Counter & Parallel Flow Heat Exchanger Tube Length Calculation

  Counter & Parallel Flow Heat Exchanger Tube Length Calculation    
  Input data in YELLOW

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HEAT-EXCHANGERS-2
 
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
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/hr-ft^2*F  
U.S. Answer: h = Btu/hr-ft^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      

 

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