Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Experimental Investigation of a Photovoltaic Thermal System With Phase Change Material(01. Izmir Institute of Technology, 2024) Karakaya, Özlem; Çetkin, ErdalÇevre dostu enerji kaynakları arasında güneş enerjisi en yaygın kullanılanlardan biridir. Fotovoltaik sistemler, güneş ışığını elektrik enerjisine dönüştürerek bu enerji kaynağını kullanmanın temel yolunu oluşturur. Ancak, PV sistemlerin verimliliği, sıcaklık artışlarıyla azalır. Bu çalışma, PV panellerin performansını artırmak için faz değiştiren malzemeler ve su soğutmalı fotovoltaik termal sistemlerin entegrasyonunu araştırmaktadır. Çalışma iki aşamadan oluşmaktadır ve her iki deney de Antalya'da gerçekleştirilmiştir. İlk aşamada, erime noktaları 25°C ve 35°C olan faz değiştiren malzemelerle entegre edilmiş PV panellerin performansı, standart PV panellerle karşılaştırılmıştır. Sonuçlar, faz değiştiren malzeme entegrasyonunun termal yönetimi iyileştirdiğini ve elektriksel verimliliği artırdığını göstermektedir. PV-PCM35 sistemi, yüksek sıcaklık koşullarında panel sıcaklığını 21.3°C oranında düşürerek, ortalama %2.16 ve maksimum %3.72 oranında verimlilik artışı sağlamıştır. İkinci aşamada, faz değiştiren malzeme ile entegre edilmiş su soğutmalı bir PV/T sistemin performansı, geleneksel PV sistemlerle karşılaştırılmıştır. Bulgular, PV/T-PCM sisteminin elektriksel verimlilikte önemli iyileştirmeler sağladığını ortaya koymaktadır. Su soğutma mekanizması, ısıyı etkili bir şekilde dağıtarak panel sıcaklıklarının düşük kalmasını sağlamış ve verimliliği artırmıştır. PV/T-PCM sistemi, maksimum elektriksel verimlilikte %3.79 ve termal verimlilikte %62.74 artış göstermiştir. Bu sonuçlar, PV/T-PCM sistemlerinin özellikle Antalya gibi yüksek sıcaklıklara sahip bölgelerde daha verimli enerji üretme potansiyeline sahip olduğunu göstermektedir.Master Thesis Design Optimization of an Industrial Oven Heat Exchanger(01. Izmir Institute of Technology, 2021) Nergiz, Güven; Çetkin, ErdalThe coating application of metals (especially in automotive and white goods sectors) is used in various fields to protect the metal against oxidation, corrosion, scratch, or high temperature to increase product lifetime. The most efficient technique in the coating application is powder coating where the powder is Epoxy-polyester. This process has three steps; surface pretreatment (washing), powder coating, and curing the coated metal. Metals may need to be dried and cured in ovens with 90°C and 200°C, respectively, for the required quality coating process. Burners are used as the heat source in the oven's heat exchangers. Due to high temperatures, the expanding heat exchanger is exposed to various thermal stresses. The stresses cause cracking and rupture problems. The regions where thermal stresses occur intensely are the surfaces with high-temperature differences. Various mass flow rates in the heat exchanger cause non-uniformity for how the energy to be transferred, thus non-uniform surface temperature distribution. In this study, a heat exchanger design provided by "ELECTRON – Sistem Teknik Makina" company has been studied. The mass flow rates in the heat transfer pipes (where the heat is mainly transferred) show deviations up to 75% from the ideal rate. With this study, deviations have been reduced to the level of ±10%. The results show that the maximum thermal stress on the heat exchanger was reduced by 24% with this improvement. In general, the uniform mass flow rates obtained in the heat transfer pipes provided a more homogeneous distribution of the surface temperatures, thus decreased thermal stresses.Master Thesis Investigation of Microchannels Heat Exchangers for Condensers(01. Izmir Institute of Technology, 2021) Sevencan, Furkan Tuğberk; Çetkin, ErdalThere are limited types of condenser types/designs in the market although there are many distinct heat exchangers available. One reason is related to the complexity of the phase-change mechanism and how it is affected by the geometric parameters of the heat exchanger. Technological requirements force the size of any component to become smaller and condensers are no exception for this trend. However, there is a limit for scaling down the current condensers, and their compactness cannot be decreased due to their serpentine design. The transition from serpentine designs to parallel microchannels is promising as the required coolant volume would decrease significantly for the same cooling due to enhanced heat exchange surface area. However, parallel channel designs are challenging to implement due to irregularities in pressure distribution which would yield phase change and condensation temperature significantly. In the present thesis, a microchannel heat exchanger was selected and the imperfections related to the pressure distribution irregularities were progressively developed numerically. Geometrical parameters were optimized to eliminate the flow maldistribution resulted from non-homogeneous pressure distribution in the condenser. The effects of header shape (from rectangular to tapered) on flow uniformity are not dramatic. Then, manifold channels were relocated with given protrusion depths which were optimized using an iterative approach. Relocating the channels enables the pressure uniformity. Finally, the condensation behavior of the design developed with the aim of enabling uniform flow resistance was documented. Under the given operational conditions, three different height channel design is 100% condensed R410a from the vapor phase into the liquid phase. A and B design were condensed the refrigerant fluid in a low Reynolds number meanwhile, C design was condensed in a high range of Reynold number. All in all, effects of maldistribution on flow regime were tried to be eliminated with new geometric design approaches and condensation effect in new geometries was able to be seen 100% at low flow rates.