Mehdi Baneshi

Numerical Study of Non-Gray Radiation and Natural Convection Using the Full-Spectrum k-Distribution Method

The interaction of non-gray radiation and natural convection in a 2-D cavity is studied numerically. The aim of this work is to analyze the thermal and flow behaviors of real cases with a small temperature difference using the full-spectrum k-distribution method. In addition, the results are obtained for different medium assumptions like pure convection, transparent medium, and gray medium to investigate which assumption is appropriate to be used instead of non-gray calculations. The results show that the gray medium assumption for radiative heat transfer is suitable to be used in cavities with normal air mixture at normal room conditions.

Infrared Radiative Properties of Thin Polyethylene Coating Pigmented With Titanium Dioxide Particles

The infrared (IR) radiative properties of TiO 2 pigment particles must be known to perform thermal analysis of a TiO 2 pigmented coating. Resins generally used in making pigmented coatings are absorbing at IR wavelengths, which means that the conventional Mie solution (MS) may not be adequate in this domain. There are two approaches to evaluating radiative properties in an absorbing medium: far field approximation (FFA) and near field approximation (NFA). In this study, after reviewing these two approaches, we evaluated the radiative properties of TiO 2 particles in polyethylene resin as an absorbing matrix in the wavelength range of 1.7-15 μm based on the MS, FFA, and NFA. We then calculated the effective scattering and absorption coefficients for different models. To investigate the effect of the particle size and volume concentration on the transmittance of IR wavelengths, we made a nongray radiative heat transfer in an anisotropic scattering monodisperse pigmented layer, with independent scattering using the radiation element method by the ray emission model. The results showed that all three approaches predicted similar results in the particle size domain and volume fraction range utilized in pigmented coatings.

Control of radiative properties of coatings pigmented with Fe 2O 3 nanoparticles

This study describes nanoparticles pigmented coatings used in controlling the radiative properties of surfaces exposed to sunlight. An optimization method that embraces both thermal and aesthetic requirements has been proposed. The proposed coatings maximize the reflectivity of the near infrared (NIR) region to reduce thermal heating, while for aesthetic appeal they minimize the visible (VIS) reflected energy. This spectral behavior can be achieved by controlling the size and concentration of pigment particles and coating thickness. In this study, both experimental and numerical approaches are applied on Fe2 O3 pigmented coating samples with 0.2 μm and 1 μm of average particle size and different particle concentrations and coating thicknesses. For numerical part the radiation analysis using the Radiation Element Method by Ray Emission Model (REM2 ) in a one dimensional parallel plane model is conducted. From the numerical results, it is shown that the optimum size of Fe2 O3 particles for our desired spectral behavior is about 0.8 μm. The experimental results also show that the samples made from 1 μm particles have better performance for our objective.Copyright

AESTHETIC AND THERMAL PERFORMANCES OF BLACK CUPRIC OXIDE AND TITANIUM DIOXIDE NANO-PARTICULATE COATINGS

Nano-particulate coatings with high reflectance against solar irradiation can control undesirable thermal heating by sunlight absorption. It can reduce the energy consumption for air conditioning of houses and cars. For the objects covered by these coatings and subjected to human sight, e.g. roofing surfaces, high dazzle of reflected visible light can offend the human eyes and spoil the fine view of covered objects. A new optimization method in designing pigmented coatings which considers both thermal and aesthetic effects by controlling the material, size and concentration of pigment particles is introduced. Our proposed coatings maximize the reflectance of near infrared (NIR) region to care the thermal effects and minimize the visible (VIS) reflected energy to keep the dark tone because of aesthetic appeal. Black cupric oxide and white titanium dioxide are considered as the pigment particles in this study. The optimum characteristics and performances of theses two pigments are obtained and compared. The results show that cupric oxide has much better performance for our objective.