纳米流体强化微槽群平板热管传热特性的研究

A flat heat pipe with microgrooves can achieve very high heat fluxes due to evaporation at thin liquid meniscus, so the heat transfer characteristics of the flat heat pipe with microgrooves can be done by changing the fluid transport properties and flow features of working fluids. Nanofluid is a new kind of working medium enhancing heat transfer. The recent findings indicate that the nanofluid as working fluid can significantly enhance thermal performance of the flat heat pipe with microgrooves. However, the mechanism of heat and mass transfer enhancement of evaporating menius using nanofluid has not been clarified, and thus the theoretical model predicting the flow and heat transfer in flat heat pipes with microgrooves of nanofluid could not be established accurately. This project uses the molecular dynamics method to investigate the mechanism of heat and mass transfer enhancement of evaporating menius using nanofluid, and the theoretical model predicting the flow and heat transfer of the evaporating menius using nanofluid is developed. Based on the above work，the theoretical model predicting the flow and heat transfer in flat heat pipes with microgrooves using nanofluid is developed, and the optimum kind of nanofluid and concentration of nanoparticle are obtained, which is used to conduct the optimum design of the flat heat pipe with microgrooves using nanofluid.

微槽群平板热管是依靠弯月面薄液膜的蒸发相变来强化传热的，因此工质的输运特性对微槽群平板热管的传热性能有强烈的影响。而纳米流体作为一种新型、高效的传热工质，可有效提高热系统的传热性能。研究表明，纳米流体作为工质可以极大增强微槽群平板热管的传热性能。但是，纳米流体强化弯月面蒸发薄液膜传热传质的机理尚未阐明，相关的理论模型及封闭方程还没有建立，纳米流体微槽群平板热管流动和传热过程的理论模型也就无法准确建立。本项目拟利用分子动力学方法探究纳米流体强化弯月面蒸发薄液膜传热传质的机理，建立适用于纳米流体弯月面蒸发薄液膜传热传质的理论模型，并在以上工作的基础上最终建立纳米流体微槽群平板热管流动和传热的理论模型，得到最佳纳米流体种类和最佳粒子浓度，用以指导纳米流体微槽群平板热管的优化设计。

电子元器件及设备正在向高效化、紧凑化、微小型化的方向发展，从而导致单位容积电子器件的发热量迅速增大。微槽群平板热管是依靠弯月面薄液膜的蒸发相变来强化传热的，在电子器件的散热和消除热点领域具有着广阔的应用前景。而纳米流体作为一种新型、高效的传热工质，可极大增强微槽群平板热管的传热能力。本项目对纳米流体强化微槽群平板热管的传热特性进行研究。基于驱动力及液膜厚度的不同，将纳米流体蒸发弯月面的蒸发薄液膜区域划分为两个不同的区域：排空区和构造区。在构造区内，液膜厚度大于纳米粒子的有效直径，纳米粒子的有序排列产生了额外的构造性脱离压力。而在排空区内，液膜的厚度小于纳米粒子的有效直径，不存在纳米粒子，产生排空力。排空力和构造性脱离压力随着纳米粒子直径的降低而增大，强化了纳米流体蒸发弯月面的传热传质能力。利用两步法制备了Al2O3-水纳米流体。确定了纳米流体的最佳制备工艺为超声分散 2 小时，此时Al2O3-水纳米流体的悬浮稳定性最好。对纳米流体微槽群平板热管的传热性能进行了试验研究。结果发现，存在一个最佳的纳米粒子体积份额为1.5%，可使纳米流体强化微槽群平板热管的传热能力最为显著。与去离子水作为工质相比，纳米流体作为工质可使微槽群平板热管的当量导热系数提高约15.6%。纳米流体是一种适用于微槽道平板热管的新型传热工质，在强化微槽群平板热管传热方面具有良好的应用前景和发展潜力。