Heat transfer perforamance

1. Thermal Energy Conversion Control Lab. Chonbuk Nat’I Univ.
Boiling heat transfer of R-22, R-134a, and CO2
in horizontal smooth minichannels*
Kwang-Il Choia, A.S. Pamitran a, Chun-Young Oh b, Jong-Taek Oh c,*
A Graduate School, Chonnam National University, San 96-1, Dunduk-Dong, Yeosu, Chonnam 550-749, Republic of Korea
B Refrigeration Research Institute, Chonnam National University, San 96-1, Dunduk-Dong, Yeosu, Chonnam 550-749, Republic of Korea
C Department of Refrigeration and Air Conditioning Engineering, Chonnam National University, San 96-1,
Dunduk-Dong, Yeosu, Chonnam 550-749, Republic of Korea
Sudheer Nandi
(Ph.D.),M.Tech,MBA.
Sustainable Energy . S.korea

2. Thermal Energy Conversion Control Lab. Chonbuk Nat’I Univ. 2
• http://www.sciencedirect.com/science/article/pii/S0140700702000403#
http://www.youtube.com/watch?v=s-YmfZNKnlU

3. Thermal Energy Conversion Control Lab. Chonbuk Nat’I Univ. 3
Qualitative classification flow regimes
.
MIT Department of Nuclear Science and Engineering

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5. Thermal Energy Conversion Control Lab. Chonbuk Nat’I Univ. 5
Heat transfer and flow regimes in a vertical heated channel. (Thermal non‐equilibrium effec
ts have been neglected in sketching the bulk temperature)

6. Thermal Energy Conversion Control Lab. Chonbuk Nat’I Univ.
Abstract
• This study examined convective boiling heat transfer in horizontal minichannels using R-22, R-134a, and CO2.
• The local heat transfer coefficients were obtained for heat fluxes ranging from 10 to 40 kW 𝑚 −2
, mass fluxes
ranging from 200 to 600 kg 𝑚−2
𝑠 −1
, a saturation temperature of 10 °C, and quality up to 1.0.
• The test section was made of stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm, and a length of
2000 mm. The section was heated uniformly by applying an electric current to the tubes directly.
• Nucleate boiling heat transfer was the main contribution, particularly at the low quality region.
• An increasing and decreasing heat transfer coefficient occurred at the lower vapor quality with increasing heat flux
and mass flux.
• The mean heat transfer coefficient ratio of R-22:R-134a:CO2 was approximately 1.0:0.8:2.0. Laminar flow was
observed in the minichannels.
• A new boiling heat transfer coefficient correlation based on the superposition model for refrigerants in
minichannels was developed with a mean deviation of 11.21%.
Keywords: Refrigerant; R-22; R-134a; R-744; Carbon dioxide; Experiment; Heat transfer; Boiling; Micro channel;
smooth tube; Horizontal tube
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8. Thermal Energy Conversion Control Lab. Chonbuk Nat’I Univ. 8
Experimental apparatus
The experimental test facility and test section.

9. Thermal Energy Conversion Control Lab. Chonbuk Nat’I Univ.
Experimental conditions
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11. Thermal Energy Conversion Control Lab. Chonbuk Nat’I Univ. 11
The effect of mass flux on heat transfer coefficient: (a)R-22, (b) R-134a, and
(c) CO2

12. Thermal Energy Conversion Control Lab. Chonbuk Nat’I Univ.
The experimental data on Wojtan et al. [20] flow pattern map for R-22.
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13. Thermal Energy Conversion Control Lab. Chonbuk Nat’I Univ. 13
The effect of heat flux on heat transfer coefficient: (a) R-22,(b) R-134a, and (c) CO2.

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The comparison of the heat transfer coefficient
The effect of inner tube diameter on heat transfer
coefficient for R-22.

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Development of a new correlation

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17. Thermal Energy Conversion Control Lab. Chonbuk Nat’I Univ. 17
Two-phase heat transfer multiplier as a function of ∅2
𝑓
Diagram of the experimental heat transfer coefficient, hexp.,
vs prediction heat transfer coefficient, hpred.
Heat transfer coefficient comparisonNucleate boiling contribution

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19. Thermal Energy Conversion Control Lab. Chonbuk Nat’I Univ.
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21. Thermal Energy Conversion Control Lab. Chonbuk Nat’I Univ. 21
Thank you for listening