Heat Transfer Coefficient of Liquid -Liquid Tubular Heater Calculation | HTC

How to find Condensate Juice Heater Heat Transfer Coefficient Calculation

The fundamental expressions relating to heat transfer coefficient in tubular heat exchangers are available in many standard texts on heat transfer and chemical engineering unit operations.

For basic concepts of overall heat transfer coefficient explained in the below following link

Fundamental  Concepts of overall heat transfer coefficient.

The Overall heat transfer coefficient ( U ) , Kcal / hr/m2/ oC or Kw/m2/ oC, of the heater determines the heat flux generated in the heater for a given temperature force, and it is most important performance factor for the unit. The overall coefficient is related to the various individula transfer coefficients encountered in the process by the expression.

1/U = 1/Hf + 1/Hs + Kt/Tk + 1/Usc

Which gives the reciprocal of  U as an overall resistance which is the sum of the individual resistance.

  • Juice film resistance (Cold media),
  • Condensate water(Hot media),
  • Tube resistance – According to MOC (material of construction) of the tube
  • Resistance of scale. ( fouling factor)

 calculation of heat transfer coefficient for shell and tube heat exchanger - condensate juice heater

Steps in calculating the heat transfer coefficient of tubular juice heater heater

Step1 : Defined the duty and calculate energy balance and flow rates of temperatures.

Step2 : Collect the physical properties of both hot and cold media.

Step3 : Assume the value of the overall coefficient Uo ass from the standard author books.

Step4 : As per the assumed HTC value from standard books  and calculate the heater parameters like heating surface , number of the tubes and its shell dia, . etc

Step5 : Estimate the tube side heat transfer coefficient.

Step6: Decide the baffle spacing and estimate shell side heat transfer coefficient.

Step7 : Calculate the Material coefficient  and Fouling factor coefficient

( Tube resistance – According to MOC (material of construction) of the tube, Resistance of scale. )

Step8: Calculating Overall heat transfer coefficient  Uo cal.

Calculate the percent of variation from Uo ass to Uo cal . The percent of variation is less than 30% then U0 cal. is Ok otherwise will be going to step 3. (i.e Again assume the Uo ass and calculate Uo cal )

In this article calculate the HTC by taking one example.

Step1 : Sugar cane juice heated by excess condensate (Hot water) available in its sugar process by shell and tube heat exchange.

Description Sign UOM Values Formula 
STEP 2 : Collection of the required data.
Juice Flow rate Qj T/hr 230
Hot water (heating media) Inlet temperature ti oC 84
Hot water (heating media) Inlet temperature to oC 62
Velocity of juice in tubes Vj m/sec 1.8
Collect the physical properties for Juice
Specific heat of the juice Cj Kcal/kg-oC 0.91 Handbook of cane sugar engineering by E.Hugot pg. no. 449
Density of juice ρj kg/M3 1048 Cane Sugar Engineering by peter rein page no. 745
Juice inlet temperature Ti oC 45
Juice outlet temperature To oC 65.00
Viscosity of juice μj Poice 0.00835 Cane Sugar Engineering by peter rein page no. 745
kg/m.hr 3.006 (1centi Poice = 1mPa.s)
Thermal conductivity of juice Kj Kcal/hr/m/oC 0.507 Principles of sugar technology by Pieter Honig Vol.1 pg. no.27
Collect the physical properties for condensate water at 85 oC
Density of water  ρw kg/M3 968
Specific heat of hot water Cw Kcal/kg-oC 1
Thermal conductivity of water Kw W/m oC 0.67281
Kcal/hr/m/oC 0.578482
Viscosity of water μw μpa.s 333
kg/m.hr 1.1988
STEP 3 : Assume OHTC and heater design parameters
Overall heat transfer coefficient given in Perry hand book for the given conditions 200 to 250 BTU/ft2/hr/o F
Heat transfer coefficient Uo ass Btu/ft2/hr/oF 225
Kcal/hr/m2/oC 1098.45
Tube OD OD mm 45
Tube Thk Tk mm 1.2
Tube plate thk Tpk mm 25
Tube ID D mm 42.6 OD – Tk
Legment Lg mm 12
Tube length L mm 4000
STEP 4 : Calculate heat balance and required quantity of how water(heating media) and then find the heater parameters.
Fundamental formula for heat balance
Heat received by Juice = Heat rejected by condensate water
Qj x Cj x ∆T (to – ti) = W x Cw x ∆T(Ti-To)
Quantity of Juice Qj Kg/hr 230000
Weight of hot water W kgs/hr 190273
Calculating number of tubes per pass
Volume of juice Qj M3/sec 0.06096 Qj / ( ρj x 3600)
Cross sectional area of one tube At M2 0.00142 (π/4) x (ID)2
Number of tubes per pass 23.77 Qj / (At x Vj )
i.e tubes/pass 24
Heating Surface  = S :  Qj x Cj x ∆T = Uo ass x  S x ∆Tm
Heat transfer coefficient Uo ass Kcal/m2/oC/hr 1098.45
∆T = To-Ti oC 20.00
∆Ti = ti – To oC 19.00
∆Te = to – Ti oC 17.00
Ln(∆Ti/∆Te) oC 0.11
∆Tm = ∆Ti -∆ Te / ( ln(∆Ti/∆Te)) 17.98
Heating Surface S m2 211.93
i.e m2 212
Number of tubes NT S = π x Dm x Ef x  NT
Mean Dia of the tube Dm mm 43.8 OD – Tk
Effective tube length Ef mm 3940 L – 2(Tpk) – 2(5)
Number of tubes NT 391.23
i.e no.s 392
Tube plate Area = 0.866 x P2 x NT / β
Pitch = OD+legment+tube tolerance+hole tolerance P 57.6
Proportional factor β 0.7
Tube plate area A 1.61
Tube plate dia / heater shell dia Ds mtrs 1.43 Sqrt (A / 0.785)
STEP 5 : Calculate the tube side heat transfer coefficient.
Tube side Juice coefficient Hf
Sieder and Tate formula  (1974)
Hf = 0.023(Kj/D) x (DG/μj)0.8 x (Cj μj/Kj)0.333 x (μj/μw)0.14
Tube side mass flux G = Qj /Aj
Area of the all tubes in pass Aj M2 0.034
Qj Kg/hr 230000.00
G kg/hr/m2 6727098
Re =Reynolds number = G D/μj
Re Taken SI units 95334.12
Pr = Prandtl number = Cj μj /Kj
Pr 5.395
Generally The value of “(μj/μw)0.14 “is negligible for low viscous materials
Tube side Juice coefficient  Hf Kcal/hr/m2/oC 5170.5
STEP 6 : Decide the baffle spacing and estimate shell side heat transfer coefficient.
Shell side heat transfer coefficient (Hs) Hs
Kern  “Process Heat transfer” page no.137
Hs = 0.36 (k/De) x Re0.55 x Pr 0.33 x  (μ /μw)0.14
Consider baffles in shell side for hot water passing B no.s 3
Re = de  Vw ρw / μw
Shell side mass velocity Vo = m/As
Cross flow As = (P – D)Ds Lb / P
Pitch P m 0.0576
OD of tube D m 0.045
Shell inside dia Ds m 1.4317
Baffle spacing Lb m 0.4772 Ds / B
Cross flow As m2 0.1495 (P – D) x Ds x  Lb / P
Fluid flow rate on the shell m kg/hr 52.854 W/3600
Qw M3/sec 0.055 m /  ρw
Velocity of water in shell side Vw m/sec 0.365 Qw / As
m/hr 1315.20
de for square pitch = 1.27( Pt 2 – 0.785 OD 2) / OD
de for triangular pitch = 1.1( Pt 2 – 0.917 OD 2) / OD
de ( here consider triangular pitch) m 0.0357
Re = de  Vw ρw/ μw 37923.04
Pr = Cw x μw / Kw 2.072
Hs = 0.36 (kj / De) x Re0.55 x Pr 0.33 x  (μj /μw)0.14
Hs Kcal/hr/m2/oC 2447.03
STEP 7 :  Calculate the Material coefficient  and Fouling factor coefficient
Material coefficient
Thickness of the tube Tk m 0.0012
Thermal conductivity SS tubes Kt Btu/Ft/hr/oF 26
Kcal/hr/m/oC 13.96
Material heat transfer coefficient Kt / Tk Kcal/hr/m2/oC 11633
Fouling factor for light hydrocarbons w/m2/oC 5000 Culson&Richanrdsons “Chemical engineering” volume 6 page no.640
Kcal/hr/m2/oC 4299
1/Usc 0.000233
STEP 8 :  Calculating Overall heat transfer coefficient  Uo cal.
 Uo cal = Overall heat transfer coefficient 1/Uo cal = 1/Hf + 1/Hs + Kt/Tk + 1/Usc
1/Hf Tube side 0.000193
1/Hs Shell side 0.000409
 Kt/Tk Wall 8.6E-05
1/Usc Fouling factor 0.000233
1/Uo cal 0.0009206
Uo cal Kcal/hr/m2/oC 1086.2

In this calculation the percent of  variation in between  Uo ass & Uo cal is less-than 30%. So Uo cal. value is correct.

Conclusion : In sugar industry the condensate heater (Duplex heater) heat tranfer coefficient will be take around 1000±100 Kcal/hr/m2/oC

Some Related Articles

For the condensate heater calculation of heating surface, number of tubes , juice inlet and outlet lines dia. ..etc,  purpose go through the below link.

Liquid- Liquid Heater Design (Condensate or Duplex juice Heater) Calculation.

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

Juice Defecator and Juice Sulphitor Design Criteria | Online Calculator

Sugar Tech | Sugar Technology related articles with online calculators

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Post Author: siva alluri

The aim of this Blog "sugarprocesstech" is Providing basic to advance knowledge in sugar process industry and providing maximum calculation regarding capacity and equipment design online calculators .

2 thoughts on “Heat Transfer Coefficient of Liquid -Liquid Tubular Heater Calculation | HTC

    Subramanyam Reddy

    (October 30, 2017 - 6:39 am)

    Excellent work which helps industry and technical person.

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