Computations of incompressible fluid flow around a long square obstacle near a wall: laminar forced flow and thermal characteristics

Computations of incompressible fluid flow and heat transfer around a square obstacle with a nearby adiabatic wall have been performed in a horizontal plane. The ranges of dimensionless control parameters considered are Prandtl number (Pr) = 10–100, Reynolds number (Re) = 1–150 and gap ratio (G) = 0.25–1. The steady-flow regime is observed up to Re = 121 for G = 0.5, and beyond this Re, time-periodic regime is observed. The shift to a time-periodic regime from a steady regime occurred at greater Re than that for an unconfined square obstacle. With increasing Pr, increase in average Nusselt number values is recorded for all Re and G studied. The heat transfer augmentation is approximately 1332% at Re = 150 (Pr = 100, G = 0.25) with regard to the corresponding values at Re = 1. Lastly, a correlation for j _h factor is determined for the preceded conditions.     

An investigation on mathematical models of the h-index

Based on two large data samples from ISI databases, the author evaluated the Hirsch model, the Egghe-Rousseau model, and the Glänzel-Schubert model of the h-index. The results support the Glänzel-Schubert model as a better estimation of the h-index at both journal and institution levels. If h _c , h _p and h _pc stand for the Hirsch estimation, Egghe-Rousseau estimation, and Glänzel-Schubert estimation, respectively, then an inequality h _p < h ～ h _pc < h _c holds in most cases.     

Experimental investigations on heat transfer characteristics of pulsating single-phase liquid flow and two-phase Taylor bubble flow through a minichannel

Experimental investigations are reported for pulsating Taylor bubble (PTB) flow through a 2.12 mm horizontal circular minichannel. Air and water are used as working fluids. A T-junction is used to generate Taylor bubble flow in a minichannel. The superficial gas velocity (U _SG ) is kept as 0.0472 m/s. The superficial liquid velocity (U _SL ) is kept as 0.0472 and 0.0708 m/s. The pulsating liquid flow is generated by developing a pulse generator circuit. The investigations are carried out for various pulsating flow frequencies of 0 Hz (continuous flow), 0.1, 0.25, 0.5, 1 and 2 Hz, which correspond to Womersley number (W _o ) 0, 0.84, 1.39, 1.88, 2.65 and 3.75, respectively. Heat transfer enhancement is found to be negligible (less than 1%) for pulsating laminar liquid flow through the minichannel. On the contrary, heat transfer is observed to decrease by 35% for PTB flow compared with continuous Taylor bubble (CTB) flow for imposed frequency of pulsation up to 1 Hz.     

Epitaxial growth and magnetic properties of <Emphasis Type="Italic">h</Emphasis>-LuFeO<Subscript>3</Subscript> thin films

In this paper, the epitaxial hexagonal LuFeO₃ (h-LuFeO₃) thin films with c-axis-oriented single phase, smooth surface were grown on YSZ (111) substrates by pulsed laser deposition method. Furthermore, a structural distortion of increased lattice constant of c is found in the epitaxial h-LuFeO₃ thin films. Moreover, the epitaxial h-LuFeO₃ thin films show room-temperature ferromagnetism. The coercive field and remnant magnetization of the epitaxial h-LuFeO₃ thin film decrease with the increase in the test temperature from 50 to 300 K. The study would be of benefit to the room-temperature single-phase multiferroic materials.     

Integral methods of calculation of heat transfer and drag under conditions of turbulent pipe flow of liquid of variable properties: Steady-state and quasi-steady-state flows in a round pipe with constant temperature on the wall

An integral method is suggested for the calculation of heat transfer and drag under conditions of flow of dropping liquid and gas in a pipe with constant wall temperature. It is found that the kind of thermal conditions on the wall (T _wall = const or q _wall = const) has insignificant effect on the Nusselt number and coefficient of friction drag for a steady-state flow of dropping liquid of variable viscosity. For a quasi-steady-state pulsating flow of dropping liquid, the thermal boundary conditions have an appreciable effect on the Nusselt number alone; in so doing, the degree of this effect increases with the oscillation amplitude and hardly depends on the temperature factor. For steady-state and quasi-steady-state flows of gas at high temperature factors, the values of heat transfer and drag at T _wall = const differ significantly from those at q _wall = const.     

Experimental modelling of free-surface dry granular flows under a centrifugal acceleration field

We investigate the dynamics of granular flows under the action of a centrifugal acceleration field. The granular flows consist of a monodisperse set of glass beads flowing down an inclined plane. The experiments are performed at variable slope angles \(\zeta \) and equivalent centrifugal accelerations \(a_\text {cf}\equiv Ng\). We study the effect of this parameters on the superficial flow velocity u and flow height h. Two trends are observed, by increasing \(\zeta \) and \(a_\text {cf}\), u increases proportionally, and h decreases asymptotically until a constant height. This relation is analysed in terms of the system potential and kinetic energy, leading to the estimation of equivalent impact forces one order of magnitude larger than those observed in small scale 1g laboratory experiments, with the possibility to reach higher forces by increasing N. Finally, considering the trend of u and h, our results suggest a scaling principle of inertial velocity proportional to \(\sqrt{N}\).     

On the Interpretation of Near-Critical Gas–Liquid Heat Capacities by L. V. Woodcock,Int. J. Thermophys. (2017) 38, 139: Comments

It is shown that: (1) the expressions for the isochoric (C_V) and isobaric (C_P) heat capacities of liquid and gas, coexisting in phase equilibrium, the heat capacities at saturation of liquid and gas (C_σ) and the heat capacity C_λ used in the article “On the Interpretation of Near-Critical Gas–Liquid Heat Capacities, L. V. Woodcock, Int. J. Thermophys. (2017) 38, 139” are incorrect; (2) the conclusions of the article based on the comparison of the incorrect C_V, C_P and C_λ with experimental data are also incorrect; (3) the lever rule cannot be used to define C_V and C_P in the two-phase coexistence region; (4) a correct expression for the isochoric heat capacity describes well the experimental data; (5) there is no misinterpretation of near-critical gas–liquid heat capacity measurements in the two-phase coexistence region; (6) there are no proofs in the article that: (a) the divergence of C_V is apparent; (b) it has not been established experimentally that the thermodynamic properties of fluids satisfy scaling laws with universal critical exponents asymptotically close to a single critical point of the vapor–liquid phase transition; and (c) there is no singular critical point on Gibbs density surface. We obtained the relations connecting the isochoric heat capacity in the two-phase region with thermodynamic properties at saturation of homogeneous liquid and gas which can be used to verify the equation of state.     

Study of the Magnetic Properties of Ni/Ag Superlattice

Thin multilayer films of alternating ultrathin Ni and Ag layers (L(Ni)=11,15,30 Å, bulk and \(L(\mathrm{Ag})=50~{\AA})\) have been prepared by evaporation in ultrahigh vacuum under controlled conditions and have been studied by the magnetic measurements. The critical temperature T _C is studied as a function of the surface exchange interaction (J _S). The dependence of T _C on the thickness L of the film has been investigated. A critical value of the surface exchange interaction in the film, above which the surface magnetism appears, is obtained. The shift of the critical temperature T _C(L) from the bulk value \([\frac{T_{\mathrm{C}}(\infty )}{T_{\mathrm{C}}(L)}-1]\) can be described by a power law L ^?λ , where \(\lambda =\frac{1}{\nu_{\mathrm{b}}}\) is the inverse of the correlation length’s exponent. The effective critical exponent associated with the magnetization M(β) is deduced for different thicknesses of Ni layers, and the thickness L(Ag) was being kept constant at 50 Å.     

Visible-light-induced hydrogen evolution reaction with WS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>

WS₂ is a promising catalyst for the hydrogen evolution reaction. We have explored photocatalytic properties of ternary sulphoselenides of tungsten (WS _x Se _2?x ) by the dye-sensitized hydrogen evolution. WS _x Se _2?x solid solutions are found to exhibit high activity reaching 2339 μmol h^?1 g^?1 for WSSe, which is three times higher than that of WS₂ alone (866 μmol h^?1 g^?1 ). The turnover frequency is also high (0.7 h^?1 ). Such synergistic effect of selenium substitution in WS₂ is noteworthy.     

Dynamic Magnetic Hysteresis Behaviors in a Mixed Spin (3/2, 2) Bilayer System with Different Crystal-Field Interactions

Dynamic magnetic hysteresis (DMH) behaviors of the mixed spin-3/2 and spin-2 Ising bilayer system with different crystal-field interactions on a two-layer square lattice is studied by the use of dynamic mean field calculations based on the Glauber-type stochastic. The hysteresis loops are obtained for different reduced temperatures (T), magnetic field amplitudes (h), frequencies (w) and interlayer coupling constants (J ₃). Influences of the T, h, w and J ₃ on the DMH properties are investigated. We also study the temperature, frequency and interlayer coupling interaction dependence of the coercive field and remanent magnetization. We compare our results with some theoretical and experimental works and observe a quantitatively good agreement with some theoretical and experimental results.     

Influence of anodic passivation on electrical characteristics of Al/<Emphasis Type="Italic">p</Emphasis>-Si/Al and Al/V<Subscript>2</Subscript>O<Subscript>5</Subscript>/<Emphasis Type="Italic">p</Emphasis>-Si/Al diodes

In this paper, the V₂O₅ thin film has been grown on the both p-type semiconductor and glass substrate by the spray pyrolysis method. For optical and structural properties of thin film, the optical absorption, SEM, AFM and XRD measurements have been done. It is observed that films exhibit polycrystalline behavior. The effects of anodic passivation on the characteristic parameters of diodes have been investigated using current–voltage (I–V) characteristics. The I–V measurements of the diodes have been performed at the room temperature in the dark. The main electrical parameters such as ideality factor (n) and barrier height (Φ _b ) of diodes have been calculated from the forward bias I–V characteristics. Likewise, the values of series resistance (R _s ) of diodes have been obtained from Norde method. It is observed that while the ideality factor decreases with anodic passivation, the barrier height increases.     

Effect of restricted geometry and external pressure on the phase transitions in ammonium hydrogen sulfate confined in a nanoporous glass matrix

A study of heat capacity, thermal dilatation, susceptibility to hydrostatic pressure, permittivity and polarization loops was carried out on NH₄HSO₄–porous glass nanocomposites (AHS?+?PG) as well as empty glass matrices. The formation of dendrite clusters of AHS with a size, d_cryst, exceeding the pore size was found. An insignificant anisotropy of thermal expansion of AHS?+?PG showing statistically uniform distribution of AHS with random orientations of nanocrystallites over the matrix was observed. The effect of internal and external pressures on thermal properties and permittivity was studied. At the phase transition P-1???Pc, a strongly nonlinear decrease in the entropy ΔS₂ and volume strain (ΔV/V)_T2 was observed with decreasing d_cryst. The linear change in temperatures of both phase transitions P-1???Pc???P2₁/c under hydrostatic pressure is accompanied by the expansion of the temperature range of existence of the ferroelectric phase Pc, while this interval narrows as d_cryst decreases.     

Wave spectrum of a conducting cylinder in an isotropic plasma

The boundary value problem of the propagation of an electromagnetic field along a cylindrical conductor in an isotropic plasma medium has been solved by the impedance method. The boundedness of the wave spectrum of such a guiding structure has been shown. The spectrum includes fast intrinsic wave E ₀₁ and extrinsic hybrid waves HE _nm and EH _nm , both fast and slow ones, their countable set being determined by the azimuthal index.     

Thermodynamic properties of (TeO<Subscript>2</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>(MoO<Subscript>3</Subscript>)<Subscript>1–<Emphasis Type="Italic">n</Emphasis></Subscript> glasses

The thermal behavior of (TeO₂) _n (MoO₃)_1–n (n = 0.75, 0.85, 0.90) tellurite glasses has been studied by differential scanning calorimetry in the range from T = 300 to T = 850 K and heat capacity has been measured in the temperature range. The thermodynamic characteristics of the devitrification process and glassy state have been determined. The experimental data obtained have been used to evaluate the standard thermodynamic functions of the system in glassy and supercooled liquid states: heat capacity C _p °(T), enthalpy H°(T)–H°(320), entropy S°(T)–S°(320), and Gibbs function G°(T)–G°(320) in the temperature range 320–630 K. The composition dependences of the glass transition temperature and thermodynamic functions for the glasses have been obtained. The thermal and thermodynamic properties of the tellurite glasses have been compared to those of previously studied (TeO₂) _n (WO₃)_1–n and (TeO₂) _n (ZnO)_1–n glasses.     

Flux Pinning with Addition of Gold Nanoparticles in CuTl-1223 Superconductor

We investigated the effects of gold (Au) nanoparticles on flux pinning in Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10?δ (CuTl-1223) superconductor by infield temperature-dependent dc-resistivity measurements. The values of \(\phantom {\dot {i}\!}T_{\mathrm {c}}^{\text {onset}}\) (K) remained almost unaffected by applying external magnetic field on (Au) _x /CuTl-1223; (x = 0～1.5 wt.%) composites samples. But a decreasing trend in T _c(0) and increasing trend in resistive broadening (ΔT) by increasing external applied magnetic field were reduced after addition of Au nanoparticles in CuTl-1223 superconducting matrix. The activation energy (U _o) was calculated according to thermally activated flux flow (TAFF) model by using the Arrhenius Law. The increase in T _c(0), U _o, and upper critical field (H _c2) indicates a strong flux pinning after the inclusion of Au nanoparticles and found optimum for x = 1.0 wt.%.     

Convective Heat Transfer at an Annular Jet Impingement on a Flat Blockage

The experimental results on heat transfer of an annular impinging jet have been. The Reynolds numbers Re = (1.2–3.6) × 10⁴, the distance S from the nozzle to a blockage, S/d₀ = 2, 4, 6, and the circular slit height d₂/d₀ = 0.51 and 0.71, where d₀ and d₂ are the internal and external nozzle diameters, have been varied. It is shown that at the same air mass flow rate, replacement of a round nozzle with an annular one results in heat-transfer intensification (up to 70% at the stagnation point). The maximum heat transfer gain occurs at a small nozzle–wall distance (S/d₀ = 2). The heat-transfer increase is accompanied by an increase in the thermal pulsation intensity. The degree of intensification of the heat exchange depends on the height of the circular slit and the nozzle–wall distance.     

Influence of coronene addition on some superconducting properties of bulk MgB<Subscript>2</Subscript>

This study reports the effect of coronene (C₂₄H₁₂) addition on some superconducting properties such as critical temperature (T_c), critical current density (J_c), flux pinning force density (F_p), irreversibility field (H_irr), upper critical magnetic field (H_c2), and activation energy (U₀), of bulk MgB₂ superconductor by means of magnetisation and magnetoresistivity measurements. Disk-shaped polycrystalline MgB₂ samples with varying C₂₄H₁₂ contents of 0, 2, 4, 6, 8, 10 wt%, were produced at 850 °C in Ar atmosphere. The obtained results show an increase in field-J_c values at 10 and 20 K resulting from the strengthened flux pinning, and a decrease in critical temperature (T_c) because of C substitution into MgB₂ lattice, with increasing amount of C₂₄H₁₂ powder. The H_c2(0) and H_irr(0) values are respectively found as 144, 181, 172 kOe, and 128, 161, 145 kOe for pure, 4 wt% and 10 wt% C₂₄H₁₂ added samples. The U₀ depending on the magnetic field curves were plotted using thermally activated flux flow model. The maximum U₀ values are respectively obtained as 0.20, 0.23 and 0.12 eV at 30 kOe for pure, 4 wt% and 10 wt% C₂₄H₁₂ added samples. As a result, the superconducting properties of bulk MgB₂ at high fields was improved using C₂₄H₁₂, active carbon source addition, because of the presence of uniformly dispersed C particles with nanometer order of magnitude, and acting as effective pinning centres in MgB₂ structure.     

Buoyancy-driven convective heat transfer from a semi-circular cylinder for various confinements

Buoyancy-driven convective heat transfer from a semi-circular cylinder for various confinements has been studied using numerical simulations for wide ranges of parameters, Reynolds numbers (1?≤?Re?≤?50), Richardson numbers (0?≤?Ri?≤?2), Prandtl numbers (0.7?≤?Pr?≤?50) and confinement ratios (0.2?≤?β?≤?0.8). A hot semi-circular cylinder is symmetrically kept in a 2D rectangular confinement. The circular side of the cylinder faces the upstream flow and the fluid flows against gravity in the channel. The governing equations are numerically solved using FLUENT and the results obtained are presented in the form of isotherms, streamlines, pressure coefficients, drag coefficients, Nusselt numbers, etc. The highest value of pressure coefficient increases with blockage ratio for all cases. The drag coefficient decreases with Re and shows complex phenomena with change in Ri and blockage ratio of the channel. Pressure drag has contributed more as compared with viscous drag in all cases. The curved surface showed more heat transfer than the flat surface of the semi-circular cylinder. The value of β also has great influence at large value of Peclect numbers (=?2500). Overall average heat transfer in terms of average Nusselt number is a function of Ri, Re, Pr and β.     

Thermodynamic Properties of Superconductor with Competing Spin-Density Wave and Charge-Density Wave

The mean field Hamiltonian describing the coexistence of the spin-density wave (SDW) and charge-density wave (CDW) for high- T _c superconductor in the underdoped region before the onset of the superconductivity was studied. From self-consistent equations for SDW and CDW gaps derived from Green’s function method, the theromodynamic properties of the superconductor were derived. Our results show the competition between the SDW and CDW state on thermodynamic properties of superconductor that deviate gap-to- T _c ratio, critical temperature, and the specific heat jump from the BCS universal value.