Vacuum Degree Research Articles

Deoxidation of Nickel-based Superalloy Using Carbon under High Vacuum Degree

Deoxidation of Nickel-based Superalloy Using Carbon under High Vacuum Degree

Effect of Radio Frequency Vacuum Drying on Drying Characteristics and Physicochemical Quality of Codonopsis pilosula Slices

In this study, the radio frequency vacuum drying (RFVD) technique was used to dry Codonopsis pilosula slices. The effects of the drying temperature, slice thickness, plate spacing, and vacuum degree on the drying characteristics and physicochemical properties of the slices were investigated. The results showed that as the drying temperature and vacuum degree increased and the slice thickness and plate distance decreased, the drying rate and effective moisture diffusion coefficient of the Codonopsis pilosula slices improved, and the required drying time was shortened by 11.11% to 29.41% compared to that after hot air drying (HAD). Through comparison, it was found that the Midilli and Weibull models could better describe the moisture variation trend during the RFVD of Codonopsis pilosula. After RFVD, the retention of lobetyolin and syringin in Codonopsis pilosula significantly increased, with maximum contents of 135.74 mg/100 g and 19.16 mg/100 g respectively, which were 75.2% and 124.28% higher than those obtained by HAD. The contents of polysaccharides, total phenolics, and total flavonoids and antioxidant performance were also enhanced. The color, shrinkage rate, and internal tissue structure were significantly improved. In conclusion, RFVD not only increases the drying speed of Codonopsis pilosula slices but also ensures the good quality of the dried products.

Photosensitized Reduction and Polymerization for One-Step Preparation of Leucomethylene Blue Hydrogel as a Visual Indicator for Both Gaseous and Dissolved Oxygen.

Oxygen is crucial for many chemical and biological processes, and its facile detection is of great significance in our daily lives. In this study, we report a leucomethylene blue (LMB)-encapsulated hydrogel visual indicator for the detection of both gaseous and dissolved Oxygen (DO). The photosensitization of methylene blue (MB) not only lead to its reduction to colorless LMB but also resulted in hydrogel polymerization, thus allowing the one-step preparation of the LMB-hydrogel. Meanwhile, the photosensitized reduction of MB was quite fast (5000-fold faster than the classical glucose reduction). In this manner, the blue color of MB could be completely decayed within only 1 min. Also, the efficient polymerization triggered by MB photosensitization ensured the rapid preparation of LMB hydrogels within 10 min. By placing the oxygen indicator in air or water, oxygen can specifically oxidize the colorless LMB-hydrogel to the blue MB-hydrogel. When coupled with a smartphone, the oxygen indicator exhibited a linear response to DO in the range 0.23-10 mg/L with a detection limit of 0.077 mg/L. The LMB-hydrogel indicator was successfully explored for visual evaluation of vacuum degree during food packaging. The LMB-hydrogel, with the advantages of low cost, ease of preparation, as well as facile use, is a promising visual indicator for both gaseous and dissolved oxygen, especially for in-house usage.

面向小粒蔬菜种子的气吸排种器排种性能试验

Vegetable precision planting agronomy is suitable for my country's current vegetable planting system, and the air-suction vegetable precision planter is currently the most important work tool in my country. This paper designs a kind of air-absorbing vegetable precision sower for the problems of small vegetable seeds with small grains, poor mobility and high difficulty in achieving uniform sowing of small seeds. First, Fluent software is used to simulate and analyze the flow field of the air chamber in the seed metering device, and the pressure and velocity of the fluid in the air chamber are analyzed. Through the comparison of the pressure distribution cloud chart and the velocity distribution cloud chart, the influence of different apertures, holes, vacuum degree, and gas chamber depth on the flow field of the gas chamber is analyzed. The air suction seed discharger test bench was set up and orthogonal test was carried out, and the test results showed that the optimal parameter combination was 3.5 kPa vacuum degree of the air chamber, 2.4 mm diameter of the type hole, and 18 r/min rotational speed of the seed discharging disk. The high-speed photographic test was carried out under the optimal parameter combination, and the results showed that leakage of suction, adsorption of 1 seed, and adsorption of multiple seeds appeared in the process of suction, and it is important for the development of the air suction precision machine for small seeded vegetables with better performance. The results showed that the phenomenon of leakage, adsorption of 1 seed and adsorption of multiple seeds occurred in the process of seed suction, which provided a reference basis for the development of a better performance of the air-absorption precision planter for small seeds.

Measurement method of vacuum degree in satellite in vacuum thermal test of spacecraft based on diaphragm gauge

Measurement method of vacuum degree in satellite in vacuum thermal test of spacecraft based on diaphragm gauge

Developing Effective Radio Frequency Vacuum Drying Processes for Moutan Cortex: Effect on Moisture Migration, Drying Kinetics, Physicochemical Quality, and Microstructure.

This study aims to maximize the post-harvest quality of Moutan Cortex and reduce energy consumption. Radio frequency vacuum (RFV) technology was used to dehydrate Moutan Cortex in this study to investigate the effects of different drying temperatures, plate spacing, and vacuum degree on the drying kinetics, physicochemical quality, and microstructure of Moutan Cortex. The results showed that RFV drying shortened the dehydration time of the Moutan Cortex by 10.71-28.57% and increased the drying rate by 15.79-54.39% compared to hot-air drying. The best color (∆E = 6.08 ± 0.28, BI = 26.97 ± 0.98) and relatively high retention of polysaccharides, total phenolics, total flavonoids, antioxidant properties, paeonol, gallic acid, paeoniflorin, and benzoylpaeoniflorin contents were observed in the dried products of Moutan Cortex at a drying temperature of 50 °C, spacing of 90 mm, and vacuum of 0.025 MPa. Analyzing the microstructure, it was found that RFV drying could effectively inhibit the shrinkage and collapse of the cellular structure, and a regular and loose honeycomb pore structure appeared inside the samples, which contributed to the rapid migration of the internal moisture. This study can provide a theoretical reference basis for the selection and application of industrialized processing methods of high-quality Moutan Cortex.

Evaluation of Thermal Insulation of Vacuum-Insulated Casing to Prevent Uncontrollable Melting of Ice and Borehole Instability in Permafrost

During oil and gas development in permafrost, hot fluids within the wellbore can cause ice melting around wellbore and a decrease in sediment strength, as well as wellbore instability. In the present work, the experimental system for evaluating the insulation effectiveness was established, and the applicability of this experimental system and methodology was verified. It was found that the difference between the experimentally obtained and actual thermal conductivity of the ordinary casings are all within 1.0 W/(m·°C). Meanwhile, the evaluation of insulation effect found that the decrease in fluid temperature, ambient temperature, and vacuum degree can improve its insulation performance. Finally, the numerical simulation was conducted on ice melting and borehole stability during the drilling operation in permafrost. The investigation results demonstrate that the use of vacuum-insulated casings significantly reduces the total heat transferred during the simulation by 86.72% compared to the ordinary casing. The utilization of vacuum-insulated casing reduces the range of ice melting around wellbore to only 16%, which occurs when using ordinary casing. The use of the vacuum-insulated casing resulted in a reduction in the final borehole enlargement rate from 52.1% to 4.2%, and wellbore instability was effectively suppressed.

Gas adsorption on activated AlGaN photocathode: A first-principle study on charge redistribution, work function variation and emission performance attenuation

AlGaN photocathode has important applications in photoelectronic imaging and vacuum electronic devices. However, The short lifetime of the photocathode results in higher costs of usage. This can be attributed to the decrease in vacuum degree and the adsorption of residual gases. In this study, first-principle study and transmission matrix are utilized to investigate five gases (H2O, CO, CO2, H2, CH4) adsorbed on Cs-activated AlGaN (100) surface. Results suggest that all these five gases are prior to deposit on the surface at low coverage of 0.25 ML with adsorption energy of -2 eV. CO has the highest adsorption possibility with its adsorption energy lower than 0 eV. Significant charge transfer occurs at Cs-gas interface, particularly near the oxygen atoms of oxygen-containing molecules. CO2 and CO exhibit a noticeable increase in work function. The increase in the work function of the H2O adsorption is primarily due to its longer dipole length rather than dipole charge by analysing the surface dipole moment. CH4 and H2 have negligible impact on surface properties. Upon gas adsorption, the electrons on the AlGaN surface flow back to the adatoms, causing the CBM shift towards higher energy and upwards band bending. Combined with the surface electron affinity, the iteration of band structures further explains the increase of work function. The open energy of free electron escaping into the vacuum after CO2 adsorption increases to the level of inactivated surface of 5.55 eV from PBE-D2. This study reveals the mechanism of performance decay of the photocathode and is expected to guide the optimization of packaging technology.

Vacuum-driven orientation of Nanostructured polystyrene-block-Poly(L-lactide) block copolymer thin films for Nanopatterning

Herein, we demonstrate a simple approach to control the orientation of cylinder-forming nanostructures in polystyrene-block-poly(L-lactide) (PS-b-PLLA) BCP thin films through thermal annealing under a high-vacuum environment. Surface tension discrepancy between the constituent blocks is critical in controlling the aimed orientation of self-assembled nanostructures in block copolymer (BCP) thin films. For BCP self-assembly, temperature has been widely utilized as a thermodynamic state variable under ambient pressure conditions, whereas the use of high vacuum (low pressure) for thermal annealing is limited. It has been observed that temperature can alter the surface tension only marginally with increasing temperature for polymeric materials; as a result, the pressure dependence of surface tension for PS and PLLA was investigated. By increasing the vacuum degree during thermal annealing, the surface tension discrepancy between the PS and PLLA blocks can be reduced significantly. Accordingly, during thermal annealing under high vacuum degree, a neutral air polymer interface can be generated for the BCP thin films, resulting in the formation of perpendicular cylinders from the neutral surface of the thin film through BCP microphase separation.

Correction: Steam turbine power prediction based on encode-decoder framework guided by the condenser vacuum degree

Correction: Steam turbine power prediction based on encode-decoder framework guided by the condenser vacuum degree

Devolatilization of high viscous fluids with high gravity technology

Volatile organic compounds (VOCs) are generally toxic and harmful substances that can cause health and environmental problems. The removal of VOCs from polymers has become a key problem. The effective devolatilization to remove VOCs from high viscous fluids such as polymer is necessary and is of great importance. In this study, the devolatilization effect of a rotating packed bed (RPB) was studied by using polydimethylsiloxane as the viscous fluid and acetone as the VOC. The devolatilization rate and liquid phase volume (KLa) have been evaluated. The results indicated that the optimum conditions were the high-gravity factor of 60, liquid flow rate of 10 L·h−1, and vacuum degree of 0.077 MPa. The dimensionless correlation of KLa was established, and the deviations between predicted and experimental values were less than ±28%. The high-gravity technology will result in lower mass transfer resistance in the devolatilization process, enhance the mass transfer process of acetone, and improve the removal effect of acetone. This work provides a promising path for the removal of volatiles from polymers in combination with high-gravity technology. It can provide the basis for the application of RPB in viscous fluids.

Intelligent control of microwave vacuum drying based on online aroma monitoring

Astragalus is a common medicinal food that has many benefits for the human body. Some medicinal components in the astragalus would decompose or volatilize at high temperature. Therefore, vacuum drying at a low temperature is a common post-harvest processing for the astragalus. The components and the internal structure of the astragalus change along with the planting range and the harvest year. Therefore, only trained experts with years’ experience can adjust the vacuum drying parameters properly based on their aroma perception, which is backward in the industrial age. In this study, astragalus aroma in microwave vacuum drying was online measured with an electronic nose. Volatiles were verified with Gas Chromatography-Mass Spectrometry (GC-MS) analysis. Drying temperature was PID controlled to maintain constant values. Microwave power was automatically regulated through a Triac circuit. Vacuum degree was adjusted instantly with a step motor. The physical and chemical quality changes of astragalus in drying process were investigated at various temperature and vacuum conditions. To optimize the drying effects, an Artificial Neural Network-based predictive control was designed to adjust the vacuum degree intelligently. The astragalus from Dingxi City, Gansu Province, China was conducted for experiments. By applying different control strategies, the astragalus quality was greatly improved, including more contents of total polysaccharides，astragaloside, total flavonoid, total saponin as well as the enhancement of beany flavor.

Effects of vacuum degree on the detonation characteristics and energy release laws of RDX explosive

To explore the detonation characteristics and energy release laws of RDX explosives under varying degrees of vacuum, the influence of vacuum degree on the fireball characteristic parameters, shock wave propagation laws and detonation performance of columnar RDX charges were studied using the air-blast experiments and AUTODYN simulations, and the fireball temperature distributions were mapped with the colorimetric thermometry technique. The experimental results indicated that as the degree of vacuum increased, the combustion duration and zone area size of the explosive fireball were both extended, while its temperature decay rate was slowed down, making the afterburning effect more pronounced. Furthermore, the peak overpressure and positive impulse of the explosion shock wave showed a downward trend, with the reductions of 56.1 % and 53.5 %, respectively, with the increasing vacuum degree. Numerical simulation was also used to reveal the energy release laws of RDX explosive, and the comparison between the experimental and numerical results showed a good degree of concordance with an average error of 6.45 %. The results of the study could provide a reference for expanding the explosion theory of explosives in plateau environment and improving the performance of explosion-proof equipment.

Clean and efficient separation of Pb-Sb alloy by vacuum gasification - Fractional condensation

The Lead (Pb) - Antimony (Sb) alloy derived from Jamesonite (Pb4FeSb6S14) using the "Roasting - Reduction Smelting" method is typically isolated through a separation method known as "High Temperature Ash Blowing - Low Temperature Ash Blowing - Electrolytic Refining". However, the "Low Temperature Ash Blowing" separation method encounters several challenges, including elevated production pressure of refined Pb, significant emissions of smoke and dust, and suboptimal separation efficiency. This study utilizes the "Vacuum Gasification - Fractional Condensation" method as an alternative to the "Low Temperature Ash Blowing" method. The experimental findings demonstrate that by implementing specific optimal experimental conditions, such as a condensation temperature range of 904–1054K, a vacuum degree of 5Pa, a gasification temperature of 1173K, a holding time of 7h, and a height-diameter ratio of 0.27, condensates with Sb content exceeding 99.5 wt% can be procured, resulting in a direct Sb yield of 33 %. The remaining residues, with an Sb content ranging from 14 to 15 wt%, serves as a valuable input for the "Electrolytic Refining" process. This utilization significantly alleviates the burden on refined Pb production during the "Electrolytic Refining" process. The treatment procedure does not require the utilization of chemical reagents, and it generates no wastewater or exhaust gas.

Modeling of low-temperature plasma inhibition and mechanism of Aspergillus flavus on corn kernels surface

ABSTRACT This study was conducted to optimize a process of low-temperature plasma treatment for the decontamination of Aspergillus flavus (A. flavus) on corn kernels. Impacts of plasma-treated time (30, 60, 90 s), plasma-treated power (300, 400, 500 W), and vacuum degree (85, 90, 95 Pa) on the decontamination effect in this process were explored. The optimal conditions included vacuum degree at 90 Pa, plasma treating time of 90 s, and plasma treating power of 500 W, under which the A. flavus spores was 4.03 log (cfu/g). Plasma treatment triggered antioxidative defense system, broke cell structures, and dispersed cell contents. A large number of free radicals act on lipids and proteins, and malondialdehyde (MDA) accumulate in large quantities, further leading to damage to cell structures.

Microstructure evolution and densification behavior of cellular Ti(C,N)-based cermets prepared by multiphase flow agglomeration and subsequent vacuum sintering

The cellular Ti(C,N)-based cermets were prepared by multiphase flow agglomeration and subsequent vacuum sintering. By precisely controlling the vacuum degree and temperature, the fine particles collided and then agglomerated together through the surface tension of bubbles generated by the dissolved gas in the slurry, forming a multiphase flow with the liquid medium as the slurry dried. Subsequently, the dried powder mixture containing the agglomerates was subjected to pressing and vacuum sintering to obtain cellular cermets. The cellular cermets were analyzed using DSC, XRD, SEM, TEM, and EDS. During the solid-phase sintering stage, the agglomerates were relatively loose and easily to be destroyed, showing large gaps with the matrix, while the gaps gradually decreased and the density slightly increased as the temperature increased. During liquid phase sintering, the grains in agglomerates were further dissolved to gain fully fine-grained agglomerates, and the interface between the agglomerates and the matrix became clear. Finally, a dense sintered body with cellular structure in which agglomerates were dispersed in the matrix was formed. Furthermore, agglomerates were mainly composed of grains with black core-gray rim and grains without obvious core/rim structure, forming distinct interfaces with the coarse-grained matrix. The cellular Ti(C,N)-based cermets exhibited superb mechanical properties, with TRS of 2184 ± 30 MPa, fracture toughness of 9.01 ± 0.3 MPa m1/2, and hardness of 93.4 ± 0.2 HRA, making them superior to traditional Ti(C,N)-based cermets.

Intensification of polyethylene devolatilization in twin‐screw extruder with additives

AbstractAiming at the problem of difficult to remove high‐carbon α‐olefin in polyethylene, the influences of operation conditions and devolatilization additives on the devolatilization of LLDPE/1‐octene system in an exhaust twin‐screw extruder are studied by headspace gas chromatography. The results showed that the devolatilization efficiency increases with the devolatilization temperature and vacuum. With the screw rotational speed, the content of liquid additives and the gas velocity of gas additives increasing, the devolatilization efficiency first increases and then decreases. The devolatilization difficulty of different grades of polyethylene varies due to the difference of the viscosities. When the volatile content is high, the effect of devolatilization additives is anhydrous ethanol > surfactant > water > nitrogen. When the volatile content is low, the effect of nitrogen on devolatilization is obviously better than anhydrous ethanol and water. Finally, a novel devolatilization process is proposed, that is, an evacuation system (vacuum degree 0.08–0.1 MPa) is set up in each stage of the devolatilization section, the anhydrous ethanol is introduced in the first stage, and high‐purity nitrogen is introduced in the second, third, and fourth stages, which can ultimately reduce the VOC content of LLDPE products to less than the target value of 50 ppm.Highlights The devolatilization process is used to remove high carbon α‐olefins from LLDPE. Each additive has an optimal injection value. Ethanol is the most effective in the foam‐dominated devolatilization stage. Nitrogen is the most effective in the diffusion‐dominated devolatilization stage. A new additive‐enhanced twin‐screw extruder devolatilization process is proposed.

增加导种条式食葵精量排种盘设计及试验

In order to solve the problems of easy seed shedding and poor seed population mobility during sowing, a precision seed metering tray for edible sunflowers with seed guide strips was designed in this paper. This article aims to adjust the adsorption posture of sunflower seeds by designing three types of structures: triangular seed guide strip, rectangular seed guide strip, and diamond seed guide strip. Seed population motion simulation and seeding performance experiments were conducted on the seeder. The experimental results show that adding a triangular seed guide strip to the seeding tray has the best disturbance effect on the seed population, with the highest proportion of seeds in the first adsorption stance seed (the seed centroid was adsorbed) and the highest qualification index. The working parameters for the best seed metering performance were obtained: the rotating speed of the seed metering disc was 8.41 r/min, and the vacuum degree was 3.5 kPa.

The growth of a single rising bubble in viscous solution and the resulting volatile removal

In the foam devolatilization, volatiles are removed accompanying with the growth of rising bubbles, and determining the amount of removed volatile is important in the design of devolatilization device. In this work, acetone and polydimethylsiloxane were used as the volatile and polymer respectively to study the single bubble growth process in the foam devolatilization. The variation of single bubble spherical equivalent radius and rising velocity in viscous solution were experimentally determined, and the effects of operational parameters (i.e., polymer viscosity, vacuum degree, solution temperature and volatile concentration) on bubble growth were evaluated. By analyzing the mechanics of bubble devolatilization, and based on the mass transfer boundary layer theory, the mass of removed volatile during bubble rising is determined, together establishing a correlation to predict the volatile removal amount.

Effect of Temperature, Vacuum Condition and Surface Roughness on Oxygen Boost Diffusion of Ti–6Al–4V Alloy

Oxygen boost diffusion (OBD) is an effective technology for improving the surface hardness of titanium and its alloys. In this present paper, the effect of temperature, vacuum condition and surface roughness on oxygen boost diffusion of Ti–6Al–4V alloy are studied. Test results show that OBD processing can be achieved at a low temperature and over long times, as well as at a high temperature and over short times. By comparing processing efficiency and mechanical properties, high temperatures and short times are preferred for OBD treatment. The influence of vacuum conditions on oxygen vacuum diffusion is significant. Under low vacuum degree conditions, relatively high oxygen content not only corrodes the OBD layer but also leads to spalling of the outmost surface of the OBD layer and the remaining oxide layer. High surface roughness can induce cracking not only in the oxide layer during the oxidation process but also in the outmost surface of the OBD layer during the vacuum diffusion process.