Ph.D. Tezi Görüntüleme | |||||||||||||||||||||
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| Summary: Convective heat transfer enhancement can be achieved by active (requiring external energy input) or passive (no external energy input) means. Using fin which is one of the passive technique are often used in the energy industry for compact heat exchangers to enhance the heat transfer rate and information on turbulent flow and heat transfer in internally finned concentric passage is rather limited in the literature. So that, in this study, turbulent flow and heat transfer characteristics in internally finned and unfinned concentric passages are investigated experimentally. Measurements are made of turbulence characteristics, mean flow, pressure drop and heat-transfer parameters in the entrance region of a concentric passage of radius ratio 0.2. In the experimental studies, hot-wire anemometer is used for the turbulence and mean flow measurements, while the liquid-crystal technique which is considered to be a new technique improved in recent years and especially preferred in complex geometries is used for the heat transfer measurements. The tests are conducted at three fin width (W=2 mm, 4 mm, 6 mm) and pitch (P=20 mm, 30 mm, 40 mm) and four height (H=2 mm, 4 mm, 6 mm, 8 mm) and Reynolds numbers ranging between 18000 and 124500 for the turbulence, mean flow and pressure drop measurements and between 16500 and 76500 for the heat transfer measurements. The heat transfer measurements are carried out on both the inner surface and the outer surface of the concentric duct and in the study, the performance analysis of the systems are also carried out. From this study, the variation of local and mean heat transfer coefficients and friction factors in the flow of the unfinned and finned concentric passages are obtained and the results for the unfinned concentric passage are compared with the data in the literature. In the flow of the finned concentric pasage, average Nusselt numbers are between 1.36 and 5.37 times the flow of the unfinned concentric passage for the finned inner surface and between 1.03 and 1.80 times for the smooth outer surface, while pressure drops are between 3.12 and 18.05. Correlations are also developed in terms of the dimensionless fin spacing, fin height, fin width and Re for the average Nusselt numbers and friction factor. Keywords :Concentric Passage, Finned Surface, Heat Transfer Coefficient, Liquid-Crystal Technique, Enhancement
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