MCQ on Refrigerator & AC 1-50

1. Freon group of refrigerants are
(A) Inflammable
(B) Toxic
(C) Non-inflammable and toxic
(D) Nontoxic and non-inflammable✔

2. The boiling point of ammonia is
(A) -10.5°C
(B) -30°C
(C) -33.3°C✔
(D) -77.7°C

3. For obtaining high COP, the pressure range of compressor should be
(A) High
(B) Low✔
(C) Optimum
(D) Any value

4. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be
(A) 1.33
(B) 2.33✔
(C) 3.33
(D) 4.33

5. Cooling water is required for following equipment in ammonia absorption plant
(A) Condenser
(B) Evaporator
(C) Absorber
(D) Condenser, absorber and separator (rectifier)✔

6. The freezing point of sulphur dioxide is
(A) -56.6°C
(B) -75.2°C✔
(C) -77.7°C
(D) -135.8°C

7. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of
(A) 1: 1
(B) 1: 9✔
(C) 9: 1
(D) 1: 3

8. In a refrigeration system, the expansion device is connected between the
(A) Compressor and condenser
(B) Condenser and receiver
(C) Receiver and evaporator✔
(D) Evaporator and compressor

9. The vapour compression refrigerator employs the following cycle
(A) Rankine
(B) Carnot
(C) Reversed Rankine
(D) Reversed Carnot✔

10. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about
(A) 1
(B) 1.25✔
(C) 2.15
(D) 5.12

11. Rating of a domestic refrigerator is of the order of
(A) 0.1 ton✔
(B) 5 tons
(C) 10 tons
(D) 40 tons

12. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the
(A) Heat dissipated to the surroundings
(B) Heat stored in the human body
(C) Sum of (A) and (B)✔
(D) Difference of (A) and (B)

13. The bank of tubes at the back of domestic refrigerator is
(A) Condenser tubes✔
(B) Evaporator tubes
(C) Refrigerant cooling tubes
(D) Capillary tubes

14. In a lithium bromide absorption refrigeration system
(A) Lithium bromide is used as a refrigerant and water as an absorbent
(B) Water is used as a refrigerant and lithium bromide as an absorbent✔
(C) Ammonia is used as a refrigerant and lithium bromide as an absorbent
(D) None of the above

15. The condition of refrigerant after passing through the condenser in a vapour compression system is
(A) Saturated liquid✔
(B) Wet vapour
(C) Dry saturated vapour
(D) Superheated vapour

16. In a refrigeration cycle, the flow of refrigerant is controlled by
(A) Compressor
(B) Condenser
(C) Evaporator
(D) Expansion valve✔

17. The colour of the flame of halide torch, in case of leakage of Freon refrigerant, will change to
(A) Bright green✔
(B) Yellow
(C) Red
(D) Orange

18. For air conditioning the operation theater in a hospital, the percentage of outside air in the air supplied is
(A) Zero
(B) 20
(C) 50
(D) 100✔

19. In vapour compression cycle using NH₃ as refrigerant, initial charge is filled at
(A) Suction of compressor
(B) Delivery of compressor
(C) High pressure side close to receiver✔
(D) Low pressure side near receiver

20. The temperature of air recorded by a thermometer, when it is not affected by the moisture present in the air, is called
(A) Wet bulb temperature
(B) Dry bulb temperature✔
(C) Dew point temperature
(D) None of these

21. Absorption system normally uses the following refrigerant
(A) Freon-11
(B) Freon-22
(C) CO2
(D) Ammonia✔

22. Which of the following statement is correct?
(A) In vapour absorption refrigerator, the compression of refrigerant is avoided.
(B) Sub-cooling can be achieved by circulating more quantity of cooling water through the condenser.
(C) In vapour compression refrigeration, the vapour is drawn in the compressor cylinder during its suction stroke and is compressed adiabatically during the compression stroke.
(D) All of the above✔

23. Allowable pressure on high pressure side or ammonia absorption system is of the order of
(A) Atmospheric pressure
(B) Slightly above atmospheric pressure
(C) 24 bars
(D) 56 bars✔

24. The C.O.P. of a Carnot refrigerator in winter will be _________ as compared to C.O.P. in summer.
(A) Same
(B) Lower
(C) Higher✔
(D) None of these

25. Chaperon equation is a relation between
(A) Temperature, pressure and enthalpy
(B) Specific volume and enthalpy
(C) Temperature and enthalpy
(D) Temperature, pressure, specific volume and enthalpy✔

26. During humidification process, __________ increases.
(A) Wet bulb temperature
(B) Relative humidity✔
(C) Dry bulb temperature
(D) Specific humidity

27. Where does the lowest temperature occur in a vapour compression cycle?
(A) Condenser
(B) Evaporator✔
(C) Compressor
(D) Expansion valve

28. The ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure, is called
(A) Humidity ratio
(B) Relative humidity✔
(C) Absolute humidity
(D) Degree of saturation

29. Under cooling in a refrigeration cycle
(A) Increases C.O.P✔
(B) Decreases C.O.P
(C) C.O.P remains unaltered
(D) Other factors decide C.O.P

30. In a domestic vapour compression refrigerator, the refrigerant commonly used is
(A) CO₂
(B) Ammonia
(C) R-12✔
(D) All of these

31. The COP of a vapour compression plant in comparison to vapour absorption plant is
(A) More✔
(B) Less
(C) Same
(D) More/less depending on size of plant

32. The fluids used in Electrolux refrigerator are
(A) Water and hydrogen
(B) Ammonia and hydrogen
(C) Ammonia, water and hydrogen✔
(D) None of these

33. Domestic refrigerator working on vapour compression cycle uses the following type of expansion device
(A) Electrically operated throttling valve
(B) Manually operated valve
(C) Thermostatic valve
(D) Capillary tube✔

34. The condition of refrigerant after passing through the expansion or throttle valve, in a vapour compression system is
(A) High pressure saturated liquid
(B) Wet vapour
(C) Very wet vapour✔
(D) Dry vapour

35. An important characteristic of absorption system of refrigeration is
(A) Noisy operation
(B) Quiet operation✔
(C) Cooling below 0°C
(D) Very little power consumption

36. The centrifugal compressors are generally used for refrigerants that require
(A) Small displacements and low condensing pressures
(B) Large displacements and high condensing pressures
(C) Small displacements and high condensing pressures
(D) Large displacements and low condensing pressures✔

37. Rick up the incorrect statement
(A) Lithium bromide used in vapour absorption cycle is non volatile
(B) Lithium bromide plant can't operate below 0°C
(C) A separator is used in lithium bromide plant to remove the unwanted water vapour by condensing✔
(D) Concentration of solution coming out of lithium bromide generator is more in comparison to that entering the generator

38. During dehumidification process, the relative humidity
(A) Remains constant
(B) Increases
(C) Decreases✔
(D) None of these

39. The refrigerant widely used in domestic refrigerators is
(A) Ammonia
(B) Carbon dioxide
(C) Sulphur dioxide
(D) R-12✔

40. The moisture in a refrigerant is removed by
(A) Evaporator
(B) Safety relief valve
(C) Dehumidifier
(D) Driers✔

41. During sensible cooling of air ________ decreases.
(A) Wet bulb temperature
(B) Relative humidity
(C) Dry bulb temperature✔
(D) Specific humidity

42. At lower temperatures and pressures, the latent heat of vaporisation of a refrigerant
(A) Decreases
(B) Increases✔
(C) Remain same
(D) Depends on other factors

43. The wet bulb depression is zero when relative humidity is
(A) Zero
(B) 0.5
(C) 0.75
(D) 1.0✔

44. The C.O.P of a refrigeration cycle with increase in evaporator temperature, keeping condenser temperature constant, will
(A) Increase✔
(B) Decrease
(C) Remain unaffected
(D) May increase or decrease depending on the type of refrigerant used

45. During humidification process, dry bulb temperature
(A) Remains constant✔
(B) Increases
(C) Decreases
(D) None of these

46. The vapour pressure of refrigerant should be
(A) Lower than atmospheric pressure
(B) Higher than atmospheric pressure✔
(C) Equal to atmospheric pressure
(D) Could be anything

47. Which of the following statement is wrong?
(A) The performance of the vapour compression refrigerator varies considerably with both vaporising and condensing temperatures.
(B) In vapour compression cycle, the useful part of the heat transfer is at the condenser.
(C) In ammonia-hydrogen (Electrolux) refrigerator, no compressor, pump or fan is required.
(D) The effect of under-cooling the liquid refrigerant is to decrease the coefficient of performance.✔

48. In a vapour compression system, the condition of refrigerant before passing through the condenser is
(A) Saturated liquid
(B) Wet vapour
(C) Dry saturated vapour
(D) Superheated vapour✔

49. For proper refrigeration in a cabinet, if the temperature and vapour pressure difference between cabinet and atmosphere is high, then
(A) Bigger cabinet should be used
(B) Smaller cabinet should be used
(C) Perfectly tight vapour seal should be used✔
(D) Refrigerant with lower evaporation temperature should be used

50. During sensible heating of air _________ decreases.
(A) Wet bulb temperature
(B) Relative humidity✔
(C) Dry bulb temperature
(D) Specific humidity

Application of magnetic materials

☆  Electrical motor and generator ☆

》 As the electric motor Electromegtets  in the spinning stator to turn . There is an electrically slippring  on the stator that directs the power to a different magnet section of the stator to achieve rotation Quick

☆Magnetic Storage ☆

》 Magnetic storage ifs magnetic recording are terms from engineering referrinv to the storage of data on a magnetized medium . Magnetic storage uses different patterns of magnetizing in a magnetizable material to store dtat and is a form of non volatile . The information access using one and more real wire head

☆Magnetic Bearing☆

》A magnetic bearing is a bearing which support a load using magnetic leviation . Magnetic bearing support moving machinery without physical contact for axample they can leviate a rotating shaft and permit leviate motion with very low friction load no mechanical wear .

☆Magnetic Resonance Image MRI☆

》A magnetic resonance algorithm is a type of magnetic resonance imaging scan that uses a magnetic field and pulses of ratio wave energy to provide picture of blood vessels inside the body . In many case MRI can provide information that can not be obtained from a x-rays ultrasound and computed tomography scan.

☆Eddy Current ☆

》 Eddy current brake like a conventional friction brake , is responsible for slowing object, as a train or a roller coaster . However unlike electromechanical brakes, which apply mechanical pressures on two separate objects eddy current brake slow an object by creating eddy current through electromagnetic induction which create resistance and turn it  either heat or electricity

Types of magnetism

☆ Diamagnetism
☆ Paramagnetsim
☆ Feromagnetsim
☆ Antiferromagnetsim

■ Diamagnetsim

• Diamagnetsim is a fundamental property of all matter, although it is usually very week. It is due to non co-operative behaviour of obtaining electrons when exposed to an applied magnetic field . Diamagnetic substance are compund of atoms which have no net magnetic moment . however when exposed to a filed .If we plot M vs H we see

■ Paramagnetism

• This class of material some of the atoms are ions in the material have a net magnetic moment due to unpaired electron in partially filled orbit . Once of the most important atoms with unpaired electrons in iron . However the individual magnetic moment do not interact magnetically, and like diamagnetism , the magnetization is zero when the field is removed . In the presence of the field there is now a partial alignment of the atomic magnetic moment in the direction of the filed resulting in a net positive magnetism and positive susceptibility

■ Ferromagnetism

When tou think magnetic materials, you probably think iron nickel or magnetic . Unlike paramagnetic materials, the atomic.moment is that materials exhibit very strong interactions. These interaction produce by electronic exchange force and result in a parallel or anti parallel alignment of atomic moment . Exchange fore are very large equivalent to a filed on the order of 1000Tesla or approximately a 100million times the strength of the earth field.

■ Antiferromagnetism
• The material moment of atoms or molecules usually to the spin of electron align in a regular pattern with neighbouring spins pointing in opposite direction . This is like ferromagnetism ,a manifestation of ordered magnetsim . Generally antiferromagnetic order may exist at sufficiently low temperature ., vanishing at and above a certain temp.The tempreature above the Neel temperature the material is typically paramagnetic.

☆Applications

•  Eletro motor ange generator
•  Magnetic storage
• Magnetic bearing
• Magnetic separator
• Medical appliance
• Magnetic Resonance Imaging MRI
• For security purpose
•Eddy current brake

Magnetic material and its properties

Magneticmaterial and its properties

》It is a common characteristics of materials . Magnetic properties of a material involve concept based on the magtnetic dipole moment . Soke of the material have the ability to create internal dipole moment . for this reason this kind of material present cpecial type of properties.

• Attracting other magnetic material.
• Inducing pole in this material.
• The polarity of teo pole are opposite
• When magnetizing occuring then some parameter of material is changed ( current I, Magnetic flux)

☆Magnetic moment :

• A vector quantity associated with the magnetic properties of electric current loops or, more generally magnets . It is equal to the amount of current flowing through the loop multiplied by the area encomlossed  by the loop, and its direction is established by the Right hand rule for rotations

☆Magnetic field or intensity ☆

• A field of force associated with changing electric fields, as when electric charge are in motion . Magnetic field exert defective force on moving electric charges.
• Most magnet have magnetic field as a result of the spinning motion of the electrons orbiting the atoms of which they are composed.
electromagnet create such field from electric current moving through coils

   ☆Magnetic Susceptibility ☆

• In electromagnetisim the magnetic susceptibility Xm is demensionless proportionally constant that indicate degree of magnetization of a material in responsee to an applied magnetic field

M=xH

                 ☆Hystersis☆

• In addition to the curie temperature and saturation magnetization ferromagnetism can retain a memory of an applied field once it is removed
 this behaviour is called Hystersis and a plot of the variation of magnetization with magnetic field is called hystersis loop

              ☆Curie Temperature☆

• Even though electronic exchange  force  in ferromagnets are very large , thermal energy eventually overcome the exchange and produce a rendomizing effect . This occur at a particular temperature called curie temperature Tc . Below the curie temperature the ferromagnet is ordered and above it, disordered. The saturation magnetization goes to zero at the curie temp. A typical plot of magnetization vs temp. for magnetic is shown below