An ice slurry system using direct contact heat transfer for cooling applications

EXPERIMENTS AND ANALYSES:
AN ICE SLURRY SYSTEM USING DIRECT CONTACT
HEAT TRANSFER FOR COOLING APPLICATIONS
















MUHAMMAD ARIFEEN WAHED
(B.Sc. (Mech. Eng.), B.U.E.T)

A THESIS SUBMITTED
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
DEPARTMENT OF MECHANICAL ENGINEERING
NATIONAL UNIVERSITY OF SINGAPORE
2009

Acknowledgements


i


ACKNOWLEDGEMENTS


In the course of this project, much assistance and services have been received form
various sources for which the author is indebted.
First of all, the author would like to express his deep gratitude to his supervisor Assoc.
Professor M.N.A. Hawlader, Department of Mechanical Engineering, National
University of Singapore for his sincere guidance, inspiration and valuable suggestions
during the course of the study. The author is also thankful to all the staff members of the
Thermal Process Laboratory.

Finally, the author would like to thank his parents and wife, Salsalina Saberat, for their
support and inspiration.




















Table of Contents

ii

Table of Contents


Acknowledgements i

Table of Contents ii
Summary v
List of Figures vii
List of Tables x
Nomenclature xi

Chapter 1 INTRODUCTION

1.1 Background: Cooling with Ice Slurry 2
1.2 Ice Slurry Technology 3
1.3 Advantages of Ice Slurry 4
1.4 Objectives 6
1.5 Scope 7


Chapter 2 LITERATURE REVIEW

2.1 Fundamentals of Ice Formation 9

2.2 Ice Slurry Production
2.2.1 Static ice production 12
2.2.2 Dynamic ice Production 16
2.2.2.1 Phase Change liquids 16
2.2.2.3 Immiscible liquid 18
2.3 Ice Slurry Heat Transfer Phenomena
2.3.1 Heat transfer through circular ducts 20
2.3.2 Heat transfer through rectangular channels 24
2.3.3 Heat transfer: industrial heat exchanger 26

Chapter 3 MATHEMATICAL MODEL

3.1 Ice Slurry Generator: Physical Arrangement 31
3.1.1 Mathematical model: ice slurry generator 32
3.1.2 Solution procedures 35

3.2 Ice Formation Analysis
3.2.1 Conception of mushy layer 42
3.2.2 Mathematical analyses 44
3.2.3 Detachment of ice layer 50
3.2.3.1 Droplet moving downward 51
3.2.3.2 Droplet moving upward 53
Table of Contents

iii

3.2.4 Mass of ice 55

3.3 Ice Slurry Extraction
3.3.1 Energy balance on cooling Coil 57
3.3.2 Pressure drop analysis 61
3.4 Solution Procedure: Flow Diagram 62


Chapter 4 EXPERIMENTS

4.1 Ice Formation: A Simulation Experiment
4.1.1 The test rig: equipment and accessories 66
4.1.2 Test procedure: ice formation 72
4.1.3 Analysis of experimental data: images 73

4.2 Ice Slurry System: Direct Contact Heat Transfer 77
4.2.1 Description of test rig 79
4.2.2 Experimental procedures 88
4.2.2.1 Charging process 88
4.2.2.2 Discharging process 90

4.3 Uncertainty Analysis 97


Chapter 5 RESULTS AND DISCUSSION

5.1 Ice Slurry Generator
5.1.1 Sensible cooling of water 100
5.1.2 Simulation results for ice slurry generator
5.1.2.1 Effect of coolant temperature 102
5.1.2.2 Effect of other parameters 103
5.1.2.3 Correlation: duration of initial cooling 105
5.1.2.4 Heat transfer between coolant and water 105

5.2 Ice Formation
5.2.1 Comparison of ice formation results 108
5.2.2 Ice formation phenomena 109
5.2.2.1 Nozzle mounted at bottom 110
5.2.2.2 Nozzle mounted at top 115

5.3 Parametric Study: Ice Formation

5.3.1 Effect of droplet diameter 120
5.3.2 Effect of coolant temperature 123

5.4 Ice Slurry Production
5.4.1 Comparison of simulation and experimental values 126
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iv

5.4.2 Parametric analysis: ice production
5.4.2.1 Effect of coolant temperature 129
5.4.2.2 Effect of nozzle diameter 131
5.4.2.3 Effect of number of nozzles 133

5.5 Ice Slurry Energy Extraction
5.5.1 Ice fraction calculation 136
5.5.2 Heat transfer coefficients for ice slurry 140
5.5.2.1 Local heat transfer coefficient 142
5.5.2.3 Average heat transfer coefficient 145
5.5.2.4 Comparison with previous studies 146
5.5.3 Parametric study: cooling capacity of ice slurry 148
5.5.4 Effectiveness of heat exchanger for
ice slurry extraction
5.5.4.1 Observation: heat transfer coefficient 150
5.5.4.2 Cooling capacity: ice slurry Vs. chilled water 152
Chapter 6 CONCLUSIONS 156

REFERENCE 160

APPENDIX A Image Analysis of Ice Formation 170
APPENDIX B Sensitivity Analysis: Duration of Initial Cooling 177
APPENDIX C Heat Transfer Characteristics of Ice Slurry 181

APPENDIX D Cooling Performance of Heat Exchanger for
Ice Slurry and Chilled Water 192
APPENDIX E Calibration and Error Analysis 199

Summary

v

Summary
The development of an ice slurry system utilizing direct contact heat transfer requires a
deeper understanding of the heat transfer process between the water and liquid in the ice
slurry generator. In order to fulfill this objective, the present study has been divided into
three parts: (i) to study the ice formation and detachment phenomena around the
supercooled liquid droplet; (ii) to design and analyze an ice slurry system to provide
better understanding of the ice production process for immiscible coolant and water; and
(iii) to evaluate the heat transfer characteristics of ice slurry utilized in the heat exchanger
for cooling applications.
Experiments and analyses were carried out to study the ice formation mechanism
between two immiscible liquids, water and coolant, FC-84, by direct contact heat
transfer. This process involves the investigation of the physical phenomenon of ice
formation around the supercooled liquid droplet and subsequent detachment from the
droplet surface under different operating conditions- upward and downward propagation
of liquid droplet in the water column. The experimental findings of ice formation show a
good agreement with analytical results. The analysis of this ice formation process is then
further extended for different parametric conditions such as droplet diameter, liquid
initial temperature and the injection velocity of coolant. The analyses show that these
parameters have significant effect on the growth of ice layer. This ice generation
knowledge is then applied to the ice production analysis of the ice slurry generator which
utilizes immiscible coolant, FC-84 and water for ice production.
To analyze the ice slurry generation process of an ice slurry generator, a mathematical

model has been developed to simulate the cooling of water and subsequent ice production
Summary

vi

in the system. Experiments are performed for both initial sensible cooling and ice
generation processes to validate the proposed model. This model is then utilized to
analyze the effect of different parameters such as initial coolant temperature, nozzle
diameter, number of nozzles, etc on the ice production of the ice slurry generator. The
analyses show that the ice generation process in the ice slurry generator can be improved
significantly by increasing the number of nozzles, decreasing the nozzle diameter, and
decreasing the initial coolant temperature in the system. Nozzle position inside the ice
slurry generator also plays an important role - more ice slurry is produced when the
nozzle is placed at the bottom than at the top. These analyses provide better
understanding of the ice slurry generator utilizing direct contact heat transfer of
immiscible liquids.
For cooling applications, heat transfer characteristics of ice slurry in a compact heat
exchanger have been discussed. To evaluate the thermodynamic and hydraulic behavior
of ice slurry for different ice fractions, corresponding experimental investigations have
been carried out for different design cooling loads and flow rates. The ice slurry heat
transfer correlation obtained from these investigations is then utilized to evaluate the
cooling performance of the heat exchanger. The analyses show that cooling performance
of the heat exchanger increases significantly when ice slurry is used instead of chilled
water at 7°C.
The analyses, therefore, assist in understanding the physical phenomena of ice formation
by direct contact heat transfer, the operational behavior of the ice slurry generator based
on this process and the utilization of ice slurry for space cooling applications.

Summary

vii

List of Figures

Figure No. Title Page No

Figure 3.1 Schematic diagram of the Ice Slurry Generator 32
Figure 3.2 Water temperature in the ice slurry generator 43
Figure 3.3 (a) Physical phenomena of ice formation 45
Figure 3.3 (b) Schematic of liquid droplet-ice-mushy-water layers. 45
Figure 3.3 (c) Cross-section of liquid droplet -ice-mushy-water layers. 45
Figure 3.4 Schematic diagram of initial ice formation process
during an infinitesimal duration 46
Figure 3.5 Ice particles accumulated over ice slurry generator 51
Figure 3.6 (a) Forces on a downward moving liquid droplet in fluid 51
Figure 3.6 (b) Forces on a upward moving liquid droplet in fluid 53
Figure 3.7 Cross section of a tube in the heat exchanger 57
Figure 3.8 Schematic diagram for energy balance inside
the tube of the heat exchanger 58
Figure 3.9 Flow diagram of simulation model 64
Figure 4.1 Schematic diagram of ice formation analysis 66
Figure 4.2 Experimental setup of ice formation analysis 67
Figure 4.3 Digital CCD camera, QImaging Retiga 2000R 68
Figure 4.4 (a) Digital zoom module, 70 XL 69
Figure 4.4 (b) Fiber optic illuminator 69
Figure 4.5 Profile of the image grabbing software (Screen Shot) 70
Figure 4.6 Profile of the image analysis software (Screen Shot) 70
Figure 4.7 Image of measurement scale for calibration purposes 71
Figure 4.8 Metallic balls for ice formation analysis 73
Figure 4.9(a) Methodology of image analysis 73

Figure 4.9(b) Ice formation phenomena (D= 50 mm, T
d
=-10
◦
C, iron ball) 74
Figure 4.10 Profile of the ice formation analysis (Screen Shot) 75
Figure 4.11 Experimental setup of ice slurry system –
ice slurry generator and ice slurry extractor 77
Figure 4.12 Schematic diagrams of ice slurry system –
ice slurry generator and ice slurry extractor 78
Figure 4.13 Glass column test section of ice slurry system 79
Figure 4.14 Cad drawing, Acrylic Base of ice slurry system 80
Figure 4.15 (a) Flange connections on Acrylic Base, top view 81
Figure 4.15 (b) Flange connections on Acrylic Base, bottom view 81


Summary

viii

List of Figures

Figure No. Title Page No
Figure 4.16 Shower spray head and connection on the
base plate of the ice slurry system 82
Figure 4.17 Cold Bath and Chiller used for the ice slurry system 82
Figure 4.18 (a) Centrifugal pump used to pump coolant 83
Figure 4.18 (b) Flow meter to measure coolant flow rate 83
Figure 4.19 Piping system of the ice slurry system 84
Figure 4.20 Extraction and return pipes to utilize ice slurry

in the heat exchanger 84
Figure 4.21 Progressive cavity pump to extract ice slurry 85
Figure 4.22 (a), (b)Fan Tubular Heat Exchanger to utilize ice slurry for
air cooling Electric Heater 86

Figure 4.23 Electric heating system – heater, rheostat, fan. 87
Figure 4.24 Flow Chart for experimental procedure showing varying
coolant flow rates in the ice slurry generator 89
Figure 4.25 (a) Pump located before Heat Exchanger 92
Figure 4.25 (b) Pump located after Heat Exchanger 92
Figure 4.26 Flow Chart for experimental procedure showing varying
Cooling Loads 94

Figure 4.27 Flow Chart for experimental procedure showing varying
ice slurry extraction rate 95
Figure 5.1 Comparison of experimented and simulated results of
temperature histograms during sensible cooling for different
coolant flow rates (8 lit/min, 10 lit/min and 12 lit/min) 101
Figure 5.2 Variation of ice formation time for coolant temperatures 102
Figure 5.3 Heat transfer coefficient of the ice slurry generator for
different coolant flow rates ( 8 lit/min, 10 lit/min, 12 lit/min) 106

Figure 5.4(a) Ice formation phenomena (D= 40 mm, T
d
=-10
◦
C, Iron ball) 107

Figure 5.4(b) Comparison of experimental and simulation results for the
ice formation process for different sizes

(Dia. = 50 mm, 40mm, 30mm) metal balls. 109
Figure 5.5 Velocity distribution of a droplet injected from a nozzle mounted
at bottom (V=0.50m/s, Dd= 4mm, Td= -10°C) 111

Figure 5.6 Effect of droplet diameter on the distance traveled by the
upward propagating liquid droplet for injection velocity 114

Figure 5.7 Velocity distribution of a droplet injected from a nozzle
mounted at top (V=0.15m/s, D
d
= 4mm, T
d
= -10ºC) 116
Figure 5.8 Effect of droplet diameter on the distance traveled by the
downward propagating liquid droplet for injection velocity 119

Figure 5.9 Effect of droplet diameter (D
d
= 4mm, 6mm, 8mm and 10mm)
on the growth of ice layer on droplet surface
(T
d
= -10ºC and V=0.15m/s) 121
Summary

ix

List of Figures

Figure No. Title Page No

Figure 5.9 Effect of droplet diameter (D
d
= 4mm, 6mm, 8mm and 10mm) on
growth of ice layer on droplet surface (T
d
= -10ºC and V=0.15m/s) 121
Figure 5.10 Effect of droplet diameter (D
d
= 4mm, 6mm, 8mm and 10mm)
on the growth of mushy layer on droplet surface
(T
d
= -10ºC and V=0.15m/s) 122
Figure 5.11 Effect of initial liquid droplet temperature (T
d
= -5ºC, -10ºC and -15ºC)
on the growth of ice layer on droplet surface
(D
d
= 10mm and V=0.15m/s) 123
Figure 5.12 Effect of initial liquid droplet temperature (T
d
= -5ºC, -10ºC and -15ºC)
on the growth of mushy layer on droplet surface
(D
d
= 10mm and V=0.15m/s) 124

Figure 5.13 Comparison of experimental and simulation results of the

generated ice slurry for ice slurry generators with nozzle
positioned at bottom. 126
Figure 5.14 Comparison of experimental and simulation results of the
generated ice slurry for ice slurry generators with nozzle top 128


Figure 5.15 Effect of ice production for different coolant temperatures
(T
d
= -5ºC, -10ºC and -15ºC) in the ice slurry generator
(Water height =1m, Cylinder Dia.= 0.3m, N
d
=1mm and N
z
=50 )
for different coolant flow rates( 8 lpm, 10 lpm and 12 lpm 129
Figure 5.16 Effect of ice production for different nozzle diameters
(N
d
= 0.8mm, 1mm and 1.2mm) in the ice slurry generator
(Water height =1m, Cylinder Dia.= 0.3m, T
d
= -10ºC and Nz =50 )
for different coolant flow rates ( 8 lpm, 10 lpm and 12 lpm) 131

Figure 5.17 Effect of ice production for different number of nozzles
(N
z
= 20, 40 and 60) in the ice slurry generator
(Water height =1m, Cylinder Dia.= 0.3m, T

d
= -10ºC and N
d
=1mm )
for different coolant flow rates ( 8 lpm, 10 lpm and 12 lpm) 134
Figure 5.18 Temperature profile of the outside surface temperature
of the heat exchanger at different locations (∆L=30 cm) 137
Figure 5.19 Ice fraction for different flow rates of ice slurry 139
Figure 5.20 Local heat transfer coefficient of ice slurry for different
ice fraction, ice slurry extraction rate 5 lpm. 143
Figure 5.21 Average heat transfer coefficient for different ice fraction
(2%, 3%, 4% and 5%) 144
Figure 5.22 Accuracy of heat transfer correlation 145
Figure 5.23 Comparison of avg. Nu. number for ice slurry flow through pipe 147
Figure 5.24 Thermal performance of ice slurry for different ice fraction
( 2% ~ 5%), Room Temperature, T
a
= 20ºC 149
Figure 5.25 Dependency of the heat transfer coefficients- air and
ice slurry on the overall heat transfer coefficient. 151
Figure 5.26 Comparative analysis of the cooling performance between ice
slurry and chilled water for different flow rates
(5lpm, 8lpm and 10lpm) 154
Summary

x

List of
Tables

Table No Title Page No

Table 3.1 Thermo-physical properties of FC-84 32
Table 4.1 Ice layer thickness, Experimentally measured
(D= 50 mm, T
d
=-10
◦
C, Iron ball) 76

Table 4.2 Heat exchanger geometric configuration 86
Table 4.3 Operating parameters for discharging experiments 93
Table 4.4 Uncertainty of the equipments 98
Table 5.1 Coefficients for different parameters to estimate the duration
of sensible cooling by direct contact heat transfer 104

Table 5.2 Ice layer thickness, Experimentally measured
(D= 40 mm, T
d
=-10
◦
C, Iron ball) 108
Table 5.3 Residence time of droplet for bottom mounted nozzle 112
Table 5.4 Residence time of droplet for top mounted nozzle 116
Table 5.4 Cooling capacity of ice slurry for different
designed cooling loads 152

Table 5.6 Cooling capacity of chilled water (7°C) for different
designed cooling loads 153

Nomenclature


xi

NOMENCLATURE

A surface area [m
2

]
C

specific heat [J.kg
-1
.K
-1
]
C
D
drag co-efficient
D drop diameter [m]
F Force [N]
h convective heat transfer
co-efficient [W.m
-2
.K
-1
]
g gravitational constant [m.s
-2
]
H
f
latent heat of fusion [J.kg
-1
]
k thermal conductivity [W.m
-1
.K

-1
]
L length / thickness of ice layer [m]
M mass [kg]
.
m
mass flow rate [kg/s]
Q total heat [W]
R radius [m]
T temperature [ºC]
t time [s]
U Overall heat transfer
Co-efficient [W.m
-2
.K
-1
]
V Volume [m
3
]
.
V
volume throughput [m
3
.s
-1
]
v velocity [m.s
-1
]

Non- dimensional group
Nu Nusselt number [-]
Pr Prandtl number [-]
Ra Rayleigh number [-]
Re Reynolds number [-]

Greek symbol
α
constant
δ
mushy layer thickness [m]
∆
difference
φ
ice fraction
µ
dynamic viscosity [kg/m.s]
η
efficiency
ρ
density [kg.m
-3
]
σ
interfacial tension [N.m
-1
]
τ
residence time [s]

ν
shear stress [N/m
2
]

Nomenclature


xii

Subscript
a air
d droplet/ diameter
D droplet
f ice/mushy layer interface
g glass
i ice/inlet/inside
I ice/inlet/inside
ins insulator
IS ice slurry
jc critical jet
m mushy layer
n nozzle
o outlet/outside
s surroundings
w water
wall pipe wall

Chapter 1 Introduction

1

CHAPTER 1
INTRODUCTION

With the invention of the vapor compression refrigeration process in 1748 by Michael
Faraday, dependency on the cooling system expands widely ranging from the food
processing to the medical applications and from the air-conditioning to the cooling of
beverages on a sunny day. At the early stage, flammable and toxic ammonia was used in
these cooling systems [1]. It was then replaced by different refrigerants,
chlorofluorocarbons (CFC) and hydro-chlorofluorocarbons (HCFC). The 1987 Montreal
Protocol, 1997 Kyoto Protocol and the United Nations Convention for Climate Change
attributed refrigerants as key players for both the depletion of ozone layer and the
potential of global warming. A very efficient solution regarding this environmental
impact is to combine a secondary cooling system with a primary refrigerant system,
which is confined in a protected area to reduce the refrigerant losses. During the last few
years, both industrial and commercial organization began to install compact chiller units
along with the secondary coolant loop instead of large charges of primary refrigerant
(CFC and HCFC) cooling system. In this secondary cooling system, chilled water is used
as coolant, which is cooled by the primary refrigerants (Ammonia and Propane). To
develop more energy efficient and cost effective thermal cooling system, research has
been focused on the development of phase change materials (PCM) to substitute the
conventional chilled water. For refrigeration and air-conditioning, coolants must have the
desired abilities such as higher thermal conductivity, higher heat transfer coefficient,
pumping ability, higher heat storage capacity, stabilized temperature, etc. For these
Chapter 1 Introduction

2

purposes, different types of phase change slurries are investigated such as carbon dioxide
slurry, shape-stabilized slurry, microencapsulated slurry and ice slurry [2,3,4]. Among
these slurries, ice slurry is a promising technology, as it involves a simple process of
conversion water into ice, obtaining very high density of enthalpy and the wide range of
cooling applications from food industries to district cooling.
1.1 Background: Cooling With Ice Slurry
Although coordinated and focused research activities on ice slurries were undertaken a
few decades ago [5], the technique has been used in various applications in different
countries from the ancient Roman times [6]. In China and other Far East countries, ice
slurry is used for the cooling of cargo railway cars. Similar techniques are used in
Germany for cooling the catering vessels in the passenger trains [7]. In Japan, ice slurry
is used in large air conditioning installations, such as the CAPCOM building, Herbis
Osaka Building, Kyoto Station Building, etc, having total floor area of more than 15,000
m
2
[8]. It is pumped to the various air handling coils directly which would save fan
energy and duct size. Similar technology for air-conditioning system is used in
commercial buildings (Techno-Mart 21, largest commercial building in Korea),
institutional buildings (Stuart C. Siegel Center, Virginia, USA, Middlesex University,
UK, etc), airport (Zurich-Kloten Airport) and many more [9, 10].
Another important sector for cooling needs by ice slurry is the mining industry. Ophir
and Koren [11] describe one such slurry plant at the Western Deep Level Gold Mine in
South Africa.
Fishermen in Chili, Netherlands and Iceland utilize ice slurry for direct chilling of fishes
and other catches [12]. They produce ice slurry from the sea water on board in their small
Chapter 1 Introduction

3

ice slurry plants. This technology is now also used in onshore fish processing plants.
Wang et al. [13] reported that the performance of ice slurry is better than the traditionally
used flake ice for the preservation of quality fish.
Ice slurry is also used for other commercial applications such as meat processing,
brewery, dairy processing, rapid cooling of vegetables, and retail food storage in different
countries. Paul [14], in Germany, describes one such meat processing plant that install ice
slurry system for cooling and air-conditioning requirements of the 3800 m
2
site. Gladis
[15] describes an ice slurry plant for processing of 90,000 kg of cheese daily located in
Hanford, California, USA.
Other future applications of ice slurries [16] are ice pigging (frequent and efficient
internal cleaning of the inside components of pipes, ducts and heat exchangers), medical
applications (treatment of cardiac arrest, sports injuries etc), fire fighting, artificial snow
production etc.
In spite of all these current applications of ice slurry systems, further research and
development are needed particularly on the generation of ice slurry in an efficient,
reliable and economic way for broad range of applications.
1.2 Ice Slurry Technology
With the invention of mechanical refrigeration, it is possible to produce ice in different
forms such as, blocks, cubes, flake, etc. The simplicity of freezing water, high latent heat
of ice and a higher degree of stratification between water and ice due to the different
densities make the application of ice slurry a promising technology for the future.
Technically, ice slurry is a mixture of small (typically 0.1 to 1 mm in diameter) ice
particles with a carrier fluid, which is generally water. This two-phase liquid stores
Chapter 1 Introduction

4

energy in the form of the latent heat of fusion (333 kJ/kg) and has the pumping capability

due to fluidity.
The key issue for using ice slurry in the cooling technology depends on the reliability,
energy efficiency and cost effectiveness for the production of ice slurry. In recent years,
several variations of ice slurry production technologies have been developed. Depending
on the ice formation mechanisms, these slurry generators are classified into two
categories: homogeneous nucleation and heterogeneous nucleation.
The first patent on the ice slurry generator based on the heterogeneous nucleation was
filed at 1976 [17]. In this method, a cylinder or a plate attached to the evaporator of a
refrigerating unit is used to cool a mixture of water and brine. It would then form a layer
of ice on the cooled surface from where ice is removed by means of mechanical scraper.
Later, based on this concept new techniques like fluidized bed technology and improved
design utilizing the drag force of the fluid for hydro-scraping of ice have been developed.
In homogeneous nucleation, cold refrigerant, either expandable gas or single phase
immiscible liquid, is dispersed into the secondary fluid, generally water. Due to the direct
contact heat transfer between two fluids, ice crystals are spontaneously dispersed in the
water. Since, no additional heat exchanger is used in this process, the method appears to
be more efficient. In 1999, Coldeco of France [18] owned a patent for commercial
manufacturing of ice slurry generator based on direct contact evaporation. However, no
unit is yet commercialized and researches have still been continuing for the development
of direct contact ice slurry generator.
1.3 Advantages of Ice Slurry
In this system, heat exchange between two immiscible fluids (Primary fluid, FC-84 and
Chapter 1 Introduction

5

secondary fluid, water) occurs. The primary immiscible fluid, which is heavier than
water, is cooled below freezing temperature of water by a conventional chiller. The fluid
is then passed through a nozzle which delivers the cooled refrigerant into the water in the
form of droplets. Ice forms when the water comes in contact with the cooled fluid

droplet. As ice is lighter than water, ice moves to the top of the tank and the heavier
immiscible fluid moves to bottom of the tank for recirculation. The advantages of the
system are as follows,
Energy Efficiency:
Unlike static ice systems, where ice forms at the heat transfer surface, ice slurry produced
in an ice slurry generator initially adheres to the droplet surface and, subsequently
detached due to buoyancy forces, resulting in higher convective and conductive heat
transfer and, hence, higher energy efficiency. Moreover, defrosting is not required to
harvest the ice for storage into tanks, resulting in higher energy efficiency.
Simplified Tank Design
Ice slurry can be pumped into storage tanks, reducing the need for extra structural support
required for ice harvesters located above the storage tanks.
Storage Flexibility
Ice slurry can be stored in tanks of any shape. As an example, the height of an ice storage
tank can be increased, resulting in a reduction of the tank footprint which leads to
valuable floor space savings. This is difficult to achieve in static and other dynamic ice
storage systems.
Chapter 1 Introduction

6

Application Flexibility
Ice packing factor of the ice slurry can be varied and it would support flexible demand
load for air conditioning applications.
Space Saving Design
Since there are no moving parts involved in this type of system, it would be compact that
saves space in the refrigeration equipment room.
Ease of Variation
Depending on the conditions, various expansions and modifications are possible in this
system. Such as, facility of installing different types of nozzles, installation of storage at a

suitable places etc.
1.4 Objectives
The objectives of this study are the following:
i. Developing a simulation model for the ice slurry generator to evaluate the ice
production phenomenon. The model would serve as a design tool for the
performance analysis of the system and assist to analyze similar type of system
for different sizes and conditions.
ii. Developing a mathematical model to simulate the growth of ice layer around the
supercooled liquid droplet by direct contact heat transfer. This model will be
extended for two different cases,
a. Nozzle located at the top of the tank and supercooled liquid droplet
moving downwards in an ice generator;
b. Nozzle located at the bottom and supercooled liquid droplet moving
upwards and downwards in an ice generator.
Chapter 1 Introduction

7

iii. Conducting experiments to measure the growth of ice layer around the
supercooled liquid droplet in contact with water and compare the experimental
values with the simulated results for the validation of the mathematical model
developed for the above mentioned cases.
iv. Developing an ice slurry system, based on the concept of direct contact heat
transfer between two immiscible liquids. An extraction system will then be
incorporated with the slurry generator to evaluate the performance of the system.
v. Analyzing the heat transfer characteristics of ice slurry for cooling applications
and investigate the viability of the ice slurry to utilize as coolant for space cooling
applications.
This study focuses on both analytical and experimental work on ice formation and ice
slurry system. An analysis of ice formation may lead to a better understanding of the

physical phenomena of ice layer growth between two immiscible liquids. In terms of
system development, an ice slurry system has been designed and fabricated for
cooling applications which would lead to an implementation of this type of new
system for future usage. The system simulation model should help other researchers
and engineers on further exploration of such system for different conditions.
Therefore, the findings of this project would inspire of the researchers to develop an
efficient and cost effective ice slurry system for commercial applications.
1.5 Scope
An introduction to the ice slurry system is included in Chapter 1, which provides a
general pre-view of the ice slurry technology for cooling applications. Chapter 2 contains
the detailed literature review of ice formation phenomena, different methodology of ice
Chapter 1 Introduction

8

slurry production, heat transfer phenomena during melting of ice slurry in heat exchanger
for cooling applications. Analytical models are discussed in Chapter 3. These include the
physical phenomenon of ice formation around the super cooled liquid droplet, system
simulation of ice slurry generator and ice slurry extractor for air cooling. Experimental
procedures together with the description of different equipments are presented in chapter
4. Design and fabrication processes of the ice slurry system – ice slurry generator and ice
slurry extractor, are also discussed. Chapter 5 presents detailed analyses of results and
discussion obtained from the experiments and analyses. Chapter 6 includes the
conclusion drawn from the analytical and experimental analyses of the ice slurry system.


Chapter 2 Literature Review

9

CHAPTER 2
LITERATURE REVIEW

In recent years, energy markets are experiencing high demand and limited supplies,
resulting in volatile and soaring prices. In response to higher energy costs, recent research
has been focused on the technologies of lower cost and higher energy-efficiency.
With this perspective, the ice slurry can be considered as a better alternative to the
conventional chilled water system, as it has the advantage of higher cooling capacity,
about five times [19], due to the latent heat of fusion of melting ice. Recently, attention
has been given to advance this ice slurry technology for successful implementation for
different applications- air conditioning, industrial and commercial refrigeration.
To implement this technology, there are several issues that need to be resolved. These are
the ice generation phenomenon, effective method of ice slurry production and the
utilization of the produced ice slurry for cooling applications. In this chapter, a review of
the published literature that addresses these issues of the ice slurry technology is
presented. The chapter comprises the following sections: the fundamentals of ice
formation, the conventional static ice generation methods, the dynamic ice generation
method- direct contact heat transfer and the investigation of the ice slurry heat transfer
during cooling applications.
2.1 Fundamentals of Ice Formation
Phase change of water to ice occurs under isothermal condition by releasing the latent
heat of fusion. This ice formation phenomena starts from a small nucleus, upon which
water molecules of the surrounding liquid phase are integrated for ice crystal growth.
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In nucleation, nuclei formation is initiated by the foreign substrate [20] associated with
the energy. The proposed theory for ice nucleation is based on the simplified
thermodynamics consideration. However, it fails to include an important factor, the

interaction and the structure of the first monolayer of the liquid in the intimate contact
with the foreign surface, which influences both the surface free energy and the volume
free energy directly. Further research had been continued to overcome the limitations of
this nucleation model. One of the proposed cases is to consider a secondary nucleation
[21], where the nucleation is induced on the seed crystal and it occurs at the surface of a
previously existing crystal. Chen et al. [22] experimentally investigated the nucleation
probability of supercooled water inside cylindrical capsules. They concluded that lower
coolant temperature, larger size of capsule and additional mass of different nucleates
agents would enhance the ice nucleation probability.
Based on the heterogeneous nucleation process, a refrigerator machine was developed. It
contains a special evaporator with a double cylinder or plate in which a part of the
water/brine mixture is cooled at the wall. The ice crystals produced were then scraped
away mechanically from the surface. To understand the phenomena of ice crystallization
on the heat exchanger surface, researchers have made significant efforts to model the
process coupled with heat and mass transfer.
Myers et al. [23] proposed a one-dimensional model for ice growth when the supercooled
fluid is impinged on a cooled surface. In this model, the ice thickness can be determined
by combining the mass balance with the phase change Stefan problem, though a number
of assumptions were made during this analysis. This model helps to understand the
physical process of ice formation. Naterer [24] presented a model to portray the
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formation processes of ice, transition and the combined ice condition; when the phase
change heat transfer occurred due to the incoming supercooled liquid droplets on heated
curved surfaces. This heat transfer model can correctly approach the simultaneously
growth of unfrozen water and ice layers under appropriate thermal conditions.
Stewart et al. [25] studied the ice crystal growth in a falling film flowing down the
surface of cooled plate. To approximate the ice growth rate, a numerical model was

suggested for supercooled liquid film, considering ice particles as equivalent heat
sources. They also discussed the effect of the parameters that control the enhancement of
heat transfer. However, this model only considered the laminar flow condition. Ismail et
al. [26] extended the previous model of ice growth for laminar falling film flowing down
a cooled vertical plate by including the effect of axial diffusion on the vertical plate.
Their work showed a rigorous analysis of the ice formation on the vertical plate because
of the in-depth analyses on the effects of the parameters that control the enhancement of
the heat transfer for ice generation. Hirata et al. [27, 28] investigated the rate of ice
formation on a cooled horizontal solid surface and its removal phenomena. In their study,
ethylene glycol solution was used to produce freezing while the cooled plates of different
materials such as polyvinyl chloride, acrylic resin, silicon resin and copper plates were
used. They reported that the ice formation and detachment from the plate were related to
the heat flux. In their study, they assumed an uniform heat flux at the interface between
ice layer and plate surface; but this assumption may not be true after the ice layer
formation on the plate surface because of the lower conduction coefficient of ice. While
there is much on the ice formation over the plate surface under various conditions, ice
formation phenomenon on immiscible super cooled liquid surface has not yet been
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investigated. In the present study ice formation, as well as the detachment of the ice layer
from the moving immiscible liquid droplet surface, is analyzed to provide better
understanding of the physical phenomena.
2.2 Ice Slurry Production
In an ice slurry system, production of ice slurry is the key concern. Much research has
been conducted on different methods of ice slurry generation during the last few decades.
An overview of these known methods is given below in this section.
2.2.1 Static ice production
Egolf and Kauffeld [29] described the scraped-surface type ice slurry generator, which is

now commercially available. It is a shell and tube heat exchanger which has a rotor or
blade assembly housed inside the tube, where the ice slurry is generated. Coolant stream
evaporates on the outer shell side of the heat exchanger. This type of generator is capable
of producing a mixture of small ice crystals and water from a binary super-cooled
solution. As it is an experimental prototype, the capital cost of this type of scraped-
surface ice slurry generator is relatively high [30]. In this system, the rate of ice
crystallization depends on log mean temperature differences between the refrigerant and
ice slurry streams inside the tube, as recommended by Russell et al. [31]. However,
continuous accumulation of ice layers on the ice slurry generator would reduce the heat
transfer rates and immediately affect the ice slurry temperature. In addition, due to the
mechanical abrasions, rotating scrappers, brushes and orbital rods would wear out over
time and need to be replaced at a given time interval. Zakeri [32,33] proposed an ice
slurry generator employing a vacuum freeze process. In this system, an evaporator cooled
by a conventional refrigerant freezes the water necessary to remove the heat of fusion