3. HEAT EXCHANGER
A heat exchanger is a device in which energy is
transferred from one fluid to another across a solid
surface. Exchanger analysis and design therefore
involve both convection and conduction. Radiative
transfer between the exchanger and the
environment can usually be neglected unless the
exchanger is uninsulated and its external surfaces
are very hot.
Heat exchangers are normally well-insulated
devices that allow energy exchange between hot
and cold fluids without mixing the fluids. The
pumps, fans, and blowers causing the fluids to flow
across the control surface are normally located
outside the control surface.
4. A basic understanding of the mechanical compenents
of a heat exchanger is important to understanding how
they function and operate.
A heat exchanger is a component that allows the
transfer of heat from one fluid (liquid org as) to another
fluid. Reasons for heat transfer include the flowwing:
1) To heat a cooler fluid by means of a hotter fluid
2) To reduce the temperature of a hot fluid by means of a
cooler fluid
3) To boil a liquid by means of a hotter fluid
4) To condense a gaseous fluid by means of a cooler fluid
5) To boil a liquid while condensing a hotter gaseous fluid
Heat exchangers can have different size and shape
depending on the application, can be made of various
materials and use various fluids for heat transfer
5. In almost any chemical ,electronic ,or mechanical
system, heat must be transferred from one place to another or
from one fluid to another.Heat is transferred between the hot
and cold medium.A heat exchanger where an exchange of
heat between two Fluids having various temperatures.In
industry, steam is often used for heating and cold water for
cooling. A variety of heat exchangers have been designed to
suit the range of heating or cooling applications
An example of a heat exchanger.
Cooling water (blue) enters at the
bottom and flows in a jacket around
the pipe containing the hot water
(red) which enters at the top.A hot
jacket could be used to heat up a
cooler liquid flowing in the pipe.
8. Heat exchangers are found in most chemical,
electrical or mechanical systems.They serve as the
system’s means of gaining or rejecting heat.Some of
the more common applications are found in heating,
power stations, power plant. Dairy and Thermal
Power Stations, chemical and petrochemical
processing plants, building heating and air
conditioning, refrigeration systems, automotive
industry, marine and space vehicles and electronic
systems, ventilation and air conditioning(HVAC)
APPLICATIONS
9. 1) TYPES OF APPLICATION
Air Conditioning
Boilers and Steam Generators
Condensers
Radiators
Evaporator
Colling Towers
13. Evaporator
Fluid approaches evaporator as a high
pressure liquid near room temperature
Heat exchanger
made from a long
metal pipe
A constriction reduces the fluid’s pressure
Fluid enters evaporator as a low pressure liquid
near room temperature
Working fluid evaporates in the
evaporator
Fluid becomes a colder gas
Breaking bonds takes energy: Thermal
energy
Heat flows from room air into colder
fluid
Fluid leaves evaporator as a low
pressure gas near room temperature
Heat has left the room!
14.
15. Compressor
Pushes gas so gas temperature rises
(law and ideal gas law)
Ordefirst red energy becomes disordered
Working fluid
enters compressor
as low pressure
gas near room
temperature
Compressor does
work on fluid:
Fluid leaves compressor as hot, high
pressure gas.
16.
17. Condenser
Heat exchanger made from long metal pipe
Fluid enters condenser as ahot, high pressure gas
Heat flows from fluid to outside air
Working Fluid condenses in the condenser Forming bonds
releases energy: Thermal energy
Fluid becomes hotter liquid
More heat flows from fluid to outside air
Fluid leaves condenser as high pressure liquid near room
temperature
Heat has reached the outside air!
18.
19. Condenser
Condensers are heat transfer devices used to convert hot gases into
liquids. Condensers are usually air-cooled, water-cooled or
evaporative (a combination of air and water cooled). Hot gaseous
vapour is passed through a tube, which is then exposed to air, or
passed through water. This exposure results in the transfer of heat,
into the cooler surrounding air or water, causing the vapour to liquid
conversion. The function of the condenser is to condense exhaust steam from
the steam turbine by rejecting the heat of vaporisation to the cooling water
passing through the condenser. The temperature of the condensate determines
the pressure in the steam/condensate side of the condenser. This pressure is
called the turbine backpressure and is usually a vacuum. Decreasing the
condensate temperature will result in a lowering of the turbine backpressure.
Note: Within limits, decreasing the turbine backpressure will increase the
thermal efficiency of the turbine
20. Types of Condensers
Air-cooled
Water-cooled
Evaporative
There are essentially three types of condensers, These
types differ in how they remove excess heat.Air-cooled
condensers remove heat by blowing air over the condenser
coil .Water-cooled condensers remove heat by pouring
water over the condenser coil.Evaporative condensers do
not typically use a refrigerant. They remove heat by
allowing water to evaporate directly into the air.Air-cooled
condensers are by far the most common type of condenser
in residential systems
24. BOILERS
The boiler has an enclosed space where the fuel combustion takes
place, usually referred to as the furnace or combustion
chamber. Air is supplied to combine with the fuel, resulting
in combustion. The heat of combustion is absorbed by the water in
the risers or circulating tubes. The density difference between hot
and cold water is the driving force to circulate the water
back to the steam drum. Eventually the water will absorb sufficient
heat to produce steam.
Boilers are vessels that allow water in contained piping to be heated
to steam by a heat source internal to the vessel. The water is heated
to the boiling point. The resulting steam separates, and the water is
heated again. Some boilers use the heat from combustion off-gasses
to further heat the steam (superheat) and/or to preheat the feedwater.
25.
26.
27.
28. RADIATORS
Radiators, as the term is normally used, are
simple heat exchangers which distribute the heat
by natural air circulation (hot air rises, so the
heated air next to the surface of a radiator rises
pulling cooler air up from the floor level). They
are simple (very little can go wrong),
easy to install and operate.
32. Evaporator
Evaporators refer to the equipment used in
evaporation, the process of boiling a liquid in
order to reduce its volume, but retain its
nutrient concentration. Evaporation is
frequently used to pre-concentrate liquid
foods, such as fruit juice and milk, prior to the
drying process.
39. Cocurrent or parallel flow
Countercurrent flow
Crossflow (single pass or multiple pass)
2) TYPES OF FLUID FLOW
40. 1.CONCURRENT OR PARALLEL FLOW HEAT
EXCHANGERS
Parallel flow, as illustrated in Figure , exists when both the
tube side fluid and the shell side fluid flow in the
same direction.
In this case, the two fluids enter the heat exchanger
from the same end with a large temperature difference. As
the fluids transfer heat, hotter to cooler, the temperatures of
the two fluids approach each other. Note that the hottest
cold-fluid temperature is always less than the coldest hot-
fluid temperature.
41.
42. Counter flow, as illustrated in Figure, exists when the two
fluids flow in opposite directions. Each of the fluids enters the heat
exchanger at opposite ends. Because the cooler fluid exits the counter
flow heat exchanger at the end where the hot fluid enters the heat
exchanger, the cooler fluid will approach the inlet temperature of the hot
fluid. Counter flow heat exchangers are the most efficient of the three
types. In contrast to the parallel flow heat exchanger, the counter flow
heat exchanger can have the hottest cold- fluid temperature greater than
the coldest hot-fluid temperatue.
2.COUNTERCURRENT FLOW HEAT EXCHANGERS
43. Cross flow, as illustrated in Figure , exists when one fluid flows perpendicular to
the second fluid; that is, one fluid flows through tubes and the second fluid passes
around the tubes at 90° angle. Cross flow heat exchangers are usually found in
applications where one of the fluids
changes state (2-phase flow). An example is a steam system's condenser, in which
the steam exiting the turbine enters the condenser shell side, and the cool water flowing
in the tubes absorbs the heat from the steam, condensing it into water. Large volumes
of vapor may be condensed using this type of heat exchanger flow. Figure Cross Flow
Heat Exchanger
3.CROSS FLOW HEAT EXCHANGERS
44.
45. Types of shape
1)TUBE (PIPE) HEAT EXCHANGERS
a)Double pipe heat exchangers
b)Spiral pipe heat exchangrs
2)PLATE HEAT EXCHANGERS
a) Plate and frame heat exchangers
c)Brazed heat exchangers
c)Welded heat exchangers
b)Spiral plate heat exchangers
3)ENLARGED SURFACE HEAT EXCHANGERS
a)Plate fin heat exchangers
b)Pipe (tube) fin heat exchangers
46. a) SHELL TUBE HEAT EXCHANGERS
This type of heat exchanger
consists of a shell (a large tube)
with a series of small tubes inside it.
Two fluids, of different starting
temperatures, flow through the
exchanger. One through the tubes
and the other through the shell. Heat
is transferred from one fluid to the
other. In this way, waste heat can be
put to use. This is a great way to
conserve energy.
51. The double pipe heat exchanger
belongs to the recuperator category
(close type heat exchangers).In this
type of exchanger, the hot and cold
fluids do not come into direct contact
with each other. The process fluid
passes through the inner tube, while
the heating or cooling media goes
through the outer tube. Because of the
large size of the product tube, these
heat exchangers have the ability to
process very large particulates
a) DOUBLE PIPE HEAT EXHANGERS or
TUBE IN TUBE HEAT EXHANGERS
52. b) SPIRAL TUBE HEAT EXCHANGERS
When considering a shell-and-tube
heat exchanger, investigate spiral
units as well. Spiral tube heat
exchangers are suitable for a number
of traditional shell-and-tube
applications.
53. A spiral tube design also may be a
good choice for as a low flow, high
purity steam generator because of the
lower cost of construction for
stainless and other exotic alloy
materials.
Preheat and Regenerative Heat
Exchangers. Spiral tube heat
exchangers also are well suited for
use as trim heaters/preheaters in a
number of processes. Because the
shell side can be removed without
disconnecting piping, heat recovery
from a fouled stream to a clean
stream is possible when higher
pressures preclude the use of a plate
heat exchanger.
54. d) TRIBLE TUBE HEAT EXCHANGER
Trible tube heat exchanger is designed with three
concentrically mounted tubes. For heat transfer
applications, the heating or cooling medium flows through
the space between the inside and outside tubes while
product travels in the opposite direction through the
middle tube
55. A plate heat exchanger consists of a series of thin
corrugated metal plates between which a number of
channels are formed, with the primary and secondary fluids
flowing through alternate channels. Heat transfer takes
place from the primary fluid steam to the secondary process
fluid in adjacent channels across the plate. Figure shows a
schematic representation of a plate heat exchanger.
2) PLATE HEAT EXCHANGERS
56.
57. BRAZED PLATE HEAT EXCHANGERS
The brazed plate heat exchanger consists of a
pack of pressed plates brazed together, thus
completely eliminating the use of gaskets.
Frame system with exception that they do not
contain gaskets and are assembled with high
temperature brazing The embossed plates are
assembled in the desired configuration with
layers of copper or nickel brazing. In a
brazed plate heat exchanger all the plates are
brazed together (normally using copper or
nickel) in a vacuum furnace.These are
carefully helium leak- tested and are ready
for use. Section Through a Brazed Plate
Heat Exchanger
58. Brazed Plate Heat Exchangers are available for process and refrigeration
applications. Made from stainless-steel plates and copper or nickel
brazing materials, they are suitable for a wide variety of heat exchanger
applications.
Typical applications include:
Refrigerant Evaporating & Condensing
Heat Pumps
Steam Heating
Engine or Hydraulic Oil Cooling
District or Zone Heating Systems
Swimming Pool Heating
Various Heating and Cooling Duties
59. WELDED PLATE HEAT EXCHANGERS
In a welded plate heat exchanger the plate
pack is held together by welded seams
between the plates. The use of laser welding
techniques allows the plate pack to be more
flexible than a brazed plate pack, enabling
the welded unit to be more resistant to
pressure pulsation and thermal cycling. The
high temperature and pressure operating
limits of the welded unit mean that these heat
exchangers normally have a higher
specification, and are more suited to heavy
duty process industry applications. They are
often used where a high pressure or
temperature performance is required, or
when viscous media such as oil and other
hydrocarbons are to be heated.
60. SPIRAL HEAT EXCHANGERS
Spiral Heat Exchangers exhibit ideal heat transfer and fluid handling
characteristics for a wide range of applications within sludge treatment
Construction and operation of the Spiral Heat Exchanger
The Spiral Heat Exchanger is composed of two long, flat plates that are
wrapped around each other, creating two concentric channels. The
channels are seal-welded on alternate sides to prevent mixing of the
fluids. Covers are fitted on both sides, with a full-faced gasket to
prevent bypassing of the fluid and leakage to the atmosphere. Full
access to the hot or cold channel is obtained simply by removing the
respective covers. The covers are frequently fitted with hinges to
facilitate opening and closing of the unit. The hot fluid flows into the
center of the unit and spirals outward towards the periphery.
Meanwhile, on the other side, the cold fluid enters at the periphery and
flows inward towards the center
63. a) Plate fin heat exchangers
b) Pipe (tube) fin heat exchangers
3)ENLARGED SURFACE HEAT
EXCHANGERS
SHAPE OF FINS
The herringbone and serrated fins provide the greatest surface area and
the highest heat transfer performance.They are particularly suitable for
applications involving close temperature approaches. Where there are
critical pressure drop requirements, the plain and perforated fins can be
used. The fins, serve as additional area for heat transfer
64. Vacuum-brazed aluminum plate-fin heat
exchangers are our highest performing heat
exchanger. They can be used for air-to-air,
air-to-liquid and liquid-to-liquid cooling.
All plate fin heat exchangers are custom
designed to match your precise
performance and size requirements.
Applications include condensers,
evaporators, environmental cooling
systems and radar cooling. Their high
performance/weight ratio also makes them
popular for airborne applications such as
cooling gearbox oil and transmission oil
with ram air or jet fuel.
a) PLATE FIN HEAT EXCHANGERS
65. Plate-fin heat exchangers consist of finned chambers separated
by flat plates that route fluid through alternating hot and cold
passages. Heat is transferred via fins in the passageways, through
the separator plate, and into the cold fluids via fin once again.
66. Generally tube-fin heat exchangers
consist of copper or stainless steel tubes
expanded into copper or aluminum fin.
Tube-fin heat exchangers are cost effective
and offer good heat removal for a wide
range of applications including lasers,
electronics, compressor cooling,
semiconductor processing equipment, and
solder reflow ovens
b) TUBE FIN HEATEXCHANGERS
67. Finned tube oil cooler replaced an existing bare
tube coil design resulting in improved thermal
performance
72. Ceramic Micro-channel Devices
Advantages
Can go up to very high temperatures
Hospitable to a wide range of catalysts
Challenges
Creation of high aspect ratio structures
Ceramic-Ceramic bonding
74. Ceramic Micro-channel Devices
Counterflow fluids in alternating
layers very effectively coupled via
fins
Individual ceramic plates, aligned, pressed together, then sintered
Fins:
Length 1.5-2.5 mm
Width at base: 300 mm
Width at tip: 200 mm
Gap Between Fins 300-400 mm
75. COOLING TOWERS
What are cooling towers?
Cooling towers are used to remove excess heat
that is generated in places such as power stations,
chemical plants and even domestically in air
conditioning units.In power stations, electricity is
generated when steam drives a turbine. This steam
must be condensed before it can be returned to the
boiler to continue the cycle of steam and electricity
generation. The condensation process happens in a
heat exchanger. Cooling water is needed in the heat
exchanger and it is this cooling water that is cycled
through the cooling tower. In this way the water for
the boilers and steam turbine is kept separate from the
cooling water. This stops impurities getting into the
turbine steam. In chemical processes excess heat can
be generated. This heat is removed using heat
exchangers and cooling water which is cycled through
a cooling tower
78. COOLING TOWERS:Many processes in chemical plants produce heat. This heat is
removed in cooling towers like these square, forced-draught cooling towers. They use
a fan to draw air through the tower. Cooling towers.Power stations generate electricity
but they also produce a lot of waste heat. This heat is removed in cooling towers
79. NATURAL DRAFT
COOLING TOWER
This photo shows a single natural
draft cooling tower as used at a
European plant. Natural draft
towers are typically about 400 ft
(120 m) high, depending on the
differential pressure between the
cold outside air and the hot humid
air on the inside of the tower as
the driving force. No fans are
used.
Whether the natural or
mechanical draft towers are used
depends on climatic and
operating requirement conditions.
80. Forced - or Natural
Draft Cooling
Tower
The green flow paths show how
the water is taken from a river
(yellow) to an intake supply basin
(green) that the Circ Water Pumps
take a suction from. The water is
then pumped to the Condenser
where the water is heated. The
water is then sent to an exit
distribution basin where the water
then can be returned to the river
and/or pumped by the Cooling
Tower Pumps to the Cooling
Towers then the water returned to
the intake supply basin where the
water can be reused
81. Natural Draft
Cooling Tower
The green flow paths
show how the warm water
leaves the plant proper, is
pumped to the natural draft
cooling tower and is
distributed.
The cooled water,
including makeup from the
lake to account for
evaporation losses to the
atmosphere, is returned to
the condenser.
Editor's Notes
Demonstration: Pump Air into a Gallon Jug with Thermometer
Hello–
My name is …
Pictured here is a close-up of the metal heat exchanger. As mentioned before liquid flow through the interior. The picture on the left is a cross section of the heat exchanger with the red arrows showing the flow of the liquid. On the right is a picture that show the flow passages on the air side. The length scale of the micropassages are on the order of 300-500 micrometers, the wall thickness is in the range of 75-150 um.
