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Final Condensers

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Condensers (Type of coolant) Water- cooled Air- cooled Tube-in- tube Shell and coil Shell and tube Natural draft Forced draft Coiled tube-in- tube Straight tube- in-tube Condensers What is condensation? Condensation is the change of the physical state of aggregation (or simply state) of matter from gaseous phase into liquid phase and the reverse of evaporation. Condensation commonly occurs when a vapor is cooled to its dew point, but the dew point can also be reached through compression. The condensed vapor is called a condensate, the laboratory or the industrial equipment used for condensation is called a condenser. Water vapor that naturally condenses on cold surfaces into liquid water is called dew. Water vapor will normally only condense onto another surface when the temperature of that surface is cooler than the temperature of the water vapor. What are condensers? Heat transfer devices used to liquefy vapors by removing their latent heat are called condensers. The latent heat is removed by absorbing it in a cooler liquid, called the coolant. Classification of condensers: Condensers can be classified into three major classes, on the basis of: 1. Type of cooling media (coolant) 2. Construction 3. Nature of process fluid There is also a further classification of above three classes of condensers.
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CondensersWhat is condensation?Condensation is the change of the physical state of aggregation (or simply state) of matter from gaseous phase into liquid phase and the reverse of evaporation. Condensation commonly occurs when a vapor is cooled to its dew point, but the dew point can also be reached through compression. The condensed vapor is called a condensate, the laboratory or the industrial equipment used for condensation is called a condenser. Water vapor that naturally condenses on cold surfaces into liquid water is called dew. Water vapor will normally only condense onto another surface when the temperature of that surface is cooler than the temperature of the water vapor.

What are condensers?Heat transfer devices used to liquefy vapors by removing their latent heat are called condensers. The latent heat is removed by absorbing it in a cooler liquid, called the coolant. Classification of condensers: Condensers can be classified into three major classes, on the basis of: 1. Type of cooling media (coolant) 2. Construction 3. Nature of process fluid There is also a further classification of above three classes of condensers.

Condensers (Type of coolant) Watercooled Aircooled

Tube-in-tube

Shell and coil

Shell and tube

Natural draft

Forced draft

Coiled tube-intube

Straight tube-intube

Condensers (constructi on) Indirect contact Shell and coil Direct contact

Tube-in-tube

Shell and tube

Coiled tube-intube Straight tube-intube Water-cooled condensers: As the name shows, these types of condensers use water as a cooling media (coolant). Water use by watercooled condensers may be: Waste water Recirculated water system.

In a waste water system, the water circulates through the condenser once, and then discharges to asewer. This system is used on small units, or in locations where large quantities of fresh inexpensive water plus a sewer system large enough to handle the waste water are available. The fresh water supply can come from city water, a well, a lake, or a river. City water is a most common source, but many states and local codes place severe restrictions on the use and disposal of condenser water.

In a recirculated water system, the same water circulates through the condenser, is cooled to removethe heat it absorbs from the condenser, and then recirculates. Therefore, this type of system requires some type of water cooling device. Cooling towers are the most common water cooling devices used in recirculated water systems. Figure shows a system that uses a cooling tower. Water pumps circulate the water through the system, and then pump the water to the cooling tower, which is usually located on the roof. Once a recirculated water system is filled with water, the only additional water it requires is makeup water. Makeup water simply replaces the water that evaporates from the cooling tower. Therefore, the recirculated water system is often required by code to conserve water and to prevent overloading of sewer systems.

Tube-in-tube condensers:Tube-in-tube condensers are the type of indirect contact and complete condensers. Water is basically used as a coolant in tube-in-tube condensers. It consists of a smaller water tube inside a larger tube. The water tube absorbs heat from the vapor, and the water absorbs the heat from the water tube. But the vapor tube is also exposed to the ambient air, thus the ambient air absorbs some heat from the condenser by natural convection. The hot vapor enters the top of the condenser, and the condensed liquid flows out at the bottom.

Coiled tube

tube-in-

condensers:Small tube-in-tube condensers are made from two continuous tubes, one inside the other, formed into coils. They are limited to about 10 ton capacity because they must be made from small, soft metal tubes that are easy to form, such as copper or aluminum. They are difficult to clean because of their shape and the small diameter of the water tube.

tube-

Straight in-tube

condensers:Straight tube-in-tube condensers are available in capacities up to 10 ton. This is the bulkiest type of watercooled condenser, and therefore other types are used for capacities above 10 ton. Header boxes are attached to each end of the condenser to control the flow of vapor and water through the condenser. Access plates bolted to the header boxes can be removed to expose the open ends of the water tubes for cleaning. This type of condenser requires a separate receiver to store condensed liquid.

Shell and coil water cooled condensers:Shell and coil water cooled condensers are the type of indirect contact and complete condensers. It is often used on small packaged A/C systems up to 15 ton capacity. Shell and coil water cooled condenser consists of one or more water coils enclosed in a welded steel shell. Both finned and bare coil types are available. The shell and coil can be either horizontal or vertical. In both the horizontal and vertical types, the hot vapor enters the top of the shell and surrounds the water coils. As the vapor condenses, it drops to the bottom of the shell, which often serves as a receiver. Most vertical types use the counter flow water system because it is more efficient than parallel water flow. In the shell and coil condenser, the coiled tubing is free to expand and contract with temperature changes because of its spring action, and can withstand any strain caused by temperature changes. Most shell and coil condensers can be cleaned only with chemicals because the shell is welded together, and mechanical cleaning devices cannot pass through the coils.

Shell and tube water cooled condensers: Shell and tube water cooled condensers are also the type of indirect contact and complete condensers. It consists of a cylindrical steel shell containing a number of straight water tubes. Tube sheets welded to each end of the shell hold the tubes in place. The water tubes are usually silver-soldered or brazed to the tube sheets. In some condensers, the tubes are expanded into grooves in the tube sheet holes to form a vapor-tight fit. Shell and tube condensers are either horizontal or open vertical type. In the horizontal type, a water box is bolted to the tube sheet at each end. The water supply and drain pipes connect to the boxes, which contain baffles that control the water flow through the tubes. The water can flow through a horizontal shell and tube condenser from 2 to 20 times, depending on the baffle arrangement in the specific condenser. The condenser tubes are made from either copper or steel, with or without fins. Steel tubes without fins are usually used in ammonia refrigerant systems because ammonia corrodes copper tubing. Tube diameters range from to 2 in, and lengths range from 4 to 18 ft. Shell diameters range from 4 to 60 in. These condensers can contain as many as 1100 tubes. The vapor enters at the top of the shell, flows

over the water tubes, and drops to the bottom of the shell as it condenses. Like a shell and coil condenser, the bottom of the shell often serves as a receiver. Most horizontal shell and tube condensers have a counter flow water system. Open vertical shell and tube condensers, are used in large ammonia systems. The vertical shells range from 16 to 60 in. in diameter, and from 10 to 16 ft tall. The shell can contain from 20 to 400 parallel water tubes. These tubes are open to a water box at the top and to a drain in the bottom. The water box is usually equipped with a perforated sheet steel distributing plate. This plate distributes the water evenly to all of the tubes, and blocks the passage of solid material large enough to clog the swirls or tubes. A curved metal plate, called a swirler, at the top of each tube causes the water to spiral as it flows down the tubes. This action forces the water against the tube wall to increase heat transfer. The water drains into a sump and is pumped to a cooling tower, or drains into a sewer.

Surface condenser: Surface condenser is the commonly used term for a water cooled shell and tubeheat exchanger installed on the exhaust steam from a steam turbine in thermal power stations. These condensers are heat exchangers which convert steam from its gaseous to its liquid state at a pressure below atmospheric pressure. Where cooling water is in short supply, an air-cooled condenser is often used. An air-cooled condenser is however significantly more expensive and cannot achieve as low a steam turbine exhaust pressure as a surface condenser. Surface condensers are also used in applications and industries other than the condensing of steam turbine exhaust in power plants . Purpose: In thermal power plants, the primary purpose of a surface condenser is to condense the exhaust steam from a steam turbine to obtain maximum efficiency and also to convert the turbine exhaust steam into pure water (referred to as steam condensate) so that it may be reused in the steam generator or boiler as boiler feed water.

The adjacent diagram depicts a typical water-cooled surface condenser as used in power stations to condense the exhaust steam from a steam turbine driving an electrical generator as well in other applications. There are many fabrication design variations depending on the manufacturer, the size of the steam turbine, and other site-specific conditions.

Other applications of surface condensers Vacuum evaporation Vacuum refrigeration Ocean Thermal Energy (OTEC) Replacing barometric condensers in steam-driven ejector systems Geothermal energy recovery Desalination systems

Capacity of Water Cooled CondensersThe capacity of a water cooled condenser depends on the temperature of the water, the amount of water circulated, and the temperature of the refrigerant gas. The capacity will increase with the temperature difference between the refrigerant gas and water. Temperature difference can be enlarged by increasing the condensation pressure, or decreasing the temperature of the water entering, or by increasing the amount of water to maintain a low water temperature.

Flow direction in condensers:Counter flow: However, the water can flow through the condensers in either direction. When the cold water enters at the bottom and flows in the direction opposite to the vapor, it is called a counter flow system. Both the water and the vapor flow in the same direction in a parallel flow system. The counter flow system is the most common in all types of water cooled condensers because it is more efficient than a parallel flow system. In the counter flow system, the coldest water is used for the final cooling of the liquid, while the warmest water absorbs heat from the hottest vapor. Thus the temperature difference between the water and the vapor stays fairly constant throughout the condenser. But as the water and vapor flow in the same direction through a parallel system, the temperature difference between them decreases. As a result, the ability of the water to absorb heat decreases as it passes through the condenser. The other flow directions include cross flow and parallel flow in which the cooling water flows in direction parallel to the direction of vapor or perpendicular (at 90 degrees) to the vapor in the latter case.

The other flow directions include cross flow and parallel flow in which the cooling water flows in direction parallel to the direction of vapor or perpendicular (at 90 degrees) to the vapor in the latter case.

Cross flow:It 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 systems 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.

Fouling in condensers:Any water used in water cooled condenser systems contains a certain amount of minerals and other foreign materials, depending on its source. These materials form deposits inside the condenser water tubes. This is called water fouling. The deposits insulate the tubes, reduce their heat transfer rate, and restrict the water flow. As the deposits build up, they also reduce the condensers capacity.

Traditional cleaning methods:The fouling of condensers not only has negative effect on heat transfer efficiency but also causes corrosion and tube narrowing phenomenon and may restrict the output or capacity of facility due to unpredicted shutdowns. The condensers may get fouled with organic deposits or with hardened process chemicals.

Scale and fouling in condensers are addressed in the following ways: 1. Chemical treatment: adding chemicals to cooling water in order to inhibit biofouling and scaling tendency. 2. Filtration systems: constantly removing suspended matters and corrosion particles from circulatory systems to prevent damage to the tubing. 3. Blowdown: regular draining of dirty water and introducing clean water to prevent scaling tendency of cooling water. 4. Manual cleaning: manually swabbing each and every condenser tube with brush to remove all scales.

Air cooled condensers:An air-cooled condenser is a coil of metal tubing through which the vapor flows. The tubing is usually attached to plate type fins to increase the surface area for heat transfer. Condenser tubes are made from copper, aluminum, or steel. They range in size from to in. outside diameter, depending on the size of the condenser. Copper tubes are most common because copper has excellent heat transfer ability, needs no protection against corrosion, and is easy to form into tubes and coils. However, either steel or aluminum condensers must be used in ammonia systems, because ammonia reacts with copper. Steel tubes must be painted to prevent corrosion. A single row of tubing provides the most efficient heat transfer. Thus is because the air temperature rises as it passes through each row of tubing. The temperature difference between the air and the vapor decreases in each additional row of tubing, and therefore each row becomes less efficient. However, single-row condensers take up more space than multiple-row condensers. Therefore, single-row condensers are usually limited to small A/C and refrigeration systems, such as domestic refrigerators and freezers, where space permits. Larger systems require a more compact condenser, a small face area and several rows of tubing stacked in depth. Although the condenser in figure has only two rows, condensers with up to six rows are common. Some condensers have seven or eight rows. However, more than eight rows of tubing are usually not efficient. This is because the air temperature would be too close to the condenser temperature to absorb any more heat after passing through eight rows of tubing.

Most air-cooled condensers have fins attached to the tubes to increase the surface area exposed to the air. This increases the amount of heat transfer from the condenser to the air. Fins are usually made from aluminum because of its light weight, but copper and steel fins are also used. The most common form of fins is the plate type. They are placed over the tubing, and the tubing is expanded, either with a mandrel or by hydraulic pressure, until the tubing fits tightly in the fins. The number of fins ranges from 4 to 30 fins per inch. The most common range on industrial and commercial condensers is 8 to 16 fins per inch. Large air- cooled condensers contain two or more circuits of tubing connected in parallel by pipes called headers. A supply of header distributes the hot vapor to the parallel circuits. The return header collects all the liquid. In this arrangement, only part of the vapor condenses in each circuit, and the condensed liquid does not fill the circuit as quickly as it does in a single circuit condenser. This gives each circuit more condensing surface, and makes the parallel circuit more efficient. Some air-cooled condensers contain a separate sub cooling circuit to increase the capacity of the system. Generally, each degree of sub cooling increases system capacity by about 0.5%. The sub-cooling circuit is usually located within the main condenser housing. However, the liquid first flows from the main condenser to the receiver, and then passes through the sub cooling circuit on its way to the metering device.

The two types of air-cooled condensers are Natural draft air-cooled condenser Forced draft air-cooled condenser In the natural draft type, heat transfers from the condenser coils to the air by natural convection. Fans-either propeller or centrifugal-in forced air condensers force the air over the condenser coils to increase its heat transfer capacity. Because the rate of heat transfer is slower on natural draft condensers, they require a larger surface area compared to a forced air type of the same capacity. Therefore, natural draft condensers are used only in small capacity applications such as household refrigerators and freezers

Forced air-cooled condensers are Base mounted Remote

Different designs are available for indoor and outdoor location. Base mounted air-cooled condensers, using propeller fans, are mounted on a base along with the compressor, receiver, and various controls. The entire arrangement is called a condensing unit. These units are used on packaged refrigeration systems of 10 ton or less, such as reach-in refrigerators and beverage coolers,and split A/C systems. Those used on refrigeration systems are usually mounted in or near the unit inside the building. Those units used for split A/C systems are usually mounted outside the building, either on a foundation on the ground or on the roof.

Remote air-cooled condensers are used on systems above 10 ton, and are available up to 125 ton.Both horizontal and vertical type air-cooled condensers are available. They can be located either inside or outside of a building. Outside, they can be mounted on a foundation on the ground, on the roof, or on the side of the building-away from walls or other obstructions to airflow. Outside condensers usually use propeller fans because they have low resistance to airflow and free air discharge. Condensers require from 600 to 1200 cfm of air per ton of capacity. Propeller fans can move this volume of air as long as the resistance to airflow is low. To prevent any resistance to airflow, the fan intake on vertical outdoor condensers usually faces the prevailing winds. If this is not possible, the air discharge side is usually covered with a shield to deflect opposing winds. Remote condensers located inside the building usually require ductwork to carry air to and from the unit. The ductwork restricts airflow to and from the condenser, and causes a high air pressure drop. Therefore, inside condensers usually use centrifugal fans which can move the necessary volume of air against the resistance to airflow.

Comparison between water-cooled and air-cooled condensers: Water-cooled condensers use water as the cooling medium, and are more common than air-cooled condensers in commercial and industrial A/C and refrigeration systems. This is because they are much smaller than air-cooled condensers of the same capacity, and therefore take up less space. For example, a 10 ton water-cooled condenser occupies about 4 cu ft, but an air-cooled condenser of the same capacity requires as much as 64 cu ft. A water-cooled condenser also has a lower condensing temperature than an air-cooled condenser. This is because the supply water temperature is normally lower than the ambient air temperature, but the differences between the condensing and cooling medium temperatures is normally the same-about 25 F (14 C ). Therefore, the compressor for a water-cooled condenser requires less horsepower for the same capacity, because it does not have to raise the pressure and temperature of the vapor as high.

Difference between in-direct contact and direct contact condensers:

In the indirect contact condensers (e.g., tube-in-tube, shell and coil, shell and tube) the condensing vapor and coolant are separated by a tubular heat transfer surface. Indirect contact condensers are also called surfaces condensers. In the direct contact condensers, the coolant and vapor streams, both of which are usually water, are physically mixed and leave the condenser as a single stream.

Direct contact condensers:Contact condensers are much smaller and cheaper than surfaces condensers (indirect contact condensers). In the figure shown, part of cooling water is sprayed into the vapor stream near the vapor inlet and the remainder is directed into a discharge throat to complete the condensation.

Dehumidifying Condensers:A condenser for a mixture of gases and non condensable gases is shown in the figure. It is set vertically and not horizontally as are most condensers for vapors containing no non condensable gases; also, vapor is condensed inside the tubes not outside, and the coolant flows through the shell. This provides the positive sweep of vapor as mixture through the tubes and avoids the formation of any stagnant pockets of inert gas that might blanket the heat transfer surface. The modified lower head acts to separate the condensate from the uncondensed vapor and gas.

There are two main categories of condenser, differentiated by the extent of condensation.

Total Condenser:In a total condenser, the entire vapor leaving the top of the column is condensed. Consequently, the composition of the vapor leaving the top tray y1 is the same as that of the liquid distillate product and reflux, XD.

Partial Condensers:In a partial condenser, the vapor is only partially liquefied. The liquid produced is returned to the column as liquid, and a vapor product stream is removed. The compositions of these three streams (V1, D, and R) are different. Normally, D (composition yD) is in equilibrium with R (composition XD). A partial condenser functions as an equilibrium separation stage, so columns with a partial condenser effectively have an extra ideal stage.

Applications of condensation:Condensation is a crucial component of distillation, an important laboratory and industrial chemistry application. Because condensation is a naturally occurring phenomenon, it can often be used to generate water in large quantities for human use. Many structures are made solely for the purpose of collecting water from condensation, such as air wells and fog fences. Such systems can often be used to retain soil moisture in areas where active desertification is occurringso much so that some organizations educate people living in affected areas about water condensers to help them deal effectively with the situation. An air well or aerial well is a structure or device that collects water by promoting the condensation of moisture from air. Designs for air wells are many and varied, but the simplest designs are completely passive, require no external energy source and have few, if any, moving parts. A fog fence or fog collector is an apparatus for collecting liquid water from fog, using of a fine mesh or array of parallel wires.

Applications of condensers: Daily life examples

Condensers in automotives:Today, as we drive our automobiles, a great many of us, can enjoy the same comfort levels that we are accustomed to at home and at work. With the push of a button or the slide of a lever, we make the seamless transition from heating to cooling and back again without ever wondering how this change occurs. CONDENSER This is the area in which heat dissipation occurs. The condenser, in many cases, will have much the same appearance as the radiator in you car as the two have very similar functions. The condenser is designed to radiate heat. Its location is usually in front of the radiator, but in some cases, due to aerodynamic improvements to the body of a vehicle, its location may differ. Condensers must have good air flow anytime

the system is in operation. On rear wheel drive vehicles; this is usually accomplished by taking advantage of your existing engine's cooling fan. On front wheel drive vehicles, condenser air flow is supplemented with one or more electric cooling fan(s). As hot compressed gasses are introduced into the top of the condenser, they are cooled off. As the gas cools, it condenses and exits the bottom of the condenser as a high pressure liquid.

Central Air Conditioning System:Air conditioners and refrigerators work the same way. Air conditioners use chemicals that easily convert from a gas to a liquid and back again. This chemical is used to transfer heat from the air inside of a home to the outside air. The parts of this system include compressor, a condenser and an evaporator. The compressor and condenser are usually located on the outside air portion of the air conditioner. The evaporator is located on the inside the house. The working fluid arrives at the compressor as a cool, low-pressure gas. The compressor squeezes the fluid. The working fluid leaves the compressor as a hot, high pressure gas and flows into the condenser. When the working fluid leaves the condenser, its temperature is much cooler and it has changed from a gas to a liquid under high pressure. The liquid goes into the evaporator through a very tiny, narrow hole. On the other side, the liquid's pressure drops. When it does it begins to evaporate into a gas. As the liquid changes to gas and evaporates, it extracts heat from the air around it. The heat in the air is needed to separate the molecules of the fluid from a liquid to a gas.By the time the working fluid leaves the evaporator; it is a cool, low pressure gas. It then returns to the compressor to begin its trip all over again.

Industrial Examples:Condensers are used in many industrial processes such as: In the nitration of propane where it is used to condense the nitroparaffins In the system for the production of concentrated nitric acid In the chlorination of pentane where it is used to condense unconverted pentane and HCL In the DDT plant


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