How Do Water Boilers Work Environmental Sciences Essay

How Do Water Boilers Work Environmental Sciences Essay A boiler is a closed vessel in which water or other liquid is heated in order to generate steam or vapor which is then used for other external processes. Water is a useful and cheap medium for transferring heat to a process. When water is boiled into steam, its volume increases about 1600 times, generating a force that is very explosive. This can be achieved by combustion of wood, natural gas, coal or oil. Electric steam boilers on the other hand use resistance to produce the required heat. The chemical energy from any of these external fuel sources is converted into heat which is then transferred to the water through radiation which is the transfer of heat from a hot body to a cold body without a conveying medium, conduction which involves the transfer of heat by actual physical contact and by convection, the transfer of heat by a conveying medium like air or water (EuropeanCommission, 2006). Since the development of the first boilers in the 18th century, boilers have evolved so as to increase their efficiency and low-cost design as well as pay more attention to air pollutant emissions like carbon monoxide and hydrogen chloride. These types of emissions depend on the type of fuel used and the load factor of the boiler. The power of a boiler is determined by the required steam mass flow rate, temperature and pressure. The amount of input fuel required depends on the fuel energy content and on the overall energy efficiency. A boilers performance is characterized by its steam pressure and temperature. Saturated steam is steam at boiling temperature for a given pressure, which is what most boilers produce and make use of. If more heat is supplied and the steam pressure rises above the saturation temperature at a given pressure, then the steam becomes superheated steam. This kind of steam though at a higher temperature, can decrease the efficiency of the steam generating plant . If more heat is supplied to the superheated steam, it becomes supercritical steam which can be used in power generation (USEPA, 2004). A closed boiler is one in which all the steam generated is returned to the vessel in form of water and is reused while an open boiler is one that does not return water to the original vessel. The boiler system comprises of three major parts which are: the feed water system, the steam system and the fuel system. The feed system supplies water to the boiler and regulates it to meet the systems demands. The steam system is responsible for collection and control of the steam produced in the boiler. This system is regulated and checked using pressure gauges and is directed to the point of use through an efficient piping system. The fuel system includes all the equipment used to generate the required heat which is dependent on the type of fuel used in the system (Hartford, 1911). There are three basic types of boilers which are used for industrial uses. These are the fire tube, the water tube and the fire box boilers. In the fire tube boilers, heat passes through the tubes which are surrounded by the water being heated. These tubes are arranged in banks so that the heat produced can pass through the vessel many times before escaping. Fire tube boilers are relatively small in size compared to the other type of boilers. In water tube boilers, heat is made to pass through the tubes which contain the water. These tubes are then interconnected to a steam outlet for distribution to the plant system. These types of boilers are the most commonly used because they are larger in size and can therefore withstand greater pressures and temperatures, though their initial and maintenance costs are higher. In a fire box boiler, the hot gases from the fire box which is the space where the fuel is burned are channeled into the tubes where they heat the water. Water is supplied to the boiler from the boiler feed water plant also known as the demineralizer plant. The demineralizer removes all salts present in the water by removal of hydrogen ions which are replaced with sulphuric acid. This water should be free of any foreign materials that could cause harm to the boiler and also decrease its performance. Some of these harmful substances include oxygen, positively charged ions of calcium, aluminum, sodium and zinc. There are also other negatively charged ions like carbonates, bicarbonates, silica and fluorides which could harm the boiler efficiency. The removal of oxygen is usually done in the de-aerator located after the ion exchanger. The de-aeration of the condensate returning from the process ensures that the water is free of oxygen bubbles that may inhibit heat transfer. In de-aeration, the dissolved gases are removed by preheating the feed water before it is allowed to enter the boiler. The removal of these gases is very important to the boiler equipment longevity as well as safety of operation. De-aeration can be done by chemical de-aeration, mechanical de-aeration or both. The chemical treatment is used to remove harmful substances that could cause build up in the heat transfer equipment. The economizer is used to preheat the water entering the boiler. This helps reduce fuel cost making the boiler more efficient (Shields, 1961). The water vessel in a boiler is connected to the heat source by metal rods which heat the water and convert it to steam. The steam is allowed to collect in the dome before exiting the boiler. The function of the dome is to force the steam to become highly condensed in order for it to exit the boiler with a large amount of pressure. A boiler also contains a drain which removes impurities from the water vessel and a chimney to allow heat to escape once it has passed the water vessel. It is vital for all boilers to have safety valves in order to allow excess steam to be released in order to prevent explosions. The heart of a boiler is a pressure vessel which is a closed container designed to hold gases or liquids at a pressure. This pressure vessel is usually made of steel or wrought iron. This pressure is obtained from an indirect source or from the application of heat from a direct or indirect source. If not properly maintained, boilers can be a source of serious injuries and can lead to huge losses in form of property destruction. Thin and brittle metals that make up some parts of the boiler could rapture or poorly welded seams could open up leading to violent eruptions of the pressurized steam. Collapsed boiler tubes could also spray the hot steam they contain into the air injuring the around (Reeves, 2001). Even with the best pretreatment programs, boiler feed water often contain some degree of impurities which normally accumulate in the boiler. The increasing accumulation of dissolved solids may lead to carry over of boiler water into the steam which may cause damage to the piping system as well as the process equipment. These suspended solids could also lead to the formation of sludge which will lead to a reduction of the boiler efficiency as well as it s heat transfer capability. In order to avoid these problems, water should often be discharged from the boiler in order to control the concentrations of the suspended and dissolved solids in the boiler. Discharging of the surface water is usually done in order to get rid of the dissolved solids while the discharging of bottom water is done in order to remove the sludge from the bottom of the boiler. Boiler blow down i.e. discharge of water from the boiler is a very important aspect of the boiler maintenance. Lack of proper blow down can lead to increased fuel consumption, extra chemical treatments for the boiler as well as increased heat loss. Also, since the blow down water has the same temperature as the boiler water, it can be reused in the boiler operations once removed. However, excessive blow down can lead to wastage of water, energy and treatment. The two major types of boiler blow downs are intermittent and continuous blow down. Intermittent blow down is done by manually fitting a valve at the bottom of the boiler which is removes the unwanted parameters. It requires large short-term increases in the amount of feed water put into the boiler which leads to a substantial amount of heat energy being lost. Alternatively, continuous blow down involves the steady and constant dispatch of small stream of concentrated boiling water being replaced with steady and constant inflow of feed water. The various energy efficiency opportunities in a boiler system can be related to combustion, heat transfer, water quality, avoidable losses and blow down. To maximize a boilers efficiency, the stack temperature should be designed to be as low as possible. Nevertheless, it should not be very low such that water vapor in the exhaust condenses on the stack walls. Automatic blow down controls that sense and respond to the boiler water conductivity and pH should be installed in order to reduce uncontrolled continuous blow down. In oil and coal fired boilers, soot should be removed as it acts as an insulator against heat transfer.

HOW IMPORTANT ARE MENTAL REPRESENTATIONS IN COGNITIVE THEORIES :: essays research papers

HOW IMPORTANT ARE MENTAL REPRESENTATIONS IN COGNITIVE THEORIES? How the world around us is represented mentally is the corner stone of cognitive architectures. It facilitates understanding of information received and perceived from our environment. The storage and retrieval of knowledge would be impossible without mental representations. Mental representations are the way in which we create ‘copies’ of the real things around us, which we perceive. A description of a representation is a symbol, sign, image or a depiction that takes the place of a real object in the real world. . Representations were broadly categorised into three. The ‘analogue representation’ the ‘propositional representation’ and ‘procedural rules’. Analogue representations are those which have an image-like copy quality to them, whereas the propositional representation are based on language-like constructs. Since the arrival of connectionism another representation has been proposed that of sub-symbolic representation. Here mental representations, according to Eysenk and Keane (2002) are â€Å"distributed† patterns of activation in a connectivist network. Historically, mental representations have been interpreted by analogy with physical representations, i.e. descriptions and classifications devised for physical representations have been applied to mental representations (Paivio, 1986). Physical representations can be picture-like or language-like (see Table). Physical and mental representations physical representations  Ã‚  Ã‚  Ã‚  Ã‚  picture-like  Ã‚  Ã‚  Ã‚  Ã‚  language-like examples  Ã‚  Ã‚  Ã‚  Ã‚  photographs drawings maps diagrams  Ã‚  Ã‚  Ã‚  Ã‚  human-language formal systems: maths, symbolic logic computer programs properties  Ã‚  Ã‚  Ã‚  Ã‚  analogue iconic continuous  Ã‚  Ã‚  Ã‚  Ã‚  non-analogue non-iconic digital/discrete Table: Types of physical representations (after Paivio, 1986) The representations need then to be categorised for storage in long -term memory. These ‘packages’ of knowledge are classed as being either procedural knowledge or declarative knowledge. Procedural knowledge is knowing how to do something or precisely what to do. It is sets of rules or procedures and skills like playing the piano. Declarative knowledge is about facts. Representations allow cognitive models to work as they are the ‘substance’ the models work on. The models for discussion share common features but are equally differentiated from each other at some level. Before looking at each of the theories mental representations it would be helpful to take a snapshot of the model structures and approaches to learning and processing to gain a fuller understanding of their strengths and weaknesses. The models compared here are Schema theory (Rummelhart and Norman 1983) ACT* Anderson) and PDP. Schema theory is said to offers a unified theory of cognition as it umbrellas all areas of cognition. It is interactive and works on stored knowledge or long-term memory. It does not address any wider structural issues. Schema is about how our learning is influenced by our previous knowledge. HOW IMPORTANT ARE MENTAL REPRESENTATIONS IN COGNITIVE THEORIES :: essays research papers HOW IMPORTANT ARE MENTAL REPRESENTATIONS IN COGNITIVE THEORIES? How the world around us is represented mentally is the corner stone of cognitive architectures. It facilitates understanding of information received and perceived from our environment. The storage and retrieval of knowledge would be impossible without mental representations. Mental representations are the way in which we create ‘copies’ of the real things around us, which we perceive. A description of a representation is a symbol, sign, image or a depiction that takes the place of a real object in the real world. . Representations were broadly categorised into three. The ‘analogue representation’ the ‘propositional representation’ and ‘procedural rules’. Analogue representations are those which have an image-like copy quality to them, whereas the propositional representation are based on language-like constructs. Since the arrival of connectionism another representation has been proposed that of sub-symbolic representation. Here mental representations, according to Eysenk and Keane (2002) are â€Å"distributed† patterns of activation in a connectivist network. Historically, mental representations have been interpreted by analogy with physical representations, i.e. descriptions and classifications devised for physical representations have been applied to mental representations (Paivio, 1986). Physical representations can be picture-like or language-like (see Table). Physical and mental representations physical representations  Ã‚  Ã‚  Ã‚  Ã‚  picture-like  Ã‚  Ã‚  Ã‚  Ã‚  language-like examples  Ã‚  Ã‚  Ã‚  Ã‚  photographs drawings maps diagrams  Ã‚  Ã‚  Ã‚  Ã‚  human-language formal systems: maths, symbolic logic computer programs properties  Ã‚  Ã‚  Ã‚  Ã‚  analogue iconic continuous  Ã‚  Ã‚  Ã‚  Ã‚  non-analogue non-iconic digital/discrete Table: Types of physical representations (after Paivio, 1986) The representations need then to be categorised for storage in long -term memory. These ‘packages’ of knowledge are classed as being either procedural knowledge or declarative knowledge. Procedural knowledge is knowing how to do something or precisely what to do. It is sets of rules or procedures and skills like playing the piano. Declarative knowledge is about facts. Representations allow cognitive models to work as they are the ‘substance’ the models work on. The models for discussion share common features but are equally differentiated from each other at some level. Before looking at each of the theories mental representations it would be helpful to take a snapshot of the model structures and approaches to learning and processing to gain a fuller understanding of their strengths and weaknesses. The models compared here are Schema theory (Rummelhart and Norman 1983) ACT* Anderson) and PDP. Schema theory is said to offers a unified theory of cognition as it umbrellas all areas of cognition. It is interactive and works on stored knowledge or long-term memory. It does not address any wider structural issues. Schema is about how our learning is influenced by our previous knowledge.

Police Administration Essay

In the general concern of police administration, strategic program evaluation is indeed important for the effectiveness of their service and function in the society. Through the thorough evaluation and analysis of their administration and programs, the police organization can understand their processes and strategies in which they can notice their challenges, pitfalls, and problems thus ensuring measures to further develop their performance and service. Another is that through evaluation, the police administration can likewise determine their strengths and advantages, which they can incorporate in their organizational development and further performance plan. Indeed, with the knowledge determined in the administration and program evaluation, the police organization can find effective solutions and strategies for the realization of further development in their function as public servants. However, for the effectiveness of the program evaluation, certain measures must be implemented to achieve the desired results and information accuracy. In this aspect, most evaluations of the police organization programs are conducted by outsiders from the said institutions who mainly represent the public sector which are the primary target of the said program. There are three reasons for this arrangement namely as inclined with humanitarian concern, neutrality view, and the awareness campaign for the fundamental characteristics of the program. Indeed, the dialogue of program evaluation by outsiders counteracting the police institutions is arranged mainly for the intention of achieving effective influence and positive results from the program for the benefit of its target namely the public sector. The arrangement placing outsiders as the evaluators of the programs and strategies of the police organizations is established based on three reasons inclined towards the effectiveness of the police function concern. The first involves humanitarian concern wherein the outside evaluation will be conducted on the perspective of its target sector and the realization of its effects on the public. In the process of outside evaluation, the examiners can thoroughly consider whether the said police program, strategy, or action will be either advantageous or detrimental to their concern. With them conducting the evaluation as the party representing the public interest, they can significantly determined if there are any abusive characteristics or grounds in the program which would be contradictory to the function and responsibility of the police department. Another reason for the said evaluation arrangement is the neutrality pursuit wherein both parties namely the police force and the public sector desire a transparent and unbiased view on the examination. Having an outside party conduct the program evaluation will result to a process free from the political nature and pressure existing inside the police organization. With this arrangement, any bias qualities inside the program can be reduced or even eliminated as both contrasting parties have reviewed and commented on the nature of the said program. The third reason for the said arrangement in police program evaluation lies in the awareness campaign and interest of the police organization. In this concern, the police group must acknowledge the presence and relevance of the public sector representation in terms of information dissemination and awareness. Manifested in the outside party evaluation, a party representing the public must be allowed to investigate and acquire knowledge regarding the program of the police organization. Having been informed of the program’s nature and characteristics, the said party can aid the public in understanding the purpose and relevance of that program thus, gaining the trust, support, and participation of the public sector. Indeed, doing the arrangement of outside party evaluation can effectively aid the interest of the program of manifesting the function of the police organization and benefit the need of the public sector. In the pursuit of achieving effectiveness in the action and performance of the police organization, programs embodying the function of the organization are created as part of their action. In the concern of achieving the beneficial interest from the police performance, the arrangement establishing outside parties to evaluate and examine the performance program of the police organization is created. This approach is developed mainly based on the reasons of humanitarian concern, transparency in the organization’s activities, and the interest of the public for awareness in the presence and activities of the police organization. In general, the development of the said arrangement as part of the procedural activity of the police organization is for the effectiveness of their function and duty of protecting the welfare of the public and promoting peace in the society.

The Great Depression Of 1929-1939 - 2217 Words

Although the Great Depression of 1929-1939 was a detrimental and hard time for America due to increases in crime rates, unemployment rates, and shortages of food, the economic collapse was also a time for President Franklin Roosevelt to reassess the economic situation in America. Roosevelt put in place laws, agencies, and legislature that better shaped the structure of the country, and ultimately created a more powerful and stronger country, both economically and socially. The new legislature that President Roosevelt put into place lead to the United States experiencing close to seven decades of economic growth and made it one of the most influential countries in the world. The American economy slipped into a depression with the Stock Market Crash of 1929. At first, people thought it would be just another depression, similar to the seventeen or more the United States had already been through, and it wasn’t referred to as ‘The Great Depression’ until much later. This time it was different though, and much more of the population was effected as the depression overwhelmed the economy a considerable amount quicker than any had before. On October 24, a day now known as ‘Black Thursday,’ more than 12.9 million shares were traded. A second rush of anxiety swept over Wall Street only five days later on a day now referred to as ‘Black Tuesday.’ Another 16 million shares were traded that day, leaving investors with nothing. The United States GDP fell thirty percent that year,Show MoreRelatedThe Great Depression ( 1929-1939 )1813 Words   |  8 PagesThe Great Depression (1929-1939) is the worst economic downtur n that the modern world has ever seen before. Beginning with the Wall Street stock market crash of 1929, the situation grew worse in the United States, in part, due to the tremendous wealth disparity between the higher class and the lower class. Wages did not grow nearly as quickly as production did during this era, so many people were unable to purchase certain goods. As a result, there was an excess in supply, which prompted layoffsRead MoreThe Causes of Canadas Great Depression of 1929-1939 Essay1679 Words   |  7 Pagesâ€Å"On the morning of October 29, 1929, panicked voices shouted over one another. Here and there, men leaned against the walls, hands over their faces as if trying to shut out the scene. In the street outside, a crowd had gathered, trying to learn the news. A man staggered out the door, clutching his hat in both hands. He looked as though he might weep. â€Å"It’s gone,â€Å" he whispered, so quietly only the few closest to him heard. â€Å"Itâ€⠄¢s all gone.†# The term ‘Great Depression’ according to Kristin Brennan evokesRead MoreThe Great Depression By Milton Freidman And Paul Samuelson1267 Words   |  6 PagesIntroduction: Background Information The Great Depression is defined as an era of hardship and was the â€Å"economic downturn in the history of the Western industrialized world† . The United States was predominantly affected by the Great Depression, soon after stock market crash of October 1929. This fiscal crisis sent Wall Street, the center of economics in New York into a state of prolonged recession that affected foreign economies. 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In 1929 the stock market had crashed which led to a higher unemployment rate and a lower income, this was called the Great Depression. A couple of years before World War I The Great Plains had been plowed then a horrible drought hit the areas that were plowed. The dry dust would blow around the plainsRead MoreHoover And Roosevelt s A ctions During The Aftermath Of The Crash Of 1929792 Words   |  4 PagesCrash of 1929. How did both administrations attempt to deal with the economic stagnation, social hardship and psychological impact of the depression? What needed to be fixed and which approach proved more successful? In your essay you should address not only the underlying economic and social problems that both administrations had to deal with and the various corrective measures they adopted, but also the underlying philosophical approaches of Hoover and Roosevelt and their supporters. The Great CrashRead MoreDecade of Despair: Winnebago County During the Great Depression by Werner E. Braatz and Thomas J. Rowland1524 Words   |  6 PagesDecade of Despair: Winnebago County During the Great Depression 1929-1939. Authors are Werner E. Braatz and Thomas J. Rowland. Copyright 2009 by University Press of America. Published Lanham, Maryland 20706. ISBN-13: 978-0761846406. The stock market crash of October 1929 drastically affected the economic growth of the entire United States. In Wisconsin the attitudes of many changed and several began to devise plans on surviving the worst depression in the Nation’s history. Wisconsin, like many