【作者】 张文成；

【导师】 江斌； 仰叶；

【作者基本信息】 合肥工业大学 ， 动力工程（专业学位）， 2021， 硕士

【摘要】 随着微型化器件的出现,高密度微型器件的散热冷却问题的解决是设备性能及工作寿命的保障。传统的换热器温度分布不均匀,流动存在死角,探索新的微尺度换热模式势在必行。因此,本文在前人的基础上提出一种用于冷热流体交换的微管换热器,即冷热管群水平置于充满介质水的封闭圆腔内进行换热。首先探究圆腔内冷热管管间距、排列方式、瑞利数对管群外自然对流强度的影响。结果表明,在不同的管间距下,管群的自然对流换热效果有差异性,瑞利数Ra在2700-5400之间时,最优管间距S在2d-2.5d之间。在不同排列方式下,当Ra在5400-270000之间以及小于2700时,斜排换热效果最为突出;当Ra在2700-5400之间时,横排换热效果最佳;当Ra大于270000时,竖排平均努塞尔数Nu_ave最大。此外,给定管间距及排列方式下,管群的Nu_ave随着Ra的增大而增大。除管群外,对方腔单管进行模拟,得到当Ra大于2×10⁵,热管的Nu_ave随着方腔的倾斜角度的增加而减小。其次,通过动网格技术研究了振动对换热的影响。模拟得出,随振幅的增加,热管的换热性能逐渐提高,但提升幅度有限。频率在0-10 Hz之间,Nu_ave几乎不变,在10-50 Hz之间,Nu_ave随着频率的增加而增加,提升幅度不超过10%;当频率超过50 Hz时,Nu_ave提升速率大幅增加。另外,当施加相同振动,Ra为2700比Ra为270的Nu_ave提高了57.14%,增幅比未施加振动的增幅多10.74%。以振动雷诺数表示时,Re_v小于5时,Nu_ave的提高较小,随着Re_v大于5以上,Nu_ave数急剧增大。最后将仿真结果与Lemlich提出的单管振动强化关联式曲线对比,发现曲线趋势一致,但本文中,振动引起的强迫对流项与自然对流项比值小于8时,强化倍数几乎为1,比值大于8时,倍数急剧上升,最大强化倍数为3.16。更多还原

【Abstract】 With the appearance of miniaturized devices,the solution of heat dissipation and cooling problem of high-density miniature devices is the guarantee of equipment performance and working life.The temperature distribution of traditional heat exchanger is not uniform and the flow has a dead angle.It is imperative to explore a new micro scale heat transfer mode.Therefore,a microtube heat exchanger for the exchange of hot and cold fluids is proposed in this paper on the basis of the predecessors,that is,the hot and cold tubes are placed horizontally in a closed circular cavity filled with medium water for heat exchange.Firstly,the influences of the distance,arrangement and Rayleigh number of the hot and cold tubes in the circular cavity on the natural convection intensity outside the tube group were investigated.The results show that the natural convection heat transfer effect of tube group is different under different tube spacing.When Rayleigh number Ra is between 2700-5400,the optimal tube spacing S is between 2d-2.5d.Under different arrangement modes,when Ra is between 5400-270000 and less than 2700,oblique row has the most prominent heat transfer effect.When Ra is between 2700 and 5400,the horizontal row has the best heat transfer effect.When Ra is greater than 270000,the average Nussel number Nu_aveof the column is the largest.In addition,given the spacing and arrangement of tubes,the Nu_aveof tube group increases with the increase of Ra.Except for the tube group,the simulation of the opposite cavity single tube shows that when Ra is greater than 2×10⁵,the Nu_aveof the heat pipe decreases with the increase of the inclination angle of the square cavity.Secondly,the influence of vibration on heat transfer is studied by moving grid technique.The simulation results show that the heat transfer performance of the heat pipe increases gradually with the increase of amplitude,but the improvement is limited.Between 0-10 Hz,Nu_avealmost stays the same;between 10-50 Hz,Nu_aveincreases with the increase of frequency,and the increase rate is less than 10%.When the frequency exceeds 50 Hz,the Nu_avelift rate increases dramatically.In addition,when the same vibration is applied,the Nu_avewith Ra of 2700 is 57.14%higher than that of Ra of 270,and the increase is 10.74%higher than that without vibration.When the vibration Reynolds number is expressed,the increase of Nu_aveis small when the Rev is less than 5,and the Nu_avenumber increases sharply when the Rev is more than 5.Finally,the simulation results were compared with Lemlich’s single tube vibration enhancement correlation curve,and it was found that the curve trend was consistent.However,in this paper,when the ratio between the forced convection term and the natural convection term induced by vibration was less than 8,the enhancement multiple was almost 1;when the ratio was greater than 8,the enhancement multiple increased sharply,and the maximum enhancement multiple was 3.16.更多还原