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Q8. With reference to the lubrication of refrigeration compressors:

a) State the advantage of using fully synthetic oils

b) Explain why oil may be carried over from the compressor

c) Describe a device which returns oil from the compressor discharge to the compressor sump

d) State the reasons why an accumulation of oil in the evaporator is undesirable.

1. Q5. a) With reference to a vapour compression refrigeration plant, explain why each of the following conditions are desirable;

(i) Superheating at the compressor suction

(ii) Undercooling at the condenser outlet

(b) Describe, with the air of a pressure-enthalpy diagram, how the evaporator cooling load is affected by the conditions stated in Q5 (a)

Q8.a) Explain with a sketch the operation of an automatic expansion valve as fitted in the direct expansion refrigeration plants. How is this valve adjusted?

b) Explain how critical temperature restricts plant operation and how these limitations can be overcome?

c) Explain how this system maintains the provision rooms at different temperatures?

Q7. With respect to the refrigeration system on board vessels, answer the following

a) Why are some TEVs fitted with an external equalizing connection?

b) What is the purpose of a back pressure valve. what will the effect if it leaks?

c)How does an electronic TEV function.

Q9. With reference to main refrigeration plants give reason for each of the following

operational irregularities and state how these are dealt with: -

(a) Rapid loss of lubricating oil from the crankcase of a “vee” block compressor; (4)

(b) Steady “fall off " in refrigeration effect over a comparatively short period of time; (4)

(c) Excessive “icing up" at compressor suction; (4)

(d) Short cycling. (4)

Q5. Describe the functional components of a reefer plant for the domestic refrigeration.
system and temperatures to be maintained in different cold rooms; (8)

i) describe the pressure switches; (2)

(ii) the tubular heat exchanger; (2)

(iii) the Oil separator and, (2)

(iv) the drier system. (2)

Q2. With reference to main refrigeration plant give reason for each of the following operational irregularities and state how these are dealt with:

a) Rapid loss of lubricating oil from the crankcase of a "vee" block compressor. (4)

b) steady "fall off" in refrigeration effect over a comparatively short period of time. (4)

c) Excessive "icing up" at compressor suction. (4)

d) Short cycling. (4)