转盘边缘黏性薄液膜不同破碎模式临界转变特性
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摘要
液膜在离心粒化器边缘的破碎模式直接决定了雾化后的液滴形态和尺寸分布,是影响物料品质的关键因素。针对转盘粒化器,提出临界转变系数表征液膜由膜状向纤维状破碎的转变条件,并拓展至其他破碎模式,建立了滴状向纤维状、完全纤维状及纤维状向膜状破碎转变的临界关系。结果表明,转盘表面润湿性对于液膜呈滴状以及滴状向纤维状模式转变影响显著,未完全润湿导致临界流量存在一定的随机性,转盘直径与临界流量间无明确规律;而完全纤维状以及膜状时,大直径转盘临界流量明显升高。转速、流量、密度及黏度的提高,破碎模式趋向于膜状;而增大表面张力,即使对于较大流量和转速,液膜也能维持纤维状或滴状模式。调整转盘直径将引起表面张力与离心力同时变化,若未打破平衡,其破碎模式不会改变。研究结果为转盘粒化器的设计与优化提供了可借鉴的理论与应用基础。
Liquid film breakup mode at disk rim of centrifuge particle generator directly determines droplet shapes and sizes,which is a key factor to affect product qualities.A critical transition coefficient for spinning disk particle generator was proposed to characterize liquid film breakup transition characteristics from film to ligament,to extend to other breakup modes,and to establish critical equations for transition from direct droplet to ligament,ligament to fully ligament,and fully ligament to sheet.The experimental results of three working fluids and two disks indicated that disk surface wettability played key role for liquid film to become direct droplet or to transit from direct droplet to ligament,which incomplete wetting caused random critical volume flow rate with no direct correlation between disk diameter and critical volume flow rate.Critical volume flow rate increased with increasing disk diameter in fully-ligament and film modes.In general,the increase of liquid flow rate,rotation speed,liquid density,and viscosity drove towards film breakup mode.However,high surface tension force maintained liquid film in direct drop or ligament even at large flow rate and rotation speed.Moreover,increasing disk diameter enhanced both centrifugal force and surface tension and breakup mode did not change unless the force balance was lost.
Liquid film breakup mode at disk rim of centrifuge particle generator directly determines droplet shapes and sizes,which is a key factor to affect product qualities.A critical transition coefficient for spinning disk particle generator was proposed to characterize liquid film breakup transition characteristics from film to ligament,to extend to other breakup modes,and to establish critical equations for transition from direct droplet to ligament,ligament to fully ligament,and fully ligament to sheet.The experimental results of three working fluids and two disks indicated that disk surface wettability played key role for liquid film to become direct droplet or to transit from direct droplet to ligament,which incomplete wetting caused random critical volume flow rate with no direct correlation between disk diameter and critical volume flow rate.Critical volume flow rate increased with increasing disk diameter in fully-ligament and film modes.In general,the increase of liquid flow rate,rotation speed,liquid density,and viscosity drove towards film breakup mode.However,high surface tension force maintained liquid film in direct drop or ligament even at large flow rate and rotation speed.Moreover,increasing disk diameter enhanced both centrifugal force and surface tension and breakup mode did not change unless the force balance was lost.
引文
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[30]WANG D X,LING X,PENG H.Theoretical analysis of free-surface film flow on the rotary granulating disk in waste heat recovery process of molten slag[J].Applied Thermal Engineering,2014,63(1):387-395.
[2]CHIANG C,CHANG M,LIU H,et al.Process intensification in the production of photocatalysts for solar hydrogen generation[J].Industrial&Engineering Chemistry Research,2012,51(14):5207-5215.
[3]何先琰,王宏,朱恂,等.铅锡合金熔融颗粒风冷相变换热特性实验研究[J].工程热物理学报,2015,36(8):1748-1751.HE X Y,WANG H,ZHU X,et al.Experiment study on air-cooled phase change heat transfer characteristics of Sn-Pb alloy droplets[J].Journal of Engineering Thermophysics,2015,36(8):1748-1751.
[4]DEHKORDI A M,VAFAEIMANESH A.Synthesis of barium sulfate nanoparticles using a spinning disk reactor:effects of supersaturation,disk rotation speed,free ion ratio,and disk diameter[J].Industrial&Engineering Chemistry Research,2009,48:7574-7580.
[5]MOHAMMADI S,HARVEY A,BOODHOO K V K.Synthesis of Ti O2 nanoparticles in a spinning disc reactor[J].Chemical Engineering Journal,2014,258:171-184.
[6]吴君军,王宏,朱恂,等.转盘离心粒化中丝状成粒特性[J].化工学报,2015,66(7):2474-2480.WU J J,WANG H,ZHU X,et al.Characteristic of ligament in centrifugal granulation by spinning disc[J].CIESC Journal,2015,66(7):2474-2480.
[7]ZHANG H,WANG H,ZHU X,et al.A review of waste heat recovery technologies towards molten slag in steel industry[J].Applied Energy,2013,112(4):956-966.
[8]BARATI M,ESFAHANI S,UTIGARD T A.Energy recovery from high temperature slags[J].Energy,2011,36(9):5440-5449.
[9]WANG D X,LING X,PENG H.Simulation of ligament mode breakup of molten slag by spinning disk in the dry granulation process[J].Applied Thermal Engineering,2015,84:437-447.
[10]WANG D X,LING X,PENG H,et al.Efficiency and optimal performance evaluation of organic Rankine cycle for low grade waste heat power generation[J].Energy,2013,50:343-352.
[11]WANG D X,PENG H,LING X.Ligament mode disintegration of liquid film at the rotary disk rim in waste heat recovery process of molten slag[J].Energy Procedia,2014,61:1824-1829.
[12]WU J J,WANG H,ZHU X,et al.Cold experiment of slag centrifugal granulation by rotary atomizer:effect of atomizer configuration[J].Applied Thermal Engineering,2017,111:1557-1564.
[13]WANG H,WU J J,ZHU X,et al.Energy-environment-economy evaluations of commercial scale systems for blast furnace slag treatment:dry slag granulation vs water quenching[J].Applied Energy,2016,171:314-324.
[14]LIU J X,YU Q B,DUAN W J,et al.Experimental investigation on ligament formation for molten slag granulation[J].Applied Thermal Engineering,2014,73(1):888-893.
[15]PENG H,WANG N,WANG D X,et al.Experimental study on critical characteristics of liquid atomization by spinning disk[J].Industrial&Engineering Chemistry Research,2016,55(21):6175-6185.
[16]王东祥,凌祥,彭浩.转盘离心粒化熔渣液膜流动特性数值模拟研究[J].南京工业大学学报(自然科学版),2015,37(3):67-73.WANG D X,LING X,PENG H.Numerical simulation of film flow characteristics of molten slag on spinning disk in centrifugal atomization process[J].Journal of Nanjing Tech University(Natural Science Edition),2015,37(3):67-73.
[17]WANG D X,LING X,PENG H,et al.Experimental investigation of ligament formation dynamics of thin viscous liquid film at spinning disk edge[J].Industrial&Engineering Chemistry Research,2016,55(34):9267-9275.
[18]HINZE J O,MILBORN H.Atomization of liquid by means of a rotating cup[J].Journal of Applied Mechanics Transactions of ASME,1950,17(2):145-153.
[19]FRASER R,DOMBROWSKI N,ROUTLY J.The filming of liquids by spinning cups[J].Chemical Engineering Science,1963,18(6):323-337.
[20]FROST A R.Rotary atomization in the ligament formation mode[J].Journal of Agricultural Engineering Research,1981,26(1):63-78.
[21]CHAMPAGNE B,ANGERS R.Rep atomization mechanisms[J].International Journal of Powder Metallurgy,1984,16(3):125-128.
[22]LIU J X,YU Q B,GUO Q.Experimental investigation of liquid disintegration by rotary cups[J].Chemical Engineering Science,2012,73(19):44-50.
[23]LIU J X,YU Q B,LI P,et al.Cold experiments on ligament formation for blast furnace slag granulation[J].Applied Thermal Engineering,2012,40:351-357.
[24]MATSUMOTO S,BELCHER D W,CROSBY E J.Rotary atomizers:performance understanding and prediction[C]//The 3rd International Conference on Liquid Atomization and Spray Systems.London:Institute of Energy,1986:1-21.
[25]KAMIYA T,KAYANO A.Disintegration of viscous fluid in the ligament state purged from a rotating disk[J].Journal of Chemical Engineering of Japan,1971,4(4):364-369.
[26]AHMED M,YOUSSEF M S.Characteristics of mean droplet size produced by spinning disk atomizers[J].Journal of Fluid Engineering,2012,134(7):1-9.
[27]AHMED M,YOUSSEF M S.Influence of spinning cup and disk atomizer configurations on droplet size and velocity characteristics[J].Chemical Engineering Science,2014,107(14):149-157.
[28]王东祥,凌祥,彭浩,等.转盘表面黏性薄液膜稳态流动特性数值模拟[J].化工学报,2017,68(6):2321-2327.WANG D X,LING X,PENG H,et al.Numerical simulation of stable flow dynamics of viscous film flow on spinning disk surface[J].CIESC Journal,2017,68(6):2321-2327.
[29]PRIELING D,STEINER H.Unsteady thin film flow on spinning disks at large Ekman numbers using an integral boundary layer method[J].International Journal of Heat and Mass Transfer,2013,65(7):10-22.
[30]WANG D X,LING X,PENG H.Theoretical analysis of free-surface film flow on the rotary granulating disk in waste heat recovery process of molten slag[J].Applied Thermal Engineering,2014,63(1):387-395.