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Why slenderness ratio is considered in design of members?
Jayesh Sharma95 and one other liked a blog entry by saurabhjain
Why slenderness ratio is considered in design of members? 1. You can answer this question 2. You can like the best answer 3. You can share the question. 
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Why do mechanical components fail? List down  Theories of Failure
Jayesh Sharma95 and one other liked a blog entry by saurabhjain
Why do mechanical components fail? List down  Theories of Failure 1. You can answer this question 2. You can like the best answer 3. You can share the question. 
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Why efficiency of Gas turbine is lower compared to IC engine ?
Timothy L Dennison and one other liked a blog entry by saurabhjain
Why efficiency of Gas turbine is lower compared to IC engine ? 1. You can answer this question 2. You can like the best answer 3. You can share the question. 
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What is the difference between knocking and detonation in IC engine?
SWAMIji and one other liked a blog entry by saurabhjain
What is the difference between knocking and detonation in IC engine? 1. You can answer this question. 2. You can like the best answer. 3. You can share the question You can get updates of new questions on Facebook linkedin twitter & google plus 
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What is the difference between refrigerator and a air conditioner ?
Muhammad Qasim liked a blog entry by admin
What is the exact difference between refrigerator and a air conditioner ? 1. You can answer this question 2. You can like the best answer 
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Why worm gear drive is used for hoists ?
Cring Ongchu liked a blog entry by saurabhjain
Why worm gear drive is used for hoists ? 1. You can answer this question 2. You can like the best answer 3. You can share the question. 
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WHY DIESEL ENGINES ARE MORE EFFICIENT THAN PETROL ENGINE
Sandip Gorai liked a blog entry by saurabhjain
You know that diesel engine is the most appropriate choice of the engineers when it comes to drive heavy automobile like trucks, aircraft, ships etc. But what makes it so torque, is it the engine design, working cycle or something else. Please share your deep analysis to answer this questions 
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State difference between AnitiFriction Bearing and Journal Bearing?
Jayesh Sharma95 liked a blog entry by saurabhjain
State difference between AnitiFriction Bearing and Journal Bearing? 1. You can answer this question 2. You can like the best answer 3. You can share the question... 
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What is an injector pressure in heavy vehicles? Why it is used?
Jairam Pal liked a blog entry by saurabhjain
What is an injector pressure in heavy vehicles? Why it is used? 1. You can answer this question 2. You can like the best answer 3. You can share the question. 
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Why tyres are made black in color?
Pradip Jadhav liked a blog entry by saurabhjain
Why tyres are made black in color? 1. You can answer this question 2. You can like the best answer 3. You can share the question. 
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Types of Hydraulic Turbines
Jayesh Sharma95 liked a blog entry by Tania Alam
Turbines are machines which convert fluid energy to mechanical energy. When the fluid used is water, they are called hydraulic turbines. Hydraulic turbines may be classified on the basis of four characteristics : On the basis of the type of energy at the turbine inlet Impulse turbine total head of the incoming fluid is converted in to a large velocity head at the exit of the supply nozzle ( entire available energy of the water is converted in to kinetic energy.) water entering the runner of a reaction turbine has only kinetic energy the rotation of runner or rotor (rotating part of the turbine) is due to impulse action Flow regulation is possible without loss Unit is installed above the tailrace Casing has no hydraulic function to perform, because the jet is unconfined and is at atmospheric pressure. Thus, casing serves only to prevent splashing of water. It is not essential that the wheel should run full and air has free access to the buckets. eg  Pelton wheel turbine ( efficient with a large head and lower flow rate.) Reaction or Pressure turbine the penstock pipe feeds water to a row of fixed blades through casing that convert a part of the pressure energy into kinetic energy before water enters the runner water entering the runner of a reaction turbine has both pressure energy and kinetic energy the rotation of runner or rotor (rotating part of the turbine) is partly due to impulse action and partly due to change in pressure over the runner blades Water leaving the turbine is still left with some energy (pressure energy and kinetic energy) It is not possible to regulate the flow without loss Unit is entirely submerged in water below the tailrace Casing is absolutely necessary, because the pressure at inlet to the turbine is much higher than the pressure at outlet. Unit has to be sealed from atmospheric pressure. Water completely fills the vane passage. eg  Francis and Kaplan turbines ( efficient with medium to low heads and high flow rates ) On the basis of the direction of flow through the runner Tangential flow turbine Direction of flow is along the tangent of the runner eg  Pelton wheel turbine. Radial flow turbine Direction of flow is in radial direction radially inwards or centripetal type, eg old Francis turbine radially outwards or centrifugal type, eg Fourneyron turbine Axial flow turbine Direction of flow is parallel to that of the axis of rotation of the runner the shaft of the turbine is vertical, lower end of the shaft is made larger which is known as hub (acts as runner) eg  Propeller turbine ( vanes are fixed to the hub and they are not adjustable ) Kaplan turbine (vanes on hub are adjustable ) Mixed flow turbine Water flows through the runner in the radial direction but leaves in a direction parallel to the axis of rotation of the runner eg Modern Francis turbine. On the basis of the head at the turbine inlet High head turbine net head varies from 150m to 2000m or even more small quantity of water required eg : Pelton wheel turbine. Medium head turbine net head varies from 30m to 150m moderate quantity of water required eg : Francis turbine. Low head turbine net head less than 30m large quantity of water required eg : Kaplan turbine. On the basis of the specific speed of the turbine Before getting into this type, one should know what the specific speed of a turbine is. It defined as, the speed of a geometrically similar turbine that would develop unit power when working under a unit head (1m head). Low specific speed turbine specific speed is less than 50. (varying from 10 to 35 for single jet and up to 50 for double jet ) eg : Pelton wheel turbine. Medium specific speed turbine specific speed varies from 50 to 250 eg : Francis turbine High specific speed turbine specific speed more than 250 eg : Kaplan turbine References : 1. Course contents on NPTEL website 2. A textbook of Fluid Mechanics and HydraulicMachines  R.K. Bansal 3. Fluid Mechanics: Including Hydraulic Machines  A.K. Jain 7 hours, 59 minutes ago 
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What should be done to prevent a safety valve to stick to its seat ?
John Matzick liked a blog entry by saurabhjain
What should be done to prevent a safety valve to stick to its seat ? 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 
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Differentiate between dial gauge slip gauge
Ram Dhani Bind liked a blog entry by saurabhjain
Differentiate between dial gauge slip gauge 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 
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What is the difference between nozzle and diffuser? Where they are used?
BM Samuvel liked a blog entry by saurabhjain
What is the difference between nozzle and diffuser? Where they are used? 1. You can answer this question. 2. You can like the best answer. 3. You can share the question. 
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Which one will cool faster??
Sk9 liked a blog entry by saurabhjain
Which one will cool faster?? You have a cold drink bottle at room temperature. In order to cool it, you place it in the refrigerator. But you want it get chilled faster. Now you have two options, place it vertical or horizontal. Assuming the effects of forced convection are negligible in your refrigerator, which way will the bottle cool fast either Horizontal or Vertical? 
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What are the advantages of hartnell over porter governor?
Rakesh Anant liked a blog entry by saurabhjain
What are advantages of hartnell over porter governor? 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 
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Experimental Analysis of an Air Washer
saurabhjain liked a blog entry by saurabh kumar tiwari
Hello World, Today i will like tell you all about my 4th year project which was on the topic of experimental analysis of an air washer. In the recent sanario the peoples are slowly getting conscious about the beast(pollution) intended to destroy our beautiful sphere(earth). This pollution had drastically spread in our world drastically in few years. It is sad to say but we are only responsible for it. The careless burning of fossil fuels, heavy growth in industries and inventions without considering about the earth safety pushed of us into this undesirable situation. But now the peoples are thinking about what they are doing and what they had done including the government which taken so many steps for the control on pollution. The scientist's also get conscious about their invention which will be in the favor the reducing pollution. In India the refrigerants like R 22 is going to be banned in upcoming few years which is one of the major reason for the depletion of the ozone layer which causes global warming and some harmful skin disease's. These things created the requirement for the replacement of old cooling systems and introduction of the new inventions which are environment friendly. My project was on the same concern me and my friends decided to try the project which can be the one of the substitute of the recent refrigeration system. On the suggestion of our professor we modified the air washer to not only work as an evaporative cooler but also can remove the sulphure dioxide from the air which is one of the gas responsible for green house effect. In my project my team was using spray type air washer with the very simple design since it become easier to modify. The spray type air washers consists of a chamber or casing containing a spray nozzle system, a sink for removing the spray water as it falls. And an eliminator section for the removal of moisture in the air. A pump recirculates water at the rate higher than the evaporation rate. Intimate contact between the spray water and the air flow causes heat and mass transfer between the air and the water. The air washer used in the industries has the basic use to clean air and control the properties of the air as per the requirement. The air washer can perform two kinds of cooling: 1. Direct evaporative cooling 2.Indirect evaporative cooling The direct evaporative cooling is done by the direct contact between sprayed water and the flowing air in the chamber. Where the indirect evaporative cooling is done by providing heat exchanger at the front of air washer. The syphon present in the heat exchanger is circulated by the cold water and the hot air is passed through the fins of the heat exchanger. Which causes heat exchange between air and water. The indirect evaporative cooling was done in my project by the use of car radiator. AIR WASHER SPECIFICATIONS BLOWER suction blower with 1HP, 3PHASE, 440 V and internal diameter 4 inch NOZZLE SECTION the nozzle section consist of: 1. 4 elbow joints (0.5 inch bore) 2. 3 distributors (0.5 inch bore) 3. 10 vertical pipes (0.5 inch bore & 50 cm length) 4. 10 holes on vertical pipe each (1 mm bore) 5. 5 holes on horizontal pipe each (1 mm bore) All the components in the nozzle section are made up of PVC material. The body of the air washer was made up of the aluminium composite pannel. Two layers of simple cellulose pad was use in the eliminator section to absorb the moisture in the air. The picture above will give you the brief and real understanding of the project. The analysis was done with the following aims: 1. circulating the water at normal temperature and analyzing the changes in the property of the air 2. circulating hot water through air washer and analyzing the change in the properties of air 3. circulating chilled water through air washer and analyzing the changes in properties of air I am providing some videos of working of my project i hope you will like it. please give reviews on my publish and don't forget to follow. your reviews are precious to me and your following will motivate to share new views thank you. 
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MACHINE DESIGN : 40 POSSIBLE QUESTIONS
Jayesh Sharma95 liked a blog entry by saurabhjain
1. What are the differences between true stress, engineering stress, proof stress. 2. What do you men by factor of safety and what is its significance 3. What do you mean by Young’s modulus, modulus of rigidity and bulk modulus. 4. What do you mean by resilience. 5. What is pure torsion and what do you mean by flexural igidity. 6. What is the difference between endurance limit stree and endurance strength. 7. What do you understand by efficiency of riveted joint. 8. What is caulking and fullering in riveted joint. 9. What do you mean by stress conc. Factor and what are the methods to reduce stress conc. 10. Why stress conc. Is more serious in brittle materials. 11. What do you mean by fatigue . 12. Springs are subjected to which type of streses. 13. What are the difference between through bolt, tap bolt and stud. 14. What is check nut and what is the function of washer. 15. Cotter and knuckle joints take which type of load and where they are used. 16. What are the difference types of couplings and what is their function. 17. What is the function of key and which type of stress they are subjected to? 18. Generally shafts are subjected to which type of stress. 19. What are the difference types of mechanical drives and which is the best for different situations. 20. What is the function of a bush why it is phosphor bronze. 21. What are difference types of threads and which threads are used for power transmission and why. 22. Why the pulley arms are elliptical in cross section and it is made up of cast iron. 23. Why it is required to change the all V belt if one of them is broken. 24. Why V belts transmit more power than flat belts. 25. What is the meaning of 6*37 or 6*7 in a rope drive. 26. What do you mean by pinion sprocket and wheel sprocket and which one is used for driving shaft. 27. What is the function of flywheel and why its material is cast iron. 28. Why the leaf springs are laminated as reducing length. 29. What is the function of clutch and is the difference between uniform wear and uniform pressure. 30. Now a days which type of clutches are used in automobiles. 31. Why disc brake is more efficient than mechanical brake. 32. What is the function of bearings and what are the different types. 33. What is bearing characteristics number and bearing modulus. 34. What is the significance of the digits of a rolling contact bearing number 6304? 35. Which type of gear drive is used for perpendicular transmission of power? 36. Why helical gears transmit more power than spur gears. 37. What do you mean by different terms like back lash, pressure angle, circular pitch in a gear drive. 38. Why involute tooth profile is better than cycloid tooth profile? 39. What is interference in gear drive and how to avoid it? 40. What do you mean by law of gearing 
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Mechanical Engineering Interview Questions & Answer  part 2
Sk9 liked a blog entry by saurabhjain
1. What is the difference between isotropic and anisotropic materials ? Ans: If a material exhibits same mechanical properties regardless of loading direction, it is isotropic, e.g., homogeneous cast materials. Materials lacking this property are anisotropic. 2. What are orthotropic materials ? Ans: It is a special class of anisotropic materials which can be described by giving their prop¬erties in three perpendicular directions e.g. wood; composites. 3. What is view factor ? Ans: View factor is dependent upon geometry of the two surfaces exchanging radiation. 4. What properties need to be considered for applications calling for following re¬quirements : (i) rigidity (ii) strength for no plastic deformation under static load (iii) strength to withstand overload without fracture. (iv) wear resistance (v) reliability and safety. Ans: (i) Rigidity—Elastic modulus and yield strength (ii) Strength (for no plastic deformation under static loading)—yield point (iii) Strength (overload)—Toughness and impact resistance (iv) Wear resistance—Hardness (v) Reliability and safety—Endurance limit and yield point. 5. Explain the effects of alloying chromium and nickel in stainless steel. Ans: Addition of nickel and chromium increases the tensile strength and increase in resistance to corrosion takes place. 6. Mention two types of dislocations. Ans: Dislocation refers to a break in the continuity of the lattice. In edge dislocation, one plane of atoms gets squeezed out. In screw dislocation the lattice atoms move fom their regular ideal positions. 7. What are the principal constituents of brass? Ans: Principal constituents of brass are copper and zinc. 8. What is Curie point ? Ans: Curie point is the temperature at which ferromagnetic materials can no longer be magnetised by outside forces. 9. Specific strength of materials is very high when they are in fibre size but lower when they are in bar form Why ? Ans: Crystal structure has ordered, repeating arrangement of atoms. Fibres are liable to maintain this and thus have high specific strength. As size increases, the condition of ordered and repeating arrangements can't be guaranteed because of several types of defects and dislocations and thus the specific strength gets lower. 10. What is the percentage of carbon in cast iron ? Ans: 2.5%. 11. Which element is added in steel to increase resistance to corrosion ? Ans: Chromium. 12. Whether individual components in composite materials retain their characteristics or not? Ans: yes. 13. An elastomer is a polymer when its percentage elongation rate is ? Ans: Greater than 100%. 14. If percentage elongation of a material is more than 200%, it is classed as ? Ans: Rubber. 15. Why is it that the maximum value which the residual stress can reach is the elastic limit of the material ? Ans: A stress in excess of elastic limit, with no external force to oppose it, will relieve itself by plastic deformation until it reaches the value of the yield stress. 16. Why fatigue strength decreases as size of a part increases beyond around 10 mm? Ans: Perfection of material conditions is possible at lower sizes and as size increases, it is not possible to attain uniform structure of the material. 17. Distinguish between creep and fatigue. Ans: Creep is low and progressive deformation of a material with time under a constant stress at high temperature applications. Fatigue is the reduced tendency of material to offer resistance to applied stress under repeated or fluctuating loading condition. 18. While normal carburising and nitriding surface treatments increase fatigue strength, excessive treatment may decrease the fatigue strength. Why ? .Ans: Normal carburising/nitriding treatments increase volume due to phase transformation at Surface and introduce residual compressive surface stress and thus increase the fatigue strength. By excessive treatment the high compressive stresses are introduced but these are balanced by high in¬ternal tensile stresses of equal value and the subsurface fatigue cracks may develop in the regions of high tensile stress and lead to early fatigue failure. 19. List at least two factors that promote transition from ductile to brittle fracture. Ans: Manner of loading, and the rate of loading promote transition from ductile to brittle frac¬ture. A machine member may have ductile failure under static loading but may fail in brittle fashion when the load is fluctuating. Similarly a material may evidence ductile failure under tensile loading at ordinary testing speed but if load is applied at a high velocity then failure may be brittle. 20. Which theories of failure are used for (a) ductile materials, and ( brittle materials ? Ans: For ductile materials, theories of failure used are maximum shear stress theory, and maximum energy of distortion theory; while for brittle materials, theory of maximum principal stress, and maximum strain are used. 21. What does thermal diffusivity of metals signify. Ans: Thermal diffusivity is associated with the speed of propagation of heat into solids during changes in temperature with time. 22. For conduction of heat, the instantaneous rate of heat flow is product of three factors. What are these ? Ans: (i) Area of the section of the heat flow path, perpendicular to the direction of heat flow. (ii) temperature gradient, i.e. change of temperature w.r.t. length of path. (ii) Thermal conductivity of material. 23. How convective heat transfer is effected and on what factors it depends ? Ans: Convective heat transfer is effected between a solid and fluid by a combination of molecular conduction within the fluid in combination with energy transport resulting from the motion of fluid particles. It depends on boundary layer configuration, fluid properties and temperature difference. 24. Which is the common element between brass and bronze ? Ans: Copper. 25. What does following alloy designation indicate FG 250 ? Ans: Grey cast iron with tensile strength of 250 MPa. 26. How is ceramic defined ? Ans: It is a solid formed by combination of metallic and nonmetallic elements. 27. Give one example of metal classified as per structure as BCC, FCC, HCP and CCP. Ans: BCC (body centred cubic) structure—Molybdenum FCC (face centred cubic) structure—Aluminium HCP (hexagonal closed packed) structure—Zinc CCP (cubic dosed packed) structureCopper. 28. What is the name of solid solution of carbon in alpha iron and delta iron ? Ans: Ferrite and austenite respectively. 29. Explain the difference between pearlite and cementile ? Ans: Pearlite is eutectoid mixture of ferrite and cementile. Cementite is chemical compound of iron and carbon. 30. Give one example each of the following proportion of materials dimensional, physical, technological and mechanical. Ans: Roughness, enthalpy, toughness, and hardness respectively. 31. For which parts the Wahl factor and Lewis form factor used ? Ans: For springs and gears respectively. 32. How oxygen can be removed from steel during melting? What are fully killed steels ? Ans: Oxygen can be removed by adding elements such as manganese, silicon or aluminium which, because of their high affinity for oxygen, react with it to form nonmetallic oxides which rise into the slag. Steels which have had most of their dissolved oxygen removed are called "fully killed steels". 33. Hydrogen cannot be removed easily from molten steel. What harm hydrogen has on property of steel ? Ans: Execessive hydrogen results in the formation of small fissures often described as hairline cracks or flakes in the steel. Large forgings in alloy steel are particularly sensitive to this phenom¬enon. 34. What is allotrope ? In what forms of cubic pattern, iron exists ? Ans: Some elements exist in more than one crystalline form. Each form is known as "allotrope". Iron exists in two forms of cubic pattern, namely body centered cubic (bcc) and facecentered cubic (fee). 35. What is the difference between alpha iron, delta iron and gamma iron ? Ans: The bcc form of iron exists between room temperature and 910°C, and between 1400°C and the melting point at 1539°C. The lower temperature form is known as "alpha"iron and the higher temperature form as "delta"iron. The facecentered cubic form existing between 910°C and 1400°C is referred to as "gammairon". 36. Metals, in general are of low strength and do not possess required physiochemical and technological properties for a definite purpose. Alloys are therefore more than metals alone. Discuss the arrangement of atoms and structures of alloys. Ans: Alloys are produced by melting or sintering two ore more metals, or metals and a nonmetal, together. Alloys possess typical properties inherent in the metallic state. The chemical elements that make up an alloy are called its components. An alloy can consist of two or more components. The phase and structures of alloys describe the constitution, transformations and properties of metals and alloys. A combination of phases in a state of equilibrium is called a system. A phase is a homogeneous portion of a system having the same composition and the same state of aggregation throughout its volume, and separated from the other portions of the system by interfaces. For instance, a homogeneous pure metal or alloy is a singlephase system. A state in which a liquid alloy (or metal) coexists with its crystals is a twophase system. Structure refers to the shape, size or the mutual arrangement of the corresponding phases in metals or alloys. The structural components of an alloy are its individual portions, each having a single structure with its characteristic features. 37. What is the difference between isotropic material and homogeneous material ? Ans: In homogeneous material the composition is same throughout and in isotropic material the elastic constants are same in all directions. 38. Explain the difference between the points of inflexion and contraflexure. Ans: At points of inflexion in a loaded beam the bending moment is zero and at points of contraflexure in loaded beam the bending moment changes sign from increasing to decreasing. 39. What is the difference between proof resilience and modulus of resilience ? Ans: Proof resilience is the maximum strain energy that can be stored in a material without permanent deformation. Modulus of resilience is the maximum strain energy stored in a material per unit volume. 40. What is the difference between column and strut ? Ans: Both column and strut carry compressive load. Column is always vertical but strut as member of structure could carry axial compressive load in any direction. 41. Explain the difference between ferrite, austenite and graphite ? Ans: Ferrite is the solid solution of carbon and other constituents in alphairon. It is soft, ductile and relatively weak. Austenite is the solid solution of carbon and other constituents in gammairon. It exists in ordinary steels at elevated temperatures, but it is also found at ordinary temperatures in some stainless steels. Graphite has a hexagonal layer lattice. ' 42. Explain the terms solid solution, eutectic, eutectoid and peritectic. Ans: Solid Solution. When a homogeneous mixture of two (or more) atomic forms exists in solid state, it is known as solid solution. Eutectic. A mixture of two (or more) phases which solidify simultaneously from the liquid al¬loy is called an eutectic. Alloys in which the components solidify simultaneously at a constant tem¬perature the lowest for the given system, are called eutectic alloys. Eutectoid. Eutectoid alloys are the alloys for which two solid phases which are completely soluble become completely insoluble on cooling before a certain temperature called eutectoid tem¬perature. Peritectic. A peritectic transformation involves a reaction between a solid and liquid that form a different and new solid phase. This three phase transformation occurs at a point called peritectic point. 43. What do you understand by critical points in iron, ironcarbide diagram ? Ans: The temperatures at which the phase changes occur are called critical points (or tem¬peratures). 45. Why PERT is preferred over CPM for evaluation of project ? Ans: PERT is based on the approach of multiple time estimates for each activity. 46. What is the percentage of chromium in 18 : 4 : 1 IISS ? Ans: 4%. 47. What is stellite ? Ans: It is a nonferrous cast alloy containing cobalt, chromium and tungsten. 48. Which rays are produced by cobalt60 in industrial radiography ? Ans: Gamma rays. 49. What are killed steels and what for these are used ? Ans: Killed steels are deoxidised in the ladle with silicon and aluminium. On solidification no gas evolution occurs in these steels because they are free from oxygen. 50. What is critical temperature in metals ? Ans: It is the temperature at which the phase change occurs in metals. 51. Car tyres are usually made of ? Ans: Styrenebutadine rubber. 52. What is the structure of pure iron and whether it is soft or hard ? Ans: Ferrite and it is soft. 53. Which elements increase the corrosion resistance of steel ? Ans: Chromium and nickel. 54. What causes hardness in steel ? How heat treatment alters properties of steel ? Ans: The shape and distribution of the carbides in the iron determines the hardness of the steel. Carbides can be dissolved in austenite is the basis of the heat treatment of steel. If steel is heated above the A critical temperature to dissolve all the carbides, and then cooled, suitable cooling through the cooling range will produce the desired size and distribution of carbides in the ferrite, imparting different properties. 55. Explain the formation of microstructures of pearlite, bainite and martensite in steel. Ans: If austenite containing about 0.80 percent carbon is slowly cooled through the critical temperature, ferrite and cementite are rejected simultaneously, forming alternate plates or lamellae. This microstructure is called pearlite. At temperatures just belot the A1, the transformation from austenite.to pearlite may take an appreciable time to initiate and complete, but the product will be lameller pearlite. As the transformation temperature is lowered, the time to initiate transformation shortens but the product is pearlite of increasing fineness, and at temperatures approaching 550°C it cannot be resolved into its lamellar constituents. Further deerease in transformation temperature causes a lengthening of the ncubation period and a change in structure of the product to a form known as "bainite". If the temperature is lowered sufficiently, the diffusion controlled nucleation and growth modes of transformation are suppressed completely and the austenite transforms by a diffusionless process in which the crystal lattice effectively shears to a new crystallographic configuration known as "martensite". This phase has a tetragonal crystal structure and contains carbon in supersaturated solid solution. 56. How with alloying of steel it is possible to a achieve properties which can not be achieved with heat treatment ? Ans: A prerequisite to the hardening of steels is that martensite should be formed on cooling, but this can only be achieved if the rate of cooling is great enough to suppress the formation of pearlite or bainite and in plain carbon steels this can be achieved by quenching relatively small specimens 57. What are the major effects of alloying elements? Ans: (1) To alter the transformation temperatures and times (2) To modify the room temperature and elevated temperature strengths of given structures by (a) stiffening the crystals and ( introducing complex precipitates which tend to harden the steel. (3) To modify the type of oxide film formed on the surface of the steel and thereby affect its corrosion resistance. 58. What is the difference between austenite stabilisers and ferrite stabilisers ? Ans: Austenite stabilisers have the effect of extending the temperature range overwhich austenite is formed. Such elements are carbon, manganese, nickel, copper and cobalt. Ferrite stabilisers have the effect of extending the temperature range over which alpha and delta ferrite are formed, which consequently reduces temperature range over which austenite is formed. Such elements are silicon, chromium, molybdenum, tungsten, titanium and niobium. 59. What are the effects of carbon on the properties of steel. Ans: In general, an increase in carbon content produces higher ultimate strength and hardness but lowers ductility and toughness of steel alloys. Carbon also increases airhardening tendencies and weld hardness, especially in the presence of chromium. In lowalloy steel for hightemperature applications, the carbon content is usually restricted to a maximum of about 0.15% in order to assure optimum ductility for welding, expanding, and bending operations. To minimize intergranular corro¬sion caused by carbide precipitation, the carbon content of austenitic (188 type) alloys is limited in commercial specifications to a maximum of 0.08%, or even less, i.e. 0.03% in the extremely lowcarbon grades used in certain corrosionresistant applications. In plain carbon steels in the normalised condition, the resistance to creep at temperatures below 440°C appears to increase with carbon content up to 0.4% carbon, at higher temperatures there is but little variation of creep properties with carbon content. An increase in carbon content lessens the thermal and electrical conductivities of steel and increases its hardness on quenching. 60. What is the role of silicon as alloying element in steels ? Ans: Silicon contributes greatly to the production of sound steel because of its deoxidizing and degasifying properties. When added in amounts up to 2.5%, the ultimate strength of the steel is increased without loss in ductility. Silicon in excess of 2.5% causes brittleness, and amounts higher than 5% make the steel nonmalleable. Resistance to oxidation and surface stability of steel are increased by the addition of silicon. These desirable effects partially compensate for the tendency of silicon to lower the creep properties of steel. Silicon increases the electrical resistivity of steel and decreases hysteresis losses. 61. Discuss the role of manganese in alloying steels. Ans: Manganese is an excellent deoxidizer and sulfur neutralizer, and improves the mechanical properties of steel, notably the ratio of yield strength to tensile strength at normal temperatures. As an alloying element, manganese serves as an inexpensive means of preventing "hot shortness". It improves rolling properties, hardenability, and resistance to wear. However manganese increases the crack sensitivity of weldments, particularly with steels of higher carbon content. 62. Define buckling factor. Ans: It is the ratio of the equivalent length of column to the minimum radius of gyration. 63. What do you understand by catenary cable ? Ans: A cable attached to the supports and carrying its own weight. 64. What is coaxing ? Ans: It is the process of improving fatigue properties by first understressing and then increasing the stress in small increments. 65. What is difference between conjugate beam and continuous beam ? Ans: A conjugate beam is an imaginary beam of same size as original beam and carrying a distributed load in accordance with the bending moment diagram. A continuous beam is one which is resting on more than two supports. 66. What is isotropic material ? Ans: It is a material having same elastic constants in all directions. 67. Explain difference between modulus of resilience and modulus of rigidity ? Ans: Modulus of resilience is the maximum strain energy stored in a material per unit volume and modulus of rigidity is the ratio of shearing stress to the shearing strain within the elastic limit. 68. What is the difference between basic hole and basic shaft ? Ans: A basic hole is one whose lower deviation is zero and in case of basic shaft the upper deviation is zero. 69. What for pyranometer is used ? Ans: It is used to measure the total hemispherical solar radiation. 70. Describe transfer machines in brief. Ans: It is an automatic machine in which workpiece alongwith fixture is transferred from one station to other automatically and several operation on workpiece are performed at each station. 71. What is burntout point ? Ans: It corresponds to maximum heat flux at which transition occurs from nucleate boiling to film boiling. 72. What do you understand by eutectic ? Ans: It is mechanical mixture of two or more phases which solidify simultaneously from the liquid alloy. 72. Explain the difference between grey iron and white iron. What is mottled iron ? Ans: The carbon in cast iron could exist at room temperature as either iron carbide, or as graphite which is the more stable form. Irons containing carbon as graphite are soft, easily machinable and are called "grey irons". Irons with carbon present as iron carbide are extremely hard, difficult to machine and are called "white" irons. Irons with fairly equal proportions of graphite and iron carbide have intermediate hardness and are called "mottled" irons. 73. The graphite in grey irons exists in the form of flakes which act as stressraisers under tensile loading and consequently grey irons have relatively low tensile strength and ductility. Still grey iron is extensively used in engineering. Why ? Ans: Grey iron is extensively used in engineering because of following characteristics. (a) Cheapness. ( Low melting point and high fluidity making it suitable for castings of intricate shape. © Relatively good erosion and corrosion resistance. (d) High damping capacity, with respect to vibration. (e) Relatively good mechanical properties under compressive loading. 74. Under what condition a convergent divergent nozzle required ? Ans: When pressure ratio is greater than critical pressure ratio. 75. What is endurance limit and what is its value for steel ? Ans: Endurance limit is the maximum level of fluctuating stress which can be tolerated indefinitely. In most steels this stress is approximately 50% of the ultimate tensile strength and it is defined as the stress which can be endured for ten million reversals of stress. 76. How the net work to drive a compressor and its volumetric efficiency behave with increase in clearance volume ? Ans: Work remains unaltered and volumetric efficiency decreases. 77. What do you understand by sulphur print ? Ans: Sulphides, when attached with dilute acid, evolve hydrogen sulphide gas which stains bromide paper and therefore can be readily detected in ordinary steels and cast irons. While sulphur is not always as harmful as is sometimes supposed, a sulphur print is a ready guide to the distribution of segregated impurities in general. 78. What is the different between brass and bronze ? Ans: Brass is an alloy of copper with zinc; and bronze is alloy of copper with tin. 79. What is the effect of addition of zinc in copper? What is the use of 70/30 brass ? Ans: By addition of zinc in copper, both tensile strength and elongation increases. The 70/30 brass has excellent deep drawing property and is used for making radiator fins. 80, What for admirality brass used ? Ans: Admirality brass with 29% zinc and 1% tin has good corrosion resistance and is used for condenser and feed heater tubes. Aluminium is also added to brass to improve corrosion resistance. 81. What is the maximum use of magnesium ? Ans: Magnesium is used to alloy with aluminium and as an additive for making SG (Spheroidal Graphite) iron. 82. What for zinc finds applications ? Ans: Galvanizing consumes the largest proportion of zinc. Zinc is resistant to corrosion but is attacked by acids and alkalies. Zinc alloy.s are suited for making die casting since the melting point is reasonably low. 83. Which factors influence the type of fracture in failure of a material ? Ans: Seven factors influencing type of failure are : (i) Type of material (inherent structure properties), (ii) Manner of loading (Static versus dynamic), (iii) Range of imposed stress, (iv) Strain rate (static, dynamic, impact), (v) Stress distribution (discontinuity in material/shape), (vi) temperature, and (vii) surface treatment. 84. What is the name given to ratio of actual cycle efficiency and ideal cycle efficiency. Ans: Efficiency ratio. 85. List two effects of manganese in plain carbon steels. , Ans: Manganese increases tensile strength and hardness. It decreases weldability. 86. Name the strongest and weakest type of atomic bonds. Ans: Metallic bond is strongest and molecular bond also known as Vander Waals bond is weakest. 87. In which process internal energy remains constant ? Ans: Isothermal process. 88. What is temper embrittlement in alloy steels and what are its effects ? Ans: Embrittlement attack is usually intergranular in metals, i.e. cracks progress between the grains of the polycrystalline material. It imparts a tendency to fail under a static load after a given period of time in those alloy steels which are susceptible to embrittlement. 89. What are whiskers ? Ans: Whiskers are very small crystals which are virtually free from imperfections and dislocations. 90. What is Bauschinger effect ? Ans: According to Bauschinger, the limit of proportionality of material does not remain constant but varies according to the direction of stress under cyclic stresses. 91. What is the difference between heat capacity and specific heat of a material ? Ans: The heat capacity of a material is the amount of heat transformed to raise unit mass of a material 1 degree in temperature. The specific heat of a material is the ratio of the amount of heat transferred to raise unit mass of a material 1 degree in temperature to that required to raise unit mass of water 1 degree of temperature at some specified temperature. For most engineering purposes, heat capacities may be assumed numerically equal to;specific heats. 92. Explain the rule to find specific heat of aqueous solutions. Ans: For aqueous solutions of salts, the specific heat can be estimated by assuming the specific heat of the solution equal to that of the water alone. Thus, for a 15% by weight solution of sodium chloride in water, the specific heat would be approximately 0.85. 93. What do you understand by latent heat ? Give four examples of latent heats. Ans: For pure substances, the heat effects accompanying changes in state at constant pressure (no temperature change being evident) are known as latent heats. Examples of latent heats are : heat of fusion, vaporisation, sublimation, and change in crystal form. 94. Define the terms free energy and free enthalpy. What is their significance and importance ? Ans: Free energy (or Helmholtz function) is defined as/= u Ts. It is equal to the work during a constantvolume isothermal reversible nonflow process. Free enthalpy (or Gibbs function) is defined as g = h  Ts (where u = internal energy, h = enthalpy, T = temperature, s = entropy) Gibbs function is of particular importance in processes where chemical changes occur. For reversible isothermal steadyflow processes or for reversible constantpressure isothermal nonflow processes, change in free energy is equal to net work. 95.Which parameter remains constant in isochoric process ? Ans: Volume. 96. What is polytropic process ? Under what conditions it approaches isobaric, isothermal, and isometric process ? In which reversible process no work is done ? Ans: A polytropic process is one that follows the equation pun = constant (index n may have values from  oc to + oo. This process approaches isobaric when n = 0, isothermal when n = 1, and isometric when n = <x>. No work is done in isometric process. 97. Whether superheated steam can be treated like ideal gas ? Ans: Yes. 98. Out of constant pressure and constant volume lines on TS diagram which line has higher slope ? And whether slope is constant or variable ? Ans: Constant volume line. Slope is variable. 99. Whether entropy is intensive property or extensive property ? Ans: Entropy is extensive property. 100. In which process fluid expands but does no work ? Ans: Throttling process. 
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What causes white smoke in two stroke locomotive engines?
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Brief History of Manifold Topology  Part 1
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[This blog is a repost from my other blog site, thought would be useful to Mechanical Engineering readers] Now every mechanical engineer uses CAD softwares. Weather software is SolidWorks, SolidEdge, Inventor or CATIA, Creo or UGNX it has same theory of CAGD and Computational Geometry. Unforuntaly we in Mechanical Engineering does not have subjects to taught this in detailed. I hope this blog series helps you to understand What Lies Benith Your CAD Software !!! Mechanical CAD solid models are consisting of geometry and topology. Geometry by virtue of its visualization capability is easy to understand and comprehend. Topology is on the other hand, more of pure virtual concept hence many find it difficult to understand. In this article brief introduction to manifold topology is illustrated. Intended audience is new CAD developers or students of computational geometry. Geometry is a part of mathematics concerned with questions of size, shape, and relative position of figures and with properties of space. Many scientists have made contribution to its theory and lot has changed since Euler first laid foundation stone of Geometry. Following is brief review of the development. Euclid 300 BC, also known as Euclid of Alexandria, was a Greek mathematician and is often referred to as the Father of Geometry. His work “Elements” is the most successful textbook in the history of mathematics. In “Elements”, the principles of what is now called Euclidean geometry were deduced from a small set of axioms. The geometrical system described in the “Elements” was long known simply as geometry, and was considered to be the only geometry possible. Today, however, that system is often referred to as Euclidean geometry to distinguish it from other socalled NonEuclidean geometries that mathematicians discovered in the 19th century. Euclid undertook a study of relationships among distances and angles, first in a plane (an idealized flat surface) and then in space. An example of such a relationship is that the sum of the angles in a triangle is always 180 degrees. Today these relationships are known as two and threedimensional Euclidean geometry. An essential property of a Euclidean space is its flatness. Important point to note is other spaces exist in geometry that are not Euclidean. For example, the surface of a sphere is not; a triangle on a sphere (suitably defined) will have angles that sum to something greater than 180 degrees. Next major contribution in Geometry came after around 2000 year by Leonhard Paul Euler (15 April 1707 – 18 September 1783). In 1736, Euler solved the problem known as the Seven Bridges of Königsberg. The city of Königsberg, Prussia was set on the Pregel River, and included two large islands which were connected to each other and the mainland by seven bridges. The problem is to decide whether it is possible to follow a path that crosses each bridge exactly once and returns to the starting point. It is not: there is no Eulerian circuit. This solution is considered to be the first theorem of graph theory, specifically of planar graph theory. In the processEuler also discovered the formula V − E + F = 2 relating the number of vertices, edges, and faces of a convex polyhedron, and hence of a planar graph. The constant in this formula is now known as the Euler characteristic for the graph (or other mathematical object), and is related to the genus of the object. The study and generalization of this formula, specifically by Cauchy and L'Huillier, is at the origin of topology. Next path breaking contribution was from Georg Friedrich Bernhard Riemann (September 17, 1826 – July 20, 1866) an extremely influential German mathematician who made important NonEuclidean geometries. This discovery was a major paradigm shift in mathematics, as it freed mathematicians from the mistaken belief that Euclid's axioms were the only way to make geometry consistent and noncontradictory. Research on these geometries led to, among other things, Einstein's theory of general relativity, which describes the universe as nonEuclidean. The subject founded by his work is Riemannian geometry. Riemann found the correct way to extend into n dimensions the differential geometry of surfaces. The fundamental object is called the Riemann curvature tensor. For the surface case, this can be reduced to a number (scalar), positive, negative or zero; the nonzero and constant cases being models of the known nonEuclidean geometries. contributions to analysis and differential geometry. He was first one to discover Riemannian geometry is the branch of differential geometry that studies Riemannian manifolds, smooth manifolds with a Riemannian metric, i.e. with an inner product on the tangent space at each point which varies smoothly from point to point. This gives in particular local notions of angle, length of curves, surface area, and volume. From those some other global quantities can be derived by integrating local contributions. Riemannian geometry deals with a broad range of geometries categorized into two standard types of NonEuclidean geometry,spherical geometry and hyperbolic geometry, as well as Euclidean geometry itself. NonEuclidean geometry describes hyperbolic and elliptic geometry, which are contrasted with Euclidean geometry. The essential difference between Euclidean and nonEuclidean geometry is the nature of parallel lines. Euclid's fifth postulate, the parallel postulate, is equivalent to Playfair's postulate, which states that, within a twodimensional plane, for any given line l and a point A, which is not on l, there is exactly one line through A that does not intersect l. In hyperbolic geometry, by contrast, there are infinitely many lines through A not intersecting l, while in elliptic geometry, any line through A intersects l. Another way to describe the differences between these geometries is as follows: Consider two straight lines indefinitely extended in a twodimensional plane that are both perpendicular to a third line. In Euclidean geometry the lines remain at a constant distance from each other, and are known as parallels. In hyperbolic geometry they "curve away" from each other, increasing in distance as one moves further from the points of intersection with the common perpendicular; these lines are often called ultra parallels. In elliptic geometry the lines "curve toward" each other and eventually intersect. We started discussing how we end up in geometry discussion? I felt it was necessary to create basic understanding of historical development of Euclidean Geometry and NonEuclidian geometry to understand next topics. As we saw earlier Euler was first one publish paper on topology in seven bridge problem demonstrating that it was impossible to find a route through the town of Königsberg that would cross each of its seven bridges exactly once. This result did not depend on the lengths of the bridges, nor on their distance from one another, but only on connectivity properties: which bridges are connected to which islands or riverbanks. In other words to solve many of geometric problems we do not need to know spatial information but what is requiring to be known is neighborhood or connectivity information termed as topology. Problems like a Möbius strip, an object with only one surface and one edge; such shapes are alos an object of study in topology. Jules Henri Poincaré (29 April 1854 – 17 July 1912) was a French mathematician and theoretical physicist, and a philosopher of science. As a mathematician and physicist, he made many original fundamental contributions to pure and applied mathematics, mathematical physics, and celestial mechanics. He was responsible for formulating the Poincaré conjecture, one of the most famous problems in mathematics. In his research on the threebody problem, Poincaré became the first person to discover a chaotic deterministic system which laid the foundations of modern chaos theory. He was a founder of topology, also known as “rubbersheet geometry,” for its focus on the intrinsic properties of spaces. From a topologist’s perspective, there is no difference between a bagel (shape like torus or from Indian menu medu wada J ) and a coffee cup with a handle. Each has a single hole and can be manipulated to resemble the other without being torn or cut. Poincaré used the term “manifold” to describe such an abstract topological space. The simplest possible twodimensional manifold is the surface of a soccer ball, which, to a topologist, is a sphere—even when it is stomped on, stretched, or crumpled. The proof that an object is a socalled twosphere, since it can take on any number of shapes, is that it is “simply connected,” meaning that no holes puncture it. Unlike a soccer ball, a bagel is not a true sphere. If you tie a slipknot around a soccer ball, you can easily pull the slipknot closed by sliding it along the surface of the ball. But if you tie a slipknot around a bagel through the hole in its middle you cannot pull the slipknot closed without tearing the bagel. Euler Poincaré equation Euler’s polyhedron formula was applicable to only simple polyhedron. This new equation from Poincaré provides relationship between topological elements for any single twomanifold body. V E + F  Li = 2(1  G) where, V : Number of vertices. E: Number of edges. F: Number of faces. Li: Number of interior loops. G: Genus, the number of closed paths on a surface which do not separate the surface into more than one region. Or, genus is the number of handles to be added to a sphere to make it homeomorphic to the object. Classification of manifolds · 0manifold is just a discrete space. Eg Point in Cartesian space corresponds to vertex in topological space. Point or set of points are zero dimensional manifolds · 1manifold is curve in Cartesian space. Eg circle, line, parabole bspline curve (non intersecting) · 2manfold is surface Cartesian space. Sphere (empty inside), torus, plane, cylinder, bspline surface (if closed empty inside, orientable and non selfintersecting ) , circular disc · 3manfold is 3 dimensional manifold. Eg Solid Objects, Solid Sphere, Solid Cylinder, Our universe J Twodimensional manifolds were well understood by the midnineteenth century. But it remained unclear whether what was true for two dimensions was also true for three. Poincaré proposed that all closed, simply connected, threedimensional manifolds—those which lack holes and are of finite extent—were spheres. The conjecture was potentially important for scientists studying the largest known threedimensional manifold: the universe. Proving it mathematically, however, was far from easy. Most attempts were merely embarrassing, but some led to important mathematical discoveries, including proofs of Dehn’s Lemma, the Sphere Theorem, and the Loop Theorem, which are now fundamental concepts in topology. By the nineteensixties, topology had become one of the most productive areas of mathematics, and young topologists were launching regular attacks on the Poincaré. To the astonishment of most mathematicians, it turned out that manifolds of the fourth, fifth, and higher dimensions were more tractable than those of the third dimension. By 1982, Poincaré’s conjecture had been proved in all dimensions except the third. In 2000, the Clay Mathematics Institute, a private foundation that promotes mathematical research, named the Poincaré one of the seven most important outstanding problems in mathematics and offered a million dollars to anyone who could prove it. After nearly a century of effort by mathematicians, Grigori Perelman sketched a proof of the conjecture in a series of papers made available in 2002 and 2003. The proof followed the program of Richard Hamilton. Several highprofile teams of mathematicians have since verified the correctness of Perelman's proof. The Poincaré conjecture was, before being proven, one of the most important open questions in topology. It is one of the seven Millennium Prize Problems, for which the Clay Mathematics Institute offered a $1,000,000 prize for the first correct solution. Perelman's work survived review and was confirmed in 2006, leading to him being offered a Fields Medal, which he declined. The Poincaré conjecture remains the only solved Millennium problem. This article was written with the help of various sources of web sources, mainly Wikipedia. Intention is to explain interesting subject such as manifold which carries paramount importance in CAD development in less mathematical and elaborative manner. Research in Manifolds is as recent as 2006 and is one of the most studied area in mathematics.