沉浸式换热器超声强化传热影响因素

Influencing factors of ultrasound enhanced heat transfer of immersed coil heat exchanger

以沉浸式换热器为研究对象,通过壁面加载超声波,比较了超声波振幅、换热器入口流速和管外压力对超声波效应及强化传热效果的影响。结果表明:超声波振幅由20μm增大至35μm时,表面对流传热系数增幅由15.67%增至26.71%;管外压力由0.1MPa增大至1.0MPa时,表面对流传热系数增幅由20.95%增至48.43%;入口流速由1.0m/s降低至0.05m/s时,表面对流传热系数增幅由1.76%增至39.01%。增大超声波振幅、环境压力和减小介质流速均能增强超声波声流现象和空化效应,有效提高超声波强化传热效果;高压环境会使同振幅、同频率超声振动作用下声功率呈指数增长,高流速会降低流体介质的声能密度,两种情况都需要匹配合适的超声波以保证强化传热最佳效果。

Taking the immersed coil heat exchanger as the research object,the ultrasonic wave was imposed by means of vibration surface,and the influence of the ultrasonic amplitude and the inlet flow rate of the heat exchanger and the pressure outside the tube on the ultrasonic effect and the heat transfer enhancement were compared.The results showed that the increase of ultrasonic amplitude from 20μm to 35μm resulted in the increase of surface heat transfer coefficient from 15.67% to 26.71%,and the increase of external pressure from 0.1MPa to 1.0MPa led to the increase of surface heat transfer coefficient from 20.95% to 48.43%.When the inlet flow rate was reduced from 1.0m/s to 0.05m/s,the surface heat transfer coefficient increased from 1.76% to 39.01%.Increasing the ultrasonic amplitude,environmental pressure and reducing the medium flow rate could all enhance the acoustic streaming and acoustic cavitation effect and effectively improved the ultrasonic heat transfer enhancement effect;the high-pressure environment will cause the sound power to increase exponentially under the same amplitude and frequency ultrasonic vibration,and the high flow rate would reduce the sound energy density of the fluid medium.Both cases needed to match the appropriate ultrasound power to ensure the best effect of enhanced heat transfer.