Understanding the coupling between the moisture loss and surface temperature in an evaporating leaf-type surface

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.

Keywords:

• Leaf
• stomata
• moisture loss
• infrared heating
• evaporation ratio

Acknowledgments

We thank CeNSE (IISc) for fabricating the desired punched plates. Thanks are due for Mr Soumya Bandyopadhyay and Mr Subin Thomas who performed preliminary experiments. Data necessary to reproduce this research can be obtained here: https://figshare.com/s/980fe0291209f87ed7d1.

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Additional information

Funding

We appreciate the funding provided by Robert Bosch Centre for Cyber Physical Systems, Indian Institute of Science under the grant number RBCCPS/ME/JHA/PC0013. We also thank financial assistance from Indian Space Research Organisation (ISRO) under the grant ISTC/MME/JHA/0374. Financial help from Ministry of Earth Sciences (Government of India) under the grant MESO/0034 is also appreciated.