SESSION 12

APPLICATIONS OF RADIATION

Chairman: S.T. Surzhikov

NEAR INFRARED SPECTROSCOPY AND IMAGING

Matthew R. Jones
Department of Aerospace & Mechanical Engineering
The University of Arizona
Tucson, Arizona 85721 USA

ABSTRACT

Advances in the area of opto-electronics which allow the detection of low intensity light have increased interest in the study of light propagation in turbid media. One of the most exciting applications of these emerging technologies is the use of near infrared spectroscopy and imaging in medicine. Since the absorption of photons by biological tissues is low in the 700-900 nm spectral region, it is feasible to use near infrared radiation as a medical probe. Few advancements have had a greater impact on medical science than the development of techniques to non-invasively determine the internal structure of biological tissues. Many view the development of near infrared spectroscopy and imaging techniques as the next important step in the continued improvement of this vital area of medical science. The use of near infrared radiation has two primary advantages over the use of x-rays. The first advantage is that near infrared light is non-ionizing, so it is safer than x-rays. The second advantage is that the near infrared absorption spectra of biological tissue depends on the functional status of the tissue, so near infrared spectroscopy and imaging can provide functional as well as structural information. However, unlike x-rays, near infrared radiation is highly scattered by biological tissues. Therefore, image reconstruction and spectroscopic techniques capable of extracting useful information from multiply scattered light are necessary. This paper describes some techniques that are being developed to measure the optical properties and to obtain images of biological tissues from an analysis of multiply scattered radiation.

RADIATION AND THERMOPHORESIS INTERACTION IN LAMINAR FREE CONVECTION

Yaman Yener and Hanlin Weng
Northeastern University, Boston, MA 02115, U.S.A.
and
Jean-Paul Magnaud
CEA-Saclay, 91191 Gif/Yvette Cedex, France

ABSTRACT

The interaction between radiation and thermophoresis in laminar free convection along a vertical cold surface is investigated. The fluid is a radiatively nonparticipating constant-property gas containing emitting, absorbing and isotropically scattering gray aerosol particles. The radiative properties of the gas-aerosol mixture are considered to be proportional to the local concentration of particles in the mixture. The vertical surface, maintained isothermal at a temperature lower than the fluid bulk temperature, assumed to be opaque, gray, and diffusely emitting and diffusely reflecting. Formal relations developed by the use of the Galerkin method are presented for the solution of the radiation part of the problem. An iterative numerical solution scheme is implemented by making use of the Keller block elimination method to solve the momentum, energy and particle concentration equations. Various results are presented in graphical forms to demonstrate the effects of thermophoresis and radiation on the velocity, temperature and particle concentration distributions.

RADIATIVE HEAT TRANSFER IN A LAYER OF ANISOTROPIC SCATTERING FOG SUBJECTED TO COLLIMATED IRRADIATION

Shigenao MARUYAMA
Institute of Fluid Science, Tohoku University
Aoba-ku, Katahira 2-1-1, Sendai 980-77, Japan

The radiation element method by ray emission model[1], REM², is applied to plane parallel and anisotropic scattering participating media. The proposed method, REM², is applicable to arbitrary thermal conditions in radiation elements and at boundary surfaces. The boundary surfaces can be specular and/or diffuse[2]. Both collimated and diffuse incident irradiation can be adopted at a boundary surface. The proposed method can be used to analyze a variety of thermal and boundary conditions, simply by changing the parameters of the radiation elements.

The provisos method [1] requires that the participating medium is isotropic. In order to include anisotropic scattering media, a delta function approximation is applied. Gas absorption due to participating gases such as H₂O and CO₂ is taken into account by employing a statistical narrow-band model.

The proposed method is applied to a modeled fog consisting of water droplets, humid air layers and a specular boundary surface subjected to an oblique collimated flux.

In the Pacific Ocean near the coast of Sendai in Japan, fog is observed on the sea surface during the summer. This fog is formed because a cold current in the sea interacts with warm humid air, resulting the formation of mist in the air. In order to simplify the model, mono-dispersed water droplets of diameter suspended in the humid air are considered. The modeled fog is illustrated in Fig. 1. The thickness of the fog layer is x_l m and the number density of water droplets is n_p m^-3.

A collimated solar flux of intensity q_c,s is irradiated onto the fog layer at an incident angle of . The specular reflectivity of the interface between the sea surface and the fog layer is approximated by the normal reflectivity of water. The value can be determined using electromagnetic theory and the complex refractive index of water .

The solar flux transmitted through the modeled fog becomes smaller as and x_l X n_p increase. The transmitted solar flux is calculated for both isotropic and anisotropic scattering phase functions. The flux of isotropic scattering particles shows smaller value than that with an anisotropic phase function.

The direction of radiation flux for a long wavelength of infrared region is from water surface towards the sky, and its intensity is about 5 to 10 % of transmitted solar flux. The radiation flux for a long wavelength is affected by gas absorption. This is negligible for the case of large particle number density and low partial pressure of water vapor. The radiation flux becomes smaller for the case of small particle density and humid air.

The temperature close to the sea surface is higher than that of the upper fog layer. The temperature jump at the interface between the sea and the fog layer is large for a optically thin fog.

REFERENCES

1. Maruyama, S. and Aihara, T., Radiation Heat Transfer of Arbitrary Three-Dimensional Absorbing, Emitting and Scattering Media and Specular and Diffuse Surfaces, ASME J. Heat Transfer, Vol. 119, pp. 129-136, (1997).
2. Maruyama, S., Radiation Heat Transfer Between Arbitrary Three-Dimensional Bodies with Specular and Diffuse Surfaces, Numerical Heat Transfer, Part A, Vol. 24, pp. 181-196, (1993).

Fig. 2 Analysis model of the sea fog irradiated by solar radiation.

OPTICAL DIAGNOSTICS OF PARTICLES IN HIGH-TEMPERATURE FLOWS

Olga S.Vaulina, Anatoli P.Nefedov, Oleg F.Petrov, Alez l. Samarian
High Energy Density Research Center
Russian Academy of Sciences, IVTAN. Izhorskaya. 13/19.
Moscow, 127412, Russia

Abstract

A combination of novel methods for determining the temperature, mean size, concentration and spectral refractive index of particles in high-temperature flows is presented. The technique is based on empirical inverting the forward-scattering transmittance and spectral emission-absorption measurements. The measurements are successfully inverted for the SiO₂, CeO₂, and ash particles in combustion flows. The particle temperature, concentration, mean size, and complex refractive index are retrieved.