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Abstract Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or in the case of closed circuit dry cooling towers rely solely on air to cool the working fluid to near the dry-bulb air temperature. Common applications include cooling the circulating water used in oil refineries, chemical plants, power stations and building cooling. Industrial cooling towers can be used to remove heat from various sources such as machinery or heated process material. The primary use of large, industrial cooling towers is to remove the heat absorbed in the circulating cooling water systems used in power plants, petroleum refineries, petrochemical plants, natural gas processing plants, food processing plants, semi-conductor plants, and for other industrial facilities such as in condensers of distillation columns, for cooling liquid in crystallization, etc. In thermal power plant one of the main parts is consider, which cools the refrigerant. When cooling the refrigerant, the cold water becomes the hot water.
The hot water temperature is reduced by cooling towers. When hot water enters into the induced draft cooling tower and sprayed by nozzles. So hot water is converted into cold water. The effective cooling of water depends upon the dry bulb temperature and wet bulb temperature, size, height of the cooling tower and velocity of air. The project deals with the performance study and analysis of induced draft cooling tower, which is one of the deciding factors used for increasing the power plant efficiency also modelling and analysis of flow using software .A cooling tower is an enclosed device for the evaporative cooling of water by contact with the air. Cooling tower is a heat rejection device. Common application includes cooling the circulating water used in oil refineries, petrochemical, and other chemical plants, thermal power stations and HVAC system for cooling buildings. Keywords Mechanical, Thermal, Cooling Tower. I.
1.1 Introduction Cooling towers are a very important part of Power plants. The primary task of a cooling tower is to reject heat into the atmosphere. Hot water from Condenser is sent to the cooling tower. The water exits the cooling tower and is sent back to the boiler or together units for further process. In cooling towers, air is passed concurrently or counter currently with water. The heat gained by air is the heat lost by water.
The efficiency of cooling tower depends on air and water flow rates and operating temperatures. In the chemical industries, utilities play an important role in plant operations. Two types of utilities are used in industries. Cooling utilities and heating utilities. Cold water is required for condenser, heat exchangers, reactors and other cooling purposes. Hot utilities include steam and other hot liquid used for heating in heat exchangers and to maintain reaction conditions. Cooling towers are used to cool the water for its various applications. The used water from various applications at higher temperature can be cooled and reused. Various types of cooling towers include Natural draft, induced draft and forced draft cooling towers. In cooling towers, air is passed concurrently or counter currently with water. The heat gained by air is the heat lost by water. The efficiency of cooling tower depends on air and water flow rates and operating temperatures. Various researchers have carried out studies and investigation on various aspects of cooling tower which influence the effectiveness and working of cooling tower.
1.2 Components of Cooling Tower
The basic components of an evaporative tower are: Frame and casing, fill, cold water basin, drift eliminators, air inlet, louvers, nozzles and fans. Frame and casing: Most towers have structural frames that support the exterior enclosures (casings), motors, fans, and other components. With some smaller designs, such as some glass fiber units, the casing may essentially be the frame. Fill: Most towers employ fills (made of plastic or wood) to facilitate heat transfer by maximizing water and air contact. Fill can either be splash or film type. With splash fill, water falls over successive layers of horizontal splash bars, continuously breaking into smaller droplets, while also wetting the fill surface. Plastic splash fill promotes better heat transfer than the wood splash fill. Film fill consists of thin, closely spaced plastic surfaces over which the water spreads, forming a thin film in contact with the air. These surfaces may be flat, corrugated, honeycombed, or other patterns. The film type of fill is the more efficient and provides same heat transfer in a smaller volume than the splash fill. Cold water basin: The cold water basin, located at or near the bottom of the tower, receives the cooled water that flows down through the tower and fill.
The basin usually has a sump or low point for the cold water discharge connection. In many tower designs, the cold water basin is beneath the entire fill .In some forced draft counter flow design, however, the water at the bottom of the fill is channelled to a perimeter trough that functions as the cold water basin. Propeller fans are mounted beneath the fill to blow the air up through the tower. With this design, the tower is mounted on legs, providing easy access to the fans and their motors. Drift eliminators: These capture water droplets entrapped in the air stream that otherwise would be lost to the atmosphere. Air inlet: This is the point of entry for the air entering a tower. The inlet may take up an entire side of a tower–cross flow design– or be located low on the side or the bottom of counter flow designs. Louvers: Generally, cross-flow towers have inlet louvers. The purpose of louvers is to equalize air flow into the fill and retain the water within the tower.
Many counter flow tower designs do not require louvers. Nozzles: These provide the water sprays to wet the fill. Uniform water distribution at the top of the fill is essential to achieve proper wetting of the entire fill surface. Nozzles can either be fixed in place and have either round or square spray patterns or can be part of a rotating assembly as found in some circular cross-section towers. Fans: Centrifugal fan is used in towers. Generally, propeller fans are used in induced draft towers and both propeller and centrifugal fans are found in forced draft towers. Depending upon their size, propeller fans can either be fixed or variable pitch. A fan having non-automatic adjustable pitch blades permits the same fan to be used over a wide range of kW with the fan adjusted to deliver the desired air flow at the lowest power consumption. Automatic variable pitch blades can vary air flow in response to changing load conditions. Digital Thermometer: 2 Digital thermometer are used to detect the inlet water temperature to the cooling tower and outlet water temperature out of the cooling tower. Figure1.2 Digital Thermometer Pump: Pump is used to lift the water from heating basin to the inlet of the cooling tower.
1.3 Tower Materials In the early days of cooling tower manufacture, towers were constructed primarily of wood. Wooden components included the frame, casing, louvers, fill, and often the cold water basin. If the basin was not of wood, it likely was of concrete. Today, tower manufacturers fabricate towers and tower components from a variety of materials. Often several materials are used to enhance corrosion resistance, reduce maintenance, and promote reliability and long service life. Galvanized steel, various grades of stainless steel, glass fibre, and concrete are widely used in tower construction as well as aluminium and various types of plastics for some components. Wood towers are still available, but they have glass fibre rather than wood panels (casing) over the wood framework. The inlet air louvers may be glass fibre, the fill may be plastic, and the cold water basin may be steel. Larger towers sometimes are made of concrete. Many towers–casings and basins–are constructed of galvanized steel or, where a corrosive atmosphere is a problem, stainless steel. Sometimes a galvanized tower has a stainless steel basin. Glass fibre is also widely used for cooling tower casings and basins, giving long life and protection from the harmful effects of many chemicals.
Plastics are widely used for fill, including PVC, polypropylene, and other polymers. T reated wood splash fill is still specified for wood towers, but plastic splash fill is also widely used when water conditions mandate the use of splash fill. Film fill, because it offers greater heat transfer efficiency, is the fill of choice for applications where the circulating water is generally free of debris that could plug the fill passageways. Plastics also find wide use as nozzle materials. Many nozzles are being made of PVC, ABS, polypropylene, and glass-filled nylon. Aluminium, glass fiber, and hot-dipped galvanized steel are commonly used fan materials. Centrifugal fans are often fabricated from galvanized steel. Propeller fans are fabricated from galvanized, aluminium, or moulded glass fibre reinforced plastic. 1.4 Preliminary Analysis of Cooling Tower Figure1.3 Temperature Analysis of water in tower Figure1.4 Pressure Analysis of water in tower Figure1.5 Velocity Analysis of water in tower Figure1.6 Pressure Analysis in fan Page | 5 Figure1.7 Velocity Analysis of air in fan Figure1.8 Velocity Analysis of air in fan II.
We have studied the way of increasing the efficiency of the cooling tower by enabling more volume of air to pass through the tower and hence more heat will be dissipated. The zigzag water flow pattern has made the water movement to slow down and longer time of water exposure to air is achieved. The importance of a cooling tower in industries has motivated us to study its performance and look for possible ways to increase its efficiency. ACKNOWLEDGMENT It gives us immense pleasure to express our sense of gratitude and sincere thanks to our respected guide prof. Suneet Mehta, Mechanical department, VIVA Institute of Technology, Virar, for his valuable guidance. We would also like to thank Dr. Arun Kumar, Principal, whole hearted support. We also wish to express our sincere thanks to prof. Niyati Raut, HOD Mechanical department, for her kind hearted support.
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