Flow boiling characteristics of refrigerant mixture R-22/R-114 in the annulus of enhanced surface tubing

This paper presents an experimental study of flow boiling heat transfer characteristics of refrigerant mixture R-22/R-114 in the annuli of a horizontal enhanced surface tubing evaporator. The geometric parameters of the test section are: inner tube bore diameter of 17.5 mm, envelope diameter of 28.6 mm and outer smooth tube of 32.3 mm I.D. The ranges of heat flux and mass velocity covered in the tests were 5–25 kW m⁻² and 180–290 kg m²⁻s⁻¹ respectively, at a pressure of 570 kPa. The enhanced surface tubing data showed a significant enhancement of the heat transfer compared to an equivalent smooth tube depending on the mixture's components and their concentrations. Correlations were proposed to predict the heat transfer characteristics such as average heat transfer coefficients as well as pressure drops of R-22/R-114 non-azeotropic refrigerant mixture flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture's pressure drop is a weak function of the mixture's composition.     

Depletion-driven four-phase coexistences in discotic systems

ABSTRACT

Free volume theory (FVT) is a versatile and tractable framework to predict the phase behaviour of mixtures of platelets and non-adsorbing polymer chains in a common solvent. Within FVT, three principal reference phases for the hard platelets are considered: isotropic (I), nematic (N) and columnar (C). We derive analytical expressions that enable us to systematically trace the different types of phase coexistences revealed upon adding depletants and confirm the predictive power of FVT by testing the calculated diagrams against phase stability scenarios from computer simulation. A wide range of multi-phase equilibria is revealed, involving two-phase isostructural transitions of all phase symmetries (INC) considered as well as the possible three-phase coexistences. Moreover, we identify the system parameters, relative disk shapes and colloid–polymer size ratios, at which four-phase equilibria are expected. These involve a remarkable coexistence of all three-phase states commonly encountered in discotics including isostructural coexistences I₁–I₂–N–C, I–N₁–N₂–C and I–N–C₁–C₂.     

Effective production of Xe<Subscript>2</Subscript>I excimer molecules by high-energy charged particles in Xe containing a small amount of C<Subscript>3</Subscript>F<Subscript>7</Subscript>I

An anomalously high efficiency of generating Xe₂I* excimer molecules in dense Xe–C₃F₇I gaseous mixtures with a small amount of C₃F₇I that are excited by a pulsed beam of fast electrons is discovered. The electron energy is 150 keV, and the beam current amplitude and duration are, respectively, 5 A and 5 ns. The temporal–spectral characteristics of spontaneous radiation from XeI* and Xe2I* excimer molecules are measured. Also, the luminescence times of the upper level for the B–X transition in the XeI* molecule (λ_max = 253 nm) and the upper level for the 4²Γ–1²Γ transition in the Xe₂I* molecule (λ = 352 nm), as well as the rate constants of quenching these levels by the gaseous mixture components, are determined. Based on the characteristics of the track structure of a high-energy plasma produced by charged particles in the dense gaseous medium, a model of plasma-chemical processes leading to the formation of XeI* (λ_max = 253 nm) and Xe₂I* (λ = 352 nmnm) excimer molecules in a Xe–C₃F₇I mixture with a small amount of an iodine atom donor is suggested.     

Role of argon in its mixture with nitrogen in deposition of nitride condensates in the Ti-Si-N system and in vacuum arc deposition processes

Arc vacuum deposition of nitride coatings in the Ti-Si-N system is carried out in an argonnitrogen mixture with variable gas concentration ratios. The resulting condensates are studied by fractographic analysis, X-ray diffraction analysis, and high-resolution scanning electron microscopy. Studied also are the elemental composition and microhardness of the condensates. At gas mixture pressure p > 5 × 10^?3 Torr, conditions are found under which the hardness of the condensates is maximal, and the dependence of the hardness on the argon percentage in the mixture is obtained. At an argon percentage of 8–12%, the hardness of the coatings reaches 50 GPa. This value is 1.7 times higher than the hardness of coatings obtained in a nitrogen atmosphere. This superhard state is explained by the nanometer size (25–30 nm) of nitride grains and a specific growing texture with a family of {100} planes that is parallel to the growth plane. Such a configuration minimizes the surface energy. Mechanisms that may increase the ionization of film-forming particles and activate chemical bonds in the presence of argon are discussed.     

5‐Fluorouracil solutions: NMR study of acid–base equilibrium in water and DMSO

A comprehensive analysis of solutions of 5‐fluorouracil (5FU) in water and an organic medium (dimethylsulfoxide, DMSO) was carried out using quantum chemical methods and nuclear magnetic resonance (NMR) spectroscopy. The details of anionic form generation in the solution of 5FU with an equimolar amount of potassium hydroxide were studied by ¹³С, ¹Н, ¹⁵N and ¹⁹F NMR. Interpretation of NMR spectral data was carried out using quantum chemical calculations at the TPSSTPSS/6‐311+G(d,p) level of theory. Specific solvation of 5FU and 1THF‐5FU was modeled in approximation using the five‐water cluster model and solvate complex including two DMSO molecules. It was established that in an alkaline medium in DMSO 5FU occurred mainly as a type of an anion with a deprotonation on N(1) position of a pyrimidine ring whereas in water alkaline solution—as a mixture of two anions with a deprotonation on N(1) and N(3) positions with a predominant content of the latter form. For the quantitative definition of the deprotonation forms of 5FU the technique based on the data of theoretical and experimental NMR ¹³C spectroscopy, tested on a model compound 1‐(tetrahydrofuranyl‐2)‐5‐fluoro‐pyrimidinedione‐2,4 (tegafur, THF‐5FU), was offered. The N(3) anion was found from spectral data to be more thermodynamically stable than the N(1) anion by 2.40 kJ mol^?1 (calculated value 2.24 kJ mol^?1) in an alkaline–water solution. Both alkaline–water and alkaline–DMSO solutions of THF‐5FU (THF‐5FU/KOH = 1/1) were characterized by the ratio of the equilibrium concentrations of the anion and diketo‐tautomer as 9:1 and 4.3:1, respectively. Copyright © 2014 John Wiley & Sons, Ltd.     

Flame propagation of nano/micron-sized aluminum particles and ice (ALICE) mixtures

Flame propagation of aluminum–ice (ALICE) mixtures is studied theoretically and experimentally. Both a mono distribution of nano aluminum particles and a bimodal distribution of nano- and micron-sized aluminum particles are considered over a pressure range of 1–10 MPa. A multi-zone theoretical framework is established to predict the burning rate and temperature distribution by solving the energy equation in each zone and matching the temperature and heat flux at the interfacial boundaries. The burning rates are measured experimentally by burning aluminum–ice strands in a constant-volume vessel. For stoichiometric ALICE mixtures with 80 nm particles, the burning rate shows a pressure dependence of r_b = aPⁿ, with an exponent of 0.33. If a portion of 80 nm particles is replaced with 5 and 20 μm particles, the burning rate is not significantly affected for a loading density up to 15–25% and decreases significantly beyond this value. The flame thickness of a bimodal-particle mixture is greater than its counterpart of a mono-dispersed particle mixture. The theoretical and experimental results support the hypothesis that the combustion of aluminum–ice mixtures is controlled by diffusion processes across the oxide layers of particles.     

Crystal structure of cholesteryl 4-[4-(4-n-hexylphenylethynyl)-phenoxy]butanoate – a liquid-crystalline unsymmetric dimer

Cholesteryl 4-[4-(4-n-hexylphenylethynyl)-phenoxy]butanoate, which exhibits the phase sequence: Cr 119.3°C (42.4?J?g^?1) SmA 196.4°C (1.1?J?g^?1) TGB–N* 202.4°C (5.4?J?g^?1) I, crystallizes in the triclinic space group P1 with unit cell parameters: a?=?10.527(1), b?=?13.151(2), c?=?16.991(2)?Å, α?=?86.13(1)°, β?=?98.96(1), γ?=?105.43(1)°, Z?=?2. The crystal structure has been solved by direct methods using single-crystal X-ray diffraction data and refined to R?=?0.0618. There are two crystallographically independent molecules, I and II, in the asymmetric unit. In both the molecules the phenyl rings are planar. The dihedral angle between the two phenyl rings is 12.16° and 18.14° for molecules I and II, respectively. In both the molecules, the six-membered rings of the cholesterol moiety are conformationally very similar. However, pronounced differences are observed in the conformation of the five-membered ring, which is intermediate between half-chair and envelope in molecule I, and half-chair in molecule II. The packing of molecules in the crystalline state is found to be a precursor to the Smectic A phase structure. The molecules in the crystal are held together by van der Waal's interactions.     

Efficient alpha particle detection by CR-39 applying 50 Hz-HV electrochemical etching method

Alpha particles can be detected by CR-39 by applying either chemical etching (CE), electrochemical etching (ECE), or combined pre-etching and ECE usually through a multi-step HF-HV ECE process at temperatures much higher than room temperature. By applying pre-etching, characteristics responses of fast-neutron-induced recoil tracks in CR-39 by HF-HV ECE versus KOH normality (N) have shown two high-sensitivity peaks around 5–6 and 15–16 N and a large-diameter peak with a minimum sensitivity around 10–11 N at 25°C. On the other hand, 50 Hz-HV ECE method recently advanced in our laboratory detects alpha particles with high efficiency and broad registration energy range with small ECE tracks in polycarbonate (PC) detectors. By taking advantage of the CR-39 sensitivity to alpha particles, efficacy of 50 Hz-HV ECE method and CR-39 exotic responses under different KOH normalities, detection characteristics of 0.8 MeV alpha particle tracks were studied in 500 μm CR-39 for different fluences, ECE duration and KOH normality. Alpha registration efficiency increased as ECE duration increased to 90 ± 2% after 6–8 h beyond which plateaus are reached. Alpha track density versus fluence is linear up to 10⁶ tracks cm⁻². The efficiency and mean track diameter versus alpha fluence up to 10⁶ alphas cm⁻² decrease as the fluence increases. Background track density and minimum detection limit are linear functions of ECE duration and increase as normality increases. The CR-39 processed for the first time in this study by 50 Hz-HV ECE method proved to provide a simple, efficient and practical alpha detection method at room temperature.     

Stark broadening measurements of some N(II) and N(III) lines

The Stark widths of seventeen N(II) and ten N(III) spectral lines, emitted from a wall-stabilized arc plasma with electron densities in the range 0.9-2.9 × 10¹⁷ cm^-3, were measured. The arc was run with a 1:1N₂:He mixture, and the electron densities were determined from the Stark widths of He(I) 5876 and 6678 A. The Stark widths of the N lines were found to scale approximately linearly with electron density.     

The extrapolation of phase equilibrium curves of mixtures in the isobaric—isothermal Gibbs ensemble

A powerful extrapolation scheme is proposed to determine the vapour—liquid and liquid—liquid equilibrium curves of mixtures by performing a single isothermal-isobaric Gibbs ensemble Monte Carlo (GEMC) simulation. The coexistence curves for the mole fraction and the density are extrapolated as functions of the temperature and the pressure by second-order Taylor series. The coefficients of the Taylor series, which are the temperature and pressure derivatives of these quantities along the coexistence curves, can be calculated from the data produced by a single GEMC simulation on the basis of fluctuation formulas. We show that the application of a Padé approximant considerably widens the temperature and pressure range where the extrapolation is accurate. Using Lennard-Jones mixtures as test systems, we show that the technique is able to produce quite accurate equilibrium curves at fixed temperature in the function of the pressure and vice versa. The procedure yields good results not only for vapour—liquid but also for liquid—liquid coexistence curves. The calculation of the vapour pressure curves at a fixed composition of the liquid side is straightforward with the method.     

Vapour-liquid equilibrium of the charged Yukawa fluid from Gibbs ensemble Monte Carlo simulations and the mean spherical approximation

A Gibbs ensemble Monte Carlo (GEMC) study supplemented by theoretical calculations using the mean spherical approximation (MSA) is reported for the charged Yukawa system. In this system the particles interact via an attractive Yukawa potential and a Coulomb potential. When the Coulomb potential is weak compared to the Yukawa attraction the results obtained for the vapour-liquid equilibrium from the GEMC and the MSA are very similar. On increasing the charge, the system becomes similar to the primitive model of electrolytes, and at high charges similar phenomena, such as ion association, are observed. At these charges, the MSA yields poorer results. Using both methods, an increase of the charge results in an increase of the critical temperature but a decrease of the critical density.     

SiMn–Graphite composites as anodes for lithium ion batteries

Two Si–Mn–C composites were obtained by sequentially ball milling the mixture of the silicon and manganese powders (atomic ratio of 3:5), followed by addition of 20 wt.% and 10 wt.% graphite, respectively. The phase structure and morphology of the composite were analyzed by X-ray diffraction (XRD) and scanning electromicroscopy (SEM). The results of XRD show that there is no new alloy phase in the composite obtained by mechanical ball milling. SEM micrographs confirm that the particle size of the Si–Mn–C composite is about 0.5–2.0 μm and the addition of graphite restrains the morphological change of active center (Si) during cycling. The Si–Mn particles are dispersed among the carbon matrix homogeneously, which ensures a good electrical contact between the active particles. Electrochemical tests show that the Si–Mn–C composite achieves better reversible capacity and cycleability. The Si–Mn–20 wt.% C composite electrode annealed at 200 °C for 2 h reveals an initial reversible capacity of 463 mAh·g^− 1 and retains 387 mAh·g^− 1 after 40 cycles.     

A15N-1H dipolar CSA solid-state NMR study of polymorphous polyglycine (-CO-CD2-15NH-)n

The solid-state¹H MAS (magic-angle spinning),²H static,¹⁵N CP (cross polarization)-MAS and¹⁵N-¹H dipolar CSA (chemical shielding anisotropy) NMR (nuclear magnetic resonance) spectra of two different modifications of C_α-deuterated^l5N-polyglycine, namely PG I and PG II (-CO-CD₂-^l5NH-)_n are measured. The data from these spectra are compared to previous NMR, infrared, Raman and inelastic neutron scattering work. The deuteration of C_α eliminates the largest intramolecular¹H-¹H dipolar coupling. The effect of the remaining (N)H-(N)H interaction (～5 kHz) is not negligible compared to the¹⁵N-¹H coupling (about 10 kHz). Its effect on the dipolar CSA spectra, described as a two-spin system, is analyzed analytically and numerically and it is shown that those parts of the powder spectrum, which correspond to orientations with a strong dipolar¹⁵N-¹H interaction, can be described as an effective two-spin system, permitting the measurement of the strength of the¹⁵N-¹H dipolar interaction and the orientation of the dipolar vector with respect to the¹⁵N CSA frame. While in the PG II system the¹⁵N CSA tensor is collinear with the amide plane, in the PG I system the CSA tensor is tilted ca. 16° with respect to the (δ₁₁δ₂₂) CSA plane.     

Structural Characterization of RF‐Sputtered a‐C:N Thin Films by Raman,IR, and X‐ray Reflectometry Spectroscopies

Abstract

Amorphous carbon nitride thin films (a‐C:N) were deposited from a carbon target, at room temperature onto silicon substrates, by reactive RF sputtering in a gas mixture of argon and nitrogen. The structural properties of these films have been studied by Raman, infrared (IR), and X‐ray reflectometry spectroscopies. Both the IR and Raman spectra of the a‐C:N films reveal the presence of C–C, C?C, C?N, and C≡N bonding types. The Raman spectra analysis shows, an increase of the C≡N triple bonds content when the concentration of nitrogen C(N₂) in the gas mixture is increased. The Raman intensities ratio between the disorder (D) and graphitic (G) bands increases with C(N₂) suggesting an increased disorder with the incorporation of nitrogen in the carbon matrix. The effect of C(N₂) on the density of a‐C:N films was also investigated by X‐ray reflectometry measurement. The increase of the nitrogen concentration C(N₂) was found to have a significant effect on the density of the films: as C(N₂) increases from 0 to 100%, the density of the a‐C:N films decreases slightly from 1.81 to 1.62 g/cm³. The low values of density of the a‐C:N films were related (i) to the absence of C–N single bonds, (ii) to the increase of disorder introduced by the incorporation of nitrogen in the carbon matrix, and (iii) to the presence of the bands around 2350 cm^?1 and 3400 cm^?1 associated with the C–O bond stretching modes and the O–H vibration, respectively, suggesting a high atmospheric contamination by oxygen and water. The presence of these bands suggests the porous character of the studied samples.     

Supercritical Fluid Propane-Butane Extraction Treatment of Oil Sludge

The extraction process with propane: butane = 3: 1 (by mass) mixture in the liquid and supercritical fluid states was used to extract petroleum products containing 12.05 mass % of anhydrous oil sludge as solid particulates. The extraction was carried out at 85–160°С and 5–50 MPa. The desired oil product contains 2.8 mass % of sulfur, it has a density of 880 kg/m³ and a kinematic viscosity of 73.75 mm²/s at 20°С as well as start and end boiling point values of 43.6 and 325°С, respectively.     

Zur mikrophysikalischen Beschreibung des schwachionisierten Säulenplasmas von Glimmentladungen in Stickstoff-Neon-Gemischen III. Bilanzierung des Säulenplasmas und Berechnung seiner inneren Parameter

For the plasma of the low current positive column in the N,-Ne-mixture the equations for the concentration of different kinds of ions and excited particles are set up. The axial electric field strength, the degree of ionization and the concentration of excited Ne-atoms and of the different kinds of ions are calculated by simultaneous solution of these balances together with the electron Boltzmann equation for this mixture and the balances for the electric current and quasineutrality of the column plasma. All these macroscopic properties of the discharge column are investigated for electric currents of 0.5 mA to 13,5 mA, for total pressures of 0,37 torr to 3,7 torr and for any mixture ratio. A comparision between measured and calculated electric field strengths shows a good agree-ment. The ionization of the N,-molecules by collisions with the metastable Ne-atoms (Penning-ionization) is of great significance for the generation of new charge carriers in such a mixture. In these investigations the collision rate zp of the Penning-ionization was obtained to 3 · 10^?11 cm³ s^?1 by the aid of a comparision between measured and calculated electric axialgradients of the column.     

Deformation and shape coexistence in medium mass nuclei

Emerging evidence for deformed structures in medium mass nuclei is reviewed. Included in this review are both nuclei that are ground state symmetric rotors and vibrational nuclei where there are deformed structures at excited energies (shape coexistence). For the first time. Nilsson configurations in odd-odd nuclei within the region of deformation are identified. Shape coexistence in nuclei that abut the medium mass region of deformation is also examined. Recent establishment of a four-particle, four-hole intruder band in the doublesubshell closure nucleus⁹⁶Zr₅₆ is presented and its relation to the Nuclear Vibron Model is discussed. Special attention is given to the N=59 nuclei where new data have led to the reanalysis of⁹⁷Sr and⁹⁹Zr and the presence of the [404 9/2] hole intruder state as isomers in these nuclei. The low energy levels of the N=59 nuclei from Z=38 to 50 are compared with recent quadrupole-phonon model calculations that can describe their transition from near-rotational to single closed shell nuclei. The odd-odd N=59 nuclei are discussed in the context of coexisting shape isomers based on the (p[303 5/2]n[404 9/2])2^– configuration. Ongoing in-beam (t.p conversion-electron) multiparameter measurements that have led to the determination of monopole matrix elements for even-even₄₂Mo nuclei are presented, and these are compared with initial estimates using lBA-2 calculations that allow mixing of normal and cross subshell excitations. Lastly, evidence for the neutron-proton³S₁ force's influence on the level structure of these nuclei is discussed within the context of recent quadrupole-phonon model calculations.Work supported by USDOE contract Nr.W-7405-Eng-48 and NATO Grant Nr.RGO565/82.     

微光高速电影摄影

低照度、低对比下的高速摄影不断增长的需要促进了新型摄影系统的发展,其中在镜头与高速运动胶片之间加入象增强器所构成的微光高速摄影可使摄影的灵敏度有显著的提高。它具有高光增益、高成家质量的优点。同时由于高速电子快门取代了机械快门,使此类摄影系统面目一新。由于高的光增益,使此摄影系统的信息记录能力大大增加,高速摄影的信息量I为: I=PFn²[log₂(1+SN)]g^2/3其中g=t_p/t_e((时间间隔)(曝光时间))当采用微光高速电影摄影时,它的信息量Γ为: Γ=PFn′²[log₂(1+S/N)](Gg)^2/3 I′/I=(n′/n)²G^2/3G通常为5×10到10⁴倍本章讨论了微光高速摄影系统中主要器件和主要技术。介绍了国外此摄影系统的发展水平与动向以及我国的应用前景。     

Phase transitions in 3,5-dichloropyridine

Abstract

Structural phase transitions in 3,5-dichloropyridine crystal have been studied by calorimetry (150–300 K), X-ray diffraction (300 K), ³⁵Cland ¹⁴N nuclear quadrupole resonance (75–300 K) and vibrational spectroscopy (20–300K). Three phases have been shown to exist: phase I, between 338 and 287.5 K, phase 11, between 287.5 and 167.5 K, and phase 111, below 167.5 K. Phase I is characterised by the space group P 2,/m and Z = 2 whereas phases I1 and 111 remain centrosymmetric but double the unit cell. All the phases are ordered and contain crystallo- graphically equivalent molecules. The I ? I1 transition is of first order and probably of the reconstructive type while the II ? III transition is believed to be displacive. Both transitions are monitored by predominantly R′_x and R′_z librational motions.     

EPR and ENDOR Studies of Shallow Donors in SiC

Recent progress in the investigation of the electronic structure of the shallow nitrogen (N) and phosphorus (P) donors in 3C–, 4H– and 6H–SiC is reviewed with focus on the applications of magnetic resonance including electron paramagnetic resonance (EPR) and other pulsed methods such as electron spin echo, pulsed electron nuclear double resonance (ENDOR), electron spin-echo envelope modulation and two-dimensional EPR. EPR and ENDOR studies of the ²⁹Si and ¹³C hyperfine interactions of the shallow N donors and their spin localization in the lattice are discussed. The use of high-frequency EPR in combination with other pulsed magnetic resonance techniques for identification of low-temperature P-related centers in P-doped 3C–, 4H– and 6H–SiC and for determination of the valley–orbit splitting of the shallow N and P donors are presented and discussed.