Kurukshetra University 2009-6th Sem B.Tech Mechanical Engineering Refrigeration and Air Conditioning (ester) - Question Paper
BT-6/M09
Refrigeration and Air Conditioning
PAPER - ME-302E
BT-6/M09 * 9780
REFRIGERATION AND AIR-CONDITIONING PaperME-302-E
Time: Three Hours] [Maximum Marks: 100
Note :Attempt FIVE questions, at least TWO from each Section. Use of Refrigerant tables and charts are allowed. Assume the suitable value of any missing data.
1. (a) Prove that the COP of Air-refrigeration cycle is given by
V y -1
. P2P3
where r = - pressure ratio.
(b) The atmospheric air at a pressure of 1 bar and temperature -5C is drawn in the cylinder of the compressor of a Bell-Coleman refrigerating machine. It is compressed isentropically to a pressure of 5 bar in the cooler. The compressed air is cooled to 15C, pressure remains the same. It is then expanded to a pressure of 1 bar in an expansion cylinder from where it is passed to the cold chamber. Find:
(i) Work done per kg of air
(ii) COP of the plant for air.
Assume the law of expansion pv12 = contt. and law of compression pv14 = contt and Cp for air = 1 kJ/kg-K.
2. (a) With the help of neat-sketch and P-H diagram, explain the
working of a simple vapour compression refrigeration cycle. Derive the expression for the COP and power required.
9780 (OL)
1
(Contd.)
(b) A vapour compression refrigerator uses R-12 as refrigerant and the liquid evaporates in the evaporator at -15C, the temperature of this refrigerant at the delivery from the compressor is 15C, when the vapour is condensed at 10C. Find the COP if
(i) There is no undercooling
(ii) The liquid is cooled by 5C before expansion by throttling.
With the help of neat sketch and P-H diagram, explain the working of two-stage Cascade System.
3. (a) (b)
4. (a) (b)
Give the nomenclature of the following refrigerants:
Water H20, Ammonia NH3, Carbon dioxide C02, Tri-chloro-monofluoromethane CC13 F, Dichloro-difluoromethane CC12F2, Methyl Chloride CHjCl, Ethyl Chloride C2H5 Cl.
With the help of neat sketch explain the working of Lithium bromide-water absorption refrigeration system.
Derive an expression for the maximum COP of vapour absorption refrigeration system.
SECTIONB Prove the following formulas:
5. (a)
Pw
W = 0-622 "pTTp-,
W
h = C t + w ((h ) + 2-3 t,)
pm vv tg'dp d7
where C = C + w C .
pm pa pv
At a certain locality, the DBT of air is 30C and RH is 40%. Determine the specific humidity, dew point and WBT of air. If this air is cooled in an air-washer using recirculated spray water and having a humidifying efficiency of 0-9, what are DBT and dew point temperature of the air leaving the air washer ?
(b)
6. (a) With the help of neat sketch, explain the working of an Air-washer. Draw the all processes on the psychrometric diagram,
(b) Explain the following:
Heat pumps, evaporative condensers, transport air-conditioning.
2
(Contd.)
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7. (a) With the help of neat sketch and P-H diagram, explain the working
of hot and dry summer Air-conditioning.
\
(b) An air-conditioning plant is designed for a small office for winter air-conditioning, outdoor conditions 10C DBT and 8C WBT. Required indoor conditions 20C DBT and 60% RH. Amount of air-circulated 0-3 m3/min/person, Seating capacity of the office 50 persons. The required condition is achieved first by heating and then by adiabatic humidifying. Find:
(i) Heating capacity of heating coil in kW and its surface temperature if the bypass factor of the coil is 0-32
(ii) Capacity of humidifier.
8. Write short notes on any THREE of the following:
(a) Comfort-Air-conditioning
(b) Adiabatic mixing of two air-streams
(c) Estimation of cooling and heating load
(d) Cooling Towers.
9780(OL)
H.
3
2000
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Attachment: |
| Earning: Approval pending. |
