Enhancing heat transfer performance of nitrogen condensation on vertical plate with microstructure

摘要

The condensation process of cryogenic fluid is mainly dominated by film condensation. In this study, microstructure surfaces are employed to enhance the nitrogen condensation heat transfer performance. The visualization experiments of nitrogen condensation on six groups of vertical microstructure plate are designed and tested in the heat flux range of 3 kW/m~2 to 27 kW/m~2. The phenomenon of rivulet at the bottom of micro fin is observed, and the rivulet velocity is close to 2-3 times of the liquid film velocity calculated by Nusselt theory. The rivulet at the bottom of the micro fin indicates the curved surface structure changes the uniform distribution of the liquid film at the top and bottom of the micro fin and accelerates condensate drainage. Besides, the heat transfer performances under different micro fin pitches, heights and fin structures are further compared and analyzed. The influence of the micro fin structure on the heat transfer performance and flow characteristics is reflected in the curvature radius and the temperature gradient from the top to the bottom of the fin. In particular, the heat transfer coefficient of micro fin with 0.3 mm height and 1 mm pitch is up to 4 times higher than that of flat plate within the condensing temperature difference range of 3.5 K. The new correlation prediction of geometric enhancement factor is in good agreement with experimental data. In engineering practice, both the thermal resistance and curvature characteristics of the micro fin in high heat fluxes should be considered when designing the micro fin with best heat transfer performance.