Geometrical and material properties of plant leaves are known to influence heat/moisture dissipation. In many species, exposed “sun” leaves are typically more dissected and possibly better convective heat dissipaters than entire shade leaves. By affecting the overall leaf boundary layer, lower-scale morphology patterns such as toothed edges can also have an important role in heat/moisture dissipation, as pointed by experiments with wetted paper models where outward teeth increased evaporative dissipation rates. Additional leaf morphological traits potentially influencing dissipation are surface corrugations, textures, trichomes and sunken stomata. Such structures can work as “dissipative” or “retaining” geometries depending on how they couple with environmental conditions and modulate leaf boundary layer. The oneweek intensive Kosmos interdisciplinary workshop at the cluster Image Knowledge Gestaltung (Berlin) was an opportunity to explore leaf design and achieve microclimate control for potential applications in technology, specifically building façades. The "Breathing skins” concept was to apply shape-related leaf dissipation strategies into folding structures that can be produced in a typical “maker-lab” setting. After a thematic introduction, participants were asked to target evapotranspiration behavior and shape-change characteristics derived from leaves, and to deliver prototypical designs using a set of prepared materials. Workshop results show the transfer of new findings in research on evapotranspiration of biological plant leaves into 3D structures for technical application. The biomimetic approach taken delivered a first translation of design abstracted from leaves into the realm of foldable geometry, for future development and technological transfer to useable products in architecture, building and fluid-assisted heat transfer systems in general.
In previous projects theromodynamics of plants was identified as an interesting field delivering concept generators for technical, especially architectural application. So leaf morphology is determined by a variety of factors, and also significant for plant water and energy balance. However, how leaf design affects evapotranspiration and, consequently, leaf thermal performance and energy budget, has not been investigated in detail. Many leaf-inspired models in the literature overlook leaf hydraulics, capillarity, wetting phenomena in porous materials and the thermal properties of cellulose. To further the knowledge in this field, we have started to research on the relation between wetting, thermal dynamics and shape. We recorded with a thermal camera free convection of wetted models made of laser-cut paper tissue, soaked in water and drying naturally. Families of shapes were abstracted from leaves of deciduous trees: white oak, for their crenations and lobes; maple, for their relatively large teeth; elm, for their smaller hierarchically-ordered serrations. In this abstracted experimental setup, we observed distinct evaporation rates for models with normalized surface area but different boundary perimeters. Outward teeth prompt dewetting nucleation in shapes only differing geometrically, shedding some light on surface designs for heat dissipation versus designs for moist microclimate retention. The biomimetic approach taken will deliver a better understanding of the biological role of leaf structure and support the enhancement of fluid-assisted heat transfer systems, for which further three-dimensional exploration and scale studies are conceptualized.