The aim of the present study is to investigate the effect of using sinusoidal profile in fins on temperature distribution and heat transfer enhancement. The longitudinal fins of rectangular, triangular, wavy rectangular and wavy triangular profiles are studied using analytical and numerical solution techniques. In addition to known profiles, wavy triangular longitudinal fins are proposed as a new fin configuration. The temperature distribution of wavy triangular fins is obtained using Shooting Method along with Cash-Karp Runge Kutta Method. Besides, CFD analyses in which laminar flow regime is concerned at different air velocities is utilized for the comparison of heat transfer rates and convective heat transfer coefficients. CFD results show that heat transfer convection coefficient values for wavy rectangular fins are the lowest ones among the investigated fins. CFD and analytical results indicate that for lower convective coefficients, the dominancy of triangular fins having wave form on plate type triangular fins is more noticeable than the dominancy of wavy rectangular fins on plate type rectangular fins. Also, further heat transfer augmentation can be provided for wavy triangular fins at higher amplitude lengths. For instance, heat transfer enhancement by 15.3 % can be achieved using wavy triangular fins with thickness of 2 cm, amplitude length of 0.21 cm and three-wave profile in comparison with triangular fins having same dimensions.
Buhar sıkıştırmalı soğutma sistemlerinde iş akışkanı olarak kullanılan R134a, küresel ısınmaya karşı alınan tedbirler kapsamında kullanımına son verilmesi planlanan soğutucu akışkanlardandır. Bu çalışmada; deneysel veriler yardımıyla EES programında geliştirilen teorik model aracılığıyla mekanik bir buhar sıkıştırmalı soğutma sisteminde R134a ve alternatifleri R1234yf, R450a, R513a ve R515b soğutucu akışkanlarının kullanımları, Termodinamiğin I. ve II. yasaları bakımından teorik olarak incelenmiştir. Analizler, sabit soğutma yükü için çeşitli buharlaşma ve yoğuşma sıcaklıklarında gerçekleştirilmiştir. Analizler sonucunda; soğutucu akışkan çeşidinin, kompresör gücüne, yoğuşturucudan birim zamandaki ısı geçiş miktarına, COP, ikinci yasa verimine ve soğutucu akışkanın debisine etkisi tespit edilmiştir. Çalışmada, R134a ve alternatiflerine ilişkin aynı şartlarda elde edilen sonuçlar karşılaştırılmıştır. Sonuç olarak, R134a ile karşılaştırıldığında kompresör gücü, R1234yf’de %5.62, R450a’da %2.35, R513a’da %3.41, R515b’de ise %2.88 oranında artmıştır. Böylece, R134a yerine R450a, R515b, R513a ve R1234yf kullanıldığında, COP’de sırasıyla %2.03, %2.80, %3.30 ve %5.32 oranlarında azalma olduğu görülmüştür. Benzer şekilde, R450a ve R515b’nin kullanılmasıyla ikinci yasa veriminde, R134a’ya kıyasla yaklaşık olarak %3, R1234yf ve R513a’nın kullanılmasıyla ise %5 oranında bir azalma tespit edilmiştir.
In this study, usage of nanolubricants containing Al2O3, graphene, and CNTs nanoparticles at various mass fractions in a refrigeration compressor was experimentally investigated. Thus, the required compressor electrical power was measured to determine effects of usage of nanolubricants. Nanoparticles, which were used preparation of nanolubricant were gradually added to the lubricant to determine optimum nanoparticle mass fraction for each nanoparticle kind. Consequently, it was observed that the compressor worked safely and efficiently with nanolubricants. Additionally, optimum mass fractions were determined as 0.750% for Al2O3, 0.250% for graphene, and 0.250% for CNTs for operating conditions of this study. As a result, the required compressor electrical power decreased by 6.26, 6.82, and 5.55% with the addition of Al2O3, graphene, and CNTs nanoparticles at optimum mass fractions of 0.750, 0.250, and 0.250% to the lubricant compared to the compressor using pure oil, respectively. Furthermore, density and dynamic viscosity of the nanolubricant samples used in experiments were also measured, and their kinematic viscosity, which are an important parameter for lubricants, were calculated. It was determined that kinematic viscosity increased continuously with the increase of the nanoparticle fraction. In conclusion, nanolubricants containing nanoparticles above optimum mass fraction increase the required compressor electrical power. It is noted that nanoparticle fractions should not be used more than optimum value in the nanolubricant applications.
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