4O LESSONS ON REFRIGERATION AND AIR CONDITIONING FROM IIT

809 Pages·2009·5.42 MB·English

4O LESSONS ON REFRIGERATION AND AIR CONDITIONING FROM IIT
KHARAGPUR. USEFUL TRAINING MATERIAL FOR MECHANICAL
ENGINEERING STUDENTS/COLLEGE, OR AS REFERENCE FOR ENGINEER.

EE IIT, Kharagpur, India
2008
Contents:
Lesson Page

Lesson 1 History Of Refrigeration [Natural Refrigeration ~ Artificial 7
Refrigeration ]

Lesson 2 History Of Refrigeration - Development Of Refrigerants And 26
Compressors [ Refrigerant development - a brief history ~ Compressor
development - a brief history ]

Lesson 3 Applications Of Refrigeration & Air Conditioning [ Application of 44
refrigeration in Food processing, preservation and distribution ~ Applications of
refrigeration in chemical and process industries ~ Special applications of refrigeration
~ Application of air conditioning ]

Lesson 4 Review of fundamental principles - Thermodynamics : Part I [ 64
Definitions ~ Thermodynamic properties ~ Fundamental laws of Thermodynamics ]

Lesson 5 Review of fundamental principles - Thermodynamics : Part II [ 78
Thermodynamic relations ~ Evaluation of thermodynamic properties ~
Thermodynamic processes ]

Lesson 6 Review of fundamentals: Fluid flow [ Fluid flow ] 93

Lesson 7 Review of fundamentals: Heat and Mass transfer [ Heat transfer ~ 104
Fundamentals of Mass transfer ~ Analogy between heat, mass and momentum
transfer ~ Multimode heat transfer ~ Heat exchangers ]

Lesson 8 Methods of producing Low Temperatures [ Sensible cooling by cold 124
medium ~ Endothermic mixing of substances ~ Phase change processes ~ Expansion
of Liquids ~ Expansion of gases ~ Thermoelectric Refrigeration ~ Adiabatic
demagnetization ]

Lesson 9 Air cycle refrigeration systems [ Air Standard Cycle analysis ~ Basic 138
concepts ~ Reversed Carnot cycle employing a gas ~ Ideal reverse Brayton cycle ~
Aircraft cooling systems ]
Lesson 10 Vapour Compression Refrigeration Systems [ Comparison 153
between gas cycles and vapor cycles ~ Vapour Compression Refrigeration Systems ~
The Carnot refrigeration cycle ~ Standard Vapour Compression Refrigeration System
(VCRS) ~ Analysis of standard vapour compression refrigeration system ]

Lesson 11 Vapour Compression Refrigeration Systems: Performance 171
Aspects And Cycle Modifications [ Performance of SSS cycle ~ Modifications to
SSS cycle ~ Effect of superheat on system COP ~ Actual VCRS systems ~ Complete
vapour compression refrigeration systems ]

Lesson 12 Multi-Stage Vapour Compression Refrigeration Systems [ Flash 193
gas removal using flash tank ~ Intercooling in multi-stage compression ~ Multi-stage
system with flash gas removal and intercooling ~ Use of flash tank for flash gas
removal ~ Use of flash tank for intercooling only ]

Lesson 13 Multi-Evaporator And Cascade Systems [ Individual evaporators 213
and a single compressor with a pressure-reducing valve ~ Multi-evaporator system
with multi-compression, intercooling and flash gas removal ~ Multi-evaporator
system with individual compressors and multiple expansion valves ~ Limitations of
multi-stage systems ~ Cascade Systems ]

Lesson 14 Vapour Absorption Refrigeration Systems [ Maximum COP of ideal 238
absorption refrigeration system ~ Properties of refrigerant-absorbent mixtures ~
Basic Vapour Absorption Refrigeration System ~ Refrigerant-absorbent combinations
for VARS ]

Lesson 15 Vapour Absorption Refrigeration Systems Based On Water- 258
Lithium Bromide Pair [ Properties of water-lithium bromide solutions ~ Steady
flow analysis of Water-Lithium Bromide Systems ~ Practical problems in water-
lithium bromide systems ~ Commercial systems ~ Heat sources for water-lithium
bromide systems ~ Minimum heat source temperatures for LiBr-Water systems ~
Capacity control ]

Lesson 16 Vapour Absorption Refrigeration Systems Based On Ammonia- 279
Water Pair [ Properties of ammonia-water solutions ~ Basic Steady-Flow Processes
with binary mixtures ]

Lesson 17 Vapour Absorption Refrigeration Systems Based On Ammonia- 301
Water Pair [ Working principle ~ Principle of rectification column and dephlegmator
~ Steady-flow analysis of the system ~ Pumpless vapour absorption refrigeration
systems ~ Solar energy driven sorption systems ~ Comparison between compression
and absorption refrigeration systems ]
Lesson 18 Refrigeration System Components: Compressors [ Compressors ~ 317
Reciprocating compressors ]

Lesson 19 Performance Of Reciprocating Compressors [ Ideal compressor 337
with clearance ~ Actual compression process ~ Capacity control of reciprocating
compressors ~ Compressor lubrication ]

Lesson 20 Rotary, Positive Displacement Type Compressors [ Rolling piston 361
(fixed vane) type compressors ~ Multiple vane type compressors ~ Characteristics of
rotary, vane type compressors ~ Rotary, screw compressors ~ Scroll compressors ]

Lesson 21 Centrifugal Compressors [ Analysis of centrifugal compressors ~ 376
Selection of impeller Speed and impeller diameter ~ Refrigerant capacity of
centrifugal compressors ~ Performance aspects of centrifugal compressor ~
Commercial refrigeration systems with centrifugal compressors ]

Lesson 22 Condensers & Evaporators [ Condensers ~ Classification of 402
condensers ~ Analysis of condensers ~ Optimum condenser pressure for lowest
running cost ]

Lesson 23 Condensers & Evaporators [ Classification ~ Natural Convection type 439
evaporator coils ~ Flooded Evaporator ~ Shell-and-Tube Liquid Chillers ~ Shell-and-
Coil type evaporator ~ Double pipe type evaporator ~ Baudelot type evaporators ~
Direct expansion fin-and-tube type ~ Plate Surface Evaporators ~ Plate type
evaporators ~ Thermal design of evaporators ~ Enhancement of heat transfer
coefficients ~ Wilson's plot ]

Lesson 24 Expansion Devices [ Capillary Tube ~ Automatic Expansion Valve (AEV) 465
~ Flow Rate through orifice ~ Thermostatic Expansion Valve (TEV) ~ Float type
expansion valves ~ Electronic Type Expansion Valve ~ Practical problems in operation
of Expansion valves ]

Lesson 25 Analysis Of Complete Vapour Compression Refrigeration 504
Systems [ Reciprocating compressor performance characteristics ~ Evaporator
Performance ~ Expansion valve Characteristics ~ Condensing unit ~ Performance of
complete system - condensing unit and evaporator ~ Effect of expansion valve ]

Lesson 26 Refrigerants [ Primary and secondary refrigerants ~ Refrigerant 523
selection criteria ~ Designation of refrigerants ~ Comparison between different
refrigerants ]
Lesson 27 Psychrometry [ Methods for estimating properties of moist air ~ 537
Measurement of psychrometric properties ~ Calculation of psychrometric properties
from p, DBT and WBT ~ Psychrometer ]

Lesson 28 Psychrometric Processes [ Important psychrometric processes ~ Air 553
Washers ~ Enthalpy potential ]

Lesson 29 Inside And Outside Design Conditions [ Selection of inside design 572
conditions ~ Thermal comfort ~ Heat balance equation for a human being ~ Factors
affecting thermal comfort ~ Indices for thermal comfort ~ Predicted Mean Vote
(PMV) and Percent People Dissatisfied (PPD) ~ Selection of outside design conditions
]

Lesson 30 Psychrometry Of Air Conditioning Systems [ Summer air 591
conditioning systems ~ Guidelines for selection of supply state and cooling coil ]

Lesson 31 Evaporative, Winter And All Year Air Conditioning Systems [ 608
Introduction to evaporative air conditioning systems ~ Classification of evaporative
cooling systems ~ Advantages and disadvantages of evaporative cooling systems ~
Applicability of evaporative cooling systems ~ Winter Air Conditioning Systems ~ All
year (complete) air conditioning systems ~ ]

Lesson 32 Cooling And Heating Load Calculations - Estimation Of Solar 626
Radiation [ Solar radiation ~ Calculation of direct, diffuse and reflected radiations ]

Lesson 33 Cooling And Heating Load Calculations -Solar Radiation 645
Through Fenestration - Ventilation And Infiltration [ Solar radiation through
fenestration ~ Estimation of solar radiation through fenestration ~ Effect of external
shading ~ Ventilation for Indoor Air Quality (IAQ) ~ Infiltration ~ Heating and cooling
loads due to ventilation and infiltration ]

Lesson 34 Cooling And Heating Load Calculations - Heat Transfer Through 660
Buildings - Fabric Heat Gain/Loss [ One-dimensional, steady state heat transfer
through buildings ~ Unsteady heat transfer through opaque walls and roofs ~ One-
dimensional, unsteady heat transfer through building walls and roof ]

Lesson 35 Cooling And Heating Load Calculations - Estimation Of 688
Required Cooling/Heating Capacity [ Heating versus cooling load calculations ~
Methods of estimating cooling and heating loads ~ Cooling load calculations ~
Estimation of the cooling capacity of the system ~ Heating load calculations ~ ]
Lesson 36 Selection Of Air Conditioning Systems [ Selection criteria for air 709
conditioning systems ~ Classification of air conditioning systems ~ All water systems ~
Air-water systems ~ Unitary refrigerant based systems ]

Lesson 37 Transmission Of Air In Air Conditioning Ducts [ Transmission of air 734
~ Flow of air through ducts ~ Estimation of pressure loss in ducts ~ Dynamic losses in
ducts ~ Static Regain ]

Lesson 38 Design Of Air Conditioning Ducts [ General rules for duct design ~ 752
Classification of duct systems ~ Commonly used duct design methods ~ Performance
of duct systems ~ System balancing and optimization ~ Fans ]

Lesson 39 Space Air Distribution [ Design of air distribution systems ~ Behaviour 772
of free-stream jet ~ Circular jets ~ Types of air distribution devices ~ Return air inlets
~ Airflow patterns inside conditioned space ~ Stratified mixing flow ~ Spot
cooling/heating ~ Selection of supply air outlets ]

Lesson 40 Ventilation For Cooling [ Natural versus mechanical ventilation ~ 797
Natural ventilation ~ Guidelines for natural ventilation ~ Forced ventilation using
electric fans ~ Interior air movement ]

Reference books for this course 809
Lesson
1
History Of Refrigeration

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Objectives of the lesson:

The objectives of this lesson are to:

1. Define refrigeration and air conditioning (Section 1.1)

2. Introduce aspects of various natural refrigeration methods, namely:

a. Use of ice transported from colder regions (Section 1.2)
b. Use of ice harvested in winter and stored in ice houses (Section 1.2)
c. Use of ice produced by nocturnal cooling (Section 1.2.1)
d. Use of evaporative cooling (Section 1.2.2)
e. Cooling by salt solutions (Section 1.2.3)

3. Introduce historical aspects of various artificial refrigeration methods, namely:

a. Vapour compression refrigeration systems, including
i. Domestic refrigeration systems (Section 1.3.1.1)
ii. Air conditioning systems (Section 1.3.1.2)
b. Vapour absorption refrigeration systems (Section 1.3.2)
c. Solar energy based refrigeration systems (Section 1.3.3)
d. Air cycle refrigeration systems (Section 1.3.4)
e. Steam and vapor jet refrigeration systems (Section 1.3.5)
f. Thermoelectric refrigeration systems (Section 1.3.6), and
g. Vortex tubes (Section 1.3.7)

At the end of the lesson the student should be able to:

1. Identify various natural and artificial methods of refrigeration

2. List salient points of various refrigeration techniques, and

3. Name important landmarks in the history of refrigeration

1.1. Introduction

Refrigeration may be defined as the process of achieving and maintaining a
temperature below that of the surroundings, the aim being to cool some product or space to
the required temperature. One of the most important applications of refrigeration has been the
preservation of perishable food products by storing them at low temperatures. Refrigeration
systems are also used extensively for providing thermal comfort to human beings by means
of air conditioning. Air Conditioning refers to the treatment of air so as to simultaneously
control its temperature, moisture content, cleanliness, odour and circulation, as required by
occupants, a process, or products in the space. The subject of refrigeration and air
conditioning has evolved out of human need for food and comfort, and its history dates back
to centuries. The history of refrigeration is very interesting since every aspect of it, the
availability of refrigerants, the prime movers and the developments in compressors and the
methods of refrigeration all are a part of it. The French scientist Roger ThÝvenot has written
an excellent book on the history of refrigeration throughout the world. Here we present only a
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brief history of the subject with special mention of the pioneers in the field and some
important events.

Q: Which of the following can be called as a refrigeration process?

a) Cooling of hot ingot from 1000oC to room temperature
b) Cooling of a pot of water by mixing it with a large block of ice
c) Cooling of human beings using a ceiling fan
d) Cooling of a hot cup of coffee by leaving it on a table
e) Cooling of hot water by mixing it with tap water
f) Cooling of water by creating vacuum over it
Ans: b) and f)
1.2. Natural Refrigeration

In olden days refrigeration was achieved by natural means such as the use of ice or
evaporative cooling. In earlier times, ice was either:

1. Transported from colder regions,
2. Harvested in winter and stored in ice houses for summer use or,
3. Made during night by cooling of water by radiation to stratosphere.

In Europe, America and Iran a number of icehouses were built to store ice. Materials
like sawdust or wood shavings were used as insulating materials in these icehouses. Later on,
cork was used as insulating material. Literature reveals that ice has always been available to
aristocracy who could afford it. In India, the Mogul emperors were very fond of ice during
the harsh summer in Delhi and Agra, and it appears that the ice used to be made by nocturnal
cooling.

In 1806, Frederic Tudor, (who was later called as the “ice king”) began the trade in
ice by cutting it from the Hudson River and ponds of Massachusetts and exporting it to
various countries including India. In India Tudor’s ice was cheaper than the locally
manufactured ice by nocturnal cooling. The ice trade in North America was a flourishing
business. Ice was transported to southern states of America in train compartments insulated
by 0.3m of cork insulation. Trading in ice was also popular in several other countries such as
Great Britain, Russia, Canada, Norway and France. In these countries ice was either
transported from colder regions or was harvested in winter and stored in icehouses for use in
summer. The ice trade reached its peak in 1872 when America alone exported 225000 tonnes
of ice to various countries as far as China and Australia. However, with the advent of
artificial refrigeration the ice trade gradually declined.

1.2.1. Art of Ice making by Nocturnal Cooling:

The art of making ice by nocturnal cooling was perfected in India. In this method ice
was made by keeping a thin layer of water in a shallow earthen tray, and then exposing the
tray to the night sky. Compacted hay of about 0.3 m thickness was used as insulation. The
water looses heat by radiation to the stratosphere, which is at around -55˚C and by early
morning hours the water in the trays freezes to ice. This method of ice production was very
popular in India.

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1.2.2. Evaporative Cooling:

As the name indicates, evaporative cooling is the process of reducing the temperature
of a system by evaporation of water. Human beings perspire and dissipate their metabolic
heat by evaporative cooling if the ambient temperature is more than skin temperature.
Animals such as the hippopotamus and buffalo coat themselves with mud for evaporative
cooling. Evaporative cooling has been used in India for centuries to obtain cold water in
summer by storing the water in earthen pots. The water permeates through the pores of
earthen vessel to its outer surface where it evaporates to the surrounding, absorbing its latent
heat in part from the vessel, which cools the water. It is said that Patliputra University
situated on the bank of river Ganges used to induce the evaporative-cooled air from the river.
Suitably located chimneys in the rooms augmented the upward flow of warm air, which was
replaced by cool air. Evaporative cooling by placing wet straw mats on the windows is also
very common in India. The straw mat made from “khus” adds its inherent perfume also to the
air. Now-a-days desert coolers are being used in hot and dry areas to provide cooling in
summer.

1.2.3. Cooling by Salt Solutions:

Certain substances such as common salt, when added to water dissolve in water and
absorb its heat of solution from water (endothermic process). This reduces the temperature of
the solution (water+salt). Sodium Chloride salt (NaCl) can yield temperatures up to -20˚C
and Calcium Chloride (CaCl ) up to - 50˚C in properly insulated containers. However, as it is
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this process has limited application, as the dissolved salt has to be recovered from its solution
by heating.

Q. The disadvantages of natural refrigeration methods are:

a) They are expensive
b) They are uncertain
c) They are not environment friendly
d) They are dependent on local conditions

Ans: b) and d)

Q. Evaporative cooling systems are ideal for:

a) Hot and dry conditions
b) Hot and humid conditions
c) Cold and humid conditions
d) Moderately hot but humid conditions

Ans: a)
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