USN 1 P E PESIT Bangalore South Campus Hosur road, 1km before ElectronicCity, Bengaluru -100 Department of Basic Science and Humanities CONTINUOUS INTERNAL EVALUATION TEST-3 Date : 15/05/2018 Marks: 60 Subject & Code : Elements of Mechanical Engineering Sec : A, B, C, D and E 17EME24 Name of faculty :SP, VNP,CM, AS and MSA Time :90 mins Note: Answer FIVE full questions, selecting any ONE full question from each part. Mark s PART 1 a Discuss the importance of engineering materials in modern age technology and classify engineering materials and give suitable examples. 8 1 b What are constituents of composites? Explain. 4 2 a How do you classify composites? Briefly explain each type. 12 PART 2 a What is soldering? Mention the types of solders. Compare welding, soldering 8 and brazing. 3 b Write short notes on the following: i) Alloy steels ii) Wrought iron 4 a Classify and explain the various types of non-ferrous metals. 8 4 b Write short notes on the following: 4 i) White cast iron. ii) Malleable cast iron. PART 3 5 a Define welding and explain electric arc welding with suitable sketch. 12 6 a Explain gas welding with a suitable sketch. What are types of flames explain 12 each with a suitable sketch PART 4 a Define the falowing: i) COP ii) Ton of refrigeration 6 8 iii) Ice making capacity b Compare vapour compression and vapour absorption refrigeration system 6 a What is the principle of refrigeration? Name the essential parts of refrigerator 8 8 and briefly explain their functions. b Define Refrigerant and list the properties of refrigerant. 4 PART 5 9 a Define refrigeration effect. Explain the construction and working of VARS. 12 10 a What is air conditioning? Explain the construction and working of Room Air 12 Conditioner
PES INSTITUTE OF TECHNOLOGY BANGALORE SOUTH CAMPUS Hosur Road, (1K.M. Before Electronic City), Bangalore 560 100 SCHEME AND SOLUTION - III INTERNAL TEST Subject : Elements of Mechanical Engineering Semester: II Sub. Code : 17EME24 Section: A,B,C,D,E Name of the faculty : SP, VNP,CM, AS and MSA Q.No PART 1 Marks 1(a) 8 1(b) The individual materials that make up composites are called constituents. Most composites have two constituents, a matrix and reinforcement. Reinforcement The reinforcement is usually much stronger and stiffer than the matrix, and that gives the composite its good properties. The matrix hold the reinforcements in an orderly pattern, the matrix also helps to transfer load among the reinforcements. Reinforcements basically come in three forms: particulate, discontinuous fiber, and 4
continuous fiber. 2(a) matrix Matrix materials are usually some type of plastic, and these composites are often called reinforced plastics. There are other types of matrices, such as metal or ceramic, but plastics are the most. The two most common plastic matrices are epoxy resins and polyester resins. Composite materials are commonly classified at two distinct levels: 1) With respect to matrix constituent Polymer matrix composite matrix is made from a polymer resin material Metal matrix composite matrix is made from a metal or alloy Ceramic matrix composite matrix is made from a ceramic material 2) With respect to reinforced constituent Fiber reinforced composite reinforcement is in the form of fiber ( thread like structure) Particle (particulate) reinforced composites reinforcement is in the form of small particles. Laminated composites reinforcement consists of layers of material. Polymer matrix composite -Composites are classified as polymer matrix composite, when the matrix is made from a polymer resin material. The reinforcement material is usually in the form of fibers made from materials like glass, carbon, graphite, boron etc and hence the name fiber reinforced polymer. 12 Metal matrix composite Matrix is made from the metal or alloy. The reinforcement material is usually in the form of fiber, or small sized particles made from ceramic or metallic materials. Most metals and alloys can be used as matrix. However light metals are responsive. Titanium, aluminum, magnesium are the popular matrix metals particularly useful for aircraft application. Ceramic matrix composite Matrix is made from a ceramic material like silicon carbide, aluminum oxide, zirconium oxide. The reinforcement material is usually in the form of fiber, and is also made from a
ceramic material like silicon carbide, aluminum oxide. It is also called as ceramic fiber reinforced ceramic (CFRC) material. With respect to reinforced constituent
PART 2 3(a) 8 3(b) Alloy Steels Alloy steel is used where significant amounts of alloying elements such as nickel, chromium, molybdenum, manganese, silicon, vanadium etc are included in addition to carbon. Alloy steels are generally more responsive to heat and mechanical treatments than carbon steels. Excellent strength, corrosion resistance, hardness and wear resistance can be improved with the alloying elements. Applications: Used in manufacturing of aircraft under carriage parts, punches and dies for cold forging, die casting and extrusion dies for aluminum, bearing elements, heavy gears, corrosion resistant containers etc. 4 Wrought iron ( means work hard ) Wrought iron is a pure form of iron consisting of about 99.5% iron and 0.05 to 0.25% carbon along with traces of sulphur, phosphorous and silicon. The low carbon content makes it soft, ductile ( easy to stretch and make a wire ) and better strength. Applications: Wrought iron is typically used for decorative applications like fences, gates and
railings, lamps etc. 4(a) COPPER AND ITS ALLOYS Copper is one of the most important non ferrous metal and is the first metal discovered by man. It is malleable, corrosion resistant and good conductor of heat and electricity. Pure copper is very ductile and relatively weak. The tensile strength and hardness can be increased by metal working, but this result in the decrease in its ductility. The properties of copper can be improved by adding alloying elements. Brass Brass is an alloy of copper and zinc, the amount of zinc varying from 5 45 % to create a range of brasses. Small amounts of other elements like lead, tin, silicon etc. can be added to brass to modify its properties so that the resulting material is fit for a given purpose. Applications: Used in the manufacture of nuts, threaded parts, taps, injectors, valve bodies etc. Bronze Bronze is a term used to define an alloy of copper and elements other than zinc. The simplest bronze is copper (88%) mixed with a small amounts of tin (not more than 11%). Various alloying elements like phosphorous, lead etc are added in small proportions to obtain favorable properties. Other elements like aluminum, silicon, beryllium are also alloyed with copper to form different types of bronzes. 8
Applications: Bronze can be rolled into wires, rods and sheets due to good ductility and malleability. They are used for springs, electrical contacts, bushes, clutch discs etc. Aluminum and its alloys Aluminum is a silverish metal extracted from Bauxite mineral. Characteristics of aluminum alloy are: Relatively light metal Easily machinable and can have a wide variety of surface finishes. Highly reflective to heat and light Good conductor of heat and electricity Can be cast, rolled, stamped, drawn, hammered, extruded and forged to any shapes. Strong resistance to corrosion. Pure aluminum is weak, very ductile material and hence cannot be used in high strength applications. When it is alloyed with other materials like copper, silicon, magnesium and tin it provides useful properties for wider applications. Applications: Being light in weight, aluminum makes itself ideal for construction of parts in aircraft, automotive vehicles, spacecrafts, marine and similar application areas where weight is a negative factor. Lead and its alloys Lead is soft, silvery white or grayish non-ferrous metal. It is malleable, ductile, corrosion resistant and the heaviest among all the common metals. However it is poor conductor of electricity and poisonous in nature. Lead is usually alloyed with tin and finds applications due to their melting characteristics. Applications: Lead and tin alloys find applications as solders (used for soldering), electrical fuses and boiler plugs. The low melting point of lead makes casting of lead easy, and therefore small arms ammunitions and shotgun pellets can be cast with minimal technical equipment Nickel and its alloys Nickel and nickel alloys are non-ferrous metals with high strength and toughness, excellent corrosion resistance, good machining properties and superior elevated temperature properties. Commercially pure nickel has a good electrical and magnetic properties. Applications: Nickel alloys are vitally important to aerospace, power generation and
petrochemical industrial applications for their high temperature characteristics. Also used in structural applications that requires specific corrosion resistant or high temperature strength properties White cast iron is produced by chilling selected areas of a casting in the mould, this prevents graphite carbon from precipitating out. The carbon remains distributed throughout the iron as iron carbide. White iron contains approximately 1.8 3.6 % carbon, 0.5 2.0 % silicon, along with sulphur, phosphorous and manganese in small amounts. Applications: White cast irons are primarily used for applications requiring wear and abrasion resistance such as mill liners, hot blasting nozzles and similar such components. 4(b) Malleable cast iron is produced by annealing- a heat treatment process, in order to transform iron carbide present in white cast iron to graphite. In the annealing process white cast iron is heated to about 900 C for long periods of time in the presence of iron oxide. Upon cooling the combined carbon separates into nodules of free graphite. Malleable cast iron contains approximately 2 3 % carbon, 0.6 1.3 % silicon, along with sulphur, phosphorous and manganese in small amounts. Applications: Malleable cast irons are used for manufacturing connecting rods and universal joint yokes, transmission gears, differential cases and certain gears, compressor, crankshafts and hubs, flanges. 4 PART 3 5(a) 12
6(a) 12
PART 4
7(a) 6 7(b) 6
In refrigeration, the heat is to be removed continuously from a system at a lower temperature and transfer it to the surroundings at a higher temperature. 8(a) This operation according to the second law of thermodynamics can only be performed by the aid of the external work. Therefore in a refrigerator, power is to be supplied to remove the heat continuously from the refrigerator cabinet to keep it cool at a temperature less than the atmosphere. 1)Evaporator: The evaporator is the heart of the refrigerator where the liquid refrigerant is evaporated by the absorption of heat from the refrigerator cabinet in which the substances which have to be cooled are kept. 2) Circulating system: Circulating devices such as compressor or pumps necessary to circulate the refrigerant to undergo the refrigeration cycle. The refrigeration enters the compressor as a vapor and is compressed to the condenser pressure 3) Condenser: The refrigerant that leaves from the compressor at a relatively high temperature and cools down and condenses as it flows through the coils of condenser by rejecting the heat to the surrounding medium. 4) Expansion device: Then the refrigerant enters a capillary tube where its temperature and pressure drops drastically due to throttling effect. 8
8(b) 4 PART 5 The rate at which the heat is absorbed in a cycle from he interior space to be cooled is called refrigerating effect. 9(a) The vapour absorption refrigerator is a heat operated system. It differs from the vapour compression system only in the manner by which the circulation of the refrigerant is achieved. In the vapour absorption system, the compressor is replaced by an absorber, a generator and a pump. The refrigerant used in this system must be highly soluble in the solution known as
'absorbent'. The system uses ammonia as the refrigerant and water as absorbent. Figure shows the line diagram of a vapour absorption system.the liquid refrigerant (ammonia) in the evaporator absorbs the heat from the medium that is to be cooled and it undergoes a change of phase form liquid to vapour. The low pressure vapour is then passed to the absorber. In the absorber, the low pressure ammonia vapour is dissolved in the weak ammonia solution producing strong ammonia solution at low pressure. The strong ammonia solution is then pumped to a generator through the heat exchanger at high pressure. While passing through the heat exchanger, the strong ammonia solution is warmed up by the hot weak ammonia solution flowing from the generator to the absorber. The warm strong ammonia solution is heated by an external source in the generator. Due to heating, the vapour gets separated from the solution. The vapour which is at high pressure and high temperature is condensed to low temperature in a condenser by cold water circulation. The high pressure liquid ammonia then passes through the expansion valve where it is expanded to low pressure and temperature. The low pressure-low temperature ammonia liquid again enters the evaporator where it absorbs the heat from the medium (cools the medium) and the cycle repeats. 10(a) Air conditioning is defined as the process of simultaneous control of temperature, humidity, cleanliness and air-motion of the confined space. Air conditioning provides comfort for human beings and also a controlled environment for industrial activities. Hence, applications of air conditioning can be broadly divided into comfort applications and process applications. An air conditioner operates on the principle of refrigeration by cooling the air drawn from the conditioned space and returning the cool, fresh air to the conditioned space. A simple room air conditioner is shown in Figure using block diagram. The system consists of a compressor, a condenser denser,, an evaporator, a capillary y tube, condenser and evaporator fans driven by the same motor. The evaporator fan and the evaporator coils of the unit always lie inside the building or space which is to be conditioned. Condenser and the condenser fan of the unit projects outside the building or space to enable heat transfer with the atmosphere. The high pressure refrigerant leaving the compressor enters the condenser coils. The latent heat of the refrigerant vapour is given to the surrounding atmosphere. Condensation takes place due to this heat transfer as the condenser fan draws air from outside the building and circulates it over the condenser coils. The high temperature liquid refrigerant enters the capillary tube and
expands in it. Partial evaporation of the refrigerant takes place in the capillary tube reducing the pressure to evaporator pressure. The cold refrigerant enters the evaporator coils. The evaporator fan continuously draws hot air from the conditioned space and circulates it over the evaporator coils. The hot air passing through the air filter comes in contact with cold evaporator coils and exchanges its heat. The cool fresh air enters the conditioned space. As a result, complete evaporation of the refrigerant takes place which enters the compressor again. The cycle repeats again and again. Desired temperature inside the room can be adjusted by thermostatic control device.