Chuang Sun

Temperature Dependence of Optical Constants for Chinese Liquid Hydrocarbon Fuels in the Near-Infrared (NIR) Region from Room Temperature to 400 K

An improved double-thickness method combined with genetic algorithm was developed to determine the optical constants of liquid hydrocarbon fuels. Different from traditional transmission measurement, it obtained the total transmittance of a window–liquid–window three-layer structure, which is the ratio of the transmission intensity of the filled cell and that of the empty sample compartment. Also, the change of the surface reflectance at the interface of the liquid sample and the optical window and the difference between forward reflection and back reflection are considered. Experiments were operated to measure spectra in the wavelength range of 0.83–2.2 µm using a Fourier transform infrared (FT-IR) spectrometer. To verify the reliability of this method, optical constants of the distilled water were determined from its experimental transmittance spectra and the results agreed well with published data. On the basis of verification, the transmittance spectra of Chinese No. -35 diesel fuel were measured at 300 K, 350 K, and 400 K with liquid sample thicknesses of 0.5 mm and 1.0 mm. Then the optical constants of the diesel sample were obtained and the temperature dependence was analyzed. Analytical results indicate that the biggest change of the extinction coefficient between 300 K and 400 K can reach 30%, while that of the refractive index is 4.7%.

Analysis on Concentrating Radiation Transfer to Solar Array with Concentrator

An algorithm of ray tracing Monte Carlo method was developed to simulate concentrating characteristics of solar radiation transfer to solar array with an ideal shape solar concentrator (ISSC). The effects of the solar angle, slope error and tracing error on the concentrated solar flux were investigated, and a uniformity factor is defined to evaluate the concentrating solar beam. The results of calculation show that the non-uniform factors lie in the range from 0.6 to 0.8 under these influencing effects.

Radiative Heat Transfer in Participating Medium and Dynamic Region Monte Carlo Method by Region Adaption

A dynamic region Monte Carlo method (DRMC) is proposed to simulate radiative heat transfer in participating medium. The basic principle and solution procedure of this method is described; radiative heat transfer in a two-dimensional rectangular region of absorbing, emitting, and/or scattering gray medium is analyzed. A comparison between DRMC and the traditional Monte Carlo method (TMC) is investigated by analyzing the simulated temperature distribution, the computing time, and the number of the sampling bundles. The investigation results show that, to compare with TMC, the DRMC can obviously reduce the computing time and storage capacity under the same solution precision for radiative transfer in optically thick medium; the DRMC allows bypassing the difficulties encountered by TMC in the limit of optically thick extinction.

Spectral backward Monte Carlo method for surface infrared image simulation

The surface infrared radiation is an important part that contributes to the infrared image of the airplane. The Monte Carlo method for the infrared image calculation is suitable for the complex geometry of targets like airplanes. The backward Monte Carlo method is prior to the forward Monte Carlo method for the usually long distance between targets and the detector. Similar to the non-gray absorbing media, the random number relation is developed for the radiation of the spectral surface. In the backward Monte Carlo method, one random number that reverses the wave length (or wave number) may result deferent wave numbers for targets’ surface elements on the track of a photon bundle. Through the manipulation of the densities of a photon bundles in arbitrary small intervals near wave numbers, all the wave lengths corresponding to one random number on the targets’ surface elements on the track of the photon bundle are kept the same to keep the balance of the energy of the photon bundle. The model developed together with the energy partition model is incorporated into the backward Monte Carlo method to form the spectral backward Monte Carlo method. The developed backward Monte Carlo method is used to calculate the infrared images of a simple configuration with two gray spectral bands, and the efficiency of it is validated by compared the results of it to that of the non-spectral backward Monte Carlo method . Then the validated spectral backward Monte Carlo method is used to simulate the infrared image of the SDM airplane model with spectral surface, and the distribution of received infrared radiation flux of pixels in the detector is analyzed.

Backward Monte Carlo analysis on stray radiation of an infrared optical system

In an infrared optical system, the thermal radiation of high temperature components is the major noise as stray radiation that degrades the system performance. Backward Monte Carlo method based on radiation distribution factor is proposed to perform the stray radiation calculation. Theoretical deduction and some techniques are presented, considering the semitransparent element like IR window as radiation emitter. The radiation distribution factors are calculated with ray tracing from the detector to radiation sources. Propagation of stray radiation and its distribution on the detector are obtained simultaneously. It is unnecessary to implement ray tracing again to study the effect of different temperatures for a given system, expect that the geometry or radiative property is changed. An infrared system is simulated using this method. Two different situations are discussed and the analysis shows that stray radiation is mainly created by IR window and lens tube.

Sensitivity Analysis of Sensor Probe for Low Thermal Diffusivity Properties Measurement

Single probe and dual probes are always taken adopt to measure the materials thermal conductivity and thermal diffusivity. The measurement principle of the two kinds of probes is different and introduced in this article. Taken the material which has low thermal diffusivity for example, the single probe and dual probes are compared by the calculation accuracy and temperature response sensitivity. Numerical simulation results show that, under the same conditions, the thermal properties obtained by the dual probes are closer to the true value for the test material, but single probe has more sensitive at temperature response.

Thermal Response Characteristics of Flat Plate Heated by High Temperature and High Speed Flow

According to the view of heat transfer, the process of the fluid flow with high temperature and high speed over a flat plate may be considered as the heat transfer process within a compressible thermal boundary layer. Based on the numerical results of thermal isolation assumption, combining the temperature comparison with modification method, a coupled method of convection heat transfer coefficient with temperature field of the plate is established, and the characteristics of the thermal response for the flat plate is dominated. Take some ribbed plates as instances, the convection heat transfer coefficient and temperature field of the plate are simulated through the provided coupled method. The results show that, not only the position and materials of the plate influence the convection heat transfer coefficient, but also the time.

Research on Temperature Field for Spacial Solar Array

The solar array which provides most of energy for the satellite plays a very important role. And the conversion coefficient of solar cell used in the solar array is directly influenced by the array temperature, which is also responsibility for the stability and safety of satellite, especially for the solar array. This paper discusses the solar array temperature fields under different situations, including the periods of the satellite operating in spring, summer and winter. Obtaining the incidence angle of the solar array in the three periods, the radiative heat flux is computed by Monte Carlo method (MCM) and the finite volume method (FVM) is employed to win the temperature field, with the harmonic mean value being used for the heat transfer at interface between different materials. The results show that, the temperature fields of the solar array are quite different for various seasons, and the highest temperature of the array is 308 K in spring, the lowest temperature is 225 K in summer, which is caused by the shadow of the earth.