Influence of air pressure on the performance of plasma synthetic jet actuator

Plasma synthetic jet actuator（PSJA） has a wide application prospect in the high-speed flow control field for its high jet velocity.In this paper,the influence of the air pressure on the performance of a two-electrode PSJA is investigated by the schlieren method in a large range from 7 k Pa to 100 k Pa.The energy consumed by the PSJA is roughly the same for all the pressure levels.Traces of the precursor shock wave velocity and the jet front velocity vary a lot for different pressures.The precursor shock wave velocity first decreases gradually and then remains at 345 m/s as the air pressure increases.The peak jet front velocity always appears at the first appearance of a jet,and it decreases gradually with the increase of the air pressure.A maximum precursor shock wave velocity of 520 m/s and a maximum jet front velocity of 440 m/s are observed at the pressure of 7 k Pa.The averaged jet velocity in one period ranges from 44 m/s to 54 m/s for all air pressures,and it drops with the rising of the air pressure.High velocities of the precursor shock wave and the jet front indicate that this type of PSJA can still be used to influence the high-speed flow field at 7 k Pa.

Two Phase Pressure Drop Performance of Refrigerant in a Small Horizontal Smooth Tube with 2.5 mm inside Diameter

Two-phase flow pressure drop measurements were made during the phase change heat transfer process of R22 in a small horizontal smooth tube with 2.5 mm inside diameter. Conclusions can be drawn that the quality corresponding to the pressure gradient peak value of small tubes became higher than that of large tubes. The effect of quality to pressure drop becomes weak as the mass flux increases. The experiment data were compared with the predicated values of the state-of-the-art correlations from the open literature. The comparisons between the data and the predictions indicate that most of the state-of-the-art correlations fails to predict the experimental data. Chisholm model shows a relatively better predictive ability than the other empirical correlations although it has a mean deviation of 26.7%. But the predicated values of Chisholm model are lower by 50% than the experimental data when the quality becomes larger.

Experimental Study on the Axial Compression Behavior of Short Columns of Steel-Fiber-Reinforced Recycled Aggregate Concrete

In order to study the axial compression performances of short columns made of recycled aggregate concrete,four samples were designed with different recycled aggregate replacement rates and carbon fibre reinforced plastics(CFRP)sheets.Then,monotonic loading was implemented to assess the variation trends of their axial compression properties.The ABAQUS finite element software was also used to determined the compression performances.Good agreement between experimental and numerical results has been found for the different parameters being considered.As shown by the results,recycled coarse aggregates result in improved ductility and better deformation performance of the specimens.The failure of specimens caused by pre damage can be compensated by using CFRP sheets,by which both the resistance to deformation and the axial carrying capacity of columns can be increased.

Determination of berberine in Phellodendron amurense from different sites of Changbai Mountain

Phellodendron amurense has been used for many years as a medical plant in traditional Chinese medicine and has shown great prospect in recent clinical trials for future applications. Berberine is an essential active compound contained in P. amurense. Our objective in this study was to quantify the content of berberine in P.amurense from sites at different elevations on Changbai Mountain. We collected samples of P. amurense from five different elevations on Changbai Mountain. Berberine in samples was extracted by ultrahigh pressure extraction（UPE）. And the quantity was measured by high performance liquid chromatography（HPLC）. First, the optimal HPLC conditions for berberine were identified with satisfactory precision（relative standard deviation, R SD／5.6 %）, good accuracy（relative error, R E／ 3.6 %） and good linear relation（R2= 0.9998） in the range of 6.576–328.8 mg L-1. Second, the combination of UPE and HPLC methods in quantitative analysis of berberine showed high repeatability（R SD= 3.28 %）, reproducibility（R SD= 4.72 %）,stability（R SD／ 1.27 %） and good recovery（99.54 %） for real plant materials. Samples from Heilongjiang Province at the lowest elevation contained the highest amount of berberine.Similarly, the lowest amount of berberine was recorded in samples from Changbai Forest Bureau of Jilin Province collected at the highest elevation in this paper. The proposed UPE–HPLC method is simple, reliable and low-cost for quantitative analysis of berberine. Content of berberine in P.amurense varied significantly by site on Changbai Mountain.

Correlations of Two-phase Friction of Refrigerant in Horizontal Smooth Tube with 2.5 mm inside Diameter

Two-phase flow pressure drop measurements are made during phase change heat transfer process of R-22 in small horizontal smooth tubes with 2.5 mm inside diameter. Conclusions are drawn that the quality corresponding to pressure gradient peak value of small tubes became higher than that of large tubes and that effects of quality on pressure drop become weak as the increase of mass flux. The experiment data are compared with predicted values of the state-of-the-art correlations from the open literature, which indicates that most of the state-of-the-art correlations fail to predict the present experimental data. Chisholm model shows a relatively better predictive ability than the other empirical correlations because it has the lowest mean deviation of 26.7%. But the predicted values of Chisholm model are 50% lower than experimental data when quality becomes higher. In this regard, an new empirical correlation based on Chisholm model is developed and this modified Chisholm correlation can describe 95% of the present data with ±20% mean deviations.

THE PERFORMANCES OF HIGH PRESSURE JET OF PURE WATER AND POLYMER SOLUTION WITH CONICAL NOZZLE

In this paper, the effects of polymer additives and nozzle shape on the proper- ties of high pressure water jet discharging into the air are investigated by theory and experiments. Criteria of judging the jet quality are put forward. And, a method that can be used in analysing the fluid flow within the nozzle is developed. Then, the calculated results are compared with the experiments that we carried out; it is shown that the degree of agreement between the two is good. At last, the mechanism to improve on the jet quality with polymer additives is discussed.

China's Cotton Textile Industry Faces Growing Pressure The analysis of economic performance of China's cotton textile industry in Jan.-Feb.(Part A)

Although the Chinese government has published a seriesof favorable policies for textile industry,the outcome of thesefiscal policies in Chinese cotton machinery industry tends to besmall at this stage,since the effects of policies is hysteresial,and the industry had extended 2009 spring holiday amid thefinancial crisis.

Analysis for pressure transient of coalbed methane reservoir based on Laplace transform finite difference method

Based on fractal geometry,fractal medium of coalbed methane mathematical model is established by Langmuir isotherm adsorption formula,Fick's diffusion law,Laplace transform formula,considering the well bore storage effect and skin effect.The Laplace transform finite difference method is used to solve the mathematical model.With Stehfest numerical inversion,the distribution of dimensionless well bore flowing pressure and its derivative was obtained in real space.According to compare with the results from the analytical method,the result from Laplace transform finite difference method turns out to be accurate.The influence factors are analyzed,including fractal dimension,fractal index,skin factor,well bore storage coefficient,energy storage ratio,interporosity flow coefficient and the adsorption factor.The calculating error of Laplace transform difference method is small.Laplace transform difference method has advantages in well-test application since any moment simulation does not rely on other moment results and space grid.

More words but less investment:Rookie CEOs and firms’digital transformations

In digital economy,firm’s digital transformation is an important means of achieving high-quality development.Adopting career concerns theory,we examine rookie CEOs’impact on firms’digital transformations,using Chinese A-share listed firms from 2007 to 2019.(1)Rookie CEOs disclose more digital transformation information,but invest less in substantial transformation,i.e.,“more words but less investment”.(2)Under high performance pressure and difficult digital transformation,rookie CEOs are more likely to adopt the above strategy.(3)Internal and external governance mechanisms help effectively monitor and mitigate such behaviors.(4)The above strategy helps CEOs decrease short-term,but not long-term,dismissal probabilities.Our findings elucidate firms’digital transformation practices and the decision styles of CEOs with different experience levels.

Thermal-Hydraulic Characteristics of Twisted Elliptical Tube Bundle in Staggered Arrangement

Based on experimental data,numerical simulations by turbulent air flowing across staggered tube bundle composed of twisted elliptical tube(TET)with constant tube wall temperature are conducted in present study.Parametric study on the thermal-hydraulic characteristics of air crossflow in TET bundles is investigated with physical parameters and Reynolds number(Re).The results show that spiral channels created by spiral deformation of TETs have a diversion effect on the air flow,which changes the flow direction of the air near the tube wall.The air in the near wall region is a three-dimensional flow,consisting of a flow perpendicular to the normal direction of the elliptical cross section and a spiral flow along the helicoid on the downstream side and the upstream side.And the interaction of the spiral channels makes the two flows and their mixing more complicated.The excellent heat transfer performance of staggered TET bundles is confirmed by the comparison of the comprehensive heat transfer performance with that of circular tube bundles.The average Nusselt number(Nu)increases with the increase of the aspect ratio(A/B)and with the increase of Re while decreases as the twist pitch(S)increases.The average Euler number(Eu)increases as A/B increases,while it decreases as Re increases and as S increases.Due to the fact that the suitable correlations for staggered TET bundles are not reported,correlations for Nu and Eu obtained from experimental data and numerical results are presented in the multiple forms.

Growth of SiC as Binder to Adhere Diamond Particle and Tribological Properties of Diamond Particles Coated SiC

The purpose of this work was to grow SiC as binder to adhere diamond particles to graphite substrate by low pressure chemical vapor deposition （LPCVD） at 1100 ℃ and 100 Pa using methyltrichlorosilane （MTS： CH3SiCl3） as precursor. The composite coatings on graphite substrates were analyzed by various techniques. Results show that a dense SiC coating with a cloud-cluster shape was formed both on the diamond particles and the substrate after deposition, The thermal stress （290.6 MPa） strengthened the interfacial bonding between the diamond particle and the SiC coating, which is advantageous for the purpose of adhering diamond particles to graphite substrate. The applied load of sliding wear test was found to affect not only the friction coefficient, but also the wear surface morphology. With increasing loads, the asperity penetration was high and the friction coefficient decreased.