heat exchanger
TRANSCRIPT
HEAT EXCHANGERS
SEMİH BEYLİKHAMİT YILDIRIM
GAZİ FIRATTAHSİN ÖZGÜR YILDIZGÖKAN KURTBEYOĞLU
HEAT EXCHANGERS
Hot In Hot Out
Cold Out Cold In
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.
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 fluid2) 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
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.
CLASSIFICATION OF HEAT EXCHANGERS
1) Types of application 2) Types of shape
3) Types of fluid flow
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
1) TYPES OF APPLICATION
Air Conditioning Boilers and Steam Generators Condensers Radiators Evaporator Colling Towers
AIR CONDITIONING
SİMPLE AİRCONDİTİONİNİG SYSTEM REFRİGERATİON AND AİR
CONDİTİONİNG
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Refrigeration Cycle
Air Conditioner
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 gasBreaking bonds takes energy: Thermal
energyHeat flows from room air into colder
fluid
Fluid leaves evaporator as a low pressure gas near room temperature Heat has left the room!
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.
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 liquidMore heat flows from fluid to outside air
Fluid leaves condenser as high pressure liquid near room temperature
Heat has reached the outside air!
CondenserCondensers 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
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
AİR-COOLED CONDENSER
WATER-COOLED CONDENSER
EVAPORATİVE
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.
RADIATORSRadiators, 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.
Automotive vehicle radiator
EvaporatorEvaporators 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.
Forced Circulation Evaporator
Falling Film Evaporator
Cocurrent or parallel flow Countercurrent flow Crossflow (single pass or multiple pass)
2) TYPES OF FLUID FLOW
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.
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
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
Types of shape1)TUBE (PIPE) HEAT EXCHANGERSa)Double pipe heat exchangersb)Spiral pipe heat exchangrs
2)PLATE HEAT EXCHANGERSa) Plate and frame heat exchangersc)Brazed heat exchangersc)Welded heat exchangersb)Spiral plate heat exchangers
3)ENLARGED SURFACE HEAT EXCHANGERSa)Plate fin heat exchangersb)Pipe (tube) fin heat exchangers
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.
HEAT EXCHANGERS, Shell and Tube
Shell-and-tube-heat exchanger with one shell pass and one tube pass; cross- counterflow operation
Hot inHot out
Cold out
Cold in
Cold in
Cold out
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 orTUBE IN TUBE HEAT EXHANGERS
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.
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.
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
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
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
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
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.
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 ExchangerThe 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
Cross Flow-Spiral Flow Heat Exchanger
Spiral Flow-Spiral Flow Heat Exchanger
Combination Cross-Flow and Spiral Flow-Spiral Flow
a) Plate fin heat exchangersb) Pipe (tube) fin heat exchangers
3)ENLARGED SURFACE HEAT EXCHANGERS
SHAPE OF FINSThe 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
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
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.
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
Finned tube oil cooler replaced an existing bare tube coil design resulting in improved thermal performance
Micro-Structured Heat Exchangers
Flow Types of Heat Exchangers
Gas – Gas Liquid – Liquid Vapor – Gas Vapor – Liquid
Micro-channels in Cross Flow Heat Exchangers
In-plane cross section
Micro Jet Cooling Array
Single phase impingement cooling >100 impinging microjets/cm2
Very high heat transfer coefficients Easily removes 1kW/cm2 of heat
Ceramic Micro-channel Devices
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
Ceramic Micro-channel Devices
500 mm x 1.5 mm structures in sintered SiN
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 mmWidth at base: 300 mmWidth at tip: 200 mmGap Between Fins 300-400 mm
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
Large cooling towers
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
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.
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
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.
