Operator Generic Fundamentals
Components – Heat Exchangers and Condensers
© Copyright 2014
Operator Generic Fundamentals
2
Heat Exchangers and Condensers
Principles of Operation
• Transfer heat from one fluid to another
– Fluids must be at different temperatures
– Fluids must come into thermal contact
– Heat flows from hotter to cooler fluid
• Maintains separation between the two fluids
© Copyright 2014
Intro
Operator Generic Fundamentals
3
Terminal Learning Objectives
At the completion of this training session, the trainee will demonstrate
mastery of this topic by passing a written exam with a grade of ≥ 80%
on the following areas:
1. Describe the purpose, construction, and principles of operation
for each major type of heat exchanger.
2. Describe the purpose, construction, and principles of operation
of condensers.
© Copyright 2014
Intro
Operator Generic Fundamentals
4
Heat Exchanger Construction & Operation
TLO 1 – Describe the purpose, construction, and principles of operation
for each major type of heat exchanger.
• Heat exchangers transfer heat from higher energy to lower energy
system
• Conduction and convection heat transfer methods
• Allows systems to maintain physical separation of processes
• Heat exchangers use different flow designs, including counter and
cross flow
© Copyright 2014
TLO 1
Operator Generic Fundamentals
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Enabling Learning Objectives for TLO 1
1. Describe the construction, effectiveness, and operation of the
following types of heat exchangers and their components (tubes,
tube sheets, baffles and shells):
a. Tube and shell
b. Plate
2. Describe hot and cold fluid flow paths in the following types of heat
exchangers:
a. Parallel flow
b. Counter flow
c. Cross flow
3. Describe the difference between the following types of heat
exchangers:
a. Single-pass versus multipass heat exchangers
b. Regenerative versus nonregenerative heat exchangers
© Copyright 2014
TLO 1
Operator Generic Fundamentals
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Enabling Learning Objectives for TLO 1
4. Describe the operation of a typical heat exchanger to include the
following:
a. Startup and shutdown
b. Control of temperature
c. Effects and control of fouling
5. Given the necessary data, calculate flow rates, and temperatures
for various types of heat exchangers.
6. Explain the consequences of heat exchanger tube failure.
© Copyright 2014
TLO 1
Operator Generic Fundamentals
7
Types of Heat Exchangers
ELO 1.1 – Describe the construction, effectiveness, and operation of the
following types of heat exchangers and their components (tubes, tube
sheets, baffles, and shells): tube and shell and plate.
• Heat exchanger construction falls into one of two categories:
– Tube and shell
– Plate
• Each type has advantages and disadvantages
© Copyright 2014
ELO 1.1
Operator Generic Fundamentals
8
Types of Heat Exchangers
Tube and Shell
• Most basic and most common type
• Consists of tubes in a container called a shell
• Fluid is separated from the shell-side fluid by the tube sheet(s)
• Tubes can withstand higher pressures than shells
• Support plates act as baffles, directing the flow of fluids
Figure: Tube and Shell Heat Exchanger
© Copyright 2014
ELO 1.1
Operator Generic Fundamentals
9
Types of Heat Exchangers
Plate Heat Exchanger
• Consists of plates instead of
tubes to separate the hot and
cold fluids
• Fluids alternate between
each of the plates
• Baffles direct the flow of fluid
between the plates
• Plates have a large surface
area and provide each of the
fluids with an extremely large
heat transfer area
Figure: Plate Heat Exchanger
© Copyright 2014
ELO 1.1
Operator Generic Fundamentals
10
Heat Exchanger Applications
• Heat exchangers are found in most chemical or mechanical systems
• Common applications are:
– Ventilation and air conditioning (HVAC) systems
– Radiators on internal combustion engines
– Boilers
– Condensers
– Preheaters or coolers
© Copyright 2014
ELO 1.1
Operator Generic Fundamentals
11
Preheaters and Feedwater Heaters
• Some heaters, such as feedwater, heat in stages verses all heat
transfer in one large heat exchanger
– Increases the plant's efficiency
– Minimizes thermal shock stress to components compared to
injecting ambient temperature liquid into a boiler (reactor) or other
device that operates at high temperatures
– In a steam system, a portion of the processed steam is tapped off
and used as heat source to preheat the feedwater in preheater
stages
© Copyright 2014
ELO 1.1
Operator Generic Fundamentals
12
Preheaters and Feedwater Heaters
• Below is an example of construction and internals of a U-tube
feedwater heat exchanger found in a preheater stage of a power plant
Figure: Feedwater Heater
© Copyright 2014
ELO 1.1
Operator Generic Fundamentals
13
Radiator
A heat exchanger is any device that transfers heat from one fluid to
another.
• Some equipment uses air-to-liquid heat exchangers
• An example of an air-to-liquid heat exchanger is a car radiator
– Coolant flowing in engine picks up heat from engine block and
carries it to radiator
• Hot coolant flows into tube side of radiator (heat exchanger)
• Relatively cool air flowing over the outside of the tubes picks up the
heat, reducing temperature of coolant
• Fins on the outside of the tubes increase surface area for heat
transfer and maximize heat transfer efficiency
© Copyright 2014
ELO 1.1
Operator Generic Fundamentals
14
AC Evaporator and Condenser
• AC units contain at least two heat exchangers, usually called
evaporator and condenser
• In each of these, refrigerant fluid flows into heat exchanger and
transfers heat, either gaining or releasing it to cooling medium, which
is commonly air or water
• In the condenser, the hot, high-pressure refrigerant gas condenses to
a subcooled liquid
• In evaporator,subcooled refrigerant flows into heat exchanger, heat
flow is reversed, cool refrigerant absorbs heat from hotter air flowing
on the outside of tubes
• Cools the air and boils refrigerants
© Copyright 2014
ELO 1.1
Operator Generic Fundamentals
15
Condenser
Condenser is a type of heat exchanger used to condense a substance
from a gaseous state to a liquid state by cooling.
• Condenser removes latent heat from the condensing fluid and
transfers it to coolant
• Normally, tube and shell heat exchanger serves as a condenser
• Baffles usually added at inlet to prevent tube impingement from
incoming gas or steam
• Frequently use large steam condensers as heat sinks for steam
system
© Copyright 2014
ELO 1.1
Operator Generic Fundamentals
16
Types of Heat Exchangers
Knowledge Check
In a tube and shell heat exchanger, the fluid flowing ________ the
tubes is called the tube-side fluid and the fluid flowing _________ of the
tubes is the shell-side fluid.
A. around; inside
B. around; outside
C. inside; outside
D. outside; inside
Correct answer is C.
© Copyright 2014
ELO 1.1
Operator Generic Fundamentals
17
Heat Exchanger Classification
ELO 1.2 – Describe hot and cold fluid flow paths in the following types of
heat exchangers: parallel flow, counter flow, and cross flow.
Parallel Flow
• Tube-side and shell-side fluid
flow in the same direction
• Fluids enter from same end
with large temperature
difference
• Heat transfers from hotter to
cooler
Figure: Parallel-Flow Heat Exchanger
– Temperatures of two fluids
approach each other
– Hottest cold-fluid
temperature is always less
than the coldest hot-fluid
temperature
© Copyright 2014
ELO 1.2
Operator Generic Fundamentals
18
Heat Exchanger Classification
Counter Flow
• Fluids flow in opposite directions and enter at opposite ends
• Cooler fluid will approach inlet temperature of the hot fluid
• Generally most efficient type of heat exchanger
• Hottest cold-fluid temperature can actually be greater than the
coldest hot-fluid temperature
Figure: Counter-Flow Heat Exchanger
© Copyright 2014
ELO 1.2
Operator Generic Fundamentals
19
Heat Exchanger Classification
Cross Flow
• Fluid flows perpendicular
• Usually used when one of the fluids changes phase
• Large volumes of vapor may be condensed
• Most efficient when comparing heat transfer rate per unit surface area
• Average difference in temperature (∆T) between two fluids over the
length of the heat exchanger is maximized
Figure: Cross-Flow Heat Exchanger
© Copyright 2014
ELO 1.2
Operator Generic Fundamentals
20
Heat Exchanger Comparison
• Compare average temperature difference across heat exchanger
• Heat exchanger with largest average temperature difference is more
efficient
• Mean (average) temperature for a heat exchanger calculated using
this equation:
∆𝑇𝑙𝑚 =
© Copyright 2014
∆𝑇2 − ∆𝑇1
∆𝑇2
𝑙𝑛
∆𝑇1
ELO 1.2
Operator Generic Fundamentals
21
Heat Exchanger Comparison
• When the values for Δ 𝑇𝑙𝑚 are determined, rate of heat transfer ( ) in
a heat exchanger is calculated using:
𝑄 = 𝑈𝑜 𝐴𝑜 ∆𝑇𝑙𝑚
Where:
• 𝑄 = heat transfer rate (BTU/hr)
• Uo = overall heat transfer coefficient (BTU/hr-ft2-°F)
• Ao = cross-sectional heat transfer area (ft2)
• ∆Tlm = log mean temperature difference (°F)
© Copyright 2014
ELO 1.2
Operator Generic Fundamentals
22
Heat Exchanger Comparison
• Consider the following example of a heat exchanger operated under
identical conditions as a counter-flow and then a parallel-flow heat
exchanger.
𝑇1 = hot fluid temperature
𝑇1 𝑖𝑛 = 200°F
𝑇1 𝑜𝑢𝑡 = 145°F
𝑈0 = 70 BTU/hr - ft2 - °F
𝐴0 = 75 ft2
𝑇2 = cold fluid temperature
𝑇2 𝑖𝑛 = 80°F
𝑇2 𝑜𝑢𝑡 = 120°F
© Copyright 2014
ELO 1.2
Operator Generic Fundamentals
23
Heat Exchanger Comparison
Counter flow:
(200℉ − 120℉) − (145℉ − 80℉)
∆Tlm =
= 72℉
200℉ − 120℉
145℉ − 80℉
∆Tlm = 72 ℉
Parallel flow:
(200℉ − 80℉) − (145℉ − 120℉)
∆Tlm =
= 61℉
200℉ − 80℉
145℉ − 120℉
∆Tlm = 61℉
© Copyright 2014
ELO 1.2
Operator Generic Fundamentals
24
Heat Exchanger Comparison
Inserting values from previous calculation into heat transfer equation
for counter-flow heat exchanger yields:
Q=
70 BTU
ℎ𝑟 − 𝑓𝑡 2 − ℉
75 𝑓𝑡 2 61℉
5
Q = 3.8 × 10 BTU/hr
Inserting values from previous calculation into heat transfer equation
for parallel-flow heat exchanger yields:
70 BTU
Q=
ℎ𝑟 − 𝑓𝑡 2 − ℉
75 𝑓𝑡 2 61℉
5
Q = 3.2 × 10 BTU/hr
© Copyright 2014
ELO 1.2
Operator Generic Fundamentals
25
Classification by Flowpath
Knowledge Check
Refer to the drawing of a lube oil heat exchanger below. The heat exchanger is
operating with the following parameters:
𝑇𝑜𝑖𝑙 𝑖𝑛 = 174°F
𝑇𝑜𝑖𝑙 𝑜𝑢𝑡 = 114°F
𝐶𝑝 𝑜𝑖𝑙 = 1.1
𝑚𝑜𝑖𝑙 = 4 x 104 lbm/hr
𝑇𝑤𝑎𝑡𝑒𝑟 𝑖𝑛 = 85°F
𝑇𝑤𝑎𝑡𝑒𝑟 𝑜𝑢𝑡 = 115°F
𝐶𝑝 𝑜𝑖𝑙 = 1.0
𝑚𝑤𝑎𝑡𝑒𝑟 = ?
What is the mass flow rate of cooling water?
A. 8.8 x 104 lbm/hr
B. 7.3 x 104 lbm/hr
C. 2.2 x 104 lbm/hr
D. 1.8 x 104 lbm/hr
© Copyright 2014
ELO 1.2
Correct answer is A.
Operator Generic Fundamentals
26
Classification by Flowpath
Knowledge Check – NRC Bank
The rate of heat transfer between two liquids in a heat exchanger will
increase if the… (Assume specific heats do not change.)
A. inlet temperature of the hotter liquid decreases by 20°F.
B. inlet temperature of the colder liquid increases by 20°F.
C. flow rates of both liquids decrease by 10 percent.
D. flow rates of both liquids increase by 10 percent.
Correct answer is D.
© Copyright 2014
ELO 1.2
Operator Generic Fundamentals
27
Other Heat Exchanger Characteristics
ELO 1.3 – Describe the difference between the following types of heat
exchangers: single-pass versus multipass heat exchangers and
regenerative versus nonregenerative heat exchangers.
• Most large heat exchangers are not purely parallel-flow, counter-flow,
or cross-flow
• Combination types maximize heat exchanger efficiency
• Having two fluids pass each other several times within a single heat
exchanger increases efficiency
© Copyright 2014
ELO 1.3
Operator Generic Fundamentals
28
Other Heat Exchanger Characteristics
• Single-pass heat exchanger
– Fluids pass each other once
• Multipass heat exchanger
– Fluids pass each other more
than once
– Reverses flow in the tubes
by use of one or more sets
of U-bends in the tubes
Figure: Single-Pass and Multipass Heat Exchangers
© Copyright 2014
• Baffles on the shell side of the
heat exchanger direct fluid back
and forth across the tubes to
achieve the multipass effect
ELO 1.3
Operator Generic Fundamentals
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Other Heat Exchanger Characteristics
• Heat exchangers are classified by their function
– Regenerative
– Nonregenerative
• Regenerative heat exchanger
– One fluid is both the cooling fluid and the cooled fluid
– Usually found in high-temperature systems
– Improves efficiency
• Nonregenerative heat exchanger
– Hot fluid is cooled by fluid from a separate system
– Energy (heat) removed is not returned to the system
© Copyright 2014
ELO 1.3
Operator Generic Fundamentals
30
Regenerative and Nonregenerative Heat
Exchanger Comparison
Figure: Regenerative Heat Exchanger
© Copyright 2014
Figure: Nonregenerative Heat Exchanger
ELO 1.3
Operator Generic Fundamentals
31
Other Heat Exchanger Characteristics
Knowledge Check
In a ________________ heat exchanger, heat from the main process
flow is ______________ the system.
A. regenerative; rejected from
B. regenerative; returned to
C. nonregenerative; stored in
D. nonregenerative; returned to
Correct answer is B.
© Copyright 2014
ELO 1.3
Operator Generic Fundamentals
32
Heat Exchanger Startup & Operation
ELO 1.4 – Describe the operation of a typical heat exchanger to include
startup and shutdown, control of temperature, and the effects and control
of fouling.
Startup
• Filled with fluid on both sides
• Cold fluid first
• Hot fluid slowly to minimize thermal shock
• Vent air and noncondensable gases (these can effectively reduce
surface area and heat transfer)
© Copyright 2014
ELO 1.4
Operator Generic Fundamentals
33
Heat Exchanger Startup & Operation
Shutdown
• Hot fluid normally stopped first
• Cold fluid stopped
• Never isolate from overpressure protection (either a discharge valve
left open or a relief valve installed)
© Copyright 2014
ELO 1.4
Operator Generic Fundamentals
34
Temperature Control
• Control the flow of either the
cooled fluid or cooling fluid
• Example – Cooling fluid flow
reduced:
– Cooling flow rate slowed,
less heat transfer, heat
exchanger outlet is higher
(less cooling of system
fluid)
Figure: Operating Water Cleanup System
© Copyright 2014
ELO 1.4
Operator Generic Fundamentals
35
Temperature Control
Refer to the drawing:
• Valves are identical and are
initially 50 percent open
• To raise the temperature at
point 7, the operator can
adjust valve D (the cooling
water throttle valve) in the
closed or shut direction
Figure: Operating Water Cleanup System
© Copyright 2014
ELO 1.4
Operator Generic Fundamentals
36
Temperature Control
• Cooled fluid
– Increasing cooled fluid flow will lower the outlet temperature
– Reverse will happen if the cooling fluid flow is slowed
© Copyright 2014
ELO 1.4
Operator Generic Fundamentals
37
Fouling of Heat Exchange Surfaces
• Foreign material (algae, scale, or debris) accumulates in a heat
exchanger
• Lowers the efficiency
• Removal by
– Hydrolancing
– Chemical cleaning
– Backwashing
• Maintaining minimum flow through heat exchanger can prevent
deposits
• Turbulent flow aids in heat transfer by agitating laminar film
• Chemicals can be added
© Copyright 2014
ELO 1.4
Operator Generic Fundamentals
38
Heat Exchanger Startup & Operation
Knowledge Check
Refer to the drawing of an operating lube oil heat exchanger below.
Increasing the oil flow rate through the heat exchanger will cause the oil
outlet temperature to _________ and the cooling water outlet
temperature to __________. (Assume cooling water flow rate remains
the same.)
A. decrease; decrease
B. decrease; increase
C. increase; decrease
D. increase; increase
Correct answer is D.
© Copyright 2014
ELO 1.4
Operator Generic Fundamentals
39
Heat Exchanger Calculations
ELO 1.5 – Given the necessary data, calculate flow rates and
temperatures for various types of heat exchangers.
Heat transfer in a heat exchanger is by conduction and convection. The
rate of heat transfer (Q) is calculated using:
𝑄 = 𝑈𝑜 𝐴𝑜 ∆𝑇𝑙𝑚
Where:
• 𝑄 = heat transfer rate
• 𝑈𝑜 = heat transfer coefficient
• 𝐴𝑜 = area
• ∆𝑇𝑙𝑚 = mean temperature
© Copyright 2014
ELO 1.5
Operator Generic Fundamentals
40
Heat Exchanger Calculations
Heat Exchanger Heat Balance
• Heat exchanger heat balance is dependent on mass flow, specific
heat capacity of the fluids, and change in temperature
𝑚1 𝐶𝑝1 ∆𝑇1 = 𝑚2 𝐶𝑝2 ∆𝑇2
Where:
• 𝑚1 = mass flow rate
• Cp = specific heat capacity
• ΔT = temperature change across heat exchanger
Using this heat balance equation, it is possible to calculate change in
mass flow rate or temperature of either fluid in a heat exchanger.
© Copyright 2014
ELO 1.5
Operator Generic Fundamentals
41
Heat Exchanger Calculations
• Use the following table to determine flow or temperature difference of
heat exchanger fluids:
Action
Formula
Determine heat transferred across
heat exchanger to or from one of
the fluids
𝑄 = 𝑈𝑜 𝐴𝑜 ∆𝑇𝑙𝑚
or
𝑄 = 𝑚𝑐𝑝 ∆𝑇
Determine log mean temperature
difference between two fluids if
necessary
∆𝑇2 − ∆𝑇1
∆𝑇𝑙𝑚 =
∆𝑇2
𝑙𝑛
∆𝑇1
Once heat transfer is known, solve
𝑚1 𝐶𝑝1 ∆𝑇1 = 𝑚2 𝐶𝑝2 ∆𝑇2
for flow or temperature difference
of other fluid
© Copyright 2014
ELO 1.5
Operator Generic Fundamentals
42
Heat Exchanger Calculations
Refer to drawing of a lube oil heat exchanger.
The heat exchanger is operating with the
following parameters:
𝑇𝑜𝑖𝑙 𝑖𝑛 = 165°F
𝑇𝑜𝑖𝑙 𝑜𝑢𝑡 = 110°F
𝐶𝑝 𝑜𝑖𝑙 = 1.1 BTU/lbm – °F
𝑚𝑜𝑖𝑙 = 3.0 x 104 lbm/hr
𝑇𝑤𝑎𝑡𝑒𝑟 𝑖𝑛 = 65°F
𝑇𝑤𝑎𝑡𝑒𝑟 𝑜𝑢𝑡 = 95°F
𝐶𝑝 𝑤𝑎𝑡𝑒𝑟 = 1.0 BTU/lbm – °F
𝑚𝑤𝑎𝑡𝑒𝑟 = ?
What is the mass flow rate of the cooling water?
© Copyright 2014
ELO 1.5
Operator Generic Fundamentals
43
Heat Exchanger Demonstration
Step
Formula
Solve for
Q oil
Q oil = moil Cp oil ∆Toil
Solution
Q = 3.0 × 104
𝑙𝑏𝑚
ℎ𝑟
1.1
𝐵𝑇𝑈
−℉
𝑙𝑏𝑚
55℉
𝐵𝑇𝑈
Q = 1.815 × 10
ℎ𝑟
6
Solve for
mwater
mwater Cp water ∆Twater
= moil Cp oil ∆Toil
1.185
× 106
= mwater
1.185 × 106
𝐵𝑇𝑈
1.0
−℉
𝑙𝑏𝑚
6.05 × 104
© Copyright 2014
ELO 1.5
𝐵𝑇𝑈
ℎ𝑟
𝐵𝑇𝑈
1.0
−℉
𝑙𝑏𝑚
𝐵𝑇𝑈
ℎ𝑟
30℉
30℉
= mwater
𝑙𝑏𝑚
= mwater
ℎ𝑟
Operator Generic Fundamentals
44
Heat Exchanger Calculations
Refer to the drawing of an operating lube oil heat exchanger below.
Given the following information:
𝑚𝑜𝑖𝑙 = 2.0 x 104 lbm/hr
𝑚𝑤𝑎𝑡𝑒𝑟 = 3.0 x 104 lbm/hr
𝐶𝑝 𝑜𝑖𝑙 = 1.1 BTU/lbm – °F
𝐶𝑝 𝑤𝑎𝑡𝑒𝑟 = 1.0 BTU/lbm – °F
𝑇𝑐𝑜𝑜𝑙𝑖𝑛𝑔 𝑤𝑎𝑡𝑒𝑟 𝑖𝑛 = 92°F
𝑇𝑐𝑜𝑜𝑙𝑖𝑛𝑔 𝑤𝑎𝑡𝑒𝑟 𝑜𝑢𝑡 = 125°F
𝑇𝑜𝑖𝑙 𝑖𝑛 = 180°F
𝑇𝑜𝑖𝑙 𝑜𝑢𝑡 = ?
Which one of the following is the temperature
A.
135°F
of the oil exiting the heat exchanger (𝑇𝑜𝑖𝑙 𝑜𝑢𝑡 )?
B.
140°F
C.
145°F
D.
150°F
Correct answer is A.
© Copyright 2014
ELO 1.5
Operator Generic Fundamentals
45
Heat Exchanger Tube Failure
ELO 1.6 – Explain the consequences of heat exchanger tube failure.
• Most common failure is a breach of the pressure boundary
• Tubes can be worn or eroded over time due to:
– High flow rates
– Particulate in the fluids passing through
• Vibration
– Caused by irregular flow pattern or flow is throttled
© Copyright 2014
ELO 1.6
Operator Generic Fundamentals
46
Heat Exchanger Failure
• Vibration could compromise seal between tubes and tube sheet or
sealing surfaces between fluids
• Failure of the heat exchanger will allow two fluids to mix
– Higher-pressure fluid forces into lower-pressure system
– Contaminated fluid is generally of low-pressure side
• Instrumentation shows an equalization of fluid temperatures at some
mid-temperature
• Lower-pressure system level should rise and increase the level in an
expansion tank and the higher-pressure system level should
decrease
© Copyright 2014
ELO 1.6
Operator Generic Fundamentals
47
Heat Exchanger Failure Example
Refer to the drawing of an operating cooling water system below. What
occurs when a tube fails in the heat exchanger?
Figure: Cooling Water System
© Copyright 2014
ELO 1.6
Operator Generic Fundamentals
48
Heat Exchanger Failure Example
Refer to the drawing of an operating cooling water system below. What
occurs when a tube fails in the heat exchanger?
• High-pressure fluid from the
tubes would force into shellside of heat exchanger
• Low-pressure system pressure
would rise and high-pressure
system surge tank level would
lower as fluid lost
• High-pressure fluid being
cooled would also add heat to
low-pressure system
Figure: Cooling Water System
© Copyright 2014
ELO 1.6
Operator Generic Fundamentals
49
Heat Exchanger Failure
Knowledge Check – NRC Bank
Borated water is flowing through the tubes of a heat exchanger being
cooled by fresh water. The shell-side pressure is less than tube-side
pressure. What will occur as a result of a tube failure?
A. Shell-side pressure will increase and the borated water system
will be diluted.
B. Shell-side pressure will decrease and the borated water
inventory will be depleted.
C. Shell-side pressure will increase and the borated water
inventory will be depleted.
D. Shell-side pressure will decrease and the borated water system
will be diluted.
Correct answer is C.
© Copyright 2014
ELO 1.6
Operator Generic Fundamentals
50
TLO 1 Summary
Now that you have completed this TLO, you should be able to do the
following:
• Describe the purpose, construction, and principles of operation for
each major type of heat exchanger.
© Copyright 2014
TLO 1
Operator Generic Fundamentals
51
TLO 1 Summary
Some important points concerning heat exchangers are as follows:
• Two methods of constructing heat exchangers are plate type and
tube type
• Heat exchangers can be classified by the following types of flow:
Parallel flow — hot fluid and coolant flow in same direction
Counter flow — hot fluid and coolant flow in opposite directions
Cross flow — hot fluid and coolant flow perpendicularly
• The four heat exchanger parts are as follows:
– Tubes/plates
– Tube sheet
– Shell
– Baffles
© Copyright 2014
TLO 1
Operator Generic Fundamentals
52
TLO 1 Summary
• Single-pass heat exchangers have fluids that pass each other once
• Multipass heat exchangers have fluids that pass each other more
than once by using U-tubes and/or baffles
• Heat exchangers should be vented when starting
• Colder fluid is supplied first to a shutdown heat exchanger
• Regenerative heat exchangers use same fluid for heating and
cooling
• Nonregenerative heat exchangers use separate fluids for heating
and cooling
• Heat exchangers are often used in the following applications:
– Preheater
– Radiator
– Air conditioning evaporator and condenser
– Steam condenser
© Copyright 2014
TLO 1
Operator Generic Fundamentals
53
NRC Exam Examples
Refer to the drawing of an
operating water cleanup system.
All valves are identical and are
initially 50 percent open. To lower
the temperature at point 7, the
operator can adjust valve
__________ in the open direction.
A.
B.
C.
D.
A
B
C
D
Correct answer is D.
© Copyright 2014
TLO 1
Operator Generic Fundamentals
54
NRC Exam Examples
Refer to the drawing of an
operating lube oil heat exchanger.
Increasing the oil flow rate through
the heat exchanger will cause the
oil outlet temperature to
__________ and the cooling water
outlet temperature to __________.
A.
B.
C.
D.
increase; increase
increase; decrease
decrease; increase
decrease; decrease
Correct answer is A.
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TLO 1
Operator Generic Fundamentals
55
NRC Exam Examples
Refer to the drawing of an
operating water cleanup system.
Valves A, B, and C are fully open.
Valve D is 80 percent open. If
valve D is throttled to 50 percent,
the temperature at point...
A.
B.
C.
D.
3 will decrease.
4 will increase.
5 will increase.
6 will decrease.
Correct answer is B.
© Copyright 2014
TLO 1
Operator Generic Fundamentals
56
TLO 1 Summary
Now that you have completed this TLO, you should be able to do the following:
1. Describe the construction, effectiveness, and operation of the following
types of heat exchangers and their components (tubes, tube sheets, baffles
and shells): tube and shell, and plate.
2. Describe hot and cold fluid flow paths in the following types of heat
exchangers: parallel flow, counter flow, and cross flow.
3. Describe the difference between the following types of heat exchangers:
single-pass versus multipass heat exchangers and regenerative versus
nonregenerative heat exchangers.
4. Describe the operation of a typical heat exchanger to include the following:
a. Startup and shutdown
b. Control of temperature
c. Effects and control of fouling
5. Given the necessary data, calculate flow rates and temperatures for various
types of heat exchangers.
6. Explain the consequences of heat exchanger tube failure.
© Copyright 2014
TLO 1
Operator Generic Fundamentals
57
Condenser Construction and Operation
TLO 2 – Describe the purpose, construction, and principles of operation
of condensers.
• Type of heat exchanger that condenses substance from a gaseous
state to a liquid state by cooling
• Removes latent heat from condensing fluid and transfers it to the
coolant
• Tube and shell heat exchanger normally used as condenser
• Baffles added at inlet, prevents tube impingement from incoming gas
or steam
• Industrial plants frequently employ large steam condensers as heat
sinks for steam system
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TLO 2
Operator Generic Fundamentals
58
Enabling Learning Objectives for TLO 2
1. State the purpose of a condenser.
2. State the definitions of hotwell and condensate depression.
3. State the reason(s) why condensers in large steam cycles operate
at a vacuum.
4. State the definition of thermal shock.
5. Describe the relationship between condenser vacuum and
backpressure.
6. Explain the process of forming a vacuum within a condenser.
© Copyright 2014
TLO 2
Operator Generic Fundamentals
59
Purpose of a Condenser
ELO 2.1 – State the purpose of a condenser.
Main Condenser
• Steam condenser is a major component of steam cycle in power
generation facilities
• Purpose of the condenser is to:
– Provide a heat sink for turbines to exhaust to give up latent heat
of vaporization
– Operating in a vacuum provides lowest heat sink, maximizing
available heat energy transfer
– Deareates condensate and feedwater, improving corrosion
protection
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Operator Generic Fundamentals
60
Purpose of a Condenser
• Gives up latent heat of vaporization
– Converts used steam into water for return to S/G
– Increases cycle's efficiency, allowing largest possible ΔT and ΔP
between heat source and heat sink
Figure: Single-Pass Condenser
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Operator Generic Fundamentals
61
Purpose of Condenser – Thermo Review
• Called latent heat of
condensation
• Specific volume
decreases drastically
• Creates a low pressure,
maintaining vacuum
• Increases plant
efficiency
Figure: Condenser
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Operator Generic Fundamentals
62
Purpose of Condenser – Thermo Review
Thermodynamic Cycle
• Liquid delivered to
condensate pump, then
feed pump where its
pressure is raised (point 1)
to the saturation pressure
corresponding to steam
generator temperature
• High-pressure liquid is
delivered to steam
generator where cycle is
repeated
© Copyright 2014
Figure: Thermodynamic Cycle
ELO 2.1
Operator Generic Fundamentals
63
Purpose of a Condenser
• Condensed steam (saturated liquid) continues to transfer heat as it
falls to the bottom of the condenser, called subcooling
– Subcooling prevents condensate pump cavitation
– Too much subcooling lowers efficiency
• Typically uses a single-pass, cross-flow condenser
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Operator Generic Fundamentals
64
Purpose of a Condenser
Knowledge Check
Condensers increase cycle efficiency by...
A. allowing the cycle to operate with the largest possible ΔT.
B. allowing the cycle to operate with the smallest possible ΔT.
C. allowing the condensate to operate with the largest possible ΔT.
D. allowing the condensate to operate with the smallest possible ΔT.
Correct answer is A.
© Copyright 2014
ELO 2.1
Operator Generic Fundamentals
65
Condenser Terms
ELO 2.2 – State the definitions of hotwell and condensate depression.
Figure: Condenser Cross-Section
© Copyright 2014
ELO 2.2
Operator Generic Fundamentals
66
Condenser Hotwell
• As steam comes in contact with tubes, it cools and condenses
• Series of baffles redirects steam to minimize direct impingement on
the cooling water tubes
• Condensed steam falls to the bottom of condenser
• Bottom area is a reservoir where condensate collects and is called
the hotwell
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Operator Generic Fundamentals
67
Condensate Depression
• As the condensate falls
towards the hotwell, it
subcools (goes below
TSAT) as it comes in
contact with tubes lower
in the condenser
• Amount of subcooling is
“condensate
depression”
• TSAT – THOTWELL = the
amount of condensate
depression
© Copyright 2014
Figure: T-v Diagram for Typical Condenser
ELO 2.2
Operator Generic Fundamentals
68
Heat Exchanger Failure
Knowledge Check
After the steam condenses, the saturated liquid continues to transfer
heat to the cooling water as it falls to the bottom of the condenser, or
hotwell. This is called ____________ and is _______________.
A. subcooling; desirable
B. subcooling; undesirable
C. latent heat; desirable
D. latent heat; undesirable
Correct answer is A.
© Copyright 2014
ELO 2.2
Operator Generic Fundamentals
69
Condenser Vacuum
ELO 2.3 – State why condensers in large steam cycles are operated at a
vacuum.
• Steam's latent heat of condensation is passed to water flowing
through tubes
• Condenser usually operated at a vacuum
• Vacuum helps increase plant efficiency by extracting more work from
the turbine
© Copyright 2014
ELO 2.3
Operator Generic Fundamentals
70
Condenser Vacuum
• Steam turbines designed to exhaust into a condenser that operates
within a specific vacuum range
• If pressure increases above these limits, physical damage will occur
to turbine blades
• When exhausted steam is condensed, its specific volume decreases,
which helps maintain vacuum
• If condensate level is allowed to rise over lower tubes of condenser,
fewer tubes are exposed for heat transfer, reducing heat transfer area
• If condenser is operating near design capacity, a reduction in
effective surface area results in difficulty maintaining condenser
vacuum
• Temperature and flow rate of cooling water through condenser control
temperature of condensate
– This in turn controls saturation pressure (vacuum) of condenser
© Copyright 2014
ELO 2.3
Operator Generic Fundamentals
71
Condenser & Noncondensable Gases
• If noncondensable gases are allowed to build up in condenser,
vacuum decreases and saturation temperature at which steam
condenses increases
• Noncondensable gases also blanket tubes of condenser, thus
reducing surface area for heat transfer in condenser
• Reduction in heat transfer surface has same effect as a reduction in
cooling water flow
© Copyright 2014
ELO 2.3
Operator Generic Fundamentals
72
Vacuum & Noncondensable Gases
• Condenser vacuum should be maintained as close to 29 inches of
Mercury (Hg) as practical
• Allows maximum expansion of steam and therefore maximum work
• If condenser perfectly airtight and no air or noncondensable gases
present in exhaust steam, only necessary to condense steam and
remove condensate to create and maintain vacuum
Figure: Condenser Cross-Section
© Copyright 2014
ELO 2.3
Operator Generic Fundamentals
73
Vacuum & Noncondensable Gases
• Sudden reduction in steam volume as it condenses creates a vacuum
– Pumping water from condenser as fast as it forms maintains
vacuum
• Not possible to prevent entrance of air and other noncondensable
gases into condenser
• Some method also needed to create initial vacuum in condenser
– Necessitates use of an air ejector and vacuum pump to establish
and help maintain condenser vacuum
© Copyright 2014
ELO 2.3
Operator Generic Fundamentals
74
Condenser Vacuum
Knowledge Check
During normal nuclear power plant operation, a main condenser
develops an air leak that decreases vacuum at a rate of 1 inch of
Hg/minimum. Which of the following will increase because of this
condition?
A. Extraction steam flow rate
B. Condenser hotwell temperature
C. Low-pressure turbine exhaust steam moisture content
D. Steam cycle efficiency
Correct answer is B.
© Copyright 2014
ELO 2.3
Operator Generic Fundamentals
75
Thermal Shock
ELO 2.4 – State the definition of thermal shock.
Thermal shock is the severe stress produced in a material upon
experiencing a sudden, unequally distributed change in temperature.
• Heat exchangers and condensers experience pressure stress and
thermal stress due to function of transferring heat
• To reduce effects of these stresses, condensers should be as close as
possible to operating temperatures prior to admitting steam from main
turbine
• If equipment is not properly preheated, severe damage can occur to
condenser tubes and the turbine
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Operator Generic Fundamentals
76
Thermal Shock
• Large temperature differences between two fluids in a heat exchanger
or between a fluid and vapor in a condenser are good from a
thermodynamic perspective
• However, they should be controlled in the system to prevent thermal
shock to components
Prevention
• Hotter fluids or vapors should be slowly admitted
• When out of service, heat exchangers are maintained, filled, and
pressurized
– Condensers steam side vented, waterside filled
© Copyright 2014
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Operator Generic Fundamentals
77
Thermal Shock
Prevention
• Main condensers must be at operating pressures (vacuum) prior to
admitting steam
• Colder fluid should be supplied to heat exchanger first, followed by
hotter fluid
• When securing a heat exchanger or condenser hot fluid, vapor is
stopped first
• Colder fluid is allowed to operate for a period of time to cool down
component(s) and reduce stress
© Copyright 2014
ELO 2.4
Operator Generic Fundamentals
78
Thermal Shock
• Heat exchangers and condensers should not be isolated in such a
manner that they do not have relief valve protection
• Liquid isolated within the heat exchanger could warm up due to
surrounding air temperature
• Increased temperature would lead to expansion of liquid and damage
to heat exchanger if not protected from overpressure
© Copyright 2014
ELO 2.4
Operator Generic Fundamentals
79
Thermal Shock
Knowledge Check
The major thermodynamic concern resulting from rapidly cooling a
reactor vessel is...
A. thermal shock.
B. stress corrosion.
C. loss of shutdown margin.
D. loss of subcooling margin.
Correct answer is A.
© Copyright 2014
ELO 2.4
Operator Generic Fundamentals
80
Vacuum Versus Backpressure
ELO 2.5 – Describe the relationship between condenser vacuum and
backpressure.
Pressure and Vacuum Relationship
• If pressure is below that of atmosphere as in case of a condenser, it
is a vacuum
• Vacuum, although a negative pressure, is normally expressed as a
positive value
© Copyright 2014
ELO 2.5
Operator Generic Fundamentals
81
Vacuum Versus Backpressure
• Pressure is a measure of force exerted per unit area on boundaries
of a substance (or system)
• Collisions of molecules of substance with boundaries of system
cause force
• Pressure is frequently expressed in units of lbf/in2 (psi) in the English
system of measurement
• Pressure can also be measured using equivalent columns of liquid,
such as water (H2O) or mercury (Hg)
– These scales use units of inches of H2O or Hg
• Height of column of liquid provides a certain pressure that can be
directly converted to force per unit area
© Copyright 2014
ELO 2.5
Operator Generic Fundamentals
82
Vacuum Versus Backpressure
• Perfect vacuum would correspond to absolute zero pressure
• Gauge pressures are positive if they are above atmospheric pressure
and negative if they are below atmospheric pressure
• Vacuum, although a negative pressure, is normally expressed as a
positive value
© Copyright 2014
ELO 2.5
Operator Generic Fundamentals
83
Vacuum Versus Backpressure
Pressure and Vacuum Relationship
Figure: Comparison of Pressure Ranges
© Copyright 2014
ELO 2.5
Operator Generic Fundamentals
84
Vacuum Versus Backpressure
Pressure and Vacuum Relationship
Pabs = Patm + Pgauge
Pabs = Patm − Pvac
Where:
Pabs = absolute pressure
Patm = atmospheric pressure
Pgauge = gauge pressure
Pvac = vacuum pressure
© Copyright 2014
ELO 2.5
Operator Generic Fundamentals
85
Vacuum Versus Backpressure
• Table shows the relationship between pressure measurements
associated with a condenser
• 29.9 inches of Hg pressure equals zero (0) inches of mercury
vacuum (HgV) and zero (0) inches of Hg equals 29.9 inches of HgV
PSIA
PSIG
Inches of HgV Inches of Hg
14.7
0
0
29.90
13.7
-1.0
2.03
27.87
12.7
-2.0
4.06
25.84
11.7
-3.0
6.09
23.81
© Copyright 2014
ELO 2.5
Operator Generic Fundamentals
86
Vacuum Versus Backpressure
• Given that a condenser pressure is 3 inches of Hg, determine the
corresponding vacuum by:
29.9 – 3 = 26.9 inches of Hg vacuum
© Copyright 2014
ELO 2.5
Operator Generic Fundamentals
87
Vacuum Versus Backpressure
Knowledge Check
A turbine has a design backpressure of 5 inches of Hg. The main
condenser is operating at 28 inches of HgV. What is the margin to
design for the turbine?
A. 24.9 inches of Hg
B. 3 inches of Hg
C. 3.1 inches of Hg
D. 24.9 inches of HgV
Correct answer is C.
© Copyright 2014
ELO 2.5
Operator Generic Fundamentals
88
Drawing a Vacuum
ELO 2.6 – Explain the process of forming a vacuum within a condenser.
• To prepare plant for startup, a vacuum must be drawn in the main
condenser
– Allows recirculation of feedwater and condensate in order to clean
up and deaerate these systems
– Allows warming of the main turbine
– Allows identification of any condenser tube leaks prior to placing
the turbine in service
© Copyright 2014
ELO 2.6
Operator Generic Fundamentals
89
Drawing a Vacuum
• Vacuum is a condition where all molecules are removed
• Allows steam cycle to exhaust to lowest possible heat sink, providing
largest enthalpy drop through the main turbine
• Consists of isolating air in-leakage paths, establishing cooling water
flow, then removing air from the condenser shell
• Mechanical vacuum pump initially removes air from condenser, then
shifts to air ejectors
• Air removal during operation is essential for efficient operation
• If air leaks into the condenser, pressure increases, temperature
increases, and plant efficiency decreases because the turbine
exhaust enthalpy increases
© Copyright 2014
ELO 2.6
Operator Generic Fundamentals
90
Drawing a Vacuum
Action Step
How
Discussion
Establish cooling flow
•Startup support cooling
systems
•Startup circulation water
system
•Startup condensate system
Various systems provide cooling for
components necessary for vacuum pull
(condensate pumps, air compressors,
mechanical vacuum pumps)
Isolate all air inleakage
paths to the main
condenser
•Complete valve lineup checks
•Close vacuum breakers
•Establish steam seal on
turbines
All possible leakage paths must be
isolated to prevent loss of condenser
pressure and temperature control. Air
leakage across turbine shaft seals is
removed via gland exhaust system.
Establish turbine seals
•Startup steam sealing system
•Startup gland exhaust system
Turbine shafts are sealed using labyrinth
seals and low-pressure steam to prevent
high-pressure steam from leaking out and
air from leaking in.
Remove air from the
condenser
•Startup the mechanical vacuum
pump (also known as a hogger)
•Shift to the air ejectors when
vacuum reaches approximately
26 inches of HgV
Mechanical vacuum pump removes air out
of main condenser. As air molecules are
removed, pressure decreases.
© Copyright 2014
ELO 2.6
Operator Generic Fundamentals
91
Drawing a Vacuum
Knowledge Check
During normal nuclear power plant operation, why does air entry into
the main condenser reduce the thermodynamic efficiency of the steam
cycle?
A. The rate of steam flow through the main turbine increases.
B. The condensate subcooling in the main condenser increases.
C. The enthalpy of the low-pressure turbine exhaust increases.
D. The air mixes with the steam and enters the condensate.
Correct answer is C.
© Copyright 2014
ELO 2.6
Operator Generic Fundamentals
92
TLO 2 Summary
Now that you have completed this TLO, you should be able to do the
following:
• Describe the purpose, construction, and principles of operation of
condensers.
© Copyright 2014
TLO 2
Operator Generic Fundamentals
93
TLO 2 Summary
• Condenser is type of heat exchanger used to condense a substance
from a gaseous state to a liquid state by cooling
• Condenser removes latent heat from fluid and transfers it to coolant
• Condenser removes latent heat of vaporization, condensing vapor
into liquid
• Hotwell is at the bottom of condenser where condensed steam is
collected and pumped back into feedwater
• Condensate depression is amount condensate is cooled below
saturation (degrees subcooled)
• Condensers operate at a vacuum to ensure temperature (thus the
pressure) of steam is as low as possible, maximizing ΔT and ΔP
between source and heat sink, ensuring highest cycle efficiency
• Thermal shock is stress produced in a body or in a material as a
result of undergoing a sudden change in temperature
© Copyright 2014
TLO 2
Operator Generic Fundamentals
94
TLO 2 Summary
Now that you have completed this TLO, you should be able to do the
following:
1. State the purpose of a condenser.
2. State the definitions of hotwell and condensate depression.
3. State the reason(s) why condensers in large steam cycles operate
at a vacuum.
4. State the definition of thermal shock.
5. Describe the relationship between condenser vacuum and
backpressure.
6. Explain the process of forming a vacuum.
© Copyright 2014
TLO 2
Operator Generic Fundamentals
95
Heat Exchangers & Condensers Summary
This module covered types of heat exchangers and condensers, their
applications and advantages, proper methods for operation, and system
responses.
Heat Exchangers
• The type of flow classifies different heat exchangers
– Parallel flow — hot fluid and coolant flow in same direction
– Counter flow — hot fluid and coolant flow in opposite directions
– Cross flow — hot fluid and coolant flow perpendicularly
• Single-pass heat exchangers have fluids that pass each other once
• Multipass heat exchangers have fluids that pass each other more than once
through using U-tubes and/or baffles
• Regenerative heat exchangers use same fluid for heating and cooling
• Nonregenerative heat exchangers use separate fluids for heating and cooling
© Copyright 2014
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96
Heat Exchangers & Condensers Summary
Condensers
Condensers perform an important function in any heat cycle. They provide a
heat sink that allows the cycle to operate at maximum efficiency.
• Condensers remove latent heat of vaporization, condensing vapor into a
liquid
• Condensers operate at a vacuum to ensure temperature (thus pressure) of
steam is as low as possible, maximizing ΔT and ΔP between source and heat
sink, ensuring highest cycle efficiency
© Copyright 2014
Operator Generic Fundamentals
97
Heat Exchangers & Condensers Summary
Now that you have completed this module, you should be able to do the
following:
1. Describe the purpose, construction, and principles of operation for
each major type of heat exchanger.
2. Describe the purpose, construction, and principles of operation of
condensers.
© Copyright 2014
Operator Generic Fundamentals