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PRESENTATION GROUPS
THERMODYNAMICS PRESENSTATION GROUPS
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Sunday 16 April 2017
Wednesday 12 April 2017
LAB RESULTS AND SOME BASICS OF HEAT TRANSFER
Fundamentals of Heat Transfer
The following is a brief overview of some
fundamental heat transfer concepts. To learn more, the reader is encouraged to
review the source publications and Web sites.
1st and 2nd Laws of Thermodynamics
The 1st Law of Thermodynamics
involves the conservation of energy. It states that - within a closed system
where no other energy material can enter or leave - energy can neither be
created nor destroyed.1, 2 Although energy cannot be created or
destroyed, it can be transferred to work other forms of energy.
Transferring heat energy is subject to the 2nd Law
of Thermodynamics.3 The 2nd Law (again applying
to a closed system) says that - for a spontaneous process - there is a net
increase in entropy4 (i.e., a measure of the disorder that
exists in a system5).
Three alternate but equivalent ways to
describe the 2nd Law are:
1.
Heat flows
spontaneously from a hot body to a cool one. (Example: A hot
microprocessor or laser diode is cooled by flow of heat into heat sink or cold
plate.)
2.
It is impossible to
convert heat completely into useful work. (Example: In a combustion
engine, a certain heat component must always be exhausted without performing
work.)
3.
Every isolated system
becomes disordered in time. (Example: In conduction when hot and cold
bodies first contact each other, the system is somewhat ordered. Hotter
molecules move faster than cooler molecules. But, once the entire system
attains a uniform temperature, this order is lost.)
Expressed in mathematical terms, any of the above
statements imply the other two.6
The 1st and 2nd Laws
of Thermodynamics govern the various modes of heat transfer: conduction,
convection and radiation.
Modes of Heat Transfer
Conduction
In conduction, heat flows from a higher
temperature region to regions of lower temperature. This occurs within solid,
liquid, or gaseous mediums or between different mediums that make direct
physical contact with each other.7 "The transfer of the
energy of motion between adjacent molecules conducts the heat. In a gas, the
'hotter' molecules, have greater energy and motions, and impart energy to
adjacent molecules at lower energy levels. This type of transfer occurs to some
extent in all solids, gases or liquids in which a temperature gradient exists.
In conduction, energy can also be transferred by "free" electrons,
which is important in metallic solids." 8 Examples of
conduction are heat transfer through the surfaces of a cold plate or
through the walls of a refrigerator.
Convection
In convection, the combined action of heat
conduction, energy storage, and mixing motion serve to transport energy.
"Convection is most important as the mechanism of energy transfer between
a solid surface and a liquid or a gas." 9 "In
forced-convection heat transfer, a pump, fan, or other mechanism forces a fluid to flow past a solid
surface. In natural or free convection, warmer or cooler fluid next to the
solid surface causes a circulation because of density differences resulting
from the temperature differences in the fluid." 10 An
example of free convection is the loss of heat into ambient air via the fins of
a heat exchanger. If a fan is used to circulate the air over
the heat exchanger fins, this becomes an example of forced
convection.
Radiation
In radiation, heat flows from a higher
temperature body to a lower temperature body when the bodies are separated in
space, even across a vacuum. 11 "The same laws that
govern the transfer of light, also govern the transfer of heat. Solids and
liquids tend to absorb the radiation being transferred through it, hence
radiation is important mainly in transfer through space or gases."12
Examples of radiation include the transfer of
heat from the sun to the earth, and from a quartz lamp to a cool object that
requires warming.
Fourier's Equation
"The basic relation for heat transfer by
conduction, proposed by the French scientist J.B.J. Fourier in 1822, states:
The rate of heat flow by conduction in a
material, qk , equals the product of the following three quantities:
k
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thermal conductivity
of the material.
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A
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area of the section
through which heat flows by conduction as measured perpendicularly to the
direction of heat flow.
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dT/dx
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temperature gradient
at the section, i.e., the rate of change of temperature T with respect to the
difference in the direction of the heat flow x.
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Writing the heat conduction equation in
mathematical form requires a sign convention; i.e., the direction of increasing
distance x is the direction of positive heat flow. According to the second law
of thermodynamics, heat will automatically flow from points of higher
temperature to points of lower temperature. Thus, heat flow will be positive
when the temperature gradient is negative. The basic equation for
one-dimensional conduction in the steady state is: qk =
-kA (dT/dx)"13
Thermal Conductivity
Thermal conductivity is a measurement of the
rate at which a given material will transfer heat.14 "The
thermal conductivity of a substance is the quantity of heat in cal/sec passing
through a body 1 cm thick with a cross section of 1 sq. cm when the temperature
difference between the hot and cold sides of the body is 1 deg. C."15 This
intrinsic property is independent of the materials size, shape, or orientation.
Thermal Resistance
Thermal resistance is the inverse of thermal
conductivity and indicates how a material inhibits the conduction of
heat. 16 Materials with a high thermal conductivity have a
low thermal resistance and have poor heat insulation qualities (e.g., copper
and aluminum). Conversely, materials with a low thermal conductivity have a
high thermal resistance, and have good heat insulation qualities (e.g., fiberglass
insulation and corkboard).17
HISTORY OF CIVIL ENGINEERING
History of the civil engineering profession
See also: History of structural engineering
Engineering has been an aspect of life since the beginnings of human existence. The earliest practice of civil engineering may have commenced between 4000 and 2000 BC in ancient Egypt, the Indus Valley Civilization, and Mesopotamia (ancient Iraq) when humans started to abandon a nomadic existence, creating a need for the construction of shelter. During this time, transportation became increasingly important leading to the development of the wheel and sailing.
Until modern times there was no clear distinction between civil engineering and architecture, and the term engineer and architect were mainly geographical variations referring to the same occupation, and often used interchangeably.[6] The construction of pyramids in Egypt (circa 2700–2500 BC) were some of the first instances of large structure constructions. Other ancient historic civil engineering constructions include the Qanat water management system (the oldest is older than 3000 years and longer than 71 km,[7]) the Parthenon by Iktinos in Ancient Greece (447–438 BC), the Appian Way by Roman engineers (c. 312 BC), the Great Wall of China by General Meng T'ien under orders from Ch'in Emperor Shih Huang Ti (c. 220 BC)[8] and the stupas constructed in ancient Sri Lanka like the Jetavanaramaya and the extensive irrigation works in Anuradhapura. The Romans developed civil structures throughout their empire, including especially aqueducts, insulae, harbors, bridges, dams and roads.
In the 18th century, the term civil engineering was coined to incorporate all things civilian as opposed to military engineering.[5] The first self-proclaimed civil engineer was John Smeaton, who constructed the Eddystone Lighthouse.[4][8] In 1771 Smeaton and some of his colleagues formed the Smeatonian Society of Civil Engineers, a group of leaders of the profession who met informally over dinner. Though there was evidence of some technical meetings, it was little more than a social society.
In 1818 the Institution of Civil Engineers was founded in London, and in 1820 the eminent engineer Thomas Telford became its first president. The institution received a Royal Charter in 1828, formally recognising civil engineering as a profession. Its charter defined civil engineering as:
History of civil engineering education[edit]
The first private college to teach civil engineering in the United States was Norwich University, founded in 1819 by Captain Alden Partridge.[10] The first degree in civil engineering in the United States was awarded by Rensselaer Polytechnic Institute in 1835.[11][12] The first such degree to be awarded to a woman was granted by Cornell University to Nora Stanton Blatch in 1905.[13]
In the UK during the early 19th century, the division between civil engineering and military engineering (served by the Royal Military Academy, Woolwich), coupled with the demands of the Industrial Revolution, spawned new engineering education initiatives: the Royal Polytechnic Institution was founded in 1838, the private College for Civil Engineers in Putney was established in 1839, and the UK's first Chair of Engineering was established at the University of Glasgow in 1840.
History of civil engineering[edit]
Civil engineering is the application of physical and scientific principles for solving the problems of society, and its history is intricately linked to advances in understanding of physics and mathematics throughout history. Because civil engineering is a wide-ranging profession, including several specialized sub-disciplines, its history is linked to knowledge of structures, materials science, geography, geology, soils, hydrology, environment, mechanics and other fields.
Throughout ancient and medieval history most architectural design and construction was carried out by artisans, such as stonemasons and carpenters, rising to the role of master builder. Knowledge was retained in guilds and seldom supplanted by advances. Structures, roads and infrastructure that existed were repetitive, and increases in scale were incremental.[14]
One of the earliest examples of a scientific approach to physical and mathematical problems applicable to civil engineering is the work of Archimedes in the 3rd century BC, including Archimedes Principle, which underpins our understanding of buoyancy, and practical solutions such as Archimedes' screw. Brahmagupta, an Indian mathematician, used arithmetic in the 7th century AD, based on Hindu-Arabic numerals, for excavation (volume) computations.[15]
The civil engineer[edit]
Education and licensure[edit]
Main article: Civil engineer
Civil engineers typically possess an academic degree in civil engineering. The length of study is three to five years, and the completed degree is designated as a bachelor of engineering, or a bachelor of science in engineering. The curriculum generally includes classes in physics, mathematics, project management, design and specific topics in civil engineering. After taking basic courses in most sub-disciplines of civil engineering, they move onto specialize in one or more sub-disciplines at advanced levels. While an undergraduate degree (BEng/BSc) normally provides successful students with industry-accredited qualification, some academic institutions offer post-graduate degrees (MEng/MSc), which allow students to further specialize in their particular area of interest.[16]
In most countries, a bachelor's degree in engineering represents the first step towards professional certification, and a professional body certifies the degree program. After completing a certified degree program, the engineer must satisfy a range of requirements (including work experience and exam requirements) before being certified. Once certified, the engineer is designated as a professional engineer (in the United States, Canada and South Africa), a chartered engineer (in most Commonwealth countries), a chartered professional engineer (in Australia and New Zealand), or a European engineer (in most countries of the European Union). There are international agreements between relevant professional bodies to allow engineers to practice across national borders.
The benefits of certification vary depending upon location. For example, in the United States and Canada, "only a licensed professional engineer may prepare, sign and seal, and submit engineering plans and drawings to a public authority for approval, or seal engineering work for public and private clients."[17] This requirement is enforced under provincial law such as the Engineers Act in Quebec.[18]
No such legislation has been enacted in other countries including the United Kingdom. In Australia, state licensing of engineers is limited to the state of Queensland. Almost all certifying bodies maintain a code of ethics which all members must abide by.[19]
Engineers must obey contract law in their contractual relationships with other parties. In cases where an engineer's work fails, he may be subject to the law of tort of negligence, and in extreme cases, criminal charges.[20] An engineer's work must also comply with numerous other rules and regulations such as building codes and environmental law.
Sub-disciplines[edit]
In general, civil engineering is concerned with the overall interface of human created fixed projects with the greater world. General civil engineers work closely with surveyors and specialized civil engineers to design grading, drainage, pavement, water supply, sewer service, dams, electric and communications supply. General civil engineering is also referred to as site engineering, a branch of civil engineering that primarily focuses on converting a tract of land from one usage to another. Site engineers spend time visiting project sites, meeting with stakeholders, and preparing construction plans. Civil engineers apply the principles of geotechnical engineering, structural engineering, environmental engineering, transportation engineering and construction engineering to residential, commercial, industrial and public works projects of all sizes and levels of construction.
Materials science and engineering[edit]
Main article: Materials science
Materials science is closely related to civil engineering. It studies fundamental characteristics of materials, and deals with ceramics such as concrete and mix asphalt concrete, strong metals such as aluminum and steel, and thermosetting polymers including polymethylmethacrylate (PMMA) and carbon fibers.
Materials engineering involves protection and prevention (paints and finishes). Alloying combines two types of metals to produce another metal with desired properties. It incorporates elements of applied physics and chemistry. With recent media attention on nanoscience and nanotechnology, materials engineering has been at the forefront of academic research. It is also an important part of forensic engineering and failure analysis.
Coastal engineering[edit]
Main articles: Coastal engineering and Coastal management
Coastal engineering is concerned with managing coastal areas. In some jurisdictions, the terms sea defense and coastal protection mean defense against flooding and erosion, respectively. The term coastal defense is the more traditional term, but coastal management has become more popular as the field has expanded to techniques that allow erosion to claim land.
Construction engineering[edit]
Main article: Construction engineering
Construction engineering involves planning and execution, transportation of materials, site development based on hydraulic, environmental, structural and geotechnical engineering. As construction firms tend to have higher business risk than other types of civil engineering firms do, construction engineers often engage in more business-like transactions, for example, drafting and reviewing contracts, evaluating logistical operations, and monitoring prices of supplies.
Earthquake engineering[edit]
Main article: Earthquake engineering
Earthquake engineering involves designing structures to withstand hazardous earthquake exposures. Earthquake engineering is a sub-discipline of structural engineering. The main objectives of earthquake engineering are[21] to understand interaction of structures on the shaky ground; foresee the consequences of possible earthquakes; and design, construct and maintain structures to perform at earthquake in compliance with building codes.
Environmental engineering[edit]
Main article: Environmental engineering
Environmental engineering is the contemporary term for sanitary engineering, though sanitary engineering traditionally had not included much of the hazardous waste management and environmental remediation work covered by environmental engineering. Public health engineering and environmental health engineering are other terms being used.
Environmental engineering deals with treatment of chemical, biological, or thermal wastes, purification of water and air, and remediation of contaminated sites after waste disposal or accidental contamination. Among the topics covered by environmental engineering are pollutant transport, water purification, waste water treatment, air pollution, solid waste treatment, and hazardous waste management. Environmental engineers administer pollution reduction, green engineering, and industrial ecology. Environmental engineers also compile information on environmental consequences of proposed actions.
Geotechnical engineering[edit]
Main article: Geotechnical engineering
Geotechnical engineering studies rock and soil supporting civil engineering systems. Knowledge from the field of soil science, materials science, mechanics, and hydraulics is applied to safely and economically design foundations, retaining walls, and other structures. Environmental efforts to protect groundwater and safely maintain landfills have spawned a new area of research called geoenvironmental engineering.[22][23]
Identification of soil properties presents challenges to geotechnical engineers. Boundary conditions are often well defined in other branches of civil engineering, but unlike steel or concrete, the material properties and behavior of soil are difficult to predict due to its variability and limitation on investigation. Furthermore, soil exhibits nonlinear (stress-dependent) strength, stiffness, and dilatancy (volume change associated with application of shear stress), making studying soil mechanics all the more difficult.[22]
Water resources engineering[edit]
See also: Hydraulic engineering and Hydrology
Water resources engineering is concerned with the collection and management of water (as a natural resource). As a discipline it therefore combines elements of hydrology, environmental science, meteorology, conservation, and resource management. This area of civil engineering relates to the prediction and management of both the quality and the quantity of water in both underground (aquifers) and above ground (lakes, rivers, and streams) resources. Water resource engineers analyze and model very small to very large areas of the earth to predict the amount and content of water as it flows into, through, or out of a facility. Although the actual design of the facility may be left to other engineers.
Hydraulic engineering is concerned with the flow and conveyance of fluids, principally water. This area of civil engineering is intimately related to the design of pipelines, water supply network, drainage facilities (including bridges, dams, channels, culverts, levees, storm sewers), and canals. Hydraulic engineers design these facilities using the concepts of fluid pressure, fluid statics, fluid dynamics, and hydraulics, among others.
Structural engineering[edit]
Main article: Structural engineering
Structural engineering is concerned with the structural design and structural analysis of buildings, bridges, towers, flyovers (overpasses), tunnels, off shore structures like oil and gas fields in the sea, aerostructure and other structures. This involves identifying the loads which act upon a structure and the forces and stresses which arise within that structure due to those loads, and then designing the structure to successfully support and resist those loads. The loads can be self weight of the structures, other dead load, live loads, moving (wheel) load, wind load, earthquake load, load from temperature change etc. The structural engineer must design structures to be safe for their users and to successfully fulfill the function they are designed for (to be serviceable). Due to the nature of some loading conditions, sub-disciplines within structural engineering have emerged, including wind engineering and earthquake engineering.[24]
Design considerations will include strength, stiffness, and stability of the structure when subjected to loads which may be static, such as furniture or self-weight, or dynamic, such as wind, seismic, crowd or vehicle loads, or transitory, such as temporary construction loads or impact. Other considerations include cost, constructability, safety, aesthetics and sustainability.
Surveying[edit]
Main articles: Surveying and Construction surveying
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Surveying is the process by which a surveyor measures certain dimensions that occur on or near the surface of the Earth. Surveying equipment, such as levels and theodolites, are used for accurate measurement of angular deviation, horizontal, vertical and slope distances. With computerisation, electronic distance measurement (EDM), total stations, GPS surveying and laser scanning have to a large extent supplanted traditional instruments. Data collected by survey measurement is converted into a graphical representation of the Earth's surface in the form of a map. This information is then used by civil engineers, contractors and realtors to design from, build on, and trade, respectively. Elements of a structure must be sized and positioned in relation to each other and to site boundaries and adjacent structures. Although surveying is a distinct profession with separate qualifications and licensing arrangements, civil engineers are trained in the basics of surveying and mapping, as well as geographic information systems. Surveyors also lay out the routes of railways, tramway tracks, highways, roads, pipelines and streets as well as position other infrastructure, such as harbors, before construction.
- Land surveying
In the United States, Canada, the United Kingdom and most Commonwealth countries land surveying is considered to be a separate and distinct profession. Land surveyors are not considered to be engineers, and have their own professional associations and licensing requirements. The services of a licensed land surveyor are generally required for boundary surveys (to establish the boundaries of a parcel using its legal description) and subdivision plans (a plot or map based on a survey of a parcel of land, with boundary lines drawn inside the larger parcel to indicate the creation of new boundary lines and roads), both of which are generally referred to as Cadastral surveying.
- Construction surveying
Construction surveying is generally performed by specialised technicians. Unlike land surveyors, the resulting plan does not have legal status. Construction surveyors perform the following tasks:
- Surveying existing conditions of the future work site, including topography, existing buildings and infrastructure, and underground infrastructure when possible;
- "lay-out" or "setting-out": placing reference points and markers that will guide the construction of new structures such as roads or buildings;
- Verifying the location of structures during construction;
- As-Built surveying: a survey conducted at the end of the construction project to verify that the work authorized was completed to the specifications set on plans.
Transportation engineering[edit]
Main article: Transportation engineering
Transportation engineering is concerned with moving people and goods efficiently, safely, and in a manner conducive to a vibrant community. This involves specifying, designing, constructing, and maintaining transportation infrastructure which includes streets, canals, highways, rail systems, airports, ports, and mass transit. It includes areas such as transportation design, transportation planning, traffic engineering, some aspects of urban engineering, queueing theory, pavement engineering, Intelligent Transportation System (ITS), and infrastructure management.
Forensic engineering[edit]
Main article: Forensic engineering
Forensic engineering is the investigation of materials, products, structures or components that fail or do not operate or function as intended, causing personal injury or damage to property. The consequences of failure are dealt with by the law of product liability. The field also deals with retracing processes and procedures leading to accidents in operation of vehicles or machinery. The subject is applied most commonly in civil law cases, although it may be of use in criminal law cases. Generally the purpose of a Forensic engineering investigation is to locate cause or causes of failure with a view to improve performance or life of a component, or to assist a court in determining the facts of an accident. It can also involve investigation of intellectual property claims, especially patents.
Municipal or urban engineering[edit]
Main article: Urban engineering
Municipal engineering is concerned with municipal infrastructure. This involves specifying, designing, constructing, and maintaining streets, sidewalks, water supply networks, sewers, street lighting, municipal solid waste management and disposal, storage depots for various bulk materials used for maintenance and public works (salt, sand, etc.), public parks and cycling infrastructure. In the case of underground utility networks, it may also include the civil portion (conduits and access chambers) of the local distribution networks of electrical and telecommunications services. It can also include the optimizing of waste collection and bus service networks. Some of these disciplines overlap with other civil engineering specialties, however municipal engineering focuses on the coordination of these infrastructure networks and services, as they are often built simultaneously, and managed by the same municipal authority. Municipal engineers may also design the site civil works for large buildings, industrial plants or campuses (i.e. access roads, parking lots, potable water supply, treatment or pretreatment of waste water, site drainage, etc.)
Control engineering[edit]
Main article: Control engineering
Control engineering (or control systems engineering) is the branch of civil engineering discipline that applies control theory to design systems with desired behaviors. The practice uses sensors to measure the output performance of the device being controlled (often a vehicle) and those measurements can be used to give feedback to the input actuators that can make corrections toward desired performance. When a device is designed to perform without the need of human inputs for correction it is called automatic control (such as cruise control for regulating a car's speed). Multidisciplinary in nature, control systems engineering activities focus on implementation of control systems mainly derived by mathematical modeling of systems of a diverse range.
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