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ACRC Technical Report 69PDF


Title:Local and Average Heat Transfer and Pressure Drop Characteristics of Annularly Finned Tube Heat Exchangers
Author(s):Kearney, S.P.; Jacobi, A.M.
Subject(s):fin heat exchangers
Abstract:Finned tube heat exchangers are important because of their direct impact on energy and material use in petrochemical, power, transportation, and HV AC/R systems. The design of effective heat exchangers has direct social, economic, and environmental ramifications. Design improvements rely on a clear understanding of the flow and heat transfer interactions in the complex flowfields which exist in heat exchangers. In this thesis, results are presented from experiments conducted to develop a more complete understanding of heat exchanger performance. Using a novel adaptation of the naphthalene sublimation method, optically measured sublimation depths are used to determine local mass transfer coefficients with very high spatial resolution. Local and average heat transfer data are inferred through the heat and mass analogy. These heat transfer data are also used to numerically compute true fin efficiencies. These true efficiencies are compared to the analytical solution of Gardner, which assumes a constant heat transfer coefficient over the entire fin surface. Pressure drop data are also presented, and thus a complete measure of heat transfer and pumping power performance for each finned tube arrangement is provided. Four different annularly finned tube banks are examined in a Reynolds number range from 5,000 to 30,000: a conventional single-row exchanger, a baffled single-row exchanger, a staggered two row exchanger and an inline two row device. The heat transfer results are compare quite well to several existing bundle correlations. In contrast to earlier work, these experiments indicate that Gardner's solution is a very good approximation to the true fin efficiency over a wide range of conditions. Reasons for this discrepancy between the current study and previous work are presented. The data for the inline and staggered tube banks surprisingly indicate that the inline configuration may be superior to the staggered arrangement for high profile fins. Justification for this conclusion is provided by comparison to other studies and analysis of the local heat/mass transfer data. Finally, this study provides the first pressure drop data for gull-wing baffling. The results indicate that the unbaffled geometry provides nearly the same heat transfer with only 20 to 25% of the pressure drop penalty in the Reynolds number range of interest.
Issue Date:1995-01
Publisher:Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report:Air Conditioning and Refrigeration Center TR-69
Genre:Technical Report
Sponsor:Air Conditioning and Refrigeration Center Project 35
Date Available in IDEALS:2009-04-17
Identifier in Online Catalog:3872752

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