Download GTU (Gujarat Technological University Ahmedabad) B.Tech/BE (Bachelor of Technology/ Bachelor of Engineering) 2020 Summer 6th Sem 2161908 Refrigeration And Air Conditioning Previous Question Paper
Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER? VI EXAMINATION ? SUMMER 2020
Subject Code: 2161908 Date:04/11/2020
Subject Name: REFRIGERATION AND AIR CONDITIONING
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Use of refrigeration and air-conditioning charts and tables is permitted.
MARKS
Q.1 (a) Establish the relationship between COP and KW per ton of
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refrigeration.
(b) A sling psychomotor reads 40?C DBT and 28?C WBT, Calculate
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the specific humidity, relative humidity, vapor density, dew point
temperature, and enthalpy using refrigeration and air
conditioning tables.
(c) An auditorium is to be air conditioned for a seating capacity of
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2000 persons for the following outdoor and indoor comfort
conditions.
Outdoor temperature 34?C, 70% RH Indoor temperature
26 ?C DBT, 50% RH, Sensible heat load=480000 K J/ hr Latent
hear load =160000 KJ/ hr. The rise in temperature of the air inside
the auditorium is limited to 7 ?C. About 70% of the room air
going to the exhaust is recirculated and mixed with 30% fresh
air. The fan is located before all the cooling and heating
equipment's and mixed air is passed through the fan. The motor
capacity is connected to the fan is 50 K W, assume 80% off the
motor efficiency is given to the air passing through the fan. The
required air conditioning is achieved first by cooling and
dehumidification and then heating the air .The dew point
temperature of cooling and humidifier coil is 12?C. Determine
the following
I) Quantity of air supplied to outdoor conditions in m3/hr per
person.
II) The capacity of the refrigeration system TOR.
III)Capacity of heating coil in K W.
IV)The bypass factor of the cooling coil.
Q.2 (a) Discuss the advantages of dense air refrigeration system over and
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open air refrigeration system
(b) A rectangular duct of 50 cm X 40 cm size carries 75 m3/min of
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air having density of 1.16 kg/m3 determine the equivalent
diameter of the circular duct if
1) the quantity of air carried in both the cases is same
2) the velocity of air in both the cases is same
Assume f= 0.01 for sheet metal, calculate the pressure loss per
100 m length of the duct.
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(c) The following data is collected regarding a space to be air-
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conditioned, room sensible heat load 42 KW, room latent heat
load 12.5 KW, outdoor condition 36 ?C DBT and 26?C WBT,
room design condition 24?C DBT and 50% RH. Ventilation of
outdoor air is 40 m3/min, assume bypass factor 0.15 determine 1)
room apparatus dew point 2) temperature of air leaving the
conditioner 3) total quantity of air supply, 4) Temperature of air
entering the coil 5) Coil dew point temperature
OR
(c) A 20 tons refrigeration load on an evaporator is taken by an
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ammonia absorption refrigeration machine. The cooling is carried
out at -30?C. The refrigerant coming out of the condenser is at
20?C and it leaves the evaporator at saturated condition.
Assume the following data
Pressure in the generator 11 bar, Temperature of strong Aqua
70?C, Temperature of weak Aqua 100 ?C, heat of one kg of
anhydrous ammonia leaving the generator =1930 K J/ kg,
concentration of weak Aqua =0.28, Concentration of strong
Aqua= 0.34 mean specific heat of aqua solution =4.7KJ / Kg?C,
Take the heat of Aqua per kg at 0?C = 4.18 kJ/ kg. heat of
absorption is given by
Q
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a= 806 - 588 Xw - 5960 Xw . Neglecting the heat loss to the
surrounding from the generator, calculate quantity of steam
required per hour for heating the strong aqua solution in the
generator if the steam is supplied at 5 bar and 0.9 dry and
condensate comes out at 130 ?C. Neglect the pressure loss in the
system.
Q.3 (a) Explain the working of refrigeration cycle with two stage
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compression. What are the advantages over single compression
system?
(b) Enumerate desirable properties of refrigerants.
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(c) With neat sketch explain working of lithium bromide water
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absorption refrigeration system also enlist major fields of
application of this refrigeration system
OR
Q.3 (a) Enumerate features of Compound compression refrigeration
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system with intercooling.
(b) Explain the following psychometric terms: Daltons Law of
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Partial Pressure, Specific Humidity, Relative humidity, Dew
point temperature
(c) Derive an expression for minimum chilled water temperature
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which can be used with sensible cooling coil in terms of dry bulb
temperature and dew point temperature of the air stream and its
relevant thermal resistance.
Q.4 (a) How selection of sound absorbing material on ducting system is
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done.
(b) Explain the significance of following psychometric processes:
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i)Cooling and dehumidification,
ii)Cooling and humidification
iii) Chemical dehumidification
iv) Adiabatic saturation
(c) What are the important considerations in the design of air
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conditioning systems?
OR
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Q.4 (a) With neat sketch explain construction and working of capillary
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tube.
(b) Explain the meaning of the terms: throw, drop, spread, and
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induction in air distribution system.
(c) Where centrifugal compressor are preferred over reciprocating
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compressor in refrigeration systems. Describe the advantages and
disadvantages of centrifugal over reciprocating compressors.
Q.5 (a) Explain the following terms related to cooling tower: range,
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approach, heat load.
(b) Describe interaction between fan and duct and the concept of
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balance in system.
(c) State the important requirements of an air conditioning duct and
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the general rules to be followed in the design of ducts
OR
Q.5 (a) Compare central air conditioning system with district air
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conditioning system
(b) State and explain the importance of fan laws, and use the
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performance of fans under off-design conditions
(c) Draw neat diagram of constant volume induction system and list
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out its merits over other systems
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This post was last modified on 04 March 2021