Cavitation flow instability of subcooled liquid nitrogen in converging–diverging nozzles

The cavitation flow instability of subcooled liquid nitrogen in two types of converging–diverging (C–D) circular nozzles with throat diameters of 1.5 and 2.0 mm was experimentally investigated. Flow observations were also performed to clarify the instability phenomenon and the differences in cavitation behavior between the two nozzles. The cavitation mode changed from continuous mode to intermittent mode as the temperature of the subcooled liquid nitrogen decreased. This change occurred in both C–D nozzles when the temperature of the liquid reached approximately 76 K. Occurrence of the intermittent mode accompanying very large pressure-oscillations was considered to be caused by a drastic reduction of the speed of sound in the single-component, vapor–liquid flow because the speed of sound restricted the throat velocity in the C–D nozzle during cavitation. Oscillation pressure values in intermittent mode were much larger than those in continuous mode, peaking between 74 and 76 K. The magnitude of the oscillation pressure in intermittent mode could be evaluated from the difference between the throat static-pressure immediately prior to the occurrence of cavitation and that during cavitation.     

Pressure drop correlation for oil–refrigerant R134a mixture flashing flow in a small diameter tube

This paper presents an experimental investigation of the ester oil ISO VG10/refrigerant R134a mixture flashing flow in a 6.0 m long, 3.22 mm ID tube, which is one of the primary steps towards the construction of a methodology for the study of the lubrication and gas leakage in refrigeration compressors. The phase change starts with solubility reduction of the refrigerant in the oil as the pressure decreases due to the friction forces. In this flashing flow the foam pattern is observed at the end of the tube as vapor quality reaches high values, and this is a particular phenomenon of this kind of mixture flow. In order to study this pressure drop, an experimental apparatus was designed to allow the measurement of both pressure and temperature profiles along the tube as well as the visualization of the flow patterns. Pressure and temperature distribution along the flow were measured for saturation pressure ranging from 450 to 650 kPa, mass flux ranging from about 2000 to 3000 kg/(m²s), temperatures around 303 K, and inlet refrigerant concentration varying between 0.2 and 0.4 kg ref/kg mixt. An available correlation proposed to predict the frictional pressure drop for a mixture composed by the mineral oil SUNISO 1GS and refrigerant R12 flowing in small diameter tubes yielded large deviations in predicting the ester oil and refrigerant R134a mixture flow. A new correlation has been proposed that fitted the experimental data with rms deviations of 24%.     

Experimental investigation and correlation of two-phase frictional pressure drop of R410A–oil mixture flow boiling in a 5 mm microfin tube

This study presents experimental two-phase frictional data for R410A-oil mixture flow boiling in an internal spiral grooved microfin tube with outside diameter of 5 mm. Experimental parameters include the evaporation temperature of 5 °C, the mass flux from 200 to 400 kg m^?2 s^?1, the heat flux from 7.46 to 14.92 kW m^?2, the inlet vapor quality from 0.1 to 0.8, and nominal oil concentration from 0 to 5%. The test results show that the frictional pressure drop of R410A initially increases with vapor quality and then decreases, presenting a local maximum in the vapor quality range between 0.7 and 0.8; the frictional pressure drop of R410A–oil mixture increases with the mass flux, the presence of oil enhances two-phase frictional pressure drop, and the effect of oil on frictional pressure drop is more evident at higher vapor qualities where the local oil concentrations are higher. The enhanced factor is always larger than unity and increases with nominal oil concentration at a given vapor quality. The range of the enhanced factor is about 1.0–2.2 at present test conditions. A new correlation to predict the local frictional pressure drop of R410A-oil mixture flow boiling inside the internal spiral grooved microfin tube is developed based on local properties of refrigerant–oil mixture, and the measured local frictional pressure drop is well correlated with the empirical equation proposed by the authors.     

Characteristics of serrated flow in commercial Cu–Be–Co alloy

Abstract

Serrated yielding in a Cu–l·8Be–0·3Co (wt-%) alloy has been studied as a function of strain rate and temperature. Serration characteristics, e.g. type, stress drop δσ, frequency ν, vacancy concentrations–strain exponent m, mobile dislocation density–strain exponent β, and activation energy Q_m for serrated yielding, have been determined. Strain rate sensitivity of flow stress δσ/? ln ? and activation volume V parameters have also been derived through strain rate change tests. The results have been interpreted in the light of the static strain aging model of the Portevin–Le Chatelier effect.

MST/540     

Influence of titanium and nitrogen on hot ductility of C–Mn–Nb–Al steels

Abstract

The influence of small additions of titanium on the hot ductility of C–Mn–Nb–Al steels has been examined. Titanium and nitrogen levels varied in the ranges 0·014–0·045 and 0·004–0·011 wt-%, respectively, so that a wide range of Ti/N ratios could be studied. The tensile specimens were cast and cooled at average cooling rates of 25, 100, and 200 K min^-1 to test temperatures in the range 1100–800°C and strained to failure at a strain rate of 2 × 10^-3 s^-1. It was found that ductility in the titanium containing niobium steels improved with a decrease in the cooling rate, an increase in the size of the titanium containing precipitates, and a decrease in the volume fraction of precipitates. Coarser particles could be obtained by increasing the Ti/N ratio above the stoichiometric ratio for TiN and by testing at higher temperatures. However, ductility was generally poor for these titanium containing steels and it was equally poor when niobium was either present or absent. For steels with ～0·005 wt-%N ductility was very poor at the stoichiometric Ti/N ratio of 3·4 : 1. Ductility was better at the higher Ti/N ratios but only two of the titanium containing niobium steels gave better ductility than the titanium free niobium containing steels and then only at temperatures below about 950–900°C. One of these steels had the lowest titanium addition (0·014 wt-%), thus limiting the volume fraction of fine Ti containing particles and the other had the highest Ti/N ratio of 8 : 1. However, even for these two steels ductility was worse than for the titanium free steels in the higher temperature range. The commercial implications of these results are discussed.     

Numerical and experimental study on the flow history effects of axial flow on the Couette–Taylor flow

In this research, experimental and numerical techniques are used to study the flow history effects of axial flow on the Couette–Taylor flow. For the experimental investigation, the flow is visualized using the PIV technique with reflective particles with a density of 1.62 g/cm³. Dispersed in a solution, the particles have a strong refraction index equal to 1.85. In this study, two protocols are adopted to study the effect of an axial flow superimposed on a Couette–Taylor flow, and of the history of the flow. The first one, the direct protocol, consists of imposing an azimuthal flow to the inner cylinder. In this case, when the regime is established, the axial flow is superimposed. The second protocol, the inverse protocol, consists of imposing first the axial flow in the gap of the system, after which an azimuthal flow is conveyed. The Couette–Taylor flow with axial flow is strongly dependent on the flow history (the protocol). Thus, the flow structures and development for different protocols are studied and analyzed here experimentally and numerically. In addition, from the numerical results, mathematical models for the two protocols are presented. For the direct protocol, a new relation between the axial Reynolds number, which stabilizes the Couette–Taylor flow, and the Taylor number is presented; for the inverse protocol, a new mathematical model for the critical Taylor number is developed as a function of the axial Reynolds number and also the first critical Taylor number without axial flow.     

Explosive welding of stainless steel–carbon steel coaxial pipes

Bi-metallic corrosion resistant steel pipes were produced through explosive welding process. The weldability window of the stainless steel pipe (inner pipe) and the carbon steel pipe (outer pipe) was determined by the use of available semi-empirical relations. The impact velocity of the pipes as the most important collision parameter was calculated by the finite element simulation. Direct effect of the explosive mass reduction on the bonding interface of the pipes was studied. Optical microscopy study showed that a transition from a wavy interface to a smooth one occurs with decrease in explosive load.     

Bioactivity potential of calcium alumino-silicate glasses and glass–ceramics containing nitrogen and fluorine

Calcium alumino-silicate glasses of general composition (in eq.%) 28Ca:57Si:15Al:[100 ? (x + y)]O:xN:yF (x = 0 or 20 and y = 0, 3 or 5) and their glass–ceramic counterparts were immersed in simulated body fluid (SBF) at 37 ± 0.5 °C for 28 days to assess their potential bioactivity. The glasses showed no Ca release or surface calcium phosphate deposition due to their high network connectivities (>2.55). The glass–ceramics all showed potential bioactivity, as the SBF became enriched in Ca and calcium phosphate deposits formed on their surfaces. This was a result of Ca release from crystalline phases (predominantly wollastonite in the case of CaSiAlOF glass–ceramics and gehlenite in the case of CaSiAlONF glass–ceramics). No aluminium was leached from the glass–ceramics into the SBF, due to its pH always exceeding 7.0.     

Comparative study of solubilities of hydrogen,nitrogen and carbon in α-iron

Solubility data of hydrogen, nitrogen and carbon in -iron are analysed on the basis of statistical thermodynamics. Present analysis appears to yield realistic values for the enthalpy term of the solutions of these interstitial elements into -Fe, while the entropy terms remain ambiguous. During the course of this analysis a parameter _x, which refers to the solubility limit of the specific interstitial element X (X=hydrogen, nitrogen or carbon), is also estimated; _H< _N< _C. This order of _X values appears to be in accord with the observation that, under normal conditions, the solubility of carbon is the highest and that of hydrogen the lowest in -Fe, while the atomic size increases with the order hydrogen相似文献   

Detailed experimental investigations on frictional pressure drop of R134a during flow boiling in 5 mm diameter channel: The influence of acceleration pressure drop component

This article presents detailed two-phase diabatic pressure drop data for refrigerant R134a at a saturation pressure of 5.5 bar corresponding to the saturation temperature of 19.4 °C. Study cases have been set for a mass flux varying from 100 to 500 kg m⁻² s⁻¹.The obtained data are used as a validation of the void fraction literature models, a set of graphs shows comparisons, for a representative set of experimental conditions, of the two-phase frictional pressure gradients for the adiabatic and diabatic flow.Verification of the acceleration pressure drop predictions for two-phase adiabatic flow showed that all correlations predict that over 60% of experimental data fit in the range of ±30%. The model proposed in this article predicts 63% of presented data within 10% error, and 96% of the data are predicted within 30% error.     

Investigation of serrated flow behaviour in Al–10Mg alloy

Abstract

In view of reported anomalies in the serrated flow behaviour of aged Al–8.6Mg alloy, characteristics of serrated flow were investigated in an Al–10Mg alloy after solution treatment as well as after aging. The material was prepared by melting and casting, and then it was extruded, solution treated, and aged at either 150 or 200°C. Strain rate sensitivity, types of serration, onset strain of serrated flow, magnitude of serrations, and frequency of serrations were studied as a function of aging and strain rate. It was found that the alloy exhibited all the usual features of serrated flow except one, i.e. the magnitude of serration increased in the overaged condition after decreasing up to peak aging.     

Modeling and Investigation of Nonstationary Pressure and Temperature Fields in a Deformable Formation During the Filtration of a Gas–Condensate Mixture

Journal of Engineering Physics and Thermophysics - A procedure and an algorithm have been proposed that allow modeling the problem of identification of parameters of a deformable formation during...     

Numerical study of solid–liquid two-phase flow and erosion in ball valves with different openings

In the coal chemical industry, petrochemical industry, and other industries, ball valve is a common and important valve due to its reliable structure. The conveying medium has particles that affect the valve surface under the drive of water flow, thereby making the ball valve face the risk of erosion and damage. In this study, the CFD-DEM method was adopted to study the influence of different openings and particle diameters on the two-phase flow and erosion characteristics inside the ball valve. The two-phase flow and particle distribution of the ball valve were analyzed, and the main erosion wall surfaces were determined. The erosion distribution of these walls was obtained. The variation rule of particle number with erosion rate was analyzed, which shows that particle number played a dominant role in erosion degree. Result also showed that in the case of small opening, the erosion decreased with the increase in particle diameter.     

Formation of core–shell network structural titanium–nitrogen alloys with different nitrogen contents

High-dense titanium alloys with a 3D network core–shell structure of different N contents were synthesized successfully by means of spark plasma sintering of the nitrided titanium particles. The microstructure investigation shows that the core–shell structure with an obvious boundary within a grain is constructed in light of different solid solution levels of nitrogen in grain boundary and grain inner. The mechanical behaviors have been experimentally assessed through compressive testing. The compacts exhibit a much enhanced strength while retaining a reasonable ductility, which can be attributed to their novel core–shell structure. With an increasing N content as well as shell thickness, the strength increases and the ductility decreases, in accordance with the morphology observations.     

Pearlite in hypoeutectoid iron–nitrogen binary alloys

In this study, hypoeutectoid Fe–N binary specimens have been prepared by gas nitriding pure iron in austenite domain at 840 °C. The slow cooling of these specimens led to the α-ferrite + γ′-Fe₄N pearlitic microstructure which is similar to the pearlite in Fe–C binary system. This pearlitic microstructure has been characterized by electron microscopy. The crystal structure of the γ′-Fe₄N nitride has been identified by electron microdiffraction and the Nishiyama–Wassermann (N–W) and near Kurdjumov–Sachs (K–S) orientation relationships have been found between the α-ferrite and the γ′-Fe₄N.     

The effect of pressure on spontaneous Rayleigh–Brillouin scattering spectrum in nitrogen

In order to study the effect of gas pressure on spontaneous Rayleigh–Brillouin scattering spectrum and verify the validity of Tenti S6 model at pressures up to 8 atm, the spontaneous Rayleigh–Brillouin scattering experiment in nitrogen was performed for a wavelength of 532 nm at the constant room temperature of 296 K and a 90° scattering angle. By comparing the experimental spectrum with the theoretical spectrum, the normalized root mean square deviation was calculated and found less than 2.2%. It is verified that Tenti S6 model can be applied to the spontaneous Rayleigh–Brillion scattering of nitrogen under higher pressures. The results of the experimental data analysis demonstrate that pressure has more effect on Brillouin peak intensity and has negligible effect on Brillouin frequency shift, and pressure retrieval based on spontaneous Rayleigh–Brillouin scattering profile is a promising method for remote of pressure, such as harsh environment applications. Some factors that caused experiment deviations are also discussed.     

Interdisciplinary relations of converging technologies: Nano–Bio–Info–Cogno (NBIC)

This paper investigates the interdisciplinary relations of nanotechnology (Nano), biotechnology (Bio), information technology (Info), and cognitive science (Cogno) (together known as NBIC converging technologies) using different bibliometric techniques. For each set of two (pairs) and three (trios) of subjects, overlaps in journal citation, authorship, publication journals, and keywords were calculated for all Iranian NBIC articles published from 2001 to 2015 in international journals. Maximum and minimum spanning trees were used to visualise the interdisciplinary relations. To determine the nature of convergence between the subjects, an expert panel categorised the shared keywords of each pair and trio of subjects using four categories of tools, material, applications and techniques. The results showed that overall the pairs of Nano–Bio and Nano–Info had the highest level of mutual interdisciplinary relations. Info–Bio and Cogno–Bio had the weakest mutual interdisciplinary relations. Among the trios, Nano–Info–Bio had the strongest relations and Cogno–Nano–Info had the weakest. The dominant type of convergence for Nano–Bio and Cogno–Bio was sharing materials. For Nano–Info the dominant type of convergence was sharing tools and techniques. For Info–Cogno, and Info–Bio sharing techniques was the dominant type of convergence, and for Nano–Cogno sharing materials and applications was most dominant. Nano–Info–Bio mostly shared materials and applications. Identifying weak and strong ties between the four NBIC fields can help plan for their further convergence at science and technology levels.     

Changes of flow stress and microstructure during hot deformation of Al–1Mg–1Mn

Abstract

Plane strain compression tests have been carried out at strain rates between 0·5 and 10 s^?1 and temperatures in the range 275–510°C, both under nominally isothermal conditions and with temperature decreasing. Also, temperature or strain rate have been changed in the interval between two deformations. In all cases, the stress–strain curves obeyed a mechanical equation of state, described by constitutive relationships in terms of strain and instantaneous value of Zener–Hollomon parameter Z. When the value of Z varies slowly during deformation, flow stress is uniquely related to subgrain size and to dislocation density within subgrains, but these relationships break down in transition structures developed after a change of Z between two deformations. The existence of an equation of state for mechanical behaviour, but not for microstructure, is considered to result from important contributions of both dislocation velocity and density to hot strength.

MST/1066     

Cyclodextrin–poloxamer aggregates as nanocarriers in eye drop formulations: dexamethasone and amphotericin B

In this present study cyclodextrin (CD)–poloxamer aggregates were characterized and developed as ophthalmic drug carriers. The combined effect of γCD/2-hydroxypropyl-γCD (HPγCD) mixtures and poloxamer on solubilization and permeability of two model drugs, dexamethasone (Dex) and amphotericin B (AmB), was investigated. The CD–poloxamer interaction and complex aggregation were examined by ¹H nuclear magnetic resonance (¹H-NMR), their solubilizing ability by high-performance liquid chromatography, and their particle size determined by dynamic light scattering and transmission electron microscopy. Formulations containing either 1.5% w/v Dex or 0.15% w/v AmB in eye drop suspensions containing various γCD/HPγCD ratios and poloxamer 407 (P407) were prepared. The solubility of the drugs, surface tension and hemolytic effect of the eye drops and drug permeation from selected formulations were determined. The ¹H-NMR study showed that P407 formed inclusion complex with CDs by inserting its poly(propylene oxide) segment into the CD cavity. P407 and γCD interacted with each other to form nanosized aggregates, and the observed concentration of dissolved γCD and P407 progressively decreased with increasing γCD and P407 concentrations. Including a high proportion of HPγCD improved the drug solubilization and reduced the hemolytic effect. The surface tension of the formulations decreased with increasing P407 concentration. Furthermore, increasing P407 content in the formulations enhanced formation of complex aggregates with consequent slower drug release. It was concluded that the drug/γCD/HPγCD complex was stabilized by P407 through formation of multi-component aggregates. Thus, CD–poloxamer aggregates are self-assembled nanocarriers from which drug delivery characteristics can be adjusted by changing the γCD/HPγCD/P407 ratios.     

Seawater effect on impact behavior of glass–epoxy composite pipes

The effect of seawater immersion on impact behavior of glass–epoxy composite pipes is experimentally investigated. Glass–epoxy pipes with [±55°]₃ orientation were fabricated using filament winding method. Composite pipes were selected for four different diameters as 50 mm, 75 mm, 100 mm, and 150 mm. The pipes were immersed in artificial seawater having a salinity of about 3.5% for 3, 6, 9, and 12 months in laboratory conditions. At the end of the conditioning period, the specimens were impacted at three distinct energy levels as 15 J, 20 J, and 25 J at ambient temperature of 20 °C. The comparisons between the dry and immersed cases were carried out by using contact force, deflection and absorbed energy data of the impact tests. Results show that moisture absorption, salt in seawater, diameter of specimen and residual stresses produced by manufacturing process of the composite pipe have significant effect on maximum contact force, maximum deflection, absorbed energy and failure of composite pipes according to exposure time to seawater.