Giorgio Galli

Analysis of thermal field within an urban canyon with variable thermophysical characteristics of the building's walls

In a typical urban configuration, a microclimatic analysis has been carried out. Using a CFD method, a N-S oriented urban street canyon, with a given H/W ratio, has been examined. The standard k-e turbulence model has been used to simulate a three-dimensional flow field and to calculate the thermo-fluid dynamics parameters that characterize the street canyon. In this study has been analyzed the thermal flow field when the walls of the building change the properties of solar radiation absorption, in particular for α=0.2 and α=0.8. Solar radiation considered is that of 21/07 in Milan in two different hours: at 11:00 a.m. and at 02:00 p.m. The study shows the importance of the thermophysical properties of a wall, in the development of the thermal field and flow field. This is a very important topic, in terms of improvement of wellbeing and the quality of the air within the cities, through the choice of materials and colors of the facades of buildings.

Speckle-Based Deflection Techniques in Diffusivity Measurements

Optical techniques have a long tradition in flow visualization, allowing both qualitative and quantitative analysis. In particular, speckle photography, introduced in 1968, has been extensively used. The aim of this work is to discuss speckle-based deflection techniques in the investigation of diffusion phenomena in liquids.

Diffusion Measurements Using DOE Schardin’s Schlieren #2 Technique

The diffusion process is very important in many engineering applications. However, there is a shortage of data about diffusion, especially between liquid mixtures (such as water and glycerin, water and salt, etc.), which justifies the search for simple and accurate experimental techniques.Optical techniques are recognized as powerful tools to investigate fluid flow phenomena in transparent media.The aim of this paper is the development of an optical experimental technique, based on Diffractive Optical Element (DOE) Schardin’s schlieren # 2, for measuring liquid diffusion coefficient. This technique is then coupled to a new data treatment, based on correlation algorithms of the Particle Image Velocimetry (PIV) type, allowing the use of displacements recorded in the entire cell rather than just between two points.Principles of the method and preliminary experimental results for the diffusion of a 1.75 M (moles/l) aqueous solution of common salt (NaCl) in pure water are given. These results are in good agreement with the literature.Copyright

Electromagnetic Transient Effects on Thermal Field for Plane Electrical Conductors

Effect of fast electromagnetic transient on the thermal field in plane conductors is evaluated by means of the numerical simulation of the one-dimensional current and temperature distributions. It was found that non negligible heating may occur along the conductor edge for electromagnetic pulse time constants lower than 10-3 s. Also, it is shown that the heat exchange coefficient ¿h¿ produces a negligible influence on temperature distribution.

First Principles Simulations of Extended Defects at Cubic SiC Surfaces and Interfaces

In this paper, we will review some recent investigations on extended def ects in cubic SiC, as obtained from first-principles molecular dynamics. As an exampl e of defects at surfaces, the formation of self-assembled nanowires, originating from coordination def ects at the Carbon terminated SiC(001) surface is discussed. Furthermore, the mechanism governing the creation of a network of edge dislocations at the SiC/Si interface is presente d. This system, characterized by a peculiar ~20% lattice mismatch, can be considered as a template of high lattice mismatched heterostructures, where an ab initio approach is still affordable. We will discuss differences and similarities between the (001) and (111) interfaces, and compare our r esults with recent experimental data.