More Ideas for Compact Double Pipe HXs

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More Ideas for Compact Double Pipe HXs

• P M V Subbarao
• Professor
• Mechanical Engineering Department
• I I T Delhi

Ideas for Creation of Compact HX!!!
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Helical Double-tube HX
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Secondary Flow in Helical Coils

• The form of the secondary flow would depend on
  the ratio of the tube diameters and other
  factors.
• A representative secondary flow pattern is shown
  below

• Thirdly, this configuration should lead to a
  more standard approach for characterizing the
  heat transfer in the exchanger.
• The ratio of the two tube diameters may be one of
  the ways to characterize the heat transfer.

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Heat Transfer in Helical Tubes
Acharya et al. (1992, 2001) developed the
following two correlations of the Nusselt number,
for Prandtl numbers less than and greater than
one, respectively.
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Heat Transfer in Helical Annulus

• Nusselt numbers for the annulus have been
  calculated and correlated to a modified Dean
  number.
• The modified dean number for the annulus is
  calculated as it would be for a normal Dean
  number, except that the curvature ratio used is
  based on the ratio of the radius of the outer
  tube to the radius of curvature of the outer
  tube, and the Reynolds number based on the
  hydraulic radius of the annulus.
• Thus the modified Dean number is

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Helical Coils Laminar flow

• De is Dean Number. DeRe (a/R)1/2.
• Srinivasan et al. (7 lt R/a lt 104)
• Manlapaz and Churchill
• Correction for vp

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• Helical coils turbulent flow

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Classification of Heat Exchangers
Creation of Variety in Anatomy of Heat
Exchanger!!!
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Creative Ideas for Techno-economic Feasibility of
a HX.

• For a viable size of a HX
• How to maximize Effective area of heat
  communication?.
• How to maximize Overall Heat transfer
  coefficient?
• How to modify the effective temperature
  difference?

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Heat Exchanger An Effective Landlord

• Creates a housing for both donor and Receiver.
• How to accommodate both in a single housing?
• Space Sharing Time sharing
• Space sharing Donor and Receiver are present
  always.
• Develop partition(s) in the house(HX).
• Time Sharing Donor And Mediator for sometime
  and Mediator and Receiver for sometime Repeat!
• Time Sharing Regenerators
• Space Sharing Recuperators
• Central Limit Theorem It is impossible to have
  time and space sharing in one system.

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A Train of External HXs in A Power Plant
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T-s Diagram of A Modern Power Plant
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Train of Shell Tube HXs.
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5
4
3
2
1
DC
GSC
3
2
5
4
1
6
GSC
DC
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Sequence of Energy Exchange from Flue Gas to Steam
FLUE GAS
PLATEN SH
EVAPORATOR
PENDENT SH
RH
ECONOMIZER
COVECTIVE SH
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4000C
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Gas Temperatures
Steam Temperatures

• Platen Super Heater
• Inlet Temperature 1236.4 0C
• Outlet Temperature 1077 0C
• Final Super Heater
• Inlet Temperature 1077 0C
• Outlet Temperature 962.4 0C
• Reheater
• Inlet Temperature 962.4 0C
• Outlet Temperature 724.3 0C
• Low Temperature Super Heater
• Inlet Temperature 724.30C
• Outlet Temperature 481.3 0C
• Economizer
• Inlet Temperature 481.3 0C
• Outlet Temperature 328.5 0C

• Platen Super Heater
• Inlet Temperature 404 0C
• Outlet Temperature 475 0C
• Final Super Heater
• Inlet Temperature 475 0C
• Outlet Temperature 540 0C
• Reheater
• Inlet Temperature 345 0C
• Outlet Temperature 5400C
• Low Temperature Super Heater
• Inlet Temperature 3590C
• Outlet Temperature 404 0C
• Economizer
• Inlet Temperature 254 0C
• Outlet Temperature 302 0C

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Flue Gas Temperature At different regions of
Furnace210 MWe)
    Design Calculated
1 Adiabatic Flame Temp (K) 1957 1966
2 FEGT (0C) 1102 1117
3 Platen SH-I Outlet (0C) 932 951
4 Platen SH-II Outlet-I outlet (0C) 859 878
5 RH 3rd 2nd outlet (0C) 595 604
6 RH 1st Stage outlet (0C) 510 531
7 Economiser outlet (0C) 385 398
8 APH Outlet (0C) 138 151
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The concept of Time Sharing

• At any time
• The overall heat transfer coefficient, U

OR

• At stead operation

OR
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Stockholm 1920The Ljungström Air Preheater
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Economic Impact of the Landmark

• The use of a Ljungström Air Preheater in a modern
  power plant saves a considerable quantity of
  fuel.
• So much that the cost of the preheater is
  generally recovered after only a few months.
• It has been estimated that the total world-wide
  fuel savings resulting from all Ljungström Air
  Preheaters which have been in service is
  equivalent to 4,500,000,000 tons of oil.
• An estimate shows that the Ljungström Air
  Preheaters in operation annually saves about 30
  Billion US.
• The distribution of thermal power capacity in
  which Ljungström Air Preheaters are installed
  over the world is shown in the table below.