1. What is the mixture of a number of gases?
a) Moist air
b) Dry air
c) Fresh air
d) Saturated air
Answer: b
Explanation: Dry air is the mixture of a number of gases like nitrogen, oxygen, carbon dioxide, hydrogen, etc. These gases have different proportion in this mixture by which the properties may alter.
2. Which of the following has the maximum contribution in the dry air?
a) Nitrogen
b) Argon
c) Carbon dioxide
d) Hydrogen
Answer: a
Explanation: Dry air is the mixture of a number of gases like nitrogen, oxygen, carbon dioxide, hydrogen, etc. In this mixture, nitrogen has the maximum contribution. Nitrogen is approximately 78.03 % by volume and 75.47 % by mass in this mixture.
3. Nitrogen and Argon have a major portion in the dry air.
a) False
b) True
Answer: a
Explanation: Dry air is the mixture of a number of gases like nitrogen, oxygen, carbon dioxide, hydrogen, etc. In this mixture, nitrogen has the maximum contribution. Nitrogen is approximately 78.03 % by volume and 75.47 % by mass in this mixture. Oxygen is approximately 20.99 % by volume and 23.19 % by mass in the mixture. But the argon has a very little portion in the mixture. So, Nitrogen and Oxygen have a major portion in the dry air.
4. Mixture of dry air and water vapor is __________
a) moist air
b) dry air
c) fresh air
d) saturated air
Answer: a
Explanation: If water vapor is present in a larger amount in the dry air, then the type of air is called as moist air. The amount of water vapor present in the air depends upon the absolute pressure and temperature of the mixture.
5. Specific humidity and absolute humidity have the same unit.
a) False
b) True
Answer: a
Explanation: Humidity ratio or Specific humidity is the mass of water vapor present in 1 kg of dry air. It is generally expressed in, g / kg of dry air and absolute humidity is the mass of water present in 1 m3 of dry air. It is generally expressed in, g / m3 of dry air.
6. The mixture of dry air and water vapor called when the air has diffused the maximum amount of water vapor into it is called ________
a) dry air
b) moist air
c) saturated air
d) specific humidity
Answer: c
Explanation: Saturated air is the mixture of dry air and water vapor when the air has diffused the maximum amount of water vapor into it. The water vapors occur in the form of superheated steam as an invisible gas.
7. What is the ratio of actual mass of water vapor in a unit mass of dry air to the mass of water vapor in the same mass of dry air when it is saturated at the same temperature?
a) Moist air
b) Dry air
c) Degree of saturation
d) Saturated air
Answer: c
Explanation: The ratio of actual mass of water vapor in a unit mass of dry air to the mass of water vapor in the same mass of dry air when it is saturated at the same temperature is called as the degree of saturation.
8. What is the mass of water vapor present in 1 kg of dry air called?
a) Specific Humidity
b) Relative humidity
c) Degree of saturation
d) Saturated air
Answer: a
Explanation: Humidity ratio or Specific humidity is the mass of water vapor present in 1 kg of dry air. It is generally expressed in, g / kg of dry air. Mathematically, W = mv / ma.
9. What is the ratio of actual mass of water vapor in a given volume of moist air to the mass of water vapor in the same volume of saturated air at the same pressure and temperature?
a) Specific Humidity
b) Relative humidity
c) Degree of saturation
d) Saturated air
Answer: b
Explanation: Relative humidity is the ratio of actual mass of water vapor in a given volume of moist air to the mass of water vapor in the same volume of saturated air. It can be represented as,
∅ = mv / ms = pv / ps.
10. What is the temperature of air recorded by a thermometer, when the moisture present in it starts condensing?
a) DBT
b) WBT
c) DPT
d) WBD
Answer: c
Explanation: DPT i.e., Dew Point Temperature is the temperature at which the moisture in it begins to condense. It can also be defined as the temperature corresponding to the partial pressure of water vapor.
11. What is the value of humidity ratio if pv = 0.387 bar and pa = 0.997 bar?
a) 0.482
b) 0.241
c) 0.122
d) 0.622
Answer: b
Explanation: Humidity ratio is the mass of water vapor present in 1 kg of dry air and has a unit g / kg of dry air.
W = 0.622 pv / pa
= 0.622 x 0.387 / 0.997
= 0.241 kg / kg of dry air.
12. What is the value of humidity ratio if mv = 1.423 and ma = 3.589?
a) 0.1
b) 0.2
c) 0.4
d) 0.5
Answer: c
Explanation: Humidity ratio is the mass of water vapor present in 1 kg of dry air and has a unit g / kg of dry air. It is also defined as the ratio of the mass of water vapor to the mass of dry air in a given volume of the air-vapor mixture. Hence, it is given as mv / ma.
W = 1.423 / 3.589 = 0.396 ≅ 0.4.
13. What is the value of relative humidity if mv = 2.901 and ms = 9.056?
a) 0.300
b) 0.330
c) 0.310
d) 0.320
Answer: d
Explanation: Relative humidity is the ratio of actual mass of water vapor in a given volume of moist air to the mass of water vapor in the same volume of saturated air. It can be represented as,
∅ = mv / ms = pv / ps = 2.901 / 9.056 = 0.320.
14. What is the value of relative humidity if pv = 0.468 bar and ps = 0.893 bar?
a) 52 %
b) 54 %
c) 56 %
d) 190 %
Answer: a
Explanation: Relative humidity is the ratio of actual mass of water vapor in a given volume of moist air to the mass of water vapor in the same volume of saturated air. It can be represented as,
∅ = mv / ms = pv / ps = 0.468 / 0.893 = 0.524 = 52.4 %.
15. What is the value of pb if pa = 1.48 bar and pv = 1.52 bar, according to Dalton’s law of partial pressures?
a) 1 bar
b) 2 bar
c) 3 bar
d) 4 bar
Answer: c
Explanation: The Dalton’s law states that the total pressure exerted by the mixture of air and water vapor is equal to the sum of the pressures, which each constituent would exert if it occupied the same space by itself. Mathematically, it can be represented as, pb = pa + pv = 1.48 + 1.52 = 3 bar.
16. If DBT = 30°C, WBT = 20°C and Barometer reading is 740 mm of Hg. Find out DPT using steam tables.
a) 5°C
b) 35°C
c) 15°C
d) 25°C
Answer: b
Explanation: For given conditions, pressure corresponding to WBT from steam table is pw = 0.02337 bar
pb = 740 mm of Hg = 740 x 133.3 / 100000 = 0.98642 bar
Pressure of water vapor = pv = pw – [(pb – pw) (td – tw) / 1544 – 1.44 tw]
= 0.02337 – [(0.98642 – 0.02337) (30 – 20) / 1544 – 1.44 x 20]
= 0.01701 bar
For 0.01701 bar water vapor pressure, dew point temperature is 15°C.
17. What do vertical and uniformly spaced lines indicate on the psychrometric chart?
a) DPT
b) WBT
c) DBT
d) Specific humidity
Answer: c
Explanation: The psychrometric chart has DBT on the x-axis. So, the vertical and uniformly spaced lines denote dry bulb temperature and spaced by 5°C.
18. Which of the following is represented by curved lines on the psychrometric chart?
a) Specific humidity
b) Relative humidity
c) WBT
d) DPT
Answer: b
Explanation: The psychrometric chart has DBT on the x-axis and specific humidity on the y-axis. The curved line on the grid shows the relative humidity. From 0 to 100 %, these lines are drawn at an interval of 10%.
19. What is represented by inclined straight lines but non-uniformly spaced on the psychrometric chart?
a) Specific humidity
b) Relative humidity
c) WBT
d) DPT
Answer: c
Explanation: The psychrometric chart has DBT on the x-axis and specific humidity on the y-axis. The inclined lines from the saturation curve and on the x-axis denote wet-bulb temperature.
20. What is represented by horizontal lines but non-uniformly spaced on the psychrometric chart?
a) Specific humidity
b) Relative humidity
c) WBT
d) DPT
Answer: d
Explanation: The psychrometric chart has DBT on the x-axis and specific humidity on the y-axis. The horizontal lines from the saturation curve and parallel to the abscissa denote dew point temperature.
21. What is represented by inclined straight lines but uniformly spaced on the psychrometric chart?
a) Enthalpy
b) Relative humidity
c) WBT
d) DPT
Answer: a
Explanation: The psychrometric chart has DBT on the x-axis and specific humidity on the y-axis. The inclined lines from the saturation curve and parallel to the wet-bulb temperature lines denote Enthalpy.
22. What is represented by obliquely inclined straight lines but uniformly spaced on the psychrometric chart?
a) Enthalpy
b) Relative humidity
c) Specific volume
d) DPT
Answer: c
Explanation: The psychrometric chart has DBT on the x-axis and specific humidity on the y-axis. The obliquely inclined lines from the saturation curve and on the dry-bulb temperature lines denote Specific volume.
23. Specific humidity lines are also known as_________
a) moisture content lines
b) relative humidity
c) specific volume
d) moist lines
Answer: a
Explanation: Specific humidity is the moisture present in the air mixture. So, specific humidity denotes moisture content. Hence, these lines are also known as moisture content lines.
24. Relative humidity on saturation curve has value of ________% at various dry bulb temperatures.
a) 0
b) 50
c) 10
d) 100
Answer: d
Explanation: Relative humidity is the ratio of actual mass of water vapor in the given volume of moist air to the mass of water vapor in the same amount of saturated air. So, on the saturation curve, for every dry bulb temperature, the value of relative humidity remains 100%.
25. Enthalpy lines and specific volume lines are the same.
a) False
b) True
Answer: a
Explanation: Though both of the lines representing given properties are inclined straight lines and uniformly spaced, but the slope of both the lines are different. The specific volume lines are obliquely inclined.
26. A psychrometric chart is a graphical representation of various physical properties of dry air.
a) True
b) False
Answer: b
Explanation: Psychrometric chart is a graphical representation of the various thermodynamic properties of moist air. This is used to find out properties of air in the field of air conditioning.
27. What is the alternate name for thermodynamic wet-bulb temperature?
a) Isobaric WBT
b) Isobaric Saturation Temperature
c) Adiabatic WBT
d) Adiabatic Saturation Temperature
Answer: d
Explanation: The thermodynamic wet-bulb temperature is also known as adiabatic saturation temperature due to the process involved in it.
28. What is the temperature at which air can be brought to saturation state adiabatically?
a) Thermodynamic WBT
b) Thermodynamic DBT
c) Thermodynamic DPT
d) DPT
Answer: a
Explanation: The temperature at which air can be brought to saturation state adiabatically is called a thermodynamic wet-bulb temperature or adiabatic saturation temperature.
29. Which of the following is carried out to obtain saturation state at the thermodynamic WBT?
a) Condensation
b) Evaporation
c) Compression
d) Expansion
Answer: b
Explanation: The temperature at which air can be brought to saturation state adiabatically is called a thermodynamic wet-bulb temperature or adiabatic saturation temperature. This state is achieved by evaporation of water into the flowing air.
30. Which of the following is the major equipment in the simplest form is used to do saturation of air?
a) Chamber
b) Vessel
c) Insulated Chamber
d) Pipe
Answer: c
Explanation: The equipment used for saturation of the air in the simplest form is an insulated chamber containing an optimum amount of water.
31. The arrangement for extra-water to flow into the chamber from its top is called as ___________
a) chamber ingot
b) chamber gate
c) make-up gate
d) make-up water
Answer: d
Explanation: The equipment used for saturation of the air in the simplest form is an insulated chamber containing an optimum amount of water. In order to get more water into the chamber, an arrangement is provided, which is called make-up water.
32. What is the ratio of humidity ratio of entering and discharging air?
a) W2 / W1 = (hs2 – hfw) + ha2 – ha1 / (hs1 – hfw)
b) W1 / W2 = (hs1 – hfw) + ha2 – ha1 / (hs2 – hfw)
c) W1 / W2 = (hs2 – hfw) + ha2 – ha1 / (hs1 – hfw)
d) W1 / W2 = (hs2 – hfw) + ha1 – ha2 / (hs1 – hfw)
Answer: c
Explanation: Balancing enthalpies, h1 – W1 hfw = h2 – W2 hfw
As, h1 = ha1 + W1 hs1 and h2 = ha2 + W2 hs2
So, by putting values we get,
W1 / W2 = (hs2 – hfw) + ha2 – ha1 / (hs1 – hfw).
33. The term (h2 – W2 hfw) is known as_________
a) sigma term
b) sigma heat
c) heat factor
d) heat term
Answer: b
Explanation: The term (h2 – W2 hfw) is known as sigma heat, and this term remains constant during the adiabatic process.
34. If h1 = 32 kJ/kg, h2 = 41 kJ/kg, hfw = 49 kJ/kg, W1 = 0.0109 kg/kg of dry air and W2 = 0.0297 kg/kg of dry air then what is the value of sigma heat?
a) 41.0865
b) 39.5447
c) 38.9013
d) 45.8775
Answer: b
Explanation: Sigma heat = (h2 – W2 hfw)
So, putting values in the formula,
Sigma heat = [41 – (49 x 0.0297)] = 39.5447.
35. Evaporation from water to flowing air is carried out adiabatically.
a) False
b) True
Answer: b
Explanation: The temperature at which air can be brought to saturation state adiabatically is called a thermodynamic wet-bulb temperature or adiabatic saturation temperature. This state is achieved by evaporation of water into the flowing air.
36. Make-up water is used to keep the water level constant.
a) True
b) False
Answer: a
Explanation: In order to get more water into the chamber, an arrangement is provided, which is called make-up water. This water is added from the top to keep the water level constant and keep the energy transfer at an optimum pace.
37. What is the By-pass factor for heating coil, if td1 = temperature at entry, td2 = temperature at exit and td3 = coil temperature?
a) td3 – td1 / td3 – td1
b) td3 – td2 / td3 – td1
c) td3 – td2 / td2 – td1
d) td3 – td2 / td1 – td2
Answer: b
Explanation: By-pass factor is the amount of air by-passed in the process. So, for heating coil,
BPF = Temperature difference between coil and exit / Temperature difference between coil and entry
= td3 – td2 / td3 – td1.
38. What is the By-pass factor for cooling coil, if td1 = temperature at entry, td2 = temperature at exit and td3 = coil temperature?
a) td3 – td1 / td3 – td1
b) td3 – td2 / td3 – td1
c) td3 – td2 / td2 – td1
d) td2 – td3 / td1 – td3
Answer: d
Explanation: By-pass factor is the amount of air by-passed in the process. So, for cooling coil,
BPF = Temperature difference between exit and coil / Temperature difference between entry and coil
= td2 – td3 / td1 – td3.
39. If the value of BPF for one row of a coil is y then what is the value of BPF for n similar rows?
a) n / y
b) n + y
c) (y)n
d) n x y
Answer: c
Explanation: BPF for multiple similar rows of a coil is the power of one BPF to the number of rows. i.e. (y)n.
40. What is the value of sensible heat given out by the coil?
a) U Ac tm
b) U Ac
c) U tm
d) U Ac2 tm
Answer: a
Explanation: Sensible heat given out by the coil is the product of overall heat transfer coefficient, the surface area of the coil and logarithmic mean temperature difference.
So, Sensible heat = U Ac tm.
41. What is the formula of logarithmic mean temperature in terms of By-pass factor?
a) Tm = td2 – td1 / loge [1/BPF]
b) Tm = td2 – td1 / log10 [BPF]
c) Tm = td2 – td1 / loge [BPF]
d) Tm = td2 – td3 / loge [BPF]
Answer: c
Explanation: Logarithmic mean temperature difference for the given arrangement is,
Tm = td2 – td1 / loge [td3 – td1 / td3 – td2]
As, BPF for the coil = [td3 – td1 / td3 – td2]
Tm = td2 – td1 / loge [BPF].
42. What is the efficiency of the coil?
a) 1 + BPF
b) 1 / BPF
c) BPF
d) 1 – BPF
Answer: d
Explanation: As the by-pass factor is the inefficiency, so the contact factor or efficiency of the coil is given by 1 – BPF.
43. What is the contact factor for heating coil, if td1 = temperature at entry, t2 = temperature at exit and td3 = coil temperature?
a) td3 – td1 / td3 – td1
b) td2 – td1 / td3 – td1
c) td3 – td2 / td2 – td1
d) td3 – td2 / td1 – td2
Answer: b
Explanation: Contact factor or efficiency of the coil is 1 – By-pass factor. So, for heating coil,
ηH = 1 – BPF
= 1 – [td3 – td2 / td3 – td1]
= td2 – td1 / td3 – td1.
44. What is the contact factor for cooling coil, if td1 = temperature at entry, td2 = temperature at exit and td3 = coil temperature?
a) td1 – td2 / td1 – td3
b) td2 – td1 / td3 – td1
c) td3 – td2 / td2 – td1
d) td3 – td2 / td1 – td2
Answer: a
Explanation: Contact factor or efficiency of the coil is 1 – By-pass factor. So, for cooling coil,
ηC = 1 – BPF
= 1 – [td2 – td3 / td1 – td3]
= td1 – td2 / td1 – td3.
45. A coil with low BPF has better performance.
a) True
b) False
Answer: a
Explanation: As BPF is the amount of air bypassed in the process and is the inefficiency of the coil. So, lower the value of BPF then better is the performance and vice-versa.
46. The value of BPF for the heating and the cooling coil is different under the same temperature conditions.
a) True
b) False
Answer: b
Explanation: BPF for heating coil is, BPF = td3 – td2 / td3 – td1
BPF for cooling coil is, BPF = td2 – td3 / td1 – td3
As the numerator and denominator are reversed in the cooling coil than the heating coil. So, the value we get for either of the coils is the same
47. Which of the following denotes Humidification process on the psychrometric chart?
a) A horizontal line with an arrow towards right
b) Vertical line with arrow upwards
c) Horizontal line with an arrow towards right
d) Vertical line with arrow downwards
Answer: b
Explanation: Psychrometric chart has DBT on the x-axis and sp. Humidity on the y-axis. So, if a process is going up on the chart, then there is an increase in relative as well as specific humidity. So, the vertical line with an arrow upwards denotes humidification process.
48. Which of the following denotes dehumidification process on the psychrometric chart?
a) A horizontal line with an arrow towards the right
b) Vertical line with arrow upwards
c) A horizontal line with an arrow towards the right
d) Vertical line with arrow downwards
Answer: d
Explanation: Psychrometric chart has DBT on the x-axis and sp. Humidity on the y-axis. So, if a process is going down on the chart, then there is a decrease in relative as well as specific humidity. So, the vertical line with an arrow downwards denotes dehumidification process.
49. Which of the following is denoted by LH = (h2 – h1) = hfg (W2 – W1)?
a) Sensible cooling
b) Sensible heating
c) Humidification
d) Dehumidification
Answer: c
Explanation: Latent heat transfer i.e., LH = (h2 – h1) = hfg (W2 – W1) denotes Humidification. As in the humidification process, there is an increase in specific humidity, so W2 > W1 and also increase in enthalpy, h2 > h1.
50. Which of the following is denoted by LH = (h1 – h2) = hfg (W1 – W2)?
a) Sensible cooling
b) Sensible heating
c) Humidification
d) Dehumidification
Answer: d
Explanation: Latent heat transfer i.e., LH = (h1 – h2) = hfg (W1 – W2) denotes dehumidification. As in the dehumidification process, there is a decrease in specific humidity, so W1 > W2 and also decrease in enthalpy, h1 > h2.
51. What is the relation between DBT and WBT if the relative humidity is 100%?
a) DBT = WBT
b) DBT > WBT
c) DBT ≫ WBT
d) DBT < WBT
Answer: a
Explanation: When the dry bulb temperature is equal to the wet-bulb temperature, then the relative humidity tends to be 100%.
52. The minimum temperature to which moist air can be cooled under ideal conditions in a spray washer is ___________
a) DPT of inlet air
b) Water inlet temperature
c) WBT of inlet air
d) Water outlet temperature
Answer: c
Explanation: Wet-bulb temperature is the minimum temperature to which moist air can be cooled under ideal conditions in a spray washer. It is an integral part of the process.
53. Which of the following process is used in winter air conditioning?
a) Humidification
b) Dehumidification
c) Heating and Humidification
d) Cooling and Dehumidification
Answer: c
Explanation: In Winter, the weather is dry and cold, so the process of heating and humidification is done to get the desired comfort conditions.
54. Which of the following process is used in summer air conditioning?
a) Humidification
b) Dehumidification
c) Heating and Humidification
d) Cooling and Dehumidification
Answer: d
Explanation: In Summer, the weather is humid and hot, so the process cooling and dehumidification is done to get the desired comfort conditions.
55. What is the value of Latent heat transfer in the process of humidification having enthalpies as 20 and 40 kJ / kg of dry air respectively?
a) 60
b) 40
c) -20
d) 20
Explanation: Latent heat transfer i.e., LH = (h2 – h1) = hfg (W2 – W1) denotes Humidification. As in the humidification process, there is an increase in specific humidity, so W2 > W1 and also increase in enthalpy, h2 > h1. So, as per given data, h1 = 40 and h2 = 20 kJ / kg of dry air.
So, latent heat transfer = h2 – h1 = 40 – 20 = 20 kJ/ kg of dry air.
56. What is the value of Latent heat transfer in the process of dehumidification having enthalpies as 19.45 and 13.67 kJ/ kg of dry air respectively?
a) 5.78
b) -5.78
c) 33.12
d) -33.12
Answer: a
Explanation: Latent heat transfer i.e., LH = (h1 – h2) = hfg (W1 – W2) denotes dehumidification. As in the dehumidification process, there is a decrease in specific humidity, so W1 > W2 and also decrease in enthalpy, h1 > h2. So, as per given data, h1 = 19.45 and h2 = 13.67 kJ / kg of dry air.
So, latent heat transfer = h1 – h2 = 19.45 – 13.67 = 20 kJ / kg of dry air.
57. What is the value of optimum effective temperature in winter?
a) 17
b) 18
c) 19
d) 20
Answer: c
Explanation: From the table of design conditions for comfort, we get to know that in winter, the optimum effective temperature is 19°C.
58. What is the value of the optimum effective temperature in summer?
a) 23
b) 22
c) 21
d) 24
Answer: b
Explanation: From the table of summer design conditions for comfort, we get to know that in summer, the optimum effective temperature is 22°C.
59. Which of the following provides the relationship between the optimum indoor effective temperature and optimum outdoor effective temperature?
a) Clothing
b) Occupants
c) Duration of stay
d) Climatic and seasonal differences
Answer: d
Explanation: As season changes, then the relationship between the optimum indoor effective temperature and optimum outdoor effective temperature changes. This affects the optimum effective temperature for comfort.
60. A person with _________ clothing needs ___________ optimum temperature.
a) heavy, higher
b) heavy, lesser
c) light, higher
d) light, lesser
Answer: d
Explanation: Clothing is one of the factors affecting the effective temperature. So, to note, a person with light clothing needs lesser optimum temperature.
61. A person with heavy clothing needs ____________ optimum temperature as compared to a person with light clothing.
a) higher
b) lesser
c) zero
d) sam
Answer: a
Explanation: Clothing is one of the factors affecting the effective temperature. So to note, a person with heavy clothing needs a higher optimum temperature than a person with light clothing.
62. Men need a higher effective temperature than women.
a) True
b) False
Answer: b
Explanation: Women actually need higher effective temperature than men to be comfortable.
63. What is the value of an increase in effective temperature do women need than men?
a) about 1°C
b) about 0.25°C
c) about 0.5°C
d) about 2°C
Answer: c
Explanation: Women actually need higher effective temperature than men to be comfortable. This value differs approximately about 0.5⁰C.
64. Which of the following is true about effective temperature between young and older people?
a) Tyoung > Told
b) Tyoung < Told
c) Tyoung ≪ Told
d) Tyoung = Told
Answer: a
Explanation: As there is a difference between effective temperature as per gender then it also happens in the age sector. Young people need a higher effective temperature than older people.
65. What is the value of an increase in effective temperature do children need than older ones in case of maternity halls?
a) 1 to 2°C
b) 2 to 3°C
c) 3 to 4°C
d) 0 to 1°C
Answer: b
Explanation: As there is a difference between effective temperature as per gender then it also happens in the age sector. Young people need a higher effective temperature than older people, i.e., Tyoung > Told
Hence, maternity halls are maintained 2 to 3°C more than the effective temperature needed for adults.
66. People living in colder climate regions feel comfortable at lower effective temperature.
a) True
b) False
Answer: a
Explanation: Climatic and seasonal differences affect the effective temperature. People living in colder climate areas are comfortable with low effective temperatures than people living in warmer areas.
67. Which of the following is true about the optimum effective temperature for human comfort?
a) Same in winter and summer
b) Not dependent on season
c) Lower in winter than in summer
d) Higher in winter than in summer
Answer: c
Explanation: Optimum effective temperature is dependent on climatic and seasonal changes. So, for human comfort, the optimum effective temperature is lower in winter than in summer.
68. The heat production from a normal healthy man when asleep is about _________
a) 50 W
b) 40 W
c) 70 W
d) 60 W
Answer: d
Explanation: A normal healthy man when asleep produces heat nearly equal to 60 W. This might vary depending on various parameters.
69. When the heat stored in the body is ________ the human body feels comfortable.
a) zero
b) infinite
c) positive
d) negative
Answer: a
Explanation: The human body feels comfortable when the heat stored in the body is zero. This is the desired comfort condition.
70. Which of the following does not mainly a factor of dependency for the degree of warmth or cold?
a) Relative humidity
b) WBT
c) Air velocity
d) DBT
Answer: d
Explanation: The degree of warmth or cold felt by the human body depends mainly on dry bulb temperature, air velocity and relative humidity.
71. The effective temperature increases with a decrease in relative humidity at the same DBT.
a) True
b) False
Answer: b
Explanation: At the same value of dry bulb temperature, the effective temperature decreases with a decrease in relative humidity to achieve desired comfort conditions.
72. What is the inefficiency of the coil to attain the desired temperature called?
a) By-pass factor
b) Effectiveness
c) Efficiency
d) By-pressure factor
Answer: a
Explanation: The DBT of air leaving the apparatus should be equal to the coil temperature, but this is not possible due to the inefficiency of the coil. This type of phenomenon is called a by-pass factor.
73. What is the number of fins provided in a unit length called?
a) By-pass
b) Distance
c) Pitch
d) Addendum
Answer: c
Explanation: By-pass factor depends upon the number of fins provided. So, the fins provided in a unit length are called as Pitch of the coil fins.
74. Which of the following is true about the effect of velocity on the by-pass factor?
a) decreases with an increase in velocity of air passing through it
b) remains unchanged with an increase in velocity of air passing through it
c) may increase or decrease with an increase in velocity of air passing through it depending upon the condition of air entering
d) increases with an increase in velocity of air passing through it
Answer: d
Explanation: The change in the velocity affects the temperature of leaving the air. Moreover, the inefficiency increases due to an increase in velocity as the by-pass factor increases.
75. The by-pass factor of the coil ___________ with _________ in fin spacing.
a) increases, increase
b) decreases, decrease
c) increases, decrease
d) decreases, increase
Answer: b
Explanation: One of the factors which affect the by-pass factor is fin spacing. If the fin spacing is not much, then the temperature leaving the apparatus becomes close to the coil temperature. So, the decrease in fin spacing results in a decrease in the by-pass factor by improving efficiency.
76. The by-pass factor of the coil ___________ with _________ in number of rows of fins.
a) increases, increase
b) decreases, decrease
c) increases, decrease
d) decreases, increase
Answer: d
Explanation: One of the factors which affect the by-pass factor is a number of rows of fins. More the number of rows of fins, better is the heat transfer rate and decreasing the inefficiency, i.e., by-pass factor. So, the increase in the number of rows results in a decrease in the by-pass factor by improving efficiency.
77. Which of the following does not affect the by-pass factor?
a) Pitch of the coil fins
b) Velocity of air
c) Weight of apparatus
d) Fin spacing
Answer: c
Explanation: The weight of the apparatus has nothing to do with the by-pass factor. Pitch of the coil does affect the by-pass factor. And the velocity of air as well as fin spacing affects the by-pass factor. These factors can reduce the efficiency of the process.
78. Number of rows of the fins in the opposite direction to the flow affects BPF.
a) False
b) True
Answer: a
Explanation: More the number of rows increases the heat transfer rate and decrease the by-pass factor. But these rows should be in the direction of flow to get desired results.
79. Air being passed by not being in contact with the coil known to be measured as BPF.
a) True
b) False
Answer: a
Explanation: When air flows, some of it gets in contact with the coil, and some passes directly unaffected. This by-pass process is measured as a by-pass factor and is affected by a lot of parameters.
80. What is the formula for m1 / m2 in terms of enthalpies for adiabatic mixing of two streams?
a) h1 – h2 / h1 – h3
b) h3 – h2 / h1 – h3
c) h3 – h2 / h2 – h3
d) h3 – h2 / h1 – h2
Answer: b
Explanation: For energy balance, m1 h1 + m2 h2 = m3 h3
m3 = m1 + m2
So, m1 h1 + m2 h2 = (m1 + m2) h3
By solving we get,
m1 / m2 = h3 – h2 / h1 – h3.
81. What is the formula for m1 / m2 in terms of specific humidity for adiabatic mixing of two streams?
a) W2 – W1 / W1 – W3
b) W3 – W1 / W1 – W3
c) W3 – W2 / W1 – W3
d) W3 – W2 / W2 – W3
Answer: c
Explanation: For energy balance, m1 W1 + m2 W2 = m3 W3
m3 = m1 + m2
So, m1 W1 + m2 W2 = (m1 + m2) W3
By solving we get,
m1 / m2 = W3 – W2 / W1 – W3.
82. Which of the following is true for the adiabatic mixing of two streams?
a) m3 = m3 – m1
b) m2 = m1 + m3
c) m1 = m3 + m2
d) m3 = m1 – m2
Answer: a
Explanation: As two streams are mixed, then the result of it is the summation of mixed masses, and using the energy balance ratio of masses can be obtained. So, m3 = m1 + m2.
83. When the adiabatic mixing is carried out, the air having ______ enthalpies and ____________ specific humidities are mixed.
a) similar, similar
b) different, similar
c) similar, different
d) different, different
Answer: d
Explanation: The two air streams getting mixed adiabatically have different enthalpies and different specific humidities to get the final condition of air.
85. What is the value of m1 / m2 if h1 = 81 kJ/ kg of dry air, h2 = 46 kJ/ kg of dry air and h3 = 58 kJ/ kg of dry air?
a) 1
b) 0
c) 0.51
d) 0.52
Answer: d
Explanation: As we know, m1 / m2 = h3 – h2 / h1 – h3
= 58 – 46 / 81 – 58
= 0.5217 = 0.52.
86. What is the value of m1 / m2 if W1 = 0.0157 kg/ kg of dry air, W2 = 0.0084 kg / kg of dry air and W3 = 0.0103 kJ/ kg of dry air?
a) 0.31
b) 0.28
c) 0.35
d) 0.52
Answer: c
Explanation: As we know, m1 / m2 = W3 – W2 / W1 – W3
= 0.0103 – 0.0084 / 0.0157 – 0.0103
= 0.0019 / 0.0054 = 0.3518 = 0.35.
87. What is the value of one of the mass before mixing if the other mass is 1.98 kg, and the final is 4.22 kg?
a) 2.24
b) 1.98
c) 4.22
d) 6.20
Answer: a
Explanation As two streams are mixed, then the result of it is the summation of mixed masses, and using the energy balance ratio of masses can be obtained. So, m3 = m1 + m2
If, m1 = 1.98 and m3 = 4.22 then, m2 = 4.22 – 1.98 = 2.24 kg.
88. What is the value of final enthalpy if the enthalpies before mixing were 50 and 28 kJ / kg of dry air respectively and m2 / m1 = 2?
a) 38.67
b) 48.67
c) 40.05
d) 52
Answer: a
Explanation: For energy balance, m1 h1 + m2 h2 = m3 h3
m3 = m1 + m2
So, m1 h1 + m2 h2 = (m1 + m2) h3
m1 / m2 = h3 – h2 / h1 – h3
0.5 = h3 – 28 / 50 – h3
50 – h3 = 2h3 – 56
3h3 = 50 + 56 = 116
h3 = 38.67.
89. Even a lesser quantity of steam may result in the formation of fog.
a) True
b) False
Answer: a
Explanation: Fog also results when steam or very fine water spray is injected into the air in a greater quantity than required to do the saturation of the air. So, even less quantity of steam without mixing properly can result in fog.
90. Fog can be cleared by cooling.
a) True
b) False
Answer: b
Explanation: Fog can be cleared by heating or mixing it with unsaturated air or mechanically separating water droplets from the air.
91. Which of the following has the highest DBT in the chart of outside summer design conditions?
a) Agra
b) Ambala
c) Banaras
d) Bangalore
Answer: b
Explanation: From the table of outside summer design conditions, the highest DBT among the given options is at Ambala with 43.3°C, whereas the temperatures of Agra, Banaras, Bangalore are 41.5°C, 40.8°C and 32.9°C respectively.
92. Which of the following has the lowest DBT in the chart of outside summer design conditions?
a) Cochin
b) Darjeeling
c) Jaipur
d) Srinagar
Answer: b
Explanation: From the table of outside summer design conditions, the lowest DBT among the given options is at Darjeeling with 17.2°C, whereas the temperatures of Cochin, Jaipur, Srinagar are 35°C, 40.8°C and 25°C respectively.
93. Which of the following has the highest WBT in the chart of outside summer design conditions?
a) Ahmednagar
b) Baroda
c) Cuttack
d) Trivandrum
Answer: a
Explanation: From the table of outside summer design conditions, the highest WBT among the given options is at Ahmednagar with 31.1°C, whereas the temperatures of Baroda, Cuttack, Trivandrum are 29.1°C, 30.6°C and 29.4°C respectively.
94. Which of the following has the lowest WBT in the chart of outside summer design conditions?
a) Cochin
b) Srinagar
c) Mahabaleshwar
d) Darjeeling
Answer: d
Explanation: From the table of outside summer design conditions, the lowest WBT among the given options is at Darjeeling with 14.5°C, whereas the temperatures of Cochin, Mahabaleshwar, Srinagar are 27.8°C, 19.2°C and 18.4°C respectively.
95. What is the value of optimum effective temperature in winter?
a) 17
b) 18
c) 19
d) 20
Answer: c
Explanation: From the table of design conditions for comfort, we get to know that in winter, the optimum effective temperature is 19°C.
96. Which of the following has the highest relative humidity in the chart of outside summer design conditions?
a) Aligarh
b) Bhopal
c) Chennai
d) Trivandrum
>Answer: d
Explanation: From the table of outside summer design conditions, the highest RH among the given options is at Trivandrum with 90% whereas, Aligarh, Bhopal, Chennai have 35%, 24% and 47% respectively.
97. Which of the following has the lowest relative humidity in the chart of outside summer design conditions?
a) Jaipur
b) Chandigarh
c) Indore
d) Mysore
Answer: a
Explanation: From the table of outside summer design conditions, the lowest RH among the given options is at Jaipur with 18% whereas, Chandigarh, Indore, Mysore have 27%, 32% and 52% respectively.
98. What is the value of the optimum effective temperature in summer?
a) 23
b) 22
c) 21
d) 24
Answer: b
Explanation: From the table of summer design conditions for comfort, we get to know that in summer, the optimum effective temperature is 22°C.
99. Which of the following has the highest effective temperature in the chart of outside summer design conditions?
a) Ahmedabad
b) Allahabad
c) Banaras
d) Cuttack
Answer: a
Explanation: From the table of outside summer design conditions, the highest ET among the given options is at Ahmedabad with 32.5°C, whereas the temperatures of Allahabad, Banaras, Cuttack are 30.8°C, 31.9°C and 32°C respectively.
100. Which of the following has the lowest effective temperature in the chart of outside summer design conditions?
a) Srinagar
b) Shimla
c) Darjeeling
d) Surat
Answer: c
Explanation: From the table of outside summer design conditions, the lowest ET among the given options is at Darjeeling with 16.8°C, whereas the temperatures of Srinagar, Shimla, Surat are 22.2°C, 19.2°C and 30.5°C respectively.
101. Which of the following is the odd man out in terms of dry bulb temperature?
a) Ambala
b) Rajpur
c) Jodhpur
d) Pune
Answer: d
Explanation: Ambala, Rajpur and Jodhpur have a similar value of dry bulb temperature, which is 43.3°C, and Pune has 37.1°C. So, the odd man out of the given options is Pune.
102. Relative humidity at Agra is _____________ the relative humidity at Kanpur.
a) higher than
b) lower than
c) equal to
d) much higher than
Answer: c
Explanation: Relative humidity at Agra is equal to the relative humidity at Kanpur, having a value of 17%.
103. Which of the cities has the lowest WBT in the chart?
a) Surat
b) Shimla
c) Lucknow
d) Mumbai
Answer: b
Explanation: From the table of outside summer design conditions, the lowest WBT is at Shimla with 12.5°C, whereas the temperatures of Surat, Lucknow, Mumbai are 21.6°C, 28.3°C and 26.7°C respectively.
104. Effective temperature at Patna, Pune, Rajpur and Surat is similar.
a) True
b) False
Answer: a
Explanation: The value of Effective temperature at Patna, Pune, Rajpur and Surat is 30.5°C.
105. Relative humidity above 30% is not desired in summer comfort cooling.
a) True
b) False
Answer: b
Explanation: In summer comfort cooling, the air of the occupied space should not have relative humidity above 60%.
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