Thermal Engineering II Set 2

Mechanical Engineering

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This set of Thermal Engineering 2 Multiple Choice Questions & Answers (MCQs) focuses on Thermal Engineering II Set 2

Q1 | Which among the following is an assumption of the compressible flow?
  • resistance to flow of object
  • no-slip condition
  • known mass flow rate
  • resistance to flow of heat
Answer: no-slip condition
Explaination:
the related assumption of a compressible fluid flow is no-slip condition. it is assumed that the flow velocity at the solid surface is equal to the velocity of the surface itself. it is in direct consequence with the continuum flow.
Q2 | What is Mach number?
  • speed of object * speed of sound
  • speed of object /speed of sound
  • speed of object + speed of sound
  • speed of object- speed of sound
Answer: speed of object /speed of sound
Explaination:
mach number is defined as the ratio of the speed of an object to the speed of sound. mach number is denoted by ‘m’.
Q3 | Which of the following kinetic friction is smaller?
  • limiting friction
  • static friction
  • rolling friction
  • sliding friction
Answer: rolling friction
Explaination:
the force which comes into play when a body rolls over the surface of another body is called rolling friction. for the same magnitude of a normal reaction, rolling friction is always greater than the sliding friction.
Q4 | A mass of 4kg rests on a horizontal plane. The plane is gradually inclined until at an angle θ= 15° with the horizontal, the mass just begins to slide. What is the coefficient of static friction between the block and the surface?
  • 0.814
  • 0.27
  • 1.5
  • 3.5
Answer: 0.27
Explaination:
θ = 15° is the angle of response.
Q5 | A scooter weighs 120kg f. Brakes are applied so that wheels stop rolling and start skidding. Find the force of friction if the coefficient of friction is 0.4.
  • 60kg f
  • 48kg f
  • 25kg f
  • 32kg f
Answer: 48kg f
Explaination:
weight of the scooter = 120kg f μ = 0.4
Q6 | How is friction due to air reduced?
  • streamlining
  • lubrication
  • by using ball bearings
  • by polishing
Answer: streamlining
Explaination:
friction due to air is considerably reduced by streamlining the shape pf the body moving through air. for example, jets have a streamline shape.
Q7 | Friction can be increased by                        
  • using air cushion
  • lubricants
  • using sand
  • using ball bearings
Answer: using sand
Explaination:
by throwing sand the force of friction between the wheels and the track becomes easier. on rainy days, we throw sand on the slippery ground. this increases the friction between our feet and the ground and reduces the chance of slipping.
Q8 | When moving along a curved path, he
  • leans inwards
  • leans outwards
  • is still
  • leans sideways
Answer: leans inwards
Explaination:
when a cyclist goes around a curved path, a centripetal force is required. the force between the tyres and the road is small to provide the necessary centripetal force. that is why a cyclist going around a curve leans inwards because the horizontal component of the normal reaction provides the necessary centripetal force.
Q9 | A train has to negotiate a curve of radius 400m. By how much should the putter rail be raised with respect to inner rail for speed of 48 km/h? The distance between the rails is 1m.
  • 0.20m
  • 0.0454m c) 0.45m
  • d) 0.020m
Answer: 0.0454m c) 0.45m
Explaination:
h = (v2 l)/rg h = 402/32 = 0.0454m.
Q10 | When a gas is pushed through a pipe, the gaseous molecules are by the pipe’s walls
  • attracted
  • absorbed
  • deflected
  • dissipated
Answer: deflected
Explaination:
this is because there is no attractive force present in the tube for the process of attraction to occur. also, the surface of pipes is not an absorbing one, hence absorption is also ruled out. a pipe is
Q11 | In fluid dynamics, the velocity of the fluid in the stagnation point is
  • zero
  • infinite
  • non-existent
  • negative
Answer: zero
Explaination:
stagnant point is a point where there is no movement of the fluid. when there is no movement, the velocity will be 0. hence the answer is 0.
Q12 | If the speed of sound is much                   than that of the gas, the gas density will stay constant.
  • smaller
  • larger
  • equal to
  • non-existent
Answer: larger
Explaination:
this is because only with speed of sound is larger, it’ll be able to compensate for the speed of gas. under such situations,
Q13 | Isentropic nozzle flow states about the movement of a gas or fluid through a narrow orifice without an increase or decrease in
  • accelerating
  • decelerating
  • equilibrium
  • exponential increase
Answer: decelerating
Explaination:
initially the flow has a velocity. in the stagnant state, the velocity is 0. for this to happen, there should be a deceleration of the velocity. hence, deceleration is the answer.
Q14 | To refrain from separation in subsonic nozzles, the expansion angle must not be more than            
  • 10 degrees
  • 20 degrees
  • 30 degrees
  • 40 degrees
Answer: 10 degrees
Explaination:
if the angle is more than 10 degrees, there will be a drift amidst the nozzle. at any angle more than 10 degrees, this separation will occur. but the minimum value is 10 degrees. so, the answer is 10 degrees.
Q15 | Gas flows through the nozzle from an area of pressure (called the chamber) to one of pressure
  • high, low
  • low, high
  • same, same
  • constant, infinite
Answer: high, low
Explaination:
anything that flows or runs moves from a region of higher value to lower value. we can take the example of any physical parameter like pressure, altitude etc.
Q16 | Converging-diverging nozzle is also known as                      
  • pascal nozzle
  • bernouille’s nozzle
  • toricelli’s nozzle
  • de laval’ nozzle
Answer: de laval’ nozzle
Explaination:
this is because this nozzle was invented by carl de laval. so, it is also named after him. hence de-laval nozzle is the option.
Q17 | When the pressure chamber is big, the flow velocities are                    
  • large
  • negligible
  • constant
  • increasing
Answer: negligible
Explaination:
when the chamber is large, the area is high. velocity is inversely proportional
Q18 | For a compressible, ideal gas, mass flow rate depends on parameters such as flow area, pressure, temperature, properties of the gas, and                    
  • avogardo’s number
  • mach number
  • reynold’s number
  • le-grange’ number
Answer: mach number
Explaination:
mass flow rate should depend on the velocity. here mach number denotes the velocity. so, the mach number gives the right answer.
Q19 | Which type of boilers use orifice to control the flow circulation?
  • natural circulation boilers
  • forced convection boilers
  • once-through boilers
  • positive forced circulation boilers
Answer: forced convection boilers
Explaination:
in these boilers water is circulated by using an additional pump. these boilers often use orifices to control the flow circulation. orifices are located at the bottom of the tubes that ensure even distribution of flow through water wall tubes. these boilers can generate steam upto about 200 bar.
Q20 | What is the advantage of having smaller ratio of water to steam space?
  • steam can be generated at a faster even if the boiler is cold
  • increases the rate of evaporation
  • water is made cyclic, i.e., from boiler drum to water tube and back to drum
  • helps in mobilizing the boiler
Answer: steam can be generated at a faster even if the boiler is cold
Explaination:
rate of evaporation is more as area of heating surface is more due to presence of large small diameter tubes. due to that smaller water ratio is allowed to steam space where in the steam can be generated as a faster rate even if the boiler is cold. as the rate of evaporation is more, it is preferred in steam power plants for power generation.
Q21 | Which are the major types of boilers that are operated in world today?
  • natural circulation boiler
  • forced circulation boiler
  • fire tube boiler
  • once through boiler
Answer: once through boiler
Explaination:
the once through boiler has higher load response characteristics due to the fact that it does not have drum and has much lower water inventory. many times load change response is dictated by the firing system and its controls rather than the boiler, per-say.
Q22 | How many level indicators are there in the water level indicator of a boiler?
  • 1
  • 2
  • 3
  • 4
Answer: 2
Explaination:
the function of the water level indicator is to indicate the level of water
Q23 | What is the function of pressure gauge in the boiler?
  • to indicate steam pressure
  • to indicate water pressure
  • to indicate air pressure
  • to indicate flue gas pressure
Answer: to indicate steam pressure
Explaination:
the function of the pressure gauge is to indicate the steam pressure inside the boiler drum in bar or in kgf in cm2 or in kn/m2 in gauge pressure. if the boiler is fitted with a superheater, one more pressure gauge fitted to the superheater header indicates the superheated steam pressure at any given instant.
Q24 | other than Steam stop valve in the boiler which is the other similar type of valve used?
  • non-reversible valve
  • transient valve
  • reversible valve
  • junction valve
Answer: junction valve
Explaination:
stop valve and junction valve are essentially same. conventionally stop valves are smaller in size whereas, junction valves are larger. when the valve is mounted on the top most portion of the steam drum, normally the valve is called junction valve. if it is connected in the steam pipe to regulate the flow of steam, the valve is known as stop valve.
Q25 | What is the function of Blow down valve of a boiler?
  • to remove sludge
  • to build sediments
  • to remove flue gas
  • to remove ash
Answer: to remove sludge
Explaination:
blow down valve is also called as blow-off-cock. the function of this valve
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