The Analysis Of Heat Transfer Mechanisms On Transpiration In Plant Leaf And Boiling Flow In Micro/Nano Scale

In the millions of years, natural plants keep evolution and choice to the environment duringthe competition for survival. Their structure, functions and the adaptive strategy almost reachedthe best, which is incomparable and beyond any artificial design. During the transpiration, plantleaves have been in continuous generation of pressure to achieve the transfer of water and heatin the evaporation, performing the excellent characteristics of heat and mass transfer. The heattransfer in microchannel heat devices has similarities with the plant system. The research onheat transfer characteristics of surface morphology and different channels plant leaves will beable to provide new inspirations for the design of the higher heat dissipation structure.Based on the updated survey of current botany research, the self-adaptive thermal structureof plant leaves had been determined as: the cross-sectional shape of leaf, the mesophyll shape,the distribution and orientation of vascular bundles, classified respectively from large scale tosmall scale. The evoluting map has been analyzed.The experiments on morphology, moisture holding and optical microscopy of five kinds ofplant leaves have been carried out to determine the response of plant leaves on thermal envi-ronment. It was found that leaf sections varied from flat to the cylindrical, the morphology ofmesophyll varied from spongy to palisade, and the vascular evolved into a ring-shaped distri-bution. The moisture-holding data showed that there was no consistency of moisture capacityin plant leaves among those who grow in different environment, which reflects the moisture-holding ability is closely related to the structure that adapted to the environment. The leaf char-acteristics in stronger moisture-holding ability is cylindrical shape, circular distribution of vas-cular, spongy mesophyll.The scanning electron microscopy experiment has been done, which is used to get the sur-face morphology and microchannel of vascular in plant leaves. The heat transfer of microchan-nel in vacular can be equivalented to the heat transfer in poros structure of microchannelthrough structural analysis. The heat transfer process under transpiration had been analyzed.Based on the numerical simulation, the heat transfer characteristics of different morphology ofmicrochannel in leaf vein have been studied. It was found through comparasion that when the convexity gap increased, the pressure drop increased first, then down, the temperature first de-creased then increased, the reflux decresed first then increased. When the ratio of gap to diam-eter of micro-cylinder is closed to1, the temperature and flow achieved the best. The study ofheat transfer characteristic of different morphologies has shown that the microchannle withpuddles (annular) shape and streaks, the pressure drop is less volatile and the temperature ismore uniformal. Puddles morphology can reduce the instabilities of flow which is claused bypressure fluctuations. The roughness has an effect on the thickness of liquid film, which is alsoaffected by its position. But the flow has a stable liquid film, which is1/3of the maximuminstable liquid film thickness.The result and mechanism of leaf morphology on the heat transfer characteristic of micro-channel was utilized to interpret the heat transfer of boiling flow in microchannel. Accordingto the experimental data and empirical formulars, the five regional heat transfer model is estab-lished. Though comparasion with experimental data and other heat transfer model, it is shownthat the five regional heat transfer model is more close to the experimental data.