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Research Papers: Evaporation, Boiling, and Condensation

Flow Boiling Visualization of R-134a in a Vertical Channel of Small Diameter

[+] Author and Article Information
Claudi Martín-Callizo

Applied Thermodynamics and Refrigeration, Royal Institute of Technology, KTH, SE100-44 Stockholm, Swedenclaudi@energy.kth.se

Björn Palm

Applied Thermodynamics and Refrigeration, Royal Institute of Technology, KTH, SE100-44 Stockholm, Swedenbpalm@energy.kth.se

Wahib Owhaib

Applied Thermodynamics and Refrigeration, Royal Institute of Technology, KTH, SE100-44 Stockholm, Swedenwahib@energy.kth.se

Rashid Ali

Applied Thermodynamics and Refrigeration, Royal Institute of Technology, KTH, SE100-44 Stockholm, Swedenrashid.ali@energy.kth.se

J. Heat Transfer 132(3), 031503 (Jan 07, 2010) (8 pages) doi:10.1115/1.4000012 History: Received February 13, 2008; Revised September 01, 2008; Published January 07, 2010

The present work reports on flow boiling visualization of refrigerant R-134a in a vertical circular channel with an internal diameter of 1.33 mm and 235 mm in heated length. A quartz tube with a homogeneous Indium Tin Oxide coating is used to allow heating and simultaneous visualization. Flow patterns have been observed along the heated length with the aid of high-speed complementary metal oxide semiconductor (CMOS) digital camera. From the flow boiling visualization, seven distinct two-phase flow patterns have been observed: isolated bubbly flow, confined bubbly flow, slug flow, churn flow, slug-annular flow, annular flow, and mist flow. Two-phase flow pattern observations are presented in the form of flow pattern maps. The effects of the saturation temperature and the inlet subcooling degree on the two-phase flow pattern transitions are elucidated. Finally, the experimental flow pattern map is compared with models developed for conventional sizes as well as to a microscale map for air-water mixtures available in literature, showing a large discrepancy.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Microscale heat transfer and visualization test rig

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Figure 2

Representative photographs of the different two-phase flow patterns observed

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Figure 3

Flow patterns inside the heated tube

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Figure 4

Flow pattern maps for R-134a: D=1.33 mm, Lhs=235 mm, Tsat=30°C, and ΔTsub,i=5°C

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Figure 5

Effect of heat flux on flow patterns of R-134a along the heated length (G=200 kg m−2 s−1, Tsat=30°C, and ΔTsub,i=5°C): SPh is the single-phase flow, IB is the isolated bubbly flow, CB is the confined bubbly flow, S is the slug flow, CH is the churn flow, S-A is the slug-annular flow, A is the annular flow, M is the mist flow

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Figure 6

Effect of saturation temperature on transition boundaries (R-134a: D=1.33 mm, Lhs=235 mm, and ΔTsub,i=5°C)

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Figure 7

Effect of inlet subcooling degree on transition boundaries (R-134a: D=1.33 mm, Lhs=235 mm, and Tsat=30°C)

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Figure 8

Comparison between the present flow pattern map (R-134a: D=1.33 mm, Lhs=235 mm, Tsat=30°C, and ΔTsub,i=5°C) and the experimental transition lines of Hewitt and Roberts (4) for low pressure air-water and high-pressure steam-water flow in vertical tubes of 10–30 mm diameter

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Figure 9

Comparison between the present flow pattern map (R-134a: D=1.33 mm, Lhs=235 mm, Tsat=30°C, and ΔTsub,i=5°C) and transition lines predicted with the model by Taitel (6) evaluated at the experimental conditions

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Figure 10

Comparison between the present flow pattern map (R-134a: D=1.33 mm, Lhs=235 mm, Tsat=30°C, and ΔTsub,i=5°C) and transition lines predicted with the model by Mishima and Ishii (7) evaluated at the experimental conditions

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Figure 11

Comparison between the present flow pattern map (R-134a: D=1.33 mm, Lhs=235 mm, Tsat=30°C, and ΔTsub,i=5°C) and the experimental transition lines of Triplett (21) for air-water flow in 1.097 mm and 1.45 mm tubes, respectively

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Figure 12

Comparison between the present flow pattern map (R-134a: D=1.33 mm, Lhs=235 mm, Tsat=30°C, and ΔTsub,i=5°C) and the transition line predicted with the correlation by Garimella (26) evaluated for D=1.33 mm

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Figure 13

Comparison between the present flow pattern map (R-134a: D=1.33 mm, Lhs=235 mm, Tsat=30°C, and ΔTsub,i=5°C) and the experimental transition lines of Chen (28) for two-phase flow of R-134a in a 1.10 mm vertical tube and pressures of 6 bar and 8 bar, respectively

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Figure 14

Comparison between the present flow pattern map (R-134a: D=1.33 mm, Lhs=235 mm, Tsat=30°C, and ΔTsub,i=5°C) and the experimental transition lines of Chen (28) for two-phase flow of R-134a in a vertical tube of 1.10 mm and 2.01 mm diameter, respectively

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