Studies on the Effect of Wind Speed on Photosynthesis

Abstract

Using a water channel and the flow visualization technique (hydrogen-bubble visual observation method), we investigated the structure and flow patterns of the boundary layer near leaves. We discussed the mass transfer through the boundary layer, which plays an important role on photosynthesis, by use of the experimental results.The shape of the boundary layer of a leaf was not flat film, but that was of the three dimensional shape which enveloped a leaf. Increasing the velocity and/or the incidence of flow on leaf, the boundary layer became turbulent, and the sectional form of that became convex on account of the edge effect at the side tip.It was observed that under fluttering condition, the transition from laminar to turbulent flow was not promoted by fluttering of leaf alone and that the structure of the boundary layer was found to be turbulent or laminar according to the conditions of flow and flutter.Generally, mass and heat transfer through the boundary layer is analyzed by using a laminar boundary layer theory, but the mass transfer estimated by our experimental results differs in following respects from that by the boundary layer theory.1. Under the flow condition parallel to the leaf, the boundary layer at the side tip becomes thin, and the estimated amount of mass transfer seems to be slightly more than that of the calculated value by the theory.2. When the incidence is 7-14°, the boundary layer on the lower surface becomes thin, and the boundary layer on the upper surface is converted into turbulent structure. The estimated amount of mass transfer becomes more than the above case 1.3. In the case of larger incidence, the resistance to diffusion at the upper surface increases as the dead water region expands. The estimated value of mass transfer is nearly equal to case 1. The feature of the boundary layer on the lower surface is the same as case 2.4. In the case that the leaf flutters, the resistance decreases when the boundary layer is turbulent. The estimated value of mass transfer is by about 60% larger than the theoretical value, but it is by only 10% larger than the theoretical value when the boundary layer is laminar.It is found that the mass and heat transfer through the boundary layer can not be dealt with without the understanding of the features of boundary layers.