Bullee Pim A, Weichert Stefan, Nore Astri, Li Leon, Ellingsen Simen Å, Hearst R Jason
Department of Energy and Process Engineering, Norwegian University of Science and Technology, Kolbjørn Hejes vei 2, 7034 Trondheim, Norway.
Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland.
Exp Fluids. 2024;65(9):132. doi: 10.1007/s00348-024-03864-3. Epub 2024 Aug 28.
We present experimental results of a study on oxygen transfer rates in a water channel facility with varying turbulence inflow conditions set by an active grid. We compare the change in gas transfer rate with different turbulence characteristics of the flow set by four different water channel and grid configurations. It was found that the change in gas transfer rate correlates best with the turbulence intensity in the vertical direction. The most turbulent cases increased the gas transfer rate by 30% compared to the low turbulence reference case. Between the two most turbulent cases studied here, the streamwise turbulence and largest length scales in the flow change, while the gas transfer rate is relatively unchanged. In contrast, for the two less turbulent cases where the magnitude of the fluctuations normal to the free surface are also smaller, the gas transfer rate is significantly reduced. Since the air-water interface plays an important role in the gas transfer process, special attention is given to the free-surface deformations. Despite taking measures to minimise it, the active grid also leaves a direct imprint on the free surface, and the majority of the waves on the surface originate from the grid itself. Surface deformations were, however, ruled out as a main driver for the increase in gas transfer because the increase in surface area is < 0.25%, which is two orders of magnitude smaller than the measured change in the gas transfer rate.
我们展示了一项关于在水通道设施中，由活动格栅设定不同湍流流入条件下的氧气传输速率的研究的实验结果。我们比较了由四种不同的水通道和格栅配置所设定的具有不同湍流特性的水流中气体传输速率的变化。结果发现，气体传输速率的变化与垂直方向上的湍流强度相关性最佳。与低湍流参考情况相比，湍流最强的情况使气体传输速率提高了30%。在这里研究的两个湍流最强的情况之间，水流中的流向湍流和最大长度尺度发生了变化，而气体传输速率相对不变。相比之下，对于另外两个湍流较弱的情况，其垂直于自由表面的波动幅度也较小，气体传输速率显著降低。由于气 - 水界面在气体传输过程中起着重要作用，因此特别关注自由表面变形。尽管采取了措施将其最小化，但活动格栅仍在自由表面留下了直接印记，并且表面上的大多数波浪都源自格栅本身。然而，表面变形被排除为气体传输增加的主要驱动因素，因为表面积的增加 < 0.25%，这比测量到的气体传输速率变化小两个数量级。
