Theoretical prediction of the anisotropic effective thermal conductivity of composite materials, Paper n.86114

The composite is made of a matrix and a fiber-reinforced material to form a non-homogeneous anisotropic material. Thermal behaviour of composite materials is very important in many applications as heat shields and heat guides. The present paper investigates theoretically a composite material made of a silica matrix and a fiber reinforcement made of steel. The steady state effective thermal conductivity in the main directions are calculated theoretically for two extreme thermal assumptions, i.e. parallel isothermal lines and parallel heat flux lines. The effective thermal conductivity of the composite is evaluated for a variable thickness of the reinforcement, i.e. for a variable volume fraction. The anisotropy degree, defined as the ratio between the thermal conductivities along the two main directions, increases with the ratio between the thermal conductivities of the reinforcement material and the matrix. The composite material, made of two homogeneous and isotropic materials, is thermally anisotropic and can be used to drive heat towards colder regions. This phenomenon is very useful when a device, such as a spacecraft, must be thermally protected

Experimental measurements of pressure, temperature and dust velocities in case of LOVA: Comparisons with a multiphase numerical model

The production of dust inside the nuclear fusion power plants is one of the safety issues of this technology. Dust is generated because of plasma-material interactions and subsequently it deposits in the bottom regions of the TOKAMAK. In case of a Loss Of Vacuum Accident (LOVA), the dust may be resuspended, threatening the functioning and the safety of these reactors. A deep study of this phenomenon is required to develop countermeasures and to improve the safety of this promising way to produce energy. The authors have studied the fluid dynamics of these accidents with a scaled experiment, called STARDUST-Upgrade. Optical techniques have been implemented to measure dust resuspension and diffusion properties, such as velocity vectors and resuspension rate. This work shows the results obtained with a new numerical model able to take into account also the dispersed phase (dust). The software uses the Euler-Euler approach, a Schiller-Naumann resistance model, and a k-ε turbulence model. The dust used is tungsten dust, that has been placed close to the inlet valve in both cases (numerical and experimental). The numerical results are analysed and compared with the experimental ones and the main agreements and differences are highlighted. The results show good accordance with the velocity vectors of dust, while the resuspension rate is overestimated in the numerical case because of the absence of adhesion and cohesion forces between dust particles and walls. This analysis is the starting point for the evolution and completion of a numerical model suitable for dust resuspension in case of LOVAs

3D numerical simulations of a LOVA reproduction inside the new facility STARDUST-UPGRADE

A loss of vacuum in a vessel, containing or not dust, is the typical case study considered in the STARDUST-UPGRADE facility of the Quantum Electronics and Plasma Group of the university of Rome Tor Vergata. This kind of accident was simulated numerically, without including the presence of dust, for two mass flow rates and three different inlet ports (C, E and F). Numerical settings are explained and the results obtained in each case are shown and discussed. At the end of the work, conclusions about what seen and further foreseen developments of this research are presented

Application of optical techniques to detect chemical and biological agents

Chemical or biological contamination, due to natural or man-made disasters, represents a severe concern for safety and security of people, and of the environment. Chemical agents (CAs) and biological agents (BAs) are commonly used for a number of civilian and military applications, and can be deployed as a weapon with terroristic purposes. Therefore, it is necessary to develop specific systems aimed at preventing or reducing the consequences of the spread of these agents. To this end, the authors have developed optical systems to detect (LIDAR) and identify (DIAL) CAs, and to detect BAs (fluorescence technique). These systems and technologies will be presented in this work together with the analysis and discussion of the results obtained