Vacuum Degrees Research Articles

Numerical simulation on the pressure, turbulence, and λ2$$ {\lambda}_2 $$ vortex characteristics within the annular symmetric jet process under different vacuum degrees

AbstractThe jet impingement flash technology represents a paramount research subject in the domain of heat and mass transfer. To augment its commercial potential, the conjunction of annular multi‐aperture jet impingement with negative pressure flash evaporation is introduced in this study. The employment of an annular nozzle array is integral to the enhancement of the heat and mass transfer efficiency between the phases. The Realizable k‐ε model is used in this study. The negative pressure flash vaporization model was also developed by introducing a mass source term and an energy source term based on the Mixture model. The flow characteristics are characterized using numerical simulation. Additionally, the λ2 vortex identification criterion is investigated the vortex structure. The simulation results exhibit good agreement with experimental findings, demonstrating that a higher initial vacuum leads to a stronger flashing effect and a more chaotic movement of the flow group within the flow field. Thus, this study provides a reference method for the structural design and optimization of annular symmetric jet impingement negative pressure deammonia chemical equipment for engineering applications.

Quantifying squeeze film damping in four-leaf clover-coupled micro-resonators: A comprehensive study under variable vacuum degrees

The squeeze film effect has a significant impact on the performance of micro-resonators when utilizing the electrostatic excitation and capacitive detection technique, due to the narrow air gaps present. It becomes the most critical damping effect that needs to be addressed. However, when micro-resonators are encapsulated in vacuum or rarefied air, squeeze film damping analysis can become considerably complex due to high-quality factors. In this study, we systematically investigate the squeeze film damping of a widely-used four-leaf clover-coupled micro-resonator under different vacuum degrees. The characteristic frequencies of micro-resonators are determined by applying the principle of mode superposition. Subsequently, the energy transfer theory is utilized to derive the theoretical formula for the quality factor caused by squeeze film damping, for varying levels of vacuum. Finite element analysis is then conducted to simulate the characteristic behavior and squeeze film damping of the resonator, confirming the accuracy of the proposed theory. In the experiment, a novel four-leaf silicon micro-resonator is fabricated using bulk anisotropic wet etching and other micromachining technologies. An experimental platform is established to study the squeeze film damping of the micro-resonator under various vacuum degrees, where the micro-resonator is excited electrostatically and detected capacitively. The frequency response and quality factor of the resonator under different vacuum degrees are measured using a house-made modal test circuit board. The experimental results demonstrate excellent agreement with the theoretical and simulated results, indicating that the proposed method can be a reliable and precise guide for understanding the squeeze film damping effect in advance, once the primary model of a micro-resonator has been designed.

Study of the cooling performance of an anti-condensation radiant cooling unit with an infrared-transparent silicon wafer

Radiant cooling systems consume a low amount of energy and provide high thermal comfort; however, the risk of condensation in hot and humid areas limits their cooling capacity and is not conducive to their application. To solve the contradiction between condensation problems and the cooling demand, this study proposes a novel anti-condensation radiant cooling unit (RCU) that uses an infrared-transparent silicon wafer (ISW) with a good mechanical strength to separate the cooling radiant panel from the humid air, thus avoiding condensation. A heat transfer model of the anti-condensation RCU was established, and experimental tests were conducted under different indoor air temperatures, humidities, and vacuum degrees in the interlayer. At a temperature of 26 °C in 50 % relative humidity, the maximum cooling capacity of the anti-condensation RCU reached 103.66 W/m2, which was 60.88 % higher than the performance of conventional RCU. When the vacuum degree of the interlayer was 0.06 Mpa, the air-contacting surface outside the ISW was approximately 1.2 °C higher than that of atmospheric pressure. The results demonstrate that the anti-condensation RCU overcomes the limitation of the dew-point temperature on the cooling capacity to a certain extent and expands its applicability in high-humidity environments.

Combined inhibition effect of vacuum chamber and inert gas on LPG explosion

In order to investigate combined inhibition effect of vacuum chamber and inert gas on Liquefied petroleum gas (LPG) explosion, the explosion experiment was carried out on the self-built gas explosion experiment pipe (L/D = 47.5). The flame propagation and explosion pressure characteristics of LPG were investigated at different vacuum degrees and 10% CO2 volume fraction (VF). The results showed that it is feasible to use a photosensitive solenoid valve to open the vacuum chamber. The Photoreceptor Solenoid Valve can open the vacuum chamber in time; Compared to add only 10% CO2, after installing the vacuum chamber, the maximum pressure peaks were all delayed; The pressure drops rapidly and a short period of negative pressure appeared, and the negative pressure duration becomes shorter as the vacuum degree increases; At various vacuum degrees levels, the maximum pressure peak value occurs at 0.06 vacuum degrees, primarily due to the combined influence of residual fuel quantity, Helmholtz oscillation, and turbulence near the flame front. The Pmax in the pipe and the flame intensity at any position is lower than that when only adding 10% CO2; high vacuum is more conducive to extinguish the flame and increase the thickness of the flame; the pumping effect of the vacuum chamber inhibits the rise of explosion pressure and flame propagation velocity. The combined explosion suppression is more effective on LPG explosions compared to add only 10% CO2. When selecting vacuum degree, it is important to consider the impact of the opening time and different vacuum degree within the vacuum chamber on pressure formation and flame propagation.

Effect of Vacuum Degrees on Interfacial Bonding Behavior of 7050 Aluminum Alloy Clad Plates During Hot-Roll Cladding

Effect of Vacuum Degrees on Interfacial Bonding Behavior of 7050 Aluminum Alloy Clad Plates During Hot-Roll Cladding

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.

Vertical Nanoscale Vacuum Channel Triodes Based on the Material System of Vacuum Electronics

Nanoscale vacuum channel triodes realize the vacuum-like transmission of electrons in the atmosphere because the transmission distance is less than the mean free path of electrons in air. This new hybrid device is the deep integration of vacuum electronics technology, micro-nano electronics technology, and optoelectronic technology. It has the advantages of both vacuum and solid-state devices and is considered to be the next generation of vacuum electronic devices. In this work, vertical nanoscale vacuum channel diodes and triodes with edge emission were fabricated using advanced micro-nano processing technology. The device materials were all based on the vacuum electronics material system. The field emission characteristics of the devices were investigated. The diode continued emitting at a bias voltage from 0 to 50 V without failure, and the current variation under different vacuum degrees was better than 2.1%. The field emission characteristics of the devices were evaluated over a wide pressure range of between 10-7 Pa and 105 Pa, and the results could explain the vacuum-like behavior of the devices when operating in air. The current variation of the triode is better than 6.1% at Vg = 8 V and Va = 10 V.

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.

The evolution behavior and constitution characteristics of interfacial oxides in the hot-rolled stainless steel clad plate

The interface oxides’ morphologies, compositions and structures of 316 L/Q235 stainless steel clad plate with different vacuum degrees of 105, 400,10 and 10−2 Pa were investigated. As the vacuum degree raises, the oxides changes from continuous coarse nodules to refined rod particles, and the constitution changes from Cr2O3, MnCr2O4 and SiO2 into amorphous Mn2SiO4. Interestingly, the shear fracture position transfers from the interface into the decarburized layer as the vacuum degree increases. Overall, the dispersed nanoscale amorphous Mn2SiO4 play an important role in strengthening and toughening interface of hot-rolled stainless steel clad plates.

Experimental Investigation and Numerical Simulation of the Fluidity of A356 Aluminum Alloy

The fluidity of A356 aluminum alloy was experimentally determined at the melt temperatures and vacuum degrees by a series of suction fluidity tests. In order to achieve different cooling rates during the test, quartz tubes, as well as stainless steel tubes, were employed as the fluidity channels. As the melt temperature increased from 650 to 730 °C, fluidity lengths either linearly increased from 26 to 36 cm or parabolically increased from 13 to 29 cm when quartz tubes or stainless steel tubes were employed, respectively. As the vacuum degree of the fluidity test increased from 0.005 to 0.03 MPa, fluidity increased from 25 to 43 cm in quartz tubes while the smaller increase in fluidity from 20 to 31 cm was observed in stainless steel tubes. Shorter fluidity lengths in stainless steel tubes than those in quartz tubes under the same fluidity measurement condition were due to faster solidification speed confirmed by microstructural analysis. In order to predict the fluidity of the A356 alloy obtained from the suction fluidity tests, a mathematical model was developed based on heat and mass transfer equations coupled with thermodynamic calculations by ChemApp software. The simulation results show good agreement with the fluidity length obtained in the present study. From a series of model calculations, the effects of casting parameters on the fluidity of the A356 melt were discussed.

Two-Mask Wafer-Level Vacuum Packaging With Bulk-Si 3D Interconnects for MEMS Devices and Its Package Performances

We present the novel 3D wafer-level vacuum packaging technology for MEMS, which only needs two masks and is realized by Au-Si eutectic bonding with a low-resistivity Si Cap wafer. Wherein, Au-Si bonding pads and rings are formed to accomplish vertical interconnects and a vacuum package respectively. Applied to resonators with two typical substrate wafers of Si and Glass, this 3D package structure has further gone through the systemic characterizations. Specifically, the high-reliable mechanic strengths of device packages are revealed from Au-Si bonding strengths measured as about 20 MPa in tensile tests. Based on analyzing parasitic capacitance networks in device packages, the feed-through effect in resonance tests can be effectively relieved by grounding on each Si layer in device package structures (i.e. the parasitic capacitance reduced from the level of pF to fF). By resonance tests, it is found that increasing the degassing duration (30 min <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\to 60$ </tex-math></inline-formula> min <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\to 100$ </tex-math></inline-formula> min) is beneficial for improving package vacuum degrees as well as consistencies (69% within 4–30 kPa <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\to 88$ </tex-math></inline-formula> % within 0.6-1.2 kPa <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\to 85$ </tex-math></inline-formula> % within 0.6-0.8 kPa), and hermetic package yields (73% <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\to 86$ </tex-math></inline-formula> % <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\to 100$ </tex-math></inline-formula> %). Besides, device packages are verified to have good long-term stability by monitoring quality factor variations in 6 months. Overall, this proposed 3D packaging technology has extensive application prospects in various MEMS devices due to its inherently-simple process, low capacitive feed-through effect, and fine package performances. Also, test results provide instructions on the realization of low-parasitic-capacitance signal interfaces and the optimization of wafer-level vacuum package processes.

Influence of vacuum degrees in rectification system on distillation characteristics of bio-oil model compounds

The batch distillation experiments of bio-oil model compounds were carried out in a pilot rectification column. The distilled fractions of bio-oil model compounds at atmospheric pressure and vacuum distillation were compared by changing the vacuum degree in the system, and the variations of each component in the fractions were analyzed and summarized. The results show that the total distillate rate of bio-oil model compounds increases, the coking rate decreases, the moisture is more likely to be evaporated, the initial distillation temperature of organics in the fraction decreases, and the distillate rate increases with the rise in the vacuum degree of the system. Therefore, increasing the vacuum degrees can effectively separate the components of the bio-oil model compounds and reduce the energy loss. When the vacuum degree is −0.08 MPa, the distillation effect of the bio-oil model compounds is optimum. The distillate rate of acetic acid and furfural can reach 99.50% and 65.88%, respectively, and the distillate rates of phenol and guaiacol are both over 25%.

Effect of Microwave Vacuum Drying on the Drying Characteristics and Chemical Compositions of Turkish Gall Residues

Recently, the secondary use of waste has received increasing attention. The raw material of Xipayi mouth rinse is Turkish gall. During the industrial production of Xipayi mouth rinse, a lot of gall residues are produced. If these drugs are directly discarded, it will cause waste of resources and also bring pressure to the ecological environment. Previous studies have found that the active ingredient content of Turkish gall residues remains high, therefore the residues are still a valuable resource for exploitation. This study aimed to evaluate the effect of the chemical compositions and drying characteristics of Turkish gall residues during microwave vacuum drying (MVD). Different vacuum degrees, sample loads and sample sizes were used to investigate the drying characteristics of Turkish gall residues, and a kinetics model was established to describe the drying characteristics. We determined gallic acid (GA), methyl gallate (MG) and ellagic acid (EA) contents, total phenolic content (TPC) and total sugar content (TSC) of dried Turkish gall residue powder and investigated the influence of different MVD conditions on components. The results showed the good fit of the Page model equation in describing the drying kinetics of Turkish gall residues during MVD. Different conditions of MVD have different effects on the main components of residue. Thus, MVD can be used to desiccate Turkish gall residues. The Page kinetics model predicts the changes in dehydration rate during MVD of Turkish gall residues, providing a proven drying method for gall residues, and provides a theoretical basis for the industrial mass production of pharmaceutical residues.

A Deep Neural Network to Identify Vacuum Degrees in Vacuum Interrupter Based on Partial Discharge Diagnosis

One of the most crucial parameters in operating a vacuum interrupter (VI) is internal pressure. The failure of switching or insulation occurs when the pressure rises above a specific level. Characteristics of partial discharge (PD) in VI can be used to measure the internal pressures of VI. This paper defines a classification problem for the degree of internal pressure in VI using PDs, which were measured using a capacitive PD coupler. Then, we propose a deep neural network to monitor the internal pressure of VI by analyzing PDs. Experimental results show that the proposed deep neural network monitors the internal pressure range, from 1.0 &#x00D7;10^-2 torr to 10 torr in VI. The classification performance of the proposed method is significantly better than those of machine learning algorithms such as support vector machines and <i>k</i>-nearest neighbor algorithm and the proposed method achieves an 100% classification accuracy.

Hydrogen permeation in a palladium membrane tube: Impacts of outlet and vacuum degree

Palladium (Pd) membranes are a crucial device for separating hydrogen and are usually operated at normal pressure on the permeate side with a single outlet. Instead of these common operating conditions, the difference between using a double outlet and a single outlet is studied. Four different vacuum degrees (15–60 kPa) are applied on the permeate side, and the results are compared with the non-vacuum operations. Situations under the vacuum and the effects of temperatures (300–400 °C) on H2 permeation are discussed. Finally, the influences of different feed gas mixtures (H2/N2, H2/CO2, and H2/CO) on the Pd membrane performance are investigated. The results show that there is no difference in H2 permeation impact the single outlet and the double outlet on the permeate side. When a vacuum is imposed on the permeate side, the H2 permeation rate and H2 recovery are efficiently intensified, that is, when the pressure difference is 9 atm, they increase from 73.21 to 84.51% and from 0.0035378 to 0.0040808 mol∙s−1, respectively. Moreover, the H2 recovery can be improved to up to 68.44% under a vacuum degree of 60 kPa. At a given Reynolds number, an increase in temperature increases the H2 permeation rate but lowers its recovery, stemming from more H2 in the feed gas. This study also investigates the feed gas of H2/N2 under a vacuum to provide a useful insight into H2 production and separation from ammonia, and the results are compared with two different feed gases of H2/CO2 and H2/CO mixtures. The results suggest that the impurities (i.e., N2, CO2, and CO) have a negative influence on the Pd membrane, which causes the H2 permeation rate to decrease, and the effect of N2 is the least significant compared to the other two.

Experimental Investigation on the Operating Characteristics of Flat-Plate CLPHP for PEMFC Cooling

Proton exchange membrane fuel cell (PEMFC) generates electricity through hydrogen and oxygen chemical reaction with the generation of much heat. According to the working temperature of PEMFC, the thermal resistance and internal relative pressure change of the flat-plate micro closed-loop pulsating heat pipe (CLPHP) are tested and analyzed at different filling ratios, vacuum degrees, and inclination angles, whose working medium is binary methanol-deionized water with a mass ratio of 5:1. The experiment results show that the higher the vacuum degree is, the better the startup and heat transfer performance of CLPHP become; the thermal resistance is less sensitive to inclination angle except for horizontal placement; the 40% volume-filling ratio can effectively avoid dry-out at high temperature. When 80 °C is the ideal working temperature of PEMFC, the thermal resistance of CLPHP is 0.093°C/W; the heat transfer heat flux is 1.59 W/cm2, and the temperature fluctuation is small. Therefore, flat-plate CLPHP has great application potential for PEMFC cooling.

Physicochemical properties of pectin extracted from navel orange peel dried by vacuum microwave

Vacuum microwave drying (VMD) technique was applied for drying fresh navel orange peel (NOP) under different vacuum degrees including 0, 25, 45, 65, and 85 kPa. Compared with the traditional hot-air drying (HAD), the drying time of VMD was remarkably reduced by 90.7–94.7%. In addition, the drying time had a negative correlation to the vacuum degree, the drying time at 85 kPa was only 5.3% of HAD. The extraction yield of VMD pectin was significantly higher than that of HAD. Comparing to HAD, the extracted pectin by VMD exhibited an increase in the degree of methoxylation, but a decline in the average molecular weight and apparent viscosity. Moreover, the VMD can promote pectin adsorption capacities to the Pb2+ with the adsorption mechanism of the pseudo-second-order kinetic model. These findings indicated that VMD is a powerful, efficient, time-saving technology for drying fresh NOP and assisting extraction of pectin from NOP.

Effects of vacuum degree, mixing speed, and water amount on the moisture distribution and rheological properties of wheat flour dough.

Effects of vacuum degrees (0.00, 0.02, 0.04, 0.06, 0.08MPa)on water distribution state, tensile properties, stress relaxation properties, and viscoelasticity of dough, as well as the effects of mixing speed (50, 70, 90rpm/min)andwater content (40%, 45%, 50%) under optimum vacuum degree were studied. The results showed that the proper vacuum degree (0.06MPa) could promote the full contact between flour and water and improved the water-holding capacity of the dough. Meanwhile, the dough had stronger tensile strength, the best viscoelasticity and the ability to recover from external deformation more quickly. Under the vacuum of 0.06MPa,with the increasing of mixing speed, the response to the external force of dough increased first and then decreased. Adding more water reduced the strength of dough, weakened the response to external forces, and led to a significant decreaseintensile resistance and tensile area of the dough, as well as a decrease in viscoelasticity (p<0.05). The propervacuum mixing allowed the preparation of dough to require more water and less energy. PRACTICAL APPLICATION: In the processing of wheat flour products, vacuum mixing is considered to be beneficial to the quality of noodles and breads. As the intermediate of these products, the dough is of great significance for the monitoring of its rheological characteristics. In this study, a moderate vacuum degree led to a significant improvement in the rheological properties of the dough, and the processing performance was the best. Under the optimal vacuum degree, the influence of mixing speed and water amount cannot be ignored. Vacuum mixing is an efficient dough preparation method, which can produce certain economic benefits.

Influence of bottom roughness and ambient pressure conditions on the emplacement of experimental dam-break granular flows

Geophysical granular flows occur at the surface of the Earth and other planets with reduced atmospheric pressure. In this paper, we investigate the run-out of dam-break flows of particle-air mixtures with fine ( $$d=75\,\upmu {\hbox {m}}$$ ) or coarse ( $$d=150\,\upmu {\hbox {m}}$$ ) grains in a flume with different bottom roughness ( $$\delta$$ ) and vacuum degrees ( $$P^*$$ ). Our results reveal an increase of the flow run-out as $$d/\delta$$ decreases for fine $$d=75 \,\upmu {\hbox {m}}$$ -particles, and run-out decreases with the dimensionless ambient pressure ( $$P^*$$ ) for a given $$d/\delta$$ . In contrast, the run-out for coarser $$d=150\,\upmu {\hbox {m}}$$ -particles, is almost invariant respect to $$P^*$$ and $$d/\delta$$ . These results show that autofluidization of fine-grained flows demonstrated by earlier works at ambient pressure also occurs at reduced pressure though being less efficient. Hence, autofluidization is a mechanism, among others, to explain long run-out of geophysical flows in different environments.

Experimental Study on the Characteristics of Air Voids of Asphalt Mixture under Vacuum Compaction

In order to improve the compaction quality of asphalt mixture, a vacuum compaction technology is studied. Under different vacuum degrees (0 MPa, -0.04 MPa, -0.06 MPa, -0.08 MPa and negative pressure), the vacuum compaction process was used to prepare asphalt mixture samples and their characteristics of air voids were tested. The test results show, when the vacuum degree increases from 0 to -0.08 MPa, the air voids decrease with the increase of vacuum degree. The middle and upper air voids are small, and between 9-25 layers, average air voids under vacuum degree of -0.08 MPa and negative pressure is 13.2%, which is 41.6% lower than that under non vacuum; The average diameter is controlled at 1.88∼2.19 mm under vacuum degree of 0.08 MPa and negative pressure, which is 43.3% less than that under non vacuum. Those results show that vacuum compaction can effectively improve the characteristics of micro air voids of asphalt mixture, which will also improve the compactness.