Tan Heping

Transient and Steady-State Combined Heat Transfer in Semi-Transparent Materials Subjected to a Pulse or a Step Irradiation

A numerical analysis based on the finite difference scheme and Hottel’s zonal method generalized by the ray tracing method is carried out to treat the one-dimensional transient and steady-state combined radiative-conductive heat transfer in non-gray Semi-Transparent Materials (STM), especially glasses, subjected to an external pulse or a step of irradiation. Coupling problems are studied for two optical boundary conditions: opaque and vitreous interfaces with specular reflections. The influence of slab thickness, spectral properties of the STM, wavelength of the incident radiation, and diffusivity coefficient are examined. It is pointed out that the application of the laser flash method in thermal metrology may give irrelevant results if the basic heat transfer model is not able to take into account radiative-conductive coupling phenomena. The effect of semi-transparency on the steady-state temperature distribution is also examined for materials ranging from fully opaque to fully transparent.

Inverse radiation problem of temperature field in three-dimensional rectangular furnaces

The discrete ordinates method is used to developed a solution to an inverse radiation problem of temperature field in rectangular furnaces. It is assumed that, with the exception of the inhomogeneous temperature field, all aspects of the radiation transport problem are known. A method is developed to determine the inhomogeneous temperature field from specified incident radiation heat fluxes at the centers of boundary walls. The inverse problem is solved using conjugate gradient method that minimize the error between the incident radiation heat fluxes calculated and the experimental data. The results of temperature estimation show that the temperature field can be estimated accurately, even with noisy data.

Inverse radiation problem in one-dimensional semitransparent plane-parallel media with opaque and specularly reflecting boundaries

Abstract The discrete ordinates method is used to develop a solution to an inverse radiation problem of source term in one-dimensional semitransparent plane-parallel media with opaque and specularly reflecting boundaries. It is assumed that, with the exception of the inhomogeneous source term, all aspects of the radiation transport problem are known. A method is developed to determine the inhomogeneous source term from specified incident radiation intensities on the boundaries. The inverse problem is solved using conjugate gradient method that minimizes the error between the incident radiation intensities calculated and the experimental data. The effects of single-scattering albedo, scattering asymmetry parameter, wall emissivity, the diffuse fraction of reflectivity, and the optical thickness on the accuracy of the inverse analyses are investigated. The results show that the source term can be estimated accurately, even with noisy data.

Effect of anisotropic scattering on radiative heat transfer in two-dimensional rectangular media

Abstract Effect of scattering on radiative heat transfer in two-dimensional rectangular media by the finite-volume method has been studied. Compared with the existing solutions, it shows that the result obtained by the finite-volume method is reliable. Furthermore, relative errors caused by the approximation that linear and nonlinear anisotropic scattering media is simplified to isotropic scattering media have been studied.

Simultaneous reconstruction of temperature distribution and radiative properties in participating media using a hybrid LSQR–PSO algorithm*

A hybrid least-square QR decomposition (LSQR)-particle swarm optimization (LSQR–PSO) algorithm was developed to estimate the three-dimensional (3D) temperature distributions and absorption coefficients simultaneously. The outgoing radiative intensities at the boundary surface of the absorbing media were simulated by the line-of-sight (LOS) method, which served as the input for the inverse analysis. The retrieval results showed that the 3D temperature distributions of the participating media with known radiative properties could be retrieved accurately using the LSQR algorithm, even with noisy data. For the participating media with unknown radiative properties, the 3D temperature distributions and absorption coefficients could be retrieved accurately using the LSQR–PSO algorithm even with measurement errors. It was also found that the temperature field could be estimated more accurately than the absorption coefficients. In order to gain insight into the effects on the accuracy of temperature distribution reconstruction, the selection of the detection direction and the angle between two detection directions was also analyzed.

Inverse Radiation Problem of Boundary Incident Radiation Heat Flux in Semitransparent Planar Slab with Semitransparent Boundaries

An inverse method is presented for estimating the unknown boundary incident radiation heat flux on one side of one-dimensional semitransparent planar slab with semitransparent boundaries from the knowledge of the radiation intensities exiting from the other side. The inverse problem is solved using conjugate gradient method of minimization based on discrete ordinates method (DOM) of radiative transfer equation. The equations of sensitivity coefficients are derived and easily solved by DOM, with the result that the complicated numerical differentiation commonly used in solving sensitivity coefficients is avoided. The effects of anisotropic scattering, absorption coefficient, scattering coefficient, boundary reflectivity, fluid temperature outside the boundaries, convection heat transfer coefficients, conduction coefficient of semitransparent media and slab thickness on the accuracy of the inverse analysis are investigated. The results show that the boundary incident radiation heat flux can be estimated accurately, even with noisy data.

Solar thermochemical hydrogen production using metallic oxides

ABSTRACT Hydrogen energy can help in solving the problem of greenhouse gas emissions which results in reduced global warming and stress on the fossil fuel supply and price, provided that hydrogen is produced by clean processes involving renewable energy. Solar hydrogen production via two-step thermochemical cycle is an appealing technique. This article attempts to present a review with aspect to solar thermochemical hydrogen production redox pairs, reactor design technology, general assessment, etc. Some novel reactors have been designed for different redox pairs in recent decade years. We give a comparison between different hydrogen technologies and summarize the problems that exist in the cycle. Though solar thermochemical hydrogen production technique is a promising and potential roacute to solve energy crisis problem, it still has many problems that need to be solved in the future.

Thermal emission of a disc body of semitransparent material

By introducing the concept of radiosity intensity to diffuse surfaces, the ray tracing method is improved to analyze the thermal emission of a disc body of gray semitransparent material. The two plane surfaces of the disc body are both specularly reflecting, and the flank surface is either diffusely reflecting or specularly reflecting. The apparent thermal emission from one plane surface is investigated with considering the influences of the characteristic optical thickness, the dimensionless radius, the refractive index of the material and the reflecting characteristics of the flank surface. The directional and hemispherical emissions show considerable differences under different reflecting characteristics of the flank surface. Moreover, in some cases, the emission not only varies with the viewing direction but also with the apparent emitting position on the plane surface. Some interesting results are presented and discussed.

First-principles study of electronic and optical properties of boron and nitrogen doped graphene

First-principles study have been performed to investigate the effects of boron (B) and nitrogen (N) co-doping and the effect of varying dopant concentration on electronic and optical properties of graphene. The band structure, density of states (DOS) plots and optical properties are calculated for BN rings doped structures. It was observed that, BN rings doped graphene structure shows a direct band gap opening which increases by increase in the number of BN rings present in the graphene sheet, also a significant red shift in absorption towards visible region is found to occur and the absorption peak at 14 eV energy reduces by increasing number of BN rings in graphene sheet. These findings can be helpful to engineer the band structure and in tailoring the optical properties in visible region for graphene.

Inverse radiation problem in one-dimensional semitransparent plane-parallel media

The discrete ordinates method is used to develop a solution to an inverse radiation problem of source term in one-dimensional semitransparent plane-parallel media with opaque and specularly reflecting boundaries. It is assumed that, with the exception of the inhomogeneous source term, all aspects of the radiation transport problem are known. A method is developed to determine the inhomogeneous source term from specified incident radiation intensities on the boundaries. The inverse problem is solved using conjugate gradient method that minimizes the error between the incident radiation intensities calculated and the experimental data. The effects of single-scattering albedo, scattering asymmetry parameter, wall emissivity, the diffuse fraction of reflectivity, and the optical thickness on the accuracy of the inverse are investigated. The results show that the source term can be estimated accurately, even with noisy data.