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

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Condensate or Duplex Heater (Liquid- Liquid Heater)  Design Calculation formulas with an online calculation sheet

• According to the in the energy conservation point of view Sugar process industry used liquid liquid heaters for raw juice  heating. It is also called condensate heater or duplex heater( for specific design).
• In liquid- liquid heater raw juice is heated with process condensate water and It has two types of designs.

1 . One is normal multi-passes arranged in a single tube plate design and it located horizontally or vertically. Generally for condensate heaters are located in a horizontal position because in the horizontal position heat transfer coefficient is high and also in this design will get a proper baffle plate arrangement for the passing of hot fluid(Condensate).

 2.  Another design is called Duplex heater. This type of design will get a maximum heat transfer coefficient up to 1200±50 Kcal/m2/hr/oC.  When compared to another liquid liquid heater design it’s having higher heat transfer value , because the passing of hot and cooled fluid is perfectly in counter-current direction from entry to leave the heater.  Another advantage is high flexibility to provide a spare heater or expand the capacity of the heater. A duplex heater is also flexible to collect the condensate (heating media) in different stages as per our process requirement.(i. e as per our required temperature we will get condensed in the middle stage of the heater).

In the sugar process industry while using vapour or steam as a heating media formulas are used for heat transfer coefficient  6 T_v \times \left( \frac{U}{1.8} \right)^{0.8} and for evaluate heating surface used \frac{M \times C_p \times \ln \left( \frac{T_v - t_i}{T_v - t_o} \right)}{K}   . But in condensate heater calculation, both are not applicable.

This article explains about calculation of condensate heater heating surface. 

Please go through the below link for the heat transfer coefficient calculation of liquid liquid heater.

Heat Transfer Coefficient of Liquid -Liquid Tubular Heater

Required data for calculation heating surface of Liquid Liquid heater

1.Crushing rate = m in T/hr

2. Juice % cane = P

3. Velocity of Juice = Vj in m/sec

4. Juice inlet temperature = ti in oC.

5. Condensate Inlet temperature = Ti in oC.

6. Condensate Outlet temperature requirement =To in oC.

7. Specific heat of juice = Cp in Kal/Kg

8. Legment = Lg in mm (Generally Legment taken for Juice heater 12mm, and for evaporators will take 10mm)

9. Tube OD = OD in mm

10. Tube Thickness = Tk in mm

11. Tube length = L in mm

12. Tube plate thickness = Tp in mm

13. Total Quantity of Condensate water percent on Mixed Juice = W

14. Heat transfer coefficient = K in Kcal/m2/hr/oC.

(Note : For Dulex Heater this value lies 1200±50 Kcal/m2/hr/oC and for Normal condensate heater with proper baffle plate arrangement lies 1000±50  Kcal/m2/hr/oC)

15. Proportional factor = β in mm

Steps in Calculation of heating surface for Liquid Liquid heater:

Quantity of juice to be heating = M  = m x P/100 in T/hr
Quantity of heating media (Condensate) = Q x W/100 in T/hr

Fundamental formula :

1 . Heat received by one  = Heat rejected by another.

2. M x Cp x (to – ti) = Q x Cw x (To- Ti)  Note : Here Cw = specific heat of heating media,  for condensate it will      take value 1)

3. Juice outlet temperature = to  ( From the above formula it can be find out the final juice outlet temperature)

Heating Surface :

For heating surface calculation  M x Cp x ΔT = S x K x ∆Tm

Heating Surface =S = [Q x Cp x ∆T]/ [ K x ∆Tm]

Here ∆Tm called as logarithmic mean temperaturelogarithmic mean temperature of liquid liquid heater -sugarprocesstech

∆T = to-ti

bigtriangleup Tm =frac{bigtriangleup Ti - bigtriangleup Te}{ Ln ( frac{bigtriangleup Ti}{bigtriangleup Te})

∆Ti = Ti-to

∆Te = To-ti

Number of tubes per pass & Number of passes:

Number of tubes per pass = frac{Volume of juice in M^3/sec }{Area of one tube in M^2 times Velocity of juice in m/sec}

(Note :while calculating the area of tube take mean dia of tube i.e Tube OD – Tube Thickness)

No. of tubes Requirement = N = S/ [π x Mean dia of tube x Tube effective length]

Number of passes = n = N / number of tubes per pass
In design point of view number of passes always should be even. According to this principle we consider the passes in even number. After the above consideration again calculates the actual heating surface and velocity of juice, it may be differ from required heating surface.

Pressure Drop and Tube Plate area calculation:

Pressure drop across the juice heater

Pressure drop across the juice heater = 0.0025 times n times U^2 times [ frac{L}{D} + 3 ]

Here pressure drop in MWC , n = number passes , U = actual velocity of juice (after considering the even passes), L = Length of the tube, D = ID of the tube (Note : L & D to be take same units)

Tube Plate Area

  1. Tube Plate Area in M^2 = frac { (0.866 times P^2 times no. of tubes)} {beta }

2. Tube Pitch (P ) = OD of the tube +Legment of the tube + tube clearance+hole clearance

3. Proportional factor(β) = Generally β value taken for multiple pass(i.e Juice heaters) 0.6 to 0.8 and for single pass(l.e evaporators or single pass duplex heater) 8 to 1.0.

4. Number of tubes will take as per the type of the heater. Suppose

For multi pass heater no. of tubes = Total number of tubes and

For Duplex having two pass in each section  than no. of tubes = No. of tubes per pass x 2

For Duplex having single pass in each section  than no. of tubes = No. of tubes per pass

(Note :Generally take extra dia in percentage on area occupied for tubes in tube plate  for partition plates arrangement, free withdrawal of condensate and noxious gases removal purpose. Its value lies in the range 10 to 20% on area occupied for tubes.)

 Heating media (Condensate water) inlet and out line dia :

1. Both inlet and outlet will take same dia meter.

2. Area required for condensate water entry (m2) =Quantity of heating media ( Q ) in M3/sec / Velocity of  Condensate water in m/sec. (Note : Velocity of condensate will take 1.8 to 2.0 m/sec while coming from the pump )

3. Dia of the condensate water in mtr = SQRT [ (Area required for condensate water in m2  x (4/π ) ]

Remaining all design parameter can be calculated as same as the normal juice heater calculation.

Online Calculator for Condensate Juice Heater (Duplex) Basic Design

Click Here

 

Liquid- Liquid Heater (Condensate or Duplex juice Heater) Calculation - sugarprocesstech

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