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DIPLOMA IN MECHANICAL ENGINEERING/ ADVANCED LEVEL CERTIFICATE COURSE IN MECHANICAL ENGINEERING (DMEVI/ ACMEVI) 02272 Term-End Examination December, 2011
BME-032 : REFRIGERATION AND AIR-CONDITIONING Maximum Marks : 70
Time : 2 hours Note :
Answer five questions. Question 1 is Compulsory.
(a) Answer the following questions. (i)
What does air conditioning 2 .comprise ?
Sketch a rotary compressor and mark 2 its parts.
Sketch a vapour absorption 3 refrigeration cycle, indicating components.
(b) Choose the correct answer from four possible choices in following questions. 1 x 7 (i) Which component of refrigeration system controls the flow of refrigerant ?
(ii) The power of a refrigeration system in kW is : (A) 3.56/ COP (B) 3.56 COP (C) COP/ 3.56 (D) none of these (iii) Sub cooling in a vapour compression refrigeration system will : (A) increase the power but reduce the size of compressor (B) reduce the power and size of compressor (C) reduce the power but increase the flow of refrigerant (D) increase the power but reduce the flow of refrigerant. (iv) A refrigerant should have : (A) low latent heat (B) high liquid sp. heat (C) high latent heat (D) high sp. volume in vapour state (v) For achieving cooling and humidification in air washer, the surface temperature of water spray : (A) must be less than dew point temp. (B) must be greater than DBT (C) must be greater than DPT but less than WBT (D) must be greater than DPT but less than DBT.
(vi) For comfort air conditioning in a house the conditions to be satisfied are : (A) Effective temp 20°C and relative humidity of 45 (B) Effective temp, 21.7°C and -DBT = 24 to 26°C (C) DBT = 25°C and RH = 45 (D) Effective temp = 21.7°C and RH= 65 (vii) What are the indication of a spoilt food ? (A) The surface of meat turns black and brittle. (B) The butter and cheese develop slimy coating. (C) Fruits develop sour and bitter taste. (D) Eggs lose weight and give very strong bad smell.
2. (a) What is a refrigerant ? On what principle 7 does it work ? Describe organic and inorganic refrigerants. (b) A refrigerator operates between — 45°C and 7 0°C. R12 is used as refrigerant. Its properties are described in the following table. Sat. temp
°C kJ/kg kJ/kg kJ/kg/K kJ/kg/K kJ/kg/K —45 —4.4 167.84 0.0190 0.7360 0 36.15 188.69 0.1420 0.7008 0.62
Draw the simple saturated cycle on T — S diagram and calculate COP and power regd.
BME 032 -
3. (a) On T —S plane show a refrigeration cycle 7 comprising isentropic compression of wet vapour (i) to saturation, (ii) condensation of saturated vapour into saturated liquid, (iii) throttling of high pressure saturated liquid into very wet vapour and (iv)
evaporation of wet vapour into Dry Vapour. Name the components in which these processes occur.
(b) In the above simple cycle if the vapour is 7 super heated before compression and liquid sub cools before throttling how will the performance be affected in terms of COP ?
4. An ice plant using water at 10°C produces 480 x 103kg of ice in 24 hours. The plant follows Carnot cycle and works between temperatures of — 5°C and higher temperature of 23°C. Calculate the capacity of plant in TR and power required. 5. (a) State and explain Dalton's law of partial pressure and Gibb's theorem . How are these used in the practice of air conditioning ? (b) Define : (i) Specific humidity (ii) Dew point temperature (iii) Relative humidity BME-032
6. (a) On a psychometric chart show following : (i)
relative humidity lines
constant specific val. lines
constant wet bulb temp. lines
constant enthalpy lines.
(b) What is adiabatic saturation ?
7. (a) What is a cold storage ? At what 4 temperatures you will store apple, banana and butter ? (b)
What is a freezer ? What are the products that are frozen ? Describe types of freezer.
Describe three means of transport 5 refrigeration.