Ries Florian, Li Yongxiang, Nishad Kaushal, Janicka Johannes, Sadiki Amsini
Institute of Energy and Power Plant Technology, Technische Universität Darmstadt, 64287 Darmstadt, Germany.
Laboratoire de Modelisation Mecanique, Energetique et Materiaux, Institut Superieur des Techniques Appliquees, B.P. 6534 Kinshasa 31 NDOLO, D.R. Congo.
Entropy (Basel). 2019 Jan 30;21(2):129. doi: 10.3390/e21020129.
In this work, entropy generation analysis is applied to characterize and optimize a turbulent impinging jet on a heated solid surface. In particular, the influence of plate inclinations and Reynolds numbers on the turbulent heat and fluid flow properties and its impact on the thermodynamic performance of such flow arrangements are numerically investigated. For this purpose, novel model equations are derived in the frame of Large Eddy Simulation (LES) that allows calculation of local entropy generation rates in a post-processing phase including the effect of unresolved subgrid-scale irreversibilities. From this LES-based study, distinctive features of heat and flow dynamics of the impinging fluid are detected and optimal operating designs for jet impingement cooling are identified. It turned out that (1) the location of the stagnation point and that of the maximal Nusselt number differ in the case of plate inclination; (2) predominantly the impinged wall acts as a strong source of irreversibility; and (3) a flow arrangement with a jet impinging normally on the heated surface allows the most efficient use of energy which is associated with lowest exergy lost. Furthermore, it is found that increasing the Reynolds number intensifies the heat transfer and upgrades the second law efficiency of such thermal systems. Thereby, the thermal efficiency enhancement can overwhelm the frictional exergy loss.
在这项工作中，应用熵产生分析来表征和优化加热固体表面上的湍流冲击射流。具体而言，数值研究了平板倾斜度和雷诺数对湍流热和流体流动特性的影响及其对此类流动布置热力性能的影响。为此，在大涡模拟（LES）框架下推导了新的模型方程，该方程允许在包括未解析亚网格尺度不可逆性影响的后处理阶段计算局部熵产生率。基于此LES研究，检测到冲击流体热和流动动力学的显著特征，并确定了射流冲击冷却的最佳运行设计。结果表明：（1）在平板倾斜的情况下，驻点位置和最大努塞尔数位置不同；（2）主要是被冲击壁是不可逆性的强源；（3）射流垂直冲击加热表面的流动布置能最有效地利用能量，且损失的可用能最低。此外，发现增加雷诺数会强化传热并提高此类热系统的第二定律效率。因此，热效率的提高可以超过摩擦可用能损失。
