universiti putra malaysia adsorption properties of...

UNIVERSITI PUTRA MALAYSIA

ADSORPTION PROPERTIES OF MALAYSIAN ACTIVATED CARBON

FOR USE IN SOLAR REFRIGERATOR

NYEIN CHAN WIN @ MOHD. ALI

FSAS 2002 32

ADSORPTION PROPERTIES OF MALAYSIAN ACTIVATED CARBON FOR USE IN SOLAR REFRIGERATOR

By

NYEIN CHAN WIN

@ l\10HD. ALI

Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, In Fulfilment of the Requirements for the Degree of Master of Science

August 2002

Abstract of thesis submitted to the Senate of Universiti Putra Malaysia in fulfilment of the requirements for the degree of M aster of Science

PROPERTIES OF MALAYSIAN ACTIVATED CARBON USE IN SOLAR ADSORPTION REFRIGERATOR

By

NYEIN CHAN WIN @ MOHO. ALI

August 2002

Chairman: Professor Mohd. Yusof Sulaiman, Ph.D.

Faculty: Science and Environmental Studies

Detail experiments and analyses have been made on the solar refrigerator

using activated charcoal and methanol adsorption cycle. A test rig was designed to

study adsorption and desorption capability of activated carbon. A comparison has

been made between adsorbability of six Malaysian commercial activated carbons. To

improve the adsorbability of the carbon a simple method was tested.

Base on Dubinin equation, some them10dynamic properties of adsorbent!

adsorbate necessary for refrigeration calculation had been obtained. In this

experiment methanol is used as the refrigerant medium. The amollnt of methanol

adsorbed by the activated carbon was measured as a function of temperature of the

activated carbon. During the experiment, the temperature of the unadsorbed

methanol was kept constant. From Dubinin-Astakhov equation, parameters of

adsorption data were determined using graphical analysis. A Claperyon P-T-X

(pressure, temperature and concentration) diagram was then constructed.

\I

The Coefficient of Perfonnance (COP) of the activated carbon was then

calculated as a function of maximum collector temperature for different condenser

and evaporator temperatures. From these results of the Coefficient of Perfonnance of

ideal adsorption refrigeration cycles applicable in solar heated adsorption

refrigerators are calculated. The results of the COP calculation for collector

temperature of 1 00°C, condenser temperature 30°C and evaporator temperature of -

1 0°C are as follows:

Activated 2030 4050 5060 6070 7080 5060(4x8)

carbon Type

COP 0.2566 0.2494 0.2563 0 .2656 0.2768 0 .2535

iii

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

SIFAT-SIFAT BUATAN MALAYSIA KARBON TERAKTIF BAG I PENJERAPAN SURIA KE A TUS PETI SEJUK

Oleh

NYEIN CHAN \VIN @ MOHO. ALI

Ogos 2002

Pengerusi: Profesor Mohd. Yusof Sulaiman, Ph.D.

Fakulti: Sains dan Pengajian Alam Sekitar

Ujikaji terperinci dan analisis telah dilaksanakan ke atas alat penyej uk yang

menggunakan kitar penjerapan karbon teraktif dan nletanol . Suatu rig nlcngujian

telah direka bentuk untuk mengkaji kebolehan karbon teraktif menjerap dan

menyahjerap. Perbandingan telah dibuat terhadap sifat penjerapan enam j enis karbon

teraktif komersial buatan Malaysia. Untuk memperbaiki sifat penjerapan karbon,

suatu kaedah mudah telah diuji.

Berpandukan ke atas persamaan Dubinin, beberapa sifat tem10dinamik

penjerap bahan terjerap yang diperlukan untuk pengiraan penyejukan telah

diperolehi. Dalam ujikaji ini metanol digunakan sebagai media pendingin . Amaun

metanol yang dijerap oleh karbon terakdit telah diukur terhdap perubahan suhu

karbon teraktif. Semasa ujikaji, suhu metanol yang tak terserap ditctapkan. Dari

persamaan Dubinin-Astakhov, parameter data penjerapan ditentukan menggunakan

analisis grad. Rajih Claperyon P-T-X (tekanan, suhu dan depadatan) kemudiannya

dibentuk.

IV

Pekali prestasi (COP) karbon teraktif dikira menurut fungsi suhu pengumpul

untuk suhu kondenser dan penyejat yan berbeza. Dari hasil pengiraan ini pre stasi

kitar penyejuk penjerapan unggul yang terpakai kepada alat penyenjuk penjerapan

yang padankyu menggunakan teuga suria dapat dikira. Hasil pengiraan COP untuk

suhu pengumpul 1 00 DC, suhu kondenser 30 DC dan suhu dan penyerat -1 0 DC adalah

seperti berikut.

Jensi karbon 2030 4050 5060 6070 7080 5060(4x8)

teraktif

COP 0.2566 0.2494 0.2563 0 .2656 0.2768 0 .2535

v

ACKNOWLEDGEMENTS

I would like to express my full thanks and sincere gratitude to Professor Dr.

Mohd. Yusof Sulaiman, chairman of my supervisory committee, for his valuable

suggestion, constructive criticism, patient guidance and repeated encouragement

throughout this work.

Similar thanks must go to Dr. Mahdi Abd W.ahab, Dr. Azmi Zakaria and

Associate Professor Dr. Zainal Abidin Sulaiman for serving as committee members,

taking interest in and offering helpful criticism and guidance throughout the research.

Thanks are also to the members and staffs in the Department of Physics who

have always willing to offer assistance and advice, in particular, En. Shaharuddin Hj .

Abd Rahman and En. Razak Haroun.

vi

I certify that an Examination Committee met on 1 ih August 2002 to conduct the final examination of Nyein Chan Win @ Mohd. Ali on his Master of Science thesis entitled "Adsorption Properties of Malaysian Activated Carbon for Use in Solar Refrigerator" in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1 980 and Universiti Pertanian Malaysia (Higher Degree) Regulations 1 98 1 . The Committee recommends that the candidate be awarded the relevant degree. Members of the Examination Committee are as follow:

ZAINAL ABIDIN T ALIB Associate Professor, Faculty of Science and Environmental Studies Universiti Putra Malaysia (Chairman)

!\lOHD. YUSOF SULAIMAN Professor, Faculty of Science and Environmental Studies Universiti Putra Malaysia (Member)

ZAINAL ABIDIN SULAIMAN Associate Professor, Faculty of Science and Environmental Studies Universiti Putra Malaysia (Member)

AZMI ZAKARlA, Ph.D. Faculty of Science and Environmental Studies Universiti Putra Malaysia (Member)

HAMSHER MOHAMAD RAMADILI, Ph.D. Professor/Deputy Dean School of Graduate Studies Universiti Putra Malaysia

Date: 9 8 0:'::: 2D02

Vll

This thesis submitted to the Senate ofUni"ersiti Putra Malaysia has been accepted as fulfilment of the requirement for the degree of Master Science. The members of the Supervisory Committee as follow:

MOHD. YUSOF SULAIMAN Professor, Faculty of Science and Environmental Studies

Universiti Putra Malaysia (Chainnan)

MAHDI ABDUL \V AHAB, Ph.D Faculty of Science and Environmental Studies

Universiti Putra Malaysia (Member)

ZAINAL ABIDIN SULAIMAN Associate Professor, Faculty of Science and Environmental Studies Universiti Putra Malaysia (Member)

AZMI ZAKARIA, Ph.D. Faculty of Science and Environmental Studies Universiti Putra Malaysia (Member)

VHI

AINI IDERIS, Ph.D. Professor/Dean School of Graduate Studies

Universiti Putra Malaysia

Date:

DECLARATION

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.

IX

� ('·o�: Q • "'\')' \L'�

NYEIN CHAN WIN @ MOHD. ALI

Date: +. 10 . tPOO;)

TABLE OF CONTENTS

ABSTRACT ABSTRAK ACKNOWLEDGEMENTS APPROVAL DECLARATION LIST OF TABLES LIST OF FIGURES LIST OF SYMBOLS AND ABBREVIATIONS

CHAPTER

I INTRODUCTION 1 . 1 Objectives of the Study 1 .2 Limitations of the Study

2 ACTIVATED CARBON 2. 1 Activated Carbon Types 2 . 1 . 1 Properties of the Activated Carbon used 2.2 Choice of the Activated Carbon-Methanol Pair 2 .3 Theory of the System 2.4 Theoretical Consideration of Adsorption 2.4. 1 Adsorption 2.4.2 Adsorption - Isotherms and Isoteres 2 .5 Literature Review 2 .5 . 1 Characterization of Carbons 2 .5 .2 Solid adsorption Solar Power Ice-makers 2 .6 Adsorption Solar Refrigeration 2 .7 Flow Chart of the Steps used in the Project

3 EXPERIMENTAL METHODS 3 . 1 Experimental Rig 3 .2 Experimental Procedure 3 .3 Presentation of the Tested Data 3 .4 Application of Clausius-Claperyon Equation 3 .5 Data Analysis 3 .6 Application of the Solar Adsorption Refrigeration Cycle 3 .6 . 1 Desorption Period (heating periods) 3 .6.2 Adsorption Period (cooling periods) 3 .7 Calculation of the ideal COP and Discussion

4 RESULTS AND DISCUSSION

5 CONCLUSION

x

PAGE

11 IV VI Vll IX Xll

XIV XVll

1 8 9

1 1 1 2 1 4 1 4 1 6 1 9 1 9 2 1 24 24 32 35 39

4 1 4 1 43 45 49 5 1 55 55 59 6 1

63

1 08

REFERENCES

VITA

XI

1 1 0

1 1 3

LIST OF TABLES

Tables Page

2. 1 Values of the Parameters in D-A Equation 30

2 .2 Values ofWo and D in the D-R Equation for the Carbons Tested 30

3 . 1 Affinity Coefficient f3 for some vapors and gases on activated carbon 48

4. 1 Adsorption data of activated carbon type 2030 (8x30) 70

4.2 Adsorption data of activated carbon type 4050 (8x30) 7 1

4.3 Adsorption data of activated carbon type 5060 (8x30) 72




4.7 Derive adsorption properties of activated carbon type 2030 (8x30) 76

4 .8 Derive adsorption properties of activated carbon type 4050 (8x30) 77

4.9 Derive adsorption properties of activated carbon type 5060 (8x30) 78

4. 1 0 Derive adsorption properties o f activated carbon type 6070 (8x30) 79

4. 1 1 Derive adsorption properties of activated carbon type 7080 (8x30) 80

4. 1 2 Derive adsorption properties of activated carbon type 5060 (4x8) 8 1

4. 1 3 Numerical values o f parameters i n the equation (4.2) 66

4. 1 4 Dubinin-Astakhov data for activated carbon type 2030 (8x30) 85





XII


4.20 Coefficient ofPerfonnances (COPs) for six types of activated carbons 94

4.2 1 Coefficient ofPerfonnances (COPs) for six types of activated carbons 94

4.22 Coefficient of Perfonnances (COPs) for six types of activated carbons 95

4.23 Coefficient ofPerfonnances (COPs) for six types of activated carbons 95





xiii

Figures

2 . 1

2 .2 .a

2 .2.b

2 .3

2 .4

2 .5

2 .6

2 .7

3 . 1

3 .2

4. 1

4.2

4.3

4.4

4.5

4.6

4.7

4 .8

4 .9

LIST OF THE FIGURES

Adsorption cycle on a Ln P vs - l iT plot

A typical complete adsorption isothenn

Types of adsorption isothenns for vapors

The straight line plot of the characteristic curve W= Wo exp (-D ( Tin Ps / P ) n

Page

1 8

23

23

27

A typical diagram depicting the 2 part structure of the characteristic curve W= WoJ exp (-DJ (T In Ps / P ) n + Wo2 exp (-D2 ( Tin Ps / P ) n 27

Deviations from linear D-R plots

Schematic diagram of a simple solar adsorption cycle

Comparison of COP between Activated Carbon-Methanol pair and Zeolite -water pair by Grenier 1 983

Schematic diagram of the experimental setup

The ideal adsorption cycle

D-R representation of activated carbon 2030 (8x30)






Dubinin-Astakhov representation of activated charcoal 2030 (n= 1 . 1 76)

Dubinin-Astakhov representation of activated charcoal 4050 (n= 1 .638)

Dubinin-Astakhov representation of activated charcoal 5060

xiv

28

38

38

42

58

82

82

83

83

84

84

88

88

(n=1 . 1 70) 89

4. 1 0 Dubinin-Astakhov representation of activated charcoal 6070 (n=1 .230) 89

4. 1 1 Dubinin-Astakhov representation of activated charcoal 7080 (n=1 .265) 90

4. 1 2 Dubinin-Astakhov representation o f activated charcoal 5060(4x8) (n=1 . 1 636) 90

4. 1 3 Claperyon diagram o f activated carbon 2030 (8x30) 9 1

4. 1 4 C1aperyon diagram o f activated carbon 4050 (8x30) 9 1

4. 1 5 C1aperyon diagram o f activated carbon 5060 (8x30) 92


4. 1 7 C1aperyon diagram of activated carbon 7080 (8x30) 93


4. 1 9 COP as a function of maximum collector temperature when Tc=25 °c and Teva= - 1 0 °C 98

4.20 COP as a function of maximum collector temperature when Tc=25 °c and Teva= -5 °C 98

4 .21 COP as a function of maximum collector temperature when Tc=25 °c and Teva= 0 °c 99

4.22 COP as a function of maximum collector temperature when Tc=25 °c and Teva= 5 °c 99

4. 23 COP as a function of maximum collector temperature when Tc=30 °c and Teva=-l 0 °C 1 00

4.24 COP as a function of maximum collector temperature when Tc=30 °c and Teva=-5 °c 1 00

4.25 COP as a function of maximum collector temperature when Tc=30 °c and Teva= 0 °c 1 0 1

4.26 COP as a function of maximum collector temperature when Tc=30 °c and Teva= 5 °c 1 01

4.27 Performance of evaporating temperature of activated carbon 2030 (8x30) at Tc=25 °C 1 02

xv

4.28 Perfonnance of evaporating temperature of activated carbon 4050 (8x30) at Tc=25 °c 1 02

4.29 Perfonnance of evaporating temperature of activated carbon 5060 (8x30) at Tc=25 °c 103


4.3 1 Perfonnance of evaporating temperature of activated carbon 7080 (8x30) at Tc=25 °c 104




4.35 Perfonnance of evaporating temperature of activated carbon 5060 (8x30) at Tc=30 °c 106




XVI

LIST OF SYMBOLS AND ABBREVIATIONS

Abbreviation Unit

COP Coefficient of Performance D-A Dubinin-Astakhov D-R Dubinin-Radushkevich TIM Transparent Insulation Material A Area m2

C Specific heat J/kgK D Parameter in D-R or D-A equations F Function H Enthalpy J L Latent heat of vaporization kJ/kg M Molecular weight kglkmol P Pressure bar Ps Saturation vapor pressure bar Q Heat flow W R Universal gas constant J/kmolK Tc Temperature of the Condenser oK or °c Teva Temperature of the evaporator oK or °c Tm Temperature of methanol oK or °c V Volume m3

W Volume filled by the adsorbate in adsorbent L/kg Wo Maximum volume available for adsorbate in

adsorbent L/kg Xmix Maximum Concentration glgl Xmin Minimum Concentration X Concentration gig

p Density kg/m3

XVll

CHAPTER!

INTRODUCTION

The limited availability of fossil energy carners and the environmental

impact of energy consumption demand mid- and long-term strategies both for the

rational use of energy and for increased renewable energy utilization. Concepts of

renewable energy conversion have been proposed and implemented during recent

decades all over the world and then remarkable potential has been demonstrated.

However, large scales implementation in the context of the requirements above has

not yet taken place.

Unlike non-renewable energy (fossil fuels), the supply of renewable energy

(solar, wind, waves, etc) is 'infinite'. Moreover the net impact of renewable energy

conversion on the environment is considerably lower than the impact of traditional

energy, which is a current concern for the whole world. As a result of the energy

crisis, attention has been focused on the need, not only to conserve conventional

sources of energy, but also to explore non-conventional sources of energy such as

solar radiation, wind, biomass, tides, geothermal sources etc. There is no reason why

these important natural resources should not be exploited for the benefit of the

developing countries, particularly solar radiation, which is relatively abundant in

most places.

During the last few decades, an increasing interest, based on research and

development has been concentrated on utilization of non-conventional energy

sources, namely solar energy, wind energy, tidal waves, biogas, geothermal energy,

hydropower, hydrogen energy, etc. Among these sources, solar energy, which is an

energy source for cooling applications, is a highly popular source due to the

following facts: direct and easy usability, renewable and continuity maintaining the

same quality, being safe, being free, being environment friendly and not being under

the monopoly of anyone.

As a future resel ve of fossil fuel becomes depleted, scientists and engineers

are responsible to develop new technologies to exploit renewable energy resources.

The sun is the major sources of renewable energy on the earth. Solar energy is one of

vital research target in the future. It is hoped that with the further improvements in

this technology, solar energy will supply not only the needs of industry but also the

everyday needs of the population in the rural and remote areas.

Some of the earliest experiments on refrigeration for preservation date back

to the fifth century (Warren, 1 979). Since then, there has been a continuous search

for cheap methods of providing could be for these purposes. At present, the most

common means of producing cold for storage purposes is by the use of vapour

compression units powered by electricity. In rural areas, this method of cold

production is not easily available because of the non-availability of electricity. This

has been affecting their standard of living. Acquisition of the appropriate capability

to produce cold in these areas, therefore, will assist significantly in improving their

standard of living. Four main options may be considered for this purpose (Critoph,

1 990)

2

(i) extension of grid connected electricity to power refrigerators,

(ii) access road for use of on board refrigerated transport,

(iii) use of photovoltaic refrigerators and

(iv) use of heat driven refrigerator or ice-maker.

Options (i) to (iii) above are too expensive to suggest that cold storage will be

available to the areas in most need of them. This leaves the heat driven ice-maker as

the most viable solution to the problem of extending cold to rural areas. The

operation of heat driven refrigerators is either continuous or intermittent. While the

continuous heat driven refrigerator still depends on electricity to power solution

pumps, the intermittent system depends only on heat for operation and does not have

any moving part. Because low-grade heat is required to power the system, it is

possible for locally available heat sources, like solar energy and fossil fuel, to be

used. This makes it very attractive in remote regions without grid connected

electricity.

Cold production using solar energy appears very attractive. This is because

cold is needed most when solar radiation is highest. Also, solar radiation is freely

available and non-polluting. Solar cooling seems to be a very attractive application

for solar energy since more cooling is necessary when more solar energy is available.

Nevertheless, to date, most efforts for promoting solar cooling have failed. Solar

cooling would be a useful technology in areas of the world where there is a demand

for cooling high isolation levels and no firm electricity supply to power conventional

systems. In tropical areCjs, domestic hot water and space heating are not necessities,

but also solar refrigeration could be used for storing agricultural products, food and

3

medicines. The most plomising applications are vaccine storage and food storage

(particularly fish). Several different solar thermal refrigeration have been studied for

some years and many refrigerators were built and tested.

There are two ways to use solar energy to operate refrigerators. The first one

IS to convert solar radiation into heat to run a thermally powered absorption or

adsorption refrigeration system. The second way is to convert solar radiation into

electricity by means of photovoltaic cells to drive a conventional refrigerator.

Photovoltaic converters and compressIOn refrigerators are currently being

developed for small-scale domestic use and for the preservation of vaccines in

isolated areas. Adsorption refrigeration systems with thermal solar collectors enjoy a

wider range of possible applications, which include air-conditioning, medium-scale

cold storage, ice manufacturing, and the same small-scale uses as the photovoltaic

systems.

The whole subject of solar powered refrigeration thus embraces a variety of

solar and refrigeration technologies, all of which are active areas of research and

development at the present time. However, none of the systems developed to date are

economically viable because they are too expensive. Efforts are being made to

improve efficiencies and bring down costs, but there is still little to choose between

the various types, and it is difficult to see which, if any, will ultimately secure

appreciable markets.

4

The direct used of solar energy as thennal power has gathered considerable

interest. Comparing with PV system, the thennal cooling system is low cost, more

maintenance free and the possibility of local production in developing countries. The

simplest fonn of thennal adsorption refrigeration cycle is intennittent which requires

low maintenance. The only complex control action needed is that the power source

cycles from the off to on start. S ince the sun automatically cycle, this complexity is

even removed. It may additional be an advantage in vaccine cooling application that

the collection of the solar energy is necessarily passive, so that the system can be

imagined to function independently of any operator input.

In the field of liquid absorption, ammonia-water and lithium bromide-water

pairs were widely used in experimental units of solar refrigeration (Ward et aI . , 1 979

and Staicovici, 1 986). Different prototypes utilizing saline ammoniac solutions

(Swartman, 1 975) as well as solid absorption reactions (Worsoe-Schmidt, 1 983) have

also been studied. As compared to the above-mentioned devices, solid adsorption

systems show some advantages: the adsorbent is not submitted to any change of

column during the sorption processes, as in solid absorption; it does not need a

rectifying column as in liquid absorption.

Efficient refrigerators based on the adsorption cycle can be perfonned using

only thennal energy. Several experimental developments have proved that adsorptive

refrigeration systems are well adapted to soft technology applications, since they can

operate without moving parts and with low-grade thennal energy from different

sources. Adsorption cooling cycles are a possible response to this problem since they

5

operate with non-toxic refrigerant fluids like water and methanol, which are fully

ecologically compatible.

S ince, adsorption techniques also allow cycling large amounts of refrigerant

fluid, adsorptive refrigerators can be most efficient, and a design of a new ice maker

using the activated carbon-methanol pair and solar regeneration is theoretically

analyzed and its behavior simulated.

Although silica gel has been used in at least one closed cycle refrigerant

system, the best majority of experience is with the zeolites or activated carbons. The

most commonly utilized adsorbents are silica gel, activated carbon, aluminas and

zeolites. Zeolite water and activated carbon-methanol are the most used adsorbent

adsorbate pairs in refrigeration systems. These two pairs have entirely different

physical and chemical properties. Methanol is easily desorbed from activated carbon

when it i s heated, while zeolite, the water is kept much longer.

Thus the activated carbon-methanol pair is best adapted to operating cycles

with small evaporating temperature variation (up to 400 C). Adsorption cycles with

the zeolite water pair need a longer evaporating temperature change (700 C or more)

to operate according to (Meunier and Douss, 1 990) . (Critoph and Vogel, 1 986)

compared zeolites and active charcoal with refrigerants R1 1 , R12 , R22 and R1 14 and

in all cases found charcoal a preferable adsorbent for solar cooling. (Meunier et aI . ,

1 990) have compared synthetic zeolite-water, synthetic zeolite-methanol, and

charcoal-methanol combinations. They find that activated charcoal-methanol gives a

better Coefficient of Performance (COP) generally, but that when the nighttime

6

ambient temperature to evaporating temperature difference is particularly higher then

a zeolite-water combination i s better. However, this will also require a higher

generating temperature to evaporating temperature from the solar collector during the

day. (Meunier, 1 990) comparing AC35-methanol with zeolite 1 3X-water, suggests

that the zeolite combination will only be superior when the temperature lift

(adsorption-evaporation temperature) exceeds 45° C. The COP is based on heat input

to the adsorbent rather than to the solar collector and so the reduced solar collector

efficiency at higher temperatures may actually make charcoal-methanol

combinations superior at even higher temperature lifts. Through the previous work of

others we know that charcoal as adsorbent, methanol as adsorbate is a suitable pair

for solar powered adsorption refrigeration.

There are other reasons for preferring charcoals:

1 . Activated charcoals are cheaper than zeolites.

2. Activated charcoals can be made with properties to suit particular applications.

3 . Activated charcoals (particularly coconut shell charcoal) can be manufactured in

the country of origin.

For these reason it was decided to concentrate on activated charcoal as an adsorbent.

The research report in this dissertation is a study of the activated charcoal

methanol solar thermally powered adsorption refrigeration system, which is

intermitted, taking advantage of the diurnal cycling of the solar source, with a view

to its eventual commercialization in developing countries in Asia. The project

included

7

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