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ACRC Technical Report 208PDF


Title:Design Tradeoffs in Microchannel Heat Exchangers
Author(s):Kulkarni, T.; Bullard, C.W.
Subject(s):microchannel heat exchangers
heat exchangers
Abstract:The present work is based on theoretical and computational investigations into microchannel heat exchangers. Microchannel heat exchangers have long been used as condensers but concerns regarding refrigerant maldistribution have so far prevented their use as evaporators. The first part of the document is devoted to identifying causes of maldistribution and suggesting ways to reduce and eventually eliminate maldistribution. To reduce maldistribution caused due to header pressure gradient, short and fat radial headers were demonstrated to be better than longitudinal headers currently used in microchannel condensers. The second part describes a way to avoid the problem associated with distributing two-phase refrigerant: passive vapor bypass. Immediately downstream of the expansion device, two-phase refrigerant is separated into vapor which is bypassed directly to the suction line through an adiabatic tube and liquid which is distributed into the evaporator. Computer simulation models were developed to explore the feasibility of this concept for a residential air-conditioning application using both sub- and transcritical cycles. The last part of the document identified tradeoffs among the first cost, operating cost and compactness of microchannel heat exchangers. Variation of air-side parameters such as fin height, thickness and pitch were considered to identify a set of designs that have the lowest first cost and another having the highest energy efficiency. The report is divided into the above sections which can be read independently, in any order at the reader’s convenience.
Issue Date:2003-02
Publisher:Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report:Air Conditioning and Refrigeration Center TR-208
Genre:Technical Report
Sponsor:Air Conditioning and Refrigeration Project 124
Date Available in IDEALS:2009-06-12

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