7.Heat exchanger sgfgfg design 4 .pptx (3).ppt

Design Temperature:
Usually 10°C higher than the maximum temperature of any
component in the heat exchanger .
Exm. Fluid temperature is near to 85°C not beyond this and
therefore we are taking 95°C as design temperature which is
10°C greater than maximum working temperature.
Design Pressure:
Generally design pressure is 5% greater than the maximum
allowable working pressure by gauge .

Maximum Allowable Stress Value:
The maximum allowable stress values for different materials can
be determined by referring Subpart 1 of ASME Section II, Part D.
Material is selected as per the fluid temperature flowing
inside exchanger.
Materials of construction Allowable fluid temperature, °C
(°F)
Carbon steel
C-Mo steel
Cr-Mo steel
Low alloy steel (< 6 % Cr)
Alloy steel (<17 % Cr)
Austenitic Cr-Ni steel
Cast iron
Brass
540 (1004)
590 (1094)
650 (1202)
590 (1094)
590 (1094)
650 (1202)
200 (392
200 (392)

Design components
The major mechanical design components of shell and tube
heat exchangers are:
• shell
•shell cover
•tube-sheet thickness,
• flanges,
•nozzles,
•gaskets,
•supports.

Shell diameter and thickness.
The nominal diameter (outside diameter) is rounded to the
nearest in the case of cylindrical pipe shell in mm:
159, 219, 267, 324, 368, 419, 457, 508,
558.8, 609.6, 660.4, 711.2, 762, 812.8, 863.6, 914.4 ,
1016.
Shell

The shell thickness ( ) can be calculated from the equation below
𝑡𝑠
based on the maximum allowable stress and corrected for joint
efficiency :
c
P
j
f
PD
t 



6
.
0
𝑡=shell thickness
𝑝= design pressure
𝐷= Shell Internal diameter
𝑓=Maximum allowable stress
of the material of construction
𝐽=Joint efficiency (usually
varies from 0.7 to 0.9)
If corrosion is possible then
On carbon steel add excess normally
ranges from 1/16" (1.6 mm) for mildly
corrosive conditions
to 1/8" (3.2 mm) for fairly severe
corrosive conditions.

TEMA HEAT EXCHANGER
LAYOUT DESIGNATION

E-Type shell- one pass shell
F-Type shell
two passes being separated by a
longitudinal baffle.
G-Type shell
the shell side pressure drop is small.
This is achieved by splitting the shell side flow.
H-Type shell
This is used for similar applications
to G-Type Shell but tends to be used
when larger units are required.

J-Type shell
The divided flow on the shell side reduces the flow velocities over
the tubes and hence reduces the pressure drop and the likelihood
of tube vibration. When there are two inlet nozzles and one outlet
nozzle this is sometimes referred to as an I-Type Shell.
K-Type shell
This is used only for reboilers to provide a large disengagement
space in order to minimize shellside liquid carry over. Alternatively
a K-Type Shell may be used as a chiller. In this case the main
process is to cool the tube side fluid by boiling a fluid on the
shellside.
X-Type shell
This is used if the maximum shellside pressure drop is exceeded by
all other shell and baffle type combinations. The main applications
are shellside condensers and gas cooler

Shell cover .
There are different types shell covers used in shell and tube
heat exchangers: flat, torispherical, hemispherical, conical
and ellipsoidal. Torispherical head is the most widely used in
chemical industries for operating pressure up to 200psi.
 
allowance
corrosion
-
c
radius
knucle
r
radius
Crown
3
4
1
2
.
0
2
i 

















i
i
i
i
R
r
R
W
c
P
j
f
W
PR
t
Torispherical head thickness:

Flat Channel cover (or head) diameter and thickness .
The thickness shall be greater of the two values: (i) shell
thickness or (ii) thickness calculated on the basis of the design
shown below.
f
P
C
D
t
10
1 


𝐷= diameter of the cover [mm] usually
same as the outside shell diameter
𝐶1= a factor which is
0.25 when the cover is bolted with full
faced gaskets and
0.3 when bolted with narrow faced or
ring type gaskets
𝑝= design pressure
𝑓= allowable stress

7.Heat exchanger sgfgfg design 4 .pptx (3).ppt

Tubes Dimensions
Tube diameters in the range 58 in. (16 mm) to 2 in. (50 mm) are
used.
The smaller diameters 5/8 to 1 in. (16 to 25 mm) are preferred for
most duties.
Larger tubes are easier to clean by mechanical methods and would
be selected for heavily fouling fluids.
The tube thickness (gauge) is selected to withstand the internal
pressure and give corrosion allowance.

The preferred lengths of tubes for heat exchangers are:
6 ft. (1.83 m),
8 ft (2.44 m),
12 ft (3.66 m),
16 ft (4.88 m)
20 ft (6.10 m),
24 ft (7.32 m).
For a given surface area, the use of longer tubes will reduce the
shell diameter; which will generally result in a lower cost
exchanger, particularly for high shell pressures.
The optimum tube length to shell diameter will usually fall within
the range of 5m to 10m.

Tube arrangements
The tubes in an exchanger are usually arranged in an equilateral
triangular, square, or rotated square pattern.

The recommended tube pitch (distance
between tube centers) is 1.25 times the
tube outside diameter.
Where a square pattern is used for ease
of cleaning, the recommended minimum
clearance between the tubes is 0.25 in.
(6.4 mm).
o
t d
P 
 25
.
1

Tube sheet .
Tube sheet is a circular flat plate with regular pattern drilled holes
according to the tube sheet layouts.
The open end of the tubes is connected to the tube sheet.
The tube sheet is fixed with the shell and channel to form the main
barrier for shell and tube side fluids.

welding (called integral
construction)
integral construction on
both sides,
The tube sheet is attached to the shell either by
One side integral
construction and other side
gasketed construction,
both sides are gasketed
construction

The minimum tube-sheet
thickness (TEMA standard) to
‘resist bending’
Where,
𝐹 =1 for fixed tube and floating type tube sheet;
𝐹=1.25 for U-tube tube sheet
Gp
1 . =diameter over which pressure is
𝐺𝑝
acting (for fixed tube sheet heat exchanger = - shell ID)
𝐺𝑝 𝐷𝑠
In a fixed tube sheet exchanger, the tube sheet is welded to the
shell.
f
k
P
FG
t
p
s
t


3
.

2. is port (narrow end
𝐺𝑝
diameter) inside diameter for
kettle type,
3.for floating tube sheet shall
𝐺𝑝
be used for stationery tube sheet.
𝑓= allowable stress for the tube sheet material

pitch
rotated
or
square
for
785
.
0
1
pitch
ular
for triang
907
.
0
1
2
2
















o
T
o
T
d
P
k
d
P
k
Pt- tube pitch

Tube-side passes (Pass partition plate)
The fluid in the tube is directed to flow back in a number of
“passes” through groups of tubes arranged in parallel, to increase
the length of the flow path.
The tubes are arranged into the number of passes required by
dividing the exchanger headers (channels) with partition plates
(pass partitions).

Pass partition plate
Pass partition plate specifies that the minimum thickness of
channel pass partition plates including corrosion allowance should
be 10 mm for both carbon steel and alloy up to channel size of 600
mm.
For higher channel size, the same should be 13 mm carbon steel
and 10 mm for alloy.
Pass partitions

Six tube passes
Two tube passes
Four tube passes

Baffles
They are fixed on the tube side between the tube bundle to
deflect the liquid or vapor-liquid mixture
Usually a metal plate about ¼ inch (6 mm) thick is used

Essentially, a shell and tube exchanger consists of a bundle of tubes
enclosed in a cylindrical shell. The ends of the tubes are fitted into
tube plate , which separate the shell-side and tube-side fluids.
Baffles are provided in the shell to direct the fluid flow and support
the tubes. The assembly of baffles and tubes is held together by
support rods and spacers.

Impingement plates
are fixed on the tube side between the tube bundle and inlet
nozzle to deflect the liquid or vapor-liquid mixture to protect
the tubes from erosion.
The protection against impingement may not be required for
the services involving non-corrosive, non-abrasive, single phase
fluids .
Usually a metal plate about ¼ inch (6 mm) thick is used as the
impingement plate.

Impingement plates
Impingement plates are fixed on the tube side
between the tube bundle and inlet nozzle to deflect
the liquid or vapor-liquid mixture to protect the tubes
from erosion.

Nozzles and branch pipes
In no case, the wall thickness of ferrous piping, excluding the
corrosion allowance shall be less than (0.04 c + 2.5) mm,
𝑑𝑜
where is the outside diameter of the connection.
𝑑𝑜𝑐
Piping connected to channel head
nozzles should be furnished with
break flanges to facilitate the
removal of channel head.

The typical nozzle size with shell ID

Gaskets
Gaskets are used to make the metal -to-metal surfaces leak-proof.
Gaskets are elasto-plastic materials and relatively softer than the
flange materials.
Deformation of gaskets under load seals the surface irregularities
between metal to metal surfaces and prevents leakage of the fluid.
For design pressures<16 kgf/cm2 and when there is no contact with
oil or oil vapor, the compressed asbestos fiber, natural or synthetic
rubber or other suitable gasket and packing materials having the
appropriate mechanical and corrosion resisting properties may be
used).

A preliminary estimation of gaskets is done using following
expression:
𝑅𝑒𝑠𝑖𝑑𝑢𝑎𝑙 𝑔𝑎𝑠𝑘𝑒𝑡 𝑓𝑜𝑟𝑐𝑒 = 𝐺𝑎𝑠𝑘𝑒𝑡 𝑠𝑒𝑎𝑡𝑖𝑛𝑔 𝑓𝑜𝑟𝑐𝑒
–( )
𝐻𝑦𝑑𝑟𝑜𝑠𝑡𝑎𝑡𝑖𝑐 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑓𝑜𝑟𝑐𝑒
This condition results the final expression in the form of:
)
1
( 



m
p
y
pm
y
D
D
ig
og
𝐷𝑂𝐺=outside gasket diameter [mm]
𝐷𝐼𝐺=inside gasket diameter [mm];

𝑝=design pressure
Y= minimum design seating stress
𝑚= gasket factor
gasket width, =(
𝑁 𝐷𝑂𝐺−𝐷𝐼𝐺)/2
The IS:4503 specifies that the minimum width of peripheral ring
gaskets for external joints shall be:
10 mm for shell sizes up to 600 mm nominal diameter and
13 mm for all larger shell sizes

7.Heat exchanger sgfgfg design 4 .pptx (3).ppt

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