Design, Simulation and Experimentation of an Axial Flow Sunﬂower-Threshing Machine with an Attached Screw Conveyor

applied sciences

Article Design, Simulation and Experimentation of an Axial Flow Sunﬂower-Threshing Machine with an Attached Screw Conveyor

Khaled Abdeen Mous Ali 1,2 , Wangyuan Zong 1,3,*, Haﬁz Md-Tahir 1 , Lina Ma 1 and Liu Yang 1

1 College of Engineering, Huazhong Agricultural University, Wuhan 430070, China; [email protected] (K.A.M.A.); [email protected] (H.M.-T.); [email protected] (L.M.); [email protected] (L.Y.) 2 College of Agricultural Engineering, AL-Azhar University, Cairo 11651, Egypt 3 Key Laboratory of Agricultural Equipment in Mid-Lower Yangtze River, Ministry of Agriculture and Rural Affairs, Wuhan 430070, China * Correspondence: [email protected]

Abstract: Sunflower threshing is one of the most interesting field processes for making the sunflower ready for seed handling, drying, cleaning and oil extraction. One of the biggest problems observed during the sunflower threshing process is the accumulation of threshed crop on the first third of the threshing roller and passing off some unthreshed parts of sunflower heads. To solve the aforementioned problem and optimize the efficiency of the sunflower threshing process, this research was focused on devising and testing a sunflower threshing machine with a close threshing box system equipped with a screw conveyor that evenly distributed the feedstock of sunflower heads on the entire length of the threshing roller. The machine was tested to assess the seed damage rate, unthreshed seed percentage, threshing efficiency, machine productivity, power requirements and Citation: Ali, K.A.M.; Zong, W.; specific energy consumption. The evaluation was done under different roller rotational speeds (150, Md-Tahir, H.; Ma, L.; Yang, L. Design, 200, 250 and 300 rpm) and feeding rates (600, 700, 800 and 900 kg/h). The obtained results revealed Simulation and Experimentation of that the threshing evaluation parameters were affected significantly by the roller rotational speed an Axial Flow Sunflower-Threshing and feeding rate. The threshing efficiency was observed to rise with the rise in the roller rotational Machine with an Attached Screw speed, and it also rose with the increasing feed rate up to 800 kg/h and then started to descend. The Conveyor. Appl. Sci. 2021, 11, 6312. unthreshed seed percentage decreased with the increase in the roller rotational speed for all feed rates, https://doi.org/10.3390/app11146312 and it decreased with the increasing feed rate up to 800 kg/h and then started to increase at the higher

Academic Editor: Nathan J. Moore feed rates. The damaged seed percentage, power requirement and machine productivity increased with the increase of the roller speed and feed rate. The Buckingham π theorem was followed to find 2 Received: 10 June 2021 an equation to predict the threshing efficiency, resulting in an equation with an R value of 0.9309. Accepted: 6 July 2021 With elimination of the blockage problem and better threshing efficiency, this machine could be a Published: 8 July 2021 good choice for small- to medium-sized sunflower farms.

Publisher’s Note: MDPI stays neutral Keywords: stationary thresher machines; axial flow thresher; screw conveyor; sunflower thresher; with regard to jurisdictional claims in performance efficiency published maps and institutional affil- iations.

1. Introduction Sunflower (Helianthus annuus L.) is one of the vital oilseed crops, grown throughout Copyright: © 2021 by the authors. the world since 4000 years ago as a source of edible oil and dietary fiber that significantly Licensee MDPI, Basel, Switzerland. enhances human health as well as livestock feed [1,2]. China plays a central role in the This article is an open access article international production of sunflower oilseed crops. In 2018, the sunflower planting area distributed under the terms and in China reached 880,000 ha with 2.42 million tons of production, mainly distributed in conditions of the Creative Commons the northeast, north and northwest regions [3]. At present, there is no specialized oil Attribution (CC BY) license (https:// sunflower combine harvester in China, and all existing models are modified based on rice creativecommons.org/licenses/by/ and wheat harvesters. Sunflower producers in many countries using rice or soya bean 4.0/).

Appl. Sci. 2021, 11, 6312. https://doi.org/10.3390/app11146312 https://www.mdpi.com/journal/applsci Appl. Sci. 2021, 11, 6312 2 of 13

threshing machines to thresh sunflower heads, resulting in seeds damages amounting to more than 4–10% and seed losses of 3–13%, while some threshers resulted in grain losses of 20–35% [4]. The main purposes of mechanized sunflower threshing are to replace reduced manual labor efforts to thresh sunflower in fields, reduce threshing time, raise the quality of threshed seed and increase threshing efficiency. Productivity, threshing efficiency, broken seeds, grain loss, power consumption, cleaning efficiency and specific energy are the indicators for a thresher’s performance [5]. In Ref. [6], it was made clear that the sunflower threshing process is affected directly by the feed rate, roller speed, concave clearance and thresher type. The seed loss percentage may reach 6% in the threshing or striking process [7]. The untraditional methods of threshing sunflowers depend upon striking, friction and concurrent striking with friction [8]. The authors of [9] made and tested a rubbing thresher machine to thresh flax and sunflower crops. The performance of the rubbing threshing machine was estimated at different threshing roller speeds, threshing belt linear speeds and concave clearances. The data showed that for the two crops, the threshing efficiency increased with the increase in the roller speed, and it decreased with the increase in the concave clearance. Furthermore, the authors of [10] assessed several typical sunflower thresher machines, with the axial flow design being used. Their study indicated that it is better to thresh sunflower at a cylinder revolving speed of 6.5 m/s with a head feeding rate of 1500–2000 kg/h at a seed moisture content of 30% (w/w). The authors of [11] developed a test bench thresher for sunflower heads, applying fundamental techniques used for seed threshers. The test outcomes illustrated that the best thresher operation occurred at a feed rate of 180 kg/h, a cylinder rotational speed of 500 rpm and a crop moisture content of 9–13%. The authors in [12] examined some engineering parameters (concave hole size, concave clearance and roller speed) to evaluate a rasp-bar thresher used in the sunflower threshing process. The authors of [13] designed and tested the performance of a pedal-operated sunflower thresher according to its threshing efficiency, cleaning efficiency, damaged seed quantity, machine productivity and the consumed specific energy under three levels of the pressure surface pressing on the friction roller (2.0, 4.0 and 6.0 kg/cm2), four levels of the friction roller speed (2.8, 3.7, 4.9 and 6.9 m/s), different radial curves of the pressure surface (330, 345 and 365 mm) and different resting times of the sunflower heads inside the threshing chamber (5, 10, and 15 s). The authors in [14] designed and fabricated a sunflower seed extraction machine to separate the seeds from the sunflower heads in order to overcome the problems faced by farmers during the manual threshing process. Many studies revealed that the broken grain percentage was increased with the increase in the thresher roller rotational speed while it was decreased with the increasing grain moisture content as well as unthreshed grains [15–17]. For axial flow threshers, about 80% of the crops are threshed in the first half of the threshing area, whereas just 20% of the crops are threshed in the other half [15], which may lead to decreased threshing efficiency and increased threshing power requirements, in addition to blockages and the machine sometimes ceasing to work. The authors of [18] evaluated the screw conveyor performance through its output productivity, volumetric efficiency, seed damage percentage and specific conveying energy. Their results concluded that some operation parameters affect the performance efficiency of conveyors, like the transported materials’ properties, the difference between conveying place levels, conveyor size, conveyor screw speed, conveyor length and the distance between the ends of the screw and the inner diameter of the conveyor cylinder. The authors of [19] investigated the effect of the transport distance on the power requirements for screw conveyors at various speeds., while in [20], the authors developed a sunflower threshing device to separate seeds under the influence of centrifugal and gravitational forces. Meanwhile, the authors of [21] tested the air-jet effect on a sunflower seed separating from its head in static conditions. Appl. Sci. 2021, 11, x FOR PEER REVIEW 3 of 13

gravitational forces. Meanwhile, the authors of [21] tested the air-jet effect on a sunflower seed separating from its head in static conditions. Despite China having an advanced place between other countries in sunflower planting, however, the mechanization of sunflower treatment in China is not at the desired level [22,23]. This research was conducted to design an axial flow sunflower threshing machine attached with a screw conveyor and study the effect of the roller rotational speed and feeding rate to evaluate its performance and select the optimal operation conditions. A mathematical equation was developed to simulate and predict the threshing efficiency of the machine, which helped to save time and other resources by reducing the number of field experiments.

2. Materials and Methods 2.1. Materials The current study was conducted at Taizi Town, Huangshi City, Hubei, China with the DW667 variety of sunflower oilseeds, which were harvested traditionally at a moisture content of 16.75% (w/w) for the seeds to test and evaluate the axial flow sunflower Appl. Sci. 2021, 11, 6312 3 of 13 threshing machine attached with a screw conveyor. The stationary sunflower threshing machine used in the current work had dimensions of 1650 mm, 1000 mm and 500 mm for its length, height and width, respectively, as shown in Figure 1. It consisted of the followingDespite parts: China having an advanced place between other countries in sunflower plant- 1. ing,The however, threshing the unit mechanization consisted of of three sunflower steel loop treatment bars attached in China with is not a atsteel the screw desired levelconveyor, [22,23]. with 120 degrees between each bar (Figure 2). Each loop bar was made fromThis steel research and was was 1305 conducted mm length, to design 30 mm an axialwide flowand sunflower10 mm thick, threshing containing machine 51 attachedsteel teeth with with a screw a tooth conveyor thickness and of study10 mm the and effect 15 mm of thehigh roller as shown rotational in Figure speed 3a,b. and feedingA steel rate screw to evaluate conveyor its contained performance five patches, and select with the a total optimal length operation of 1350 mm, conditions. a patch A mathematicallength of 260 equation mm and was an outer developed diameter to simulate of 310 mm, and attached predict the to loop threshing bars. There efficiency wasof thea machine,vertical gap which between helped the to highest save time point and of other the teeth resources and the by reducingouter diameter the number of the of fieldscrew experiments. equaling 15 mm to allow sunflower heads to pass between the teeth and the inner wall of the threshing unit. 2. Materials and Methods 2. The threshing box was a rectangular box with a semicircle base. It contained the 2.1. Materials threshing unit and a feed opening 335 mm in length and 250 mm wide, and it also hadThe an current outlet hole study below was the conducted next end at of Taizi the Town,box with Huangshi dimensions City, of Hubei, 335 × 200 China mm. with 3. theThe DW667 mainframe variety was of sunflower constructed oilseeds, from 45-mm which weresquare harvested steel pipes traditionally to carry the at threshing a moisture contentbox, threshing of 16.75% (unit,w/w )power for the source seeds to and test po andwer evaluate transmission the axial system. flow sunflower The power threshing was machine attached with a screw conveyor. The stationary sunflower threshing machine transmitted from a three-phase electric motor (3 kW and 1700 rpm) to the threshing used in the current work had dimensions of 1650 mm, 1000 mm and 500 mm for its length, unit by two aluminum pulleys and a V-belt with a reducing gearing ratio of 0.50 height and width, respectively, as shown in Figure1. It consisted of the following parts: between the motor and roller.

(a) (b)

Figure 1. Designed model (a) and prototype (b) of the sunﬂower threshing machine, consisting of the following functional parts: the power source (1), power transmission system (2), feed opening (3), cover (4), threshing box (5), output opening and tray (6) and thresher frame (7).

The threshing unit consisted of three steel loop bars attached with a steel screw conveyor, with 120 degrees between each bar (Figure2). Each loop bar was made from steel and was 1305 mm length, 30 mm wide and 10 mm thick, containing 51 steel teeth with a tooth thickness of 10 mm and 15 mm high as shown in Figure3a,b. A steel screw conveyor contained ﬁve patches, with a total length of 1350 mm, a patch length of 260 mm and an outer diameter of 310 mm, attached to loop bars. There was a vertical gap between the highest point of the teeth and the outer diameter of the screw equaling 15 mm to allow sunﬂower heads to pass between the teeth and the inner wall of the threshing unit. The threshing box was a rectangular box with a semicircle base. It contained the threshing unit and a feed opening 335 mm in length and 250 mm wide, and it also had an outlet hole below the next end of the box with dimensions of 335 × 200 mm. The mainframe was constructed from 45-mm square steel pipes to carry the threshing box, threshing unit, power source and power transmission system. The power was transmitted from a three-phase electric motor (3 kW and 1700 rpm) to the threshing unit by two aluminum pulleys and a V-belt with a reducing gearing ratio of 0.50 between the motor and roller. Appl.Appl. Sci.Sci. 20212021,, 1111,, xx FORFOR PEERPEER REVIEWREVIEW 44 ofof 1313

FigureFigure 1.1. DesignedDesigned modelmodel ((aa)) andand prototypeprototype ((bb)) ofof thethe sunflowersunflower threshingthreshing machine,machine, consistingconsisting ofof Appl. Sci. 2021, 11, 6312 thethe followingfollowing functionalfunctional parts:parts: thethe powerpower sourcesource (1(1),), powerpower transmissiontransmission systemsystem (2),(2), feedfeed openingopening4 of 13 (3),(3), covercover (4),(4), threshingthreshing boxbox (5),(5), outputoutput opopeningening andand traytray (6)(6) andand thresherthresher frameframe (7).(7).

((aa)) ((bb)) FigureFigureFigure 2.2. 2. DesignedDesignedDesigned modelmodel model ((a (aa)) ) andand and prototypeprototype prototype ((b (bb)) ) ofof of thethe the threshingthreshing threshing rollerroller roller andand and thethe the screwscrew screw conveyor,conveyor, conveyor, showingshowing showing thethe the looploop loop threshingthreshing threshing barbarbar (1),(1), (1), thethe the screwscrew screw conveyorconveyor conveyor (2)(2) (2) anan anddd thethe the mainmain main threshingthreshing threshing shaftshaft (3).(3).

((aa)) ((bb))

FigureFigureFigure 3.3. 3. ((aa()a) )TheThe The looploop loop threshingthreshing threshing barbar bar andand and ((b (bb)) ) aa a threshingthreshing threshing tooth.tooth. tooth.

TheTheThe rollerroller roller rotationalrotational rotational speedspeed speed waswas was determineddetermined determined byby by aa a digitaldigital digital tachometertachometer tachometer withwith with anan an accuracyaccuracy accuracy ofofof ±0.05%±0.05%±0.05% ++ 1,+1, 1,rangingranging ranging fromfrom from 11 to 1to to 19,99919,999 19,999 rprp rpmmm (Shenzhen(Shenzhen (Shenzhen VictorVictor Victor Hi-THi-T Hi-Techechech Co,Co, Co, Ltd.;Ltd.; Ltd.; DM6234PDM6234P DM6234P+++;; ; Guangzhou,Guangzhou,Guangzhou, Shenzhen,Shenzhen, Shenzhen, China).China). China). AnAn An electricalelectrical electrical speedspeed speed converterconverter converter waswas was usedused used toto to controlcontrol control thethe the motormotormotor revolvingrevolvingrevolving speed, speed,speed, which whichwhich led toledled controlling toto controllingcontrolling the roller thethe rotational rollerroller rotational speed.rotational A CALDIPREE speed.speed. AA CALDIPREECALDIPREEBM822A digital BM822ABM822A DC/AC digitaldigital clamp DC/ACDC/AC meter clampclamp and mete multi-metermeterr andand multi-metermulti-meter (Shenzhen (Shenzhen(Shenzhen Binjiang Electronic BinjiangBinjiang ElectronicElectronicTechnology TechnologyTechnology Co, Ltd.; BM822A, Co,Co, Ltd.;Ltd.; Guangzhou, BM822A,BM822A, GuGu Shenzhen,angzhou,angzhou, China) Shenzhen,Shenzhen, capable China)China) of measuring capablecapable theofof measuringmeasuringvoltage in thethe volts voltagevoltage (V), current inin voltsvolts in(V),(V), amperes currentcurrent in(A)in amperesamperes and resistance (A)(A) andand inresistanceresistance ohms ( Ω inin) ohmsohms with a((ΩΩ current)) withwith aaaccuracy currentcurrent accuracyaccuracy of ±2% A ofof was ±2%±2% used AA waswas to measure usedused toto thememeasureasure current thethe (A) currentcurrent to the (A)(A) power toto thethe source powerpower (motor) sourcesource to (motor)(motor)determine toto determinedetermine the required thethepower requiredrequired for powerpower the threshing forfor thethe threshing process.threshing process.process. 2.2. Methods 2.2.2.2. MethodsMethods 2.2.1. Experiments Design 2.2.1.2.2.1. ExperimentsExperiments DesignDesign The platform was tested under four roller rotational speeds (150, 200, 250 and 300 rpm The platform was tested under four roller rotational speeds (150, 200, 250 and 300 (1.39,The 2.77, platform 3.47 and was 4.2 m/s))tested and under four four levels roller of feeding rotational rates speeds (10, 11.66, (150, 13.33 200, and 250 15 and kg/min) 300 rpm (1.39, 2.77, 3.47 and 4.2 m/s)) and four levels of feeding rates (10, 11.66, 13.33 and 15 rpmwere (1.39, used 2.77, to achieve 3.47 and feeding 4.2 m/s)) rates ofand 600, four 700, leve 800ls and of feeding 900 kg/h, rates respectively. (10, 11.66, All 13.33 treatments and 15 kg/min) were used to achieve feeding rates of 600, 700, 800 and 900 kg/h, respectively. All kg/min)were replicated were used thrice, to achieve and the feeding threshing rates time of 600, was 700, recorded 800 and for 900 each kg/h, experimental respectively. test. All treatmentstreatments werewere replicatedreplicated thrice,thrice, andand ththee threshingthreshing timetime waswas recordedrecorded forfor eacheach experimentalexperimental2.2.2. Theoretical test.test. Equations Threshing Force 2.2.2.2.2.2. TheoreticalTheoretical EquationsEquations Separating seeds from, for example, pods, spikes or heads requires a detachment force ThreshingThreshingF, which can ForceForce be expressed as a function of the cylinder’s linear speed, the friction coefﬁcient betweenSeparatingSeparating crop parts seedsseeds and from,from, the friction forfor example,example, coefﬁcient pods,pods, between spikesspikes the oror crops headsheads and requiresrequires the thresher aa detachmentdetachment parts [24]: forceforce F,F, whichwhich cancan bebe expressedexpressed asas aa functionfunction ofof thethe cylinder’scylinder’s linearlinear speed,speed, thethe frictionfriction F = Fc + Fr (1)

where F is the total threshing force (N), Fc is the cylinder’s impact force (N) and Fr represents the friction forces. Appl. Sci. 2021, 11, 6312 5 of 13

The cylinder impact force can be calculated as a function of the feeding rate and the crop linear speed inside the threshing unit with the following equation [8]:

Fc = q(v 2 − v1) (2)

where q is the crop feeding rate in kg/s, v2 is the crop speed at the end of the cylinder in m/s and v1 is the crop speed as it enters the cylinder in m/s. Usually, v2 depends upon the cylinder’s linear speed, and it can be predicted from the following equation: v2 = a v (3) where a is an empirical ﬁgure related to the cylinder length, straw moisture content, threshing bar shape, feeding rate and physical properties of the thresher. For a thresher 0.8 m in length with a moisture content of 15–25% and a feeding rate of 12,600 kg/h, the coefﬁcient a was determined equal to 0.70–0.85 [25], and v is the linear speed of the cylinder:

Fr = f F (4)

where f is a coefﬁcient for the rasp-bar thresher type, which is equal to (0.65–0.75) [8], and F is the force needed for threshing crops (i.e., the total threshing force) [26]. By inserting Equations (2)–(4) into Equation (1), the resulting equation is as follows:

F = q (a v − v1) + f F (5)

The required threshing force to overcome the seed’s attachment force can be calculated from Equation (6). According to this equation, the diameter of the threshing roller and the critical roller rotational speed are estimated, as well as the range of the feeding rate. It was taken into account that the directed force of the seeds should not exceed 8.5 N (the lowest average breaking force for under-studying seed at the same moisture content, which was determined by using a TMS-PRO texture analyzer device (Spectronic CamSpec Ltd., TMS-PRO, Chicago, IL, USA)): q(av − v ) F = 1 (6) 1 − f The following equation is used to determine the suitable diameter of the steel shafts with almost no axial load [26], and it was designed with a safety factor of 3.81: q 3 16 n 2 2 d = (Kt Mt) + (Kb Mb) (7) πτmax

where n is a safety factor, τmax is the allowable stress (40–55 MPa), Kt and Kb are the combined shock and fatigue factors applied to bending and torsional moment, respectively, Mt is the torsional moment (N.mm) and Mb is the bending moment (N.mm). Kb = 1.2–2.0, and Kt = 1.0–1.5 [26].

The Seed Damage Percentage The seed damage percentage was measured from the following equation:

d Seed damage percentage = × 100 (8) t where d is the mass of the damaged seed (g) and t is the total mass of the sample (g).

The Percentage of Unthreshed Seed The percentage of unthreshed seed was calculated with the following equation:

Utm Utl = × 100 (9) Utm + Soutlet + dameged seed Appl. Sci. 2021, 11, 6312 6 of 13

where Utl is the percentage of unthreshed seed, Utm is the mass of the unthreshed seed (g) and Soutlet is the mass of the threshed seeds at the main seed outlet.

Threshing Efﬁciency By knowing the damaged seed percentage and unthreshed seed percentage (total seed losses), the threshing efﬁciency can be calculated from the following equation:

Threshing ef ficiency % = 100 − total seed losses (10)

Thresher Productivity (kg/h) The thresher’s working productivity was calculated by using the recorded threshed quantity of sunflower heads and experiment running time according to the following equation:

S × 3600 Thresher productivity = w (11) T

where Sw is the mass of the threshed sunﬂower heads (kg) and T is the threshing time (s).

Power Requirements For three-phase motors, by measuring the average value of the current line (in amperes) going to power source and the recorded voltage, the consumed power can be calculated by inserting these values in the following equation [27]: √ 3 I.V. η cos θ P = (12) 1000 where P is the power requirements (kW), I is the line current strength in amperes (A), V is the potential difference (V), which was equal to 380 V, η is the√ mechanical efficiency, which was assumed to be 95%, cos θ is the power factor (85%) and 3 is the coefficient of consumed three-phase current (η, cos θ motor specifications).

The Speciﬁc Energy The speciﬁc consumed energy (kW.h/ton) was calculated according to the following equation: consumed power ∗ 1000 specific energy = (13) Productivity Randomized complete block design (RCBD) analysis was conducted to design and analyze the experiments, with three replicates for each treatment and making use of the SPSS software program (SPSS Inc., version 20, Chicago, IL, USA), following the two-way ANOVA test method with the L.S.D at a 5% probability level.

Mathematical Modeling According to Buckingham’s π theorem, the following dimensionless groups were obtained to predict the threshing efficiency during the threshing process: π = η π = vT π = FRT η v 1 , 2 L and 3 L3 ρ , where is the threshing efficiency, is the roller speed (m/s), T is the threshing time (s), L is the roller length (m), FR is the feed rate (kg/s) and ρ is the sunflower bulk density (kg/m3).

threshing time (s), L is the roller length (m), FR is the feed rate (kg/s) and 𝜌 is the sunflower bulk density (kg/m3).

3. Results and Discussion 3.1. Effect of the Roller’s Rotational Speed on the Damaged Seed Percentage at Different Feed Rates The experimental results obtained from the current study are represented by line charts. As is shown in Figure 4, the damaged seed percentage increased from 0.36% to Appl. Sci. 2021, 11, 6312 0.88%, 0.46% to 0.98%, 0.73% to 1.15% and 0.92% to 1.28% with the increase of the roller’s7 of 13 rotational speed to 150, 200, 250 and 300 rpm for 600 kg/h, 700 kg/h, 800 kg/h and 900 kg/h feed rates, respectively. At higher roller rotational speeds, the threshing bars struck the sunflowerstruck the heads sunﬂower and seeds heads more and strongly, seeds more breaking strongly, more breaking seeds, morewhich seeds, was why which higher was speedswhy higher resulted speeds in higher resulted damaged in higher seed damaged percentages. seed percentages. The results The of resultsthe seed of damage the seed percentagedamage percentage of this study of this coincided study coincided with withthose those in previous in previous studies studies [8,28], [8,28 ],while while the the accumulationaccumulation of of sunflower sunﬂower heads heads inside inside the the thre threshingshing box box at at high high feed feed rates rates also also led led to to a a riserise in in the the broken broken seed seed percentage. percentage.

1.4 at 600 kg/h at 700 kg/h at 800 kg/h at 900 kg/h

1.2

1.0

0.8

0.6

0.4

0.2 Damaged seed percentage (%) 0.0 100 150 200 250 300 350 Roller rotational speed (rpm)

FigureFigure 4. Effect 4. Effect of the of theroller’s roller’s rotational rotational speed speed (rpm) (rpm) on the on thedamaged damaged seed seed percentage percentage (%) (%)at different at different feeding feeding rates rates.

3.2.3.2. Effect Effect of of the the Roller’s Roller’s Rotational Rotational Speed Speed on on the the Unthreshed Unthreshed Seed Seed Percentage Percentage at at Different Different Feed RatesFeed Rates TheThe unthreshed seedseed percentagepercentage decreased decreased with with the the increase increase of roller of roller rotational rotational speed speedfor all for feeding all feeding rates. rates. It decreased It decreased from 3.67%from 3.67% to 2.09%, to 2.09%, 3.11% 3.11% to 1.65%, to 1.65%, 2.55% 2.55% to 1.21% to and 2.87% to 1.47% with increasing roller rotational speeds of 150, 200, 250 and 300 rpm 1.21% and 2.87% to 1.47% with increasing roller rotational speeds of 150, 200, 250 and 300 at feed rates of 600 kg/h, 700 kg/h, 800 kg/h and 900 kg/h, respectively, as shown rpm at feed rates of 600 kg/h, 700 kg/h, 800 kg/h and 900 kg/h, respectively, as shown in in Figure5). These results were in agreement with previous studies [ 8] in the same Figure 5). These results were in agreement with previous studies [8] in the same operational conditions, while the obtained data of that study showed that the unthreshed operational conditions, while the obtained data of that study showed that the unthreshed seed decreased with the increase of the feed rate from 600 kg/h to 800 kg/h and then seed decreased with the increase of the feed rate from 600 kg/h to 800 kg/h and then increased with the increase of the feed rate from 800 kg/h to 900 kg/h. The increase increased with the increase of the feed rate from 800 kg/h to 900 kg/h. The increase in the in the roller’s rotational speed may lead to increased sunflower head friction with the roller’s rotational speed may lead to increased sunflower head friction with the threshing threshing bars and the threshing box wall, increasing the sunflower heads’s contact with bars and the threshing box wall, increasing the sunflower heads’s contact with each other each other and leading to a reduction of the unthreshed seed percentage. On the other and leading to a reduction of the unthreshed seed percentage. On the other hand, hand, increasing the feed rate also led to an increase in the friction action between the increasingsunflower the heads feed up rate to also a limited led to point. an increase in the friction action between the sunflower heads up to a limited point. 3.3. Effect of the Roller’s Rotational Speed on the Threshing Efficiency at Different Feed Rates As is represented in Figure6, the threshing efficiency increased with the increase in the roller’s rotational speed. It also increased with the increase of the feed rate from 600 kg/h to 800 kg/h, but it began to decrease with the feed rate increasing from 800 kg/h to 900 kg/h. The threshing efficiency increased from 95.98% to 97.03%, 96.43% to 97.37%, 96.72% to 97.64% and 96.21% to 97.25% for feed rates of 600 kg/h, 700 kg/h, 800 kg/h and 900 kg/h, respectively, which was in line with previous studies [8,28]. These results recorded a high threshing efficiency compared with the reported results [4]. The threshing efficiency was calculated from Equation (9), which included the unthreshed seed and damaged seed percentages. As the quantity of unthreshed seed was more than the damaged seed, the threshing efficiency was more highly affected by the unthreshed seed percentage than the damaged seed percentage. Appl. Sci. 2021, 11, x FOR PEER REVIEW 8 of 13

4.5 4.0 at 600 kg/h at 700 kg/h at 800 kg/h at 900 kg/h 3.5 3.0 2.5 2.0 1.5 1.0 Appl.Appl. Sci. Sci. 20212021, ,1111, ,x 6312 FOR PEER REVIEW 88 of of 13 13 0.5 Unthreshed seed percentage (%) Unthreshed seed percentage 0.0 100 150 200 250 300 350 4.5 Roller rotational speed (rpm) 4.0 at 600 kg/h at 700 kg/h at 800 kg/h at 900 kg/h

Figure 5. Effect of the roller’s3.5 rotational speed (rpm) on the unthreshed seed percentage (%) at different feed rates (kg/h). 3.0 3.3. Effect of the Roller’s Rotational Speed on the Threshing Efficiency at Different Feed Rates 2.5 As is represented in Figure 6, the threshing efficiency increased with the increase in 2.0 the roller’s rotational speed. It also increased with the increase of the feed rate from 600 1.5 kg/h to 800 kg/h, but it began to decrease with the feed rate increasing from 800 kg/h to 900 kg/h. The threshing efficiency increased from 95.98% to 97.03%, 96.43% to 97.37%, 1.0 96.72% to 97.64% and 96.21% to 97.25% for feed rates of 600 kg/h, 700 kg/h, 800 kg/h and 0.5 900 kg/h, respectively, which was in line with previous studies [8,28]. These results Unthreshed seed percentage (%) Unthreshed seed percentage 0.0 recorded a high threshing efficiency compared with the reported results [4]. The threshing 100efficiency was 150 calculated from 200 Equation (9 250), which included 300 the unthreshed 350 seed and damaged seed percentages. As the quantity of unthreshed seed was more than the damaged seed, the threshingRoller efficiency rotational was speed more (rpm) highly affected by the unthreshed seed

Figure 5. Effect of thepercentage roller’s rotational than the speed damaged (rpm) on seed the unthreshed percentage. seed percentage (%) at different feed rates (kg/h). Figure 5. Effect of the roller’s rotational speed (rpm) on the unthreshed seed percentage (%) at different feed rates (kg/h).

97.8 3.3.at Effect 600 kg/hof the Roller’s Rotaat 700tional kg/h Speed on the atThreshing 800 kg/h Efficiency atat Different 900 kg/h Feed Rates 97.6 As is represented in Figure 6, the threshing efficiency increased with the increase in 97.4 the roller’s rotational speed. It also increased with the increase of the feed rate from 600 97.2 kg/h to 800 kg/h, but it began to decrease with the feed rate increasing from 800 kg/h to 97.0 900 kg/h. The threshing efficiency increased from 95.98% to 97.03%, 96.43% to 97.37%, 96.8 96.72% to 97.64% and 96.21% to 97.25% for feed rates of 600 kg/h, 700 kg/h, 800 kg/h and 96.6 900 kg/h, respectively, which was in line with previous studies [8,28]. These results 96.4 recorded a high threshing efficiency compared with the reported results [4]. The threshing 96.2 efficiency was calculated from Equation (9), which included the unthreshed seed and Threshing efficiency (%) Threshing efficiency damaged seed percentages. As the quantity of unthreshed seed was more than the 96.0 damaged seed, the threshing efficiency was more highly affected by the unthreshed seed 95.8 percentage than the damaged seed percentage. 100 150 200 250 300 350 Roller rotational speed (rpm) 97.8 at 600 kg/h at 700 kg/h at 800 kg/h at 900 kg/h FigureFigure 6. Effect 6. Effectof the97.6 ofroller’s the roller’s rotational rotational speed speed(rpm) (rpm)on the on threshing the threshing efficiency efﬁciency (%) at(%) different at different feed rates feed (kg/h). rates (kg/h). 97.4 3.4. Effect of the Roller’s Rotational Speed on the Machine’s Productivity at Different Feed Rates 97.2 3.4. Effect of the Roller’s Rotational Speed on the Machine’s Productivity at Different Feed Rates Figure 7 explains that the sunflower threshing machine’s output productivity was 97.0 Figure7 explains that the sunﬂower threshing machine’s output productivity was increased with the increase of both the roller’s rotational speed and feeding rate. This 96.8 increased with the increase of both the roller’s rotational speed and feeding rate. This result resultagreed agreed with with [29 [29]] for for the the same same range rang of operationale of operational conditions. conditions. The machine’s The machine’s productivity 96.6 increased from 522.16 kg/h to 592.34 kg/h, 618.24 kg/h to 692.46 kg/h, 714.30 kg/h to 96.4 785.46 kg/h and 811.35 kg/h to 880.45 kg/h when the roller’s rotational speed increased to 96.2

Threshing efficiency (%) Threshing efficiency 150 rpm, 200 rpm, 250 rpm and 300 rpm at feed rate levels of 600 kg/h, 700 kg/h, 800 kg/h 96.0 and 900 kg/h, respectively. The increase in the machine’s productivity with the increased 95.8 roller revolving speed may have been due to the action of the screw conveyor, which was 100affected directly 150 by the rotational 200 speed for 250its calculated productivity. 300 350 Roller rotational speed (rpm) Figure 6. Effect of the roller’s rotational speed (rpm) on the threshing efficiency (%) at different feed rates (kg/h).

3.4. Effect of the Roller’s Rotational Speed on the Machine’s Productivity at Different Feed Rates Figure 7 explains that the sunflower threshing machine’s output productivity was increased with the increase of both the roller’s rotational speed and feeding rate. This result agreed with [29] for the same range of operational conditions. The machine’s Appl. Sci. 2021, 11, x FOR PEER REVIEW 9 of 13

Appl. Sci. 2021, 11, x FOR PEER REVIEW 9 of 13

productivity increased from 522.16 kg/h to 592.34 kg/h, 618.24 kg/h to 692.46 kg/h, 714.30 kg/hproductivity to 785.46 increasedkg/h and from811.35 522.16 kg/h kg/h to 880.45 to 592 .34kg/h kg/h, when 618.24 the kg/hroller’s to 692.46rotational kg/h, speed 714.30 increasedkg/h to 785.46to 150 rpm,kg/h 200and rpm, 811.35 250 kg/h rpm to and 880.45 300 rpmkg/h at when feed ratethe roller’slevels of rotational 600 kg/h, speed 700 kg/h,increased 800 kg/h to and150 rpm,900 kg/h, 200 rpm,respectively. 250 rpm The and increase 300 rpm in at the feed machine’s rate levels productivity of 600 kg/h, with 700 thekg/h, increased 800 kg/h roller and 900revolving kg/h, respectively. speed may The have increase been indue the to machine’s the action productivity of the screw with Appl. Sci. 2021, 11, 6312 conveyor,the increased which roller was revolvingaffected speeddirectly may by havethe rotationalbeen due tospeed the actionfor its ofcalculated the screw9 of 13 productivity.conveyor, which was affected directly by the rotational speed for its calculated productivity. at 600 kg/h at 700 kg/h at 800 kg/h at 900 kg/h 1000 at 600 kg/h at 700 kg/h at 800 kg/h at 900 kg/h 1000 900 900 800 800 700 700 600 600 500 Machine productivtiy Machine productivtiy (kg/h) 500

Machine productivtiy Machine productivtiy (kg/h) 100 150 200 250 300 350 100 150Roller rotational 200 speed 250 (rpm) 300 350 Roller rotational speed (rpm) Figure 7. Effect of the roller’s rotational speed (rpm) on the machine’s productivity (kg/h) at different feed rates (kg/h). FigureFigure 7.7. EffectEffect ofof thethe roller’sroller’s rotationalrotational speedspeed (rpm)(rpm) onon thethe machine’smachine’sproductivity productivity (kg/h) (kg/h) at different feedfeed ratesrates (kg/h).(kg/h). 3.5. Effect of the Roller’s Rotational Speed on Power Requirements at Different Feed Rates 3.5.Figure Effect of 8 explainsthe Roller’s that Rotational the power Speed requiremen on Power t Requirements increased with at Differentthe increase FeedFeed in RatesRates both the roller’sFigure rotational8 8 explains explains speed thatthat and thethe the powerpower feeding requirementrequiremen rate. Thist increasedincreased result is withinwith line thethe with increaseincrease the in resultsin both both theinthe [28,29].roller’s With rotationalrotational the roller speedspeed rotational and and the the speeds feeding feeding increasing rate. rate. This This resultto 150 result is rpm, in is line 200in with linerpm, thewith 250 results rpmthe resultsand in [28 300,29 in ]. rpm,With[28,29]. the the powerWith roller the requirement rotational roller rotational speeds increased increasing speeds from increasing to1.68 150 kW rpm, to 1502.41 200 rpm, rpm,kW, 2.01200 250 rpm, rpmkW to and250 2.59 rpm 300 kW, rpm, and 2.42 300 the kWpowerrpm, to 3 the kW requirement power and 2.70 requirement kW increased to 3.51 increased from kW for 1.68 feed kWfrom rate to 1. 2.4168 levels kW kW, ofto 2.01 6002.41 kW kg/h, kW, to 2.592.01700 kW,kg/h,kW 2.42to 800 2.59 kW kg/h kW, to and 3 2.42 kW 900kWand kg/h, to 2.70 3 kWrespectively. kW and to 3.51 2.70 kW kWThe for to increasing feed3.51 kW rate for levelspower feed of ratere 600quirements levels kg/h, of 700 600 with kg/h, kg/h, the 800 700increase kg/h kg/h, and in800 both 900kg/h kg/h,the and roller’s900respectively. kg/h, rotational respectively. The speed increasing andThe the increasing power feeding requirements powerrate was re duequirements with to the the increased with increase the load increase in both on the thein electricboth roller’s the motor.roller’srotational rotational speed and speed the and feeding the feeding rate was rate due was to thedue increased to the increased load on load the electric on the motor.electric motor. 4.0 at 600 kg/h at 700 kg/h at 800 kg/h at 900 kg/h 4.0 at 600 kg/h at 700 kg/h at 800 kg/h at 900 kg/h

3.0 3.0

2.0 2.0

1.0

Power requirements (kW) Power requirements 1.0 Power requirements (kW) Power requirements 0.0 0.0100 150 200 250 300 350 100 150Roller rotatonal 200 speed 250 (rpm) 300 350

Roller rotatonal speed (rpm) FigureFigure 8. 8.EffectEffect of of the the roller’s roller’s rotational rotational speed speed (rpm) (rpm) on on the the power power requirements requirements (k (kW)W) at at different different feed feed rates rates (kg/h). (kg/h). Figure 8. Effect of the roller’s rotational speed (rpm) on the power requirements (kW) at different feed rates (kg/h). 3.6. Effect of the Roller’s Rotational Speed on the Specific Energy at Different Feed Rates The consumed specific energy increased with the increase of the roller’s rotational speed for all feeding rates, while the effect of the feeding rate on the consumed specific energy was non-significant, which caused an unclear impression on the diagram (Figure9 ). It is noted that the consumed specific energy increased from 3.23 kW.h/ton to 4.06 kW.h/ton, 3.27 kW.h/ton to 3.74 kW.h/ton kW, 3.40 kW.h/ton to 3.80 kW.h/ton and 3.34 kW.h/ton to 3.98 kW.h/ton with the increasing roller rotational speed of 150 rpm, 200 rpm, 250 rpm and 300 rpm at feed rate levels of 600 kg/h, 700 kg/h, 800 kg/h and 900 kg/h, respectively. The unclear influence of the feed rate on the specific energy may have been due to the specific Appl. Sci. 2021, 11, x FOR PEER REVIEW 10 of 13

3.6. Effect of the Roller’s Rotational Speed on the Specific Energy at Different Feed Rates The consumed specific energy increased with the increase of the roller’s rotational speed for all feeding rates, while the effect of the feeding rate on the consumed specific energy was non-significant, which caused an unclear impression on the diagram (Figure 9). It is noted that the consumed specific energy increased from 3.23 kW.h/ton to 4.06 kW.h/ton, 3.27 kW.h/ton to 3.74 kW.h/ton kW, 3.40 kW.h/ton to 3.80 kW.h/ton and 3.34 Appl. Sci. 2021, 11, 6312 kW.h/ton to 3.98 kW.h/ton with the increasing roller rotational speed of 150 rpm, 200 10rpm, of 13 250 rpm and 300 rpm at feed rate levels of 600 kg/h, 700 kg/h, 800 kg/h and 900 kg/h, respectively. The unclear influence of the feed rate on the specific energy may have been dueenergy, to the which specific depends energy, upon which the machine’sdepends upon productivity the machine’s and power productivity requirements, and power while requirements,the increase of while the speciﬁc the increase energy of the with specific the increasing energy with roller the rotational increasing speed roller was rotational because speedof the was rate because of the power of the requirementrate of the power rising re withquirement the increasing rising with roller the speed, increasing which roller was speed,higher which than thewas increase higher than in the the machine’s increase productivityin the machine’s rate. productivity rate.

4.2 at 600 kg/h at 700 kg/h at 800 kg/h at 900 kg/h

4.0

3.8

3.6

3.4 Spesific energy (kW.h/ton) 3.2

3.0 150 200 250 300 Roller rotation epeed (rpm) FigureFigure 9. 9. EffectEffect of of the the roller’s roller’s rotational rotational speed speed (rpm) (rpm) on on the the specific speciﬁc energy energy (kg.h/ton) (kg.h/ton) at at different different feedfeed rates rates (kg/h). (kg/h).

3.7.3.7. Statistical Statistical Analysis Analysis TableTable 11 represents represents the the analysis analysis of variance of variance for the for significance the significance of the study of parametersthe study parametersin relation in to relation the performance to the performance of the sunflower of the sunflower threshing threshing machine. machine. It is clear It thatis clear the thatdamaged the damaged seed percentage seed percentage was affected was affected significantly significantly at the at probabilitythe probability level level of of 1% 1% by byincreasing increasing both both the the roller’s roller’s rotational rotational speed speed and theand feed the rate. feed A rate. higher A effecthigher was effect recorded was recordedfor the feedfor the rate feed than rate the roller’sthan the rotational roller’s rotational speed, while speed, the while effect the of the effect interaction of the interactionbetween the between feed rate the and feed the rate rotational and the speed rotational was non-significant. speed was non-significant. The unthreshed The seed unthreshedwas affected seed significantly was affected at asignificantly probability levelat a probability of 1% by both level the of roller’s1% by both rotational the roller’s speed rotationaland the feed speed rate, and with the a feed greater rate, effect with for a greater the roller’s effect rotational for the roller’s speed thanrotational the feed speed rate thanand the without feed arate significant and without effect a for significant the interaction effect betweenfor the interaction the roller’s between revolving the speed roller’s and revolvingthe feed rate.speed The and threshing the feed efficiency rate. The wasthreshin affectedg efficiency significantly was ataffected a probability significantly level of at 1%a probabilityby both of thelevel study of 1% variables, by both with of the a greater study impactvariables, from with the roller’sa greater rotational impact speedfrom thanthe roller’sthe feed rotational rate, while speed the interaction than the betweenfeed rate, the while study the variables interaction had a non-significantbetween the study effect on the threshing efficiency. The machine’s productivity was influenced remarkably at a variables had a non-significant effect on the threshing efficiency. The machine’s probability of 1% by the roller’s rotating speed and the feeding rate, with a high effect from productivity was influenced remarkably at a probability of 1% by the roller’s rotating the feed rate. Otherwise, the effect of the interaction between the feed rate and the roller’s speed and the feeding rate, with a high effect from the feed rate. Otherwise, the effect of revolving speed had no significant effect. The power requirement was affected significantly the interaction between the feed rate and the roller’s revolving speed had no significant at a probability of 1% by the feed rate and the roller’s rotational speed, with a significance effect. The power requirement was affected significantly at a probability of 1% by the feed level for the feed rate greater than the roller’s rotational speed, while the effect of the rate and the roller’s rotational speed, with a significance level for the feed rate greater than interaction between the feed rate and the roller’s rotational speed was non-significant. The obtained data show that the specific energy was affected significantly at a probability level of 1% by the roller’s rotational speed values, while the effect of the feed rate and the interaction between the roller’s rotational speed and the feed rate was non-significant. The obtained data represented that the operational conditions of 300 rpm with 800 kg/h recorded the highest threshing efficiency, a close value to the lowest consumed specific energy and the closest value to the highest production efficiency. Therefore, this operation conditions was considered the optimal operation condition. Appl. Sci. 2021, 11, x FOR PEER REVIEW 11 of 13

the roller’s rotational speed, while the effect of the interaction between the feed rate and the roller’s rotational speed was non-significant. The obtained data show that the specific energy was affected significantly at a probability level of 1% by the roller’s rotational speed values, while the effect of the feed rate and the interaction between the roller’s rotational speed and the feed rate was non-significant. The obtained data represented that the operational conditions of 300 rpm with 800 kg/h recorded the highest threshing efficiency, a close value to the lowest consumed specific energy and the closest value to Appl. Sci. 2021, 11, 6312 11 of 13 the highest production efficiency. Therefore, this operation conditions was considered the optimal operation condition.

TableTable 1. 1.AnalysisAnalysis of ofvariance variance for for the the effectiveness effectiveness of ofthe the study study parameters parameters on on the the performance performance of ofthe the sunflower sunflower threshing threshing machine.machine. F Value Source of F Value df Damagedd f Unthreshed Threshing Power VariationSource of Variation Damaged Unthreshed Threshing Power Re- Specific Productivity Productivity Specific Energy Seed SeedSeed EfficiencySeed Efficiency Requirementquirement Energy Replication 3 Replication 3 Roller speedRoller A speed 3 A 189.192 ** 3 218.947 189.192 ** ** 99. 218.947361 ** ** 21.73499.361 **** 21.734 142.358 ** ** 142.358 ** 15.666 15.666 ** ** Feed rateFeed B rate B 3 237.355 ** 3 101.616 237.355 ** ** 37.474 101.616 ** ** 325.654 37.474 ** ** 325.654 365.822 ** ** 365.822 ** 1.092 1.092ns ns ns ns ns ns ns ns A × B A × B 9 1.407 ns 91.877 1.407 ns 1.6251.877 ns 1.6250.032 ns 0.0321.26 ns 1.26 0.414 0.414ns Error Error32 32 ns ** Significant** Significant at a level at a level of 1%. of 1%. * Significant * Significant at at a alevel level of of 5%. ns Non-significant.Non-significant.

3.8.3.8. Mathematical Mathematical Modelin Modelingg for forThreshing Threshing Efficiency Efficiency TheThe most most important important evaluation evaluation parameter parameter for for threshing threshing machines machines is isthe the threshing threshing efficiency.efficiency. In Inthis this study, study, the the Buckingham Buckingham π πtheoremtheorem was was followed followed to tofind find an an equation equation connectingconnecting the the factors factors affecting affecting the the threshing threshing process process to topredict predict the the threshing threshing efficacy. efficacy. ThisThis will will help help to toreduce reduce the the number number of offield field experiments experiments that that are are necessary necessary to toassess assess the the threshingthreshing efficiency efficiency [30]. [30 The]. The following following innovative innovative mathematical mathematical equation equation simulates simulates the the threshingthreshing process process for for calculating calculating the the threshing threshing efficiency: efficiency:

2 vT𝑣𝑇 𝐹F𝑇T 𝐹F𝑇 T ηη= =0.00015 0.00015( ) ++ (−753.08 (−753.08 R ++ 21.16521.165 R + 0.8124+ 0.8124 (14) (14) L𝐿 𝐿L3 𝜌ρ 𝐿L 𝜌3 ρ

FigureFigure 10 10 presents presents the relationrelation between between the the observed observed and and predicted predicted threshing threshing efﬁcien- 2 efficienciescies with with a correlation a correlation coefﬁcient coefficient R2 of R 0.9309. of 0.9309.

0.98 0.98 R² = 0.9309 0.97 0.97 0.96 0.96 Predicted efficiency (%) Predicted efficiency 0.96 0.96 0.97 0.97 0.98 0.98 Observed efficency (%)

Figure 10. The relationship between the observed and predicted threshing efficiencies (%). Figure 10. The relationship between the observed and predicted threshing efficiencies (%). 4. Conclusions 4. 1.ConclusionsThe thrreshing efficiency increased with the increase in the roller’s rotational speed 1. Theand thrreshing feed rate efficiency up to a feed increased rate level with of 800the increase kg/h. The in maximumthe roller’s threshing rotational efficiency speed and(97.64%) feed rate was up recordedto a feed rate at a level roller of rotational 800 kg/h. speedThe maximum of 300 rpm threshing and a feedefficiency rate of 800 kg/h. The power requirements and machine productivity increased with the increases of both the roller’s rotational speed and the feed rate. The maximum power consumption value (3.51 kW) and maximum machine productivity value (880.45 kg/h) were recorded at a 300 rpm roller rotational speed and a 900 kg/h feed rate. 2. Because it recorded the highest threshing efficiency (97.64%) and the closest value of the lowest consumed specific energy (3.80 kW.h/ton), the operational condition of 300 rpm roller rotational speed with 800 kg/h feed rate was considered as the optimal operation condition. Appl. Sci. 2021, 11, 6312 12 of 13

2 η = vT + (− FRT + FRT + 3. The equation of 0.00015 L 753.08 L3 ρ 21.165 L3 ρ 0.8124 can be used to predict the threshing efficiency of the machine under examination with a correlation coefficient of 0.9309. 4. With better threshing efficiency, the newly designed sunflower threshing machine with the new add-on of a screw conveyer to avoid blockage problems, compared with the rice and soya bean threshing machines used in threshing sunflower crops, is considered suitable threshing equipment for farmers who have small- and medium- sized sunflower cultivation areas.

Author Contributions: Conceptualization, W.Z. and K.A.M.A.; methodology, K.A.M.A.; software, L.Y.; validation, W.Z., L.M. and K.A.M.A.; formal analysis, K.A.M.A.; investigation, W.Z.; resources, L.Y.; data curation, K.A.M.A.; writing—original draft preparation, K.A.M.A.; writing—review and editing, H.M.-T.; visualization, L.M.; supervision, W.Z.; project administration, W.Z.; funding acquisi- tion, W.Z. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the National Key Research and Development, grant number 2016YFD0702104. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available on demand from the first author at ([email protected]). Conflicts of Interest: The authors declare no conflict of interest.

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