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ACRC Technical Report 91PDF


Title:An Experimental Study of Flow and Heat Transfer in Offset Strip and Louvered-Fin Heat Exchangers
Author(s):DeJong, N.C.; Jacobi, A.M.
Subject(s):louvered-fin heat exchangers
Abstract:The efficiency of heat exchangers is important in the HV ACIR industry. Driven by high energy standards and increasing competition, manufacturers are seeking to decrease air-side resistance in heat exchangers by increasing the heat transfer coefficient. Offset strip and louvered fins increase the heat transfer coefficient through two methods -- boundary layer restarting and the initiation of self-sustained oscillations. The purpose of this thesis is to develop a better understanding of flow and heat transfer in offset strip and louvered fins so that design guidelines may be developed. Five geometries are analyzed in this study -- two offset strip and three louvered with a 25- angle of incidence -- over a Reynolds number range of 100 to 12000. Heat transfer is inferred from mass transfer data acquired using the naphthalene sublimation method, and pressure drop across each array is detennined using conventional methods. Flow visualization studies are performed to develop a more complete understanding of the actual flow mechanisms. The results show that vortex shedding in the periodic regime increases heat transfer significantly. Measurements of local mass transfer along a fin show that local heat transfer behavior on a fin is different for offset strip and louvered fins, and these results are used to develop design guidelines Because of the flow structures at work, short louvered fins may be especially advantageous. Studies of overall behavior show that at a given Reynolds number, louvered fins require less area for a given heat duty than do offset strip fms. However, pumping power is significantly higher for louvered fins. Therefore, if heat exchanger efficiency is more important than heat exchanger size, offset strip fins may be just as desirable if not more desirable than louvered fins for certain exchanger geometries and operating conditions.
Issue Date:1995-10
Publisher:Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report:Air Conditioning and Refrigeration Center TR-91
Genre:Technical Report
Sponsor:Air Conditioning and Refrigeration Center Project 38
Date Available in IDEALS:2009-04-20
Identifier in Online Catalog:3953517

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