Definition Manufacturing Technology - Case Study Example

Manufacturing Technology This design report concerning the overall system efficiencies and associated with advanced cooling systems in the current market to provide a tool can be used in selecting systems for a given installation. The objective of this study was to review cooling technologies available in the current market and to promote the introduction of advanced cooling technologies. Metals owe their importance to their unique mechanical properties, the combination of high strength with the ability to change shape plastically ductility and malleability). This plasticity enables them to be shaped, e.g. into motor car bodies, tin cans and girders, by processes of mechanical working such as pressing, drawing, rolling and forging. Even more important, this same plasticity gives strong metals their extraordinary toughness, the ability to endure all the knocks and shocks of long rough service without breaking or crumbling away. Corrosion properties are the materials compatibile for the components used for the following items such as compressor, piping, evaporator, and condenser. Safety considerations include toxicity and flammability. With the introduction of Freon, sulfur dioxide rapidly disappeared from the market. Ammonia is still used in some large commercial plants, well away from residential areas, where a leak will not cause widespread injuries.With the Use of highly purified propane gas as a refrigerant is gaining favor, in systems designed for R-12, R-22 or R-134a. Now it is marketed under the trade name Duracool® and it is designated as R-290.. Moreover, propane is nontoxic. The powerful Emissions from automotive air-conditioning are a growing concern because of their impact on climate changet a great extent.. The European Union will phase out refrigerants with a global warming potential (GWP) of more than 150 in automotive air conditioning and other air conditioning sstems from 2011 onwards. According to this it will ban potent greenhouse gases such as the refrigerant to promote safe and energy-efficient refrigerants as HFC-134a—which has a GWP of 1410. The natural refrigerant CO2 (R-744)is the most promising alternative. Carbon dioxide is toxic and potentially lethal in concentrations above 5% by volume non-flammable, non-ozone depleting, has a global warming potential of 1. For cars, residential air conditioning, hot water pumps, commercial refrigeration, and vending machines R-744 can be used as a working fluid in climate control systems. Spray Water with Recirculation and Heating or Cooling To achieve the desired air condition Spray-type humidifiers may use heating or cooling equipment. The heat supplied to or gained from the system is: The ADP (Apparatus Dew-Point Temperature) will be higher than the adiabatic process when the heat is supplied to the system. The contact factor of humidification depends on the process line. In some cases the increase in moisture content is accompanied by sensible cooling and in some others by sensible heating. The ADP (Apparatus Dew-Point Temperature) will be higher than the adiabatic process when the heat is supplied to the system. The contact factor of humidification depends on the process line. In some cases the increase in moisture content is accompanied by sensible cooling and in some others by sensible heating. METALLURGY AND MANUFACTURING Metallurgy today is an applied science. Its fascination lies in the challenge of using science to give mankind the best engineering materials that the laws of nature and the Earth's natural resources will allow. The applied science of metallurgy links the science of metals to the metal industries. This link is only maintained and strengthened by deliberate care and attention, for there is always a tendency for the scientific and industrial sides to drift apart. to commit himself totally to the electrical characteristics of these materials are extremely sensitive to the presence of minute concentrations of impurity atoms, which concentrations may be controlled over very small spatial regions is as natural for the research man. The advent of integrated circuitry that has totally revolutionized the electronics and computer industries and semiconductors have made possible. ENGINEERING REQUIREMENTS OF MATERIALS The same can be successfully used for making engineering components such a rankshaft, spanner, etc. so that engineering requirements of a material mean as what is expected of from the material. he goes in search of that material which possesses such properties as will permit the component part to perform its functions successfully while in use When an engineer thinks of deciding and fabricating an engineering part,. For example, one may select high speed steel for making a milling cutter or a power hack-saw blade. The main engineering requirements of materials fall under three categories such as Fabrication requirements Service requirements Economic requirements. Fabrication requirements mean that the material should be able to get shaped (e.g., cast, forged, formed, machined, sintered etc.) and joined (e.g., welded, brazed, etc.) easily. Fabrication requirements relate themselves with material's machinability, ductility, castability, heat-treatability, weldability, etc. There is proper strength, wear resistance; corrosion resistance, etc. are examples to Service requirements imply that the material selected for the purpose must stand up to service demands. The engineering part should be made with minimum overall cost which is Economic requirements demand. Proper selection of both technical and marketing variables can achieve Minimum overall cost may be achieved. Properties of Engineering Materials Property of a material (or Material Property) is a factor that influences qualitatively or quantitatively the response of a given material to imposed stimuli and constraints, e.g., forces, temperatures, etc. Properties render a material suitable or unsuitable for particular use in industry. The material property is independent of the dimension or shape of the material, e.g., tensile strength of annealed, fine grained pure aluminium will be around 4.8 x 107 N/m2 irrespective of the dimensions of the specimen tested. In principle all material properties have a statistical behaviour. Different material properties are : Mechanical properties Thermal properties Electrical properties Magnetic properties Chemical properties Optical properties Physical properties Technological properties. MECHANICAL PROPERTIES Mechanical properties include those characteristics of material that describe its behaviour under the action of external forces. In order to construct a mechanically sound structure such as a bridge on the river the knowledge of mechanical properties of materials is very essential. By conducting experimental tests on the material specimen Mechanical properties can be determined. Under applied forces and loads Mechanical properties determine the behaviour of engineering materials. The response of the materials to applied forces will depend on the type of bonding, the structural arrangement of atoms or molecules and the type and number of imperfections, which are always present in solids except in rare circumstances. For this reason, mechanical properties are very sensitive to manufacturing processes and operations, which may result in highly variable characteristics even in materials of the same chemical composition. — Various mechanical properties are : Elasticity A liquid or gas adapts itself to the shape of its container, but a solid has a shape of its own, which it tends to preserve. Loading a solid will change its dimensions, but the resulting deformation will disappear upon unloading. This tendency of a deformed solid to seek its original dimensions upon unloading is ascribed to a property called elasticity. The recovery from the distorting effects of the loads may be instantaneous or gradual, complete or partial. A solid is called perfectly elastic if this recovery is instantaneous and complete; it is said to exhibit delayed elasticity or inelastic effects, respectively, if the recovery is gradual or incomplete. Accurate measurements reveal some delayed elasticity and inelastic effects in all solids. Giving a precise definition of elasticity and setting forth the rudiments of the theory of elasticity require a discussion of the concepts of strain, stress and modulus of elasticity. Stress Plasticity Plasticity is that property of a material by virtue of which it may be permanently deformed when it has been subjected to an externally applied force great enough to exceed the elastic limit. The subject of plasticity is of great importance to an engineer for it is this property that, in most cases, enables him to shape (e.g., roll, forge) metals in the solid state. The minimum stress that should cause permanent deformation can be computed from a knowledge of the bond strength. The result of such computations gives values that are from 100 to 1000 times the stress required to initiate plastic deformation of a crystal as determined by testing. For most materials, the plastic deformation follows the elastic deformation. Referring to stress-strain curve a material obeys the law of elastic solids for stresses below the yield stress and this is followed by the plastic deformation. The mechanism of plastic deformation is essentially different in crystalline materials and amorphous materials. Crystalline materials undergo plastic deformation as the result of slip along definite crystallographic planes whereas, in amorphous materials, plastic deformation occurs when individual molecules or groups of molecules slide past one another. Toughness What is Toughness? To withstand bending or the application of shear stresses without fracture, it is the ability of the material to absorb energy during plastic deformation up to fracture. It is the ability of a material. Resilience Resilience is usually measured by determining the rebound of a pendulum or ball after a single impact. It represents the ratio of energy given up on recovery from deformation to energy required to produce deformation. Bearing Materials Bearings support moving parts, such as shafts and spindles, of a machine or mechanism. Bearings may be classed as (i) Rolling contact (i.e., Ball and roller) bearings. («) Plain bearings. Rolling contact bearings are almost invariably made of steel that can be hardened after machining. Both plain carbon and alloy (Ni, Cr, Mo) steels are employed for different applications. For making plain bearings, an extremely wide range of materials is available and will be discussed below. PROPERTIES OF BEARING MATERIALS A bearing material should: (i) Possess low coefficient of friction. (if) Provide hard, wear resistant surface with a tough core. (iii) Have high compressive strength, (j'v) Have high fatigue strength, (v) Be able to bear shocks and vibrations, (vi) (vii) Possess adequate plasticity under bearing load. (viii) Possess adequate strength at high temperatures. (ix) Be such that it can be easily fabricated. (x) Possess resistance to corrosion. (xi) Be such that it does not cause excessive wear of the shaft rotating in it, i.e., bearing material should be softer than the shaft material. (Xii) Possess antiseizure characteristics. (xiii) Be having small pieces of a comparatively hard metal embedded in a soft metal. (xiv) Maintain a continuous film of oil between shaft and bearing in order to avoid metal to metal contact. (xv) Possess ability to embed in itself any dirt, etc., present in lubricating oil. (xvi) Should be cheap and easily available. TYPES OF BEARING MATERIALS They are Lead or tin-based alloys. Cadmium-based alloys. Aluminium based alloys. Silver-based alloys. Copper-based alloys. Sintered bearing materials. Non-metallic bearing materials. Lead or tin based alloys (Babbitt metals) They may be divided as The high tin alloys with more than 80% tin and little or no lead. The high lead alloys with about 80% lead and 1-12% tin. The alloys with intermediate percentages of tin and lead. In addition to lead and tin, these bearing alloys contain antimony and copper also. Typical compositions of A lead based alloy A tin based alloy Pb 75% Sn 88% Sbl5% Sb 8% Snl0% Cu 4% Lead base alloys are softer and brittle than the tin base alloys. Lead base alloys are cheaper than tin base alloys. Tin base alloys have a low coefficient of friction as compared to lead base alloys. Lead base alloys are suitable for light and medium loads, whereas tin base alloys are preferred for higher loads and speeds. Whereas tin base alloys find applications in high speed engines, steam turbines, lead base alloys are used in rail road freight cars. Solidus temperature of Tin base alloys — Approx. 222°C Solidus temperature of Lead base alloys —Approx. 240°C Besides, both these alloys possess Good ability to embed dirt Good conformability to journal Good corrosion resistance Very good seizure resistance, etc. White metals are tin base or lead base bearing alloys and are usually referred to as babbitts. Sintered bearing materials Copper powder with 8 to 10% tin and sometimes with 1 to 3% graphite is used for making porous sintered bronze bearings. Besides using bronze powder, iron powder has also been tried for making sintered iron bearings. Such bearings possess greater strength. Non-metallic bearing materials They are Teflon (poly tetrafluoroethylene) It has coefficient of friction < 0.04, without lubrication. It has good stability at high temperatures. It is chemically inert to water and many chemicals and solvents. Fillers like glass and graphite increase the resistance to deformation. SELF LUBRICATING/POROUS BEARINGS The self lubricating or porous bearing is made by sintering powder- ed metal and then impregnating it with oil. As the name suggests, the bearing is self lubricating. Various compositions of bronze are in wide use. Iron is used to a less extent. The porous bearings contain volume of between 17% and 30%. — Refrigerators, air-conditioners, washing machines etc., contain self lubricating bearings. — The lubricants in a porous bearing operate through the following two mechanisms: Hydrodynamic lubrication, and Boundary film lubrication Hydrodynamic lubrication, propounded by Morgan, is made possible only with the help of a pump during starting. When the shaft rotates in a self lubricated bearing, circulation of oil occurs around the shaft. This circulation prevents heat build up. Hydrodynamic theory is applied only to the regime where there is sufficient oil to form a continuous film. This theory is limited to low bearing pressure where it operates well. In general, part of the entire load is also carried by the sliding contact between the bearing and shaft surfaces, which is separated by a thin film of lubricant known as Boundary film lubrication. In this case, the bearing performance depends on the ability of the lubricant to maintain a boundary film under load. The transition from hydrodynamic to boundary condition extends over a wide range; it is neither sudden nor precisely defined. Self-lubricating bearing materials The following are Various types of bearings incorporating metal powders . Steel-backed materials with a non-porous sintered lining to form engine bearings and wrapped bushes. Unbacked porous sintered metallic parts impregnated with oil for self-lubricating bearings, bushes or washers. Steel-backed materials with a porous sintered lining impregnated with plastic for dry operation or operation with a limited supply of lubricant. Unbacked nonporous sintered metallic parts containing graphite as a dry lubricant for use under poor lubrication conditions. Sintered polytetrafluoroethylene (P.T.F.E.), parts incorporating metal powders to form a material suitable for non-lubricated applications. Bearings mentioned at (1) and (2) above are produced and used in bulk, while the remaining three are used in smaller amounts because of their specialized applications. Steel-backed materials with a non-porous sintered lining —For engine bearings, there are three main classes of lining materials: Lead or tin-based white metal (Babbit), Copper-based alloys, Aluminium-based alloys. Since white metal does not possess sufficient strength to carry the load for most of the modern engines, copper-based alloys, for example, copper-lead and lead bronze OR aluminium-based alloys such as aluminium-tin are preferred. Copper-lead bearings have a lead content of 40-45% by weight. Their fatigue strength is 50% greater than that of a similar thickness of white metal lining. Cu-Pb bearings are widely employed in automotive engines and they have replaced most of the conventional solid phosphor-bronze bushes. Sintered Copper-based Bearing Linings Oil-impregnated porous bearings They should possess sufficient interconnected porosity to contain and retain in use the maximum possible amount of oil. They find applications in positions not easily accessible for lubrication. Steel-backed materials with a porous-plastic impregnated lining There are two types of bearing materials; the first are those which are impregnated with a mixture of P.T.F.E. (polytetrafluoroethylene) and lead, and are employed as a dry bearing material due to extremely high degree of wear resistance of this P.T.F.E./lead/bronze surface. ., The second, in which the impregnant is thermoplastic acetal co polymer, is particularly suitable for operation with a minimum lubricant supply. Porous bearings are usually made of bronze, with or without the addition of graphite or other dry lubricant. Although iron, brass or aluminium alloys may be employed, bronze holds a predominant position in this field. They are marketed either impregnated with oil or in dry condition. Advantages of porous bearings The ease with which it is possible to prepare low cost duplex or two-phase materials (metal-metal, metal-plastic, metal-non metallic lubricant, metal-liquid lubricant) with controlled and better mechanical properties Capacity to work without continuous lubrication Resistance to corrosion No machining is required to manufacture the bearing, Can be used in positions which are not easily accessible for lubricating and maintaining the bearings. Preferred where there is dirt contamination in the surrounding atmosphere. Where there is absence or limited supply of lubricant where, it is required that lubricants must not get into the products (e.g., food, textile, etc.). It is more economical to mass production, than bearings produced by casting and the machining processes. Disadvantages of porous bearings Low yield strength and fatigue strength when compared to other bearing materials. High coefficient of expansion when compared to steel The Performance Parameters The performance parameters that have been used in the evaluation of various systems as this study describe. The system COP is the main performance parameter of concern for this study. The COP limits for real cycles, systems COP limits and ideal systems were developed. For various systems and can be compared to manufacturer rated COP information these can give an indication of the theoretical and practical maximum COP values. Here the effect of Tc and Te on COP is also discussed in detail. It is the desiccant systems that are introduced .Their use and method of rating are investigated. For possible consideration the novel systems such as heat pumps, thermoelectric units, and others are presented. those for a heat pump based on shaft work or a heat source and the coefficient of performance for cooling based on shaft work or a heat or fuel source, can be briefed as follows. The coefficient of performance for refrigeration based on shaft work to remove heat at a temperature Tc is: COP Q W / Eq 1 Here W is the shaft work and Qc is the heat removed that can be supplied by an electric motor or engine. The cold body takes the form of chilled water in many systems. On the power consumption per ton of refrigeration, some manufacturers provide information. This can be related to the 2.(COPc)e by: kW ton COP c e / 3.516 / Eq 2 The energy efficiency ratio is another performance measure sometimes cited in manufacturer’s literature is (EER in Btu/W). This can be converted to a 3.COP value by: COP EERc e / 3.413 Eq 3 Based on a heat source (either gas fired or steam) the coefficient of performance for a refrigeration system is: COP Q Q c e c s / Eq 4 where Qc is the heat removed and Qs is the heat supplied by the heat source. This definition is directly applicable to absorption type systems. The matrix in Table 1 lists the rated COP quoted by manufacturers of various systems. The vapor-compression systems use (COPc)e and the absorption systems use (COPc)s as defined above. The two COPs can be related by the efficiency of the power generation facility defined as e, where: 5.he Wout / Qs Eq 5 We can see that: COP Q W W Q COP c c in out s c e e / / h Eq 6 in the refrigeration mode, e is based on the ambient temperature. For a system driven by shaft work that can act as a heat pump, the coefficient of performance in the heating mode can be determined by: COP Q Q h s h s / Equation 7 Here Win is as previously defined and Qh is the heat supplied. This formula can be reduced to the following form: COP COP h e c e 1 Eq 8 With the engine driven by a heat supply, the COP of a heat pump can be defined as: COP Q Q h s h s / Equation 9 Here Qs is the heat provided by the heat source and the Qh is the heat supplied to the conditioned space. This relation can then be manipulated to the form: COP COP COP h s h e e c s e h ' h ' Equation 10 Here based on the ambient temperature in the heat pump mode eis the engine efficiency. For a heat pump based on an absorption system using steam or a direct-fired heat source, the coefficient of performance can be defined by: COP Q Q h s h s / Eq 11 The above relation can be described as: COP COP h s c s 1 Eq 12 It is only because the use of the heat rejected in both the condenser and the absorber. Carnot Cycle No heat engine can be more efficient than a reversible heat engine working between two fixed temperature limits, by using the second law of thermodynamics it is possible to show. This heat engine is known as Carnot cycle and consists of the following processes: 1 to 2: Isentropic expansion 2 to 3: Isothermal heat rejection 3 to 4: Isentropic compression 4 to 1: Isothermal heat supply To the cycle per unit mass the flow of supplied heat is: Q1 = T1 s To the cycle per unit mass the flow of rejected heat is: Q2 = T2 s To the cycle, by applying the first law of thermodynamics we obtain: Q1 - Q2 - W = 0 The Cycle’s thermal efficiency is : = W/Q1 = 1 - T2/T1 no cycle can achieve this efficiency due to mechanical friction and other irreversibility. Here the work done by the system is: Wg = W41 + W12 and work ratio is defined as the ratio of the net work, W, to the gross work output, Wg, i.e. W / Wg for power generation theoretically, it can not be used in practice. This is the most efficient system. Ideal Cycle Four thermodynamic processes are the key factors in an ideal cycle. 1. A reversible isothermal process in which heat is transferred to a working fluid from a high temperature reservoir 2. There is a reversible adiabatic process in which the temperature of the working fluid decreases from the high temperature to the low temperature. 3. There is a reversible isothermal process in which heat is transferred to a low temperature reservoir. 4. a reversible adiabatic process in which the temperature of the working fluid increases from the low temperature to the high temperature Carnot cycle is well described by all these 4 steps. It converts heat into work. For a refrigeration cycle, the performance is measured by the coefficient of performance (COP), which is the amount of heat removed from the low temperature reservoir divided by the net work input. For the Carnot refrigeration system described, the performance can be defined as: COP T T T T T T c s c s o s o c / Eq 13 in which (COPc)s is the coefficient of performance for cooling based on a heat input, Tc is the chilled water temperature, Ts is the temperature of the heat source that drives the system, and To is the temperature of the surroundings or heat sink (for the condenser of a refrigerator) or source (for the evaporator of a heat pump). For a heat pump, this ultimate performance is given by the relation: COP T T T T T T h s h s o s h o / Eq 14 In this relation (COPh)s is the coefficient of performance for heating based on a heat source, Ts and To are as described for Eq. 13, and Th is the temperature at which heat is delivered by the heat pump. For example, giving Ts = 2,000 R, To = 500 R, and Th = 550 R, (COPh)s = 8.25, i.e., for one Btu applied at 2,000 R, 8.25 Btu would be available at 550 R or 90 F. Heat conduction The Fourier's law,( law of heat conduction,)states that the time rate of heat transfer through a material is proportional to the negative gradient to that gradient, through which the heat is flowing in the temperature and to the area at right angles: where Q is the amount of heat transferred, t is the time taken, k is the material's conductivity. S is the surface through which the heat is flowing, T is the temperature. Heat pump Thermodynamic heat pump is the models for heat pumps. The heat pumps are intended to keep a place warm and refrigerators designed to cool it that is the difference between the two. Technically a refrigerator cycle is also a heat pump cycle. when heat is removed from a low-temperature with the help of external mechanical work space or source and rejected to a high-temperature sink. the thermodynamic power cycle the inverse of the heat pump cycle. Although absorption heat pumps are used in a minority of applications,the most common types of heat pump systems use the reverse-Rankine vapor-compression refrigeration cycle . Heat pump can be classified as: 1. Vapor cycle, 2. Gas cycle, and 3. Stirling cycle Vapor cycle refrigeration can further be classified as: 1. Vapor compression refrigeration 2. Gas absorption refrigeration Here we look at Vapor-Compression Cycle only as it is widely used. Figure 2:Temperature–Entropy diagram . Thermodynamic cycle To its initial state, thermodynamic cycle is a series of thermodynamic processes which returns a system. making the cycle an important concept in thermodynamics the repeating nature of the process path allows for continuous operation,. to model the workings of actual devices Thermodynamic cycles often use quasistatic processes . P-V diagram of a thermodynamic cycle is an Example . on a P-V diagram thermodynamic cycle is a closed loop. A P-V diagrams X axis shows volume (V) and Y axis shows pressure (P). by the process, the area enclosed by the loop is the work (W) done: . Transferred into the system this work is equal to the balance of heat (Q): . to an isothermal process Equation (2) makes a cyclic process similar: during the course of the cyclic process, even though the internal energy changes. The system's energy is the same as the energy it had when the process began when the cyclic process finishes. then it represents a heat engine, and W will be positive if the cyclic process moves clockwise around the loop. then it represents a heat pump, and W will be negative if it moves counterclockwise. Operating Concerns There is an increased chance for the Li-Br salt to begin to crystallize as the concentration of LiBr in the solution increases and the vapor pressure drops. The crystallization limits also have an impact on the liquid-to-liquid heat exchanger that is used to preheat the solution going to the generator. The solution coming from the generator has a relatively high mass concentration of LiBr (e.g., 65 percent). The pressure in the absorber is less than that in the generator, and the heat exchanger will lower the temperature of the returning strong solution. If the returning solution temperature is lowered too much in the heat exchanger, crystallization will begin to occur. This limits the amount of heat that can be recovered from the returning strong solution and thus also limits the performance capabilities of the system. The position in the system where crystallization is most likely to occur is the heat exchanger; low condensing pressures are conducive to crystallization. One method for controlling crystallization is to maintain artificially high condensing pressures even when low temperature cooling water is available. Between the two generator stages double-effect chillers have additional parameters associated with the flow distribution. References 1. Angrist, S.W., Direct Energy Conversion (The Allyn and Bacon, Inc., Boston, MA, 1971). 2. Aphornratana, S., “Thermodynamic Analysis of Absorption Refrigeration Cycles Using the Second Law of Thermodynamics Method,” International Journal of Refrigeration, vol 18, No. 4 (1995), pp 244-252. 3. Wikipedia – Heat Pump and Refrigeration Cycle http://en.wikipedia.org/wiki/Heat_pump_and_refrigeration_cycle 4. Wikipedia – Fourier’s law http://en.wikipedia.org/wiki/Fourier%27s_law 5. http://www.cartage.org.lb/en/themes/Sciences/Physics/Thermodynamics/AppliedThermodynamics/Airconditioners/Airconditioners.htm 6. Wikipedia – Thermodynamic Cycle http://en.wikipedia.org/wiki/Thermodynamic_cycle 7. Thermodynamics - http://www.taftan.com/thermodynamics/ 8. Costa, S., Miranda M., Varum H. and Teixeira-Dias F., 2006, On the evolution of the mechanical behaviour of structural elements, Materials science forum, vol 514-516, pp709-833 9. Schlaich, Mike, et al., Guidelines for the Design, International Federation for Structural Concrete, 2005, 10. Schlaich, Mike, Source: International Journal of Space Structures, Volume 22, Number 1, March 2007 11. Mechanical behaviour of materials, UBC, Vancouver, Canada, July 21-23, 2007. 12. http://pitp.physics.ubc.ca/confs/glass07/ 13. Case Studies for the Use of Post Consumer Glass as a Construction Aggregate, CWC report GL97-5rpt, 1997. Issue Date / Update: November 1996 http://www.chihuly.com/bridgeofglass/projectdescription.html Read More