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+clc;
+clear;
+//Example 3.23
+vfr=1200  ;  //Water flow rate in [l/h]
+rho=0.98 ;   //Density of water in g/[cubic cm]
+m_dot=vfr*rho    //Mass flow rate of water [kg/h]
+m_dot2=m_dot/3600    //[kg/s]
+Cp=4.187*10^3 ;   //[J/kg.K]
+Di=0.025  ;  //Diameter in [m]
+mu=0.0006 ;   //[kg/(m.s)]
+Ai=%pi*((Di/2)^2)    //Area of cross-section in [m^2]
+Nre=(Di/mu)*(m_dot2/Ai)    //Reynolds number
+k=0.63 ; //for metal wall in [W/(m.K)]
+Npr=Cp*mu/k;    //Prandtl number
+//Since Nre>10000
+//therefore ,Dittus boelter eqn for heating is 
+Nnu=0.023*(Nre^(0.8))*(Npr^(0.4))
+ho=5800   ; //Film heat coefficientW/(m^2.K)
+hi=Nnu*k/Di    //Heat transfer coeffcient in [W/(sq m.K)]
+Do=0.028 ;   //[m]
+Di=0.025 ;   //[m]
+xw=(Do-Di)/2;    //[m]
+Dw=(Do-Di)/log(Do/Di);    //[m]
+k=50  ;  //for metal wall in [W/(m.K)]
+Uo=1/(1/ho+Do/(hi*Di)+xw*Do/(k*Dw));    //in [W/sq m.K]
+dT=343-303 ; //[K]
+dT1=393-303 ;   //[K]
+dT2=393-343 ;   //[K]
+dTm=(dT1-dT2)/log(dT1/dT2);    //[K]
+Cp=Cp/1000;  //[in [kJ/kg.K]]
+Q=m_dot*Cp*dT;    //Rate of heat transfer in [kJ/h]
+Q=Q*1000/3600;    //[J/s] or [W]
+Ao=Q/(Uo*dTm);    //Heat transfer area in [sq m]
+//Also,..Ao=%pi*Do*L    ..implies that
+L=Ao/(%pi*Do)    //[m]
+printf("Length of tube required is %f m",round(L));