The Brutal Realities of War Expressed in Poetry Essay Example for Free

The Brutal Realities of War Expressed in Poetry Essay The poet’s confronts a very poetic perception of life and death by which he incorporated a very distinct mood in his poetry. He particularly engrosses himself to make a point of comparison between the life of those free animals and the soldiers. The speaker is English soldier, perhaps Isaac Rosenberg himself. The poetry has a touch of humor from the speaker’s observation towards the rat and the poppy in the first half of the poem. A rat in the trenches has caught the poet’s eye. He was amused with the fact that this animal is equally at home and comfortable to leap in both German and British trenches. ‘Now you have touched this English hand/ You will do the same to a German’ (Line 9-10) that says that the rat can freely pass between the English and German lines and is more likely to survive than those strong soldiers. In war, the soldiers’ life is of little value compared to the insects and animals roaming around. The speaker assumed that the rat as it passes both the German and English trenches wonders of what is happening to human beings specially of those soldiers who have ‘Strong eyes, fine limbs†¦Ã¢â‚¬â„¢ and those ‘haughty athletes,’ (Line 14). The Rear-Guard by Siegfried Sassoon The Rear Guard gives a realistic approach of the experience of being in war through a soldier’s perspective. The poem is a piece of description that concentrates towards the horror of war. It aims to give information regarding the realities of war from a soldier who descends from Hell. The poet in this masterpiece uses figurative language to convey war’s horror, complexities and confusion. In the fourth and fifth line ‘Tins, boxes, bottles, shapes to vague to know/ A mirror smashed, the mattress from a bed’, the writer provides many figurative objects to illustrate the busy and confused nature of war. The following lines illustrate the painful agony of the soldiers. The ‘Unloading hell behind him step by step’, mentioned in the last line says that on earth through war there is also hell, that even after war the ending point is still hell in eternity. Strange Meeting by Wilfred Owen The narrator of this poem is a soldier found himself in hell. Throughout the poetry, he is conversing with another soldier who distinguished himself as the narrator’s enemy, ‘I am the enemy you killed, my friend. / I knew you in this dark: for you frowned/ Yesterday through me as you jabbed and killed’ (Line 36-39). The narrator refers to the other soldier as a ‘Strange friend†¦Ã¢â‚¬â„¢ (Line 14) which means both were from opposing parties and therefore were strangers to each other. But in hell, they were able to call themselves friends by which they can freely reveal their emotions and thoughts without fear. What common theme is present in all three of these poems and what common message do the poems convey? War is often associated with the physical imagery of violence and political conflict. History itself says that the intentions of war trail into the purpose of acquiring a greater power in terms of position, territory, resources, rights and rewards. Conflict of interest in any form if it will not be settled diplomatically may result to violence and hostility. There is always a participation of military and soldiers to show and define who the stronger party is. Soldiers as land forces play an important role in providing honor and success in one political party. Soldiers with their capability, bravery, sense of commitment and the things they carry defines a group’s strength. Since there is always an involvement of armed conflict between military forces, non participant of warfare which means those who are not engage in the actual combat simply perceive war as brutal and fierce, a battle of life and death that ends either in victory or lost. When the war ends, they perceive that everything is over. However for those who experience it, there is a greater battle that not everybody understands. To truly define war, it is significant to acquire the perspective of those who are mostly affected and those who are mostly involve. The three poems apparently illustrate the brutal realities of war especially for those participants. The writers of the poems were literally participants of war or combat. They show war ugly truths which are often in contrast to the ideas of glory, courage and heroism associated with war. War is ambiguous and illogical because it forces human beings into extreme situations that give no choice in the process. Both the narrator of the â€Å"Strange Meeting† and â€Å"The Rear-Guard† poetry found themselves in Hell which suggests that war not only destroys physical life and property nor ruin the psychological aspects of those participants, but war steals one’s opportunity to possibly experience eternal life in heaven. The fact that both narrators indulge Hell in their poetry demonstrates their belief in religion. In war, there is always a distorted line about religious concept of humanity and duty. The concept of right and wrong, guilt and emotions does not matter in the middle of combat because what matters most is personal survival. The brutalities of war are not so much about the glory and victory of the political party the soldiers’ represent but it is more on personal survival. How does the text of each manifest that message and what significance does this message hold about war in general? The three poetry used powerful language and figures of speech to make a point of comparison. For example, the used of Hell as the main setting of the poem ‘Strange Meeting’ and ‘The Rear-Guard’ suggest that war is man’s product of wickedness. ‘Break of Day in the Trenches’ on the other hand used animals as a powerful imagery to illustrate that man’s life in the middle of combat is of little value compared to any other living animals or insects that enjoy freedom. War in this poetry suggests that those participants in combat have no choice but to fight for their survival. They are prison literally. The poets also used powerful language to evoke the reader’s emotions. The used of ambiguity, irony, wits and symbolism leave the poems the possibility of multiple interpretation. The emotions however are almost common which makes the poems more realistic. In these poems, it can be realized that to really know the real concept of war, one must relate and accumulate the truths from experience of those soldiers. They are the one who can completely and truly define the irrationality and irony of war. Reference: Rosenberg, Isaac (1916). Break of Day in the Trenches. Harrison and Stuart Clark (Ed. ) Peace and War (p. 102). Berlin. (Reprinted from New York, 1989, Oxford University Press) Sasoon, Siegfried (1918). The Rear Guard. Parini (Ed. ). The Wadsworth Anthology of Poetry (p. 1126). Canada. (Reprinted from Canada, 2005, Thomson Wadsworth). Owen, Wilfred (1920). Strange Meeting. Parini (Ed. ). The Wadsworth Anthology of Poetry (p. 776). Canada. (Reprinted from Canada, 2005, Thomson Wadsworth).

The Trail of Tears :: essays research papers

The Trail Of Tears Gloria Jahoda, the author of The Trail of Tears talks about how Indian populations dropped and how white people are the ones responsible for the drop of their population. The white men are not responsible for the drop of the Indian population. Johoda makes all Indians sound like defenseless children. Johoda is making excuses for Indians because Indians let the white man take over their lives and life style. Indians would do everything that was asked of them by the white man instead of standing up for themselves. The Choctaws were granted citizenship in the exception of them not living their everyday life style. Under citizenship, the tribal government of the Choctaws was abolished. Choctaws was given heavy fines and even jail time if the Choctaws dishonored the demands of the white man for their citizenship. Chief Moshulatubbee was shocked so he decided to run for congress. Mississippians took Moshulatubbee wanting to run for congress as a joke. Moshulatubbee lost. The lost started a civil war among the Choctaws. No matter what the Choctaws did they did not get their way. When leaving Mississippi some of the Choctaws died of diseases and of hunger. So the Choctaws gave in and again let the white man take control of them. One of the presidents of the United States, Andrew Jackson went to war with Indians hopping to get rid of the Indians. Black Hawk was a 62-year-old Indian who hated Americans. Black Hawk says that American promises are empty. When ever Americans told Black Hawk that they would do something for the Indians the Americans would never do what they promised. Black Hawk decided to take the side of the British. When ever the British said they would do something for the Indians the British would always do what they promised. Black Hawk always carried a British medal around his neck he respected the British a great deal. Andrew Jackson the president of the United States at the time came face to face with Black Hawk. The president asked Black Hawk, â€Å"why did you go to war,† Black Hawk did not answer. It was said that maybe the sac chief did not understand the question, but I say it’s just another excuse for Indians being naà ¯ve and letting the Americans do what they would l ike with the Indians. This book educates the audience on how there were brave Indians.

Heat Exchanger

Heat exchanger An interchangeable plate heat exchanger Tubular 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. [1] 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. Contents| Flow arrangement Countercurrent (A) and parallel (B) flows * Fig. 1: Shell and tube heat exchanger, single pass (1–1 parallel flow) * Fig. 2: Shell and tube heat exchanger, 2-pass tube side (1–2 crossflow) * Fig. : Shell and tube heat exchanger, 2- pass shell side, 2-pass tube side (2-2 countercurrent) There are three primary classifications of heat exchangers according to their flow arrangement. In parallel-flow heat exchangers, the two fluids enter the exchanger at the same end, and travel in parallel to one another to the other side. In counter-flow heat exchangers the fluids enter the exchanger from opposite ends. The counter current design is the most efficient, in that it can transfer the most heat from the heat (transfer) medium due to the fact that the average temperature difference along any unit length is greater.See countercurrent exchange. In a cross-flow heat exchanger, the fluids travel roughly perpendicular to one another through the exchanger. For efficiency, heat exchangers are designed to maximize the surface area of the wall between the two fluids, while minimizing resistance to fluid flow through the exchanger. The exchanger's performance can also be affected by the addition of fins or corrugations in one o r both directions, which increase surface area and may channel fluid flow or induce turbulence. The driving temperature across the heat transfer surface varies with position, but an appropriate mean temperature can be defined.In most simple systems this is the â€Å"log mean temperature difference† (LMTD). Sometimes direct knowledge of the LMTD is not available and the NTU method is used. Types of heat exchangers Shell and tube heat exchanger A Shell and Tube heat exchanger Main article: 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  Ã‚ °C). [2] This is because the shell and tube heat exchangers are robust due to their shape. Several thermal design features must be considered when designing the tubes in the shell and tube heat exchangers: * 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 tub e 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 space available at the installation site and the need to ensure tubes are available in lengths that are twice the required length (so they can be withdrawn and replaced).Also, 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, in creases 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 f luid 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. An outer, wider baffle looks like a donut, whilst the inner baffle is shaped like a disk.This type of baffle forces the fluid to pass around each side of the disk then through the donut baffle generati ng a different type of fluid flow. Fixed tube liquid-cooled heat exchangers especially suitable for marine and harsh applications can be assembled with brass shells, copper tubes, brass baffles, and forged brass integral end hubs. [3] (See: Copper in heat exchangers). 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 Main article: Plate heat exchangerAnother 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, vacuum-brazed, and welded 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 â€Å"chevron†, dimpled, or other patterns, where others may have machined fins and/or grooves. Plate and shell heat exchanger A third type of heat exchanger is a plate and shell heat exchanger, which combines plate heat exchanger with shell and tube heat exchanger technologies.The heart of the heat exchanger contains a fully welded circular plate pack made by pressing and cutting round plates and welding them together. Nozzles carry flow in and out of the platepack (the ‘Plate side' flowpat h). The fully welded platepack is assembled into an outer shell that 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 Main article: Plate fin heat exchanger This type of heat exchanger uses â€Å"sandwiched† passages containing fins to increase the effectiveness of the unit.The designs include crossflow and counterflow cou pled 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 high 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 plat e 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 use 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. They can also be integrated into a heatcatcher system that allows an ORC[further explanation needed] generator to produce waste heat to power. Dynamic scraped surface heat exchanger Another type of heat exchanger is called â€Å"(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 th e 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. 4][5] Distillation set-ups typically use condensers to condense distillate vapors back into liquid. Power plants that use 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 exchan gers pass heat from the primary (reactor plant) system to the secondary (steam plant) system, producing steam from water in the process. These 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. [6][7] To conserve energy and cooling capacity in chemical and other plants, regenerative heat exchangers can transfer heat from a stream that must be cooled to another stream that must 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. [8] 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. [9] Phases[10]| Continuous phase| Driving force| Change of phase| Examples| Gas – Liquid| Gas| Gravity| No| Spray columns, packed columns| | | | Yes| Cooling towers, falling droplet evaporators| | | Forced| No| Spray coolers/quenchers| | Liquid flow| Yes| Spray condensers/evaporati on, jet condensers| | Liquid| Gravity| No| Bubble columns, perforated tray columns| | | | Yes| Bubble column condensers| | | Forced| No| Gas spargers| | | Gas flow| Yes| Direct contact evaporators, submerged combustion| HVAC air coils One of the widest uses of heat exchangers is for air conditioning of buildings and vehicles. This class of heat exchangers is commonly called air coils, or just coils due to their often-serpentine internal tubing. Liquid-to-air, or air-to-liquid HVAC coils are typically of modified crossflow arrangement. In vehicles, heat coils are often called heater cores.On the liquid side of these heat exchangers, the common fluids are water, a water-glycol solution, steam, or a refrigerant. For heating coils, hot water and steam are the most common, and this heated fluid is supplied by boilers, for example. For cooling coils, chilled water and refrigerant are most common. Chilled water is supplied from a chiller that is potentially located very far away, but refri gerant must come from a nearby condensing unit. When a refrigerant is used, the cooling coil is the evaporator in the vapor-compression refrigeration cycle. HVAC coils that use this direct-expansion of refrigerants are commonly called DX coils.Some DX coils are â€Å"microchannel† type. [11] On the air side of HVAC coils a significant difference exists between those used for heating, and those for cooling. Due to psychrometrics, air that is cooled often has moisture condensing out of it, except with extremely dry air flows. Heating some air increases that airflow's capacity to hold water. So heating coils need not consider moisture condensation on their air-side, but cooling coils must be adequately designed and selected to handle their particular latent (moisture) as well as the sensible (cooling) loads.The water that is removed is called condensate. For many climates, water or steam HVAC coils can be exposed to freezing conditions. Because water expands upon freezing, these somewhat expensive and difficult to replace thin-walled heat exchangers can easily be damaged or destroyed by just one freeze. As such, freeze protection of coils is a major concern of HVAC designers, installers, and operators. The introduction of indentations placed within the heat exchange fins controlled condensation, allowing water molecules to remain in the cooled air.This invention allowed for refrigeration without icing of the cooling mechanism. [12] The heat exchangers in direct-combustion furnaces, typical in many residences, are not ‘coils'. They are, instead, gas-to-air heat exchangers that are typically made of stamped steel sheet metal. The combustion products pass on one side of these heat exchangers, and air to heat on the other. A cracked heat exchanger is therefore a dangerous situation that requires immediate attention because combustion products may enter living space. Spiral heat exchangers Schematic drawing of a spiral heat exchanger.A spiral heat exchang er (SHE), may refer to a helical (coiled) tube configuration, more generally, the term refers to a pair of flat surfaces that are coiled to form the two channels in a counter-flow arrangement. Each of the two channels has one long curved path. A pair of fluid ports are connected tangentially to the outer arms of the spiral, and axial ports are common, but optional. [13] The main advantage of the SHE is its highly efficient use of space. This attribute is often leveraged and partially reallocated to gain other improvements in performance, according to well known tradeoffs in heat exchanger design. A notable tradeoff is capital cost vs operating cost. ) A compact SHE may be used to have a smaller footprint and thus lower all-around capital costs, or an over-sized SHE may be used to have less pressure drop, less pumping energy, higher thermal efficiency, and lower energy costs. Construction The distance between the sheets in the spiral channels are maintained by using spacer studs that were welded prior to rolling. Once the main spiral pack has been rolled, alternate top and bottom edges are welded and each end closed by a gasketed flat or conical cover bolted to the body.This ensures no mixing of the two fluids occurs. Any leakage is from the periphery cover to the atmosphere, or to a passage that contains the same fluid. [14] Self cleaning SHEs are often used in the heating of fluids that contain solids and thus tend to foul the inside of the heat exchanger. The low pressure drop lets the SHE handle fouling more easily. The SHE uses a â€Å"self cleaning† mechanism, whereby fouled surfaces cause a localized increase in fluid velocity, thus increasing the drag (or fluid friction) on the fouled surface, thus helping to dislodge the blockage and keep the heat exchanger clean. The internal walls that make up the heat transfer surface are often rather thick, which makes the SHE very robust, and able to last a long time in demanding environments. † They are also easily cleaned, opening out like an oven where any build up of foulant can be removed by pressure washing. Self-Cleaning Water filters are used to keep the system clean and running without the need to shut down or replace cartridges and bags. Flow arrangements Concurrent and countercurrent flow. There are three main types of flows in a spiral heat exchanger: 1. Counter-current Flow: Fluids flow in opposite directions.These are used for liquid-liquid, condensing and gas cooling applications. Units are usually mounted vertically when condensing vapour and mounted horizontally when handling high concentrations of solids. 2. Spiral Flow/Cross Flow: One fluid is in spiral flow and the other in a cross flow. Spiral flow passages are welded at each side for this type of spiral heat exchanger. This type of flow is suitable for handling low density gas, which passes through the cross flow, avoiding pressure loss. It can be used for liquid-liquid applications if one liquid has a cons iderably greater flow rate than the other. . Distributed Vapour/Spiral flow: This design is that of a condenser, and is usually mounted vertically. It is designed to cater for the sub-cooling of both condensate and non-condensables. The coolant moves in a spiral and leaves via the top. Hot gases that enter leave as condensate via the bottom outlet. Applications The SHE is good for applications such as pasteurization, digester heating, heat recovery, pre-heating (see: recuperator), and effluent cooling. For sludge treatment, SHEs are generally smaller than other types of heat exchangers. [citation needed] SelectionDue to the many variables involved, selecting optimal heat exchangers is challenging. Hand calculations are possible, but many iterations are typically needed. As such, heat exchangers are most often selected via computer programs, either by system designers, who are typically engineers, or by equipment vendors. To select an appropriate heat exchanger, the system designers (or equipment vendors) would firstly consider the design limitations for each heat exchanger type. Though cost is often the primary criterion, several other selection criteria are important: * High/low pressure limits * Thermal performance Temperature ranges * Product mix (liquid/liquid, particulates or high-solids liquid) * Pressure drops across the exchanger * Fluid flow capacity * Cleanability, maintenance and repair * Materials required for construction * Ability and ease of future expansion * Material selection, such as copper, aluminum, carbon steel, stainless steel, nickel alloys, and titanium. Small-diameter coil technologies are becoming more popular in modern air conditioning and refrigeration systems because they have better rates of heat transfer than conventional sized condenser and evaporator coils with round copper tubes and aluminium or opper fin that have been the standard in the HVAC industry. Small diameter coils can withstand the higher pressures required by the new generation of environmentally friendlier refrigerants. Two small diameter coil technologies are currently available for air conditioning and refrigeration products: copper microgroove[15] and brazed aluminium microchannel. [16] Choosing the right heat exchanger (HX) requires some knowledge of the different heat exchanger types, as well as the environment where the unit must operate.Typically in the manufacturing industry, several differing types of heat exchangers are used for just the one process or system to derive the final product. For example, a kettle HX for pre-heating, a double pipe HX for the ‘carrier’ fluid and a plate and frame HX for final cooling. With sufficient knowledge of heat exchanger types and operating requirements, an appropriate selection can be made to optimise the process. [17] Monitoring and maintenance Online monitoring of commercial heat exchangers is done by tracking the overall heat transfer coefficient. The overall heat transfer coeffi cient tends to decline over time due to fouling.U=Q/A? Tlm By periodically calculating the overall heat transfer coefficient from exchanger flow rates and temperatures, the owner of the heat exchanger can estimate when cleaning the heat exchanger is economically attractive. Integrity inspection of plate and tubular heat exchanger can be tested in situ by the conductivity or helium gas methods. These methods confirm the integrity of the plates or tubes to prevent any cross contamination and the condition of the gaskets. Mechanical integrity monitoring of heat exchanger tubes may be conducted through Nondestructive methods such as eddy current testing.Fouling Main article: Fouling A heat exchanger in a steam power station contaminated with macrofouling. Fouling occurs when impurities deposit on the heat exchange surface. Deposition of these impurities can decrease heat transfer effectiveness significantly over time and are caused by: * Low wall shear stress * Low fluid velocities * Hi gh fluid velocities * Reaction product solid precipitation * Precipitation of dissolved impurities due to elevated wall temperatures The rate of heat exchanger fouling is determined by the rate of particle deposition less re-entrainment/suppression.This model was originally proposed in 1959 by Kern and Seaton. Crude Oil Exchanger Fouling. In commercial crude oil refining, crude oil is heated from 21  °C to 343  °C prior to entering the distillation column. A series of shell and tube heat exchangers typically exchange heat between crude oil and other oil streams to heat the crude to 260  °C prior to heating in a furnace. Fouling occurs on the crude side of these exchangers due to asphaltene insolubility. The nature of asphaltene solubility in crude oil was successfully modeled by Wiehe and Kennedy. 18] The precipitation of insoluble asphaltenes in crude preheat trains has been successfully modeled as a first order reaction by Ebert and Panchal[19] who expanded on the work of Ke rn and Seaton. Cooling Water Fouling. Cooling water systems are susceptible to fouling. Cooling water typically has a high total dissolved solids content and suspended colloidal solids. Localized precipitation of dissolved solids occurs at the heat exchange surface due to wall temperatures higher than bulk fluid temperature. Low fluid velocities (less than 3  ft/s) allow suspended solids to settle on the heat exchange surface.Cooling water is typically on the tube side of a shell and tube exchanger because it's easy to clean. To prevent fouling, designers typically ensure that cooling water velocity is greater than 0. 9 m/s and bulk fluid temperature is maintained less than 60  °C. Other approaches to control fouling control combine the â€Å"blind† application of biocides and anti-scale chemicals with periodic lab testing. Maintenance Plate heat exchangers must be disassembled and cleaned periodically. Tubular heat exchangers can be cleaned by such methods as acid cleani ng, sandblasting, high-pressure water jet, bullet cleaning, or drill rods.In large-scale cooling water systems for heat exchangers, water treatment such as purification, addition of chemicals, and testing, is used to minimize fouling of the heat exchange equipment. Other water treatment is also used in steam systems for power plants, etc. to minimize fouling and corrosion of the heat exchange and other equipment. A variety of companies have started using water borne oscillations technology to prevent biofouling. Without the use of chemicals, this type of technology has helped in providing a low-pressure drop in heat exchangers. In nature HumansThe human nasal passages serve as a heat exchanger, which warms air being inhaled and cools air being exhaled. You can demonstrate its effectiveness by putting your hand in front of your face and exhaling, first through your nose and then through your mouth. Air exhaled through your nose is substantially cooler. [20][21] In species that have e xternal testes (such as humans), the artery to the testis is surrounded by a mesh of veins called the pampiniform plexus. This cools the blood heading to the testis, while reheating the returning blood. Birds, fish, marine mammalsCountercurrent exchange conservation circuit Further information: Countercurrent exchange in biological systems â€Å"Countercurrent† heat exchangers occur naturally in the circulation system of fish, whales and other marine mammals. Arteries to the skin carrying warm blood are intertwined with veins from the skin carrying cold blood, causing the warm arterial blood to exchange heat with the cold venous blood. This reduces the overall heat loss in cold waters. Heat exchangers are also present in the tongue of baleen whales as large volumes of water flow through their mouths. 22][23] Wading birds use a similar system to limit heat losses from their body through their legs into the water. Carotid rete The carotid rete is a counter-current heat exchangi ng organ in some ungulates. The blood ascending the carotid arteries on its way to the brain, flows via a network of vessels where heat is discharged to the veins of cooler blood descending from the nasal passages. The carotid rete allows Thomson's gazelle to maintain its brain almost 3 °C cooler than the rest of the body, and therefore aids in tolerating bursts in metabolic heat roduction such as associated with outrunning cheetahs (during which the body temperature exceeds the maximum temperature at which the brain could function). [24] In industry Heat exchangers are widely used in industry both for cooling and heating large scale industrial processes. The type and size of heat exchanger used can be tailored to suit a process depending on the type of fluid, its phase, temperature, density, viscosity, pressures, chemical composition and various other thermodynamic properties.In many industrial processes there is waste of energy or a heat stream that is being exhausted, heat exch angers can be used to recover this heat and put it to use by heating a different stream in the process. This practice saves a lot of money in industry, as the heat supplied to other streams from the heat exchangers would otherwise come from an external source that is more expensive and more harmful to the environment. Heat exchangers are used in many industries, including: * Waste water treatment Refrigeration * Wine and beer making * Petroleum refining In waste water treatment, heat exchangers play a vital role in maintaining optimal temperatures within anaerobic digesters to promote the growth of microbes that remove pollutants. Common types of heat exchangers used in this application are the double pipe heat exchanger as well as the plate and frame heat exchanger. In aircraft In commercial aircraft heat exchangers are used to take heat from the engine's oil system to heat cold fuel. 25] This improves fuel efficiency, as well as reduces the possibility of water entrapped in the fu el freezing in components. [26] Early 2008, a Boeing 777 flying as British Airways Flight 38 crashed just short of the runway. In an early-2009 Boeing-update sent to aircraft operators, the problem was identified as specific to the Rolls-Royce engine oil-fuel flow heat exchangers. [26] Other heat exchangers, or Boeing 777 aircraft powered by GE or Pratt and Whitney engines, were not affected by the problem. [26]

Native Americans and Diabetes Essay - 2359 Words

Native Americans and Diabetes Since the arrival of Columbus in 1492, American Indians have been in a continuous struggle with diseases. It may not be small pox anymore, but illnesses are still haunting the native population. According to statistics, Native Americans have much higher rates of disease than the overall population. This includes a higher death rate from alcoholism, tuberculosis, and diabetes than any other racial or ethnic group. Recent studies by Indian health experts show that diabetes among Indian youth ages 15-19 has increased 54% since 1996 and 40% of Indian children are overweight. Even though diabetes rates vary considerably among the Native American population, deaths caused from diabetes are 230 percent greater†¦show more content†¦When the Native Americans were forced onto reservations they stopped hunting and preparing their own food. Instead the United States government gave them food that their bodies were not used to digesting. Indians were not used to eating flour, lard, cann ed meats and poultry that are swimming in fat, and canned fruits and vegetables packed in sugary syrup. Native Americans’ bodies could not handle the extra fat and sugar in their diet. This, coupled with a decrease in intense exercise, increased obesity and brought on the rise of diabetes. The sudden lack of exercise resulted in a significant weight increase in the Native American community. Indians were used to roaming the countryside. They had to follow the buffalo or move to warmer weather. Now, they were put into permanent homes and bought their food. This created an overweight, obese group of people. Studies estimated that the overall occurrence of obesity among Native Americans was 13.7 percent for men and 16.5 percent for women. These are higher than the United States’ rates of 9.1 percent and 8.2 percent, respectively. 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