Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2018 Winter 6th Sem New 2161406 Food Refrigeration And Air Conditioning Previous Question Paper
1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VI (NEW) EXAMINATION ? WINTER 2018
Subject Code:2161406 Date:30/11/2018
Subject Name:Food Refrigeration & Air - Conditioning
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1 (a) Answer the following: 03
(i) How is leakage of halocarbons detected?
(ii) How do CFC?s deplete the ozone layer of stratosphere?
(i)
(iii) Give safety criteria for selection of refrigerants.
(b) Answer the following: 04
(i) Work out the R-designation of C2H6.
(ii) What are azeotropes? Give examples.
(iii) Two metric tons of water at 0
o
C is converted to ice at 0
o
C in 12 hours.
Calculate the refrigeration capacity in TR. [Cpw = 4.2 kJ/kgK]
(iv) What is ?Green House Effect??
(c) A cold storage of 10 TR capacity based on simple VCR system of is operating on the
following conditions:
Evaporating temperature = - 10
o
C, Condensing temperature = 36
o
C
Compressor discharge temperature = 40
o
C
Avg. Specific heat of superheated vapours = 1.12 kJ/kgK
COP of the system = 4.0
Calculate the following:
i. Mass flow rate of the refrigerant in kg/s.
ii. Compressor power requirement in kW.
iii. Quality of refrigerant entering the evaporator.
iv. Heat rejected at Condenser in kW
v. Carnot COP of the system.
vi. Refrigeration efficiency in %
vii. If ?vol= 90%, calculate actual piston displacement in m
3
.
t
(
o
C)
hg
kJ/kg
hf
kJ/kg
vg
m
3
/kg
?f
kg/ m
3
CPv
kJ/Kk
g
- 10 382 183 0.11 1330 0.84
36 412 250 0.023 1160 1.12
40 420 260 0.019 1140 1.15
07
Q.2 (a) A heat pump based on simple VCRS of 200 kW heating capacity working between
evaporating and condensing temperatures of ? 10
o
C and 30
o
C respectively has COP
of 4.5. If the enthalpy of saturated vapours entering the compressor is 400 kJ/kg and
the enthalpy of liquid refrigerant entering the expansion valve is 250 kJ/kg, calculate
(i) Compressor power in kW
(ii) Heat rejection ratio (HRR)
(iii) Refrigeration efficiency
03
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1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VI (NEW) EXAMINATION ? WINTER 2018
Subject Code:2161406 Date:30/11/2018
Subject Name:Food Refrigeration & Air - Conditioning
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1 (a) Answer the following: 03
(i) How is leakage of halocarbons detected?
(ii) How do CFC?s deplete the ozone layer of stratosphere?
(i)
(iii) Give safety criteria for selection of refrigerants.
(b) Answer the following: 04
(i) Work out the R-designation of C2H6.
(ii) What are azeotropes? Give examples.
(iii) Two metric tons of water at 0
o
C is converted to ice at 0
o
C in 12 hours.
Calculate the refrigeration capacity in TR. [Cpw = 4.2 kJ/kgK]
(iv) What is ?Green House Effect??
(c) A cold storage of 10 TR capacity based on simple VCR system of is operating on the
following conditions:
Evaporating temperature = - 10
o
C, Condensing temperature = 36
o
C
Compressor discharge temperature = 40
o
C
Avg. Specific heat of superheated vapours = 1.12 kJ/kgK
COP of the system = 4.0
Calculate the following:
i. Mass flow rate of the refrigerant in kg/s.
ii. Compressor power requirement in kW.
iii. Quality of refrigerant entering the evaporator.
iv. Heat rejected at Condenser in kW
v. Carnot COP of the system.
vi. Refrigeration efficiency in %
vii. If ?vol= 90%, calculate actual piston displacement in m
3
.
t
(
o
C)
hg
kJ/kg
hf
kJ/kg
vg
m
3
/kg
?f
kg/ m
3
CPv
kJ/Kk
g
- 10 382 183 0.11 1330 0.84
36 412 250 0.023 1160 1.12
40 420 260 0.019 1140 1.15
07
Q.2 (a) A heat pump based on simple VCRS of 200 kW heating capacity working between
evaporating and condensing temperatures of ? 10
o
C and 30
o
C respectively has COP
of 4.5. If the enthalpy of saturated vapours entering the compressor is 400 kJ/kg and
the enthalpy of liquid refrigerant entering the expansion valve is 250 kJ/kg, calculate
(i) Compressor power in kW
(ii) Heat rejection ratio (HRR)
(iii) Refrigeration efficiency
03
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2
(b) In a vapour absorption type refrigeration system, heating, cooling and refrigeration
takes place at temperatures of 100?C, 20?C and -10?C respectively.
(i) Find the theoretical COP of the system.
(ii) If the heating temperature is increased to 180?C and the refrigeration temperature
is decreased to -30?C, find the percent change in the COP.
04
(c) Explain the operation of simple VCRS with the help of P-h & T-s diagrams. Explain
the effect of the following on the performance of vapour compression cycle:
(i) Liquid sub-cooling
(ii) Compressor volumetric efficiency
(iii) Reduction in suction temperature.
07
OR
(c) Explain the functions of different components of a simple vapour compression
refrigeration system with the help of a neat flow diagram. Also draw T-s diagram for
the vapour compression cycle indicating various state points. Why is it desirable to
slightly superheat the vapours before it enters the compressor? If the condensed
refrigerant liquid exiting the condenser is slightly sub-cooled, how will it affect the
volumetric efficiency and COP of the system?
07
Q.3 (a) Define cascade refrigeration system. For a 2-stage cascade refrigeration system, the
COP of low and high cascade sides are 1.5 and 4.5 respectively. Calculate the COP of
the system.
03
(b) In an absorption type refrigerator heat is supplied to generator by condensing saturated
steam at 2 bar. Calculate the maximum COP possible of the system if the temperature
to be maintained inside the refrigerator is ? 5
o
C. The atmospheric temperature is 32
o
C.
If the refrigeration load is 5 TR and the actual COP is 90% of maximum COP,
calculate the mass of steam required per hour. Assume that only latent heat of
condensation of steam is used for heating purpose. Given: Saturation temperature of
steam at 2 bar = 120
o
C; hfg = 2230 kJ/kg
04
(c) Explain the construction and working of simple VAR system based on LiBr ?Water. 07
OR
Q.3 (a) Explain the operation and applications of of a 2- stage cascade refrigeration system
with a p-h diagram.
03
(b) ?An ideal vapour absorption refrigeration system may be considered as a heat-operated
refrigerating machine combining a heat engine and a mechanical refrigerator working
together to produce the desired refrigeration effect?. Justify the statement with help of
schematic diagram and mathematical relations.
04
(c) Draw a neat diagram of NH3?Water based practical VARS. Explain the function of
various components of this cycle and derive an expression for maximum COP.
07
Q.4 (a) Define ?Draft?, ?Blow? and ?Throw? as related to air flow with the help of a neat
diagram.
03
(b) Answer the following:
i. Briefly describe types of supply air outlets in air conditioning.
ii. State important considerations while choosing a fan.
04
(c) Classify condensers and give the criteria for their selection. A water-cooled condenser
is sized to reject 50 kW heat at a condensing temperature of 40?C when the maximum
outdoor temperature is 36?C. What will be the approximate condensing temperature
07
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1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VI (NEW) EXAMINATION ? WINTER 2018
Subject Code:2161406 Date:30/11/2018
Subject Name:Food Refrigeration & Air - Conditioning
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1 (a) Answer the following: 03
(i) How is leakage of halocarbons detected?
(ii) How do CFC?s deplete the ozone layer of stratosphere?
(i)
(iii) Give safety criteria for selection of refrigerants.
(b) Answer the following: 04
(i) Work out the R-designation of C2H6.
(ii) What are azeotropes? Give examples.
(iii) Two metric tons of water at 0
o
C is converted to ice at 0
o
C in 12 hours.
Calculate the refrigeration capacity in TR. [Cpw = 4.2 kJ/kgK]
(iv) What is ?Green House Effect??
(c) A cold storage of 10 TR capacity based on simple VCR system of is operating on the
following conditions:
Evaporating temperature = - 10
o
C, Condensing temperature = 36
o
C
Compressor discharge temperature = 40
o
C
Avg. Specific heat of superheated vapours = 1.12 kJ/kgK
COP of the system = 4.0
Calculate the following:
i. Mass flow rate of the refrigerant in kg/s.
ii. Compressor power requirement in kW.
iii. Quality of refrigerant entering the evaporator.
iv. Heat rejected at Condenser in kW
v. Carnot COP of the system.
vi. Refrigeration efficiency in %
vii. If ?vol= 90%, calculate actual piston displacement in m
3
.
t
(
o
C)
hg
kJ/kg
hf
kJ/kg
vg
m
3
/kg
?f
kg/ m
3
CPv
kJ/Kk
g
- 10 382 183 0.11 1330 0.84
36 412 250 0.023 1160 1.12
40 420 260 0.019 1140 1.15
07
Q.2 (a) A heat pump based on simple VCRS of 200 kW heating capacity working between
evaporating and condensing temperatures of ? 10
o
C and 30
o
C respectively has COP
of 4.5. If the enthalpy of saturated vapours entering the compressor is 400 kJ/kg and
the enthalpy of liquid refrigerant entering the expansion valve is 250 kJ/kg, calculate
(i) Compressor power in kW
(ii) Heat rejection ratio (HRR)
(iii) Refrigeration efficiency
03
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2
(b) In a vapour absorption type refrigeration system, heating, cooling and refrigeration
takes place at temperatures of 100?C, 20?C and -10?C respectively.
(i) Find the theoretical COP of the system.
(ii) If the heating temperature is increased to 180?C and the refrigeration temperature
is decreased to -30?C, find the percent change in the COP.
04
(c) Explain the operation of simple VCRS with the help of P-h & T-s diagrams. Explain
the effect of the following on the performance of vapour compression cycle:
(i) Liquid sub-cooling
(ii) Compressor volumetric efficiency
(iii) Reduction in suction temperature.
07
OR
(c) Explain the functions of different components of a simple vapour compression
refrigeration system with the help of a neat flow diagram. Also draw T-s diagram for
the vapour compression cycle indicating various state points. Why is it desirable to
slightly superheat the vapours before it enters the compressor? If the condensed
refrigerant liquid exiting the condenser is slightly sub-cooled, how will it affect the
volumetric efficiency and COP of the system?
07
Q.3 (a) Define cascade refrigeration system. For a 2-stage cascade refrigeration system, the
COP of low and high cascade sides are 1.5 and 4.5 respectively. Calculate the COP of
the system.
03
(b) In an absorption type refrigerator heat is supplied to generator by condensing saturated
steam at 2 bar. Calculate the maximum COP possible of the system if the temperature
to be maintained inside the refrigerator is ? 5
o
C. The atmospheric temperature is 32
o
C.
If the refrigeration load is 5 TR and the actual COP is 90% of maximum COP,
calculate the mass of steam required per hour. Assume that only latent heat of
condensation of steam is used for heating purpose. Given: Saturation temperature of
steam at 2 bar = 120
o
C; hfg = 2230 kJ/kg
04
(c) Explain the construction and working of simple VAR system based on LiBr ?Water. 07
OR
Q.3 (a) Explain the operation and applications of of a 2- stage cascade refrigeration system
with a p-h diagram.
03
(b) ?An ideal vapour absorption refrigeration system may be considered as a heat-operated
refrigerating machine combining a heat engine and a mechanical refrigerator working
together to produce the desired refrigeration effect?. Justify the statement with help of
schematic diagram and mathematical relations.
04
(c) Draw a neat diagram of NH3?Water based practical VARS. Explain the function of
various components of this cycle and derive an expression for maximum COP.
07
Q.4 (a) Define ?Draft?, ?Blow? and ?Throw? as related to air flow with the help of a neat
diagram.
03
(b) Answer the following:
i. Briefly describe types of supply air outlets in air conditioning.
ii. State important considerations while choosing a fan.
04
(c) Classify condensers and give the criteria for their selection. A water-cooled condenser
is sized to reject 50 kW heat at a condensing temperature of 40?C when the maximum
outdoor temperature is 36?C. What will be the approximate condensing temperature
07
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3
when the outdoor temperature is at 18?C and the load is reduced to 20 kW?
OR
Q.4 (a) State fan laws Give measures to improve fan efficiency? A centrifugal fan running at
960 RPM consumes 880W power and delivers 105 cmm of air at 1 atm static pressure.
If the fan speed is doubled, calculate
(i) The power required. (ii)Air flow rate in m
3
/minute
03
(b) What are air washers? An air-filtration system receives dusty air from a plant having a
dust loading of 0.003 kg/m
3
of air. The exhaust air has a dust loading of 0.255 g/m
3
of
air. Calculate the weight of dust collected by the filter in 10 hours if the air-filtration
system handles 500 m
3
/minute of air. What is the filtration efficiency of the system?
04
(c) Explain the principle and working of any one :
(i) Flooded type evaporator with a neat diagram.
(ii) Evaporative condensers
07
Q.5 (a) What are cooling towers? Explain its operation with a neat diagram. 03
(b) Give the classification of compressors. Explain hermetic compressor. 04
(c) Define cooling, freezing, refrigeration and chilling. Calculate the refrigeration load
expressed in TR which balances the heat loss from the four side walls of a small cold
room 3 m ? 3.0 m ? 2.5 m. The walls are made of 24 cm brickwork, 25 cm hard board
and 1.32cm cement. The inside wall temperature is -15?C and outside wall temperature
is 30?C. Consider a safety factor of 2 for losses through joints etc. The thermal
conductivities of brick, board and cement plaster are 0.62 W/m?C, 0.05 W/m?C and
0.82 W/m?C respectively.
07
OR
Q.5 (a) Explain the following in brief: (i) TEV (ii) IQF 03
(b) Write brief notes on the following with figures if required:
i. Axial flow fans
ii. Time switches
iii. Automatic humidity control
iv. Types of temperature sensors
04
(c) Discuss the need for low temperature storage of foods. Give the basic design criteria
for cold stores and list basic components of a cold storage plant including safety
equipment. What is the need for an ?Ante Room??
07
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This post was last modified on 20 February 2020