Here we have mentioned most frequently asked Mechanical Engineering Interview Questions and Answers specially for freshers and experienced.
1. Explain the second law of thermodynamics.
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The entropy of the universe increases over time and moves towards a maximum value.
2. What kinds of pipes are used for steam lines?
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Normally galvanized pipes are not used for steam. Mild steel with screwed or welded fittings are the norm. Pressure and temperature are very important factors to be considered in what type of materials to be used. Steam even at low pressures can be extremely dangerous.
3. What is the difference between shear center flexural center of twist and elastic center?
Ans:
The shear center is the centroid of a cross-section. The flexural center is the center of twist, which is the point on a beam that you can add a load without torsion. The elastic center is located at the center of gravity. If the object is homogeneous and symmetrical in both directions of the cross-section then they are all equivalent.
4. What is ferrite?
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Magnetic iron rock
5. What is the difference between projectile motion and a rocket motion?
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A projectile has no motor/rocket on it, so all of its momentum is given to it as it is launched. An example of a projectile would be pen that you throw across a room.
A rocket or missile does have a motor/rocket on it so it can accelerate itself while moving and so resist other forces such as gravity.
6. What is a cotter joint?
Ans:
These types of joints are used to connect two rods, which are under compressive or tensile stress. The ends of the rods are in the manner of a socket and shaft that fit together and the cotter is driven into a slot that is common to both pieces drawing them tightly together. The tensile strength of the steel is proportionate to the strength needed to offset the stress on the material divided by the number of joints employed.
7. What is the alloy of tin and lead?
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A tin and lead alloy is commonly called solder. Usually solder is a wire with a rosin core used for soldering. The rosin core acts as a flux.
8. What does F.O.F. stand for in piping design?
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FOF stands for Face of Flange. A flange has either of the two types of faces:
a) Raised face
b) Flat face
The F.O.F is used to know the accurate dimension of the flange in order to avoid the minute errors in measurement in case of vertical or horizontal pipelines.
9. Explain Otto cycle.
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Otto cycle can be explained by a pressure volume relationship diagram. It shows the functioning cycle of a four stroke engine. The cycle starts with an intake stroke, closing the intake and moving to the compression stroke, starting of combustion, power stroke, heat exchange stroke where heat is rejected and the exhaust stroke. It was designed by Nicolas Otto, a German engineer.
10. What is gear ratio?
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It is the ratio of the number of revolutions of the pinion gear to one revolution of the idler gear.
11. What is annealing?
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It is a process of heating a material above the re-crystallization temperature and cooling after a specific time interval. This increases the hardness and strength if the material.
12. What is ductile-brittle transition temperature?
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It is the temperature below which the tendency of a material to fracture increases rather than forming. Below this temperature the material loses its ductility. It is also called Nil Ductility Temperature.
13. What is a uniformly distributed load?
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A UDL or uniformly distributed load is a load, which is spread over a beam in such a way that each unit length is loaded to the same extent.
14. What are the differences between pneumatics and hydraulics?
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a) Working fluid: Pneumatics use air, Hydraulics use Oil
b) Power: Pneumatic power less than hydraulic power
c) Size: P components are smaller than H components
d) Leakage: Leaks in hydraulics cause fluid to be sticking around the components. In pneumatics, air is leaked into the atmosphere.
e) Pneumatics obtain power from an air compressor while hydraulics require a pump
f) Air is compressible, hydraulic oil is not
15. What is enthalpy?
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Enthalpy is the heat content of a chemical system.
16. What is a positive displacement pump?
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A positive displacement pump causes a liquid or gas to move by trapping a fixed amount of fluid or gas and then forcing (displacing) that trapped volume into the discharge pipe. Positive displacement pumps can be further classified as either rotary-type (for example the rotary vane) or lobe pumps similar to oil pumps used in car engines. These pumps give a non-pulsating output or displacement unlike the reciprocating pumps. Hence, they are called positive displacement pumps.
17. Why would you use hydraulics rather than pneumatics?
Ans:
Hydraulics is suitable for higher forces & precise motion than pneumatics. This is because hydraulic systems generally run at significantly higher pressures than pneumatics systems. Movements are more precise (repeatable) because hydraulics uses an incompressible liquid to transfer power whilst pneumatics uses gases.
Pneumatic systems have some advantages too. They are usually significantly cheaper than hydraulic systems, can move faster (gas much less viscous than oil) and do not leak oil if they develop a leak.
18. What is isometric drawing?
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It is a 3-D drawing used by draftsmen, architects etc
19. What are the advantages of gear drive?
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In general, gear drive is useful for power transmission between two shafts, which are near to each other (at most at 1m distance). In addition, it has maximum efficiency while transmitting power. It is durable compare to other such as belts chain drives etc. You can change the power to speed ratio.
Advantages: –
It is used to get various speeds in different load conditions.
It increases fuel efficiency.
Increases engine efficiency.
Need less power input when operated manually.
20. Which conducts heat faster steel copper or brass?
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Copper conducts heat faster than steel or brass. Any material that is good for conducting heat is also good for electricity in most cases. Wood terrible for transferring heat thus is also insulator for electric.
21. How pipe flanges are electrically insulated?
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Pipe flanges are protected from corrosion by means of electrolysis, with dielectric flanges. The piping system is electrically insulated by what is called a sacrificial anode. A bag of readily corrodible metal is buried in the ground with a wire running from the pipe to the bag so that the sacrificial anode will corrode first. If any electrical current charges the pipe, it also serves as a ground.
22. What is a Process Flow Diagram?
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A Process Flow Diagram (or System Flow Diagram) shows the relationships between the major components in the system. It also has basic information concerning the material balance for the process.
23. Where pneumatic system is used?
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Any system needs redundancy in work needs pneumatics, because the compressor of the pneumatic system has periodical operations (intermittent work, not as hydraulic pump). The compressed air could be accumulated in tanks with high pressures and used even if the compressor failed.
24. Why gas containers are mostly cylindrical in shape?
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The most efficient shape for withstanding high pressure is a sphere but that would be costly to manufacture. A cylinder with a domed top and a domed bottom (look underneath, the flat base is actually welded around the outside, the bottom of the gas container is actually domed) is a much cheaper shape to manufacture whilst still having good strength to resist the internal gas pressure.
25. How is martensite structure formed in steel?
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Martensite transformation begins when austenite is cooled below a certain critical temperature, called the matrensite start temperature. As we go below the martensite start temperature, more and more martensite forms and complete transformation occurs only at a temperature called martensire finish temperature. Formation of martensite requires that the austenite phase must be cooled rapidly.
26. What is an ortographic drawing?
Ans:
Orthographic projections are views of a 3D object, showing 3 faces of it. The 3 drawings are aligned so that if the page were folded, it would create part of the shape. It is also called multiview projections.
The 3 faces of an object consist of its plan view, front view and side view. There are 2 types of orthographic projection, which are 1st angle projection and 3rd angle projection.
27. What is representative elementary volume?
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Smallest volume over which measurements can be made that will yield a representative of the whole.
28. Why are LNG pipes curved?
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LNG pipes are curved because LNG is condensed gas (-164 deg cel) so it can expand the pipes that is what engineers designed the LNG pipes are curve type.
29. What does angular momentum mean?
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Angular momentum is an expression of an objects mass and rotational speed.
Momentum is the velocity of an object times it is mass, or how fast something is moving how much it weigh. Therefore, angular momentum is the objects mass times the angular velocity where angular velocity is how fast something is rotating expressed in terms like revolutions per minute or radians per second or degrees per second.
30. Can you use motor oil in a hydraulic system?
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Hydraulic fluid has to pass a different set of standards than motor oil. Motor oil has tackifiers, lower sulfur content, and other ingredients that could prove harmful to the seals and other components in a hydraulic system. If it is an emergency only should you do it.
31. What causes white smoke in two stroke locomotive engines?
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That is the engine running too lean (lack of fuel). This condition will lead to overheating and failure of the engine.
32. What is the role of nitrogen in welding?
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Nitrogen is used to prevent porosity in the welding member by preventing oxygen and air from entering the molten metal during the welding process. Other gases are also used for this purpose such as Argon, Helium, Carbon Dioxide, and the gases given off when the flux burns away during SMAW (stick) welding.
33. What does Green field project mean?
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Green field projects are those projects, which do not create any environmental nuisance (pollution), follows environmental management system and EIA (environment impact assessment). These projects are usually of big magnitude.
34. Is it the stress that, produces strain or strain produces stress?
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A Force applied to an object will cause a displacement. Strain is effectively a measure of this displacement (change in length divided by original length).
Stress is the Force applied divided by the area it is applied. (E.g. pounds per square inch)
Therefore, to answer the question, the applied force produces both ?Stress and Strain?. ?Stress and Strain? are linked together by various material properties such as Poisson’s ratio and Young’s Modulus.
35. How does iron ore turn into steel?
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To make Steel, Iron Ore is refined into iron and all the carbon is burned away using very high heat (Bessemer). A percentage of Carbon (and other trace elements) are added back to make steel.
36. What is knurling?
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Knurling is a machining process normally carried our on a centre lathe. The act of Knurling creates a raised criss-cross pattern on a smooth round bar that could be used as a handle or something that requires extra grip.
37. What is the mechanical advantage of a double pulley?
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It only takes half the effort to move an object but twice the distance.
38. What is extrued aluminum?
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Extrusion is the process where a metal or a metal bar is pulled through a mandrel to elongate it and/or give it a final shape.
Extruded Aluminum is a common form of making small aluminum wire, bars or beams and many varieties of small non-structural, decorative pieces.
39. What is a Newtonian fluid?
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A Newtonian fluid possesses a linear stress strain relationship curve and it passes through the origin. The fluid properties of a Newtonian fluid do not change when any force acts upon it.
40. What are the points in the stress strain curve for steel?
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Proportional limit, elastic limit or yield point, ultimate stress and stress at failure.
41. What Is Extrued Aluminum?
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Extrusion is the process where a metal or a metal bar is pulled through a mandrel to elongate it and/or give it a final shape.
Extruded Aluminum is a common form of making small aluminum wire, bars or beams and many varieties of small non-structural, decorative pieces.
42. What Is The Mechanical Advantage Of A Double Pulley?
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It only takes half the effort to move an object but twice the distance.
43. What Is Knurling?
Ans:
Knurling is a machining process normally carried our on a centre lathe. The act of Knurling creates a raised criss-cross pattern on a smooth round bar that could be used as a handle or something that requires extra grip.
44. How Does Hydraulic Clutches Work?
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By using a non-compressible fluid, it acts like a solid push rod.
45. Why Is Over-pressurizing An Air Conditioning System Bad?
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Overcharging a refrigeration or air conditioning system can result in an explosion. To avoid serious injury or death, never overcharge the system. Always use proper charging techniques. Limit charge amounts to those specified on the system equipment serial label or in the original equipment manufacturer’s service information.
Overcharging the system immerses the compressor motor, piston, connecting rods, and cylinders in liquid refrigerant. This creates a hydraulic block preventing the compressor from starting. The hydraulic block is also known as locked rotor.
Continued supply of electricity to the system causes heat to build in the compressor. This heat will eventually vaporize the refrigerant and rapidly increase system pressure. If, for any reason, the thermal protector fails to open the electrical circuit, system pressure can raise to high enough levels to cause a compressor-housing explosion.
46. Will A Steel Cable Become Longer If It Is Heated While Under Load?
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Even the heaviest steel cables stretch under load, whether they heat or not. Heating the cable will certainly elongate it. Friction caused by guides or pulleys can greatly increase the temperature of a cable under load.
You might consider the possibility of total failure if the heat is high enough and I am not sure but the cable might act in unpredictable ways when it fails. Applying heat to a steel cable under load is probably dangerous to your health and the health of anyone nearby.
When steel is heated, steel expands. It does not need to be under load. That is the reason that in the old days before advanced electronics and optics surveyors used chains rather than cables for measuring land. Had they used cable they would have gotten different measurements in summer and winter based on the difference in temperature and the coefficient of expansion of the material. The coefficient of expansion is a number that informs just how much a given material will expand or contract for a given change in temperature.
To find the coefficient of expansion and other interesting information consult a materials handbook, available in better libraries or your local college of engineering. Another example of expanding steel and the necessity for dealing with this characteristic is the overlapping slip joint found on bridges that allows horizontal structural members to expand and contract without damaging the bridge.
47. What Is The Congressional Space Medal Of Honor?
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The medal was created in 1969, designed by Congress for “any astronaut who in the performance of his duties has distinguished himself by exceptionally meritorious efforts and contributions to the welfare of the Nation and mankind.
48. What Is The Law Of Thermodynamics?
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There are actually 3 Laws of Thermodynamics (the actual number is debatable, but the number ranges from 3-5, depending on your adding skills).
49. Is It The Stress That, Produces Strain Or Strain Produces Stress?
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A Force applied to an object will cause a displacement. Strain is effectively a measure of this displacement (change in length divided by original length).
Stress is the Force applied divided by the area it is applied. (E.g. pounds per square inch)
Therefore, to answer the question, the applied force produces both “Stress and Strain”. “Stress and Strain” are linked together by various material properties such as Poisson’s ratio and Young’s Modulus.
50. How Does A Super Charger Work In A Car?
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A supercharger is a used to increase the volume of air dragged into each cylinder per stroke.
In combustion engines, there are only really two ways to increase power, firstly increase the amount of fuel in the engine (either increase the displacement, or add more cylinders) or increase the amount of air in the engine (for a more effective explosion of the fuel)
Superchargers are powered by the engines crankshaft, which is connected usually by a belt drive. This rotational power turns a fan, which sucks air into the intake manifold similar in effect to turbochargers, with reduced lag. However, superchargers take more energy out the engine, so swings and roundabouts.
51. Why Do The Radiators In Your House Click When You Start The Heating System?
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They are clicking because they are heating up. The heat causes expansion and that is why you hear clicking.
52. How Can I See Where Pipes Are Behind The Wall?
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By using radio waves.
53. How Are The Pneumatic System And The Hydraulic System Similar?
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Pneumatics use gases such as air or nitrogen, hydraulics use oil or water, both systems use pressure to act on a specific application.
54. What Is The Difference Between An Electric Motor And An Electric Generator?
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There is no fundamental difference between an electric motor and an electric generator or dynamo. In normal use, all motors behave as generators, and all generators behave as motors. DC Motors act like generators because they use less electrical energy when allowed to spin fast. DC generators act like motors because they become easier to spin when less electrical energy is drawn from their terminals.
For example, connect two small DC magnet motors together. Then if you spin the shaft of the first motor, the second motor’s shaft will start spinning too. One acts as a DC generator, and the other acts as a DC motor. Alternatively, spin the second one’s shaft, and the first one will start spinning.
Another example: If you connect a small DC motor to a small battery, then an electric current will appear in the motor’s coils, and the motor starts spinning. However, if you spin the motor’s shaft slightly faster than the normal speed, the direction of current in the circuit will reverse, and the battery starts taking in energy from the motor. The motor has become a generator, and it is recharging the battery.
55. What Are Some Examples Of A Periscope?
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It is an optical instrument for viewing objects, which are above the level of direct sight; mostly used in submarines.
56. What Does Green Field Project Mean?
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Green field projects are those projects, which do not create any environmental nuisance (pollution), follows environmental management system and EIA (environment impact assessment). These projects are usually of big magnitude.
57. Is Pipe Round Because It Provides The Least Area To Volume Ratio?
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More likely because it is easier to manufacture, much easier to put threads on, you do not have to worry about orientation when you put them together, and they have no weak spots created by corners.
My gutter pipes are rectangular because they do not stick out as far from the house as a circular one with the same area. However, they are low enough in the pressure they contain that they can be formed from sheet metal with a crimped seam. Making a water supply pipe, that way would be impossible.
In addition, it is easy to keep them aligned to the house. Running a rectangular water main under a street would be a major pain.
58. Who Built The Trans Alaska Pipelene?
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The pipe was constructed in six sections by five different contractors employing 21,000 people at the peak of work.
59. How Is A Submarine Able To Submerge And Surface?
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Submarines have ballast tanks. The tanks can hold air, or they can be “vented” and water can flow into them and fill them completely. When the tanks are full of air, the submarine is buoyant and floats. When the main vents are opened, the tanks are flooded and the submarine submerges. When the submarine is submerged, wants to surface, air can be injected at high pressure into the ballast tanks to force out water, again make the submarine buoyant, and cause it to rise to the surface and float.
In practice, when a submarine surfaces, it doesn’t use a lot of air from its high pressure air tanks to “blow the ballast tanks” because it takes a long time to pump up the high pressure air tanks again. What happens is that all the ballast tanks are given a “good shot” of high-pressure air (a few seconds), and then the planes are used in conjunction with the screw (which some call a propellor) to actually drive a submarine to the surface. Once there, something called a low-pressure blower system can be used to finish blowing the ballast tanks (while the high-pressure air compressors are running to pump the high-pressure air tanks back up).
60. What Is Railroad Track Ballast?
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That being said railroad track ballast is the cover for the subgrade. Ballast has several functions:
It enables water to drain from the track.
It assists in helping control the thermal expansion of continues welded rail.
As a train passes the rails, it supports the train.
It distributes the weight of the train from the track structure to the sub grade.
Maintains a smooth running surface for the train to run on.
As ballast becomes contaminated with other materials, it looses its ability to do some or all of these jobs.
61. What Is A Turboprop Engine?
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The combination of the words turbine and propeller in techno jargon will give you the word “turboprop”. A turboprop engine is a turbojet (gas turbine) engine, which powers the propeller/s.
A conventional jet engine produces its thrust in large part due to the heated gasses escaping out the rear of the engine. While this is very useful for aircraft, which fly at high speeds and high altitudes, it is less desirable for aircraft, which are designed to fly at slower speeds and take off from smaller runways.
A turboprop engine is a jet engine, which converts the bulk of its thrust into rotational energy for powering a propeller. This allows jet engines, which are a high-rpm low-torque engine to be used in situations where low-rpm and high-torque are needed instead.
The higher reliability and efficiency of a jet or turboprop engine as compared to an internal combustion engine makes them very desirable for aircraft designs, which, in the past, would have utilized internal combustion engines.
62. What Are Examples Of Mechanisms?
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Examples of mechanisms are the workings of a clock, a light switch, and a nail clipper.
63. What Color Are Thermal Oil Piping Lines?
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Brownish and sort of grey.
64. How Does Hydraulics Work?
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A positive displacement pump (gear, vane, or piston pump) is driven by a prime mover (Electrical Motor or Engine) it sucks fluid from reservoir and delivers oil to system. During loading, a resistance to flow creates the pressure, which is utilized to do the work through cylinder for linear motion, or through hydraulic motor for rotary motion, Direction of flow is changed with help of direction control valve & system pressure is regulated by pressure control valve & flow is regulated by flow control valve.
65. What Is The Role Of Nitrogen In Welding?
Ans:
Nitrogen is used to prevent porosity in the welding member by preventing oxygen and air from entering the molten metal during the welding process. Other gases are also used for this purpose such as Argon, Helium, Carbon Dioxide, and the gases given off when the flux burns away during SMAW (stick) welding.
66. What Causes White Smoke In Two Stroke Locomotive Engines?
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That is the engine running too lean (lack of fuel). This condition will lead to overheating and failure of the engine.
67. What Is The Difference Between Hydraulic Oil And Engine Oil?
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Both the hydraulic and engine oils are made from base oils with additives mixed in. The additives used change the characteristics of the oils so that they function differently.
Generally, hydraulic oils (final product including additives) are expected to have very low compressibility and very predictable friction and viscosity stability under pressure.
Generally engine oils (Engine Lubrication Oils anyway) are intended to have high resistance to heat (degradation including chemical and viscosity due to heat) resistance to burning and resistance to absorption of fuels and chemical compounds produced during combustion.
Both classes of oils are likely to have additives intended to provide detergency and to reduce foaming.
Base oils are most commonly petroleum oil bases due to cost, but other bases oil can be used including mineral oils (especially for hydraulic oils) and plant oils (especially for engine oils) and oils from animal sources.
68. Can You Use Motor Oil In A Hydraulic System?
Ans:
Hydraulic fluid has to pass a different set of standards than motor oil. Motor oil has tackifiers, lower sulfur content, and other ingredients that could prove harmful to the seals and other components in a hydraulic system. If it is an emergency only should you do it.
69. What Does Angular Momentum Mean?
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Angular momentum is an expression of an objects mass and rotational speed.
Momentum is the velocity of an object times it is mass, or how fast something is moving how much it weigh. Therefore, angular momentum is the objects mass times the angular velocity where angular velocity is how fast something is rotating expressed in terms like revolutions per minute or radians per second or degrees per second.
70. What Is The Difference Between Upstream And Downstream In A Refinery?
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The total process of a the refining business starts at the oil field or gas field and runs all the way to the sending of processed hydrocarbon to a final user.
Upstream applies to the operation of exploration, drilling, hydrocarbon production, and transmission via truck, rail or ship or pipeline to the refinery intake valve.
Downstream includes all work done at the refinery, distillation, cracking, reforming, blending storage, mixing and shipping.
The case of heavy oil processing (oil sands etc.) and gas plant operation tend to cross the boundaries somewhat. Most are regarded as upstream operations even though downstream type operations are part of the processes. The production of chemical side products at gas plants (e.g. sulfur) is not generally segregated as a “Chemical Plant” operation.
Additional hydrocarbon production operations such as saddle plants, which remove a component from pipeline gas, are generally lumped with upstream.
71. What Does A Rolling Offset Look Like?
Ans:
Rolling offsets are used in the piping and sheet metal (ductwork) trades, a rolling offset changes the elevation and locaton of the piping or duct usually by using two fittings to offset around obstacles. Rolling offsets are used mostly when you are limited to the size of the fittings in order to change your elevation and location.
72. What Kind Of Paper Airplane Flies The Farthest?
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Thickest paper has the greatest mass and therefore potential energy. Potential energy equals kinetic energy (speed). Speed equals lift. Lift equals a greater flight distance. Thicker planes fly farther.
73. How Does An Equal-arm Balance Work?
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Two pans of equal balances are placed at the end of the beam, one at each end. A long pointer attached at right angles to the beam at the point of support. Zero on a scale indicates the beam is at rest.
74. What Is Wet Corrosion And Galvanic Corrosion?
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Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially when in electrical contact with a different type of metal and both metals are immersed in an electrolyte.
When two or more different sorts of metal come into contact in the presence of an electrolyte, a galvanic couple is set up as different metals have different electrode potentials. The electrolyte provides a means for ion migration whereby metallic ions can move from the anode to the cathode. This leads to the anodic metal corroding more quickly than it otherwise would; the corrosion of the cathodic metal is retarded even to the point of stopping. The presence of electrolyte and a conducting path between the metals may cause corrosion where otherwise neither metal alone would have corroded.
Wet Corrosion: The main feature of corrosion of a divalent metal M in an aqueous solution containing oxygen is because of the corrosion process consists of an anodic and a cathodic reaction. In the anodic reaction (oxidation), the metal is dissolved and transferred to the solution as ions M2+. The cathodic reaction in the example is reduction of oxygen. It is seen that the process makes an electrical circuit without any accumulation of charges.
The electrons released by the anodic reaction are conducted through the metal to the cathodic area where they are consumed in the cathodic reaction. A necessary condition for such a corrosion process is that the environment is a conducting liquid (an electrolyte) that is in contact with the metal. The electrical circuit is closed by ion conduction through the electrolyte. In accordance with the conditions, this dissolution process is called wet corrosion, and the mechanism is typically electrochemical.
75. How Do Concrete Pumps Work?
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liquid (fluid) concrete has a big viscosity, how the pump overcomes this big viscosity. every couple seconds maybe 4-5 seconds the machine emits a loud thump. sound come from pnomatic part of the machine.
76. What Is Representative Elementary Volume?
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Smallest volume over which measurements can be made that will yield a representative of the whole.
77. How Can You Convert Air Mass To Air Volume?
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Mass = density * volume.
Air density is p/RT, where R is the gas constant for air (287 J/kg-K), T is the absolute temperature, and p is the pressure, equal to 101325 Pa at sea level.
At sea level and room temperature, the density of air is rho 101325 N/m2/ (287 N-m/ (kg-K)*293 K or about a) 2 kg/mc)
78. What Are Different Types Of Gate Valves?
Ans:
There are a few different designs:
Parallel disk gate valves use two disks with a spring in between them, sliding into the seats. At low pressure, the spring forces the disks outward against the seats, sealing off the valve. At high pressure, all the sealing is accomplished by the downstream disk.
Wedge gate valves use a tapered disk that slides into two seats set at a slight, converging angle. The wedging action provides the sealing force between the disk and the seat.
Single disk gate valves are used where the flow is always one-way (like sluices on dams). There is some flexibility in the attachment of the disk to the stem, so the differential pressure on the disk pushes it against the seat, sealing it off.
79. What Is The Density Of Plastic?
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Plastics are the general term for a wide range of synthetic or semisynthetic polymerization products. There are many different plastics; all have their own density!
Most common plastics, however, have a density between .035 and .045 lb/cu in.
80. What Is An Ortographic Drawing?
Ans:
Orthographic projections are views of a 3D object, showing 3 faces of it. The 3 drawings are aligned so that if the page were folded, it would create part of the shape. It is also called multiview projections.
The 3 faces of an object consist of its plan view, front view and side view. There are 2 types of orthographic projection, which are 1st angle projection and 3rd angle projection.
81. What is mechanism?
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A mechanism is an assembly of different parts which perform a complete motion and is often part of a machine.
82. State Newton’s three laws of Motion.
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– The law of inertia: Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.
– Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object). Force=Mass times acceleration.
– For every action there is an equal and opposite reaction.
83. State the laws of thermodynamics and its importance of in Mechanical Engineering.
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Thermodynamics is a physical science which studies the interrelation between heat, work and the internal energy of any system. Thermodynamics helps study all the systems of mechanical engineering. There are three laws of thermodynamics.
First Law: Energy can be neither created nor destroyed. It can only change forms. In any process in an isolated system, the total energy remains the same.
Eg: turning on a light would seem to produce energy; however, it is electrical energy that is converted.
Second Law: The second law of thermodynamics states that the entropy of any isolated system not in thermal equilibrium almost always increases.
Eg: A car that has run out of gas will not run again until you walk 10 miles to a gas station and refuel the car.
Third Law: As temperature approaches absolute zero, the entropy of a system approaches a minimum.
Eg: Water in gas form has molecules that can move around very freely. Water vapor has very high entropy (randomness). As the gas cools, it becomes liquid which can still move around but not as freely. At this point they have lost some entropy. On cooling further it becomes solid ice where molecules can no longer move freely but can only vibrate within the ice crystals. The entropy is now very low. As the water nears absolute zero, the vibration of the molecules diminishes. If the solid water reaches absolute zero, all molecular motion would stop completely. And at this point the water would have no entropy at all.
84. What is Hess law?
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According to the Hess law the energy transfer is simply independent of the way being followed. If the reactant and the product of the whole process are the same then same amount of energy will be dissipated or absorbed.
85. What is PS?
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Personal Statement. It is something that gives an informative background about an individual.
86. What is a bearing? What are the different types of bearings?
Ans:
Bearing is a device that helps smoother movement with minimal friction which in turn helps enhances efficiency and speed. Considering two types of loading, radial and thrust, there are different types of bearings which help handle these loads. The basic difference in the types of loads is essentially due to their ability to handle weight and different kinds of loads for various applications. Different types of bearings are:
-Ball bearing
-Roller bearing
-Ball Thrust bearing
-Roller thrust bearing
-Tapered roller bearing
-Magnetic bearings
-Giant Roller Bearing
87. What is a process flow diagram?
Ans:
A Process Flow Diagram is a user friendly, simplified sketch which illustrates general plant streams, major equipments and key central loops and shows the relationship between major components in the system. By using symbols to identify instruments and vessels it describes the primary flow course. They also provide e detail of mass/energy balance data along with stream composition and physical properties, however do not show minor components.
88. What is a time and motion theory?
Ans:
Frederick Taylor was pioneer of the time and motion theory. This technique monitors the amount of time required to complete a task along with observing the steps taken by a worker to complete the given task.
89. Which is the hardest material on earth?
Ans:
Diamond is currently the hardest material, made up of carbon atoms which cannot move. Carbon is the only atom that can have four electrons in the second shell surrounding the carbon nucleus, precisely why making a diamond the hardest material. However, there also are claims by a few to a new rare material called Wurtzite Boron Nitride which has a structure similar to a diamond but has some other atoms in place of carbon.
90. One unit of BTU is how many Joules?
Ans:
1 BTU=1055.06 Joules
91. What does a pump develop? Give reason to support your answer.
Ans:
Pump is a device that is used to transfer fluid from one place to another place which means it develops flow not pressure.
92. Explain the difference between pipe and a tube.
Ans:
A pipe is measured based on its inner diameter (ID) whereas a tube is measured based on the outer diameter (OD). Other than the dimensions there is no major difference between the two.
93. Explain the formula of heat loss in a pipe.
Ans:
In order to find total heat loss through the pipes it is imperative to know the thermal conductivity and the differing thicknesses of each layer. The ground that surrounds the pipe also acts as a layer of insulation. Considering this, the thermal properties of the stoneless sand is included in the heat loss calculation.
94. What kind of pipes are used for steam lines?
Ans:
Pressure and temperature are two of the most important factors to be considered before selecting the type of material to be used. Steam is a compressible gas due to which the capacity of the pipe line depends on the size of the pipes and pressure of the steam. Since steam at even low pressure can be dangerous, extra care is to be taken. Galvanized pipes are usually not used for steam. Pipes made of mild steel with welded fittings are instead largely used.
95. Who invented the four stroke engine? According to you which one is more efficient, four stroke engine or a two stroke engine and why?
Ans:
Nikolaus Otto invented the four stroke engine. Both, two stroke and four stroke have their own advantages and disadvantages. 4 stroke is more fuel efficient. However, 2 stroke produces more power.
96. What do you understand by the concept of a 6 stroke engine? Explain how it works.
Ans:
The six stroke engine is based on the concept of four stroke engine but built with an intention of improvising the efficiency in reducing emission. Every cycle of a four stroke engine involves the upward and downward movement of the piston which happens twice in the chamber, resulting in four total strokes and one of which is the power stroke which provides the torque to move the vehicle. A six stroke engine works similarly except that there are two power strokes.
97. Explain what is torque
Ans:
Torque is the force that causes rotation. It is a measure of how much force is acting on an object making it rotate.
98. What is the difference between torque and power?
Ans:
While power determines the speed of a vehicle, torque determines the time in which that speed can be reached. The greater the
torque figure, the faster the acceleration. The more torque in the engine, the faster you accelerate. Power is the rate at which work is done, so it is basically the potential of the engine.
99. Explain why diesel engine is known as high torque and petrol engine as high speed engine?
Ans:
Each power stroke in a petrol engine releases more heat and is converted into mechanical energy due to a higher rate of burning. This is the reason petrol engine has higher power and acceleration.
Diesel engine is a compression ignition engine with higher compression ratio, therefore extreme pressure is high. Since the piston of a diesel engine is larger, more torque is delivered in produced.
100. Why do heavy vehicles use diesel engine?
Ans:
The compression ratio of diesel engine is higher than the petrol engine, the reason for producing higher torque. The efficiency of diesel engine increases with load. Diesel produces slow energy on burning of fuel and the efficiency of the engine increases with load which is why diesel engine is suitable and largely used for heavy vehicles.
101. Explain the difference between projectile motion and rocket motion.
Ans:
The major difference is that a projectile has no motor or a rocket on it, due to which the momentum is given to it as it is launched. A pen thrown across a room is a classic example of a projectile motion. On the other hand, a rocket or missile has a motor on it which helps in accelerating while moving. This helps in resisting other forces such as gravity. A projectile does not have any specific shape, it is a point mass, whereas rocket has a particular shape having its center of gravity situated at a particular point on its body. Thus rocket motion comes under kinetics and projectile comes under kinematics.
102. Between steel, copper and brass, which conduct faster heat.
Ans:
Copper conducts heat faster than steel or brass. In most cases, material that is good for conducting heat is also good for electricity.
103. Explain the types of sensors.
Ans:
(i) Temperature Sensor- This device collects information about the temperature from a source and converts it to a form which is understandable by another device or person. Glass thermometer is the best example where mercury acts as the temperature sensor.
(ii) IR Sensors- This device detects and/or emits infrared radiation to sense a particular phase in the environment. Mostly thermal radiation is emitted by all the objects in the infrared spectrum. This type of radiation is not visible to the human eye but the infrared sensor detects it.
(iii) UV Sensors- These sensors measure the intensity of the ultraviolet radiation. This form of electromagnetic radiation has wavelengths which are longer than x-rays yet shorter than visible radiation. UV sensors can discover the exposure of environment to ultraviolet radiation.
(iV) Touch Sensor- A touch sensor acts as a variable resistor based on the location where it is sensed. Proximity Sensor- A proximity sensor detects the presence of objects that are placed in close proximity without any point of contact.
104. What minerals are used in the manufacture of cars?
Ans:
Cars are made from many various minerals. The steel body is made from the iron-rich minerals like magnetite and hematite. Door handles and badges are often coated in chromium which comes from chromite. Some of the other minerals used are aluminum, quartz, copper, magnesium, zinc, tin etc.
105. Which instrument measures speed in a car?
Ans:
A speedometer helps measure the speed in the car.
106. What are the advantage and disadvantage of using LPG in a car?
Ans:
Advantages:
The high octane rate enables it to blend better with air and to burn completely, generating less carbon. With less carbon buildup, spark plugs often last longer and oil changes are needed less frequently.
Since it burns in the gaseous phase, it results in less corrosion and engine wear.
In case of a spill, LPG evaporates quickly.
Disadvantages
The LPG requires servicing at approximately once a year.
Since complete combustion occurs, more heat is liberated which is not advised for a long journey as the engine will get over heated.
Installation of LPG is rather difficult.
107. Why gas containers are mostly in a cylindrical shape?
Ans:
The ideal shape would be a sphere. The container must have the capacity to withstand the extremely high pressure of liquefied gas. A spherical shape helps in distributing these forces uniformly.
108. Explain why re-heater is used in gas turbine
Ans:
The advantage of reheater is that it significantly increases the thrust; which is a prime reason for its use in gas turbines.
109. How many types of suspensions are used in automobiles?
Ans:
McPherson struts
Leaf spring
Coil spring
Torsion beam
Wishbone
Air Suspension
110. What is DTSI? Why it is used in motor bikes?
Ans:
Digital Twin Spark Ignition. This is used for a better fuel combustion in the cylinder head which helps provide better efficiency and optimum use of fuel.
111. What are the advantages of DTSI over normal engines?
Ans:
The cylinder head has two spark plugs, instead of the usual one. When two sparks are generated at either ends of the combustion chamber, the air-fuel mixture is ignited in a way that creates two flame fronts. A higher rate of combustion is achieved leading to higher rise in pressure. The outcome of this is more torque, better fuel efficiency and lower emissions.
112. What is meant by gear ratio?
Ans:
A gear ratio is a direct measure of ratio of the rotational speeds of two or more interlocking gears.
113. What is the ratio of specific heat of air?
Ans:
The ratio of specific heat ?=CP/CV is a factor in adiabatic engine processes and in determining the speed of sound in gas. This ratio ?=1.66 for an ideal monoatomic gas and ?=1.4 for air, which is predominantly a diatomic gas.
114. What is the percentage of carbon present in pig iron?
Ans:
Carbon content is generally 3.5-4.5%.
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