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Structure optimization of separating nozzle for waste plastic recycling
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Procedia CIRP 00 (2018) 000–000
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Procedia CIRP 00 (2017) 000–000 Procedia CIRP 80 (2019) 572–577
26th CIRP Life Cycle Engineering (LCE) Conference
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26th CIRP Life Cycle Engineering (LCE) Conference
Structure optimization of separating nozzle for waste plastic recycling Structure optimization of separating for waste plastic recycling 28th CIRP Design Conference,nozzle May 2018, Nantes, France Fengfu Yin*, Lianlian Xue, Zhen Liu , Lin Li, Chuansheng Wang College of Electromechanical Engineering, Qingdao University and Technology, Qingdao 266061,China Fengfu Yin*, Xue, Liuof,Science Lin Li, Chuansheng Wang A new methodology toLianlian analyze theZhen functional and physical architecture of * Corresponding author. Tel.:1-358-322-9902; fax: +0-532-889-57388. E-mail address: [email protected] College of Electromechanical Qingdao University of Science and Technology, Qingdao 266061,China existing products for anEngineering, assembly oriented product family identification * Corresponding author. Tel.:1-358-322-9902; fax: +0-532-889-57388. E-mail address: [email protected]
Paul Stief *, Jean-Yves Dantan, Alain Etienne, Ali Siadat
Abstract
École Nationale Supérieure d’Arts et Métiers, Arts et Métiers ParisTech, LCFC EA 4495, 4 Rue Augustin Fresnel, Metz 57078, France
Abstract The wide application of plastic products had led to a large amount of waste plastics, which brought serious environmental
pollution problems. Although separation is the first step of waste plastic recycling, the injection separating device is still not fully serious environmental section, total length of pollutionand problems. is theonfirst step ofseparating waste plastic recycling, the injection separating is still notusing fully nozzle, distanceAlthough betweenseparation two nozzles plastic device were systematically simulateddevice and analyzed optimized. In this paper, the influences of nozzleBased outleton diameter, contraction ratio, length of parameters contraction combination section, total of length of computational fluid dynamics (CFD) software. the Witozinsky curve,the optimal nozzle nozzle, and distance between two nozzles on plasticsection, separating device were systematically analyzed using4 outlet diameter, contraction ratio, length of contraction and distance between two nozzlessimulated were foundand to be 6 mm, 1.6, Abstract computational Based on the optimalresult parameters combination of nozzle mm, and ＜12fluid mm. dynamics Therefore,(CFD) a newsoftware. streamlined nozzle wasWitozinsky designed. curve,the Best separation was also obtained under this outlet diameter, contraction ratio, length of section,between and distance betweendata two and nozzles were found to be 6 mm, 1.6, 4 parameters combination, which indicated thecontraction good agreements experimental simulation results. In today’s business environment, the trend towards more product variety and customization is unbroken. Due to this development, the need of mm, and ＜12 mm. Therefore, a new streamlined nozzle was designed. Best separation result was also obtained under this agile andThe reconfigurable production systems B.V. emerged to cope with various products and product To design and optimize production © 2019 Authors. Published by Elsevier is agreements an open access article under the CC BY-NC-ND license parameters combination, which indicated theThis good between experimental datafamilies. and simulation results. *The Corresponding Tel.:of +33 3 87 37 54 30; E-mail address: [email protected] wide application plastic products had ledoutlet to a diameter, large amount of waste plastics, brought optimized. Inauthor. this paper, the influences of nozzle contraction ratio, lengthwhich of contraction
systems as well as to choose the optimal product matches, product analysis methods are needed. Indeed, most of the known methods aim to (http://creativecommons.org/licenses/by-nc-nd/3.0/). © 2019 2019aThe The Authors. Published by Elsevier Elsevier B.V. This an access article CC license analyze product or one product family on the physical level. Different families, may differ largely in terms of the number and © Authors. Published by B.V. This is is an open open accessproduct article under under the thehowever, CC BY-NC-ND BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/) Peer-review under responsibility of the scientific committee of the 26th CIRP Life Cycle Engineering nature of components. This fact impedes an efficient comparison and choice of appropriate product(LCE) familyConference. combinations for the production (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review responsibility of the scientific committee of the 26th Life Cycle Engineering (LCE) Conference. system. A newunder methodology is proposed to analyze existing products in CIRP view of their functional and physical architecture. The aim is to cluster Peer-review under responsibility of spectrum; the scientific committee of the 26thPlastics; CIRPofLife Cycleassembly Engineering Conference. Keywords: Spray Near infrared Sorting technology; Wasted Computational Fluid Dynamic these products in nozzle; new assembly oriented product families for the optimization existing lines(LCE) and(CFD) the creation of future reconfigurable assembly systems. Based on Datum Flow Chain, the physical structure of the products is analyzed. Functional subassemblies are identified, and nozzle; infrared Moreover, spectrum; Sorting technology; Wasted Computational Dynamic (CFD)is the output which depicts the a Keywords: functionalSpray analysis is Near performed. a hybrid functional andPlastics; physical architectureFluid graph (HyFPAG) 1. Introduction fluorescence sorting [15], laser designers. induced Anbreakdown similarity between product families by providing design support to both, production system planners and product illustrative [16] on andtwosoproduct on, based onofthe differences in example of a nail-clipper is used to explain the proposed methodology. Anspectroscopy industrial case study families steering columns of 1. Recycling Introduction fluorescence sorting [15], The laser breakdown and France reusingisof waste plastics is one of the most evaluation opticalof signal identification. typesinduced of plastics can be thyssenkrupp Presta then carried out to give a first industrial the proposed approach. spectroscopy [16] andbysocollecting on, basedtheonspectral the differences in ©important 2017 The branches Authors. Published by Elsevier B.V. of resource utilization with extremely high accurately identified, information Recycling and reusing of waste plastics is one of the most optical signal identification. The types of plastics can be Peer-review of the the scientific committee of the 28th Design economic under valueresponsibility [1]. However, development level of CIRP which canConference reflect the2018. characteristics of different plastics and
important of resourcefor utilization with extremely technologybranches and equipment waste plastic recyclinghigh is
accurately collecting spectrum. the spectralPhotoelectric information comparing identified, with theby standard which can reflect the characteristics of different plastics separation, especially the near-infrared spectral separation,and is technology and equipment for waste plastic recycling is comparing with the standard spectrum. Photoelectric plastics with different properties duing waste plastic colleting, gradually becoming a research hotspot in separation industry nowhere nearofenough 3]. As ahas result of mixing various separation, especially the near-infrared separation, is the reusing mixed[2,plastics become the offirst and benifiting from its advantages includingspectral pollution-free, high plastics with different properties duing waste plastic colleting, gradually becoming a research hotspot in separation industry problem for waste plastic recycling [4, 5]. Therefore, automation level, continuous operation, manufactured and high separation 1.foremost Introduction of the product range and characteristics and/or the separation reusing ofof mixed become thefirst first benifiting fromseparating its advantages including pollution-free, high the differentplastics kinds ofhas plastics is the stepand of efficiency.The nozzle is one of the most critical assembled in this system. In this context, the main challenge in foremost problem for waste plastic recycling [4, 5]. Therefore, automation level, continuous operation, and high separation waste recycling. There are several formixed componentand in analysis separation process using tothe method nearDue plastic to the fast development in methods the domain of modelling is now not only cope with single the separation of different kinds of plastics is the[6], firstflotation step of efficiency.The separating nozzle is one ofairthe critical plastics separation, density separation infrared spectrum High-speed jet most fromfamilies, nozzle communication and including an ongoing trend of digitization and products, a limited separation. product range or existing product waste plastic recycling. There are several methods formixed component in separation process using the method nearseparation [7, 8], electric separation [9,10], and photoelectric provides moving power for separated targeting plastics digitalization, manufacturing enterprises are facing important but also tospectrum be able toseparation. analyze and to compareairproducts to nozzle define plastics separation, including density separation [6], flotation infrared High-speed jet from separation, inetc.. Among theseenvironments: separation methods, the [17].Because of the Itimportant role ofthat nozzles in existing plastic challenges today’s market aphotoelectric continuing new product families. can for be observed classical separation [7,separation 8], electric separation [9,10], andclassified provides moving power separated targeting plastics photoelectric method can be further into separation, a lot of researches on the influences of nozzle tendency towards ofthese product development times and product familiesofarethe regrouped in function clients orinfeatures. separation, etc..asreduction Among separation methods, the [17].Because important role ofofproperties, nozzles plastic subtypes, such color sorting [11], near-infrared spectral shape, nozzle size, and internal fluid etc. on shortened product lifecycles. In addition, there isclassified an increasing However, assembly product families are hardly find. photoelectric separation method can besorting further into separation, a lot oforiented researches onbeen the influences of to nozzle sorting [12], mid-infrared spectral [13], Raman separation efficiency have already done in recent years. demand of such customization, being at[11], the same time in aspectral global On the product family level, products differ mainlyetc. in two subtypes, as [14], color X-ray sorting near-infrared shape, size, and internal fluid on spectral sorting perspective sorting, X-ray He etcharacteristics: al.nozzle [18] studied the influence ofcomponents theproperties, internal and streamline competition with competitors all over the world. This trend, main (i) the number of (ii) the sorting [12], mid-infrared spectral sorting [13], Raman separation efficiency have already been done in recent years. which the development from macro to micro type components (e.g. electronical). spectralis inducing sorting [14], X-ray perspective sorting, X-ray He etofal. [18] studied themechanical, influence ofelectrical, the internal streamline markets, results in diminished lot sizes due to augmenting Classical methodologies considering mainly single products 2212-8271 © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license product varieties (high-volume to low-volume production) [1]. or solitary, already existing product families analyze the (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review responsibility thevariety scientific CIRP Life Cycle (LCE) To cope with this ascommittee wellB.V. asofThis tothebe able toaccess product structure on aConference. physical level (components level) which 2212-8271 ©under 2019 Theaugmenting Authors. of Published by Elsevier is26th an open articleEngineering under the CC BY-NC-ND license doi:10.1016/j.procir.2017.04.009 (http://creativecommons.org/licenses/by-nc-nd/3.0/). identify possible optimization potentials in the existing causes difficulties regarding an efficient definition and Peer-review under responsibility of the scientific committee of the 26th CIRP Life Cycle Engineering Conference. production system, it is important to have a precise knowledge comparison of(LCE) different product families. Addressing this Keywords: Design method; identification economic value [1]. [2, However, development of nowhere Assembly; near enough 3]. AsFamily a the result of mixing oflevel various
doi:10.1016/j.procir.2017.04.009
2212-8271 © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/) 2212-8271 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of scientific the scientific committee theCIRP 26thDesign CIRP Conference Life Cycle 2018. Engineering (LCE) Conference. Peer-review under responsibility of the committee of the of 28th 10.1016/j.procir.2019.01.042
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shape in the contraction nozzle on jet flow field under several different kinds of turbulence models.The application of Witozinsky curve in nozzle design in subsonic flow was also investigated. Xu et al. [19] simulated the influence of the contraction angle on water jet nozzle using Fluent software. The results showed remarkable negative correlation between jet velocity and contraction angle of the nozzle. Zhou and coworkers [20] analyzed the hydrodynamics characteristics of high-pressure water jet. The flow field inside and outside the nozzle, which has a certain guiding significance for nozzle designation, was simulated systematically. Hu et al. [21,22] claimed that the optimal nozzle structure for plastic separation was 3.5 mm in radius and 60 mm in length. Hu’s simulation model considered only three factors: diameter, length and contraction angle. The near-infrared plasticseparating equipment was mainly composed of identification, controlling and separation systems. It is very important for separating device to receive the signals form controller and perform injection function to separate different materials. However, the injection separating device was still not fully optimized till now since the research focus of plastic separating device was mainly on the improvement of the identification and controlling systems. The efficiency and accuracy of the near-infrared plastic separating device were limited by its deficiencies, such as high energy consumption, high air consumption, inaccurate injection, high noisy, etc. [22]. In this paper, a streamlined nozzle was designed basing on the Witozinsky curve. Computational fluid dynamics (CFD) software was used to simulate and optimize the streamlined nozzle in detail to explore the optimized nozzle parameters combination with lower energy consumption and higher precision for plastic separation,.
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was applied [23]. After setting the turbulence intensity, the calculation equation of turbulence can be expressed as: I =0.16 Re
1 8
(1)
, where Re is the Reynolds number. Taking straightcontraction 2 nozzle as an example, the velocity vector graph basing on simulation result was shown in Fig. 2.
Fig.2. The velocity vector graph of the straight-contraction 2 nozzle.
The jet flow shapes of all five different nozzles were found to be linear type, which could meet the requirements of plastic separating devices, according to the simulated velocity vector graphs. However, the internal flow field, maximum velocity, and length of the jet core section for different nozzles under the pressure of 0.2 MPa were totally different. The jet core section was the concentrated part with high velocity in jet flow field (red area in Fig.2).Longer length and more concentrated of the jet core section were both beneficial to precise separation of plastics [24].
The comparative analysis of axial velocities of five different nozzles under 0.2 MPa inlet pressure was shown in Fig. 3. The maximum velocity of the five nozzles were all around 340 m/s. In addition, the maximum velocities of the two contraction nozzles and the straight nozzle were slightly 2. The Witozinsky curve higher than those of the two straight-contraction nozzles. The The influence of different shapes of nozzles on separation platform of the maximum velocities in Fig. 3 represented the result was studied and an optimum nozzle shape for plastic length of jet core section. It can be seen that the length of jet separation was found in this paper. As shown in Fig. 1, five core section of the straight nozzle was significantly lower than typical nozzle shapes with same lengthes of 25 mm and outlet those of the other four nozzles, while the length of jet core diameters of 4 mm were selected for analyzing and comparing. sections of nozzles 2 to 5 were in same length. The straightThe contraction angles for these five nozzles were 0°（No.1， contraction nozzle presented a slower velocity attenuation and straight ） , 5° （ No.2 ， contraction 1 ） , 20° （ No.3 ， better performance. As can be seen from Fig. 4, two straightcontraction 2）, 30°（No.4， straight-contraction 1）, and contraction nozzles consumed less air than others. Furtherly, 60°（No.5， straight-contraction 2）, respectively. the air consumption of the straight-contraction nozzle with a contraction angle of 60° was only 83% of that with a contraction angle of 20°.
Fig.1. Cross-sectional views of five different nozzles
The grid file was generated using Fluent software after drawing with GAMBIT software. The inlet and oulet pressure were set at 0.2 MPa and atmospheric pressure, respectively. Steady-state conditions were applied on account of the observation of steady-state data of air consumption and the shape of the jet flow.The outlet diameter was set as hydraulic diameter while reliable k-e model with better performance
Fig. 3. Axial velocities comparison of five different nozzles
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The following results were obtained after simulating the velocity vectors of smooth contraction nozzle and contraction nozzle with sharp corners using Fluent software. The fluid state in the outlet section of the smooth nozzle was laminar flow with orderly flow field, while that of the nozzle with sharp corners was turbulence flow with unstable flow directions and velocity distributions.That is, smoother outlet section would lead to better jetting and separation effects. Therefore, smooth streamlined nozzles with linear contraction characteristic were selected based on the Witozinsky curve. In addition, the flow channel was designed using the line shape of the Witozinsky curve, which presented positive effects in aircraft and wind tunnel design[25].
Fig.4. Air consumption of nozzles with different shapes under the pressure of 0.2 MPa.
The equation of Witozinsky curve can be expressed as follows x [1 ( ) 2 ]2 r* 2 1 l ( ) 1 (1 ) y C [1 1 ( x ) 2 ]3 3 l
(2)
3
application and installation requirements, the total lengths of the nozzles were set at 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, and 50 mm, respectively. The value of other parameters were set according to Case 1 in Table 1. Table 1. Setting of the nozzle parameters. Parameter
Case 1
Case 2
Case 3
Case 4
Case 5
Outlet diameter
6 mm
6 mm
6 mm
/
6 mm
Length of the contraction section
5 mm
/
5 mm
4 mm
5 mm
Shrinkage ratio
1.6
1.6
/
1.6
1.6
Total length of the nozzle
/
25 mm
25 mm
25 mm
25 mm
Inlet pressure
0.2 MPa
Outlet pressure
0 MPa
Air temperature
300 K
Fig. 6 showed the axial velocities comparison of nozzles with different total lengths. The coordinates of each curve were changed to prevent them from overlapping. It can be seen that the variations of the length, axial velocity, and maximum velocity of the jet core section were almost the same under each unit length interval. Fig. 7 presented the comparison of air consumption among nozzles with different lengths. Similar amount of air consumption among different nozzles demonstrated that the total length of nozzles had little influence on nozzle property. That is, total length of nozzle was not a main factor.
, where C represents the contraction ratio (i.e. 𝐶𝐶 = r 0/r*), r0 is the inlet radius, r* is the outlet radius, and l is the length of the contraction section, x and y are the coordinate values of discrete points (as shown in Fig. 5).
Fig. 6. Axial velocities comparison of nozzles with different total lengths.
Fig. 5. Schematic diagram of the Witozinsky curve.
3. Result and discussion Two-dimensional and three-dimensional models of the nozzle was built using CFD software after choosing streamlined nozzles based on the Witozinsky curve. The influences of various parameters on nozzles were analyzed from the points of jet velocity, length of core section, and air consumption to explore the optimal parameters of the nozzle, including total length of the nozzle [26], the length of the contraction section, outlet diameter [27], shrinkage ratio[28], and nozzle spacing. 3.1. Total length of the nozzle Total length of the nozzle is one of the most important parameters of the nozzle structure. According to actual
Fig. 7. Comparison of air consumption among nozzles with different lengths.
The fluid flowing process was affected by the resistance along the pipeline, including fluid internal friction, and the friction between fluid and inner surface of nozzle. Total length of nozzle was not a main factor basing on the simulation results. However, the friction of inner wall was not considered during modelling and simulating. Therefore, a numerical method was introduced below to calculate the onway resistance to make the simulation results more reliable.
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The loss caused by on-way resistance of the pressure flow along the circular pipe was generally calculated by the DarcyWeissbach equation: hf
1 v2 d 2g
(3)
, where λ is the on-way resistance coefficient, l is the length of the nozzle, d is the diameter of the nozzle, and v is the velocity. It can be seen from this equation that the energy loss causing by on-way resistance varied directly as the length of the nozzle. That is, shorter total length of the nozzle was beneficial for the reducing of mechanical energy losses under the same condition. Therefore, the total length of the nozzle was determined to be 25 mm after overall considering the aforementioned conditions and the simplicity of installation. 3.2. The length of the contraction section According to the referential structure parameters, the lengths of the contraction section of nozzles were set at 3, 4, 5, 6, and 7 mm, respectively. The value of other parameters were set according to Case 2 in Table 1. The numerical simulations were carried out using the two-dimensional model. It can be seen from Fig. 8 that the velocities of jet flow of nozzles with different contraction sections in length were almost the same. Therefore, the length of the contraction section had little influence on the velocity of jet flow. The air consumption comparison of nozzles with different contraction sections in length was shown in Fig. 9. The results showed that the amount of air consumption would increase with the increasing of the length of contraction section. In the case of similar performance, lower energy consumption should be chosen. In view of the manufacturing, 4 mm was chosen as the length of contraction section.
Fig. 8. Velocities of jet flow with different contraction sections in length.
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3.3. Shrinkage ratio The shrinkage ratios of nozzles were set at 1.2, 1.4, 1.6, 1.8, 2, 3, and 4, respectively. Other parameters were set according to Case 3 in Table 1. The simulations in this part were also performed using the two-dimensional model. Fig.10 showed the axis velocities comparison of nozzles with different shrinkage ratios. The results showed that the jet velocities of nozzles with different shrinkage ratios presented little differences under certain pressure, while the lengths of jet core sections were different. Besides, the lengths of the jet core sections were much longer than others when the shrinkage ratios were set at 1.6 and 4. Fig.11 presented the air consumption comparison of nozzles with different shrinkage ratios. Minimum air consumption was achieved at the shrinkage ratio of 4. No significant variation of air consumption amount was found when the shrinkage ratio was in the range of 1.6 to 4. Additionally, the inlet diameter of the nozzle was too large when the shrinkage ratio was set at 4, which will bring inconvenient to manufacturing and installation. Taking all these factors, the optimal shrinkage ratio was determined as 1.6.
Fig. 10. Axis velocities comparison of nozzles with different shrinkage ratios.
Fig. 11. Air consumption comparison of nozzles with different shrinkage ratios.
3.4. Outlet diameter
Fig. 9. Air consumption comparison of nozzles with different contraction sections in length.
The outlet radii of nozzles were sequentially set at 1, 1.5, 2, 2.5, 3, 4, and 5 mm. According to the simulation data of different outlet diameters, the optimal nozzle's parameters suitable for the sorting equipment were obtained. The value of other parameters were set according to Case 4 in Table 1. It can be clearly seen from the axis velocities comparison in Fig. 12 that different outlet diameters had great influences on maximum velocities of jet flows and the lengths of jet core
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sections. The maximum velocity presented obvious increasing with the increase of radius from 1 to 2.5 cm, while the maximum velocity remained essentially unchanged when the radius varied from 2.5 to 5 cm. Besides, except for the velocity fluctuation caused by nozzle expansion, the velocity of the jet core section kept constant at 350 m/s. Therefore, the length jet core section increased obviously with the increasing of radius. The distance between nozzle central axis and selected target should be set within the length range of undifferentiated jet flow field, i.e. the length of jet core section (75 mm). In addition, due to the limitation of the actual installation of the equipment, the distance should be larger than 30 mm to reduce accidental collision of materials on nozzles and provide enough space for equipment installation. Considering the influence of nozzle number on maintenance and equipment cost, the optimal vertical distance between nozzle and separation target should be 50 mm. Obviously, the nozzles with radius of 1 cm, 1.5 cm and 2 cm could not meet the design requirements.
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target was simulated using the three-dimensional model. Different center offsets and nozzle watersheds (both internal and external) were established in this three-dimensional model. The negative direction of Z axis was set to be the direction of gravity. Kept the center offsets of X and Z axis to 0, the center offset of Y axis was set at 0mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, respectively. The optimal vertical distance between the separation target and the nozzle was 50 mm based on the analysis results above, and the rest parameters were set according to Case 5 in Table 1. Fig. 14 showed a comparison of the deviations between target on each coordinate direction and axis when the target was ejected to 200 mm in height at different central deviations. It can be seen from Fig. 14 that the deviations in X and Y directions would increase with the increase of center offset. The deviation of X direction was not obvious when the center offset was in the range of 0 to 2 mm, while the deviation presented sharp increasing when the center offset was in the range of 3 to 5 mm. No obvious regularity can be found when the center offset was larger than 6 mm. The deviation of Y direction increased gradually with the center offset from 0 to 6 mm. Obvious trajectory deviation can be obtained under larger center offsets.
Fig. 12. Axis velocities comparison of nozzles with different outlet diameters.
According to the air consumption comparison in Fig. 13, the air consumption increased gradually with the increase of the nozzle radius. Therefore, smaller outlet diameter should be chosen to minimize the air consumption on the basis of satisfying the jet velocity for separation and the length of jet core section. Thus, optimized outlet diameter of nozzle was determined as 6 mm.
Fig. 13. Air consumption comparison of nozzles with different outlet diameters.
3.5. Nozzle spacing The offset between gravity center of the target and nozzle axis was the center offset. The flight trajectory of plastic, and the time and air consumption amount for reaching the preset position under different center offsets were investigated using simulation methods. Furthermore, the flight trajectory of the
Fig. 14. Comparison of deviations of target coordinate at a height of 0.2m (Z=200mm).
Small deviations of X and Y directions were obtained when the center offset was 7 mm, which were not in line with the expected growth trend. This is because the target had already been turned over several times. The target was sucked in due to the low pressure in high-speed region of jet flow, and finally resulted in small deviations in both directions. In other words, this should be considered as a failure of separation. When the center offset was 8 mm, the boundary of the calculation model was exceeded because of oversized deviation in Y direction, which should also be also considered as a failure of separation. To sum up, the sepration requirements can be satisfied when the center offset was less than 6 mm. Thus, the design of nozzle spacing should limit the center offset to less than 6 mm, and the distance between two nozzles should be no more than 12 mm. However, it should be noted that the layout distance was determined after determing the nozzle parameters, especially the outlet diameter of nozzle (6 mm) and the distance between the separation target and the nozzle (50 mm). The optimal nozzle spacing also should be redetermined if relevant parameters were changed.
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4. Conclusions Separation nozzles with different shapes and parameters were simulated by CFD software. The simulation results showed that the streamline nozzle based on Witozinsky curve had the advantages of long jet core section, slow velocity attenuation, low air consumption, low turbulence and energy saving. The total length of the nozzle had little effect on the its performance, but the on-way resistance would decrease with the increase of total length. Optimal total length was found to be 25 mm. The length of the contraction section also presented little effect on the performance of the nozzle. The length of the contraction section was positively correlated with the air consumption. Therefore, optimal length of the contraction section was 4 mm under similar performance. The jet velocities of nozzles with different shrinkage ratios were almost the same, while the core sections of jet flows were different. Longer jet core sections for nozzles, which were benefitful for manufacturing and installation, can be obtained under the shrinkage ratio of 1.6. The outlet diameter showed a significant influence on the jet flow of the nozzle, and the length of jet core section and amount of air consumption would increase with the increase of outlet diameter. The nozzle could meet the plastic separation requirement with less air consumption when the outlet diameter was set at 6 mm. Optimal injection accuracy was obtained when the distance between separation target and nozzle axis was 50 mm. Furthermore, the nozzle spacing should be no less than 12 mm since the optimal nozzle spacing was significantly affected by other parameters of the nozzle. The significance of numerical simulation research using CFD software in this paper was to provide basis for the design of the injection separation device, and to define the reasonable ranges of various parameters of the nozzle. Strong supporting for products optimization and improvement also could be obtained using this method. Best separation result was obtained under optimal parameters combination according to the simulation results. The experimental data were also in good agreements with the simulation results. Acknowledgements This study was supported by the National Natural Science Foundation of China (No. 51575287) and Shandong Natural Science Foundation (No. ZR2016XJ003). References [1] Mwanza BG , Mbohwa C , Telukdarie A.Strategies for the recovery and recycling of plastic solid waste (PSW): A Focus on plastic manufacturing companies. Proc Manuf,2018, 21:686-693. [2] Zheng WH, Qu MH. Waste waste recycling status and future trends in China. Chin Resour Compr Utiliz 2018;36:75-77. [3] Zhao Y B,Lv X D ,Ni HG.Solvent-based separation and recycling of waste plastics: A review. Chemosphere 2018;209 :707-720. [4] Yang YL.Classification of waste plastics in simple ways. Renew resour circ econ2009;2:38-41. [5] Zheng Y, Bai JR, Xu JN, Li XY, et al. A discrimination model in waste plastics sorting using NIR hyperspectral imaging system. Waste Manage 2018;72:87-98.
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[6] Dodbiba G, Haruki N, Shibayama A, et al. Combination of sink-float separation and flotation technique for purification of shredded PETbottle from PE or PP flakes. Int. J. Miner. Process 2002;65:748-755. [7] Wang CQ, Wang H, Zhao X. Research progress in the separation of waste plastics by flotation. Chin Plast 2013;27:96-102. [8] Shen HT, Forssberg E, Pugh R. Selective flotation separation of plastics by chemical conditioning with methylcellulose. Resour conserv recy 2002; 35:229-241． [9] Amar T, Karim M, Mohamed Y, et al. Roll-type versus free-fall electrostatic separation of tribocharged plastic particles. IEEE T Ind Appl 2010; 46:1564-1569. [10] Wu GQ.Triboelectrostatic separation for granular plastic waste.Shanghai Jiao Tong University,China:2013. [11] Huang Y, Li JB, Wang YB. Introduction of photoelectric color sorting machine. Mod Agric Equip 2007(10):60-61. [12] Yin FF, Yan L, Han QX, et al. Revive on application of near infrared spectroscopy technology (NIR) in plastic sorting. Environ Eng 2017;35: 134-138. [13] Wang D, Ma ZH, Zhao L, et al. Comparative research on the NIR and MIR micro-imaging of two similar plastic materials. Spectros Spectr Anal 2011;35:2377-2382. [14] Dou YL, Zhang WX, Zhang YJ, et al. Identification of plastics by fourier transform raman and infrared spectroscopy. Anal Chem 2006(11):16151618. [15] Aldriana A, Lederstegerb A, Pombergera R. Monitoring of WEEE plastics in regards to brominated flame retardants using handheld XRF. Waste Manage 2015;24:297-304. [16] Sun QQ, Du M, Guo LB, et al. Fast identification of plastics with laserinduced breakdown spectroscopy. Spectros Spectral Anal 2017;37:22052209. [17] Hu B,Zhang SH,Tang GL,et al.Development of automatic identification and sorting unit for waste mixed plastics. Lift Transp Machin 2015 (06):38-41. [18] He F, Xie JS, Yang JL. Influence of channel profile of Nozzle inside on Jet Flow Field. Chin J Appl Mech 2001;18:114-119. [19] Xu R，DU CL, Zeng R, et al. Study on jet simulation of nozzles with different contraction Angles. Min Mach 2011;39:36-39. [20] Zhou WH. Numerical simulation of internal and external flow fields of high pressure water jet nozzles. Lanzhou University of Technology, China: 2008. [21]Hu B,Wang ST,Yang JY, et al. Experimental research on nozzle device in mixed waste plastic automatic identification separator. J Tianjin Univer of Technol 2013;29:8-9. [22] Hu B, Wang ST, Tang GL, et al. Design of accurate sorting device for waste plastics based on fluent. Chin J Appl Mech 2015;32:10751081+1109. DOI：10.11776/cjam.32.06.D048 [23] Lee H, Wray T, Agarwal RK. CFD performance of turbulence models for flow from supersonic nozzle exhausts. 34th AIAA Appl Aerodyn Confer. Dallas:2016. [24] Yang Y, Zhu R, Zhao F. Numerical Simulation on Effect of Curve on Supersonic Oxygen Jet Characteristic. J Ind Heat 2016;45:9-12. [25] Li MX, Li XH, Chen PH. A method study on unfloded of practical wind tunnel contraction stages of witozinsky curve. Appl Energ Technol 2010; 01:1-4. [26] Jia WW. Jet impingement analysis of different length nozzles based on ANSYS Fluent. Metall Equip 2016;01:33-36. [27] Wang ZG, Ran CY, Deng B, et al. Study on the jet characteristics of the remote flushing nozzle based on FLUENT. Hydraul Pneum Seal 2016;36: 31-34. [28] Pang SM, Chen PM. Taper nozzle design on CFD. Mech Manuf Autom 2011; 40:41-42.
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Structure optimization of separating nozzle for waste plastic recycling Structure optimization of separating for waste plastic recycling 28th CIRP Design Conference,nozzle May 2018, Nantes, France Fengfu Yin*, Lianlian Xue, Zhen Liu , Lin Li, Chuansheng Wang College of Electromechanical Engineering, Qingdao University and Technology, Qingdao 266061,China Fengfu Yin*, Xue, Liuof,Science Lin Li, Chuansheng Wang A new methodology toLianlian analyze theZhen functional and physical architecture of * Corresponding author. Tel.:1-358-322-9902; fax: +0-532-889-57388. E-mail address: [email protected] College of Electromechanical Qingdao University of Science and Technology, Qingdao 266061,China existing products for anEngineering, assembly oriented product family identification * Corresponding author. Tel.:1-358-322-9902; fax: +0-532-889-57388. E-mail address: [email protected]
Paul Stief *, Jean-Yves Dantan, Alain Etienne, Ali Siadat
Abstract
École Nationale Supérieure d’Arts et Métiers, Arts et Métiers ParisTech, LCFC EA 4495, 4 Rue Augustin Fresnel, Metz 57078, France
Abstract The wide application of plastic products had led to a large amount of waste plastics, which brought serious environmental
pollution problems. Although separation is the first step of waste plastic recycling, the injection separating device is still not fully serious environmental section, total length of pollutionand problems. is theonfirst step ofseparating waste plastic recycling, the injection separating is still notusing fully nozzle, distanceAlthough betweenseparation two nozzles plastic device were systematically simulateddevice and analyzed optimized. In this paper, the influences of nozzleBased outleton diameter, contraction ratio, length of parameters contraction combination section, total of length of computational fluid dynamics (CFD) software. the Witozinsky curve,the optimal nozzle nozzle, and distance between two nozzles on plasticsection, separating device were systematically analyzed using4 outlet diameter, contraction ratio, length of contraction and distance between two nozzlessimulated were foundand to be 6 mm, 1.6, Abstract computational Based on the optimalresult parameters combination of nozzle mm, and ＜12fluid mm. dynamics Therefore,(CFD) a newsoftware. streamlined nozzle wasWitozinsky designed. curve,the Best separation was also obtained under this outlet diameter, contraction ratio, length of section,between and distance betweendata two and nozzles were found to be 6 mm, 1.6, 4 parameters combination, which indicated thecontraction good agreements experimental simulation results. In today’s business environment, the trend towards more product variety and customization is unbroken. Due to this development, the need of mm, and ＜12 mm. Therefore, a new streamlined nozzle was designed. Best separation result was also obtained under this agile andThe reconfigurable production systems B.V. emerged to cope with various products and product To design and optimize production © 2019 Authors. Published by Elsevier is agreements an open access article under the CC BY-NC-ND license parameters combination, which indicated theThis good between experimental datafamilies. and simulation results. *The Corresponding Tel.:of +33 3 87 37 54 30; E-mail address: [email protected] wide application plastic products had ledoutlet to a diameter, large amount of waste plastics, brought optimized. Inauthor. this paper, the influences of nozzle contraction ratio, lengthwhich of contraction
systems as well as to choose the optimal product matches, product analysis methods are needed. Indeed, most of the known methods aim to (http://creativecommons.org/licenses/by-nc-nd/3.0/). © 2019 2019aThe The Authors. Published by Elsevier Elsevier B.V. This an access article CC license analyze product or one product family on the physical level. Different families, may differ largely in terms of the number and © Authors. Published by B.V. This is is an open open accessproduct article under under the thehowever, CC BY-NC-ND BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/) Peer-review under responsibility of the scientific committee of the 26th CIRP Life Cycle Engineering nature of components. This fact impedes an efficient comparison and choice of appropriate product(LCE) familyConference. combinations for the production (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review responsibility of the scientific committee of the 26th Life Cycle Engineering (LCE) Conference. system. A newunder methodology is proposed to analyze existing products in CIRP view of their functional and physical architecture. The aim is to cluster Peer-review under responsibility of spectrum; the scientific committee of the 26thPlastics; CIRPofLife Cycleassembly Engineering Conference. Keywords: Spray Near infrared Sorting technology; Wasted Computational Fluid Dynamic these products in nozzle; new assembly oriented product families for the optimization existing lines(LCE) and(CFD) the creation of future reconfigurable assembly systems. Based on Datum Flow Chain, the physical structure of the products is analyzed. Functional subassemblies are identified, and nozzle; infrared Moreover, spectrum; Sorting technology; Wasted Computational Dynamic (CFD)is the output which depicts the a Keywords: functionalSpray analysis is Near performed. a hybrid functional andPlastics; physical architectureFluid graph (HyFPAG) 1. Introduction fluorescence sorting [15], laser designers. induced Anbreakdown similarity between product families by providing design support to both, production system planners and product illustrative [16] on andtwosoproduct on, based onofthe differences in example of a nail-clipper is used to explain the proposed methodology. Anspectroscopy industrial case study families steering columns of 1. Recycling Introduction fluorescence sorting [15], The laser breakdown and France reusingisof waste plastics is one of the most evaluation opticalof signal identification. typesinduced of plastics can be thyssenkrupp Presta then carried out to give a first industrial the proposed approach. spectroscopy [16] andbysocollecting on, basedtheonspectral the differences in ©important 2017 The branches Authors. Published by Elsevier B.V. of resource utilization with extremely high accurately identified, information Recycling and reusing of waste plastics is one of the most optical signal identification. The types of plastics can be Peer-review of the the scientific committee of the 28th Design economic under valueresponsibility [1]. However, development level of CIRP which canConference reflect the2018. characteristics of different plastics and
important of resourcefor utilization with extremely technologybranches and equipment waste plastic recyclinghigh is
accurately collecting spectrum. the spectralPhotoelectric information comparing identified, with theby standard which can reflect the characteristics of different plastics separation, especially the near-infrared spectral separation,and is technology and equipment for waste plastic recycling is comparing with the standard spectrum. Photoelectric plastics with different properties duing waste plastic colleting, gradually becoming a research hotspot in separation industry nowhere nearofenough 3]. As ahas result of mixing various separation, especially the near-infrared separation, is the reusing mixed[2,plastics become the offirst and benifiting from its advantages includingspectral pollution-free, high plastics with different properties duing waste plastic colleting, gradually becoming a research hotspot in separation industry problem for waste plastic recycling [4, 5]. Therefore, automation level, continuous operation, manufactured and high separation 1.foremost Introduction of the product range and characteristics and/or the separation reusing ofof mixed become thefirst first benifiting fromseparating its advantages including pollution-free, high the differentplastics kinds ofhas plastics is the stepand of efficiency.The nozzle is one of the most critical assembled in this system. In this context, the main challenge in foremost problem for waste plastic recycling [4, 5]. Therefore, automation level, continuous operation, and high separation waste recycling. There are several formixed componentand in analysis separation process using tothe method nearDue plastic to the fast development in methods the domain of modelling is now not only cope with single the separation of different kinds of plastics is the[6], firstflotation step of efficiency.The separating nozzle is one ofairthe critical plastics separation, density separation infrared spectrum High-speed jet most fromfamilies, nozzle communication and including an ongoing trend of digitization and products, a limited separation. product range or existing product waste plastic recycling. There are several methods formixed component in separation process using the method nearseparation [7, 8], electric separation [9,10], and photoelectric provides moving power for separated targeting plastics digitalization, manufacturing enterprises are facing important but also tospectrum be able toseparation. analyze and to compareairproducts to nozzle define plastics separation, including density separation [6], flotation infrared High-speed jet from separation, inetc.. Among theseenvironments: separation methods, the [17].Because of the Itimportant role ofthat nozzles in existing plastic challenges today’s market aphotoelectric continuing new product families. can for be observed classical separation [7,separation 8], electric separation [9,10], andclassified provides moving power separated targeting plastics photoelectric method can be further into separation, a lot of researches on the influences of nozzle tendency towards ofthese product development times and product familiesofarethe regrouped in function clients orinfeatures. separation, etc..asreduction Among separation methods, the [17].Because important role ofofproperties, nozzles plastic subtypes, such color sorting [11], near-infrared spectral shape, nozzle size, and internal fluid etc. on shortened product lifecycles. In addition, there isclassified an increasing However, assembly product families are hardly find. photoelectric separation method can besorting further into separation, a lot oforiented researches onbeen the influences of to nozzle sorting [12], mid-infrared spectral [13], Raman separation efficiency have already done in recent years. demand of such customization, being at[11], the same time in aspectral global On the product family level, products differ mainlyetc. in two subtypes, as [14], color X-ray sorting near-infrared shape, size, and internal fluid on spectral sorting perspective sorting, X-ray He etcharacteristics: al.nozzle [18] studied the influence ofcomponents theproperties, internal and streamline competition with competitors all over the world. This trend, main (i) the number of (ii) the sorting [12], mid-infrared spectral sorting [13], Raman separation efficiency have already been done in recent years. which the development from macro to micro type components (e.g. electronical). spectralis inducing sorting [14], X-ray perspective sorting, X-ray He etofal. [18] studied themechanical, influence ofelectrical, the internal streamline markets, results in diminished lot sizes due to augmenting Classical methodologies considering mainly single products 2212-8271 © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license product varieties (high-volume to low-volume production) [1]. or solitary, already existing product families analyze the (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review responsibility thevariety scientific CIRP Life Cycle (LCE) To cope with this ascommittee wellB.V. asofThis tothebe able toaccess product structure on aConference. physical level (components level) which 2212-8271 ©under 2019 Theaugmenting Authors. of Published by Elsevier is26th an open articleEngineering under the CC BY-NC-ND license doi:10.1016/j.procir.2017.04.009 (http://creativecommons.org/licenses/by-nc-nd/3.0/). identify possible optimization potentials in the existing causes difficulties regarding an efficient definition and Peer-review under responsibility of the scientific committee of the 26th CIRP Life Cycle Engineering Conference. production system, it is important to have a precise knowledge comparison of(LCE) different product families. Addressing this Keywords: Design method; identification economic value [1]. [2, However, development of nowhere Assembly; near enough 3]. AsFamily a the result of mixing oflevel various
doi:10.1016/j.procir.2017.04.009
2212-8271 © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/) 2212-8271 © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of scientific the scientific committee theCIRP 26thDesign CIRP Conference Life Cycle 2018. Engineering (LCE) Conference. Peer-review under responsibility of the committee of the of 28th 10.1016/j.procir.2019.01.042
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Fengfu Yin et al. / Procedia CIRP 80 (2019) 572–577 Fengfu Yin et al./ Procedia CIRP 00 (2019) 000–000
shape in the contraction nozzle on jet flow field under several different kinds of turbulence models.The application of Witozinsky curve in nozzle design in subsonic flow was also investigated. Xu et al. [19] simulated the influence of the contraction angle on water jet nozzle using Fluent software. The results showed remarkable negative correlation between jet velocity and contraction angle of the nozzle. Zhou and coworkers [20] analyzed the hydrodynamics characteristics of high-pressure water jet. The flow field inside and outside the nozzle, which has a certain guiding significance for nozzle designation, was simulated systematically. Hu et al. [21,22] claimed that the optimal nozzle structure for plastic separation was 3.5 mm in radius and 60 mm in length. Hu’s simulation model considered only three factors: diameter, length and contraction angle. The near-infrared plasticseparating equipment was mainly composed of identification, controlling and separation systems. It is very important for separating device to receive the signals form controller and perform injection function to separate different materials. However, the injection separating device was still not fully optimized till now since the research focus of plastic separating device was mainly on the improvement of the identification and controlling systems. The efficiency and accuracy of the near-infrared plastic separating device were limited by its deficiencies, such as high energy consumption, high air consumption, inaccurate injection, high noisy, etc. [22]. In this paper, a streamlined nozzle was designed basing on the Witozinsky curve. Computational fluid dynamics (CFD) software was used to simulate and optimize the streamlined nozzle in detail to explore the optimized nozzle parameters combination with lower energy consumption and higher precision for plastic separation,.
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was applied [23]. After setting the turbulence intensity, the calculation equation of turbulence can be expressed as: I =0.16 Re
1 8
(1)
, where Re is the Reynolds number. Taking straightcontraction 2 nozzle as an example, the velocity vector graph basing on simulation result was shown in Fig. 2.
Fig.2. The velocity vector graph of the straight-contraction 2 nozzle.
The jet flow shapes of all five different nozzles were found to be linear type, which could meet the requirements of plastic separating devices, according to the simulated velocity vector graphs. However, the internal flow field, maximum velocity, and length of the jet core section for different nozzles under the pressure of 0.2 MPa were totally different. The jet core section was the concentrated part with high velocity in jet flow field (red area in Fig.2).Longer length and more concentrated of the jet core section were both beneficial to precise separation of plastics [24].
The comparative analysis of axial velocities of five different nozzles under 0.2 MPa inlet pressure was shown in Fig. 3. The maximum velocity of the five nozzles were all around 340 m/s. In addition, the maximum velocities of the two contraction nozzles and the straight nozzle were slightly 2. The Witozinsky curve higher than those of the two straight-contraction nozzles. The The influence of different shapes of nozzles on separation platform of the maximum velocities in Fig. 3 represented the result was studied and an optimum nozzle shape for plastic length of jet core section. It can be seen that the length of jet separation was found in this paper. As shown in Fig. 1, five core section of the straight nozzle was significantly lower than typical nozzle shapes with same lengthes of 25 mm and outlet those of the other four nozzles, while the length of jet core diameters of 4 mm were selected for analyzing and comparing. sections of nozzles 2 to 5 were in same length. The straightThe contraction angles for these five nozzles were 0°（No.1， contraction nozzle presented a slower velocity attenuation and straight ） , 5° （ No.2 ， contraction 1 ） , 20° （ No.3 ， better performance. As can be seen from Fig. 4, two straightcontraction 2）, 30°（No.4， straight-contraction 1）, and contraction nozzles consumed less air than others. Furtherly, 60°（No.5， straight-contraction 2）, respectively. the air consumption of the straight-contraction nozzle with a contraction angle of 60° was only 83% of that with a contraction angle of 20°.
Fig.1. Cross-sectional views of five different nozzles
The grid file was generated using Fluent software after drawing with GAMBIT software. The inlet and oulet pressure were set at 0.2 MPa and atmospheric pressure, respectively. Steady-state conditions were applied on account of the observation of steady-state data of air consumption and the shape of the jet flow.The outlet diameter was set as hydraulic diameter while reliable k-e model with better performance
Fig. 3. Axial velocities comparison of five different nozzles
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The following results were obtained after simulating the velocity vectors of smooth contraction nozzle and contraction nozzle with sharp corners using Fluent software. The fluid state in the outlet section of the smooth nozzle was laminar flow with orderly flow field, while that of the nozzle with sharp corners was turbulence flow with unstable flow directions and velocity distributions.That is, smoother outlet section would lead to better jetting and separation effects. Therefore, smooth streamlined nozzles with linear contraction characteristic were selected based on the Witozinsky curve. In addition, the flow channel was designed using the line shape of the Witozinsky curve, which presented positive effects in aircraft and wind tunnel design[25].
Fig.4. Air consumption of nozzles with different shapes under the pressure of 0.2 MPa.
The equation of Witozinsky curve can be expressed as follows x [1 ( ) 2 ]2 r* 2 1 l ( ) 1 (1 ) y C [1 1 ( x ) 2 ]3 3 l
(2)
3
application and installation requirements, the total lengths of the nozzles were set at 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, and 50 mm, respectively. The value of other parameters were set according to Case 1 in Table 1. Table 1. Setting of the nozzle parameters. Parameter
Case 1
Case 2
Case 3
Case 4
Case 5
Outlet diameter
6 mm
6 mm
6 mm
/
6 mm
Length of the contraction section
5 mm
/
5 mm
4 mm
5 mm
Shrinkage ratio
1.6
1.6
/
1.6
1.6
Total length of the nozzle
/
25 mm
25 mm
25 mm
25 mm
Inlet pressure
0.2 MPa
Outlet pressure
0 MPa
Air temperature
300 K
Fig. 6 showed the axial velocities comparison of nozzles with different total lengths. The coordinates of each curve were changed to prevent them from overlapping. It can be seen that the variations of the length, axial velocity, and maximum velocity of the jet core section were almost the same under each unit length interval. Fig. 7 presented the comparison of air consumption among nozzles with different lengths. Similar amount of air consumption among different nozzles demonstrated that the total length of nozzles had little influence on nozzle property. That is, total length of nozzle was not a main factor.
, where C represents the contraction ratio (i.e. 𝐶𝐶 = r 0/r*), r0 is the inlet radius, r* is the outlet radius, and l is the length of the contraction section, x and y are the coordinate values of discrete points (as shown in Fig. 5).
Fig. 6. Axial velocities comparison of nozzles with different total lengths.
Fig. 5. Schematic diagram of the Witozinsky curve.
3. Result and discussion Two-dimensional and three-dimensional models of the nozzle was built using CFD software after choosing streamlined nozzles based on the Witozinsky curve. The influences of various parameters on nozzles were analyzed from the points of jet velocity, length of core section, and air consumption to explore the optimal parameters of the nozzle, including total length of the nozzle [26], the length of the contraction section, outlet diameter [27], shrinkage ratio[28], and nozzle spacing. 3.1. Total length of the nozzle Total length of the nozzle is one of the most important parameters of the nozzle structure. According to actual
Fig. 7. Comparison of air consumption among nozzles with different lengths.
The fluid flowing process was affected by the resistance along the pipeline, including fluid internal friction, and the friction between fluid and inner surface of nozzle. Total length of nozzle was not a main factor basing on the simulation results. However, the friction of inner wall was not considered during modelling and simulating. Therefore, a numerical method was introduced below to calculate the onway resistance to make the simulation results more reliable.
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The loss caused by on-way resistance of the pressure flow along the circular pipe was generally calculated by the DarcyWeissbach equation: hf
1 v2 d 2g
(3)
, where λ is the on-way resistance coefficient, l is the length of the nozzle, d is the diameter of the nozzle, and v is the velocity. It can be seen from this equation that the energy loss causing by on-way resistance varied directly as the length of the nozzle. That is, shorter total length of the nozzle was beneficial for the reducing of mechanical energy losses under the same condition. Therefore, the total length of the nozzle was determined to be 25 mm after overall considering the aforementioned conditions and the simplicity of installation. 3.2. The length of the contraction section According to the referential structure parameters, the lengths of the contraction section of nozzles were set at 3, 4, 5, 6, and 7 mm, respectively. The value of other parameters were set according to Case 2 in Table 1. The numerical simulations were carried out using the two-dimensional model. It can be seen from Fig. 8 that the velocities of jet flow of nozzles with different contraction sections in length were almost the same. Therefore, the length of the contraction section had little influence on the velocity of jet flow. The air consumption comparison of nozzles with different contraction sections in length was shown in Fig. 9. The results showed that the amount of air consumption would increase with the increasing of the length of contraction section. In the case of similar performance, lower energy consumption should be chosen. In view of the manufacturing, 4 mm was chosen as the length of contraction section.
Fig. 8. Velocities of jet flow with different contraction sections in length.
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3.3. Shrinkage ratio The shrinkage ratios of nozzles were set at 1.2, 1.4, 1.6, 1.8, 2, 3, and 4, respectively. Other parameters were set according to Case 3 in Table 1. The simulations in this part were also performed using the two-dimensional model. Fig.10 showed the axis velocities comparison of nozzles with different shrinkage ratios. The results showed that the jet velocities of nozzles with different shrinkage ratios presented little differences under certain pressure, while the lengths of jet core sections were different. Besides, the lengths of the jet core sections were much longer than others when the shrinkage ratios were set at 1.6 and 4. Fig.11 presented the air consumption comparison of nozzles with different shrinkage ratios. Minimum air consumption was achieved at the shrinkage ratio of 4. No significant variation of air consumption amount was found when the shrinkage ratio was in the range of 1.6 to 4. Additionally, the inlet diameter of the nozzle was too large when the shrinkage ratio was set at 4, which will bring inconvenient to manufacturing and installation. Taking all these factors, the optimal shrinkage ratio was determined as 1.6.
Fig. 10. Axis velocities comparison of nozzles with different shrinkage ratios.
Fig. 11. Air consumption comparison of nozzles with different shrinkage ratios.
3.4. Outlet diameter
Fig. 9. Air consumption comparison of nozzles with different contraction sections in length.
The outlet radii of nozzles were sequentially set at 1, 1.5, 2, 2.5, 3, 4, and 5 mm. According to the simulation data of different outlet diameters, the optimal nozzle's parameters suitable for the sorting equipment were obtained. The value of other parameters were set according to Case 4 in Table 1. It can be clearly seen from the axis velocities comparison in Fig. 12 that different outlet diameters had great influences on maximum velocities of jet flows and the lengths of jet core
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sections. The maximum velocity presented obvious increasing with the increase of radius from 1 to 2.5 cm, while the maximum velocity remained essentially unchanged when the radius varied from 2.5 to 5 cm. Besides, except for the velocity fluctuation caused by nozzle expansion, the velocity of the jet core section kept constant at 350 m/s. Therefore, the length jet core section increased obviously with the increasing of radius. The distance between nozzle central axis and selected target should be set within the length range of undifferentiated jet flow field, i.e. the length of jet core section (75 mm). In addition, due to the limitation of the actual installation of the equipment, the distance should be larger than 30 mm to reduce accidental collision of materials on nozzles and provide enough space for equipment installation. Considering the influence of nozzle number on maintenance and equipment cost, the optimal vertical distance between nozzle and separation target should be 50 mm. Obviously, the nozzles with radius of 1 cm, 1.5 cm and 2 cm could not meet the design requirements.
5
target was simulated using the three-dimensional model. Different center offsets and nozzle watersheds (both internal and external) were established in this three-dimensional model. The negative direction of Z axis was set to be the direction of gravity. Kept the center offsets of X and Z axis to 0, the center offset of Y axis was set at 0mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, respectively. The optimal vertical distance between the separation target and the nozzle was 50 mm based on the analysis results above, and the rest parameters were set according to Case 5 in Table 1. Fig. 14 showed a comparison of the deviations between target on each coordinate direction and axis when the target was ejected to 200 mm in height at different central deviations. It can be seen from Fig. 14 that the deviations in X and Y directions would increase with the increase of center offset. The deviation of X direction was not obvious when the center offset was in the range of 0 to 2 mm, while the deviation presented sharp increasing when the center offset was in the range of 3 to 5 mm. No obvious regularity can be found when the center offset was larger than 6 mm. The deviation of Y direction increased gradually with the center offset from 0 to 6 mm. Obvious trajectory deviation can be obtained under larger center offsets.
Fig. 12. Axis velocities comparison of nozzles with different outlet diameters.
According to the air consumption comparison in Fig. 13, the air consumption increased gradually with the increase of the nozzle radius. Therefore, smaller outlet diameter should be chosen to minimize the air consumption on the basis of satisfying the jet velocity for separation and the length of jet core section. Thus, optimized outlet diameter of nozzle was determined as 6 mm.
Fig. 13. Air consumption comparison of nozzles with different outlet diameters.
3.5. Nozzle spacing The offset between gravity center of the target and nozzle axis was the center offset. The flight trajectory of plastic, and the time and air consumption amount for reaching the preset position under different center offsets were investigated using simulation methods. Furthermore, the flight trajectory of the
Fig. 14. Comparison of deviations of target coordinate at a height of 0.2m (Z=200mm).
Small deviations of X and Y directions were obtained when the center offset was 7 mm, which were not in line with the expected growth trend. This is because the target had already been turned over several times. The target was sucked in due to the low pressure in high-speed region of jet flow, and finally resulted in small deviations in both directions. In other words, this should be considered as a failure of separation. When the center offset was 8 mm, the boundary of the calculation model was exceeded because of oversized deviation in Y direction, which should also be also considered as a failure of separation. To sum up, the sepration requirements can be satisfied when the center offset was less than 6 mm. Thus, the design of nozzle spacing should limit the center offset to less than 6 mm, and the distance between two nozzles should be no more than 12 mm. However, it should be noted that the layout distance was determined after determing the nozzle parameters, especially the outlet diameter of nozzle (6 mm) and the distance between the separation target and the nozzle (50 mm). The optimal nozzle spacing also should be redetermined if relevant parameters were changed.
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4. Conclusions Separation nozzles with different shapes and parameters were simulated by CFD software. The simulation results showed that the streamline nozzle based on Witozinsky curve had the advantages of long jet core section, slow velocity attenuation, low air consumption, low turbulence and energy saving. The total length of the nozzle had little effect on the its performance, but the on-way resistance would decrease with the increase of total length. Optimal total length was found to be 25 mm. The length of the contraction section also presented little effect on the performance of the nozzle. The length of the contraction section was positively correlated with the air consumption. Therefore, optimal length of the contraction section was 4 mm under similar performance. The jet velocities of nozzles with different shrinkage ratios were almost the same, while the core sections of jet flows were different. Longer jet core sections for nozzles, which were benefitful for manufacturing and installation, can be obtained under the shrinkage ratio of 1.6. The outlet diameter showed a significant influence on the jet flow of the nozzle, and the length of jet core section and amount of air consumption would increase with the increase of outlet diameter. The nozzle could meet the plastic separation requirement with less air consumption when the outlet diameter was set at 6 mm. Optimal injection accuracy was obtained when the distance between separation target and nozzle axis was 50 mm. Furthermore, the nozzle spacing should be no less than 12 mm since the optimal nozzle spacing was significantly affected by other parameters of the nozzle. The significance of numerical simulation research using CFD software in this paper was to provide basis for the design of the injection separation device, and to define the reasonable ranges of various parameters of the nozzle. Strong supporting for products optimization and improvement also could be obtained using this method. Best separation result was obtained under optimal parameters combination according to the simulation results. The experimental data were also in good agreements with the simulation results. Acknowledgements This study was supported by the National Natural Science Foundation of China (No. 51575287) and Shandong Natural Science Foundation (No. ZR2016XJ003). References [1] Mwanza BG , Mbohwa C , Telukdarie A.Strategies for the recovery and recycling of plastic solid waste (PSW): A Focus on plastic manufacturing companies. Proc Manuf,2018, 21:686-693. [2] Zheng WH, Qu MH. Waste waste recycling status and future trends in China. Chin Resour Compr Utiliz 2018;36:75-77. [3] Zhao Y B,Lv X D ,Ni HG.Solvent-based separation and recycling of waste plastics: A review. Chemosphere 2018;209 :707-720. [4] Yang YL.Classification of waste plastics in simple ways. Renew resour circ econ2009;2:38-41. [5] Zheng Y, Bai JR, Xu JN, Li XY, et al. A discrimination model in waste plastics sorting using NIR hyperspectral imaging system. Waste Manage 2018;72:87-98.
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