| Herringbone tube, which has a V shaped groove pattern, are widely used in heat exchanger, not only because of the larger surface for heat transfer, but because the microfins may strengthen the disturbance and carry liquid in two different flow directions, which can greatly improve the two-phase heat transfer. The EHT tube, which enhanced heat transfer surface produces a combination of more nucleation sites, increased turbulence, boundary layer disruption, secondary flow generation and increased heat transfer surface area, is a newly-developed tube. It is hoped that a better utilization of this two type tubes can be get from my experiment research.At first a literature review of two-phase flow on tubes was completed in this paper. Secondly, experiment facility was improvement for outside tube condensation. Finally the experimental data analysis and condensation characteristics comparison were carried out.Smooth tube was also tested for comparison, and two kinds of casings with 17mm and 25.4mm inner diameter respectively were settled. Experiment was performed to evaluate convective condensation of R22 and R410A on a smooth tube (outer diameter 12.7 mm), a herringbone tube (fin root diameter 12.7 mm) and a newly developed enhanced surface EHT tube (outer diameter 12.7 mm) at 318.15K (±0.5K) saturation temperature, with inlet and outlet qualities of 0.8 (±0.05) and 0.1 (± 0.05), respectively. The results suggest that the heat transfer coefficient in 17mm casing of the herringbone tube is 1.95 times larger than a smooth tube and the EHT tube is 1.67 times that of the smooth tube for R410a condensation. And for R22 condensation, the heat transfer coefficient of the herringbone tube is 1.83 times larger than a smooth tube and the EHT tube is 1.52 times that of the smooth tube. And in 25.4mm casing, the herringbone tube provides the best heat transfer performance for both two refrigerants, and the heat transfer coefficient of EHT tube is worse than smooth tube. |
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