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WorksheetsTHERMAL ENGINEERING II MCQ (MODEL EXAM - 2)
Total questions: 50
Worksheet time: 50mins
Consider the following statements: A psychrometer measures,
a. wet bulb temperature
b. dew point temperature
c. dry bulb temperature.
On these statements......is/are correct
a
b
c
Vapour can be treated a gas when
Temperature of vapour > critical temperature
Pressure of vapour < 10 kpa
Temperature of vapour = critical temperature
Pressure of vapour is > critical pressure
In the case of sensible cooling of air, the coil efficiency is given by (BPF = Bypass factor)
BPF-1
1-BPF
BPF
1 + BPF
In air-conditioning design for summer months, the condition inside a factory where heavy work is performed as compared to a factory in which light work is performed should have
lower dry bulb temperature and lower relative humidity
lower dry bulb temperature and higher relative humidity
lower dry bulb temperature and same relative humidity
same dry bulb temperature and same relative humidity
Which one of the following statements is correct
The sensible heat gain is due to the difference in humidity
The latent heat gain is due to the temperature difference between the fresh air through unconditioned space in the building adds to the sensible heat gain
The heat gain through the walls of ducts carrying conditioned air through unconditioned space in the building adds to the sensible heat gain
Maximum heat gain to a building occurs through walls
Which of the following statements are true?
I. The air conditioning duct should have high aspect ratio for good performance
II. If the air conditioning duct is diverging then the angle of divergence should be as small as possible to reduce pressure loss
III. To minimize the noise and vibration air should flow with low velocity
IV. All of the above
I
II
III
IV
Which of the followings is a Volatile organic compound (VOC)
Aromatic hydrocarbons
Hydrocarbons
Ethers
A cold storage is to be maintained at – 5°C while the surroundings are at 35°C. The heat leakage from the surroundings into the cold storage is estimated to be 29 kW. The actual C.O.P. of the refrigeration plant used is one third that of an ideal plant working between the same temperatures. Find the power required to drive the plant
11.58 kJ/s
12.98 kJ/s
12.90 kJ/s
10.98 kJ/s
Dry ice refrigeration process uses
Dry air
Pure water
Carbon di oxide
Nitrogen
With reciprocating compressor in vapour compression refrigeration system, wet compression is not desirable because
Liquid trapped up in the head of cylinder may damage the compressor valves
COP of the cycle decreases
Volumetric efficiency of compressor decreases
Mass flow rate per ton of refrigerant increases
Which one of the following statements is correct for reciprocating air compressor
Its volumetric efficiency increases with increasing clearance ratio
Its volumetric efficiency increases with increasing pressure ratio
Its volumetric efficiency does not vary with change in clearance ratio and pressure ratio
Its volumetric efficiency decreases with increasing clearance ratio and pressure ratio, both
Which of the following statements is not correct
A topping cycle plant generates electricity or mechanical power first
A bottoming cycle plant generates heat first
Both a and b
A bottoming cycle plant generates electricity or mechanical power first
What is a typical efficiency of a cogeneration system?
58%
85%
68%
95%
In a combined cycle power plant consisting of gas turbine and waste heat boiler, the exhaust gas temperature is ____.
around 150 °C
around 500 °C
around 300 °C
around 400 °C
Which of the following depends on physical properties of fluids as well as geometry of the heat exchanger?
Fouling coefficient
Overall heat transfer coefficient
LMTD (Log Mean Temperature Difference)
Effectiveness
The major limitation of metallic recuperator is -------
limitation of handling COx, NOx etc.
limitation of reduced life for handling temperature more than 1000°C
manufacturing difficulty of the required design
none of the above
Combined cycle is a combination of
conventional boiler first followed by cogeneration system
Rankine cycle first followed by a Brayton cycle
Brayton cycle first followed by a standard Rankine cycle
extraction in the first portion and then a condensing cycle
The efficiency of a stand-alone gas turbine without any heat recovery system will be in the range of
10 –15 %
15 –20 %
20 – 25 %
35 – 40 %
Ceramic recuperators can withstand gas side temperature up to
400°C
1300°C
1000°C
1700°C
The waste heat recovery equipment in a combustion system will be more economical when the exit flue gases are at a temperature of
200°C
400°C
600°C
800°C
A heat pipe can transfer up to ____ times more thermal energy than copper
10
20
50
100
In an industry, exhaust gas from the furnace is used for power generation by installing waste heat recovery steam boiler and a steam turbine. This type of co- generation is termed as
combined cycle
Brayton cycle
topping cycle
bottoming cycle
The most economic insulation is the thickness where …..
depreciation costs of insulation and energy cost due to losses are the same
the sum of energy cost due to losses and insulation depreciation cost is minimum
energy losses are minimized
energy cost due to losses are minimized.
The major limitation of metallic recuperator is
handling COx, NOx etc.
reduced life for handling temperature more than 650°C
manufacturing difficulty of the required design
none of the above
In a cogeneration system, with extraction condensing turbine, the highest heat rate is recorded when;
maximum power output and maximum extraction to process
maximum power output and normal extraction to process
maximum power output and minimum extraction to process
none of the above
In a process plant 200 kg/hr of hot condensate at 6 bar(g) having a sensible heat of 166 kCal/kg is discharged. The plant also requires low pressure steam at a pressure of 1 bar(g) for heating application. Find out the quantity of flash steam generated in the flash vessel in kg/hr. The condensate at a pressure of 1 bar(g) has a sensible heat of 120 kCal/ kg and a latent heat of 526 kCal/kg
15.5 kg/hr
16.5 kg/hr
17.5 kg/hr
18.5 kg/hr
Oxidation of carbon to CO2 yields 8084 kcal/kg of carbon. Oxidation of carbon to CO in the flue gas yields 2430 kcal/kg of carbon. Oxidation of CO to CO2 will yield
5464 kCal
5654 kCal
5800 kCal
540 kCal
The flow of steam is supersonic .........
At the entrance to the nozzle
At the throat of the nozzle
In the convergent portion of the nozzle
In the divergent portion of the nozzle
The maximum velocity attainable at the throat of a steam nozzle is......
less than sonic velocity
Sonic velocity
more than sonic velocity
Supersonic velocity
Which of the following devices uses wilson's line in determining flow through it.......
Steam engine
Steam nozzle
Reaction turbine
Impulse turbine
Nozzle efficiency is described as.......
Isentropic heat drop/useful heat drop
useful heat drop/isentropic heat drop
saturation temperature/supersaturation temperature
supersaturation temperature/saturation temperature
The steam leaves the nozzle at a.........
High pressure and low velocity
High-pressure and high velocity
Low pressure and low velocity
Low pressure and high velocity
The flow of steam is supersonic.........
At the entrance to the nozzle
At the throat of the nozzle
In the convergent portion of the nozzle
In the divergent portion of the nozzle
The maximum velocity attainable at the throat of a steam nozzle is......
Much less than sonic velocity
Slightly less then sonic velocity
Sonic velocity
Slightly more than sonic velocity
Supersonic velocity
The effect of friction in nozzle is to .......
Keep dryness fraction constant
Increase dryness fraction
Decrease dryness fraction
First increase dryness fraction up to certain limit and then decrease it
The critical pressure ratio for initially superheated steam is.......as compared to initially dry saturated steam
More
Less
Same
None of the above
A nozzle is said to be choked when .......
Flow-through it is zero
Flow is attained at maximum value corresponding to critical exit pressure
It is not possible to increase the flow by increasing inlet pressure
It is discharging into atmosphere
In an impulse turbine.......
The steam is expanded in nozzles only and there is a pressure drop and heat drop
The steam is expanded both in fixed and moving blades continuously
The steam is expanded in moving blades only
The pressure and temperature of steam remains constant
The reheating of steam in a turbine........
Increases the work done through the turbine
Increases the efficiency of the turbine
Reduces wear on the blades
All of the above
Da-laval turbines are mostly used.......
Where low speeds are required
For small power purposes and and low speeds
For small power purposes and and high speeds
For large power purposes
The degree of reaction is defined as the ratio........
Heat drop in the fixed blades to the heat drop in the moving blades
Heat drop in the moving blades to the heat drop in the fixed blades
Heat drop in the moving blades to the total heat drop in the fixed blades
Heat drop in the fixed blades to the total heat drop in the moving blades
There is enthalpy drop only in.......blades in case of an impulse steam turbine
Fixed
Rotating
Moving
All of the above
In a reaction turbine........
The steam is allowed to expand in the nozzle, where it gives a high velocity before it enters the moving blades
The expansion of steam takes place partly in the fixed blades and partly in the moving blades
The steam is expanded from a high pressure to a condenser pressure in one or more nozzles
The pressure and temperature of steam remains constant
In an impulse turbine
The steam is expanded in nozzles only and there is a pressure drop and heat drop
The steam is expanded both in fixed and moving blades continuously
The steam is expanded in moving blades only
The pressure and temperature of steam remains constant
In a reaction turbine, when steam flows through the fixed blades
Pressure increases while velocity decreases
Pressure decreases while velocity increases
Pressure and velocity both decreases
Pressure and velocity both increases
The relative efficiency is defined as the
Ratio of thermal efficiency to Rankine efficiency
Ratio of brake power to the indicated power
Ratio of heat equivalent to indicated power to the energy supplied in steam
Product of thermal efficiency and Rankine efficiency
A throttle governed steam engine develops 15 kW with 280 kg per hour of steam and 35 kW with 520 kg per hour of steam. The steam consumption in kg per hour when developing 20 kW will be nearly
150 kg/h
210 kg/h
280 kg/h
340 kg/h
In the following table, boiler components (left side) and different functions of boiler operation (Right side) are given. Determine correct functions corresponding to boiler component and select suitable option.
1B-2A-3D-4C
1C-2D-3A-2B
1D-2B-3C-4A
1A-2C-3B-4D
In a gas power cycle, hot combustion gas having specific heat 0.98 kJ/Kg-K enters the turbine at 25 bar, 1300 K and exits at 1 bar. The ratio of specific heat of the working fluid is 1.3. The isentropic efficiency of the turbine is 92%. The work developed (kJ/kg) by the turbine is
614.44
725.95
667.87
576.82
when fuel oil with 84.9 % carbon, 11.4 % hydrogen, 3.2 % Sulphur, 0.4 % oxygen and 0.1 % ash by weight is burnt with 20 % excess air, assume complete combustion calculate Total air supplied
6.42 kg/kg of fuel
9.24 kg/kg of fuel
16.72 kg/kg of fuel
19.52 kg/kg of fuel
