Vacuum Degree Research Articles

Heat Transfer Characteristics of Vacuum Insulated Pipe due to Change in Vacuum Degree

Heat Transfer Characteristics of Vacuum Insulated Pipe due to Change in Vacuum Degree

Vacuum preloading combined with surcharge preloading method for consolidation of clay-slurry ground: A case study

A reclamation project was undertaken in Zhuhai, China, covering an area of 11.35 km2 with a clay-slurry thickness of 30 m. It is interesting to find a good reinforcement method, which is more suitable for strengthening such a large-scale dredged clay-slurry ground. Evidence from engineering practice shows that vacuum preloading or vacuum preloading combined with surcharge preloading method technology has certain advantages. However, further data is required to verify their performance in the field. This paper presents a case study using the conventional vacuum preloading and vacuum preloading combined with surcharge preloading method (vacuum pressure of 90 kPa, surcharge height of 3 m) to improve the thick clay-slurry ground for a subgrade engineering project in Zhuhai, China. A series of field monitoring, in-situ tests, and laboratory tests were performed to evaluate their treatment effect by analysis of vacuum degree, ground surface settlement, layered settlement, consolidation degree, lateral displacement, excess pore water pressure dissipation, and vane shear strength. The results showed that the ground treated via vacuum preloading combined with surcharge preloading method was more effective than conventional vacuum preloading. The vacuum degree of vacuum preloading combined with surcharge preloading method was slightly lower than that of conventional vacuum preloading, decreasing with depth. The settlement is increased by 55.56%, average consolidation degree is enlarged by 40.9%, lateral displacement can be augmented by 2.4 times, pore water pressure coefficient is less than 0.6, and undrained shear strength is amplified by 22.2%. These findings can be used to guide the design of the combined preloading method of the subgrade engineering project along the east coast of China.

Clearance distribution design and thermal deformation analysis of variable-pitch screw rotors for twin-screw vacuum pumps

Clearance distributions between a pair of intermeshing screw rotors greatly affect the gas leakage and pump performance of twin-screw vacuum pumps. Screw rotors generated by the traditional clearance design method have unreasonable clearance distributions and then affect the vacuum degree, especially for variable-pitch screw rotors. Aiming at solving the above problem, this paper presented a novel clearance design method, and designed a pair of intermeshing variable-pitch screw rotors with reasonable clearance distributions at each meshing surface. In addition, thermal deformations of intermeshing screw rotors were simulated, and variations of each clearance were analyzed. Two kinds of screw rotors, the novel and traditional screw rotors, respectively designed by the novel and traditional clearance design methods were manufactured, and their ultimate vacuum degrees of two corresponding twin-screw vacuum pumps were tested. It is found that clearance distributions of the novel screw rotor are superior to the traditional screw rotor designed by the traditional method; the novel screw rotor reduces the value of the reserved circumferential clearance by 41.67%, and the corresponding twin-screw vacuum pump with this screw rotor achieves a higher ultimate vacuum degree as 0.1Pa, while the pump with the traditional screw rotor just achieves the value of 8.4Pa.

A Method for Detecting the Vacuum Degree of Vacuum Glass Based on Digital Holography.

The vacuum degree is the key parameter reflecting the quality and performance of vacuum glass. This investigation proposed a novel method, based on digital holography, to detect the vacuum degree of vacuum glass. The detection system was composed of an optical pressure sensor, a Mach-Zehnder interferometer and software. The results showed that the deformation of monocrystalline silicon film in an optical pressure sensor could respond to the attenuation of the vacuum degree of vacuum glass. Using 239 groups of experimental data, pressure differences were shown to have a good linear relationship with the optical pressure sensor's deformations; pressure differences were linearly fitted to obtain the numerical relationship between pressure difference and deformation and to calculate the vacuum degree of the vacuum glass. Measuring the vacuum degree of vacuum glass under three different conditions proved that the digital holographic detection system could measure the vacuum degree of vacuum glass quickly and accurately. The optical pressure sensor's deformation measuring range was less than 4.5 μm, the measuring range of the corresponding pressure difference was less than 2600 pa, and the measuring accuracy's order of magnitude was 10 pa. This method has potential market applications.

Simulation study of the thermal insulation performance of a vacuum‐insulated tube inside an electrically heated device

AbstractTo realize stable heating of a heated cigarette while effectively controlling the outer‐wall temperature of an electric heating‐type appliance, a vacuum‐insulated tube (VIT) is currently widely used for thermal insulation against the heating element. The effects of the critical parameters of the VIT, gases at different pressures, wall thickness, and material on its thermal insulation performance, were simulated using Fluent to provide guidance on the structure and performance optimization of the EHD. When the absolute pressure of gas in the VIT was <0.5 Pa, increasing the degree of vacuum did not improve the thermal insulation performance. The thermal insulation performance of VITs made from different materials (stainless steel, copper, aluminium, brass, and titanium alloy) was closely related to the emissivity and thermal conductivity of the material. Stainless steel yielded better overall thermal insulation owing to its low thermal conductivity and emissivity. Highly emissive materials, such as brass and titanium alloy, contributed to higher heat transfers through the radiation inside the vacuum chamber and external radiation from the VIT, decreasing the thermal insulation performance of the VIT. Stainless steel VITs yielded an improved thermal insulation performance as the wall thickness decreased, but at the cost of decreased mechanical stability. For a wall thickness of 0.05–0.30 mm, stainless steel yielded the best structural stability. VITs with different wall thicknesses were made from stainless steel, copper, and aluminium, and the thermal insulation performance and structural stability of the EHD were optimized.

Research and application of digital technology of film coating equipment

At present, most of the coating production still adopts relatively backward traditional methods, there are its equipment status, operation, production, repair and maintenance information of digital technology application less problems. In view of this problem, a data acquisition module and data processing system are developed to realize the data acquisition and real-time monitoring of the equipment temperature, vacuum degree, rotation speed, target material, film thickness and surface condition. The data acquisition module consists of a self-organized network system formed by the sensor nodes deployed in the detection area and installed on the device, combined with / wireless communication. Through the development of the system to achieve the digital and intelligent application of coating equipment.

Numerical investigation of the ground-based thermal environment experimental approaches to reveal the ice-sublimation phenomenon inside lunar regolith

In recent years, the Moon, as the closest celestial body to the Earth, has become the foremost target of human exploration outward. Some lunar exploration missions and studies have shown that ice may exist in the polar regions of the Moon. Water is very important for human survival. The ice mining and utilization is based on the understanding of the sublimation mechanism. Simulation of ground-based tests is an effective means to explore the sublimation of ice. Therefore, in this paper, the thermal environment of Shackleton Crater and the particle size distribution of typical lunar soils are analyzed as the basis of parameter settings for the ground test. Four operating conditions are established for ground tests, including the influence of heat sink temperature, vacuum level, particle size distribution and dry soil density. The larger the radiation heat flow, the higher the heat sink temperature, the smaller the vacuum degree, the larger the average particle size, resulting in a larger sublimation rate. The decrease of density makes the sublimation process faster and then slower. The sublimation process proceeds fastest when the dry soil density is 1200 kg/m3. The heat sink temperature has the greatest effect on the sublimation process, and the vacuum has the least effect. When the radiation heat flow ranges from 39.01 W/m2 to 45.63 W/m2 at the heat sink temperature of 120 K, the maximum sublimation rate is 5.79E-15 kg/s, the maximum sublimation area is 1.93E-9 m2 and the maximum sublimation heat flow is 1.59E-8 W. However, the effect of vacuum degree and particle size distribution on the sample temperature variation is not significant, due to the small order of magnitude of the sublimation heat flow compared to the radiation and conduction heat flows. This paper gives a range of parameters for ground-based simulation experiments and points out the microscopic changes of the ice sublimation process, which provides ideas for the next ground-based experiments and the exploitation of water-ice resources on the Moon.

Revolutionary encapsulating solution of solar PV panels: vacuum glazing with zero H2O and O2 replacing EVA/PVB films

AbstractDue to the shortage of energy in the world, solar energy has received widespread attention as an inexhaustible new green energy and as one of the main sources of power. Many researchers have studied the various materials and efficiencies of solar cells; however, how to extend the life of solar cells has rarely been studied. At present, the main encapsulating method of solar cells is to seal their surface with films such as ethylene-vinyl acetate and polyvinyl butyral. The main problem that has been encountered is that the erosion of water and oxygen leads to a reduction in the service life and efficiency of solar cells. Inspired by the solar panels of satellites in space, a revolutionary vacuum-glazing encapsulating solution with zero H2O and O2 has been invented. The experimental results have nearly doubled the 30–35-year service life of solar cells, based on deep learning predictions. Therefore, the building integrated photovoltaic can be used for the 70-year life of a building. The method is applicable to various solar cells, such as crystalline Si cells, CIGS, CdTe and perovskite film cells, etc. In practice, the main problems encountered in the encapsulation of vacuum glazing include the following: ensuring that the supporting pillar does not pierce the thin film PV and that it is placed accurately between the band gaps; ensuring that the emission of heat is not conducted in a vacuum; ensuring that the sealing sheet covers cover the exhausting port on the glass accurately; maintaining the vacuum degree for a long time; insulating the edge of the sealing materials, as well as other issues. The above problems have been solved perfectly through machine learning of computer vision and the design structure of the thin film PV.

Performance and kinetics study of glycerol ketal synthesis from biomass‐based platform chemicals catalyzed by metal salts

AbstractBackgroundMethyl levulinate glycerol ketal (MLK) is a new kind of glycerol ketal with a wide range of applications. The efficient and green synthesis of MLK from biomass‐based platform chemicals including methyl levulinate (ML) and glycerol (GLY) catalyzed by cheap metal salts was investigated. Effects of different reaction conditions on the GLY conversion and the MLK yield were discussed, and the optimization and the kinetics of ketal preparation were further developed.ResultsThe reaction time, amount of catalyst and ML:GLY molar ratio were optimized based on Box–Behnken experimental design. The average MLK yield of 97.6% could be obtained under the optimum reaction conditions of ML:GLY molar ratio 4:3, vacuum degree 90 kPa, AlCl3 1.8 g, temperature 126 °C and reaction time 2 h, and the AlCl3 could be reused ten times without deactivation. On this basis, the kinetics studies showed that the ketal reaction conforms to the pseudo‐second‐order kinetics model, and the values of pre‐referential factor and activation energy were 1.824 × 104 mol·(g·h)−1 and 90.69 kJ mol−1. A reaction pathway for the ketalization reaction was proposed.ConclusionsThese results provide references for the scale‐up of MLK synthesis and the development of a new glycerol ketal. © 2023 Society of Chemical Industry (SCI).

Design and Experimental Research on Centralized Lubrication and Waste Oil Recovery System for Wind Turbines

Lubrication plays a key role in increasing availability of wind turbines, extending unit life and reducing operating costs. In view of the problems of valve core lag, grease hardening and difficulty in removing waste oil in a centralized lubrication system, an improved centralized lubrication system and waste oil recovery system were designed in this study. Discharge of waste grease in the bearing cavity was simulated under different vacuum conditions. It was shown that vacuum degree of bearing cavity is proportional to oil output speed of waste grease. Performance and fatigue reliability tests of the waste grease suction and drainer device test platform were conducted over 12,000 fatigue cycles. The results show that the vacuum degree error of the waste grease suction and drainer device before and after the test is less than 5%, and the power oil pressure, oil output pressure and oil output quantity of the test product are stable, indicating that the designed waste grease suction and drainer device has excellent sealing and reliability. The waste grease suction and drainer device can eliminate grease discharge resistance in the bearing cavity, facilitating discharge of waste oil and improving wind turbine operation efficiency.

Heat and mass transfer law during microwave vacuum drying of rice

In order to obtain the microwave vacuum drying characteristics of rice and the change in law of temperature and humidity, the mechanism of water diffusion and migration in the drying process was analyzed based on the multiphase flow in porous media, the change model of moisture content was established, and the microwave heating process coupled with electromagnetic field and mass heat field was simulated. The accuracy of the multiphase porous medium model was verified by measuring the moisture changes during rice drying under different vacuum degrees. The results show that the temperature distribution of rice during heating is high in the center and low around, and the vacuum degree hardly affects the change in rice temperature. The capillary pressure in rice gradually increases, and the equilibrium vapor pressure gradually decreases during drying. The estimated moisture content reduced from 0.25 to 0.189, 0.177, and 0.169, and the experimental value decreased from 0.25 to 0.186, 0.177, and 0.167 after drying the rice for 60 min at vacuum of 0.02 MPa, 0.04 MPa, and 0.06 MPa, respectively. The experimental value was in agreement with the calculated value. The higher the vacuum degree, the faster the drying speed, and this finding provided a new idea for improving the drying efficiency.

Charge Density-Based Pyroelectric Vacuum Sensor.

A traditional thermal conductivity vacuum gauge mainly detects low pressure (the degree of vacuum) by measuring the temperature change of a filament heated by the electric current. We propose a novel pyroelectric vacuum sensor that utilizes the effect of ambient thermal conductivity on the pyroelectric effect to detect vacuum through the charge density of ferroelectric materials under radiation. The functional relationship between the charge density and low pressure is derived, which is validated in a suspended (Pb,La)(Zr,Ti,Ni)O3 (PLZTN) ferroelectric ceramic-based device. The charge density of the indium tin oxide/PLZTN/Ag device under 405 nm of 60.5 mW cm-2 radiation at low pressure reaches 4.48 μC cm-2, which is increased by about 3.0 times compared with that at atmospheric pressure. The vacuum can improve the charge density without increasing the radiation energy, confirming the important role of ambient thermal conductivity on the pyroelectric effect. This research provides a demonstration for ambient thermal conductivity effectively tuning pyroelectric performance, a theoretical basis for pyroelectric vacuum sensors, and a feasible route for further optimizing the performance of pyroelectric photoelectric devices.

Drying Characteristics and Odor Concentration in Tail Gas in Vacuum Drying of Municipal Sewage Sludge

As one of the most common solid wastes, municipal sewage sludge needs to be dried before its disposal and resource reuse. In this study, the effects of vacuum degree, heat source temperature and sludge thickness on drying rate and odor concentration in tail gas were studied through orthogonal experiments carried out on the lab-scale vacuum heat-conductive sludge drying device; The effects of heat source temperature on drying rate and odor concentration in tail gas were studied through comparative experiments of atmospheric state and vacuum state (-0.08MPa). The results show that the sludge thickness is the main factor affecting the sludge static drying rate, and the vacuum degree is the main factor affecting the odor concentration in the tail gas of sludge static drying. Under vacuum state (-0.08MPa), sludge can be dried efficiently while using low-grade heat source. In addition, while maintaining a high drying rate, the odor concentration in the tail gas will also be significantly reduced by reducing the generation of volatile sulphur compounds (VSCs).

Surface-modified silicalite-1-filled PDMS membranes for pervaporation dehydration of trichloroethylene.

In this study, the impact of silane coupling agents, namely 3-aminopropyltrimethoxysilane (APTMS), trimethylchlorosilane (TMCS), and 1,1,3,3-tetramethyldisilazane (TMDS), on the hydrophobicity of silicalite-1 zeolite was investigated to enhance the pervaporation separation performance of mixed matrix membranes (MMMs) for trichloroethylene (TCE). The hydrophobicity of TMCS@silicalite-1 and TMDS@silicalite-1 particles exhibited significant improvement, as evidenced by the increase in water contact angle from 96.1° to 101.9° and 109.1°, respectively. Conversely, the water contact angle of APTMS@silicalite-1 particles decreased to 85.2°. Silane-modified silicalite-1 particles were incorporated into polydimethylsiloxane (PDMS) to prepare mixed matrix membranes (MMMs), resulting in a significant enhancement in the adsorption selectivity of trichloroethylene (TCE) on membranes containing TMCS@silicalite-1 and TMDS@silicalite-1 particles. The experimental findings demonstrated that the PDMS membrane with a TMDS@silicalite-1 particle loading of 40 wt% exhibited the most favorable pervaporation performance. Under the conditions of a temperature of 30 °C, a flow rate of 100 mL min-1, and a vacuum degree of 30 kPa, the separation factor and total flux of a 3 × 10-7 wt% TCE aqueous solution were found to be 139 and 242 g m-2 h-1, respectively. In comparison to the unmodified silicalite-1/PDMS, the separation factor exhibited a 44% increase, while the TCE flux increased by 16%. Similarly, when compared to the pure PDMS membrane, the separation factor showed an 83% increase, and the TCE flux increased by 20%. These findings provide evidence that the hydrophobic modification of inorganic fillers can significantly enhance the separation performance of PDMS membranes for TCE.

The Production Practice of Ultra-pure and Ultra-low-carbon Stainless Steel 07Cr17Ni12Mo2 by LF-VOD+ESR Steelmaking Process

By reasonably controlling the vacuum degree, oxygen supply intensity, oxygen lance position, and other process parameters of Vacuum Oxygen Decarburization (VOD) refining furnace (60t), and according to the blowing situation, combined with the oxygen concentration difference potential, exhaust gas temperature and CO concentration, accurately determine the blowing end point, and then further remove inclusions in steel by Electro-Slag Remelting (ESR), making the end point C less than or equal to 0.06 %, the total content of (As + Sn + Pb + Sb + Bi) is less than or equal to 150 ppm, total oxygen content is less than or equal to 30 ppm. The content of class A, B, C and D inclusions is less than or equal to grade 1.0 and the total inclusion grade is less than or equal to grade 2.0.

Drying characteristics, quality changes, parameters optimization and flavor analysis for microwave vacuum drying of garlic (Allium sativum L.) slices

The influence factors such as microwave power, vacuum degree and temperature were investigated using the color L*, thiosulfinate content, rehydration ratio and comprehensive score of garlic slices as responses. The microwave vacuum drying (MVD) parameters of garlic slices were optimized by response surface methodology. The electronic nose was used to compare the flavor differences between fresh garlic and dried garlic slices. The results showed that the drying curve and rate curve of MVD garlics accorded with the drying characteristics of foods, the optimum MVD conditions of garlic slices were microwave power 260 W, vacuum degree 81 kPa, and temperature 49.5 °C. Under these conditions, the color L*, the thiosulfinate content, the rehydration ratio and the comprehensive score of garlic slices were 82.26, 3.0378 mg/100 g, 2.796 and 0.9265, respectively. The principal component analysis results of electronic nose demonstrated that there was no difference in the composition between the dried garlic slices and fresh garlic, while the linear discriminant analysis of electronic nose could distinguish them. There was no significant difference in the volatile components of dried garlic slices under different drying conditions. Therefore, MVD process could be an effective drying method and quite suitable for garlic.

Design and construction of the magnetic perturbation magnets of the space plasma environment research facility for simulating the geomagnetic storm on the ground

Geomagnetic storm in the magnetosphere of the earth is significant in understanding the basic space plasma processes such as wave-particle interaction and predicting the space weather related to the human activity. Due to defects involved in the space observation and theoretical modeling, it is urgent to investigate it in the laboratory based on a simulation facility. To that end, two circular magnetic perturbation magnets are proposed in the SPERF (Space Plasma Environment Research Facility) to generate the magnetic disturbances with different characteristic times for studying the response of the inner magnetosphere to the geomagnetic storm. The paper focuses on the engineering design and construction of the magnets. The scaling relation for geomagnetic storm simulation is presented, serving as the design requirement of the magnets. Then, starting with giving the designed parameters of the magnets satisfying the requirement and analyzing the crucial issues facing their engineering design, the design results, manufacturing procedure, and test results are presented, with emphasize on the measures to improve the insulation, vacuum degree, and plasma quality. Then, mechanical analyses are done to evaluate the strength of the supporting mechanism of the magnets under the magnetic force and torque caused by the possible deviation from the concentricity with the dipole magnet. Afterwards, a connection scheme is designed to make the coaxial cables connecting to the magnet's leads go through the vacuum vessel considering the constraints of the magnetic-force impact, thermal burden, and motion requirement. One of the magnetic perturbation magnets has been installed in the SPERF, and is now being tested combined with the pulsed power supply.

Comparative Study on Preparation Methods for Transparent Conductive Films Based on Silver Nanowires.

Silver nanowires, which have high optoelectronic properties, have the potential to supersede indium tin oxide in the field of electrocatalysis, stretchable electronic, and solar cells. Herein, four mainstream experimental methods, including Mayer-rod coating, spin coating, spray coating, and vacuum filtration methods, are employed to fabricate transparent conductive films based on the same silver nanowires to clarify the significance of preparation methods on the performance of the films. The surface morphology, conductive property, uniformity, and flexible stability of these four Ag NW-based films, are analyzed and compared to explore the advantages of these methods. The transparent conductive films produced by the vacuum filtration method have the most outstanding performance in terms of surface roughness and uniformity, benefitting from the stronger welding of NW-NW junctions after the press procedure. However, limited by the size of the membrane and the vacuum degree of the equipment, the small-size Ag films used in precious devices are appropriate to obtain through this method. Similarly, the spin coating method is suited to prepare Ag NWs films with small sizes, which shows excellent stability after the bending test. In comparison, much larger-size films could be obtained through Mayer-rod coating and spray coating methods. The pull-down speed and force among the Mayer-rod coating process, as well as the spray distance and traveling speed among the spray coating process, are essential to the uniformity of Ag NW films. After being treated with NaBH4 and polymethyl methacrylate (PMMA), the obtained Ag NW/PMMA films show great potential in the field of film defogging due to the Joule heating effect. Taken together, based on the advantages of each preparation method, the Ag NW-based films with desired size and performances are easier to prepare, meeting the requirements of different application fields.

Development of Vacuum Tube Well Dewatering Test Device and Study on Vacuum Degree Transfer Law

Vacuum tube well dewatering technology has gradually become an effective means to deal with low-permeability soil groundwater. The vacuum degree transfer law is an important element in the study of the mechanism of deep foundation pit vacuum tube well dewatering. To further study the transfer law of vacuum degree in vacuum tube well dewatering, a laboratory test setup for vacuum tube well dewatering was developed, and vacuum tube well dewatering tests were conducted under various in-well vacuum values, tube diameter, depth of tube well, and other factors. The variation law of vacuum degree under various working condition coupling was thoroughly analyzed in this research. The results show that with the increase of vacuum value in the well, the radial vacuum degree and vertical vacuum degree have about 14.9~47.7% and 14.9~32.4% increase, respectively, and transmission attenuation of radial vacuum degree, transmission attenuation of vertical vacuum degree, and the range of the vacuum field all increase to some extent. With the outward transmission of the vacuum degree, the transmission attenuation of the radial vacuum degree decreases rapidly and then tends to be stable, and the transmission attenuation of the vertical vacuum degree decreases gradually. The radial vacuum degree, the transmission attenuation of the radial vacuum degree, and the range of the radial vacuum field are not affected by the buried depth of the tube well. The study’s conclusions can serve as a foundation and point of reference for projects involving the design and implementation of deep foundation pit vacuum tube well dewatering.

Vacuum Carbon Reducing Iron Oxide Scale to Prepare Porous 316 Stainless Steel

In order to improve the added value of iron oxide scale and reduce the manufacturing cost of porous stainless steel, steel rolling iron oxide scale as an iron-containing raw material was used to prepare porous 316 stainless steel by high-temperature sintering under vacuum conditions, while carbon was used as a reducing agent and pore-forming agent, and the necessary metal powders were added. In our work, the specific reduction system was confirmed, including the sintering temperature, sintering time, vacuum degree and carbon amount, through thermodynamic calculation combined with experiments. Thermodynamic analysis results showed that the transformation process of the chromium element in the raw materials at 10−4 atm and 300~1600 °C was FeCr2O4 + Cr3O4→Cr2O3 + Cr3O4 + Cr23C6→Cr23C6 + Cr7C3 + FCC→FCC + Cr23C6→FCC→FCC + BCC→Cr(liq). The FCC phase with qualified carbon content could be obtained at 10−4 atm and 1200 °C, while 90.88 g iron oxide scale, 17.17 g carbon, 17.00 g metal chromium, 12.00 g metal nickel and 2.5 g metal molybdenum were necessary to produce 100 g porous 316 stainless steel. The porous 316 stainless steel with a carbon content of 0.025% could be obtained at 10−4 atm and 1200 °C for 180 min, while the chromium element underwent the transformation of metal, Cr→FeCr2O4→Cr23C6→Austenite. The porosity of the porous 316 stainless steel was 42.07%. The maximum size of impurity particles was 5 μm when the holding time reached 180 min. Magnetic separation was an effective method to reduce impurities in the porous stainless steel.