Determination of the Critical Temperature and Critical Pressure of Five Compounds

The critical properties of five compounds, including propanal,butanal, 1-pentanal, 2-methel butanal and trimer of ethanal, weredetermined for the first time by a new capillary quick-flow method.The apparatus was improved with a capillary tube and checked withhexane and 10heptene as standard reagents. The experimental resultsproved that the determination of critical properties by quick-flowmethod with a capillary tube apparatus was successful.

Research on the Critical Buckling Pressure of Bucket Foundations with Inner Compartments for Offshore Wind Turbines

In the process of suction penetration of bucket foundations with inner compartments for offshore wind turbines,most researches focus on soil seepage failure and soil plugs,while the buckling of foundations is rarely investigated.Therefore,theoretical calculation methods for critical buckling pressures of the skirt and bulkheads of the bucket foundation are first presented according to the stability theory of a cylindrical shell and the small deflection theory of a thin plate,respectively.Furthermore,two types of models with and without considering the skirt-soil interaction are developed for the calculation of critical buckling pressure of the bucket foundation.Taking a practical project as an example,theoretical and numerical methods are used to obtain the critical buckling pressures of a bucket foundation.In this work,the theoretical method and the finite element model considering the skirt-soil interaction for calculating the critical buckling pressure of bucket foundations are firstly proposed.The results can help to optimize the design process of offshore wind turbine foundations and improve the safety of offshore wind power systems.

Critical and Impeding Pressures of Al Evaporation during ISM Processing of NiAl

In this paper, the critical pressure pcrit and impeding pressure pimpe of the elemental evaporation were defined and studied based on the calculation of the relationship between the evaporation loss rate Nm and the chamber pressure p during melting of NiAl alloys. When the chamber pressure is lower than pcrit or higher than Pimpe Nm tends to be the maximum or minimum value and remains almost unchanged. However, declines sharply with the increase of the chamber pressure when pcrit<P<Pimpe. A method has been put forward to calculate the pcrit and pimpe of Al evaporation in a Ni-XAI (x=25-50 at. pct) melt. The calculation result shows that the pcrit or pimpe is a second-order function of the molar percentage of Al and the melting temperature.

Experimental Analysis of the Flow Characteristics of an Adjustable Critical-Flow Venturi Nozzle

The response of an adjustable critical-flow Venturi nozzle is investigated through a set indoor experiments aimed to determine the related critical flow rate,critical pressure ratio,and discharge coefficient.The effect of a variation in the cone displacement and liquid content on the critical flow characteristics is examined in detail and it is shown that the former can be used to effectively adjust the critical flow rate.The critical pressure ratio of the considered nozzle is above 0.85,and the critical flow control deviation of the gas flow is within±3%.Liquid flow can reduce the gas critical mass flow rate accordingly,especially for the cases with larger liquid volume and lower inlet pressure.The set of results and conclusions provided are intended to support the optimization of steam injection techniques in the context of heavy oil recovery processes.

Determination of Critical Parameters of Carbon Dioxide+Butyraldehyde System with Different Compositions

Supercritical carbon dioxide（SC-CO2 ） is considered in green chemistry as a substitute for conventional solvents in chemical reactions due to its environmentally benign character. Recently we have reported the homogeneous hydroformylation of propylene in supercritical carbon dioxide（ SC-CO2 ） , which is an example of this kind of application of carbon dioxide. The determination for the critical parameters of carbon dioxide ＋ butyraldehyde mixtures is necessary for this reaction design which is the focus of the present paper. The critical parameters of the binary systems were determined via the static visual method at a constant volume with the molar fraction of butyraldehyde ranging from 1.0% to 2. 2% and the pressure ranging from 5 to 10 MPa. The experimental results show that the critical pressure and temperature increased with increasing the molar fraction of butyraldehyde. The bubble（dew） temperatures and the bubble （dew） pressures for the binary systems were also determined experimentally. The p-T Figures at different compositions of the binary systems were described. In addition, the critical compressibility factors Zc of the binary systems at different concentrations of n-butyraldehyde were calculated. It was found that the critical compressibility factor values of the binary systems decreased with increasing the molar fraction of n-butyraldehyde in the experimental range.

An improved apparent permeability model considering full pore pressure range,variable intrinsic permeability and slippage coefficient

Although the slippage effect has been extensively studied,most of the previous studies focused on the impact of the slippage effect on apparent permeability within a low pore pressure range,resulting in the inability of matching the evolution of permeability in the remaining pressure range.In this paper,a new apparent permeability model that reveals the evolution of permeability under the combined action of effective stress and slippage in the full pore pressure range was proposed.In this model,both intrinsic permeability and slippage coefficient are stress dependent.Three experimental tests with pore pressure lower than 2 MPa and a test with pore pressure at about 10 MPa using cores from the same origin under constant confining stress and constant effective stress are conducted.By comparing experimental data and another apparent permeability model,we proved the fidelity of our newly developed model.Furthermore,the contribution factor of the slippage effect Rslip is used to determine the low pore pressure limit with significant slippage effect.Our results show that both narrow initial pore size and high effective stress increase the critical pore pressure.Finally,the evolutions of the slippage coefficient and the intrinsic permeability under different boundary conditions were analyzed.

Logistic Regression Analysis and Nursing Interventions for High-risk Factors for Pressure Sores in Patients in a Surgical Intensive Care Unit

Objective： To investigate the risk factors related to the development of pressure sores in critically ill surgical patients and to establish a basis for the formulation of effective precautions. Methods： A questionnaire regarding the factors for pressure sores in critically ill surgical patients was created using a case control study with reference to the pertinent literature. After being exam- ined and validated by experts, the questionnaire was used to collect data about critically ill surgical patients in a grade A tertiary hospital. Among the 47 patients enrolled into the study, the 14 who developed nosocomial pressure sores were allocated to the pressure sore group, and the remaining 33 patients who met the inclusion criteria and did not exhibit pressure sores were allocated to the control group. Univariate and multivariate logistic regression analyses were employed to examine the differences in 22 indicators between the two groups in an attempt to identify the risk factors for pressure sores. Results： According to the univariate analyses, the maximum value of lactic acid in the arterial blood, the number of days of norepinephrine use, the number of days of mechanical ventilation, the number of days of blood purification, and the number of days of bowel incontinence were statistically greater in the pressure sore group than in the control group （P〈0.05）. The multivariate logistic regression analysis revealed that the number of days of norepinephrine use and the level of lactic acid in the arterial blood were high risk-factors for pressure sores （P〈0.05）. Conclusions： The best method for preventing and control pressure sores in surgical critically ill patients is to strongly emphasize the duration of the critical status and to give special attention to patients in a continuous state of shock. The adoption of measures specific to high-risk patient groups and risk factors, including the active control of primary diseases and the application of decompression measures during the treatment of the patients, are helpful for improving the quality of care in the prevention and control of pressure sores in critically ill patients.

Rapidly Estimating Natural Gas Compressibility Factor

Natural gases containing sour components exhibit different gas compressibility factor （Z） behavior than do sweet gases. Therefore, a new accurate method should be developed to account for these differences. Several methods are available today for calculating the Z-factor from an equation of state. However, these equations are more complex than the foregoing correlations, involving a large number of parameters, which require more complicated and longer computations. The aim of this study is to develop a simplified calculation method for a rapid estimating Z-factor for sour natural gases containing as much as 90% total acid gas. In this article, two new correlations are first presented for calculating the pseudo- critical pressure and temperature of the gas mixture as a function of the gas specific gravity. Then, a simple correlation on the basis of the standard gas compressibility factor chart is introduced for a quick estimation of sweet gases＇ compressibility factor as a function of reduced pressure and temperature. Finally, a new corrective term related to the mole fractions of carbon dioxide and hydrogen sulfide is developed.

Orifice plate cavitation mechanism and its influencing factors

The orifice plate energy dissipater is an economic and highly efficient dissipater. However, there is a risk of cavitaion around the orifice plate flow： In order to provide references for engineering practice, we examined the cavitation mechanism around the orifice plate and its influencing factors by utilizing mathematical analysis methods to analyze the flow conditions around the orifice plate in view of gas bubble dynamics. Through the research presented in this paper, the following can be observed： The critical radius and the critical pressure of the gas nucleus in orifice plate flow increase with its initial state parameter r0 ; the development speed of bubbles stabilizes at a certain value after experiencing a peak value and a small valley value; and the orifice plate cavitation is closely related to the distribution of the gas nucleus in flow. For computing the orifice plate cavitation number, we ought to take into account the effects of pressure fluctuation. The development time of the gas nucleus from the initial radius to the critical radius is about 107-10-5 s; therefore, the gas nucleus has sufficient time to develop into bubbles in the negative half-cycle of flow fluctuation. The orifice critical cavitation number is closely related to the orifice plate size, and especially closely related with the ratio of the orifice plate radius to the tunnel radius. The approximate formula for the critical cavitation number of the square orifice plate that only considers the main influencing factor was obtained by model experiments.

Hydrodynamic deep drawing of double layered conical cups

Hydrodynamic deep drawing assisted by radial pressure is an advanced sheet forming technology with great advantages such as higher drawing ratio, good surface quality and higher dimensional accuracy. In this process, both the bottom surface and the peripheral edge of sheets are under hydrodynamic pressure, so that the forming procedure is more uniform with low failure probability. Multi-layered sheets with complex geometries could be formed more easily with this technique compared with other traditional methods. Rupture is the main irrecoverable failure form in sheet forming processes. Prediction of rupture occurrence is of great importance for determining and optimizing the proper process parameters. In this research, a theoretical model was proposed to calculate the critical rupture pressure in production of double layered conical parts with hydrodynamic deep drawing process assisted by radial pressure. The effects of other process parameters on critical rupture pressure, such as punch tip radius, drawing ratio, coefficient of friction, sheet thickness and material properties were also discussed. The proposed model was compared with finite element simulation and validated by experiments on Al1050/St13 double layered sheets, where a good agreement was found with analytical results.

MATERIAL FRACTURE TOUGHNESS DETERMINATION FOR POLYETHYLENE PIPE MATERIALS USING SMALL SCALE TEST RESULTS

The Small-Scale Steady State (S4) test has been recently developed in order to assess the fracture behaviour of polyethylene (PE) gas distribution pipe material during rapid axial crack propagation. Based on an investigation of the S4 test, a simulation model of S4 test has been developed. This paper describes the use of the results obtained from the S4 test and program modified from PFRAC (Pipeline Fracture Analysis Code) to evaluate the fracture toughness of the material, G(d), which could not be directly obtained from the test, and to predict critical pressure, p(c), for rapid crack propagation (RCP) in a full scale PE pipe. The algorithms for contact conditions are developed to consider the opening pipe wall impact against a series containment rings and the capabilities of PFRAC are also extended. When G(d) is evaluated, investigations are made on the effect of temperature, wall thickness and crack velocity. In addition, procedures to evaluate the critical pressure for the S4 test pipe are also discussed.

Elastoplastic Analysis of Circular Tunnel in Saturated Ground Under Different Load Conditions

When a tunnel is excavated below the groundwater table,groundwater flows in through the excavated wall of the tunnel and seepage forces act on it.These forces significantly affect the ground reaction curve,which is defined as the relationship between the internal pressure and radial displacement of the tunnel wall.This study investigates analytical solutions for seepage forces acting on the lining of a circular tunnel under steady-state groundwater flow.Considering the tunnel’s construction or service period and boundary conditions,the direction of maximum principal stress changes,and the input stress of the Mohr-Coulomb criterion varies.The stress distribution and yield range of the surrounding soils and linings are studied.The first,second,and third critical inner pressures are defined and evaluated.The influence of the seepage field on the plastic radius,first critical pressure,and stress distribution of the tunnel is analyzed.It is shown that during the construction period,the seepage force promotes the expansion of the yield area,whereas during the service period,the opposite is the case.The first critical pressure increases nearly linearly with the distant water pressure.The radial stress distribution decreases clearly in comparison with that when the seepage force is not considered,and the reduction is more prominent when internal pressure increases.The tangential stress distribution increases clearly compared with that when the seepage force is not considered.

Face stability of shield tunnels considering a kinematically admissible velocity field of soil arching

Existing mechanism of simulating soil movement at tunnel face is generally based on the translational or rotational velocity field,which is,to some extent,different from the real soil movement in the arching zone.Numerical simulations are carried out first to investigate the characteristics of the velocity distribution at tunnel face and above tunnel vault.Then a new kinematically admissible velocity field is proposed to improve the description of the soil movement according to the results of the numerical simulation.Based on the proposed velocity field,an improved failure mechanism is constructed adopting the spatial discretization technique,which takes into account soil arching effect and plastic deformation within soil mass.Finally,the critical face pressure and the proposed mechanism are compared with the results of the numerical simulation,existing analytical studies and experimental tests to verify the accuracy and improvement of the presented method.The proposed mechanism can serve as an alternative approach for the face stability analysis.

Geologically controlling factors on coal bed methane （CBM） productivity in Liulin

It is of great significance to forecast high yield of CBM wells and analyze dynamic production by having an overall study on the characteristics of the produced CBM and determining the main factors influencing the productivity of CBM. With the test report and the related geological parameters of a single well, methods of combining the productivity data and typical production curves were used to analyze different geological factors and how to influence the capacity of a single layer. Then, the paper proposed a new understanding about capacity characteristics of the study area and geological control factors： First, the Shanxi formation production capacity characteristics was divided into two-stages, showing signs of gas and gas break- through for 100 days. Second, two parameters, which include potential of gas production and gas production capacity, were bet- ter than the single parameter, such as gas content, coal thickness, and penetration to analyze affecting factors of single well pro- duction. Finally, comprehensive analysis concluded that the ratio of critical desorption pressure to reservoir pressure has greater influence on the production of vertical CBM wells. Besides, the potential of gas production capacity has greater impact at stage of showing gas signs; the coal reservoir pressure and gas production capacity have greater impact at stage of gas breakthrough for 100 days. Thus, to seek the coal bed methane with high ratio of critical desorption pressure to reservoir pressure and high yield of gas will be important guarantee to the success of the coal bed methane exploration and development.

Theoretical analysis on water-inrush mechanism of concealed collapse pillars in floor

In order to study the water-inrush mechanism of concealed collapse pillars from the mechanical view, a mechanical model for water-inrush of collapse pillars has been established based on thick plate theory of elastic mechanics in this paper.By solving this model the deformation of water-resistant rock strata under the action of water pressure and the expression of critical water pressure for collapse pillar waterinrush have been obtained The research results indicate that：the boundary conditions and strength of water-resistant strata play important roles in influencing water-inrush of collapse pillars.The critical water-inrush pressure is determined by both relative thickness and absolute thickness of water-resistant strata.

Evolution characteristics of precursor information of coal and gas outburst in deep rock cross‑cut coal uncovering

As mines become deeper,the potential for coal and gas outbursts in deep rock cross-cut coal uncovering is enhanced.The outburst precursors are unclear,which restricts the effectiveness and reliability of warning systems.To reveal the evolution characteristics of coal and gas outburst precursor information in deep rock cross-cut coal uncovering,briquette specimens are constructed and experiments are conducted using a self-developed true triaxial outburst test system.Using acoustic emission monitoring technology,the dynamic failure of coal is monitored,and variations in the root mean square(RMS)of the acoustic emissions allow the effective cracking time and effective cracking gas pressure to be defined.These characteristics are obviously different in deep and shallow coal.The characteristic parameters of gas outburst exhibit stepwise variations at different depths.The RMS and cumulative RMS have stepped failure characteristics with respect to changes in gas pressure.The characteristic parameters of coal failure are negatively correlated with the average in-situ stress and effective stress,but positively correlated with the lateral pressure coefficient of in-situ stress and the critical gas pressure.The transition characteristics are highly sensitive in all cases.The critical depth between deep and shallow coal and gas outbursts is 1700 m.The expansion multiple of acoustic emission intensity from the microfracture stage to the sharp-fracture stage of coal is defined as the outburst risk index,N1.For depths of 1100–1700 m,N1≥7 denotes a higher risk of outburst,whereas at depths of 1700–2500 m,N1≥3 indicates enhanced risk.

Interplay of superconductivity and d-f correlation in CeFeAs_(1-x)P_xO_(1-y)F_y

The recent discovery of high-temperature superconductivity in iron-based pnictides （chalcogenides） not only trig- gers tremendous enthusiasm in searching for new superconducting materials, but also opens a new avenue to the study of the Kondo physics. CeFeAsO is a parent compound of the 1111-type iron-based superconductors. It shows 3d- antiferromagnetic （AFM） ordering below 139 K and 4f-AFM ordering below 4 K. On the other hand, the phosphide CeFePO is a ferromagnetically corelated heavy-fermion （HF） metal with Kondo scale TK 10 K. These properties set up a new platform for research of the interplay among magnetism, Kondo effect, and superconductivity （SC）. In this review, we present the recent progress in the study of chemical pressure effect in CeFeAsOl_yFy （y = 0 and 0.05）. This P/As-doping in CeFeAsO serves as an effective controlling parameter which leads to two magnetic critical points, Xcl -- 0.4 and Xc2 - 0.92, associated with suppression of 3d and 4f magnetism, respectively. We also observe a turning point of AFM-FM ordering of Ce3＋ moment at Xc3 - 0.37. The SC is absent in the phase diagram, which is attributed to the destruction to Cooper pair by Ce-FM fluctuations in the vicinity of Xcl. We continue to investigate CeFeAsl-xPxO0.95Fo.os. With the separation of xcl and xc3, this chemical pressure results in a broad SC region 0〈 x 〈 0.53, while the original HF behavior is driven away by 5% F- doping. Different roles of P and F dopings are addressed, and the interplay between SC and Ce-4f magnetism is also discussed.

Experimental study on detonation parameters and cellular structures of fuel cloud

In this paper, detonation parameters of fuel cloud, such as propylene oxide （PO）, isopropyl nitrate （IPN）, hex- ane, 90# oil and decane were measured in a self-designed and constructed vertical shock tube. Results show that the deto- nation pressure and velocity of PO increase to a peak value and then decrease smoothly with increasing equivalence ra- tio. Several nitrate sensitizers were added into PO to make fuel mixtures, and test results indicated that the additives can efficiently enhance detonation velocity and pressure of fuel cloud and one type of additive n-propyl nitrate （NPN） played the best in the improvement. The critical initiation energy that directly initiated detonation of all the test liquid fuel clouds showed a U-shape curve relationship with equiva- lence ratios. The optimum concentration lies on the rich-fuel side （;b 〉 1）. The critical initiation energy is closely related to molecular structure and volatility of fuels. IPN and PO have similar critical values while that of alkanes are larger. Detonation cell sizes of PO were respectively investigated at 25;C, 35;C and 50;C with smoked foil technique. The cell width shows a U-shape curve relationship with equivalence ratios at all temperatures. The minimal cell width also lies on the rich-fuel side （;b 〉 1）. The cell width of PO vapor is slightly larger than that of PO cloud. Therefore, the deto- nation reaction of PO at normal temperature is controlled by gas phase reaction.

Study for the Gas Flow through a Critical Nozzle

In the present study, computational work using the axisymmetric, compressible, Navier-Stokes equations is carried out to predict the discharge coefficient and critical pressure ratio of gas flow through a critical nozzle. The Reynolds number effects are investigated with several nozzles with different throat diameter. Diffuser angle is varied to investigate the effects on the discharge coefficient and critical pressure ratio. The computational results are compared with the previous experimental ones. It is known that the discharge coefficient and critical pressure ratio are given by functions of the Reynolds number and boundary layer integral properties. It is also found that diffuser angle affects the critical pressure ratio.

Buckling analysis of ring stiffened thin cylindrical shell under external pressure

Submarine pressure hulls,fire-tube boilers,vacuum tanks,oil well casings,submersibles,underground pipelines,tunnels,rocket motor casing,etc.,are some of the examples of thin cylindrical shell structures which collapse due to buckling under uniform pressure.To enhance the buckling strength of bare cylin-drical shells,one of the best solutions is to stiffen them with ring stiffeners.In this work in order to predict the shell instability failure mode(SIFM)and general instability failure mode(GIFM)FE models are generated and analysed using buckling analysis of general-purpose FE software ANSYS.The numeri-cal results obtained using FE analysis are compared with published analytical and experimental results.Hence in the present study effort s are taken to develop FE models to predict global and shell instability failure modes of externally ring stiffened cylindrical shells by using linear FE analysis.It is proposed to use full/half bare cylindrical shell FE models(L/R ratio upto 200)to determine SIFM and FE models with shell281-Beam189(for stiffeners)can be used to determine GIFM.The developed FE models are vali-dated by comparing numerical results with experimental results published by Seleim and Roorda[25].By using both proposed FE models it is possible to predict the failure modes namely SIFM and GIFM,comparing their values of critical buckling pressures.The lower pressure value can indicate the possible failure mode.