Chemical Engineering   PDF generated using the open source mwlib toolkit. See http://code.pediapress.com/ for more informa...
ContentsArticles   Chemical engineering                        1   History of chemical engineering             8   Chemica...
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Being Chemical Engineer
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Being Chemical Engineer

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Awesome guide for all "Chemical Engineers". I strongly believe that this Book should be with all chemical engineers.

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Being Chemical Engineer

  1. 1. Chemical Engineering PDF generated using the open source mwlib toolkit. See http://code.pediapress.com/ for more information. PDF generated at: Sun, 06 May 2012 13:54:05 UTC
  2. 2. ContentsArticles Chemical engineering 1 History of chemical engineering 8 Chemical engineer 11 Unit operation 15 Unit process 18 Process integration 19 Momentum transfer 21 Heat transfer 23 Mass transfer 34 Chemical process 36 Chemical reaction engineering 38 Chemical kinetics 40 Chemical process modeling 44 Chemical thermodynamics 45 Chemical plant 51 Process engineering 58 Process control 60 Process design 62 Fluid mechanics 65 Fluid dynamics 69 Transport phenomena 76 List of chemical process simulators 81 Outline of chemical engineering 84 Education for Chemical Engineers 87 Index of chemical engineering articles 88 List of chemical engineering societies 91References Article Sources and Contributors 94 Image Sources, Licenses and Contributors 96Article Licenses License 97
  3. 3. Chemical engineering 1 Chemical engineering Chemical engineering is the branch of engineering that deals with physical science (e.g., chemistry and physics), and life sciences (e.g., biology, microbiology and biochemistry) with mathematics and economics, to the process of converting raw materials or chemicals into more useful or valuable forms. In addition, modern chemical engineers are also concerned with pioneering valuable new materials and related techniques – which are often essential to related fields such as nanotechnology, fuel cells and biomedical [1] engineering. Within chemical engineering, two broad subgroups include 1) design, manufacture, and operation of plants and machinery in industrial chemical and related processes ("chemical process engineers"); and 2) development of new or adapted substances for products ranging from foods and beverages to cosmetics to cleaners to pharmaceutical ingredients, among many other products ("chemical product engineers"). Process engineers design, construct and operate plants Etymology A 1996 British Journal for the History of Science article cites James F. Donnelly for mentioning a 1839 reference to chemical engineering in relation to the production of sulfuric acid.[2] In the same paper however, George E. Davis, an English consultant, was credited for having coined the term.[3] The History of Science in United States: An Encyclopedia puts this at around 1880.[4] "Chemical engineering", describing the use of mechanical equipment in the chemical industry, became common vocabulary in England after 1850.[5] By 1910, the profession, "chemical engineer", was already in common use in Britain and the United States.[6] History Chemical engineering emerged upon the development of unit operations, a George E. Davis fundamental concept of the discipline. Most authors agree that Davis invented unit operations if not substantially developed it.[7] He gave a series of lectures on unit operations at the Manchester Technical School (University of Manchester today) in 1887, considered to be one of the earliest such about chemical engineering.[8] Three years before Davis lectures, Henry Edward Armstrong taught a degree course in chemical engineering at the City and Guilds of London Institute. Armstrongs course "failed simply because its graduates ... were not especially attractive to employers." Employers of the time would
  4. 4. Chemical engineering 2 have rather hired chemists and mechanical engineers.[4] Courses in chemical engineering offered by Massachusetts Institute of Technology (MIT) in the United States, Owens College in Manchester, England and University College London suffered under similar circumstances.[9] Starting from 1888,[10] Lewis M. Norton taught at MIT the first chemical engineering course in the United States. Nortons course was contemporaneous and essentially similar with Armstrongs course. Both courses, however, simply merged chemistry and engineering subjects. "Its practitioners had difficulty convincing engineers that they were engineers and chemists that they were not simply chemists."[4] Unit Students inside an industrial chemistry laboratory at MIT operations was introduced into the course by William Hultz Walker in 1905.[11] By the early 1920s, unit operations became an important aspect of chemical engineering at MIT and other US universities, as well as at Imperial College London.[12] The American Institute of Chemical Engineers (AIChE), established in 1908, played a key role in making chemical engineering considered an independent science, and unit operations central to chemical engineering. For instance, it defined chemical engineering to be a "science of itself, the basis of which is ... unit operations" in a 1922 report; and with which principle, it had published a list of academic institutions which offered "satisfactory" chemical engineering courses.[13] Meanwhile, promoting chemical engineering as a distinct science in Britain lead to the establishment of the Institution of Chemical Engineers (IChemE) in 1922.[14] IChemE likewise helped make unit operations considered essential to the discipline.[15] New concepts and innovations By the 1940s, it became clear that unit operations alone was insufficient in developing chemical reactors. While the predominance of unit operations in chemical engineering courses in Britain and the United States continued until the 1960s, transport phenomena started to experience greater focus.[16] Along with other novel concepts, such process systems engineering (PSE), a "second paradigm" was defined.[17][18] Transport phenomena gave an analytical approach to chemical engineering[19] while PSE focused on its synthetic elements, such as control system and process design.[20] Developments in chemical engineering before and after World War II were mainly incited by the petrochemical industry,[21] however, advances in other fields were made as well. Advancements in biochemical engineering in the 1940s, for example, found application in the pharmaceutical industry, and allowed for the mass production of various antibiotics, including penicillin and streptomycin.[22] Meanwhile, progress in polymer science in the 1950s paved way for the "age of plastics".[23] Lag and environmental awareness The years after the 1950s are viewed{ to have lacked major chemical innovations.[24] Additional uncertainty was presented by declining prices of energy and raw materials between 1950 and 1973. Concerns regarding the safety and environmental impact of large-scale chemical manufacturing facilities were also raised during this period. Silent Spring, published in 1962, alerted its readers to the harmful effects of DDT, a potent insecticide. The 1974 Flixborough disaster in the United The Union Carbide India Limited plant where the Kingdom resulted in 28 deaths, as well as damage to a chemical plant 1984 explosion originated and three nearby villages. The 1984 Bhopal disaster in India resulted in
  5. 5. Chemical engineering 3 almost 4,000 deaths . These incidents, along with other incidents, affected the reputation of the trade as industrial safety and environmental protection were given more focus.[25] In response, the IChemE required safety to be part of every degree course that it accredited after 1982. By the 1970s, legislation and monitoring agencies were instituted in various countries, such as France, Germany, and the United States.[26] Recent progress Advancements in computer science found applications designing and managing plants, simplifying calculations and drawings that previously had to be done manually. The completion of the Human Genome Project is also seen as a major development, not only advancing chemical engineering but genetic engineering and genomics as well.[27] Chemical engineering principles were used to produce DNA sequences in large quantities.[28] While the application of chemical engineering principles to these fields only began in the 1990s, Rice University researchers see this as a trend towards biotechnology.[29] Concepts Part of a series on Chemical engineering History Concepts Unit operations Unit processes Chemical engineer Chemical process Process integration Unit operations Momentum transfer Heat transfer Mass transfer Mechanical operations Unit process Chemical reaction engineering Chemical kinetics Chemical process modeling Chemical technology Process Control Process integration Branches Process design  · Fluid mechanics Process systems engineering Chemical plant design Chemical thermodynamics Transport phenomena  · *More*
  6. 6. Chemical engineering 4 Others Outline of chemical engineering Index of chemical engineering articles Education for chemical engineers List of chemical engineers List of chemical engineering societies List of chemical process simulators Perrys Chemical Engineers Handbook Category:Chemical engineering Chemical engineering involves the application of several principles. Key concepts are presented below. Chemical reaction engineering Chemical reactions engineering involves managing plant processes and conditions to ensure optimal plant operation. Chemical reaction engineers construct models for reactor analysis and design using laboratory data and physical parameters, such as chemical thermodynamics, to solve problems and predict reactor performance.[30] Plant design Chemical engineering design concerns the creation of plans and specification, and income projection of plants. Chemical engineers generate designs according to the clients needs. Design is limited by a number of factors, including funding, government regulations and safety standards. These constraints dictate a plants choice of process, materials and equipment.[31] Process design A unit operation is a physical step in an individual chemical engineering process. Unit operations (such as crystallization, drying and evaporation) are used to prepare reactants, purifying and separating its products, recycling unspent reactants, and controlling energy transfer in reactors.[32] On the other hand, a unit process is the chemical equivalent of a unit operation. Along with unit operations, unit processes constitute a process operation. Unit processes (such as nitration and oxidation) involve the conversion of material by biochemical, thermochemical and other means. Chemical engineers responsible for these are called process engineers.[33]
  7. 7. Chemical engineering 5 Transport phenomena Transport phenomena occur frequently in industrial problems. These include fluid dynamics, heat transfer and mass transfer, which mainly concern momentum transfer, energy transfer and transport of chemical species respectively. Basic equations for describing the three transport phenomena in the macroscopic, microscopic and molecular levels are very similar. Thus, understanding transport phenomena requires thorough understanding of mathematics.[34] Applications and practice Chemical engineers "develop economic ways of using materials and energy"[36] as opposed to chemists who are more interested in the basic composition of materials and synthesizing products from such. Chemical engineers use chemistry and engineering to turn raw materials into usable products, such as medicine, petrochemicals and plastics. They are also involved in waste management and research. Both applied and research facets make extensive use of computers.[35] Chemical engineers use computers to manage [35] automated systems in plants. A chemical engineer may be involved in industry or university research where he or she is tasked in designing and performing experiments to create new and better ways of production, controlling pollution, conserving resources and making these processes safer. He/she may be involved in designing and constructing plants as a project engineer. In this field, the chemical engineer uses his/her knowledge in selecting plant equipment and the optimum method of production to minimize costs and increase profitability. After its Operators in a chemical plant using an older construction, he/she may help in upgrading its equipment. He/she may analog control board, seen in Germany, 1986. also be involved in its daily operations. [37] Related fields and topics Today, the field of chemical engineering is a diverse one, covering areas from biotechnology and nanotechnology to mineral processing.
  8. 8. Chemical engineering 6 • Biochemical engineering • Heat transfer • Process design • Bioinformatics • Industrial gas • Process development • Biomedical engineering • Industrial catalysts • Process Systems Engineering • Biomolecular engineering • Mass transfer • Process miniaturization • Biotechnology • Materials science • Paper engineering • Ceramics • Metallurgy • Safety engineering • Chemical process modeling • Microfluidics • Semiconductor device fabrication • Chemical Technologist • Mineral processing • Separation processes (see also: separation of mixture) • Crystallization processes • Distillation processes • Membrane processes • Chemical reactor • Nanotechnology • Textile engineering • Chemical weapons • Natural environment • Thermodynamics • Cheminformatics • Natural gas processing • Transport phenomena • Computational fluid dynamics • Nuclear reprocessing • Unit operations • Corrosion engineering • Oil exploration • Water technology • Cost estimation • Oil refinery • Electrochemistry • Pharmaceutical engineering • Environmental engineering • Plastics engineering • Earthquake engineering • Polymers • Fluid dynamics • Process control • Food engineering • Fuel cell References [1] From Petroleum to Penicillin. The First Hundred Years of Modern Chemical Engineering: 1859–1959. – Burnett, J. N. [2] Cohen 1996, p. 172 [3] Cohen 1996, p. 174 [4] Reynolds 2001, p. 176 [5] Cohen 1996, p. 186 [6] Perkins 2003, p. 20 [7] Cohen 1996, pp. 172–173 [8] Cohen 1996, p. 175 [9] Cohen 1996, p. 178 [10] Cohen 1996, p. 180 [11] Cohen 1996, p. 183 [12] Cohen 1996, p. 184 [13] Cohen 1996, p. 187 [14] Cohen 1996, p. 189 [15] Cohen 1996, p. 190 [16] Cohen 1996, p. 185 [17] Ogawa 2007, p. 2 [18] Perkins 2003, p. 29 [19] Perkins 2003, p. 30 [20] Perkins 2003, p. 31 [21] Reynolds 2001, p. 177 [22] Perkins 2003, pp. 32–33 [23] Kim 2002, p. 7S [24] Perkins 2003, p. 34 [25] Kim 2002, p. 8S [26] Perkins 2003, p. 35 [27] Kim 2002, p. 9S [28] American Institute of Chemical Engineers 2003a
  9. 9. Chemical engineering 7 [29] Rice University [30] Carberry 2001, pp. 1–2 [31] Towler & Sinnott 2008, pp. 2–3 [32] McCabe, Smith & Hariott 1993, p. 4 [33] Silla 2003, pp. 8–9 [34] Bird, Stewart & Lightfoot 2002, pp. 1–2 [35] Garner 2003, pp. 47–48 [36] American Institute of Chemical Engineers 2003, Article III [37] Garner 2003, pp. 49–50 Bibliography • American Institute of Chemical Engineers (2003-01-17), AIChE Constitution (http://www.aiche.org/About/ WhoWeAre/Governance/Constitution.aspx), retrieved 2011-08-13. • Bird, R. Byron; Stewart, Warren E.; Lightfoot, Edwin N. (2002), Kulek, Petrina, ed., Transport Phenomena (http://books.google.com/books?id=L5FnNlIaGfcC) (2nd ed.), United States: John Wiley & Sons, ISBN 0-471-41077-2, LCC QA929.B% 2001, LCCN 2001-23739. • Carberry, James J., Chemical and Catalytic Reaction Engineering (http://books.google.com/ books?id=arJLaKa4yDQC), McGraw-Hill Chemical Engineering Series, Canada: General Publishing Company, ISBN 0-486-41736-0, LCC TP155.7.C37 2001, LCCN 2001-17315. • Cohen, Clive (June 1996), "The Early History of Chemical Engineering: A Reassessment" (http://www.ruf.rice. edu/~che/links/The early history of chemical engineering- a reassessment.pdf), The British Journal for the History of Science (Cambridge University Press) 29 (2), JSTOR 4027832. • Rice University, Engineering the Future of Biology and Biotechnology (http://www.ruf.rice.edu/~che/ research/white_paper_1.html), retrieved 2011-08-07. • Garner, Geraldine O. (2003), Careers in engineering (http://books.google.com/books?id=6-c4P223B1YC), VGM Professional Career Series (2nd ed.), United States: McGraw-Hill, ISBN 0-07-139041-3, LCC TA157.G3267 2002, LCCN 2002-27208. • Kim, Irene (January 2002), "Chemical engineering: A rich and diverse history" (http://www.clarkson.edu/ ~wilcox/Design/evolvche.pdf), Chemical Engineering Progress (Philadelphia: American Institute of Chemical Engineers) 98 (1), ISSN 0360-7275. • McCabe, Warren L.; Smith, Julian C.; Hariott, Peter (1993), Clark, B.J.; Castellano, Eleanor, eds., Unit Operations of Chemical Engineering, McGraw-Hill Chemical Engineering Series (5th ed.), Singapore: McGraw-Hill, ISBN 0-07-044844-2, LCC TP155.7.M393 1993, LCCN 92-unknown operator: u.. • Ogawa, Kōhei (2007), "Chapter 1: Information Entropy" (http://books.google.com/ books?id=3oWkzyazNCgC), Chemical engineering: a new perspective (1st ed.), Netherlands: Elsevier, ISBN 978-0-444-53096-7. • Perkins, J.D. (2003), "Chapter 2: Chemical Engineering — the First 100 Years" (http://www.scribd.com/doc/ 7011048/Chemical-Engineering-the-First-1-O0-Years), in Darton, R.C.; Prince, R.G.H.; Wood, D.G., Chemical Engineering: Visions of the World (http://books.google.com/books?id=VCLt0shyTQMC) (1st ed.), Netherlands: Elsevier Science, ISBN 0 444 51309 4. • Reynolds, Terry S. (2001), "Engineering, Chemical" (http://books.google.com/books?id=K1fXRZIosJMC), in Rothenberg, Marc, History of Science in United States: An Encyclopedia, New York City: Garland Publishing, ISBN 0-8153-0762-4, LCC Q127.U6 H57 2000, LCCN 99-43757. • Silla, Harry (2003), Chemical Process Engineering: Design and Economics (http://books.google.com/ books?id=lWmIX0r-XggC), New York City: Marcel Dekker, ISBN 0-8247-4274-5. • American Institute of Chemical Engineers (2003a), "Speeding up the human genome project" (http://www. clarkson.edu/~wilcox/Design/evolvche.pdf), Chemical Engineering Progress (Philadelphia) 99 (1), ISSN 0360-7275.
  10. 10. Chemical engineering 8 • Towler, Gavin; Sinnott, Ray (2008), Chemical engineering design: principles, practice and economics of plant and process design (http://books.google.com/books?id=EkK8X54BsTIC), United States: Elsevier, ISBN 978-0-7506-8423-1. History of chemical engineering Part of a series on Chemical engineering History Concepts Unit operations Unit processes Chemical engineer Chemical process Process integration Unit operations Momentum transfer Heat transfer Mass transfer Mechanical operations Unit process Chemical reaction engineering Chemical kinetics Chemical process modeling Chemical technology Process Control Process integration Branches Process design  · Fluid mechanics Process systems engineering Chemical plant design Chemical thermodynamics Transport phenomena  · *More* Others Outline of chemical engineering Index of chemical engineering articles Education for chemical engineers List of chemical engineers List of chemical engineering societies List of chemical process simulators Perrys Chemical Engineers Handbook Category:Chemical engineering
  11. 11. History of chemical engineering 9 Chemical engineering as a discipline is a little over one hundred years old. It grew out of mechanical engineering in the last part of the 19th century, because of a need for chemical processors. Before the Industrial Revolution (18th century), industrial chemicals were mainly produced through batch processing. Batch processing is similar to cooking. Individuals mix ingredients in a vessel, heat or pressurize the mixture, test it, and purify it to get a saleable product. Batch processes are still performed today on expensive products, such as perfumes, or pure maple syrups, where one can still turn a profit, despite batch methods being slow and inefficient. Most chemicals today are produced through a continuous "assembly line" chemical process. The Industrial Revolution was when this shift from batch to continuous processing occurred. Origin The Industrial Revolution led to an unprecedented escalation in demand, both with regard to quantity and quality, for bulk chemicals such as sulfuric acid and soda ash. This meant two things: one, the size of the activity and the efficiency of operation had to be enlarged, and two, serious alternatives to batch processing, such as continuous operation, had to be examined. This created the need for an engineer who was not only conversant with how machines behaved, but also understood chemical reactions and transport phenomena (how substances came together to react, how the required conditions could be achieved, etc.), and the influence the equipment had on how these processes operated on the large scale. Thus, Chemical Engineering was born as a distinct discipline; distinct from both Mechanical Engineering on one hand and industrial chemistry on the other. Professional associations These early programmes married industrial chemistry with mechanical engineering, with the emphasis most decidedly on engineering. But chemical engineers still needed to clearly define their activity as something more than a mishmash of chemistry and engineering. To emphasize their identity and thus help the growth of their profession, chemical engineers formed the American Institute of Chemical Engineers in 1908. The Institution of Chemical Engineers was founded in 1922 and awarded a Royal Charter in 1957. In 1959, the Instituto Mexicano de Ingenieros Quimicos (IMIQ) was founded in Mexico.[1] Definitions For the other established branches of engineering, there were ready associations in the mind of the common man: Mechanical Engineering meant machines, Electrical Engineering meant circuitry, and Civil Engineering meant structures. So chemical engineering can be symbolised as chemicals production. Unit operation The answer, provided by Arthur D. Little to the President of MIT, was to emphasize the approach chemical engineers took to the design and analysis of processes rather than a process or a product. The concept of Unit operations was developed to emphasize the underlying unity among seemingly different operations. For example, the principles are the same whether one is concerned about separating alcohol from water in a fermenter, or separating gasoline from diesel in a refinery, as long as the basis of separation is generation of a vapor of a different composition from the liquid. Therefore such separation processes can be studied together as a unit operation (in this case called distillation). The concept has stood the profession in good stead in its phase of growth, and has even been used to understand the way the human body functions.
  12. 12. History of chemical engineering 10 Unit processes In the early part of the last century, a parallel concept called Unit Processes was used to classify reactive processes. Thus oxidations, reductions, alkylations etc. formed separate unit processes and were studied as such. This was natural considering the close affinity of chemical engineering to industrial chemistry at its inception. Gradually however, the subject of chemical reaction engineering has largely replaced the unit process concept. This subject looks at the entire body of chemical reactions as having a personality of its own, independent of the particular chemical species or chemical bonds involved. The latter does contribute to this personality in no small measure, but to design and operate chemical reactors, a knowledge of characteristics such as rate behaviour, thermodynamics, single or multiphase nature, etc. are more important. The emergence of chemical reaction engineering as a discipline truly signaled the severance of the umbilical cord connecting chemical engineering to industrial chemistry, and served to cement the truly unique character of this discipline. References [1] "History" (http:/ / web. imiq. org/ index. php?option=com_content& view=article& id=47& Itemid=57& lang=en). . Retrieved May 18, 2010., External links • "History of ChEn: Struggle for Survival" (http://web.boun.edu.tr/akman/history/h_surviv.html) • "About AIChE" (http://www.stevens-tech.edu/aiche/about_aiche.html) (from www.stevens-tech.edu) • Chemical Achievers: Chemical Engineering (http://www.chemheritage.org/classroom/chemach/engineering/ index.html), discusses several individuals associated with defining the field of chemical engineering during its early stages
  13. 13. Chemical engineer 11 Chemical engineer Chemical engineers design, construct and operate plants Part of a series on Chemical engineering History Concepts Unit operations Unit processes Chemical engineer Chemical process Process integration Unit operations Momentum transfer Heat transfer Mass transfer Mechanical operations Unit process Chemical reaction engineering Chemical kinetics Chemical process modeling Chemical technology Process Control Process integration
  14. 14. Chemical engineer 12 Branches Process design  · Fluid mechanics Process systems engineering Chemical plant design Chemical thermodynamics Transport phenomena  · *More* Others Outline of chemical engineering Index of chemical engineering articles Education for chemical engineers List of chemical engineers List of chemical engineering societies List of chemical process simulators Perrys Chemical Engineers Handbook Category:Chemical engineering In the field of engineering, a chemical engineer is the profession in which one works principally in the chemical industry to convert basic raw materials into a variety of products, and deals with the design and operation of plants and equipment to perform such work.[1] In general, a chemical engineer is one who applies and uses principles of chemical engineering in any of its various practical applications; these often include 1) design, manufacture, and operation of plants and machinery in industrial chemical and related processes ("chemical process engineers"); 2) development of new or adapted substances for products ranging from foods and beverages to cosmetics to cleaners to pharmaceutical ingredients, among many other products ("chemical product engineers"); and 3) development of new technologies such as fuel cells, hydrogen power and nanotechnology, as well as working in fields wholly or partially derived from Chemical Engineering such as materials science, polymer engineering, and biomedical engineering. History The term appeared in print in 1839, though from the context it suggests a person with mechanical engineering knowledge working in the chemical industry.[2] In 1880, George E. Davis wrote in a letter to Chemical News A Chemical Engineer is a person who possesses chemical and mechanical knowledge, and who applies that knowledge to the utilisation, on a manufacturing scale, of chemical action. He proposed the name Society of Chemical Engineers, for what was in fact constituted as the Society of Chemical Industry. At the first General Meeting of the Society in 1882, some 15 of the 300 members described themselves as chemical engineers, but the Societys formation of a Chemical Engineering Group in 1918 attracted about 400 members.[3] In 1905 a publication called The Chemical Engineer was founded in the USA, and in 1908 the American Institute of Chemical Engineers was established.[4] In 1924 the Institution of Chemical Engineers adopted the following definition A chemical engineer is a professional man experienced in the design, construction and operation of plant and works in which matter undergoes a change of state and composition.[5] (The first female member joined in 1942.)[6] As can be seen from the later definition, the occupation is not limited to the chemical industry, but more generally the process industries, or other situations in which complex physical and/or chemical processes are to be managed. In 1951 the President of the Institution of Chemical Engineers said in his Presidential Address "I believe most of us would be willing to regard Edward Charles Howard (1774-1816) as the first chemical engineer of any eminence".[7] Others have suggested Johann Rudolf Glauber (1604–1670) for his development of processes for the manufacture of the major industrial acids.[8]
  15. 15. Chemical engineer 13 Overview Historically, the chemical engineer has been primarily concerned with process engineering. The modern discipline of chemical engineering, however, encompasses much more than just process engineering. Chemical engineers are now engaged in the development and production of a diverse range of products, as well as in commodity and specialty chemicals. These products include high performance materials needed for aerospace, automotive, biomedical, electronic, environmental and military applications. Examples include ultra-strong fibers, fabrics, adhesives and composites for vehicles, bio-compatible materials for implants and prosthetics, gels for medical applications, pharmaceuticals, and films with special dielectric, optical or spectroscopic properties for opto-electronic devices. Additionally, chemical engineering is often intertwined with biology and biomedical engineering. Many chemical engineers work on biological projects such as understanding biopolymers (proteins) and mapping the human genome. Employment and Salaries In the United States of America, the Department of Labor estimated in 2008 the number of chemical engineers to be 31,000. According to a 2011 salary survey by the American Institution of Chemical Engineers (AIChE), the median annual salary for a chemical engineer was approximately $110,000.[9] In one salary survey, chemical engineering was found to be highest-paying degree for first employment of college graduates.[10]Chemical engineering has been successively ranked in the Top 2 places in the Most Lucrative Degrees Survey by CNN Money in the United States of America.[11][12][13] In the UK, the Institution of Chemical Engineers 2006 Salary Survey reported an average salary of approximately £53,000, with a starting salary for a graduate averaging £24,000.[14] Chemical engineering is a male-dominated field: as of 2009, only 17.1% of professional chemical engineers are women.[15] However, that trend is expected to shift as the number of female students in the field continues to increase.[16] References [1] Licker, Mark, D. (2003). Dictionary of Engineering", McGraw-Hill, 2nd Ed. [2] Ure, Andrew (1839) A Dictionary of Arts Manufactures and Mines, London: Longman, Orme, Brown, Green & Longman, page 1220 [3] Colin Duvall and Sean F, Johnston (2000) Scaling Up: The Institution of Chemical Engineers and the Rise of a New Profession Kluwer Academic Publishers [4] John C. Olsen (December 1932), Chemical Engineering As A Profession: Origin and Early Growth of the American Institute of Chemical Engineers (http:/ / www. aiche. org/ uploadedFiles/ About/ Centennial/ CE_Profession-A. pdf) [5] Transactions of the Institution of Chemical Engineers volume 2 page 23 (1924) [6] Colin Duvall and Sean F, Johnston (2000)Scaling Up: The Institution of Chemical Engineers and the Rise of a New Profession Kluwer Academic Publishers [7] Transactions of the IChemE (1951) Volume 29 page 163 [8] Herman Skolnik in W. F. Furter (ed) (1982) A Century of Chemical Engineering ISBN 0-306-40895-3 page 230 [9] U.S. Department of Labor, Bureau of Labor Statistics: Chemical Engineers (http:/ / www. bls. gov/ oes/ current/ oes172041. htm) [10] Chemical Engineering Ranked Highest Paying Degree (http:/ / chemical. princeton. edu/ news/ news_info. shtml?id=57), Department of Chemical Engineering, Princeton University, February 15, 2006 [11] (http:/ / money. cnn. com/ 2009/ 07/ 24/ news/ economy/ highest_starting_salaries/ index. htm), 2009 [12] (http:/ / money. cnn. com/ 2006/ 02/ 13/ pf/ college/ starting_salaries/ index. htm), 2006 [13] (http:/ / money. cnn. com/ 2007/ 07/ 11/ pf/ college/ starting_salaries/ index. htm), 2007 [14] Institution of Chemical Engineers Annual Review 2006 [15] "Chemical Engineer Careers: Employment & Salary Trends for Aspiring Chemical Engineers" (http:/ / www. collegedegreereport. com/ articles/ chemical-engineer-careers-employment-salary-trends-aspiring-chemical-engineers). CollegeDegreeReport.com. . [16] http:/ / www. intstudy. com/ articles/ sl275a43. htm
  16. 16. Chemical engineer 14 External links • American Institute of Chemical Engineers (USA) (http://www.aiche.org/) • Institution of Chemical Engineers (UK) (http://www.icheme.org) • Canadian Society for Chemical Engineers (http://www.cheminst.ca/csche_home__e.htm) • Engineers Australia (AUS) (http://www.ieaust.org/)
  17. 17. Unit operation 15 Unit operation An ore extraction process broken into its constituent unit operations (Quincy Mine, Hancock, MI ca. 1900) Part of a series on Chemical engineering History Concepts Unit operations Unit processes Chemical engineer Chemical process Process integration Unit operations Momentum transfer Heat transfer Mass transfer Mechanical operations
  18. 18. Unit operation 16 Unit process Chemical reaction engineering Chemical kinetics Chemical process modeling Chemical technology Process Control Process integration Branches Process design  · Fluid mechanics Process systems engineering Chemical plant design Chemical thermodynamics Transport phenomena  · *More* Others Outline of chemical engineering Index of chemical engineering articles Education for chemical engineers List of chemical engineers List of chemical engineering societies List of chemical process simulators Perrys Chemical Engineers Handbook Category:Chemical engineering In chemical engineering and related fields, a unit operation is a basic step in a process. Unit operations involve bringing a physical change such as separation, crystallization, evaporation, filtration etc. For example, in milk processing, homogenization, pasteurization, chilling, and packaging are each unit operations which are connected to create the overall process. A process may have many unit operations to obtain the desired product. Historically, the different chemical industries were regarded as different industrial processes and with different principles. Arthur Dehon Little propounded the concept of "unit operations" to explain industrial chemistry processes in 1916.[1] In 1923, William H.Walker, Warren K. Lewis and William H. McAdams wrote the book The Principles of Chemical Engineering[2] and explained the variety of chemical industries have processes which follow the same physical laws. They summed-up these similar processes into unit operations. Each unit operation follows the same physical laws and may be used in all chemical industries. The unit operations form the fundamental principles of chemical engineering. Chemical engineering unit operations consist of five classes: 1. Fluid flow processes, including fluids transportation, filtration, solids fluidization 2. Heat transfer processes, including evaporation, condensation 3. Mass transfer processes, including gas absorption, distillation, extraction, adsorption, drying 4. Thermodynamic processes, including gas liquefaction, refrigeration 5. Mechanical processes, including solids transportation, crushing and pulverization, screening and sieving Chemical engineering unit operations also fall in the following categories: • Combination (mixing) • Separation (distillation) • Reaction (chemical reaction)
  19. 19. Unit operation 17 Chemical engineering unit operations and chemical engineering unit processing form the main principles of all kinds of chemical industries and are the foundation of designs of chemical plants, factories, and equipment used. References [1] "The MIT Connection"http:/ / libraries. mit. edu/ archives/ exhibits/ adlittle/ mit-connection. html Retrieved March 6, 2010. [2] The Encyclopedia of Earth. "Walker, William H. http:/ / www. eoearth. org/ article/ Walker,_William_H. Accessed April 4, 2010.
  20. 20. Unit process 18 Unit process Part of a series on Chemical engineering History Concepts Unit operations Unit processes Chemical engineer Chemical process Process integration Unit operations Momentum transfer Heat transfer Mass transfer Mechanical operations Unit process Chemical reaction engineering Chemical kinetics Chemical process modeling Chemical technology Process Control Process integration Branches Process design  · Fluid mechanics Process systems engineering Chemical plant design Chemical thermodynamics Transport phenomena  · *More* Others Outline of chemical engineering Index of chemical engineering articles Education for chemical engineers List of chemical engineers List of chemical engineering societies List of chemical process simulators Perrys Chemical Engineers Handbook Category:Chemical engineering A Unit Process is a step in manufacturing in which chemical reaction takes place, e.g, the oxidation of paraxylene to terephthalic acid is a unit process, the hydrogenation of vegetable oil to ghee is a unit process. In 1930 P.H. Groggins introduced Unit processes in order to classify and standardize chemical reactions.[1]
  21. 21. Unit process 19 References [1] Austen, George (1984). Shreves Chemical Process Industries. Mc-Graw Hill. pp. 1. ISBN 0-07-066167-7. • Review of What are Unit manufacturing processes from the National Academies Press (http://www.nap.edu/ nap-cgi/skimit.cgi?recid=4827&chap=19-30) Process integration Process integration is a term in chemical engineering which has two possible meanings. 1. A holistic approach to process design which emphasizes the unity of the process and considers the interactions between different unit operations from the outset, rather than optimising them separately. This can also be called integrated process design or process synthesis. El-Halwagi (1997 and 2006) and Smith (2005) describe the approach well. An important first step is often product design (Cussler and Moggridge 2003) which develops the specification for the product to fulfil its required purpose. 2. Pinch analysis, a technique for designing a process to minimise energy consumption and maximise heat recovery, also known as heat integration, energy integration or pinch technology. The technique calculates thermodynamically attainable energy targets for a given process and identifies how to achieve them. A key insight is the pinch temperature, which is the most constrained point in the process. The most detailed explanation of the techniques is by Linnhoff et al. (1982), Shenoy (1995) and Kemp (2006). This definition reflects the fact that the first major success for process integration was the thermal pinch analysis addressing energy problems and pioneered by Linnhoff and co-workers. Later, other pinch analyses were developed for several applications such as mass-exchange networks (El-Halwagi and Manousiouthakis, 1989), water minimization (Wang and Smith, 1994), and material recycle (El-Halwagi et al., 2003). A very successful extension was "Hydrogen Pinch", which was applied to refinery hydrogen management (Nick Hallale et al., 2002 and 2003). This allowed refiners to minimise the capital and operating costs of hydrogen supply to meet ever stricter environmental regulations and also increase hydrotreater yields. In the context of chemical engineering, Process Integration can be defined as a holistic approach to process design and optimization, which exploits the interactions between different units in order to employ resources effectively and minimize costs. Note that Process Integration is not limited to the design of new plants, but it also covers retrofit design (e.g. new units to be installed in an old plant) and the operation of existing systems. Nick Hallale (2001), in his article in Chemical Engineering Progress provided a state of the art review. He explained that process integration far wider scope and touches every area of process design. Industries are making more money from their raw materials and capital assets while becoming cleaner and more sustainable. Source: http://www.allbusiness.com/manufacturing/chemical-manufacturing/1128450-1.html#ixzz1Wij9OVl5 The main advantage of process integration is to consider a system as a whole (i.e. integrated or holistic approach) in order to improve their design and/or operation. In contrast, an analytical approach would attempt to improve or optimize process units separately without necessarily taking advantage of potential interactions among them. For instance, by using process integration techniques it might be possible to identify that a process can use the heat rejected by another unit and reduce the overall energy consumption, even if the units are not running at optimum conditions on their own. Such an opportunity would be missed with an analytical approach, as it would seek to optimize each unit, and thereafter it wouldn’t be possible to re-use the heat internally. Typically, process integration techniques are employed at the beginning of a project (e.g. a new plant or the improvement of an existing one) to screen out promising options to optimize the design and/or operation of a process plant.
  22. 22. Process integration 20 Also it is often employed, in conjunction with simulation and mathematical optimization tools to identify opportunities in order to better integrate a system (new or existing) and reduce capital and/or operating costs. Most process integration techniques employ Pinch analysis or Pinch Tools to evaluate several processes as a whole system. Therefore, strictly speaking, both concepts are not the same, even if in certain contexts they are used interchangeably. The review by Nick Hallale (2001) explains that in the future, several trends are to be expected in the field. In the future, it seems probable that the boundary between targets and design will be blurred and that these will be based on more structural information regarding the process network. Second, it is likely that we will see a much wider range of applications of process integration. There is still much work to be carried out in the area of separation, not only in complex distillation systems, but also in mixed types of separation systems. This includes processes involving solids, such as flotation and crystallization. The use of process integration techniques for reactor design has seen rapid progress, but is still in its early stages. Third, a new generation of software tools is expected. The emergence of commercial software for process integration is fundamental to its wider application in process design. OA References Cussler, E.L. and Moggridge, G.D. (2001). Chemical Product Design. Cambridge University Press (Cambridge Series in Chemical Engineering). ISBN 0521791839 El-Halwagi, M. M., (2006) "Process Integration", Elsevier El-Halwagi, M. M., (1997) "Pollution Prevention through Process Integration", Academic Press El-Halwagi, M. M., F. Gabriel, and D. Harell, (2003) “Rigorous Graphical Targeting for Resource Conservation via Material Recycle/Reuse Networks”, Ind. Eng. Chem. Res., 42, 4319-4328 El-Halwagi, M. M., and Manousiouthakis, V. (1989). Synthesis of mass exchange networks. AIChE J. 35(8), 1233-1244. Hallale, Nick, (2001), "Burning Bright: Trends in Process Integration", Chemical Engineering Progress, July 2001 Nick Hallale, I Moore, D. Vauk (2002), "Hydrogen: Liability or Asset?", Chemical Engineering Progress, September 2002 [1] Hallale, N. Ian Moore, Dennis Vauk, "Hydrogen optimization at minimal investment", Petroleum Technology Quarterly (PTQ), Spring (2003) Kemp, I.C. (2006). Pinch Analysis and Process Integration: A User Guide on Process Integration for the Efficient Use of Energy, 2nd edition. Butterworth-Heinemann. ISBN 0750682604. Includes downloadable spreadsheet software. Linnhoff, B., D.W. Townsend, D. Boland, G.F. Hewitt, B.E.A. Thomas, A.R. Guy and R.H. Marsland, (1982) “A User Guide on Process Integration for the Efficient Use of Energy," IChemE UK Shenoy, U.V. (1995). "Heat Exchanger Network Synthesis: Process Optimization by Energy and Resource Analysis". Includes two computer disks. Gulf Publishing Company, Houston, TX, USA. ISBN 0884153916. Smith, R. (2005). Chemical Process Design and Integration. John Wiley and Sons. ISBN 0471486809 Wang, Y. P. and R. Smith (1994). Wastewater Minimisation. Chem. Eng. Sci., 49, 981-1006
  23. 23. Process integration 21 References [1] http:/ / www. allbusiness. com/ manufacturing/ chemical-manufacturing/ 1000302-1. html Momentum transfer Part of a series on Chemical engineering History Concepts Unit operations Unit processes Chemical engineer Chemical process Process integration Unit operations Momentum transfer Heat transfer Mass transfer Mechanical operations Unit process Chemical reaction engineering Chemical kinetics Chemical process modeling Chemical technology Process Control Process integration Branches Process design  · Fluid mechanics Process systems engineering Chemical plant design Chemical thermodynamics Transport phenomena  · *More* Others Outline of chemical engineering Index of chemical engineering articles Education for chemical engineers List of chemical engineers List of chemical engineering societies List of chemical process simulators Perrys Chemical Engineers Handbook Category:Chemical engineering In particle physics, wave mechanics and optics, momentum transfer is the amount of momentum that one particle gives to another particle.
  24. 24. Momentum transfer 22 In the simplest example of scattering of two colliding particles with initial momenta , resulting in final momenta , the momentum transfer is given by where the last identity expresses momentum conservation. Momentum transfer is an important quantity because is a better measure for the typical distance resolution of the reaction than the momenta themselves. Wave mechanics and optics A wave has a momentum and is a vectorial quantity. The difference of the momentum of the scattered wave to the incident wave is called momentum transfer. The wave number k is the absolute of the wave vector and is related to the wavelength . Often, momentum transfer is given in wavenumber units in reciprocal length Diffraction The momentum transfer plays an important role in the evaluation of neutron, X-ray and electron diffraction for the investigation of condensed matter. Bragg diffraction occurs on the atomic crystal lattice, conserves the wave energy and thus is called elastic scattering, where the wave numbers final and incident particles, and , respectively, are equal and just the direction changes by a reciprocal lattice vector with the relation to the lattice spacing . As momentum is conserved, the transfer of momentum occurs to crystal momentum. The presentation in -space is generic and does not depend on the type of radiation and wavelength used but only on the sample system, which allows to compare results obtained from the many different methods. Some established communities such as powder diffraction employ the diffraction angle as the independent variable, which worked fine in the early years when only a few characteristic wavelengths such as Cu-K were available. The relationship to -space is and basically states that larger corresponds to larger .
  25. 25. Heat transfer 23 Heat transfer Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy and heat between physical systems. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species, either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system. Heat conduction, also called diffusion, is the direct microscopic exchange of kinetic energy of particles through the boundary between two systems. When an object is at a different temperature from another body or its surroundings, heat flows so that the body and the surroundings reach the same temperature, at which point they are in thermal equilibrium. Such spontaneous heat transfer always occurs from a region of high temperature to another region of lower temperature, as required by the second law of thermodynamics. Heat convection occurs when bulk flow of a fluid (gas or liquid) carries heat along with the flow of matter in the fluid. The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is often called "natural convection". All convective processes also move heat partly by diffusion, as well. Another form of convection is forced convection. In this case the fluid is forced to flow by use of a pump, fan or other mechanical means. The final major form of heat transfer is by radiation, which occurs in any transparent medium (solid or fluid) but may also even occur across vacuum (as when the Sun heats the Earth). Radiation is the transfer of energy through space by means of electromagnetic waves in much the same way as electromagnetic light waves transfer light. The same laws that govern the transfer of light govern the radiant transfer of heat.[1] Overview Heat is defined in physics as the transfer of thermal energy across a well-defined boundary around a thermodynamic system. It is a characteristic of a process and is not statically contained in matter. In engineering contexts, however, the term heat transfer has acquired a specific usage, despite its literal redundancy of the characterization of transfer. In these contexts, heat is taken as synonymous to thermal energy. This usage has its origin in the historical interpretation of heat as a fluid (caloric) that can be transferred by various causes,[2] and that is also common in the language of laymen and everyday life. Fundamental methods of heat transfer in engineering include conduction, convection, and radiation. Physical laws describe the behavior and characteristics of each of these methods. Real systems often exhibit a complicated combination of them. Heat transfer methods are used in numerous disciplines, such as automotive engineering, thermal management of electronic devices and systems, climate control, insulation, materials processing, and power plant engineering. Various mathematical methods have been developed to solve or approximate the results of heat transfer in systems. Heat transfer is a path function (or process quantity), as opposed to a state quantity; therefore, the amount of heat transferred in a thermodynamic process that changes the state of a system depends on how that process occurs, not only the net difference between the initial and final states of the process. Heat flux is a quantitative, vectorial representation of the heat flow through a surface.[3] Heat transfer is typically studied as part of a general chemical engineering or mechanical engineering curriculum. Typically, thermodynamics is a prerequisite for heat transfer courses, as the laws of thermodynamics are essential to the mechanism of heat transfer.[3] Other courses related to heat transfer include energy conversion, thermofluids, and mass transfer.
  26. 26. Heat transfer 24 The transport equations for thermal energy (Fouriers law), mechanical momentum (Newtons law for fluids), and mass transfer (Ficks laws of diffusion) are similar[4][5] and analogies among these three transport processes have been developed to facilitate prediction of conversion from any one to the others.[5] Mechanisms The fundamental modes of heat transfer are: Conduction or diffusion The transfer of energy between objects that are in physical contact Convection The transfer of energy between an object and its environment, due to fluid motion Radiation The transfer of energy to or from a body by means of the emission or absorption of electromagnetic radiation Advection The transfer of energy from one location to another as a side effect of physically moving an object containing that energy Conduction On a microscopic scale, heat conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their energy (heat) to these neighboring particles. In other words, heat is transferred by conduction when adjacent atoms vibrate against one another, or as electrons move from one atom to another. Conduction is the most significant means of heat transfer within a solid or between solid objects in thermal contact. Fluids—especially gases—are less conductive. Thermal contact conductance is the study of heat conduction between solid bodies in contact.[6] Steady state conduction (see Fouriers law) is a form of conduction that happens when the temperature difference driving the conduction is constant, so that after an equilibration time, the spatial distribution of temperatures in the conducting object does not change any further.[7] In steady state conduction, the amount of heat entering a section is equal to amount of heat coming out.[6] Transient conduction (see Heat equation) occurs when the temperature within an object changes as a function of time. Analysis of transient systems is more complex and often calls for the application of approximation theories or numerical analysis by computer.[6] Convection Convective heat transfer, or convection, is the transfer of heat from one place to another by the movement of fluids, a process that is essentially transfer of heat via mass transfer. (In physics, the term fluid means any substance that deforms under shear stress; it includes liquids, gases, plasmas, and some plastic solids.) Bulk motion of fluid enhances heat transfer in many physical situations, such as (for example) between a solid surface and the fluid.[8] Convection is usually the dominant form of heat transfer in liquids and gases. Although sometimes discussed as a third method of heat transfer, convection is usually used to describe the combined effects of heat conduction within the fluid (diffusion) and heat transference by bulk fluid flow streaming.[9] The process of transport by fluid streaming is known as advection, but pure advection is a term that is generally associated only with mass transport in fluids, such as advection of pebbles in a river. In the case of heat transfer in fluids, where transport by advection in a fluid is always also accompanied by transport via heat diffusion (also known as heat conduction) the process of heat convection is understood to refer to the sum of heat transport by advection and diffusion/conduction.
  27. 27. Heat transfer 25 Free, or natural, convection occurs when bulk fluid motion (steams and currents) are caused by buoyancy forces that result from density variations due to variations of temperature in the fluid. Forced convection is a term used when the streams and currents in the fluid are induced by external means—such as fans, stirrers, and pumps—creating an artificially induced convection current.[10] Convective heating or cooling in some circumstances may be described by Newtons law of cooling: "The rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings." However, by definition, the validity of Newtons law of cooling requires that the rate of heat loss from convection be a linear function of ("proportional to") the temperature difference that drives heat transfer, and in convective cooling this is sometimes not the case. In general, convection is not linearly dependent on temperature gradients, and in some cases is strongly nonlinear. In these cases, Newtons law does not apply. Radiation Thermal radiation is energy emitted by matter as electromagnetic waves due to the pool of thermal energy that all matter possesses that has a temperature above absolute zero. Thermal radiation propagates without the presence of matter through the vacuum of space.[11] Thermal radiation is a direct result of the random movements of atoms and molecules in matter. Since these atoms and molecules are composed of charged particles (protons and electrons), their movement results in the emission of electromagnetic radiation, which carries energy away from A red-hot iron object, transferring heat to the surrounding the surface. environment primarily through thermal radiation. Unlike conductive and convective forms of heat transfer, thermal radiation can be concentrated in a small spot by using reflecting mirrors, which is exploited in concentrating solar power generation. For example, the sunlight reflected from mirrors heats the PS10 solar power tower and during the day it can heat water to 285 °C (unknown operator: ustrong °F). Advection By transferring matter, energy—including thermal energy—is moved by the physical transfer of a hot or cold object from one place to another.[12] This can be as simple as placing hot water in a bottle and heating a bed, or the movement of an iceberg in changing ocean currents. A practical example is thermal hydraulics. This can be described by the formula Convection vs. conduction In a body of fluid that is heated from underneath its container, conduction and convection can be considered to compete for dominance. If heat conduction is too great, fluid moving down by convection is heated by conduction so fast that its downward movement will be stopped due to its buoyancy, while fluid moving up by convection is cooled by conduction so fast that its driving buoyancy will diminish. On the other hand, if heat conduction is very low, a large temperature gradient may be formed and convection might be very strong. The Rayleigh number ( ) is a measure determining the result of this competition.
  28. 28. Heat transfer 26 where • g is acceleration due to gravity • ρ is the density with being the density difference between the lower and upper ends • μ is the dynamic viscosity • α is the Thermal diffusivity • β is the volume thermal expansivity (sometimes denoted α elsewhere) • T is the temperature and • ν is the kinematic viscosity. The Rayleigh number can be understood as the ratio between the rate of heat transfer by convection to the rate of heat transfer by conduction; or, equivalently, the ratio between the corresponding timescales (i.e. conduction timescale divided by convection timescale), up to a numerical factor. This can be seen as follows, where all calculations are up to numerical factors depending on the geometry of the system. The buoyancy force driving the convection is roughly , so the corresponding pressure is roughly . In steady state, this is canceled by the shear stress due to viscosity, and therefore roughly equals , where V is the typical fluid velocity due to convection and the order of its timescale. The conduction timescale, on the other hand, is of the order of . Convection occurs when the Rayleigh number is above 1,000–2,000. For example, the Earths mantle, exhibiting non-stable convection, has Rayleigh number of the order of 1,000, and Tconv as calculated above is around 100 million years. Phase changes Transfer of heat through a phase transition in the medium—such as water-to-ice, water-to-steam, steam-to-water, or ice-to-water—involves significant energy and is exploited in many ways: steam engines, refrigerators, etc.[13] For example, the Mason equation is an approximate analytical expression for the growth of a water droplet based on the effects of heat transport on evaporation and condensation. Boiling Heat transfer in boiling fluids is complex, but of considerable technical importance. It is characterized by an S-shaped curve relating heat flux to surface temperature difference.[14] At low driving temperatures, no boiling occurs and the heat transfer rate is controlled by the usual single-phase mechanisms. As the surface temperature is increased, local boiling occurs and vapor bubbles nucleate, grow into the surrounding cooler fluid, and collapse. This is sub-cooled nucleate boiling, and is a very efficient heat transfer mechanism. At high bubble generation rates, the bubbles begin to interfere and the heat flux no longer increases rapidly with surface temperature (this is the departure from nucleate boiling, or DNB). At higher temperatures still, a maximum in the heat flux is reached (the critical heat flux, or CHF). The regime of falling heat transfer that follows is not easy to study, but is believed to be characterized by alternate periods of nucleate and film boiling. Nucleate boiling slows the heat transfer due to gas bubbles on the heaters surface; as mentioned, gas-phase thermal conductivity is much lower than liquid-phase thermal conductivity, so the outcome is a kind of "gas thermal barrier". At higher temperatures still, the hydrodynamically-quieter regime of film boiling is reached. Heat fluxes across the stable vapor layers are low, but rise slowly with temperature. Any contact between fluid and the surface that may be seen probably leads to the extremely rapid nucleation of a fresh vapor layer ("spontaneous nucleation").
  29. 29. Heat transfer 27 Condensation Condensation occurs when a vapor is cooled and changes its phase to a liquid. Condensation heat transfer, like boiling, is of great significance in industry. During condensation, the latent heat of vaporization must be released. The amount of the heat is the same as that absorbed during vaporization at the same fluid pressure. There are several types of condensation: • Homogeneous condensation, as during a formation of fog. • Condensation in direct contact with subcooled liquid. • Condensation on direct contact with a cooling wall of a heat exchanger: This is the most common mode used in industry: • Filmwise condensation is when a liquid film is formed on the subcooled surface, and usually occurs when the liquid wets the surface. • Dropwise condensation is when liquid drops are formed on the subcooled surface, and usually occurs when the liquid does not wet the surface. Dropwise condensation is difficult to sustain reliably; therefore, industrial equipment is normally designed to operate in filmwise condensation mode. Modeling approaches Complex heat transfer phenomena can be modeled in different ways. Heat equation The heat equation is an important partial differential equation that describes the distribution of heat (or variation in temperature) in a given region over time. In some cases, exact solutions of the equation are available; in other cases the equation must be solved numerically using computational methods. For example, simplified climate models may use Newtonian cooling, instead of a full (and computationally expensive) radiation code, to maintain atmospheric temperatures. Lumped system analysis System analysis by the lumped capacitance model is a common approximation in transient conduction that may be used whenever heat conduction within an object is much faster than heat conduction across the boundary of the object. This is a method of approximation that reduces one aspect of the transient conduction system—that within the object—to an equivalent steady state system. That is, the method assumes that the temperature within the object is completely uniform, although its value may be changing in time. In this method, the ratio of the conductive heat resistance within the object to the convective heat transfer resistance across the objects boundary, known as the Biot number, is calculated. For small Biot numbers, the approximation of spatially uniform temperature within the object can be used: it can be presumed that heat transferred into the object has time to uniformly distribute itself, due to the lower resistance to doing so, as compared with the resistance to heat entering the object. Lumped system analysis often reduces the complexity of the equations to one first-order linear differential equation, in which case heating and cooling are described by a simple exponential solution, often referred to as Newtons law of cooling.
  30. 30. Heat transfer 28 Applications and techniques Heat transfer has broad application to the functioning of numerous devices and systems. Heat-transfer principles may be used to preserve, increase, or decrease temperature in a wide variety of circumstances. Insulation and radiant barriers Thermal insulators are materials specifically designed to reduce the flow of heat by limiting conduction, convection, or both. Radiant barriers are materials that reflect radiation, and therefore reduce the flow of heat from radiation sources. Good insulators are not necessarily good radiant barriers, and vice versa. Metal, for instance, is an excellent reflector and a poor insulator. The effectiveness of an insulator is indicated by its R-value, or resistance value. The R-value of a material is the inverse of the conduction coefficient (k) multiplied by the thickness Car exhausts usually require some form of heat barrier, especially high performance exhausts where a ceramic coating (d) of the insulator. In most of the world, R-values are is often applied. measured in SI units: square-meter kelvins per watt (m²·K/W). In the United States, R-values are customarily given in units of British thermal units per hour per square-foot degrees Fahrenheit (Btu/h·ft²·°F). Rigid fiberglass, a common insulation material, has an R-value of four per inch, while poured concrete, a poor insulator, has an R-value of 0.08 per inch.[15] The tog is a measure of thermal resistance, commonly used Heat exposure as part of a fire test for firestop products. in the textile industry, and often seen quoted on, for example, duvets and carpet underlay. The effectiveness of a radiant barrier is indicated by its reflectivity, which is the fraction of radiation reflected. A material with a high reflectivity (at a given wavelength) has a low emissivity (at that same wavelength), and vice versa. At any specific wavelength, reflectivity = 1 - emissivity. An ideal radiant barrier would have a reflectivity of 1, and would therefore reflect 100 percent of incoming radiation. Vacuum flasks, or Dewars, are silvered to approach this ideal. In the vacuum of space, satellites use multi-layer insulation, which consists of many layers of aluminized (shiny) Mylar to greatly reduce radiation heat transfer and control satellite temperature.
  31. 31. Heat transfer 29 Critical insulation thickness Low thermal conductivity (k) materials reduce heat fluxes. The smaller the k value, the larger the corresponding thermal resistance (R) value. Thermal conductivity is measured in watts-per-meter per kelvin (W·m−1·K−1), represented as k. As the thickness of insulating material increases, the thermal resistance—or R-value—also increases. However, adding layers of insulation has the potential of increasing the surface area, and hence the thermal convection area. For example, as thicker insulation is added to a cylindrical pipe, the outer radius of the pipe-and-insulation system increases, and therefore surface area increases. The point where the added resistance of increasing insulation thickness becomes overshadowed by the effect of increased surface area is called the critical insulation thickness. In simple cylindrical pipes, this is calculated as a radius:[16] Heat exchangers A heat exchanger is a tool built for efficient heat transfer from one fluid to another, whether the fluids are separated by a solid wall so that they never mix, or the fluids are in direct contact. Heat exchangers are widely used in refrigeration, air conditioning, space heating, power generation, and chemical processing. One common example of a heat exchanger is a cars radiator, in which the hot coolant fluid is cooled by the flow of air over the radiators surface. Common types of heat exchanger flows include parallel flow, counter flow, and cross flow. In parallel flow, both fluids move in the same direction while transferring heat; in counter flow, the fluids move in opposite directions; and in cross flow, the fluids move at right angles to each other. Common constructions for heat exchanger include shell and tube, double pipe, extruded finned pipe, spiral fin pipe, u-tube, and stacked plate. When engineers calculate the theoretical heat transfer in a heat exchanger, they must contend with the fact that the driving temperature difference between the two fluids varies with position. To account for this in simple systems, the log mean temperature difference (LMTD) is often used as an "average" temperature. In more complex systems, direct knowledge of the LMTD is not available, and the number of transfer units (NTU) method can be used instead. Heat dissipation A heat sink is a component that transfers heat generated within a solid material to a fluid medium, such as air or a liquid. Examples of heat sinks are the heat exchangers used in refrigeration and air conditioning systems, and the radiator in a car (which is also a heat exchanger). Heat sinks also help to cool electronic and optoelectronic devices such as CPUs, higher-power lasers, and light-emitting diodes (LEDs). A heat sink uses its extended surfaces to increase the surface area in contact with the cooling fluid. Buildings In cold climates, houses with their heating systems form dissipative systems, often resulting in a loss of energy (known colloquially as "Heat Bleed") that makes home interiors uncomfortably cool or cold. For the comfort of the inhabitants, the interiors must be maintained out of thermal equilibrium with the external surroundings. In effect, these domestic residences are islands of warmth in a sea of cold, and the thermal gradient between the inside and outside is often quite steep. This can lead to problems such as condensation and uncomfortable air currents, which—if left unaddressed—can cause cosmetic or structural damage to the property. Such issues can be prevented through the execution of an energy audit, and the implementation of recommended corrective procedures (such as the installation of adequate insulation, the air sealing of structural leaks, and the
  32. 32. Heat transfer 30 addition of energy-efficient windows and doors.[17] Thermal transmittance is the rate of transfer of heat through a structure divided by the difference in temperature across the structure. It is expressed in watts per square meter per kelvin, or W/m²K. Well-insulated parts of a building have a low thermal transmittance, whereas poorly-insulated parts of a building have a high thermal transmittance. A thermostat is a device capable of starting the heating system when the houses interior falls below a set temperature, and of stopping that same system when another (higher) set temperature has been achieved. Thus, the thermostat controls the flow of energy into the house, that energy eventually being dissipated to the exterior. Thermal energy storage Thermal energy storage refers to technologies that store energy in a thermal reservoir for later use. They can be employed to balance energy demand between daytime and nighttime. The thermal reservoir may be maintained at a temperature above (hotter) or below (colder) than that of the ambient environment. Applications include later use in space heating, domestic or process hot water, or to generate electricity. Most practical active solar heating systems have storage for a few hours to a days worth of heat collected. Evaporative cooling Evaporative cooling is a physical phenomenon in which evaporation of a liquid, typically into surrounding air, cools an object or a liquid in contact with it. Latent heat describes the amount of heat that is needed to evaporate the liquid; this heat comes from the liquid itself and the surrounding gas and surfaces. The greater the difference between the two temperatures, the greater the evaporative cooling effect. When the temperatures are the same, no net evaporation of water in air occurs; thus, there is no cooling effect. A simple example of natural evaporative cooling is perspiration, or sweat, which the body secretes in order to cool itself. An evaporative cooler is a device that cools air through the simple evaporation of water. Radiative cooling Radiative cooling is the process by which a body loses heat by radiation. It is an important effect in the Earths atmosphere. In the case of the Earth-atmosphere system, it refers to the process by which long-wave (infrared) radiation is emitted to balance the absorption of short-wave (visible) energy from the Sun. Convective transport of heat and evaporative transport of latent heat both remove heat from the surface and redistribute it in the atmosphere, making it available for radiative transport at higher altitudes. Laser cooling Laser cooling refers to techniques in which atomic and molecular samples are cooled through the interaction with one or more laser light fields. The most common method of laser cooling is Doppler cooling. In Doppler cooling, the frequency of the laser light is tuned slightly below an electronic transition in the atom. Thus, the atoms would absorb more photons if they moved towards the light source, due to the Doppler effect. If an excited atom then emits a photon spontaneously, it will be accelerated. The result of the absorption and emission process is to reduce the speed of the atom. Eventually the mean velocity, and therefore the kinetic energy of the atoms, will be reduced. Since the temperature of an ensemble of atoms is a measure of the random internal kinetic energy, this is equivalent to cooling the atoms. Sympathetic cooling is a process in which particles of one type cool particles of another type. Typically, atomic ions that can be directly laser-cooled are used to cool nearby ions or atoms. This technique allows cooling of ions and atoms that cannot be laser cooled directly.

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