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1第一题一管壳式换热器，单壳程、双管程，用渣油预热原油。渣油的质量流量是，入口温度为，原油的质量流量是入口温度为，求原油的出口温度，换热器的总传热系数，传热效率。换热器的结构参数如下：传热面积A=130m2壳体直径D=0.7m管子规格Φ25×2.5mm管中心距P=32mm，正方形排列管长L=6m管程通道截面积AT=0.0459m2壳程通道截面积AS=0.0525m2渣油侧的污垢热阻R渣油＝0.0005m2·K/W原油侧的污垢热阻R原油＝0.0001m2·K/W解：1初设出口温度Th2或Tc2。1）设定热容流率较小一侧流体的出口温度。 Wh=68250㎏/hWc=175000㎏/h显然：Wh〈WcWhCph〈WcCpc即：热流体一侧热容流率较小，所以设热流体一侧出口温度。2）进一步估算冷流体出口温度Tc2=Tc1+Wh/Wc（Th1-Th2）=275+68250/175000（382-328.5）=295.9(℃)故初设：Th2=328.5(℃)Tc2=295.9(℃)2.计算物性参数及传热系数；1）定性温度：Tmc=（Tc2+Tc1)/2=（295.9+275)/2=285.5(℃)Tmh=(Th2+Th1)/2=(382+328.5)/2=355.25(℃)2)计算物性参数:密度、比热、导热系数、粘度。相对密度D式中X=1+t/100;t－定性温度；A密度：D20－20℃时油品相对密度，D20渣油＝0.919，D20原油＝0.850hkgWh/68250CToh382hkgWc/175000CTco2755.328)275382(5.03825.0)11(12TcThThTh)exp(556.0312.00841.0)(174.0248.0942.02020220XDXXDDXDD1000855.310015525.41001TXTXch2Dh=0.6866同理Dc=0.6227。比热Cp式中，K为油品特性因数，可查取或实测对渣油，K渣油＝12.5对原油，K原油＝12.5Cph=0.7857Cpc=0.7499导热系数λ单位粘度υ(单位为cSt1cSt=10-6m2/s)注意区别动力粘度和运动粘度，运动粘度单位:cSt式中：z－渣油;y－原油)exp(556.0312.00841.02)^20(174.0248.0942.02020hhhhhhhhXDXDXDXD)/()35.0055.0(318.0)000551.000147.0(7072.02020CkgkcalKDtDCpoCkgKcalCkgKcal)/(/00054.011008.020hCmkcalDto1003.0)00054.01(1008.008864.0)00054.01(1008.02020cchhDTmcDTmh)(hCmKcalcsttba22.1)273ln(expexp1312010090150050273273ln/)22.1ln()22.1ln(ln)273ln()22.1ln(ln222111212111yzyzttttbtba3SI单位为:㎡/s3、据换热器的结构尺寸求a、安排流程：管程：I，h，渣油—热流体，易结垢，粘度大，管内易清洗，热损失少。壳程：O，C原油—冷流体。b、分别计算管程和壳程的流速。注意单位：由（㎏/h）换算为u的单位（m/s）单位是：m/sc、计算Re，Pr准数。其中：di=0.025-2×0.0025=0.02d、计算0，i；6^106013.06^10617.1chKi,,0602.03600hihhhhNAWAWui487.100cAWcu1193.41Pr9.67285Re66.7455Re000hhhphhhphiccehiihhiiCCuddudi69.11Pr0cccpcccpcuCC02718.0025.0)2^025.042^032.0(4)2^42^(400ddpdeo14.0)^/(33.0Pr^8.0Re^023.0wiuuda14.0)^/(33.0Pr^55.0Re^36.00wuudea4e、进行壁温校正：Qc=WcCpc（Tc2-Tc1）Qh=WhCph（Th1-Th2）据：冷侧：Twc＞TmcTwc=（Tc1+Tc2）/2+Qc/（0×A0）热侧：Twh＜TmhTwh=（Th1+Th2）/2－Qh/（i×Ai）Qc=WcCpc(Tc2–Tc1)=3.18×10^6J/sQH=WhCph(Th1–Th2)=3.3×10^6J/s只估算一侧壁温，认为Twc=Twhf、求K0：1K0=R0+1/0+(d0/di)Ri+(d0/di)1/0=215.41g、求=0.37464、计算TH2：TH2’=TH1-（TH1–TC1）=382-0.3746(382-275)=341.90CTH2’-TH2>0.1所以重新计算TC2、Tmc、Tmh、物性参数等等。第一次计算数据：48.435PrRe023.0.........365.1352PrRe527.0Re36.033.0^8.0^33.0^05.0^055.0^0002000Re2000ReiiihiecddLLiodnAdnAio2)^(1maxminCCNTUmin)(WCpAKNTU))(^1()(^12max)^min(1max)min(12eeCCCC5Th1Th2TmhD20hXhDhCph382328.5355.250.9194.55250.6866430.785686Tc1Tc2TmcD20cXcDcCpc275295.9285.450.853.85450.6226930.749927λhazbzυhυhAtWh0.08864318.917-2.92961.616731.6167*10^-60.045968250λcaybyυcυcAsWc0.10030922.81-3.68710.6013640.6013*10^-60.0525175000UidiReiPriαiCmax0.6015290.027441.29841.19797435.0817131237.2U0de0Re0Pr0α0KCmin1.4869690.027267256.3911.721811352.365215.271653623.08NTUτεTh2’0.5218890.5637730.374406341.9386第一次迭代过程及结果：Th1Th2TmhD20hXhDhCph382341.9386361.96930.9194.6196930.6805840.7...