heat exchanger ppt
TRANSCRIPT
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HEAT EXCHANGERS
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INTRODUCTION:
Shell and tube heat exchangers are one of the most
common equipment found in all plants
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How it works?
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WHAT ARE THEY USED FOR?
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Heat Exchanger
Cooler
Heater
Condenser
Reboiler
Both sides single phase and process stream
One stream process fluid and the other cooling water or air
One stream process fluid and heating utility as steam
One stream condensing vapor and the other cooling water or air
One stream bottom stream from a distillation column and the other a hot utilityor process stream
Classification according to service .
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DESIGN CODES:
Code
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Standard
Specifications
Is recommended method of doing something
ASME BPV – TEMA
is the degree of excellence required
API 660-ASME B16.5–ASME B36.10M–ASME B36.19-ASME B16.9–ASME B16.11
Is a detailed description of construction, materials,… etc
Contractor or Owner specifications
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MAIN COMPONENTS
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2- Channel
3- Channel Flange
4- Pass Partition
5- Stationary Tubesheet
6- Shell Flange
7- Tube
8- Shell
9- Baffles
10- Floating Head backing Device
11- Floating Tubesheet
12- Floating Head
13- Floating Head Flange
14 –Shell Cover
1- Channel Cover
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TEMA
HEAT
EXCHANGER
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TEMA HEAT EXCHANGER
Front Head Type
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A - Type B - Type C - Type
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TEMA HEAT EXCHANGER
Shell Type
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E - Type F - Type
J - TypeK - Type
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TEMA HEAT EXCHANGER
Rear End Head Types
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M - Type S - Type T - Type
Fixed Tubesheet Floating Head Pull-Through Floating Head
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CLASSIFICATION:
U-Tube Heat Exchanger
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Fixed Tubesheet Heat Exchanger
Floating Tubesheet Heat exchanger
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EXAMPLE
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AKT
EXAMPLE
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HEAT EXCHANGERS MECHANICAL
DESIGN
Terminology
Design data
Material selection
Codes overview
Sample calculations
Hydrostatic test
Sample drawing
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DESIGN DATA
Heat Exchanger Data Sheet :
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Design pressure
Design temperature
Dimensions / passes
Tubes ( dimensions, pattern)
Nozzles & Connections
TEMA type
Baffles (No. & Type)
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MATERIAL SELECTION
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Material
Selection
Strength
Corrosion Resistance
Fabricability
Cost
&Availabilit
y
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HEAT EXCHANGERS:
DESIGN CONSIDERATIONS
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TYPES
Heat Exchanger Types
Heat exchangers are used to energy conversion and utilization. They
involve heat exchange between two fluids separated by a solid and
encompass a wide range of flow configurations.
• Concentric-Tube Heat Exchangers
Parallel Flow Counterflow
Simplest configuration.
Superior performance associated with counter flow.
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TYPES (CONT.)
• Cross-flow Heat Exchangers
Finned-Both Fluids
Unmixed
Unfinned-One Fluid Mixed
the Other Unmixed
For cross-flow over the tubes, fluid motion, and hence mixing, in the
transverse direction (y) is prevented for the finned tubes, but occurs
for the un-finned condition.
Heat exchanger performance is influenced by mixing.
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TYPES (CONT.)
• Shell-and-Tube Heat Exchangers
One Shell Pass and One Tube Pass
Baffles are used to establish a cross-flow and to induce turbulent mixing of the
shell-side fluid, both of which enhance convection.
The number of tube and shell passes may be varied, e.g.:
One Shell Pass,
Two Tube Passes
Two Shell Passes,
Four Tube Passes
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TYPES (CONT.)
• Compact Heat Exchangers
Widely used to achieve large heat rates per unit volume, particularly
when one or both fluids is a gas.
Characterized by large heat transfer surface areas per unit volume, small
flow passages, and laminar flow.
(a) Fin-tube (flat tubes, continuous plate fins)
(b) Fin-tube (circular tubes, continuous plate fins)
(c) Fin-tube (circular tubes, circular fins)
(d) Plate-fin (single pass)
(e) Plate-fin (multipass)
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OVERALL COEFFICIENT
Overall Heat Transfer Coefficient
• An essential requirement for heat exchanger design or performance calculations.
• Contributing factors include convection and conduction associated with the
two fluids and the intermediate solid, as well as the potential use of fins on
both sides and the effects of time-dependent surface fouling.
• With subscripts c and h used to designate the hot and cold fluids, respectively,
the most general expression for the overall coefficient is:
, ,
1 1 1
1 1
c h
f c f h
w
o o o oc c h h
UA UA UA
R RR
hA A A hA
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OVERALL COEFFICIENT
o,
Overall surface efficiency of fin array (Section 3.6.5)
1 1
o
f
c or h f
c or h
A
A
total surface area (fins and exposed base) surface area of fins only
t
f
A AA
Assuming an adiabatic tip, the fin efficiency is
,
tanhf c or h
c or h
mL
mL
2 /c or h p w c or hm U k t
, partial overall coe1
fficientp c or h
f c or h
hUhR
2 for a unit surfFouling fact ace area (m W)or K/fR
Table 11.1
conduction resistan Wall (K/Wce )wR
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LMTD METHOD
A Methodology for Heat Exchanger
Design Calculations- The Log Mean Temperature Difference (LMTD) Method -
• A form of Newton’s Law of Cooling may be applied to heat exchangers by
using a log-mean value of the temperature difference between the two fluids:
1mq U A T
1 2
1
1 21n /m
T TT
T T
Evaluation of depends on the heat exchanger type.1 2 and T T
• Counter-Flow Heat Exchanger:
1 ,1 ,1
, ,
h c
h i c o
T T T
T T
2 ,2 ,2
, ,
h c
h o c i
T T T
T T
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LMTD METHOD (CONT.)
• Parallel-Flow Heat Exchanger:
1 ,1 ,1
, ,
h c
h i c i
T T T
T T
2 ,2 ,2
, ,
h c
h o c o
T T TT T
Note that Tc,o can not exceed Th,o for a PF HX, but can do so for a CF HX.
For equivalent values of UA and inlet temperatures,
1 , 1 ,m CF m PFT T
• Shell-and-Tube and Cross-Flow Heat Exchangers:
1 1 ,m m CFT F T
Figures 11.10 - 11.13F
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ENERGY BALANCE
Overall Energy Balance
• Assume negligible heat transfer between the exchanger and its surroundings
and negligible potential and kinetic energy changes for each fluid.
, ,h i h ohq m i i
, ,c c o c iq m i i
fluid enthalpyi
• Assuming no l/v phase change and constant specific heats,
, , ,p h h i h ohq m c T T
, ,h h i h oC T T
, , ,c p c c o c iq m c T T
, ,c c o c iC T T
, Heat capacity r s ateh cC C
• Application to the hot (h) and cold (c) fluids:
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SPECIAL CONDITIONS
Special Operating Conditions
Case (a): Ch>>Cc or h is a condensing vapor .hC
– Negligible or no change in , , .h h o h iT T T
Case (b): Cc>>Ch or c is an evaporating liquid .cC
– Negligible or no change in , , .c c o c iT T T
Case (c): Ch=Cc.
1 2 1mT T T –
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PROBLEM: OCEAN THERMAL ENERGY
CONVERSION
Design of a two-pass, shell-and-tube heat exchanger to supply
vapor for the turbine of an ocean thermal energy conversion
system based on a standard (Rankine) power cycle. The power
cycle is to generate 2 MWe at an efficiency of 3%. Ocean water
enters the tubes of the exchanger at 300K, and its desired outlet
temperature is 292K. The working fluid of the power cycle is
evaporated in the tubes of the exchanger at its phase change
temperature of 290K, and the overall heat transfer coefficient is
known.
FIND: (a) Evaporator area, (b) Water flow rate.
SCHEMATIC:
Problem :