Valve

A valve is a device that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure.

The simplest, and very ancient, valve is simply a freely hinged flap which drops to obstruct fluid (gas or liquid) flow in one direction, but is pushed open by flow in the opposite direction.

Valves are used in a variety of contexts, including industrial, military, commercial, residential, and transport. The industries in which the majority of valves are used are oil and gas, power generation, mining, water reticulation, sewage and chemical manufacturing.[citation needed]

In daily life, most noticeable are plumbing valves, such as taps for tap water. Other familiar examples include gas control valves on cookers, small valves fitted to washing machines and dishwashers, safety devices fitted to hot water systems, and valves in car engines. In nature, veins acting as valves are controlling the blood circulation; heart valves control the flow of blood in the chambers of the heart and maintain the correct pumping action.

Valves play a vital role in industrial applications ranging from transportation of drinking water to control of ignition in a rocket engine.

Valves may be operated manually, either by a handle, lever or pedal. Valves may also be automatic, driven by changes in pressure, temperature, or flow. These changes may act upon a diaphragm or a piston which in turn activates the valve, examples of this type of valve found commonly are safety valves fitted to hot water systems or boilers.

More complex control systems using valves requiring automatic control based on an external input (i.e., regulating flow through a pipe to a changing set point) require an actuator. An actuator will stroke the valve depending on its input and set-up, allowing the valve to be positioned accurately, and allowing control over a variety of requirements.

Types Of Heat Exchanger

Shell And Tube Heat Exchanger
Shell and tube heat exchangers consist of a series of tubes. One set of these tubes contains the fluid that must be either heated or cooled. The second fluid runs over the tubes that are being heated or cooled so that it can either provide the heat or absorb the heat required. A set of tubes is called the tube bundle and can be made up of several types of tubes: plain, longitudinally finned, etc. Shell and tube heat exchangers are typically used for high-pressure applications (with pressures greater than 30 bar and temperatures greater than 260 °C).[2] This is because the shell and tube heat exchangers are robust due to their shape.
There are several thermal design features that are to be taken into account when designing the tubes in the shell and tube heat exchangers. These include:
Tube diameter: Using a small tube diameter makes the heat exchanger both economical and compact. However, it is more likely for the heat exchanger to foul up faster and the small size makes mechanical cleaning of the fouling difficult. To prevail over the fouling and cleaning problems, larger tube diameters can be used. Thus to determine the tube diameter, the available space, cost and the fouling nature of the fluids must be considered.
Tube thickness: The thickness of the wall of the tubes is usually determined to ensure:
There is enough room for corrosion
That flow-induced vibration has resistance
Axial strength
Availability of spare parts
Hoop strength (to withstand internal tube pressure)
Buckling strength (to withstand overpressure in the shell)
Tube length: heat exchangers are usually cheaper when they have a smaller shell diameter and a long tube length. Thus, typically there is an aim to make the heat exchanger as long as physically possible whilst not exceeding production capabilities. However, there are many limitations for this, including the space available at the site where it is going to be used and the need to ensure that there are tubes available in lengths that are twice the required length (so that the tubes can be withdrawn and replaced). Also, it has to be remembered that long, thin tubes are difficult to take out and replace.
Tube pitch: when designing the tubes, it is practical to ensure that the tube pitch (i.e., the centre-centre distance of adjoining tubes) is not less than 1.25 times the tubes' outside diameter. A larger tube pitch leads to a larger overall shell diameter which leads to a more expensive heat exchanger.
Tube corrugation: this type of tubes, mainly used for the inner tubes, increases the turbulence of the fluids and the effect is very important in the heat transfer giving a better performance.
Tube Layout: refers to how tubes are positioned within the shell. There are four main types of tube layout, which are, triangular (30°), rotated triangular (60°), square (90°) and rotated square (45°). The triangular patterns are employed to give greater heat transfer as they force the fluid to flow in a more turbulent fashion around the piping. Square patterns are employed where high fouling is experienced and cleaning is more regular.
Baffle Design: baffles are used in shell and tube heat exchangers to direct fluid across the tube bundle. They run perpendicularly to the shell and hold the bundle, preventing the tubes from sagging over a long length. They can also prevent the tubes from vibrating. The most common type of baffle is the segmental baffle. The semicircular segmental baffles are oriented at 180 degrees to the adjacent baffles forcing the fluid to flow upward and downwards between the tube bundle. Baffle spacing is of large thermodynamic concern when designing shell and tube heat exchangers. Baffles must be spaced with consideration for the conversion of pressure drop and heat transfer. For thermo economic optimization it is suggested that the baffles be spaced no closer than 20% of the shell’s inner diameter. Having baffles spaced too closely causes a greater pressure drop because of flow redirection. Consequently having the baffles spaced too far apart means that there may be cooler spots in the corners between baffles. It is also important to ensure the baffles are spaced close enough that the tubes do not sag. The other main type of baffle is the disc and donut baffle which consists of two concentric baffles, the outer wider baffle looks like a donut, whilst the inner baffle is shaped as a disk. This type of baffle forces the fluid to pass around each side of the disk then through the donut baffle generating a different type of fluid flow.

Conceptual diagram of a plate and frame heat exchanger.

A single plate heat exchanger

An interchangeable plate heat exchanger applied to the system of a swimming pool

Plate heat exchanger

Another type of heat exchanger is the plate heat exchanger. One is composed of multiple, thin, slightly separated plates that have very large surface areas and fluid flow passages for heat transfer. This stacked-plate arrangement can be more effective, in a given space, than the shell and tube heat exchanger. Advances in gasket and brazing technology have made the plate-type heat exchanger increasingly practical. In HVAC applications, large heat exchangers of this type are called plate-and-frame; when used in open loops, these heat exchangers are normally of the gasket type to allow periodic disassembly, cleaning, and inspection. There are many types of permanently bonded plate heat exchangers, such as dip-brazed and vacuum-brazed plate varieties, and they are often specified for closed-loop applications such as refrigeration. Plate heat exchangers also differ in the types of plates that are used, and in the configurations of those plates. Some plates may be stamped with "chevron" or other patterns, where others may have machined fins and/or grooves.

Plate & shell heat exchanger

A third type of heat exchanger is plate & shell heat exchanger which combines plate heat exchanger and shell & tube heat exchanger technologies. In the heart of the heat exchanger there are a fully welded circular plate pack which is made by pressing and cutting round plates and welding them together. Nozzles are added which carry flow in and out of the platepack (the 'Plate side' flowpath).The fully welded platepack is assembled into an outer shell which creates a second flowpath ( the 'Shell side'). Plate and shell technology offers high heat transfer, high pressure, high operating temperature, compact size, low fouling and close approach temperature. In particular, it does completely without gaskets, which provides security against leakage at high pressures and temperatures.

Adiabatic wheel heat exchanger

A fourth type of heat exchanger uses an intermediate fluid or solid store to hold heat, which is then moved to the other side of the heat exchanger to be released. Two examples of this are adiabatic wheels, which consist of a large wheel with fine threads rotating through the hot and cold fluids, and fluid heat exchangers.

Plate fin heat exchanger

This type of heat exchanger uses "sandwiched" passages containing fins to increase the effectivity of the unit. The designs include crossflow and counterflow coupled with various fin configurations such as straight fins, offset fins and wavy fins.

Plate and fin heat exchangers are usually made of aluminium alloys which provide higher heat transfer efficiency. The material enables the system to operate at a lower temperature and reduce the weight of the equipment. Plate and fin heat exchangers are mostly used for low temperature services such as natural gas, helium and oxygen liquefaction plants, air separation plants and transport industries such as motor and aircraft engines.

Advantages of plate and fin heat exchangers:
High heat transfer efficiency especially in gas treatment
Larger heat transfer area
Approximately 5 times lighter in weight than that of shell and tube heat exchanger.
Able to withstand high pressure

Disadvantages of plate and fin heat exchangers:
Might cause clogging as the pathways are very narrow
Difficult to clean the pathways
Aluminum alloys are susceptible to Mercury Liquid Embrittlement Failure

Pillow plate heat exchanger

A pillow plate exchanger is commonly used in the dairy industry for cooling milk in large direct-expansion stainless steel bulk tanks. The pillow plate allows for cooling across nearly the entire surface area of the tank, without gaps that would occur between pipes welded to the exterior of the tank.

The pillow plate is constructed using a thin sheet of metal spot-welded to the surface of another thicker sheet of metal. The thin plate is welded in a regular pattern of dots or with a serpentine pattern of weld lines. After welding the enclosed space is pressurized with sufficient force to cause the thin metal to bulge out around the welds, providing a space for heat exchanger liquids to flow, and creating a characteristic appearance of a swelled pillow formed out of metal.

Fluid heat exchangers

This is a heat exchanger with a gas passing upwards through a shower of fluid (often water), and the fluid is then taken elsewhere before being cooled. This is commonly used for cooling gases whilst also removing certain impurities, thus solving two problems at once. It is widely used in espresso machines as an energy-saving method of cooling super-heated water to be used in the extraction of espresso.

Waste heat recovery units

A Waste Heat Recovery Unit (WHRU) is a heat exchanger that recovers heat from a hot gas stream while transferring it to a working medium, typically water or oils. The hot gas stream can be the exhaust gas from a gas turbine or a diesel engine or a waste gas from industry or refinery.

Dynamic scraped surface heat exchanger

Another type of heat exchanger is called "(dynamic) scraped surface heat exchanger". This is mainly used for heating or cooling with high-viscosity products, crystallization processes, evaporation and high-fouling applications. Long running times are achieved due to the continuous scraping of the surface, thus avoiding fouling and achieving a sustainable heat transfer rate during the process.

Phase-change heat exchangers

Typical kettle reboiler used for industrial distillation towers

Typical water-cooled surface condenser

In addition to heating up or cooling down fluids in just a single phase, heat exchangers can be used either to heat a liquid to evaporate (or boil) it or used as condensers to cool a vapor and condense it to a liquid. In chemical plants and refineries, reboilers used to heat incoming feed for distillation towers are often heat exchangers.

Distillation set-ups typically use condensers to condense distillate vapors back into liquid.

Power plants which have steam-driven turbines commonly use heat exchangers to boil water into steam. Heat exchangers or similar units for producing steam from water are often called boilers or steam generators.

In the nuclear power plants called pressurized water reactors, special large heat exchangers which pass heat from the primary (reactor plant) system to the secondary (steam plant) system, producing steam from water in the process, are called steam generators. All fossil-fueled and nuclear power plants using steam-driven turbines have surface condensers to convert the exhaust steam from the turbines into condensate (water) for re-use.

To conserve energy and cooling capacity in chemical and other plants, regenerative heat exchangers can be used to transfer heat from one stream that needs to be cooled to another stream that needs to be heated, such as distillate cooling and reboiler feed pre-heating.

This term can also refer to heat exchangers that contain a material within their structure that has a change of phase. This is usually a solid to liquid phase due to the small volume difference between these states. This change of phase effectively acts as a buffer because it occurs at a constant temperature but still allows for the heat exchanger to accept additional heat. One example where this has been investigated is for use in high power aircraft electronics.

Direct contact heat exchangers

Direct contact heat exchangers involve heat transfer between hot and cold streams of two phases in the absence of a separating wall. Thus such heat exchangers can be classified as:
Gas – liquid
Immiscible liquid – liquid
Solid-liquid or solid – gas

Most direct contact heat exchangers fall under the Gas- Liquid category, where heat is transferred between a gas and liquid in the form of drops, films or sprays. [2]

Such types of heat exchangers are used predominantly in air conditioning, humidification, industrial hot water heating, water cooling and condensing plants.[

Heat Exchanger

A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, natural gas processing, and sewage treatment. The classic example of a heat exchanger is found in an internal combustion engine in which a circulating fluid known as engine coolant flows through radiator coils and air flows past the coils, which cools the coolant and heats the incoming air.

Arfa Karim

February 1995 – 14 January 2012), was a Pakistani student and computer prodigy, who in 2004 at the age of nine years became the youngest Microsoft Certified Professional (MCP) in the world, a title she kept until 2008. She was invited by Bill Gates to visit the Microsoft Headquarters in USA. A Science park in Lahore was named after her as Arfa Karim Technology Park.
Early life
Arfa was born in a family that hailed from the village of Chak No. 4JB Ram Dewali in Faisalabad, Punjab. After returning to Pakistan from a visit to Microsoft headquarters, Arfa had numerous interviews with television and newspapers. S. Somasegar, the vice president of the Software Development Division, wrote about her in his blog. On 2 August 2005, Arfa Karim was presented the Fatimah Jinnah Gold Medal in the field of Science and Technology by the then Prime Minister of Pakistan Shaukat Aziz on the occasion of 113th birth anniversary of Fatima Jinnah. She also received the Salaam Pakistan Youth Award again in August 2005 by the President of Pakistan. Arfa Karim is also the recipient of the President's Award for Pride of Performance, a civil award granted to people who have shown excellence in their respective fields over a long period of time. She is the youngest recipient of this award. In recognition of her achievement Arfa was made brand ambassador for Pakistan Telecommunication Company's 3G Wireless Broadband service named EVO in January 2010.
Representation at international forums
Arfa Karim has also represented Pakistan on various international forums, she was invited by the Pakistan Information Technology Professionals Forum for a stay of two weeks in Dubai. A dinner reception was hosted for her there, which was attended by the dignitaries of Dubai including the Ambassador of Pakistan. During that trip, Arfa was presented with various awards and gifts including a laptop. During the same tour she also flew a plane in a flying club at the age of 10 and received the first flight certificate. In November 2006, Arfa attended the Tech-Ed Developers conference themed Get ahead of the game held in Barcelona on an invitation from Microsoft. She was the only Pakistani among over 5000 developers in that conference.
Cardiac arrest
In 2011, at the age of 16, Arfa Karim was studying at the Lahore Grammar School Paragon Campus in her second year of A Levels. She suffered a cardiac arrest after an epileptic seizure which damaged her brain on 22 December 2011, and was admitted to Lahore's Combined Military Hospital (CMH) in critical condition.
Offer by Bill Gates
On 9 January 2012, Bill Gates, Chairman of Microsoft, made contact with Arfa's parents, and directed his doctors to adopt "every kind of measure" for her treatment. Gates set up a special panel of international doctors who remained in contact with her local doctors through teleconference. The panel received details about her illness and provided assistance in diagnosis and treatment. Local doctors dismissed the option of Arfa being moved to another hospital due to her being on a ventilator and in critical condition. Relatives and family members of Arfa have lauded Bill Gates for offering to bear her treatment expenses.
Signs of improvement
On 13 January 2012, Arfa Karim started to improve and some parts of her brain showed signs of improvement. Her father, Amjad Karim Randhawa, said Microsoft had raised the possibility of flying Arfa to the US for care.
Death
On 14 January 2012, 16-year-old Arfa Karim died at 9:50 PM (Pakistan Standard Time) at Combined Military Hospital (CMH) Lahore. Her Namaz-e-Janaza was offered in Cavalry Ground Lahore at 10 AM on 15 January 2012, and later at Faisalabad the same day. The funeral was attended by Chief Minister of Punjab Shahbaz Sharif. She was buried at her ancestral village Chak No. 4JB Ram Dewali, Faisalabad.
Arfa Software Technology Park
On 15 January 2012, Chief Minister Shahbaz Sharif announced that the name of Lahore Technology Park would be changed to Arfa Software Technology Park.

Bharat Ratna

Bharat Ratna , translates to Jewel of India or Gem of India in English) is the Republic of India's highest civilian award, awarded for the highest degrees of national service. This service includes artistic, literary, and scientific achievements, as well as "recognition of public service of the highest order.         In 2011, the Minister for Home Affairs and Prime Minister of India agreed to change the eligibility criteria to allow sportspersons to receive the award.

The holders of the Bharat Ratna rank 7th in the Indian order of precedence; however, unlike knights they do not carry any special title nor any other honorifics.
History
The order was established by Rajendra Prasad, President of India, on 2 January 1954. The original statutes of January 1954 did not make allowance for posthumous awards (and this perhaps explains why the decoration was never awarded to Mahatma Gandhi), though this provision was added in the January 1955 statute. Subsequently, there have been twelve posthumous awards, including the award to Subhash Chandra Bose in 1992, which was later withdrawn due to a legal technicality, the only case of an award being withdrawn. The award was briefly suspended from 13 July 1977 to 26 January 1980.

While there was no formal provision that recipients of the Bharat Ratna should be Indian citizens, this seems to have been the general assumption.[citation needed] Of the 41 awards so far, there has been one award to a naturalised Indian citizen, Mother Teresa (1980), and to two non-Indians, Khan Abdul Ghaffar Khan (1987) and Nelson Mandela (1990). The awarding of this honour has frequently been the subject of litigation questioning the constitutional basis of such.

Originally, the specifications for the award called for a circular gold medal carrying the state emblem and motto, among other things. It is uncertain if a design in accordance with the original specifications was ever made. The actual award is designed in the shape of a peepul leaf and carries with the words "Bharat Ratna", inscribed in Devanagari script. The reverse side of the medal carries the state emblem and motto. The award is attached to a 2-inch-wide (51 mm) ribbon, and was designed to be worn around the recipient's neck.

Abraham Lincoin Ghost

There have been several stories about ghosts of former Presidents revisiting the White House. However, the most common and popular is that of Abraham Lincoln. Lincoln's Ghost, or to others as The White House Ghost, is said to have haunted the White House since his death. It is widely believed that when he was president, Lincoln might have known of his assassination before he died

The dream

Lincoln had a dream on April 14, 1865, the day that he was assassinated by John Wilkes Booth. As he told his Cabinet that day:

"In the dream, I was awakened by a faint moaning coming from somewhere nearby. I stood, and began hunting the noise, finally finding my way to the east room, where men and women were shrouded in funeral shawls. I saw a coffin on a dais, and soldiers at either end. A captain stood nearby, and I addressed him 'Who is dead in the White House' say I. 'The President,' is his answer, 'he was killed by an assassin.' In the coffin was a corpse in funeral vestments, but the face was obscured."

Sightings

Lyndon B. Johnson is supposed to have spoken with the ghost of Mr. Lincoln. Johnson, standing in the second floor room that had been Lincoln's office (Lincoln had used the Oval Office as a library), asked "You had a war, you had a Civil Rights movement, you had protesters and critics, what can I do?" And the story goes, the response was "Don't go to the theater." This story is a humorous yarn originated by an anonymous humorist on the staff of Bob Hope.

Lincoln's ghost can see the future, according to some witnesses, mainly White House Press Secretary Marlin Fitzwater in 1990.

In an unkind variant of the story, Lincoln advises his successor that he should go to the theater. The unfriendly variant has been told of many subsequent presidents

Abraham Lincoin Bedroom

Young Willie Lincoln (age 11) died in the White House in the bed now in the Lincoln Bedroom at about 5:00 P.M. on February 20, 1862. Both Theodore Roosevelt and Dwight D. Eisenhower claimed they felt the powerful presence of Abraham Lincoln in this room. Eleanor Roosevelt said, "Sometimes when I worked at my desk late at night I'd get a feeling that someone was standing behind me. I'd have to turn around and look." Rumors were that Winston Churchill had a Lincoln sighting in the room. Amy Carter, during sleepovers with her friends, waited up at night for the ghost of Mr. Lincoln to appear. Once the girls tried to get in touch with him with a Ouija board to no avail. Ronald Reagan's dog would bark outside the room but never enter. Maureen Reagan said she saw mysterious apparitions there. Actor Richard Dreyfess reported having scary dreams about a portrait of Mr. Lincoln that hangs in the room. "A high percentage of people who work here won't go in the Lincoln Bedroom," said President Bill Clinton's White House social secretary, Capricia Marshall. White House maids and butlers have sworn they had seen Lincoln’s ghost.

The Lincoln Bedroom was in the news during Bill Clinton's term because of its use as a bedroom for White House guests. But it wasn't always used as a bedroom. When Abraham Lincoln was president, it was used as his personal office and Cabinet room. (It was used in this manner by all presidents between 1830 and 1902.) During the Lincoln presidency, the walls were covered with Civil War maps. It had dark green wallpaper, and the carpeting was also dark green. Newspapers were stacked on the desk and tables along with large amounts of mail and requests from office seekers. Two large wicker wastebaskets were filled with debris. Mr. Lincoln signed the Emancipation Proclamation in this room on January 1, 1863.
In 1902 the room became a bedroom when all the second floor offices were moved to the West Wing during the Roosevelt renovation. It was named the Lincoln Bedroom in 1945 when President and Mrs. Truman moved in the bed and other furniture. Mary Todd Lincoln purchased the large bed, measuring eight feet long by six feet wide, in 1861 as part of her refurbishing of the White House. (The photograph of the bed is from the Meserve-Kunhardt Collection.) It was a part of a set of furniture she purchased for the Prince of Wales Room (besides the bed which had purple-and-gold satin curtains, the set included matching draperies, a marble-topped table, and six chairs). Several presidents used the bed including Theodore Roosevelt and Woodrow Wilson. Never used by Abraham Lincoln himself, it is made of carved rosewood. The original mattress was made of horsehair. Barbara Bush replaced the mattress, but guests still report it's lumpy.

Many of the Victorian pieces in the bedroom were placed there by the Trumans when the Brussels carpet and the Lincoln bed were installed in 1945. The chandelier, which was acquired in 1972, resembles the one hanging there when Lincoln was president. The sofa and matching chairs, a gift to the White House in 1954, are believed to have been there during Lincoln's presidency. One of the chairs in the room, upholstered in antique yellow-and-green Morris velvet, was sold after Lincoln's assassination but was returned to the White House as a gift in 1961. The rocking chair near the window is similar to the one Lincoln was sitting in when he was shot by John Wilkes Booth.


Along the west wall are four chairs used by Lincoln's Cabinet members. They are believed to have been purchased for the White House when James Polk was president. To the left of the fireplace is a desk that Lincoln used at the Soldiers' Home (where he often stayed to escape the heat of Washington's summers).


President Lincoln's Cottage at the Soldiers' Home
On this desk is a copy of the Gettysburg Address that is signed, dated, and titled by Abraham Lincoln. Lincoln originally gave this copy to Colonel Alexander Bliss.

To the left of the bed is a portrait of Andrew Jackson that was a favorite of Lincoln's. The portrait of Mary Todd Lincoln, hanging to the right of the bed, was given to the White House by Mrs. Robert Todd Lincoln. It was painted from photographs by Katherine Helm, daughter of Mary Todd's half-sister, Emily Todd Helm. To the right of the mantel is an engraving of Francis B. Carpenter's 1864 painting titled First Reading of the Emancipation Proclamation before Lincoln's Cabinet.

Hanging above the desk is an 1865 lithograph titled Abraham Lincoln's Last Reception. It depicts Mr. and Mrs. Lincoln greeting guests, including Cabinet members, in the East Room. On the north wall hangs a portrait of Lincoln by Stephen Arnold Douglas Volk based on a bust his father (Leonard Volk) had done from real life. Other objects associated with Lincoln, including books he read, have also been placed about the room.
** Mrs. John F. Kennedy

Thank you to Sarah Norton Ramberg for creating the idea for this page. Sources used: The White House: An Historic Guide by the White House Historical Association in cooperation with The National Geographic Society; How the White House Works by George Sullivan; Lincoln in American Memory by Merrill D. Peterson; The White House: Cornerstone of a Nation by Judith St. George; The White House by Patricia Ryon Quiri; and the March 17th, 1997, issue of People Weekly.

Although the bed was not actually used by President Lincoln, the late author Dr. Merrill D. Peterson wrote on p. 324 of Lincoln in American Memory: “When President Truman told his aged mother, an unreconstructed Confederate, that she would sleep in Lincoln’s bed when visiting him in the capital, she told him in no uncertain terms that she would sleep on the floor instead.”

Diesel Cycle - Ideal Cycle for Compression-ignition Engines

Isentropic Compression (1-2) Click to View Movie (25.0 kB)		The only difference between ideal Otto cycle and ideal Diesel cycle is the heat addition process. Instead of constant volume heat addition process in SI engine, heat is added to the air in the Diesel engine at constant pressure. The four processes are: 1-2 Isentropic compression 2-3 Constant pressure heat addition 3-4 Isentropic expansion 4-1 Constant volume heat rejection
Constant Pressure Heat Addition (2-3) Click to View Movie (45 kB) Isentropic Expansion (3-4) Click to View Movie (29 kB) Constant Volume Heat Rejection (4-1) Click to View Movie (35 kB)		Noting that the ideal Diesel cycle is executed in a closed system and the working fluid is air according to the air-standard assumption. Also, changes in kinetic and potential energies are negligible. No heat transfer is involved in the two isentropic processes. The energy balances for these two processes are:       -w12 = u2 - u1       -w34 = u4 - u3 w12 is negative since work is needed to compress the air in the cylinder and w34 is positive since air does work to the surroundings during its expansion. In the constant pressure heat addition process, air is expanded to keep the pressure as constant during the heat addition. The expansion work equals       w23 = P2(v3 - v2) The energy balances for this process is:       q23 = u3 - u2 + w23 = h3 - h2 In the constant volume heat rejection process, no work interaction is involved since no volume change occurs. The energy balances for this process is:           q41 = u1 - u4 q23 is positive since heat is added to the air and q41 is negative since heat is rejected to the surroundings during this process. For the whole cycle, the energy balance can be determined by adding the energy balance of its four processes. That is,       q23 + q41 - w12 - w34 = 0
		The thermal efficiency of an ideal Otto cycle is       ηth,Diesel = wnet/qin According to the analysis above, the net work output is       wnet = w34 + w12 = q23 + q41       qin = q23       ηth, Diesel = 1+ q41/q23 Under the cold air-standard assumption, the thermal efficiency of an ideal Diesel cycle is
		In order to simplify the above equation, the cutoff ratio rc is defined as rc = v3/v2 Process 1-2 and process 3-4 are isentropic. Thus,        The thermal efficiency relation reduces to

Thermodynamics(Auto cycle, Diesel cycle,Brayton cycle,Gay-Lussac's Law,Efficiency of Heat Engine formulas)

Thermodynamics is a branch of physics which deals with the energy and work of a system. It was born in the 19th century as scientists were first discovering how to build and operate steam engines. Thermodynamics deals only with the large scale response of a system which we can observe and measure in experiments. As aerodynamicists, we are most interested in the thermodynamics of propulsion systems and high speed flows. On this page we consider the thermodynamics of a four-stroke internal combustion engine. Today, most general aviation or private airplanes are powered by internal combustion (IC) engines, much like the engine in your family automobile.
There are two main parts to engine operation: the mechanical operation of the engine parts, and the thermodynamics through which the engine produces work and power. On this page we discuss the basic thermodynamic equations that allow you to design and predict engine performance.
In an internal combustion engine, fuel and air are ignited inside a cylinder. The hot exhaust pushes a piston which is connected to a crankshaft to produce power. The burning of fuel is not a continuous process, but occurs very quickly at regular time intervals. Between ignitions, the engine parts move in a repeated sequence called a cycle. The engine is called a four stroke engine because there are four movements, or strokes, of the piston during one cycle.
On the figure we show a plot of pressure versus gas volume throughout one cycle. We have broken the cycle into six numbered stages based on the mechanical operation of the engine. For the ideal four stroke engine, the intake stroke (1-2) and exhaust stroke (6-1) are done at constant pressure and do not contribute to the generation of power by the engine. During the compression stroke (2-3), work is done on the gas by the piston. If we assume that no heat enters the gas during the compression, we know the relations between the change in volume and the change in pressure and temperature from our solutions of the entropy equation for a gas. We call the ratio of the volume at the beginning of compression to the volume at the end of compression the compression ratio, r. Then
p3 / p2 = r ^ gamma
T3 / T2 = r ^ (gamma - 1)
where p is the pressure, T is the temperature, and gamma is the ratio of specific heats. During the combustion process (3-4), the volume is held constant and heat is released. The change in temperature is given by
T4 = T3 + f * Q /cv
where Q is the heat released per pound of fuel which depends on the fuel,f is the fuel/air ratio for combustion which depends on several factors associated with the design and temperature in the combustion chamber, and cv is the specific heat at constant volume. From the equation of state, we know that:
p4 = p3 * (T4 /T3)
During the power stroke (4-5), work is done by the gas on the piston. The expansion ratio is the reciprocal of the compression ratio and we can use the same relations used during the compression stroke:
p5 / p4 = r ^ (-gamma)
T5 / T4 = r ^ (1 - gamma)
Between stage 5 and stage 6, residual heat is transferred to the surroundings so that the temperature and pressure return to the initial conditions of stage 1 (or 2).
During the cycle, work is done on the gas by the piston between stages 2 and 3. Work is done by the gas on the piston between stages 4 and 5. The difference between the work done by the gas and the work done on the gas is shown in yellow and is the work produced by the cycle. We can calculate the work by determining the area enclosed by the cycle on the p-V diagram. But since the processes 2-3 and 4-5 are curves, this is a difficult calculation. We can also evaluate the work W by the difference of the heat into the gas minus the heat rejected by the gas. Knowing the temperatures, this is an easier calculation.
W = cv * [(T4 - T3) - (T5 - T2)]
The work times the rate of the cycle (cycles per second cps) is equal to the power P produced by the engine.
P = W * cps

On this page we have shown an ideal Otto cycle in which there is no heat entering (or leaving) the gas during the compression and power strokes, no friction losses, and instantaneous burning occurring at constant volume. In reality, the ideal cycle does not occur and there are many losses associated with each process. These losses are normally accounted for by efficiency factors which multiply and modify the ideal result. For a real cycle, the shape of the p-V diagram is similar to the ideal, but the area (work) is always less than the ideal value.

Diesel Cycle

Rudolph Diesel
	Rudolph Diesel was born in Paris of Bavarian parents in 1858. As a budding mechanical engineer at the Technical University in Munich, he became fascinated by the 2nd law of thermodynamics and the maximum efficiency of a Carnot process and attempted to improve the existing thermal engines of the day on the basis of purely theoretical considerations. His first prototype engine was built in 1893, a year after he applied for his initial patent, but it wasn't until the third prototype was built in 1897 that theory was put into practice with the first 'Diesel' engine.
Diesel Cycle Operation
The Diesel cycle is the cycle used in the Diesel (compression-ignition) engine. In this cycle the heat is transferred to the working fluid at constant pressure. The process corresponds to the injection and burning of the fuel in the actual engine. The cycle in an internal combustion engine consists of induction, compression, power and exhaust strokes.
Run Diesel Cycle Animation
	Induction Stroke The induction stroke in a Diesel engine is used to draw in a new volume of charge air into the cylinder. As the power generated in an engine is dependent on the quantity of fuel burnt during combustion and that in turn is determined by the volume of air (oxygen) present, most diesel engines use turbochargers to force air into the cylinder during the induction stroke. From a theoretical perspective, each of the strokes in the cycle complete at Top Dead Centre (TDC) or Bottom Dead Centre (BDC), but in practicality, in order to overcome mechanical valve delays and the inertia of the new charge air, and to take advantage of the momentum of the exhaust gases, each of the strokes invariably begin and end outside the 0, 180, 360, 540 and 720 (0) degree crank positions (see valve timing chart).
	Compression Stroke The compression stroke begins as the inlet valve closes and the piston is driven upwards in the cylinder bore by the momentum of the crankshaft and flywheel. The purpose of the compression stroke in a Diesel engine is to raise the temperature of the charge air to the point where fuel injected into the cylinder spontaneously ignites. In this cycle, the separation of fuel from the charge air eliminates problems with auto-ignition and therefore allows Diesel engines to operate at much higher compression ratios than those currently in production with the Otto Cycle.
	Compression Ignition Compression ignition takes place when the fuel from the high pressure fuel injector spontaneously ignites in the cylinder. In the theoretical cycle, fuel is injected at TDC, but as there is a finite time for the fuel to ignite (ignition lag) in practical engines, fuel is injected into the cylinder before the piston reaches TDC to ensure that maximum power can be achieved. This is synonymous with automatic spark ignition advance used in Otto cycle engines.
	Power Stroke The power stroke begins as the injected fuel spontaneously ignites with the air in the cylinder. As the rapidly burning mixture attempts to expand within the cylinder walls, it generates a high pressure which forces the piston down the cylinder bore. The linear motion of the piston is converted into rotary motion through the crankshaft. The rotational energy is imparted as momentum to the flywheel which not only provides power for the end use, but also overcomes the work of compression and mechanical losses incurred in the cycle (valve opening and closing, alternator, fuel injector pump, water pump, etc.).
	Exhaust Stroke The exhaust stroke is as critical to the smooth and efficient operation of the engine as that of induction. As the name suggests, it's the stroke during which the gases formed during combustion are ejected from the cylinder. This needs to be as complete a process as possible, as any remaining gases displace an equivalent volume of the new charge air and leads to a reduction in the maximum possible power.
	Exhaust and Inlet Valve Overlap Exhaust and inlet valve overlap is the transition between the exhaust and inlet strokes and is a practical necessity for the efficient running of any internal combustion engine. Given the constraints imposed by the operation of mechanical valves and the inertia of the air in the inlet manifold, it is necessary to begin opening the inlet valve before the piston reaches Top Dead Centre (TDC) on the exhaust stroke. Likewise, in order to effectively remove all of the combustion gases, the exhaust valve remains open until after TDC. Thus, there is a point in each full cycle when both exhaust and inlet valves are open. The number of degrees over which this occurs and the proportional split across TDC is very much dependent on the engine design and the speed at which it operates.