Comparison and Validation of in-Tube CO2 Boiling Heat Transfer Correlations
Jahar Sarkar1, Souvik Bhattacharyya2,a and M. Ram Gopal2,b
1Department of Mechanical Engineering, IT-BHU, Varanasi 221 005, India.
jahar_s@hotmail.com
2Department of Mechanical Engineering, IIT Kharagpur, Kharagpur 721 302, India.
asouvik@mech.iitkgp.ac.in
bramg@mech.iitkgp.ac.in
ABSTRACT
High pressure, very low viscosity and surface tension, and near critical operation make the flow boiling heat transfer and pressure drop phenomenon of carbon dioxide distinct from conventional refrigerants. Distinct film break down and dryout phenomena make most of the general correlation unusable. The measured CO2 flow boiling heat transfer coefficient is significantly higher than that predicted from general correlation and the variation trend with the vapor quality is also opposite. This study presents a review and detailed comparison of evaporative heat transfer correlations available for carbon dioxide flow boiling in mini tubes.
The recently developed heat transfer correlations for CO2 flow boiling are based on the limited set of operating conditions and tube dimensions. So the correlations are required to be validated for other dimensions and flow conditions to use with minimum error for the heat exchanger design. The in-tube CO2 flow boiling with water as heating medium has been experimentally investigated. Subsequently the correlations have been validated for boiling heat transfer coefficient with the experimental heat transfer data. This study is expected to help the appropriate design of evaporator to be employed in transcritical CO2 cycle based cooling or heating systems.
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