Yüzey aktif maddelerin nanoakışkanların termal özellikleri ve ısı transferi üzerindeki etkilerinin deneysel incelenmesi
Küçük Resim Yok
Tarih
2020
Yazarlar
Dergi Başlığı
Dergi ISSN
Cilt Başlığı
Yayıncı
Bursa Teknik Üniversitesi
Erişim Hakkı
info:eu-repo/semantics/openAccess
Özet
Son yıllarda, ısı transfer verimliliğini artırmak için yenilikçi bir yaklaşım olan nanoakışkan kullanımı hakkında çalışmalar hızla artmaktadır; fakat nanoakışkan kullanımını sınırlayan bazı faktörler bulunmaktadır. Bu faktörlerden en önemlisi uzun süre nanoakışkan kararlılığını sağlayamamaktır; ancak bu doğrultuda farklı yöntemler geliştirilmiştir. Bu yöntemlerden bir tanesi ise sürfaktan kullanmaktır. Bu deneysel çalışma kapsamında ilk aşamada üç farklı sürfaktanın, temel akışkan olarak seçilen saf suyun termofiziksel özellikleri üzerine etkilerinin incelenmesi, ardından nano boyutlarda Al2O3 partikülleri ile elde edilen nanoakışkanların fiziksel özelliklerinin ve kararlılığının ölçülmesi ve son aşamada ise hazırlanan nanoakışkanın gövde boru tipi bir ısı değiştirici kullanılarak ısı transfer karakteristiğinin belirlenmesi amaçlanmıştır. Bu amaçlar doğrultusunda SDS, NP 10 ve Tween 80 olmak üzere 3 farklı sürfaktan kütlece %0,2 %0,4 %0,6 ve %0,8 oranlarında saf su ile karıştırılıp, çözeltiler oluşturulmuştur. Bu çözeltilerin 25 °C, 35 °C, 45 °C, 55 °C ve 65 °C olmak üzere 5 farklı sıcaklıkta yoğunluk, viskozite ve termal iletkenlik ölçümleri gerçekleştirilmiştir. Ardından ortalama partikül boyutu 18 nm olan Al2O3 partikülleri kullanılarak hacimce %0,3 %0,5 %0,7 %0,9 ve %1,1'lik nanoakışkanlar hazırlanmıştır. Nanoakışkan kararlılığını artırmak için sürfaktan ve ultrasonik homojenizatör kullanılmıştır. Elde edilen nanoakışkanların 25 °C, 35 °C, 45 °C, 55 °C ve 65 °C sıcaklıktaki yoğunluk, viskozite ve termal iletkenlikleri ölçülmüştür. Aynı zamanda hazırlanan nanoakışkanların kararlılığının belirlenmesi için sedimentasyon metodu kullanılmıştır. Isı transfer performansının incelenmesi için sırasıyla su ve %0,2 Tween 80 ve %0,3 Al2O3 ile hazırlanan nanoakışkan gövde borulu bir ısı değiştiricinin boru kısmından 2, 3 L/dk, 4 L/dk ve 5 L/dk olmak üzere 4 farklı debide beslenmiş ve toplam ısı transfer katsayıları hesaplanmıştır. Çalışmalar sonucunda sürfaktan kullanılmadan hazırlanan nanoakışkanların termofiziksel özelliklerinin literatürle büyük oranda uyumlu olduğu gözlemlenmiştir. Tüm konsantrasyonlarda hazırlanan nanoakışkanlar için partikül miktarı ile nanoakışkanın yoğunluğunun doğru orantılı arttığı görülmüştür. Ayrıca akışkanın viskozitesi nanopartikül eklenmesi ile artmış fakat partikül kümelenmesinden dolayı düzenli bir artış gözlemlenememiştir. Farklı oranlarda hazırlanan nanoakışkanların termal iletkenlik değerlerinin suyun değerlerinden yüksek olduğu tespit edilmiştir. Sıcaklık arttıkça termal iletkenlik değerleri artmış ve 25 oC sıcaklıkta elde edilen maksimum termal iletkenlik değeri, hacimce %1,1 Al2O3 ve kütlece %0,2 Tween 80 kullanılarak hazırlanan nanoakışkan ile sağlanmıştır. SDS sürfaktanının, nanoakışkan kararlılığı üzerinde negatif etkisi olduğu görülmüş olup en iyi kararlılığa Tween 80 sürfaktanı ile ulaşılmıştır. Nanoakışkan kullanımı ile ısı transfer katsayısı artmış ve ısı transfer katsayısındaki maksimum artış %11,54 olarak hesaplanmıştır. Ayrıca debi arttıkça toplam ısı transfer katsayısında artış görülmüştür.
In recent years, studies on th use of nanofluids, an innovative approach to enhance heat transfer efficiency, have been increasing rapidly. However, some factors limit the use of nanofluids. The most important of these factors is not being able to provide nanofluid stability for a long time, but different methods have been developed accordingly. One of these methods is to use surfactant as a dispersant. Within the scope of this experimental study, it was aimed to determine the effects of three different surfactants on the thermophysical properties of the pure water which was selected as the base fluid, the physical properties and stability of the nanofluids obtained by using nano-sized Al2O3 particles, and the heat transfer characteristic of the prepared nanofluid using a shell and tube heat exchanger. For these purposes, 3 different surfactants, SDS, NP 10, and Tween 80, were mixed to pure water with a ratio of 0.2% 0.4% 0.6% and 0.8% by weight, and solutions were obtained. Density, viscosity, and thermal conductivity measurements of these solutions at 25 °C, 35 °C, 45 °C, 55 °C and 65 °C were carried out. Afterward, using the Al2O3 particles with an average particle size of 18 nm, nanofluids were prepared with a volumetric ratio of 0.3%, 0.5%, 0.7%, 0.9%, and 1.1%. Surfactant and ultrasonic homogenizer were used to increase the stability of nanofluids. Density, viscosity, and thermal conductivity of the obtained nanofluids at 25 °C, 35 °C, 45 °C, 55 °C and 65 °C were measured. Meanwhile, the sedimentation method was used to determine the stability of the prepared nanofluids. To investigate the heat transfer performance, water and nanofluids, containing Al2O3 and Tween 80 with the ratio of 0.3% and 0.2% respectively, were fed to the tube side of the heat exchanger at 4 different flow rates (2, 3, 4 and 5 L/min) and the total heat transfer coefficient was calculated. As a result of the study, it has been observed that the thermophysical properties of nanofluids prepared without the use of surfactants are substantially compatible with the literature. It was seen that densities of the nanofluids at all concentrations increased with the concentration of particles proportionally. Besides, the viscosity of the fluid increased with the addition of nanoparticles, but no regular increase was observed due to particle aggregation. It has been determined that the thermal conductivity values of nanofluids prepared at different rates are higher than the values of water. As the temperature increased, the thermal conductivity values of the fluids increased and the maximum thermal conductivity value obtained at 25 oC was achieved with nanofluid prepared using 1.1% Al2O3 by volumetric and 0.2% Tween 80 by weight ratio. SDS surfactant was found to have a negative effect on the stability of nanofluids, and the best stability was achieved with the Tween 80 surfactant. Besides, the use of nanofluid improved the total heat transfer coefficient and its maximum value was calculated as 11.54%. When the flow rate of fluids fed to the heat exchanger increased, the total heat transfer coefficient enhanced.
In recent years, studies on th use of nanofluids, an innovative approach to enhance heat transfer efficiency, have been increasing rapidly. However, some factors limit the use of nanofluids. The most important of these factors is not being able to provide nanofluid stability for a long time, but different methods have been developed accordingly. One of these methods is to use surfactant as a dispersant. Within the scope of this experimental study, it was aimed to determine the effects of three different surfactants on the thermophysical properties of the pure water which was selected as the base fluid, the physical properties and stability of the nanofluids obtained by using nano-sized Al2O3 particles, and the heat transfer characteristic of the prepared nanofluid using a shell and tube heat exchanger. For these purposes, 3 different surfactants, SDS, NP 10, and Tween 80, were mixed to pure water with a ratio of 0.2% 0.4% 0.6% and 0.8% by weight, and solutions were obtained. Density, viscosity, and thermal conductivity measurements of these solutions at 25 °C, 35 °C, 45 °C, 55 °C and 65 °C were carried out. Afterward, using the Al2O3 particles with an average particle size of 18 nm, nanofluids were prepared with a volumetric ratio of 0.3%, 0.5%, 0.7%, 0.9%, and 1.1%. Surfactant and ultrasonic homogenizer were used to increase the stability of nanofluids. Density, viscosity, and thermal conductivity of the obtained nanofluids at 25 °C, 35 °C, 45 °C, 55 °C and 65 °C were measured. Meanwhile, the sedimentation method was used to determine the stability of the prepared nanofluids. To investigate the heat transfer performance, water and nanofluids, containing Al2O3 and Tween 80 with the ratio of 0.3% and 0.2% respectively, were fed to the tube side of the heat exchanger at 4 different flow rates (2, 3, 4 and 5 L/min) and the total heat transfer coefficient was calculated. As a result of the study, it has been observed that the thermophysical properties of nanofluids prepared without the use of surfactants are substantially compatible with the literature. It was seen that densities of the nanofluids at all concentrations increased with the concentration of particles proportionally. Besides, the viscosity of the fluid increased with the addition of nanoparticles, but no regular increase was observed due to particle aggregation. It has been determined that the thermal conductivity values of nanofluids prepared at different rates are higher than the values of water. As the temperature increased, the thermal conductivity values of the fluids increased and the maximum thermal conductivity value obtained at 25 oC was achieved with nanofluid prepared using 1.1% Al2O3 by volumetric and 0.2% Tween 80 by weight ratio. SDS surfactant was found to have a negative effect on the stability of nanofluids, and the best stability was achieved with the Tween 80 surfactant. Besides, the use of nanofluid improved the total heat transfer coefficient and its maximum value was calculated as 11.54%. When the flow rate of fluids fed to the heat exchanger increased, the total heat transfer coefficient enhanced.
Açıklama
Fen Bilimleri Enstitüsü, Kimya Mühendisliği Ana Bilim Dalı
Anahtar Kelimeler
Kimya Mühendisliği, Chemical Engineering
