ME 304 6th Sem
May 2005
REFRIGERATION AND AIR CONDITIONING
Max Marks 60
Max Time 3 Hours
Note: Section A is compulsory. Attempt any four questions each carrying 5 marks from section B and any two each carrying 10 marks from section C.
Section A (10 x 2 = 20)
1
(a) Enumerate important refrigeration applications
(b) State merits of an air refrigeration system.
(c) Show the vapour compression cycle as a T-S diagram when the vapour is dry and saturated at the end of compression.
(d) What is the importance of hydrogen in Electolux refrigerator?
(e) What is the function of flash intercooler provided in a compound vapour compression refrigeration system?
(f) State the applications of vortex tube.
(g) How are refrigerants classified?
(h) Define Relative humidity and Specific humidity.
(i) How are the fans classified?
(j) List the components of cooling load estimate
Section B (4 x 5 = 20)
II An air refrigerator works between pressure limits of 1 and 4 bar. The temperature of the air entering the compressor is 15 oC and entering the expansion cylinder is 30 oC.
The expansion follows the law PV1.25 = constant.
Take for air cp = 1 kJ/kg K and Cv = 0.7 kJ/kg K. Find the following:
(a) COP of the refrigerating cycle.
(b) If the air in circulation through the system is 25 kg/ min, find the refrigeration capacity of the system.
III State the effect and causes of moisture in refrigerant of refrigeration system. How can it be removed from the system?
IV Describe briefly the method used for liquefaction of hydrogen.
V 20 m3 of air per minute at 30 oC and 60% RH is cooled to 22 oC DBT maintaining specific humidity constant. Find the following:
(a) Heat removed from air
(b) R.H. of cooled air
(c) WBT of the cooled air.
Take air pressure = 1 bar.
VI Discuss briefly a split air- conditioner.
Section C (2 x 10 = 20)
VII (a) What is sub cooling and super heating? Explain with the help of a diagram. Why is super heating considered to be good in certain cases?
(b) A refrigerating unit is working between 40 oC and –10 oC. The load on the unit is 5 tons. Find:
(i) COP of the system
(ii) Power required to run system.
Assume that the refrigerant is dry and saturated vapour leaving the evaporator and compression is isentropic. The refrigerant used is MHz.
If the temperature of the refrigerant required in the evaporator is –20 oC, then, find the change in COP of the system and the power required.
VIII Draw a neat diagram of lithium bromide water absorption system and explain its working. List the major field application of this system.
IX The following are the design data for an air conditioning system prepared for a restaurant:
Outdoor condition = 34o DBT and 28 oDBT
Indoor condition = 24o DBT and 50 RH
Solar heat gain through walls roof and floor = 4.4 kW
Occupants = 25
Sensible heat gain per person = 85 W
Latent heat gain per person =105 W
Internal lighting load = 15 lamps of 100 watts capacity each
plus 10 fluorescent fixtures of 80 W each.
Sensible heat gain from other sources = 11.6 kW
Infiltration air = 14 m3 /min
Coil by ass factor = 0.15
If the return and outdoor are adiabatically mixed in the ratio 3:2 (by bass) and then passed through the conditioner: determine:
(a) dry bulb temperature and wet bulb temperature of supply air
(b) apparatus, dew point
(c) capacity of the air –conditioning plant.
May 2005
REFRIGERATION AND AIR CONDITIONING
Max Marks 60
Max Time 3 Hours
Note: Section A is compulsory. Attempt any four questions each carrying 5 marks from section B and any two each carrying 10 marks from section C.
Section A (10 x 2 = 20)
1
(a) Enumerate important refrigeration applications
(b) State merits of an air refrigeration system.
(c) Show the vapour compression cycle as a T-S diagram when the vapour is dry and saturated at the end of compression.
(d) What is the importance of hydrogen in Electolux refrigerator?
(e) What is the function of flash intercooler provided in a compound vapour compression refrigeration system?
(f) State the applications of vortex tube.
(g) How are refrigerants classified?
(h) Define Relative humidity and Specific humidity.
(i) How are the fans classified?
(j) List the components of cooling load estimate
Section B (4 x 5 = 20)
II An air refrigerator works between pressure limits of 1 and 4 bar. The temperature of the air entering the compressor is 15 oC and entering the expansion cylinder is 30 oC.
The expansion follows the law PV1.25 = constant.
Take for air cp = 1 kJ/kg K and Cv = 0.7 kJ/kg K. Find the following:
(a) COP of the refrigerating cycle.
(b) If the air in circulation through the system is 25 kg/ min, find the refrigeration capacity of the system.
III State the effect and causes of moisture in refrigerant of refrigeration system. How can it be removed from the system?
IV Describe briefly the method used for liquefaction of hydrogen.
V 20 m3 of air per minute at 30 oC and 60% RH is cooled to 22 oC DBT maintaining specific humidity constant. Find the following:
(a) Heat removed from air
(b) R.H. of cooled air
(c) WBT of the cooled air.
Take air pressure = 1 bar.
VI Discuss briefly a split air- conditioner.
Section C (2 x 10 = 20)
VII (a) What is sub cooling and super heating? Explain with the help of a diagram. Why is super heating considered to be good in certain cases?
(b) A refrigerating unit is working between 40 oC and –10 oC. The load on the unit is 5 tons. Find:
(i) COP of the system
(ii) Power required to run system.
Assume that the refrigerant is dry and saturated vapour leaving the evaporator and compression is isentropic. The refrigerant used is MHz.
If the temperature of the refrigerant required in the evaporator is –20 oC, then, find the change in COP of the system and the power required.
VIII Draw a neat diagram of lithium bromide water absorption system and explain its working. List the major field application of this system.
IX The following are the design data for an air conditioning system prepared for a restaurant:
Outdoor condition = 34o DBT and 28 oDBT
Indoor condition = 24o DBT and 50 RH
Solar heat gain through walls roof and floor = 4.4 kW
Occupants = 25
Sensible heat gain per person = 85 W
Latent heat gain per person =105 W
Internal lighting load = 15 lamps of 100 watts capacity each
plus 10 fluorescent fixtures of 80 W each.
Sensible heat gain from other sources = 11.6 kW
Infiltration air = 14 m3 /min
Coil by ass factor = 0.15
If the return and outdoor are adiabatically mixed in the ratio 3:2 (by bass) and then passed through the conditioner: determine:
(a) dry bulb temperature and wet bulb temperature of supply air
(b) apparatus, dew point
(c) capacity of the air –conditioning plant.