Search Results (50)

In recent decades, international interest has grown in the design and implementation of evolutionary reactors based on passive systems. The design of such systems requires reliable and validated numerical tools capable of simulating phenomena driven by very small forces, especially when compared to active systems. For this reason, several international research projects aim to assess the capabilities and limitations of numerical tools in modelling passive systems and their associated physical phenomena. The HERO-2 facility was designed to provide preliminary experimental data for characterizing bayonet tubes and exploring their potential application as Steam Generators (SGs) in advanced nuclear reactor designs, such as Small Modular Reactors (SMRs). Following the agreement between the Italian Ministry of Economic Development and the ENEA, multiple experimental campaigns were conducted, and a RELAP5 (R5) input deck of the facility has been developed. Considering the RELAP5 limits in simulating condensation phenomena encountered in previous studies, the primary objective of this study is to enhance the capabilities of the code in simulating condensation phenomena in horizontal pipes under natural circulation conditions with the implementation of Thome correlation and, in the second instance, to re-evaluate the numerical model of the HERO-2 facility. Moreover, a comprehensive uncertainty analysis (UA) is carried out to identify the key parameters influencing the simulations. The analysis revealed that the simulation results are strongly affected by the filling ratio uncertainties, a given initial condition that, together with the power supplied, determines the most important thermal-hydraulic (T/H) test parameters, such as the saturation pressure, the void fraction, mass flow rate, etc. Overall, the study provides a deeper understanding of the factors governing passive system performance and highlights the importance of accurately characterizing the experimental boundary and initial conditions in the verification and validation activities of a T/H code. Full article

Pressurized chemical looping combustion (PCLC) provides the benefit of simplifying the carbon capture process by generating a flue gas stream with high CO₂ concentration. However, flue gas polishing is required to remove the residual impurities for pipeline transport. The intensified heat exchanger reactor (IHXR) is a promising method for flue gas polishing while maximizing useful heat recovery that incorporates alternating catalytic packed beds with interstage cooling via printed circuit heat exchangers (PCHE). This work offers a design process for an IHXR capable of polishing a flue gas stream from a 100 MWth natural gas-fired PCLC unit while recovering 1.6 MW of useful heat in the form of saturated steam at 180 °C. Simulation work performed in Aspen HYSYS was used to determine the polished flue gas outlet species concentrations as well as the required number and size of the packed bed sections. The PCHEs for interstage cooling were sized via a thermal circuit approach. The final IHXR consists of six packed beds at 0.06 m in length and five PCHEs at 0.265 m in length, combining to a total IHXR length of 1.685 m. The height and width of the IHXR is shared between the packed beds and PCHEs at 0.91 m and 0.45 m, respectively. The resulting IHXR is capable of recovering heat at a rate of approximately 2.3 MW/m³. Full article

To explore the influence of cooking methods on the flavor parameters of Tibetan sheep, various techniques such as atmospheric-pressure (AP), high-pressure (HP), atmospheric-pressure high-pressure (APHP), and high-pressure atmospheric-pressure (HPAP) cooking were tested. The results indicated that APHP and HP cooking yielded the best sensory qualities, accounting for 26.15% and 25.51%, respectively. The HP group had the highest amino acid content at 34%, enhancing the meat’s sweet taste due to alanine, glycine, arginine, and methionine. Among 40 detected fatty acids, the order of saturated fatty acid (SFA), monounsaturated fatty acid (MUFA), polyunsaturated fatty acid (PUFA), and n-6/n-3 content was AP > APHP > HPAP > HP (p < 0.05). An electronic tongue and nose identified aroma components across the four cooking methods. Similarities in aroma were observed among the samples after cooking, while significant differences were found in the aroma components between the AP group and the other three cooking methods (p < 0.05). The gas chromatography–ion mobility spectrometry (GC–IMS) and gas chromatography–mass spectrometry (GC–MS) analyses of the meat in the four groups indicated that there were significant differences in volatile compounds among meat cooked with different methods (p < 0.05), with 56 and 365 flavor compounds detected by the two analytical techniques, respectively. Moreover, the GC–MS results indicated that the flavor substance content in the HP group accounted for 30.80% among these four sample groups. This comprehensive analysis showed that high-pressure steaming could significantly improve the flavor quality of Tibetan sheep, providing a theoretical basis and empirical reference for the optimization of pre-treatment conditions and the processing of Tibetan sheep. Full article

To enhance the steam parameters of steam injection boilers during the thermal recovery of heavy oil while ensuring the safe and stable operation of boiler pipelines, this study conducted two-phase flow boiling numerical simulations in a horizontal heated tube with an inner diameter of 65 mm, using water and water vapor as working fluids. The analysis focused on the gas–liquid phase distribution, temperature profiles, near-wall fluid velocity, and pressure drop along both the axial and radial directions of the tube. Furthermore, the effects of heat flux density, mass flow rate, and inlet subcooling on these parameters were systematically investigated. The results reveal that higher heat fluxes intensify the velocity difference between the upper and lower tube walls and enlarge the temperature gradient across the wall surface. A reduction in mass flow rate increases the gas phase fraction within the tube and causes the occurrence of identical flow patterns at earlier axial positions. Additionally, the onset of nucleate boiling shifts upstream, accompanied by an increase and upstream movement of the wall’s maximum temperature. An increase in inlet subcooling prolongs the time required for the working fluid mixture to reach saturation, thereby decreasing the gas phase fraction and delaying the appearance of the same flow patterns. Finally, preventive and control strategies for ensuring the safe operation of steam injection boiler pipelines during heavy oil recovery are proposed from the perspective of flow pattern regulation. Full article

The paper presents changes in the color and acidity of beech wood with false heartwood in the process of pressure steaming at the temperature interval t = 105 °C and 125 °C during τ = 6 to 24 h. The light white-gray color of sapwood with a yellow tint changes to pale pink and red-brown to brown-red color during the steaming process. The color of beech wood with false heartwood changed to brown-gray color shades during 24 h of steaming with saturated water steam. From the measured data, as well as the visual evaluation of the color of the wood, I can conclude that, in the process of steaming beech wood with false heartwood, we can achieve color unification between false heartwood and sapwood in mode at temperature t = 105 °C for time τ = 18 h and in mode at temperature t = 125 °C for time τ = 12 h. Due to the influence of hemicellulose hydrolysis, the acidity of beech wood changes in the process of steaming. The decrease in acidity of beech wood in the temperature interval t = 105–125 °C and time τ = 6–24 h is in the range of values pH_sapwood = 5.2 to 3.6 and pH_{false heartwood} = 5.0 to 3.9. The relationship between the total color difference ∆E and the acidity change in beech sapwood and false heartwood is expressed by a second-degree polynomial function. The above mathematical relations represent a useful tool for evaluating the achieved color shade before further technological processing. Full article

Soil organic pollution poses a significant threat to agricultural safety in China, underscoring the critical importance of developing efficient remediation technologies for soil environmental protection. Steam injection, a promising method for removing organic pollutants from soil, has yet to be thoroughly investigated in terms of its energy efficiency. A novel steam injection system with horizontal wells is proposed to remediate soil xylene pollution, and a corresponding numerical model is established and solved through TOUGH2-T2VOC codes. The energy efficiency characteristics and main influencing factors of the system are analyzed. The results demonstrate that steam injection is an effective method to remediate xylene pollution. It is evaluated that during the first 1.5 years of the 5-year operation period, production xylene saturation gradually decreases from 0.3 to 0.05, and the production xylene mass flow rate gradually decreases from 0.179 kg/s to 2.448 × 10⁻⁴ kg/s. Pump power consumption gradually increases from 17.23 kW to 30.67 kW, while energy efficiency gradually decreases from 7.73 × 10⁻⁴ kg/kJ to 1.00 × 10⁻⁶ kg/kJ. Sensitivity analyses indicate that the main factors affecting the xylene mass flow rate are formation permeability, production pressure and the initial xylene saturation, and the main factors affecting energy efficiency are the steam injection flow rate, formation permeability, production pressure and initial xylene saturation. This has significant practical significance for the optimal design of the steam injection remediation scheme for soil organic pollution. Full article

The SAGP (steam and gas push) process is an effective enhanced oil recovery (EOR) method for heavy oil reservoirs. Understanding the microscopic interactions among steam, non-condensable gasses (NCGs), and heavy oil under reservoir conditions in SAGP processes is important for their EOR applications. In this study, molecular simulations were performed to investigate the microscopic interactions among steam, NCG, and heavy oil under reservoir conditions in SAGP processes. In addition, the microscopic EOR mechanisms during SAGP processes and the effects of operational parameters (NCG type, NCG–steam mole ratio, temperature, and pressure) were discussed. The results show that the diffusion and dissolution of CH₄ molecules and the extraction of steam molecules cause the molecules of saturates with light molecular weights in the oil globules to stretch and gradually detach from one another, resulting in the swelling of heavy oil. Compared with N₂, CH₄ has a stronger ability to diffuse and dissolve in heavy oil, swell the heavy oil, and reduce the density and viscosity of heavy oil. For this reason, compared with cases where N₂ is used, SAGP processes perform better when CH₄ is used, indicating that CH₄ can be used as the injected NCG in the SAGP process to improve heavy oil recovery. As the NCG–steam mole ratio and injection pressure increase, the diffusion and solubility abilities of CH₄ in heavy oil increase, enabling CH₄ to perform better in swelling the heavy oil and reducing the density and viscosity of heavy oil. Hence, increasing the NCG–steam mole ratio and injection pressure is helpful in improving the performance of SAGP processes in heavy oil reservoirs. However, the NCG–steam mole ratio and injection pressure should be reasonably determined based on actual field conditions because excessively high NCG–steam mole ratios and injection pressures lead to higher operation costs. Increasing the temperature is favorable for increasing the diffusion coefficient of CH₄ in heavy oil, swelling heavy oil, and reducing the oil density and viscosity. However, high temperatures can result in intensified thermal motion of CH₄ molecules, reduce the interaction energy between CH₄ molecules and heavy oil molecules, and increase the difference in the Hildebrand solubility parameter between heavy oil and CH₄–steam mixtures, which is unfavorable for the dissolution of CH₄ in heavy oil. This study can help readers deeply understand the microscopic interactions among steam, NCG, and heavy oil under reservoir conditions in SAGP processes and its results can provide valuable information for the actual application of SAGP processes in enhancing heavy oil recovery. Full article

The pulp and paper industry is under increasing pressure to reduce its energy consumption and carbon footprint. This study examines the feasibility of integrating high-temperature heat pumps (HTHP) into tissue paper production to enhance energy efficiency and decarbonization. Focusing on the energy-intensive drying process, the study uses data from a typical tissue paper mill to simulate and optimize an HTHP system producing four tons per hour of nine-bar saturated steam. It also addresses necessary modifications for HTHP integration applicable across the sector. Various refrigerants were analyzed, achieving a maximum coefficient of performance (COP) of 2.01. Results showed that HTHP can reduce energy consumption and emissions by up to 17% and 40%, respectively, based on the European electricity mix. Although steam production costs increase by 55% compared to fossil fuel-based systems, HTHP is more cost-effective than direct electric resistance heating, which raises costs by 196%. With a CO₂ price of EUR 100/t, HTHP offers a 12% cost reduction. However, without public funding, capital expenditures may be unsustainable in many regions, though viable in countries with favorable gas and electricity price differentials. The paper underscores the need for advancements in HTHP technology and cost reductions, emphasizing industry adaptation for seamless HTHP integration. Full article

A kettle reboiler uses the latent heat from the condensation of high-temperature and high-pressure steam in the tube to produce low-pressure saturated steam in the outer shell. The deposition of particles on the tube may change the boiling heat transfer mode from nucleate boiling to natural convection, thereby deteriorating the heat transfer performance of the kettle reboiler. Therefore, it is very important to explore the deposition characteristics of particles in the kettle reboiler. In this study, the RPI boiling model based on the Euler–Euler method is used to analyze the water boiling process on the surface of the tube bundle. The DRW model and critical adhesion velocity model based on the Euler–Lagrangian method are used to calculate the motion of particles during the boiling process and the deposition (rebound) behavior. The results show that the boiling of liquid water enhances the local flow velocity of the fluid, so that the maximum flow velocity appears around the near-wall region. The local high-speed flow disperses the particles in the wake flow of the tube bundle, which inhibits the impact of particles on the wall. As the particle size increases, the wall adhesion and fluid drag on the particles are weakened, and the gravity effect gradually becomes dominant, increasing the residence time of the particles in the tube bundle and the frequency of particle impact on the wall. The particle deposition ratio first decreases and then increases. Ultimately, most particles will be deposited in the low-speed area at the end of the tube bundle. Full article

Volatile organic compounds (VOCs) are pollutants that pose significant health and environmental risks, necessitating effective mitigation strategies. Catalytic oxidation emerges as a viable method for converting VOCs into non-toxic end products. This study focuses on synthesizing a catalyst based on calcium silicate hydrates with chromium ions in the CaO-SiO₂-Cr(NO₃)₃-H₂O system under hydrothermal conditions and evaluating its thermal stability and catalytic performance. A catalyst with varying concentrations of chromium ions (10, 25, 50, 100 mg/g Cr³⁺) was synthesized in unstirred suspensions under saturated steam pressure at a temperature of 220 °C. Isothermal curing durations were 8 h, 16 h, and 48 h. Results of X-ray diffraction and atomic absorption spectroscopy showed that hydrothermal synthesis is effective for incorporating up to 100 mg/g Cr³⁺ into calcium silicate hydrates. The catalyst with Cr³⁺ ions (50 mg/g) remained stable up to 550 °C, beyond which chromatite was formed. Catalytic oxidation experiments with propanol and propyl acetate revealed that the Cr³⁺ catalyst supported on calcium silicate hydrates enhances oxygen exchange during the heterogeneous oxidation process. Kinetic calculations indicated that the synthesized catalyst is active, with an activation energy lower than 65 kJ/mol. This study highlights the potential of Cr³⁺-intercalated calcium silicate hydrates as efficient catalysts for VOC oxidation. Full article

An alternative to the existing method of processing secondary magnesium raw materials by remelting in a salt furnace can be distillation separation into volatile metals (Mg, Zn and Cd), low-volatile metals (Al, Mn and Zr) and rare earth elements. The separation of metals may be tracked based on phase diagrams where the field boundaries of the vapor–liquid equilibrium are plotted. Due to the fact that Mg, Zn and Cd have comparable saturated vapor pressures, the possibility of the distillation separation of Mg–Zn and Mg–Cd systems using full state diagrams including the melt–vapor phase transition boundaries were determined in this work. The boundaries of these systems were calculated based on the partial values of saturated vapor, determined by the boiling point method, and presented in the form of temperature–concentration dependencies with the indicated boundaries. The field boundaries were calculated (L + V) at atmospheric pressure (101.33 kPa) and in vacuum (1.33 kPa and 0.7 kPa,) supposing the implementation of the process. The possibility of the separate extraction of zinc and cadmium from magnesium was considered using complete phase diagrams including the boundaries of the melt–steam phase transition. When considering the boundaries of the vapor–liquid equilibrium in the binary systems Mg–Zn and Mg–Cd, it was established that it is impossible to separate metals in one “evaporation–condensation” cycle in a vacuum of 1.33 and 0.7 kPa. The problem is caused by the small size of the fields (L + V) at the temperature, which suggests processes of the re-evaporation of the condensate from the previous distillation stage. The separation of zinc and cadmium from liquid alloys with magnesium under equilibrium conditions requires several repetitions of the condensate distillation process. In non-equilibrium conditions, the real processes will require a larger number of conversions. This implies the expediency of the joint evaporation of magnesium with zinc and cadmium and the use of condensate for additional charging to liquid magnesium, and the remainder of the distillation, where volatile metals such as Al, Mn, Zr and rare earth elements will be concentrated, should be directed to the preparation of ligatures for special magnesium-based alloys. Full article

Bamboo–wood composites have found extensive applications in the container flooring, furniture, and construction industries. However, commonly utilized bamboo units such as four-side-planed rectangular bamboo strips and bamboo scrimber suffer from either low utilization rates or high adhesive content. The recently developed bamboo-flattening technology, which employs softening methods with saturated high-pressure steam, may improve the utilization rate and reduce the adhesive content, but its complex processes and high cost restrict its widespread application. This study introduces a novel bamboo–wood composite utilizing high-utilization, easy-to-manufacture bamboo units processed through a straightforward flattening-and-grooving method. However, the stress concentration introduced by the grooving treatment may affect the mechanical properties and stability of the bamboo–wood composites. In order to optimize the mechanical properties and bonding performance, response surface methodology based on a central composite rotatable design was used to map the effects of hot-pressing parameters (time, temperature, and pressure) on the mechanical properties. The bamboo-woodbamboo–wood composites prepared with optimized conditions of 1.18 min/mm pressing time, 1.47 MPa pressure, and a 150 °C temperature had a 121.51 MPa modulus of rupture and an 11.85 GPa modulus of elasticity, which exhibited an error of only ~5% between the experimental and model predictions. Finite element analysis revealed that, in comparison to homogeneous flat bamboo composites, grooved bamboo composites exhibited distinct tensile ductility and toughness due to discontinuous stress fields and alternating rigid–soft layers, which alter the stress transmission and energy dissipation mechanisms. Additionally, grooving treatment not only effectively improved the surface wettability of the bamboo plants, thus enhancing the permeability of the adhesive, but also facilitated adhesive penetration into parenchymal cells and fibers. This led to the formation of a more robust glue–nail structure and chemical bonding. Full article

Highly valued for their nutritional benefits, sprouts are characterized by high water content, which promotes microbial proliferation, potentially leading to toxicity and a reduced shelf life. To address this challenge, the present study explores the application of a novel drying–texturizing approach, named IVDV (Intensification of Vaporization by Decompression to the Vacuum), to sprouts. This technique would enable faster drying of the sprouts and better preservation of their nutritional content, compared to traditional hot-air drying. Using Response Surface Methodology, optimal IVDV parameters (saturated steam pressure P, processing time t, and water content W) for wheat sprouts were defined, with a focus on preserving vitamins, proteins, and lipids, and optimizing the expansion ratio. This optimization process identified optimal experimental conditions at 5.5 bars, a duration of 15 s, and 8.8% d.b. water content. Under these conditions, the use of IVDV endowed the expanded sprouts with a crunchier and more friable texture. In addition, it significantly improved the preservation of vitamins B6 and E by 412% and 42%, respectively, compared to traditional mild hot-air drying, without significantly affecting vitamin B2, proteins, and lipids. When combined with conventional hot-air drying, IVDV not only enhanced the preservation of the sprouts’ nutritional content but also reduced drying time and energy consumption. This marks a significant advancement in sprouts preservation techniques, paving the way for novel potential applications. Full article

In this paper, under the background of low-temperature steam waste heat recovery technology, the pressure oscillation characteristics of direct-contact condensation between continuously falling droplets and saturated steam at sub-atmosphere pressure were studied. An experimental device of pressure oscillation based on an acceleration oscillation sensor was established to investigate the influence of vapor pressure and fluid velocity on the oscillation characteristics of direct-contact condensation. The results showed that as the absolute pressure increases, the peak value of oscillation decreases gradually and the time-domain periodic waveform becomes fluctuating. When the liquid flow rate is low, the condensation oscillation shows a single-peak waveform and the dominant frequency moves towards a higher frequency. When the liquid velocity increases gradually, the RMS (root mean square) of pressure oscillation remains unchanged at first and then decreases obviously. The dominant frequency of oscillation decreases from 23.68 Hz to 7.16 Hz continuously, and the amplitude of oscillation decreases in a parabolic pattern. The auto power spectrum showed that the frequencies with higher energy become unconcentrated and show fluctuation characteristics. The amplitude of the dominant frequency is about 0.0004 (m/s²)², while that of the other peak frequencies is about 0.00010–0.00015 (m/s²)². In practical applications, excessive flow velocity and reduced vacuum degree should be avoided to prevent low-frequency vibration, which may lead to fatigue damage or even failure of the equipment due to resonance. In addition, the direct-contact condensation state can be inferred from the vibration signal to reduce environmental noise. Full article

Given the global pressure of climate change and ecological equilibrium, there is an urgent need to develop effective carbon dioxide (CO₂) capture technology. Due to its comprehensiveness and flexibility, Direct Air Capture (DAC) technology has emerged as a vital supplement to traditional emission reduction methods. This study aims to innovate Direct Air Capture (DAC) technology by utilizing the ultrasonic impregnation method to load Tetraethylenepentamine (TEPA) onto alumina (Al₂O₃) as the adsorbent. Furthermore, high gravity adsorption technology is integrated to significantly enhance the efficiency of DAC. Characterization tests, including BET, FTIR, TG, XRD, and SEM-EDS, confirm the structural stability and high capture capacity of the adsorbent. Additionally, this study demonstrates the rapid and efficient capture of CO₂ from the air using TEPA-Al₂O₃ adsorbent under high gravity conditions for the first time. Under optimal conditions with TEPA loading at 15.06%, a high gravity factor of 2.67, and a gas flow rate of 30 L/min, TEPA-Al₂O₃ achieves a CO₂ adsorption capacity of 48.5 mg/g in RAB, which is an improvement of 15.56 mg/g compared to traditional fixed-bed technology. Moreover, it reaches adsorption saturation faster under high gravity conditions, exhibiting a significantly higher adsorption rate compared to traditional fixed-bed systems. Furthermore, the adsorption process better conforms to the Avrami model. Steam stripping regeneration is utilized to regenerate the adsorbent, demonstrating excellent regeneration performance and stable adsorption capacity, thereby proving its feasibility and economic benefits as a DAC technology. Full article