•Experimental and numerical analyses of a novel micromixer with two-layer crossing channels were performed.•The micromixer showed at least 96% mixing throughout a Reynolds number range (0.2–120).•At ...low Reynolds numbers (0.2–10), the micromixer showed about 99% mixing at the exit.•The proposed micromixer showed lower pressure drop than TLCCM for Re larger than 10.
A novel design is presented for a chaotic micromixer using two-layer serpentine crossing microchannels. The performance of the micromixer was analyzed both numerically and experimentally. The numerical analysis was performed using three-dimensional Navier-Stokes equations with a convection–diffusion model for the species concentration in a Reynolds number range of 0.2–120. An experimental model of the micromixer was fabricated by soft lithography with polydimethylsiloxane (PDMS). Two working fluids, water and dye-water mixture were used for numerical analysis except for the experimental validation of numerical results. Both the numerical and experimental analyses confirm that the micromixer achieves a high level of mixing over a wide range of Reynolds numbers through splitting, enlarging, recombination, and folding mechanisms. The micromixer showed over 95% mixing throughout the tested range of Reynolds number. Especially, about 99% mixing was achieved at Reynolds numbers less than ten. Thus, the proposed micromixer can be used in microfluidic systems which require fast mixing at low Reynolds numbers.
•A novel hybrid power-unit based on a passive fuel cell/battery system is proposed.•The hybrid power-unit consists of 5 fuel cell stacks and 6 battery modules.•A dedicated test bench has been ...realized for reproducing the Artemis duty-cycle.•The fuel cell unit produces about the 51% of the energy request by the load.•The average efficiency of the fuel cell unit during the Artemis duty-cycle is 47%.
Hybrid fuel cell/battery power-unit configurations are gaining growing attention; in fact, they offer advantages in terms of fuel cell downsizing, higher efficiency and fast fueling. In these configurations, the power-sharing is actively controlled employing power electronics, mainly boost converters, that affect the costs and performance of the system. In this work, a novel hybrid power-unit based on a passive fuel cell/battery system is proposed for a lightweight electric vehicle (5 kW nominal power). This configuration eliminates the need for costly power converters, and increases the overall performance. The hybrid power-unit consists of 5 fuel cell stacks, 6 battery modules and two resistors that allow safe fuel cell start-up and shut-down. The power profile requested by the electric motor is derived from an ARTEMIS drive cycle and tested by means of two electronic loads.
The analysis on the power-unit behavior and performance has been carried out by means of a numerical model and experimental activities.
The power-unit response has been analyzed focusing on: i) start-up operation; ii) drive cycle operation; iii) shut-down operation. During the whole test, the fuel cell produced about 51% of the total requested energy while the battery pack about 49%. The average stack efficiency during operation resulted to be 47%, while it dropped to 41% considering also start-up and shut-down.
Results proved the technical feasibility as well as the safety of the system and showed that the developed power-unit has promising features for practical applications.
Hydrogen refueling stations (HRSs) are key infrastructures rapidly spreading out to support the deployment of fuel cell electric vehicles for several mobility purposes. The research interest in these ...energy systems is increasing, focusing on different research branches: research on innovation on equipment and technology, proposal and development of station layout, and research aiming to provide experimental data sets for performance investigation. The present manuscript aims to present an overview of the most recent literature on hydrogen stations, by presenting the technological status of the system at the global level, and their research enhancement on the involved components and processes. After the review of the mentioned aspects, this paper will present the already existing layouts and the potential configurations of such infrastructures, considering several options of the delivery routes, the end-user destination, and hydrogen storage thermodynamic status, whether liquid or gaseous.
•Overview of the most recent literature on HRS operation and experimental activities•Discussion on already existing layouts of hydrogen refueling stations•Hydrogen storage thermodynamic status, liquid or gaseous, and related HRS layout•Research enhancement on the involved components and processes
Rubber self-compacting concrete (RSCC), recognized as an environmentally friendly material, possesses excellent resistance to impact. However, the inclusion of rubber particles significantly ...decreases its compressive strength. This study investigated the compressive properties of RSCC with rubber particles substituting for fine aggregate volume percentages of 0 %, 10 %, 20 %, and 30 % after exposure at 25, 300, 600, and 900 °C for 3 h. The interface conditions among the rubber particles and the mortar were examined using scanning electron microscopy (SEM). The findings reveal that: (1) Both the compressive strength and the modulus of elasticity of RSCC exhibit a pronounced decline as the exposure elevates, with the maximum reduction reaching 84.25 % and 89.42 % respectively (where the substitution percentage of rubber particles is 30 %), compared to values at room temperature. Conversely, the peak strain exhibited an increase of 130.41 % (with the substitution percentage of rubber particles being 30 %). (2) As the substitution percentage of rubber particles increases, the decline in RSCC's compressive strength and elastic modulus after cooling at elevated temperatures is less noticeable than at room temperature, and the peak strain of RSCC exhibits negligible increase after being subjected to high temperatures. (3) Prediction equations and constitutive models for the compressive strength and peak strain of RSCC post-high temperature exposure are proposed in light of the experimental data. The comparison shows an obvious connection between the experimental outcomes and the predictive results.
•The mechanical properties of the RSCC fell dramatically as the temperature increased.•RSCC loses less compressive strength after elevated temperatures with increased substitution percentage of rubber particles.•The increase in peak strain of RSCC post-high temperature was negligible with the elevation of rubber particle substitution.•Prediction formulas for the stress–strain constitutive of RSCC after high-temperature treatment were proposed.
The present paper deals with the influence of different hydrogen enrichment on oxy-fuel combustion of natural gas, enabling important insights regarding decarbonization of high-temperature processes. ...Experiments were conducted using a high-impulse multifuel burner for industrial applications for hydrogen contents between 0–100%. The fuel input varied between 100 and 140 kW, while water-cooled lances were used to simulatethermal loads. The analysis included temperature measurement points, atomic and energy balances and the cooling capacity of the thermal load for steady-state operation. The obtained results show that the flue gas temperature decreases by up to 126 K for pure hydrogen, while the cooling capacities of the thermal load increased by up to 16.3% at constant calorific energy input. The flames for different hydrogen enrichments were also compared visually. Overall, all investigated fuel blends were highly interchangeable with the investigated burner and showed high potential for a timely decarbonization of industrial heating.
•Oxy-fuel combustion of hydrogen-enriched natural gas with 0 to 100 % H2.•Experimental analysis of a semi-industrial scale furnace at steady state conditions.•How the flame length, heat distribution and flow rates depend on H2 content in NG.•Analysis of mass and energy fluxes with positive pressure within the furnace.•Promising solution for timely CO2 reduction in high-temperature processes.
This paper presents an extensive experimental investigation of the circular recycled aggregate concrete filled steel tubes (RACFST) stub columns under to axial compression to assess their ...cross-section behaviour. Recycled aggregate concrete is a sustainable concrete produced with recycled coarse aggregate (RAC) from demolition wastes generally used to fabricate non-structural elements. When compared with natural coarse aggregate (NCA), the recycled coarse aggregate presents lower mechanical properties due to physical and chemical changes that occurred during the recycling process, and thus the resulting RAC possess lower strength than the conventional natural aggregate concrete. However, the confinement provided by the circular steel tube can increase the strength and ductility of RAC in recycled aggregate concrete filled steel tubes (RACFST) columns. The test programme presented in this paper comprised twenty-three composite columns with replacement ratios (the mass percentages of the NCA replaced by RCA in concrete) corresponding to 0% (nature coarse aggregate), 30 and 50% (recycled aggregate concrete), plus four steel columns used for comparison. The experiments have shown that, as anticipated, the concrete core enhances the composite section load-carrying capacity. However, the control over the contents of this concrete core influences the composite section's ductility. If the fill material presents a brittle behaviour, stress redistributions occur in both steel and concrete to compensate for this effect. Since the behaviour of natural aggregate concrete filled steel tubes (NACFST) and RACFST columns are similar, the present paper starts from a study based on a comparative assessment of the recommendations presented in ABNT NBR 8800, ABNT NBR 16239, AISC 360–16, Eurocode 4 and Australian/New Zealand AS/NZS 2327 design standards. These design recommendations proved to be consistent and in line with the performed experiments. Additionally, the results indicated that the cross-section slenderness ratio (D/t) and the confinement ratio directly influence the composite section response.
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•An experimental programme was carried out comprising recycled aggregate concrete-filled steel tubular (RACFST) columns.•Different replacement ratios of the nature coarse aggregate replaced by recycled aggregate concrete were assessed.•The steel tubes were produced using a high-frequency induction welding process minimizing the residual stress effects.•The RACFST stub columns presented similar resistances with NACFST stub columns due to confinement contribution.•EC4 and AS/NZS 2327 predictions provide a good approach to be used to RACFST stub columns’ design.•NBR 8800 and AISC 360-16 presented very conservative predictions for the columns’ strength.
A small subset of education studies analyzes school data collected seasonally (separating the summer from the school year). At first, this work was primarily known for documenting learning loss in ...the summers, but scholars have since recognized that observing how inequality changes between summer and school periods provides leverage for understanding how schools influence inequality. Results based on this analytic technique confirm current views in some ways, but in other ways the patterns challenge existing wisdom. For example, Black/White gaps in math and reading skills often grow faster when school is in versus out, consistent with the view that schools exacerbate racial inequality. But socioeconomic gaps produce the opposite pattern, suggesting that schools are compensatory across this dimension. In this review, I consider the logic behind seasonal research, the empirical patterns it has produced, and the kinds of new questions it motivates.
A new absorber surface is designed for solar air heaters to make them compact and enhance heat transfer parameters. The current paper presents the novel absorber design using a tubular surface having ...three-pass in counter-flow. The absorber tubes are constructed from thin sheets of aluminium; 15 tubes are closely spaced in line with each other to establish three-pass, i.e. five tubes per pass. The research paper investigates numerically and experimentally the thermo-hydraulic performance of a Tubular Three-pass Solar Air Heater (TTPSAH). The numerical model was developed using MATLAB to predict the performance and outlet air temperature. The error in numerical and experimental evaluation is approximately 5%, showing promising results. It was found that the TTPSAH accelerates heat transfer in a compact surface area. The maximum thermal efficiency was evaluated as 60.04%, 41% and 33.3% for an airflow rate of 0.006 kg/s, 0.004 kg/s, and 0.002 kg/s respectively. Thermal enhancement with a maximum outlet air temperature of 110.6 °C, 91.4 °C and 80.2 °C was recorded at a mass flow rate of 0.002 kg/s, 0.004 kg/s and 0.006 kg/s in glazed conditions. Furthermore, the research includes an estimation of the energy cost per kilowatt-hour (kWh), which amounts to $0.017, $0.025, and $0.0311 for mass flow rates of 0.006 kg/s, 0.004 kg/s, and 0.002 kg/s, respectively.
•To increase the applicability of solar energy a novel tubular three-pass solar air heaters was designed.•The mathematical model and experimental results are in good agreement.•The maximum outlet air temperature of 110.6 °C attained for a flow rate of 0.002 kg/s.•The thermohydraulic performance parameters of TTPSAH was also studied.
