doi: 10.3850/978-981-08-7614-2_IMPRES052

ABSTRACT

Experiments on flow pattern and flow boiling heat transfer of pure CO₂ and CO₂-oil mixtures in horizontal thin smooth and micro-fin tubes were carried out. The test smooth tube is a stainless steel tube, and the test micro-fin tube is an inner grooved copper tube. The test tubes are about 2 mm in mean inner diameter and 1 m in length. Experiments were conducted at mass velocities from 380 to 1500 kg/(m²s), a saturation temperature of 10°C, heat fluxes from 10 to 43.3 kW/m². The observed flow patterns in both the tubes were compared with the flow pattern map, and the measured local heat transfer coefficients for both the tubes were compared with those calculated from the prediction correlations proposed by Cheng et al. for smooth tubes. As the results, the flow patterns in both the tubes agree well with the flow pattern map. For pure CO₂, the prediction model agrees well with the experimental data of the smooth tube, and the measured local heat transfer coefficients of the micro-fin tube are about 31% higher than those of the smooth tube. For CO₂-oil mixtures, the experimental data of both the tubes are much lower than those of pure CO₂. The dryout inception qualities of the micro-fin tube are much higher than those of the smooth tube. And the dryout inception qualities of the micro-fin tube increase with the increase in mass velocity, while those of the smooth tube decrease with the increase in mass velocity.

Keywords: Carbon dioxide, Flow pattern, Flow boiling, Heat transfer, Dryout, Lubricating oil.

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