Air Conditioner Using Engine Exhaust Heat

Air Conditioner Using Engine Exhaust Heat This paper describes the development possible in the field of vehicle air conditioning based on vapour absorption cooling. The cooling effect is produced by waste heat energy recovered from engine exhaust. The advantages of such a system are drastic reduction of fuel over consumption and emissions associated with vehicle air conditioner usage. The current air conditioning system used in automobile is based on vapour compression cycle which necessarily consists of a compressor driven by engine output and thus increases fuel consumption rate and pollution proportion. The introduction of vehicle air conditioning using vapour absorption cycle eliminates the need for compressor; here compressor is replaced by generator and absorber unit. Engine waste heat from exhaust gases is used as heat source for generator of vapour absorption system. This paper describes the development possible in the field of vehicle air conditioning based on vapour absorption cooling. Some limitations are outlined and suggestions for future improvement are pointed out. Keywords Vapour Absorption Refrigeration Cycle, Vapour Compression Refrigeration Cycle. Introduction Motivating factors for the designing this system is continuous optimization of the performance of internal combustion engines and the increasing utilization of air conditioning in vehicles, as it reaches the status of essential need for modern life. Internal combustion engines are potential energy sources for absorption refrigeration systems, as about one third of the energy availability in the combustion processes wasted through the exhaust gas. Thus, use of the exhaust gas in an absorption refrigeration system can increase the overall system efficiency. An automobile engine utilizes only about 35% of available energy and rests are lost to cooling and exhaust system. If one is adding conventional air conditioning system to automobile, it further utilizes about 5% of the total energy. Therefore automobile becomes costlier, uneconomical and less efficient. It also decreases the life of engine and increases the fuel consumption. For very small cars compressor needs 3 to 4 bhp, a significant ratio of the power output. Keeping these problems in mind, a car air conditioning system is proposed from recovery of engine waste heat using engine exhaust as source of generator for VARS. Introduction to VARS: Figure 1 Schematics of Ammonia Water Absorption Refrigeration System Fig. 1 shows a schematic of the basic aqua-ammonia refrigeration cycle. High pressure ammonia vapor enters the condenser, where it transfers heat to the neighborhood. Liquid ammonia leaves the condenser and passes through an expansion valve, reaching the evaporator pressure. The refrigerant then enters the evaporator, where it receives heat from the cold source, turning into low pressure vapor. In the sequence, ammonia vapor enters the absorber, where a weak solution of water and low concentration ammonia absorbs the refrigerant and, at the same time, transfers heat to the neighborhood. The solution has now a high ammonia concentration, and is pumped to the vapor generator, where it receives heat from an external source. The ammonia in the solution then evaporates, separating from water and flowing to the condenser to start a new cycle. A weak water-ammonia solution leaves the vapor generator and enters the absorber to absorb ammonia vapor from the evaporator. A heat exchanger betwee n the absorber and the vapor generator transfers heat from the weak solution leaving the vapor generator to the high ammonia concentration solution going into the vapor generator. The coefficient of performance (COP) of the absorption system is usually much lower in magnitude then the compression system. But this low value of the former is not of much importance since it uses the waste heat such as engine exhaust heat. The most important thing about VARS is even if the evaporator temperature falls, the same COP can be maintained by elevating the generator temperature .Hence the capacity of the system remains almost the same. Design procedure of heat extraction device: Since VARS is heat operated cycle we need heat extraction device to extract heat from high temperature source and to deliver this heat to the generator of system. In order to enhance the performance of the refrigeration cycle we need to optimize the design of the Heat Extraction device. Because of its simplicity in operation, less installation as well as maintenance cost, we select Heat Exchanger as heat extraction device. C:UsersLENOVODesktopA4heatex.jpg Figure2- Schematic of Heat Exchanger In order to find the dimensions of the Heat Exchanger we have to assume certain cooling capacity of the cooling system. Lets assume it as 2.5 kW that is Qref = 2.5 kW. Calculations for Heat Extraction Device that is in our case a Heat Exchanger are as follows Calculation for Ammonia site: Calculation of mass flow rate Qref = à ¡Ã‚ ¹Ã‚ *cp*(Tg Te ) (1) Where , cp specific heat capacity Tg Temperature of the generator Te Temperature of evaporator à ¡Ã‚ ¹Ã‚  Mass flow rate From this equation we can determine mass flow rate of refrigerant. Calculation of velocity à ¡Ã‚ ¹Ã‚ =A*v*à Ã‚  (2) Where, à Ã‚  = density of the refrigerant (taken from design data book) A Flow Area for Refrigerant Ammonia In order to find A we have to take diameter of the tube according to availability in the market. v is the velocity of the refrigerant . Calculation of Reynolds number Re = (à Ã‚ *v*D)/ µ (3) Where D = diameter of the refrigerant tube  µ = dynamic viscosity of refrigerant at mean temperature (taken from design data book) Calculation of Prandtl number Pr = ( µ*Cp)/ k (4) Where, Cp = specific heat of the refrigerant k = thermal conductivity of the refrigerant Calculation of Nusselt number Calculation of the Nusselt number is based on the co-relations and the selection of the co-relation is based on the magnitude of the Re ,Pr , and the nature of the heat transfer surface. In our particular condition we select Gnielinski co-relation, since it involves less uncertainty (6%) so mathematical result will be more accurate. Nu = ((Æ’/2)* (Re 1000)*Pr)/ (1+12.7* (Æ’/2)1/2*((Pr)2/3 1)) (5) Where, Æ’ = friction factor its value depends on the Re Æ’= 0.079(Re)-0.25 4*103 Æ’=0.046(Re)-0.2 3*104 Calculation of convective heat transfer co-efficient Nu = (hr*D)/k (8) Where, hr = Convective heat transfer co-efficient k = Thermal conductivity of the ammonia Similar way we can find out these parameters for exhaust gases by following the same procedure. Calculation of Log Mean Temperature Difference (LMTD) à ¢Ã‹â€ Ã¢â‚¬  Tm = (à ¢Ã‹â€ Ã¢â‚¬  T1-à ¢Ã‹â€ Ã¢â‚¬  T2) / ln(à ¢Ã‹â€ Ã¢â‚¬  T1/à ¢Ã‹â€ Ã¢â‚¬  T2) (9) Where, à ¢Ã‹â€ Ã¢â‚¬  T1 = Temperature difference between the exhaust inlet temperature and refrigerant exit temperature à ¢Ã‹â€ Ã¢â‚¬  T2 = Temperature difference between exhaust outlet temperature and refrigerant inlet temperature Calculation of Total Thermal Resistance Qref =U*A *à ¢Ã‹â€ Ã¢â‚¬  Tm (10) Since à ¢Ã‹â€ Ã¢â‚¬  Tm / Qref is the total thermal resistance we will get the value of 1/ U*A Calculation of the length of heat exchanger Rtotal = Rconv.+Rcond.+Rconv. (11) 1/(U*A)= 1/(he*A) + (ln( ro/ri)) /(2à Ã¢â€š ¬*L*k) + 1/(href*A) (12) Where, he = Convective heat transfer coefficient of the exhaust gasses href = Convective heat transfer coefficient of the refrigerant A = Heat Transfer Area From equation (12) we can easily calculate optimum value of the length of heat exchanger. Now Effectiveness of Heat Exchanger changes as Inlet Temperature Difference between hot exhaust gases and cool refrigerant varies. Effectiveness of Heat exchanger can be calculated by following procedure. Calculation of the effectiveness of the heat exchanger In case of the counter flow the effectiveness Ɇº is given by Ɇº = (1-EXP((-1+C)*NTU) /(1- C* EXP( (-1-C)*NTU)) (13) Where, NTU = Number of Transfer Unit NTU = (U*A)/(à ¡Ã‚ ¹Ã‚  * CP)min. (14) C = Capacity Ratio C = (à ¡Ã‚ ¹Ã‚  * CP)min / (à ¡Ã‚ ¹Ã‚  * CP)max (15) Calculation of amount of heat transfer to the generator Ɇº = (actual heat transfer / maximum heat transfer) (16) Maximum heat transfer Qmax = à ¡Ã‚ ¹Ã‚ *CP*à ¢Ã‹â€ Ã¢â‚¬  Tmax (17) Where, à ¢Ã‹â€ Ã¢â‚¬  Tmax = Maximum temperature difference between hot exhaust gases and cold refrigerant Using Equations (14) (15) we can calculate actual heat transferred to the generator of the VARS. Calculation of Coefficient of Performance (COP) of VARS COP= (Cooling Effect Produced / Heat Energy Input to Generator) (18) Since COP is the function of temperature we can calculate the COP by using following relation also, COP= (Te*(Tg-Ta))/ (Tg*(Ta-Te)) (19) Where Te = Temperature of the evaporator Tg = Temperature of the generator Ta = Temperature of absorber Results and Discussion: For optimization of design of heat extraction device, we need to determine and fix some parameters. Assume desired heat transfer to be 3 kW. Also we need to find out the specific temperature or temperature range of VARS generator so as to have optimum COP. Graph 1: Generator Temperature Vs COP of VARS From graph 1, it is clear that VARS system will have maximum COP in the generator temperature range of 118 °c (391 K) to 127 °c (400 K). Now we can fix the refrigerant outlet temperature. Furthermore we cannot reduce the exhaust gas temperature below certain level. Sudden drop in exhaust temperature will cause the exhaust gas to slow down. The drop in exhaust temperature can be accommodated by reducing the exhaust pipe diameter. After fixing the generator temperature i.e. , refrigerant outlet temperature, exhaust gas outlet temperature and refrigerant inlet temperature, the only parameter remaining is exhaust gas inlet temperature. Exhaust temperature varies with load conditions (no load to full load conditions) and driving conditions (idling to power mode). This results in to change in LMTD, due to which the overall heat transferred to refrigerant changes. As a result of change in exhaust gas inlet temperature the effectiveness of heat exchanger changes. As exhaust temperature increases effective heat transfer area required decreases as well as effectiveness of heat exchanger reduces. Optimum heat transfer area and effectiveness of heat exchanger is represented by graph 2. Graph 2: Optimum Heat Transfer Area, Effectiveness Vs Inlet Temperature Difference Effectiveness is the function of temperature difference between hot exhaust gases and cold refrigerant at inlet. As this temperature difference increases, effectiveness of heat exchanger decreases. Effectiveness of heat exchanger is not of prime concern. We can maintain the effectiveness to certain level by varying refrigerant inlet temperature by some means, for example, electric heating. It will maintain the temperature difference between two fluids at inlet. Small amount of energy will be utilized to elevate the refrigerant temperature. Prime concern of the study is to obtain desired cooling effect by utilizing exhaust waste heat. So effectiveness of heat exchanger can be compromised to certain level. Practically, COP of system will be much lower as compared to mathematically obtained values but sufficient to produce desired cooling effect efficiently. Graph 1 represents the theoretical values of COP obtained by equation (19). We have used these values to determine optimum generator temperature. After fixing the parameters of heat extraction device (Heat Exchanger), the practical values of COP are obtained by using equation (18). Graph 3 represents the practical values of COP. It is clear from graph 3 that as generator temperature rises from 118 °c to 127 °c, COP values drops to 73% and cooling effect obtained at a point is 2.8 kW and effectiveness of heat exchanger is about 50%. Graph 3: Generator Temperature Vs COP Conclusion From the above results we can say that it is possible to extract waste heat of the engine exhaust using heat exchanger. In order to increase the performance of VARS we have to operate heat exchanger at the optimum condition mentions in results. Some precaution we have to take care such as at the initial stages of engine operation performance of VARS is low, hence to get the same cooling effect we have heat ammonia generator using heating coil.

My Cultural Identity Essay -- Cultural Identity Essays

My culture identity, as I know it as is African American. My culture can be seen in food, literature, religion, language, the community, family structure, the individual, music, dance, art, and could be summed up as the symbolic level. Symbolic, because faith plays a major role in our daily lives through song, prayer, praise and worship. When I’m happy I rely on my faith, same as when I’m sad, for I know things will get better as they have before. There are different disciplines within the humanities, but there is one that I feel that has influenced my cultural identity the most†¦music. I say music because from the start music told my culture’s history; informed others about deeds or events that had taken place, also, music was and continues to be important in comforting, healing, and during labor. â€Å"African American music has evolved through various eras and styles; the powerful melodic lines and the rhythm (the all-important rhythm) remained prominent and influential† (Powell, 2007, p.1). One way that I’ve celebrated and tried to connect with what I know as my culture is to attend Juneteenth Festival of the Carolinas. â€Å"According to Welcome to Juneteenth, â€Å"this is an annual four day event celebrated in the month of June at Independence Park, in Charlotte, North Carolina, hosted by Pape Ndiaye, proprietor of the House of Africa located in Charlotte, NC since 1997† (Juneteenth, n.d.). This family event unifies Africans, African-American, and non-African people and is celebrated with drummers, dancers, faith communities, local talent, special guests, and vendors that sell clothing, jewelry, food, books, art, music, furniture, purses, and much more. One may say we already have a day set aside to celebrate freedom. The Junete... ...x.php?option=com_content&view=article&id=133&Itemid=10 Lumbee Tribe of North Carolina (n.d.). Who Are The Lumbee? Retrieved March 7, 2014, from http://www.lumbeetribe.com/index.php?option=com_content&view=article&id=135&Itemid=115 Powell, A. (2007). The Music of African Americans and its Impact on the American Culture in the 1960’s and the 1970’s. Miller African Centered Academy, 1. Retrieved from http://www.chatham.edu/pti/curriculum/units/2007/Powell.pdf Main Section | Community Tool Box. (n.d.). Retrieved March 4, 2014, from http://ctb.ku.edu/en/table-of-contents/culture/cultural-competence/culture-and-diversity/main Welcome to Juneteenth. (n.d.). Retrieved March 7, 2014, from http://www.juneteenthofthecarolinas.com/ Whirty, R. (2007, March/April). The Lost Colony of Roanoke. Natives People. Retrieved from http://www.lost-colony.com/magazineNP.html

The Development of Multi-Faceted Literacy in American Culture

Though many theories have been formulated about literacy and how to apply proper education to it, few seem to grasp the fact that true literacy involves lots of different aspects. Though many educators have tried to put the term literacy into a strict definition, it is best understood as a complex educational aspect. Literacy combines elements of culture, both nation and international. It involves picking up essential skills that can be taught in the classroom, as well. In addition to all of that, it involves a person learning the advanced art of articulation. Speaking well, writing well, and understanding how to get a point across are three things that should be included in that discussion, as well. How a person understands literacy is dependent upon which of these theories that person accepts as being the standard. According to Dr. Robert Needlman, literacy needs to be understood in a broad sense, as it is very important to all other forms of learning. In a recent article on the matter, Needlman wrote, â€Å"Literacy is more than just being able to read and write. Literate children see reading as fun and exciting. They use reading to learn about a wide range of subjects, and they use writing to share their ideas† (Needlman). This means that teachers must learn to teach their students how to read and write at the most basic level, but that is rarely enough. True literacy can not be gained without a wide application of many different principles. One position that has become very popular among educators in recent years is one that employs a strategy of teaching students to communicate. Learning how to frame words in sentences and paragraphs is not enough in order to truly teach someone to be literate. In order to be literate, a person has to be able to take those words and put them into coherent thoughts. This position is probably the one that most closely represents what today’s educators should be aiming for when they frame curriculums for students. Skills based literacy is the building block from which all other things have to come. This is generally accepted by most educators out there. The problem is that some of these educators are not going beyond that. Though literacy starts with the basic skills, it certainly cannot stop there. It can only be effective if it is combined with a literacy program that teaches students cultural literacy and communications skills, as well. Teaching one without taking the time to teach the other is like teaching a person how to fish, giving them all of the equipment, and then forgetting to tell them where the pond is located. Though learning the actual skill of reading and writing is obviously an important part of the process, the cultural aspects are even more important. Especially in the United States, cultural literacy has not been nearly as much of a concern as other aspects of education. This is partly because teachers have been teaching with their eye on standardized tests and partly because no real value has been placed on cultural literacy. Now, the value and importance of both understanding how to read and write and understand how to put those things into context is being stressed more and more in schools and to America’s youth. Certain school districts have taken the initiative of instilling this sort of program within their curriculum for students. According to literature put out by the Poway Unified School District, cultural literacy is important to the development of students. Their website states, â€Å"The best lessons for cultural literacy come from the many students who sit in front of us each day in our classrooms. Their cultures, heritage, and stories formulate the most powerful cultural literacy curriculum† (Poway Unified School District). Elementary schools are not the only ones taking notice in this. College writing programs have implemented strategies as well to give their students a chance to become fully literate. Reed College, for example, has an entire writing program that is dedicated to teaching students the proper rules for communicating in their writing. This program not only focuses on writing, but it also teaches the value of things like drama and other liberal arts. Hampden-Sydney College is another college in the United States that has put an emphasis on this type of education. Their rhetoric program must be completed by all students who come through the school, whether those students are business majors or history majors. In the full context of a college liberal arts program, writing takes on a huge level of importance. Universities that offer these programs need to instill a writing intensive program across the board. This does not mean that just journalism or English students should have to concentrate on refining their skills. It means that in history courses, religion courses, philosophy courses, and other sorts of classes, a bunch of writing should be required. By incorporating writing into the curriculum of these other subjects, students will further learn how to communicate with their writing and they will become better at the other subjects, as well. Without an emphasis on writing, a liberal arts program is doomed to failure. Successful communication is a necessary aspect of these programs, as well. That cannot be gained without learning how to write critically, though. As E.D Hirsch is quick to point out, the English language lends itself to much interesting diction for writers. In his book, Hirsch wrote, â€Å"Literature in English excels in every kind of writing. Its particular glory is its poetry. For historical reasons, the English language acquired a vocabulary that is unusually rich and nuanced, combining words of Germanic root (such as see and glimpse) with words of Latin root (such as perceive and envision)† (Hirsch). There are quite a few different approaches to organizing a program such as this. Some colleges have started specific writing courses that teach students how to put their ideas into writing. More times than not, these classes are put into freshman year experience programs. These are the programs that teach students how to learn and how to be good college students. More times than not, these classes are taught alongside a study skills course. After all, most students are going to have to write multiple essays when they enter college and writing will be an essential part of their life. It only makes sense to preach the importance of writing from the very beginning of the college experience. This is not enough, though. In today’s world, being able to write and communicate is essentially important. Just about everything revolves around it, including the business world. According to the Educational Testing Service, which handles much of the student testing in the United States, the situation is extremely dire. They state, â€Å"As society becomes more technologically advanced, the quantity and types of written materials are growing. Adults are expected to use information from these materials in new and more complex ways and to maintain and enhance their literacy skills through lifelong learning activities. Literacy skills are critical not only for the personal achievement of individuals, but also for the social and economic development of each nation. These skills are no longer linked to a single threshold that separates the literate from the nonliterate† (Educational Testing Service). This quotation does much to state the overall importance of literacy in society and it also hammers home the point that literacy is becoming more important and more relevant, despite what some might think. In fact, it is dire, according to C.H. Knoblauch. In his Literacy and the Politics of Education, Knoblauch writes, â€Å"However, if literacy today is perceived as a compelling value, the reason lies not in such self-interested justifications but in its continuing association with forms of social reality that depend on its primacy† (Knoblauch). In addition to that, there is sentiment from other literary sources about the American situation. The Formation of National Cultures states, â€Å"In America, the reality is that we have not yet properly achieved monoliteracy, much less multiliteracy† (Foundation of National Cultures). This means that the United States still has to work on both the simple parts of literacy, as well as the more advanced aspects. One of the staples of any liberal arts program is a good history department. History courses are interesting because of the fact that they incorporate many different aspects of reading, writing, critical thinking, and lots of other skills. Students are not only forced to write and read critically, but they are often forced to do these things in a cultural sense. History courses not only teach what happened and when it happened, but they study cultural trends. Writing and reading have to be a huge part of any history course. Framing a history course with an eye on literacy is easy. In fact, it would be very difficult to even consider teaching any sort of history class without the inclusion of these things. As far as the actual setup of a course is concerned, it would not be all that difficult to integrate. The course would need a strong textbook, which must be read each and every night. In addition to that, the instructor of the course would teach the class in a lecture/discussion format, where students have to get used to both critical listening and critical communication. During each class period, students would have to listen to an instructor and take notes on what that professor is saying. This is one way to not only teach students the art of writing, but it also teaches students to think about the most important things that they are hearing. From that, they will react to that knowledge. The course would not be taught with only lectures, though. There would obviously be some grading that would be required. Writing would be integrated into the course in both essays and in tests. For the essays, students would be required to submit a number of them, depending upon length. This would give students a chance to not only explore the liberal arts staple of history, but it would also make them learn how to express themselves in a logical way. Essays would require proper writing skills, as well as good organization and good understanding of the material at hand. This would be an appropriate test of the knowledge and a good way to further integrate literary skills into the course. When it came time to give the test, writing would be on that, as well. Some part of the test would include an essay, where students would have to prepare a concise thought without too much time to research the issue. By doing these things, writing, reading, and critical communication could take their rightful place of importance in the liberal arts field. Without them, the courses would be naked and barren. By including writing and reading in liberal arts programs, a university would not be precluded from also offering advanced writing courses. Traditional definitions of literacy have come up with the conclusion that it is actually a skill that must be learned and mastered. Though the cultural literacy idea has become much more popular in recent years, the idea of literacy being a skill has still not been lost. With the right amount of instruction, students can learn how to both read and write at a very high level. Like with other subjects in a curriculum, writing programs must take the opportunity to teach both the basics and the advanced aspects of writing and reading. Colleges would be well advised to offer a literacy major or minor within their course catalog. With this program, the university could offer tens of classes on writing and reading. Everything from critical writing to business writing could be offered within this major. With that knowledge, a student would be able to go on to many different careers, since it has been established that writing and reading is such a large part of the business culture today. As long as literacy is a skill, it is something that must be harnessed and taught in universities and in lower levels of schools, as well. Elementary, middle, and high schools would be smart to adopt similar programs, which would further prepare students for the rigors of college literacy programs. In short, this would take a concerted effort at every level of academia if it is going to be successful. This is something that Allan Bloom takes very seriously in his book, The Closing of the American Mind. In there, Bloom writes, â€Å"I used to think that young Americans began whatever education they were to get at the age of eighteen, that their early lives were spiritually empty and they arrived at the university clean slate unaware of their deeper selves and the world beyond their superficial experience† (Bloom). The need for education at early levels is of the utmost importance to people like Bloom. No matter what definition of literacy a person subscribes to, the fact remains that it is a very important part of education that must be addressed. At current standing, schools are not doing nearly enough to teach the skills and to instill the type of cultural knowledge that is essential in order to truly communicate. Literacy is far more complicated than many educators have been willing to give it credit for. The first step to truly teaching literacy in a correct way is to understand that it is a changing thing. According to the folks at the Perkins School for the Blind, literacy includes many different aspects that must be accounted for. Their website reads, â€Å"The development of literacy is founded upon our experiences – beginning with birth – and our interactions with the world and those around us. Over time, these experiences enable us to develop the ability to connect meaning to words and letters. First, though, the path to literacy requires establishing communication and connecting meaning to objects, events and people in our world† (Perkins School for the Blind). This means that literacy is constantly being learned by everyone, each and every day. With this sort of knowledge in hand, it is easy to conclude that literacy must be included in every aspect of education. When talking about a classic liberal arts education, this is especially true. No matter if the skills-based literacy interpretation is correct or the other interpretations are correct, one must concede that all aspects of the idea should be considered. When shaping the plan for literacy training within a liberal arts program, lots of things must be considered. Luckily for those people who frame curriculums,   many liberal arts classes already require many pieces of literacy to be included to begin with. From critical writing to reading to other forms of communication, literacy will always be a part of history, philosophy, English, and the other subjects within liberal arts. With that in mind, the key is to highlight those skills and make sure that students are given an opportunity to enhance them. Works Cited Bloom, Allan. Closing of the American Mind. Educational Training Service. What is Literacy? http://www.nocheating.org/portal/site/ets/menuitem.c988ba0e5dd572bada20bc47c3921509/?vgnextoid=2a8eaf5e44df4010VgnVCM10000022f95190RCRD&vgnextchannel=6773e3b5f64f4010VgnVCM10000022f95190RCRD Hirsch, E.D. Cultural Literacy. Knoblauch, C.H. Literacy and the Politics of Education. Perkins School for the Blind. Perkins Panda Early Literacy Kit. http://www.perkins.org/literacy/panda/ Poway Unified School District. Cultural Literacy. http://www.powayusd.com/projects/edtechcentralnew/culturallit.htm â€Å"Formation of National Cultures† Needlman, Robert. What is Literacy? http://www.drspock.com/article/0,1510,5133,00.html         

A Collection of Traditional and Literary Ballad Poems

The ballad is at the intersection of poetry and song, from traditional folk ballads crystallizing out of the mists of ancient oral traditions to modern literary ballads in which poets use the old narrative forms to retell traditional legends or to tell stories of their own.   The Evolution of Balladry A ballad is simply a narrative poem or song, and there are many variations on balladry. Traditional folk ballads began with the anonymous wandering minstrels of the Middle Ages, who handed down stories and legends in these poem-songs, using a structure of stanzas and repeated refrains to remember, retell, and embellish local tales. Many of these folk ballads were collected in the 17th and 18th centuries by scholars like Harvard professor Francis James Child and poets like  Robert Burns  and Sir Walter Scott. Two of the ballads in this collection are examples of this type of traditional ballad, anonymous retellings of local legends: the spooky fairy tale â€Å"Tam Lin† and â€Å"Lord Randall,† which reveals the story of a murder in the question-and-answer dialogue between a mother and son. Folk ballads also told love stories both tragic and happy, tales of religion and the supernatural, and recountings of historical events. After the 16th-century invention of inexpensive printing, ballads moved from the oral tradition onto newsprint.  Broadside ballads  were â€Å"poetry as news,† commenting on the events of the day—although many of the older traditional folk ballads were also distributed as broadsides in print. Literary Ballads by Known Poets In the 18th and 19th centuries, Romantic and Victorian poets took hold of this folk-song form and wrote literary ballads, telling their own stories, as Robert Burns did in â€Å"The Lass That Made the Bed to Me† and Christina Rossetti did in â€Å"Maude Clare†Ã¢â‚¬â€or reimagining old legends, as Alfred, Lord Tennyson did with part of the Arthurian story in â€Å"The Lady of Shalott.† Ballads carry tales of tragic romance (Edgar Allan Poe’s â€Å"Annabel Lee†), of the honor of warriors (Rudyard Kipling’s â€Å"The Ballad of East and West†), of the despair of poverty (William Butler Yeats’ â€Å"The Ballad of Moll  Magee†), of the secrets of brewing (Robert Louis Stevenson’s â€Å"Heather Ale: A Galloway Legend†), and of conversations across the divide between life and death (Thomas Hardy’s â€Å"Her Immortality†). The ballads combination of narrative propulsion implied melody (ballads are often and very naturally set to music), and archetypal stories are irresistible.    The Varied Structures of Ballads Most ballads are structured in short stanzas, often the quatrain form that has come to be known as â€Å"ballad measure†Ã¢â‚¬â€alternating lines of  iambic  tetrameter (four stressed beats, da DUM da DUM da DUM da DUM) and iambic trimeter (three stressed beats, da DUM da DUM da DUM), rhyming the second and fourth lines of each stanza. Other ballads combine the four lines into two, forming rhymed couplets of seven-stress lines that are sometimes called â€Å"fourteeners.† But the word â€Å"ballad† refers to a general type of poem, not necessarily a fixed poetic form, and many ballad poems take liberties with the ballad stanza or abandon it altogether. Examples of Ballads In chronological order, some classic ballads are as follows; Anonymous, â€Å"Tam Lin† (traditional folk ballad, written down by James Child in 1729)Anonymous, â€Å"Lord Randall† (traditional ballad published by Sir Walter Scott in 1803)Robert Burns, â€Å"John Barleycorn: A Ballad† (1782)Robert Burns,  Ã¢â‚¬Å"The Lass That Made the Bed to Me† (1795)Samuel Taylor Coleridge, â€Å"The Rime of the Ancient Mariner† (1798)William Wordsworth, â€Å"Lucy Gray, or Solitude† (1799)John Keats,  Ã¢â‚¬Å"La Belle Dame sans Merci† (1820)Samuel Taylor Coleridge, â€Å"The Ballad of the Dark Ladie† (1834)Alfred, Lord Tennyson, â€Å"The Lady of Shalott† (1842)Edgar Allan Poe, â€Å"Annabel Lee† (1849)Christina Rossetti, â€Å"Maude Clare† (1862)Algernon Charles Swinburne, â€Å"A Ballad of Burdens† (1866)Christina Rossetti,  Ã¢â‚¬Å"A Ballad of Boding† (1881)Rudyard Kipling, â€Å"The Ballad of East and West† (1889)William Butler Yeats, â€Å"The Ballad of M oll Magee† (1889)Robert Louis Stevenson, â€Å"Heather Ale: A Galloway Legend† (1890)Oscar Wilde, â€Å"The Ballad of Reading Gaol† (1898)Thomas Hardy, â€Å"Her Immortality† (1898)William Butler Yeats, â€Å"The Host of the Air† (1899)Ezra Pound, â€Å"Ballad of the Goodly Fere† (1909)