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GUJARAT TECHNOLOGICAL UNIVERSITY

MECHANICAL ENGINEERING (19)

REFRIGERATION AND AIRCONDITIONING

SUBJECT CODE: 2161908

B.E. 6th SEMESTER Type of course: Core course

Prerequisite: Thermodynamics

Rationale: The course is designed to give fundamental knowledge of types of refrigeration, refrigeration

cycles, refrigerants and behavior under various conditions, different air conditioning terms and load

calculation, designing of components of air distribution system.

Teaching and Examination Scheme:

Teaching Scheme Credits Examination Marks Total

Marks L T P C Theory Marks Practical Marks

ESE

(E)

PA (M) ESE (V) PA

(I) PA ALA ESE OEP

3 0 2 5 70 20 10 20 10 20 150

Content:

Sr.

No.

Content Total

Hrs

%

Weight

age

1 Introduction: Brief history and need of refrigeration and air conditioning,

methods of producing cooling, ton of refrigeration, coefficient of performance,

types and application of refrigeration and air condensing systems.

2 3

2 Refrigerants: Classification, nomenclature, desirable properties, secondary

refrigerants, future industrial refrigerants

2 4

3 Air refrigeration: Reversed Carnot cycle and its limitation, Bell-Coleman

cycle, aircraft refrigeration, working and analysis of Simple; Bootstrap; Reduced

ambient and Regenerative air refrigeration systems

4 8

4 Vapour Compression system: Simple system on P-h and T-s diagrams, analysis

of the simple cycle, factors affecting the performance of the cycle, actual cycle

Compound Compression System: Compound compression with intercooler,

flash gas removal and flash intercooler, multiple evaporators with back pressure

valves and with multiple expansion valves without flash inter cooling, analysis

of two evaporators with flash intercooler and individual expansion valve and

multiple expansion valve, cascade refrigeration system

7 16

5 Absorption refrigeration system: Desirable characteristics of refrigerant,

selection of pair, practical H2O -NH3 cycle, LiBr – H2O system and its working,

h-x diagram and simple calculation of various process like adiabatic mixing and

mixing with heat transfer, throttling, Electrolux refrigeration system*

3 8

6 Refrigeration system components: Types; construction; working; comparison

and selection of compressors*; condensers; expansion devices; and evaporators,

refrigeration piping accessories*, evacuation and charging of refrigerant*,

properties and classification of thermal insulation

5 12

7 Psychrometry: Dalton’s law of partial pressure, Properties of moist air,

temperature and humidity measuring instruments, psychrometric chart,

psychrometric processes such as sensible heating and cooling, heating and

humidification cooling and dehumidification, chemical dehumidification,

adiabatic saturation

5 13

8 Human comfort: Selection of inside design conditions, thermal comfort, heat

balance equation for a human being, factors affecting thermal comfort, Effective

temperature, comfort chart and factors governing effective temperature, selection

of outside design conditions

1 3

9 Load analysis: Site survey, outdoor and indoor design conditions, classification 6 15

of loads, flywheel effect of building material and its use in design, effect of wall

construction on cooling load, instantaneous heat gain (IHG) and instantaneous

cooling load (ICL) heat transmission through sunlit and shaded glass using

tables, method of reduction of solar heat gain through glass, calculations of

cooling load TETD due to sunlit and shaded roof and walls using tables,

ventilation and air infiltration, load due to outside air, heat gain from occupants;

electric lights; product; electric motor and appliances, load calculations for

automobiles, use of load estimation sheet*, introduction of CLTD method

10 Duct design and air distribution: Function; classification and economic factors

influencing duct layout, equal friction method of duct design, use of friction

chart, dynamic losses and its determination, Requirements of air distribution

system, air distribution, grills, outlets, application, location

4 10

11 Air-conditioning systems: Classification, system components, all air; all water;

and air-water systems, room air conditioners, packaged air conditioning plant,

central air conditioning systems, split air conditioning systems

3 8

* To be covered in practical sessions only.

Suggested Specification table with Marks (Theory):

Distribution of Theory Marks

R Level U Level A Level N Level E Level C Level

10 20 15 10 10 5

Legends: R: Remembrance; U: Understanding; A: Application, N: Analyze and E: Evaluate and above

Levels (Revised Bloom’s Taxonomy)

Note: This specification table shall be treated as a general guideline for students and teachers. The actual

distribution of marks in the question paper may vary slightly from above table

Reference Books:

1. Refrigeration and Air Conditioning by C P Arora, McGraw-Hill India Publishing Ltd.

2. Refrigeration and Air-conditioning by Ramesh Arora , Prentice Hall of India

3. Refrigeration and Air Conditioning by Manohar Prasad, New Age International Publisher

4. Principles of Refrigeration by Roy. J Dossat, Pearson Education

5. Refrigeration and Air Conditioning by Jordon and Prister, Prentice Hall of India Pvt. Ltd.

6. Refrigeration and Air Conditioning by W.F. Stocker and J. W. Jones, McGraw-Hill

7. Refrigeration and Air Conditioning by Ameen Ahmadul, PHI India

8. Automobile Air conditioning by Crouse and Anglin, McGraw Hill Publications

Course Outcome:

After learning the course the students should be able to:

● Understand the basic concepts of refrigeration and air conditioning systems

● Understand and analysis of various refrigeration cycles

● Make basic calculation of psychometric properties and process

● Do basic calculations of heating and cooling load requirements of a room.

● Apply scientific and engineering principles to analyze and design aspects of engineering systems that

relate to refrigeration and air conditioning.

List of laboratory experiments: (Any 10 of the following experiments to be performed)

1. To understand different components of VCR system and to determine its COP

2. To understand working of Electrolux refrigerator and to determine its COP.

3. To understand construction and working of reciprocating, rotary and centrifugal compressor used for

R&AC.

4. To understand various tools used for refrigeration tubing and and to perform various operations like

flaring, swaging, bending, brazing etc.

5. To perform different psychrometric processes and analyze the same using psychrometric chart.

6. To understand construction and working of window air-conditioner/ split air-conditioner and to determine

its capacity.

7. To determine COP and apparatus dew point of an air conditioning test rig.

8. To calculate cooling load of a confined space using table and compare the same with load estimation

sheet.

9. Study of domestic refrigerator and to determine % running time at different thermostat settings.

10. To determine (COP)C and (COP)H of heat pump

11. To determine saturation efficiency of air cooler/air washer

12. Study of packaged plant

Design based Problems (DP)/Open Ended Problem:

● Calculation of cooling load for a shopping mall or a large building.

● Make calculation of thermal insulation for a small cabin to prevent heat loss.

● Design and construction of a personal cooler.

● Determine evaporative cooling capacity of a desert cooler.

● Prepare duct layout for a shopping mall or a large building using any one method. (Different groups can

take one method for same building and discuss the results).

● Thermal design of condenser used for R&AC

Major Equipment:

● Vapor compression test rig

● Vapor absorption test rig

● Sectional models of various type of compressors

● Air conditioning test rig

● Air cooler apparatus

● Apparatus to perform various psychrometric processes

● Tools for refrigeration tubing

● Mechanical heat pump

List of Open Source Software/learning website:

1. http://nptel.ac.in/

2. www.learnerstv.com

ACTIVE LEARNING ASSIGNMENTS: Preparation of power-point slides, which include videos,

animations, pictures, graphics for better understanding theory and practical work – The faculty will allocate

chapters/ parts of chapters to groups of students so that the entire syllabus to be covered. The power-point

slides should be put up on the web-site of the College/ Institute, along with the names of the students of the

group, the name of the faculty, Department and College on the first slide. The best three works should submit

to GTU.

ASSIGNMENT: 1 Name of Subject: REFRIGERATION & AIR CONDITIONING Subject Code: 2161908

Chapter/Unit: 1

1 Define refrigeration. Discussed various methods of producing cooling.

2 Define and explain below terms: 1.Ton of refrigeration (TR) 2.COP of refrigerator

3 Give applications of refrigeration and air conditioning

ASSIGNMENT: 2 Chapter/Unit: 2

1 What is refrigerant? Give classification of refrigerants.

2 How refrigerants are designated? Explain designation of any two refrigerants CCl2F2and C2Cl2F4

3 Give the list of desirable properties of refrigerants. Explain each briefly. OR Explain thermodynamic, chemical and physical properties of refrigerants.

4 What are the secondary refrigerants? How they differentiate from primary refrigerant? Give examples and applications of few recently used refrigerants.

ASSIGNMENT: 3

Chapter/Unit: 3

1 Explain air refrigerator working on reversed Carnot cycle and give comments on its limitations.

2

Derive an expression for COP of Bell-Coleman cycle (Reversed Brayton OR Reversed Joule cycle). Discuss the merits and demerits of the open cycle and close (dense) Bell-Coleman cycle.

3

Explain working and analysis of following aircraft cooling (refrigeration) systems with schematic and T-s diagram 1.Boot strap air cooling system 2.Regenerative air cooling system

4

The atmospheric air at pressure 1 bar and temperature -5 0C 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 15 0C, pressure remaining 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: (1) The work done per kg of air, and (2) C.O.P of the plant. For air assume law for expansion pv1.2 = constant; law for compression pv1.4 = constant and Cpa = 1 kJ/kg K.

5

A boot-strap cooling system of 10 TR capacities is used in an aeroplane. The Ambient air temperature and pressure are 20⁰C and 0.85 bar respectively. The pressure of air discharged from the main compressor is 3 bar. The discharge pressure of air from auxiliary compressor is 4 bar. The isentropic efficiency of each of the compressor is 80%, while that of turbine is 85%. 50% of the enthalpy of air discharged from the main compressor is removed in the first heat exchanger and 30% of the enthalpy of air discharged from the auxiliary compressor is removed in the second heat exchanger using rammed air. Assuming the ramming action to be isentropic, the required cabin pressure are 0.9 bar and temperature of the air leaving the cabin not more than 20⁰C. Find: 1. The power required to operate the system; and 2. The C.O.P of the system. Draw the schematic and T-s diagram of the system. Take γ = 1.4 and cp= 1 kJ/kg K.

ASSIGNMENT: 4 Chapter/Unit: 4

Explain mechanism of a simple vapour compression refrigeration system with neat sketch and p-h and T-s diagram. Mention the advantages and disadvantages of vapour compression system over air refrigeration system.

1

How actual vapour compression refrigeration cycle differs from theoretical vapour compression refrigeration cycle?Explain with T-s diagram.

2

Explain following types of compound vapour compression with intercooler with schematic and p-h diagram: 1.Two stage compression with flash chamber 2.Two stage compression with water intercooler, liquid subcooler and liquid flash chamber

3

The temperature limits of an ammonia refrigeration system are 25⁰C and -10⁰C. If the gas is dry at the end of compression. Calculate the coefficient of performance of the cycle assuming no undercooling of the liquid ammonia. Use the following table for properties of ammonia:

4

A single compressor using R-12 as refrigerant has three evaporators of capacity 30 TR, 20 TR and 10 TR. All the evaporators operate at -10⁰C, 5⁰C and 10⁰C respectively. The condenser pressure is 9.609 bar. The liquid refrigerant leaving the condenser is subcooled to 30⁰C. The vapour leaving the evaporators is dry and saturated. Assuming isentropic compression, find: 1. The mass of refrigerant flowing through each evaporator; 2. The power required to drive the compressor; and 3. The C.O.P. of the system.

5

ASSIGNMENT: 5

Chapter/Unit: 5

Explain construction and working of simple vapour absorption refrigeration system with schematic diagram. 1

Advantages of vapour absorption refrigeration system over vapour compression Refrigeration system. 2

Describe with neat sketch Li-Br and water system. What are its limitations? 3

Prove the expression for C.O.P for ideal vapour absorption refrigeration system 4

ASSIGNMENT: 6

Chapter/Unit: 6

Explain construction and working of following types of refrigerant compressors with neat sketch: a. Reciprocation compressor (hermetically sealed) b. Centrifugal compressor c .Rotary compressor (e.g rolling piston type, rotating vane type, screw type)

1

State the functions of expansion device. Explain construction and working of on following types of expansion devices with neat sketch.

a. Capillary tube d. Thermostatic expansion valve 2

Explain working of an evaporator. Describe the factor affecting heat transfer Capacity of an evaporator. 3

Write short note on following water cooled refrigerant condensers with neat sketch: a. Double tube or tube-in-tube type b.Shell and coil type, Shell and tube type

4

ASSIGNMENT: 7

Chapter/Unit: 7

Define following terms: Saturated air (ii) Specific humidity (iii) Relative humidity (iv) Absolute humidity (v) Dry bulb temperature (vi) Dew point temperature (vii) Wet bulb depression

1

Moist air at 30°C, 1.01325 bar has a relative humidity of 80%. Determine without using the psychometric chart 1) Partial pressures of water vapour and air 2) Specific humidity 3) Specific Volume and 4) Dew point temperature

2

With neat sketch explain construction and working of any one type of humidifier. 3

Laxmi Institute of Technology , Sarigam Approved by AICTE, New Delhi; Affiliated to Gujarat Technological University, Ahmedabad

Academic Year 2018-19

Centre Code: 086 Examination : Mid Sem Branch: Automobile Semester: 6 Sub Code: 2161908 Sub: RAC Date: 28/1/2019 Time: 9.00-10.00 AM Marks: 20

Q 1 Q 1

A R22 vapour compression refrigeration system operates between -100C and 45oC. The refrigerant is subcooled by 50C before entering the expansion valve and vapour is superheated by 5 0C before entering the compressor. By using Pressure-enthalpy chart, Calculate (i) Refrigeration effect per kg.(ii) Mass flow rate of refrigerant for 5 TR capacity and(iii) COP of the system.

OR An NH3 refrigerator produces 30 tonnes of ice from and at 0 0C. The temperature range in the compressor is from 26 0C to -14 0C. the vapour is dry saturated at the end of the compression. Actual C.O.P. is 60 % of the theoretical. Calculate the power required for the compressor. The latent heat of ice = 335 kJ/kg. Use following table.

5

Q 2 Define Ton of refrigeration , State the Name of different types of system used for cooling of aircraft cabin, Also Explain with schematic diagram Bootstrap air Refrigeration system.

5

Q 3 Define Refrigeration. State types of refrigeration systems. Explain Reverse Carnot cycle. 5 Q 4 Q 4

A dense air refrigeration machine operating on Bell-Coleman cycle works between 3.4 bar and 17 bar. The temperature of air after the cooler is 15oC and after refrigeration is 6oC, for a refrigeration capacity of 6 tons calculate 1. Temperature after compression and expansion 2. Air circulation required in cycle per minute 3. Work of compression. 4. Theoretical COP.

OR The Following data is used in aero plane using a boot-strap cooling system: Capacity = 20 TR The ambient air temperature = -50C The ambient air pressure = 0.8 bar The increase in pressure due to isentropic ramming =1 bar The compression ratio = 4 The discharge pressure of the air from the auxiliary compressor =5 bar The isentropic efficiency of each compressor = 80% The isentropic efficiency of the turbine = 85% The removal of enthalpy by first heat exchanger = 50% of the enthalpy of air discharged from the auxiliary compressor. The removal of enthalpy by second heat exchanger using rammed sir = 30% of the enthalpy of air discharged from the auxiliary compressor. The required cabin pressure = 0.9 bar The temperature of the air leaving the cabin = 250C. Calculate (i) COP (ii) power required to operate the system Take γ = 1.4 and Cp=1.005 KJ/kg K. Assume ram efficiency =100%.

5

Laxmi Institute of Technology , Sarigam Approved by AICTE, New Delhi; Affiliated to Gujarat Technological

University, Ahmedabad Academic Year 2016-17

Centre Code: 086 Examination : Mid Sem 2 Branch: Auto Semester: 6 Sub Code: 2161908 Sub: RAC Date: 4/4/2017

Time: 9:00 AM to 10:00 PM Marks: 20

Q 1 Define following terms: (i) Saturated air (ii) Specific humidity (iii) Relative humidity (iv) Absolute humidity (v) Dry bulb temperature (vi) Dew point temperature (vii) Wet bulb depression

5

Q 2 Explain mechanism of a simple vapour compression refrigeration system with neat sketch and p-h and T-s diagram. Mention the advantages and disadvantages of vapour compression system over air refrigeration system.

5

Q3 The temperature limits of an ammonia refrigeration system are 25⁰C and -10⁰C. If the gas is dry at the end of compression. Calculate the coefficient of performance of the cycle assuming no undercooling of the liquid ammonia. Use the following table for properties of ammonia:

5

Q4 Describe with neat sketch Li-Br and water system. What are its limitations? OR Prove the expression for C.O.P for ideal vapour absorption refrigeration system

5

1

Seat No.: ________ Enrolment No.___________

GUJARAT TECHNOLOGICAL UNIVERSITY BE - SEMESTER–VI (NEW) EXAMINATION – WINTER 2017

Subject Code: 2161908 Date:28/11/2017 Subject Name:Refrigeration and Air Conditioning Time:02:30 PM TO 05:00PM 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) Define refrigeration, air conditioning and COP. 03

(b) Explain the method of designation of refrigerant with example. 04

(c) Explain standard VCR cycle with T-S and P-H diagrams.

07

Q.2 (a) Why aircrafts require cooling? 03

(b) Differentiate dry and wet compression. 04

(c) Discuss the effect of suction pressure and sub-cooling on the performance of a

vapour compression system. 07

OR

(c) Explain Boot strap air refrigeration system with neat diagram. 07

Q.3 (a) Explain working of Electrolux VAR system with neat sketch. 03

(b) Explain hermetically sealed compressor. 04

(c) An NH3 refrigerator produces 30 tonnes of ice from and at 00 C. The

temperature range in the compressor is from 260 C to -140 C. the vapour is dry

saturated at the end of the compression. Actual C.O.P. is 60 % of the

theoretical. Calculate the power required for the compressor. The latent heat

of ice = 335 kJ/kg. Use following table.

Temp.,0

C

Enthalpy

kJ/kg,

Vapour

Enthalpy

kJ/kg,

Liquid

Entropy

kJ/kg K,

SL

Entropy

kJ/kg K,

Sv

26 1483.72 322.73 1.4257 5.3066

-14 1445.47 135.82 0.7599 4.8137

07

OR

Q.3 (a) Enlist properties required for an ideal refrigerant-absorbent

combination. 03

(b) Explain construction and working of Thermostatic Expansion valve with neat

sketch. 04

(c) Briefly explain the working of Two stage vapour compression system with

water intercooler and liquid sub-cooler. 07

Q.4 (a) Explain human comfort. 03

(b) Explain Adiabatic saturation process with neat sketch. 04

(c) Explain equal friction loss (pressure loss) method for duct design. 07 OR

Q.4 (a) Explain cooling and dehumidification process. 03

(b) Explain flywheel effect as applied to cooling load calculation with neat

labeled diagram. 04

(c) 50 m3/min of air at 270 c DBT and 200 C WBT flows through a cooing coil

and leaves the coil at 120 C DBT and 8 gm/kg of moisture content. Determine:

(i) Apparatus dew point (ii) Contact factor (iii) Cooling load.

07

Q.5 (a) Differentiate instantaneous heat gain (IHG) and instantaneous cooling

load (ICL). 03

(b) Explain central air conditioning system 04

(c) Explain all air system. 07

OR

Q.5 (a) Explain air washer. 03

2

(b) Explain construction and working of any one type humidifier with neat sketch. 04

(c) Define effective temperature. Explain briefly various factors governing it. 07

*************

1

Seat No.: ________ Enrolment No.___________

GUJARAT TECHNOLOGICAL UNIVERSITY BE - SEMESTER–VI (NEW) - EXAMINATION – SUMMER 2016

Subject Code:2161908 Date:17/05/2016 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 Air-Conditioning charts and Steam tables is permitted.

Q.1 (a) Explain the effect of evaporator pressure, condenser pressure and liquid sub-

cooling on performance of vapour compressor refrigeration system using P-H diagram.

07

(b) A dense air refrigeration machine operating on Bell-Coleman cycle works between 3.4 bar and 7 bar. The temperature of air after the cooler is 15oC and after refrigeration is 6oC, for a refrigeration capacity of 6 tons calculate 1. Temperature after compression and expansion 2. Air circulation required in cycle per minute 3. Work of compression and expansion 4. Theoretical COP 5. Rate of water circulation required in the cooler in Kg/min if rate of temperature rise is limited to 30oC. For air take Cp=1.005 kJ/kg K, γ = 1.4. for water Cp = 4.18 kJ/kg K.

07

Q.2 (a) Define refrigeration, State the Name of different types of system used for cooling of aircraft cabin, Also Explain with schematic diagram Bootstrap air Refrigeration system.

07

(b) A R22 vapour compression refrigeration system operates between -100C and 450C. The refrigerant is subcooled by 50C before entering the expansion valve and vapour is superheated by 50C before entering the compressor. By using Pressure-enthalpy chart, Calculate (i) Refrigeration effect per kg.(ii) Mass flow rate of refrigerant for 5 TR capacity and(iii) COP of the system.

07

OR (b) A refrigeration machine is required to produce ice at 0oC from water at 20oC.

The machine has a condenser temperature of 25oC while evaporator temperature is -50C. The relative efficiency of the machine is 50% and 6 kg of Freon-12 is circulated through the system per minute. The refrigerant enters in the compressor with dryness fraction of 0.6. Calculate the amount of ice produced in 24 hrs. Take latent heat of ice 335 kJ/kg. Temperature ( 0C)

Liquid heat ( KJ/kg)

Latent heat ( KJ/kg)

Entropy of liquid ( KJ/kg-K)

25 59.7 138 0.2232 -5 31.4 154 0.1251

07

Q.3 (a) Explain with neat sketch working of ammonia-hydrogen refrigerator also explain significance of Hydrogen used in system.

07

(b) Explain construction, working, advantages and disadvantages of Thermostatic Expansion valve with neat sketch.

07

OR

2

Q.3 (a) Explain Thermodynamic, Chemical and Physical properties of an Ideal Refrigerant.

07

(b) State and explain various heat loads to be considered for cooling load calculation of typical building.

07

Q.4 (a) Define following term related to psychrometry (i) wet bulb temperature (ii) psychrometry (iii) Relative humidity (iv) By pass factor (v) dew point temperature (vi) apparatus dew point temperature (vii) sensible heat factor

07

(b) Explain various methods used for design of the duct. 07

OR Q.4 (a) Explain with neat sketch the Cascade refrigeration system. 07

(b) A circular duct of 40 cm is selected to carry air in an air conditioned space at a velocity of 440 m/min to keep the noise level at desired level. If this duct is replaced by a rectangular duct of aspect ratio of 1.5, find out the size of rectangular duct for equal friction method when (a) the velocity of air in two ducts is same, (b) the discharge rate of air in two ducts is same.

07

Q.5 (a) Classify air conditioning systems. Explain Central air conditioning system with a neat sketch.

07

(b) Explain in brief the following: (i) Ice Making plant. (ii) Effective Temperature.

07

OR Q.5 (a) Classify Fan used in air-conditioning system. Explain selection of the an using

fan characteristic curve. 07

(b) Explain working of Li-Br vapour absorption refrigeration system with neat sketch.

07

*************

1

Seat No.: ________ Enrolment No.___________

GUJARAT TECHNOLOGICAL UNIVERSITY BE – SEMESTER – VI (NEW).EXAMINATION – WINTER 2016

Subject Code: 2161908 Date: 22/10/2016

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 psychrometric chart and steam table is permissible.

Q.1 (a) Explain with neat schematic diagram simple air refrigeration system also draws its

T-s plot.

07

(b) Explain following terms

(1) Flash chamber (5) Hermetically sealed compressor

(2) Aspect ratio (6) Grand Sensible Heat Factor

(3) Humidity ratio (7) Secondary refrigerant

(4) Dew point temperature

07

Q.2 (a) A food storage requires a refrigeration capacity of 12 TR and works between the

evaporative temperature of -8OC and condensing temperature of 30OC. The

refrigerant R-12 is sub cooled by 5OC before entering expansion device and

vapour is superheated to -2OC before leaving to evaporator coil. (1) Draw p-h

diagram for the process and find out (2) C.O.P. (3) power required in kW/TR.

Saturation

Temperature

Saturation

Pressure

Enthalpy

(kJ/kg)

Entropy

(kJ/kg K)

(OC) (bar) Liquid Vapor Liquid Vapor

-8 2.354 28.72 184.07 0.1149 0.7007

30 7.451 64.59 199.62 0.24 0.6853

Take specific heat of liquid R-12 as 1.235 kJ/kg K and vapour R-12 as 0.733 kJ/kg

K

07

(b) Explain with neat schematic diagram, working of two stage compression system

with water intercooler, liquid subcooler and flash intercooler. Also draw p-h

diagram.

07

OR

(b) A dense air refrigerator operating on Bell-Coleman cycle works between 3 bar and

15 bar. The temperature of air after the evaporator and after cooler is 5OC and 20

OC respectively. The evaporator extracts 2000 kg/min of heat from the space to be

cooled. Calculate (1) amount of air required in the cycle per minute, (2) power

required to run the system, (3) COP and (4) mass flow rate of water per minute in

cooler if rise in temperature of water is 20 OC.

Assume isentropic compression and expansion, Cp=1.008kJ/kg K, γ=1.4 for air

and for water Cp=4.18 kJ/kg K.

07

Q.3 (a) Explain working of theoretical aqua ammonia vapour absorption refrigeration

system with neat sketch. Also state few selection criteria for vapor absorption

refrigeration system.

07

(b) The barometer for air reads 750 mm of Hg. The DBT and WBT measured using

sling psychrometer is 33OC and 23OC respectively. Calculate (1) Vapor pressure

(2) Relative humidity (3) Humidity ratio (4) Dew point temperature (5) specific

enthalpy (6) wet bulb depression and (7) dew point depression

07

2

OR

Q.3 (a) What is the function of expansion device? Explain automatic expansion valve with

neat sketch.

07

(b) Air at 30OC DBT and 60% RH enters over cooling coil at rate 250m3/min. If

effective surface temperature of coil is 12OC and bypass factor is 0.1 then name

the process undergone by air and calculate temperature of air leaving coil,

refrigerating effect in TR, mass of water vapor condensed and SHF.

07

Q.4 (a) List out applications of refrigeration and explain ice plant with neat sketch 07

(b) Derive the formula of equivalent diameter of circular duct for rectangular duct

when (1) the quantity of air carries in both the ducts is same and (2) the velocity of

air in both the ducts is same.

07

OR

Q.4 (a) List out factors governing human comfort. Define Effective Temperature. Explain

five factors governing optimum effective temperature.

07

(b) Classify refrigerants briefly and explain four thermodynamic properties of

refrigerants.

07

Q.5 (a) What are IHG and ICL? Explain flywheel effect of building material on peak load

and time lag of heat load with neat sketch.

07

(b) Explain ventilation and infiltration in brief. Also calculate total infiltration air in

m3/min and load due to outside air for the Restaurant. Take Inside design

condition 26 OC DBT, specific humidity 11.1 gm/kg of dry air and Outside design

condition 42 OC DBT, specific humidity 16.4 gm/kg of dry air. Size of room is

18x18x4 meter, No. of air changes required/hr is 1.5, No. of occupants 100, door

open/hr/occupant is 3 and usage factor for swinging door is 3.

07

OR

Q.5 (a) List out methods for duct design and explain equal friction loss method with its

advantages and disadvantages.

07

(b) Classify air conditioning systems and explain summer air conditioning system

with neat sketch.

07

*************