Modes of Heat Transfer

DEFINITION OF HEAT TRANSFER| Heat transfer is energy in transit due to temperature difference . Whenever there exists a temperature difference in a medium or between media, heat transfer must occur. The basic requirement for heat transfer is the presence of temperature difference . There can be no net heat transfer between two mediums that are at the same temperature. The temperature difference is the driving force for heat transfer, just as the voltage difference is the driving force for electric current flow and pressure difference is the driving force for fluid flow.The rate of heat transfer in a certain direction depends on the magnitude of the temperature gradient (the temperature difference per unit length or the rate of change of temperature) in that direction. The larger the temperature gradient, the higher the rate of heat transfer| PHYSICAL ORIGINS AND RATE EQUATIONS:It is important to understand the physical mechanisms which underlie the heat transfer modes and that we are able to use the rate equations that quantify the amount of energy being transferred per unit time.Conduction:Conduction can be imagined as a atomic or molecular activity which involves the transfer of energy from the more energetic to the less energetic particles of a substance due to interactions between the particles. |   | Explanation: The physical mechanism of conduction is explained as follows: Consider a gas in which there exists a temperature gradient and assume that there is no bulk motion. The gas may occupy the space between two surfaces that are maintained at different temperatures, as shown in Figure 1. 2.The temperature at any point is associated with the energy of gas molecules in proximity to the point. This energy is related to the random translational motion, as well as to the internal rotational and vibrational motions, of the molecules. | Higher temperatures are associated with higher molecular energies, and when neighboring molecules collide, as they are const antly doing, a transfer of energy from the more energetic to the less energetic molecules must occur. In the presence of the temperature gradient, energy transfer by conduction must then occur in the direction of decreasing temperature.This transfer is evident in the Figure 1. 2. The hypothetical plane at xo is constantly being crossed by molecules from above and below due to their random motion. However, molecules from above are associated with a larger temperature than those from below, in which case there must be a net transfer of energy in the positive x- direction. Hence, the net transfer of energy by random molecular motion may be thought of as diffusion of energy. It is possible to quantify heat transfer processes in terms of appropriate rate equations.These equations may be used to compute the amount of energy being transferred per unit time. The rate equation for heat conduction is known as Fourier's Law. The rate equation for the one dimensional plane wall shown in Figure below, having a temperature distribution T(x) is given by | (1. 1) | The heat flux (W/m2) is the heat transfer rate in the x -direction per unit area perpendicular to the direction of transfer, and it is proportional to the the temperature gradient, dT/dx , in this direction. The proportionality constant k is a transport property known as the thermal conductivity (W/m.K) and is a characteristic of the wall material. The minus sign is a consequence of the fact that the heat is transferred in the direction of decreasing temperature. Under the steady state conditions shown in Figure 1. 3, where the temperature distribution is linear, the temperature gradient may be expressed as | (1. 2) | and the heat flux then | (1. 3) | or | (1. 4) | This equation provides a heat flux , that is, the rate of heat transfer per unit area. The heat rate by conduction qx(W), through a plane wall of area A is then the product of the flux and the area qx= . A.Convection takes place when energy is transferre d from a surface to a fluid flowing over it as a result of a difference between the temperatures of the surface and the fluid. Convection heat transfer mode is comprised of two mechanisms * Energy transfer due to random molecular motion (diffusion) * Energy transferred by the bulk or macroscopic motion of the fluid ( advection) This fluid motion is associated with the aggregate or collective movement of the large number of molecules. Such motion, in the presence of temperature gradient, contributes to the heat transfer.Because the molecules in the aggregate retain their random motion, the total heat transfer is then due to a superposition of energy transport by the random motion of the molecules and by the bulk motion of the fluid. Convection heat transfer may be classified according to the nature of the flow. * Forced convection takes place when the flow is caused by an external agent such as fan, pump or atmospheric winds. For example, consider the use of a fan to provide forced c onvection air cooling of hot electrical components on a stack of printed circuit boards. Natural convection takes place when the flow is induced by density differences caused by the temperature variations in the fluid. For example, consider heat transfer that occurs from hot components on a vertical array of circuit boards in still air. * The rate equation for convection is known as Newton's law of cooling. This is given by | (1. 5) | * q† is the convective heat flux (W/m2). Convective heat flux is proportional to the difference between the surface and temperatures, Ts and , respectively.The proportionality constant is termed the convection heat transfer coefficient. It depends on the surface geometry, the nature of the fluid motion, and the fluid involved. Any study of convection ultimately reduces to a study of the means by which h may be determined. Although consideration of these means is postponed to Chapter 6, convection heat transfer will frequently appear as a boundary condition in the solution of conduction problems. In the solution of such problems we presume h to be known, using typical values gven in Table. * RADIATION: Thermal radiation is energy emitted by matter that is at a finite temperature. Radiation occurs not only from solid surfaces but also from liquids and gases. Regardless of the form of the matter, the emission may be attributed to changes in the electron configurations of the constituent atoms or molecules. The energy of the radiation field is transported by electromagnetic waves. While the transfer of energy by conduction and convection requires the presence of a material medium, radiation does not. In fact, radiation transfer occurs most efficiently in a vacuum. Consider radiation transfer processes for the surface of Figure. 1. 4. Radiation that is emitted by the surface originates from the thermal energy of matter bounded by the surface, and the rate at which the energy is released per unit area (W/m2) is termed the surface emissive power E. * There is an upper limit to the emissive power, which is prescribed by the Stefan-Boltzmann law | (1. 6) | * where Ts is the absolute temperature (K) of the surface and is the Stefan-Boltzmann constant ( = 5. 67 x 10-8 W/m2K 4). Such a surface is called an ideal radiator or black body. *

‘Journal on Gryphon” by Charles Baxter Essay

The short story Gryphon by Charles Baxter has an unusual character, a new substitute teacher at the rural community of Five Oaks in Michigan. The students meet with the strange lady who brings them strange yet fascinating lectures. Miss Ferenczi could be an exceptional teacher in a suitable environment, with her willingness to break the boundary in teaching method, her lectures on new materials never presented in textbooks, and her influence to help the students explore new things. I wonder if there would be any teacher daring enough to tell the class â€Å"six times eleven could be sixty eight.† Miss Ferenczi accepts the normal mathematical answer, but she also provides a different view and solution to the math problem, because â€Å"it’s more interesting that way.† When the narrator boy could not spell â€Å"balcony† she whispered to him; that the word is ugly and if he does not like a word, he does not have to use it. The students who have the wrong answer and the wrong spelling would always remember the right answers that way; moreover they do not feel ashamed of their wrong reply. They feel better when they are accepted and gently guided toward the right knowledge. Miss Ferenczi hates the way teachers are supposed to follow the rules, timeline, and the material presented readily in textbooks. When she told the children to open the book she herself â€Å"was staring at some object just outside the window.† She refuses to have lunch with other teachers since she wants to stay close with her students. Miss Ferenczi feels comfortable only when she can teach in her own way, not to be directed by any rules or any inflexible method or limit, which makes the students less distracted at the same boring way they have always been taught. The new substitute teacher appeared in the class surprising the students as much as her strange stories. The kids have never heard of the Antipode stone that would blind people, the Hope diamond, or the plant that can eat meat. The things they get to learn in textbooks are boring numbers and parched tiresome text. Miss Ferenczi knows the kids will love her stories, as she exposes them to amazing facts. Whether true, mythic or untrue, the information she provides is wide outside the schoolbook. They are the historical, cultural, social, and scientific lessons of the world that her students have never been told. The knowledge she gives the members of the  class is not only taken from what the school requires, but everything worthwhile to inform them about the universe. Her outstanding, broad collection of matters in different fields reveals a brand new world to the students. Children at fourth grade normally would blow their nose into notebook paper when there is nobody around, sit in class just to watch the teacher’s actions, and go home to play. It is amazing how Miss Ferenczi captures the kids’ interest, make them focus to a point that â€Å"no one even went to the bathroom.† With their old teacher Mr. Hibler, the students would chatter and whisper during the lecture, but with Miss Ferenczi they sit still and are fascinated with her lecturing. They are astounded at a plant that can kill animals, they are eager to discuss whether a half bird and half lion monster is real. They go home excitedly and dig up the dictionary to find out and feel â€Å"fabulous† to discover a new myth. She creates an â€Å"information hunger† in the children to explore, to discover new things that most teachers can hardly ever do. Since Miss Ferenczi’s appearance, the students have changed their view. She brings a fresh perspective of life, a strange way to present her lecture, and makes the students eager to go to class. It is because of her that after she got fired, during the lecture, the students pay close attention to the insects unlike they had ever done before. Miss Ferenczi accomplishes what all teachers are supposed to achieve, she is the most wonderful teacher every kid dreams to have. Works Cited Baxter, Charles. Gryphon.1985. Rpt. in Compact Literature ReadingReacting Writing. By Kirszner and Mandell. 6th ed. 2007. â€Å"Gryphon: Often Asked Questions.† Rev. of Gryphon, by Charles Baxter. CharlesBaxter. 3 June 2009 .

Why is civilty dead Essay Example | Topics and Well Written Essays - 500 words

Why is civilty dead - Essay Example These are the indications from the media, the public and political life. Admittedly, people have to have the freedom to speak for themselves, however the era of mass information and technology made our sense desensitized. After off the cruelty pouring out from the media it is difficult for us to control ourselves and to express our feelings without passing the border of the good manners. We are used to watching and listening to politicians who try to discredit their opponents on the public space. We also know that their verbal disruption polarizes and poisons the debate. We no longer perceive political animosity as something unusual. By now we heard how the Congressman Joe Wilson yelled to President Obama and called him "liar". However the lack of courteous behavior in politics is not the most troubling one, now that it moved to the public realm. Television helped a lot in showing foul language and numbing our sensibility with constant broadcasting of rude behavior. In addition the anonymity of the internet allows people to launch freely their anger. Mass media likes to focus its attention on nasty personal attacks performed by celebrities. The U.S society has a deep fascination with celebrities and I believe that their world- wide broadcast of indiscretions forced society to ask if civility is no more.

Beethovens Hair Research Paper Example | Topics and Well Written Essays - 1000 words

Beethovens Hair - Research Paper Example Along with these theories of Beethoven’s music composition style, number of theories are being put forward and even tested by the researchers on what exactly caused deafness in him. It was around 1800s, by the age of 26, when Beethoven began lose hearing in both his ears. Initially, he suffered from a serious form of ear disease called Tinnitus, because of which he mainly heard ‘ringing’ sound in his ears, thereby making it difficult for him to hear the music. Then, over time, mainly around early 1820s, his hearing loss became more intense, with Beethoven not able to even acknowledge the tumultuous applause, which he received from a huge crowd at a concert, as he was not facing the crowd and mainly because he was not able to hear it. (Colles and Grove). Although, he gave up conducting public concerts, he continued to compose and that resulted in many of his celebrated works. The exact cause of his deafness is unknown, but based on the study of old literature and importantly on the current researches being conducted by prestigious institutions, certain probable causes are being put forward. In addition, the recovery of Beethoven’s hair and advanced testing of it including Forensic testing have unlocked details about various facets of his life, particularly the physical as well as social factors, which could have contributed to his deafness. â€Å"Scientists tested a lock of Beethovens hair in hopes that, at last, the world would have explanation for the composers deafness.† (Martin and Nibley 30). Before this testing was done, various causes was attributed to his hearing loss and that included otosclerosis or abnormal growth of bone in his inner ear, typhus, syphilis and lead poisoning. Among these four causes, the first two were discounted earlier or could not be proved, with the later two being discussed through current researches. Otoscl erosis is a disease which happens when there is â€Å"new bone formation either in the area of

2000 Concorde Accident Essay Example | Topics and Well Written Essays - 1500 words

2000 Concorde Accident - Essay Example This theory proceeds from the perspective that business environments are socially determined. Therefore, the levels of success of business enterprises are directly proportional to the level of attachment that exists between the social order and the company’s actions and reactions. On this score, some of the issues that have been used to determine the course of action are mostly tied to the capacity to relate to issues of general interest. Multiple perspectives agree on the fact that legitimacy theory harmonizes the relationships and connections between the society and the business in ways that provide synergies that enable the sustainability of the business environment (Buys, 2010, pp. 55-61). Other theorists suggest that the proper adoption of this theory has the effect of easing the chain of supply as the streamlined social environment provides the necessary support for easing the processes of the firm. This study shall engage the theory of legitimacy in understanding the reactions that followed the 2000 Concorde Crash. Air France reacted in various ways to the tragedy but this paper will concern itself with the formal responses as obtained from press releases, official comment, news reports, and other kinds of responses that followed the disaster (Buyck, 2010, p. 67). The assumption is that the responses could be reduced into the company’s demonstration of an underlying commitment to the service of certain values, mores, ethics, and traditions that regulate its policy framework and on which its operational framework is based. Essentially, the reactions by Air France to the disaster could be interpreted as an outward manifestation of its framework as understood within the aspect of corporate management. The case in point for discussion concerns the disastrous crash of the French Concorde flight also known as Air France Flight 4590. This paper will limit itself to some specific responses of the management of Air France to the 2000 crash of the Concorde.

Re sit assessment Essay Example | Topics and Well Written Essays - 1000 words

Re sit assessment - Essay Example This issue can be resolved by an examination of the intention of the parties to the contract. Through the landmark case of Heilbut, Symons & Co v Buckleton,1 the House of Lords had established that whether or not a statement is a term of the contract shall be decided by employing the intention of the parties as the overall guide. This intention shall be ascertained under the four tests of timing, importance of the statement, reduction of terms to writing, and possession of special knowledge or skills. First, under the test of timing, the use of cream Welsh slate can be considered as a term of the contract if the reverend’s statement was made within a short interval of time from the writing of the contract. Otherwise, if there was a long lapse of time, then it is a mere representation and not part of the terms of the contract.2 The second test that could be used to determine the true intention of the parties is the importance of the statement. If the court determines that the s tatement was the principal reason for the aggrieved party to enter into the contract in question, then it is a term. Otherwise, if it was not the essential cause for the conclusion of the contract, then it is a mere representation. ... It is established that when a contract is reduced into writing, it contains all the stipulations agreed by the parties and all those not mentioned on paper are deemed not part of the contract. However this rule admits of some exceptions where statements were considered as part of the terms of the contract although they were omitted in the written contract.4 The final test for the intentions of the parties is the possession of special knowledge or skills. If the person who made the disputed statement has special knowledge or skills thus placing him in a better position to know the truth or validity of his claim than the other party, then the statement is a term of the contract. For example, between a veteran car dealer and a first-time car owner, the statements made by the former about the conditions of the car shall be considered as part of the terms of the contract.5 If after applying the foregoing tests it shall be found that the statement about the use of cream Welsh slate is a te rm of contract, it shall then be determined whether the term is one of condition or warranty. A condition is a key term of the contract which is important to its very existence while a warranty is a minor term which does not affect the main purpose for the contract. In addition, a breach of condition entitles the injured party to repudiate the contract and to claim damages6 while a breach of warranty only entitles the injured party to a claim for damages without the remedy of repudiation.7 Moreover, despite the breach of condition, the aggrieved party has the option to simply demand for damages and just proceed with the execution of the contract. Finally, a breach of condition gives rise to a remedy for

Business Law Essay Example | Topics and Well Written Essays - 1500 words - 4

Business Law - Essay Example This method of justice strives to create an alternative forum away from the Courts which is more relaxed in nature, which allows for a more chilled out atmosphere and where the procedural importance given to the cases is reduced in order to allow the human touch a greater importance. Following is the definition of Alternate Dispute Resolution: â€Å"Procedures for settling disputes by means other than litigation; e.g., by arbitration, mediation, or minitrials. Such procedures, which are usually less costly and more expeditious than litigation, are increasingly being used in commercial and labor disputes, Divorce actions, in resolving motor vehicle and Medical Malpractice tort claims, and in other disputes that would likely otherwise involve court litigation.†1 Reading and understanding from the above definition, it can be interpreted that ADR is an alternate mechanism for justice which is less costly and more expeditious. Alternate Dispute Resolution consists of Arbitration, M ediation and Conciliation. Arbitration is a process by which the parties to the dispute appoint an independent Arbitrator who judges the case for the respective parties. This independent arbitrator is appointed on the behest of both the parties. Once the arbitrator is decided, the venue for the arbitration depends upon the parties to the matter. ... These systems envisage a concept where the parties mediate and conciliate with the other parties on their own without the admission of an arbitrator. The process of Mediation and Conciliation is considered to be more in the zone of a personal conversation rather than a legal case going on.2 The idea of ADR has always been to allow a more open and calm approach towards justice delivery system. And it has ben quite successful in the Europe and UK with a streamlined method of arbitration, medication and conciliation process in practice. The ADR Group is a world-renowned commercial arbitration organization, which indulges in systematic approach towards the problem solving of arbitration. ADR, thus, improves the judicial system in the following ways: 1. Less Burden on the courts 2. Less expensive than litigation 3. Less time consuming than litigation 4. Less stressful than litigation 5. More freedom to the parties to represent their case 6. Greater opportunity for the party to be heard 7. More chances of better justice delivery since every argument is taken into proper consideration Tribunals The UK Tribunal system is extremely diligent in nature. The UK Tribunal system is part of the administrative justice system, which is the place for justice delivery. It is known as Non-Departmental Public Bodies. The Tribunals take the parallel role of dealing with issues ranging to different areas of law, such as Competition Law, Environmental Law, Taxation Law etc. The Tribunals are quasi judicial bodies which are responsible for granting justice as a means away from the basic court justice delivery system. â€Å"The tribunals are managed by the Tribunals Service, which is an executive agency of the Ministry of Justice. Recently, the tribunals have been re-organized, so that

Operations and logistics management Essay Example | Topics and Well Written Essays - 3000 words

Operations and logistics management - Essay Example as internet as a channel of business and communication has gained a strong footing, internet retailing is becoming an option to expand business across new horizon; synergies need to be established in the multi channel retailing strategy or moving across boundaries with pure brick and mortar model. With huge business empire build up decision should made with respect to the organizational structure, centralization vs decentralization of operations, use of technology in the operations such as Radio Frequency Identification (RFID), data mining, point of sales (POS) terminals etc. eBay transformed this experience into a virtual market place. The internet marketplace as an industry is rapidly growing, and the industry is becoming very competitive, with loads of user demand increasing continuously. This use of technology revolutionized the brick and mortar business concept to the virtual network of business. Hence, then evolved various business models for the online business solutions; three of them mainly include – the e-commerce model, the content-rich model and the membership/subscription model. The companies selling products, goods and services over the internet, make use of the e-commerce business model; providing advertising spaces on websites that attract visitors and subscribers is the domain of content rich model and lastly, web pages that provide subscription and membership to access different parts or items contained on the site by charging a certain amount of fee is another of the model. With the passage of time the aggregator business model, with aggressive infrastructure built up by many entrants to the industry gained popularity – but not all survived. The need be achieving and capitalizing on economies of scale for myriad of services to be offered at the cheapest offers to the customer. eBay provides both product and service. The service as distinguished from a good has certain characteristics viz. intangibility, inseparability, heterogeneity or

Human Resources in action Essay Example | Topics and Well Written Essays - 1000 words

Human Resources in action - Essay Example One of the main processes in the recruitment process is the selection process. The Selection process refers to the exercise of matching an organization requirement with the right skills and qualification of the people. The paper will identify two of the sources that Four Season Hotel can use to recruit the right candidate for a front desk receptionist position and the step that can be used to ensure the best candidate is selected. There are two main method of recruitment available to Four Season Hotel; one, the hotel can advertise the position to the existing employees. Another method that the hotel can use is the external source, for example, posting on job portals. Both methods have advantages and drawbacks. First, advertising the Front desk receptionist position to the existing employees is cheaper and less time-consuming (Catano, Fitzgerald, Hackett, Wiesner, & Methot, 2009). Companies spend a lot of money on advertisement for new positions. The Hotel will drastically reduce this cost since the information can be easily circulated in the organization. The Hotel also has a unique culture and hence hiring an existing employee drastically reduces the in job training costs. Hiring the existing employees, ensure that the organization culture is maintained. It is of paramount importance for the employee to give personalized services to the guests and treat them with respect and dignity. And given the front desk receptionist will be welcoming and handling the guest most of the time, it is vital the receptionist to have good understanding of the company. Not only does internal advertising maintains organization culture but also builds a strong relationship among employees. It also motivates the employees. Internal hiring will ensure that the employees build a strong relationship with themselves and management. The hotel mission and vision statements will be well understood by the employees. Furthermore, the employees are motivated to work hard so that