Effects Of Vacuum Degree Research Articles

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.

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.

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).

High Efficiency Compound Vacuum Oil Gas Separation Technology Based on Integrated Oil Filter of Ultra-High Voltage Transformer

In order to improve the filtering effect of vacuum oil purifier, the author proposes the research and application of high-efficiency compound vacuum oil-gas separation technology based on electric ultra-high voltage transformer integrated oil purifier. The author studies under the condition of constant oil temperature and flow rate, the effect of vacuum degree on the filtering effect of transformer oil vacuum oil filter. Using the research results, a frequency conversion automatic vacuum oil filter is designed, which makes the processing process have the characteristics of simple operation, high degree of automation, and high work efficiency. The test results show that if the transformer oil processed by the variable frequency automatic vacuum oil purifier is new oil, its water content is less than 45 mg/kg and the gas content is less than 12%; when the breakdown voltage is greater than 25 kV, the transformer oil index can meet the following requirements after the equipment is filtered for one cycle: breakdown voltage ≥75 kV; water content ≤5 mg/kg; and gas content ≤0.1% (volume ratio). After one cycle (after 100 min), the variable frequency automatic (three-stage) vacuum oil filter can greatly shorten the time of transformer oil circulating and filtering. Conclusion. The designed frequency conversion automatic vacuum oil purifier is obviously better than other transformer oil vacuum oil purifiers.

Preparation and characterization of building insulation material based on SiO2 aerogel and its composite with expanded perlite

This article aims to complement the advantages of SiO2 aerogel and expanded perlite (EP) to prepare high-performance building insulation materials. SiO2 aerogels were prepared via acid/base two-step catalytic process followed by ambient pressure drying (APD) process. The two-step surface modification method is used to improve hydrophobicity of aerogel. And SiO2 aerogel/EP thermal insulation composites were obtained via introducing wet gel into EP. The effects of the amount of water, the amount of anhydrous alcohol and the pH value of sol on the properties of aerogels were analyzed. And the effects of vacuum degree and adsorption time on the thermal conductivity and compressive strength of SiO2/EP composite were studied. The pore size distribution and chemical structure of SiO2 aerogel were characterized by N2 adsorption-desorption test and Fourier transform infrared spectroscopy (FTIR). The micromorphology, crystal structure of SiO2 aerogel and SiO2/EP composite were characterized by scanning electron microscope, X-Ray diffraction. The results show that the thermal conductivity of SiO2 aerogel prepared with tetraethoxysilane (TEOS): methyltriethoxysilane (MTES): ethanol (EtOH):H2O = 1:0.3:14:6 (mole ratio) was as low as 0.0212 W/(m·K), the aerogel had high porosity (95.05%) and super hydrophobicity(the contact angle is 158.7°). Meanwhile, it was found that SiO2 aerogel is stably distributed in the pores of the EP and effectively reduces its thermal conductivity and water absorption. The minimum thermal conductivity of SiO2/EP composite was 0.036 W/(m·K), the minimum water absorption was 9.2% and the compressive strength was 214.35 kPa. Hence, SiO2 aerogel/EP with good performance and low cost has great potential in the field of building insulation.

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.

Effect of vacuum degree and T6 treatment on the microstructure and mechanical properties of Al–Si–Cu alloy die castings

This study investigated the effect of T6 treatment on the microstructure and mechanical properties of a die-cast Al–Si–Cu alloy at three vacuum degrees: 1013, 200, and 100 mbar. Corresponding microstructure and mechanical properties were performed. At the as-cast state, the eutectic Si sizes increased unexpectedly with increasing vacuum degree because oxides can act as heterogeneous nucleation sites for the eutectic Si at atmospheric pressure. Also, the increasing vacuum level from 1013 mbar to 100 mbar decreased pore size and porosity, which was the main reason for 12% and 55% increases in tensile strength and elongation, respectively. After T6 treatment, the decreasing pore size and porosity prevented the formation of blister. In addition, numerous θ′ phases were precipitated to strengthen the α-Al grains, evidently improving the tensile strength. The fractography of alloys under 1013 mbar revealed transgranular fractures because the spheroidized eutectic Si reduced the stress concentration at the grain boundaries. In contrast, the fractography of the alloys under 200 and 100 mbar showed coexistence of transgranular fractures and intergranular fractures due to the eutectic Si phase with coarse morphology presented at the grain boundaries.

Effect of vacuum degree on adhesion strength and corrosion resistance of magnetron sputtered aluminum coating on NdFeB magnet

A pure aluminum (Al) coating was deposited by direct current (DC) magnetron sputtering onto sintered NdFeB magnet coupons and glass slides at different vacuum degrees. The effect of vacuum degree on adhesion strength and corrosion resistance of the coating was investigated. The results showed that the adhesion strength between the Al coating and the substrate NdFeB magnet increased first and then decreased while the corrosion resistance of the Al coating increased with increasing vacuum degree. The Al coating formed at the low vacuum degree fractured within the coating when being peeled off because of a relatively high density of coating defects, while that formed at the high vacuum degree was mainly debonded along the coating/substrate interface. The decreased adhesion strength when the vacuum degree further increased could be attributed to excessive internal stress. The Al coating deposited at high vacuum degree was more corrosion resistant than that formed at low vacuum as the coating becomes less porous. Due to the presence of the micro defects, the corrosion behavior of the Al coating was accelerated on the substrate NdFeB magnet through the galvanic effect via these defects.

Effects of vacuum degree on the water status, physicochemical properties and microstructure of fast frozen dumpling wrappers

SummaryVacuum mixing is a new method of dough making, and little literature is available regarding its effects on the product quality of frozen food. This research studied the effects of different degrees of vacuum (0.00, −0.02, −0.04, −0.06, −0.08 MPa) on the water state, thermal properties, cooking characteristics and microstructure of fast frozen dumpling wrappers during different storage times (0, 14 and 30 days). Vacuum mixing significantly decreased the spin–spin relaxation times (T2) and freezing water content, thus indicating that it decreased the mobility of moisture and enhanced the binding of dough components with water molecules. Furthermore, the increases in the cooking loss rate and hardness of fast frozen dumpling wrappers during storage were inhibited by vacuum mixing, especially after storage for 30 days, possibly because vacuum mixing formed a more continuous and compacted dough structure, thereby generating a smaller ice crystal structure. These results should provide a theoretical basis for the application of vacuum mixing to fast frozen dumplings.

The effect of vacuum degree on the porosity and mechanical properties of die cast AlSi9Cu3(Fe) alloy

AlSi9Cu3(Fe) aluminum alloy specimens were produced by conventional high-pressure die casting (HPDC) and vacuum-assisted high-pressure die casting (VPDC) processes under atmospheric and 3 different...

Effect of magnetron sputtering parameters on adhesion properties of tungsten-rhenium thin film thermocouples

Tungsten-Rhenium (W-Re) thin films were grown on alumina ceramic substrate using the magnetron sputtering technique. The feasibility and reliability of the tungsten-rhenium thin film thermocouples application are largely dependent on the adhesion properties between the W-Re film and substrate. In order to get the good adhesion, we researched the effect of magnetron sputtering parameters on adhesion properties of tungsten-rhenium thin film thermocouples. With the help of three factors and three levels orthogonal table, nine orthogonal experiments were designed to study the influences of argon flow rate, sputtering power and vacuum degree on the performance of adhesion. The result showed that the effect of vacuum degree on adhesion properties was the largest, then come sputtering power, while the effect of the argon flow rate was the least and the optimal parameters combination was: argon flow rate 30 Sccm, sputtering power 400 W and vacuum degree 0.7 × 10−6 Torr.

Water regeneration from human urine by vacuum membrane distillation and analysis of membrane fouling characteristics

As a potential high-efficiency water circulation technique in some fields, such as space station that is abundant with vacuum and cooling resources and solar power, vacuum membrane distillation (VMD) process was employed for water regeneration from human urine. Particularly, membrane fouling characteristics were investigated. The separation performances including the membrane flux as well as the chemical oxygen demand (COD), ammonia-nitrogen concentration, and conductivity value of distillates were studied experimentally. The results indicated the flux increased with increasing feed temperature, but decreased with time. In the distillates, the COD reduced with time and went up with increasing feed temperature, the ammonia-nitrogen and conductivity increased gradually with time and rose up with increasing feed temperature due to the thermal decomposition of urea. The VMD processes of 500mL urine feed after 16-h operation had high COD removal rates of 99.3–99.5%, and the removals of ammonia-nitrogen reached 40.6–75.1%. The corresponding yields of water were 31.9–48.6%. Furthermore, the effects of vacuum degree in the permeate side, cross-flow flowrate and feed temperature on membrane flux were experimentally evaluated. The results showed that the critical fouling operating conditions (CFOCs) existed in the urine VMD processes. From the scanning electron microscopy photographs, it was confirmed that organic fouling accompanied by salt crystals on membrane surface can be restrained effectively when the urine VMD processes were carried out within the CFOCs. The organics, salt ions, and ammonia-nitrogens could be removed effectively under appropriate VMD conditions, such as relatively low temperature, sufficient membrane area and short heating time.

Effect of Vacuum Degree on Pinhole of Vacuum Counter-Pressure Casting Molten Aluminum Alloy

During vacuum counter-pressure casting, the vacuumization is an important stage for thin-wall and complicated aluminum alloy castings. Through testing and an analyzing numbers of pinhole and pinhole grade of aluminum alloy samples under different vacuum degree, the effect of vacuum degree on pinhole of vacuum counter- pressure casting molten aluminum alloy is studied. The results indicate vacuum degree has greater effect on pinhole of molten aluminum alloy in vacuumizing process. The smaller vacuum degree is, the more numbers of pinhole of the samples are, and the higher pinhole grade of the samples is. Therefore, when vacuum degree is small, pinhole of molten aluminum alloy appears easily. So the vacuum degree doesn’t choose too small, but for thin-wall and complicated aluminum alloy castings, the vacuum degree doesn’t choose too big either. Appropriate vacuum degree is from 20 KPa to 40 KPa.

Research on Open-Cell Rigid Polyurethane Foam as Vacuum Insulated Panel Core

Open-cell rigid polyurethane foam was taken as core material of the vacuum insulated panel, and the effects of open-cell ratio, density, cell-diameter and intensity on adiabatic performance of the vacuum insulated panel were simply discussed. The effect of vacuum degree on it is also discussed. The pre-treated craft of vacuum insulated panel manufacture is introduced too. If the open-cell rigid polyurethane foam was taken as the core-material and pretreated craft was carried, the vacuum insulated panel’s thermal conductivity can be less than 10mW/(m•K).

Predict Model for Water Content of Dredged Sludge under the Aeration-Vacuum Condition

The clogging problem occurs in the dewatering projects of sludge with high water content and high clay particles content can be solved by the aeration-vacuum dewatering method. And the water in the sludge can be separated out quickly. Through the dewatering model test of the sludge with this method, the effects of vacuum degree and aeration rate on the dewatering results are studied. The relationship between the initial and final water content is got under the aeration-vacuum condition. Through the fitting analysis of the dewatering curves, the predict model for water content of dredged sludge is presented. And the effect mechanism of the vacuum degree and aeration rate are analyzed.

Predict Model for Water Content of Dredged Sludge under the Aeration-Vacuum Condition

The clogging problem occurs in the dewatering projects of sludge with high water content and high clay particles content can be solved by the aeration-vacuum dewatering method. And the water in the sludge can be separated out quickly. Through the dewatering model test of the sludge with this method, the effects of vacuum degree and aeration rate on the dewatering results are studied. The relationship between the initial and final water content is got under the aeration-vacuum condition. Through the fitting analysis of the dewatering curves, the predict model for water content of dredged sludge is presented. And the effect mechanism of the vacuum degree and aeration rate are analyzed.

Effects of vacuum degree on tribological behavior of TiB 2/Al composites

The effects of vacuum degree on the tribological behavior of TiB 2/Al composites were investigated by a pin-on-disc tribometer under five vacuum degrees of 0.01, 0.03, 0.05, 0.07 and 0.1 MPa, respectively. The results show that the friction coefficient decreases with the increase of vacuum degree, while the wear rates change little. EDS spectra of composites wear surfaces show that Fe element content decreases with the increase of vacuum, which is consistent with the change of friction coefficients.

Effect of vacuum degree and aeration rate on sludge dewatering behavior with the aeration-vacuum method

Due to large-scale dredging operations, a large amount of sludge is inevitably produced. Large areas of land are occupied when the dredged sludge is discarded in the disposal site as waste material. The sludge dewatering with aeration-vacuum (SDAV) method is suit for treating the sludge with high water content and high clay content in the disposal site. The water in the sludge can be discharged out. The volume of the sludge can be reduced quickly, and the recycling of the land can be accelerated by this method. Most importantly, this technique is an efficient way to deal with clogging problems when pumping water from high water content, high clay content dredged sludge. Vacuum degree range tests, the aeration rate range tests, and the influencing factors of sludge dewatering behavior tests were conducted with a self-developed SDAV model test device. Sludge samples were taken from the South-to-North Water Diversion East Line Project in Huai’an White-Horse Lake disposal site, Jiangsu Province, China. The optimal range of vacuum degree and aeration rate were obtained through the test results, and the mechanisms for how the two factors work and how they affect the sludge dewatering behavior were analyzed. The suitable vacuum degree range in SDAV is below 50 kPa, and the suitable aeration rate is about 1.0 m3/h. The low-vacuum degree contributes to reduce the adsorption effect of micro-channels on soil particles in filter material and to maintain the arch structures. Aeration has the effects of expansion, disturbance, changing Reynolds number, and dynamic sieve separating. The pump quantity of water per meter of filter tube (Δm) has different change rules as the vacuum degree changes under different aeration rates. The reason is that the formed arch structures’ conformation and permeability differ greatly under different combined-conditions of vacuum degree and aeration rate. The optimal combined-condition for dewatering the sludge is 35 kPa with 1.0 m3/h.

Determination of paclitaxel and its analogues in the needles of Taxus species by using negative pressure cavitation extraction followed by HPLC‐MS‐MS

A new separation method, negative pressure cavitation (NPC) extraction followed by HPLC-MS-MS for the determination of paclitaxel and its analogues in the needles of Taxus species is described in this study. Compared with three conventional extraction methods, NPC is a more effective, economical, and facile method for the separation of nature compounds from herbal plants. In contrast to high-temperature extraction, NPC at low temperature can minimize undesirable reactions such as thermal decomposition or degradation. In addition, the extraction mechanism of NPC was also illuminated. The effects of vacuum degree, extraction solvent, ratio of solid to liquid, time, and times extraction were studied and optimized. The optimum extraction conditions were as follows: vacuum degree -0.03 MPa, solvent 80% v/v alcohol, ratio of material to liquid 1:15 (g/mL), extraction time 60 min, extraction (x3). Using these conditions, the recoveries of 10-deacetyl-7-xylosylpaclitaxel, 10-deacetylpaclitaxel, cephalomannine, and paclitaxel were higher than 95.88, 95.82, 94.85, and 96.18%, respectively. The contents of paclitaxel, 10-deacetyl-7-xylosylpaclitaxel, 10-deacetylpaclitaxel, and cephalomannine for Taxus chinensis were 0.0053, 0.0467, 0.0132, and 0.0076%, and 0.0067, 0.0153, 0.0047, and 0.0064% for Taxus cuspidata, respectively. Furthermore, a comparison of SEM images observed the morphological changes of microstructures and cellular damage in yew needles.

Synthesis and pervaporation properties of NaA zeolite membranes prepared with vacuum-assisted method

Uniform and dense NaA zeolite membranes were synthesized on the tubular α-Al 2O 3 support with a vacuum-assisted method by using low vacuum. The effect of vacuum degree on the formation of the NaA zeolite membrane was investigated. With the assistance of the vacuum, the negative influence of the gravitation force could be effectively reduced. Therefore, the zeolite particles could transport to cover the entire area of the support surface homogeneously, which facilitated formation of uniform and dense zeolite membranes. With the assistance of the vacuum, most zeolite particles migrated to the support surface for membrane formation, and the amount of crystals forming in the liquid phase could be greatly reduced. In addition, zeolite particles could be transported to the support surface rapidly, increasing the rate of dense membrane formation. The pervaporation properties of the as-synthesized zeolite membranes were evaluated by dehydration of 95 wt.% isopropanol/water mixtures at 343 K. The as-synthesized NaA zeolite membrane prepared with the vacuum-assisted method (i.e., with the assistance of 10 mmHg vacuum degrees), showed good pervaporation properties. The separation factor (water/isopropanol) was 3781 and the flux was 1.49 kg/m 2h, respectively. Based on the observed results, the formation mechanism of zeolite membrane with vacuum-assisted method was discussed.