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 KoreaC 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

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• http://www.sciencedirect.com/science/article/pii/S0140700702000403#

http://www.youtube.com/watch?v=s-YmfZNKnlU

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Qualitative classification flow regimes.

MIT Department of Nuclear Science and Engineering

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Heat transfer and flow regimes in a vertical heated channel. (Thermal non‐equilibrium ef-fects have been neglected in sketching the bulk temperature)

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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 , mass fluxes ranging from 200 to 600 kg , 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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Experimental apparatus

The experimental test facility and test section.

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Experimental conditions

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The effect of mass flux on heat transfer coefficient: (a)R-22, (b) R-134a, and (c) CO2

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The experimental data on Wojtan et al. [20] flow pattern map for R-22.

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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 coefficientThe 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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Two-phase heat transfer multiplier as a function of Diagram of the experimental heat transfer coefficient, hexp.,vs prediction heat transfer coefficient, hpred.

Heat transfer coefficient comparisonNucleate boiling contribution

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