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PLATE AND FRAME HEAT EXCHANGER

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Title: PLATE AND FRAME HEAT EXCHANGER


1
PLATE AND FRAME HEAT EXCHANGER
2
PRESENTED BY
  • HAFEERA SHABBIR 06-CHEM-19
  • MUBASHRA LATIF 06-CHEM-23
  • PAKEEZA TARIQ MEER 06-CHEM-65
  • MAHPARA MUGHAL 06-CHEM-69

3
OUTLINE
  • Introduction
  • Construction
  • Principle of Operation
  • Applications
  • Advantages
  • Limitations of Operation
  • Comparison of with STH
  • Design steps with Solved example

4
Introduction
  • It is a type of compact heat exchanger
  • A plate heat exchanger is a type of heat
    exchanger that uses metal plates to transfer heat
    between two fluids


5
CONSTRUCTION
  • Based on their construction plate and frame heat
    exchangers are classified into
  • (a) Gasketedplate
  • (b) Welded-plate

6
GASKETED-PLATE HEAT EXCHANGER(GPHE)
  • Parallel corrugated plates clamped in a frame
    with each plate sealed by gaskets and with four
    corners ports, one pair for each of the two
    fluids.
  • The fluids are at all times separated by 2
    gaskets, each open to the atmosphere. Gasket
    failure cannot result in fluid intermixing but
    merely in leakage to atmosphere, hence a
    protective cover is there.

7
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9
Construction of GPHE
  • Plates
  • Gaskets
  • Plate frame

10
PLATES
  • Plate thickness is 0.4 to 0.8 mm
  • Channel lengths are 2-3 meters
  • Plates are available in Stainless Steel,
    Titanium, Titanium-Palladium, Nickel

11
PLATES
  • PATTERNS
  • 1)Induce turbulence for high HT coefficient
  • 2)Reinforcement and plate support points that
    maintains inter-plate separation.
  • TYPES OF PATTERNS
  • Mainly 2 types of patterns (corrugations) are
    used
  • 1)Intermating or washboard corrugations
  • 2)Chevron or herringbone corrugations

12
CHEVRON OR HERRINGBONE
  • Most common type
  • Corrugations are pressed to same depth as plate
    spacing
  • Operate at High pressure
  • Corrugation depth 3mm to 5mm
  • Velocity 0.1 to 1 m/s

13
CHEVRON CORRUGATIONS
14
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15
  • INTERMATING TROUGH PATTERNS
  • Pressed deeper than spacing
  • Fewer connection points
  • Operate at Lower pressure
  • Max channel gap 3mm to 5mm
  • Min channel gap 1.5 mm to 3 mm
  • Velocity range in turbulent region is 0.2 to 3
    m/s

16
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17
DIMPLE CORRUGATIONS
18
GASKETS
  • They limit the maximum operating temperature for
    a plate heat exchanger. Material selection
    depends upon
  • 1)Chemical resistance
  • 2)Temperature resistance
  • 3)Sealing properties
  • 4)Shape over an acceptable period of time

19
GASKET MATERIALS
  • Typical gasket materials are
  • Natural rubber styrene
  • Resin cured butyl
  • Compressed asbestos fiber gaskets

20
FRAMES
  • Materials
  • 1)Carbon steel with a synthetic resin finish
  • 2)stainless steel

21
WELDED PLATE HEAT EXCHAGERS(WPHE)
  • Developed to overcome the limitations of the
    gasket in GPHE
  • Inabilty of heat transfer area inspection and
    mechanical cleaning of that surface

22
OPERATION
  • Channels are formed between the plates and corner
    ports are arranged so that the two media flow
    through alternate channels.
  • The heat is transferred through the thin plate
    between the channels, and complete counter
    current flow is created for highest possible
    efficiency. No intermixing of the media or
    leakage to the surroundings will take place as
    gaskets around the edges of the plates seal the
    unit.

23
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24
APPLICATIONS
  • 3 major applications
  • (1)liquid-liquid services
  • (2)condensing and evaporative
  • (3)Central cooling

25
LIQUID-LIQUID SERVICES
  • It is well-suited to liquid/liquid duties in
    turbulent flow, i.e. a fluid sufficiently viscous
    to produce laminar flow in a smooth surface heat
    exchanger may well be in turbulent flow in PHE.
  • It has major applications in the food industry.

26
CONDENSATION AND VAPORIZATION
  • Condensation of vapor (including steam) at
    moderate pressure, say 6 to 60 Psi, is also
    economically handled by PHEs, but duties
    involving large volumes of very low pressure gas
    or vapor are better suited to other forms of heat
    exchangers

27
CENTRAL COOLING
  • It is the cooling of a closed circuit of fresh
    non-corrosive and non-fouling water for use
    inside a plant, by means of brackish water.
    Central coolers are made of titanium, to
    withstand the brackish water

28
ADVANTAGES
  • Compactness
  • Flexibility
  • Very high heat transfer coefficients on both
    sides of the exchanger
  • Close approach temperatures and fully
    counter-current flow
  • Ease of maintenance. Heat transfer area can be
    added or subtracted with out complete dismantling
    the equipment

29
CONTD..
  • Ease of inspection on both sides
  • Ease of cleaning
  • Savings in required flow area
  • Low hold-up volume
  • Low cost
  • No Local over heating and possibility of stagnant
    zones is also reduced
  • Fouling tendency is less

30
LIMITATIONS
  • Low Pressure
  • upto 300 psi
  • Low temperature
  • upto 300 F
  • Limited capacity
  • Limited plate size
  • 0.02 sq.m to 1.5 sq.m

31
  • Large difference b/w flow rates cant be handled
  • High pressure drop
  • Potential for leakage

32
COMPARISON BETWEEN PHE AND STHE
FEATURES Multiple duty Hold up volume Gaskets modifications PHE Possible Low On each plate Easy by adding or removing plates STHE Impossible High On flanged joints impossible
33
FEATURES PHE STHE
Repair Detection of leakage Access for inspection Time reqd. for opening Fouling Easy to replace plates and gaskets Easy to detect On each side of plate 15 min 15 to 20 of STHE Requires tube plugging Difficult to detect Limited 60 to 90 min
34
FEATURES PHE STHE
Sensitivity to vibrations Not sensitive sensitive
35
  • DESIGN STEPS WITH SOLVED EXAMPLE

36
STATEMENT OF PROBLEM
  • A plate heat exchanger was use to preheat 4 kg/s
    of dowtherm from 10 to 70?C with a hot water
    condensate that was cooled from 95 to
    60?C.Determine the number of plates required for
    a single-pass counter flow plate and frame
    exchanger. Assume that each mild stainless-steel
    plate kw45j/s.m.Khas a length of 1.0m and a
    width of 0.25m with a spacing between the plates
    of 0.005m.Also,estimate the pressure drop of the
    hot water stream as it flows through the
    exchanger.

37
DATA REQUIRED
  • The performance characteristics for the chevron
    configuration selected for the plates are shown .
    For
  • Re gt 100,Nu and f can be represented by the
    following relationships
  • Nu 0.4 Re0.64Pr0.4
  • f 2.78Re-0.18

38
ASSUMPTIONS
  • The plate heat exchanger operates under steady
    state
  • conditions.
  • No phase change occurs both fluids are single
    phase and are unmixed.
  • Heat losses are negligible the exchanger shell
    is
  • adiabatic.
  • The temperature in the fluid streams is uniform
    over
  • the flow cross section.
  • There is no thermal energy source or sink in the
    heat
  • exchanger.
  • The fluids have constant specific heats.
  • The fouling resistance is negligible.

39
Properties of each fluid at the mean temperature
in the exchanger are
property
Dowtherm at 40
?C
Water at 77?C
4.198103J/kg.K
Heat capacity CP
1.622103 J/kg.K
0.138
J/.m.K
Thermal conductivity k
0.668J/s.m.K
Viscosity µ
3.7210-4Pa.s
2.7010-3Pa.s
Density ?
1.044102kg/m3
9.74102kg/m3
40
SOLUTION
  • APPROACH TO THE PROBLEM
  • To avoid an iterative calculation because of the
    interdependency between the heat transfer area
    and the total flow area, use the NTU approach to
    determine the NTUmin required, noting that
    NTUminUA/(mCp)min.the area of the plate and
    frame exchanger can be calculated once the
    overall heat transfer coefficient has been
    evaluated.

41
CALCULATION OF HT AREA
  • For a single pass configuration with Np plates
    and NP1 flow passages ,solution of the problem
    can be simplified mathematically by assuming n
    flow passages and n-1 plates ,since flow
    velocities involve flow passages and not plates.
    with this modification, the heat transfer surface
    area of the exchanger in terms of n is
  • A(n-1)LW(n-1)(1)(0.25)0.25(n-1)m2

42
CALCULATION OF FLOW AREA
  • The flow area for each stream with n/2flow
    passages is given by
  • Sn/2(W)(b)
  • n/2(0.25)(0.005)
  • (6.2510-4)n.

43
CALCULATION OF HEAT DUTY AND FLOW RATES
  • TOTAL RATE OF HEAT TRANSFER
  • FOR DOWTHERM
  • q (mCp?T)c
  • 4(1.622103)(70-10)
  • 3.89105W
  • THE MASS FLOW RATE OF WATER
  • mhq/(CP?T)h
  • 3.89105/(4.198103)(95-60)
  • 2.65 Kg/s
  • VELOCITY OF WATER
  • Vh mh /?hS
  • 2.65/(9.74102)(6.2510-4)n
  • (4.35/n)m/s

44
  • EQUIVALENT DIAMETER
  • De2b
  • 0.01m

45
CALCULATION OF HOT SIDE HT COEFFICIENT
  • REYNOLD NUMBER
  • RehDeVh?h /µh
  • 0.01(4.35/n)(9.74102)/(3.7210-4)
  • 1.139105/n
  • This indicates that Reynold number is greater
    than 100 and correlation for Nu can be used.
  • Pr NUMBER
  • Prh Cpµ/k
  • (4.198103)(3.7210-4)/0.668
  • 2.34
  • hh (0.4)(kh/De)Re0.64Pr0.4
  • 0.668/0.011.139105/n0.64(2.34)0
    .4
  • 6.467104/n0.64W/m2.K

46
CALCULATION OF COLD SIDE HT COEFFICIENT
  • The same calculations are repeated for cold
    stream.
  • Vmc/?c S
  • 4.0/(1.044103)(6.2510-4)n
  • 6.13/n
  • ReDeVc?c/µc
  • 0.01(6.13/n)(1.044103)/(2.7010-3)
  • 2.37104/n
  • Prc(1.622103)(2.7010-3)/(0.138)
  • 31.73
  • This also indicates that Regt100
  • hc(0.4)(kc/De)Re0.64Pr0.4
  • (0.4)(0.138/0.01)(237104/n)0.64
    (31.73)0.4
  • 1.388104 /n0.64 W/m2.K

47
CALCULATION OF OVERALL HT COEFFICIENT
  • The overall heat transfer coefficient can now be
    determined in terms of n. Since the surface areas
    on either side of the plate are the same, no
    correction for area is required.
  • Assume a thickness of the plate xw of 0.0032m
  • 1/U1/hhxw/kw1/hc
  • n0.64/(6.467104)(0.0032)/(45)n0.64/(1.38810
    4)
  • 8.75110-5n0.6477.1110-5 m. K/W

48
USING THE NTU METHOD
  • A NTUmin for cold stream with a minimum mcp is
    defined
  • NTUminUA/(Mcp)min
  • Tc,outTc,in/ f?T?,log
    mean
  • LOG MEAN TEMPERATURE DIFF
  • ?T?,log mean

    (Th,in-Tc,out)-(Th,out
    Tc,in)/ln(Th,in-Tc,out)/Th,out-Tc,in)
  • (95-70)-(60-10)/ln(95-70)/(60-10)
  • 36.067 K.
  • For a single pass counter flow plate and frame
    heat exchanger ,F1.

49
  • NTU 70-10/36.067
  • 1.664
  • To satisfy the other NTU definition of UA/(Mc) in
    terms of results in the relation

1
0.25(n-1)


1.664
(
)(

)


8.751105n0.647.1110-5
4.0(1.622103)
50
ITERATIVE METHOD
  • This equation can be solved with itreration to
    indicate that n51.Thus 50 plates are required to
    meet to the heat transfer needs to preheat 4kg/s
    of dowtherm from 10 to 70?C.

51
HYDRAULIC DESIGN
  • PRESSURE DROP IN WATER STREAM
  • Vh 4.35/510.0853m/s
  • Reh1.139105/512233
  • Since Regt100
  • f 2.78Re-0.18
  • 2.78(2233)-0.18
  • 0.694

52
CONTD..
  • Neglecting friction due to entrance and exit
    losses as well as temperature effects on the
    viscosity between the wall and the bulk fluids.
  • So pressure drop is calculated from the following
    equation
  • ?P4f(L/De)?h Vh2 /2
  • 4(0.694)(1/0.01) (9.74102)(0.0853)2/2
  • 984N/m2
  • 984Pa

53
CONCLUSION
  • Since the entrance and exit losses will be small,
    the pressure drop per plate
  • is small, and a new configuration with modified
    dimensions should be considered.
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