热管换热器计算.doc

热管换热器计算.doc 热管换热器设计 一台锅炉排烟温度为160?，要求设计一台热管换热器，用烟气余热加热进 3Vu,气以提高锅炉效率。已知参数:锅炉排烟量=189000m/h，迎风面风速 ff t,t,2.9m/s，排烟温度160?，设定出口烟气温度118?。需要空气的流量f1f2 3v,2.9m/sV=120000m/h，进气温度，空气风速为 t,25?lfl1 选取圆片翅片强化换热。翅片管材料选择碳钢(w=1%)。热管参数:热管C ,蒸发段长取l=3.16m，管外径d=34mm，管内径d=29mm，壁厚=2.5mm， 翅00i0 ,s,6.4mm片高度H=12mm，翅片厚度=2mm，翅片间距，那么翅片的节距f s',,，s,8.4mm，每根管肋片数为n=3160/8.4=376片。管排选用叉排布置，fff S,0.115mS,S,0.115m迎面横向管子距离设定为，翅片管纵向距离。由于TLT 烟气和空气的物性很相近，取相同的蒸发器和冷凝器结构参数。 1. 总换热量计算 t，t160，118f1f2定性温度tfm= ,,139?22 查物性得: 3,62,2,,0.8712kg/mc，,1.0793kJ/(kg,K)Pr，,0.682，,,25.931，10m/s，,,3.473，10W/(m,K)fpfff ,6,,22*10Pa,s f 烟气放热量 Q,cm,t,c,V,t,1.0793*1000*0.8712*189000*42/3600,2073330.983Wpfpfff 2.计算迎风面积A和迎风管排数B y V189000f2迎风面积 A,,,18.10myu2.9*3600f A18.10y迎风面宽度 E,,,5.73ml3.160 E5.73迎风面管子数 B,,,49.8，取B,50根S0.115T 3.冷空气出口温度及对数平均温差 Q冷空气出口温度: t,，tl2l1,cVplll 80，25?t,80?假设，则 t,,52.5l2lm2 3?,,1.085kg/m，c,1005J/(kg,K)水的物性参数: 查得52.5lpl Q2073330.983则: t,，t,*3600，25,82.0?l2l1,cV1005*1.085*120000plll 82，25t,82?再假设冷空气出口温度为，则 t,,53.5?l2lm2 3?,,1.081kg/m，c,1005J/(kg,K)查得53.5空气的物性参数: lpl Q2073330.983则: t,，t,*3600，25,82.2?l2l1,cV1005*1.081*150000plll t,82?冷空气出口温度为: l2 82，25空气侧定性温度为: t,,53.5?lm2 物性: 3,6,,1.081kg/m，c,1005J/(kg,K)，,,0.0285W/(m,K),,,19.8*10,Pr,0.698lpllll ,t,118-25,93?，,t,160-82,78? 12 ,t-,t93,7812对数平均温差,t,,,85.3? ,mo,t93,,1ln()ln,,,t78,,2 4.计算总传热系数 ?管束最小流通截面积NFA 2NFA=[(S-d)-2H,n]lB,[(0.115,0.034),2*0.012*0.002*376]*3.16*50,9.946mT0f0 h ?烟气侧换热系数 f V,0.8712*189000ff22 G,,,16555.08kg/(m,h)=4.5986kg/(m,s),maxfNFA9.946 6Re=Gd/ ,=4.5986*0.034*10/22=7106.93 ff,max0f 0.63381/30.63381/3Nu,0.137RePr,0.137*7106.93*0.682,33.31 fff Nu,hd/,又 ff0f Nu,ff2故烟气侧换热系数 h,,33.31*0.03473/0.034,34.02W/(m,K)fd0 h?空气侧换热系数 l V,1.081*12000022ll G,,,13042.43kg/(m,h)=3.6229kg/(m,s)l,maxNFA9.946 6Re=Gd/ ,=3.6229*0.034*10/19.8=6221.14 ll,max0f 0.63381/30.63381/3Nu,0.137RePr,0.137*6221.14*0.698,30.85 lll Nu,hd/,又 ll0l Nu,2ll故空气侧换热系数 h,,30.85*0.0285/0.034,25.86W/(m,K)ld0 ?单根热管表面积A 由肋片的参数查传热学书(杨世铭，陶文铨 编著)P65图2-20得: ,,0.89，,,0.90肋效率 fl ,222肋片表面积 A,376*(2*((d，2H),d)，,(d，2H),),1.4411mf0004 肋片之间的根部表面积为 2A,,d(l,n*,),3.14*0.034*(3.16,376*0.002),0.2572m rf00 2A,A，A,0.2572，1.4411,1.6983m热管外总表面积 rf h?蒸发管外有效换热系数 fe h(A，A),33.31*(0.2572，0.89*1.4411)frff2 h,,,30.20W/(m,K)feA1.6983 h冷凝管外有效换热系数 ?le h(A，A),25.86*(0.2572，0.9*1.4411)lrlf2 h,,,23.67W/(m,K)leA1.6983?热管内换热系数h i 热管蒸发段内壁加热的热流密度: Q2073330.9832 q,,,6497.142W/m,,nld1109*3.16**0.029i0 热管内蒸发段换热系数h计算使用imura’s correction: i 0.30.650.30.70.40.2,,,,cgq,,Pwwplesat,,,,h,0.32 i0.250.40.1,,,,P,h,a,,vfgw,, t,106?假设热管蒸发段蒸汽温度为，查饱和水和饱和蒸汽的热物理性质表v 得: 3,6c,4.2278kJ/(kg,K,),,953.96kg/m,,,0.6842W/(m,K),,,268.4，10Pa,splwww 35,,0.73498kg/m,h,2240.78kJ/kg，P,1.26482，10Pa vfgsat 2代入上述h公式计算得:h=5402.567W/(mK) ii ?总换热系数h ,0.00252忽略污垢热阻，导热热阻:(翅片管导 r,,,0.000058m,K/Ww,43.2w ,43.2W/(m,K),热系数) w h总传热系数 111A1A ,，，2r，2whhhAhAfelewii 其中 22A,,dl,3.14*0.034*3.16,0.337m,A,,dl,3.14*0.029*3.16,0.288mwii000 1111.698311.6983则 ,，，2*0.000058，2*,0.078128h30.2023.670.3375402.5670.288 2h,12.9W/(m,K)故 5.热管换热器管数、排数计算 Q,hA,t由，有: 0m,o Q2073330.9832总换热面积为 A,,,1884.21m0h,t12.9*85.3mo, A1884.210蒸发热管总数根 n,,,1109A1.6983 n1109换热器排数 m,,,22.1排B50 18,,,,,,,取22排，排列为 50,5050,51,,50,51,50,50？ 6.管内蒸汽温度计算 Q2073330.983平均壁面温度: t,t,,139,,108.5:CwfmhAn30.2*1.6983*1109fe t,105?假设热管蒸发段蒸汽温度为，查饱和水和饱和蒸汽的热物理性质表v 得: 3,6c,4.2265kJ/(kg,K),,,954.7kg/m,,,0.684W/(m,K),,,270.75，10Pa,swwwpl 35,,0.7121kg/m,h,2243.5kJ/kg，P,1.22285，10Pa vfgsat 2代入hi公式算得:hi=5384.373072 W/(mK)，则: Q2073330.983 t,t,,108.5,,104.7:Cvw,hA5384.373*352**3.16*0.029ii t,104.7:C假设的温度和算得的温度相差较小，则饱和蒸汽的温度为，符合v 要求 7(压降计算 ,p蒸发器压降计算 f 0.316,0.9270.515,,,dG,,,,SS0.034*4.59860.115f0,max0.3160.927TT,,,,,,,,f,37.86,37.86*()()6,,,,,,,,dS22*100.034fL0,,,,,, 0.1150.515(),0.7420.115 22nGf0.7424*15666.08f,max,p,,,171.4Pa,250Pa，符合要求7,2g21.3*10*0.8712cf ,p冷凝器压降计算 l 0.3160.9270.515,,dG,,,,,,SS0.034*3.62290.115l0,max0.3160.927,,TT,,,,,,f,37.86,37.86*()()6,,,,,,,,dS19.8*100.034lL0,,,,,,0.1150.515(),0.7740.115 22nGf0.7744*13042.43l,max,p,,,103.1Pa,250Pa，符合要求7,2g21.3*10*1.081cl