Jump to content
Mechanical Engineering Community

Leaderboard


Popular Content

Showing content with the highest reputation since 02/20/2018 in all areas

  1. 5 points

    Version 1.1.0

    30,249 downloads

    A COMPLETE INSTRUCTOR AND STUDENT SUPPLEMENT PACKAGE - Continued These ppts are set of instructor and student supplements. . A FOCUS ON DIAGNOSIS AND PROBLEM SOLVING The primary focus of these ppts is to satisfy the need for problem diagnosis. Time and again, the author has heard that technicians need more training in diagnostic procedures and skill development. To meet this need and to help illustrate how real problems are solved, diagnostic stories are included throughout. Each new topic covers the parts involved as well as their purpose, function, and operation, and how to test and diagnose each system.
  2. 4 points
    Selection of material is an important aspect for manufacturing industries . The quality of product is highly depends upon its material properties. These properties are used to distinguish materials from each other. For Example: A harder material is used to make tools.A ductile material is used to draw wires. So the knowledge of mechanical properties of material is desirable for any mechanical student or for any person belongs to mechanical industries. This post brings top 18 mechanical properties. Mechanical properties of material: There are mainly two types of materials. First one is metal and other one is non metals. Metals are classified into two types : Ferrous metals and Non-ferrous metals. Ferrous metals mainly consist iron with comparatively small addition of other materials. It includes iron and its alloy such as cast iron, steel, HSS etc. Ferrous metals are widely used in mechanical industries for its various advantages. Nonferrous metals contain little or no iron. It includes aluminum, magnesium, copper, zinc etc. Most Mechanical properties are associated with metals. These are #1. Strength: The ability of material to withstand load without failure is known as strength. If a material can bear more load, it means it has more strength. Strength of any material mainly depends on type of loading and deformation before fracture. According to loading types, strength can be classified into three types. a. Tensile strength: b. Compressive strength: 3. Shear strength: According to the deformation before fracture, strength can be classified into three types. a. Elastic strength: b. Yield strength: c. Ultimate strength: #2. Homogeneity: If a material has same properties throughout its geometry, known as homogeneous material and the property is known as homogeneity. It is an ideal situation but practically no material is homogeneous. #3. Isotropy: A material which has same elastic properties along its all loading direction known as isotropic material. #4. Anisotropy: A material which exhibits different elastic properties in different loading direction known as an-isotropic material. #5. Elasticity: If a material regain its original dimension after removal of load, it is known as elastic material and the property by virtue of which it regains its original shape is known as elasticity. Every material possess some elasticity. It is measure as the ratio of stress to strain under elastic limit. #6. Plasticity: The ability of material to undergo some degree of permanent deformation without failure after removal of load is known as plasticity. This property is used for shaping material by metal working. It is mainly depends on temperature and elastic strength of material. #7. Ductility: Ductility is a property by virtue of which metal can be drawn into wires. It can also define as a property which permits permanent deformation before fracture under tensile loading. The amount of permanent deformation (measure in percentage elongation) decides either the material is ductile or not. Percentage elongation = (Final Gauge Length – Original Gauge Length )*100/ Original Gauge Length If the percentage elongation is greater than 5% in a gauge length 50 mm, the material is ductile and if it less than 5% it is not. #8. Brittleness: Brittleness is a property by virtue of which, a material will fail under loading without significant change in dimension. Glass and cast iron are well known brittle materials. #9. Stiffness: The ability of material to resist elastic deformation or deflection during loading, known as stiffness. A material which offers small change in dimension during loading is more stiffer. For example steel is stiffer than aluminum. #10. Hardness: The property of a material to resist penetration is known as hardness. It is an ability to resist scratching, abrasion or cutting. It is also define as an ability to resist fracture under point loading. #11. Toughness: Toughness is defined as an ability to withstand with plastic or elastic deformation without failure. It is defined as the amount of energy absorbed before actual fracture. #12. Malleability: A property by virtue of which a metal can flatten into thin sheets, known as malleability. It is also define as a property which permits plastic deformation under compression loading. #13. Machinability: A property by virtue of which a material can be cut easily. #14. Damping: The ability of metal to dissipate the energy of vibration or cyclic stress is called damping. Cast iron has good damping property, that’s why most of machines body made by cast iron. #15. Creep: The slow and progressive change in dimension of a material under influence of its safe working stress for long time is known as creep. Creep is mainly depend on time and temperature. The maximum amount of stress under which a material withstand during infinite time is known as creep strength. #16. Resilience: The amount of energy absorb under elastic limit during loading is called resilience. The maximum amount of the energy absorb under elastic limit is called proof resilience. #17. Fatigue Strength: The failure of a work piece under cyclic load or repeated load below its ultimate limit is known as fatigue. The maximum amount of cyclic load which a work piece can bear for infinite number of cycle is called fatigue strength. Fatigue strength is also depend on work piece shape, geometry, surface finish etc. #18. Embrittlement: The loss of ductility of a metal caused by physical or chemical changes, which make it brittle, is called embrittlement.
  3. 4 points
    tractors and Backhoe loaders are supposed to maintain a constant depth in ploughing/digging. For this it requires the movement of the body to be restricted so that we dont disturb the main tractor functions. If we have a suspended tractor which bounces too much over undulations in a field then we cannot expect the implement to have a constant ploughing depth which is a requirement in agriculture.
  4. 4 points
    1. It's not oil the best name is brake fluid as it consists a lot of material inside such as (silicone, glycol ether/borate ester, mineral oil) 2. One of the main things for BF, it must have a high boiling point to avoid vaporizing in the lines this is why we need to change the brake fluid from time to time as it has tendency to absorb water which will lower its boiling temperature leading to change part of the fluid into moisture and vapour inside the brake circuits and this will create vapour lock leading to being compressible and once it became compressible the brake foot force will not be transferred to the other brake parts (cylinders,brake pistons, ...) We have many types of BF each has its own dry/wet boiling temperature such as:- DOT3 (dry 205C/401F- wet 140C/284F) DOT4 (dry 230C/446F - wet 150C/311F) DOT5 (dry 260C/500F - wet 180C/365F) *Hygroscopic means (water absorbing)
  5. 3 points
    Get a chance to win - Religion Engineer Caste Mechanical Tshirt You can also buy it from https://teespring.com/mechanical-engineering-tees_eu What you need to do Reply only once the following Your name Your Engineering College Year of completing the degree Make sure the t-shirt image is not posted again in your reply..... Last Date to receive entries for T-shirts - Oct 8th 2018 Number of Tees will be given as per the received entries 100 to 499 Entries received 1 T-shirt 500 to 999 Entries 2 T-shirts 1000 or more Entries 5 T-shirts There will be lucky draw to find the winners...and name of Winners will be informed on Oct 10th. This is only available to mechanical engineering professionals. This give away is to encourage participation among members. All rights and decisions are reserved with team of the website. Lets start introduction... Just follow the rules... Do not post anything in between... just be professional.
  6. 3 points
    Pre-heat is required for the following reasons: (1) It lowers the cooling rate in the weld metal and base metal, producing a more ductile metallurgical structure with greater resistant to cracking. (2) The slower cooling rate provides an opportunity for any hydrogen that may be present to diffuse out harmlessly without causing cracking. (3) It reduces the shrinkage stresses in the weld and adjacent base metal, which is especially important in highly restrained joints. (4) It raises some steels above the temperature at which brittle fracture would occur in fabrication. Post heating is required to remove further residual stresses present in the weld pool after heat treatment process also. If post heating is not done, then residual stresses develops as cracks and propagates throughout, resulting in the failure of the material. Also Preheat/Post weld heat treatment can be used to help ensure specific mechanical properties, such as notch and toughness.
  7. 2 points
    1. What is the difference between scavenging and supercharging ? Ans: Scavenging is process of flushing out burnt gases from engine cylinder by introducing fresh air in the cylinder before exhaust stroke ends. Supercharging is the process of supplying higher mass of air by compressing the atmospheric air. 2. What are the names given to constant temperature, constant pressure, constant volume, constant internal energy, constant enthalpy, and constant entropy processes.Ans: Isothermal, isochroic, isobaric, free expression, throttling and adiabatic processes respectively. 3. In a Rankine cycle if maximum steam pressure is increased keeping steam temperature and condenser pressure same, what will happen to dryness fraction of steam after expansion ?Ans: It will decrease. 4. Why entropy change for a reversible adiabatic process is zero ? Ans: Because there is no heat transfer in this process. 5. What are two essential conditions of perfect gas ? Ans: It satisfies equation of state and its specific heats are constant. 6. Enthalpy and entropy are functions of one single parameter. Which is that ? Ans: Temperature. 7. Why rate of condensation is higher on a polished surface compared to rusty surface ? Ans: Polished surface promotes drop wise condensation and does not wet the surface. 8. How much resistance is offered to heat flow by drop wise condensation ? Ans: Nil How are these questions - please do add comments and if you like them please do share this post on facebook, linkedin, twitter and google plus. 9. What is the relationship between COP of heating and cooling ? Ans: COP of heating is one(unity) more than COP of cooling. 10. How much is the work done in isochoric process ? Ans: Zero. 11. When maximum discharge is obtained in nozzle ? Ans: At the critical pressure ratio. 1. Under what condition the work done in reciprocating compressor will be least ? Ans: It is least when compression process approaches isothermal. For this purpose, attempts are made to cool the air during compression. 13. What is the difference between stalling and surging in rotary compressions ? Ans: Stalling is a local phenomenon and it occurs when How breaks away from the blades. Surging causes complete breakdown of flow and as such it affects the whole machine. 14. Why the electric motor of a fan with backward curved blades is never got overloaded under any condition ? Ans: The maximum power is consumed at about 70% of maximum flow in case'of fan with backward blades. For higher flow, power consumption gets lower. 15. Why the work per kg of air flow in axial flow compressor is less compared to centrifugal compressor for same pressure ratio ? Ans: Isentropic efficiency of axial flow compressor is higher. 16. What is the name given to portion of thermal energy to be necessarily rejected to environment ? Ans: Anergy. 17. What is pitting ? How it is caused ? Ans: Non uniform corrosion over the entire metal surface, but occuring only in small pits is called pitting. It is caused by lack of uniformity in metal. 18. What is caustic embrittlement ? Ans: It is the actual physical change in metal that makes it extremely brittle and filled with minute cracks. It occurs particularly in the seams of rivetted joints and around the rivet holes. 19. Which impurities form hard scale and which impurities soft scale ? Ans: Sulphates and chlorides of lime and magnesium form hard scale, and carbonates of lime and magnesium form soft scale. 20. What is the difference between hard water and soft water ? Ans: Hard water contains excess of scale forming impurities and soft water contains very little or no scale forming substances. 21. Which two elements in feed water can cause corrosion of tubes and plates in boiler ? ' Ans: Acid and oxygen in feed water lead to corrosion. 22. What should be done to prevent a safety valve to stick to its seat ? Ans: Safety valve should be blown off periodically so that no corrosion can take place on valve and valve seat. 23. Why large boilers are water tube type ? Ans: Water tube boilers raise steam fast because of large heat transfer area and positive water circulation. Thus they respond faster to fluctuations in demand. Further single tube failure does not lead to catastrophy. 24. What type of boiler does not need a steam drum ? Ans: Super-critical pressure boiler. 25. Why manholes in vessels are usually elliptical in shape ? Ans: Elliptical shape has minimum area of opening and thus plate is weakened the least. Further it is very convenient to insert and take out the cover plate from elliptical opening. 26. Low water in boiler drum is unsafe because it may result in overheating of water tubes in furnace. Why it is unsafe to have high water condition in boiler drum ? Ans: High drum level does not allow steam separation to be effective and some water can be carried over with steam which is not desirable for steam turbine. 27. Why boiler is purged everytime before starting firing of fuel ? Ans: Purging ensures that any unburnt fuel in furnace is removed, otherwise it may lead to explosion. 28. What is the principle of mechanical refrigeration ? Axis. A volatile liquid will boil under the proper conditions and in so doing will absorb heat from surrounding objects. 29. Why high latent heat of vaporisation is desirable in a refrigerant ? Ans: A high latent heat of vaporisation of refrigerant results in small amount of refrigerant and thus lesser circulation system of refrigerant for same tonnage. 30. What is the critical temperature of a refrigerant ? Ans: Critical temperature is the maximum temperature of a refrigerantrat which it can be condensed into liquid and beyond this it remains gas irrespective of pressure applied. 31. Maximum combustion temperature in gas turbines is of the order of 1100 to 10°C whereas same is around 00°C in I.C. engine ? Why ? Ans: High temperature in I.C. engine can be tolerated because it lasts for a fraction of second but gas turbines have to face it continuously which metals can't withstand. 32. Why efficiency of gas turbines is lower compared to I.C. engines ? Ans: In gas turbines, 70% of the output of gas turbine is consumed by compressor. I.C. engines have much lower auxiliary consumption. Further combustion temperature of I.C. engines is much higher compared to gas turbine. 33. What do you understand by timed cylinder lubrication ? Ans: For effective lubrication, lub oil needs to be injected between two piston rings when piston is at bottom of stroke so that piston rides in oi during upward movement. This way lot of lub oil can be saved and used properly. 34. What is IIUCR in relation to petrol engine ? Ans: HUCR is highest useful compression ratio at which the fuel can be used in a specific test engine, under specified operating conditions, without knocking. 35. In some engines glycerine is used in place of water for cooling of engine. Why ? Ans: Glycerine has boiling point of 90°C which increases its heat carrying capacity. Thus weight of coolant gets reduced and smaller riadiator can be used. 36. Why consumption of lubricating oil is more in two-stroke cycle petrol engine than four-stroke cycle petrol engine ? Ans: In two-stroke engine lub oil is mixed with petrol and thus some lub oil is blown out through the exhaust valves by scavenging and charging air. There is no such wastage in four stroke petrol engine. 37. As compression ratio increases, thermal n increases. How is thermal n affected by weak and rich mixture strength ? Ans: Thermal n is high for weak mixture and it decreases as mixture strength becomes rich. 38. How engine design needs to be changed to burn lean mixture ? Ans: Engine to burn lean mixture uses high compression ratio and the highly turbulent move¬ment of the charge is produced by the geometry of the combustion chamber. 39. Horse power of I.C. engines can be expressed as RAC rating, SAE rating, or DIN rating. To which countries these standards belong ? Ans: U.K., USA and Germany respectively. 40. What is the use of flash chamber in a vapour compression refrigeration cycle to improve the COP of refrigeration cycle ? Ans: When liquid refrigerant as obtained from condenser is throttled, there are some vapours. These vapours if carried through the evaporator will not contribute to refrigerating effect. Using a flash chamber at some intermediate pressure, the flash vapour at this pressure can be bled off and fed back to the compression process. The throttling process is then carried out in stages. Similarly compression process is also done in two separate compressor stages. 41. Why pistons are usually dished at top ? Ans: Pistons are usually hollowed at top to (i) provide greater spa'e for combustion, (ii) increase surface for flue gases to act upon, and (iii) better distribution of stresses. 42. What is the function of thermostat in cooling system of an engine ? Ans: Thermostat ensures optimum cooling because excessive cooling decreases the overall efficiency. It allows cooling water to go to radiator beyond a predetermined temperature. 43. What are the causes of failure of boiler tubes ? Ans: Boiler tubes, usually are made from carbon steel and are subject to (a) high rates of heat transfer,( b ). bending stresses due to uneven heating, especially at expanded or welded joints into headers or drums, © external erosion from burners and flue gas, (d) possible corrosion on the boiler side, and (e) occasional manufacturing defects. Failure may occur due to following reasons : (a) High thermal ratings may lead to rapid failure if the internal fluid flow is reduced for any reason. The resultant overheating leads to a failure by creep, characterised by the bulging of the tube with the eventual development of a longitudinal split. (b ) Fatigue cracking due to bending stresses occur. These are associated with change of section and/or weld undercut, where tubes are expanded or welded into headers. © Failure may arise due to overstressing of a reduced section of metal. (d) Sudden failure of the boiler tube due to corrosion arises from embrittlement of the carbon steel due to interaction between atomic hydrogen from the corrosion process and the iron carbide present in the steel. (e) Defects in tube manufacture, although far from being a regular occurrence, can be a cause of serious trouble. Lamination in boiler tubes or score marks arising from the cold drawing of tubes, give rise to premature failure and may promote corrosion at these regions. 44. What are the causes of failure of superheater tubes ? Ans: Superheater tubes are subjected to the most severe combination of stress, temperature and corrosive environment. In addition to high-temperature strength, resistance to corrosion is also important. For example, low-alloy ferritic steel such as -1/% Cr, 1% Mo would not be used at metal temperatures above 580°C because of inadequate resistance to corrosion and oxidation over a full service life of 100,000/150,000 hr. Failures in superheater tubes may arise from : (a) Prior fabrication history (b ) Faulty heat treatment © Consequences of welding (d) Overheating of the tube metal (e) Gas-side corrosion (f) Stress corrosion (austenitic steels). 45. Why supercritical boilers use less amount of steel compared to non-supercritical boilers ? Ans: Supercritical boilers do not head heavy drum for separation of steam from mixture of water and steam. 46. Out of electric heater and heat pump, which is economical in operation ? Ans: Heat pump. 47. Which furnace burns low-ash fusion coal and retains most of the coal ash in the slag? Ans: Cyclone furnace. 48. How the thickness of thermal boundary layer and thickness of hydrodynamic boundary layer related ? Ans: Ratio of their thickness = (Prandtl number)-1/3. 49. What is the effect of friction on flow of steam through a nozzle ? Ans: To decrease both mass flow rate and wetness of steam. 50. Why gas turbine power plant needs efficient compressor ? Ans: Because a large portion of turbine work is eaten away by compressor and its inefficiency will affect net power output and cost of generation. 51. Why rockets using liquid hydrogen have higher specific impulse compared to liquid hydrocarbon ? Ans: Liquid hydrogen has higher burning velocity. 52. Why axial flow compressor is preferred for gas turbines for aeroplanes ? Ans: Because it has low frontal area. 53. What is the effect of inter cooling in gas turbines ? Ans: It decreases thermal efficiency but increases net output. 54. Why iso-octane is chosen as reference fuel for S.I. engines and allotted 100 value for its octane number ? Ans: Iso-octane permits highest compression without causing knocking. 55. Why thermal efficiency of I.C. engines is more than that of gas turbine plant ? Ans: In I.C. engine maximum temperature attained is higher than in gas turbine. 56. Which are the reference fuels for knock rating of S.I. engines ? Ans: n-heptane and ISO-octane. 57. When effect of variations in specific heats is considered then how do maximum temperature and pressure vary compared to air standard cycle ? Ans: Temperature increases and pressure decreases. 58. Quantities like pressure, temperature, density, viscosity, etc. are independent of mass. What are these called ? Ans: Intensive properties. 59. The amount of radiation emitted per scm per sec is called .... ? Ans: Emissive power. 60. In convection heat transfer, if heat flux intensity is doubled then temperature difference between solid surface and fluid will ? Ans: Get doubled. 61. How you can define coal ? Ans: Coal is a naturally occurring hydrocarbon that consists of the fossilised remains of buried plant debris that have undergone progressive physical and chemical alteration, called coalification, in the course of geologic time. 62. Which pollutant is major greenhouse gas and what is its effect ? Ans: CO is major greenhouse gas and it traps the radiation of heat from the sun within earth's atmosphere. 63. In order to increase efficiency and reduce CO emissions and other emissions, clear coal technologies are receiving major attention. What are these ? Ans: (i) Advanced pulverised and pressurised pulverised fuel combustion. (ii) Atmospheric fluidised bed combustion and pressurised fluidised bed combustion. (iii) Supercritical boilers. (iv) Integrated gasification combined cycle systems. (v) Advanced integrated gasification, including fuel cell systems. (vi) Magneto hydrodynamic electricity generation. 64. What are the important operational performance parameters in design of fuel firing equipment ? Ans: Fuel flexibility, electrical load following capability, reliability, availability, and maintenance ease. 65. What is the differenc between total moisture and inherent moisture in coal ? Ans: The moisture content of the bulk as sampled is referred to as total moisture, and that of the air dried sample is called inherent moisture. 66. Proximity analysis of coal provides data for a first, general assessment of a coal's quality and type. What elements it reports ? Ans: Moisture, volatile matter, ash and fixed carbon. 67. Ultimate analysis of coal is elementary analysis. What it is concerned with ? Ans: Carbon, hydrogen, nitrogen, and sulphur in coal on a weight percentage basis. 68. Explain the difference between AFBC, BFBC, PFBC and PCFB in regard to fluidised bed technologies. Ans: AFBC (Atmospheric fluidised bed combustion) process consists of forming a bed of inert materials like finely sized ash or ash mixed with sand, limestone (for sulphur removal), and solid fuel particles in a combustor and fluidising it by forcing combustion air up through the bed mixture. The gas flows thorugh bed without disturbing particles significantly but gas velocity is high enough to support the total weight of bed (fluidisation). At slightly higher velocity excess gas passes through the bed as bubbles (fluidised bed) and gives the bed the appearance of a boiling liquid. Bubbling fluidised bed combustion (BFBC) has a defined height of bed material and operates at or near atmospheric pressure in the furnace. Pressurised fluidised bed combustion (PFBC) system operates the bed at elevated pressure. Exhaust gases have sufficient energy to power a gas turbine, of course, gases need to be cleaned. In fluidised combustion, as ash is removed some unburned carbon is also removed resulting in lower efficiency. In circulating fluidised bed combustion (CFBC) system, bed is operated at higher pressure leading to high heat transfer, higher combustion efficiency, and better fuel feed. Circulating fluidised beds operate with relatively high gas velocities and fine particle sizes. The maintenance of steady state conditions in a fast fluidised bed requires the continuous recycle of particles removed by the gas stream (circulating bed). The term circulating bed is often used to include fluidised bed sys¬tems containing multiple conventional bubbling beds between which bed material is exchanged. 69. What for Schmidt plot for is used in heat transfer problems ? Ans: Schmidt plot is a graphical method for determining the temperature at any point in a body at a specified time during the transient heating or cooling period. 70. In which reactor the coolant and moderator are the same ? Ans: Pressurised water reactor. 71. Which reactor has no moderator ? Ans: Fast breeder reactor. 72. What are thermal neutrons ? Ans: Thermal neutrons are slow neutrons (having energy below 1 eV) which are in thermal equilibrium with their surroundings. 73. What is big advantage of fast breeder reactor ? Ans: It has rapid self breeding of fissile fuel during the operation of the reactor, and thus, it offers about sixty times the output with same natural uranium resources through ordinary non-breeder nuclear reactor. 74. What is the purpose of biological shield in nuclear plants ? Ans: Biological shield of heavy concrete prevents exposure to neutrons, beta rays and gamma rays which kill living things. 75. Which two elements have same percentage in proximate and ultimate analysis of coal? Ans: Moisture and ash. 76. On which analysis is based the Dulong's formula for the heating value of fuel ? Ans: On ultimate analysis. 77. Which element causes difference in higher and lower heating values of fuel ? Ans: Hydrogen. 78. Which heating value is indicated by a calorimeter and why ? Ans: Gross heating value because steam is condensed and heat of vapour formed is recovered. 79. State the difference between ultimate and proximate analysis of coal ? Ans: In ultimate analysis, chemical determination of following elements is made by weight: Fixed and combined carbon, H, O, N, S, water and ash. Heating value is due to C, H and S. In proximate analysis following constituents are mechanically determined by weight. Moisture, volatile matter, fixed carbon and ash. Heating value is due to fixed carbon and volatile matter. 80. What is fuel ratio ? Ans: Fuel ratio is the ratio of its % age of fixed carbon to volatile matter. 81. How the analyses and calorific values of fuels can be reported ? Ans: It may be reported as (a) as received or fired (wet) basis (b ) dry or moisture free basis © combustible or ash and moisture free basis 82. What is the difference between nuclear fission and fission chain reaction. Ans: The process of splitting of nucleus into two almost equal fragments accompanied by re¬lease of heat is nuclear fission. Self sustained, continuing, sequence of fission reactions in a con¬trolled manner is fission chain reaction. 83. Explain difference between fissile and fertile materials. Ans: The materials which can give nuclear fission e.g. U 35, Pu 39, U 33 are fissile materi¬als. Fertile material itself is not fissionable, but it can be converted to a fissionable material by irradiation of neutrons in a nuclear reactor. 84. What do you understand by fuel cycle in nuclear plants ? Ans: Fuel cycle a series of sequential steps involved in supplying fuel to a nuclear power reactor. The steps include : Mining, refining uranium, fabrication of fuel elements, their use in nuclear reactor, chemical processing to recover remaining fissionable material, re-enrichment of fuel from recovered material, refabrication of new fuel elements, waste storage etc. 85. What is heavy water and what is its use in nuclear plants ? Ans: Water containing heavy isotopes of hydrogen (Deuterium) is known as heavy water. Heavy water is used as a moderator. Heavy water has low cross section for absorption of neutrons than ordinary water. Heavy water slows down the fast neutrons and thus moderates the chain reaction. 86. What is a converter reactor ? Ans: A reactor plant which is designed to produce more fuel than it consumes. The breeding is obtained by converting fertile material to fissile material. 87. Explain nuclear reactor in brief. Ans: A plant which initiates, sustains, controls and maintains nuclear fission chain reaction and provides shielding against radioactive radiation is nuclear reactor. 88. What is the difference between conversion and enrichment ? Ans: The process of converting the non fissile U 38 to fissile U-35 is also called "Conversion". The material like U 38 which can be converted to a fissile material by the neutron flux is called "fertile material". The conversion is obtained within the nuclear reactor during the chain reaction. Enrichment is the process by which the proportion of fissile uranium isotope (U-35) is increased above 0.7% (original % in natural uranium). The concentration of U-35 in the uranium hexafluoride is increased from the 0.7% in natural uranium to to 4%. This is called enrichment and is accomplished in an enrichment plant. 89. Disposal of radioactive waste materials and spent fuel is a major and important technology. How the waste radioactive material is disposed off ? Ans: Nonusable fission products are radioactive and take short/medium/long time for radioactive decay to reach safe level of radioactivity. Accordingly three methods of disposal are : (a) Zero or low radioactivity material is dispersed or stored without elaborate shielding. (b ) Medium radioactivity material is stored for short duration of about 5 years to allow decay of radioactivity. © High radioactive material. They are stored in water for several months to permit radioactive decay to an accepetable low level. 90. Which nuclear reactor uses water as a coolant, moderator and reflector ? Ans: Pressurised water reactor. 91. Which reactor produces more fissionable material than it consumes ? Ans: Breeder reactor. 92. Which reactor uses natural uranium as fuel ? Ans: Gas cooled reacator. 93. Which reactor uses heavy water as moderator ? Ans: CANDU. 94. Which reactor requires no moderator ? Ans: Breeder reactor. 95. Which reactor uses primary coolant as fluoride salts of lithium, beryllium, thorium and uranium ? Ans: Molten salt breeder reactor. 96. Why an increase in area is required to produce an increase of velocity in case of supersonic flow ? Ans: Increase in area for increase in velocity for supersonic flow is required because the density decreases faster than velocity increases at supersonic speeds and to maintain continuity of mass, area must increase. 97. Under what circumstances would there be an increase in pressure in a diver¬gent nozzle ? Ans: For subsonic flow at inlet section of a diffuser a lower velocity and higher pressure will exist at the exit section. For supersonic isentropic flow at the inlet section a higher velocity and lower pressure will exist at the exit but if a shock wave occurs in the diffuser then a higher pressure will exist at the exit. 98. Why water can't be used as refrigerant for small refrigerating equipment ? Ans: The refrigerant should be such that vapour volume is low so that pumping work will be low. Water vapour volume is around 4000 times compared to R- for a given mass. 99. Which parameter remains constant in a throttling process ? Ans: Enthalpy. 100. What is the difference between isentropic process and throttlinglprocess ? Ans: In isentropic process, heat transfer takes place and in throttling process, enthalpy before and after the process is same.
  8. 2 points
    AKS15

    Mechanical Engineering Quiz 1

    How will the balance reading remain same in that "Bucket-Spring balance" question. Reading should increase perhaps.
  9. 2 points
  10. 2 points
    • Graded Mode
    • 10 minutes
    • 20 Questions
    • 111 Players
    lets check your knowledge on production engineering We will be starting the online quiz series This is the first among the same...We are testing the system One lucky winner among the top scorer will get "I am a Mechanical engineer t-shirt" The winner will be choose from lucky draw This t-shirt Please encourage all your friends to participate... More the participants...more prizes will be offered in the coming quiz series. All the best
  11. 2 points
    Thanks for writing here,welcome on https://mechanical-engg.com/ look forward for your active participation.
  12. 2 points
    Concept of heating is just simple with respect to welding. Majorly Pre or post heating in welding is to relieve stresses which are used to developed during welding. Pre heating: Power saving - by pre heating, heat gradient can be reduced and so to control heat generation, low heat input can be given and so process characteristics can be reduced accordingly Reduction in internal residual stresses - the stresses will are already inside the material can reduce the strength of the weld, to avoid that, pre treatment can be used Post heating: Post heating or annealing or normalizing is done mainly to reduce the thermal stresses developed during welding To relieve Hydrogen embrittlement in which Hydrogen has entrapped during welding from moisture or the filler material
  13. 2 points
    Welding is a process of joining similar and dissimilar metals or other material by application of heat with or without application of pressure and addition of filler material. It is used as permanent fasteners. Welding is essential process of every manufacturing industries. In fact, the future of any new metal may depend on how far it would lend itself to fabrication by welding. The weldability has been defined as the capacity of being welded into inseparable joints having specified properties such as definite weld strength proper structure. The weldability of any metal depends on five major factors. These are melting point, thermal conductivity, thermal expansion, surface condition, and change in microstructure. Types of welding: Basically welding may be classified into three types. 1. Plastic welding: In plastic welding or pressure welding process, the pieces of metal to be joined are heated to a plastic state and then forced together by external pressure. These welding are also known as liquid-solid welding process. This procedure is used in forge welding and resistance welding. 2. Fusion welding: In the fusion welding or no pressure welding process, the material at the joint is heated to a molten state and allowed to solidify. These welding are also known as liquid state welding process. This includes gas welding, arc welding, thermite welding etc. 3. Cold welding: In this welding process, the joints are produced without application of heat, but by applying pressure which results diffusion or inter-surface molecular fusion of the parts to be joined. It is also known as solid state welding process. This process is mainly used for welding nonferrous sheet metal, particularly aluminum and its alloys. This includes ultrasonic welding, friction welding, Explosive welding etc. 4 Main Welding Processes: 1. Arc Welding (Fusion Welding): In this type of welding process, weld metal melted from the edges to be joined and allow to solidifies from the liquid state and usually below the recrystallization temperature without any applied deformation. Arc welding is most extensively employed method of joining metal parts by fusion. In this welding the arc column is generated between an anode, which is the positive pole of power supply, and the cathode, the negative pole. When these two conductors of an electric circuit are brought together and separated for a small distance such that the current continues to flow through a path of ionized particles called plasma, an electric arc is formed. This ionized gas column acts as a high resistance conductor that enables more ions to flow from the anode to the cathode. Heat is generated as the ions strike the cathode. This heat used as melting of metal to be joined or melting the filler metal which further used as joining material of welding metal. The electrode is either consumable or non-consumable as per welding requirement. The temperature at the center of the arc being 6000 OC to 7000OC 2. Gas Welding: The gas welding is done by burning of combustible gas with air or oxygen in a concentrated flame of high temperature. As with other welding methods, the purpose of the flame is to heat and melt the parent metal and filler rod of a joint. It can weld most common materials 3. Gas Metal arc welding (MIG): This welding is also known as metal inert gas welding. In this type of welding a metal rod is used as one electrode, while the work being welded is used as another electrode. It is a gas shielded metal arc welding which uses the high heat of an electric arc between a continuously fed, consumable electrode wire and the material to be welded. Metal is transferred through protected arc column to the work. In this process the wire is fed continuously from a reel through a gun to constant surface imparts a current upon the wire. In this welding the welding area is flooded with a gas which will not combine with the metal. The rate of flow gas is sufficient to keep the oxygen of the air away from the hot metal surface while welding is being done. 4. Gas Tungsten Arc Welding (TIG): This welding is also known as tungsten inert gas welding is similar to the MIG in that is uses the gases for shielding. This arc welding process uses the intense heat of an electric arc between a no consumable tungsten electrode and the material to be welded. In this process the electrode is not consumable during welding process and gas is used to protect the weld area form atmospheric air.
  14. 2 points
    They both are the metal forming processes. When plastic deformation of metal is carried out at temperature above the recrystallization temperature the process, the process is known as hot working. If this deformation is done below the recrystallization temperature the process is known as cold working. There are many other differences between these processes which are described as below. Difference between Hot Working and Cold Working: S.No. Cold working Hot working 1 It is done at a temperature below the recrystallization temperature. Hot working is done at a temperature above recrystallization temperature. 2. It is done below recrystallization temperature so it is accomplished by strain hardening. Hardening due to plastic deformation is completely eliminated. 3. Cold working decreases mechanical properties of metal like elongation, reduction of area and impact values. It increases mechanical properties. 4. Crystallization does not take place. Crystallization takes place. 5. Material is not uniform after this working. Material is uniform thought. 6. There is more risk of cracks. There is less risk of cracks. 7. Cold working increases ultimate tensile strength, yield point hardness and fatigue strength but decreases resistance to corrosion. In hot working, ultimate tensile strength, yield point, corrosion resistance are unaffected. 8. Internal and residual stresses are produced. Internal and residual stresses are not produced. 9. Cold working required more energy for plastic deformation. It requires less energy for plastic deformation because at higher temperature metal become more ductile and soft. 10. More stress is required. Less stress required. 11. It does not require pickling because no oxidation of metal takes place. Heavy oxidation occurs during hot working so pickling is required to remove oxide. 12. Embrittlement does not occur in cold working due to no reaction with oxygen at lower temperature. There is chance of embrittlement by oxygen in hot working hence metal working is done at inert atmosphere for reactive metals.
  15. 2 points
    saurabhjain

    Engines

    We welcome comments on each picture of engines...
  16. 2 points

    Version

    6,533 downloads

    Powerpoint Notes on Metal forming Topic includes— Hot &Cold working Forging Extrusion Rolling Drawing
  17. 2 points
    Diesel Engines we dont need the Spark Plug the Calorific value of the Diesel is more when compared with petrol Engine. For less colorific value we do not get more horse power. But diesel natually have more heat developed during combustion thus developing more power than petrol engines.
  18. 2 points
    HAI Amit kumar, This is hari can u please explin me in breif About this line"To reduce the internal pressure"
  19. 1 point
    Define coefficient of Drag. 1. You can answer this question 2. You can like the best answer 3. You can share the question...
  20. 1 point
    If a idler pulley is necessary, there are rules as to the diameter that should be used so as not the "break the back" of the belt, I assume you are talking v-belts. Then when tensioning the drive belts your need to apply about a 1% stretch to the cords in the belt, assumption is std belts with polyester cords. If you are thinking to firstly correctly tension the belts, then apply an idler, the whole drive could be over tensioned and damage the shaft and bearings. You have to tension the drive the same as you would with the idler in the system, Both Carlisle Belts and Gates have very good drive design programs for designing and provide tensioning information. This is not a simple procedure and the larger the drive the bigger the loads, also life and efficiency are very important.
  21. 1 point
    • Graded Mode
    • 10 minutes
    • 17 Questions
    • 33 Players
    Mechanical Engineering Quiz 8
  22. 1 point

    From the album: Engineering images 10

    Overhead valve, also commonly called pushrod, engines are a simplified V-style design. These are built to be compact and resistant to oil contamination and are often used in small displacement racing.In consumer automotive, however, the pushrod engine has largely been replaced by the SOHC and DOHC designs....
  23. 1 point
    What should be done to avoid tension loading in column ?
  24. 1 point

    Version 1.0.0

    875 downloads

    Detailed presentation about Flywheels and governors. Including 3 videos for proper explanation.
  25. 1 point
  26. 1 point

    From the album: All in a picture!

    All of the basic hydraulic valves and their symbols
  27. 1 point
    What is the purpose of using the governor in CI engine? Which are the two major type of governors? You can answer this question. You can like the best answer. You can share the question You can get updates of new questions on Facebook linkedin twitter & google plus
  28. 1 point

    Version

    12,117 downloads

    Geometric Dimensioning and Tolerance ppt Five powerpoint presentations
  29. 1 point
    Hetal Patel

    Machine Design Methods

    It is a process done for producing a device that is needed to solve a real world problem by use of scientific principles, technical knowledge, designing softwares and manufacturing techniques. Design procedure Specifications of product according to market survey. Selection of mechanism Block diagram showing layout of selected configuration and joining processes. Design of individual components Forces Material Failure mode Geometric dimensions 5. Drawings of parts and assembly. And then this drawings are sent to manufacturing department
  30. 1 point
    Hetal Patel

    CAD software to use?

    First I would advice you to go to basics for learning (AutoCAD) then switch to other softwares if you are just starting. I you already have some insite on using basic softwares then it totally depends on you what further process or operation you want to do and according te softwares changes.
  31. 1 point
    Great collection thanks for sharing
  32. 1 point

    Version Ed. 1, 2006

    59 downloads

    AISC Steel Design Guide 21: Welded Connections—A Primer for Engineers
  33. 1 point
    In an open loop system input is independent of output. They are simple and fast process... In closed loop system input is dependent on output. They are complex and slow process... Closed loop system in general are provided with sensors that serve the purpose of controlling the input..
  34. 1 point
  35. 1 point
    Define "Mechanical property" of engineering material State any 6 mechanical properties, give their definition and one example of material possessing the property You can answer this question. You can like the best answer. You can share the question You can get updates of new questions on Facebook linkedin twitter & google plus
  36. 1 point
    DrD

    Explain why washers are used?

    My comment above, quoted by Pandit Shivam shukla, is in the wrong discussion and should be disregarded. I'm not sure how it got here. It was intended for a thread related to a six stroke engine, if I recall correctly. I regret the error in this posting. DrD
  37. 1 point
    There are lots of them out there, just to name a few: . Maximum principal stress theory (Rankine's theory) Maximum shear stress theory (Guest's theory) Maximum principal strain theory (Saint's theory) Maximum strain energy theory (Haigh's theory) Maximum distortion energy theory (Hencky&Von Mises theory) This presentation is a good starting point.
  38. 1 point
    Jay shah

    What is mohr's circle used for ?

    Mohr circle is used to determine the value of state of stress in the planes of different orientation.
  39. 1 point

    From the album: Example model simulations for Packaging Machine Design.

    Case Erector Mechanism opens case as it loads conveyor This mechanism is used to erect pre-glued cases from a magazine and place on an indexing conveyor. The mechanism forces the case to open as it is pulled from the magazine. Conjugate Cams eliminate backlash and reduce overall cam stress If a disk cam drives the mechanism, then unless gravity is sufficient to hold the roller on the cam, a spring or air cylinder is needed to keep the roller in contact. This will effectively double the contact stress on the cam and increase the required drive torque and induce drive speed fluctuations. Alternatively a groove cam could be used. This will prevent a possibility of the cam roller bouncing, however, there will inevitably be backlash which will be traversed during acceleration reversals. When backlash is traversed, the roller looses contact with one flank and smashes into the other flank. This can cause vibrations and lead to premature failure and reduced precision in the tool motion. Conjugate cams, although more expensive, overcome most of these problems. Two separate cams with separate followers that are preloaded onto the cam flank to eliminate backlash. Springs are not required reducing the contact stress on bearing forces. The cams should ideally be machined in the same setup so that both profiles are truly conjugate.
  40. 1 point

    Version

    303 downloads

    Materials Numerical Quantities-Forms Tables designed for the metal trade are intended for use, mostly by vocational schools, and companies. Individuals of different experience levels will greatly benefit from this book, whether novice or specialized workers. In total, this book contains 7 chapters, each of which cover fundamental aspects of the subject. The chapters in this book include Measures And Weights, Metal Cutting Operations, Engineering Components, Mechanics, Numbers, Materials, and Engineering Drawings. Simply, this is a book similar to design data book which contains some requisite information on Metal Trade. I have scanned the pages and made a ebook. You can also buy it. Just 120 Rupees. Worth it!!
  41. 1 point
    What is/are the function of a clutch and its working principal ? How is different from flywheel? 1. You can answer this question 2. You can like the best answer 3. You can share the question.....
  42. 1 point
    A diesel engine's compression ratio produces temperatures approx.. 210 deg C which is near the auto flash point of diesel fuel, this therefore causes combustion
  43. 1 point
    Hi Joshua, I've just read your message and I couldn't agree with you more. The Diesel engine and the gas engine ARE both internal combustion engines. It's a very amateurish mistake that I've made and I apologise to anyone who may have been misled by this. I can't imagine what I was thinking of when I wrote it. Thanks for your correction. Roger
  44. 1 point
    In welding, similar materials are used to melt together a seam creating a bond that is the same as the original material. In Brazing, it is akin to gluing, where a second material is melted and wets to the surface of the first, but not melting the original, creating a mechanical bond between the two. This is a quick description, because there are grey areas that can in fact melt and bond dissimilar materials with and without fluxes. Basically welding makes two parts into one, brazing is like gluing two parts together.
  45. 1 point
    First and third angle projections depict a 3D object in a 2D yet second and fourth angle projections show one view of the object. In other words first and third angle projections are more elaborate than second and fourth angle projections.
  46. 1 point
    Tractors are designed for agricultral purpose,so when the exhaust is at bottom there may damage due to water etc in field .so it mounted on top of engine
  47. 1 point
    Petrol get ignited with at low temp. But for diesel high temp is required for combustion. ..This sole purpose is not achieved by spark plugs so we go with compression ignition. ...thus we don't have spark plugs in diesel engine. ..
  48. 1 point
    Aakarshan Satheesh Kumar

    Explain why washers are used?

    Washers are used when bolting to make stronger the joint and to reduce bolt fatigue due to inconsistent loads. Any stretch or flattening of parts is likely to be less than the compression of the washer thus, the bolt won't loosen much.
  49. 1 point
    Arpit.v

    What is the function of a bearing?

    Reduce surface contact to Point contact of balls thus reduces friction and allows smoth rotation.
  50. 1 point
    saurabhjain

    Difference between pump and compressor

    Basically a Pump is used for liquid or fluid to transform it to a much high pressure head while a Compressor is used for gases to transform from low to a much high pressure. From Mechanical Engineering point of view liquid is incompressible so Compressor cannot be used for liquid substances. Posted by AbdulQadir Abba Sheriff on linkedin


×
×
  • Create New...