Experiments on flows in channels with spatially distributed heating
Experiments on flows in channels with spatially distributed heating
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DOI：
10.1017/jfm.2019.332
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发表时间：
2019-06
影响因子：
3.7
通讯作者：
A. Inasawa;K. Taneda;J. M. Floryan
中科院分区：
文献类型：
--
作者：
A. Inasawa;K. Taneda;J. M. Floryan
研究了受空间分布加热的通道内的流动。这种流动是有意义的，因为理论分析表明加热导致压力损失的减少。构造了一种特殊的装置，该装置提供了用于产生具有所需强度的良好控制的空间周期性加热以及精确控制具有小雷诺数的流动中的流速的手段。该设备与空气一起工作，并提供对流动内部的光学访问。将有关理论推广到处理实验中测得的温度场。实验在雷诺数Re<20$和单一Rayleigh数下进行，峰-峰温差和通道半高Ra_{p}=3500$。流动可视化和粒子图像测速仪测量表明，形成的二维稳定辊的大小是由$Re$，与最大的辊观察到的最小的$Re$和辊的大小逐渐减少，因为$Re$增加，直到他们完全消除在最大的$Re$在实验中使用。理论和实验测定的复杂流场之间的一个很好的协议被发现。壁面剪应力提取的速度测量符合他们的理论对应在预期的精度。实验速度场与理论速度场的一致性以及它们与相应压力场的唯一关系间接验证了加热诱导压力梯度降低效应。
Flows in channels exposed to spatially distributed heating were investigated. Such flows are of interest as theoretical analyses suggest that heating leads to the reduction of pressure losses. A special apparatus providing the means for the creation of well-controlled spatially periodic heating with the desired intensity as well as precise control of the flow rate in flows with small Reynolds numbers was constructed. The apparatus works with air and provides optical access to the flow interior. The relevant theory has been generalized to handle the temperature fields measured in the experiments. The experiments were carried out for Reynolds numbers $Re<20$ and at a single Rayleigh number based on the peak-to-peak temperature difference and channel half-height of $Ra_{p}=3500$ . Flow visualization and particle image velocimetry measurements demonstrated the formation of two-dimensional steady rolls whose size was dictated by $Re$ , with the largest rolls observed for the smallest $Re$ and the roll size being gradually reduced as $Re$ increased until their complete elimination at the largest $Re$ used in the experiment. An excellent agreement between the theoretically and experimentally determined complex flow fields was found. Wall shear stresses extracted from the velocity measurements agree with their theoretical counterparts within the expected accuracy. The agreement between the experimental and theoretical velocity fields and their unique relation with the corresponding pressure fields indirectly verify the heating-induced pressure-gradient-reducing effect.