Magnetohydrodynamic Effects On Mixed Convection Flows In Channels And Ducts

This work focuses on magnetohydrodynamic (MHD) mixed convection flow of electrically conducting fluids enclosed in simple 1D and 2D geometries in steady periodic regime. In particular, in Chapter one a short overview is given about the history of MHD, with reference to papers available in literature, and a listing of some of its most common technological applications, whereas Chapter two deals with the analytical formulation of the MHD problem, starting from the fluid dynamic and energy equations and adding the effects of an external imposed magnetic field using the Ohm's law and the definition of the Lorentz force. Moreover a description of the various kinds of boundary conditions is given, with particular emphasis given to their practical realization. Chapter three, four and five describe the solution procedure of mixed convective flows with MHD effects. In all cases a uniform parallel magnetic field is supposed to be present in the whole fluid domain transverse with respect to the velocity field. The steady-periodic regime will be analyzed, where the periodicity is induced by wall temperature boundary conditions, which vary in time with a sinusoidal law. Local balance equations of momentum, energy and charge will be solved analytically and numerically using as parameters either geometrical ratios or material properties. In particular, in Chapter three the solution method for the mixed convective flow in a 1D vertical parallel channel with MHD effects is illustrated. The influence of a transverse magnetic field will be studied in the steady periodic regime induced by an oscillating wall temperature. Analytical and numerical solutions will be provided in terms of velocity and temperature profiles, wall friction factors and average heat fluxes for several values of the governing parameters. In Chapter four the 2D problem of the mixed convective flow in a vertical round pipe with MHD effects is analyzed. Again, a transverse magnetic field influences the steady periodic regime induced by the oscillating wall temperature of the wall. A numerical solution is presented, obtained using a finite element approach, and as a result velocity and temperature profiles, wall friction factors and average heat fluxes are derived for several values of the Hartmann and Prandtl numbers. In Chapter five the 2D problem of the mixed convective flow in a vertical rectangular duct with MHD effects is discussed. As seen in the previous chapters, a transverse magnetic field influences the steady periodic regime induced by the oscillating wall temperature of the four walls. The numerical solution obtained using a finite element approach is presented, and a collection of results, including velocity and temperature profiles, wall friction factors and average heat fluxes, is provided for several values of, among other parameters, the duct aspect ratio. A comparison with analytical solutions is also provided, as a proof of the validity of the numerical method. Chapter six is the concluding chapter, where some reflections on the MHD effects on mixed convection flow will be made, in agreement with the experience and the results gathered in the analyses presented in the previous chapters. In the appendices special auxiliary functions and FORTRAN program listings are reported, to support the formulations used in the solution chapters.

Advanced solutions for authenticity and quality of virgin olive oils

This Ph.D. project aimed to the development and improvement of analytical solutions for control of quality and authenticity of virgin olive oils. According to this main objective, different research activities were carried out: concerning the quality control of olive oil, two of the official parameters defined by regulations (free acidity and fatty acid ethyl esters) were taken into account, and more sustainable and easier analytical solutions were developed and validated in-house. Regarding authenticity, two different issues were faced: verification of the geographical origin of extra virgin (EVOOs) and virgin olive oils (VOOs), and assessment of soft-deodorized oils illegally mixed with EVOOs. About fatty acid ethyl esters, a revised method based on the application of off-line HPLC-GC-FID (with PTV injector), revising both the preparative phase and the GC injector required in the official method, was developed. Next, the method was in-house validated evaluating several parameters. Concerning free acidity, a portable system suitable for in-situ measurements of VOO free acidity was developed and in-house validated. Its working principle is based on the estimation of the olive oil free acidity by measuring the conductance of an emulsion between a hydro-alcoholic solution and the sample to be tested. The procedure is very quick and easy and, therefore, suitable for people without specific training. Another study developed during the Ph.D. was about the application of flash gas chromatography for volatile compounds analysis, combined with untargeted chemometric data elaborations, for discrimination of EVOOs and VOOs of different geographical origin. A set of 210 samples coming from different EU member states and extra-EU countries were collected and analyzed. Data were elaborated applying two different classification techniques, one linear (PLS-DA) and one non-linear (ANN). Finally, a preliminary study about the application of GC-IMS (Gas Chromatograph - Ion Mobility Spectrometer) for assessment of soft-deodorized olive oils was carried out.