Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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  • Master Thesis
    Numerical Investigation of Thermal Management in Photovoltaic Cells With Phase Changing Materials (pcm) and High Conductivity Inserts
    (01. Izmir Institute of Technology, 2021) Çetkin, Erdal; Çetkin, Erdal; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Photovoltaic cells' electrical conversion efficiency from incident solar radiation heavily depends on the cell temperature. A novel thermal management strategy aimed at keeping the cell temperature in the same order to maximize PV cell electrical conversion efficiency is proposed in this study. The study compares four solar module configurations: a conventional photovoltaic module (PVT module), a hybrid of conventional with PCM (PVT/PCM-I), an internally finned configuration with PCM (PVT/PCM-II), and a configuration where the bottom surface of PVT/PCM-II was cooled via convection (PVT/PCM-III). The developed 3D numerical model was solved via ANSYS software involving the solar ray tracing radiation model for incident solar radiations and a transient melting-solidification thermo-fluid model for modeling of the PCM. Numerical results were validated by comparing them against experimental results published in the literature. Results show that the conversion efficiency of PV cells reaches 16.84%, 18.65%, 18.83%, and 18.98% after 120 minutes for PVT module, PVT/PCM-I, PVT/PCM-II, and PVT/PCM-III, respectively while the specific electrical power produced reaches 75.30W/m2, 83.39W/m2, 84.19W/m2, and 89.42W/m2 for solar radiation of 540W/m2 and 26°C ambient temperature. A 5 mm increase in the fin height for PVT/PCM-II results in a 0.22% increase in efficiency while a 0.5m/s increase in the inlet velocity of the cooling air for PVT/PCM-III results in about 0.06% efficiency increase. Furthermore, performance evaluation of PVT/PCM-III was carried out with sample weather data of the Indian Institute of Technology-Delhi and the Algiers site. The hourly average of overall conversion efficiency for the respective sites reaches 16.70% and 16.84% for a conventional PV module and 19.04% and 19.19% for PVT/PCM-III where the conversion efficiency increases by 14% and 13.7% respectively.
  • Master Thesis
    Computational Fluid Dynamics (cfd) Analysis of Latent Heat Storage in Heat Exchangers by Using Phase Change Materials (pcm)
    (Izmir Institute of Technology, 2020) Çetkin, Erdal; Çetkin, Erdal; Rocha, Luiz Aberto Oliveira; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    The development of TES applications and materials takes the attention of many researchers, but the current literature rarely involves studies concerning medium temperature applications. This thesis compares available phase change materials (PCMs) for the medium temperature range. For this aim, Erythritol was defined as PCM in the numerical analyses. The effect of heat transfer fluid (HTF) tube position and shell shape on the melting time and sensible energy requirement for melting a phase change material (PCM) in a latent heat thermal energy storage (LHTES) application were investigated. Tube location and shell shape are essential due to the shape of the melted region, i.e., similar to the boundary layer. Results show that the S-curve of melting becomes steeper if the tubes are distributed such that the intersection of melted regions is delayed. Therefore, melted regions should be packed into a finite space which uncovers the shape of the shell that minimizes melting time and required sensible energy. Results show that, rectangular-shaped shell design where the tubes located near the bottom end decreases melting time and sensible energy from 67 minutes to 32 minutes and from 161.8 kJ/kg to 136.3 kJ/kg for %72.3 liquid fraction relative to the circular-shaped shell, respectively. In the four-tube cases, then the required melting time and sensible energy decrease 80% and 3.8% through the rectangular-shaped shell design for the PCM to melt completely, respectively. Overall, the results show that sensible energy storage and especially melting time can be decreased greatly by just varying the design.
  • Master Thesis
    Investigation of the Effect of Pase-Change Metarials on the Performance of Household Refrigerators
    (Izmir Institute of Technology, 2014) Coşkun, Çağlar; Özkol, Ünver; Özkol, Ünver; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    The main problem that this study deals with is the issues of thermal effectiveness of phase change materials (or PCM) application to household refrigerators and investigating the performance improvement with numerical methods. PCMs are materials that store thermal energy in latent heat form between its solidus and liquidus points. By this way, these materials can store large amount of heat in a narrow temperature range, which made them to gain popularity in recent years. By exploiting this feature of PCMs, it is thought that using these materials in household refrigerators could increase the energy efficiency, thus energy class of a refrigerator. Because, keeping the cold energy inside the refrigerated space as latent heat will decrease the number of stop and start cycles of the compressor. Decreasing the number of stop and start cycles is beneficial since the distribution of refrigerant fluid in the refrigeration cycle breaks down every time compressor is stopped and established again on the next start, which is the main inefficiency source. In this study, at first, the steady temperature contours are extracted by steady state numerical simulations to see the possible locations for the application of PCMs. Then, transient simulations are conducted to understand the transient thermal behavior of the refrigerated space and these transient results are validated with experimental data. In the light of these steady and transient thermal pictures, PCMs having proper phase change temperatures are placed in appropriate places on the walls of the refrigerator and transient simulations are conducted to see the effects of PCMs. Since radiative heat transfer cannot be ignored in household refrigerators, all simulations are conducted with and without radiation and effects of radiation are also presented. The well – known commercial computational fluid dynamics (CFD) code, FLUENT is employed for the numerical simulations.