performance. The breakthrough pressure and water saturation tests indicate that nano-GDLs with uniform and gradient structures have higher breakthrough pressures and lower water saturation compared with those of the commercial Toray GDL, which facilitates back diffusion of water through the membrane and water discharge in the GDL. Specifically, among the nano-GDLs with a gradient structure, the three-layer medium-gradient nano-GDL sample (3-MG) possesses the maximum breakthrough pressure and minimum water saturation ratio. The fuel cell test determined that the maximum power density of the 3-MG nano-GDL sample is 14% higher than that with commercial Toray GDL without cathode humidification. • Electrospinning can fabricate gas diffusion layers with gradient pore sizes. • The nano-GDL pore size is much smaller than that of commercial Toray GDL. • The 3-MG nano-GDL has higher breakthrough pressure and lower water saturation. • The power density of 3-MG nano-GDL is 14% higher than commercial Toray GDL. [ABSTRACT FROM AUTHOR]

Ionic thermoregulated osmotic energy conversion in nanochannels synergistically utilizes osmotic and thermal energy for power generation based on ionic selective transport in charged nano-membranes under salinity gradients and thermal regulations. Currently, no explicit general dimensionless formulas exist that reflect the relationship between impact factors and performance to guide performance designs. In this study, data-driven insight is presented to establish a framework for obtaining explicit and general relational expressions based on data augmentation using the similarity principle and deep learning. The original database is derived from a finite element simulation with 10,000 dimensional samples, then augmented to 30,000 dimensional samples via similarity principle-based data augmentation. Subsequently, a deep neural network model with decay algorithms is employed to expand the database to new 300,000 dimensional samples with a prediction accuracy exceeding 98 %, which are further converted to dimensionless forms for multiple linear regression. Three dimensionless and explicit formulas for the electrical potential, output power, and energy conversion efficiency are obtained, which indicate determination coefficients of 0.91, 0.93, and 0.92, respectively. Furthermore, considering actual experimental and application situations, the modified dimensionless formula of the output power predicts the experimental results with an average error of 7.80 %. This study efficiently alleviates experimental burden and facilitates engineering applications. [Display omitted] • Data-driven insight is presented to establish a framework for general formulas. • Primary data augmentation is achieved by similarity principle. • Secondary data augmentation is realized by deep learning. • Explicit dimensionless formulas with high determination coefficients are obtained. [ABSTRACT FROM AUTHOR]

The internal water and thermal state and performance of an air-cooled proton exchange membrane (PEM) fuel cell stack are strongly determined by the fan arrangement and operational characteristics. This study presents an innovative method to investigate the influence of fan on stack performance through integration of fan's full morphology, including the fan blade, grill between the fan and stack, etc. into a three-dimensional (3D) multiphase stack model. The multiple reference frame (MRF) model is implemented to simulate the air flow field caused by the rotation of fan and the multiple transfers coupled with electrochemical reactions is considered in the 3D stack model in detail. Through this integrated model, the influence of the air supply mode, fan number and duty ratio on stack performance and the distribution characteristics are investigated in detail. It is found that the air flowing into each cell in the fan-cooled stack is highly non-uniform, which increases the variations of oxygen concentration, temperature, and voltage in the stack. In comparison with the blowing mode, the suction mode helps to promote the uniformity of air supply with a lower air flow velocity. [ABSTRACT FROM AUTHOR]

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]

Segmented proton exchange membrane (PEM) fuel cells are widely implemented in measuring their internal spatially distributed variables (e.g. current density and temperature). However, the difference between the segmented and ordinary fuel cells in spatial distribution characteristics has not been fully understood. In this work, we studied the spatial distribution characteristics in segmented fuel cells (cell area: 366.6 cm2) utilizing a three-dimensional (3D) large-scale fuel cell model that considers the full morphologies of metallic bipolar plates (BPs) and dot-matrix hydrogen, air and coolant flow distribution zones, including the current density, temperature, water content, etc., and compared with those in ordinary fuel cells. It is found that placing a segmented print circuit board (PCB) next to the bipolar plate (BP) component has little influence on fuel cell performance and internal distribution characteristics, whereas the measured current density distribution in the PCB still has inconsistency with that in the ordinary fuel cell, indicating that the influence of segmentation on electron conduction cannot be neglected. In the fuel cell with segmented BP and PCB, the fuel cell performance decreases significantly mainly due to increased electrical and ionic ohmic loss. In addition, the BP's segmentation significantly influences on the water and thermal state inside the whole fuel cell, leading to inconsistency in the measured temperature, relative humidity (RH) and current density distributions with ordinary fuel cells. [ABSTRACT FROM AUTHOR]

Reducing Pt catalysts amount without sacrificing the performance and durability is critical for the commercialization of proton exchange membrane fuel cells (PEMFCs). Pt degradation in the cathode catalyst layer (CCL) decreases the electrochemically active surface area (ECSA), and Pt precipitation, especially Pt band formation, has a significant effect on proton exchange membrane (PEM) stability, resulting in severe PEMFC degradation during long-term operation. In this study, a one-dimensional model is developed focusing on Pt catalyst degradation and precipitation, including Ostwald-ripening, mass loss, precipitation in the PEM from nucleation, particle size growth, to Pt band formation. The model accuracy is comprehensively validated against the corresponding experimental data, including ECSA loss and particle size distribution (PSD) evolution in the CCL under different operating conditions (temperature, relative humidity, and loading mode), as well as the precipitated Pt size distribution characteristics and local potential in the PEM. Using this model, the Pt band formation process is comprehensively analyzed, and the effects of operating conditions on Pt degradation and Pt band formation are investigated in detail. It is found that the nucleation stage is brief, and then the significant inhomogeneity at the size growth stage causes Pt band formation. In addition, the high activation enthalpy of dissolution under low humidity can effectively inhibit Pt degradation, and Ostwald-ripening is the mean cause of Pt degradation, which is likely to occur during the rapid voltage change period. [ABSTRACT FROM AUTHOR]

Direct CO 2 electroreduction of flue gas is a technology that simplifies CO 2 capture and purification process and directly utilizes CO 2 in flue gas. Low CO 2 reduction reaction selectivity caused by the low CO 2 partial pressure and side reactions competition is the challenge. In this study, a direct CO 2 electroreduction system for multicomponent flue gases was established. A two-dimensional steady model was developed by considering major electrode reactions of flue gas in Cu x O-based catalysts. General influence criteria and optimum operation window for the potential, temperature, and pressure were proposed. In addition, a techno-economic analysis of the flue gas electrolysis system was conducted. The results demonstrated that the CO 2 electroreduction reaction performances are weak at atmospheric pressure owing to the side reaction competition and small reactant concentration. A method involving pressurization and catholyte inlet temperature declination is proposed to break the stalemate of tiny reactant concentrations and ensure the dominance of the CO 2 electroreduction reaction. The selectivity and current density of the CO 2 reduction reaction were 71% and − 148 mA/cm2 at −1.17 V vs. reversible hydrogen electrode potential (RHE), respectively, under the conditions of an inlet electrolyte temperature of 273 K and an operating pressure of 20 atm. C 1 products with excellent yields are the dominant products. Furthermore, the techno-economic analysis showed that the flue gas electrolysis system has higher profitability and lower cost than the purified CO 2 electrolysis system. The present results can be used to optimize the electrolyzer operating parameters and construct CO 2 reduction systems. • Direct CO 2 electroreduction system for multicomponent flue gas is established. • Performance and electrochemical conditions of flue gas electrolysis are analyzed. • Pressurization and temperature control are proposed to improve flue gas electrolysis. • Flue gas electrolysis is more economic and lucrative than purified CO 2 electrolysis. [ABSTRACT FROM AUTHOR]

• A fast battery preheating method based on inductive heating is proposed. • Heating performance of inductive heating and conventional methods are compared. • Numerical model for battery inductive heating is established. • Inductive heating provides better temperature uniformity and heating efficiency. • Inductive heating is improved with lower current frequency and battery thickness. The fast preheating of lithium ion batteries (LIBs) is a challenge hindering its wide application in cold climate. This study proposes a new preheating method that employs an inductive heating operation. The performance of inductive heating on LIB is evaluated and compared with conventional heating methods using metal resistance film (MRF) and positive temperature coefficient (PTC) elements. Subsequently, an inductive heating numerical model is established to investigate the influence of critical factors, including current frequency and battery thickness, on the inductive heating performance. Results show that conventional MRF and PTC heating cannot provide safe fast preheating of LIBs owing to significant temperature difference inside battery. In comparison, inductive heating offers a better battery preheating performance with fast temperature increment, uniform temperature distribution and high efficiency. The battery utilizing sandwich inductive heating achieves a temperature increase rate up to 71.4 °C/min, an insignificant temperature deviation less than 6 °C, and a heating efficiency of 79.2% in the experimental test. The higher temperature uniformity of inductive heating is attributed to the fact that heat is generated within the battery electrode layers and that the contact thermal resistance induced by battery case can be eliminated. Moreover, the inductive heating performance is highly related with current frequency and battery thickness. The inductive heating of LIB is more suitable for operations at low frequencies, such as 10 kHz, as the skin effect of inductive heating can be decreased, and the temperature uniformity is increased. The battery thickness less than 4 mm is recommended as the maximum temperature deviation is less than 2 °C. This paper provides a preliminary investigation into the feasibility of LIB inductive preheating technology and offers new insights into the thermal management design of LIB application in cold climates. [ABSTRACT FROM AUTHOR]

• An adaptive strategy for active thermal convective cloak via heat gain and loss is proposed. • Adaptive heat sources have been demonstrated to be feasible for heat convection. • An inverse process is built to calculate the heat source via conjugate gradient method. • Thermal cloak is experimentally validated using a heat source matrix. Thermal metamaterials, known for their effective and directional heat control and management strategy, have garnered significant attention leading to the investigation of various functional thermal conductive metadevices. Nevertheless, conventional thermal convective metadevices resort to artificial structures in the flow field, which face the challenge of the coupling of heat and mass transfer and unstable flow field. Herein, we report an adaptive strategy for fabricating an active thermal convective cloak via tunable heat gain and loss. Adaptive body and surface heat sources, rather than graded structures inside functional regions, have been demonstrated to be feasible for heat convection. Accompanied by the active manipulation scheme, an inverse design process was constructed to calculate the heat source distributions based on the knowledge of the target temperature fields. The proof-of-concept heat source matrix, using well-laid out resistance heaters and thermoelectric components, experimentally validated the thermal cloaking pattern in the flow field. The active scheme overcomes the limitations of the complex engineered structures required for conventional thermal convective metadevices. Thus, in this study, we establish a new paradigm for thermal convective camouflage and pave the way for active thermal management in heat convection. [ABSTRACT FROM AUTHOR]

Osmotic energy conversion is a promising method of sustainable electricity generation using seawater and river water. Artificial pure NaCl solutions are commonly used, whereas the effects of multivalent-ion ingredients present in natural seawater on osmotic power generation remain unclear. In this study, the impacts of coexisting ions in multicomponent seawater (MS) are experimentally assessed using graphene oxide membrane (GOM). Divalent cation in MS shows inferior transport to monovalent cation, thereby presenting a lower power density than when using pure NaCl solutions. Inspired by experimental results, an interfacial binding rope theory is proposed to clarify ion-wall interactions and cation transport in sub-nanochannels with hydrophilic functional groups. The binding rope networks include direct cation-wall connections mediated by composition-changed hydration shells, indirect connections by H-bonds linking solvated water molecules and functional groups, and electrostatic attractions between cations and negatively charged surfaces. The theory feasibility is confirmed by first-principles calculations focusing on the charge distribution, binding site and length, surface electrification, and cation diffusivity and selectivity in GOM sub-nanochannels. Divalent cation diffuses slower than monovalent cation in both pure solutions and confined channels. For the mixed solution in channels, both monovalent and divalent cations show worse diffusivities due to additional monovalent-divalent electrostatic repulsions, as well as inferior cation selectivity due to weakened deprotonation reactions. Bridged by environment-controlled interfacial potential distribution, ion diffusivity, and ion selectivity, this theory guides the improvement of MS-based osmotic performance under regulations of concentration gradient, pH, and temperature. A power density of 8.52 W m–2 and stable output within 27 days are achieved. The interfacial binding rope theory could be popularized to refine the transport mechanisms of various cations in diverse hydrophilic sub-nanochannel materials, promoting the application of osmotic power generation and other nanoscale technologies. [Display omitted] • Multicomponent seawater shows lower osmotic power density than pure NaCl solution. • Interfacial binding rope theory for ion transport in sub-nanochannels is inspired. • This theory is verified by first-principles calculations. • The theory guides the improvement of osmotic power density. [ABSTRACT FROM AUTHOR]

• The SPCF with a combination of staggered structures and fins is proposed. • The enhanced reflection of the SPCF is attributed to the shift of the peak position. • The improved sound insulation performance is attributed to the structural coupling effect. Noise is associated with physical and mental health and well-being. Sound insulation materials allowing ventilation are in demand. A staggered phononic crystal with fins (SPCF), which is a combination of staggered structures and fins, is proposed to improve the sound insulation performance and meanwhile allow ventilation. The maximum peak value (5.2 dB) of the experimentally measured transmission loss of the SPCF is higher than the peak values of the reference samples. The improved sound insulation performance of the SPCF compared with reference samples is attributed to the frequency shift effect and structural coupling effect. The dissipated energy caused by the thermal effect in the SPCF accounts for about 20 %-26 % of the total dissipated energy, suggesting that the thermal effect must be considered to obtain an accurate total dissipated energy. The SPCF sets up a new strategy for the next-generation sound insulation materials allowing ventilation. [ABSTRACT FROM AUTHOR]

The water management capacity of the gas diffusion layer (GDL) is a crucial factor in improving the performance of polymer electrolyte membrane fuel cells at high current densities. Owing to different hydrophobic properties, the distribution of polytetrafluoroethylene (PTFE) significantly adjusts the distribution of liquid water within the GDL. Moreover, the combined optimization of the pore structure and hydrophobicity further affects the water discharge behavior in the GDL. In this study, an improved stochastic method is proposed to reconstruct the realistic GDL porous structure with in-plane gradient distributed porosity and a microporous layer (MPL) with bending cracks. Subsequently, two forms of nonuniform PTFE distributions in the in-plane and through-plane directions were designed. A three-dimensional multi-relaxation time D3Q19 pseudopotential multicomponent multiphase Lattice Boltzmann Method (LBM) was adopted to numerically explore the liquid water dynamic behavior in coupled GDL and MPL systems with different combinations of the gradient porosity and gradient wettability distribution. The numerical results indicated that the pore structure water-collection effect, caused by the graded distributed porosity, drives liquid water to accumulate in the layer with relatively large pores. Whereas, the hydrophilic water-collection effect, caused by the graded distributed wettability, drives liquid water to move towards and accumulate in the relatively hydrophilic layer. For in-plane distribution wettability, the coordination of the pore structure and hydrophilic water-collection effect is realized by arranging the layer with a relatively large porosity into a relatively hydrophilic layer. Then the concentration effect of liquid water and the drainage rate is enhanced. For through-plane distribution wettability, the liquid content at the GDL/MPL interface could be significantly reduced by increasing the hydrophobicity of the region in the GDL close to the MPL/GDL interface. The present study consolidates our understanding of the influence mechanism of different PTFE distributions on liquid water transport in GDL/MPL systems, contributing to the optimization of the structural design of the GDL. [Display omitted] • An improved stochastic method is proposed to reconstruct porous GDL and MPL. • A 3D pore scale LBM is adopted to explore liquid water transport in GDL with PTFE. • Coordination for pore structure and hydrophilic water-collection effect is realized. • The gradient distribution wettability can reduce liquid content at GDL/MPL interface. [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]

Accurate prediction of the effective thermal conductivities of aerogel nano-porous materials has remained to be a challenging problem. A new method to predict their insulation performance is proposed in this paper. Firstly, a random generation-growth method, following the solid-phase growth principle, is used to reconstruct the two-dimensional open-cell mesoscopic structures. The pore size of aerogel can be controlled preliminarily and the similarity between reconstructive and real structures can be enhanced with this generation method. On the basis of the generated structure, the lattice Boltzmann method D2Q9 is adopted to predict the effective thermal conductivity. The results are agreed well with published data, which demonstrate that this method can not only guarantee the stochastic character of the aerogel structure but also is reliable for practical applications. Furthermore, the effects of porosity, ambient pressure and temperature on the heat transfer performance are investigated. There exists an optimal density making the effective thermal conductivity being minimum and the optimal density is different under various temperatures. The effective thermal conductivity decreases with the ambient pressure decrease and then remains a constant value. Finally, the contributions of gas phase, solid phase and radiative heat transfer to the effective thermal conductivity are separated by decomposition method. [ABSTRACT FROM AUTHOR]

The moisture separator is widely used in nuclear power plants to remove entrained water droplets from two phase flow. The present work presents a comparative analysis of the performance of three types of separators with corrugated plates. The effects of inlet velocity and plate spacing on the pressure drop and separation efficiency have been numerically investigated by applying the realizable k - ɛ model and discrete phase model. The results show that the pressure drop and separation efficiency of the separator with hooks is the highest of the three types of separators at the same inlet velocity and plate spacing. The predicted pressure drop and separation efficiency for the three types of separators are enhanced with the increase of inlet velocity. And the reduction in plate spacing increases the pressure drop and separation efficiency. Besides, the separation efficiency of the large-scale droplets is higher than that of the small-scale droplets for the same inlet velocity. [ABSTRACT FROM AUTHOR]

• ANR consisting of rectangular units in nanochannels is proposed. • ANR enhances ion selectivity by increasing the concave region's EDL overlap degree. • The osmotic energy conversion performance can be divided into three zones. • The ANR distributed in the rear region generates higher osmotic power. • ANR geometry is optimized by manipulating the height and reducing the width/pitch. Nanofluidic osmotic energy conversion is widely regarded as a promising technology for the conversion of clean salinity-gradient energy into electricity. Surface roughness can increase the surface charge of nanochannels, but its effect on the ion flux and osmotic energy generation has rarely been investigated. In this study, we propose artificial nanoroughness with rectangular units in nanochannels to enhance ion selectivity and osmotic energy conversion of nanochannels without obvious influence on the ion flux. The osmotic energy conversion performance is separated into an ion selectivity-sufficient zone, a driving force-sufficient zone, and a transition region called balanced zone according to the ion concentration ratio. The artificial nanoroughness significantly increases the ion selectivity in the balanced zone and the driving force-sufficient zone by improving the space charge density in the concave region. The artificial nanoroughness distributed in the rear region of the nanochannel can generate higher osmotic power than that in the frontal region. Moreover, either the maximum osmotic power or energy conversion efficiency can be realized by manipulating the height of artificial nanoroughness under a concentration ratio less than 100, whereas both of them can be achieved simultaneously by reducing the width or pitch of the artificial nanoroughness under all concentration ratios. The current work paves a promising path to consolidate ion selectivity and osmotic power generation through the interfacial design of nanochannels. [ABSTRACT FROM AUTHOR]

• Full-scale 3D simulation for air-cooled PEM fuel cell stack was presented; • The stack polarization curve and temperature distribution were validated; • Oxygen content becomes lower at a higher temperature site in the stack; • Thermal behavior has a decisive effect on the distributions of temperature, gas, etc.; • Increasing the air flow rate benefits the uniform distribution of oxygen, water, etc. This study presents one of the first full-scale stack three-dimensional (3D) simulations for proton exchange membrane (PEM) fuel cell to investigate temperature distribution, cell/stack performance, and impact of air cooling. The stack consists of 30 cells with the active area of 50 mm × 200 mm for each fuel cell. The manifold and all the basic components are included in the computational domain, while the flow field structure is treated as porous media in order to reduce the computational burden. The model predictions are validated against the experimentally measured voltage and detailed temperature distribution under different currents. It is found that significant differences in temperature are present between the fuel cells at the two sides and that in the middle, and the oxygen content becomes lower at a higher temperature site due to the local increased water vapor concentration. As a consequence, thermal behavior has a decisive effect on the distributions of temperature, reactant concentration, membrane hydration, current density, etc., inside this air-cooled stack. It is also found that increasing the cooling air flow rate not only decreases the stack temperature, but also reduces the temperature variation, which further benefit the uniform distributions of oxygen, water vapor, etc. in the stack. [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]

Highlights: [•] The flame temperature was significantly affected by heat input at lower flame speed. [•] The flame temperature was affected by heat loss at higher flame velocity. [•] The flame temperature of foams was lower than that of packed beads and honeycombs. [•] The CO emission was mainly determined by the flame temperature. [•] The HC emission was mainly controlled by the mixing uniformity of fuel/air. [Copyright &y& Elsevier]

Abstract: The natural convection on metallic foam-sintered plate at different inclination angles was experimentally studied. Seven copper foam samples with different pore densities (10–40 pore per inch), porosities (0.90–0.95), and aspect ratios (the ratio of foam thickness to sample length, 0.1–0.5) were measured at inclination angles of 0° (vertical orientation), 15°, 30°, 45°, 60°, 75°, 90° (horizontal orientation). The heat conduction and natural convection inside the foam both contributed to the total heat transfer. Although, the form and viscous drag, which are influenced by permeability and viscous friction in the thermal boundary layer respectively, tend to suppress the natural convection, the heat transfer was finally enhanced by the foam sintered surface due to large surface area extension. Optimum inclination range 60–75° corresponding to maximum average Nu number was found in the heat flux range of 600–1800W/m2. The sintered foam surface with lower porosity and pore density was recommended for heat transfer enhancement. Particularly, the sample with porosity 0.9, pore density of 10PPI, aspect ratio of 0.5 offered the highest average Nu number among the studied samples. An empirical correlation for modified Nusselt number at isoflux boundary condition considering the foam morphology parameter and inclination angle was proposed within deviation ±15% between the correlation and the experimental data. [Copyright &y& Elsevier]