Basic mechanical engineering interview questions and answers pdf


 

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Basic Mechanical Engineering Interview Questions And Answers Pdf

+ Mechanical Engineering Interview Questions and Answers, Question1: What is Both the hydraulic and engine oils are made from base oils with additives. Download Mechanical Engineering Interview Questions PDF from here and prepare accordingly Check More: Interview Questions and Answers It also has basic information concerning the material balance for the process. Basic Mechanical Interview Questions With Answers in pdf format – A Mechanical Engineer who sits for an interview is expected to be well.

Question How Does Hydraulics Work? Answer : 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. Answer : 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. Answer : That is the engine running too lean lack of fuel. This condition will lead to overheating and failure of the engine. Answer : 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. Answer : Hydraulic fluid has to pass a different set of standards than motor oil.

High damping capacity, with respect to vibration. Relatively good mechanical properties under compressive loading. Under what condition a convergent divergent nozzle required? When pressure ratio is greater than critical pressure ratio. What is endurance limit and what is its value for steel? Endurance limit is the maximum level of fluctuating stress which can be tolerated indefinitely.

How the net work to drive a compressor and its volumetric efficiency behave with increase in clearance volume? Work remains unaltered and volumetric efficiency decreases. What do you understand by sulphur print? 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.

What is the different between brass and bronze? Brass is an alloy of copper with zinc; and bronze is alloy of copper with tin. What is the effect of addition of zinc in copper? By addition of zinc in copper, both tensile strength and elongation increases. What for admirality brass used? Aluminium is also added to brass to improve corrosion resistance. What is the maximum use of magnesium?

Magnesium is used to alloy with aluminium and as an additive for making SG Spheroidal Graphite iron. What for zinc finds applications? Galvanizing consumes the largest proportion of zinc. Zinc is resistant to corrosion but is attacked by acids and alkalies. Zinc alloy. Which factors influence the type of fracture in failure of a material? What is the name given to ratio of actual cycle efficiency and ideal cycle efficiency. Efficiency ratio. List two effects of manganese in plain carbon steels.

Manganese increases tensile strength and hardness. It decreases weldability. Name the strongest and weakest type of atomic bonds. Metallic bond is strongest and molecular bond also known as Vander Waals bond is weakest. In which process internal energy remains constant? Isothermal process. What is temper embrittlement in alloy steels and what are its effects? Embrittlement attack is usually intergranular in metals, i. 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.

What are whiskers? Whiskers are very small crystals which are virtually free from imperfections and dislocations. What is Bauschinger effect?

600 TOP MECHANICAL ENGINEERING Interview Questions and Answers PDF

According to Bauschinger, the limit of proportionality of material does not remain constant but varies according to the direction of stress under cyclic stresses. What is the difference between heat capacity and specific heat of a material? 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. Explain the rule to find specific heat of aqueous solutions.

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. What do you understand by latent heat? Give four examples of latent heats.

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. Define the terms free energy and free enthalpy. What is their significance and importance? It is equal to the work during a constant-volume isothermal reversible nonflow process.

For reversible isothermal steady-flow processes or for reversible constant-pressure isothermal nonflow processes, change in free energy is equal to net work. Which parameter remains constant in isochoric process? What is polytropic process? Under what conditions it approaches isobaric, isothermal, and isometric process? In which reversible process no work is done? No work is done in isometric process.

Whether superheated steam can be treated like ideal gas? Out of constant pressure and constant volume lines on TS diagram which line has higher slope? And whether slope is constant or variable? Constant volume line. Slope is variable. Whether entropy is intensive property or extensive property? Entropy is extensive property. In which process fluid expands but does no work? Throttling process. What is the difference between scavenging and supercharging? Scavenging is process of flushing out burnt gases from engine cylinder by introducing fresh air in the cylinder before exhaust stroke ends.

Supercharging is the process of supplying higher mass of air by compressing the atmospheric air.

Mechanical Engineering Interview Questions & Answers

What are the names given to constant temperature, constant pressure, constant volume, constant internal energy, constant enthalpy, and constant entropy processes. Isothermal, isochroic, isobaric, free expression, throttling and adiabatic processes respectively. In a Rankine cycle if maximum steam pressure is increased keeping steam temperature and condenser pressure same, what will happen to dryness fraction of steam after expansion?

It will decrease. Why entropy change for a reversible adiabatic process is zero? Because there is no heat transfer in this process. What are two essential conditions of perfect gas? It satisfies equation of state and its specific heats are constant. Enthalpy and entropy are functions of one single parameter. Which is that? Why rate of condensation is higher on a polished surface compared to rusty surface? Polished surface promotes drop wise condensation and does not wet the surface.

How much resistance is offered to heat flow by drop wise condensation? Nil What is the relationship between COP of heating and cooling? How much is the work done in isochoric process? When maximum discharge is obtained in nozzle?

At the critical pressure ratio. Under what condition the work done in reciprocating compressor will be least? It is least when compression process approaches isothermal. For this purpose, attempts are made to cool the air during compression. What is the difference between stalling and surging in rotary compressions? Stalling is a local phenomenon and it occurs when How breaks away from the blades.

Surging causes complete breakdown of flow and as such it affects the whole machine. Why the electric motor of a fan with backward curved blades is never got overloaded under any condition? For higher flow, power consumption gets lower. Why the work per kg of air flow in axial flow compressor is less compared to centrifugal compressor for same pressure ratio? Isentropic efficiency of axial flow compressor is higher.

What is the name given to portion of thermal energy to be necessarily rejected to environment? What is pitting? How it is caused? Non uniform corrosion over the entire metal surface, but occuring only in small pits is called pitting. It is caused by lack of uniformity in metal. What is caustic embrittlement? It is the actual physical change in metal that makes it extremely brittle and filled with minute cracks.

It occurs particularly in the seams of rivetted joints and around the rivet holes. Which impurities form hard scale and which impurities soft scale? Sulphates and chlorides of lime and magnesium form hard scale, and carbonates of lime and magnesium form soft scale. What is the difference between hard water and soft water? Hard water contains excess of scale forming impurities and soft water contains very little or no scale forming substances.

Which two elements in feed water can cause corrosion of tubes and plates in boiler? Acid and oxygen in feed water lead to corrosion. What should be done to prevent a safety valve to stick to its seat?

Safety valve should be blown off periodically so that no corrosion can take place on valve and valve seat. Why large boilers are water tube type?

Water tube boilers raise steam fast because of large heat transfer area and positive water circulation. Thus they respond faster to fluctuations in demand. Further single tube failure does not lead to catastrophy. What type of boiler does not need a steam drum? Super-critical pressure boiler. Why manholes in vessels are usually elliptical in shape? Elliptical shape has minimum area of opening and thus plate is weakened the least. Further it is very convenient to insert and take out the cover plate from elliptical opening.

Low water in boiler drum is unsafe because it may result in overheating of water tubes in furnace. Why it is unsafe to have high water condition in boiler drum?

High drum level does not allow steam separation to be effective and some water can be carried over with steam which is not desirable for steam turbine. Why boiler is purged every time before starting firing of fuel? Purging ensures that any unburnt fuel in furnace is removed, otherwise it may lead to explosion.

What is the principle of mechanical refrigeration?

A volatile liquid will boil under the proper conditions and in so doing will absorb heat from surrounding objects. Why high latent heat of vaporisation is desirable in a refrigerant? A high latent heat of vaporisation of refrigerant results in small amount of refrigerant and thus lesser circulation system of refrigerant for same tonnage. What is the critical temperature of a refrigerant? Critical temperature is the maximum temperature of a refrigerantrat which it can be condensed into liquid and beyond this it remains gas irrespective of pressure applied.

High temperature in I. Why efficiency of gas turbines is lower compared to I. Further combustion temperature of I. What do you understand by timed cylinder lubrication? For effective lubrication, lub oil needs to be injected between two piston rings when piston is at bottom of stroke so that piston rides in oi during upward movement. This way lot of lub oil can be saved and used properly.

HUCR is highest useful compression ratio at which the fuel can be used in a specific test engine, under specified operating conditions, without knocking. In some engines glycerine is used in place of water for cooling of engine.

Mechanical engineering interview questions.pdf

Thus weight of coolant gets reduced and smaller riadiator can be used. Why consumption of lubricating oil is more in two-stroke cycle petrol engine than four-stroke cycle petrol engine? In two-stroke engine lub oil is mixed with petrol and thus some lub oil is blown out through the exhaust valves by scavenging and charging air.

There is no such wastage in four stroke petrol engine. As compression ratio increases, thermal n increases. How is thermal n affected by weak and rich mixture strength? Thermal n is high for weak mixture and it decreases as mixture strength becomes rich. How engine design needs to be changed to burn lean mixture? Engine to burn lean mixture uses high compression ratio and the highly turbulent movement of the charge is produced by the geometry of the combustion chamber.

Horse power of I. To which countries these standards belong? What is the use of flash chamber in a vapour compression refrigeration cycle to improve the COP of refrigeration cycle? When liquid refrigerant as obtained from condenser is throttled, there are some vapours. These vapours if carried through the evaporator will not contribute to refrigerating effect.

Using a flash chamber at some intermediate pressure, the flash vapour at this pressure can be bled off and fed back to the compression process. The throttling process is then carried out in stages. Similarly compression process is also done in two separate compressor stages. Why pistons are usually dished at top? What is the function of thermostat in cooling system of an engine? Thermostat ensures optimum cooling because excessive cooling decreases the overall efficiency.

It allows cooling water to go to radiator beyond a predetermined temperature. What are the causes of failure of boiler tubes? Boiler tubes, usually are made from carbon steel and are subject to a high rates of heat transfer, b bending stresses due to uneven heating, especially at expanded or welded joints into headers or drums, c external erosion from burners and flue gas, d possible corrosion on the boiler side, and e occasional manufacturing defects.

Failure may occur due to following reasons : a High thermal ratings may lead to rapid failure if the internal fluid flow is reduced for any reason. The resultant overheating leads to a failure by creep, characterised by the bulging of the tube with the eventual development of a longitudinal split. Lamination in boiler tubes or score marks arising from the cold drawing of tubes, give rise to premature failure and may promote corrosion at these regions. What are the causes of failure of superheater tubes?

Superheater tubes are subjected to the most severe combination of stress, temperature and corrosive environment. In addition to high-temperature strength, resistance to corrosion is also important. Failures in superheater tubes may arise from : a Prior fabrication history b Faulty heat treatment c Consequences of welding d Overheating of the tube metal e Gas-side corrosion f Stress corrosion austenitic steels.

Why supercritical boilers use less amount of steel compared to non-supercritical boilers? Supercritical boilers do not head heavy drum for separation of steam from mixture of water and steam. Out of electric heater and heat pump, which is economical in operation? Heat pump. Which furnace burns low-ash fusion coal and retains most of the coal ash in the slag? Cyclone furnace. How the thickness of thermal boundary layer and thickness of hydrodynamic boundary layer related?

What is the effect of friction on flow of steam through a nozzle? To decrease both mass flow rate and wetness of steam. Why gas turbine power plant needs efficient compressor? Because a large portion of turbine work is eaten away by compressor and its inefficiency will affect net power output and cost of generation.

Why rockets using liquid hydrogen have higher specific impulse compared to liquid hydrocarbon? Liquid hydrogen has higher burning velocity. Why axial flow compressor is preferred for gas turbines for aeroplanes? Because it has low frontal area. What is the effect of inter cooling in gas turbines?

It decreases thermal efficiency but increases net output. Why iso-octane is chosen as reference fuel for S. Iso-octane permits highest compression without causing knocking. Why thermal efficiency of I. Which are the reference fuels for knock rating of S. When effect of variations in specific heats is considered then how do maximum temperature and pressure vary compared to air standard cycle?

Temperature increases and pressure decreases. Quantities like pressure, temperature, density, viscosity, etc. What are these called? Intensive properties. The amount of radiation emitted per scm per sec is called …. Emissive power. Get doubled. How you can define coal? Coal is a naturally occurring hydrocarbon that consists of the fossilised remains of buried plant debris that have undergone progressive physical and chemical alteration, called coalification, in the course of geologic time.

Which pollutant is major greenhouse gas and what is its effect? In order to increase efficiency and reduce CO emissions and other emissions, clear coal technologies are receiving major attention.

Advanced pulverised and pressurised pulverised fuel combustion. Atmospheric fluidised bed combustion and pressurised fluidised bed combustion. Supercritical boilers. Integrated gasification combined cycle systems. Advanced integrated gasification, including fuel cell systems.

+ TOP MECHANICAL ENGINEERING Interview Questions & Answers

Magneto hydrodynamic electricity generation. What are the important operational performance parameters in design of fuel firing equipment? Fuel flexibility, electrical load following capability, reliability, availability, and maintenance ease. What is the difference between total moisture and inherent moisture in coal? The moisture content of the bulk as sampled is referred to as total moisture, and that of the air dried sample is called inherent moisture. What elements it reports?

Moisture, volatile matter, ash and fixed carbon. Ultimate analysis of coal is elementary analysis. What it is concerned with? Carbon, hydrogen, nitrogen, and sulphur in coal on a weight percentage basis. AFBC Atmospheric fluidised bed combustion process consists of forming a bed of inert materials like finely sized ash or ash mixed with sand, limestone for sulphur removal , and solid fuel particles in a combustor and fluidising it by forcing combustion air up through the bed mixture.

The gas flows thorugh bed without disturbing particles significantly but gas velocity is high enough to support the total weight of bed fluidisation. At slightly higher velocity excess gas passes through the bed as bubbles fluidised bed and gives the bed the appearance of a boiling liquid.

Bubbling fluidised bed combustion BFBC has a defined height of bed material and operates at or near atmospheric pressure in the furnace. Pressurised fluidised bed combustion PFBC system operates the bed at elevated pressure. Exhaust gases have sufficient energy to power a gas turbine, of course, gases need to be cleaned. In fluidised combustion, as ash is removed some unburned carbon is also removed resulting in lower efficiency.

In circulating fluidised bed combustion CFBC system, bed is operated at higher pressure leading to high heat transfer, higher combustion efficiency, and better fuel feed. Circulating fluidised beds operate with relatively high gas velocities and fine particle sizes. The maintenance of steady state conditions in a fast fluidised bed requires the continuous recycle of particles removed by the gas stream circulating bed. The term circulating bed is often used to include fluidised bed systems containing multiple conventional bubbling beds between which bed material is exchanged.

What for Schmidt plot for is used in heat transfer problems? Schmidt plot is a graphical method for determining the temperature at any point in a body at a specified time during the transient heating or cooling period.

In which reactor the coolant and moderator are the same? Pressurised water reactor. Which reactor has no moderator? Fast breeder reactor. What are thermal neutrons? Thermal neutrons are slow neutrons having energy below 1 eV which are in thermal equilibrium with their surroundings.

What is big advantage of fast breeder reactor? It has rapid self breeding of fissile fuel during the operation of the reactor, and thus, it offers about sixty times the output with same natural uranium resources through ordinary non-breeder nuclear reactor.

What is the purpose of biological shield in nuclear plants? Biological shield of heavy concrete prevents exposure to neutrons, beta rays and gamma rays which kill living things. Which two elements have same percentage in proximate and ultimate analysis of coal? Moisture and ash. On ultimate analysis. Which element causes difference in higher and lower heating values of fuel?

Which heating value is indicated by a calorimeter and why? Gross heating value because steam is condensed and heat of vapour formed is recovered.

State the difference between ultimate and proximate analysis of coal? In ultimate analysis, chemical determination of following elements is made by weight: Fixed and combined carbon, H, O, N, S, water and ash. Heating value is due to C, H and S. Mechanical has always remained immune to such short-lived craze, proving its everlasting effect in the mechanics of the world.

To get a little bit more technical, Mechanical Engineering is the discipline involved with the application of engineering mechanics and principles to design, analyze, build and maintain mechanical systems. One might wonder what compels a mechanical engineer to take up this underestimated disciple.

The fundamental idea as to how a seemingly simple volume of strange looking fluid is helping a relatively enormous vehicle move or how a basic concept of friction in a rope and pulley arrangement is being used to operate a lift is what motivates a mechanical engineer. We have enlisted a book which contains Mechanical Interview Questions and Answers in pdf format.

This branch of engineering has its effect so large and widely prevalent, that there are a number of different areas that make up this branch such as Engineering Mechanics, Heat Transfer, Refrigeration and Air conditioning, Mechanics of Solids, Design of Machinery, Metallurgy, Engineering Design, and Fluid Mechanics to name a few.

In a field so vast, it is unlikely that a student can become an expert in every field. The student is advised to be particularly well versed with the subject that is relevant to the firm which conducts the interview, be it a design firm or a manufacturing firm. It is also highly recommended that the student study through a bunch of Mechanical interview questions that test the students understanding and knowledge of each of the different topics of study.

The proper understanding of these topics and a healthy level of confidence is all that is needed to ace any kind of interview for a Mechanical Engineer. Below we have provided more information regarding this and provided Mechanical Interview Questions with Answers which can be easily downloaded in pdf format. Also, we have included a few most important frequently asked aptitude questions as well.

So check out these question and we are sure it will help you prepare the Interview, no matters whether you are a fresher or having relevant experience, in all cases these will surely help you.

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