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Shell and Tube Multipass Heat Exchanger Design | Tubular juice heater

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Tubular juice heater design calculation with online calculator

The shell and tube multipass tubular juice heater consists of an assembly of tubes, the juice circulates through the tubes, and the vapour outside them. The juice to pass a certain number of times from bottom to top and from top to bottom of the heater by restricting the juice each time to a few of the tubes.

There are two principal designs of tubular juice heaters, the horizontal and the vertical, both are use in sugar Industry. The Vertical juice heaters are preferred because they occupy less floor space, are subject to less formation of scales and provide better facilities for cleaning.

Shell and Tube Multipass Heat Exchanger Design | Tubular juice heater design calculation with online calculator

Construction Parameters of Tubular Juice heater:

  • The cylindrical shell containing the tube plates is extended at each end beyond the tube plate, the extended portion being divided into compartments by baffles.
  • The heated media (juice) circulates through out tubes and heating media (vapours) circulated on shell side.
  • The first compartment which is for juice inlet and last compartment which is for juice outlet. These two are located upper portion each compartment provides for two passes of upward and downward flow. If there are 22 tubes per pass, for example, there will be 44 tubes for each compartment, 22 for upward and 22 for downward flow.
  • The shell and doors are material of construction( MOC ) consider as MS mild steel and for tube generally used Brass or SS304.
  • Heat transfer coefficient plays an important role to find the heating surface calculation of the heater.
  • Number of passes always should be consider even number.
  • The legment of the tube plate generally consider 12mm for juice heater design.
  • The prapotional factor of the tubes consider 0.6 to 0.8 for multiple passes of heater.
  • Air vents and drain cocks shell be provide for each compartment.
  • Juice velocity in tubes generally consider from 1.6 t0 2.0 m/sec. And heating media velocity consider as per the bleed vapour. The lower velocity of the juice in heater would foul more rapidly. For the high velocities the passage of the juice through the heater causes a marked pressure drop, which rapidly becomes prohibitive.
  • Tubes have a diameter in the range of 38 to 50 mm. Tube lengths may vary between 3 m and 6 m. Longer tube designs lead to lower pressure drops at the same liquid velocity because of the reduced number of passes.
  • The temperature different between outlet of the heated media(Juice) and condensate of the heating meadia(vapour) is called approach of the heater.
  • The approach temperature depends upon heating media (bleed vapour), type of heater (Dead end or dynamic type). It is vary from 5 to 12oC.
  • For dynamic or vapour line juice heater the approach temperature comes upto 5 to 8oC. For turbine exhaust or 1st bleed vapours the approach comes 5 to 8oC. The lower bleed vapours the temperature approach taken 8 to 12oC
  • Efficient removed to be required for condensate water and non condensable gases.
  •  Condensate outlets from the heater should be sufficient to ensure that the velocity of flow of the water does not exceed 1 m/s.
  • The non condensible gases (NCG) removal purpose to be provide for every 10m2 heating surface area required minimum 1cm2 area.
  • Heaters are tested, according to the intended permissible working pressure is 2.5 bars on shell side means vapour side and  6 bars on tube side means juice side.
  • The dynamic type tubular juice heater having outlet vapour line along with the inlet vapour line. So the heating media having two connections of inlet and outlet. The heat transfer coefficient is higher in the dynamic type heater due vapour sweeping effect.
  • In the dynamic type tubular juice heater outlet vapour line dia design for 70 to 100% on total vapour demand. So for the inlet vapour line dia designed for 70 to 200% on total vapour demand of the juice heater. 

Shell and Tube Multipass Heat Exchanger Design | Tubular juice heater design calculation with online calculatorShell and Tube Multipass Heat Exchanger Design | Tubular juice heater design calculation with online calculator

Heat Transfer Coefficient:

To know about fundamental concepts of heat transfer coefficient purpose go through the below link.

Heat transfer coefficient for shell and tube heat exchanger.

HTC depends upon

  • Thermal conductivity of the tube metal.
  • Diameter and the thickness of the tube.
  • Clean lines of the tube surface from the inside and outside.
  • Density, Velocity, viscosity & temperature of Juice to be heated.
  • Efficient removal of condensate water and non- condensable gases.
  • Scale formation and its thickness over the tube surface

For complete information of Heat transfer coefficient calculation purpose please go through the below link

Juice Heater Heat Transfer Coefficient Calculation.

Thermal conductivity for different metals

  • Material                             Thermal conductivity in  Kcal/m2/hr/oC
  • Copper                                 324.74
  • Aluminum                           177.04
  • Brass                                    84.30
  • M.S                                       38.70
  • S.S                                        14.00

For simplification of the finding heat transfer coefficient (HTC) purpose, our technologist proposed number formulas. Out of that the below mentioned formula is most popular for dead-end type juice heaters. This formula have taken from HANDBOOK OF CANE SUGAR ENGINEERING by E. HUGOT.

K  = 6 x Tv x [U / 1.8] 0.8

This formula is applicable only for dead-end type sugar industry juice heater design.

Here

  • K = HTC in Kcal/m2/hr/oC
  • Tv = vapour temperature in oC
  • U = Velocity of juice in m/sec

Heating Surface calculation of tubular juice heater

Fundamental formula :

Heat received by heated media(juice) = Heat rejected by heating media( vapour)

Q =M x Cp x ΔT = K x S x ΔTm

Where

  • Q = Heat transferred in  kCal/hr
  • M= Quantity of material to be heating or cooling in kg/hr
  • Cp = Specific heat of material in Kcal/kg/oC
  • ΔT = Temperature difference from inlet to outlet of the heated material in oC
  • S = Heat transfer surface area in m2
  • ΔTm = LMTD = Log Mean Temperature Difference
  •   K = Overall heat transfer Coefficient Kcal/m2/hr/oC.
  • Ti / To = Hot fluid inlet/outlet (vapour)
  • ti / to = Cold fluid inlet/outlet (Juice)

ΔT = to – ti

\Delta T_m = \frac{\Delta T_{\text{inlet}} - \Delta T_{\text{outlet}}}{\ln \left( \frac{\Delta T_{\text{inlet}}}{\Delta T_{\text{outlet}}} \right)}

  • ΔTinlet = Ti – ti ( Co current Flow)
  • ΔT outlet = To – to (Co current Flow)

Here Heating media is vapour and utilizes only the latent heat so the heating media inlet and outlet temperatures are the same. So it is to be taken as Tv

M \times C_p \times \Delta T = S \times K \times \frac{(T_v - t_i) - (T_v - t_o)}{\ln \left( \frac{T_v - t_i}{T_v - t_o} \right)}

S \times K = M \times C_p \times \ln \left( \frac{T_v - t_i}{T_v - t_o} \right)

 

Design formulas of shell and tube multipass heater

Here we calculate by considering the example.

To find the heat transfer coefficient by using the above formula i.e K  = 6 x Tv x [U / 1.8] 0.8

or to be calculated as per the standard formulas below

Shell and tube Heater Heat Transfer Coefficient Calculation.

According to the heat transfer coefficient, we can heat surface easily by the above formula.

S.no Particulars Sign and formulas Values UOM
Data to be required for calculation
1 Crushing rate TCH 210 TCH
2 Juice % cane P 102 %
3 Velocity of Juice Vj 1.8 m/sec
4 Density of juice ρ 1.06 gm / ml3
5 Tube OD OD 45 mm
6 Tube Thickness Tk 1.2 mm
7 Tube ID ID 42.6 mm
8 Tube length L 4000 mm
9 Specific heat of juice Cp 0.9 Kcal/Kg/oC
10 Legment Lg 12 mm
11 Vapour inlet temperature Tv 85 oC
12 Juice inlet temperature ti 60 oC
13 Juice outlet temperature to 75 oC
14 Tube plate thickness Tb 25 mm
15 Velocity of vapour Vv 40 m/sec
16 Heater Heating Surface S 250 m2
17 Velocity of condensate Vc 1 m/sec
18 Proportional factor β = 0.7 to 0.8 0.7  
19 Latent heat of vapour
 
548.24 kcal/Kg
20 Specific volume of vapour μ 2.83 M3/kg
         
Calculation part  
         
1 Number of tubes per pass      
  Volume of the juice M = (TCH x P) / ( ρ x 3600) 0.0561 M3/sec
  Area of the one tube A = 0.785 x ID2 0.0014 M2
    M / ( A x Vj) 21.89 tubes/pass
    i.e 22.00  
2 Number of the tubes      
  Mean Dia Dm = OD – Tk 43.8  
  Effective tube length L m = L – 2 x Tb – 2 x 5 3940  
  Number of the tubes  N t = S / ( π  x Dm x Lm ) 461.36  
    i.e 462.00 no.s
3 Number of Passes n = Nt / tubes per pass 21.00  
3 Number of passes should be always taken even number ( n ) 22  
         
         
  As Per Even number of passes Heater parameters to be calculated
4 No. of compartments Top side = n/2 +1 12  
    Bottom side = n/2 11  
5 Actual number of tubes Nt = n x tubes per pass 484 no.s
         
6 Actual heating surface S = π x Dm x Lm x Nt
 262 m2
         
7 Actual velocity Vj = M /  Area of one pass 1.79 m/sec
8 pressure drop across the juice heater 0.0025 x n x Vj2 x ( L/ ID +3) 17.10 MWC
         
9 Tube plate dia      
  Pitch Pt = OD + Legment + Tube Tolerance(0.5mm) + Hole Tolerance(0.1mm) 57.6  
  Tube plate Area At = 0.866 x Pt 2 x Nt /  β 1.99 m2
    Take 10% extra 2.19 m2
  Tube plate dia Dt = SQRT ( At / 0.785) 1668 mm
10 Dia of juice inlet pipe      
    Area Aj = M / Vj 0.031 m2
    Dj = SQRT ( Aj / 0.785) 0.199 mtrs
    i.e 200 NB
11 Vapour inlet Dia Qj x Cp x ΔT = W x λ   mtrs
    Qj = TCH x P x 1000 214200 Kg/hr
    ΔT  = to -ti 15 oC
    W = weight of the vapour 5274.515 kg/hr
    Qv = W x μ /3600 4.146 M3/ sec
    Av = Qv / Vv 0.104 m2
    Take 10% extra 0.114 m2
    Dv = SQRT ( Av / 0.785) 0.381 mtrs
    i.e 400 NB
12 Condensate pipe Dia      
    Qc = weight of the condensate = W 0.00147 M3/sec
    Ac = Qc/ Vc 0.00147 M2
    Take 50% extra for free removal 0.00220 M2
    Dc = SQRT ( Ac /0.785) 0.053 mtrs
    i.e 75 mm
13 NCG pipe line dia      
  Cross section area of pipe For every 10m2 Heating surface required 1 cm2 area to be required ( An ) 26.23 cm2
    SQRT (( An/4) / 0.785) 2.89 cm
  NCG pipe line dia 4 no.s NCG points and each having 32 mm
14 Calendria shell thickness (P*  Di / (2*F*J – P) ) + C    
  Maximum allowable pressure P (Hydraulic test pressure) 3 kg/cm2
  ID of the Juice heater Di 1668 mm
  Allowable stress F 1400 kg/cm2
  Welding Joint efficiency J 0.75  
  Corrosion allowance C = 1.5 for calendria shell 1.5 mm
  Calendria shell thickness   3.89 mm
  Say   4 mm
  But as per standard specification 12mm for longitude of equipment
         
15 Tube plate thickness f x G x SQRT((0.25 x P)/F) + C    
  Corrosion allowance C = 3.0mm for tube plate 3 mm
  Allowable stress F 1400 kg/cm2
  Maximum allowable pressure P 3 kg/cm2
  Modulus factor for MS sheet Es 2100000 kg/cm2
  Modulus factor for SS sheet Et 1900000 kg/cm2
  ID of the shell G 1668 mm
  Thickness of the shell ts 12 mm
  Thickness of tube tt 1.22 mm
  OD of the tube do 45 mm
  Do = OD of the calendria sheet Do = ID + 2 x shell thickness 1692 mm
  Number of tubes Nt 484 no.s
  K K =( Es x ts x (Do -ts)) /(Nt x Et x tt x(do -tt)) 0.862174  
  f = safety factor f = SQRT ( K / (2 + 3K)) 0.433567  
  Tube plate thickness   19.74 mm
  But as per standard specification 25mm for tube plate
         
16 Thickness of the cover plate tc = Gc x SQRT ( K x P /f ) + C.A    
  ID of the shell Gc 1668 mm
  For flat joint K = 0.3 0.3  
  Design Pressure P 3 kg/cm2
  Allowable stress f 1400 kg/cm2
  Corrosion allowance C = 1.5mm for cover plate 1.5 mm
  Thickness of the cover plate   43.79 mm
  But as per the Indian practice to given 32mm cover plate with adequate stiffening is sufficient

Tubular juice heater online calculator

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