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摘要
The maximum droplet radius during dropwise condensation can significantly influence the heat transfer characteristics. On the dropwise-filmwise hybrid surface, droplets on the dropwise region can remove through filmwise region spontaneously driven by the surface free energy difference between the dropwise and filmwise regions, and thus the maximum droplet radius (equivalent to the departure radius for the complete dropwise condensation) can be adjusted by the configurations of hybrid surface. The condensation heat transfer enhancement of steam with hybrid surface is investigated in this paper by integrating the dropwise and filmwise condensation heat transfer models. The influence of maximum droplet radius on heat flux of dropwise region, the liquid film thickness and heat flux of filmwise region are investigated, respectively. Accordingly, the heat transfer contributions of two regions to the heat transfer characteristics of hybrid surface are analyzed. Finally, the influences of surface subcooling degree, contact angle and contact angle hysteresis on heat transfer characteristics of hybrid surface are discussed. The results indicate that an optimum value of the maximum droplet radius exists to enhance the condensation heat transfer of steam with the hybrid surface, which is dependent on surface subcooling degree, filmwise region width and contact angle while independent on contact angle hysteresis. With the surface subcooling degree increases ranging from 1.0 K to 10 K, the optimum maximum radius of droplet on dropwise region increases from about 0.2 mm to 0.375 mm. The optimum maximum radius of droplet increases from about 0.25 mm to 0.5 mm when the filmwise region width increases from 0.5 mm to 1.0 mm. The optimum maximum radius of droplet decreases with the increase of the contact angle. Therefore, steam condensation heat transfer performance can be regulated and optimized by designing the hybrid surface appropriately. The results also indicate that heat transfer enhancement factor for the hybrid surface is larger than 1.0 for the low surface subcooling or the condensing surface with small contact angle or large contact angle hysteresis. Therefore, the hybrid surface can effectively enhance the condensation heat transfer for the special cases, such as those with low surface subcooling degree, or with small contact angle and large contact angle hysteresis. For the case discussed in this paper, the maximum enhancement factor can approach up to about 1.18.
- 出版日期2014-10
- 单位大连理工大学
