Proposte di tesi di Laurea Magistrale
Structured surfaces for heat transfer enhancement in forced convection
Work description and objectives: Heat transfer in forced convection inside rectangular channels is a very interesting matter for industry as it is encountered in critical heat transfer applications like gas-turbine blade cooling, and in devices largely used such as plate-fin compact heat exchangers. In designing these devices, high values of heat transfer area per unit volume are searched for; however, if this parameter is increased over a given value, thermal performances start worsening. In fact, the higher the surface-to-volume ratio the narrower the passages, so air velocity has to be lowered to maintain acceptable the pressure drops; however, narrow passages and low air velocities lead to laminar flows, that are characterized by a rather poor convective coefficient which eventually defeats completely the area increase benefits. To overcome this limit, heat transfer is enhanced by configuring surfaces with a large variety of fins, ribs and corrugated surfaces, which are an efficient and cost-effective solution. Two experimental research lines are carried out in parallel at the ThermALab, along with Computational Fluid Dynamics (CFD) simulations, on forced convection inside rectangular channels with walls structured with a variety of ribs configurations.
The proposed topics and the main tasks of the work are:
1) Pressure drops and overall heat transfer characteristics in forced-convection inside ribbed rectangular channels
- Experimental analysis of average heat transfer coefficients and pressure drops in rectangular channels with various shapes of enhanced surfaces, by means of conventional instruments (thermocouples, RTDs, micromanometer and mass flow meters)
- Comparison of performance parameters, namely, average Nusselt number, friction factor, figures of merit, between different configurations. Comparison could be also carried out by clustering data analysis techniques, searching for configurations with different geometry while performing in quite similar way.
- Identification of design criteria to project enhanced surfaces according to given specifications.
2) Experimental analysis by IR-thermography of local heat tranfer characteristics inside ribbed rectangular channels
- Experimental analysis by IR-thermography of spatial distribution of convective heat transfer coefficient in rectangular channels with various shapes of enhanced surfaces,
- DNS CFD simulations of flows for the same geometry and operating condition experimentally investigated.
- Comparison between numerical and experimental results.
Both topics are available as subjects of MSc thesis. The activity must include a preliminary literature review, and experiments have to be carried out at the ThermALab laboratory, Department of Energy, Campus Bovisa.
Required skills: Attitude towards experimental activity, and heat and mass transfer problems. LabView knowledge is a plus for local measurements.
Non Destructive Testing by IR thermography
Work description and objectives: Non Destructive Testing (NDT) methods are used every day as a fundamental quality control and maintenance tool in many industrial applications, from aerospace composites materials to electronic components, from pipelines to buildings. IR-thermography based NDT methods use the propagation of heat pseudo-waves as a mean to identify the presence and the geometry of internal defects by recording the surface temperature field of the specimen after, or during, a thermal stimulus. In photovoltaic solar panels, cell defects are proven to give a local temperature increase. Research activity in the ThermALab is focused on low conductivity non-metallic samples. MSc thesis available topics are thermographic image treatment algorithms, curved and composite samples analysis, and FEM parametric models and simulations. The activity must include a preliminary literature review, and experiments have to be carried out at the ThermALab laboratory, Department of Energy, Campus Bovisa.
The available topics and activities are:
1) IR non-destructive testing on composite materials
- Experimental study on the identification of different typologies of internal defects in composite panels of different materials by means of IR thermography
- Implementation and testing of new ways of processing thermogram sequences, as an alternative to the phase analysis.
- Numerical modeling by means of a commercial code of multiphysics of heat transfer diffusion inside orthotropic materials, and results validation against experimental data.
2) IR non-destructive testing on photovoltaic panels
- Experimental analysis of different types of photovoltaic panels (PV) in operative conditions or in laboratory by means of electroluminescence effects
- Link between experimental measurements and defect typology
- Diagnostic system proposal or analysis of the defect influence on global performance and safety of PV panels.
Required skills: Attitude towards experimental activity, and heat and mass transfer problems. Matlab knowledge. Any experience with COMSOL Multiphisics would be a plus.
Radiometric proprieties evaluation
Work description and objectives:
In recent years, solar protection systems are used and studied as a promising energy saving technology for buildings, both for cold and hot climates. Many solutions have already been proposed, and some of them are already adopted and show interesting results, especially in reducing the air conditioning power consumption during hot seasons. Standard measurements are defined to evaluate global radiometric characteristics of semi-transparent surfaces, however those standard are often incapable of describing new surfaces or complex interaction between various media.
Another field of interest is the study of the surface properties of laser machined samples. Laser machining is employed more and more by the industry world for its highly controllable outcomes, and for the possibility of automatization. Surface machining can yield dramatic changes in roughness and optical parameters, like texture and color, and multiangle spectrophotometry is the technique of choice for the evaluation of these changes
The ThermALab is equipped with a top-grade UV-Vis-NIR (solar range) spectrophotometer, and with TracePRO software, which is the standard in radiative heat transfer simulations. A second spectrophotometer operates within the medium and far IR wavelength range. The latter spectrophotometer will allow to extend measurements of spectral reflectivity and emissivity to the whole IR range. The MSc thesis subject is the experimental and theoretical study of radiometric proprieties of innovative semi-transparent media, smart films or surface finishing; modeling simulations could be possibly carried out on the basis of experimental data.
The available thesis topics is:
Multi-angle spectrophotomoetry on laser-machined metallic samples.
- Experimental analysis on metallic laser-treated surfaces, made in several controlled atmospheric environments, by means of multi-angle spectrophotometry
- Analysis of optical properties variations as a function of the laser machining parameters, aimed at finding links between them.
- Development of an optical model to understand the effects of laser machining techniques of surfaces on their radiometric properties as experimentally found.
The activity must include a preliminary literature review, and experiments have to be carried out at the ThermALab laboratory, Department of Energy, Campus Bovisa.
Required skills: Attitude towards experimental activity, good knowledge of radiative heat transfer.