Mechanical Engineering Interview Questions with Answers on Thermodynamics, Power Plant Engg, Heat & Mass Transfer, I.C Engine, Automobile, Refrigeration & Air-Conditioning: Set 02
Question No. 51
Difference
between Boiling Point and Melting Point.
Answer:
(A) The melting point is a defined for solids
when it transfers from solid state to liquid state.
(B) The boiling point is defined for liquids
for a state change from liquid to gas.
(C) Boiling point is highly dependent on the
external pressure whereas the melting point is independent of the external
pressure.
Question No. 52
State
Laws of conservation of energy?
Answer:
According to the laws of conservation of energy, “energy can neither be created nor be destroyed. It can only be transformed from one form to another.”
According to the laws of conservation of energy, “energy can neither be created nor be destroyed. It can only be transformed from one form to another.”
Question No. 53
Is the
boiler a closed system?
Answer:
Yes definitely the boiler is a closed system.
Yes definitely the boiler is a closed system.
Question No. 54
What is
Carnot engine?
Answer:
It was being designed by Carnot and Carnot engine is an imaginary engine which follows the Carnot cycle and provides 100% efficiency.
It was being designed by Carnot and Carnot engine is an imaginary engine which follows the Carnot cycle and provides 100% efficiency.
Question No. 55
What is the use of flash chamber in a vapour
compression refrigeration cycle to improve the COP of refrigeration cycle?
Answer:
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.
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.
Question No. 56
Why pistons are usually dished at top?
Answer:
Pistons are usually hollowed at top to
Pistons are usually hollowed at top to
(A) Provide
greater space for combustion
(B) Increase
surface for flue gases to act upon, and
(C) Better distribution
of stresses.
Question No. 57
What is the function of thermostat in cooling
system of an engine?
Answer:
Thermostat ensures optimum cooling because excessive cooling decreases the overall efficiency. It allows cooling water to go to radiator beyond a predetermined temperature.
Thermostat ensures optimum cooling because excessive cooling decreases the overall efficiency. It allows cooling water to go to radiator beyond a predetermined temperature.
Question No. 58
Which
formula forms a link between the Thermodynamics and Electro chemistry?
Answer:
Gibbs Helmholtz formula is the formula which forms the link between the thermodynamics and electromagnetism.
Gibbs Helmholtz formula is the formula which forms the link between the thermodynamics and electromagnetism.
∆Hs/R = [∂ ln.p /∂(1/T)] (x)
Where: x – mole fraction of CO₂ in the liquid
phase
p – CO₂ partial pressure (kPa)
T – Temperature (K)
R – Universal gas constant
α – mole ratio in the liquid phase (mole CO₂
per mole of amines)
Question No. 59
What is
Hess Law?
Answer:
According to the Hess law the energy transfer is simply independent of the path being followed.
According to the Hess law the energy transfer is simply independent of the path 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.
Question No. 60
Which has
more efficiency: Diesel engine or Petrol engines?
Answer:
Off course Diesel engine has the better efficiency out of two.
Off course Diesel engine has the better efficiency out of two.
Question No. 61
Explain
Otto cycle.
Answer:
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.
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.
Question No. 62
Why iso-octane is chosen as reference fuel for S.I.
engines and allotted 100 values for its octane number?
Answer:
Iso-octane permits highest compression without causing knocking.
Iso-octane permits highest compression without causing knocking.
Question No. 63
Why thermal efficiency of I.C. engines is more
than that of gas turbine plant?
Answer:
In I.C. engine maximum temperature attained is higher than in gas turbine.
In I.C. engine maximum temperature attained is higher than in gas turbine.
Question No. 64
Which are the reference fuels for knock rating of
S.I. engines?
Answer:
n-heptane and ISO-octane.
n-heptane and ISO-octane.
Question No. 65
What will
be the position of Piston Ring?
Answer:
In 180 degree angle the Top ring, Second ring and Oil ring are fixed. Position the ring approximately 1 inch gap below the neck.
In 180 degree angle the Top ring, Second ring and Oil ring are fixed. Position the ring approximately 1 inch gap below the neck.
Question No. 66
What is
Heat rate of a Power plant?
Answer:
Heat rate is a measure of the turbine efficiency. It is determined from the total energy input supplied to the Turbine divided by the electrical energy output.
Heat rate is a measure of the turbine efficiency. It is determined from the total energy input supplied to the Turbine divided by the electrical energy output.
Question No. 67
When effect of variations in specific heats is considered
then how do maximum temperature and pressure vary compared to air standard
cycle?
Answer:
Temperature increases and pressure decreases.
Temperature increases and pressure decreases.
Question No. 68
Quantities like pressure, temperature, density,
viscosity, etc. are independent of mass. What are these called?
Answer:
Intensive properties.
Intensive properties.
Question No. 69
Why we do not use same technology to start both SI /CI engine?
Answer:
The S.I. or spark ignition engine uses petrol as a fuel and the C.I. or compression ignition engine uses diesel as a fuel. Both the fuels has different compression ratio. In SI engine the compression ratio is 8-12:1. In CI engine the compression ratio is 16-22:1. So in case of SI engine, the compression ratio is not sufficient for fuel to burn so a spark plug is used, whereas in CI engine, the compression ratio is so high that due to its internal heat the fuel is combusted so there is no need for a spark plug. So the technology used in SI engine is different from CI engine.
The S.I. or spark ignition engine uses petrol as a fuel and the C.I. or compression ignition engine uses diesel as a fuel. Both the fuels has different compression ratio. In SI engine the compression ratio is 8-12:1. In CI engine the compression ratio is 16-22:1. So in case of SI engine, the compression ratio is not sufficient for fuel to burn so a spark plug is used, whereas in CI engine, the compression ratio is so high that due to its internal heat the fuel is combusted so there is no need for a spark plug. So the technology used in SI engine is different from CI engine.
Question No. 70
What VVTi written on new cars of Toyota stands for?
Answer:
VVTi: Variable Valve Timing with Intelligence. It is the advanced version of the VVT engine.
VVTi: Variable Valve Timing with Intelligence. It is the advanced version of the VVT engine.
It changes
the cam shaft position by using oil pressure. It is similar to CVVT in Hyundai.
Question No. 71
In convection heat transfer, if heat flux
intensity is doubled then temperature difference between solid surface and
fluid will?
Answer:
Get doubled.
Get doubled.
Question No. 72
How you can define coal?
Answer:
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.
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.
Question No. 73
Why is the Suction pipe of Vapour Compression Refrigeration system
insulated?
Answer:
(A) It
prevents the suction line from sweating and dripping water inside the house.
(B) The insulation also prevents the
suction line attracting heat from the outdoors on its way to the condenser
coil.
Question No. 74
How to determine the capacity of Refrigeration system? How we use
Condenser coils, Compressor, Capillarity?
Answer:
To determine the Refrigeration system by test of C.O.P and use the Condenser coils, Compressor, Capillarity, based on the properties
To determine the Refrigeration system by test of C.O.P and use the Condenser coils, Compressor, Capillarity, based on the properties
Question No. 75
What do you mean by super critical above 500 MW in Thermal power plant?
Answer:
In super critical boiler means all the steam to convert in to superheated steam at outlet of boiler no need to sent to super heater once again.
In super critical boiler means all the steam to convert in to superheated steam at outlet of boiler no need to sent to super heater once again.
Question No. 76
Which pollutant is major greenhouse gas and what
is its effect?
Answer:
CO is major greenhouse gas and it traps the radiation of heat from the sun within earth's atmosphere.
CO is major greenhouse gas and it traps the radiation of heat from the sun within earth's atmosphere.
Question No. 77
In order to increase efficiency and reduce CO
emissions and other emissions, clear coal technologies are receiving major
attention. What are these?
Answer:
(A)
Advanced pulverized and pressurized pulverized fuel combustion.
(B)
Atmospheric fluidized bed combustion and pressurized fluidized bed combustion.
(C)
Supercritical boilers.
(D)
Integrated gasification combined cycle systems.
(E)
Advanced integrated gasification, including fuel cell systems.
(F) Magneto
hydrodynamic electricity generation.
Question No. 78
What does CC Stand for?
Answer:
CC is the abbreviated form of cubic centimeter. It is the unit by which the capacity of an engine is designated. It is the volume between TDC and BDC. It represents the quantity of fuel-air mix or exhaust gas that is pumped out in a single piston stroke. Alternatively it can represent the volume of the cylinder itself.
CC is the abbreviated form of cubic centimeter. It is the unit by which the capacity of an engine is designated. It is the volume between TDC and BDC. It represents the quantity of fuel-air mix or exhaust gas that is pumped out in a single piston stroke. Alternatively it can represent the volume of the cylinder itself.
Question No. 79
State the difference between ultimate and
proximate analysis of coal?
Answer:
In ultimate analysis, chemical determination of following elements is made by weight: Fixed and combined carbon, H, O, N, S, water and ash. Heating value is due to C, H and S.
In ultimate analysis, chemical determination of following elements is made by weight: Fixed and combined carbon, H, O, N, S, water and ash. Heating value is due to C, H and S.
In
proximate analysis following constituents are mechanically determined by
weight. Moisture, volatile matter, fixed carbon and ash heating value is due to
fixed carbon and volatile matter.
Question No. 80
What is fuel ratio?
Answer:
Fuel ratio is the ratio of its percentage (%) of fixed carbon to volatile matter.
Fuel ratio is the ratio of its percentage (%) of fixed carbon to volatile matter.
Question No. 81
How the analyses and calorific values of fuels
can be reported?
Answer:
It may be reported as:
It may be reported as:
(A) As
received or fired (wet) basis
(B) Dry or
moisture free basis
(C)
Combustible or ash and moisture free basis
Question No. 82
We have read that when the piston goes up and down then the engine works
i.e. the suction, compression etc. then what happens in the case of big
vehicles, which start at stable condition, i.e. how does their piston moves
when they are at rest. How suction, compression etc?
Answer:
Smaller vehicles like bikes, cars are started with the help of motors. Initially, motors turn the crank shaft till sufficient suction pressure is reached. When sufficient suction pressure is reached, the engine starts to suck the fuel in and then the cycle begins when the fuel is taken in and ignited. Similarly, for huge engines, instead of motors, we use starting air. air at a pressure of 10-30 bar is fed to the engine which is at rest. This air rotates the engine till it attains sufficient suction pressure. Once the pressure is reached, the cycle starts and it starts firing.
Smaller vehicles like bikes, cars are started with the help of motors. Initially, motors turn the crank shaft till sufficient suction pressure is reached. When sufficient suction pressure is reached, the engine starts to suck the fuel in and then the cycle begins when the fuel is taken in and ignited. Similarly, for huge engines, instead of motors, we use starting air. air at a pressure of 10-30 bar is fed to the engine which is at rest. This air rotates the engine till it attains sufficient suction pressure. Once the pressure is reached, the cycle starts and it starts firing.
Question No. 83
The Compression ratio of Petrol engine is always less than Compression
Ratio of Diesel engine why?
Answer:
Petrol is not self igniting; it needs spark to flame up in chamber. Whereas diesel is self igniting in diesel engine, to attain that state it requires high temp &pressure. This temperature & pressure is more than what’s required in Petrol Engines by property of that fluid.
Petrol is not self igniting; it needs spark to flame up in chamber. Whereas diesel is self igniting in diesel engine, to attain that state it requires high temp &pressure. This temperature & pressure is more than what’s required in Petrol Engines by property of that fluid.
Question No. 84
What are the important operational performance
parameters in design of fuel firing equipment?
Answer:
Fuel flexibility, electrical load following capability, reliability, availability, and maintenance ease.
Fuel flexibility, electrical load following capability, reliability, availability, and maintenance ease.
Question No. 85
What is the difference between total moisture and
inherent moisture in coal?
Answer:
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.
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.
Question No. 86
What is the temperature of space?
Answer:
The short answer is that the temperature in space is approximately 2.725 Kelvin. That means the universe is generally just shy of three degrees above absolute zero, the temperature at which molecules themselves stop moving. That’s almost -270 degrees Celsius, or -455 Fahrenheit.
The short answer is that the temperature in space is approximately 2.725 Kelvin. That means the universe is generally just shy of three degrees above absolute zero, the temperature at which molecules themselves stop moving. That’s almost -270 degrees Celsius, or -455 Fahrenheit.
Question No. 87
Proximity analysis of coal provides data for a
first, general assessment of a coal's quality and type. What elements it
reports?
Answer:
Moisture, volatile matter, ash and fixed carbon.
Moisture, volatile matter, ash and fixed carbon.
Question No. 88
Ultimate analysis of coal is elementary analysis.
What it is concerned with?
Answer:
Carbon, hydrogen, nitrogen, and sulfur in coal on a weight percentage basis.
Carbon, hydrogen, nitrogen, and sulfur in coal on a weight percentage basis.
Question No. 89
What are the causes of main engine black smoke?
Answer:
There is many cause of black smoke.
There is many cause of black smoke.
(A) Is
improper mixture of fuel supply by carburettor like very rich mixture so the
fuel improper burn.
(B) It is when piston or piston ring is fail so
back side cooling oil release in combustion chamber it cause black smoke.
(C) Improper
ignition system like not sufficient time of pressure rise delay period.
Question No. 90
What is the significance of torque (in Nm) given in the engine
specification?
Answer:
It give the moment about any point or simple rotation.
It give the moment about any point or simple rotation.
Question No. 91
Explain the difference between AFBC, BFBC, PFBC
and CFBC in regard to fluidized bed technologies.
Answer:
AFBC (Atmospheric fluidized bed combustion) process consists of forming a bed of inert materials like finely
sized ash or ash mixed with sand, limestone (for sulfur removal), and solid
fuel particles in a combustor and fluidising it by forcing combustion air up
through the bed mixture. The gas flows through 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 (fluidized bed) and gives the bed the appearance of a boiling
liquid.
BFBC (Bubbling fluidized bed combustion) has a defined height of bed material and operates at or near
atmospheric pressure in the furnace.
PFBC (Pressurized fluidized bed combustion) 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 fluidized combustion, as ash is removed some unburned carbon is also removed
resulting in lower efficiency.
CFBC (circulating fluidized bed combustion) system, bed is operated at higher pressure leading to high heat
transfer, higher combustion efficiency, and better fuel feed. Circulating fluidized beds operate
with relatively high gas velocities and fine particle sizes. The maintenance of
steady state conditions in a fast fluidized bed requires the continuous recycle of particles removed by the gas stream
(circulating bed). The term circulating bed is often used to include fluidized bed systems
containing multiple conventional bubbling beds between which bed material is
exchanged.
Question No. 92
What is the difference between nuclear fission
and fission chain reaction?
Answer:
The process of splitting of nucleus into two almost equal fragments accompanied by release of heat is nuclear fission. Self sustained, continuing, sequence of fission reactions in a controlled manner is fission chain reaction.
The process of splitting of nucleus into two almost equal fragments accompanied by release of heat is nuclear fission. Self sustained, continuing, sequence of fission reactions in a controlled manner is fission chain reaction.
Question No. 93
What is BHP?
Answer:
Brake horsepower is the amount of work generated by a motor under ideal conditions. This work is calculated without the consideration of effects of any auxiliary component that may slow down the actual speed of the motor. Brake horsepower is measured within the engines output shaft and was originally designed to calculate and compare the output of steam engines.
Brake horsepower is the amount of work generated by a motor under ideal conditions. This work is calculated without the consideration of effects of any auxiliary component that may slow down the actual speed of the motor. Brake horsepower is measured within the engines output shaft and was originally designed to calculate and compare the output of steam engines.
As per the
conventions, 1 BHP equals to:
(1) 745.5
watts
(2) 1.01389
ps
(3) 33,000
ft lbf/min
(4) 42.2 BTU/min
Question No. 94
Which parameter remains constant in a throttling
process?
Answer:
Enthalpy.
Enthalpy.
Question No. 95
What is the difference between isentropic process
and throttling process?
Answer:
In isentropic process, heat transfer takes place and in throttling process, enthalpy before and after the process is same.
In isentropic process, heat transfer takes place and in throttling process, enthalpy before and after the process is same.
Question No.96
What is D-4D Technology used in Toyota Vigo?
Answer:
D-4D is widely recognized as one of the most advanced diesel technologies on the market today. Diesel engines relied on relatively simple technology with a low-pressure mechanical injector delivering fuel to a pre-combustion chamber in the cylinder head where a single ignition fired by the intense heat of high compression takes place.
D-4D is widely recognized as one of the most advanced diesel technologies on the market today. Diesel engines relied on relatively simple technology with a low-pressure mechanical injector delivering fuel to a pre-combustion chamber in the cylinder head where a single ignition fired by the intense heat of high compression takes place.
Question No. 97
What for Schmidt plot for is used in heat
transfer problems?
Answer:
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.
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.
Question No. 98
What is ATFT Technology used in Honda Hunk?
Answer:
ATFT means Advance Tumble Flow Induction Technology, Tumble flow means swirling. In this technology, fuel air mixture from the carburettor into the engine cylinder with a swirl action. The advantage being one gets a more efficient burning of fuel hence more power and better fuel economy with lesser emissions.
ATFT means Advance Tumble Flow Induction Technology, Tumble flow means swirling. In this technology, fuel air mixture from the carburettor into the engine cylinder with a swirl action. The advantage being one gets a more efficient burning of fuel hence more power and better fuel economy with lesser emissions.
Question No. 99
What is big advantage of fast breeder reactor?
Answer:
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.
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.
Question No. 100
What is the purpose of biological shield in nuclear
plants?
Answer:
Biological shield of heavy concrete prevents exposure to neutrons, beta rays and gamma rays which kill living things.
Biological shield of heavy concrete prevents exposure to neutrons, beta rays and gamma rays which kill living things.