Punjab University 2005 B.Tech REFRIGERATION AND AIR CONDITIONING - Question Paper

REFRIGERATION AND AIR CONDITIONING

Max Marks 60

Max Time three Hours

Note: part A is compulsory. Attempt any 4 ques. every carrying five marks from part B and any 2 every carrying 10 marks from part C.

part A (10 x two = 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 given in a compound vapour compression refrigeration system?
(f) State the applications of vortex tube.
(g) How are refrigerants classified?
(h) describe Relative humidity and Specific humidity.
(i) How are the fans classified?
(j) List the components of cooling load estimate

part B (4 x five = 20)

II An air refrigerator works ranging from pressure limits of one and four bar. The temperature of the air entering the compressor is 15 oC and entering the expansion cylinder is 30 oC.
The expansion follows the legal regulations PV1.25 = constant.
Take for air cp = one kJ/kg K and Cv = 0.7 kJ/kg K. obtain the following:
(a) COP of the refrigerating cycle.
(b) If the air in circulation through the system is 25 kg/ min, obtain 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 define 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. obtain the following:
(a) Heat removed from air
(b) R.H. of cooled air
(c) WBT of the cooled air.
Take air pressure = one bar.

VI explain briefly a split air- conditioner.

part C (2 x 10 = 20)

VII (a) What is sub cooling and super heating? discuss with the help of a diagram. Why is super heating considered to be good in certain cases?
(b) A refrigerating unit is working ranging from 40 oC and –10 oC. The load on the unit is five tons. Find:
(i) COP of the system
(ii) Power needed to run system.
presume 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 needed in the evaporator is –20 oC, then, obtain the change in COP of the system and the power needed.

VIII Draw a neat diagram of lithium bromide water absorption system and discuss its working. List the major field application of this system.

IX The subsequent 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 every
plus 10 fluorescent fixtures of 80 W every.
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.

Earning:   Approval pending.