UNIVERSITI PUTRA MALAYSIA

DESIGN, CONSTRUCTION AND TESTING OF FREEZE CONCENTRATOR

ROSNAH BT HAJI SHAMSUDIN

FK 2000 46

DESIGN, CONSTRUCl'ION AND TESTING OF FREEZE CONCENTRATOR

ROSNAH BT HAJJ SHAMSUDIN

MASTER OF SCIENCE UNIVERSm PUTRA MALAYSIA

2000

To the most beloved ones:

Mak, Abah dan adik .....

Thanks for your continuos support and encouragement

My husband Azmi bin Peryatin .. ...

For the aspiration and inspiration

My daughter Nurul Izzah . ....

Ease my stress and tension

My parent in law and Brothers in law ... . .

Thanks for a great understanding

Syaiful, Yus, Mai, Azie, Das, Ros, Kak Zai and Aidy

Thanks for your helpful and comment

ii

Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment of the requirement for the degree of Master of Science

DESIGN, CONSTRUCTION AND TESTING OF FREEZE CONCENTRATOR

By

ROSNAH BT BAJI SHAMSUDIN

November 2000

Chairman: Hishamuddin bin Jamaludin, MSc

Faculty: Engineering

The main aspects of this study, were the design, construction and

performance of a freeze concentrator. The design process consists of three main

parts: a vertical tube heat exchanger, an auger to scrape the ice formed and a

refrigeration unit to bring the temperature to below freezing.

Basically, the freeze concentration process used involves ice formation from

a juice solution at the surface of a vertical tube heat exchanger. The ice will be

scraped by a rotating auger, which pushes it out through a window and collected in a

reservoir. This results in a product of higher solute concentration than its

concentration in the feed.

The potential application of the freeze concentrator was experimented using

sugar solutions at three different feed concentrations i.e. 7.5%, 10.3% and 12% brix,

as well as pineapple juice at 11.4% brix. The freezing point depression for the

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solutions were respectively -l.Ore, -l.15°e, -1.49°e and -1.49°e. The feed flow

rates used for the solutions were respectively 0.65 Vmin, 0.5 Vmin, 0.43 Vmin and

0.45 Vmin. Using these process parameters, the total mass of ice after 180 min is

1.75kg for a feed of 7.5% brix and 1.46kg for a feed of 12% brix. From theoretical

analysis, the expected total mass of ice produced is 2.6kg for the 7.5% brix and

1.97kg for the 12% brix solution. Therefore, the performance efficiency for the

freeze concentrator is around 67% of theory for all three sugar solutions.

Base on the heat balance analysis, the overall thermal performance of this

freeze concentration process for the three different feed concentrations shows that

about 80010 of the refrigeration load is loss. If these losses were not considered, about

87% of the cooling energy transferred is for sensible heat removal and 13% for ice

formation.

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Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk Ijazah Master Sains

REKABENTUK, PEMBINAAN DAN UJIAN KEATAS ALAT PEMEKATAN JUS SECARAS�BEKU

Oleh

ROSNAH BT HAJI SBAMSUDIN

November 1000

Pengerusi: Hishamuddin bin Jamaludin, MSc

Fakulti: Kejuruteraan

Perkara utama di dalam kajian ini merangkumi aspek rekabentuk, pembinaan

dan prestasi alat pemekat sejuk beku. Proses merekabentuk pemekat sejuk beku ini

terbahagi kepada tiga bahagian utama iaitu turus tegak penukar haba, auger untuk

mengikis ais yang terbentuk dan unit penyejuk untuk menurunkan suhu bawah takat

beku.

Pada asasnya, proses pemekat sejuk beku ini bermula dengan pembentukan

ais di penukar haba. Ais akan dikikis oleh auger yang berpusing ke saluran keluar

dan dikumpulkan ditakungan yang disediakan. Ini menghasilkan produk yang

mempunyai kepekatan yang lebih tinggi dari kepekatan bahan suap.

Keupayaan pemekat sejuk beku ini diuji dengan menggunakan larutan gula

pada tiga kepekatan yang berlainan iaitu 7.5%, 10.3% dan 12.0010 brix disamping jus

nenas (11.4% brix) juga digunakan. Tirik penyejukbekuan pada 7.5%, 10.3% dan

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12.0% brix serta jus nenas masing-masing ialah -1.01'C, -1.15°C, -1.49°C dan

-1.49°C.

Bagi kepekatan bahan suap 7.5%, 10.3% dan 12% brix dan jus nenas masing­

masing kadar alir yang digunakan adalah 0.65 llmin, 0.5 lImin, 0.43 lImin dan 0.45

Vmin.

Dengan parameter proses tersebut dan masa operasi 180 min jumlah berat ais

yang diperolehi ialah 1.75kg dengan suapan 7.5% brix manakala l.46kg dengan

suapan 12% brix. Manakala secara pengiraan pula berat ais yang patut diperolehi

ialah 2.6kg di 7.5% brix dan 1.97kg di 12% brix. Maka pada keseluruhannya

keputusan menunjukan keupayaan kecekapan alat pemekat sejuk heku ini adalah

lebih kurang 67010 berbanding teori bagi ketiga-tiga kepekatan yang berlainan.

Berdasarkan analisis keseimbangan haba, prestasi terma menunjukan alat

pemekat sejuk beku tersebut mengalami kehilangan haba sebanyak 80%. Jika

kehilangan ini diabaikan, didapati 87% haba efektif digunakan bagi pemindahan

haba pelakuran manakala selebihnya digunakan bagi pembentukan ais.

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ACKNOWLEDGEMENTS

In the name of Allah, the Most Gracious, the Most Merciful, I would like to

express my gratitude and appreciation to my supervisor, Mr. Hishamuddin bin

Jamaludin, for his invaluable guidance, advice, constructive and suggestions throughout

the period of my project.

I would like to make special mention of help from Mr. Dzulkifli bin Mat Hashim

of Faculty Food Science and Biotecknology, for his information's, assistance and for

allowing me to use the relevant apparatus in carrying out the tests.

My appreciation to all Faculty of Engineering staff, especially to Mr. Nasharudin

Mohamad and Mr. Anuar Ariffin for their assistance's in my work. Special recognition

is also extended to Mr. Soib, Mr. Azman and Mr. Amran from Faculty Food Science and

Biotechnology for their comment, helpful hands and encouragement during my project.

Last but not least, I would like to express my utmost appreciation and love to my

family especially my parent and my husband Azmi bin Peryatin for their cares,

encouragement and understanding during my studies.

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I certify that an Examination Committee met on 22nd November 2000 to conduct the final examination of Rosnah bt Haji Shamsudin on her Master of Science thesis entitled "Design, Construction and Testing of Freeze Concentrator" in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti Pertanian Malaysia (Higher Degree) Regulations 1981. The Committee recommends that candidate be awarded the relevant degree. Members of the Examination Committee are as follows:

HUSSAIN MOBD. SALLEH, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Chairman)

mSHAMUDDIN B JAMALUDIN, M.Sc. Faculty of Engineering Universiti Putra Malaysia (Member)

DZULKIFL Y B HASHIM, M.Sc. Faculty of Food Science & Biotechnology Universiti Putra Malaysia (Member)

WAN MOBAMAD B WAN ABDULLAH, PhD Faculty of Engineering Universiti Putra Malaysia (Member)

--------�-----------------------

--.-_,-.HAZALt MOHAYIDIN, Ph.D. Professor Deputy Dean of Graduate School Universiti Putra Malaysia

Date: 0 9 DEC 2000

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This thesis submitted to the Senate of Universiti Putra Malaysia has been accepted as fulfilment of the requirements for the degree of Master of Science.

��---.------------�-��-----------------------------

KAMIS AW ANG, Ph.D. Associate Professor Dean of Graduate School Universiti Putra Malaysia

Date: 1 1 JAN ZOOl

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I hereby declare that the thesis is based on my original work except for quotations and citations, which have been duly acknowledged. I also declare that it has not been previously or concurrently submitted for any other degree at UPM or other institutions.

(Ros

Date: 0 9 DEC 2000

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TABLE OF CONTENTS

DEDICATION ABSTRACT ABSTRAK ACKNOWLEDGEMENTS APPROVAL SHEETS LIST OF FIGURES LIST OF TABLES LIST OF ABBREVIATIONS

CHAPTER

I INSTRODUCTION The Advantages of Freeze Concentration The Disadvantages of Freeze Concentration The Objectives

II LITERATURE REVIEW Definitions Freeze Concentration of Foods

The Freezing Point The Freezing Times of Food

Ice Crystallization Nucleation of Crystal Formation Crystal Growth

Types of Freeze Concentration Crystallization Unit

Separation Unit Refrigeration Requirements in Freezing Foods

Mechanical Refrigeration Principles

ill METHODOLOGY DESIGN and CONSTRUCTION General Design and Fabrication of Freeze Concentrator

The Vertical Tube Heat Exchanger The Construction of the Column The Construction of the Auger

The Cooling Unit System A Split-System Air-Conditioning A Coolant Tank

11 111 V V1I V111 X111 xv XVI

1 1 2 4

5 6 6 9 10 10 11 12 12 16 18 18

21 21 22 22 22 22

27 28 28

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The Copper Coil Coolant

Selection of Construction Materials Process Support Equipment

Thermostat Temperature Scanner The Storage Tank Circulating Pump Flow Meter Electrical Power Supply Circuit Box Auxiliary Cooling Unit

Platform Test Method

Preliminary Tests

PROPERTIES OF PINEAPPLE JUICE Preparation of Samples (pineapple Juice) Proximate Analysis

Thermal Properties Specific Heat of Juice (Cp) Thermal Conductivity of Juice (k) Density of Juice (p)

Freezing Point Viscosity Determination of Sugar Determination of pH Total Soluble Solid

IV RESULTS AND DISCUSSION General Properties of Pineapple Juice Proximate Analysis Freezing Point Other Properties Test run with pineapple Juice Material balances analysis Heat balances analysis

V CONCLUSION

REFERENCES APPENDICES BIODATA OF THE AUTHOR

29 31 32 33 33 33 34 34 35 36 37 41 41 41

45 45 45 45 45 46 47 49 50 50 51 51

52 52 52 54 57 58 64 68

81

83 86 148

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Figure 2.1 2.2

2.3

2.4 3.l 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9

3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.19 3.20 3.21

3.22

4.1 4.2 4.3 4.4

4.5

4.6

4.7

4.8(a) 4.8(b) 4.8(c)

4.9 4.10(a) 4.10(b)

LIST OF FIGURES

Diagram of a basic freeze concentration process Comparison of freezing curves for pure water and an aqueous solution containing one solute Typical phase diagram showing eutectic point for sugar-water system Schematic diagram of a simple refrigeration system Schematic diagram of Freeze Concentrator Top End Cap and Bottom End cap The Auger Drive Assembly Drive Pulley Shaping the Washer to Form the Auger Completed Auger with Three Solid Stainless Steel as a Support Finished Components of the Heat Exchanger Split-System Air Conditioning Evaporator Coil Arrangement (Type A) Position a Evaporator Coil and Thermostat in the Coolant Tank A Evaporator Coil Arrangement (Type B) Temperature Scanner and Digital Thermometer Placement of Pump & Flow Meter Auxiliary Cooling Unit The circuit diagram of single-phase power supply Electrical Power Supply Circuit Box Views of the Freeze Concentrator Design of Auger The cooling coil in the feed tank Position of temperature sensors from the temperature logger at point 1,2 and 3 Schematic illustration of temperature versus time for the determination of initial freezing point Freezing point vs concentration of sugar solution Feed flow rate of sugar solution The area of ice formation Water content In concentrate for different initial feed concentration Changes in feed concentration for sugar solution and pineapple juice Changes of sugar concentration in ice at different concentration of sugar solution Changes in sugar concentration in ice with respect to changes of inlet feed concentration Mass of ice at 7.5% brix (Experimental and theoretical) Mass of ice at 10.3% brix (Experimental and theoretical) Mass of ice at 12.0% brix (Experimental and theoretical) Percentage error mass of ice between experiment and theory result Changes in inlet and outlet temperature of coolant at 7.5% brix Changes in inlet and outlet temperature of coolant at 10.3% brix

Page 6 7

9

20 23 24 25 25 26 26 27 28 29 31 32 35 36 37 38 39 40 44 44 49

50

56 59 60 61

62

63

64

65 66 66 67 69 69

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4.10(c) Changes in inlet and outlet temperature of coolant at 12.0% brix 70 4.1O(d) Rate of heat transfer from coolant to solution at different 70

concentration of sugar solution 4.11(a) Changes in inlet and outlet temperature of feed at 7.5% brix 72 4. 11 (b) Changes in inlet and outlet temperature of feed at 10.3% brix 72 4.11(c) Changes in inlet and outlet temperature of feed at 12.0010 brix 73 4. 11 (d) Rate of sensible heat transfer to solution at different concentration 73

of sugar solution 4.12 Rate of heat transfer in the formation of ice at different 74

concentration of sugar solution 4.13 Rate of heat loss at different concentration of sugar solution 75 4.14 Overall thermal performance of freeze concentrator 76 4.15 The log mean temperature difference at different concentration of 78

sugar solution 4.16(a) Changes in overall heat transfer coefficient during cooling at 79

different feed concentration 4.16(b) Changes in overall heat transfer coefficient during freezing at 80

different feed concentration

xiv

LIST OF TABLES

Table Page

2.1 Classification of crystallizers used in Freeze Concentration 9

3.1 The specific heat of pure components as a function of 46 Temperature

3.2 The thermal conductivity of pure components as a function of 47 temperature

3.3 The density of pure components as a function of temperature 48

4.1 Proximate content of pineapple juice 53

4.2 The thermal properties of pineapple juice 54

4.3 The thermal properties of sugar solution 54

4.4 The initial freezing point based on concentration and position of 55 temperature probe

4. 5 (a) Energy analysis included losses 77

4.5(b) Energy analysis excluded losses 77

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LISTS OF ABBREVIA nONS

A = Latent heat of fusion, kJ/kg

PI = Density of ice, kg/m3

ps = Density of the solution, kglm3

P = Density, kglm3

pa = Density of ash, kg/m3

Pc = Density of carbohydrate, kglm3

PF = Density of fat, kg/m3

PP = Density of protein, kglm3

Pw = Density of water, kglm3

pc = Density of coolant, kg/m3

Pj = Density of juice, kg/m3

I.1c = Viscosity of coolant, kg/ms

J.lj = Viscosity of juice, kg/ms

ATIn = logarithmic mean temperature difference, 0 C A = logarithmic mean area heat transferring wall, m2

Ac = cross - sectional area of tube heat exchanger, m2

Aj = cross - sectional area of product, m2

C = Concentrate, % brix

c;, = Specific heat, kJ/kg K c;"e = Specific heat of coolant, kJ/kg K

c;,,j = Specific heat of juice, kJ/kg K Cp,a = Specific heat of ash, kJ/kg K Cp,e = Specific heat of carbohydrate, kJ/kg K Cp,F = Specific heat of fat, kJ/kg K Cp,p = Specific heat of protein, kJ/kg K Cp,w = Specific heat of water, kJ/kg K Cb = Bulk solute concentration Ci = Interfacial concentration of solute

(dC/dT)eq = Freezing point depression constant de = diameter of the tube heat exchanger, m ds = shaft diameter, m cit = inside diameter product cylinder, m Fe = Flow rate of coolant, Vmin F- = Flow rate of juice, IImin 1 h = Heat transfer coefficient, W Im2K he = Heat transfer coefficient of coolant, W/m2K hj = Heat transfer coefficient at product Guice) side, W Im2K I = Ice, % brix I = Current flow, A k e = Mass transfer coefficients k = Thermal conductivity, W/mK ke = Thermal conductivity of coolant, W ImK

kj = Thermal conductivity of juice, W ImK ka = Thermal conductivity of ash, W/mK ke = Thermal conductivity of carbohydrate, W/mK kF = Thermal conductivity of fat, W/mK

kp = Thermal conductivity of protein, W/mK

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kw = Thermal conductivity of water, W/mK e = Length of heat transfer, m

mA = Fraction of product moisture content ms = Fraction of products solids ma = Mass fraction of ash Il1c = Mass fraction of carbohydrate mF = Mass fraction of fat

Illp = Mass fraction of protein 1l1w = Mass fraction of water ·IIlc = Mass flow rate of coolant, kg/sec .mj = Mass flow rate of juice, kg/sec

. mice = Mass flow rate of ice, kg/sec MA = Molecular weight of water Ms = Molecular weight of product solids n = number of rows of scraper blades N = Shaft speed, rev/sec

Nu = Nusselt - number P = Power required to rotate blade, W Pr = Prandtl- number Qc = Total heat transfer from coolant to solution, W Qsol = Rate of sensible heat transfer to solution, W Qice = Rate of heat transfer in the formation of ice, W Qloss = Rate of heat loss, W Re = Reynolds - number Rg = Universal gas constant Re = External radius heat transferring wall, m R = Internal radius heat transferring wall, m TA = Actual freezing point, 0 C TAo = Freezing point of pure water, 0 C Tb = Bulk temperature, 0 C Tl = Outlet temperature of ice, 0 C

T2, Tc,out = Surface temperature of coolant out, 0 C T3 T· = Inlet temperature of feed/juice, 0 C , J,m T4, Tc,in = Surface temperature of coolant in, 0 C

Ts = Inlet temperature of coolant tank, 0 C T6, !i,out = Outlet temperature of feed/juice, 0 C

T = Average temperature of coolant, 0 C U = Overall heat transfer coefficient, W/m2K Uc = Velocity of coolant, m1sec Uj = Average flow velocity, m1sec V = Voltage flow, V

XB = Mole fraction of water XA = Mole fraction of water within the product

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CHAPTER I

INTRODUCTION

Water is removed from foods to provide microbiological stability, to reduce

deteriorative chemical reactions and to reduce storage and transportation costs.

This water can be removed by heating and cooling. Distillation or evaporation by

addition of heat is not the only method of removing water from fruit juices. Water

may also be removed from juices by freezing out as crystals of solid ice. This

process is called Freeze Concentration. In freeze concentration water is partly

separated from the aqueous solution by crystallization and the ice is then separated

from the concentrated liquid phase (Maguer et ai, 1986).

Freeze concentration has been used to concentrate fruit juices, coffee

extract, vinegar, beer, wine, pickling brines and liquid smoke, to recover potable

water from brackish water and sea water and to concentrate toxic wastes and paper­

mill black liquor.

1.1 The Advantages of Freeze Concentration

Conventional method of concentration processes such as evaporation or

distillation has some disadvantages. During evaporation of water from aqueous

solutions the volatile responsible for aroma and fragrance are also driven off While

equipment to condense and return this desirable volatile has been developed, the

recombined end product is inferior to the starting material.

1

Distillation requires the addition of heat This heat brings about a

breakdown in the chemical structure of the food liquid causing a change in flavour,

a diminution of vitamin contents and other nutritive property Even when essence

recovery systems are employed and all volatile condensed and added back to the

concentrate, the original flavor is not restored (Norman et al, 1977) Other methods

for the removal of water are reverse osmosis (hyper filtration) and ultra filtration

In these methods water and some solutes in a solution are selectively removed

through a semi permeable membrane (Fellows, 1988)

Freeze concentration involves the concentration of an aqueous solution by

partial freezing and subsequent separation of the resulting ice crystals It is

considered to be one of the most advantageous concentration processes because of

the many positive characteristics related with its application It is capable of

concentrating various comestible liquids without appreciable change in flavor,

aroma, color or nutritive value The concentrate contains almost all the original

amounts of solutes present in the liquid food (Tasoula et aI, 1990) These low

temperatures are needed to preserve texture of the food by retarding chemical

changes, by retarding the action of food enzymes and by eliminating the growth of

microorganisms capable of growth near or below 0 °c

1.2 The Disadvantages of Freeze Concentration

Freeze concentration process involves the fractional crystallization

of ice from liquid foods Although this process is traditional (it has long been used

2

to enhance the alcoholic content of cider) it has found only limited and spasmodic

use in the food industry (Brennan et al, 1990).

Freeze concentration disadvantages are threefold. Firstly, the degree of

concentration achievable is limited. Secondly, suspended matter in the feed can

serve as heterogeneous nuclei. This can lead to concentrates, which are pale in

colour and lacking in flavour since pigmented particles, and suspended essential

oils are removed from the system at the center of ice crystals. Thirdly, the process

has proven to be more expensive than evaporation. The capital cost of the plant is

not the only feature contributing to the economics of the process, since the fraction

of the soluble solids of the feed material discharged with the ice crystals or the

melted water rather than with the concentrate is highly important (Brennan et al,

1990).

Process improvements over the years have been directed to cost-effective

reduction of this loss. The problem to be solved is the generation of ice crystals

substantially free of inclusions of mother liquor and the separation of these from

the system clean of any adhering concentrate (Brennan et al, 1990).

3

1.3 Objective

The objectives of this project are:

1. To design and construct a Freeze Concentrator for the concentration of sugar

solution.

2. To test and evaluate the performance of the Freeze Concentrator in freezing

sugar solution at various feed concentrations.

3. To determine the rate of ice formation with a shell in tube heat exchanger that

is provided with an auger scraper at various feed concentrations.

4

2.1 Definitions

CHAPTER II

LITERATURE REVIEW

In freeze concentration water is first partly segregated from the aqueous

solution by crystallization and thereupon the ice is separated from the concentrated

liquid phase. The crystallization and separation operations can be performed in the

same apparatus. In actual practice, however, these operations are performed in two

separate apparatus (Thijssen, 1974b). These are the crystallizer and separator.

Schwartzberg (1972), described freeze concentration as a process in which:

a) cooling is used to selectively freeze solvent from solutions� b) solute

concentrations in residual solution consequently increase� and c) concentrated

solution and solidified solvent are separated when desired concentrations are

reached.

Freeze concentration involves partial freezing of the product and removal of

the pure ice crystals, thus leaving behind all of the non aqueous constituents in

diminished quantity of water The major limitations of the process include relatively

high cost, difficulties in effective separation of ice crystals without loss of food

solids and a relatively low upper limit on total solid concentration in the product

(Fennema, 1975).

5

2.2 Freeze Concentration of Foods

The basic components of a freeze concentration system is as shown in figure

2.1. A refrigeration unit is required to provide the driving force for ice

crystallization.

FEED

� I CRYSTAL NUCLEATION I �,

CRYSTAL GROWTH

CRYSTAL SL URRY

�r SEPARATION -+ ICE

�r CONCENTRATE

Figure 2.1: Diagram of a basic freeze concentration process

2.2.1 The Freezing Point

The freezing point of a liquid is that temperature at which the liquid is in

equilibrium with the solid. The freezing point of a solution is lower than that of a

pure solvent. The freezing point of food is lower than that of pure water. The

addition of a nonvolatile solute (sugar) to water lowers the vapor pressure of the

6

water solution of sugar and the freezing point of the water solution will be lower than

that of pure water. Because of the high content of water in most foods, most of them

freezes solidly at temperatures between 00 and _30 C (Norman et ai, 1978).

The actual freezing process in food products is somewhat more complex than

freezing of pure water. Figure 2.2 compares the freezing curves of water with

aqueous solution containing a solute. In water, the temperature decreases as heat is

removed from the system until the freezing point is reached. After a smail amount of

supercooling, the temperature remains constant as the latent heat is removed from the

water system. Following this latent heat removal, the temperature decreases again as

energy is removed (Heldman, 1979).

Temperature

Eutectic point

Initial freezing point

Time

water

Solution

Figure 2.2: Comparison of freezing curves for pure water and an aqueous solution containing one solute

7