Total and local heat transfer from a smooth circular cylinder in cross-flow at high reynolds number

The total and local heat transfer from a smooth circular cylinder to the cross flow of air has been measured over the Reynolds number range 3 × 10⁴ < Re < 4 × 10⁶. The interaction between flow and heat transfer is discussed. In particular, the boundary-layer effects on the heat transfer, such as transition from laminar to turbulent flow or boundary-layer separation, are considered in conjunction with the distributions of local static pressure and skin friction.     

Estimation of convective mass transfer in solar distillation systems

In this article a thermal model has been developed to determine the convective mass transfer for different Grashof Number range in solar distillatiOn process. The model is based on simple regression analysis. Based on the experimental data obtained from the rigorous outdoor experimentation on passive and active distillation systems for summer climatic conditions, the values of C and n have been calculated. The modified values of C and n for Nu=C(GrPr)ⁿ, are proposed as C=0.0322; N=0.4114 for 1.794 × 10⁶6 in a passive solar still and C=0.0538; N=0.383 for 5.498 × 10⁶6 in an active solar still. The percentage deviation between experimental and theoretical results are found within an accuracy of 12%.     

Electrical and optical properties of F-doped textured SnO2 films deposited by APCVD

This paper presents the structural, electrical and optical properties of transparent conducting F-doped textured SnO₂ films prepared by atmosphere pressure chemical vapour deposition (APCVD). Polycrystalline SnO₂:F films having a variable preferred orientation have been obtained with resistivity as low as 5 × 10⁻⁴ Ωcm, with carrier concentrations between 3.5 × 10²⁰ and 7 × 10²⁰ cm⁻³, and Hall mobilities from 15.7 to 20.1 cm²/V/s. The average transmittance (including diffusion transmittance) is as high as 94% in the wavelength range of the visible spectrum and the maximum infrared reflectance reaches 92% for a film 655 nm thick. The figure of merit ƒ_TC = T10/_sh, (7.12 × 10⁻² S) of these films is the highest amongst the results reported on doped SnO₂ films.     

A group of improved heat and mass transfer correlations in solar stills

Based on the analogy of heat and mass transfer and an empirical correlation, a group of improved heat and mass transfer correlations in basin type solar stills is established. In order to validate the correlation group, a multi-stage stacked tray solar still with basin area of 0.665×0.650 m² is constructed of aluminum sheets. By comparison of the calculated results with the measurement results, which were obtained from our steady state simulated experiments and reported in previous literature, it is found that the correlation group developed in this work can provide better predictions for the evaporation rate of basin type solar stills at the wide range of Rayleigh number (3.5×10³<Ra<2.26×10⁷) and temperature (35<T_w<86 °C).     

Preparation and properties of transparent conducting zinc oxide and aluminium-doped zinc oxide films prepared by evaporating method

Undoped and aluminium-doped zinc oxide films have been prepared by thermal evaporation of zinc acetate [Zn(CH₃COO)₂ 2H₂O] and aluminium chloride [AlCl₃] onto a heated glass substrate. The structural and optoelectrical properties of the films have been studied. The effects of heat treatment for the as-deposited films in air and vaccum are investigated. Highly transparent films with conductivity as low as 2×10⁻³ Ω cm can be produced by controlling the deposition parameters. The electron carrier densities are in the range 0.2–7×10¹⁹ cm⁻³ with mobilities of 22–58 cm² V⁻¹ s⁻¹.     

Heat transfer of a plate in a liquid flow

The paper presents results of the experimental investigation of heat transfer of a plate in a flow of air, water and transformer oil at different directions of heat flow over the range of Re_f numbers from 2 × 10⁴ to 3 × 10⁷ and that of Pr_f—from 0.701 to 380. Formulae were obtained to calculate heat transfer of a plate in a liquid flow.     

Influence of free-stream turbulence intensity on heat transfer in the two-dimensional turbulent boundary layer of an accelerated compressible flow

For the accelerated compressible flow in a two-dimensional convergent-divergent nozzle the influence of free-stream turbulence on heat transfer in the turbulent boundary layer has been investigated empirically. The turbulence intensity varied from nearly zero to about 20%, the nozzle entrance Reynolds number reached up to about 10⁷. The experimental set-up and the turbulence measurement technique are carefully described. For three different loading cases the measured data of free-stream turbulence intensity and fluctuation are given along the nozzle axial length as well as the local Stanton number in comparison to those of accelerated flow without free stream turbulence. For low Reynolds numbers (Re_x < 10⁶) no clear change of heat transfer has been observed, while for Re_x < 10⁶ a weak and nearly linear dependency of Stanton number on free-stream turbulence intensity can be pointed out.     

A correlation for heat transfer by natural convection from horizontal cylinders that accounts for viscous dissipation

Eight previously published correlation equations plus one new correlation for heat transfer by natural convection from horizontal isothermal cylinders are tested against a fairly extensive body of experimental data culled from the literature for 10⁻⁸ < Ra < 10⁸ and 0.7 < Pr < 4 × 10⁴. The new equation, which represents the Nusselt number as a function of the Prandtl and Rayleigh numbers plus an additional dimensionless parameter that accounts for viscous dissipation, is shown to correlate the experimental data more accurately than does any one of the eight previously published equations. It is concluded that viscous dissipation may not be neglected in all cases of natural convection from horizontal cylinders, and further, that the inclusion of a viscous dissipation term in certain related problems, such as natural convection in porous media, may lead to more accurate correlation equations.     

The calculation of wall and fluid temperatures for the incompressible turbulent boundary layer, with arbitrary distribution of wall heat flux

Numerical solution of the partial differential equation for heat transfer in the incompressible turbulent boundary layer has been obtained for uniform (q_w/ρC_pu_i)/√(c_f/2) and for Prandtl numbers 0–7, 1 and 7. The Spalding boundary-layer velocity law was assumed, and the Schmidt method of integration used. Boundary-layer temperature distributions up to x⁺ = 10⁶ are presented, together with the “Spalding function” St/√(c_f/2). A method is given for the application of the solutions to the case of arbitrary distribution of heat flux at the wall.     

Synthesis and characterization of CuInSe2 thin films from Cu, In and Se stacked layers using a closed graphite box

Various techniques have been used to produce CuInSe₂ but the problem of producing films with the desired properties for efficient device fabrication over large areas has always persisted. The Stacked Elemental Layer (SEL) technique has been demonstrated as a method for producing films over a large area, but the films normally annealed in vacuum or in Se ambient, mostly exhibited poor morphology with small grain sizes which result in poor devices. A method of synthesizing CuInSe₂ films by annealing or selenization of the Cu, In and Se elemental layers using a closed graphite box was developed. SEM, EDX, XRD, spectrophotometric and Hall measurements were used to characterize all annealed films. Results have shown single phase chalcopyrite films with improved crystal sizes of about 4 μm The film composition varied from Cu-rich to In-rich with electrical resistivities of 10⁻³ to 10⁴ Ωcm, cattier concentrations of 5 × 10¹⁵ to 10¹⁷ cm⁻³ and mobilities of 0.6 to 7.8 cm² V⁻¹ s⁻¹ An energy band gap of 0.99 eV and 1.02 eV was obtained for a Cu-rich and near stoichiometric In-rich films respectively. Heterojunction devices using the structure ZnO/CdS/CuInSe₂ were fabricated with electrical conversion efficiencies of 6.5%.     

Waste incineration and energy recovery

We discuss the implications of waste incineration on energy production at currently achieved conversion efficiencies to electricity and for realistic estimates of incinerable fractions of municipal, hazardous, and biomedical wastes. We find approximate steady-state contributions in the U.S. of 6.1 × 10³, (3.0–3.9) × 10³ and 0.5 × 10³ MW_e for these three technologies, respectively. A combustion-research agenda for waste incinerators is summarized briefly. Its implementation may be expected to contribute to the efficacious development of waste-incineration technologies and associated energy recovery.     

Out of the cell performance of reforming catalysts for direct molten carbonate fuel cells (DMCFC)

Nickel catalysts supported on commercial MgO and LiAlO₂ have been tested and compared in the methane steam reforming reaction at temperatures ranging from 798 to 923 K and GHSV from 5.4 × 10⁶s⁻¹ to 5.4 × 10⁸s⁻¹. Initial molar ratio of the reactants, R = P_H2O/P_CH4 was 2.54. Results of the influence of the catalyst reduction temperature have been reported. Preliminary results of the reaction kinetic analysis, adopting first order pseudohomogeneous model, are given. The suitability of using these catalysts into the molten carbonate fuel cells (MCFC), to generate hydrogen directly by the methane steam reforming, is discussed.     

Chimney effect in a “T” form cavity with heated isothermal blocks: The blocks height effect

In this paper, a numerical study of natural convection from a two dimensional “T” form cavity with rectangular heated blocks is conducted. The blocks are identical, and the domain presents a symmetry with respect to a vertical axis passing through the middle of the opening. The governing equations are solved using a control volume method, and the SIMPLER algorithm for the velocity–pressure coupling is employed. Special emphasis is given to detail the effect of Rayleigh number and block height on the heat transfer and the flow rate generated by the chimney effect. The results are given for the parameters of control as, 10⁴Ra3×10⁶, Pr=0.71, opening diameter (C=l^′/H^′=0.15), blocks gap (D=d^′/H^′=0.5) and blocks height (1/8B=h^′/H^′1/2). These results show that the heat transfer variation with Ra is in the same manner as those met in the case of the vertical smooth or ribbed channels.     

Some aspects of free-convective heat transfer in eddy flow through a horizontal tube

Experimental investigation of unsteady-state free convection in a horizontal cylindrical channel is carried out for the case of non-uniform distribution of heat flux along a channel at a constant temperature on the wall. The averaged temperature field in a gas was investigated on a Mach-Zender interferometer. Hydrodynamic structures were investigated by the smoke visualization technique. Heat fluxes were calculated on the basis of thermocouple measurements. In the case of non-uniform heat flux on the channel wall, the existence of longitudinal large scale hydrodynamic structures has been noted. Longitudinal and lateral Rayleigh numbers varied from 0 to 4 × 10⁹ and from 0.8 × 10⁴to 1.2 × 10⁵, respectively. Investigations were carried out with air, carbon dioxide and helium flows.     

Chemical storage of solar energy kinetics of heterogeneous SO3 and H2O reaction—Reaction analysis and reactor design

The first energy recovery step in the ammonium hydrogen sulfate (AHS) cycle is the formation of H₂SO₄(l) from H₂O(g) and SO₃(g). It has been determined that the optimum way to accomplish this is by the use of a double pipe tubular reactor. In this paper, a mathematical model for the reactor is presented, applied to the three reaction zones, and a method of numerical solution discussed. Three horizontal pilot-scale configurations, 0.234 × 10⁶ to 5.863 × 10⁶ kJ/h energy release, are discussed and sizing presented. Also, the results for a vertical configuration are presented. The need for additional work on two-phase gas-liquid flow in condensing systems and in annuli has been identified. The most important conclusion is that a high temperature can be achieved in the reactor by the use of a front end adiabatic section followed by nonadiabatic sections to recover the heat released.     

Heat and mass transfer laws for fully turbulent wall flows

The general method of Izakson and Millikan for the derivation of the well-known Prandtl-Nikuradse skin friction law is applied to the analysis of turbulent heat and mass transfer in pipes, channels, and boundary layers. The formula for the heat (or mass) transfer coefficient (or the Nusselt number) is obtained which contains the dimensionless coefficients of the universal logarithmic equations for the velocity and temperature profiles as parameters of the formula. One of these parameters is a universal function of Prandtl (or Schmidt) number and all the others are constants. The existing velocity and temperature profile measurements in various turbulent wall flows permit the determination of all the necessary coefficients with fair accuracy. The resulting calculations are in satisfactory agreement with numerous experiments on heat and mass transfer in pipes and boundary layers on a flat plate over the Prandtl (or Schmidt) number range from 6 × 10⁻³ to 10⁶ and over two orders of magnitude of Reynolds (or Péclét) number variations.     

Optical and electrochemical characteristics of niobium oxide films prepared by sol-gel process and magnetron sputtering A comparison

Electrochromic niobia (Nb₂0₅) coatings were prepared by the sot-gel spin-coating and d.c. magnetron sputtering techniques. Parameters were investigated for the process fabrication of sol-gel spin coated Nb₂0₅ films exhibiting high coloration efficiency comparable with that d.c. magnetron sputtered niobia films. X-ray diffraction studies (XRD) showed that the sot-gel deposited and magnetron sputtered films heat treated at temperatures below 450°C, were amorphous, whereas those heat treated at higher temperatures were slightly crystalline. X-ray photoelectron spectroscopy (XPS) studies showed that the stoichiometry of the films was Nb₂0₅. The refractive index and electrochromic coloration were found to depend on the preparation technique. Both films showed low absorption and high transparency in the visible range. We found that the n, k values of the sot-gel deposited films to be lower than for the sputtered films. The n and k values were n = 1.82 and k = 3 × 10⁻³, and n = 2.28 and K = 4 × 10⁻³ at 530 urn for sot-gel deposited and sputtered films, respectively. The electrochemical behavior and structural changes were investigated in 1 M LiC10₄/propylene carbonate solution. Using the electrochemical measurements and X-ray photoelectron spectroscopy, the probable electrode reaction with the lithiation and delithiation is Nb₂O₅ + x Li⁺ + x e⁻ ↔ Li_xNb₂0₅. Cyclic voltametric (CV) measurements showed that both Nb₂0₅ films exhibits electrochemical reversibility beyond 1200 cycles without change in performance. “In situ” optical measurement revealed that those films exhibit an electrochromic effect in the spectral range 300 < λ < 2100 nm but remain unchanged in the infrared spectral range. The change in visible transmittance was 40% for 250 nm thick electrodes. Spectroelectrochemical measurements showed that spin coated films were essentially electrochemically equivalent to those prepared by d.c. magnetron sputter deposition.     

High temperature rate coefficient for the reaction of O(P) with H2 obtained by the resonance absorption of O and H atoms

The reaction of O(³P) with H₂ has been studied behind reflected shock waves in the temperature range of 1713–3532K at total pressures of about 1.4–2.0 bar by Atomic Resonance Absorption Spectroscopy using mixtures of N₂O and H₂ highly diluted in Ar. The O atoms were generated by the fast thermal decomposition of N₂O and the reaction with H₂ was followed by monitoring the time dependent O and H atom concentrations in the postshock reaction zone. For the experimental conditions chosen, the measured O and H atom concentrations were primarily sensitive to the well-known N₂O dissociation and to the studied reaction and hence its rate coefficient could be deduced. The measured rate coefficient data are fitted by the least-squares method to obtain the following three parameter expression: K₄=3.72×10⁶(T/K)^2.17exp(−4080K/T)cm³ mol⁻¹8⁻, which is in excellent agreement with the recent ab initio calculations for the rate coefficient of this reaction in the overlapping temperature range. The present result is also compared to the experimental results reported by earlier investigators.     

Assessment of oil and natural gas resources in the Gulf Cooperation Council countries

This paper deals with the assessment of oil and natural gas resources in the Gulf Cooperation Council. Currently, the reserves of oil and natural gas are estimated at 461.70 × 10⁹ barrels and 615.58 × 10¹² SCF, respectively. Data are given and analyzed on reserves and production for the period 1978–1989.     

Natural convection heat transfer enhancement in horizontal concentric annuli using nanofluids

Heat transfer enhancement in horizontal annuli using nanofluids is investigated. Water-based nanofluid containing various volume fractions of Cu, Ag, Al₂O₃ and TiO₂ nanoparticles is used. The addition of the different types and different volume fractions of nanoparticles were found to have adverse effects on heat transfer characteristics. For high values of Rayleigh number and high L/D ratio, nanoparticles with high thermal conductivity cause significant enhancement of heat transfer characteristics. On the other hand, for intermediate values of Rayleigh number, nanoparticles with low thermal conductivity cause a reduction in heat transfer. For Ra = 10³ and Ra = 10⁵ the addition of Al₂O₃ nanoparticles improves heat transfer. However, for Ra = 10⁴, the addition of nanoparticles has a very minor effect on heat transfer characteristics.