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//Variable declaration:
uC = 3.7*10**-4 //Viscosity of benzene (lb/ft.s)
uH = 2.05*10**-4 //Viscosity of water @200 . (lb/ft.s)
u2 = 2.16*10**-4 //Viscosity of water @192 . (lb/ft.s)
pC = 54.8 //Density of benzene (lb/ft^3)
pH = 60.13 //Density of water (lb/ft^3)
cpC = 0.415 //Specific heat capacity of benzene (Btu/lb..)
cpH = 1 //Specific heat capacity of water (Btu/lb..)
sgC = 0.879
kC = 0.092 //Thermal conductivity of benzene (Btu/h.ft..)
kH = 0.392 //Thermal conductivity of water @200 . (Btu/h.ft..)
k2 = 0.390 //Thermal conductivity of water @192 . (Btu/h.ft..)
mC = 2500 //Flow rate of benzene (lb/s)
mH = 4000 //Flow rate of water (lb/s)
Re = 13000 //Reynolds number
dTc = 120-60 //Difference in temperature heating for benzene
Tw = 200 //Temperatperature of hot water (.)
//For 2-inch schedule 40 pipe
Ai = 0.541 //Inside area of pipe (ft^2/ft)
Ao = 0.622 //Outside area of pipe (ft^2/ft)
Di = 2.067 //Inside diameter of pipe (inch)
Do = 2.375 //Outside diameter of pipe (inch)
Si = 0.0233 //Inside surface area of pipe (ft^2)
dXw = 0.128 //Width of pipe (ft)
pi = %pi
//For 4-inch schedule 40 pipe
Dio = 4.026 //Inside diameter of pipe (inch)
Doi = Do //Outside diameter of pipe (inch)
kw = 26
//Calculations:
function [a] = St(Re,Pr) //Dittus Boelter equation
a = 0.023*Re**-0.2*Pr**-0.667
endfunction
//For inside tubes:
Dicalc = 4*mC/(Re*pi*uC)/3600 //Inside diameter (ft)
mHcalc = Re*pi*uH*(Doi+Dio)/4*3600/12 //Mass flow rate of water (lb/h)
Q = mC*cpC*dTc //Heat in water (Btu/h)
dTH = Q/mH //Temperature difference of water (.)
THo = Tw - dTH //Outlet temperature of water (.)
THav = (Tw+THo)/2 //Average temperature of water (.)
//For benzene:
PrC = cpC*uC/kC*3600 //Prandtl number
StC = round(St(13000, PrC) * 10**5)/10**5 //Stanton number
hi = StC*cpC*mC/Si //Heat transfer coefficient (Btu/h.ft^2..)
//For water:
ReH = 4*mH/3600/(pi*u2*(Doi+Dio)/12) //Reynolds number
PrH = cpH*(u2)/k2*3600 //Prandtl number
StH = round(St(ReH, PrH) * 10**5)/10**5 //Stanton number
Sann = pi/4*(Dio**2-Doi**2)/144 //Surface area of annulus (ft^2)
ho = round(StH*cpH*mH/Sann) //Heat transfer coefficient (Btu/h.ft^2..)
//For pipe:
Dlm = (Do-Di)/log(Do/Di)*12 //Log mean difference in diameter (ft)
Uo = 1/(Do/Di/hi + dXw*Do/kw/Dlm + 1/ho) //Overall heat transfer coefficient (Btu/h.ft^2..)
dTlm = (124.4-80)/log(124.4/80) //Log mean temperature difference (.)
L = Q/(Uo*0.622*dTlm) //Length of pipe (ft)
//Result:
printf("The required length of pipe: %.1f ft",L)
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