A novel thin film organic bionic leaf was prepared by a solution-casting method to simulate the thermal effect of transpi- ration and solar spectrum reflection characteristics of plant leaves. The main components of the bionic leaf are polyvinyl alcohol （PVA）, lithium chloride （LiCl） and chromium sesquioxide （Cr2O3）. The thin film was modified by chemical cross-linking, and its surface was modified by alkylsilane to prevent excessive swelling. The thin film can simulate the thermal effect of natural leaf transpiration because that the hygroscopic PVA and LiCI can absorb and desorb water due to the high and low humidity of the ambient air at night and day, respectively. The thin film has the similar solar spectrum reflection characteristics to those of plant leaves due to the Cr2O3 and the water content of the hygroscopic materials. The measured diurnal maximum radiation temperature difference between the organic bionic leaf and the Osmanthus fragrans leaf was only 0.55 ℃. In addition, the solar spectrum reflection measurements revealed that the organic bionic leaf could precisely simulate the key solar spectrum reflec- tion characteristics of plant leaves.
A one-dimensional thermophysical model is used to investigate the simulation of the infrared thermal signature of mental plate with phase change material(PCM)plate theoretically.The optimized parameters are obtained by the theoretical calculations.Based on the calculation results,a kind of organic PCM is selected to experimentally verify the model,and the good match between the theoretical and experimental results is achieved.The results of this investigation provide the design rules and key materials for the application of PCMs in false target.
Understanding the heat and mass transfer processes of plant leaves is essential for plant bionic engineering. A general thermophysical model was established for a plant leaf with particular emphasis on the transpiration process. The model was verified by the field measured stomatal resistance and temperature of a camphor leaf. A dynamical simulation revealed that diurnal transpiration water consumption is dominated by the solar irradiance and the day-average temperature of the leaf is dominated by the ambient air temperature; transpiration plays an important role in the cooling of the leaf, in average it could dissipate around 32.9% of the total solar energy absorbed by the leaf in summer. To imitate the thermal infared characteristic of the real leaf, the up surface of the bionic leaf must have emissivity and solar absorptivity close to those of a real leaf and its shape and surface roughness must be similar to those of the real leaf. The key point is that the bionic leaf must be able to evaporate water to simulate the transpiration of a plant leaf, appropriate adsorbent can be used to realize this function.
