
Counter & Parallel Flow Heat Exchanger Tube Length Calculation 


Input data in YELLOW
Update and Reset funtions at bottom of page. 













































Heat transfer, Q = 
U*A*∆Tm 








Plane wall heat transfer coefficient, U = 
1 / (1/ho + L/K + 1/h1 




Cylindrical wall heat transfer coefficient, U = 
1 / (1/hi + [RoLn(Ro/Ri)]/K + Ri/Ro) 



i and o refer to inside and outside tube surfaces. 




Large temperature difference, ΔTbc = 
Ta  Td 

ΔTbc = 

From Input Data below. 

Small temperature difference, ΔTad = 
Tb  Tc 


ΔTad = 

From Input Data below. 

Logarithmic mean temp. difference, ΔTm = 
(ΔTbc  ΔTad)/ln(Tbc/ΔTad) 

Answer: ΔTm = 

deg C 



The added resistance to heat transfer caused by corrosion is called fouling. 

Fouling factor, R ranges between 0.0005 and 0.002. See manufactures data. 

Fouling factor, R = 
(1/Udirty)  (1/Uclean) 




Forced Convection  in Coiled Tube Heat Exchangers 

Turbulent flow in coiled tube. 
Input Data 

Temp. of Fluid (Liquid) flowing in, Ta = 

deg C 



Temp. of Fluid (Liquid) flowing out, Tb = 

deg C 


Tc = 

deg C 



Td = 

deg C 


Tube inside diameter, Di = 

mm 


Tube outside diameter, Do = 

mm 


Velocity of Fluid (Liquid) in tube, V = 

m / s 





Water properties at temperature Tb deg C from the table above: 

Fluid (Liquid) density, ρ = 

kg / m^3 



Cp = 

k*J/kg*K 



Fluid (Liquid) dynamic viscosity, μ = 

kg / m*s 



Fluid (Liquid) conductivity, k = 

W / m*K 



Prandtl number, Pr = 

 



Factor, n = 





Velocity of Fluid (Liquid) in tube, V = 

m / s 







Results 


Fluid (Liquid) bulk temperature, Tb = 
(Tin + Tout) / 2 
deg C 

Answer: Tb = 

deg C 

Reynolds Number, Re = 
V*D / ν 



or, Re = 
V*D*ρ / μ 


Answer: Re = 

Turbulent 
Re >4000 



Convective heat transfer coefficient, h = 
0.023*(Re^.8)*(Pr^n)*(k/d) 


S.I. Answer: h = 

W / m^2*K 

U.S. Answer: h = 
(W/m^2*K)/5.5956 
Btu/hrft^2*F 

U.S. Answer: h = 

Btu/hrft^2*F 



S.I. Answer from above: h = 

W / m^2*K 

Large temperature difference, ΔTbc = 
Tb  Tc 


Answer: ΔTbc= 

deg C 







Small temperature difference, ΔTad = 
Ta  Td 




Answer: ΔTad = 

deg C 






Logarithmic temperature difference, ΔTm = 
(ΔTbc  ΔTad)/ln(Tbc/ΔTad) 

Answer: ΔTm = 

deg C 




Overall heat transfer coefficient = 
Uo 


Heat flow rate, Q = 
Uo*A*ΔTm 


Heat flow rate thru inside tube wall, Qi = 
Uo*π*di*L*ΔTm 


Heat flow rate thru outside tube wall, Qo = 
Uo*π*do*L*ΔTm 


Uo = 
h *Ai / Ao 






Tube inside area, Ai = 
π*di*L 



Tube outside area, Ao = 
π*do*L 


Overall heat transfer coefficient, Uo = 
h *di / do 



Answer: Uo = 

W / m^2*K 






Cp = 
Cp*1000 
1000*J/kJ 



Answer: Cp = 

J/kg*K 






Disregarding tube fouling, determine the tube length required: 



The tube length required, L = 
ρ*V*(di)^2*Cp*(Tout Tin) / (4*Uo*do*ΔTm) 

Answer: L = 

m 


