微通道内纳米流体空化流动特性及其复合强化传热机理研究

In many workplaces with high heat fluxes, it is difficult to meet the cooling requirement by only one kind of heat transfer enhancement technology. Therefore, developing high efficient compound enhancement technologies has become one of the focuses in the heat transfer field. Both hydrodynamic cavitation and nanofluids are the new methods proposed to enhance heat transfer in the microchannel heat sink. The combination of these two methods will further improve the heat transfer effect. The phenomenon of heat transfer enhancement with cavitating flow of nanofluid involves heat and mass transfer among the gas, liquid and solid phases. The mechanism and influential factors for this physical process are extremely complex, which is of great scientific significance for the research. In the project, several typical kinds of nanofluids will be selected as the working medium. Based on the bubble dynamics theory, the interaction between nanoparticles and cavitation bubbles is investigated from the micro perspective, and its effects on heat transfer are further analyzed. Meanwhile, by means of visualization experiments and numerical simulations, the synergy mechanism of the nanofluid in combination with cavitating flow for heat transfer enhancement is clarified at the macro level. The momentum and energy transmission model will be established to investigate the flow and heat transfer characteristics, as well as the mechanism of compound heat transfer enhancement in the microchannel heat sink. The present research lays a solid theoretical foundation for the practical application of this technique in the future.

在许多高热流密度工作场合，单一强化传热技术已很难满足其冷却要求，发展新型高效复合强化技术成为传热领域学者研究的热点。水力空化与纳米流体都是近年来新涌现的微通道热沉强化传热方法，将两者有机结合，取长补短，可进一步提升换热效果。微通道热沉内纳米流体空化强化传热现象涉及气-液-固三相热质传递过程, 其机理及影响因素非常复杂，相关研究具有重要科学意义。本课题拟选取几种典型的纳米流体，借助空泡动力学基本理论，从微观角度阐明纳米颗粒和空化泡之间的相互作用规律及其与强化传热的内在联系；同时，通过可视化实验和数值模拟手段，从宏观层面阐明微通道热沉内纳米流体空化流动强化传热协同机制，建立合理描述动量与能量传递过程的数理模型，探明影响微通道热沉流动和传热特性的关键因素，揭示纳米流体空化流动复合强化传热机理，为相关技术的实际应用奠定坚实的理论基础。

随着电子信息技术的迅速发展，芯片工作时的热流密度越来越高，传统的散热技术已经不能满足热管理的需求。微通道热沉因具有换热面积大、结构紧凑和传热系数高等优良特性，得到广泛应用。为进一步提升微通道的散热性能，国内外学者不断尝试新的强化传热思路，如改用换热性能更好的流体工质以及改变流体流动状态。本项目创新性的提出纳米流体和水力空化相结合的方法并开展研究。首先，从微观空泡动力学角度出发，对纳米流体空化过程的微观流动及传热特性开展研究，阐明纳米颗粒和空化泡之间的相互作用规律及其与强化传热的内在关联。研究结果表明，纳米颗粒的存在导致了流体密度和粘性的增加，相较去离子水，对空化泡的生长和溃灭过程有抑制作用。同时，在微通道有限空间内，空化泡的生长和溃灭受到壁面的阻碍，空化射流强度明显下降，因此壁面传热强化区域变小。同时，由于空化泡与壁面的距离更近，引入传热热阻。因此，在空化泡壁与壁面距离较近的局部区域，甚至出现传热恶化的情况。在上述研究基础上，通过实验和数值模拟方法，对纳米流体宏观流动和传热特性开展研究。结果进一步印证纳米流体的空化强度低于去离子水。随着空化强度的增加，微通道内纳米流体的换热效果得到提升。但是，空化诱发结构局部壁面附近由于空化泡的附着，导致对流换热系数出现下降。此外，讨论了空化诱发结构、入口压力和出口压力等因素的影响，结果表明当圆弧形（R=0.3 mm）空化诱发结构下，纳米流体的空化强度以及对流换热系数最高。上述研究揭示了微通道内纳米流体的空化动力学特性和强化传热机理，探明了影响空化流动和传热的因素，为促进微尺度高效复合强化传热技术的发展和进步奠定基础，具有重要的学术意义和广阔的应用前景。