Value Of Ρ0 Research Articles

Formation Mechanism and Characteristics of a Liquid Microlayer in Microchannel Boiling System

Experiments were performed using the laser extinction method to measure the thickness of the liquid film formed by growing flattened bubbles in a microchannel for gap sizes of 0.5 mm, 0.3 mm, and 0.15 mm. Water, ethanol, and toluene were used as test fluids. A high-speed camera was also used to simultaneously measure the bubble growth process. It was confirmed that the gap size and bubble forefront velocity determined the initial microlayer thickness. The variation trend of the microlayer thickness relative to the velocity of the interface was divided into two regions: region I, where the velocity is small and the thickness increases linearly with increasing velocity, and region II, where the thickness is almost constant or decreased slightly with increasing velocity. Furthermore, a nondimensional correlation for investigating the effects of test materials and gap sizes on microlayer thickness is presented. An analysis of the results showed that the boundaries of the two regions correspond to a Weber number of approximately 110, and in the region where the Weber number was smaller than 110, the thickness of the microlayer was thinner for the liquid whose value of ρ0.62ν0.42σ−0.62 was relatively small. However, for the region where Weber number was larger than 110, the smaller the kinematic viscosity of the liquid, the thinner the microlayer became.

An estimation of hydrophilic and hydrophobic interaction of aqueous urea, methylurea, dimethylurea and tetramethylurea from density and apparent molal volume at 30.0°C

Density (ρ) for 0.20–1.0 mol kg−1 of urea, 1-methylurea, 1,3-dimethylurea and 1,1,3,3-tetramethylurea solutions have been measured at an interval of 0.2 mol kg−1. Apparent molal volume (V φ, cm3 mol−1) is calculated from ρ values. Primary data were regressed and extrapolated to zero concentration for the limiting density (ρ0) and limiting apparent molal volume values for solute–solvent interactions.–CH3 (methyl) groups of N-methylureas weaken hydrophilic interaction and enhance hydrophobic interaction. The value of ρ0 and reflect the intermolecular forces due to electrostatic charge. The decreasing value of ρ0 and increasing value of with increasing number of–CH3 groups suggest some weak hydrophilic and strong hydrophobic interactions, so that the structure-breaking effect decreases. It was also found that with increasing concentration, the hydrophilic or hydrophobic interactions become stronger.

Three typical sizes of spherical drops in vapor phase

The effects of the molecular theory of distorted vapor-liquid boundary surfaces are discussed within the framework of the lattice gas model for spherical drops that are present in the vapor phase. It is shown that three typical scales of drop size ρ can be defined, corresponding to: (1) the critical value of ρ0 at the beginning of phase formation related to the emergence of surface tension of the dense phase; (2) the value of radius ρt, above which the thermodynamic description of surface tension of a drop is reasonable and both discreteness of the compound and contributions of spontaneous fluctuations can be ignored; and (3) the value of radius ρb, above which the values of surface tension are close to the volume value, upon small surface distortions of large drops.

Density changes of iron during morphological healing evolution of internal fatigue microcracks

Plastic-strain-controlled fatigue was performed on pure iron specimens with uniaxial symmetric tension-compression loadings at room temperature. The as-fatigued specimens were then annealed in vacuum at 1173 K from 1 to 7 hours. The morphologies of internal fatigue microcracks were observed by scanning electron microscopy (SEM) in the as-fatigued and as-annealed specimens. The density of the specimens was measured with an electronic analytical balance. The density of the as-fatigued specimens decreased continuously as the fractional fatigue life increased, and was nearly constant when the specimens were annealed up to 2 hours at 1173 K, but increased gradually after 2 hours of annealing time. The density of some specimens eventually approximates to the value of ρ0, the initial density, at 7 hours of annealing time. This suggests that the initial decrease in density is due to crack initiation and propagation in the as-fatigued specimens. At the early stage of annealing, the specimen density is nearly constant because the crack morphological change is controlled by surface diffusion. At the later stages, the density increases and finally returns to the initial density because the spherical voids evolved from the parent crack are reduced by volume diffusion coupled with grain-boundary diffusion. A combined model is presented to predict the shrinkage of the spherical voids within the specimens, and is in broad agreement with the experimental data.

An investigation of a correlation/covariance method of signal extraction

A harmonic correlation technique has been used effectively to isolate a primary signal from two independent data sets each of which is contaminated by the presence of interfering signals. Each of the two data sets is decomposed by a harmonic analysis, and then the correlation coefficients and amplitude ratios between the two decompositions are computed for each harmonic. Only harmonics which satisfy predetermined selection criteria are retained. Those criteria are in the form of requiring the correlation coefficient to exceed some magnitude, say, ρ0, and the amplitude ratio not to exceed some value, say, R0. The resulting pair of retained signals are then typically highly correlated. It is suggested that appropriate values of ρ0 lie between 0.25 and 0.6 and of R0 between 3.0 and 6.0, depending on the relative amplitudes of the primary and interfering signals. Critical examination of the technique shows that under many conditions it can be an effective tool for eliminating signals which are not a good approximation to the primary signal. This conclusion is confirmed by simulated examples of satellite magnetic anomaly data with interfering fields from ionospheric currents.

Effect of notches and microstructure on the fracture toughness of TiAl-based alloys

The effects of notches and microstructure on the fracture behavior of TiAl-based alloys are systematically investigated. It has been determined that the apparent fracture toughness, KA, for four typical microstructures—which include fully lamellar, nearly lamellar, duplex, and nearly gamma microstructures—exhibits similar variational trends with the notch root radius. KA is independent of the notch root radius ρ when ρ is smaller than the critical radius ρ0, and increases linearly with ρ12 when ρ is larger than ρ0. The value of ρ0 is of the same order of magnitude as the grain size, and the slope of the KA-ρ12 curve is dependent on the microstructure type. The good agreement between the statistical data of the crack initiation site in the blunt bent bar and the peak stress location indicates that the fracture of TiAl-based alloys is controlled by the maximum tensile stress rather than the strain or strain gradients as in Ti3Al-Nb-based alloys. By using the Tetelman model of stress-controlled fracture, the effect of the notch root radius on the apparent fracture toughness can be explained very well.

Variable‐Range Hopping in Neutron‐Transmutation‐Doped Gallium Arsenide

AbstractFirst investigations are reported on the temperature dependence of the dc‐conductivity at T = = 0.05 to 300 K on neutron‐transmutation‐doped (NTD) n‐GaAs in the vicinity of the metalinsulator transition (MIT). At a medium compensation of K = 0.60 to 0.77 the MIT takes place at the critical electron concentration of nc = 2.3 × 1016 cm−3. On the dielectric side of the MIT in the variable‐range hopping regime (VRH) at T ≦ 10 K the conductivity obeys the equation σ(T) = σ0exp [— (T1/T)1/2] and not the Mottlaw. The experimental values T1 are for all samples much smaller than T1theor for isolated shallow impurities and scale down according to T1 = = T1*(1 ‐ n/nc)1.6±0.4 with T1* = 5.9 K by approaching the MIT. This behaviour is due to the divergency of the localization radius a and the static DK ϵ0 at the MIT. The obtained linear In σ — T−1/2 law over about 2.5 orders of magnitude in temperature variation and more than three orders of magnitude of variation in conductivity is interpreted in the frame of a Coulomb gap with vanishing density of states at the Fermi level, as predicted by Efros and Shklovskii. The pre‐exponential factor ϱ0 = σ0−1 shows also scaling behaviour according to ϱ0 = ϱ0*(1 ‐ n/nc)1.2±0.4 and a value of ϱ0* = 2.2 Ω cm. At n → nc σ0 = ϱ0−1 reaches the value of Mott's minimal metallic conductivity of σMM = (Ce2/h) nc1/3, with 0.025 ≦ C ≦ 0.05.

Electrical properties of GaAs layers irradiated by H4 ions

The quantitiesρ(D) andρ(T) are studied in n- and p-GaAs, irradiated at T = 300°K by H+ ions (5 MeV). It is shown that the resistance of lightly doped GaAs specimens increases from original values ofρ0 to\(\bar \rho _{{\text{max}}} \) ≈109 Ω·cm upon irradiation by H+ ions (5 MeV) to integral fluxes up to D* − 1015 H+/cm2. For D > D* the layer resistance decreases from 109 Ω·cm to ∿ 1 Ω·cm at 300°K. It was found that all the GaAs specimens intensely irradiated by H+ ions had p-type conductivity near 300°K. Isochronic annealing of radiation defects was studied in the temperature interval 20–700°C.

An analysis of non-propagating fatigue cracks

An analysis for the formation of nonpropagating fatigue cracks at (the base of V-shaped) notch roots, based on the considerations of the extent of the critically stressed region ahead of a notch or a crack tip, and the resulting volumetric strength effect, is developed. Assuming that the minimum local cyclic stress required for crack initiation from a notch root is equal to the unnotched fatigue limit, σe, and that the minimum local cyclic stress required for the propagation of the crack is equal to the theoretical strength of the material, σe, a model of notch fatigue limit is proposed that shows that nonpropagating cracks should form at the notch base if ρ≤ ρ0, a critical root radius, provided the notch is sufficiently deep,i.e. d ≥ ρ0. The radius ρ0 is a material constant and can be estimated from known material properties. The estimated values of ρ0 are in fairly good agreement with available experimental values for steels and pure copper. For stresses near the notch fatigue limit it is suggested that p0 be regarded as a radius above which notch fatigue limit is essentially initiation controlled and below which essentially propagation controlled. The notch fatigue limit based on complete fracture can then be estimated more accurately with mild as well as sharp notches.

Density and Pressure in the Chapman–Jouguet Plane as Functions of Initial Density of Explosives

IN an ideal detonation in condensed explosives, the relation between the density in the Chapman–Jouguet plane (ρ1) and the initial density of the explosive (ρ0) seems to be a single straight line common to most explosives. Mader1 has calculated ρ1 for a great number of explosives at different values of ρ0 ⩾ 1 g/cm3, using the semi-empirical Becker–Kistiakowsky–Wilson equation of state.