Eğrisel kanal içerisine bilye yerleştirilerek oluşturulan gözenekli ortamlarda akış ve ısı geçişinin deneysel incelenmesi
Eğrisel kanal içerisine bilye yerleştirilerek oluşturulan gözenekli ortamlarda akış ve ısı geçişinin deneysel incelenmesi
Dosyalar
Tarih
2021
Yazarlar
Gökaslan, Mustafa Yasin
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
Lisansüstü Eğitim Enstitüsü
Özet
Kanala kavis verildiğinde veya kanal içerisine gözenekli ortam yerleştirildiğinde ısı geçişinde iyileşmeler söz konusudur. Eğrisel kanallarda akışkanın kanal içerisindeki akış hareketinden kaynaklı ikincil akışlar meydana gelmektedir. Gözenekli ortamda ise gözeneklerin varlığı, akış hareketini karıştırmakta ve katı ile akışkan temas alanını arttırmaktadır. Eğrisel kanallar veya gözenekli ortamlar, petrolün çıkartılmasında, kimyasal ve nükleer reaktörlerin tasarımında, nükleer atıkların depolanmasında, elektronik parçaların soğutulmasında, ısı değiştiricilerinde, yalıtım uygulamalarında ve uzay araçlarının soğutulması gibi pek çok bilimsel alanda kullanılmaktadır. Eğrisel kanalda veya gözenekli kanalda yapılan akış ve ısı geçişi sonuçları, eğrisel gözenekli kanalda akış ve ısı geçişi sonuçları için geçerlilik sağlamayabilir. Bu iki farklı durumdaki ısı geçişini iyileştiren parametrelerin bir arada olması durumunda, ısı geçişine nasıl etkileyeceği bilinmemektedir. Bu nedenle eğrisel gözenekli kanalda akış ve ısı geçişini anlayabilmek için teorik, sayısal ve deneysel verilere ihtiyaç duyulmaktadır. Bu bilimsel açığı aydınlatmak için bu çalışmada, kanalın hem eğrisel hem de içerisinde gözenekli ortam bulunması durumunda kanaldaki akış ve ısı geçişi deneysel olarak incelenmiştir. Eğrisel kanal parametrelerinden olan eğrilik yarıçapının üç farklı değeri ile gözenekli ortamın parametrelerinden olan bilye çapının üç farklı değerinde akış ve ısı geçişi incelenmiştir. Ayrıca aynı eğrilik yarıçapında kanal genişliğinin akış ve ısı geçişine etkisi iki farklı kanal genişliği için incelenmiştir. Eğrisel kanal olarak 1 turdan oluşan Arşimet spirali seçilmiştir. Dört farklı deney odasının her birinin boş ve içerisinde 2.00, 2.38 ve 3.17 mm çapında bilyelerden oluşturulan 16 farklı deney kombinasyonunda akış ve ısı geçişi deneysel olarak incelenmiştir. Her bir paket yatak için gözeneklilik ve özgül yüzey alanları incelenmiş ve literatürden elde edilen denklemlerle kıyaslanmıştır. Oluşturulan paket yatakların her biri için geçirgenlik, Forchheimer katsayıları ve Ergün sabitlerine karşılık gelen katsayılar deneysel olarak hesaplanmıştır. Hesaplanan bu katsayıların bağımsız değişkenlerin hataları da dikkate alınarak Ergün denkleminden elde edilen sonuçlarla kıyaslanmıştır. Eğrisel gözenekli kanallarda, eğriselliğin etkisini daha iyi anlamak için boyutsuz bir sayı tanımlanmış ve bütün deney verilerinden elde edilen basınç düşüşü korelasyonu sunulmuştur. Sunulan bu korelasyonda tanımlanan boyutsuz sayı (değiştirilmiş Dean sayısı) sayesinde kavis oranı ihmal edildiğinde verilen basınç düşüşü denklemi düz paket yataklar için kullanıma uygun hale dönüşmektedir. Spiral kanalın içerisine bilye yerleştirilmeden önce dört farklı deney odası için sabit ısı akısında ve sistem termodinamik olarak dengeye ulaştığında ısı geçişi deneyleri gerçekleştirilmiştir. Boş spiral kanalda ikincil akışlar sayesinde iç ve dış yüzeyde sıcaklık dağılımı farkı görülmüş olup, her iki yüzey için farklı Nusselt sayıları veren denklemler sunulmuştur. Ayrıca aynı açıda, iç ve dış yüzey sıcaklıkların ortalaması alınarak ortalama Nusselt sayısını veren denklem de sunulmuştur. Boş spiral kanal için elde edilen Nusselt sayısını veren denklemler literatürle kıyaslanmış ve literatürle uyum içerisinde olduğu görülmüştür. Böylece spiral paket yatakta ısı geçişi deneyleri yapılmadan önce deney tesisatının güvenirliliği test edilmiştir. Spiral kanal bilye yerleştirerek oluşturulan spiral paket yataklarda ısı geçişi de her iki yüzeye sabit ısı akısı uygulayarak gerçekleştirilmiştir. Bütün deney verilerinden hesaplanan Nusselt sayısı ile değiştirilmiş Dean sayısı arasındaki ilişki verilmiştir. Basınç düşüşünde olduğu gibi kavis oranının ihmal edilmesi durumunda, literatürde sunulan düz paket yataklar için Nusselt sayısı değerlerine yakınsamaktadır. Gözenekli eğrisel kanallarda hem basınç düşüşünde hem de ısı geçişinde eğriselliğin etkisi düşük hızlarda ihmal edilebilir seviyedeyken, hızın artmasıyla eğrisellik önem kazanmaktadır. Kanal genişliği ısı geçişinde önemli bir parametre olup, kanal genişliği düştükçe yüzeyden geçen ısı geçişinin arttığı sonucuna ulaşılmıştır. Bilye çapı ise hem basınç düşüşünü hem de ısı geçişini önemli ölçüde etkilemektedir. Özgül yüzey alanının, basınç düşüşü ve ısı geçişine etkisi önemlidir. Özgül yüzey alanı arttıkça basınç düşüşü ve ısı geçişi artmaktadır.
When the channel is curved or porous media is located inside the channel, there are improvements in heat transfer. Studies have been carried out on heat transfer and pressure drop in curvilinear channels and porous media for many years. Secondary flows occur in curvilinear channels due to the flow movement of the fluid in the channel. In porous media, the presence of pores mixes the fluid flow and increases the solid-fluid contact area. While curvilinear channels are generally used in areas such as blood flow and cell analysis and heat exchangers, porous media are used in many scientific fields such as drill for oil, design of chemical and nuclear reactors, storage of nuclear wastes, cooling of electronic parts, insulation applications and cooling of spacecraft. The results of flow and heat transfer in the curvilinear channel or porous medium may not be valid for the results of flow and heat transfer in the curvilinear porous channel. Therefore, experimental data or theoretical results or numerical results are needed to understand the flow and heat transfer in the curvilinear porous channel. It is not known how the parameters that improve the heat transfer in these two different situations will affect the heat transfer in case of coexistence. In order to illuminate this scientific gap, in this study, flow and heat transfer in the channel are experimentally investigated in the case of both curvilinear and porous media in the channel. The flow and heat transfer with three different values of the radius of curvature, which is one of the curvilinear channel parameters, three different ball diameter, which is one of the parameters of the porous medium, are investigated. In addition, in order to determine flow and heat transfer in the effect of the channel width on the same curvature radius, two different channel widths with the same radius of curvature are examined. Archimedes spiral, consisting of 1 turn (2π), is chosen as the curvilinear channel. Flow and heat transfer is experimentally investigated in 16 different experimental combinations in each of four different test chambers unfilled and packed beds formed by filling 2.00, 2.38 and 3.17 mm diameter balls. The experimental setup consists of 3 main compartments: air straightener section, test chamber and air intake chamber. Thanks to the blower, the sucked air passes through the flow straightener section. The air first passes through the nozzle and enters the 40 mm diameter plexiglass pipe. The average velocity of the air is measured by the anemometer after the flow straightener located just below the nozzle. are available. The inlet pressure from the pressure socket is measured before entering the air inlet header passing through the flow straightening unit. Then, the air entering the inlet header moves in a curvilinear channel and moves in spiral channel. After exiting the spiral channel, it passes through the air outlet header and enters the outlet plexiglass pipe. The outlet pressure is measured by the pressure socket on this outlet plexiglass pipe. There are 40 thermocouples in each test chamber. There are film heaters on both surfaces of the spiral channel and constant heat flux is applied to the surfaces thanks to the DC power supplies. The porosity and specific surface areas for each packed beds are examined and compared with equations obtained from the available literature. Pressure drop experiments for steady flow are carried out by measuring the air velocity and pressure drop simultaneously. The coefficients corresponding to the permeability, Forchheimer coefficients and Ergün constants for each packed bed formed were experimentally calculated. The permeability, Forchheimer coefficients and coefficients corresponding to Ergün's constants are experimentally calculated for each packed beds. These calculated coefficients are compared with the results obtained from Ergün's equation, taking into account the errors of the independent variables. In curvilinear porous channels, a dimensionless number which is modified Dean number is defined to better understand the effect of curvature ratio. The pressure drop correlation obtained from all experimental data is presented. Thanks to the modified Dean number defined in this correlation, when the curvature ratio is neglected, the pressure drop becomes suitable for use for straight packed beds. Before the balls are located inside the spiral channel, heat transfer experiments are carried out for unfilled spiral channels at constant heat flux and when the system reached thermodynamically equilibrium. In the unfilled spiral channel, it is observed that there is a difference in temperature distribution on the inner and outer surfaces due to the secondary flows. The balance of thermal energy equation is written in the channel and the best-fit heat transfer coefficient that fits the experimental data with the theoretical equation is determined by the method of least squares. The relations between Nusselt numbers and modified Dean numbers for inner and outer surfaces are presented. In addition, using the average surface temperature obtained by averaging the inner and outer surface temperatures at the same angle, the equation giving the Nusselt number is also presented. The Nusselt numbers correlations are determined for the inner surface, outer surface and average surface temperature. For the unfilled spiral channel, the Nusselt numbers obtained from the experiments are compared with the available literature and found to be in agreement. Thus, the reliability of the experimental setup is tested before conducting the heat transfer experiments in the spiral bed. The heat transfers in spiral packed beds formed by filling balls in spiral channels is also achieved by applying equal constant heat flux to both surfaces. There is no temperature difference on the inner and outer surfaces of the spiral packed beds and it is almost the same temperature on both surfaces at the same angle. The relation between Nusselt number obtained from all experimental data and modified Dean number is given. If the curvature ratio is neglected as in the pressure drop correlation, it converges to the heat transfer values obtained from straight packed beds in the available literature. In case the curvature ratio is neglected in both heat transfer and pressure drop correlations, the presented equations are suitable for straight packed beds. In porous curvilinear channels, the effect of curvature ratio on both pressure drop and heat transfer is negligible at low velocities, while curvature ratio gains importance as velocity increases. Channel width is an important parameter in heat transfer and it is concluded that as the channel width decreases, the higher the heat transfer on the surface. Ball diameter significantly affects both pressure drop and heat transfer. Specific surface area has an important effect on pressure drop and heat transfer and as the specific surface area increases, pressure drop and heat transfer increase.
When the channel is curved or porous media is located inside the channel, there are improvements in heat transfer. Studies have been carried out on heat transfer and pressure drop in curvilinear channels and porous media for many years. Secondary flows occur in curvilinear channels due to the flow movement of the fluid in the channel. In porous media, the presence of pores mixes the fluid flow and increases the solid-fluid contact area. While curvilinear channels are generally used in areas such as blood flow and cell analysis and heat exchangers, porous media are used in many scientific fields such as drill for oil, design of chemical and nuclear reactors, storage of nuclear wastes, cooling of electronic parts, insulation applications and cooling of spacecraft. The results of flow and heat transfer in the curvilinear channel or porous medium may not be valid for the results of flow and heat transfer in the curvilinear porous channel. Therefore, experimental data or theoretical results or numerical results are needed to understand the flow and heat transfer in the curvilinear porous channel. It is not known how the parameters that improve the heat transfer in these two different situations will affect the heat transfer in case of coexistence. In order to illuminate this scientific gap, in this study, flow and heat transfer in the channel are experimentally investigated in the case of both curvilinear and porous media in the channel. The flow and heat transfer with three different values of the radius of curvature, which is one of the curvilinear channel parameters, three different ball diameter, which is one of the parameters of the porous medium, are investigated. In addition, in order to determine flow and heat transfer in the effect of the channel width on the same curvature radius, two different channel widths with the same radius of curvature are examined. Archimedes spiral, consisting of 1 turn (2π), is chosen as the curvilinear channel. Flow and heat transfer is experimentally investigated in 16 different experimental combinations in each of four different test chambers unfilled and packed beds formed by filling 2.00, 2.38 and 3.17 mm diameter balls. The experimental setup consists of 3 main compartments: air straightener section, test chamber and air intake chamber. Thanks to the blower, the sucked air passes through the flow straightener section. The air first passes through the nozzle and enters the 40 mm diameter plexiglass pipe. The average velocity of the air is measured by the anemometer after the flow straightener located just below the nozzle. are available. The inlet pressure from the pressure socket is measured before entering the air inlet header passing through the flow straightening unit. Then, the air entering the inlet header moves in a curvilinear channel and moves in spiral channel. After exiting the spiral channel, it passes through the air outlet header and enters the outlet plexiglass pipe. The outlet pressure is measured by the pressure socket on this outlet plexiglass pipe. There are 40 thermocouples in each test chamber. There are film heaters on both surfaces of the spiral channel and constant heat flux is applied to the surfaces thanks to the DC power supplies. The porosity and specific surface areas for each packed beds are examined and compared with equations obtained from the available literature. Pressure drop experiments for steady flow are carried out by measuring the air velocity and pressure drop simultaneously. The coefficients corresponding to the permeability, Forchheimer coefficients and Ergün constants for each packed bed formed were experimentally calculated. The permeability, Forchheimer coefficients and coefficients corresponding to Ergün's constants are experimentally calculated for each packed beds. These calculated coefficients are compared with the results obtained from Ergün's equation, taking into account the errors of the independent variables. In curvilinear porous channels, a dimensionless number which is modified Dean number is defined to better understand the effect of curvature ratio. The pressure drop correlation obtained from all experimental data is presented. Thanks to the modified Dean number defined in this correlation, when the curvature ratio is neglected, the pressure drop becomes suitable for use for straight packed beds. Before the balls are located inside the spiral channel, heat transfer experiments are carried out for unfilled spiral channels at constant heat flux and when the system reached thermodynamically equilibrium. In the unfilled spiral channel, it is observed that there is a difference in temperature distribution on the inner and outer surfaces due to the secondary flows. The balance of thermal energy equation is written in the channel and the best-fit heat transfer coefficient that fits the experimental data with the theoretical equation is determined by the method of least squares. The relations between Nusselt numbers and modified Dean numbers for inner and outer surfaces are presented. In addition, using the average surface temperature obtained by averaging the inner and outer surface temperatures at the same angle, the equation giving the Nusselt number is also presented. The Nusselt numbers correlations are determined for the inner surface, outer surface and average surface temperature. For the unfilled spiral channel, the Nusselt numbers obtained from the experiments are compared with the available literature and found to be in agreement. Thus, the reliability of the experimental setup is tested before conducting the heat transfer experiments in the spiral bed. The heat transfers in spiral packed beds formed by filling balls in spiral channels is also achieved by applying equal constant heat flux to both surfaces. There is no temperature difference on the inner and outer surfaces of the spiral packed beds and it is almost the same temperature on both surfaces at the same angle. The relation between Nusselt number obtained from all experimental data and modified Dean number is given. If the curvature ratio is neglected as in the pressure drop correlation, it converges to the heat transfer values obtained from straight packed beds in the available literature. In case the curvature ratio is neglected in both heat transfer and pressure drop correlations, the presented equations are suitable for straight packed beds. In porous curvilinear channels, the effect of curvature ratio on both pressure drop and heat transfer is negligible at low velocities, while curvature ratio gains importance as velocity increases. Channel width is an important parameter in heat transfer and it is concluded that as the channel width decreases, the higher the heat transfer on the surface. Ball diameter significantly affects both pressure drop and heat transfer. Specific surface area has an important effect on pressure drop and heat transfer and as the specific surface area increases, pressure drop and heat transfer increase.
Açıklama
Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2021
Anahtar kelimeler
Gözenekli malzemeler,
Porous materials,
Isı,
Heat