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MCQOPTIONS
This section includes 346 Mcqs, each offering curated multiple-choice questions to sharpen your GATE (Mechanical Engineering) knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
A room having dimensions of 5 m × 5 m × 3 m contains air at 25°C and 100 kPa at a relative humidity of 75%. The corresponding value of ps is 3.169 kPa. The partial pressure of dry air will be nearly |
| A. | 106 kPa |
| B. | 98 kPa |
| C. | 86 kPa |
| D. | 78 kPa |
| Answer» C. 86 kPa | |
| 2. |
For an air-conditioned space, RTH = 100 kW, RSHF = 0.75, volume flow rate of air is 100 m3/minute and room specific humidity is 0.01 kg/kg of dry air. The specific humidity of supply air in kg/kg of dry air is |
| A. | 0.01 |
| B. | 0.0075 |
| C. | 0.005 |
| D. | 0.0025 |
| Answer» D. 0.0025 | |
| 3. |
A thin layer of water in field is formed after a farmer has watered it. The ambient air conditions are: temperature 20 ° C and relative humidity 5%. An extract of steam tables is given below.Temperature (°C)-15-10-50.015101520Saturation pressure (kPa)0.100.260.400.610.871.231.712.34Neglecting the heat transfer between the water and the ground, the water temperature in the field after phase equilibrium is reached equals |
| A. | 10.3 °C |
| B. | -10.3 °C |
| C. | -14.5 °C |
| D. | 14.5 °C |
| Answer» D. 14.5 °C | |
| 4. |
In air-conditioning systems, air may be cooled and dehumidified by1. Spraying chilled water to air in the form of fine mist.2. Circulating chilled water or brine in a tube placed across the air flow3. Placing the evaporator coil across the air flow.Which of the above statements are correct? |
| A. | 1 and 2 only |
| B. | 1 and 3 only |
| C. | 2 and 3 only |
| D. | 1, 2 and 3 |
| Answer» E. | |
| 5. |
During the evaporation cooling process, wet bulb temperature: |
| A. | increases |
| B. | decreases |
| C. | remains constant |
| D. | unpredictable |
| Answer» D. unpredictable | |
| 6. |
Air (at atmospheric pressure) at a dry bulb temperature of 40°C and wet bulb temperature of 20°C is humidified in an air washer operating with continuous water recirculation. The wet bulb depression (i.e. the difference between the dry and wet bulb temperatures) at the exit is 25% of that at the inlet. The dry bulb temperature at the exit of the air washer is closest to |
| A. | 10°C |
| B. | 20°C |
| C. | 25°C |
| D. | 30°C |
| Answer» D. 30°C | |
| 7. |
During the chemical dehumidification process of air |
| A. | dry bulb temperature and specific humidity decreases |
| B. | dry bulb temperature increases and specific humidity decreases |
| C. | dry bulb temperature decreases and specific humidity increases |
| D. | dry bulb temperature and specific humidity increases |
| Answer» C. dry bulb temperature decreases and specific humidity increases | |
| 8. |
If a mass of moist air in an airtight vessel heated to a higher temperature, then |
| A. | Specific humidity of the air increases |
| B. | Specific humidity of the air decreases |
| C. | Relative humidity of the air increases |
| D. | Relative humidity of the air decreases |
| Answer» E. | |
| 9. |
If a certain mass of moist air in an air tight vessel is heated to a higher temperature, then |
| A. | Specific humidity of the air increases |
| B. | Specific humidity of the air decreases |
| C. | Relative humidity of the air increases |
| D. | Relative humidity of the air decreases |
| Answer» E. | |
| 10. |
Dew point temperature is the temperature at which condensation begins when the air is cooled at constant |
| A. | Volume |
| B. | Entropy |
| C. | Pressure |
| D. | Enthalpy |
| Answer» D. Enthalpy | |
| 11. |
If ma = mass of dry air and mw = mass of water vapour in the air-water vapour mixture, then humidity ratio is given by- |
| A. | mw / ma |
| B. | ma / mw |
| C. | (mw + ma) / mw |
| D. | ma / (ma + mw) |
| Answer» B. ma / mw | |
| 12. |
In order to have a low by-pass factor of cooling coil, the fin spacing and the number of tubes rows should be respectively |
| A. | wide apart and high |
| B. | wide apart and low |
| C. | close and low |
| D. | close and high |
| Answer» E. | |
| 13. |
In an air-conditioning plant, air enters the cooling coil at 27°C. The coil surface temperature is -5°C. If the bypass factor of the unit is 0.4, the air will leave the coil at: |
| A. | 5.6°C |
| B. | 7.8°C |
| C. | 9.2°C |
| D. | 11.2°C |
| Answer» C. 9.2°C | |
| 14. |
A large cylindrical vessel was sealed in summer. What is likely to happen to it in winter? |
| A. | nothing |
| B. | become lighter |
| C. | buckle end collapse |
| D. | seal getting loosened |
| Answer» D. seal getting loosened | |
| 15. |
On a psychometric chart, what does a vertical line represent? |
| A. | Adiabatic saturation |
| B. | Sensible cooling |
| C. | Dehumidification |
| D. | Humidification |
| Answer» D. Humidification | |
| 16. |
During an air-conditioning of a plant, the room sensible heat load is 40 kW and room latent heat load is 10 kW, ventilation air is 25% of supply air. At full load, the room sensible heat factor will be |
| A. | 0.9 |
| B. | 0.8 |
| C. | 0.7 |
| D. | 0.6 |
| Answer» C. 0.7 | |
| 17. |
For 'Infiltration' and ‘Ventilation' terms in air-conditioning, which is a false statement? |
| A. | Both are putting cooling / heating load on plant |
| B. | Ventilation is deliberately provided, however infiltration occurs in an unwanted way |
| C. | Ventilation can be made zero |
| D. | Infiltration air quantity reduces ventilation air quantity |
| Answer» D. Infiltration air quantity reduces ventilation air quantity | |
| 18. |
A measure of feeling warmth or coolness by the human body in response to the air temperature, moisture content and air motion is called |
| A. | Dry bulb temperature |
| B. | Effective temperature |
| C. | Wet bulb temperature |
| D. | Dew point temperature |
| Answer» C. Wet bulb temperature | |
| 19. |
Dew point temperature is always an indication of ________. |
| A. | Dryness of air |
| B. | Latent heat |
| C. | Moisture content of the air |
| D. | Coolness of air |
| Answer» D. Coolness of air | |
| 20. |
During the adiabatic cooling of moist air which of the following remains constant? |
| A. | DBT |
| B. | Specific humidity |
| C. | Relative humidity |
| D. | WBT |
| Answer» E. | |
| 21. |
Air is normally dehumidified by _____. |
| A. | Injecting water |
| B. | Passing steam |
| C. | Heating |
| D. | Cooling |
| Answer» E. | |
| 22. |
For winter air conditioning, the relative humidity should not be more than: |
| A. | 60% |
| B. | 75% |
| C. | 40% |
| D. | 90% |
| Answer» D. 90% | |
| 23. |
As warm air cools, it's relative humidity |
| A. | Increases |
| B. | Decreases |
| C. | Remains same |
| D. | Depends on wet bulb temperature |
| Answer» B. Decreases | |
| 24. |
If the by – pass factor is 0.30, what will be the efficiency of the cooling coil or the contact factor? |
| A. | 0.3 |
| B. | 0.15 |
| C. | 0.66 |
| D. | 0.7 |
| Answer» E. | |
| 25. |
Consider the following statements for sensible heating. In this process:1) Wet bulb temperature increases2) Relative humidity decreases3) Vapour pressure remains constantWhich of the above statements are correct? |
| A. | 1, 2 and 3 |
| B. | 1 and 2 only |
| C. | 1 and 3 only |
| D. | 2 and 3 only |
| Answer» B. 1 and 2 only | |
| 26. |
On psychometric chart, wet bulb temperature lines are ________. |
| A. | Horizontal |
| B. | Vertical |
| C. | Straight inclined sloping downward to the right |
| D. | Curved |
| Answer» D. Curved | |
| 27. |
For summer air-conditioning, the relative humidity should not be less than |
| A. | 40% |
| B. | 60% |
| C. | 75% |
| D. | 90% |
| Answer» C. 75% | |
| 28. |
A desert cooler having a cooling efficiency of 70% reduces the temperature of atmospheric air from 37°C to 30°C. The wet bulb temperature of the air is |
| A. | 24°C |
| B. | 25°C |
| C. | 26°C |
| D. | 27°C |
| Answer» E. | |
| 29. |
If the atmospheric conditions are 20°C, 1.013 bar and specific humidity of 0.0095 kg/kg of dry air, the partial pressure of vapour will be nearly |
| A. | 0.076 bar |
| B. | 0.056 bar |
| C. | 0.036 bar |
| D. | 0.016 bar |
| Answer» E. | |
| 30. |
Consider the following statements for the appropriate context:1. The Relative Humidity of air remains constant during sensible heating or cooling2. The Dew Point Temperature of air remains constant during sensible heating or cooling3. The total enthalpy of air remains constant during adiabatic cooling4. It is necessary to cool the air below its Dew Point Temperature for dehumidifyingWhich of the above statements are correct? |
| A. | 1, 2 and 3 |
| B. | 1, 2 and 4 |
| C. | 3 and 4 only |
| D. | 2, 3 and 4 |
| Answer» E. | |
| 31. |
A moist air sample has dry bulb temperature of 30ºC and specific humidity of 11.5g water vapour per kg dry air. Assume molecular weight of air as 28.93. If the saturation vapour pressure of water at 30ºC is 4.24 kPa and the total pressure is 90kPa, then the relative humidity (in %) of air sample is |
| A. | 50.5 |
| B. | 38.5 |
| C. | 56.5 |
| D. | 68.5 |
| Answer» C. 56.5 | |
| 32. |
Air at 25°C DBT and 80% RH is passed over a cooling coil whose surface temperature is 10°C which is below DPT of the air. If the air temperature coming out of the cooling coil is 15°C, then the bypass factor of the cooling coil is: |
| A. | 0.56 |
| B. | 0.33 |
| C. | 0.76 |
| D. | 0.87 |
| Answer» C. 0.76 | |
| 33. |
During the sensible cooling process _____. |
| A. | Specific humidity remains constant |
| B. | Specific humidity increases |
| C. | Specific humidity decreases |
| D. | Specific humidity is unpredictable |
| Answer» B. Specific humidity increases | |
| 34. |
If a thermometer is used to measure temperature in moving steam in a nozzle, it measures __________ temperature. |
| A. | dynamic |
| B. | static |
| C. | stagnation |
| D. | wet-bulb |
| Answer» D. wet-bulb | |
| 35. |
Moist air at 35°C and 100% relative humidity is entering a psychometric device and leaving at 25°C and 100% relative humidity. The name of the device is |
| A. | Humidifier |
| B. | Dehumidifier |
| C. | Sensible heater |
| D. | Sensible cooler |
| Answer» C. Sensible heater | |
| 36. |
If the volume of most air with 50% RH is isothermally reduced to half its original volume then relative humidity of moist air becomes |
| A. | 25% |
| B. | 60% |
| C. | 70% |
| D. | 100% |
| Answer» E. | |
| 37. |
Ambient pressure, temperature and relative humidity at a location are 101 kPa, 300 K, and 60% respectively. The saturation pressure of water at 300 K is 3.6 kPa. The specific humidity of ambient air is _______ g/kg of dry air. |
| A. | 35.1 |
| B. | 21.9 |
| C. | 13.6 |
| D. | 21.4 |
| Answer» D. 21.4 | |
| 38. |
In sensible cooling of moist air, its physical properties vary as follows:1. The wet bulb temperature decreases2. The dew point: temperature remains constant3. The relative humidity increasesWhich of the above statements are correct? |
| A. | 1, 2 and 3 |
| B. | 1 and 2 only |
| C. | 1 and 3 only |
| D. | 2 and 3 only |
| Answer» B. 1 and 2 only | |
| 39. |
In a psychometric chart, what does a vertical downward line represent |
| A. | Sensible cooling process |
| B. | Adiabatic saturation process |
| C. | Humidification process |
| D. | Dehumidification process |
| Answer» E. | |
| 40. |
_________ is defined as the amount of dry saturated steam generated from feed water at 100°C at normal atmospheric pressure. |
| A. | Equivalent evaporation |
| B. | Degree of superheat |
| C. | Boiler thermal efficiency |
| D. | Dryness fraction |
| Answer» B. Degree of superheat | |
| 41. |
At 100% RH, the three characteristics DBT (Dry Bulb Temperature), WBT (Wet Bulb Temperature) & DPT (Dew Point Temperature) are |
| A. | Different |
| B. | Equal |
| C. | Any two are equal |
| D. | None of the above |
| Answer» C. Any two are equal | |
| 42. |
If air at dry bulb temperature of 35°C and dew point temperature of 20°C passes through an air washer in which water is sprayed at 25°C, then the process would be |
| A. | sensible cooling |
| B. | cooling and dehumidification |
| C. | cooling and humidification |
| D. | cooling and constant dew point temperature |
| Answer» D. cooling and constant dew point temperature | |
| 43. |
For air with a relative humidity of 80% _____. |
| A. | Dry bulb temperature is less than the wet bulb temperature |
| B. | Dew point temperature is less than wet bulb temperature |
| C. | Dew point and wet bulb temperatures are equal |
| D. | Dry bulb and dew point temperatures are equal |
| Answer» C. Dew point and wet bulb temperatures are equal | |
| 44. |
Dew point temperature is the temperature at which condensation begins when the air is cooled at constant |
| A. | volume |
| B. | entropy |
| C. | pressure |
| D. | enthalpy |
| E. | temperature |
| Answer» D. enthalpy | |
| 45. |
In operation theater air conditioning application, recirculation air percentage will be |
| A. | 20% |
| B. | 50% |
| C. | 0 % |
| D. | 80% |
| Answer» D. 80% | |
| 46. |
If sensible and latent heating transfer in an air conditioning process is 2.5kW and 1.5 kW respectively. Then sensible heat factor (SHF) will be |
| A. | 0.5 |
| B. | 1 |
| C. | 0.625 |
| D. | Zero |
| Answer» D. Zero | |
| 47. |
In a Psychometric chart, which of the following statement/s is/are correct? |
| A. | It is used to determine properties of refrigerants |
| B. | It cannot determine WBT and DBT |
| C. | It is seldom used for air conditioning design |
| D. | It provides plots for moist air conditioning |
| Answer» E. | |
| 48. |
During air conditioning in winter: |
| A. | The air is cooled and dehumidified |
| B. | The air is cooled and humidified. |
| C. | The air is heated and humidified. |
| D. | The air is heated and dehumidified. |
| Answer» D. The air is heated and dehumidified. | |
| 49. |
1 kg of moist air of RH 70% at 21°C is cooled at a constant pressure of 1 bar to 5°C. The vapor pressure at 21°C and 5°C are 0.025 bar and 0.0087 bar. The percentage of water vapor that condenses into water, at 5°C is |
| A. | 66% |
| B. | 85% |
| C. | 51% |
| D. | 17% |
| Answer» B. 85% | |
| 50. |
Moist air at a pressure of 100 kPa is compressed to 500 kPa and then cooled to 35°C in an aftercooler. The air at the entry to the aftercooler is unsaturated and becomes just saturated at the exit of the aftercooler. The saturation pressure of water at 35°C is 5.628 kPa. The partial pressure of water vapour (in kPa) in the moist air entering the compressor is closest to |
| A. | 0.57 |
| B. | 1.13 |
| C. | 2.26 |
| D. | 4.52 |
| Answer» C. 2.26 | |