Modeling and Simulation on Thermo-fluid Behaviors in Gas-Liquid Two-phase Flow Systems
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|Publisher:||The Iron and Steel Institute of Japan|
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03 Dec. (Last 30 Days)
Kouji TAKATANI, Yuji IWANAGA
The gasification rates of three kinds of coke having different reactivity were measured by the use of thermobalance. Next, a non-isothermal mathematical model was developed considering the effect of structural changes of coke due to the gasification and reaction heat.
By the use of above mathematical model, rate parameters were determined from the experimental results and the difference of reaction style between CO2 gas and H2O gas was investigated.
Haruo KOKUBU, Toshihiro INATANI, Tsutomu NOZAKI, Hirotoshi FUJIMORI, Masanobu MASUKAWA, Yasuaki OOMORI
The reactions in the shaft type Ferromanganese smelting furnace operated in stream on 24 June 1985 at Mizushima Ferro Alloy Co. were investigated by use of vertical sonde and shaft gas sampler. The results obtained are as follows ; 1) High coke ratio of high carbon ferromanganese operation is attributable to high direct reduction ratio, high amount of heat of MnO reduction, high heat loss and low blast temperature. 2) The Boudouard reaction is nearly in equilibrium in the temperature above 700°C. 3) Mn, K2O and SiO2 are enriched in fume dust and its diameter is 0.30.7 μm. 4) 1030% of fume dust generated at hearth is discharged from the top of the furnace and the rest is trapped by charged materials and circulates in the furnace. 5) Fume dust trap mainly occurs when the dust is melt in the temperature above 1 200°C.
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Nagayasu BESSHO, Shuji TAKEUCHI, Tetsuya FUJII, Kyoji NAKANISHI, Hajime BADA, Jun MORI
The decarburization rate in the 230t bottom blowing converter was studied by using a mass spectrometer in order to predict the final carbon content in the bath and to achieve an efficient recovery of the off-gas. The followings are the major remarks obtained :
(1) The fraction of oxygen which reacts with carbon in the bath (η) depends on the silicon content in the steel. The value of η keeps 100% during the decarburization period, but begins to decrease at the final stage of blowing, and indicates about 15% at the carbon content of 0.045%.
(2) When the iron ore reacts with carbon in the bath, time lag is observed, but the decarburization efficiency of oxygen in iron ore is the same as that of the oxygen gas blown.
(3) Using the waste gas analysis system, the end point carbon was predicted within the accuracy of ± 0.018%.
(4) The volume and compositions of waste gas evolved from the bath can be predicted with the decarburization model, and it is possible to form the inert gas layer more stably and more rapidly and to extend the time of gas recovery.
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Tetsu-to-Hagané Vol.75(1989), No.12
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Tetsu-to-Hagané Vol.75(1989), No.10
Keiji OKUMURA, Mamoru KUWABARA, Kensuke SASSA, Iwao MUCHI
Double diffusive phenomena which causes various types of convection in a fluid phase stems from two coexisting diffusive components with different diffusivities relating to heat or mass. Typical convection regimes due to the double diffusive phenomena are the finger interface and the diffusive interface.
On the basis of a set of governing equations which describes the double diffusive phenomena, thermal Rayleigh number (RaT) and solutal Rayleigh number (RaC) were extracted as the controlling dimensionless numbers. Various convection regimes were classified on a RaT vs. RaC diagram. A cold model experiment using NH4Cl-H20 system has been conducted to confirm the relationship on the RaT vs. RaC diagram. Transitional changes in the finger and the diffusive interfaces were visualized by the shadowgraph method. The convection regimes observed in the experimental system were successfully simulated by numerical computation of the governing equations.
Double diffusive phenomena during unidirectional solidification in the vertical direction was investigated based on both the numerical simulations and experiments for the NH4Cl-H2O system and Sn-Pb system. Observations and theoretical predictions suggested that finger type upward flows which selectively grow in liquid phase in the first stage of solidification induce channels in mushy zone and which in turn resulted in freckles in solidified ingot.
Hung Chuan CHEN, Kenji TOMOKIYO, Hidenori ERA, Mineo SHIMIZU
The carbide distribution prior to cold rolling was studied to know its effect on mechanical properties with respect to retained austenite (γR) in 0.2%C-1.4%Si-1.0%Mn-0.05%P steel cold rolled and intercritically annealed and isothermally held at bainitic transformation temperature. The microstructures after final heat-treatment were of ferrite, γR, bainite and/or martensite. In general, the steel with prior ferrite/pearlite structure (FP steel) gave more amount of γR and better mechanical properties such as strength, elongation, etc. than that with prior ferrite/cementite one (FC steel). The excellent mechanical properties in FP steel were based on a large amount of γR which transforms to martensite during deformation, giving rise to a high work hardening rate. The experimental results also showed that an increase in intercritical annealing temperature and/or time brought about a similar amount of γR in FC steel as in FP steel. However, FP steel still exhibited a superior elongation compared with FC steel. The reason for this is that the former contained a relatively large amount of small (about 2 μ, m) γR with stacking fault which would originate from fine cementites prior to cold rolling. It was concluded that the mechanical properties were strongly affected not only by the amount of γR but also by the γR size and configuration.
Michiharu NARAZAKI, Sadakatsu FUCHIZAWA, Masaaki USUBA
The characteristic temperature during quenching of cylindrical and spherical silver specimens in stiee subcooled water has been investigated to clarify the cause of the scattering and discrepancy of the data which have been reported by many investigators. The following results were obtained,
1) The local premature collapse of vapor blanket at the sharp corner of ends of cylindrical specimen or at the support tube significantly affects the values of characteristic temperature and it's dependence on liquid subcooling.
2) If the hemispherical geometry of both ends of cylinders or spherical geometry were selected to eliminate the local collapse of vapor blanket and if the premature collapse at support tube was prevented, the values of characteristic temperature did not exceed the maximum temperature predicted by the thermodynamic model by LIENHARD and agreed well with the value predicted by the hydrodynamic model by BERENSON regardless of liquid subcooling and specimen geometry.
3) It can therefore be presumed that the scattering and discrepancy of the reported values of characteristic temperature might have arisen from the local premature collapse of the vapor blanket at the corner of the ends of cylindrical specimens or at the support tube.
Ikuo OCHIAI, Hiroshi OHBA
A study has been made on the effect of the addition of titanium to reduce strain aging of low-carbon steel wire rod during cold forming. The effects of the conditions of wire rod rolling and subsequent cooling on the precipitation behavior of TiC and also the effect of the reduction of strain aging on both flow stress and work hardening have been investigated by adding titanium to low-carbon steels of carbon contents of 0.005 and 0.02 mass%. The results obtained are as follows.
(1) The precipitation rate of TiC in ferrite phase is highest at approximately 1 073K. The precipitates observed are pure TiC and the complex precipitates of TiC nucleated on Ti4C2S2 or Ti2S precipitates.
(2) When a small amount of titanium is added to the low-carbon steel wire rod, the strength of the wire rod is increased by the precipitation hardening caused by TiC.
(3) In the case of ordinary rolling, the minimum amount of titanium for the prevention of strain aging is over three times more than the stoichiometric amount for 0.005 mass% carbon steels, and is approximately twice as much as the stoichiometric amount for 0.02 mass% carbon steels. The minimum amount of titanium is remarkably reduced by controlled rolling.
(4) The amount of work hardening by wire drawing and flow stress in the high-speed compression test were reduced by approximately 27% and 15%, respectively, by the prevention of strain aging.
Toshihiko KAZINO, Toshihiro HAYASHI, Toshiro KOBAYASHI
Static fracture toughness test at room temperature and -196°C was carried out on JIS SS41 steel specimens which had different notch root radii and microstructures, then, effect of microstructural factor on ductile and brittle fracture toughnesses were examined.
At room temperature, it was observed that the local model of ductile fracture initiation criterion was valid. Characteristic distance in ductile fracture has nearly corresponded to void initiation distance ahead of the crack tip and the spacing of inclusion, therefore, it was presumed that a microstructural factor associated with the ductile fracture was mainly inclusions. Ductile crack initiation toughness and crack propagation toughness were measured. It was observed that the crack propagation toughness rather than the crack initiation toughness was susceptible to variation of microstructure.
At very low temperature, it has been shown that the variation of the fracture toughness with notch root radius follows the theoretical formula presented by Williams. Characteristic distance in brittle fracture has corresponded to a multiple of martensite packet size or spacing of precipitated carbide, therefore, it was presumed that a microstructural factor associated with the brittle fracture was mainly carbides. Brittle fracture initiation model taking the process zone at the crack tip and distribution of carbides into consideration was presented.
Hisahiro SAKAI, Shouichi OCHIAI, Manabu UENO
The purpose of this work is to present results on the mechanical properties of SUJ 2 bearing steel improved by a cyclic heat treatment. The structure of thermally cycled steel consists of fine-grained ferrite particles of the size under about 2 μm containing fine cementite particles of the size about 0.2μm. Thermally cycled steel was found to be superplastic at 710°C, just below A1 temperature, at an initial strain rate of 1.67 × 10 -4s -1, i.e. elongation to failure was about 500% and the strain rate sensitivity, m value, was about 0.4. The activation energy of about 180 kJ/mol, which is nearly equal to that of grain boundary diffusion of Fe atoms in α-iron, was obtained for this plastic deformation.
Furthermore the rolling contact fatigue life test was performed at room temperature under constant load. The fatigue life of SUJ 2 steel thermally cycled was found to be prolonged (about 2.5 times) as compared with that of conventional one.
Yoshio MONMA, Hiroshi ITOH, Mitsuru EGASHIRA, Eiji BABA, Hideko MIYAZAKI, Chiaki TANAKA
The drift (or decrease) of electromotive force (EMF) in the calibration of PR thermocouples used for long-time creep testing at various temperatures up to 100 000h in air is investigated. The magnitude of resistivity, ρ, which is considered to be one of indices to the inhomogeneity of thermocouples, and its distribution from the measuring junction are measured. The change in p together with the results of X-ray diffraction and spectroscopic analysis indicate that the inhomogeneity is very small in Pt but considerable in Pt-12.8%Rh limbs.
The oxides found on the surface of thermocouples with notable drifts are the mixture of Rh2O3 types. The effect of drift on the measured temperature is rather small if the ratio of immersion depth is less than unity (when it is more than unity, the scatter in the drift among thermocouples after virtually same times is pronounced). For the thermocouples used 30 000 to 50 000h at 1 000°C the drift is also responsible to the evaporation of Pt and Rh elements.
For the thermocouples with the immersion depth of 250 mm, the annealing treatment is effective to recover the drift provided that the test temperature is below 500°C ; above 500°C it is recommended to cut off a part of thermocouple limbs up to 100 mm from the measuring junction in order to get the complete recovery of EMF.
Toshinori OZAKI, Yuichi ISHIKAWA
Environmental embrittlement of 17-4PH martensitic stainless steel castings for sea water use is studied. Failure analysis, stress corrosion cracking test, and crevice corrosion test yield the following results.
1) It is suggested that failure of the 17-4PH steel sliding contact components may be due to the hydrogen embrittlement cracking initiated at pits. Furthermore it seems that a rather high frequency of failure occurrence in an initial few year period may be caused by the initial presence of some factors responsible for the failure.
2) The cracking susceptibility persists at an applied stress lower than 15kgf/mm2 when the hardness of the steel exceeds HV = 310. On the other hand when the hardness is lower than 310, the steel remains uncracked even at an applied stress higher than 60 kgf/mm2. The cracking susceptibility is slightly affected by chemical composition and microstructure of the steel.
Based on these findings, following countermeasures are taken. The steel should be aged so as to be the hardness below 310 HV and the compressive stress is induced at the component surface by shrink fitting. Moreover the injection of fresh water into a shaft casing during the shut-off period is recommended.
No failure has been reported for over ten years since the countermeasures had been adapted.
Takehiko ITAGAKI, Toshiharu KOBAYASHI, Jung Wei SHIH, Takashi ARAI, Michio YAMAZAKI
Exposure experiments of some metallic materials were carried out in the fluidized bed low-BTU coal gasification pilot-plant of Coal Mining Research Center. The test materials contains a carbon steel, chromium-molybdenum steels, stainless steels and superalloys along with the aluminum- or chromium-coated materials. These materials were attacked mainly with oxidation and sulfidation and the major factor of corrosion was sulfidation. It was found that the corrosion behavior of alloys was strongly dependent on the chromium content in the alloys. It was also found that alloys with lower chromium contents such as 2.25Cr-1Mo steel and SUS410 are hardly applicable for the coal gas atmosphere. SUS347 gave comparatively good results rather than the other austenitic stainless steels containing 18% chromium.
In superalloys the scaling losses of Hastelloy X, 50Ni-50Cr and S-816 were extremely low. Then it can be concluded that the chromiun content in the alloys should be increased more than 20% in order to give a good corrosion performance in the coal gas environment. It was also revealed that the chromium-coated material resulted in a high corrosion resistance, whilst the aluminum-coated alloys did not show sufficient resistance to high temperature corrosion. Aluminum as an alloying element also had little effect for the increased corrosion resistance.
Tomoo TAKAHARI, Susumu OHTSUKA
Colouring solution (composed with CrO3 : 250g/l and H2SO4 : 500g/l) used to colouring method for stainless steels that was developed at Birmingham research institute of International Nickel Corp. is deteriorated according to increase of amounts of colouring treatments.
Deteriorated colouring solution caused troubles of elongation of colouring time e.g. falldown of production efficiency and missing clarity of coloured films So, deterioration behavior and restoration method of colouring ability of the colouring solution were studied. The results are as follows;
(1) Deterioration was caused by comsuptions of chromic and sulfuric acid that were main components of the colouring solution.
(2) And more than 12 g/l of chromium (III) ion, the colouring solution deteriorated the colouring times delayed.
(3) Colouring times turned back to the former level when amounts of comsumed chromic and sulfuric acids were added into the deteriorated colouring solution.
(4) But the colouring times were not recovered for the solutions contained with more than 12 g/l chromium (III) ions even if chromic and sulfuric acids were added.
03 Dec. (Last 30 Days)
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MATERIALS TRANSACTIONS Vol.64(2023), No.11
Tetsu-to-Hagané Vol.109(2023), No.11
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