Spunbond-nanolif-spunbond (SNS) teknolojisi ile nitelikli hava filtresi üreten bir sistemin çekici ünitesinin tasarımı ve geliştirilmesi

Nanofibers are effective materials, which have frequently been investigated to produce high quality air filters. As an environmental approach, our aim is to achieve nanofibers by melting. In spun-bond systems extruder, spin-pump, nozzle package and attenuator are used. Molten polymer which flows from extruder is made steady by spin-pump. Regular melt passes through nozzle holes and forms fibers under high pressure. The fibers pulled from nozzle are shrunk to micron size by an attenuator; after solidification, they are collected on a conveyor. In this research, different designs of attenuator systems have been studied; also CFD analysis have been done on these different designs. Afterwards, one of these designs tested and finally some optimizations have been done to reduce pressure drop and increase air velocity. As a nanofiber production method, electrospinning has intensively been investigated recently. However, lots of solvent are used in traditional electrospinning method which reduces production rate. Moreover, this method increases production costs. Therefore, melting system was invented as a basic method for SNS nanofiber layer fabrics production. In this system, extruder, nozzle package and high-voltage power supply are essential devices. Mixture or molten polymer is put in a funner which has one or more holes. In this process polymer granules are fed by funner which are melted and moved on by extruder. After extruder, granules are driven to a nozzle which has numerous holes and are converted to fibers. Coat- Hanger die has been designed and selected to be used in this research. Its primitive representation has been designed by an analytical method. After nozzle, molten polymer is solidified by cold air. In attenuation region fibers are attenuated by high speed air. Depending on the polymer characteristics and production rate, air velocity reaches 1000 to 8000 m/min. For instance, polypropylene (PP) usually needs a 2000 m/min velocity where this amount is about 4000 m/min for polyamide (PA). Through cooling and protracting process, parameters such as humidity and temperature should be controlled. Fibers diameter and its homogeneity are two main factors which determine performance of produced filter. In order to achieve this goal polymer pressure in the nozzle and also air pressure distribution at jet section must be uniform. By inspecting so many different references and patents, a primitive design for attenuator has been developed. The design had to be done at a state which guaranties high velocity with lowest vibration. Vibration is an important factor in attenuator design; it results in agglomerated nanofibers and subsequently non-uniformity. A primitive design of attenuator has been created and some analysys have been done to probe velocity and pressure drop in it. Selected design has been drawn and meshed in ANSYS-ICEM CFD. The mesh method which has been used in this process is a very accurate one which uses blocks instead of automatic meshing. Selected design has been manufactured and a fan with 0.07 bar output pressure has been purchased in the sake of experiments. Manufactured attenuator has been mounted on the fan and jet velocity tests have been done on it. There was a very close overlapping between experimental and simulation results where max deviation is 8%. Therefore, some optimizations could be done based on simulation results. However, sometimes there would be needs for higher velocities which would requests fans with higher output pressure and subsequently higher powers. In this situation, demanded fan will be very large and expensive. Moreover, less pressure drop will guarantee less vibration. So it is needed to obtain higher velocities with lower pressure drop by doing some optimizations on attenuator interior design which affects pressure drop significantly. Therefore, some researches has been done on this matter and a new interior design has been developed. This process should be done on a layout which guarantees smooth narrowing throughout air path; so the least possible amount of pressure drop will be obtained. In this process, to reduce pressure drop, a larger input has been selected which is as large as fan output. As mentioned before, there was a large amount of pressure drop at the wall next to inlet pipe; this pressure drop was the product of high velocity in the pipe which was a result of small diameter; this problem was conquered by enlarging inlet gap. Moreover, there was a significant pressure drop at the pipe itself which was very long; to eliminate this, the pipe removed from representation. Also interior design has been made in a case which has a smooth narrowing layout. At first, some air channels with a slight angle have represented; these angles would provide a perfect narrowing at channels; but as a matter of fact, it was very difficult to manufacture such channels; so the angles have been eliminated and some other methods employed to compensate the lack of inclined designed. Air partitions have been made vertical and by using longer partitions in every path, smooth narrowing made possible. There was a significant pressure drop because of sharp exit on jet; severe colliding of air to the plate next to jet had caused in mentioned pressure drop; so it has been changed to a 45 degrees exit on bottom edge of jet gap. In order of comparisons, a simulation with the same properties of former one has been done on this layout. This will guarantee an accurate comparison between two designs, which will lead to a realistic conclusion. By using same inlet properties, there was a 60 m/s growth in jet velocity which is about 90 m/s. In addition, pressure drop at the wall next to inlet and jet have been eliminated. There was a large amount of pressure drop at interior part of attenuator unit which have been reduced significantly by changing some design parameters. Also by using the same properties of inlet a three times larger amount of velocity has been obtained at jet section which will help to protract nanofibers more than before. Also by using smooth narrowing method at interior part there will be less vibration which will help to obtain more uniform spun-bonds. Finally, in order to find out the effect of fibers on airflow, other CFD analysis have been done considering fibers at cross sections. There are 396 exit holes on manufactured die with a diameter of 0.35 mm which brought some hardships during meshing process. This geometry has been meshed using advanced method of structured mesh and analyzed in FLUENT. Results of these analysis shows a slight effect of fibers on airflow, which is not so great to consider in attenuator design. A UDF code has been developed during this project to consider fibers movements between two attenuator units; the method which is used in this analysis is deforming mesh which is brought in FLUENT. However, this analysis would need a computer with very high ram capacity and a great CPU; so because of lack of computational resources, it wasn't possible to do such an analysis. It is obvious that changing a design representation slightly could have a significant effect on pressure drop and production factors. In this way, the most important part in this project was drawer unit. Slight changes at interior or exterior parts of drawers would has a significant effect on pressure drop. It is necessary to consider the cost of production at first steps, which includes fan as an expensive component. Using analytical methods could help to prevent large amount of financial wastes, if it is done using a true and useful method.