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authorprashantsinalkar2017-10-10 12:27:19 +0530
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+//Example 14-3
+clc;clear;
+// Given values
+P_atm=101.3*1000; // Pa
+g=9.81;// m/s^2
+alpha=1.05;
+eps=0.02*0.0254;//Roughness in m
+D=4*0.0254;// in 'm' converted from 'in'
+L=10.5*0.3048;//in 'm' converted from 'ft'
+gradz=1.219;// grad z=(z_1-z_2) in m
+
+// Calculation
+A=((%pi*D^2)/4);//Area in m^2
+v=300:10:700;//Volume flow rate in gpm
+T=[25 60];//Temperature matrix
+for j=1:1:length(T)
+ //Water properties at T = 25°C and 60°C respectively
+ if T(j)==25 then
+ rho=997.0;// kg/m^3
+ nu=8.91*10^-4;// Kinematic viscosity in kg/m.s
+ mu=nu/rho;
+ P_v=3.169*1000;// Pa
+ else
+ rho=983.3;// kg/m^3
+ nu=4.67*10^-4;// Kinematic viscosity in kg/m.s
+ mu=nu/rho;
+ P_v=19.94*1000;// Pa
+
+ end
+
+for i=1:1:length(v);
+
+ v_(i)=(6.309*10^-5)*v(i); //Volume flow rate in m3^s converted from gpm
+ V(i)=v_(i)/A;//Velocity in m/s
+ Re=(4*v_(i))/(mu*%pi*D);//Reynolds number
+
+ function [X]=fric(f)
+ X=-2.0*log10(((eps)/(3.7*D))+((2.51)/(Re*sqrt(f))))-1/sqrt(f); //Friction factor as a implicit function of Re using Colebrook equation
+ endfunction
+
+ f=0.00001; //Initial guess to solve X
+ fr=fsolve(f,fric);//Calculating friction factor
+
+ sigmaK_l=0.5+(3*0.3)+6.0;// Minor losses
+ H_l=((fr*L)/D+sigmaK_l)*(V(i)^2/(2*g));//The required net head of the fan at the minimum flow rate
+
+ NPSH(j,i)=((P_atm-P_v)/(rho*g))+(gradz)-(H_l)-((alpha-1)*(V(i)^2)/(2*g));
+end
+end
+F=[300 400 500 600 680];//Flow rate in gpm
+N=[3.8 4.44 5.06 6.13 7.0];//minimum NPSH required approximately taken from Fig.14-21
+plot(v',NPSH'*3.28,'r',F,N,'-o');
+xlabel('v,gpm');
+ylabel('NPSH,ft');
+legend('Available NPSH, 25°C','Available NPSH, 60°C','Required NPSH');
+printf('\nCavitation occurs at flow rates above approximately 600 gpm. \nThe maximum volume flow rate without cavitation decreases with temperature.')