Module name: Refrigeration and Air conditioning Effetive Date 1Augt 2016 Tasks:

Question

Module name: Refrigeration and Air conditioning

Effetive Date 1Augt 2016 Tasks: Section A Answer ALL questions. 1. Purposes of each component: (a) What is the function of the evaporator in a refrigeration or air-conditioning system? (b) What does the compressor do in the refrigeration system? (30 marks) 2. Theories: (a) A refrigerator manufactured by one manufacturing cornpany works between 400 C and -5o C. The manufacturer claims that coefficient of performance of that refrigerator is 7.0. Do you agree with his statement? Justify your answer (b) What is the relationship between pressure and the boiling point of liquids? (30 marks) Section B Answer ONE question. 3. Concepts: (a) What is the relation between refrigeration and air conditioning? (b) How does a heat pump resemble a refrigeration system? (e) Describe the desirable characteristics for the working fluid used in a power plant why water suits the criteria. (40 marks) Cause and effect: (a) What effect does a slight amount of liquid refrigerant have on a compressor over a 4. long period of time? (b) What happens to the refrigerant and refrigerant heat in the condenser? (e) What condition does the automatic expansion valve maintain in the evaporator? (40 marks) S. Problems and precautions: (a) Name two problems a refrigeration system may have if the condensing unit is esposed to a low-ambient condition when not equipped with a low-ambieat head pressure control valve. (b) What are the important issues to be considered in the design of refrigeration systems? (c) Discuss how the system could be improved to reduce the electricity input nceded to provide the heat output for the operating conditions described (40 marko)

Explanation / Answer

(1)

(a)

Evaporator is the part of refrigerator or AC where heat is absorbed by refrigerant

Evaporator carries low temperature liquid refrigerant inside cooling coil surrounded by fins, where liquid refrigerant changes liquid phase to vapour phase , this results in absorption of heat to maintain low temperature.

(1)

(b)

The main function of compressor in refrigerator or AC , is to increase the pressure and corresponding saturation temperature of the vapour refrigerant to high enough so that it can condensed into liquid phase by rejecting heat to the condenser.

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