Дисертації: "Tecnica industriale e commerciale"

1

Nardotto, Daniele. "ANALISI SPERIMENTALE E MODELLIZZAZIONE DI CIRCUITI FRIGORIFERI CON COMPRESSORE AD INVERTER IMPIEGATI NELLA REFRIGERAZIONE COMMERCIALE." Doctoral thesis, Università degli studi di Padova, 2010. http://hdl.handle.net/11577/3426975.

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This report explains a comparison between two possible commercial refrigeration systems. The first system considers a display cabinet flooded and refrigerated by a traditional centralized plant with a remote air cooled roof top condenser and a refrigerant distribution pipe network (high pressure liquid lines, low pressure vapor lines). The plant utilizes R404A refrigerant. The second system is composed by a display cabinet equipped with an on board inverter DC-compressor for R404A. This system is water condensed by a centralized hydraulic system with a roof top water-air heat exchanger. Adopting inverter DC-compressor enables an appreciable energy saving, because the system is designed for allowing a floating refrigerant evaporation temperature, in function of some parameters as: air curtain temperature, compressor speed and refrigerant condensation temperature. Moreover, the system uses an electronic expansion valve, too. The vapor superheating in the compressor suction line is the minimum value for the system stability in order to minimize the refrigerant side dry area in the evaporator coil. This study is supported by an experimental work with two display cabinets tested in Carel Thermodynamics Laboratory. This data acquisition campaign has permitted a comparison with a finite element model, developed in order to reproduce the refrigerant system behavior under frosting condition and for studying the compressor frequency effects in the refrigeration cycle. The conclusions define some guideline for controlling the compressor, in order to minimize the electrical power consumption.
In questo lavoro si espone un confronto fra due tipologie d'impianti di refrigerazione destinati alle superfici commerciali. Il primo sistema riguarda un impianto centralizzato con condensatore remoto raffreddato ad aria e con le classiche linee di refrigerante (linea in alta pressione del liquido, linea in bassa pressione del vapore surriscaldato) sviluppate in lunghezza nell’area di vendita dei prodotti. L'impianto è a R404A. Il secondo sistema è un banco frigorifero con un compressore a bordo dotato di motore brushless e utilizzante R404A. Questo sistema è raffreddato ad acqua con un gruppo idraulico centralizzato. Tale tipologia di circuito permette un interessante risparmio energetico, poiché adotta la temperatura di evaporazione flottante, determinata in valore dal setpoint della lama d’aria, della frequenza di rotazione del compressore e dalla temperatura di condensazione. Il sistema è dotato di una valvola di espansione del refrigerante a retroazione elettronica. Il compressore in tal modo è in grado di lavorare con un surriscaldamento minimo e stabile, utile a ottimizzare l’uso dell’evaporatore. Questo lavoro è basato su dati sperimentali, ottenuti grazie alle prove eseguite presso il Laboratorio di Termodinamica di Carel S.p.A.. Questa campagna di dati ha permesso il confronto con un modello ai volumi finiti, sviluppato per riprodurre in comportamento del sistema sotto l’effetto del brinamento e utile a studiare anche l’effetto sul circuito della frequenza del compressore. Nella parte finale di questo report sono date alcune direttive per controllare il ciclo frigorifero in modo ottimale dal punto di vista energetico.

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2

GELMI, Ornella. "Storia e caratteri dell'istruzione tecnica industriale bergamasca." Doctoral thesis, Università degli studi di Bergamo, 2011. http://hdl.handle.net/10446/864.

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3

Bovo, Sara <1978&gt. "Fragranze di interesse commerciale via catalisi asimmetrica." Doctoral thesis, Università Ca' Foscari Venezia, 2007. http://hdl.handle.net/10579/898.

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4

LIVI, GIANLUCA. "Il software, tra diritto d’autore e brevetto industriale." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2013. http://hdl.handle.net/2108/202101.

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5

Romanato, Nicolo' <1985&gt. "Tutela, valorizzazione e trasferimento del segreto industriale." Doctoral thesis, Università Ca' Foscari Venezia, 2014. http://hdl.handle.net/10579/5653.

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Il presente elaborato si prefigge proprio lo scopo di analizzare questo istituto e, in particolare, in che cosa consista il “segreto industriale” o “trade secrets”, distinguendo in due distinti capitoli, i diversi interventi normativi – con i conseguenti riflessi sul profilo dogmatico – che si sono succeduti nel tempo (capitolo 1 e 2). In seguito verranno analizzati gli strumenti attraverso i quali il segreto industriale può essere efficamente tutelato a fronte di condotte appropriative di terzi, anche non diretti concorrenti e soprattutto, dai dipendenti (capitolo 3). Verrà poi indicato il metodo con cui questo know-how deve essere contabilizzato (capitolo 4), prima di procedere a verificare quale tutela sia per lo stesso apprestata dagli ordinamenti stranieri (capitolo 5) e, infine, con quali strumenti contrattuali possa essere trasferito (capitolo 6).

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6

Paglialunga, Stefano. "Road Safety Review della porzione sud della zona industriale-commerciale di Casalecchio di Reno." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.

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In questo elebarato si è analazzato e studiato una porzione dell'infrastruttura viaria del quartiere Arcobaleno del comune di Casalecchio di Reno. In particolare è stato effettuato un'analisi della sicurezza delle vie A. De Curtis, Giovannini e F. Coppi e delle relative intersezioni. Sono state utilizzate le linee guida contenute nel decreto legislativo n° 35/2011 riguardanti il Road Safety Review. E' stata altresì effettuata un'analisi approfondita criticità locali non presenti nelle linee guida del decreto.

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7

Terzi, Luigi Andrea <1972&gt. "Nuove prospettive per la produzione energetica." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/205/1/PhDTesiTerzi.pdf.

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8

Terzi, Luigi Andrea <1972&gt. "Nuove prospettive per la produzione energetica." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/205/.

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9

Pieri, Stefano <1977&gt. "Multi-objective optimization of microgas turbine recuperatos." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/415/1/Tesi_Pieri_Stefano.pdf.

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10

Pieri, Stefano <1977&gt. "Multi-objective optimization of microgas turbine recuperatos." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/415/.

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11

Pinto, Francesco <1978&gt. "Application of evolutionary techniques to energy transfer efficiency in heat transfer problems and low consumption buildings." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/419/1/Pinto.pdf.

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12

Pinto, Francesco <1978&gt. "Application of evolutionary techniques to energy transfer efficiency in heat transfer problems and low consumption buildings." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/419/.

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13

Copiello, Diego <1980&gt. "Multiobjective genetic algorithms applied to heat transfer problems." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1218/1/copiello_diego_tesi.pdf.

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In the present work, the multi-objective optimization by genetic algorithms is investigated and applied to heat transfer problems. Firstly, the work aims to compare different reproduction processes employed by genetic algorithms and two new promising processes are suggested. Secondly, in this work two heat transfer problems are studied under the multi-objective point of view. Specifically, the two cases studied are the wavy fins and the corrugated wall channel. Both these cases have already been studied by a single objective optimizer. Therefore, this work aims to extend the previous works in a more comprehensive study.

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14

Copiello, Diego <1980&gt. "Multiobjective genetic algorithms applied to heat transfer problems." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1218/.

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In the present work, the multi-objective optimization by genetic algorithms is investigated and applied to heat transfer problems. Firstly, the work aims to compare different reproduction processes employed by genetic algorithms and two new promising processes are suggested. Secondly, in this work two heat transfer problems are studied under the multi-objective point of view. Specifically, the two cases studied are the wavy fins and the corrugated wall channel. Both these cases have already been studied by a single objective optimizer. Therefore, this work aims to extend the previous works in a more comprehensive study.

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15

Tomarchio, Valerio <1978&gt. "Magnetohydrodynamic Effects On Mixed Convection Flows In Channels And Ducts." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1411/1/tomarchio_valerio_tesi.pdf.

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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.

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16

Tomarchio, Valerio <1978&gt. "Magnetohydrodynamic Effects On Mixed Convection Flows In Channels And Ducts." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1411/.

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Анотація:

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.

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17

Celli, Michele <1980&gt. "Stability, viscous dissipation and local thermal non-equilibrium in fluid saturated porous media." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2010. http://amsdottorato.unibo.it/2485/1/Celli_Michele_PhD_Thesis.pdf.

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In this thesis, the field of study related to the stability analysis of fluid saturated porous media is investigated. In particular the contribution of the viscous heating to the onset of convective instability in the flow through ducts is analysed. In order to evaluate the contribution of the viscous dissipation, different geometries, different models describing the balance equations and different boundary conditions are used. Moreover, the local thermal non-equilibrium model is used to study the evolution of the temperature differences between the fluid and the solid matrix in a thermal boundary layer problem. On studying the onset of instability, different techniques for eigenvalue problems has been used. Analytical solutions, asymptotic analyses and numerical solutions by means of original and commercial codes are carried out.

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18

Celli, Michele <1980&gt. "Stability, viscous dissipation and local thermal non-equilibrium in fluid saturated porous media." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2010. http://amsdottorato.unibo.it/2485/.

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In this thesis, the field of study related to the stability analysis of fluid saturated porous media is investigated. In particular the contribution of the viscous heating to the onset of convective instability in the flow through ducts is analysed. In order to evaluate the contribution of the viscous dissipation, different geometries, different models describing the balance equations and different boundary conditions are used. Moreover, the local thermal non-equilibrium model is used to study the evolution of the temperature differences between the fluid and the solid matrix in a thermal boundary layer problem. On studying the onset of instability, different techniques for eigenvalue problems has been used. Analytical solutions, asymptotic analyses and numerical solutions by means of original and commercial codes are carried out.

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19

Ragazzini, Chiara <1980&gt. "Studio teorico e computazionale legato agli aspetti fluidodinamici in idrodinamica navale." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2010. http://amsdottorato.unibo.it/2564/1/ragazzini_chiara_tesi.pdf.

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20

Ragazzini, Chiara <1980&gt. "Studio teorico e computazionale legato agli aspetti fluidodinamici in idrodinamica navale." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2010. http://amsdottorato.unibo.it/2564/.

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21

Terlizzese, Tiziano <1974&gt. "Second law analysis and simulation techniques for the energy optimization of buildings." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2010. http://amsdottorato.unibo.it/2743/1/terlizzese_tiziano_tesi.pdf.

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The research activity described in this thesis is focused mainly on the study of finite-element techniques applied to thermo-fluid dynamic problems of plant components and on the study of dynamic simulation techniques applied to integrated building design in order to enhance the energy performance of the building. The first part of this doctorate thesis is a broad dissertation on second law analysis of thermodynamic processes with the purpose of including the issue of the energy efficiency of buildings within a wider cultural context which is usually not considered by professionals in the energy sector. In particular, the first chapter includes, a rigorous scheme for the deduction of the expressions for molar exergy and molar flow exergy of pure chemical fuels. The study shows that molar exergy and molar flow exergy coincide when the temperature and pressure of the fuel are equal to those of the environment in which the combustion reaction takes place. A simple method to determine the Gibbs free energy for non-standard values of the temperature and pressure of the environment is then clarified. For hydrogen, carbon dioxide, and several hydrocarbons, the dependence of the molar exergy on the temperature and relative humidity of the environment is reported, together with an evaluation of molar exergy and molar flow exergy when the temperature and pressure of the fuel are different from those of the environment. As an application of second law analysis, a comparison of the thermodynamic efficiency of a condensing boiler and of a heat pump is also reported. The second chapter presents a study of borehole heat exchangers, that is, a polyethylene piping network buried in the soil which allows a ground-coupled heat pump to exchange heat with the ground. After a brief overview of low-enthalpy geothermal plants, an apparatus designed and assembled by the author to carry out thermal response tests is presented. Data obtained by means of in situ thermal response tests are reported and evaluated by means of a finite-element simulation method, implemented through the software package COMSOL Multyphysics. The simulation method allows the determination of the precise value of the effective thermal properties of the ground and of the grout, which are essential for the design of borehole heat exchangers. In addition to the study of a single plant component, namely the borehole heat exchanger, in the third chapter is presented a thorough process for the plant design of a zero carbon building complex. The plant is composed of: 1) a ground-coupled heat pump system for space heating and cooling, with electricity supplied by photovoltaic solar collectors; 2) air dehumidifiers; 3) thermal solar collectors to match 70% of domestic hot water energy use, and a wood pellet boiler for the remaining domestic hot water energy use and for exceptional winter peaks. This chapter includes the design methodology adopted: 1) dynamic simulation of the building complex with the software package TRNSYS for evaluating the energy requirements of the building complex; 2) ground-coupled heat pumps modelled by means of TRNSYS; and 3) evaluation of the total length of the borehole heat exchanger by an iterative method developed by the author. An economic feasibility and an exergy analysis of the proposed plant, compared with two other plants, are reported. The exergy analysis was performed by considering the embodied energy of the components of each plant and the exergy loss during the functioning of the plants.

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22

Terlizzese, Tiziano <1974&gt. "Second law analysis and simulation techniques for the energy optimization of buildings." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2010. http://amsdottorato.unibo.it/2743/.

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Анотація:

The research activity described in this thesis is focused mainly on the study of finite-element techniques applied to thermo-fluid dynamic problems of plant components and on the study of dynamic simulation techniques applied to integrated building design in order to enhance the energy performance of the building. The first part of this doctorate thesis is a broad dissertation on second law analysis of thermodynamic processes with the purpose of including the issue of the energy efficiency of buildings within a wider cultural context which is usually not considered by professionals in the energy sector. In particular, the first chapter includes, a rigorous scheme for the deduction of the expressions for molar exergy and molar flow exergy of pure chemical fuels. The study shows that molar exergy and molar flow exergy coincide when the temperature and pressure of the fuel are equal to those of the environment in which the combustion reaction takes place. A simple method to determine the Gibbs free energy for non-standard values of the temperature and pressure of the environment is then clarified. For hydrogen, carbon dioxide, and several hydrocarbons, the dependence of the molar exergy on the temperature and relative humidity of the environment is reported, together with an evaluation of molar exergy and molar flow exergy when the temperature and pressure of the fuel are different from those of the environment. As an application of second law analysis, a comparison of the thermodynamic efficiency of a condensing boiler and of a heat pump is also reported. The second chapter presents a study of borehole heat exchangers, that is, a polyethylene piping network buried in the soil which allows a ground-coupled heat pump to exchange heat with the ground. After a brief overview of low-enthalpy geothermal plants, an apparatus designed and assembled by the author to carry out thermal response tests is presented. Data obtained by means of in situ thermal response tests are reported and evaluated by means of a finite-element simulation method, implemented through the software package COMSOL Multyphysics. The simulation method allows the determination of the precise value of the effective thermal properties of the ground and of the grout, which are essential for the design of borehole heat exchangers. In addition to the study of a single plant component, namely the borehole heat exchanger, in the third chapter is presented a thorough process for the plant design of a zero carbon building complex. The plant is composed of: 1) a ground-coupled heat pump system for space heating and cooling, with electricity supplied by photovoltaic solar collectors; 2) air dehumidifiers; 3) thermal solar collectors to match 70% of domestic hot water energy use, and a wood pellet boiler for the remaining domestic hot water energy use and for exceptional winter peaks. This chapter includes the design methodology adopted: 1) dynamic simulation of the building complex with the software package TRNSYS for evaluating the energy requirements of the building complex; 2) ground-coupled heat pumps modelled by means of TRNSYS; and 3) evaluation of the total length of the borehole heat exchanger by an iterative method developed by the author. An economic feasibility and an exergy analysis of the proposed plant, compared with two other plants, are reported. The exergy analysis was performed by considering the embodied energy of the components of each plant and the exergy loss during the functioning of the plants.

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23

Flacco, Giuseppe <1981&gt. "Edificio-Impianto: ruolo dell'involucro e dell'impiantistica. Miglioramento delle prestazioni energetiche degli edifici attraverso progetti innovativi che anticipano l'applicazione della Direttiva CE 2010/31." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3359/1/FLACCO_GIUSEPPE_TESI.pdf.

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La tematica del presente scritto è l’analisi teorico-sperimentale del sistema edificio-impianto, che è funzione delle soluzioni progettuali adottate, dei componenti scelti e del tipo di conduzione prevista. La Direttiva 2010/31/CE sulle prestazioni energetiche degli edifici, entrata in vigore l’8 luglio 2010, pubblicata sulla Gazzetta Europea del 18 giugno 2010, sostituirà, dal 1º febbraio 2012, la direttiva 2002/91/CE. La direttiva prevede che vengano redatti piani nazionali destinati ad aumentare il numero di “edifici a energia quasi zero” e che entro il 31 dicembre 2020 tutti gli edifici di nuova costruzione dovranno essere “edifici a energia quasi zero”, per gli edifici pubblici questa scadenza è anticipata al 31 dicembre 2018. In questa prospettiva sono stati progettati due “edifici a energia quasi zero”, una villa monofamiliare e un complesso scolastico (scuola dell’infanzia, elementare, media inferiore) attualmente in via di realizzazione, con l’obiettivo principale di fornire un caso studio unico per ogni tipologia in quanto anche modulare e replicabile nella realtà del nostro territorio, che anticipano gli obiettivi fissati dalla Direttiva 2010/31/CE. I risultati ottenibili dai suddetti progetti, esposti nella tesi, sono il frutto di un attenta e proficua progettazione integrata, connubio tra progettazione architettonica ed energetico/impiantistica. La stessa progettazione ha esaminato le tecnologie, i materiali e le soluzioni tecniche “mirate” ai fini del comfort ambientale e di un’elevata prestazione energetica dell’edificio. Inoltre è stato dedicato ampio rilievo alla diagnosi energetica degli edifici esistenti attraverso 4 casi studio, i principali svolti durante i tre anni di dottorato di ricerca, esemplari del patrimonio edilizio italiano. Per ogni caso studio è stata condotta una diagnosi energetica dell’edificio, valutati i risultati e definita la classe energetica, ed in seguito sono stati presi in considerazione i possibili interventi migliorativi sia da un punto di vista qualitativo sia economico tenendo conto degli incentivi statali per l’incremento dell’efficienza energetica.

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24

Flacco, Giuseppe <1981&gt. "Edificio-Impianto: ruolo dell'involucro e dell'impiantistica. Miglioramento delle prestazioni energetiche degli edifici attraverso progetti innovativi che anticipano l'applicazione della Direttiva CE 2010/31." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3359/.

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La tematica del presente scritto è l’analisi teorico-sperimentale del sistema edificio-impianto, che è funzione delle soluzioni progettuali adottate, dei componenti scelti e del tipo di conduzione prevista. La Direttiva 2010/31/CE sulle prestazioni energetiche degli edifici, entrata in vigore l’8 luglio 2010, pubblicata sulla Gazzetta Europea del 18 giugno 2010, sostituirà, dal 1º febbraio 2012, la direttiva 2002/91/CE. La direttiva prevede che vengano redatti piani nazionali destinati ad aumentare il numero di “edifici a energia quasi zero” e che entro il 31 dicembre 2020 tutti gli edifici di nuova costruzione dovranno essere “edifici a energia quasi zero”, per gli edifici pubblici questa scadenza è anticipata al 31 dicembre 2018. In questa prospettiva sono stati progettati due “edifici a energia quasi zero”, una villa monofamiliare e un complesso scolastico (scuola dell’infanzia, elementare, media inferiore) attualmente in via di realizzazione, con l’obiettivo principale di fornire un caso studio unico per ogni tipologia in quanto anche modulare e replicabile nella realtà del nostro territorio, che anticipano gli obiettivi fissati dalla Direttiva 2010/31/CE. I risultati ottenibili dai suddetti progetti, esposti nella tesi, sono il frutto di un attenta e proficua progettazione integrata, connubio tra progettazione architettonica ed energetico/impiantistica. La stessa progettazione ha esaminato le tecnologie, i materiali e le soluzioni tecniche “mirate” ai fini del comfort ambientale e di un’elevata prestazione energetica dell’edificio. Inoltre è stato dedicato ampio rilievo alla diagnosi energetica degli edifici esistenti attraverso 4 casi studio, i principali svolti durante i tre anni di dottorato di ricerca, esemplari del patrimonio edilizio italiano. Per ogni caso studio è stata condotta una diagnosi energetica dell’edificio, valutati i risultati e definita la classe energetica, ed in seguito sono stati presi in considerazione i possibili interventi migliorativi sia da un punto di vista qualitativo sia economico tenendo conto degli incentivi statali per l’incremento dell’efficienza energetica.

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25

Conti, Alessandra <1979&gt. "Fluidodinamica biomedica computazionale del flusso sanguigno in presenza di affezioni strumentali e/o patologiche." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4328/1/Tesi_Dottorato_Alessandra_Conti_mod2.pdf.

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La tesi di Dottorato studia il flusso sanguigno tramite un codice agli elementi finiti (COMSOL Multiphysics). Nell’arteria è presente un catetere Doppler (in posizione concentrica o decentrata rispetto all’asse di simmetria) o di stenosi di varia forma ed estensione. Le arterie sono solidi cilindrici rigidi, elastici o iperelastici. Le arterie hanno diametri di 6 mm, 5 mm, 4 mm e 2 mm. Il flusso ematico è in regime laminare stazionario e transitorio, ed il sangue è un fluido non-Newtoniano di Casson, modificato secondo la formulazione di Gonzales & Moraga. Le analisi numeriche sono realizzate in domini tridimensionali e bidimensionali, in quest’ultimo caso analizzando l’interazione fluido-strutturale. Nei casi tridimensionali, le arterie (simulazioni fluidodinamiche) sono infinitamente rigide: ricavato il campo di pressione si procede quindi all’analisi strutturale, per determinare le variazioni di sezione e la permanenza del disturbo sul flusso. La portata sanguigna è determinata nei casi tridimensionali con catetere individuando tre valori (massimo, minimo e medio); mentre per i casi 2D e tridimensionali con arterie stenotiche la legge di pressione riproduce l’impulso ematico. La mesh è triangolare (2D) o tetraedrica (3D), infittita alla parete ed a valle dell’ostacolo, per catturare le ricircolazioni. Alla tesi sono allegate due appendici, che studiano con codici CFD la trasmissione del calore in microcanali e l’ evaporazione di gocce d’acqua in sistemi non confinati. La fluidodinamica nei microcanali è analoga all’emodinamica nei capillari. Il metodo Euleriano-Lagrangiano (simulazioni dell’evaporazione) schematizza la natura mista del sangue. La parte inerente ai microcanali analizza il transitorio a seguito dell’applicazione di un flusso termico variabile nel tempo, variando velocità in ingresso e dimensioni del microcanale. L’indagine sull’evaporazione di gocce è un’analisi parametrica in 3D, che esamina il peso del singolo parametro (temperatura esterna, diametro iniziale, umidità relativa, velocità iniziale, coefficiente di diffusione) per individuare quello che influenza maggiormente il fenomeno.
The present work analyzes the haematic flow through a finite element code (COMSOL Multiphysics). Artery is affected by Doppler catheter (whose position inside is concentric or non-concentric, and also inclined with respect to the vessel’s axis) or stenoses of different shape and extension. Solid artery is a rigid, elastic or hyperelastic cylinder. Blood vessel’s diameters are assumed to be 2 mm, 4 mm, 5 mm and 6 mm. Haematic laminar flow, both in stationary and transient regime, is established, and blood is a non-Newtonian cassonian fluid, modified according to Gonzales & Moraga formulation. Numerical analysis are on three-dimensional and bidimensional models, the latter one also introducing fluid-structure interaction. Fluid dynamic three-dimensional models consider rigid artery to compute pressure field, then this is introduced as input datum in the structural-mechanics simulation, in order to determine cross-sectional variation and disturbance length on flow. Three dimensional models affected by the catheter’s presence consider three blood flow rates (maximum, minimum and averaged), while bi-dimensional and stenotic three-dimensional artery’s models introduce a pressure time-dependent function representing the haematic wave. Geometric domains are discretized by triangles (2D) and tetrahedrons (3D), also improving mesh near walls and downstream obstacles, to resolve recirculation. Two appendices are attached to the present dissertation, dealing with results from CFD simulations of conjugate heat transfer in microchannels and droplet evaporation in non-confined systems. Fluid dynamics in microchannel is analogous to the flow analysis in the capillary system; while the Eulerian-Lagrangian approach, which models evaporation, could represent blood multiphase nature. Microchannel’s appendix analyzes the transient condition following time-dependent heat flux rising, also varying inlet velocity and microchannel’s geometry. Investigation on droplet evaporation is a parametric three-dimensional analysis, that examines every parameter’s weight (external temperature, initial diameter, relative humidity, initial velocity and diffusion coefficient) in order to find the most influencing parameter on evaporation.

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26

Conti, Alessandra <1979&gt. "Fluidodinamica biomedica computazionale del flusso sanguigno in presenza di affezioni strumentali e/o patologiche." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4328/.

Повний текст джерела

Анотація:

La tesi di Dottorato studia il flusso sanguigno tramite un codice agli elementi finiti (COMSOL Multiphysics). Nell’arteria è presente un catetere Doppler (in posizione concentrica o decentrata rispetto all’asse di simmetria) o di stenosi di varia forma ed estensione. Le arterie sono solidi cilindrici rigidi, elastici o iperelastici. Le arterie hanno diametri di 6 mm, 5 mm, 4 mm e 2 mm. Il flusso ematico è in regime laminare stazionario e transitorio, ed il sangue è un fluido non-Newtoniano di Casson, modificato secondo la formulazione di Gonzales & Moraga. Le analisi numeriche sono realizzate in domini tridimensionali e bidimensionali, in quest’ultimo caso analizzando l’interazione fluido-strutturale. Nei casi tridimensionali, le arterie (simulazioni fluidodinamiche) sono infinitamente rigide: ricavato il campo di pressione si procede quindi all’analisi strutturale, per determinare le variazioni di sezione e la permanenza del disturbo sul flusso. La portata sanguigna è determinata nei casi tridimensionali con catetere individuando tre valori (massimo, minimo e medio); mentre per i casi 2D e tridimensionali con arterie stenotiche la legge di pressione riproduce l’impulso ematico. La mesh è triangolare (2D) o tetraedrica (3D), infittita alla parete ed a valle dell’ostacolo, per catturare le ricircolazioni. Alla tesi sono allegate due appendici, che studiano con codici CFD la trasmissione del calore in microcanali e l’ evaporazione di gocce d’acqua in sistemi non confinati. La fluidodinamica nei microcanali è analoga all’emodinamica nei capillari. Il metodo Euleriano-Lagrangiano (simulazioni dell’evaporazione) schematizza la natura mista del sangue. La parte inerente ai microcanali analizza il transitorio a seguito dell’applicazione di un flusso termico variabile nel tempo, variando velocità in ingresso e dimensioni del microcanale. L’indagine sull’evaporazione di gocce è un’analisi parametrica in 3D, che esamina il peso del singolo parametro (temperatura esterna, diametro iniziale, umidità relativa, velocità iniziale, coefficiente di diffusione) per individuare quello che influenza maggiormente il fenomeno.
The present work analyzes the haematic flow through a finite element code (COMSOL Multiphysics). Artery is affected by Doppler catheter (whose position inside is concentric or non-concentric, and also inclined with respect to the vessel’s axis) or stenoses of different shape and extension. Solid artery is a rigid, elastic or hyperelastic cylinder. Blood vessel’s diameters are assumed to be 2 mm, 4 mm, 5 mm and 6 mm. Haematic laminar flow, both in stationary and transient regime, is established, and blood is a non-Newtonian cassonian fluid, modified according to Gonzales & Moraga formulation. Numerical analysis are on three-dimensional and bidimensional models, the latter one also introducing fluid-structure interaction. Fluid dynamic three-dimensional models consider rigid artery to compute pressure field, then this is introduced as input datum in the structural-mechanics simulation, in order to determine cross-sectional variation and disturbance length on flow. Three dimensional models affected by the catheter’s presence consider three blood flow rates (maximum, minimum and averaged), while bi-dimensional and stenotic three-dimensional artery’s models introduce a pressure time-dependent function representing the haematic wave. Geometric domains are discretized by triangles (2D) and tetrahedrons (3D), also improving mesh near walls and downstream obstacles, to resolve recirculation. Two appendices are attached to the present dissertation, dealing with results from CFD simulations of conjugate heat transfer in microchannels and droplet evaporation in non-confined systems. Fluid dynamics in microchannel is analogous to the flow analysis in the capillary system; while the Eulerian-Lagrangian approach, which models evaporation, could represent blood multiphase nature. Microchannel’s appendix analyzes the transient condition following time-dependent heat flux rising, also varying inlet velocity and microchannel’s geometry. Investigation on droplet evaporation is a parametric three-dimensional analysis, that examines every parameter’s weight (external temperature, initial diameter, relative humidity, initial velocity and diffusion coefficient) in order to find the most influencing parameter on evaporation.

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27

Magnini, Mirco <1982&gt. "CFD modeling of two-phase boiling flows in the slug flow regime with an interface capturing technique." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4437/1/Magnini_Mirco_tesi.pdf.

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Анотація:

The objective of this thesis was to improve the commercial CFD software Ansys Fluent to obtain a tool able to perform accurate simulations of flow boiling in the slug flow regime. The achievement of a reliable numerical framework allows a better understanding of the bubble and flow dynamics induced by the evaporation and makes possible the prediction of the wall heat transfer trends. In order to save computational time, the flow is modeled with an axisymmetrical formulation. Vapor and liquid phases are treated as incompressible and in laminar flow. By means of a single fluid approach, the flow equations are written as for a single phase flow, but discontinuities at the interface and interfacial effects need to be accounted for and discretized properly. Ansys Fluent provides a Volume Of Fluid technique to advect the interface and to map the discontinuous fluid properties throughout the flow domain. The interfacial effects are dominant in the boiling slug flow and the accuracy of their estimation is fundamental for the reliability of the solver. Self-implemented functions, developed ad-hoc, are introduced within the numerical code to compute the surface tension force and the rates of mass and energy exchange at the interface related to the evaporation. Several validation benchmarks assess the better performances of the improved software. Various adiabatic configurations are simulated in order to test the capability of the numerical framework in modeling actual flows and the comparison with experimental results is very positive. The simulation of a single evaporating bubble underlines the dominant effect on the global heat transfer rate of the local transient heat convection in the liquid after the bubble transit. The simulation of multiple evaporating bubbles flowing in sequence shows that their mutual influence can strongly enhance the heat transfer coefficient, up to twice the single phase flow value.
Questa tesi si è posta l'obiettivo di migliorare il codice commerciale CFD Ansys Fluent, per ottenere un solutore in grado di compiere simulazioni accurate di flussi in ebollizione nel regime slug flow. Un codice numerico affidabile permette una miglior comprensione della dinamica della bolla causata dall'evaporazione, rendendo possibile la stima dello scambio termico alla parete. Per limitare il costo computazionale delle simulazioni, il problema è modellato con una formulazione assialsimmetrica. Le fasi liquido e vapore sono incomprimibili ed in moto laminare. Attraverso un approccio di tipo single fluid, le equazioni che governano il moto sono scritte come per un flusso a fase singola, tuttavia discontinuità ed effetti di interfaccia vanno introdotti e discretizzati propriamente. Fluent dispone di una tecnica di tipo Volume-of-Fluid per l'avvezione dell'interfaccia e per mappare le discontinue proprietà del fluido su tutto il dominio. Nello slug flow gli effetti di interfaccia sono dominanti, di conseguenza l'accuratezza con cui essi sono calcolati è fondamentale per la veridicità del solutore. A tale scopo, sono state introdotte nel codice numerico delle funzioni esterne, sviluppate appositamente per il calcolo della tensione superficiale e dello scambio di massa ed energia all'interfaccia come conseguenza dell'evaporazione. Le migliori prestazioni del codice modificato rispetto a quello originale sono dimostrate attraverso numerosi casi test. Per provare la validità del nuovo codice numerico nella riproduzione di reali configurazioni di flusso, sono stati simulati diversi flussi adiabatici ed il confronto con i risultati sperimentali è molto positivo. La simulazione dell'evaporazione di una bolla singola evidenzia che la convezione transitoria nel liquido, successivamente al passaggio della bolla, ha un effetto dominante sul coefficiente di scambio termico globale. La simulazione di bolle multiple che evaporano in sequenza mostra che la loro influenza reciproca migliora notevolmente il coefficiente di scambio, fino a due volte il valore a fase singola.

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28

Magnini, Mirco <1982&gt. "CFD modeling of two-phase boiling flows in the slug flow regime with an interface capturing technique." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4437/.

Повний текст джерела

Анотація:

The objective of this thesis was to improve the commercial CFD software Ansys Fluent to obtain a tool able to perform accurate simulations of flow boiling in the slug flow regime. The achievement of a reliable numerical framework allows a better understanding of the bubble and flow dynamics induced by the evaporation and makes possible the prediction of the wall heat transfer trends. In order to save computational time, the flow is modeled with an axisymmetrical formulation. Vapor and liquid phases are treated as incompressible and in laminar flow. By means of a single fluid approach, the flow equations are written as for a single phase flow, but discontinuities at the interface and interfacial effects need to be accounted for and discretized properly. Ansys Fluent provides a Volume Of Fluid technique to advect the interface and to map the discontinuous fluid properties throughout the flow domain. The interfacial effects are dominant in the boiling slug flow and the accuracy of their estimation is fundamental for the reliability of the solver. Self-implemented functions, developed ad-hoc, are introduced within the numerical code to compute the surface tension force and the rates of mass and energy exchange at the interface related to the evaporation. Several validation benchmarks assess the better performances of the improved software. Various adiabatic configurations are simulated in order to test the capability of the numerical framework in modeling actual flows and the comparison with experimental results is very positive. The simulation of a single evaporating bubble underlines the dominant effect on the global heat transfer rate of the local transient heat convection in the liquid after the bubble transit. The simulation of multiple evaporating bubbles flowing in sequence shows that their mutual influence can strongly enhance the heat transfer coefficient, up to twice the single phase flow value.
Questa tesi si è posta l'obiettivo di migliorare il codice commerciale CFD Ansys Fluent, per ottenere un solutore in grado di compiere simulazioni accurate di flussi in ebollizione nel regime slug flow. Un codice numerico affidabile permette una miglior comprensione della dinamica della bolla causata dall'evaporazione, rendendo possibile la stima dello scambio termico alla parete. Per limitare il costo computazionale delle simulazioni, il problema è modellato con una formulazione assialsimmetrica. Le fasi liquido e vapore sono incomprimibili ed in moto laminare. Attraverso un approccio di tipo single fluid, le equazioni che governano il moto sono scritte come per un flusso a fase singola, tuttavia discontinuità ed effetti di interfaccia vanno introdotti e discretizzati propriamente. Fluent dispone di una tecnica di tipo Volume-of-Fluid per l'avvezione dell'interfaccia e per mappare le discontinue proprietà del fluido su tutto il dominio. Nello slug flow gli effetti di interfaccia sono dominanti, di conseguenza l'accuratezza con cui essi sono calcolati è fondamentale per la veridicità del solutore. A tale scopo, sono state introdotte nel codice numerico delle funzioni esterne, sviluppate appositamente per il calcolo della tensione superficiale e dello scambio di massa ed energia all'interfaccia come conseguenza dell'evaporazione. Le migliori prestazioni del codice modificato rispetto a quello originale sono dimostrate attraverso numerosi casi test. Per provare la validità del nuovo codice numerico nella riproduzione di reali configurazioni di flusso, sono stati simulati diversi flussi adiabatici ed il confronto con i risultati sperimentali è molto positivo. La simulazione dell'evaporazione di una bolla singola evidenzia che la convezione transitoria nel liquido, successivamente al passaggio della bolla, ha un effetto dominante sul coefficiente di scambio termico globale. La simulazione di bolle multiple che evaporano in sequenza mostra che la loro influenza reciproca migliora notevolmente il coefficiente di scambio, fino a due volte il valore a fase singola.

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29

Morsiani, Riccardo <1983&gt. "Analisi sperimentale dell'influenza dei parametri di processo sulla resistenza di contatto tra polimero e stampo durante la formatura." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4890/1/Morsiani_Riccardo_Tesi.pdf.

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Анотація:

Con gli strumenti informatici disponibili oggi per le industrie, in particolar modo coi software CAE, le possibile simulare in maniera più che soddisfacente i fenomeni fisici presenti in natura. Anche il raffreddamento di un manufatto in polimero può venire simulato, a patto che si conoscano tutti i dati dei materiali e delle condizioni al contorno. Per quanto riguarda i dati dei materiali, i produttori di polimeri sono molto spesso in grado di fornirli, mentre le condizioni al contorno devono essere padroneggiate dal detentore della tecnologia. Nella pratica, tale conoscenza è al più incompleta, quindi si fanno ipotesi per colmare le lacune. Una tra le ipotesi più forti fatte è quella di una perfetta conduzione all'interfaccia tra due corpi. Questo è un vincolo troppo forte, se paragonato alla precisione di tutti gli altri dati necessari alla simulazione, e quindi si è deciso di eseguire una campagna sperimentale per stimare la resistenza al passaggio flusso termico all'interfaccia polimero-stampo ovvero determinare la conduttanza termica di contatto. L'attività svolta in questa tesi di dottorato ha come scopo quello di fornire un contributo significativo allo sviluppo e al miglioramento dell'efficienza termica degli stampi di formatura dei polimeri termoplastici con tecnologia a compressione.
Today's computational resources allow a more than satisfactory simulation of most industrial processes, including closure manufacturing. The cooling and cristalization step of the manufacturing process may be simulated, provided all polymer data, process parameters and boundary conditions are known. As to the latter two issues, it is the manufacturer's task to gain the necessary information, but this knowledge is in practice lacking at best, which makes assumptions compulsory. One of the strongest assumptions is that of perfect thermal contact at the interface between mold and polymer, too limiting a hypothesis if compared to the precision with which other conditions and parameters are known. To fill this gap an experimental campaign was devised, starting from scratch, to determine by means of inverse thermal analysis the value of the thermal contact conductance in the case of two families of polymeric materials and its dependence on the main process parameters at play in compression molding. The results, both qualitative and quantitative highlighted which aspects may be discarded and which play a fundamental role in the cooling process.

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30

Morsiani, Riccardo <1983&gt. "Analisi sperimentale dell'influenza dei parametri di processo sulla resistenza di contatto tra polimero e stampo durante la formatura." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4890/.

Повний текст джерела

Анотація:

Con gli strumenti informatici disponibili oggi per le industrie, in particolar modo coi software CAE, le possibile simulare in maniera più che soddisfacente i fenomeni fisici presenti in natura. Anche il raffreddamento di un manufatto in polimero può venire simulato, a patto che si conoscano tutti i dati dei materiali e delle condizioni al contorno. Per quanto riguarda i dati dei materiali, i produttori di polimeri sono molto spesso in grado di fornirli, mentre le condizioni al contorno devono essere padroneggiate dal detentore della tecnologia. Nella pratica, tale conoscenza è al più incompleta, quindi si fanno ipotesi per colmare le lacune. Una tra le ipotesi più forti fatte è quella di una perfetta conduzione all'interfaccia tra due corpi. Questo è un vincolo troppo forte, se paragonato alla precisione di tutti gli altri dati necessari alla simulazione, e quindi si è deciso di eseguire una campagna sperimentale per stimare la resistenza al passaggio flusso termico all'interfaccia polimero-stampo ovvero determinare la conduttanza termica di contatto. L'attività svolta in questa tesi di dottorato ha come scopo quello di fornire un contributo significativo allo sviluppo e al miglioramento dell'efficienza termica degli stampi di formatura dei polimeri termoplastici con tecnologia a compressione.
Today's computational resources allow a more than satisfactory simulation of most industrial processes, including closure manufacturing. The cooling and cristalization step of the manufacturing process may be simulated, provided all polymer data, process parameters and boundary conditions are known. As to the latter two issues, it is the manufacturer's task to gain the necessary information, but this knowledge is in practice lacking at best, which makes assumptions compulsory. One of the strongest assumptions is that of perfect thermal contact at the interface between mold and polymer, too limiting a hypothesis if compared to the precision with which other conditions and parameters are known. To fill this gap an experimental campaign was devised, starting from scratch, to determine by means of inverse thermal analysis the value of the thermal contact conductance in the case of two families of polymeric materials and its dependence on the main process parameters at play in compression molding. The results, both qualitative and quantitative highlighted which aspects may be discarded and which play a fundamental role in the cooling process.

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31

Greppi, Matteo <1985&gt. "Numerical optimization,modeling and system evaluation of a thermophotovoltaic hybrid panel." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5415/1/Greppi_Matteo_Tesi.pdf.

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Анотація:

Photovoltaic (PV) solar panels generally produce electricity in the 6% to 16% efficiency range, the rest being dissipated in thermal losses. To recover this amount, hybrid photovoltaic thermal systems (PVT) have been devised. These are devices that simultaneously convert solar energy into electricity and heat. It is thus interesting to study the PVT system globally from different point of views in order to evaluate advantages and disadvantages of this technology and its possible uses. In particular in Chapter II, the development of the PVT absorber numerical optimization by a genetic algorithm has been carried out analyzing different internal channel profiles in order to find a right compromise between performance and technical and economical feasibility. Therefore in Chapter III ,thanks to a mobile structure built into the university lab, it has been compared experimentally electrical and thermal output power from PVT panels with separated photovoltaic and solar thermal productions. Collecting a lot of experimental data based on different seasonal conditions (ambient temperature,irradiation, wind...),the aim of this mobile structure has been to evaluate average both thermal and electrical increasing and decreasing efficiency values obtained respect to separate productions through the year. In Chapter IV , new PVT and solar thermal equation based models in steady state conditions have been developed by software Dymola that uses Modelica language. This permits ,in a simplified way respect to previous system modelling softwares, to model and evaluate different concepts about PVT panel regarding its structure before prototyping and measuring it. Chapter V concerns instead the definition of PVT boundary conditions into a HVAC system . This was made trough year simulations by software Polysun in order to finally assess the best solar assisted integrated structure thanks to F_save(solar saving energy)factor. Finally, Chapter VI presents the conclusion and the perspectives of this PhD work.

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32

Greppi, Matteo <1985&gt. "Numerical optimization,modeling and system evaluation of a thermophotovoltaic hybrid panel." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5415/.

Повний текст джерела

Анотація:

Photovoltaic (PV) solar panels generally produce electricity in the 6% to 16% efficiency range, the rest being dissipated in thermal losses. To recover this amount, hybrid photovoltaic thermal systems (PVT) have been devised. These are devices that simultaneously convert solar energy into electricity and heat. It is thus interesting to study the PVT system globally from different point of views in order to evaluate advantages and disadvantages of this technology and its possible uses. In particular in Chapter II, the development of the PVT absorber numerical optimization by a genetic algorithm has been carried out analyzing different internal channel profiles in order to find a right compromise between performance and technical and economical feasibility. Therefore in Chapter III ,thanks to a mobile structure built into the university lab, it has been compared experimentally electrical and thermal output power from PVT panels with separated photovoltaic and solar thermal productions. Collecting a lot of experimental data based on different seasonal conditions (ambient temperature,irradiation, wind...),the aim of this mobile structure has been to evaluate average both thermal and electrical increasing and decreasing efficiency values obtained respect to separate productions through the year. In Chapter IV , new PVT and solar thermal equation based models in steady state conditions have been developed by software Dymola that uses Modelica language. This permits ,in a simplified way respect to previous system modelling softwares, to model and evaluate different concepts about PVT panel regarding its structure before prototyping and measuring it. Chapter V concerns instead the definition of PVT boundary conditions into a HVAC system . This was made trough year simulations by software Polysun in order to finally assess the best solar assisted integrated structure thanks to F_save(solar saving energy)factor. Finally, Chapter VI presents the conclusion and the perspectives of this PhD work.

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33

Yang, Yahui <1984&gt. "Experimental and Numerical Analysis of Gas Forced Convection through Microtubes and Micro Heat Exchangers." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5751/1/Yang_Yahui_tesi.pdf.

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Анотація:

The last decade has witnessed very fast development in microfabrication technologies. The increasing industrial applications of microfluidic systems call for more intensive and systematic knowledge on this newly emerging field. Especially for gaseous flow and heat transfer at microscale, the applicability of conventional theories developed at macro scale is not yet completely validated; this is mainly due to scarce experimental data available in literature for gas flows. The objective of this thesis is to investigate these unclear elements by analyzing forced convection for gaseous flows through microtubes and micro heat exchangers. Experimental tests have been performed with microtubes having various inner diameters, namely 750 m, 510 m and 170 m, over a wide range of Reynolds number covering the laminar region, the transitional zone and also the onset region of the turbulent regime. The results show that conventional theory is able to predict the flow friction factor when flow compressibility does not appear and the effect of fluid temperature-dependent properties is insignificant. A double-layered microchannel heat exchanger has been designed in order to study experimentally the efficiency of a gas-to-gas micro heat exchanger. This microdevice contains 133 parallel microchannels machined into polished PEEK plates for both the hot side and the cold side. The microchannels are 200 µm high, 200 µm wide and 39.8 mm long. The design of the micro device has been made in order to be able to test different materials as partition foil with flexible thickness. Experimental tests have been carried out for five different partition foils, with various mass flow rates and flow configurations. The experimental results indicate that the thermal performance of the countercurrent and cross flow micro heat exchanger can be strongly influenced by axial conduction in the partition foil separating the hot gas flow and cold gas flow.

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Yang, Yahui <1984&gt. "Experimental and Numerical Analysis of Gas Forced Convection through Microtubes and Micro Heat Exchangers." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5751/.

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Анотація:

The last decade has witnessed very fast development in microfabrication technologies. The increasing industrial applications of microfluidic systems call for more intensive and systematic knowledge on this newly emerging field. Especially for gaseous flow and heat transfer at microscale, the applicability of conventional theories developed at macro scale is not yet completely validated; this is mainly due to scarce experimental data available in literature for gas flows. The objective of this thesis is to investigate these unclear elements by analyzing forced convection for gaseous flows through microtubes and micro heat exchangers. Experimental tests have been performed with microtubes having various inner diameters, namely 750 m, 510 m and 170 m, over a wide range of Reynolds number covering the laminar region, the transitional zone and also the onset region of the turbulent regime. The results show that conventional theory is able to predict the flow friction factor when flow compressibility does not appear and the effect of fluid temperature-dependent properties is insignificant. A double-layered microchannel heat exchanger has been designed in order to study experimentally the efficiency of a gas-to-gas micro heat exchanger. This microdevice contains 133 parallel microchannels machined into polished PEEK plates for both the hot side and the cold side. The microchannels are 200 µm high, 200 µm wide and 39.8 mm long. The design of the micro device has been made in order to be able to test different materials as partition foil with flexible thickness. Experimental tests have been carried out for five different partition foils, with various mass flow rates and flow configurations. The experimental results indicate that the thermal performance of the countercurrent and cross flow micro heat exchanger can be strongly influenced by axial conduction in the partition foil separating the hot gas flow and cold gas flow.

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Naldi, Claudia <1987&gt. "Development and Applications of Simulation Codes for Air-to-Water and Ground-Coupled Heat Pump Systems." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7438/1/Naldi_Claudia_tesi.pdf.

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In this Thesis, new simulation codes for the evaluation of a heat pump system seasonal performance are presented. The codes apply to electric air-to-water and ground-coupled heat pump systems based on a vapor compression cycle, used for building heating, cooling and domestic hot water production. Numerical models are developed to simulate different kinds of air-to-water heat pumps by means of the bin-method. The models take into account the different operating modes of mono-compressor on-off, multi-compressor and inverter-driven heat pumps. The heat pump system seasonal performance is analyzed in terms of SCOP and SEER in relation to the thermal characteristics of the building, the climate of the location and the kind of heat pump control system. Furthermore, numerical codes for the hourly simulation of air-to-water heat pump systems are developed. The dynamic codes are implemented in the software MATLAB and apply to on-off and inverter-driven heat pumps for building heating, cooling and domestic hot water production, coupled with storage tanks and integrated by a gas boiler or electric heaters. The codes are used, in particular, to evaluate the seasonal performance and the primary energy consumption of the inverter-driven air-to-water heat pump employed in the retrofit of a residential building in Bologna (Italy). A code for the hourly simulation of ground-coupled heat pump systems is developed. The code, implemented in MATLAB, employs g-functions expressed in analytic form and applies to on-off and inverter-driven heat pumps, used for building heating and/or cooling. The whole system, composed by the heat pump and the coupled borehole heat exchanger field, can be simulated for several years. The code is applied to analyze the effects of the inverter and of the total length of the borehole field on the mean seasonal performance of a ground-coupled heat pump system designed for a residential house with dominant heating loads.

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Naldi, Claudia <1987&gt. "Development and Applications of Simulation Codes for Air-to-Water and Ground-Coupled Heat Pump Systems." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7438/.

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Анотація:

In this Thesis, new simulation codes for the evaluation of a heat pump system seasonal performance are presented. The codes apply to electric air-to-water and ground-coupled heat pump systems based on a vapor compression cycle, used for building heating, cooling and domestic hot water production. Numerical models are developed to simulate different kinds of air-to-water heat pumps by means of the bin-method. The models take into account the different operating modes of mono-compressor on-off, multi-compressor and inverter-driven heat pumps. The heat pump system seasonal performance is analyzed in terms of SCOP and SEER in relation to the thermal characteristics of the building, the climate of the location and the kind of heat pump control system. Furthermore, numerical codes for the hourly simulation of air-to-water heat pump systems are developed. The dynamic codes are implemented in the software MATLAB and apply to on-off and inverter-driven heat pumps for building heating, cooling and domestic hot water production, coupled with storage tanks and integrated by a gas boiler or electric heaters. The codes are used, in particular, to evaluate the seasonal performance and the primary energy consumption of the inverter-driven air-to-water heat pump employed in the retrofit of a residential building in Bologna (Italy). A code for the hourly simulation of ground-coupled heat pump systems is developed. The code, implemented in MATLAB, employs g-functions expressed in analytic form and applies to on-off and inverter-driven heat pumps, used for building heating and/or cooling. The whole system, composed by the heat pump and the coupled borehole heat exchanger field, can be simulated for several years. The code is applied to analyze the effects of the inverter and of the total length of the borehole field on the mean seasonal performance of a ground-coupled heat pump system designed for a residential house with dominant heating loads.

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37

Puccetti, Giacomo <1988&gt. "Optical Techniques for Experimental Tests in Microfluidics." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7534/1/Puccetti_Giacomo_tesi.pdf.

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This PhD dissertation deals with the use of optical, non-invasive measurement techniques for the investigation of single and two-phase flows in microchannels. Different experimental techniques are presented and the achieved results are critically discussed. Firstly, the inverse use of the micro Particle Image Velocimetry technique for the detection of the real shape of the inner cross-section of an optical accessible microchannel is shown by putting in evidence the capability of this technique to individuate the presence of singularities along the wetted perimeter of the microchannel. Then, the experimental measurement of the local fluid temperature using non-encapsulated Thermochromic Liquid Crystal particles is discussed. A deep analysis of the stability of the color of these particles when exposed to different levels of shear stress has been conducted by demonstrating that these particles can be used for simultaneous measurements of velocity and temperature in water laminar flows characterized by low Reynolds numbers (Re < 10). A preliminary experiment where the TLC thermography is coupled to the APTV method for the simultaneous measurement of the three-dimensional velocity and temperature distribution in a microchannel is shown. Finally, an experimental analysis of the different flow patterns observed for an adiabatic air-water mixture generated by means of a micro T-junction is discussed. The main air-water mixture features have been deeply observed in 195 different experimental conditions in which values of superficial velocity ranging between 0.01 m/s and 0.15 m/s for both the inlet flows (air and water) are imposed. The flow patterns of the air-water mixture are strongly influenced by the value of the water superficial velocity; on the contrary, the air superficial velocity plays a secondary role for the determination of the characteristics of the bubbles (i.e. length).

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38

Puccetti, Giacomo <1988&gt. "Optical Techniques for Experimental Tests in Microfluidics." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7534/.

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This PhD dissertation deals with the use of optical, non-invasive measurement techniques for the investigation of single and two-phase flows in microchannels. Different experimental techniques are presented and the achieved results are critically discussed. Firstly, the inverse use of the micro Particle Image Velocimetry technique for the detection of the real shape of the inner cross-section of an optical accessible microchannel is shown by putting in evidence the capability of this technique to individuate the presence of singularities along the wetted perimeter of the microchannel. Then, the experimental measurement of the local fluid temperature using non-encapsulated Thermochromic Liquid Crystal particles is discussed. A deep analysis of the stability of the color of these particles when exposed to different levels of shear stress has been conducted by demonstrating that these particles can be used for simultaneous measurements of velocity and temperature in water laminar flows characterized by low Reynolds numbers (Re < 10). A preliminary experiment where the TLC thermography is coupled to the APTV method for the simultaneous measurement of the three-dimensional velocity and temperature distribution in a microchannel is shown. Finally, an experimental analysis of the different flow patterns observed for an adiabatic air-water mixture generated by means of a micro T-junction is discussed. The main air-water mixture features have been deeply observed in 195 different experimental conditions in which values of superficial velocity ranging between 0.01 m/s and 0.15 m/s for both the inlet flows (air and water) are imposed. The flow patterns of the air-water mixture are strongly influenced by the value of the water superficial velocity; on the contrary, the air superficial velocity plays a secondary role for the determination of the characteristics of the bubbles (i.e. length).

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39

Jahanbin, Aminhossein <1987&gt. "Finite element analysis of heat transfer in double U-tube borehole heat exchangers." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amsdottorato.unibo.it/7844/1/Thesis.pdf.

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The present Ph.D. dissertation deals with the finite element analysis of the heat transfer processes in double U-tube Borehole Heat Exchangers, called BHEs. In the evaluation of thermal response tests (TRTs), in the design of the BHE fields, and in the dynamic simulation of ground-coupled heat pumps (GCHPs), the mean temperature Tm of the working fluid in a BHE, is usually approximated by the arithmetic mean of inlet and outlet temperatures. In TRTs, this approximation causes an overestimation of the thermal resistance of the heat exchanger. In the dynamic simulation of GCHPs, this approximation introduces an error in the evaluation of the outlet temperature from the ground heat exchangers. In the present thesis, by means of 3D finite element simulations, firstly, the analysis of the fluid temperature distribution is carried out, then, correlations are proposed to determine the mean fluid temperature, for double U-tube BHEs. Tables of a dimensionless coefficient are provided that allows an immediate evaluation of Tm in any working condition, with reference to double U-BHEs with a typical geometry. In addition, the effects of the surface temperature distribution on the thermal resistance of a double U-tube BHE are investigated. It is shown that the thermal resistance of a BHE cross section (2D) is not influenced by the bulk-temperature difference between pairs of tubes, but is influenced by the thermal conductivity of the ground when the shank spacing is high. Then it is shown that, if the real mean values of the bulk fluid temperature and of the BHE external surface are considered, the 3D thermal resistance of the BHE coincides with the thermal resistance of a BHE cross section, provided that the latter is invariant along the BHE.
La presente Tesi di Dottorato tratta dell’analisi agli elementi finite dei processi di trasmissione del calore in scambiatori verticali con il terreno detti “Borehole Heat Exchangers”, BHEs, con riferimento a BHEs a doppio tubo a U. Nella valutazione di Test di Risposta Termica (TRTs), per il progetto di campi di BHEs, e nella simulazione dinamica di pompe di calore accoppiate al terreno (Ground-Coupled Heat Pumps, GCHPs), la temperatura media Tm del fluido operatore in un BHE è abitualmente approssimata dalla media aritmetica della temperatura in ingresso e di quella in uscita del fluido. Nei TRT, questa approssimazione causa una sovrastima della resistenza termica dello scambiatore. Nella simulazione dinamica delle GCHPs, questa approssimazione introduce un errore nel calcolo della temperatura in uscita dallo scambiatore di calore. In questa Tesi, la distribuzione di temperatura del fluido nello scambiatore viene studiata mediante accurate simulazioni 3D agli elementi finiti, quindi vengono proposte semplici correlazioni adimensionali che consentono di determinare la temperatura media Tm del fluido in qualsiasi condizione operativa, date le temperature in entrata e in uscita e la portata in volume del fluido e la conducibilità termica della malta sigillante. Vengono inoltre analizzati gli effetti della distribuzione di temperatura superficiale dello scambiatore sulla resistenza termica dello stesso. Si mostra che la resistenza termica 2D di una sezione trasversale non è influenzata dalla differenza della temperatura di bulk fra coppie di tubi, ma è influenzata dalla conducibilità termica del terreno circostante se l’interasse fra i tubi è elevato. Si mostra anche che, se vengono considerati i veri valori della temperatura media di bulk del fluido e della temperatura alla superficie esterna dello scambiatore, la resistenza termica 3D dello scambiatore coincide con quella 2D di una sezione trasversale, a condizione che questa possa essere considerata invariante lungo lo scambiatore.

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Dongellini, Matteo <1988&gt. "Dynamic Modeling and Seasonal Performance Evaluation of Air-to-Water Heat Pump Systems." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amsdottorato.unibo.it/7901/1/Dynamic%20modeling%20and%20seasonal%20performance%20evaluation%20of%20air-to-water%20heat%20pump%20systems.pdf.

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In this Thesis a series of numerical models for the evaluation of the seasonal performance of reversible air-to-water heat pump systems coupled to residential and non-residential buildings are presented. The exploitation of the energy saving potential linked to the adoption of heat pumps is a hard task for designers due to the influence on their energy performance of several factors, like the external climate variability, the heat pump modulation capacity, the system control strategy and the hydronic loop configuration. The aim of this work is to study in detail all these aspects. In the first part of this Thesis a series of models which use a temperature class approach for the prediction of the seasonal performance of reversible air source heat pumps are shown. An innovative methodology for the calculation of the seasonal performance of an air-to-water heat pump has been proposed as an extension of the procedure reported by the European standard EN 14825. This methodology can be applied not only to air-to-water single-stage heat pumps (On-off HPs) but also to multi-stage (MSHPs) and inverter-driven units (IDHPs). In the second part, dynamic simulation has been used with the aim to optimize the control systems of the heat pump and of the HVAC plant. A series of dynamic models, developed by means of TRNSYS, are presented to study the behavior of On-off HPs, MSHPs and IDHPs. The main goal of these dynamic simulations is to show the influence of the heat pump control strategies and of the lay-out of the hydronic loop used to couple the heat pump to the emitters on the seasonal performance of the system. A particular focus is given to the modeling of the energy losses linked to on-off cycling.
Questa Tesi presenta una serie di modelli numerici sviluppati per la valutazione delle prestazioni stagionali di sistemi basati su pompe di calore reversibili di tipo aria-acqua accoppiate a edifici residenziali e non residenziali. Lo sfruttamento del potenziale risparmio energetico legato all'adozione di pompe di calore èun compito difficile per i progettisti, in quanto diversi fattori come la variabilità delle condizioni climatiche esterne, la capacità delle pompe di calore di modulare la potenza termica/frigorifera erogata, la logica di controllo del sistema e la configurazione impiantistica utilizzata influiscono sulle prestazioni energetiche ottenibili. Lo scopo di questo lavoro è quello di studiare in dettaglio tutti questi aspetti. Nella prima parte della Tesi viene presentata una serie di modelli basati su un approccio di tipo "temperature class" per la previsione delle prestazioni stagionali di una pompa di calore reversibile aria-acqua. Viene proposta un'innovativa procedura di calcolo per la determinazione dell'efficienza stagionale della pompa di calore costruita come un'estensione della metodologia riportata dalla norma europea EN 14825. Tale procedura può essere applicata non solo per lo studio di pompe di calore mono-compressore (On-off HPs), ma anche di pompe di calore multi-compressore (MSHPs) ed a velocità variabile (IDHPs). Nella seconda parte della Tesi la simulazione dinamica è stata utilizzata allo scopo di ottimizzare il sistema di controllo della pompa di calore e dell’impianto. I modelli dinamici sono stati realizzati utilizzando il software TRNSYS e permettono di simulare il comportamento dinamico di On-off HPs, MSHPs e IDHPs. Lo scopo principale dei modelli dinamici presentati è quello di evidenziare l'influenza dei sistemi di regolazione della pompa di calore e della configurazione del circuito idronico utilizzato per accoppiare la pompa di calore ai terminali sulle prestazioni stagionali dell'impianto. Particolare attenzione è stata rivolta alla modellazione delle perdite energetiche legate ai cicli di on-off della pompa di calore.

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Rostami, Behnam <1986&gt. "Experimental Analysis of Droplet Generation in Presence of Newtonian and non-Newtonian Flows within Microjunctions." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amsdottorato.unibo.it/8600/1/Thesis_final_Behnam%20Rostami.pdf.

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Microdroplets have attracted increasing interest among researchers due to the wide spread of promising technological applications such as biological analysis, cancer diagnosis, drug discovery and chemical reactions. With respect to traditional emulsion methods which are usually able to produce droplets with a broad size variation (polydispersed emulsions), microfluidic devices have been developed to produce monodispersed microdroplets with a controllable size. The diameter and size variation of droplets are controlled by a series of parameters, including the geometries and dimensions of the microfluidic devices, properties of the liquids, flow rates and surfactant concentrations. In this Ph.D. thesis, droplet formation has been analyzed experimentally, thanks to a series of specific tests on simple microfluidic devices devoted to droplet generation based on the use of T-junctions or micro cross-junctions. The experimental work has been focused on the analysis of the control of droplet regime which can be activated in a microfluidic droplet generator in presence of Newtonian and non-Newtonian dispersed phases, with or without the addition of surfactants. The mechanism of the droplet formation has been studied by following the evolution of the interface between the immiscible liquids at the microjunction thanks to the post processing of images acquired by using a speed camera connected to an inverted microscope. In order to study the behavior of non-Newtonian shear thinning liquids during droplet formation, Xanthan gum aqueous solutions have been used because their rheological properties are very similar to those of blood. The effect on the droplet regimes of the main controlling parameters, such as the flow rates of the immiscible liquids introduced in the microfluidic device, fluid viscosity and interfacial tension has been studied with the aim to individuate the range of these controlling parameters for which the microfluidic device is able to produce monodispersed droplets with an assigned volume and frequency.

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Campana, Jean Pierre <1990&gt. "ALMABEST: a new whole building energy simulation Simulink-based tool for NZEB design." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amsdottorato.unibo.it/8993/3/TESI%20Campana.pdf.

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In this Thesis the new tool ALMABEST for the dynamic energy simulation of the whole building coupled to HVAC systems is presented. This tool, developed in the Matlab environment, consists of two libraries, ALMABuild and ALMAHVAC, dedicated to the building and HVAC system modelling respectively; this Thesis is focused in particular on ALMABuild. In the first part of this Thesis, the description of ALMABuild, which consists of a Simulink library and a set of Graphical User Interfaces (GUIs), is presented. It is emphasized how the use of these GUIs allows to overcome the drawback of other Simulink-based tools in terms of introduction of building data and of implementation of the model in the Simulink desktop. The benchmark of ALMABuild has been performed following the BESTEST procedure. In the second part of this work, applications of the ALMABEST tool are illustrated with the aim to highlight the main features of this tool. In particular, the detailed evaluation of the spatial distribution of radiative, indoor air and operative temperature obtained by means of ALMABEST has been used in order to compare the indoor local comfort conditions obtained by six different emitters. Furthermore, the impact of the temperature sensor position in a room on the local indoor comfort conditions and on the dynamic response of the emitters has been analysed. The coupling of the Matlab Optimization Toolbox with ALMABuild is illustrated by means of a series of single and multi-objective optimizations in which the total annual energy demand is minimized by modifying a series of specific building parameters. Finally, the impact of occupant interactions with windows on comfort and heating energy consumptions is analysed. Results emphasize how the presence of occupants and their active behaviour cannot be ignored if an accurate and realistic evaluation of the building performance have to be obtained.

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Lucchi, Michael <1989&gt. "Dynamic models for the analysis of vapour-compression refrigerating machines." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amsdottorato.unibo.it/9359/1/Michael%20Lucchi%20-%20Cycle%20XXXII.pdf.

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Vapour-compression refrigeration systems represent one of the most relevant fields in terms of energy consumption. Among the research works aimed at reducing their environmental impact, those related to control systems are appealing, since they usually involve lower costs than interventions at system level and directly affects the energy consumption. In this work, a library of models able to reproduce the dynamics of the main components of a vapour-compression refrigeration machine has been developed in Matlab/SIMULINK to supply the building blocks to investigate the effects of different control strategies on the energy performance and on the control quality of the system. To obtain models with low computational cost, the switched moving-boundary approach was adopted for the mathematical model of the heat exchangers. Firstly, the models were numerically verified, using the Matlab toolbox Thermosys as a benchmark. A good agreement between the predictions of the two models was highlighted in the simulation of an air-to-air refrigerating machine; moreover the in-house models showed a better repeatability in the prediction of important quantities like refrigerant superheating, subcooling and charge. The dynamic models were also experimentally validated, comparing their predictions with the experimental data acquired on a water-to-water refrigerating machine equipped with brazed-plate heat exchangers. Results showed a very good agreement between numerical and experimental data, also in terms of electric power absorption and COP, thus proving the model usefulness in transient energy analysis. The effects of the suction accumulator and liquid receiver on the dynamics of the machine were also investigated. A novel lumped-parameter model combining the dynamics of the condenser and of the receiver was developed, allowing the coexistence of a non-zero subcooling at the condenser outlet and a partial filling condition of the receiver. An improvement in the prediction of the refrigerant pressure and temperature at the compressor outlet was highlighted.

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Rehman, Danish <1988&gt. "Experimental and Numerical Analysis of Gas Flows in Microchannels and Micro Heat Exchanger." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amsdottorato.unibo.it/9405/1/RehmanDanish_Ciclo32_Thesis.pdf.

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Due to increased interest in miniaturization, great attention has been given in the recent decade to the micro heat exchanging systems. Literature survey suggests that there is still a limited understanding of gas flows in micro heat exchanging systems. The aim of the current thesis is to further the understanding of fluid flow and heat transfer phenomenon inside such geometries when a compressible working fluid is utilized. A combined experimental and numerical approach has been utilized in order to overcome the lack of employable sensors for micro dimensional channels. After conducting a detailed comparison between various data reduction methodologies employed in the literature, the best suited methodology for gas microflow experimentalists is proposed. A transitional turbulence model is extensively validated against the experimental results of the microtubes and microchannels under adiabatic wall conditions. Heat transfer analysis of single microtubes showed that when the compressible working fluid is used, Nusselt number results are in partial disagreement with the conventional theory at highly turbulent flow regime for microtubes having a hydraulic diameter less than 250 microns. Experimental and numerical analysis on a prototype double layer microchannel heat exchanger showed that compressibility is detrimental to the thermal performance. It has been found that compressibility effects for micro heat exchangers are significant when the average Mach number at the outlet of the microchannel is greater than 0.1 compared to the adiabatic limit of 0.3. Lastly, to avoid a staggering amount of the computational power needed to simulate the micro heat exchanging systems with hundreds of microchannels, a reduced order model based on the porous medium has been developed that considers the compressibility of the gas inside microchannels. The validation of the proposed model against experimental results of average thermal effectiveness and the pressure loss showed an excellent match between the two.

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45

Vayssière, Brandão Pedro <1993&gt. "Linear and nonlinear thermal instability of Newtonian and non-Newtonian fluid saturated porous media." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amsdottorato.unibo.it/10143/1/VayssiereBrandao_Pedro_PhD_Thesis.pdf.

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The present work aims to investigate the influence of different aspects, such as non-standard steady solutions, complex fluid rheologies and non-standard porous-channel geometries, on the stability of a Darcy-Bénard system. In order to do so, both linear and nonlinear stability theories are considered. A linear analysis focuses on studying the dynamics of the single disturbance wave present in the system, while its nonlinear counterpart takes into consideration the interactions among the single modes. The scope of the stability analysis is to obtain information regarding the transition from an equilibrium solution to another one, and also information regarding the transition nature and the emergent solution after the transition. The disturbance governing equations are solved analytically, whenever possible, and numerical by considering different approaches. Among other important results, it is found that a cylinder cross-section does not affect the thermal instability threshold, but just the linear pattern selection for dilatant and pseudoplastic fluid saturated porous media. A new rheological model is proposed as a solution for singular issues involving the power-law model. Also, a generalised class of one parameter basic solutions is proposed as an alternative description of the isoflux Darcy--Bénard problem. Its stability is investigated.

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Zanini, Luigi <1991&gt. "Analisi sulla tecnica esecutiva del pittore Giovanni Bonconsiglio e studio di tempere grasse contenenti azzurrite, previo invecchiamento artificiale." Master's Degree Thesis, Università Ca' Foscari Venezia, 2017. http://hdl.handle.net/10579/10416.

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Il presente lavoro di tesi è partito dallo studio di sei dipinti, appartenenti alle collezioni dei Musei Civici di Palazzo Chiericati a Vicenza (cinque su supporto ligneo, uno su tela), tutte opere attribuite al pittore vicentino Giovanni Bonconsiglio, detto Marescalco, attivo in area veneta tra la fine del XV e l’inizio del XVI secolo, di cui si sono così approfondire le conoscenze relative alla tecnica d’esecuzione pittorica. Di particolare interesse è stato lo studio, attraverso gascromatografia abbinata alla spettrometria di massa GCMS, della frazione organica dei microcampioni prelevati dalle opere, in particolare del legante pittorico, poiché l’arco di tempo a cavallo tra XV e XVI secolo fu un periodo di sperimentazione in cui è possibile riscontrare l’impiego di tempere grasse, ovvero leganti pittorici a base di miscele di sostanze lipidiche e proteiche, scelta intermedia tra l’antica e tradizionale tempera a solo materiale proteico e l’innovazione apportata dall’uso di solo olio siccativo. Oltre al legante, sono stati indagati, tramite analisi al Microscopio Elettronico a Scansione SEM, i diversi sistemi stratigrafici dei campioni inglobati in resina, mentre con l’accoppiamento del SEM alla sonda EDS (Spettrometria a Dispersione di Energia) si sono raccolti i dati sull’analisi elementare per ciascun strato pittorico, utili per la caratterizzazione dei pigmenti impiegati dall’artista. Tramite spettroscopia FTIR-ATR (Spettroscopia Infrarosso in Trasformata di Fourier - Riflettanza Totale Attenuata) sono stati analizzati i residui dei microprelievi non inglobati in resina, troppo piccoli per essere inglobati o ottenuti frammentando microcampioni di dimensioni più consistenti. La parte sperimentale è partita indagando un aspetto suggerito dalla stessa pellicola pittorica di alcuni tra i dipinti qui analizzati, vale a dire l’influsso del pigmento azzurrite sull’invecchiamento artificiale (termico, UV e a elevata umidità) di diverse formulazioni di tempera, basate su varie miscele di colla di coniglio, olio di semi di lino, tuorlo d’uovo e resina mastice. A tale scopo, sono stati eseguiti ad hoc dei campioni in serie, preparati direttamente su vetrini o su supporti lignei preparati, secondo la prassi tradizionale, a gesso e colla animale: la prima serie si compone di diverse tempere pure, senza pigmento, mentre la seconda serie è a base delle medesime tempere, alle quali è stato addizionato il pigmento azzurrite. I risultati ottenuti su questi provini tramite GCMS, analisi DART-MS (Direct Analysis in Real Time accoppiata a spettrometria di massa) e spettroscopia FTIR-ATR sui campioni di solo legante a tempera, invecchiati e non, sono messi a confronto con i dati raccolti con le medesime strumentazioni sui campioni, invecchiati e non, che presentano al loro interno legante miscelato a pigmento. Sono inoltre affiancati i dati colorimetrici, ottenuti prima e dopo invecchiamento sia per i campioni con solo legante che per quelli composti di legante miscelato a pigmento, per avere in mano un dato oggettivo sulle variazioni cromatiche e di luminosità pre e post invecchiamento, oltre che sull’influsso del diverso legante sulla cromia della pellicola pittorica non sottoposta a invecchiamento.

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47

Preti, Lorenzo. "Microincapsulazione di nanoparticelle di argento tramite tecnica spray-freeze-drying." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/10019/.

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Per limitare gli effetti tossici delle Ag-NPs, si è pensato che esse possano essere utilizzate in forma di microincapsulati, in quanto le microcapsule possono avere una certa velocità di rilascio sotto specifiche condizioni. Incapsulando quindi le Ag-NPs, posso ottenere un rilascio controllato di esse, in modo da ottenere una concentrazione di esse utile allo scopo per cui vengono impiegate, evitando un sovradosaggio che non porterebbe alcun beneficio ma solo a una maggior probabilità di causare effetti tossici.

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BISIGHINI, Alfio. "Single and double drop impacts onto deep and thick liquid layers." Doctoral thesis, Università degli studi di Bergamo, 2010. http://hdl.handle.net/10446/609.

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The present experimental and analytical study deals with single and double drop impacts onto a deep pool or liquid layers of finite thickness, with a general purpose of understanding the complex flows generated by spray impacts. The study is focused mainly on the observation of the evolution of the crater formed by the drop impacts and the description of the associated flow in the liquid layer. A test rig for the high-speed-visualization of interface phenomena has been built and experimental investigations using highspeed-imaging and image processing have been performed. Single drop impacts onto a deep pool have been studied in relation with the extensive existing literature. A new classification of the flow regimes has been suggested and a new “trampoline” regime has been detected and described. The phenomenon of the closure of the crown above the crater, typical of terminal speed impacts, has been obtained with unprecedented low impact parameters and it has been observed to be promoted by the sphericity of the impacting drop, while it does not take place if the drop is oblate. A phenomenological investigation of double drop impacts onto a deep pool has been for the first time performed. The phenomena arising have been observed to be characterized by several interactions, which have been described and discussed. The two craters and the two jets ejected from the craters may merge each other. New complex hollow shapes of the crater or of the jet resulting from the merging may be produced and a new mechanism of bubble entrapment has been detected. A test case for the validation of numerical codes has also been proposed, since the simultaneous impact of two identical drops represents a new example of three dimensional free surface flow, instead of the axial symmetry typical of a single drop impact. The influence of a finite value of the depth of the target liquid layer has been investigated in comparison with single drop impacts onto a deep pool, with particular attention on the crater evolution. The presence of the wall has been observed to reduce the velocity of penetration of the crater, but to do not significatively change its maximum depth, which is only reached later. For this reason the maximum crater depth of a deep pool impact has been chosen as reference parameter for the usual classification in thin films, thick films and deep pools of the depth of the target liquid layers in relation with the parameters of the impacting drop. This choice has a more physical significance, since it accounts for the kinetic energy of the impacting drop instead of only its diameter. The crater formed by the impact of a drop onto a deep pool has been characterized for several impact parameters. A new theoretical model for its evolution has been formulated. Potential flow theory has been used to model the flow around the crater as the velocity field given by a moving expanding sphere, whose equations of motion have been obtained through a balance of stresses at the crater interface and include the effects of inertia, gravity, surface tension and viscosity. Agreement with experimental data from the present study and from literature is rather good. A map of the predicted values of the maximum crater depth as a function of the impact parameters has been produced.
The present experimental and analytical study deals with single and double drop impacts onto a deep pool or liquid layers of finite thickness, with a general purpose of understanding the complex flows generated by spray impacts. The study is focused mainly on the observation of the evolution of the crater formed by the drop impacts and the description of the associated flow in the liquid layer.

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49

DALL'OLIO, Stefano. "Boiling of the R134a inside a glass minichannel : a new approach of flow pattern characterization based on flow visualization." Doctoral thesis, Università degli studi di Bergamo, 2009. http://hdl.handle.net/10446/84.

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50

VILLA, Fabio. "Effect of Wettability on Phase Change Phenomena." Doctoral thesis, Università degli studi di Bergamo, 2017. http://hdl.handle.net/10446/89510.

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