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采用分子动力学方法模拟纳米尺度下液体在固体壁面上发生核化沸腾的过程，主要研究壁面浸润性对气泡初始核化过程和气泡生长速率的影响以及固-液界面效应在液体核化沸腾的能量传递过程中所起到的作用.研究结果发现：壁面浸润性越强，气泡在固壁处越容易核化.该结果与经典核化理论中“疏水壁面易于产生气泡”的现象产生了明显的区别.其根本原因是在纳米尺度下，固-液界面热阻效应不能被忽略.一方面，在相同的壁温下，通过增强固-液相互作用，可以显著降低界面热阻，使得热量传递效率提高，导致靠近壁面处的流体温度升高，气泡核化等待时间缩短，有利于液体沸腾核化.另一方面，气泡的生长速率随着壁面浸润性的增强而明显升高.当气泡体积生长到一定程度时，会在壁面处形成气膜，从而导致壁面传热性能恶化.因此，通过壁面的热流密度呈现出先增大后减小的规律.With the rapid development of nanotechnology, nucleate boiling has been widely applied to the thermal management of nanoelectronics, owing to its highly-efficient heat transfer characteristics. Considering the scale effects, such as temperature jump at solid-liquid interface, a further study of nucleation boiling mechanism at a microscopic level is needed. At present, extensive studies have been carried out for providing a significant insight into the formation of nano-bubbles in a nanoscale thermal system, but the effect of heat transfer efficiency affected by the surface wettability on bubble nucleation over solid substrate is rarely available in the literature. Therefore, in this paper, the effect of surface wettability on the initial nucleation process and growth rate of bubbles are investigated and the mechanism of bubble nucleation on a nanoscale is analyzed, by the molecular dynamics simulation. The modified Lennard-Jones potential is used for investigating the solid-liquid interaction. Changing the potential parameters α and β can obtain different surface wettability. The atomic sites, liquid density profiles and bubble nucleus volumes are computed to compare the processes of bubble nucleation on different surfaces. The variation of liquid temperature, potential and absorbed heat flux with heating time are evaluated to explore the mechanism of bubble nucleation. The simulation results show that the surface wettability influences the bubble nucleation and heat transfer at liquid-solid interface significantly. On the one hand, the bubble nucleation is promoted by properly increasing the liquid-solid interaction, which is distinctly different from the existing classical theory related to nano-bubble preferably formed on a hydrophobic surface. This is because the thermal resistance of the solid-liquid interface on a nanoscale cannot be neglected. The interface thermal resistance will decrease with the increase of wettability. Therefore, the heat transfer efficiency is higher for a stronger liquid-solid interaction so that the liquid over the hot wall obtains more energy to make bubble nucleus generated earlier. On the other hand, the surface wettability also influences the bubble growth rate. The stronger the liquid-solid interaction, the faster the bubble grows. When the volume of bubble reaches a certain value, a vapor film is formed on the substrate, leading to film boiling. Furthermore, it also illustrates that initial heat flux increases with time. In this stage, the heat flux curve shows two kinds of slopes, corresponding to the occurrence of evaporation and bubble nucleation, respectively. Then, after a certain time, the heat flux profile presents a declining trend, indicating a change into film boiling.
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Keywords:
- nanoscale /
- bubble nucleation /
- wettability /
- interface effect
[1] Agostini B, Fabbri M, Park J E, Wojtan L, Thome J R, Michel B 2007 Heat Transfer Eng. 28 258
[2] Riofrío M C, Caney N, Gruss J A 2016 Appl. Therm. Eng. 104 333
[3] Zhang S W, Yuan W, Tang Y, Chen J L, Li Z T 2016 Appl. Therm. Eng. 104 659
[4] Marable D C, Shin S, Nobakht A Y 2017 Int. J. Heat Mass Transf. 109 28
[5] Xu J L, Li Y X 2007 Int. J. Heat Mass Transf. 50 2571
[6] bin Saleman A R, Chilukoti H K, Kikugawa G, Shibahara M, Ohara T 2017 Int. J. Therm. Sci. 120 273
[7] Bourdon B, Bertrand E, di Marco P, Marengo M, Rioboo R, de Coninck J 2015 Adv. Colloid Interface Sci. 221 34
[8] Jo H J, Ahn H S, Kang S H, Kim M H 2011 Int. J. Heat Mass Transf. 54 5643
[9] Quan X J, Chen G, Cheng P 2011 Int. J. Heat Mass Transf. 54 4762
[10] Xu X P, Qian T Z 2014 Phys. Rev. E 89 063002
[11] Kinjo T, Matsumoto M 1998 Fluid Phase Equilib. 144 343
[12] Kimura T, Maruyama S 2002 Microscale Thermophys. Eng. 6 3
[13] Kinjo T, Gao G T, Zeng X C 2000 Prog. Theor. Phys. Suppl. 138 732
[14] Mao Y J, Zhang Y W 2013 Nanoscale Microscale Thermophys. Eng. 17 79
[15] Theofanous T G, Tu J P, Dinh A T, Dinh T N 2002 Exp. Therm. Fluid Sci. 26 775
[16] Nagayama G, Tsuruta T, Cheng P 2006 Int. J. Heat Mass Transf. 49 4437
[17] Bai B F, Li S J 2010 Proceedings of the 14th International Heat Transfer Conference Washington, United States of America, August 8-13, 2010 p177
[18] Novak B R, Maginn E J, McCready M J 2008 J. Heat Transfer 130 042411
[19] Carey V P, Wemhoff A P 2005 Int. J. Heat Mass Transf. 48 5431
[20] Hens A, Agarwal R, Biswas G 2014 Int. J. Heat Mass Transf. 71 303
[21] Yamamoto T, Matsumoto M 2012 J. Therm. Sci. Technol. Jpn. 7 334
[22] Nagayama G, Kawagoe M, Tokunaga A, Tsuruta T 2010 Int. J. Therm. Sci. 49 59
[23] Phan H T, Caney N, Marty P, Colasson S, Gavillet J 2009 Int. J. Heat Mass Transf. 52 5459
[24] Gong S, Cheng P 2015 Int. J. Heat Mass Transf. 85 635
[25] Leroy F, MüllerPlathe F 2010 J. Chem. Phys. 133 044110
[26] Okumura H, Ito N 2003 Phys. Rev. E 67 045301
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[1] Agostini B, Fabbri M, Park J E, Wojtan L, Thome J R, Michel B 2007 Heat Transfer Eng. 28 258
[2] Riofrío M C, Caney N, Gruss J A 2016 Appl. Therm. Eng. 104 333
[3] Zhang S W, Yuan W, Tang Y, Chen J L, Li Z T 2016 Appl. Therm. Eng. 104 659
[4] Marable D C, Shin S, Nobakht A Y 2017 Int. J. Heat Mass Transf. 109 28
[5] Xu J L, Li Y X 2007 Int. J. Heat Mass Transf. 50 2571
[6] bin Saleman A R, Chilukoti H K, Kikugawa G, Shibahara M, Ohara T 2017 Int. J. Therm. Sci. 120 273
[7] Bourdon B, Bertrand E, di Marco P, Marengo M, Rioboo R, de Coninck J 2015 Adv. Colloid Interface Sci. 221 34
[8] Jo H J, Ahn H S, Kang S H, Kim M H 2011 Int. J. Heat Mass Transf. 54 5643
[9] Quan X J, Chen G, Cheng P 2011 Int. J. Heat Mass Transf. 54 4762
[10] Xu X P, Qian T Z 2014 Phys. Rev. E 89 063002
[11] Kinjo T, Matsumoto M 1998 Fluid Phase Equilib. 144 343
[12] Kimura T, Maruyama S 2002 Microscale Thermophys. Eng. 6 3
[13] Kinjo T, Gao G T, Zeng X C 2000 Prog. Theor. Phys. Suppl. 138 732
[14] Mao Y J, Zhang Y W 2013 Nanoscale Microscale Thermophys. Eng. 17 79
[15] Theofanous T G, Tu J P, Dinh A T, Dinh T N 2002 Exp. Therm. Fluid Sci. 26 775
[16] Nagayama G, Tsuruta T, Cheng P 2006 Int. J. Heat Mass Transf. 49 4437
[17] Bai B F, Li S J 2010 Proceedings of the 14th International Heat Transfer Conference Washington, United States of America, August 8-13, 2010 p177
[18] Novak B R, Maginn E J, McCready M J 2008 J. Heat Transfer 130 042411
[19] Carey V P, Wemhoff A P 2005 Int. J. Heat Mass Transf. 48 5431
[20] Hens A, Agarwal R, Biswas G 2014 Int. J. Heat Mass Transf. 71 303
[21] Yamamoto T, Matsumoto M 2012 J. Therm. Sci. Technol. Jpn. 7 334
[22] Nagayama G, Kawagoe M, Tokunaga A, Tsuruta T 2010 Int. J. Therm. Sci. 49 59
[23] Phan H T, Caney N, Marty P, Colasson S, Gavillet J 2009 Int. J. Heat Mass Transf. 52 5459
[24] Gong S, Cheng P 2015 Int. J. Heat Mass Transf. 85 635
[25] Leroy F, MüllerPlathe F 2010 J. Chem. Phys. 133 044110
[26] Okumura H, Ito N 2003 Phys. Rev. E 67 045301
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