非线性声流作用下并列双换热管流动传热特性研究

A study on flow heat transfer characteristics of side-by-side double heat exchanger tubes under nonlinear acoustic streaming

为研究强声波作用下时均非线性声流引起的流动传热问题,建立并列双换热管周围非线性声流耦合非均匀温度场的数值模型,采用雷诺应力法计算不同声频率(20~2 000 Hz)和声压级(123.31~140.21 dB)下非线性声流对管束周围温度场和管壁换热系数的影响规律。结果表明:高强声形成的畸变性非线性声流效应对换热管束的传热过程具有显著调制作用;换热管平均努塞尔数随着声频率、声压级的增大分别呈指数形式减小、增大;管束间隙区域非线性声流旋涡对热量具有捕集效应,使间隙区域平均努塞尔数较小,且局部努塞尔数总是呈“U”型分布;与高频强声相比,20 Hz和140.21 dB的低频强声产生的非线性声流效应具有更显著的传热强化效果,平均努塞尔数比1 000Hz提高了2倍、比123.31 dB提高了2.37倍。

In order to study the flow and heat transfer caused by time-averaged nonlinear acoustic streaming under the action of strong sound waves,a numerical model of nonlinear acoustic streaming coupled non-uniform temperature field around a side-by-side double heat exchanger tube was established.The Reynolds stress method was used to calculate the effects of nonlinear acoustic streaming on the temperature field and heat transfer coefficient around the tube bundle under different sound frequencies(20-2000 Hz)and sound pressure levels(123.31-140.21 dB).Results show that the distortion nonlinear acoustic streaming effect formed by high intensity sound has a significant modulating effect on the flow and heat transfer process of the heat exchanger tube bundle.The average Nusselt number of the heat exchanger tube decreases and increases exponentially with sound frequency and sound pressure level,respectively.The nonlinear acoustic streaming vortex in the gap region of the tube bundle has a heat-trapping effect,so the average Nusselt number is small,and the local Nusselt number in the gap area of the tube bundle always has a“U”distribution.Compared with high-frequency strong sound,the nonlinear acoustic streaming effect produced by 20 Hz and 140.21 dB low-frequency strong sound has a more significant heat transfer enhancement effect,and the average Nusselt number is 2 times higher than 1000 Hz and 2.37 times higher than 123.31 dB.