Water Transport Characteristics Of Plant Xylem Structure And Design Of Bionic Emitter

In the soil-plant-atmosphere continuum(SPAC)system,the water transmission mechanism in plants has always been regarded as the core element of the system water cycle and has received widely attention.The internal structure of xylem determines the water transport capacity of plants.The vessels,tracheids,perforation plates,pits and other structures in xylem constitute an interlaced pipe system.It is difficult to calculate the water transport characteristics of the xylem structure because of its small structure size.At present,computational fluid dynamics methods were used to explore the internal flow characteristics of the xylem.There were three problems in the application: 1.There were few studies on the structure of xylem(reticulated thickening,pitted thickening),and the water transport characteristics of the combination of multiple tissue structures were ignored.2.Different tissue structural parameters of plant xylem were not obtained by experiments,which led to the inaccuracy of the model construction.3.The flow resistance characteristics of various tissue structures in plant xylem were not considered in engineering application.In order to solve the above problems,the mechanism of water transport in plants was studied more deeply,and its tissue structure was applied on engineering through bionic design,this article mainly focused on the following aspects:(1)A model of the reticulated spirals number distribution was proposed to analyze the flow resistance characteristics of reticulated thickening vessel,the variation in the reticulated structural parameters(number of spirals,spiral spacing,reticulated height,reticulated width,vessel inner diameter)on the internal flow of the vessel was analyzed.It is concluded that the interaction between the reticulated structure and the recirculation region,especially the recirculation region,was mainly responsible for the effects of the secondary wall thickening on the water transport.At the same time,the structural flow resistance of reticular thickening vessel was the largest,followed by annual thickening vessel,and helical thickening vessel was the least.(2)Based on the experimental data and analysis of water transport characteristics of multi tissue structure vessel,taking angiosperm Jatropha curcas L tree as the research object,the structural parameters of Jatropha curcas L with perforation plate and pitted thickening were obtained by botanical slices.The 3Dmodel analysis showed that the xylem vessel flow resistance was composed of three elements: smooth vessel,pitted thickening and perforation plate,and the flow resistance of smooth vessel was the largest,followed by the pitted thickening,and perforated plate was the least.The flow resistance of the vessel model was positively correlated with the pit depth,perforation plate height and perforation plate width and negatively correlated with the vessel inner diameter and pit membrane permeability.The vessel inner diameter and the pit depth had a great influence on the flow resistance.The pit structure in pitted thickening caused the vessel to be transported radially,the pit membrane permeability had the greatest influence on the radial transmission efficiency,which was 0%-5.09%.(3)Based on the experimental data,taking the gymnospermous Sabina Chinensis tree as the research object,the structural parameters of the torus-margo bordered pit structure(TPS)in root and stem tracheid were obtained from the botanical section.The 3D model analysis showed that the size of the TPS in the root and stem was different,but the proportion of TPS flow resistance components was similar.The margo contributed a relatively large fraction of flow resistance,then the torus and the border,and the secondary cell wall formed a small fraction.The size and position of the pores in the margo had a significant effect on the fluid velocity.The flow resistance of the TPS was positively correlated with the torus diameter,the middle width and the upper width of the torus,while the flow resistance of the TPS was negatively correlated with the margo permeability.The change of its structural parameters had a greater impact on the smaller TPS(stem).(4)The single tracheid flow resistance calculation model was established by experiments.The single tracheid structural parameters(tracheid width,tracheid length,number of pits)were obtained by isolation.The model analysis showed the tracheid lumen resistance was determined by the tracheid width and tracheid length.The total pit flow resistance was determined by the number of pits and single pit structure flow resistance.The power curve,S-curve and inverse curve fitted the scatter plot of total pit flow resistance,total flow resistance and total resistance rate of single tracheid and tracheid length at the same time.It was found that there was a negative correlation between them.The three kinds of flow resistance values were larger in the stem than in the root,indicating that the single tracheid structure in the root was more conducive to water transport than the stem.The ratio of tracheid lumen resistance to total pit flow resistance mainly was less than 0.6 in the stem and less than 1 in the root,indicating that the pit resistance was dominant in the total flow resistance of the stem and root.(5)A new pit drip irrigation emitter was constructed by means of the pit structure in the water transport tracheids of bionic plants,and four structural optimization models were designed.Experiments and simulations were carried out on the flow index,energy dissipation coefficient and anti-clogging ability.The results showed that the optimized design models 3 and 4 had better performance by reducing the flow area at the upper and lower ends of the pit drip irrigation emitter model and increasing the resistance on both sides of the torus edge.The flow index was between0.4817 to 0.4862(Experiment value),and the energy dissipation coefficient was 843 to 912(Experiment value).The optimizations improved the anti-clogging ability by increasing the structure resistance and reducing the low velocity vortex zone.The experimental error compared with the numerical simulation for the flow index and the energy dissipation coefficient were less than 3%.It indicated that the analysis method of numerical simulation combined with experimental verification was reliable.