换热管周围声流强化对流传热的数值模拟

Numerical Simulation of Convective Heat Transfer Enhanced by Acoustic Streaming Around Heat Exchanger Tubes

为研究稳态声流成分对换热管对流换热特性的影响,建立了行波场中单换热管外声流强化传热的数值计算模型。采用分离时间尺度的数值方法模拟了声流和非均匀温度场的耦合作用,分析了换热管局部努塞尔数和平均努塞尔数在不同激励频率(10~1500 Hz)和声压级(103~127 dB)作用下的变化规律。结果表明:平均努塞尔数随着激励频率的增加呈指数形式减小,随着声压级的增大呈指数形式增大;低频声波形成的内涡流和高频声波形成的外涡流决定了不同的局部努塞尔数分布规律;低频高强度声波可在换热管热黏性边界层内、外形成强烈的声流扰动,极大地强化了换热管的热传输过程。

In order to study the effect of steady-state acoustic streaming components on the convective heat transfer characteristics of heat exchange tubes,a numerical calculation model for the enhancement of heat transfer by acoustic streaming outside a single heat exchange tube in a traveling wave field was established.The coupling effect of acoustic streaming and non-uniform temperature field is calculated by using the numerical method of separating time scale,and the variation rules of local Nusselt number and average Nusselt number of heat exchanger tube under different excitation frequencies(10-1500 Hz)and sound pressure levels(103-127 dB)were analyzed.Results show that the average Nusselt number decreases exponentially with the increase of excitation frequency,and increases exponentially with the increase of sound pressure level.The inner streaming formed by low-frequency sound waves and the outer streaming formed by high-frequency sound waves determine different local Nusselt number distribution laws.Low-frequency and high-intensity sound waves can form a strong acoustic streaming disturbance inside and outside the thermal viscous boundary layer of the heat exchanger tube,which greatly strengthens the heat transfer process of the heat exchanger tube.