| Industrial textiles have become the most promising and strategic branch of the textile industry and hydro entanglement is considered to be the fastest growing non-woven technology. In the past decade, the average annual growth rate of hydroentangled nonwoven manufacturing capacity in China reached more than30%. Hydroentangling process provides nonwoven excellent strength, hand-feeling, air permeability and free of chemical binders by exploring the impact force of the high-energy water jets. Therefore, hydroentangled nonwovens are widely used in medical, health, personal care, apparel, household and other areas because of their unique performance.However, the high energy consumption of generating high-energy water jets and recycled water purifiction is one of the key factors for the high cost of hydroentangled nonwovens, which it constrains remains further development of hydroentanglement technique. For example, a spunlace line with a production capacity of10～15t per day has a water150-250t per hour. Therefore, the study on effective utilization of high-pressure water becomes important for water and energy savings.High-pressure manifold is the key equipment for distributing and utilizing the energy of high-pressure water in hydroentangling process, it is reported the distribution and utilization have an important effect on the hydroentangled nonwoven properties and energy consumption. However, as a closed high-pressure flow field inside the manifold during the production, experimental observation and measurement of the flow distribution inside the manifold is impossible. In this study, Computational fluid dynamics (CFD) simulation is employed to investigate the flow distribution inside the drilled type and slot type manifolds, and then its impacts on the hydroentangling nonwovens properties and engineering energy consumption were analyzed to verify the credibility of the CFD simulation results, which provided the theoretical basis for optimizing of the manifold structure.This study mainly covers three parts:First, theoretical analysis and numerical simulation of fluid dynamics. CFD simulation is employed to analyze and characterize the three dimensional flow fields inside drilled type and slot type manifolds, and then the effects of the main geometry parameters of the manifolds on the flow distribution were studied. The evolutionary strategy is used to optimize the design of manifolds as well. Second, the impacts of manifold geometry on hydroentangling nonwovens properties were analyzed to verify the credibility of the CFD simulation results. Third, the impacts of manifold geometry on the engineering energy consumption of the hydroentangling system were investigated to further verify the credibility of the CFD simulation results and provide theoretical basis for energy saving of the hydroentangling system.The main content and conclusions of each part are as follows:(1) CFD models of the high-pressure flow field inside drilled type and slot type manifolds were established; the control equations of the models were dispersed by finite volume method; the steady state, implicit solver, k-ε Realizable model, and the SIMPLE algorithm based on staggered grids were employed to simulate the flow distribution inside the two types manifolds with water pressure of8.0to12.0MPa by FLUENT software; the flow field distribution inside the two types manifolds were analyzed and the coefficient values (CVs) of the velocity and pressure along the central line of the outflow surfaces were evaluated; furthermore, the direction the various structural parameters need to be optimized were analyzed by single factor analysis method. The results show that the velocity CVs along the outflow surface of slot type manifold is almost twice of drilled type manifold, and the difference becomes bigger with the process pressure increasing, while, the CVs of the drilled type manifold is almost constant with the process pressure increasing; both the pressure CVs are almost equal when the process pressure is8.0MPa. However, with the increase of the process pressure, the pressure CVs along the outflow surface of the slot type manifold show gradually increasing also; while that of the drilled type manifold is almost constant. It is worth noting that all of the CVs are very small, order of the magnitude is10-3. On the basis of the single factor analysis, evolutionary strategy was used to optimize drilled and slot type manifolds combined with three-dimensional numerical simulation. The velocity CV along with the centerline of the outflow surface was taken as objective function, the central distance of the adjacent vertical cylindrical holes D2and the ratio of the radius of the rod and the lower chamber R3/R2were taken as objective variables of drilled type manifold, the internal radius of the cartridge R3’and the width of the outlet D’ were taken as objective variables of slot type manifold.(3,12)-ES evolutionary strategy was employed to search the optimum objective variables; for each pair of variables, the corresponding objective functions would be obtained by establish and simulate new manifold models, and the searching and numerical simulation operation would be continued until meets the prescribed terminal condition. Finally, the optimum variables (D2=18.4227mm, R3=9.9830mm) of drilled type manifold were found after evolved14generations, and the optimum variables (R3’=25.5444, D’=2.3759) of slot type manifold were found after evolved17generations. The optimized velocity CVs are0.9681%and1.7033%for drilled type and slot type manifold, respectively.(2) Fifteen group hydroentangled materials with different basis weight and fabric structure were made by drilled type and slot type manifolds, respectively, under different process pressure to investigate the impacts of the manifold geometry on the properties of the hydroentangled materials. Tensile strength, bonding strength index, permeability and pore size distribution of the materials were tested. Experimental results indicate that, with the same inlet pressure for manifolds, the hydroentangling nonwovens made from the drilled type manifold have higher strength in cross direction (CD) and bonding strength index than that from the slot type manifold. The results also show that the hydroentangling nonwovens made from the drilled type manifold exhibit more uniform air permeability in CD and its pore sizes are smaller. Correspondingly, the numerical simulation results showed that the fluid flow distribution inside the drilled type manifold is more uniform than slot type manifold, and the velocity and pressure CVs at the drilled type manifold outlet are smaller.(3) The impacts of the manifold geometry on the energy consumption during practical hydroentanlging project were studied. The production volume, water and power consumption of six production lines (including3lines equipped with drilled type manifolds and3with sot type manifolds) among18moths were tracked. It is found that the water and power consumption, as well as comprehensive energy consumption per standard unit production of the lines with drilled type manifolds is smaller than that with slot type manifolds. The reasons can be summarized as follows:firstly, the production lines equipped with slot type manifold need more high-pressure water for bonding the same specification webs than the lines with drilled type manifold because of the non-uniform distribution and more pressure loss inside the slot type manifolds; secondly, more water consumption and circulation require more frequency cleaning of the filtration system, so as to consume more water. Thirdly, more water remains in the bonded material from the lines with slot type manifold when it left the hydroentangling area than that with drilled type manifolds. The results show that the engineering energy consumption of the hydroentanlging project is related to the manifold geometry. |
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