压电风扇对管内局部受迫对流换热的强化效果研究

Local heat transfer enhancement induced by a piezoelectric fan in a channel with axial flow

目的:电子设备的局部过热问题对散热系统的设计提出了新的考验。针对传统被动式散热技术调节困难、调节代价大等问题,本文提出使用压电风扇作为控制元件对管内局部过热区域进行主动对流换热效果强化的方案,期望通过实验与数值模拟研究掌握压电风扇在管内横流作用下的流动控制特性及强化传热机理,为压电风扇在实际工程中的应用提供理论指导。创新点:1.通过基于等温设计的实验系统测试加热面在压电风扇作用下的时均努塞尔数,并证明压电风扇对管内局部区域对流换热效果的强化能力;2.通过数值模拟分析压电风扇的纵向涡产生特性并解释纵向涡对局部对流换热效果的强化机理。方法:1.利用铜热沉导热快、热容大等特性建立定常的等温换热面,并测量得到等温壁面在压电风扇作用下的时均努塞尔数;2.使用基于动网格技术的数值模拟,得到压电风扇作用下的流场与温度场信息,分析压电风扇的流动控制特性,并解释压电风扇强化局部对流换热的机理;3.通过参数化研究说明振幅和来流雷诺数对压电风扇强化对流换热效果的影响。结论:1.压电风扇的振动可以显著地强化管内局部区域的对流换热性能;2.压电风扇引起的对流换热强化主要来自其振动产生的纵向涡对;3.压电风扇的振动对管内流动压降的影响较小。

The present work experimentally and numerically investigates the local heat transfer enhancement induced by a piezoelectric fan interacting with a cross flow in a local heated channel.The piezoelectric fan is placed along the flow direction and tested under different amplitudes and flow rates.In the simulations,a spring-based smoothing method and a local remeshing technique are used to handle the moving boundary problems.Hybrid mesh is used to reduce the size of dynamic mesh domain and to improve computational efficiency.The experimental and numerical values of the time-averaged mean Nusselt number are found to be in good agreement,with deviations of less than 10%.The experimental result shows that the heat transfer performance of the heated surfaces is substantially enhanced with a vibrating piezoelectric fan.The numerical result shows that the heat transfer enhancement comes from the strong longitudinal vortex pairs generated by the piezoelectric fan,which significantly promote heat exchange between the main flow and the near-wall flow.In the case of a=0.66(a is the dimensionless amplitude)and Re=1820,the enhancement ratio of the time-averaged mean Nusselt number reaches 119.9%.