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COMPETITIVE EXAMINATIONS QUESTIONS 915

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51. Hydrogen is essential in an Electrolux refrigeration system, because
    (a) it acts as a catalyst in the evaporator
    (b) the reaction between hydrogen and ammonia is endothermic in evaporator and exothermic
    in absorber
    (c) the cooled hydrogen leaving the heat exchanger cools the refrigerant entering the
    evaporator
    (d) it helps in maintaining a low partial pressure for the evaporating ammonia.


52. In an ideal refrigeration (reversed Carnot) cycle, the condenser and evaporator tempera-
    tures are 27°C and – 13°C respectively. The COP of this cycle would be
    (a) 6.5 (b) 7.5
    (c) 10.5 (d) 15.0.


53. A single-stage vapour compression refrigeration system cannot be used to produce ultra low
    temperatures because
    (a) refrigerants for ultra-low temperatures are not available
    (b) lubricants for ultra-low temperatures are not available
    (c) volumetric efficiency will decrease considerably
    (d) heat leakage into the system will be excessive.


54. Vapour absorption refrigeration system works using the
    (a) ability of a substance to get easily condensed or evaporated
    (b) ability of a vapour to get compressed or expanded
    (c) affinity of a substance for another substance
    (d) absorptivity of a substance.


55. Which one of the following statements regarding ammonia absorption system is correct?
    The solubility of ammonia in water is
    (a) a function of the temperature and pressure of the solution
    (b) a function of the pressure of the solution irrespective of the temperature
    (c) a function of the temperature of the solution alone
    (d) independent of the temperature and pressure of the solution.


56. Consider the following statements :
    In thermoelectric refrigeration, the coefficient of performance is a function of
    
    
    1. electrical conductivity of materials.
    
    
    2. Peltier coefficient.
    
    
    3. Seebeck coefficient.
    
    
    4. temperature at cold and hot junctions.
    
    
    5. thermal conductivity of materials.
       Of these statements :
       (a) 1, 3, 4 and 5 are correct (b) 1, 2, 3 and 5 are correct
       (c) 1, 2, 4 and 5 are correct (d) 2, 3, 4 and 5 are correct.
    
    
    
    


57. Air cooling is used for freon compressors whereas water jacketing is adopted for cooling
    ammonia compressors. This is because
    (a) latent heat of ammonia is higher than that of a freon
    (b) thermal conductivity of water is higher than that of air
    (c) specific heat of water is higher than that of air
    (d) of the larger superheat horn of ammonia compression cycle.