Study On Water Evaporation And Transport Mechanism Of Reed Porous Materials

Reed is a kind of plant that grows in the swamps and lakes,it can continuously transport water to leaves through evaporation,showing significant anti-gravity water transport capacity.Efficient water transport of reed is not only related to the fluid characteristics and negative pressure generated by transpiration,but also to the xylem microchannel structure and the wettability of xylem conduit.Studying its structural characteristics and the influence of the wettability of xylem vessel on the water transport and evaporation efficiency,which has a guiding significance to design a high-performance evaporator based on water evaporation of the reeds.Therefore,reed was selected with different structures as the experimental research object,and the structural characteristics,water transport capacity and water evaporation performance of reed was studied in this thesis,and the main contents include:（1）This paper introduced the concept of surface tension,contact Angle,expounded the capillary flow phenomenon and mechanism of the porous materials,analyzed the contribution of four different forces which make up capillary forces at the flow process,divided each flow stage and the flow time of each stage was determined.The theoretical model of capillary flow revealed the factors affecting the water transport capacity,and the water transport capacity can be improved by changing related parameters.（2）The factors affecting water evaporation of reed were explored through experiments.The morphology and wettability of the samples after delignification of different reeds were characterized by environmental scanning electron microscopy（SEM）and contact angle measuring instrument.Studied the evaporation performance of natural reed and delignified reed,solid reed and hollow reed which from different regions,based on the above experiments,studied the effect of length changes on the evaporation performance of natural reed and delignified reed.The experimental results showed that delignification can could improve the water transport capacity of reed,increased the micropore size of reed and effectively improved the evaporation performance.In terms of reed structure,hollow structure is more conducive to transporting and evaporating water than solid structure.Reed stem length has an impact on evaporation performance,with the increase of length,the evaporation performance of reed increased continuously.When the length increased to 23 cm,the evaporation rate reached the maximum value of 0.15 kg·m^-2·h^-1,which was 11.5 times that of natural reed with the same length.（3）The heat and humidity transfer process in reed porous media with hollow structure were studied by using finite element simulation analysis,the effects of single factor changes such as porosity,wall thickness,temperature and humidity and multiple factor changes in temperature and humidity on the heat and water transfer of reed evaporation were analyzed respectively.The simulation results showed that the water evaporation of the hollow reed began from the front and back ends locally,there are water concentration differences between the front end and the back end,the upper surface and the lower surface of the reed.The evaporation of water in reed porous media increases with the increase of porosity,and increases with the decrease of wall thickness.When the wall thickness（i.e.,the ratio of inner and outer pores）was 0.9,the evaporation reached the highest.Through the orthogonal simulation experiment,it was concluded that when the ambient temperature is 60℃and the relative humidity is 20%,the internal water distribution of reed porous material is relatively uniform,and the internal water can be completely evaporated after 11 hours of evaporation.