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PLATE HEAT EXCHANGER

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... Total pressure drop Pt Pt = Pc + Pp = 26,547 + 50,999 = 77546 N/m2 0.78 bar engineering-resource.com Thank You engineering -resource.com ... – PowerPoint PPT presentation

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Title: PLATE HEAT EXCHANGER


1
PLATE HEAT EXCHANGER
2
GROUP MEMBERS
  • Nadeem Akhtar (2006-chem-22)
  • Matloob Ahmed (2006-chem-26)
  • Zohaib Atiq Khan (2006-chem-40)

3
Introduction to PHE
  • Second abundantly used HEX after STHE.
  • Fall in the category of compact heat exchangers.
  • Mostly used in food industry like milk, beverages
    and juices industry.
  • Is usually comprised of a stack of corrugated or
    embossed metal plates in mutual contact.

4
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5
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6
Facts and figures on Plate Heat Exchanger

7
1-Size range for unit and plates
  • For unit

Size 1540-2500m2
Number of plates Up to 700
Port size Up to 39 cm
8
1-Size range for unit and plates
  • (b) For plates

Thickness. 0.5 1.2mm
Size. 0.03 2.2m
Spacing. 1.5 5mm
Corrugation depth. 3 5mm
9
2-Standrad performance limits
Max. operating pressure. 30 bar. Or 360psi.
Max. operating temperature. 200oC. Or 390 0F
Max. flow rate. 3600 m3/hr. Or 950,000USG/min.
Heat transfer coefficient. 3500 7500 W/m2 .oC Or 600 1300 BTU/ft2 hr of
10
2-Standrad performance limits
Heat transfer area. 0.1 2200 m2 or 2 24,000 ft 2
NTU. 0.3 0.4
Pressure drop. 30kpa per NTU
Temperature approach. As low as 2 oC
Heat recovery. As high as 93
11
Mechanical parts of PHE
  • Plates (provide heat transfer area)
  • Gasket (prevents leakage of fluids).
  • Frame (for enclosure, on front).
  • Pressure plate (to press the plates on rare
    side).
  • Support column (to support the exchanger).
  • Splitter (plate dividing the PHE in parts in
    case of multi-streaming)
  • Tightening bolts

12
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13
Multi streaming using splitter plate
14
Material of construction
  • (1) Plates
  • As plates are very thin (0.5 1.2mm) So we can
    not compromise on material of construction plates
    are usually made of very strong materials,
    depending on operatin conditions
  • (a) stainless steel AISI 304
  • (b) stainless steel AISI 316
  • (c) Hastelloy B
  • (d) Hastelloy c-276
  • (e) alluminium brass 76/22/2
  • (f) incoloy 825

15
Material of construction
  • (2) Gaskets

Nitrile rubber. Used up to 110 oC for mineral oils, dilute mineral acids, and aliphatic hydrocarbons.
EPDM. (ethylene-propylene-diene monomer) Used up to 160 oC for mineral acids, or bases, aqeuous solutions or steam
Viton. ( copolymer of vinylidine flouride and hexafluoro-propylene) Used up to 100 oC for hydrocarbons and chlorinated hydrocarbons
16
Classification of PHES
  • Plate heat exchangers can be classified based on
  • Joints
  • Plate corrugations.
  • Flow arrangements.

17
Classification of PHES
  • Based on joints PHES are classified in to three
    types
  • Gasketted.
  • Brazed.
  • Welded.

18
Classification of PHES
  • (1) gasketted.

19
Classification of PHES
  • (2) brazed.

20
Classification of PHES
  • (3) Welded plate.

21
Classification of PHES
  • Based on corrugation two types of PHES exist
  • (a) Wash board.
  • (b) Chevron.

22
Classification of PHES
  • Based on flow arrangement
  • Series flow
  • U-arrangement

23
Advantages of PHE
  1. A PHE offers very high heat transfer coefficient.
    Increase in H.T coefficient is three to five
    times.
  2. Is suitable even for a close approach temperature
    as low as 2 oC, and for a large temperature
    cross.
  3. Offers ease of inspection, cleaning and
    maintenace.
  4. Heat transfer area can be increased or decreased
    by adding or removing some plates.
  5. Conveniently performs multiple heat exchange
    duties in a single exchanger.
  6. Requires much less floor soace.
  7. Costs less than shell and tube heat exchanger
    especially when expensive material of
    construction is used.

24
Disadvantages
  1. Effect of fouling because of scaling, deposition
    of solids by crystallization, corrosion, and even
    by biological materials is quite significant in
    PHES
  2. Large over design is required. For example in an
    STHEX for a fouling resistance of 1.7610-4
    will increase the required surface area by 35 in
    case of STHEX but will increase the required
    surface area of a PHE by about 100.
  3. The allowable fouling resistance in PHE is one
    tenth of that in STHEX.

25
Applications
  • Dairy industry
  • Pharmaceuticals
  • Food processing
  • Petroleum and chemical industries
  • Pulp and paper industry
  • Power generation
  • Reboiling or condensing services

26
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27
Applications for which PHES are not recommended
  1. Gas-to-gas applications
  2. Fluids with very high viscosities may pose to
    distribution problems, flow velocities less than
    0.1m/s are not used because of low H.T
    coefficient.
  3. Less suitable for vapours condensing under vacuum

28
Design of Plate Heat Exchanger
29
Thermal Design Steps
  • Step 1
  • Calculate properties of fluids i.e
  • density, viscosity, thermal conductivity,
    specific heat
  • Also determine fluids unknown inlet and outlet
    temperatures and flow rates

30
  • Step 2
  • Calculate heat duty, the rate of heat transfer
    required
  • Qc (mcp)c (t2-t1)
  • Qh (mcp)h (T2-T1)

31
Step 3
  • Calculate the log mean temperature difference,
    LMTD
  • LMTD (T1-t2) (T2-t1)
  • ln(T1-t2)/(T2-t1)

32
Step 4
  • Determine the log mean temperature correction
    factor, Ft
  • NTU ( To- Ti )
  • LMTD
  • Where
  • Ti stream inlet temperature C
  • To stream outlet temperature C
  • LMTD log mean temperature difference C

33
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34
Step 5
  • Calculate the corrected mean temperature
    difference
  • ?Tm Ft x LMTD

35
Step 6
  • Select specific construction of the plates
    suitable for the required service like
  • Plate material
  • Port diameter
  • Gasket material

36
Step 6 contd
  • Corrugation type

Washboard pattern
Chevron pattern
37
Step 6 contd
  • Effective length
  • Width
  • Plate pitch

38
Step 7
  • Estimate the overall heat transfer coefficient

39
Step 8
  • Calculate the surface area required
  • Q UA (Ft x LMTD )
  • A Q
  • U (Ft x LMTD )

40
Step 9
  • Determine the number of plates required
  • Number of plates Total surface area
  • Area of one plate

41
Area of one plate
A (L D) x W
42
Step 10
  • Decide the flow arrangement and number of passes

43
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44
Step 11
  • Calculate the film heat transfer coefficients for
    each stream
  • Nu C Ren Prm (µ/µw)x
  • Typical reported values are
  • C 0.15-0.40
  • n 0.65-0.85
  • m 0.30-0.45 (usually 0.333)
  • x 0.05-0.20

45
Step 11 continued
  • Most popular correlation for preliminary estimate
    of area is
  • (hde/kf) 0.26 Re0.65 Pr0.4 (µ/µw)0.14
  • Also we can use general relation
  • (hde/kf) Ch Ren Pr1/3 (µ/µw)0.17

46
Ch n values
47
Step 12
  • Calculate the overall coefficient, allowing for
    fouling factors
  • 1 1 1 t Rfh Rfc
  • Ud hh hc kw

48
Step 13
  • Compare the calculated with the assumed overall
    coefficient.
  • If satisfactory, say - 0 to 10 error,
    proceed. If unsatisfactory return to step 7 and
    estimate another value of overall heat transfer
    coefficient U

49
Hydraulic Design
  • Pressure Drop Calculations

50
Step 14
  • Check the pressure drop for each stream
  • Channel pressure drop
  • ?Pc 8 f Lp ?up2
  • de 2
  • f 0.6 Re-0.3

51
Step 14 continued
  • We can also use
  • ?Pc 4 f LpNp Gc2 (µ/µw)- 0.17
  • de 2?
  • f Kp
  • Rem

52
Kp m values
53
Step 14 continued
  • Port pressure drop
  • ?Pp 1.3Np?upt2
  • 2
  • upt the velocity through the ports w/?Ap, m/s,
  • w mass flow through the ports, kg/s,
  • Ap area of the port (3.14xd2pt)/4, m2,
  • dpt port diameter, m,
  • Np number of passes

54
Step 14 continued
  • Total pressure drop ?Pt
  • ?Pt ?Pc ?Pp

55
Design Problem
56
Statement
  • Design a gasketed plate heat exchanger to cool
    methanol from 95 C to 40C. Flow-rate of
    methanol is 100,000 kg/h. Brackish water is used
    as coolant, with a temperature rise from 25 to
    40C.

57
Step 1
Physical properties of fluids Methanol Water
Density (kg/m3) 750 995
Viscosity (mNm-2s) 3.4 0.8
Specific Heat Cp (kJ/kg oC) 2.84 4.2
Thermal conductivity (W/moC) 0.19 0.59
58
Step 2
  • Heat duty of hot fluid (methanol)
  • Qh (mcp)h (T2-T1)
  • 100000 x 2.84 x (95 - 40)
  • 3600
  • 4340 kW

59
Step 2 contd.
  • Mass flow rate of cold fluid (Water)
  • As Qh Qc
  • mc Qh
  • Cpc x (t2 t1)
  • 4340
  • 4.2 x (40 - 25)
  • 68.9 kg/s

60
Step 3
  • LMTD Calculation
  • (Methanol) 95 0C 40 0C
  • (Water) 40 0C 25 0C
  • LMTD (T1-t2) (T2-t1)
  • ln(T1-t2)/(T2-t1)
  • (95 40 ) (40 - 25)
  • ln(95 40 )/(40 - 25)
  • 31 oC

61
Step 4
  • Correction factor Ft
  • NTU ( To- Ti ) 95 - 40
  • LMTD 31
  • 1.77
  • From figure 12.62
  • try 1 1 pass
  • Ft 0.96

62
0.96
1.77
63
Step 5
  • ?Tm Ft x LMTD
  • 0.96 x 31
  • 29.76 0C

64
Step 6
  • Estimate the overall heat transfer coefficient

65
Step 7
  • Calculate the surface area required
  • A Q
  • U (Ft x LMTD )
  • 4340000
  • 2000 x (0.96 x 31)
  • 72.92 m2

66
Step 8
  • Select area of one plate
  • Assuming
  • effective Length of plate 1.5 m
  • effective width of plate 0.5 m
  • plate spacing 3 mm
  • then
  • effective area of plate 0.75 m2

67
Step 8
  • Determine the number of plates required
  • Number of plates total surface area
  • area of one plate
  • 72.92
  • 0.75
  • 97

68
Step 8
  • No need to adjust this, 97 will give an even
    number of channels per pass, allowing for an end
    plate
  • Number of channels per pass (N) (97 - 1 )/2
  • 48
  • Channel cross-sectional area (Ac) 3 x 10-3 x
    0.5
  • 0.0015 m2
  • hydraulic mean diameter (de) 2 x 3 x 10-3
  • 6 x 10-3 m

69
Step 9
  • Selection of flow arrangement and number of
    passes
  • No of passes 1 - 1
  • Flow arrangement U - Arrangement

70
Step 10
  • (Methanol) film heat transfer coefficient hh
  • Channel velocity m
  • ? x Ac x N
  • 27.8
  • 750 x 0.0015 x 48
  • 0.51 m/s

71
(Methanol) film heat transfer coefficient hh
  • Re ? x up x de
  • µ
  • 750 x 0.51 x 6x10-3
  • 0.34x10-3
  • 6750

72
(Methanol) film heat transfer coefficient hh
  • hh 0.26 Re0.65 Pr0.4 (µ/µw)0.14kf/de
  • Pr µCp/k 5.1
  • hh 0.26 (6750)0.65 (5.1)0.4 0.19/6x10-3
  • 4870 W/m2oC

73
(Water) film heat transfer coefficient hc
  • Channel velocity m
  • ? x Ac x N
  • 68.9
  • 995 x 0.0015 x 48
  • 0.96 m/s

74
(Water) film heat transfer coefficient hc
  • Re ? x up x de
  • µ
  • 995 x 0.96 x 6x10-3
  • 0.8x10-3
  • 6876

75
(Water) film heat transfer coefficient hc
  • hc 0.26 Re0.65 Pr0.4 (µ/µw)0.14kf/de
  • Pr µCp/k 5.7
  • hc 0.26 (6876)0.65 (5.7)0.4 0.59/6x10-3
  • 16,009 W/m2 0C

76
Step 11
  • Overall heat transfer coefficient Ud
  • 1 1 1 t Rfh Rfc
  • Ud hh hc kw
  • 1 1 0.75x10-3 0.0001 0.00017
  • 4870 16,009 21
  • Ud 1754 W/m2 0C
  • (too low than 2000 W/m2 0C )

77
Fouling Factors
78
Step 12
  • The value of design overall coefficient i.e 1754
    W/m2 0C is too low than assumed or estimated
    value i.e 2000 W/m2 0C )

79
Iterative procedure
  • Again assume U(estimated)
  • U(estimated) 1600 W/m2 0C
  • Area (A) 91.94 m2
  • Number of plates 121
  • hh 4215 W/m2 0C
  • hc 13,846 W/m2 0C
  • Ud 1634 W/m2 0C
  • Ud U(estimated)

80
  • Hence
  • Number of plate per pass (121 1) / 2
  • 60

81
Step 13a
  • Pressure drop calculations
  • Channel pressure drop (Methanol)
  • f 0.6 Re-0.3
  • f 0.60(5400)-0.3 0.046
  • ?Pc 8 f Lp ?up2
  • de 2
  • Path length Lp plate length x number of passes
  • 1.5 x 1 1.5 m.

82
Channel pressure drop (Methanol)
  • up 0.41 m/s
  • ? 750 kg / m3
  • de 6x10-3 m
  • ?Pc 5799 N / m2

83
Port pressure drop (methanol)
  • ?Pp 1.3Np?upt2
  • 2
  • Port diameter dpt 100 mm
  • Port area 3.14xd2pt/4 0.00785 m2
  • Port velocity 27.8/(750 x0.00785 )
  • 4.72 ms-1
  • ?Pp 10,860 Nm-2

84
Pressure drop (Methanol)
  • Total pressure drop ?Pt
  • ?Pt ?Pc ?Pp
  • 5799 10,860
  • 16,659 N/m2 0.16 bar

85
Step 13b
  • Channel pressure drop (water)
  • f 0.6 Re-0.3
  • f 0.60(5501)-0.3 0.045
  • ?Pc 8 f Lp ?up2
  • de 2
  • Path length Lp plate length x number of passes
  • 1.5 x 1 1.5 m.

86
Channel pressure drop (water)
  • up 0.77 m/s
  • ? 995 kg / m3
  • de 6x10-3 m
  • ?Pc 26,547 N / m2

87
Port pressure drop (water)
  • ?Pp 1.3Np?upt2
  • 2
  • Port diameter dpt 100 mm
  • Port area 3.14xd2pt/4 0.0078 m2
  • Port velocity 68.9/(995 x 0.0078 )
  • 8.88 ms-1
  • ?Pp 50,999 Nm-2

88
Pressure drop (water)
  • Total pressure drop ?Pt
  • ?Pt ?Pc ?Pp
  • 26,547 50,999
  • 77546 N/m2 0.78 bar

89
Thank You
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