Natural gas liquifier based on an EGD-generator-expander

Versions are considered for preparing liquefied natural gas (LNG) in liquefiers with different cold producing units; with a throttle valve, a vortex tube, a turbo-expander. A short analysis is given for their efficiency, and disadvantages and advantages are noted. It is proposed to use as a cold producing unit in liquid gas liquefiers an electrogasdynamic (EGD) generator-expander (G-E) using (utilization) the energy of pipeline natural gas. Schemes are provided for a new stage and the construction of a multistage EGD G-E. Versions are shown for inclusion in a natural gas liquefier whose operational analysis shows that they are not surpassed in efficiency by liquefiers with a turbo-expander. __________ Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 6, pp. 17–20, June, 2007.     

Riga hydroelectric power plant—25 Years: Provision for safe operation of water-development works and hydromechanical equipment

Conclusions The 25-year service of the Riga hydroelectric power plant has demonstrated reliable operation of the installed power-generating and hydromechanical equipment. The condition of the water-development works has also given no cause for special concern from the standpoint of ensuring their safe operation. A large amount of the monitoring-measuring equipment installed by service personnel are completely preserved and provide for reliable monitoring of structure behavior. Data derived from field observations have completely confirmed the correctness of solutions adopted in the design of both the earth and concrete structures. The computerized information-diagnostics system installed at the plant has made it possible to develop a data base of observational results, and process and analyze them on a qualitatively higher level. Service personnel have the capacity to assess independently the safe condition of a structure for the adoption of timely measures to prevent emergency situations. Translated from Gidrotekhnicheskoe Stroitel’stvo, No. 12, pp. 11–16, December, 1999.     

Effect of in-situ formed MgO on the microstructure of thixomolded AZ91 magnesium alloy

ABSTRACT

In-situ magnesium matrix nano-composites were produced through a reaction of CO₂ with the AZ91 alloy at a semi-solid temperature range. The process was performed at 595°C, which corresponded to about 10% of solid fraction, under shear and mixing conditions generated by a screw-barrel system. As a result, nano-scale native MgO (30–50?nm) and a small amount of Al₄C₃ carbide within an eutectic consisting of α(Mg), β-Mg₁₇Al₁₂ were formed. Homogeneously distributed α(Mg) globular grains with volume 8–12% were visible. AZ91 composites revealed yield strength of 220?MPa at compression strength of 460?MPa and hardness 103?±?2?HV.     

Evolution of Globular Microstructure and Rheological Properties of Stellite™ 21 Alloy after Heating to Semisolid State

Metal alloys can be successfully thixoformed in the partially liquid state if they display non-dendritic near-globular microstructures. The article presents the development of feedstock with such non-dendritic microstructure produced through the solid-state route of strain-induced melt-activated (SIMA) method, for a Stellite? 21 alloy. Stellite? alloys are a range of cobalt-chromium alloys designed for wear and corrosion resistance, currently shaped by casting, powder metallurgy or forging processes, but semisolid-state processing offers the possibility of a near-net-shaping method for these alloys. In this work, sprayformed followed by extrusion samples were heated to the temperature range at which the liquid and solid phases coexist in the material and spheroidal shape solid particles in a liquid matrix were obtained as required for semisolid processing. Microstructural investigations were carried out using scanning electron microscopy (SEM) in combination with energy-dispersive spectroscopy (EDS), with a further objective of analyzing the rheological properties of Stellite? 21 alloy in the semisolid state, providing results to be used for identification of a processing window of temperature and viscosity ranges for thixoforming this alloy.     

Dual-band infrared detectors

IntroductionMulticolor capabilities are highly desirable foradvance infrared(IR) systems.Systems that gatherdata in separate IR spectral bands can discriminateboth absolute temperature and unique signatures ofobjects in the scene.By providing this new dimensionof contrast,multiband detection also enables ad-vanced color processing algorithms to further im-prove sensitivity above that of single- color devices.This is extremely important for the process of identi-fying temperature difference b…     

Structure and properties of composites prepared from partially amorphous ZrCuNiTi and nanocrystalline silver

Alloys of composition Zr40Cu40Ni10Ti10 and Zr48,5Cu32.5Ni9Ti10 (in at.%) were ball milled for 40 h starting from elemental powders or melt spun from cast ingots. In both cases amorphous structure was obtained, however in the case of ribbons, larger crystals of Cu₁₀Zr₇ or Ni₇Zr₂ phases of size of a few hundred nm were observed. In the case of milled alloys much finer intermetallic phases such as Zr₂Cu or Cu₁₀Zr₇ were identified within the amorphous matrix using X-ray diffraction or HRTEM. In both alloys DSC studies have shown higher crystallization temperature for the powder, than for the ribbon. It was explained by a different structure of preexisting intermetallic nuclei crystallizing in milled powders. The milled amorphous powder was also used as a matrix for composites containing 20% or 50% of nanocrystalline silver powder, prepared from silver powder by ball milling. The composites hot pressed at the same temperature as the amorphous samples show in some places very narrow transition phase enriched in silver containing also other elements of the amorphous phase. Composites containing more silver show lower hardness and strength, but exhibit a few percent of plastic deformation in the compression test. Scanning electron studies of deformed composite samples show crack initiation within the amorphous phase, not at the components interfaces.     

Homopolycondensation of thiophenol

A homopolycondensation of thiophenol in a medium of concentrated sulphuric acid has been investigated. As a result, two types of poly(phenylene sulphide), melting at 130°–135°C and 310°–330°C have been obtained. Linear and branched structures and a mechanism for the reaction are proposed. The thermal properties of the polymers were studied by thermal gravimetric analysis (t.g.a.).     

Heat Treatment of Thixo-Formed Hypereutectic X210CrW12 Tool Steel

Steel is a particularly challenging material to semisolid process because of the high temperatures involved and the potential for surface oxidation. Hot-rolled X210CrW12 tool steel was applied as a feedstock for thixoforming. The samples were heated up to 1525?K (1250?°C) to obtain 30?pct of the liquid phase. They were pressed in the semisolid state into a die preheated up to 473?K (200?°C) using a device based on a high-pressure die casting machine. As a result, a series of main bucket tooth thixo-casts for a mining combine was obtained. The microstructure of the thixo-cast consisted of austenite globular grains (average grain size 46 ??m) surrounded by a eutectic mixture (ferrite, austenite, and M₇C₃ carbides). The average hardness of primary austenite grains was 470?HV_0.02 and that of eutectic 551?HV_0.02. The X-ray analysis confirmed the presence of 11.8?pct ??-Fe, 82.4?pct ??-Fe, and 5.8?pct M₇C₃ carbides in the thixo-cast samples. Thermal and dilatometric effects were registered in the solid state, and the analysis of curves enabled the determination of characteristic temperatures of heat treatment: 503?K, 598?K, 693?K, 798?K, 828?K, 903?K, and 953?K (230?°C, 325?°C, 420?°C, 525?°C, 555?°C, 630?°C, 680?°C). The thixo-casts were annealed at these temperatures for 2?hours. During annealing in the temperature range 503?K to 693?K (230?°C to 420?°C), the hardness of primary globular grains continuously decreased down to 385HV_0.02. The X-ray diffraction showed a slight shift of peaks responsible for the tension release. Moreover, after the treatment at 693?K (420?°C), an additional peak from precipitated carbides was observed in the X-ray diffraction. Thin plates of perlite (average hardness 820?HV_0.02) with carbide precipitates appeared at the boundaries of globular grains at 798?K (525?°C). They occupied 17?pct of the grain area. Plates of martensite were found in the center of grains, while the retained austenite was observed among them (average hardness of center grains was 512?HV_0.02). A nearly complete decomposition of metastable austenite was achieved after tempering at 828?K (555?°C) due to prevailing lamellar pearlite structure starting at grain boundaries and the martensite located in the center of the grains. The X-ray analysis confirmed the presence of 3.4?pct ??-Fe, 84.6?pct ??-Fe, and 12?pct M₇C₃ carbides. The dilatometric analysis showed that the transformation of metastable austenite into martensite took place during cooling from 828?K (555?°C). The additional annealing at 523?K (250?°C) for 2?hours after heat treatment at 828?K (555?°C) caused the precipitation of carbides from the martensite. After tempering at 903?K (630?°C), the thixo-cast microstructure showed globular grains consisting mainly of thick lamellar perlite of the average hardness 555?HV_0.02.