Asymmetry of Hawking Radiation of Dirac Particles in a Charged Vaidya–de Sitter Black Hole

The Hawking radiation of Dirac particles in a charged Vaidya–de Sitter black hole is investigated by using the method of generalized tortoise coordinate transformation. It is shown that the Hawking radiation of Dirac particles does not exist for P₁, Q₂ components, but for P₂, Q₁ components it does. Both the location and the temperature of the event horizon change with time. The thermal radiation spectrum of Dirac particles is the same as that of Klein-Gordon particles.     

Infrared spectral radiative properties of high temperature gas with multi-component

The shock layer of high-speed missiles is a highly uneven gas medium with multi-component and high temperature. Its spectral radiation effects degrade and distort the remote sensing images of infrared sensors. The exact numerical calculating method of the shock wave thermal radiation noise has been developed in this paper. With the multi-temperature model and the rectangular grid recursive method of ray tracing, atomic-molecular absorption and emission spectra of CO₂, H₂O and N₂ were obtained along the line of sight along the seeker detectors. Based on image degradation evaluation criteria and the wind tunnel experimental results, how images blurred by the proposed model were verified. The relations between the shock wave thermal radiation noise and flow parameters were also analyzed. For the 3–8 μm infrared band, shock wave thermal radiation noise is little effected by flight altitude, and close relations with Mach number, as the empirical formula given.     

Numerical prediction of heat transfer by natural convection and radiation in an enclosure filled with an isotropic scattering medium

This paper deals with the numerical solution for natural convection and volumetric radiation in an isotropic scattering medium within a heated square cavity using a hybrid thermal lattice Boltzmann method (HTLBM). The multiple relaxation time lattice Boltzmann method (MRT-LBM) has been coupled to the finite difference method (FDM) to solve momentum and energy equations, while the discrete ordinates method (DOM) has been adopted to solve the radiative transfer equation (RTE) using the S8 quadrature. Based on these approaches, the effects of various influencing parameters such as the Rayleigh number (Ra), the wall emissivity (ε_ι), the Planck number (Pl), and the scattering albedo (ω), have been considered. The results presented in terms of isotherms, streamlines and averaged Nusselt number, show that in absence of radiation, the temperature and the flow fields are centro-symmetrics and the cavity core is thermally stratified. However, radiation causes an overall increase in the temperature and velocity gradients along both thermally active walls. The maximum heat transfer rate is obtained when the surfaces of the enclosure walls are regarded as blackbodies. It is also seen that the scattering medium can generate a multicellular flow.     

Unsteady boundary layer flow of a nanofluid over a stretching sheet with variable fluid properties in the presence of thermal radiation

In this paper, we investigated numerically an unsteady boundary layer flow of a nanofluid over a stretching sheet in the presence of thermal radiation with variable fluid properties. Using a set of suitable similarity transformations, the governing partial differential equations are reduced into a set of nonlinear ordinary differential equations. System of the nonlinear ordinary differential equations are then solved by the Keller-box method. The physical parameters taken into consideration for the present study are: Prandtl number Pr, Lewis number Le, Brownian motion parameter N _b, thermophoresis parameter N _t, radiation parameter N _r, unsteady parameter M. In addition to these parameters, two more new parameters namely variable thermophoretic diffusion coefficient parameter e and variable Brownian motion diffusion coefficient parameter β have been introduced in the present study. Effects of these parameters on temperature, volume fraction of the nanoparticles, surface heat and mass transfer rates are presented graphically and discussed briefly. To validate our method, we have compared the present results with some previously reported results in the literature. The results are found to be in a very good agreement.     

Species and temperature predictions in a semi-industrial MILD furnace using a non-adiabatic conditional source-term estimation formulation

A Reynolds-Averaged Navier–Stokes (RANS) simulation of the semi-industrial International Flame Research Foundation (IFRF) furnace is performed using a non-adiabatic Conditional Source-term Estimation (CSE) formulation. This represents the first time that a CSE formulation, which accounts for the effect of radiation on the conditional reaction rates, has been applied to a large scale semi-industrial furnace. The objective of the current study is to assess the capabilities of CSE to accurately reproduce the velocity field, temperature, species concentration and nitrogen oxides (NO_x) emission for the IFRF furnace. The flow field is solved using the standard k–ε turbulence model and detailed chemistry is included. NO_x emissions are calculated using two different methods. Predicted velocity profiles are in good agreement with the experimental data. The predicted peak temperature occurs closer to the centreline, as compared to the experimental observations, suggesting that the mixing between the fuel jet and vitiated air jet may be overestimated. Good agreement between the species concentrations, including NO_x, and the experimental data is observed near the burner exit. Farther downstream, the centreline oxygen concentration is found to be underpredicted. Predicted NO_x concentrations are in good agreement with experimental data when calculated using the method of Peters and Weber. The current study indicates that RANS-CSE can accurately predict the main characteristics seen in a semi-industrial IFRF furnace.     

The solution of inverse radiation problems using an efficient computational technique

In our previous work (Park, Kim, JQSRT 58 (1) (1997) 115), an efficient computational technique for solving the radiative transfer equations for participating media has been devised, which is as accurate as the S₄ method but consumes much less computer time. In the present investigation, we employ this technique to solve an inverse radiation problem of determining the time-varying strength of a heat source, which mimics flames in a furnace, from temperature measurements in three-dimensional participating media where radiation and conduction occurs simultaneously. The present technique is found to identify the strength of the heat source efficiently without a priori information about the unknown function to be estimated.     

Investigation of the Radiation Mechanism of Microwave Excited Cluster Lamps

Experimental and theoretical investigations towards a better understanding of the radiation mechanisms in WO₂Br₂-discharges, so-called “cluster lamps” are presented. The main purpose of the investigation is to find out whether a major part of the continuum emitted from these discharges, which in the past has been interpreted as thermal cluster radiation, could also originate from molecular band radiation, in particular from triatomic molecules in colder discharge regions. Comparing emission spectra of WO₂Br₂-discharges from different plasma regions, using lamps operated at different vapor pressures and power levels (i.e. non-LTE and LTE-discharges), we conclude that by far the major part of the strong continuum radiation emitted from WO₂Br₂ lamps is indeed thermal radiation of hot tungsten cluster particles. WO— (below 550 nm) and WO₂-molecular radiation (above 650 nm), which is superimposed on the cluster continuum, also contribute to the total radiation output, but to a lesser degree. A crude model for WO₂ molecular emission is presented. Unfortunately, the WO₂ emission component greatly impedes proper fitting of the measured cluster continuum to a thermal cluster model.     

Dimensionless heat transfer correlations for estimating edge heat loss in a flat plate absorber

Data obtained from heat transfer relations discretized with the finite element method were used in developing dimensionless correlations, which led to determining prediction equations for the average edge temperature of a flat plate absorber. For a prescribed flux, if parameters like the incident radiation intensity, edge insulation thermal conductivity and ambient temperature are known, the value of the edge temperature variable is immediately determined. A range of edge-to-absorptive area ratios is considered, as well as the effects of the edge insulation on enhancing thermal performance. Notably, the edge loss is high in absorbers with high edge-to-absorptive area ratios and ambient conditions with low h _a and T _a . In extreme operating conditions, however, the loss can be employed of a high proportion. As a result, prediction equations are obtained, which can be employed in design and simulation so as to minimize useful energy losses and thereby improve efficiency.     

Nanocrystals formation on Ho doped strontium barium niobate glass

The study of two different methods to obtain strontium barium niobate nanocrystals immersed in a glass matrix has been carried out. Ho₂O₃-doped SrO-BaO-Nb₂O₅-B₂O₃ glasses were fabricated using the melt quenching method. Glass ceramic samples were obtained from the precursor glass by thermal treatment in a furnace and by laser irradiation. These glass ceramic samples are formed by a glassy phase and a crystalline phase of strontium barium niobate nanocrystals. This structure was confirmed by X-ray diffraction and Atomic Force Microscope images. The incorporation of Ho³⁺ ions in the strontium barium niobate nanocrystals were corroborated by optical measurements, which produced an increment in the luminescence intensity compared to the precursor glass.     

Three-dimensional non-grey gas radiative transfer analyses using the statistical narrow-band model

Three-dimensional non-grey gas radiation analyses were conducted using the statistical narrow-band model with updated band parameters and three implementation methods: the exact or the correlated formulation, the non-correlated expression, and the grey-band approximation with the absorption coefficient estimated using the local properties. The accuracy of the two approximate narrow-band implementation methods was evaluated for both low-resolution spectral intensity and spectrally integrated radiative source term and wall heat flux in a rectangular enclosure containing (1) isothermal pure water and (2) a CO₂/H₂O/N₂ mixture with a furnace type gas temperature distribution. For spectrally integrated quantities, results of the grey-band approximation are very close to those of the non-correlated formulation and are in qualitative agreement with the results of the correlated formulation. The two approximate methods are capable of predicting qualitatively correct and fairly accurate distributions of low-resolution spectral radiation intensities for the isothermal case. However, they predict less accurate low-resolution spectral intensities for the non-isothermal case.     

Utilization of blast furnace slag nano-fluids in two-phase closed thermos-syphon heat pipes for enhancing heat transfer

This article deals with utilization of blast furnace slag nano-fluids in two-phase closed thermo-syphon heat pipes for enhancing heat transfer at various states of operation. The utilization of nano-fluids obtained from X₂O₃-, XO-, XO₂-, and X₂O-type oxides, such as Al₂O₃, Fe₂O₃, CaO, SiO₂, MgO, MnO, K₂O, and Na₂O, on the improvement of heat pipe performance has been separately reported in a number of studies in the literature. The present study experimentally demonstrated the effect of using a nano-fluid obtained from blast furnace slag comprised of various types of metal oxides in varying ratios on improving the performance of a heat pipe. The slag was obtained from the iron blast furnace of Karabük Iron Steel Workings (Turkey). Triton X-100 (Dow Chemical Company) dispersant was used in the study to produce the blast furnace slag/water nano-fluid via direct-synthesis. The 2 wt% concentration of blast furnace slag/water nano-fluid was used as the working fluid in heat pipes. A straight copper tube with an inner diameter of 13 mm, outer diameter of 15 mm, and length of 1 m was used as the heat pipe in the present experimental study. The nano-fluid filled 33.3% (44.2 ml) of the volume of the two-phase closed thermo-syphon. Three heating power levels (200, 300, and 400 W) were used in the experiments with three different flow rates of cooling water (5, 7.5, and 10 g/s) used in the condenser for cooling the system. An increase of 22% was achieved in thermal performance of the two-phase closed thermo-syphon when 2 wt% blast furnace slag containing nano-fluid was used to replace pure water at a heat load of 200 W with a cooling water flow rate of 5 g/s.     

X-ray investigation of the mean square thermal displacements in VDx, NbHx and TaHx interstitial alloys

X-Ray measurements of the integrated Bragg intensities from V, Nb and Ta single crystals as a function of hydrogen (D) concentration and temperature have been carried out. Two different methods were applied: (i) the usual angular dispersive method using MoK_α1 characteristic radiation; and (ii) the energy dispersive method using the white spectrum of the Mo tube and an intrinsic Ge detector. From the results the thermal Debye-Waller factor for the three metals and its change with hydrogen concentration are determined. The mean square of the thermal displacements (u²) decreases with hydrogen (D) concentration. For NbH_x(D_x) this agrees well with (u²) values as determined from measured phonon density of states spectra. The results are also given in terms of a Debye temperature depending on H(D) concentration.     

Pulsed laser deposition and annealing of Dy-Fe-B thin films on melt-spun Nd-Fe-B ribbons for improved magnetic performance

Pulsed laser deposition of 250-nm thick, amorphous Dy₂Fe₁₄B layers on 40-μm thick Nd₂Fe₁₄B melt-spun ribbons was conducted to improve coercivity and energy product. The coated ribbons were subsequently annealed by two methods: (1) furnace annealing in an inert-gas controlled quartz furnace using tantalum foil at 1173 K for 2 h; (2) laser annealing using a continuous wave CO₂ laser with power varying from 10 to 20 W for 0.2 s (estimated temperatures using a thermal model were 993-1528 K). X-ray diffraction was used to identify the microstructural phases and grain size. Magnetic hysteresis tests were conducted at 300 K using a SQUID magnetometer with a maximum field of 5.0 T. Results showed a 10% increase in coercivity and 30% increase in energy product in coated over uncoated samples that were furnace-annealed. However, the coated and laser-annealed samples exhibited soft magnetic behavior with almost zero coercivity. The incomplete crystallization of amorphous phase and precipitation of α-Fe during laser annealing are found to be responsible for the observation of poor magnetic performance.     

A CFD assisted control system design with applications to NO x control in a FGR furnace

In this paper, a novel technique to design control systems for industrial processes with non-linear distributed parameters is proposed. The technique utilizes computational fluid dynamics (CFD) simulation to extract the most essential characteristics from the non-linear industrial process, and then represent them as a set of linear dynamic models around a specific operating point. Based on the linear dynamic representation, a closed-loop feedback linear control system can be designed to maintain the desired performance for the system around the chosen operating point. To illustrate such a design process, an industrial reheating furnace with flue gas recirculation (FGR) is selected herein. The method involves the numerical solution of the partial differential equations describing the fluid flow, heat transfer and combustion process in the furnace. The resulting dynamic relations between the furnace inputs and outputs can then be represented in terms of a multi-input and multi-output transfer function matrix. The objective of the control system is then to maintain the optimally selected furnace operating conditions and compensate for any deviations caused by disturbances to minimize the nitric oxides (NO _x ) emission through feedback mechanisms. The performance of the closed-loop controlled furnace is evaluated not only in the linear domain, but also with the detailed full-scale non-linear CFD model. The results have shown that the proposed method is viable and the designed control system can indeed minimize the deviation of the furnace from the desired operating conditions and hence to prevent any excessive NO _x formation in the combustion process.     

Growth of large La2−xSrxCuO4 single crystals using tilting-mirror-type infrared heating image furnace

Large single crystals of La_2−xSr_xCuO₄ (LSCO) high-T_c superconductors were grown by the infrared heating floating zone (IR-FZ) method using a tilting-mirror-type image furnace. The maximum diameter of the LSCO crystals increased to 10 mm in the tilting-mirror-type image furnace from 6 mm in the conventional image furnace. CuO rich feeds were required for the crystal growth using the tilting-mirror-type image furnace to compensate for the lack of CuO caused by the significant evaporation of CuO during the growth. The evaporation of CuO was affected by the tilting angle of the mirrors of the image furnace and by feed diameter. The optimized growth conditions were as follows: mirror tilting angle, 20°; feed diameter, 10 mm∅; and feed composition 50.7 mol% CuO.     

High precision materials processing using a novel Q-switched CO2 laser

Holes with diameters of about 400 µm have been laser trepanned in Ti6Al4V and carbon fibre reinforced polymer (CFRP) thin sheets with a thickness of 0.5 mm. A commercial CO₂ laser (SM1500E, FEHA LaserTec, Germany) and a novel Q-switched CO₂ laser (µ-storm, IAI, Netherlands) were used as radiation sources. Optical microscopy, scanning electron microscopy and replicas of the processed holes were used to investigate the influence of the CO₂ laser pulse parameters (e.g. pulse energy, duration and peak power) on the processing quality. It was shown that melt formation and high temperature oxidation reactions of Ti6Al4V during thermal laser processing were reduced significantly by using short and high intense Q-switched CO₂ laser pulses. During trepanning of CFRP heat affected zones resulting from the extremely different thermal properties (melting and vaporisation temperature, heat conduction) of the reinforcing carbon fibres and the polymer matrix were reduced significantly by using the Q-switched CO₂ laser. The results demonstrate that Ti6Al4V and CFRP can be processed very precisely with CO₂ laser radiation and air as processing gas without melt formation and thermal damage.     

Numerical investigation of the partial oxidation process in porous media based reformer

Numerical investigation of the thermal partial oxidation process of Methane in porous media based reformer is performed. A finite volume based CFD code, including radiation modeling, in combination with a detailed chemical kinetics scheme is used to perform the numerical simulation. A heterogeneous approach for the heat transport modeling in porous media (separate coupled energy equations for the gas and solid phases) was used. Validation of the model with experimental data is also performed. The model was able to predict the temperature behavior in the reformer reasonably well. However, the concentrations of H₂ and CO were under predicted while the H₂O concentration was over predicted.     

Rare-earth doped (Lu0.85Y0.15)2SiO5 nanocrystalline powders obtained by polymer assisted sol–gel synthesis

In the present work we explored the possibility of obtaining nanocrystalline (Lu_0.85Y_0.15)₂SiO₅ (LYSO) powders using polymer assisted sol–gel method. The synthesis started from TEOS as alkoxide precursor while polyethylene glycol with average molecular weight of 4000 was used as fuel. The resulting powders were obtained by firing gels in two ways: in conventional furnace and in microwave oven, with further annealing. This modified sol–gel synthetic route enabled production of pure phase LYSO powders at much lower temperatures (1050 °C) compared to classical, -solid-state methods (1400 °C). Crystallization kinetics are examined using differential thermal analysis, and rather low values of crystallization activation energies (around 12 kJ/mol) were found, revealing good potential of this method for low-temperature production of LYSO powder.     

Evaluation of downstream-mixing scheme for 9.4-µm CO2 gasdynamic laser

A theoretical analysis of a downstream-mixing 16-μm CO₂ gasdynamic laser revealed the possibility of utilizing the downstream-mixing scheme for the generation of 9.4-μm radiation using a CO₂ gasdynamic laser. The flow-field has been analyzed using complete two-dimensional, unsteady laminar form of Navier-Stokes equations coupled with the finite rate vibrational kinetic equations. The analysis showed that integrated small-signal gain of 11.5m⁻¹ for Lorentzian broadening and 4.8m⁻¹ considering Voigt function can be obtained for N₂ reservoir temperature of 2000°K and velocity ratio 1:1 between the CO₂ and N₂ mixing streams. These results (presented in graphs) clearly highlight the large potential of downstream-mixing CO₂ gasdynamic laser for 9.4-μm laser generation.