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Q3. Explain the following briefly with reference to a domestic refrigeration system on board a ship. (16)

(a) Ingress of air into the freon system.

(b) Loss of refrigerant from a condenser.

(c) Water in the freon system.

(d) Icing of condenser external surface.

Q5) With regard to a reciprocating refrigerator compressor.

(a) Sketch the mechanical shaft seal showing its component parts and how it is lubricated (8)

(b) Describe the sealing arrangement stating the materials used for the component parts (4)

(c) State the effect on the environment of the release of refrigerants into the atmosphere (4)

Q8. (a) Explain 'short cycling' in the context of refrigeration and air conditioning systems onboard ship. State its causes and how it can be avoided. (6)
(b) State the symptoms of 'overcharging' and 'undercharging' in refrigeration system. What are its effects and state remedial measures (5)
(c) What are the visible indicators of oil in refrigeration system. What would be its effects? State remedial measures (5)

Q6. With Respect to Container Ship: -

A. Sketch a ship’s indirect refrigeration system arranged for cooling containers stowed in stacks in the hold;

B. Describe the refrigeration system sketched in (A);

C. State the advantages of the system described in (A) compared with containers with their own refrigeration self-contained units.

Q5. With respect to refrigeration gases used on-board vessels, answer the following:

A. Explain Ozone Depleting Potential (ODP) and Global warming potential (GWP) of conventional refrigerant gases.

B. Name the alternate refrigerant gases available and being used onboard.

C. Explain the steps you will take to ensure that release of refrigerant gases from the plant in minimized during normal operation and during maintenance activities.

Q3. Explain vapor compression refrigeration cycle on T-S and PH diagram and explain the purpose of EACH of the following:

(a) Expansion valve

(b) Room thermostat

(c) High pressure cut out.

(d) Equalizing line.

Q9. With respect to the refrigeration system on board vessels, answer the following
a) Why are some TEVs fitted with an external equalising 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.

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)