An experimental investigation on comparison of synthetic and continuous jets impingement heat transfer
An experimental investigation on comparison of synthetic and continuous jets impingement heat transfer
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DOI：
10.1016/j.ijheatmasstransfer.2015.06.065
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发表时间：
2015-11
影响因子：
5.2
通讯作者：
Xiao-ming Tan;Jing-zhou Zhang;Shan Yong;G. Xie
中科院分区：
文献类型：
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作者：
Xiao-ming Tan;Jing-zhou Zhang;Shan Yong;G. Xie
本研究通过实验研究了由活塞致动器驱动的正常合成射流冲击下的对流换热特性。特别关注合成射流和连续射流之间详细的局部和横向平均传热比较，以及孔口形状对合成射流冲击的影响。单圆形、单方形和单矩形三种喷射孔被设计成具有大致相同的出口面积。此外，进一步确定了在大冲程长度到射流到表面间距的情况下合成射流冲击的传热方式。目前，等效对流传热系数是根据目标温度与环境温度之间的差值来定义的。结果表明，在驻点附近，连续射流比合成射流表现出更强的局部传热。然而，合成射流在表面上产生更平坦和更均匀的局部传热系数分布，这表明其在较大射流与表面间距下横向平均对流换热增强方面优于连续射流。对于具有低激励频率和大冲程长度的活塞驱动合成射流，有证据表明停滞努塞尔数和射流雷诺数之间存在幂律关系，指数约为0.32。观察到两种传热方式，并且无论孔口形状如何，冲程长度与射流到表面间距的临界比率大约为 18。孔口形状对对流换热具有中等影响。单矩形合成射流产生比其他孔口稍好的驻点传热。源自圆孔孔口的合成射流似乎带来了良好的整体对流换热效果。对于方孔孔口，与相应的连续射流相比，合成射流冲击的优点相对减弱。
The convective heat transfer characteristics under a normally synthetic jet impingement driven by a piston actuator are investigated experimentally in the present study. Particular attentions are paid to present the detailed local and laterally-averaged heat transfer comparison between synthetic jet and continuous jet, as well as the effect of orifice shape on the synthetic jet impingement. Three jet orifices including single-round, single-square, and single-rectangular are designed to have the approximately same exit area. In additional, heat transfer regimes for the synthetic jet impingement in the situation of large stroke length to jet-to-surface spacing are further identified. In the present, the equivalent convective heat transfer coefficient is defined in terms of the difference between target temperature and ambient temperature. The results show that continuous jet exhibits stronger local heat transfer than the synthetic jet in the vicinity of stagnation point. However, the synthetic jet produces much flatter and more uniform local heat transfer coefficient distributions over the surface, showing its advantage over the continuous jet on laterally-averaged convective heat transfer enhancement at a larger jet-to-surface spacing. For the piston-driven synthetic jet featured by low excitation frequency and large stroke length, there is evidence for a power law relationship between stagnation Nusselt number and jet Reynolds number with an exponent of approximately 0.32. Two kinds of heat transfer regimes are observed and a critical ratio of stroke length to jet-to-surface spacing is identified as 18 approximately regardless of orifice shape. The orifice shape has a moderate effect on the convective heat transfer. The single-rectangular synthetic jet produces a slightly better stagnation point heat transfer than the other orifices. The synthetic jet originated from the round-hole orifice seems to introduce favorable overall convective heat transfer achievement. The advantage of synthetic jet impingement in comparison to the corresponding continuous jet is relatively degraded for the square-hole orifice.