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Öğe Alüminyum Köpüklerde İki Boyutlu Isı Transferinin Deneysel ve Sayısal Olarak İncelenmesi(2016) Sertkaya, Ahmet Ali; Akbaba, BurakBu çalışmada açık hücreli alüminyum köpükler ısı değiştirici formuna getirilip iki boyutlu ısı transferi deneysel ve sayısal olarak incelenmiştir. 10, 20 ve 30 PPI (Number of Pores Per Inch) gözenek yoğunluklarına sahip açık hücre alüminyum köpükler sabit ısı akısı için ısı değiştiricinin kanatlarını oluşturmuştur. Alüminyum köpük üzerinde, X-Y düzleminde özellikle ısıtıcıya yakın bölgelerde sık olarak yerleştirilen ısıl çiftlerle sıcaklıklar ölçülmüştür. Elde edilen sıcaklıklar yardımıyla bütün yüzey üzerindeki sıcaklık dağılımı bulunmuştur. Grafikler, yüzey sıcaklıkları ve giriş sıcaklığı (?T) arasındaki farka dayalı olarak çizilmiştir. Ayrıca her üç ısı değiştirici için basınç düşüşü bulunmuştur. Sistem için iki boyutlu ısı transferi denklemleri sayısal olarak elde edilmiştir. Elde edilen denklemler merkezi fark yöntemi kullanılarak çözülmüştür.Öğe EXPERIMENTAL AND NUMERICAL ANALYSIS OF A TWO DIMENSIONAL HEAT TRANSFER ON OPEN CELL ALUMINUM FOAMS(Gazi Univ, Fac Engineering Architecture, 2016) Sertkaya, Ahmet Ali; Akbaba, BurakIn this study, heat transfer was investigated in open cell aluminum foams formed into a heat exchanger experimentally and numerically as two dimensional. The open cell aluminum foams with pore density of 10, 20, 30 PPI were used as the heat exchanger fins formed for a constant heat flow. Temperatures were measured using thermocouples located on several points in the X-Y planes of the aluminum foams especially on areas near the heaters. The temperature distribution for the whole area was obtained from the measured temperatures,. The graphs were plotted based on the difference between the surface temperatures and the inlet temperature (Delta T). In adition for each of the three heat exchanger pressure drop was found. Two dimensional heat transfer equations for the system were derived in the numerical solution. Then the obtained equations were discretized by using the central difference method and finally solved.Öğe Experimental and Numerical Analysis of one Dimensional Heat Transfer on Open Cell Aluminum Foams(Gazi Univ, 2015) Sertkaya, Ahmet Ali; Ates, Ali; Altinisik, Kemal; Dincer, KevserIn this study, one dimensional heat transfer of open cell aluminum metal foams is investigated both experimentally and by using numerical methods as well. Open cell aluminum foams with pore densities of 10, 20 and 30 (Number of Pores Per Inch) PPI were shaped into heat exchangers. The foams having sizes of 200 x 100 x 20 mm were insulated on their three faces. Steady heat flux was maintained on the base section of the foam by heating a plate shaped coil electrically. Temperature distributions on the vertical sections and mostly on locations near heaters were measured with the thermocouples located on the aluminum foams. With the help of the recorded temperatures from the tests the graphs of open cell aluminum foams with pore densities of 10, 20 and 30 were plotted. First of all, one dimensional heat transfer equations were derived for the numerical solution of the system. The governing equations obtained were then discretized by using the Central Difference Method and finally solved with the Finite Difference Method. The results obtained were converted into graphs and compared with the empirical results obtained beforehand. The fastest drop in temperature close to the heater was observed at the foam with 10 PPI while the lowest falling rate took place at the foam with 30 PPI pore density. At an interval of three aluminum foams, the temperature difference was found to be higher near the heater and lower away from the heater. It was found that both experimental and numerical results are closely related.Öğe Experimental Investigation of Heat Transfer Depending on Inclination Angle of Unfinned, Axial Finned and Radial Finned Heat Exchangers(Pergamon-Elsevier Science Ltd, 2021) Sertkaya, Ahmet Ali; Sari, SinanIn this study, effects of axial and radial fins on a circular pipe and inclination angle were investigated experimentally for natural convection heat transfer. An unfinned circular pipe was utilized as reference. Experiments were carried out at 0 degrees,30 degrees,60 degrees and 90 degrees pipe inclination angles to measure natural convection heat transfer. Hot water was used as heat source during the experiments. The water in a storage tank was kept at a constant temperature and it was circulated through heat exchanger. Radiation heat transfer was also taken into consideration. Rayleigh number varied between Ra approximate to 10 x 10(6) and 60 x 10(6). The highest calculated Nusselt number was found as about Nu:A08 for axial finned heat exchanger. All finned surfaces and inclination angles lead to better heat transfer performances comparing to the unfinned heat exchanger. (C) 2020 Elsevier Ltd. All rights reserved.Öğe Rule-based Mamdani-type fuzzy modelling of thermal performance of fintube evaporator under frost conditions(E D P Sciences, 2016) Ozen, Dilek Nur; Altinisik, Kemal; Dincer, Kevser; Ates, Ali; Sertkaya, Ahmet Ali; Tolu, Muhammed EminFrost formation brings about insulating effects over the surface of a heat exchanger and thereby deteriorating total heat transfer of the heat exchanger. In this study, a fin-tube evaporator is modeled by making use of Rule-based Mamdani-Type Fuzzy (RBMTF) logic where total heat transfer, air inlet temperature of 2 degrees C to 7 degrees C and four different fluid speed groups (ual=1; 1.44; 1.88 m s-1, ua2=2.32; 2.76 m s-1, ua3=3.2; 3.64 m s-1, ua4=4.08; 4.52; 4.96 m s-1) for the evaporator were taken into consideration. In the developed RBMTF system, outlet parameter UA was determined using inlet parameters Ta and ua. The RBMTF was trained and tested by using MATLAB (R) fuzzy logic toolbox. R-2 (%) for the training data and test data were found to be 99.91%. With this study, it has been shown that RBMTF model can be reliably used in determination of a total heat transfer of a fm-tube evaporator.
