合成双射流垂直冲击沸腾单气泡数值研究

Numerical study of boiling single bubble in vertical impact of dual synthetic jets

  • 摘要: 针对航空航天、电子设备散热等领域对新型相变换热技术的迫切需求,传统沸腾换热中气泡脱离频率低的问题是制约其性能的关键。因此,本研究采用数值模拟方法,对合成双射流垂直冲击沸腾单气泡进行了数值研究,分析射流冲击对沸腾单气泡生长、脱离的影响。相较于冲击前,射流冲击后气泡脱离频率显著提高,脱离体积减小。同时,射流能有效吹除近壁面气泡,破坏近壁面热边界层,高效地将冷流体从主流区卷吸到壁面附近,在降低表面气泡覆盖的同时将对流传热系数稳定在一个较高的值。在振幅为1.4 m/s,频率为50 Hz,冲击距离为15 mm的条件下,平均气泡覆盖率下降7.64%,对流传热系数提升32.18%。此外,分析合成双射流振幅、频率和冲击距离对冲击效果的影响:振幅的变化直接决定射流速度,对冲击效果影响更大,振幅为0.8 m/s时换热提升最小21.33%,振幅为1.1 m/s时最大可达41.32%,同时射流速度是决定气泡水平位移大小的主要因素;频率的变化也会影响冲击效果,但与振幅变化相比影响较小,且始终能保持较好的强化换热效果,频率范围10~90 Hz之间的换热提升相差不到10%。冲击距离越小,削弱温度边界层能力越强,但同时也会对气泡生长脱离产生抑制作用,冲击距离为11 mm时提升最小,传热系数提升16.34%;冲击距离为15 mm时提升最大,传热系数提升31.97%。

     

    Abstract: In response to the new active enhanced heat transfer technologies required for current aerospace and electronic device cooling, a numerical study was conducted on dual synthetic jets vertical impact boiling single bubble, analyzing the effects of jets impact on bubble growth and detachment during boiling. Compared with not impacted, the bubble detachment frequency significantly increased after the jets impact, while the detachment volume decreased. At the same time, the jets can effectively remove near-wall bubbles, disrupt the near-wall thermal boundary layer, efficiently draw cold fluid from the mainstream region to near the wall, and reduce bubble coverage \phi . It was found that the larger the bubble coverage, the smaller the convective heat transfer coefficient. Dual synthetic jets impact can transform the original boiling from a violently oscillating unstable state to a relatively stable and controllable state, reducing surface bubble coverage while stabilizing the convective heat transfer coefficient at a relatively high value. Under the conditions of an amplitude of 1.4 m/s, a frequency of 50 Hz, and an impact distance of 15 mm, the average bubble coverage decreased by 7.64%, and the convective heat transfer coefficient increased by 32.18%. In addition, the effects of Dual synthetic jets amplitude, frequency and impact distance on the impact performance were analyzed: changes in amplitude directly determine the jet velocity and have a greater effect on the impact, the minimum heat transfer improvement is 21.33% when the amplitude is 0.8 m/s, and the maximum can reach 41.32% when the amplitude is 1.1 m/s. Meanwhile, jet velocity is the main factor determining the horizontal displacement of bubble.The change in frequency also affects the impact effect, its influence is relatively small compared with the change in amplitude. Moreover, it can always maintain a good heat transfer enhancement effect, the heat transfer enhancement within the frequency range of 10 Hz to 90 Hz differs by less than 10%. There exists an optimal impact distance that can achieve the best heat transfer enhancement effect. When the impact distance is 11 mm, the improvement is minimal, and the heat transfer coefficient increases by 16.34%; The maximum improvement is achieved when the impact distance is 15 mm, and the heat transfer coefficient increases by 31.97%.

     

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