Convective boiling performance of refrigerant R-134a in herringbone and microfin copper tubes |
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Authors: | Enio P. Bandarra Filho,Jos M. Saiz Jabardo |
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Affiliation: | aFaculdade de Engenharia Mecânica, Universidade Federal de Uberlândia, Av. João Naves de Ávila, 2160 Bloco 1M, Santa Mônica, Uberlândia, MG, Brasil;bEscuela Politécnica Superior, Universidad de la Coruña, Calle Mendizábal s/n, 15403 Ferrol, España, Spain |
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Abstract: | This paper reports an experimental investigation of convective boiling heat transfer and pressure drop of refrigerant R-134a in smooth, standard microfin and herringbone copper tubes of 9.52 mm external diameter. Tests have been conducted under the following conditions: inlet saturation temperature of 5 °C, qualities from 5 to 90%, mass velocity from 100 to 500 kg s−1 m−2, and a heat flux of 5 kW m−2. Experimental results indicate that the herringbone tube has a distinct heat transfer performance over the mass velocity range considered in the present study. Thermal performance of the herringbone tube has been found better than that of the standard microfin in the high range of mass velocities, and worst for the smallest mass velocity (G=100 kg s−1 m−2) at qualities higher than 50%. The herringbone tube pressure drop is higher than that of the standard microfin tube over the whole range of mass velocities and qualities. The enhancement parameter is higher than one for both tubes for mass velocities lower than 200 kg s−1 m−2. Values lower than one have been obtained for both tubes in the mass velocity upper range as a result of a significant pressure drop increment not followed by a correspondent increment in the heat transfer coefficient. |
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Keywords: | Experiment Evaporation R-134a Microfin tube Wavy tube Heat transfer Pressure dropMots clé s: Expé rimentation É vaporation R-134a Tube microaileté Tube ondulé Transfert de chaleur Chute de pression |
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