1999 Fiscal Year Final Research Report Summary
Enhancement of Condensation of a HFC-Refrigerant in a Horizontal Microfin Tube
| Project/Area Number |
09650252
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Thermal engineering
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| Research Institution | Okayama Prefectural University |
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Principal Investigator |
NOZU Shigeru Okayama Prefectural University, Department of Systems Engineering, Professor, 情報工学部, 教授 (10135957)
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| Co-Investigator(Kenkyū-buntansha) |
FUJIWARA Wataru Okayama Prefectural University, Department of Systems Engineering, Research Associate, 情報工学部, 教務職員 (40275376)
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| Project Period (FY) |
1997 – 1999
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| Keywords | Condensation / Heat Transfer Enhancement / Microfin Tube / Refrigerant / Flow observation / Annular and stratified regimes / Theoretical model / Experiment |
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| Research Abstract |
Experimental and theoretical studies have been performed for the condensation of refrigerant vapor in horizontal microfin tubes. The experiments includes the local heat transfer and pressure drop measurements, and flow observation study by use of an industrial borescope during condensation of HCFC123 in horizontal, smooth and herringbone tubes. The condensate flow from the fin surface to the drainage gutters located at the top and bottom of the tube seems quite well in the low condensate with high vapor velocity regime. The measured local heat transfer data for the herringbone tube decreased as the condensation proceeds, taking a maximum heat transfer enhancement ratio of ten.
A theoretical model of film condensation in spirally grooved, horizontal microfin tubes has been developed. The annular flow regime and the stratified flow regime were considered on the basis of the flow observation studies performed by the present and previous investigators. The annular flow model assumes that al
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l the laminar condensate flow occurs through the grooves. The condensate film is segmented into thin and thick film regions. In the thin film region formed on the fin surface, the condensate is assumed to be drained by the combined surface tension and vapor shear forces. In the thick film region formed in the groove, on the other hand, the condensate is assumed to be driven by the vapor shear force. For the stratified flow regime, the height of stratified condensate was determined by a modified Taitel and Dukler model. For the upper part of the tube, numerical calculation of laminar film condensation considering the combined effects of gravity and surface tension forces was conducted. The heat transfer coefficient at the lower part of the tube was estimated by an empirical equation for the internally finned tubes developed by Carnavos.
The theoretical predictions of the circumferential average heat transfer coefficient by the two theoretical models were compared with available experimental data for four refrigerants and four tubes. Generally, the annular flow model gave a higher heat transfer coefficient than the stratified flow model in the high quality region, whereas the stratified flow model gave a higher heat transfer coefficient in the low quality region. Most of the experimental data agreed within ±20% with the higher of the two theoretical predictions. Less
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