Disadvantages Of The Open Cycle Configuration Environmental Sciences Essay

Disadvantages Of The Open Cycle Configuration Environmental Sciences Essay The main problems of todays society are; the ever increasing demand in energy, a possible resource shortage and environmental pollution. Therefore a lot of money is spent in research to find alternative ways of producing energy using Earths natural resources like wind, sun and the ocean. This report is a study on Ocean Thermal Energy Conversion (OTEC) which might be the answer to the energy and environmental problem our world has to face. A basic description and an introduction to the types and principles of operation of closed cycle, open cycle and hybrids of OTEC technology is given in this report. Emphasis is shown on the hybrid cycle which has advantages compared to other single purpose plants for fresh water production or power generation. The process of desalination of sea water can prove vital for countries which have water shortage. This report is focused on the technology that would be suited for a hybrid cycle OTEC plant situated in Cyprus. Contents Table of Figures 1. Aims and Objectives The aim of this project is to investigate the characteristics of a dual purpose plant for simultaneous production of desalinated water and electric power. An attempt will be made to state the conditions and criteria for adjusting the ratio of desalinated water to power production and also how this ratio is affected by a variation in seawater temperature and pressure. In addition, different design considerations of the hybrid cycle particularly suitable for an OTEC plant operating in Cyprus will be discussed. 2. Introduction The ocean surface absorbs more heat from the sun in one square mile than could be produced by burning 7000 barrels of oil (Avery Wu, 1994). Therefore the solar energy absorbed per day by the surface waters can be used to provide a green, zero-emission production of electricity. Ocean Thermal Energy Conversion or OTEC is the technology that meets the technical requirements and is economically viable for harvesting the solar energy absorbed by the ocean. OTEC plants make use of the thermal gradient that exists between the surface of the ocean and the deep cold waters to initiate a power producing cycle. The warm tropical surface waters (at a temperature of à ¢Ã¢â‚¬ °Ã‹â€ 22 °C) and the deep ocean waters (at a depth of 1000m a temperature of à ¢Ã¢â‚¬ °Ã‹â€ 4 °C) are used as a source of thermal energy to vaporize and condense the working fluid of a turbine-generator system. The thermodynamic cycle for this heat engine is the called the Rankine cycle. OTEC systems maybe either clos ed cycle, open cycle or a combination of the two also known as hybrid systems. In the closed cycle, seawater is used to vaporize and condense a working fluid, such as ammonia, which drives a turbine-generator in a closed loop, producing electricity. In the open cycle, surface water is flash-evaporated in a vacuum chamber. The resulting low-pressure steam is used to drive a turbine-generator. Cold seawater is used to condense the steam after it has passed through the turbine. The open cycle can, therefore, be configured to produce fresh water as well as electricity. The hybrid cycle consists of both the closed cycle system and the open cycle system. The system is interconnected and arranged in such a manner that the former cycle provides electricity and the latter yields desalinated water. Such a system has promising potential in countries which have issues with lack of water. 3. Literature Review 3.1 Closed Cycle OTEC System 3.1.1 Principle of Operation The closed cycle was first proposed in 1881, by DArsonval in France, and was demonstrated in 1979, when a small plant mounted on a barge off Hawaii (Mini-OTEC) produced 50 kW of gross power, for several months, with a net output of 18 kW (Vega, 1992). The principle of operation of the closed OTEC system is demonstrated in figure 1 below. Figure : Principle of operation of a closed cycle OTEC system (National Renewable Energy Laboratory) In the closed cycle, the OTEC system utilizes the warm surface seawater to vaporize a working fluid, such as ammonia, which flows through a heat exchanger (evaporator). The vapor expands at modest pressures and drives a turbine which is coupled to a generator that produces electricity. The vapor then passes through another heat exchanger (condenser) where it is condensed back into a liquid using cold seawater from pumped from the oceans depths through a cold water pipe. A pressurizer or feed pump is used to pump the condensed working fluid back to the evaporator to complete the cycle, producing continuous power generation as long as the warm water and cold water continue to flow. The closed OTEC cycle is basically the same as the conventional Rankine cycle employed in steam engines, in which the steam is condensed and returned to the boiler after driving a piston or steam turbine, OTEC differs by using a different working fluid and lower pressures and temperatures (Avery Wu, 1994). The four processes of the ideal Rankine cycle are listed below: 1. Isentropic expansion (Turbine) 2. Isobaric heat rejection (Condenser) 3. Isentropic compression (Pump) 4. Isobaric heat addition (Evaporator) 3.2 Open Cycle OTEC System 3.2.1 Principle of Operation The open cycle concept was first proposed in the 1920s and demonstrated in 1930, off Cuba by its inventor, a Frenchman by the name of Georges Claude (Vega, 1992). In the open cycle, the warm seawater is the working fluid. The warm seawater is pumped into a vacuum chamber where it is flash- evaporated to produce steam at an absolute pressure of about 2.4kPa. The steam passes through a low pressure turbine which in turn drives a generator to produce electricity. The steam exiting the turbine flows is condensed by cold seawater pumped from the oceans depths through a cold-water pipe. In this open cycle configuration a surface condenser can be used and therefore the condensed steam remains separated from the cold seawater and provides a supply of desalinated water. Figure 2 below shows the principle of operation of the open cycle OTEC system. Figure : Principle of operation of an open cycle OTEC system (National Renewable Energy Laboratory) 3.2.2 Disadvantages of the Open Cycle Configuration This type of configuration produces less power than the closed cycle alternative but it is attractive in places where water shortage is an issue. In addition, the very low pressure at which the system operates means that connections must be carefully sealed to prevent atmospheric air from entering the system, which could bring the operation to a halt. Another disadvantage compared to the closed cycle system is that the specific volume of the low-pressure steam is very large compared to the pressurized working fluid used in the closed cycle system. Therefore the components must have large flow areas to ensure that steam flow does not reach a high enough velocity which could damage the turbine. Also, a large turbine is required to accommodate the very high volumetric flow rates of the low-pressure steam in order to generate a sufficient amount of electrical power. 3.3 Hybrid Cycle OTEC System 3.3.1 Principle of Operation A hybrid cycle combines the features of both the closed-cycle and open-cycle systems. In a hybrid OTEC system, warm seawater enters a vacuum chamber where it is flash-evaporated into steam, which is similar to the open-cycle evaporation process. The steam vaporizes the working fluid of a closed-cycle loop on the other side of an ammonia vaporizer. The vaporized fluid then drives a turbine that produces electricity. The steam condenses within the heat exchanger and provides desalinated water. Figure 3 is an illustration of the hybrid cycle OTEC system. Figure : Principle of operation of a hybrid cycle OTEC system (National Renewable Energy Laboratory) The electricity produced by the system can be delivered to a utility grid or used to manufacture methanol, hydrogen, refined metals, ammonia, and similar products. 3.4 OTEC Components The main components of an OTEC system are described below- namely, heat exchangers, evaporators, turbines and condensers. 3.4.1 Heat Exchangers for Closed Cycle OTEC Systems The design of heat exchangers to meet industrial requirements for efficiency, durability, ease of manufacture, packaging, system integration reliability and cost has led to an extensive technology devoted just to this subject. The special requirements of OTEC can be met by heat exchangers with different operating characteristics than conventional designs. Also, research has been done to increase the overall heat transfer coefficients in ways that will reduce the heat exchanger costs per kilowatt of net power generated. This has led to the investigation of various potential types of heat exchangers with features designed to be optimal for OTEC applications. Some of these are briefly described below. Shell and Tube Heat Exchangers: This is the most widely used type of heat exchanger for industrial evaporator and condenser applications. As the name implies, this type consists of a shell and a bundle of tubes inside it. Specifically for OTEC applications, water flows through the tubes and the working fluid flows across the tube bank in the middle section. In conventional ones, seawater flows through the tubes, and the working fluid evaporates or condenses in a shell around them. This design can be enhanced by using fluted tubes: the working fluid flows into the grooves and over the crests, producing a thin film that evaporates more effectively. Plate Heat Exchangers: Another type of heat exchanger that would offer advantages in performance and cost is the plate heat exchanger. The plate type heat exchanger is more compact than the shell and tube configuration. In this type, the seawater and the working fluid flow in alternate channels separated by parallel plates. Suitable manifolds are used to guide the fluid into the proper channels. With this type of heat exchanger the gains in heat transfer coefficient can be up to 100-200%, compared with the conventional shell and tube designs. The material which heat exchangers are made of is very important in terms of cost and performance. Titanium was the original material chosen for closed-cycle heat exchangers because it resists corrosion. However, it is an expensive option for plants that use large heat exchangers. Therefore other cheaper materials such as corrosion-resistant copper-nickel alloys can be used to protect platform and cold-water pipes, but are not compatible with ammonia, the most common working fluid. A suitable alternative is aluminium which performs well under marine conditions and results indicate that selected aluminium alloys may last 20 years in seawater (Thomas Hills, 1989). Marine organisms and slime can quickly grow on surfaces exposed to warm seawater- a buildup known as biofouling- and this reduces the heat transfer efficiency. Laboratory experiments indicate that the addition of chlorine in the pipes can prevent biofouling (Panchal, Larsen-Basse, Little, 1984). 3.4.2 Evaporators for Open Cycle OTEC Systems Open-cycle flash-evaporators include those with open-channel flow, falling films, and falling jets. These conventional evaporators typically perform to within 70% to 80% of the maximum thermodynamic performance at acceptable hydraulic losses. The technological development led to a vertical-spout evaporator that can perform to within 90% of the thermodynamic limit (National Renewable Energy Laboratory). In this evaporator, water is drawn upward through a vertical pipe (a spout) and violently sprayed outward by escaping steam (Bharathan Penney, 1984). To enhance performance, the spray may fall on screens that further break up the droplets and increase the evaporation rate. To avoid pressure loss, the evaporator has simple intake and exit systems that separate the steam from the discharge. Steam continues through the system, and the remaining seawater is discharged from the bottom of the evaporator. Violent flashing in a spout evaporator causes seawater droplets to be entrained by the steam. If they are not removed, these droplets can cause erosion and stress-corrosion cracking in turbine blades and contaminate the desalinated water discharge as well. Passing the steam through the commercially available mist eliminators used in the process industry removes a sufficient quantity of these seawater droplets (Bharathan Penney, 1984). 3.4.3 Turbines In the open cycle process, after the droplets are removed, steam flows through large, low-pressure turbines, entering at a pressure of about 2.4 kPa. These turbines must be able to handle the large steam flows necessary to produce a significant amount of electric power. Multistage turbines used in nuclear or coal-fired power plants are already available. The low-pressure stages of these turbines typically operate at conditions close to those needed in an open-cycle OTEC plant. In close cycle OTEC systems the turbine needs not be so large because it works with vapor at elevated pressures. 3.4.4 Condensers for Open Cycle OTEC Systems Once the steam passes through the turbines, it can be condensed in direct-contact condensers or surface condensers. A surface condenser consists of an intermediate solid wall, which is absent in direct-contact condensers and therefore the latter provides more effective condensation (Bharathan, Parsons, Althof 1988). In one design-a two-stage condenser (see figure 4 below) developed at Solar Energy Research Institute-cold seawater is distributed through two open-ended vessels filled with a commercially available structured packing material. About 80% of the steam is condensed as it flows through the first vessel in the same direction as the cold seawater. The remaining steam is routed into the bottom of the second vessel and flows through it in the opposite direction to the seawater. At the top of the second vessel, a vacuum system pumps out the non-condensable (inert) gases along with any uncondensed steam (National Renewable Energy Laboratory). Figure : Illustration of a two stage condenser (National Renewable Energy Laboratory) Surface condensers keep the cooling seawater separate from the spent steam during condensation. By using indirect contact, the condensers produce desalinated water that is relatively free of seawater impurities. The surface condensers considered for use in OTEC systems are similar to those used in conventional power plants; however, these surface condensers must operate under lower pressures and with higher amounts of non-condensable gases in the steam. These non-condensable gases which are present in the open cycle system are released from the seawater when it is exposed to low pressures under vacuum and are namely oxygen, nitrogen and carbon dioxide. Air can also enter the open cycle vacuum chamber through leaks therefore decent construction techniques can reduce the rate of air leakage to very low levels. These gases, if are not removed from the vacuum vessel, they can build up enough pressure to stop evaporation. An exhaust compressor is usually used to remove these non-condensab le gases. The compressor however requires about 10% of the total power generated by the system (Parsons, Bharathan, Althof, 1985). 4. Methodology In this section, pending work and project plan summary will be described. For the final project, the literature review might be expanded a bit more to include the various types of working fluids that can be used. Furthermore, a section explaining the thermodynamics behind the operation of the OTEC cycle (Carnot efficiency and Rankine cycle) will be added, followed by a more realistic calculation on the OTEC actual thermal efficiency, net power output and production of desalinated water. Once these calculations are carried out, a reasonably concise section on the application of solar heating on OTEC will be written. Then an investigation on the effect of increasing water inlet temperature on power generation and fresh water production will be carried out. In addition, the effect of an increase in pressure on power generation and fresh water production will also be included. Computational software such as Wolframalpha or Matlab will help in determining the relationship between variable temperatures and pressures on power generation and desalinated water production. If time allows it, simulation software such as Simul8 will be used to find the optimum conditions for the hybrid cycle OTEC plant. A section of discussion and analysis of results will follow explaining the obtained results, including suggestions for improving the design. Finally, a segment explaining by what means the proposed hybrid cycle OTEC plant is suitable for operation in Cyprus. This segment will include the economic factors involved (need for finance, government subsidies etc.), drawbacks and benefits such a plant will have on the island. 5. Gantt Chart The Gantt Chart below represents the plan for completion of the project including important deadline dates for presentations and submission of the report. Figure : Figure showing the Gantt Chart 6. Conclusion Water and energy are essential for human life. A steady supply of energy and water is indispensable for improving the living standard and economic stability of any country, especially countries which face water shortage problems like Cyprus. The goal of this report is to demonstrate the characteristics of a dual purpose OTEC plant and through various design considerations find the optimum conditions for such a plant to be as productive and as efficient as possible and at the same time be economically viable to attract investors.

Much Ado About Nothing :: essays research papers

I wasn’t able to attend the play in Spring Green, WI, so I will be giving an explanation of one of the characters of the play. I have chosen to talk about Beatrice, and I hope I can make it two whole pages.   Ã‚  Ã‚  Ã‚  Ã‚  Beatrice is the niece of Leonato, who is am influential figure in Messina, where the story, Much Ado About Nothing, takes place. He is also a good friend with Don Pedro who leads an army, which has just come back from battle.   Ã‚  Ã‚  Ã‚  Ã‚  She is a very pretty young woman, with a very outgoing attitude. She tells it like it is, and doesn’t care what people think about her. Everyone loves her, and she is quite the entertainer. Beatrice makes everyone laugh, with her witty remarks. She’s a very intelligent person, and she knows it. So does everyone else for that matter.   Ã‚  Ã‚  Ã‚  Ã‚  Beatrice always says, throughout almost the entire play that she could never get married, because she would never be able to find a man that could make her happy, in fact she is almost sure that the perfect man for her doesn’t exist. She doesn’t need a man in her life, and she’s perfectly happy being without a husband. Now don’t get me wrong, she isn’t a mean person, she’s just really independent.   Ã‚  Ã‚  Ã‚  Ã‚  Well that was until Benedick, a very handsome military man with an attitude equal to Beatrice’s, came along. They bickered back and forth and spoke constantly about how much they hated each other, and butted heads whenever possible. So, it was obvious to everyone around them that they were perfect for eachother. There was a little trickery and they ended up falling head over heals in love with one another.   Ã‚  Ã‚  Ã‚  Ã‚  So, even though she wasn’t looking for a man and never planned to, she got him.

Scalar Vector

Acceleration is the rate of change of velocity with time. Velocity is a vector physical quantity; both magnitude and direction are required to define it. The length of an imaginary straight path, typically distinct from the path actually traveled by P. Distance is a numerical description of how far apart objects are. In physics or everyday usage, distance may refer to a physical length, or an estimation Time in physics is defined by its measurement Formula Acceleration= change in velocity / time intervalAverage velocity= displacement/time Oz (square root of) squared plus y squared D=ext X=d/t Units The gal, sometimes called Galileo, (symbol Gal) The SSL unit of speed and velocity is the ratio of two -? the mutterer second. The standard unit of displacement in the International System Of Units ( SSL ) is the meter (m). Meter (m) In the International System of Units (SSL), the unit of time is the second (symbol: Examples At an amusement park, when you ride a reallocates is starts slowl y, then faster, then slows down again.If you walk to a campsite 1 mile away and then jack to your start point within 1 hour: Your average speed would be: total distance/time = 2 miles/ 1 hour or 2 miles per hour How far does the earth travel in one year? In terms of distance, quite far (the circumference of the earth's orbit is nearly one trillion meters), but in terms of displacement, not far at all (zero, actually). At the end of a year's time the earth is right back where it started from. It hasn't gone anywhere.

The Technique In The Great Gat essays

The Technique In The Great Gat essays The Great Gatsby is Fitzgeralds finest novel, it was published in1925, and Eliot considered it to be the first step that America has taken since Henry James1. It is a sensitive and symbolic treatment of themes of contemporary life related with irony and pathos to the legendry of American dream. Nick Carraway, a young Midwesterner who sells bonds in New York, lives at West Egg, Long Islands, which is separated from the city by an ashdump, whose distinctive feature is an oculists faded billboard with a pair of great staring eyes behind yellow spectacles, symbolic of an obscenely futile world. Nicks neighbor is mysterious Jay Gatsby, whose mansion and fabulous entertainments are financed by bootlegging and other criminal activities. As a poor army lieutenant, Gatsby had fallen in love with Nicks cousin Daisy, who later married Tom Buchanan, an unintelligent, brutal man of wealth. Through Nick, he manages to meet Daisy again, impresses her by his extravagant devotion, and makes her his mistress. Her husband takes as his mistress Myrtle Wilson, sensual wife of a garage man. When her husband becomes jealous and imprisons her in her room, Myrtle escapes, runs out on the highway, and is accidentally hit by Daisy, who drives on. Gatsby tries to protect Daisy, and Tom, to whom she h as become reconciled, brings his hatred of her lover to a climax by telling Myrtles husband that it was Gatsby who killed her. Wilson shoots Gatsby and then himself. At the end of the story, Nick leaves the East and returns to the Mid-west. The Great Gatsby is the subject of many and diverse critical assessments and reappraisals that have elevated the novel to its current prominent position in American literature2. In this novel, Fitzgerald used many techniques: the controlled and detached point of view, the crafted structure and symbolism, all these distinguish The Great Gatsby from the style of h...

Thomas Jefferson Out-federalized the Federalists essays

Thomas Jefferson Out-federalized the Federalists essays During the time surrounding the ratification of the constitution, Thomas Jefferson was quite possibly the most pronounced and respected Democratic-Republican. His strict opposition of an overly industrious America, coupled with his fear of a tyrannical government, illustrated Jeffersons purely Republican views. However, during his presidency, his actions didnt always mirror his ideals. Turning towards Federalist views to solve some of the major problems occurring during his reign, Jefferson actually ended up Out-federalizing the Federalists. These Federalist views started to become evident even before Jefferson was elected president. In 1776, he designed and composed a Constitution for the state of Virginia. The plan included an effective system of checks and balances, including a lower house which was to be elected by the people, and a senate which was to be elected by the members of the house. When a different constitution was chosen, his criticisms emulated that of a strict federalist. Jefferson complained that the chosen system lacked a good system of checks. His reasoning was that the senate and house were both chosen by voters, thus making them too alike. This is when Jefferson concluded that the government, even when chosen by the people, still had too much power(Madaras and SoRelle 179). Perhaps the most prevalent shift of views occurred with the Louisiana Purchase. When Napoleon and the French signed the Treaty of San Ildefonso they regained title to Louisiana from the Spanish. Jeffersons initial feelings towards this movement were those of excitement because of his admiration and support of the French. These notions quickly and drastically changed when he realized that whoever inhabited New Orleans was, by sheer geographical location, Americas enemy. This area was the outlet where all of the produce of the western region of America left the country and traveled to markets a...

Undecided Essay Example | Topics and Well Written Essays - 1500 words

Undecided - Essay Example According to Foucault, achieving control over the individuals is one of fundamental motives in exercising discipline. Attaining power also acts as a means of transforming the behavior of subjects. Detainees get essential services from their closets and do not have the freedom to interact (Foucault, 2008). Foucault also elaborated the effects of discipline given the control that it attracts on subjects. He related discipline and control to the Panopticon designed by Bentham. The Panopticon was an effective structure in conducting day and night surveillance of prisoners without their awareness. The structure had several prison cells surrounding a high observation tower, with masked windows to hide the surveillance unit officers. It was challenging to realize the presence of any light inside the tower to keep prisoners guessing. The masking of tower’s windows would hide anyone inside. Control, according to Foucault, is achievable from discipline instilled and is the center of att aining power over subjects. The design was to keep the prisoners unaware of any surveillance going on in the tower, at any time. The design of the Panopticon gained dominance in design of most present day prisons. The effectiveness of the design in enabling observation of prisoners, while they remain unaware, was the main reason for its adoption. Current security measures as the observation cameras also use the same design in surveillance. Panopticism is an avenue of achieving power over the conduct of humans and an avenue where exercise of power takes place. The Panopticon is a representation of the modern society utilizing discipline and punishment. Although Foucault appreciates the freedom of members of any society, he maintains that control and examination are vital for institutions and governments to undertake as an avenue of control. Directed by M. Scorsese and adapted by L. Kalogridis in 2010, Shutter Island is an American masterpiece thriller movie that attracted a plausible number of viewers. The movie setting is in 1954 and it features investigative roles by Teddy Daniels. Shutter Island is a facility for the criminally insane, converted from its former function as a fortress used by Civil War fighters. Daniels has long experience in investigation given his role throughout the Second World War. Daniel’s role is to find out the loss of a patient from the facility on the Island. The patient, Rachel Solando, was under medication at the hospital of the mentally insane. The investigator has to perform against several constraints including denied access to crucial documents at the facility that would be important for the investigation. The facility management does not cooperate with Daniels and the mission turns challenging from the beginning. Their mission faces many distractions including the great storm that separates the two, Daniels and Chuck Aule, his partner. They find it stressful but do not stop at that. Their investigation skills are super b to allow them access shocking information about the facility’s illegal operations. Although Daniels is on a mission to investigate the case of a disappeared patient at the facility, he has other interests as well. He holds the belief that he may find credible information surrounding the horrible death of his wife, at the medical facility. The chief at the prison, Dr. Cawley, holds exceptional authority to command what favors him most. This further complicates the whole process of investigation. The

Discussion Topics for Management Course - United States Essay

Discussion Topics for Management Course - United States - Essay Example In this case, employees feel motivated and increase their dedication business practices, something that enhances its chances of success and quality outcomes. It is important for business executives to understand that risk and uncertainty are not actually similar. Uncertainty often concerns possible results and outcomes, which are not known to the business managers. On the other hand, risks can be described as certain kinds of uncertainties that involve actual probabilities of loss for various outcomes (Ferrell & Fraedrich, 2005). In this case, it is evident that situations involving risks can be accounted for easily as compared to those involving uncertainties. The process of making decisions based on risky conditions has to seek, where possible to provide a definite identification of risks, quantifying and absorbing them. In this case, business executives have to understand that the quantity of a risk is often equivalent to the total of all the probabilities relating to the particular risky outcome, alongside the expected loss from the outcome. From the foregone discussion it is evident that business managers are better placed to account for the management outcomes that are made under risky situations that those involving certainties. One of the most important aspects of a business’ management decision-making process is accounting for the outcomes. Accountability, in this case is needed in the process of making assessments and evaluations, which are important in the growth and development stages of the business (Ferrell & Fraedrich, 2005). Business managers are expected to avoid uncertainty situations in the business, this is because, they often lead to many losses in the management process. Risky situations can often bring positive outcomes depending on the effectiveness of the decisions made in the business. This is the reason why business managers that make effective decisions over