papermaking part2 drying（下）

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1、Chapter8Steamandcondensatesystems¢p=C¢1=2½v2(22)a;p3l0¢p=k½U2(1+nM)(23)b;ppll¢p=³¢1=2½U2(1+M)(1+nM)(24)c;pllC=1+M[1+E2ln(1+1=E2)](25)1+nME=Ul(1+nM)(26)v0whereΔppispressurelossinarotarysiphonΔpa,ppressurelosscausedbycentrifugalforceΔpb,ppressurelosscausedbyaccelerationofconde

2、nsateΔpc,ppressurelosscausedbyflowresistancenρl/ρhM_mh/_mlρldensityofcondensateρhdensityofsteamm_lmassflowofcondensatem_hmassflowofsteamUlcondensatespeedinthesiphon,if_mh=0v0circumferentialspeedofdryerkpexperimentalcoefficient(kp>>ks>1)ζresistancecoefficientofthesiphon.Thisa

3、pproachiscomplicatedandhastobecombinedwithexperimentalvalues(Fig.20).Asimplifiedapproachusingtwocomponentsdescribethepressureloss7:¢pp=¢pf+¢pc(27)whereΔpfispressurelossinarotarysiphonΔpfpressurelosscausedbyflowresistanceΔpcpressurelosscausedbycentrifugalforce.Equations28and2

4、9cancalculatethepressurelosscausedbyflowresistance7:¡¢¢p=¢p1+C1+1(28)flXX2qX=¢pl(29)¢phwhereΔpfispressurelosscausedbyflowresistanceΔplpressurelossifonlycondensateflowsinthepipeΔphpressurelossifonlysteamflowsinthepipeXtheMartinellinumber.Calculationofthepressurelossofahomogen

5、eousflowusesthefollowingformula9:¢p=³1=2½U2(30)whereΔpispressurelossPapermakingPart2,Drying-Page150Chapter8SteamandcondensatesystemsζresistancecoefficientρdensityofflowingliquidUflowspeed.Sinceonecanassumethatcentrifugalforceprimarilyaffectsthecondensatedrops,knowingthemasso

6、fwaterinthesiphonisnecessary.Thisisobviouslynotthesameasthemassofwaterinentryandexit.Estimationusesthefollowingformula/7/:³´2¡¢1=1+C1+1(31)RlXX2Thisgivesthepressurelosscausedbythecentrifugalforceasfollows:¢p=R1/2½v2(32)cll0Figure20.Characteristiccurveofarotarysiphondependson

7、machinespeedaccordingtoEqs.21−26.Figure21.Dependenceofthecharacteristiccurveofarotatingsiphononcondensateload.Figure22.Dependenceofthecharacteristiccurveofarotatingsiphononmachinespeed.Thefollowingformulathengivesthetotalpressureloss:¡¢¢p=¢p1+9:3+1+R1/2½v2(33)plXX2ll0whereΔp

8、pistotalpressurelossΔplpressurelossifonlycondensateflowsinthepipeRlshareofc