Heat transfer from a cylindrical,heavily finned surface

The transfer of heat from a strongly heated, heavily finned surface is examined. The material of the surface and of the fins has high thermal conductivity (copper), while the heat transfer fluid has comparatively low thermal conductivity (oil). Under these conditions, increase in the number of fins and reduction of the distance between them makes possible a high value of the coefficient of heat transfer from the heated surface to the fluid.Notation R₂ and r₁ radii of cylindrical surface at tip and base of fins, respectively - r, z coordinate axes - angle between planes of adjacent slots - x slot width - b anda coordinates of tip and base of fin - thermal conductivity of fin material - t fin temperature - u mean fluid temperature over slot width - coefficient of heat transfer from fin surface to fluid - c specific heat of fluid - v fluid velocity (since the viscosity is considered constant over the flow, v is also constant) - q density of heat flux through base of fin - specific weight of fluid - ¯t, ¯u Laplace transforms - p Laplace transform parameter, s-auxiliary quantity determined from equation (13) - I, K, J, Y Bessel functions - u⁰ mean fluid temperature over height of slot     

Growth and Properties of Double-Sided YBCO Films Deposited by Off-Axis Sputtering for Microwave Applications

The double-sided YBa₂Cu₃O _y (YBCO) films were grown on LaAlO₃ (LAO) substrates by an off-axis magnetron sputtering system with two 2-inch sputtering guns. High-quality YBCO films within a 50-mm-diameter area were obtained. The homogeneous YBCO films revealed transition temperature T _c(R=0) of 86K and a critical current density J _c (zero field) of 1.5×10⁶ A/cm² at 77 K. Thesurface impedance of YBCO films was measured using a probe-coupling type microstripline resonator method. The surface resistance R _S of 1.8 was obtained at 77 K around 2180 MHz. Additionally, a HTS three pole bandpass filter was fabricated and revealed a good microwave characteristic. The influence of surface roughness on microwave properties of YBCO films was discussed.     

Influence of stefan flow on heat and mass transfer and kinetics of chemical reactions of a carbon particle in air

With account taken of Stefan flow, an analysis of the interrelated heat and mass transfer of a carbon particle in parallel reactions on its surface is performed.Notation T temperature, K - t time, sec - density, kg/m³ - c specific heat, J/(kg·K) - d diameter - R particle radius, m - thermal conductivity coefficient, W/(m·K) - particle emissivity - v Stefan flow velocity, m/sec - r radial coordinate - C _j relative mass concentration of the jth component - µ _j molar weight, kg/mole - k ₁,k ₂ constants of the first and the second reaction rates, m/sec - k ₀₁ andk ₀₂ preexponents - E ₁,E ₂ activation energies, J/mole - D diffusion coefficient, m²/sec - =v _RR/D dimensionless value of the Stefan flow velocity - Q _x surface power of heat release, W/m² - Q _st density of the heat flux via heat conduction and Stefan flow, W/m² - Q _r density of the heat flux via radiation - j _j mass flux density - W rate of the heterogeneous chemical reaction in O₂, kg/(m²·sec). Indexes - 1 particle - 2 gas - w wall - st Stefan - infinitely distant - in initial - R on the particle surface - by heat conduction - r by radiation - j 1, O₂ - j 2, CO₂ - j 3, CO - j 4, N₂ Odessa State University. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 4, pp. 576–582, July–August 1995.     

Proton Conductivity in H2 – x (NH4) x V9Mo3O32.5 – δ · nH2O Xerogel Films

The electrical conductivity of _{2 – x} (NH₄) _x V₉Mo₃O_{32.5 –} · nH₂O xerogel films containing different amounts of ammonium ions and water was measured as a function of temperature. The results demonstrate that, in a wide temperature range, the proton conductivity of the films reaches a maximum atx= 1.5. The activation energy of conductivity in the films, equal to 0.1–0.2 eV at low temperatures, rises upon partial dehydration above 100°C. The possible mechanisms of proton formation and transport are discussed.     

Analytic study of the temperature change in the flowing molten metal in sand casting

A system of differential equations is given for the heat transfer in the flow of a liquid alloy in the channels in casting sand, and a formula is derived for the temperature of the alloy at any given point at an arbitrary instant.Notation c₁ specific heat of liquid alloy, J/kg · deg - ₁ density of alloy, kg/m³ - heat transfer coefficient, W/m² · deg - ₁ effective heat transfer coefficient, W/m² · deg - P channel cross-section circumference, m - F cross-section of channel - t_g temperature at inner channel surface, °K - w flow velocity, m/sec - R half-thickness of channel, m - t₂ temperature of mold wall, °K - _sta time from start of alloy flowing in channel, sec - ₂ thermal conductivity of mold material, W/m · deg - t₀ initial mold temperature, °K - c₂ specific heat of mold material, J/kg · deg - ₂ density of mold, kg/m³ - a₂ thermal diffusivity, m₂/sec - km, b_a coefficients of heat accumulation by mold and alloy, W/sec^1/2/m² · deg - t_in temperature of alloy at inlet, °K Translated from Inzhenerno-Fizicheskii Zhurnal, vol. 20, No. 5, pp. 872–878, May, 1971.     

Study of thermal properties of glass system 77% B2O3-23% PbO doped with ZnO in the temperature range 300 to 700 K

The thermal properties: specific heat capacity (C _p), thermal conductivity (), and thermal diffusivity (a) of the glass system 77% B₂O₃-23% PbO doped with ZnO, were measured in the temperature range 300 to 700 K. It was found that electronic conduction has no significant contribution to the thermal conductivity. The main mechanism of heat transfer is therefore due to both phonons and photons. A discussion of the results is made in view of various theoretical aspects.     

Nonlinear hydromagnetic stability analysis of condensation film flow down a vertical plate

Summary In the present paper, the nonlinear stability of electrically conductive liquid condensation film that flows down a vertical flat plate is investigated analytically. The generalized kinematic equations for the film thickness with phase change at the interface is modified to take into account the effect of an uniform magnetic field applied transversely to the plate. The results show that both the supercritical stability and the subcritical instability still can be found in the magnetic fluid film flow system. The effect of the magnetic field (which was revealed as a Hartmann number,m) is to stabilize the film flow. Therefore, the instability could be counteracted by controlling the applied magnetic field. Moreover, this paper presents more accurate assessment for the instability of electrically conductive liquid film flow in a magnetic field.Nomenclature B ₀ strength of magnetic field - C _p specific heat of liquid - d d _r +id _i , complex wave celerity - g gravitational acceleration - h film thickness - h ₀ local base flow film thickness - h _fg latent heat - K liquid thermal conductivity - m , Hartmann number - Nd - W , dimensionless surface tension - p liquid pressure - p _g vapor pressure - Pe =Pr·Re, local Peclet number - Pr =C _p /K, Prandtl number - Re =u ₀ h ₀/, Reynolds number - S surface tension of liquid - t time - T liquid temperature - T _s vapor saturation temperature - T _w wall temperature - u ₀ , reference velocity - u, v velocity alongx- andy-direction, respectively - x, y coordinate along and transverse to the plate Greek symbols wave number - =C _p (T _s –T _w )/h _fg . Knudsen number - dimensionless disturbance film thickness - dimensionless temperature - fluid kinematic viscosity - liquid density - _s vapor density - electrical conductivity coefficient - liquid stream function - disturbance wavelength Supercripts * dimensionless quantities     

Perovskite-type lanthanum chromium-based oxide films prepared by ultrasonic spray pyrolysis

Ultrasonic spray pyrolysis was used to form 2–8 m thick LaCrO₃ films on different substrates from La(CrO₄)(NO₃)·nH₂O precursor films. There was an optimum substrate temperature for the formation of uniform precursor films by the spray pyrolysis. When the substrate temperature was lower than 250 °C, dry precursor films were not formed, while above 250 °C the deposition rate decreased with substrate temperature. The precursor films were converted to perovskite-type oxide films by heat treatment at 800 °C in a nitrogen atmosphere. Both A-site substituted (La_0.8Ca_0.2) CrO₃ and B-site substituted La(Cr_0.5Mn_0.5)O₃ oxide films were formed in a similar manner. Electronic conductivity of the oxide films was improved by repetitions of the spray pyrolysis and heat treatment in nitrogen.     

Preparation of high-T c superconducting film in the system of Bi-Sr-Ca-Cu-O from sol-gel process and its properties

High-T _c superconducting Bi₂Sr₂CaCu₂O_x films withT _c ^off =80 K were prepared by the dipping method of sol-gel processing using inorganic salts. The influence of the preparation conditions on the superconducting properties of the derived material is reviewed. Bi, Sr, Ca and Cu nitrates were used as raw materials. Glycerol was used as solvent. The thickness of films made by the dip method was about 0.5 m. The films were crystallized by heat-treatment at 830°C for 10 min.T _c ^off of films was 80 K andJ _c at 77 K was more than 8 kA cm^–2. Synthesis of high-T _c superconducting films was very easy and the crystallization of films was possible with a relatively low heat-treatment temperature.     

Microwave properties of highly oriented YBa2Cu3O7-δ superconducting thin films

We have performed millimeter-wave frequency (94 GHz) measurements on high-quality YBa₂Cu₃O₇- superconducting films on yttrium-stabilized (100) ZrO₂ and MgO substrates. The 0.2m thin films fabricated by magnetron sputteringin situ with the YBa₂Cu₃O₇- powders as target exhibit superconducting transition temperatures up to 88 K. The critical current density of 6×10⁵ A/cm² at 77 K and the X-ray diffraction spectrum as well as scanning electron microscope photographs indicate these thin films are fullyc-axis oriented, extremely high in density, and universally homogeneous. Millimeter-wave surface resistances have been measured on a hemisphere open resonator in the temperature range of 20 K toT _c and beyond. The surface resistance at 94 GHz and 77 K for these films is found to be about 30 m, nearly 1/4 that for copper, and a drop of two orders in the surface resistance within 4 K is observed, which indicates that these films are good materials for applications in the millimeter-wave range, especially for fabricating microwave devices. We observed such low surface resistance in these thin films due to the near absence of grain and phase boundaries coupled with a high degree of crystalline orientation.     

Thermopower measurements on SiO x thin films

Thermopower and d.c. electrical conductivity measurements have been carried out between 125 and 625 K on SiO _x thin films, 130 nm thick, deposited on to Corning 7059 substratesin vacuo 1 mPa at 1.5 nm sec^–1. The thermopower, d.c. conductivity and their respective activation energies are fitted to a polynomial expression in 1/T. Below 400 K, the thermopower is negative, at 400 K the thermopower activation energy is approximately zero and the dominant current carriers are holes at the valence band edge, between 400 and 470 they are polaronic holes, between 470 and 590 K non-polaronic holes, and above 590 K electrons. Energy band diagrams are proposed for each temperature range studied.     

Measurement of Thermal Conductivity of TiO2 Thin Films Using 3ω Method

TiO₂ film has been used in many industrial components such as laser filters, protection mirrors, chemical sensors, and optical catalysts. Therefore, the thermal properties of TiO₂ thin films are important in, e.g., reducing the thermal conductivity of ceramic coatings in gas turbines and increasing the laser damage threshold of antireflection coatings. The thermal conductivity of four kinds of TiO₂ thin films, prepared by dc magnetron sputtering, was measured using the 3 method in the temperature range from 80 K to room temperature. The results showed that the thermal conductivity of TiO₂ thin films strongly depends on the thickness and the microstructure of the films. The films with smaller grain size and thinner thickness have smaller thermal conductivities.     

Measurement of the effective thermal conductivity of agricultural products

This paper reports new measurements of the effective thermal conductivity of agricultural materials such as grains by means of the transient heat flow method using a line heat source. The effect of a probe diameter used for the transient heat flow method on the effective thermal conductivity was studied using standard spherical particles and some grains. It was concluded that the transient heat flow method can be applied to the measurement of the effective thermal conductivity of agricultural materials such as grains provided that the ratio of the probe diameter to the diameter of the particles of the specimen is greater than unity.Nomenclature A Area of heating surface - d Diameter of particles of the specimen - d _e Hydrodynamic diameter of particles of the specimen - E Error - H Distance between hot and cold walls - L Probe length - M Moisture content - N Number of contact points of particles of the speciment to the probe surface - Q Net heat flux - q Heat flux per probe length added to probe - R Probe radius - r Radial distance - T Temperature - T _h Surface temperature of the hot wall - T _c Surface temperature of the cold wall - t Time - _a Thermal conductivity of air - _eff Effective thermal conductivity - _s Thermal conductivity of a single kernel - Thermal diffusivity - _s Thermal diffusivity of a single kernel - Porosity - Euler constant (=0.5775...) - Angle Invited paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Comprehensive determination of potential-dependent heat- and mass-transfer characteristics of disperse materials

A method is proposed for parametric identification of a mathematical model of coupled heat and mass transfer (HMT) in a disperse medium.Notation T temperature of the medium, K - U concentration of substances distributed in the medium, kg/kg - a _m diffusion, m₂/sec - a _m ^T thermodiffusion, m²/(sec·K) - C, C₀, C_q specific heat capacity of the medium, the medium at U=0, and the substance distributed in the medium, J/(kg·K) - y₀ density of the dry material, kg/m³ - thermal conductivity, W/(m·K) - a diffusivity, m²/sec - j_m ^u, j_m ^T, j_m density of the diffusion, thermodiffusion, and total fluxes of the substances, kg/(m²·sec) - q heat flux, W/m² - x space coordinate - time Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 56, No. 5, pp. 773–779, May, 1989.     

Characteristics of nanostructure and electrical properties of Ti thin films as a function of substrate temperature and film thickness

Titanium films of different thickness at different substrate temperatures are prepared using PVD method. The nanostructure of these films was obtained using X-ray diffraction (XRD) and AFM, while the thicknesses were measured by means of Rutherford back scattering (RBS) technique. Resistivity, Hall coefficient, concentration of carriers and the mobility in these films are obtained. The results show that, the rutile phase of TiO₂ is formed which is initially amorphous and as the film thickness increases it tends to become textured in (020) direction, which is more pronounced at higher temperatures and possibly transforms to anatase TiO₂ with (112) orientation for thickest films of 224 nm. The conductivity and concentration of carriers increase with thickness, while the Hall coefficient and the mobility decrease. The activation energies in these samples were obtained from the Arrhenius plots of σ and R _H. For thinner films ( eV) and for thickest film (224 nm) a break point is observed at about 500 K, which is consistent with the idea of more processes becoming activated at higher temperatures.     

Transport properties of CdGa2Se4 thin films

The d.c. conductivity was determined for CdGa₂Se₄ thin films in the temperature range 300–625 K for as-deposited and heat-treated films. The conductivity at room temperature of films of thickness 326 nm prepared at a temperature of 573 K was found to be 10^–12 ( cm)^–1. The dependence of the electrical conductivity on the annealing temperature in a vacuum of 1 Pa for a thin film of thickness 140 nm, shows that the electrical conductivity increases with increasing annealing temperature. However, the activation energies E and E decrease with increasing annealing temperature. The data of these annealed films are in agreement with the Meyer–Neldel rule. The thermoelectric power measurements indicate p-type conduction in the as-deposited films as well as for the heat-treated films. The p-type conduction is due to the cadmium deficiency as indicated by EDX. The difference between the value of the activation energy calculated from the thermoelectric power E _S and that obtained from the conductivity E indicates the presence of long-range potential fluctuations.     

Thermocapillary stability during gravity flow of a liquid film

Thermocapillary rupture of a film under conditions of turbulent undulatory flow is associated with the buildup of wave motion on its surface. Here an approximate solution to the problem and criterial relations are obtained for determining the limits of stable film flow.Notation _min, kg/m·sec minimum irrigation intensity at which no film rupture occurs - ₁, kg/m· sec irrigation intensity at which the first dry spot appears - q, W/m² thermal flux density - _D, °C temperature at the rupture section - x, m space coordinate along the warm surface in the direction of flow - y, m coordinate in the direction normal to the warm surface - _o, m mean thickness of the film between large waves - _c, m thickness of the continuous layer - _cr, m critical film thickness - _o=/_o andl _o=l _o/_o dimensionless initial amplitude and length of a wave - , sec^–1 recurrence frequency of large waves - t_cr, sec time till thermocapillary rupture of a film - t_p, sec time of penetration of a thermal perturbation through the film thickness - u, m/sec velocity of thermocapillary flow of the liquid - , W/m·°C thermal conductivity - c_p, kJ/kg·°C specific heat - , kg/m linear density - , N·sec/m² dynamic viscosity - a, m²/sec thermal diffusivity - , N/m surface tension - , N/m² tangential stress at the film surface - L, m length of the warm pipe segment - L_o, m distance from the inlet to the section where wave motion at the film surface occurs - ¯w, m/sec mean velocity of downward flow of liquid in the film - , m mean thickness of the laminar layer - g, m²/sec free-fall acceleration due to gravity Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 4, pp. 581–591, October, 1980.     

Interaction of Pb and Sn with Thin Films of Their Oxides on Single-Crystal Silicon

Experimental data are presented on the interactions between Pb and thin SnO and SnO₂ films and between Sn and thin PbO films during vacuum annealing and subsequent heat treatment in flowing oxygen. The Pb and Sn films were deposited by magnetron sputtering onto single-crystal Si substrates; the SnO and SnO₂ films were produced by heat-treating Sn in flowing oxygen at 470 and 870 K, respectively; and the PbO films were obtained by heat-treating Pb films at 520 K. During annealing of Pb/SnO₂/Si heterostructures at 870 K in a vacuum of 0.33 × 10^–2 Pa, Pb reacts with lead oxides to form PbSnO₃, whereas vacuum annealing of Sn/PbO/Si heterostructures leads to the formation of SnO and Pb metal. The lead stannates forming in vacuum persist during subsequent heat treatment in flowing oxygen at atmospheric pressure at temperatures of up to 1120 K.     

Studies on microbridges of superconducting YBCO thin film

Critical current densities of the superconducting Y-Ba-Cu-O (YBCO) films have been observed to decrease with the increase of power of microwave radiation. Presence of Josephson type of junctions in the microbridges has been established from the microwave irradiation and magnetic field studies. BCS energy gap parameter (2/kT _c ) has been calculated from thedI/dV characteristics and found to be 3.7 at 13 K.     

Influence of radiation on the limits of heterogeneous combustion of a particle in two parallel reactions on its surface

The influence of radiation on critical parameters of heterogeneous ignition and extinction of a carbon particle in air is analyzed with allowance for two heterogeneous reactions.Notation Q _chem surface power of heat release through chemical reactions, W/m² - Q _h overall density of heat flux by molecular convectionQ _m.c. and radiationQ _i, W/m² - d particle diameter, m - t time, sec - T ₁,T ₂,T ₂,T _w particle gas, and reaction chamber wall temperature respectively, K - ₁, ₂ particle and gas density, kg/m³ - c ₁,c ₂ specific heat of particle and gas, J/(kg·K) - n _ox relative mass concentration of oxidant in the gaseous medium - q _i thermal effect of the first (i=1, C+O₂=CO₂) and the second (i=2, 2C+O₂=2CO) chemical reactions, J/kg - _i stoichiometric coefficient - E activation energy, J/mole - k _0i preexponential factor, m/sec - R universal gas constant, J/(mole·K) - Nu Nusselt number - ₂ thermal conductivity coefficient of gas, W/(m·K) - D ₂ diffusion coefficient of gas, m²/sec - ₂₀, ₂₀,D ₀ density, thermal conductivity, and diffusion coefficients of gas atT ₀ - emissivity coefficient - Stefan-Boltzmann constant, W/(m²·K⁴) - , heat- and mass-transfer coefficients, W/(m²·K), m/sec. Indexes: 1, particle - 2 gas - ign ignition - ext extinction - w wall - st steady - cr critical - in initial - c combustion - m maximum - lim limiting I. I. Mechnikov Odessa State University. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 3, pp. 466–473, 1995.