http://repositorio.jesuita.org.br/handle/UNISINOS/1682 PPG Engenharia Mecânica Wed, 15 Apr 2026 16:25:37 GMT 2026-04-15T16:25:37Z http://repositorio.jesuita.org.br/handle/UNISINOS/13988 Análise experimental da mudança de fase de bioPCM em espuma metálica de geometria retangular e perfilada Becker, Fábio As a result of the gradual energy transition, with the increasing use of cleaner energy sources, energy storage becomes inevitable, mainly due to the seasonality of generation from such sources. In this context, one of the main existing alternatives is energy storage through latent heat. The main characteristic of this type of storage is its high energy storage density at a virtually constant temperature—that is, at the temperature at which the phase change occurs—which makes it possible to use it in numerous applications. Materials based on this form of storage are known as Phase Change Materials (PCMs). Due to their wide range of applications, the use of bio-based PCMs (bioPCMs) is important to mitigate potential environmental impacts. However, PCMs generally have low thermal conductivity, which may limit some applications. Therefore, methods that can improve heat transfer are necessary. The incorporation of metallic foams with different morphological characteristics into PCM is an efficient alternative that has been investigated due to its high heat exchange surface area and improved thermal conductivity. In this context, this research proposes a study with different foam geometries, along with the use of palm wax as bioPCM. Thus, two nickel foam geometries were used: one rectangular and the other profiled, which resembles a fin geometry. This allows for increased heat transfer and efficiency with a smaller foam volume. Furthermore, the influence of changing the reservoir orientation, analogous to the tilt of a photovoltaic module, was also analyzed. The main results showed that the case containing rectangular foam reduced the charging (fusion) time by 7.5% and the discharging (solidification) time by 4%, compared to the case without foam, while the case containing the profiled geometry reduced the charging time by 7.1% and increased the discharging time by 10%. The inclusion of foam also improved the energy storage rate by approximately 8.1% for the rectangular geometry and by 7.6% for the profiled geometry. Thu, 27 Nov 2025 00:00:00 GMT http://repositorio.jesuita.org.br/handle/UNISINOS/13988 2025-11-27T00:00:00Z http://repositorio.jesuita.org.br/handle/UNISINOS/13987 Análise experimental e numérica do escoamento em coletores solares de tubo a vácuo sob diferentes inclinações Spengler, Fernando Claudio This thesis presents an integrated experimental and numerical investigation of the thermal and fluid dynamic behavior of water in evacuated tube solar collectors operating under natural circulation (thermosiphon regime). The study focuses on the influence of the tube set inclination on the internal circulation of the thermal fluid and the stability of the flow. The experimental methodology involved test bench trials under real operating conditions, with continuous monitoring of temperature and mass flow rate for inclinations of 20°, 30°, and 45°. In parallel, numerical simulations were conducted using CFD (Computational Fluid Dynamics), employing validated numerical models to analyze the local velocity and temperature fields inside the tubes. The results indicate that inclinations higher than 30° enhance natural convection but also induce transient flow instabilities, characterized by abrupt oscillations in the mass flow rate. The coupled analysis confirmed the consistency between experimental and numerical patterns, revealing internal mechanisms associated with the breakdown of thermal stratification and the formation of recirculation. The daily global efficiency of the system was calculated for each inclination configuration, resulting in the following efficiency values: 46.4% for 20°, 69.5% for 30°, and 54.4% for 45°. These results highlight that the 30° inclination provided the highest overall thermal efficiency, due to its more stable behavior throughout the daily cycle. Although the 45° inclination promoted the highest values of flow rate and temperature increase, the system’s behavior did not remain stable at this elevated level throughout the day, which resulted in a lower efficiency compared to the 30° inclination. The conclusions highlight the importance of inclination adjustment to optimize the thermal performance of the collectors and demonstrate that the combination of numerical and experimental methods is effective in understanding the phenomena involved. Tue, 22 Jul 2025 00:00:00 GMT http://repositorio.jesuita.org.br/handle/UNISINOS/13987 2025-07-22T00:00:00Z http://repositorio.jesuita.org.br/handle/UNISINOS/13917 Análise teórico: experimental de um concentrador solar tipo Fresnel Linear Scalco, Patricia Solar radiation, an abundant and renewable source, can be harnessed through solar concentrators, which direct and concentrate incident radiation into small areas, converting it into heat for electricity generation or to supply industrial processes requiring medium to high temperatures. One of the technologies that apply this concept is the Linear Fresnel Reflector (LFR), which uses parallel rows of flat (or slightly curved) mirrors that move throughout the day following the movement of the Sun. Solar radiation strikes the mirrors and is reflected to an absorber, where the radiation is converted into thermal energy. In this context, this thesis presents a theoretical and experimental analysis of the performance of an LFR system with a trapezoidal cavity receiver, installed at the Renewable Sources Laboratory of the University of Vale do Rio dos Sinos (UNISINOS). The study was structured in three main stages: geometric and analytical modeling, thermal analysis of the receiver, and experimental validation. The first step involved characterizing the mirror array and receiver, applying the gap angle concept to redistribute the mirror rows to minimize blocking and shading losses. Subsequently, a thermal model was developed to simulate heat transfer in the receiver: heat balances were applied to each of the surfaces involved in the heat exchange, properties of the Paratherm HE thermal fluid, conduction, convection, and radiation losses. Subsequently, experimental tests were conducted on different days and flow rates, enabling comparison with theoretical results. The analysis revealed that, although the thermal model accurately predicts thermal trends, discrepancies occur due to operational instabilities and limitations in experimental control. Furthermore, the results showed that the trapezoidal cavity receiver achieved an optical efficiency of 77% and a CAP of 0.24, values higher than those obtained with the CPC combined with the evacuated tube (63% and CAP of 0.10). Mirror redistribution using the gap angle criterion increased efficiency to 89%, albeit with a smaller angular tolerance. Experimental tests confirmed the influence of operating conditions and thermal losses, while the theoretical model adequately reproduced the receiver's behavior, highlighting the importance of convection and radiation losses at high temperatures. Thu, 17 Jul 2025 00:00:00 GMT http://repositorio.jesuita.org.br/handle/UNISINOS/13917 2025-07-17T00:00:00Z http://repositorio.jesuita.org.br/handle/UNISINOS/13574 Análise teórico-experimental de métodos de vitrificação para aplicações de criopreservação de sêmen Silva, Álisson Renan Stochero da The success of a cell cryopreservation procedure is directly related to the method of preparing the biological material, the freezing protocol, the sample volume and the relationship between the cooling rate and the concentration/type of cryoprotective agents (CPA). In order to avoid the formation of ice crystals, the sample cooling rate must be greater than the crystal formation rate. Through the vitrification method, it is possible to achieve high cooling rates, making the direct transition from the liquid state to the vitrified and amorphous state, without the formation of ice crystals. The probability of vitrification increases with higher cooling rates, higher viscosity and smaller sample volume. Vitrification is most used when working with biological materials with a small volume and low concentration of intracellular water, such as semen cryopreservation applications. In this work, two semen cryopreservation methods were developed, the direct immersion vitrification method and the contact droplet vitrification method. An experimental and numerical investigation was conducted, through the design and construction of benches and equipment, computer simulations, evaluation and proposal of methodologies. For the contact droplet vitrification method, solidification advancement behavior, cooling rates, contact angle, geometry and material of the cooling surface were investigated. For the direct immersion vitrification method, the influence of the cooling medium was investigated, comparing immersion in liquid nitrogen (LN2) with nitrogen slush (SN2). The effect of the type of container for sample allocation was also evaluated, comparing cryotubes with PDMS chips, comparing different concentrations of CPA and the impact of volume on the cryopreservation process. Biological tests with semen investigated the influence of the processing method (simple washing and swim-up), and freezing protocol, on the cooling rate, viability and motility. The results in this work support the improvement and development of new methods and protocols for cryopreservation of biological materials, especially for semen vitrification applications. Fri, 28 Jun 2024 00:00:00 GMT http://repositorio.jesuita.org.br/handle/UNISINOS/13574 2024-06-28T00:00:00Z http://repositorio.jesuita.org.br/handle/UNISINOS/13452 Desing construtal aplicado à convecção de calor em cavidades com obstáculos Borahel, Rafael da Silveira From the perspective of the constructal design, this work investigated the convection process in a lid-driven cavity with an isothermal block (BI) inside, with the aim of maximizing the dimensionless heat transfer rate (𝑞∗) on the walls of the block. Keeping the BI vertically centred (𝑦0∗ = 0,5) in the cavity, the degrees of freedom (GL) considered for the system were the cavity and BI aspect ratios (𝐴𝑅 and 𝐴𝑅0, respectively), combined with the dimensionless horizontal position of the BI inside the cavity (𝑥0∗ ). In addition to these parameters, the size of the isothermal block – symbolized by  – was also considered a key parameter of the system. For this purpose, four different sizes were considered to the BI ( = 1/4, 1/8, 1/16 and 1/32), making it possible to analyze their effects on the flow and convective heat transfer inside the system. By varying these parameters, a total of 280 different designs were generated and tested for the system, which were evaluated in the dominant forced, mixed, and natural convection scenarios, resulting in 840 analyzed cases. The convective flow inside the cavity was considered Newtonian, two-dimensional, laminar, incompressible and steady-state The mathematical model consisted of the conservation equations of mass, momentum (in 𝑥 and 𝑦 directions) and energy. All the equations were solved computationally through numerical simulations carried out in ANSYS FLUENT 2023 R1, which uses the finite volume method (MVF). Among the 280 different designs created and tested for the system, the one that proved to be the most effective in promoting 𝑞∗ was characterized by 𝐴𝑅 = 0.35 (horizontal cavity) and 𝐴0 = 1 (square). Through this design, giving to the BI its largest size ( = 1/4), the maximum value of 𝑞∗ (31,19) was achieved with the BI subtly shifted to the right (𝑥0 ∗ = 0,6) in the forced convection scenario. In general, this system configuration stood out in promoting 𝑞∗ due to having a larger lid, which moves a greater amount of fluid, thus increasing the momentum of the flow. In addition, the horizontal shape of the cavity narrows its upper gap, bringing the top wall of the BI closer to the sliding lid and thus reducing the thickness of the thermal boundary layer that forms there, which benefits heat transfer. Thu, 22 Feb 2024 00:00:00 GMT http://repositorio.jesuita.org.br/handle/UNISINOS/13452 2024-02-22T00:00:00Z http://repositorio.jesuita.org.br/handle/UNISINOS/13451 Avaliação geométrica de três aletas inseridas em uma cavidade aplicando design construtal e o método superfície de resposta Rodrigues, Priscila Martta Lid-driven cavities are often used as a simplified case to study and understand various complex engineering problems, such as heat exchangers and heat sinks, in order to identify which geometry offers the best performance. In this context, the present work conducted a numerical study and geometric evaluation of a mixed convection flow with heat transfer. The objective was to assess the effects of the geometry of three fins inserted inside a lid-driven cavity subjected to mixed convection on the heat transfer between the fins and the fluid, indicating the configurations with the best performance under different conditions through the application of the Constructal Design method. The study involved the investigation of the following stages: (i) evaluating the effect of the aspect ratios of each of the three fins on the heat transfer rate; (ii) evaluating the effect of the fin area fractions (ϕ1, ϕ2, and ϕ3), keeping the left fin area fraction (ϕ1) and the ratio H1/L1 fixed, associated with a search space screening; (iii) evaluating the effect of different total area fractions (ϕT = 0.05, 0.1, and 0.2) for different fin area ratios for Ri = 0.1 and 1, using the Response Surface Methodology (RSM) combined with Design of Experiments; (iv) comparing the system performance for different Richardson numbers. When associated with a search space screening, the results indicated that the best performance was achieved when fin 3 (ϕ3) has the largest area and the highest H3/L3 ratio, suggesting that the dominance of fin 3 enhances thermal exchange, particularly for higher H3/L3 ratios, while the predominance of fin 2 is observed for lower H3/L3 ratios. The best geometry found was H1/L1 = 0.1, H2/L2 = 0.5, and H3/L3 = 19, resulting in the highest heat transfer rate for the configuration ϕ1 = 0.05, ϕ2 = 0.04, ϕ3 = 0.01. The evaluation of Constructal Design combined with RSM allowed for the determination of the geometry that achieves the best thermal performance by varying the fraction of the area occupied by the fins. The results showed that the largest total area fraction provides the most favorable performance, attributed to the increase in the heat exchange area provided by the fins. The best thermal performance for Ri = 0.1 was 32% higher compared to the best performance for Ri = 1. It was observed that the use of Constructal Design associated with RSM required fewer simulations compared to a search space sweep for similar aspect ratios (Hn/Ln). Tue, 17 Sep 2024 00:00:00 GMT http://repositorio.jesuita.org.br/handle/UNISINOS/13451 2024-09-17T00:00:00Z http://repositorio.jesuita.org.br/handle/UNISINOS/13450 Avaliação de um sistema micro CHP experimental para veículos recreativos Pinto, Daniel Vieira Recreational vehicles (RVs) are homes on wheels that can be pulled by a motor vehicle, in the case of trailers, or can be self-propelled, like a motorhome. For comfortable use of an RV, there is a need for an electrical supply to recharge its batteries and operate the appliances and equipment installed, as well as thermal energy, for heating water and possibly air conditioning. A conventional and widely used solution for supplying electrical energy is the installation of photovoltaic modules combined with a connection to an electrical grid, when possible, although in some cases combustion engine generators are used. Water heating is generally done by means of gas-fired instantaneous heaters or hybrid gas/electric storage heaters. In general, air conditioning in RVs is done by means of split-type air conditioning and gas or diesel heating. In order to develop an alternative to the currently available energy supply methods, combined with the search for more efficient and environmentally friendly means of energy use, this work proposes the creation of a cogeneration system (heat and electric power) for RVs. A systematic literature review (SLR) was carried out, covering scientific articles on combined heat and power (CHP) systems. The SLR was preceded by a search for documents on cogeneration and energy use in RVs, both in scientific databases and in intellectual property banks. A research gap was identified on micro CHP devices for RVs. In the development of this work, an experimental micro CHP device (mCHP-Ex) was created, with 980 W of maximum electrical power, consisting of a single-cylinder internal combustion engine, an automotive alternator and heat exchangers for thermal recovery. The prototype was enclosed and instrumented, enablingmeasurements of the thermal power available in the water flow (from exhaust gases, lubricating oil and cooling air heat recovery systems) in addition to the electrical power of the alternator. To quantify the availability of electrical and thermal power, as well as the efficiency and operation parameters of the system, tests were performed in 46 different operating conditions, combining variations between 2000 rpm and 3600 rpm in the engine rotation frequency and the levels of electrical load imposed on the alternator, from no load to 100% load. The electrical efficiency of the mCHP-Ex reached 10.18% ± 0.2% at 3008 rpm with 83% load. Maximum electrical output was 0.746 kW ±0.015 kW at 3637 rpm and 100% load. Maximum thermal energy recovery rate was 3.267 kW ±0.039 kW. Utilization factor reached 65.57% ±0.22%. Compared to commercial micro CHP systems seen at RSL, mCHP-Ex can be up to 48% lighter. Compared to traditional means of providing separate electrical and thermal power for RVs, mCHP-Ex provides 63% greater primary energy utilization when the demand is for electrical power and space heating. However, for conditions where the demand is for electrical power and water heating, or even electrical power alone, current solutions available are still more efficient. Wed, 19 Jun 2024 00:00:00 GMT http://repositorio.jesuita.org.br/handle/UNISINOS/13450 2024-06-19T00:00:00Z http://repositorio.jesuita.org.br/handle/UNISINOS/13214 Comparative study on the performance of photovoltaic modules and their sensitivity to external parameters based on an experimental analysis Abe, Caio Felippe In this thesis, four photovoltaic (PV) technologies were experimentally compared, aiming to quantify the impact of the external parameters on PV performance. Two of the technologies studied are quite common in the market: polycrystalline (p-Si) and monocrystalline (m-Si). The third technology, bifacial, allows the conversion of the solar radiation reaching the back face of the modules, providing a yield gain. Modules with multijunction cells under concentration (HCPV) were also included in the analysis. They use a larger solar spectrum range and lenses to concentrate the beam radiation thanks to a 2-axis tracker constantly following the Sun. The PV modules were tested and had their ratings experimentally determined using modeling approaches developed in this thesis. All modules were assembled on the PV tracker to provide the same operating conditions, and the measurement campaign was carried out for 12 months. The experimental records, at one-minute timestep, were checked for synchronicity, interpolated, and aggregated. Several filtering approaches were discussed and applied to provide an adequate balance between noise removal and data retention. The PV arrays were then studied concerning their particularities, starting with the identification of the most influencing operating parameters, in order of relevance, and their impact on the output power. Then, the effect of the operating temperature was assessed, and the actual temperature coefficients for the DC power were determined. Finally, a sensitivity analysis targeting the DC power relative to the operating parameters was performed based on filters and mathematical models developed for each PV array. Special attention was given to the bifacial array since this technology is very promising due to its interesting cost-benefit relation; novel methods to determine the effective irradiance and the bifacial gain were also developed. Two different methods were applied to characterize the PV modules. It was found that their actual performance is not as good as reported on the datasheets. The m-Si array was the least sensitive to the operating temperature, followed by the p-Si and bifacial modules. In turn, the HCPV devices were the most impaired by the temperature, air mass, and humidity. The wind speed influence was small for the HCPV modules; the arrays most benefited by the wind were the p-Si and m-Si. The bifacial array presented the greatest final yield (with a bifacial gain of 6.2 %), followed by m-Si and p-Si. In turn, the HCPV array presented the poorest yield, mainly due to their responsiveness only to the beam irradiance and the high temperature coefficient for the DC power.; Dans cette thèse, quatre technologies photovoltaïques (PV) ont été comparées expérimentalement afin de quantifier l'impact des paramètres externes sur leurs performances. Deux des technologies étudiées sont courantes sur le marché : le polycristallin (p-Si) et le monocristallin (m-Si). La troisième technologie, bifaciale, convertit également le rayonnement solaire atteignant la face arrière des modules, apportant ainsi un gain de rendement. Enfin, des modules à cellules multi-jonctions sous concentration (HCPV), permettant d’utiliser un plus large spectre solaire, sont également étudiés ; ils utilisent des lentilles pour concentrer le rayonnement et ont besoin d’un tracker biaxial pour recevoir et convertir le rayonnement direct perpendiculaire au plan des modules. Les modules PV ont été testés et leurs caractéristiques déterminées expérimentalement à l'aide d'approches de modélisation développées dans cette thèse. Tous les modules ont été assemblés sur le même tracker pour offrir les mêmes conditions de fonctionnement, et la campagne de mesures a duré 12 mois. Les enregistrements expérimentaux – mesurés à un pas de temps d'une minute – ont été vérifiés pour leur synchronicité, interpolés et agrégés. Plusieurs approches de filtrage ont été appliquées et discutées pour atteindre un équilibre adéquat entre suppression du bruit et conservation des données. Les paramètres les plus influents, par ordre de pertinence, et leur impact sur la puissance des quatre générateurs PV ont été étudiés. L'effet de la température a été évalué et les coefficients de température réels ont été déterminés. Une analyse de sensibilité de la puissance par rapport aux paramètres de fonctionnement a été réalisée sur la base de filtres et de modèles mathématiques développés pour chaque générateur PV. Une attention particulière a été accordée aux modules bifaciaux car cette technologie est très prometteuse du fait de son bon rapport coût-bénéfice ; de nouvelles méthodes pour déterminer l’irradiance efficace et le gain bifacial ont été développées. Deux méthodes ont été appliquées pour caractériser les modules PV. Il a été constaté que leurs performances réelles n’étaient pas aussi bonnes que celles indiquées sur les fiches techniques. La technologie m-Si était la moins sensible à la température, suivi des modules pSi et bifaciaux. Les modules HCPV étaient les plus altérés par la température, la masse d’air et l’humidité. L’influence du vent est moins marquée pour les modules HCPV mais plus importante pour le p-Si et le m-Si. Les modules bifaciaux ont des performances plus élevées (gain bifacial de 6,2 %), suivi du m-Si et du p-Si. Le générateur HCPV présentait la production la plus faible, principalement en raison de l’utilisation de la seule composante directe du rayonnement et du coefficient de température élevé. Tue, 05 Mar 2024 00:00:00 GMT http://repositorio.jesuita.org.br/handle/UNISINOS/13214 2024-03-05T00:00:00Z http://repositorio.jesuita.org.br/handle/UNISINOS/12937 Síntese de nanopartículas metálicas e uso de grafeno para tintas condutivas aplicadas a blindagem eletromagnética Bobsin, Alexsandro The development of conductive inks has increased recently, especially in the microelectronics industry. Micro and nanoparticles of copper or silver are generally used in the composition of inks, but the high cost of silver and the oxidation of copper are challenges for industrial use. Another option is the use of particles with a copper core covered by silver (Cu-Ag), also called core-shell, as it overcomes both limitations of the pure metals mentioned. Graphene is another conductive nanomaterial emphasized in scientific studies to formulate new inks. A silver ink painting of the system in a package (SiP) chip is a technology that produces a conductive film covering these devices against electromagnetic interference (EMI). This is an alternative method to metal cans that have been used in the shielding of these microchips. Nevertheless, painting with Cu-Ag or graphene inks can reduce the amount of silver, becoming an opportunity for innovation. Furthermore, it reduces production costs and generates environmental gains through metal cans. Therefore, this research proposes using conductive inks with these nanomaterials as an alternative to forming films for electromagnetic shielding and painting SiP chips to cover it. The objective was to synthesize and disperse Cu-Ag particles for the formulation of metallic paints and a water-based graphene suspension for electromagnetic shielding. The morphology, size, chemical composition, and crystalline phases of the particles used techniques of atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), light diffraction, and X-ray diffraction (DRX). Films were produced by casting and spray painting to measure resistivity, test substrate adhesion, and electromagnetic shielding, including evaluating coverage on SiP chips. The Cu-Ag particles had different shapes with complete and partial coverage of silver on copper. The few-layer and multilayer graphene were used. The Cu-Ag ink showed an electrical resistivity of 10-04 Ω.cm at 200 °C, while the graphene suspension 10-02 Ω.cm at 300°C. PET presented better adhesion in the test on different substrates according to standard d3359. The shielding efficiency was -44 dB for CU-Ag ink and -9 dB for graphene suspension, according to ASTM d4935. Mon, 18 Sep 2023 00:00:00 GMT http://repositorio.jesuita.org.br/handle/UNISINOS/12937 2023-09-18T00:00:00Z