Search Results (521)

The paper presents the experimental study of the zeolite heat storage unit discharging process in a laboratory scale. The Authors focused on the discharging process, which utilizes adsorption of water, in the form of steam, on zeolite, because the adsorption process is considered as more challenging in terms of reaction kinetics and heat transfer. The Authors designed and built a laboratory stand with a sorption heat storage unit filled with 13X zeolite and with a separated heat transfer fluid system, where air was used for discharging. Dynamic parameters including the temperature of inlet and outlet air and the temperature distribution inside the zeolite bed during the discharging process were investigated. The gathered measurement data were used to determine the heat fluxes and to compute dynamic heat balance of the thermal storage unit including internal and external heat losses. It was demonstrated that the applied design and scale of the thermal storage unit allows to reach the thermal power over 300 W and heat the discharging air from 40 °C to over 110 °C. The innovative aspect of the study is the improvement of operational stability of the sorption heat storage unit through the implementation of a heat exchanger design that separates the heat transfer fluid from the zeolite bed, as well as a control system with a neural network layer for predicting the mass flow rate of steam. Full article

Based on a realistic three-dimensional geometric model, this study numerically investigates the influence of yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) on the aerothermal performance of an annular combustor by employing a conjugate heat transfer (CHT) and non-premixed reactive flow coupling approach. Considering the inner and outer liners, double-wall exhaust bends, and the full configuration of cooling holes, two cases—with and without the TBCs—were analyzed. The results reveal that the application of TBCs markedly modifies the near-wall flow structures and heat transfer characteristics. The cooling air mass flow rate decreases from 0.1211 kg/s to 0.1023 kg/s, corresponding to a 15.5% reduction in cooling load. The main recirculation zone becomes more compact, with enhanced vortex intensity, smoother velocity distribution, and improved flame stability. The high-temperature core region extends further downstream, and the peak temperature increases by approximately 80–100 K, indicating more complete combustion and greater heat retention. The outlet temperature distribution factor (OTDF) decreases from 57.34% to 44.48%, leading to a 22.4% improvement in temperature uniformity. The average wall temperatures of the inner liner, outer liner, and exhaust bend decrease by 3.7%, 8.8%, and 7.5%, respectively, with local peak reductions exceeding 250 K. The study demonstrates that the YSZ TBCs enhances the combustor’s thermal protection capability, flow stability, and temperature uniformity through a coupled mechanism of “thermal insulation–flow reconstruction–energy redistribution.” It should be noted that this study considers only the effect of the ceramic top coat of the TBCs, excluding the metallic bond coat and the thermally grown oxide (TGO) layer. Full article

Alfalfa, as a high-quality forage crop, undergoes a drying process that is critical to its product quality and commercial value. This paper systematically reviews research progress on alfalfa drying technologies and equipment throughout the entire process. First, it proposes a comprehensive production technology model covering three core stages: drying pretreatment, drying conditioning and optimization, and product quality control. This model emphasizes adaptability to material characteristics, processing methods, product quality, and economic efficiency. Second, it delves into the drying mechanisms of alfalfa, detailing the forms of water presence (free water or bound water), migration pathways, and the three-stage water loss periods: constant rate, first falling rate, and second falling rate. It identifies “asynchronous drying of stems and leaves” as the core issue causing nutrient loss and technical challenges. Subsequently, a comprehensive review was conducted on pre-treatment equipment such as mowing and flattening, as well as various drying methods including natural drying, hot-air drying, solar drying, and microwave drying. The principles, characteristics, and impacts of these methods on alfalfa quality were evaluated. Additionally, a comprehensive quality assessment system for alfalfa hay was summarized, incorporating physical, chemical, and biological methods. Finally, future development directions are proposed: developing domestically produced, intelligent drying equipment; integrating clean energy to reduce energy consumption; and achieving precise control of drying processes through establishing multi-scale heat and mass transfer models. These efforts will advance China’s alfalfa drying industry toward standardization, integration, and intelligence, ensuring a stable supply of high-quality hay. Full article

Understanding heat and mass transfer phenomena is fundamental to successful roasting practices. These phenomena can be quantified via an energy balance over the roaster, whereby heat and mass transfer equations can be formulated. Through rigorous calibration of the simulation with experimentally derived data obtained using a spouted bed roaster, a zero-dimensional, batch-scale model of coffee roasting was developed to predict time–temperature roasting profiles. Calibration involved implementation of (i) an airflow calibration to determine the air mass flow rate and velocity of air input to the roaster, (ii) kinetic models and empirical correlations to describe coffee’s physicochemical development during roasting and (iii) a non-linear least squares fitting procedure to estimate system-dependent parameters—such as the thermal response coefficient and heat transfer effectiveness—that are otherwise difficult to determine. In this way, user inputs of roasting parameters relevant for spouted bed roasters—batch size, airflow and inlet air temperature—were probed to capture the full kinetics of coffee roasting under various process conditions, from which rate constants for mass loss kinetics were determined. In this study, development of the zero-dimensional, batch-scale simulation is described, alongside rigorous calibration with pilot-scale roasting trials. These simulations are application-ready and can be used by product and process developers to roast coffee in silico, providing not just an informative tool, but one that can be instructive and predict requirements for raw material (green coffee) properties, roasting process conditions, or roasted coffee properties. Full article

Soil moisture exhibits high spatio-temporal variability that necessitates dense monitoring networks, yet the cost of commercial sensors often limits widespread deployment. Despite the mass production of low-cost capacitive soil moisture sensors driven by IoT applications, significant gaps remain in their robust characterisation and in the availability of open-source, reproducible monitoring systems. This study pursues two primary objectives: (1) to develop an open-source, low-cost, off-grid soil moisture monitoring station (picoSMMS) and (2) to conduct a sensor-unit-specific calibration of a popular low-cost capacitive soil moisture sensor (LCSMS; DFRobot SEN0193) by relating its raw output to bulk static relative dielectric permittivity (${ϵ}_s$), with the additional aim of transferring technological gains from consumer electronics to hydrological monitoring while fostering community-driven improvements. The picoSMMS was built using readily available consumer electronics and programmed in MicroPython. Laboratory calibration followed standardised protocols using reference media spanning permittivities from 1.0 (air) to approximately 80.0 (water) under non-conducting, non-relaxing conditions at 25 ± 1 °C with temperature-dependency characterisation. Models were developed relating the sensor’s output and temperature to ${ϵ}_s$. Within the target permittivity range (2.5–35.5), the LCSMS achieved a mean absolute error of 1.29 ± 1.07, corresponding to an absolute error of 0.02 ± 0.01 in volumetric water content (VWC). Benchmarking revealed that the LCSMS is competitive with the ML2 ThetaProbe, and outperforms the PR2/6 ProfileProbe, but is less accurate than the SMT100. Notably, applying the air–water normalisation procedure to benchmark sensors significantly improved their performance, particularly for the ML2 ThetaProbe and PR2/6 ProfileProbe. A brief field deployment demonstrated the picoSMMS’s ability to closely track co-located HydraProbe sensors. Important limitations include the following: inter-sensor variability assessment was limited by the small sensor ensemble (only two units), and with a larger sample size, the LCSMS may exhibit greater variability, potentially resulting in larger prediction errors; the characterisation was conducted under non-saline conditions and may not apply to peat or high-clay soils; the calibration is best suited for the target permittivity range (2.5–35.5) typical of mineral soils; and the brief field deployment was insufficient for long-term validation. Future work should assess inter-sensor variability across larger sensor populations, characterise the LCSMS under varying salinity, and conduct long-term field validation. Full article

The formation of bubbles at an orifice is a key problem in gas–liquid two-phase flow. In the electronic atomizer, the bubble size and generation frequency formed at the gas exchange port are important factors affecting the heat and mass transfer efficiency and two-phase flow in the atomization process. Therefore, it is of great theoretical and practical significance to study the process of bubble growth and detachment at the orifice. In this work, the dynamic change in bubble volume during the periodic growth of the orifice is analyzed by visual experiments. The effects of outlet liquid flow rate, orifice parameter, and liquid properties on bubble detachment volume and detachment frequency are discussed. It is found that under different orifice diameters and outlet liquid flow rates, the bubble generation period can be divided into three forms: single-, double-, and triple-bubble periodicities based on the number of bubbles in the period. The detachment frequency and detachment volume of bubbles increase with the increase the in outlet flow rate. The change in liquid properties also affects the bubble growth and detachment characteristics. This work provides a theoretical basis for the design of an air exchange structure in an electronic atomizer. Full article

Methane is a potent greenhouse gas that requires its emissions to be mitigated. A significant source for methane emissions is in the form of the biogas that is produced from anaerobic digestion in wastewater reclamation and landfill facilities. Biogas has a high valorization potential in the form of its bioconversion into ectoines, an active ingredient in skin care products, by halotolerant alkaliphilic methanotrophs. Cultures of Methylotuvimicrobium alcaliphilum 20Z were grown in bench scale stirred-tank reactors to determine factors to improve methane uptake and removal. Tangential flow filtration was also implemented for a bio-milking method to recover ectoine from culture media. Methane uptake and reactor productivity increased, with a temperature of 28 °C compared with 21 °C. Decreasing the methane gas bubble diameter by decreasing the sparger pore size from 1 mm to 0.5 µm significantly improved methane removal and reactor productivity by increasing mass transfer. Premixing methane and air before sparging into the reactor saw a higher removal of methane, while sparging methane and air separately created an increase in reactor productivity. Maximum methane removal efficiency was observed to be 70.56% ± 0.54 which translated to a CH₄-EC of 93.82 ± 3.36 g CH₄ m⁻³ h⁻¹. Maximum ectoine yields was observed to be 0.579 mg ectoine L⁻¹ h⁻¹. Full article

A greenhouse solar dryer was used to study the drying behavior of mesquite pods, and a radiation model for participating media was numerically solved to predict the air temperature in the dryer. The model was solved for a stationary state by considering the environmental conditions. The transfer coefficients were calculated for natural and forced convection. In the case of forced convection, an average airflow of 0.5668 m/s (SD = 0.1121) was provided over the trays. The weight of the pods, their temperature, air temperature, ambient temperature, relative humidity, and solar irradiation were recorded. The average heat transfer coefficients for natural and forced convection were 2.9294 W/m² °C and 6.3772 W/m² °C, respectively. The average mass transfer coefficients for natural and forced convection were 0.002987 kg/m² s and 0.00601 kg/m² s, respectively. The greenhouse dryer showed a high dependence on the weather conditions, showing important disturbances to air temperature. For the experiment with forced convection, a reabsorption of moisture was observed during the night; nevertheless, the final moisture content of the pods was below 0.05 g moisture/g dry matter, which was convenient for the subsequent grinding process. The radiation model correctly describes the average air temperature in the greenhouse volume. A reduction in thermal fluctuations will be important to improve the process. Full article

The economic viability of solar drying mainly depends on the appropriate design of air collectors, which are the main parts of a solar dryer. Although the V-groove collector has been reported to have one of the highest efficiencies, no comprehensive parameter analysis on this collector has been reported in the literature. This detailed study investigates the influence of different operating and design variables on the outlet temperature and the efficiency of the air collector. The parameter analysis also contributed to the development of the most effective design guidelines. The parameters examined include solar radiation, airflow rate, incoming air temperature, collector length, height of the vee, the spacing between the top of the vee and the transparent cover, number of such covers, and the thickness of the back insulation. The airflow rate is identified to be the essential operating parameter that affects the efficiency, and a better heat transfer rate is noticed in the intermediate flow state. It is also found that to achieve the best performance, it is necessary to maintain a mass airflow rate between 0.015 and 0.055 kg/m²s, to have incoming air at a near-atmospheric temperature, and to have two transparent covers on top. Full article

This paper reports a novel effort to estimate and evaluate the coefficients of Hg transfer across the water/air interface in lakes such as Cane Creek Lake (CCL, Cookeville, TN, USA). This was accomplished by calculating the coefficients (k_w) using the Two-Thin Film (TTF) Model for Hg transfer together with the field-measured data of Hg emission flux (F), dissolved gaseous mercury concentration (DGM), air Hg concentration (C_a), and water temperature for Henry’s coefficient (K_H) obtained from a separate field study at the CCL. The daily mean k_w values range from 0.045 to 0.21 m h⁻¹, with the min. at 0.0025–0.14 and the max. at 0.079–0.41 m h⁻¹, generally higher for the summer, and from 0.0092 to 0.15, with the min. at 0.0032–0.033 and the max. at 0.017–0.31 m h⁻¹, generally lower for the fall and winter, exhibiting an apparent seasonal trend. The highest k_w values occur in August (mean: 0.21, max.: 0.41 m h⁻¹). Our k_w results add to and enrich the aquatic interfacial Hg transfer coefficient database and provide an alternative avenue to evaluate and select the coefficients for the TTF Model’s application. The k_w results are of value in gaining insights into the Hg transfer actually occurring across the water/air interface under environmental influences (e.g., wind/wave, solar radiation). Our k_w results do not show a clear, consistent correlation of k_w with wind/wave effect, nor sunlight effect, in spite of some correlations in sporadic cases. Generally, the k_w values do not exbibit the trends prescribed by the model sensitivity study. The comparisons of our k_w results with those obtained using wind-based transfer models (the Liss/Merlivat Model, the Wanninkhof Model, and the modified linear model) show that they depart from each other. The findings of this study indicate that the TTF Model has limitations and weaknesses. One major assumption of the TTF Model is the equilibrium of the Hg distribution between the air and water films across the water/air interface. The predominant oversaturation of DGM shown by our DGM data evidently challenges this assumption. This study suggests that aquatic interfacial Hg transfer is considerably more complicated, involving a group of factors, more than just wind and wave. Full article

This study addresses the operational challenges of conventional packed cooling towers in seawater applications, where salt deposition and blockage significantly impair performance. A packing-free shower cooling tower (SCT) utilizing droplet-based heat and mass transfer is proposed as a robust alternative for high-salinity applications where conventional packed towers are prone to fouling and blockage. A comprehensive numerical model was developed and validated experimentally, showing a maximum error of less than 6% in predicting outlet water temperature. The analysis demonstrates that increasing salinity markedly reduces cooling efficiency—for instance, at threefold concentration (S ≈ 57.96 g/kg), efficiency decreased by 5.59% in summer and 4.91% in winter compared to freshwater, due to reduced vapor pressure and inhibited evaporation. However, elevating the inlet water temperature and air-to-water ratio partially counteracted these effects by enhancing evaporative and convective transfer. Larger droplet diameters also adversely affected performance, with cooling efficiency dropping from 75.87% (1 mm droplets) to 28.92% (3.5 mm droplets) in freshwater summer conditions. Notably, seasonal variations influenced the magnitude of salinity-related performance loss, with winter operations exhibiting less degradation. These findings provide critical insights and a reliable predictive tool for the design and optimization of high-salinity cooling systems. Full article

Lithium-oxygen batteries (LOBs) are limited by sluggish oxygen redox kinetics and cathode instability. Herein, we report a cobalt particle catalyst encapsulated in nitrogen-doped carbon (Co@NC) with a three-dimensional hierarchical architecture, synthesized via a chitosan-derived hierarchical porous carbon framework. This innovative design integrates uniformly dispersed ultra-thin carbon shells (11.7 nm), pyridinic nitrogen doping, and Co particles (1.41 μm) stabilized through carbon-support electronic coupling. The hierarchical porosity facilitates rapid O₂/Li⁺ mass transport, while pyridinic N sites act as dual-function electrocatalytic centers for Li₂O₂ nucleation and charge transfer kinetics. Co@NC achieves 11,213 mAh g⁻¹ at 200 mA g⁻¹ (126.5% higher than nitrogen-doped carbon) and maintains 1.54 V overpotential (500 mAh g⁻¹). These metrics outperform benchmark catalysts, addressing kinetic and stability challenges in LOBs. The study advances electrocatalyst design by integrating structural optimization, heteroatom doping, and electronic coupling strategies for high-performance metal–air batteries. Full article

Inefficient drying of alfalfa round bales causes significant nutrient loss (up to 50%) and quality degradation due primarily to uneven drying in existing processing methods. To address this challenge requiring dedicated equipment and optimized processes, this study developed a specialized hot-air drying test bench (CGT-1). A coupled heat and mass transfer model was established, and 3D dynamic simulations of temperature, humidity, and wind speed distributions within bales were performed using COMSOL multiphysics to evaluate drying inhomogeneity. Single-factor experiments and multi-factor response surface methodology (RSM) based on Box–Behnken design were employed to investigate the effects of hot air temperature (50–65 °C), wind speed (2–5 m/s), and air duct opening diameter (400–600 mm) on moisture content, drying rate, and energy consumption. Results demonstrated that larger duct diameters (600 mm) and higher wind speeds (5 m/s) significantly enhanced field uniformity. RSM optimization identified optimal parameters: temperature at 65 °C, wind speed of 5 m/s, and duct diameter of 600 mm, achieving a drying time of 119.2 min and a drying rate of 0.62 kg/(kg·min). Validation experiments confirmed the model’s accuracy. These findings provide a solid theoretical foundation and technical support for designing and optimizing alfalfa round-bale drying equipment. Future work should explore segmented drying strategies to enhance energy efficiency. Full article

The development of a prototype of a cooking device based on catalytic hydrogen combustion (CHC) is presented in this research. CHC is the catalytic reaction between hydrogen (H₂) and oxygen (O₂), generating heat and water vapour as the only by-product. In the developed prototype, only H₂ gas is fed to the catalytic surface while air is entrained from the environment by convection (i.e., passive approach). Therefore, the convective mass transfer during the exothermic reaction between H₂ and O₂ allows a continuous H₂/air mixture supply to the catalytic surface. In this prototype, 30 g of Pt/Al₂O₃ (0.5 wt% Pt) catalyst is used for the H₂ combustion. The developed prototype performance was evaluated by determining its combustion temperature, H₂ slip (amount of unreacted H₂ in the flue gas), and flue gas composition with respect to NO_x formation. Tests were performed at inlet H₂ flows of 1–5 normal (N) L/min, which equates to a power output of 0.18–0.90 kW, respectively. The observed combustion temperature of the catalyst surface, determined using an IR camera, was in the range of 324.5 °C (at 1 NL/min) to 611.2 °C (at 5 NL/min). The H₂ slip of <1.75 vol% was observed during CHC at 1–5 NL/min H₂ flow. The maximum efficiency of 42% was determined at 1 NL/min H₂ flow and a power output of 0.18 kW. Full article

The secondary air system plays important roles in gas turbines, such as cooling hot-end components, sealing the rim, and balancing axial forces. In this paper, the flow structure and the heat transfer characteristics of the rotating disk cavity with two inlets and single outlet is studied by CFD (Computational Fluid Dynamics) approach. The effect and mechanism under higher rotational speed and larger mass flow rate are also discussed. The results show that a large-scale vortex is induced by the central inlet jet in the low-radius region of the cavity, while the flow structure in the high-radius region is significantly influenced by rotational speed and flow rate. Increasing the rotational speed generally enhances heat transfer because it amplifies the differential rotational linear velocity between the disk surface and nearby wall flow, consequently thinning the boundary layer. Increasing the mass flow rate enhances heat transfer through two primary mechanisms: firstly, it elevates the turbulence intensity of the near-wall fluid; secondly, the higher radial velocity results in a thinner boundary layer. Full article