Refrigeration and AC Mechanic MCQ Quiz - Objective Question with Answer for Refrigeration and AC Mechanic - Download Free PDF

The correct answer is Measuring high temperatures.

Key Points

Pyrometer:

• Pyrometer is a device for measuring relatively high temperatures, such as are encountered in furnaces.
• Most pyrometers work by measuring radiation from the body whose temperature is to be measured.
• Radiation devices have the advantage of not having to touch the material being measured.
• Radiation Pyrometers are used to measure the temperature of red hot metals up to 3000°C.

Concept:

• A ton of refrigeration (TR), also called a refrigeration ton (RT), is a unit of power used, especially to describe the heat-extraction capacity of refrigeration and air conditioning equipment.
• It is defined as the rate of heat transfer that results in the melting of 1 ton of pure ice at 0°C in 24 hours.
• The unit conversions is:
  • 1 TR = 210 kJ/min = 3.5 kW 
  • 1 kCal = 4.18 kJ
  • ∴ 1 kJ = 0.239 kCal
  • ∴ 210 kJ = 50.19 kCal
  • ∴ 1 TR = 50.19 kCal/min = 3011.52 kCal/hr

Explanation:

Various reasons and effects of multi-split AC are following.

Explanation:

The naming of refrigerant (Saturated hydrocarbon):

• The saturated refrigerant consists of carbon, hydrogen, fluorine, and chlorine and is represented as:

C_mH_nF_pCl_q 

Where, m, n, p, and q are the number of carbon, hydrogen, fluorine, and chlorine atoms.

• The refrigerant HFC 134a is represented as C₂H₂F₄, whereas the refrigerant CFC 12 is defined as CF₂Cl₂.
• The chlorine element present in the refrigerant CFC 12 dissociates in the presence of sunlight when the refrigerant leaks out from the system. 
• The chlorine reacts with the ozone molecules in the ozone layer situated in the stratosphere and starts damaging the ozone layer.
• The refrigerant HFC 134a does not consist of ant chlorine element due to which the ozone depletion potential (ODP) of HFC 134a is zero, making HFC 134a a possible substitute for CFC 12.
• The ozone layer filters the harmful ultraviolet radiations coming from the sun. Therefore the depletion of the ozone layer is undesirable. For this reason, the refrigerants containing chlorine elements are now replaced. 

Thus, option (4) is the correct answer.

Additional Information
Ozone Depletion Potential (ODP):

• Ozone Depletion Potential (ODP) indicates how much the chemical compounds can degrade the ozone layer.

Global Warming Potential  (GWP):

• Global Warming Potential indicates how much the chemical compounds contribute to global warming.

Explanation:

The characteristics of a good refrigerant should have the following properties

1. Low boiling point
2. High latent heat value
3. Low freezing point
4. Non-flammable and non-toxic
5. High di-electric strength
6. Not affected by moisture
7. Non-corrosive to metals
8. Mixes well with compressor oil

The correct answer is Measuring high temperatures.

Key Points

Pyrometer:

• Pyrometer is a device for measuring relatively high temperatures, such as are encountered in furnaces.
• Most pyrometers work by measuring radiation from the body whose temperature is to be measured.
• Radiation devices have the advantage of not having to touch the material being measured.
• Radiation Pyrometers are used to measure the temperature of red hot metals up to 3000°C.

Sensible heating: It is the process of increasing the Dry bulb temperature at constant specific humidity.

Effects of sensible heating:

i) Dry bulb temperature increases

ii) Sp. Humidity or humidity ratio remains constant

iii) Dew point temperature is constant

iv) Relative humidity decreases

v) Enthalpy increases

vi) Specific Volume Increases

vii) Wet bulb temperature increases

The difference between a rectifier diode and a Zener diode are:

• Compared to normal rectifier diodes, Zener diodes are heavily doped
• Unlike ordinary diodes which do not work in breakdown region, Zener didoes work only in the breakdown region
• General rectifier didoes are used in forward biased condition, whereas Zener diodes are always used in reverse bias condition
• The reverse breakdown voltage of Zener didoes is very much less (3 to 18 V) compared to rectifier diodes (minimum 50 V)

Explanation:

The turbine is a prime mover that converts the energy of high pressure, high-temperature fluid supplied by the boiler into shaft work with the low-temperature steam exhausted to a condenser. 

The turbine trip is the shutdown of a power generation turbine due to unexpected events like turbine over-speeding, low vacuum in the condenser, etc.

1. The power pant remains hot even after the turbine trip. 
2. The system needs to be gradually cooled.
3. The extremely hot steam generated during the turbine trip needs to be condensed.
4. Hence, the cooling water supply to the condenser should be stopped after 15-30 minutes for the overall cold system.
5. The damaging effect of the hot steam on other components of the power plant is also reduced. 
6. Cooled also helps in safe and easy repair operations.

Condenser:- It is a device in a steam power plant in which steam condenses and heat released by steam is absorbed by water.

The condensation of steam in a close vessel produces a partial vacuum due to a great reduction in the volume of low-pressure steam.

• An electrical tong tester is also known as clamp meter
• It is used to measure current in a circuit in amperes
• It can measure large AC currents up to 1000 amperes

The correct answer is Will decrease.

• If the humidity in the atmosphere is high, the rate of evaporation is low because the air is filled with water vapor and is not able to take up more humidity. Thus, the evaporation process slows down.

Key Points

• Evaporation is a form of vaporization that usually occurs at the surface of a liquid and involves the transition of liquid particles to the gaseous phase.
  • Therefore, this process is said to involve a change in the state of the fluid.
  • The surrounding gas should not saturate with the substance to be evaporated.
  • The rate of evaporation is greater at higher temperatures because as the temperature rises, the amount of energy required for evaporation decreases.
  • Water loss by evaporation in sunny, warm weather is greater than in cloudy and cool weather.
  • The moisture content of the air, or water vapor content, also has an effect on evaporation.
  • The lower the relative humidity, the drier the air, and the higher the rate of evaporation.
  • The more moist the air, the closer the air is to saturation, and the less evaporation can take place.
  • Also, warm air can have a higher concentration of water vapor, so you might think that warm air has more room to store more water vapor than cool air.

Watt hour meter or energy meter is an instrument which measures amount of electrical energy used. It measures the instantaneous voltage and current and calculate its product to find power.

A voltmeter is used to measure the potential difference. Therefore, it must be connected in parallel to the circuit of which the potential difference is to be measured. A voltmeter must have high resistance otherwise it will take heavy current.