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1.
The problem of freezing of pure water in a round pipe is treated with due regard for convection under asymmetric thermal boundary conditions in the absence of motion along the pipe. The problem is solved numerically using the control volume approach, SIMPLER algorithm, and the enthalpy method. Results are obtained for three Grashof (Gr) and six Biot (Bi) numbers: Gr = 1.55 × 106, Bi = 0.305 (0 < ), Bi = 0.044 ( < 2); Gr = 1.24 × 107, Bi = 0.610 (0 < ), Bi = 0.087 ( < 2); Gr = 9.89 × 107, Bi = 1.220 (0 < ), Bi = 0.174 ( < 2). The correctness of calculation of the problem disregarding free-convection flows is analyzed. 相似文献
2.
Ageing characteristics of cast Zn-Al based alloy (ZnAl7Cu3) 总被引:1,自引:0,他引:1
Microstructure and ageing characteristics of a cast Zn-Al based alloy (ZnAl7Cu3) were studied using X-ray diffraction, electron scanning microscopy and back-scattered diffraction techniques. Two stages of phase transformation, i.e., decomposition of zinc rich phase and four phase transformation, + T + , were detected during ageing at 150°C. Electron back-scattered diffraction technique was applied in distinguishing both zinc rich and phases. 相似文献
3.
P. V. Tsoi S. Yu. Yusunov N. R. Korpeev 《Journal of Engineering Physics and Thermophysics》1984,47(1):860-864
Analytical solutions of the direct and inverse problems of nonstationary heat conduction in a thin semiinfinite rod are given for the case of radiative heat fluxes at the lateral surfaces and a partial outflow of heat by convection and radiation through the end of the rod.Notation
thermal diffusivity
- x1
coordinate along the length of the rod
- t1
time
- t=t1/d2
dimensionless time (Fourier number)
- x=X1/d
relative coordinate
- To
initial temperature
-
Boltzmann constant
- Sk=aTc
3d/
Stark number
- Bi=d/
reduced Biot number
-
emissivity
Translated from Inzhenero-Fizicheskii Zhurnal, Vol. 47, No. 1, pp. 148–153, July, 1984. 相似文献
4.
A two-dimensional gasdynamic model of a plasma generator is proposed. A numerical solution of the problem is obtained, and peculiarities of the gasdynamic flow are considered. Results are compared with experiment.Notation T
temperature
- p
pressure
- N
number of gas particles per unit volume
- w
gas mass velocity vector with components wz=u and wr=v
- z
axial coordinate
- r
radial coordinate
- t
time
- E
total specific energy of gas
-
specific internal energy
-
density
- V
plate velocity
- Ein
initial plate energy
- M
plate mass
- S
plate area
- p
pressure difference between left and right sides of plate
- t, z, r
time and space steps
- k<1
Courant number
- c
velocity of sound in the gas
Indices 0
initial value
- *
characteristic dimensional quantities
- i, j
grid cell indices along z and r
- n
number of time step
- ()
symbol denoting intermediate values of gasdynamic variables in a time layer
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 5, pp. 859–867, November, 1979. 相似文献
5.
The error of measurements of the dielectric parameters and tan in a cylindrical cavity resonator supporting the H
01p
mode by varying the length of the resonator at a constant resonance frequency is considered. The errors in measuring and tanare investigated numerically as a function of the electric thickness of the sample being investigated and its permittivity . 相似文献
6.
J. R. White 《Journal of Materials Science》1981,16(12):3249-3262
The two-site model is developed for the analysis of stress relaxation data. It is shown that the product of d In (–
)/d and (-
i) is constant where is the applied stress,
i is the (deformation-induced) internal stress and
= d/dt. The quantity d In (
)/d is often presented in the literature as the (experimental) activation volume, and there are many examples in which the above relationship with (-
i) holds true. This is in apparent contradiction to the arguments that lead to the association of the quantity d In (–
)/d with the activation volume, since these normally start with the premise that the activation volume is independent of stress. In the modified theory presented here the source of this anomaly is apparent. Similar anomalies arise in the estimation of activation volume from creep or constant strain rate tests and these are also examined from the standpoint of the site model theory. In the derivation presented here full account is taken of the site population distribution and this is the major difference compared to most other analyses. The predicted behaviour is identical to that obtained with the standard linear solid. Consideration is also given to the orientation-dependence of stress-aided activation. 相似文献
7.
Complex microstructural changes in as-cast eutectoid Zn-Al alloy 总被引:4,自引:0,他引:4
Phase transformations and microstructural changes of an as-cast eutectoid Zn-Al alloy (ZnAl22Cu2) were investigated during isothermal holding. The typical dendritic structures consisted of s phase as a core with the edge of decomposed s phase and decomposed s in the interdendritic regions. A series of complex phase transformations was observed. Both decompositions of s and s were determined at an early stage of ageing and a four-phase transformation, f+T+, was observed at the boundaries of f phase and the phase, instead of clearly observed at the boundaries of phase, in a solution-treated Zn-Al alloy during prolonged ageing. 相似文献
8.
Martensitic transformations in Ti-Mo alloys 总被引:5,自引:0,他引:5
A detailed investigation has been made of the structure of alloys of the Ti-Mo system containing up to 10wt% Mo, water-quenched from the-phase region. With increase in molybdenum content, the martensite structure changes from hexagonal () to orthorhombic () at 4 wt% Mo, and at 10 wt% Mo, the structure is completely retained . For alloy compositions <4 wt% Mo, there is a diffusional component in the transformation of the -phase at the quench rates employed. There is a transition, with increase in molybdenum content, in morphology (from massive to acicular) and in substructure (from dislocations to twins). However, the transitions in crystallography, morphology and sub-structure are not directly related to one another except for an abrupt loss of dislocation substructure at the/ transition. The to crystallographic transition has the characteristics of a second order transformation, and evidence has been obtained of the existence of a spinodal within the metastable orthorhombic system. The orthorhombic martensites of Ti-6 and 8 wt% Mo decompose during quenching producing a fine modulated structure within the martensite plates, consistent with a proposed spinodal mode of decomposition. 相似文献
9.
M. M. Talianker 《Journal of Materials Science》1982,17(11):3097-3100
The athermal transformation in Zr-2 at.% Nb alloy has been investigated by transmission electron microscopy. Analysis of the selected-area diffraction pattern has shown that the orientation relationships between the omega and the parent-phase in quenched Zr-2 at.% Nb alloy are the same as have been previously observed for the reaction in pure zirconium. Thus it was deduced that the direct transition has taken place in the alloy during cooling. The-originated -particles were visualized using the dark-field technique. The formation of the athermal omega in the-region of-stabilized Zr-Nb alloy is discussed in terms of the relative positions of the free energy equilibrium curvesT
0
,T
0
,T
0
and the correspondingM
s
,M
s
andT
s
start curves. It is concluded that the omega phase can occur over a much wider range of alloy compositions than is usually recognized on the basis of transformation data. 相似文献
10.
The oxidation of dispersed aluminium oxynitride particles in an alumina matrix has been studied. The kinetics law of this reaction is linear and the activation energy is 420±40 kJ mol–1 (100±10 kcal mo–1). A-alumina layer is formed and leads to-alumina above 1200° C. The-alumina formation produces surface compressive stresses, and thus the mechanical properties (
f, HV) are improved. We have proved that the formation of-alumina in the Al2O3-AION composite can lead to the best properties for this ceramic. A-alumina layer has a very interesting effect on the wear resistance of this material. 相似文献
11.
Summary The hypersonic small-disturbance theory is reexamined in this study. A systematic and rigorous approach is proposed to obtain the nonlinear asymptotic equation from the Taylor-Maccoll equation for hypersonic flow past a circular cone. Using this approach, consideration is made of a general asymptotic expansion of the unified supersonic-hypersonic similarity parameter together with the stretched coordinate. Moreover, the successive approximate solutions of the nonlinear hypersonic smalldisturbance equation are solved by iteration. Both of these approximations provide a closed-form solution, which is suitable for the analysis of various related flow problems. Besides the velocity components, the shock location and other thermodynamic properties are presented. Comparisons are also made of the zeroth-order with first-order approximations for shock location and pressure coefficient on the cone surface, respectively. The latter (including the nonlinear effects) demonstrates better correlation with exact solution than the zeroth-order approximation. This approach offers further insight into the fundamental features of hypersonic small-disturbance theory.Notation
a
speed of sound
-
H
unified supersonic-hypersonic similarity parameter,
-
K
hypersonic similarity parameter, M
- M
freestream Mach number
-
P
pressure
-
T
temperature
-
S
entropy
-
u, v
radial, polar velocities
-
V
freestream velocity
-
shock angle
-
cone angle
-
density
-
density ratio, /()
-
ratio of specific heats
-
polar angle
-
stretched polar angle, /
- (), (), ()
gage functions 相似文献
12.
We present data on the copper isotope effect (63Cu-65Cu), Cu =-nTc/nmCu, for two isotopic pairs of oxygen-deficient YBa2Cu3O7–, where varies between 0.06 and 0.52. Cu is below 0.01 at =0.06 (fully oxygenated), it takes values between –0.14 and –0.34 in the 60 K plateau. Larger negative values of Cu are observed away from the plateau. The dependence of Cu is similar to that of the pressure effect dnTc/dP. 相似文献
13.
Z. Y. Cheng X. W. Du Jing Zhu C. X. Cao F. S. Sun 《Journal of Materials Science》2000,35(18):4501-4505
The 2 phase transformation in fractured high temperature stress rupture Ti-48Al-2Nb(at.%) alloy has been studied by analytical electron microscopy. 2 and phases were found at grain boundaries. 2 layers that suspended in layers and interfacial ledge higher than 2d
(111) at /2 interfaces were observed in the lamellar grains. These facts indicated that 2 phase transformation and dynamic recrystallization have occurred during high temperature stress rupture deformation. It can be concluded that deformation induced 2 phase transformation and dynamic recrystallization resulted in the presence of particles at grain boundaries. A structural and compositional transition area between deformation-induced 2(or ) and its adjacently original (or 2) phases was found by HREM and EDS and is suggested as a way to transform between and 2 phase during high temperature stress rupture deformation. The transition area was formed by slide of partial dislocations on close-packed planes and diffusion of atoms. 相似文献
14.
E. M. Godzhaev A. M. Nazarov Kh. S. Khalilova A. M. Suleimanova 《Inorganic Materials》2001,37(11):1104-1105
The thermal expansion coefficient () and isothermal compressibility (
T
) of TlIn1 – x
Nd
x
Se2(0 x 0.08) crystals were measured between 77 and 400 K. In the range 77–160 K, both and
T
increase with temperature, the increase in being much steeper. At higher temperatures, and
T
change very little. The observed composition dependences of and
T
are interpreted in terms of energy-band structure. 相似文献
15.
J. S. Thorp A. B. Ahmad B. L. J. Kulesza S. V. J. Kenmuir 《Journal of Materials Science》1984,19(10):3211-3216
Recently developed coaxial line techniques [1] have been used to determine, at room temperature, the values of the real () and imaginary (') parts of the dielectric constants for some Mg-Al-Si, Ca-Al-Si and Y-Al-Si oxynitride glasses over the frequency range 500 MHz to 5 GHz. The frequency dependencies of and ' are consistent with the universal law of dielectric response in that (-t8)(n–1) and '(n–1) for all glass compositions; the high experimental value of the exponent (n=1.0±0.1) suggests the limiting form of lattice loss [2] situation. In this frequency range, as previously reported [3] at longer wavelengths, the addition of nitrogen increases the dielectric constant, (); in both the oxide and oxynitride glasses is also influenced by the cation, being increased with cation type in the order magnesium, yttrium, calcium as at lower frequencies. 相似文献
16.
M. M. Elkholy 《Journal of Materials Science: Materials in Electronics》1994,5(3):157-162
The a.c. conductivity for the TeO2-P2O5 glassy system was measured in the temperature range 300–573 K and in the frequency range 100 Hz to 10 kHz. The a.c. conductivity () increased with frequency according to the relation ()s. The frequency exponent s was found to decrease with increasing temperature. The composition dependence of the conductivity was also investigated. The density of states was also calculated using the Elliott model. The a.c. conductivity increased over the studied temperature range. The obtained experimental data have been analysed with reference to various theoretical models. The analysis shows that the correlated barrier hopping (CBH) model is the most appropriate mechanism for conduction in the TeO2-P2O5 glass system. 相似文献
17.
Kazutaka Kudo Takashi Noji Yoji Koike Terukazu Nishizaki Norio Kobayashi 《Journal of Low Temperature Physics》2003,131(3-4):725-729
We have investigated the magnetic susceptibility, , and the thermal conductivity, , in magnetic fields for the four-leg spin-ladder system La2Cu2O5 single crystal. The in a magnetic field parallel to the ladder exhibits a kink at 130 K in correspondence to the magnetic ordering. The along the ladder exhibits a peak at 25 K and a shoulder at 14 K, which are probably related to the thermal conductivity due to magnons, magnon, and that due to phonons, phonon, respectively. The perpendicular to the ladder, on the other hand, exhibits only one broad peak related to phonon. The observed large anisotropy of has been explained based upon the anisotropy of magnon. 相似文献
18.
A new rationale is presented for various decomposition products obtained from the metastable -phase found in Ti-6A1-4V alloy produced by hot isostatic pressing comminuted melt-spun fibres and cooled to room temperature by furnace cooling. This alloy has an -matrix with about 8 vol% retained -phase, which is supersaturated with -stabilizers to such an extent that the martensitic transformation has been suppressed. The metastable -phase decomposes by different modes during continuous cooling, depending on the actual composition of individual -grains. Less enrichment of vanadium and iron favours the direct formation of the equilibrium -phase from the -matrix, while greater enrichment of vanadium and iron leads to a spinodal decomposition of the metastable -phase, resulting in a + two-phase structure. During further continuous cooling, the -phase which is lean in -stabilizers will transform into isothermal -phase. In addition, an unknown phase has also been observed in the -phase, which is typified by the appearance of 1/2{112} reflections in the SAD patterns. 相似文献
19.
Conclusions 1. For thin absorbers, the Landau theory incorporating certain above-listed corrections is a general-purpose one and is in good agreement with experiment both for heavy and light charged particles 0.01. 2. For intermediate layers (0.01 1 and 1), exact solutions are provided by the Vavilov theory [11]. 3. The numerical-analytic method of plotting the energy loss distribution function proposed in [13] is suitable for very thin ( 0.01) absorbers.Translated from Izmeritel'naya Tekhnika, No. 3, pp. 60–62, March, 1970. 相似文献
20.
Why it is easier to cut with even the sharpest knife when pressing down and sliding than when merely pressing down alone is explained. A variety of cases of cutting where the blade and workpiece have different relative motions is analysed and it is shown that the greater the slice/push ratio given by (blade speed parallel to the cutting edge/blade speed perpendicular to the cutting edge), the lower the cutting forces. However, friction limits the reductions attainable at the highest . The analysis is applied to the geometry of a wheel cutting device (delicatessan slicer) and experiments with a cheddar cheese and a salami using such an instrumented device confirm the general predictions. 相似文献