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Charge Minimization of Microchannel Heat Exchangers

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PDF TR251.pdf (2MB) ACRC Technical Report 251 PDF
Title: Charge Minimization of Microchannel Heat Exchangers
Author(s): Traeger, K.M.; Hrnjak, P.S.
Subject(s): microchannel heat exchangers charge minimization small systems
Abstract: This thesis focuses on microchannel heat exchangers, and the methods used to try and reduce the charge contained in them. First, four condensers were designed and manufactured with the same air side characteristics and same tube design (with the exception of some blocked ports in one design) so that any difference in charge, capacity, pressure drop etc. can be attributed to flow geometry. These designs were a two circuit serpentine design, a two pass parallel flow design, and two one pass parallel flow designs. The difference between the two one pass designs were the number of microchannel ports in the tubes, one with 19 ports and the other with 10. The one pass design with 10 ports contained the least amount of charge, on average about 20 g, while the other one pass design contained the most charge, about 28 g. The reason for this difference was not only because the smaller tube volume, but an increase in mass flux also decrease the amount of charge in the exit header by 20- 30%. The serpentine condenser also had very low charge amounts, but pressure drop was about ten times higher than in the parallel flow designs. This caused a 4% lower COP than what was given with the one pass design. Two serpentine evaporators have also been examined. The evaporators had similar core volumes of about 870 cm3. One evaporator had double the fin length by using a “splitter” fin, which reduced the length of the evaporator tube and therefore reduced the internal volume. Both evaporators performed almost exactly the same, but the splitter fin evaporator had less of a pressure drop and contained 15% less charge. Finally, the models developed for this thesis were used to theoretically compare the performance and charge of six different refrigerants, propane (which was the refrigerant used for experiments), R22, R134a, isobutane, ammonia, and R410A in a condenser. A pressure drop based on a 1% decrease of Carnot COP was found for each refrigerant. Ammonia was found to be able to have same capacity as the other refrigerants, but able to achieve the capacity with a much smaller cross sectional area and a very small amount of charge.
Issue Date: 2005-06
Publisher: Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report: Air Conditioning and Refrigeration Center TR-251
Genre: Technical Report
Type: Text
Language: English
URI: http://hdl.handle.net/2142/12911
Sponsor: Air Conditioning and Refrigeration Project 179
Date Available in IDEALS: 2009-06-24
 

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