Impact of Heat Shield Structure in the Growth Process of Czochralski Silicon Derived from Numerical Simulation

Further development of the photovoltaic industry is restricted by the productivity of mono-crystalline silicon technology due to its requirements of low cost and high efficient photocells. The heat shield is not only the important part of the thermal field in Czochralski（Cz） mono-crystalline silicon furnace, but also one of the most important factors influencing the silicon crystal growth. Large-diameter Cz-Si crystal growth process is taken as the study object, Based on FEM numerical simulation, different heat shield structures are analyzed to investigate the heater power, the melt-crystal interface shape, the argon flow field, and the oxygen concentration at the melt-crystal interface in the process of large Cz-Si crystal growth. The impact of these factors on the growth efficiency and crystal quality are analyzed. The results show that the oxygen concentration on the melt-crystal interface and the power consumption of the heater stay high due to the lack of a heat shield in the crystal growth system. Argon circumfluence is generated on the external side of the right angle heat shield. By the right-angle heat shield, the speed of gas flow is lowered on the melt free surface, and the temperature gradient of the free surface is increased around the melt-crystal interface. It is not conducive for the stable growth of crystal. The shape of the melt-crystal interface and the argon circulation above the melt free surface are improved by the inclined heat shield. Compared with the others, the system pulling rate is increased and the lowest oxygen concentration is achieved at the melt-crystal interface with the composite heat shield. By the adoption of the optimized composite heat shield in experiment, the real melt-crystal interface shapes and its deformation laws obtained by Quick Pull Separation Method at different pulling rates agree with the simulation results. The results show that the method of simulation is feasible. The proposed research provides the theoretical foundation for the thermal field design of the large diameter Cz-Si monocrystalline growth.

Some Aerothermodynamic Aspects of ESA Entry Probes

Two different entry vehicles are presented here： the Inflatable Reentry and Descent Demonstrator （IRDT）, and Huygens. Both missions involve （re）entries at conditions close to orbital, and have been performed in 2005. Specific aspects of the design and the mission of IRDT are briefly outlined. The preliminary results of the recent flight of IRDT and the methodology followed at ESTEC for the assessment of radiative fluxes for Huygens are summarised.

Study on release rate of latent heat in Czochralski silicon growth

The pulling rate in czochralski silicon (CZSi) growth is important for reducing the cost of solar cell. In this paper, double-heater, heat shield and composite argon duct system were introduced in the Ф450 mm hot zone of a Czochralski furnace. The pulling rate under different thermal system was recorded in experiments. Argon flow and temperature fields were simulated by finite element method(FEM). Experimental results and numerical simulation indicate that double-heater and composite argon duct system can enhance obviously the release rate of latent heat. In Φ 200 mm Czochralski silicon (CZSi) growth, average pulling rate can increase from 0.6 mm·min-1 in the conventional hot zone to 0.8 mm·min-1 in the modified hot zone.

CONTROL OF TRANSPIRATION COOLING SYSTEM AND ITS CHARACTERISTICS

The mathematical model of three-dimensional transpiration cooling control system in heat shield was given, in general, it's a nonlinear control system on variable-domain mixed up with both distributed and concentrated parameters. It was pointed out that the thermal and ablative problems of the shield can be solved solely when the coolant flow is one-dimensional and incompressible or one-dimensional and steady. In regard to the surface ablating problem of the thermal shield, the control schemes of the system, including its simplified condition and the characteristics of one-dimensional point control, were suggested here. As far as the coolant is concerned, the solutions of the equilibrium state were given with or without the phase change.

Numerical and Experimental Characterizations of SiFRP Ablator for the Application to Liquid Rocket Engine Combustors

The ablative material is supposed to be one of good candidates for LRE （liquid rocket engine） combustion chamber to achieve both high reliability and low cost and a numerical analysis for the ablator is considered to be a potentially efficient tool to reduce cost as well. So far, ablators have been successfully applied for many SRM （solid rocket motors）, but the application to LRE is still quite limited in Japan. The authors believe that this is primarily because of the unpredictable nature of the heat load from combustion gases to the combustor wall. Indeed, reliable thermal design of ablative combustion chamber, namely reliable prediction of thermal performance, needs both reliable heat load model and reliable ablator response model. This paper elaborates our research activities and our recent research findings.

Hydrothermal Synthesis of Cs_xWO_3 and the Effects of N_2 Annealing on its Microstructure and Heat Shielding Properties

Cesium tungsten bronze （CsxW03） powders were synthesized by hydrothermal reaction at 190 ℃ by using sodium tungstate and cesium carbonate as raw materials, and the effects of N2 annealing on the microstructure and near-infrared （NIR） shielding as well as heat insulation properties of CsxW03 were investigated. The results indicated that the synthesized CsxW03 powders exhibited hexagohal CSo.32WO3 crystal structure, and subsequent N2 annealing could further improve the crystallinity of CsxW03 particles. Moreover, the NIR shielding and heat insulation properties of CsxW03 could be further improved after N2 annealing at appropriate temperature for a period of time. Particularly, the 500 ℃-annealed CsxW03 products in the N2 atmosphere showed the best NIR shielding and heat insulation properties. When the N2 annealing temperature was higher than 700 ℃, the NIR shielding properties decreased again. The 800 ℃-annealed samples in the N2 atmosphere showed higher visible light transmittance, however, the NIR shielding properties were lower than that of the non-annealed samples.

Heat Shielding Effects in the Earth＇s Crust

Knowledge of heat flow and associated variations of temperature with depth is crucial for understanding how the Earth functions. Here, we demonstrate possible heat shielding effects that result from the occurrence of mafic intrusions/layers（granulitic rocks） within a dominantly granitic middle crust and/or ultramafic intrusions/layers（peridotitic rocks） within a dominantly granulitic lower crust; heat shielding is a familiar phenomenon in heat engineering and thermal metamaterials. Simple one-dimensional calculations suggest that heat shielding due to the intercalation of granitic, granulitic and peridotitic rocks will increase Moho temperatures substantially. This study may lead to a rethinking of numerous proposed lower crustal processes.