Abstract

We experimentally report evaporation characteristics from leaf-like surfaces having low open (exposed) area ratio. Even at much lower (1–10%) exposed areas, higher transpiration rates (60–70% compared to a bare water source) are sustained by a leaf. We mimic stomata, tiny openings present on the leaves using holes punched on silicon wafers (SW). The leaf-mimics have different opening diameters, ranging from$50\mathrm{\mu }\mathrm{m}$ to$400\mathrm{\mu }\mathrm{m},$ but nearly the same open area of$\sim 25\mathrm{m}{\mathrm{m}}^2.$ The leaf-mimic with the smallest opening size was found to evaporate the most, while for the larger opening sizes it seems to decrease. In all the cases, evaporation ratio (ratio of the evaporation rate from the leaf-mimic to that of from a bare water surface at the same net incident radiation) increased with decreasing pore sizes; we compute this ratio based on three different definitions including one for the isothermal cases. In non-isothermal cases, we recognized that the variation in surface temperature led to nonlinear variation in the surface water vapor concentration. The effect of increased surface temperature, compared to a bare water surface in similar conditions, is missing in defining the evaporation ratios in previous approaches and thus we include it.

摘要

我们通过实验报告了具有低开放（暴露）面积比的叶状表面的蒸发特征。即使在低得多（1-10%）的暴露区域，叶子也能维持较高的蒸腾速率（与裸水源相比为 60-70%）。我们使用在硅片 (SW) 上打孔来模拟气孔，即叶子上存在的微小开口。叶模拟物具有不同的开口直径，范围从$50\mathrm{\mu }\mathrm{米}$到$400\mathrm{\mu }\mathrm{米},$但几乎相同的开放区域$～25\mathrm{米}{\mathrm{米}}^2.$发现具有最小开口尺寸的叶子模拟物蒸发最多，而对于较大开口尺寸，它似乎减少了。在所有情况下，蒸发率（在相同净入射辐射下，模拟叶片的蒸发率与裸露水面的蒸发率之比）随着孔径的减小而增加；我们根据三种不同的定义来计算这个比率，包括一个用于等温情况的定义。在非等温情况下，我们认识到地表温度的变化导致地表水蒸气浓度的非线性变化。与类似条件下的裸水表面相比，增加的表面温度的影响在定义先前方法中的蒸发率时缺失，因此我们将其包括在内。