【作者】 王伟；

【导师】 徐进良； 李智；

【作者基本信息】 华北电力大学(北京) ， 工程硕士（专业学位）， 2023， 硕士

【摘要】 随着现代电子设备的尺寸不断减小,单位体积的散热量迅速增加。压电风扇作为一种创新的设计和可行的解决方案,可用于便携式电子产品的微电子系统散热。压电风扇属于主动冷却装置,它能以较低的功耗增强传热。本文采用数值模拟、理论分析的方法对压电风扇散热系统的流动及传热特征展开探究,主要研究内容如下:首先,基于Ansys Fluent软件并采用动网格技术,对压电风扇激励产生的三维瞬态空气流场进了数值分析。通过获得压电风扇激励流场内静压和速度矢量分布,揭示压力变化对涡流发展的影响;对具体叶片尺寸和振动频率的压电风扇P-Q特性进行了计算,并讨论了叶片宽度及振动频率对风扇P-Q特性的影响。计算结果表明,压电风扇叶片振动形成的负压区尺度以及最小负压值严重影响着叶片激励空气涡流的强度以及气流流量的大小,并且其P-Q特性曲线呈现出与轴流风扇相似的特点。其次,五种通道布置方案的流动及传热特性通过数值模拟的方法被分别探究。时间平均速度分布揭示了由叶根形成的两股高速冷却气流的流动特性,即冷却流逐渐在叶尖中部汇聚并向下游扩散。由于负压区和正压区的卷吸和驱动作用最强,方案5的最高速度为8 m/s。方案1-5的通风量范围为1.21×10-3至2.07×10-3 m3/s。对于方案1-4,最大通风量始终来自顶部边界,百分比超过80%。在所有方案中,方案1的最高温度最低,为467.401 K。然而,在方案1中获得了最高的时空平均传热系数,高达54.02 W/(m2·K)。最后,为了获得双压电风扇系统在有限体积内传热性能的理论极限,通过三维模拟详细研究了叶片位置对其的影响。在此,叶片间距范围为风扇宽度的1.6至4.2倍,并分别获得了对应四个振动相位角(0°,60°,120°,180°)的叶片间距最佳值。对于所有振动模式,风量变化曲线随叶片节距呈抛物线趋势。当风扇以同相模式运行时,可获得最大的风量。此外,在同相和反相模式下都观察到了局部热点现象。对于同相模式,局部热点之间的距离随着叶片间距的增加而变大,而对于反相模式,则保持基本恒定。本文的工作通过数值模拟和理论分析为压电风扇的实际传热优化提供了设计指导,将有助于对压电风扇系统热管理的理论理解和应用。更多还原

【Abstract】 As the size of modern electronic devices continues to decrease,the amount of heat dissipation per unit volume increases rapidly.Piezoelectric fans are used as an innovative design and a viable solution for cooling microelectronic systems in portable electronics.Piezoelectric fans are active cooling devices that can enhance heat transfer with low power consumption.In this paper,the flow and heat transfer characteristics of a piezoelectric fan cooling system are investigated using numerical simulations and theoretical analysis,the details are as follows:First,based on the Ansys Fluent software and using the dynamic mesh technique,the three-dimensional transient air flow field generated by the piezoelectric fan excitation is numerically analyzed.By obtaining the static pressure and velocity vector distributions in the piezoelectric fan excitation flow field,the influence of pressure changes on the vortex development is revealed;the P-Q characteristics of the piezoelectric fan are calculated for specific blade sizes and vibration frequencies,and the effects of blade width and vibration frequency on the P-Q characteristics of the fan are discussed.The calculation results show that the scale of the negative pressure zone formed by the piezoelectric fan blade vibration and the minimum negative pressure value seriously affect the intensity of the air vortex excited by the blade and the magnitude of the airflow,and its P-Q characteristic curve shows similar characteristics to those of the axial fan.Second,the flow and heat transfer characteristics of each of the five channel arrangement schemes were investigated by numerical simulation.The time-averaged velocity distribution reveals the flow characteristics of two high-speed cooling streams formed by the blade roots,i.e.,the cooling streams gradually converge in the middle of the blade tip and spread downstream.The highest velocity for scheme 5 is 8 m/s due to the strongest coiling and driving effect in the negative and positive pressure zones.The ventilation air volume for schemes 1-5 ranges from 1.21 × 10-3 to 2.07 ×10-3 m3/s.For schemes 1-4,the maximum ventilation volume always comes from the top boundary with a percentage exceeding 80%.Among all schemes,the highest temperature value of scheme 1 was the lowest,that is 467.401 K.However,the highest time-space average heat transfer coefficient was obtained in scheme 1,up to 54.02 W/(m2·K).Finally,in order to obtain the theoretical limits of the heat transfer performance of the dual piezoelectric fan system in a finite volume,the influence of the blade position was investigated in detail by 3D simulations.Here,the blade pitch ranges from 1.6 to 4.2 times the fan width,and the optimum values of blade pitch are obtained for each of the four vibration phase angles(0°,60°,120°,180°).For all vibration modes,the air volume variation curve follows a parabolic trend with blade pitch.The maximum air volume is obtained when the fan is operated in in-phase mode.In addition,the local hot spot phenomenon was observed in both in-phase and counter-phase modes.For the in-phase mode,the distance between the local hot spots becomes larger with increasing blade pitch,while for the counter-phase mode,it remains essentially constant.The work in this paper provides a design guide for practical heat transfer optimization of piezoelectric fans through numerical simulation and theoretical analysis,which will contribute to the theoretical understanding and application of thermal management of piezoelectric fan systems.更多还原