Mechanical Engineering / Makina Mühendisliği

Permanent URI for this collectionhttps://hdl.handle.net/11147/4129

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Author: search.filters.author.Çetkin, ErdalSubject: search.filters.subject.Heat transfer

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  • Article
    Gemi Sevk Gücü ve Isı Transferinin Yapısal Gelişim Teorisi ile İlişkisi
    (TMMOB Gemi Mühendisleri Odası, 2022) Güneş, Ümit; Çetkin, Erdal; Şahin, Bahri
    Yapısal Gelişim Teorisi 1996 yılında literatüre kazandırılmış olup tabiattaki ve mühendislikteki tasarım prensiplerini açıklar. Teori, yeryüzündeki akış sistemlerini bütüncül bir şekilde ele alır. Akışın (hareketin) olmadığı yerde çoğu zaman canlılıktan bahsetmemiz dahi mümkün olmamaktadır. Akış sistemlerinin çözümünde anahtar davranış biçimi bu sistemlerin minimum dirençli yol ile hareketini sürdürmesidir. Belli bir zaman dilimi için minimum direnç ile hareket eden sistem zaman geçtikçe kendine yeni yollar (kanallar) bulmakta ya da bazı yolları hiç kullanmayarak yönünü değiştirmektedir. Yapısal Gelişim Teorisi ise hayati öneme sahip olan akış sistemlerinin fiziksel arka planını ortaya koymaktadır. Bu makalede özellikle mühendislik çözümlerinin başında gelen akış sistemlerinin yapısı (gemilerde kurulu ana makine gücü ve ısı transferi örnekleri özelinde) ve Yapısal Gelişim Teorisi’ne göre ilişkisi araştırılmıştır. Bunun için 1085 adet petrol tankeri için DWT ile bu tankerler için gerekli olan güç ilişkisi nonlineer regresyon ile analiz edilmiştir. Sonuç olarak gemilerdeki genel gelişimin ve ısı transferinin yapısal gelişim prensiplerine uygun şekilde gerçekleştiği gösterilmiştir.
  • Article
    Citation - WoS: 35
    Citation - Scopus: 38
    Heat Transfer Enhancement in a Microchannel Heat Sink: Nanofluids And/Or Micro Pin Fins
    (Taylor & Francis, 2020) Coşkun, Turgay; Çetkin, Erdal
    Here, we show that overall thermal conductance in a rectangular microchannel heat sink can be maximized with the combination of nanofluids and micro pin fins. We uncover the effect of micro pin fins and nanofluids both separately and simultaneously in order to uncover their effect on the thermal conductance (i.e., thermal resistance). Both nanofluids and micro pin fins decrease the overall thermal resistance due to increase in the average thermal conductivity of the flow system. In addition, they increase the heat transfer surface area of the solid interacting with the fluid. However, the pumping power (pressure drop) increases in both methods due to the increase in the resistances to the fluid flow. The results document what should be the nanoparticle volume fraction mixed into the base fluid and the micro pin fin volume in order to minimize thermal resistance. If the thermal conductivity of the nanoparticles and micro pin fins are the same, the thermal conductance becomes the maximum with 4% and 0.14% volume fractions for the nanofluid and micro pin fins, respectively. This result shows that inserting micro pin fins and using nanofluids with a given volume fraction ratio maximize the overall thermal conductance. © 2019, © 2019 Taylor & Francis Group, LLC.
  • Article
    Citation - WoS: 33
    Citation - Scopus: 35
    Experimental and Numerical Investigation of Constructal Vascular Channels for Self-Cooling: Parallel Channels, Tree-Shaped and Hybrid Designs
    (Elsevier Ltd., 2016) Yenigün, Onur; Çetkin, Erdal
    In this paper, we show experimentally and numerically how a plate which is subjected to a constant heat load can be kept under an allowable temperature limit. Vascular channels in which coolant fluid flows have been embedded in the plate. Three types of vascular channel designs were compared: parallel channels, tree-shaped and their hybrid. The effects of channel design on the thermal performance for different volume fractions (the fluid volume over the solid volume) are documented. In addition, the effects of the number of channels on cooling performance have been documented. Changing the design from parallel channels to tree-shaped designs decreases the order of pressure drop. Hence increase in the order of the convective heat transfer coefficient is achieved. However, tree-shaped designs do not bathe the entire domain, which increases the conductive resistances. Therefore, additional channels were inserted at the uncooled regions in the tree-shaped design (hybrid design). The best features of both parallel channels and tree-shaped designs are combined in the hybrid of them: the flow resistances to the fluid and heat flow become almost as low as the tree-shaped and parallel channels designs, respectively. The effect of design on the maximum temperature shows that there should be an optimum design for a distinct set of boundary conditions, and this design should be varied as the boundary conditions change. This result is in accord with the constructal law, i.e. the shape should be varied in order to minimize resistances to the flows.