702 插秧機系統(tǒng)設計

702 插秧機系統(tǒng)設計,插秧機,系統(tǒng),設計 performance,form17pressurecomparing the performance of a double inlet cyclone withPowder Technology 145 (2004)operation. However, the increasing emphasis on environ-ment protection and gas–solid separation is indicating thatfiner and finer particles must be removed. To meet thischallenge, the improvement of cyclone geometry and per-formance is required rather than having to resort to alterna-tive units. Many researchers have contributed to largevolume of work on improving the cyclone performance,by introducing new inlet design and operation variables.These include studies of testing a cyclonic fractionator forresearchers, was developed, and the experimental study onaddressing the effect of inlet type on cyclone performanceswas presented.2. ExperimentalThree kinds of cyclone separators with various inletgeometries, including conventional tangential single inlethave became one of most important particle removal devicethat preferably is utilized in both engineering and processclean air by Lim et al. [6]. In this paper, the new inlet type,which is different type of inlet from that used by formersimplicity to fabricate, low cost to operate, and well adapt-ability to extremely harsh conditions, cyclone separatorsKeywords: Cyclone; Symmetrical spiral inlet; Collection efficiency; Pressure drop1. IntroductionCyclone separators are widely used in the field of airpollution control and gas–solid separation for aerosolsampling and industrial applications [1]. Due to relative[2], developing a mathematic model to predict the collectionefficiency of small cylindrical multiport cyclone by DeOtte[3], testing a multiple inlet cyclones based on Lapple’ typegeometry by Moore and Mcfarland [4], designing andtesting a respirable multiinlet cyclone sampler that minimizethe orientation bias by Gautam and Streenath [5],andparticle size and flow rate in this paper. Experimental result indicated that the symmetrical spiral inlet (SSI), especially CSSI inletgeometry, has effect on significantly increasing collection efficiency with insignificantly increasing pressure drop. In addition, theresults of collection efficiency and pressure drop comparison between the experimental data and the theoretical model were alsoinvolved.Short communiDevelopment of a symmetricalcyclone separatorBingtao Zhao*, HenggenDepartment of Environmental Engineering, Donghua UniversityReceived 28 October 2003; received in revisedAvailable onlineAbstractThree cyclone separators with different inlet geometry were designed,direct symmetrical spiral inlet (DSSI), and a converging symmetricalperformance characteristics, including the collection efficiency andsampling that used multiple inlet vanes by Wedding et al.* Corresponding author. Tel.: +86-21-62373718; fax: +86-21-62373482.E-mail address: zhaobingtao@mail.dhu.edu.cn (B. Zhao).Shen, Yanming KangNo. 1882, Yanan Rd., Shanghai, Shanghai 200051, China24 February 2004; accepted 3 June 2004July 2004which include a conventional tangential single inlet (CTSI), aspiral inlet (CSSI). The effects of inlet type on cyclonedrop, were investigated and compared as a function ofcationspiral inlet to improve47–50(CTSI), direct symmetrical spiral inlet (DSSI), and converg-ing symmetrical spiral inlet (CSSI), were manufactured andstudied. The geometries and dimensions these cyclones arepresented in Fig. 1 and Table 1. To examine the effects ofinlet type, all other dimensions were designed to remain thesame but only the inlet geometry.The pressure drops were measured between two pressuretaps on the cyclone inlet and outlet tube by use of a digitalby 0.15–1.15% and 0.40–2.40% in the tested velocityrange.Fig. 4(a)–(d) compares the grade collection efficiency ofthe cyclones with various inlet types at the flow rate of3Fig. 2. Schematic diagram of experimental system setup.B. Zhao et al. / Powder Technology 145 (2004) 47–5048micromanometer (SINAP, DP1000-IIIC). The collectionefficiency was calculated by the particle size distribution,by use of microparticle size analyzer (SPSI, LKY-2). Due tohaving the same symmetrical inlet in Model B or C, the flowrate of each inlet of multiple cyclone was equal to anotherand controlled by valve; two nozzle-type screw feeders wereused in same operating conditions to disperse the particleswith a concentration of 5.0 g/m3in inlet tube. The solidparticles used were talcum powder obeyed by log-normalsize distribution with skeletal density of 2700 kg/m3, mass–mean diameter of 5.97 Am, and geometric deviation of 2.08.The mean atmospheric pressure, ambient temperature, andrelative humidity during the tests were 99.93 kPa, 293 K,and less than 75%, respectively.3. Results and discussionThe experimental system setup is shown in Fig. 2.Fig. 1. Schematic diagram of cyclones geometries: (a) conventionaltangential single inlet, Model A; (b) direct symmetrical spiral inlet, ModelB; (c) converging symmetrical spiral inlet, Model C.3.1. Collection efficiencyFig. 3 shows the measured overall efficiencies of thecyclones as a function of flow rates or inlet velocities. It isusually expected that collection efficiency increase with theentrance velocity. However, the overall efficiency of thecyclone with symmetrical spiral inlet both Models B and Cwas always higher than the efficiency of the cyclone withconventional single inlet Model A at the same velocity; andespecially, the cyclone with CSSI, Model C has a highestoverall efficiency. These effects of improved inlet geometrycontribute to the increase in overall efficiency of the cycloneTable 1Dimensions of cyclones studied (unit: mm)DDehH B Sab300 150 450 1200 1125 150 150 60388.34, 519.80, 653.67, and 772.62 m /h, with the inletvelocities of11.99, 16.04,20.18, and23.85m/s,respectively.As expected, the frictional efficiencies of all the cyclonesare seen to increase with increase in particle size. Theshapes of the grade collection efficiency curves of allmodels have a so-called ‘‘S’’ shape. The friction efficienciesof the DSSI (Model B) and CSSI cyclones (Model C) aregreater by 2–10% and 5–20% than that for the CTSIcyclone (Model A), respectively. This indicates that theinlet type or geometry to the cyclone plays an importantrole in the collection efficiency. It was expected thatparticles introduced to the cyclone with symmetrical spiralinlet (Models B and C) would easily be collected on thecyclone wall because they only have to move a shortdistance, and especially, the CSSI (Model C) changes theparticle concentration distribution and makes the particlepreseparated from the gas before entering the main body ofcyclone.Fig. 5 compares the experimental data at a flow rate of653.67 m3/h (inlet velocity of 20.18 m/s) with existingclassical theories [7–11]. Apparently, the efficiency curvesbased on Mothes and Loffler’ model and Iozia and Leith’smethod match the experimental curves much closer thanother theories do. This result corresponds with the studycarried out by Dirgo and Leith [12] and Xiang et al. [13].Fig. 3. Overall efficiency of the cyclones at different inlet velocities.velocityB. Zhao et al. / Powder Technology 145 (2004) 47–50 49Fig. 4. Grade efficiency of the cyclones at different inlet velocities. (a) Inlet(d) Inlet velocity=23.85 m/s.The comparison show that some model can predict atheoretical result that closed the experimental data, but thechanges of flow pattern and particle concentration distribu-tion induced by symmetrical spiral inlet having effects oncyclone performance were not taken into account adequatelyin developed theories.To examine the effects of the symmetrical spiral inlet oncyclone performance more clearly, Fig. 6 was prepared,depicting the 50% cut size for all models with varying theflow rate or inlet velocity. The 50% cut size of Models Cand B are lower than that of Model A at the same inletFig. 5. Comparison of experimental grade efficiency with theories.=11.99 m/s. (b) Inlet velocity=16.04 m/s. (c) Inlet velocity=20.18 m/s.velocity. As the inlet velocity is decreased, the 50% cut sizeis approximately decreased linearly. With inlet velocity20.18 m/s, for example, the decrease rate of 50% cut sizeis up to 9.88% for Model B and 24.62% for Model C. Thisindicated that the new inlet type can help to enhance thecyclone collection efficiency.3.2. Pressure dropThe pressure drop across cyclone is commonly expressedas a number gas inlet velocity heads DH named the pressureFig. 6. The 50% cut size of the cyclones.inlet velocity are presented in Table 2.Obviously, higher pressure drop is associated with higherBarth5.18B. Zhao et al. / Powder Technology 145 (2004) 47–5050flow rate for a given cyclone. However, specifying a flowrate or inlet velocity, the difference of pressure drop coef-ficient between Models B, C, and A is less significant, andvaried between 5.21 and 5.76, with an average value 5.63,for Model B, 5.22–5.76, with an average value 5.67, forModel C, and 5.16–5.70, with an average value 5.55, forModel A, calculated by regression analysis. This is animportant point because it is possible to increase the cyclonecollection efficiency without increasing the pressure dropsignificantly.The experimental data of pressure drop were alsocompared with current theories [14–20], and results arepresented in Table 3. The results show that the model ofAlexander and Barth provided the better fit to theexperimental data, although for some cyclones the modelsof Shepherd and Lapple and Dirgo predicted equallywell.4. ConclusionsA new kind of cyclone with symmetrical spiral inletdrop coefficient, which is the division of the pressure dropby inlet kinetic pressure qgmi2/2. The pressure drop coeffi-cient values for the three cyclones corresponding to differentTable 2Pressure drop coefficient of the cyclonesCyclone Inlet velocity (m/s)model11.99 16.04A 5.16 5.18B 5.21 5.27C 5.22 5.35Table 3Comparison of pressure drop coefficient with theoriesTheory Shepherd Alexander First StairmandValue 6.40 5.62 6.18 5.01(SSI) including DSSI and CSSI was developed, and theeffects of these inlet types on cyclone performance weretested and compared. Experimental results show the overallefficiency the DSSI cyclone and CSSI is greater by 0.15–1.15% and 0.40–2.40% than that for CTSI cyclone, and thegrade efficiency is greater by 2–10% and 5–20%. Inaddition, the pressure drop coefficient is 5.63 for DSSIcyclone, 5.67 for CSSI, and 5.55 for CTSI cyclone. Despitethat the multiple inlet increases the complicity and the costof the cyclone separators, the cyclones with SSI, especiallyCSSI, can yield a better collection efficiency, obviously witha minor increase in pressure drop. This presents the possi-bility of obtaining a better performance cyclone by means ofimproving its inlet geometry design.References[1] Y.F. Zhu, K.W. Lee, Experimental study on small cyclones operatingat high flowrates, Aerosol Sci. Technol. 30 (10) (1999) 1303–1315.[2] J.B. Wedding, M.A. Weigand, T.A. Carney, A 10Am cutpoint inlet forthe dichotomous sampler, Environ. Sci. Technol. 16 (1982) 602–606.[3] R.E. DeOtte, A model for the prediction of the collection efficiencycharacteristics of a small, cylindrical aerosol sampling cyclone, Aero-sol Sci. Technol. 12 (1990) 1055–1066.[4] M.E. Moore, A.R. Mcfarland, Design methodology for multiple inletcyclones, Environ. Sci. Technol. 30 (1996) 271–276.[5] M. Gautam, A. Streenath, Performance of a respirable multi-inletcyclone sampler, J. Aerosol Sci. 28 (7) (1997) 1265–1281.[6] K.S. Lim, S.B. Kwon, K.W. Lee, Characteristics of the collectionefficiency for a double inlet cyclone with clean air, J. Aerosol Sci.34 (2003) 1085–1095.[7] D. 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