Adsorptive Properties of Activated Charcoal Methanol Combinations

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Renewable Ener tv

Vo[. 3, No.

6/7,

pp. 567-575, 1993 096(~1481/93 $6. 00+ .00

Printed in Grea t Bri tai n (' 1993 Pergamon Press Ltd

ADSORPTIVE PROPERTIES OF ACTIVATED

CHARCOAL/METHANOL COMBINATIONS

HU JING and R. H. B. EXELL

Division of Energy Technology, Asian Institute of Technology, P.O. Box 2754,

Bangkok 10501, Thailand

( R ec e i ved 26 N o v e m b e r 1992;a c c ep ted 17 December 1992)

Abstract---The adsorptive properties of several activated charcoal/methanol combinations were measured

in the laboratory. The Dubinin.-.Astakhov quation is used to analyze the data, and pressure temperature

concentration diagrams are given. From these results the coefficients of performance of ideal adsorption

refrigeration cycles applicable in solar heated adsorption refrigerators are calculated. It was found that

extruded samples from the U.K. and China had similar properties, but the best results were given by

granular samples from Thailand. There is some evidence hat small grain sizes (1 mm) are better than large

grain sizes (5 mm).

I. INTRODUCTION

Among the intermittent solid adsorption cycles for

solar ice-making refrigerators operating in a daily

cycle, the charcoal/methanol combination appears to

have advantages over other combinations. The advan-

tages include chemical stabil ity, better coefficient o f

performance (COP) [1], and relatively inexpensive

materials locally available in developing countries.

The pore structure of adsorptive solids is divided

into three approximate classes: micropores (radii

<a bo ut 15 A), transi tiona l pores (radii 15-200 A.),

and macropores (radii > 200 ~) [2]. The basis of this

classification is the behavior of each type of pore in

the process of vapor adsorption. However, although

meaningful informat ion about pore size distribution

in transitional pores and macropores can be obtained

[2], there is no satisfactory method of estimating the

size distr ibut ion in micropores. The pores in activated

charcoal are in the micropore range. Since it is there-

fore impossible to estimate theoretically the adsorp-

tive properties of the activated charcoal/methanol

combi nation, and since there are big variat ions in the

quality of activated charcoals available from different

sources, it is necessary to measure the adsorptive

properties of methanol on these different charcoals in

order to choose the one that is most suitable for mak-

ing solar refrigerators in particular circumstances.

Such measurements have been made by Passos

e t a l .

in France [3], by determining the isosters, and by

Sridhar in the Asian Institute of Technology (AIT)

[4] by determining the isobars.

In this paper, we describe some new measuremen ts

of the adsorptive properties of activated charcoals from

several different sources with the help of the simple,

but effective, experimental rig developed at AIT. The

results are compared with each other by the Dub inin

Radushkevich (D-R ) and Dubin in Astakhov (D A)

representations. In addition, the pressure-temperature

concentration (P T-X) diagrams derived from the

test results are given for each kind of activated char-

coal in a form that is convenient for specifying and

analyzing adsorption refrigeration cycles. The dia-

grams were used to calculate and compare the COPs

of a number of ideal cycles using these activated

charcoals.

2 . E X P E R I M E N T A L W O R K

The experimental rig for testing the adsorptive

properties of activated charcoal and methanol is

shown in Fig. 1. The charcoal sample (250 g) is con-

tained in the stainless steel cylinder container (A)

immersed in an oil bath with a temperature controller.

Temperature gradients inside the charcoal are reduced

by the central pipe of container A that allows warm

oil to circulate and heat the charcoal from the center.

The temperatures of the charcoal sample and the oil

are measured by the thermocouples. The pressure of

the system is indicated by the vacuum gauge and mer-

cury U-tube. The quick release coupling enables one

to remove container A from the system easily, for

changing the charcoal sample.

The graduated glass cylinder conta iner (B) is used

as a methanol receiver and evaporator ; it is immersed

in a glass water bath whose temperature is held con-

stant by means of flowing tap water or ice. The quan-

567



568 H. JING and R. H. B. EXELL

V a c u u m

P u m p

V a c u u m g a u g e

V~alve

, ( ~ M e r c u r y U t u b e T e m p e r a t u r e c o n tr o l

Fig. 1. Diagram of experimental rig.

tity (volume) of methanol adsorbed can be read

directly from the graduations, and the temperature

of the methanol is measured by the thermocouple.

Several valves are used to isolate and evacuate parts

of the system when necessary.

After introducing a measured amoun t of the char-

coal sample (about 250 g) into container A and

enough methanol into container B, the tests are car-

ried out according to the following three steps.

(1) The charcoal sample is degassed at 120 C under

vacuum and the air is flushed from container B by

means of the vacuum pump while part o f the methanol

is evaporated.

(2) The two containers are connected, keeping the

methanol in container B at a constant temperature

Tin, while cooling container A with charcoal sample

in ~ 10 ~' steps from an initial temperature of abou t

120°C to a final temperature o f abou t 30°C. A t each

step, a sufficiently long time is allowed for equi librium

to be reached between the charcoal sample and the

methanol. The temperatures of A and B and the level

of methanol in B are recorded in order to obtain the

adsorption isobar at the saturation vapor pressure of

methanol at temperature Tin.

(3) Similar data are taken while reheating the char-

coal sample in steps of 10° back to 120°C to obtain

the desorption i sobar at the same pressure.

Theoretically, the desorption isobar is the same as

the corresponding adsorpt ion isobar. However, in our

experiments only the adsorption isobar was reliable

because during desorption some methano l condensed

in the connecting pipe instead of in container B. For

each sample two isobars were measured by fixing Tm

at tap water temperature (about 30°C) and at iced

water temperature (about 5°C).

The activated charcoal samples measured came

from the U.K., China and Thailand. The descriptions

of the charcoal samples are listed in Table 1.

3. PRESENTATION OF THE TEST DATA

Based on the potential theory, a description of

adsorption in activated charcoal was proposed by

Polyani [5]. Dubinin and Raduskhevich originally

gave the fundamental state equation for the adsorp-

tion (D-R equation) as follows :

W= Woexp[-D TlnPs/P)2],

(1)

where W is the adsorbed volume (liters of methano l

per kilogram of charcoal) at temperature T (K) and

pressure P (bar) ; Ps is the saturated vapor pressure of

the adsorbate at temperature T; Wo is the maximum

volume of the adsorption space ; and D is a constant

for the charcoal sample. Because it is found that there



Adsorptive properties of activated charcoal/methanol

Table 1. The charcoal samples

569

Charcoal sample Country Description

207 E4* U.K

LSZ-40t China

LSZ-30t China

MD6070~. Thailand

MD5060~: Thailand

Normal charcoal Thailand

Coconut shell based, extruded

Coal based CCL4 > 55%, extruded

Coal based CCL4 > 65%, extruded

Coconut shell based, granular, mesh size = 4 x 8

Coconut shell based, granular, mesh size = 8 x 30

Coal based, not activated

* Sutcliffe Speakman Carbon Ltd, U.K.

t Beijing Beijiao Activated Carbon Manufacturing Co., China.

~. UDP Chemical Co. Ltd, Thailand.

are some deviations from the above D-R expression,

Dubinin and Astakhov [6] have introduced an

improved equation (the D-A equation) to fit the

experimental data better. The D- A equation contains

a third parameter, n :

W = W o e x p [ - D ( T l n P ~ / P ) " ] .

(2)

Although it has been pointed out [7, 8] that the D -

A equation still deviates from the experimental data

near s atura tion [namely, for very small and very large

values of (T In

Ps/P)'],

it is considered to be accurate

enough for comparing the adsorptive properties of

different charcoals and for use as a tool in correlating

adsorpt ion data for engineering purposes.

Figure 2 shows the D R representat ions of the char-

coal we tested in the temperature range 30-120°C

at two different pressures. All the activated charcoal

samples yield a curve that is convex downwards. This

is typical of highly activated charcoal in contrast to

the unactivated charcoal, for which the graph appears

convex upwards. This implies that eqn (1) cannot

express the adsorptive properties of activated char-

coal/methanol well. To analyze the data in terms of

the D-A equation the parameter n is allowed to vary

and the value that gives the best linear correlation

between In W and (TIn

Ps/P)"

is found. Figure 3 shows

the resulting D-A representations of the charcoal

samples. Though there are still some slight deviations

from the straight lines, the D-A presentations of eqn

(2) renders the experimental data with sufficient accu-

racy for use in engineering design.

Table 2 gives the numerical values of the pa rameters

in eqn (2) for each of the combinations studied. The

parameter Wo is an indicator for the degree of acti-

vation, since it gives the volume of micropores (per

unit mass of charcoal) available for adsorption. The

parameter n decreases as the degree of activation

increases, with the exception of charcoal MD5060,

which consists of grains much smaller in size (< 1 mm

diameter) than the grains of the other samples (4-5

mm diameter). The parameter D increases with the

degree of activation, again with the exception of char-

coal MD5060. The exception in the case of MD5060

may be due to the fact that the small spaces between

the grains provide an additional conribution to the

volume available for adsorption, for the observed

value of Wo in MD5060 is approximately twice the

value that would be expected from the relation con-

necting n and D with Wo in the other samples.

From eqn (2) we find that In P and -

1/T

are lin-

early related along an isoster (W = constant) if we

omit the quadratic and higher terms in the expansion

of In P~. Therefore, with the experimentally deter-

mined parameters in eqn (2), we can ob tain an isoster

as a straight line on a In P versus - 1/T plot by con-

necting two corresponding points with the same W.

Figure 4 shows the isosters derived for the charcoal

samples studied, where W has been replaced by the

more familiar symbol X as the concentra tion of meth-

anol adsorbed in the charcoal (kg methanol per kg

charcoal).

4. CYCLE PERFORMANCE WITH THE

CHARCOALS

The In P versus - 1 / T diagram is convenient to

describe the principle of the adsorption refrigeration

cycle. Theoretically, the cycle consists of two isosters

and two isobars (Fig. 5).

The process starts at point 1, where all the adsorbate

(methanol) is adsorbed on the adsorbent (charcoal)

at the ambient temperature, Td, and pressure P~. As

the adsorben t is heated, the temperature and pressure

increase along the isoster while the concentration of

the adsorbate in the adsor bent remains at Xm~,, unti l

point 2 is reached. At point 2 the generation process

starts on the isobar for the saturat ion vapor pressure,

P2,

of the adsorba te at the condenser temperature, T~.

During generation the adsorbate is driven from the

adsorbent and the adsorbent temperature increases

along the isobar to a maxi mum value, Tm~, at point

3. During this process the adsorbate vapor condenses



5 7 0 H . J 1 N G a n d R . H . B . E X E L L

- 1 ,

C h a r c o a l 2 0 7 E 4

~ 112~k~,~ c2 P = 0.1 96 ba r

-1 "n ~ + P = 0.05 ba r

\

- 2 . 4 t \

- 2 .6 p

-2 .8 F x ~

_ :~E '\

- 3 .4 L + ' x , L

- 3 6 i ~ - ~

X f ~ - ~

o 2 1 ~ ; ~ - ~ 2 5

- - 3 o - -

(T In (Ps /P ) ) ~ , 1 ~

_5

C h a r c o a l L S Z 4 0

-1115 ~

r J P = 0 . 183 ba r

2 1 . X ~ + P = O . O S b a r

i:i \

0 5 1 0 1 1 5 2'0 215 3'0

(T In(P s/P) ) 2 lo- '

3 5

- 1


-1.5

-2

-2 .5

- 3 ~

i

- 3 .5 1

I

- 4 ~

-4 .5

P = 0 . 1 9 0 b a r

+ P = 0 . 05 bar

~ - . . &

1 0 - - 1 5 2 '0 2 5 3 0 - - - -

(T In(Ps /P) ) 2 ,o- '

3 5

-0 ,6

-0 ,8

-1

-1 .2

-1 ,4

-1 .6

-1 ,8

-2

-2 .2

-2 .4

-2 .6

-2 .8

-3

-3 .2

-3 .4

-3 .6

-3 .8

- 4 - -

0

C h a r c o a l M D 6 0 7 0

y [3 P = 0 . 157 bar

~ - ~ 0 ; 5 2 0 2'5 3 0

(T In (Ps /P ) ) 2 ~1 ~

3 8

5

- 0 . 6 .

C h a r c o a l M D 5 0 6 0

o : ] ~ \ = P = o , , 3 b a r

- 1 2 P b

, : 4 t \ o = o o 5 ~,

- I

.6 ~ " ~

- 2 . 2 i - ~ .

- 2 . 4 i

" , ,

-2.6F N

- 3 .2 ~ " q

o T s Y o ~ 1 5 2 0 2 ; £

( m h ' l ( P ~ t P ) ) 2 ~ i o 5

35

Unac t i v a ted c h a rc oa l

, ~

-2"1

- 2 "2 ~ - " ~ o = P = 0 . 1 6 0 b a r

-2.6

-2.7

-2.8

- 2 .

-3.2

-3.3

-3.4

-3.5

-3.6

-3.7

-3.8

-3-~L

1'0 115 2'0 215 3'0

( T I n ( P s /P ) ) 2 , l ~

F i g . 2. D R r e p r e s e n t a t i o n o f s i x c h a r c o a l s a m p l e s . - - , B e s t fi t p a r a b o l i c r e g r e s s i o n c u r v e s .

3 5



A d s o r p t i v e p r o p e r t i e s o f a c t i v a te d c h a r c o a l / m e t h a n o l 5 71

5

C h a r c o a l 2 0 7 E 4

- 0 . 5 . . . . . . .

-I I~)'~. n = 1 . 3 4

1 5 t ~ , ~ {3 P : 0 . t 9 6 b a r

- 2 . 5

- 3 ~ ~ \

- 3 . s '

I

-4 .5 ~ r ~ i - ' ~ - ~ - 4

0 0 .02 0 .04 0 .060 .0% .0 . % .; 4 0 .% .1 8 0 . 2 0 .~ 2 0 . 2 4

(T In( Ps/P ))~, l o ~


- 1 °

_ ~ P = 0 . 1 8 3 b a r

-2.5.3 -- "

-3 .5

-4

-4.5

- 5 i i i b i i . l l i i

o o ? ° & o ~ ° & o ~ & o g ° & o # • o .1 7 1 ~ 4 • ~

(T In (PsJP ) )*, o "


-1 I -

- 1 . 5 n = 1 . 26

- 2 ' k n p = 0 . 1 9 0 b a r

- 2 .5 L

- 3 . 5

- 4 j

- 4 . 5

5 ~ o o O y ~ ; ~ o ~ ~ o 1 1 O ~ 3

(T In(Ps/P )) , 1~,

C h a r c o a l M D 6 0 7 0

-0 .6

- 0 .8 t r 3 ~ + ~ i 1

- 1 = 1 . 1 2

- 1 . 2

- 1 . 4 E l P = 0 , 1 5 7 b a r

- 1 .6 + ~ . . + P = 0 . 0 5 b a r

- 1 . 8

-2

- 2 . 2

- 2 . 4 I

- 2 . 6 L

- 2 , 8 ~ 1

-3

- 3 . 4

-3 .61 '~ .

. 3 .8 k \ ' L

4 F - q

o o ~ . . . . ~ 1 . . . . . . T - -

5 0 . 0 1 5 0 . 0 2 5 0 . 0 3 5 0 . 0 4 5

0 .01 0 .02 0 ,03 0 .04

(T In (P s /P) ) " , o ,

-0.5

C h a r c o a l M D 5 0 6 0

-1

-1 .5

-2

. 2 . 5

-3

- 3 . 5

. 4

- 4 . 5

u • o + n

1 . 5 0

Q P

=

0 . 1 4 3 b a r

0 1 0 : 2 0 3 0 : 4 0 5 o : 6 0 7 -

T In (P s /P) ) " , ~o

F i g . 3. D - A r e p r e s e n t a t i o n o f a c t i v e c h a r c o a l s a m p l e s . , B e s t f it l i n e a r r e g r e s s i o n c u r v e s .

0 .8



572

H . J I N 6 and R. H. B. EXELL

i n t h e c o n d e n s e r a n d i s c o l l e c t e d i n a re c e i ve r , a n d

t h e c o n c e n t r a t i o n o f t h e a d s o r b a t e i n t h e a d s o r b e n t

d e c r ea s e s t o i ts m i n i m u m X , , . . T h e r e ce i v er is t h e n

i s o l at e d f r o m t h e a d s o r b e n t , a n d t h e a d s o r b e n t is

c o o l e d a l o n g t h e i s o s t e r a t c o n s t a n t c o n c e n t r a t i o n ,

X m ~,, t o p o i n t 4 w h e r e t h e p r e s s u r e i s a g a i n P , . A t t h i s

p o i n t t h e r e c e iv e r is c o n n e c t e d a g a i n t o t h e a d s o r b e n t

t o a l lo w t h e a d s o r p t i o n p r o c e s s t o s ta r t . D u r i n g t h i s

p r o c e s s t h e l i q u i d a d s o r b a t e c o l l e c t e d i n t h e r e c e i v e r

e v a p o r a t e s a n d a b s o r b s h e a t a t t h e r e f r i g e r a ti o n t e m -

p e r a t u r e , T ~ ,. , o f t h e e v a p o r a t o r w h i l e t h e c o n -

c e n t r a t i o n o f t h e a d s o r b a t e i n t h e a d s o r b e n t i n c r e as e s

0 . 2

0 :1

0 . 0 9

0 . 0 8

o.gz.

0 . 0 6

.I.

o o ~

~ , _ - -

0 . 0 4 .

o . Q _ ~ .

o 9?

harcoal 2 0 7 E 4

[ I

' , /

_ _ . _ , / _ .

-

7 - - ~

- - -

- - - ' H - ' - 4 ~

___ _

_ I i

' i 1

/ I I i

I ° , c I = ° > I ° ' c I

- 3 . 7 - 3 . 5 - & 3 - 3 .1

I

I ' I

I j

I

i I , -

L

I I

I I

I I

I I

- 2 . 9 - 2 . 7 - 2 - 5

- I / T x l O 3 ( K - I }

0 . 2

0 . 1 5

9.A ___

o

_ 9 _

o.9_8

o _ o

o . _ o _ s

o.o_5

o .2 _

o . _ o ~ _ _7

0 . 0 2

- & 7

harcoal L S Z 4 0

/ / / / / / / / / I

- I--- -I- l- -

- - T N i T T i - T T - r i - q - -

I I

I I

I I

I I

- & 5 - 3 . 5 - & l - 2 . 9 - 2 . 7 - 2 . 5

3 - I

- I / T x l 0 ( K )

0 . 2

0 . 1 9

0 , 1 5

o-9P_

0 . 0 8

o #

0 . 0 6

~. o _

o 4_

0 . 0 ~ _

0 . 0 2

harcoal L S Z 3 0

I

I

I

I

I

- 3 . 5

I

2 - - i -

' I - -

I I

I I

I I

I I

I I

- & 3 - :5 .1 - 2 . 9 - 2 . 7 - 2 . 5

. l I T x 1 0 3 ( K - i l

harcoal M D 6 0 7 0

0 . 2

° i

o.osq_ ,_ d _ p _ ,___l.f lH ¢t_f_7_~_~L__

-~ o . o ~ _ _ + # _ + _ ' ~ _ ~l / _ k / _ l _ d _ _

- ~ o o , I @ / i

; _ f lY J ~ J _ Y _ _ _

oo-q--]7-7-

L_

"- - -1 - - Z ~ ,- q / I / i l l / ~ I

0 . 0 4 / { ;

J I J J I I2 L L _ _ L L _ _

I i I i i i I

/ i I i I

/ I I i I

o._o_2t i i I ~ I i

- 3 . 6 - 3 . 4 - 3 . 2 - 3 . 0 - 2 . 8 - 2 . 6 - 2 . 4

- I / T x 1 0 3 ( K - I~

F ig . 4 . Expe r im enta l i sos te r s on a In P ver sus - 1 /T p lo t . Va lues of X a re 0 .02 , 0 .04 . . . . 0 .18 , 0 .20 .



A d s o r p t i v e p r o p e r ti e s o f a c t i v a t ed c h a r c o a l / m e t h a n o l

573

0 . 2

0 . 1 5

0_._1_

0 . 0 9

o.o_8_

o . o L

o.9_6_

0 9 _ _

o _ o _ 4 _

o ._o~

0 0 2

C h a r c o a l M D 5 0 6 0

, t /

I / ' 1

V

I , / i I ,

I / I I ~ = o z /

- - - ~ - - r e - - - r - ' : - ~

i / I I

/ / /

- -

I I

- - W t J

- -

1 1

o : I c l o 9 ° ° e l

- 3 . 6 - 3 . 4 - 3 . 2 - 3 D - 2 . 8 - 2 . 6 - 2 . 4

3 - I

- I / T x l O K )

Fig. 4.

(continued)

t o X ~ ,,~ a t p o i n t 1. A t t h e s a m e t i m e , t h e a d s o r b e n t

c o o l s t o 7-..,b y r e j e c t i n g t h e s e n s i b le h e a t a n d t h e h e a t

o f a d s o r p t i o n .

I n o u r s i m u l a t i o n c a l c u l a t i o n t o c o m p a r e t h e s y s t em

p e r f o r m a n c e s w i t h d i ff e r e n t c h a r c o a l s w e a s s u m e d t h e

h e a t c a p a c i t y o f t h e m e t a l c h a r c o a l c o n t a i n e r t o b e

1 .0 1 k J / K p e r k g c h a r c o a l a n d t h e f in a l a d s o r p t i o n

t e m p e r a t u r e t o b e 3 0~ C . T h e p h y s i c a l p r o p e r t i e s ( d e n -

s i ty , s p e c if i c h e a t c a p a c i t y , e t c . ) o f c h a r c o a l s a r e

a s s u m e d t o b e th e s a m e . T h e D - A e q u a t i o n ( 2)

w a s u s e d a s t h e s t a te e q u a t i o n w i t h t h e p a r a m e t e r s i n

T a b l e 2 .

I n P

P 2

P1

J

. . . . . . . . . .

:

3

|

Y e v T a T C T m a x - 1F T

Fig . 5 . P T X d iag ram o f th e s imp le ad so rp t io n cy c le . T~ ,

ev ap o ra to r t emp era tu re ; T , , amb ien t t emp era tu re , T~ ,

c o n d e n s e r t e m p e r a t u r e ; T ~ ,, ~, m a x i m u m t e m p e r a t u r e o f

ch arco a l .

T h e c o e f fi c i e nt o f p e r f o r m a n c e ( C O P ) i s d e f i n e d a s :

C O P = L / ( Q ~e , + Qde~)

w h e r e L i s t h e u s e f u l h e a t o f r e f r i g e r a t i o n e x t r a c t e d a t

t h e e v a p o r a t o r t e m p e r a t u r e , T o , ; Q ~ e , i s t h e s e n s i b l e

h e a t n e e d e d t o h e a t t h e m e t a l c o n t a i n e r a n d t h e c h a r -

c o a l t o t h e t e m p e r a t u r e , T m ,x ; a n d Q a ,~ i s t h e h e a t o f

d e s o r p t i o n .

T h e c a s e s i n v e s t i g a t e d i n c l u d e e v a p o r a t o r t e m -

p e r a t u r e s o f 0 a n d - 1 0 C , w h i c h a r e t y p i c a l f o r c o o l

s t o r a g e a n d i c e - m a k i n g , r e s p e c ti v e ly . T h e c o n d e n s e r

t e m p e r a t u r e s , T o, a r e 25 , 35 a n d 5 O C c o r r e s p o n d i n g

t o a c o n d e n s e r i n c i r c u l a t i n g w a t e r , a c o n d e n s e r i n

s t a ti c w a t e r a n d a n a i r - c o o l e d c o n d e n s e r , r e s p e c t i v e ly .

T h e s i m u l a t i o n r e s u lt s a r e s h o w n i n F i g s 6 a n d 7 .

C h a r c o a l M D 6 0 7 0 h a s t h e b es t p e r f o r m a n c e i n a ll

c a se s , f o l l o w e d b y c h a r c o a l M D 5 0 6 0 . T h e s e t w o c h a r -

c o a l s a re g r a n u l a r w i t h o u t e x t r u s i o n a n d h a v e a W,,

m u c h h i g h e r t h a n t h e o t h e r s a m p l e s ( se e T a b l e 2 ) .

T h e t w o c h a r c o a l s L S Z 3 0 a n d L S Z 4 0 h a v e s i m i l a r

p e r f o r m a n c e s i n a ll c a s e s b e c a u s e t h e n u m e r i c a l v a l u e s

o f t h e p a r a m e t e r s W o , D a n d n i n e q n ( 2) a r e s i m i l a r .

T h e c h a r c o a l 2 0 7 E 4 f r o m t h e U . K . h a s a s im i l a r p er -

f o r m a n c e w h e n T ¢, = 0 ' C , b u t i s b e t t e r w h e n

T ~,. = - 1 0 ° C a n d h i g h e r v a l u e s o f T m , x a r e a t t a i n e d .

F r o m t h e r es u lt s o f t h e C O P c o m p u t a t i o n s w e fi nd

t h a t l a r g e r v a l u e s o f W o n o r m a l l y g i v e b e t t e r C O P s .

H o w e v e r , t h e C O P i s i n f l u e nc e d b y th e o p e r a t i n g t e m -

p e r a t u r e s . T h e s m a l l e r v a l u e s o f D a n d l a r g e r v a lu e s

o f n g i v e s m a l l e r v a r i a t i o n s o f th e C O P a s t h e p e a k

t e m p e r a t u r e T m ,x i n c re a s e s, s o f o r s o m e c h a r c o a l s w i t h

c l o s e v a l u e s o f W o , n a n d D i t i s n o t a l w a y s t r u e t h a t

l a r g e v a l u e s o f W 0 g i v e b e t t e r v a l u e s o f t h e C O P .

5 . C O N C L U S I O N

T h e a d s o r p t i v e p r o p e r t i e s o f s e v e ra l c h a r c o a l /

m e t h a n o l c o m b i n a t i o n s ( T a b l e 2 ) h a v e b e e n d e t e r -

m i n e d e x p e r i m e n t a l l y . T h e c o r r e s p o n d i n g D A p re -

s e n t a t i o n s a n d t h e P T - X d i a g r a m s t h a t a re n e c e s s a ry

t o d e s i g n a s o l a r r e f r i g e r a t i o n c y c l e a r e a l s o g i v e n .

S i m p l e p e r f o r m a n c e s i m u l a t i o ns s h o w e d t h a t t h e

Tab le 2 . Nu m er ica l v a lu es o f p a ramete r s in eqn (2)

W,, Temperature

Ch arco al (1 /kg) n D x l0 s range ( 'C)

207E4 0 .365 1 .3 4 14 .962 30~1 I0

LSZ40 0.384 1 .28 28.814 30 110

LSZ3 0 0 .405 1 .1 6 31 . 972 30-- 110

MD 6070 0 .989 1 .12 88 .9 82 30 120

M D 5 0 6 0 0 .5 3 5 1 .5 0 4 .5 8 95 3 0 , 1 20

No rm al 0 .1 5 6 9 2 .0 0 .1 9 82 3 0 -1 1 0



5 7 4 H . J 1 N G a n d R . H . B . E X EL L

( T o = 2 5 " C )

0 5 . . . . . . . . . . . . . . . ~

0 4 . . . . . . . I I I . . ~

0 2

0.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

070 1~0 1

0 g o 1 0 0 1 ~ 'o 1 3 0 1 4 0 1 5 0

Tm~ ~)

0 . 6 [ f r c = 3 5 C )

O 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

O 4 . . . . . . . . . . . . . . . . . . . . . . . . . . .

~ 0 3

O 2 . . . . . . . . . . . . . . . . . . . . . . . . . .

0 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Q

7 0 8 0 9 0 1 0 0 1 1 0

1 2 0 1 3 0 1 4 0 1 5 0

T m a x ( ° C )

0 5 I ( T c = 2 5 C )

0 4 . . . . . . . . . . . . . . . . .

0 3 . . . . . . . . .

0 2 . . . . . . . . . . . .

0 1

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

0

7 0 8 0 9 0 1 0 0 1 1 0 1 2 0 1 3 0 1 4 0 1 5 0

"fma× (~C)

O3

0 2

( T c = 3 5 " C ) 1

0

7 0 8 0 9 0 1 0 0 1 1 0 1 2 0 1 3 0 1 4 0 1 5 0

T m a x ( " C )

0 4

0 3

0 2

0 . 1

( T o = 5 0 C }

0 7 0 8 0 9 0 1 0 0 1 1 0 1 2 0 1 3 0 1 4 0 1 5 0

T m ax (~C)

F i g . 6 . C O P a s a f u n c t i o n o f m a x i m u m c h a r c o a l t e m p e r a t u r e ,

w h e n T, .v 0 C . - - , U n a c t i v a t e d c h a r c o a l ; ÷ , M D 6 0 7 0 :

A , M D 5 0 6 0 ; I I , 2 0 7 E 4 ; × , L S Z 3 0 ; V , L S Z4 0 .

f r C 5 0 C )

0 3

0 2 5

0 2

0 1 5

0 1

0 0 5

0 7 0 8 0 9 0 l O G 1 1 0 1 2 0 1 3 G 1 4 0 , 5 0

Tmax ( ° C )

F i g . 7. C O P a s a fu n c t i o n o f m a x i m u m c h a r c o a l t e m p e r a t u r e ,

w h e n T ~,. - - 1 0 ~ C. , U n a c t i v a t e d c h a r c o a l ; + , M D 6 0 7 0 ;

A , M D 5 0 6 0 ; I I , 2 07 E 4 ; x , L S Z 3 0 ; ~ ' , L S Z 4 0.



A d s o r p t i v e p r o p e r t ie s o f a c t i v a te d c h a r c o a l / m e t h a n o l

575

g r a n u l a r a c t i v a t e d c h a r c o a l g i v es a b e t t e r p e r-

f o r m a n c e t h a n e x t r u d e d a c t i v a t e d c h a rc o a l . T h e T h a i

c o c o n u t s h e ll b a s e d M D 6 0 7 0 g r a n u l a r a c t i v a t e d c h a r -

c o a l g a v e t h e b e s t p e r f o r m a n c e i n t h e s a m p l e s t e s t e d .

T h e r e i s a n i n d i c a t i o n i n t h e o t h e r T h a i s a m p l e

( M D 5 0 6 0 ) t h a t a s m a l l e r g r a i n si ze (1 m m ) i s b e t t e r

t h a n a l a r g e r g r a i n s i z e ( 5 m m ) . A g e n e r a l r e s u l t i s

t h a t t h e U . K . a n d C h i n e s e s o u r c e s p r o v i d e a c t i v a t e d

c h a r c o a l s o f e q u a l q u a l i t y , a n d t h e T h a i s o u r c e p r o -

v i d e s e v e n b e t t e r a c t i v a t e d c h a r c o a l f o r u s e i n a d s o r p -

t i o n r e f r i g e r a ti o n . T h i s i s o f i n t e r e s t t o A s i a n c o u n t r i e s

i n t e r e st e d i n th e f u t u r e d e v e l o p m e n t a n d l o c a l p r o -

d u c t i o n o f s o l a r a d s o r p t i o n r e f r i g e ra t o r s .

R E F E R E N C E S

I . M . Po n s an d J . J . Gu i l l em in o t , Des ig n o f an ex p er ime n ta l

so la r p o wered so l id ad so rp t io n i ce mak er . J. Solar Enerqy

Enq.

108. 332 (1986).

2 . H . M arsh , Th e ch arac te r iz a t io n o f m ic ro p o ro u s ca rb o n s

b y m e a n s o f t h e D u b i n in R a d u s h k e v i c h e q u a t i o n . J. Col-

lo idlnter face Sc i . 33, 101 (1970).

3 . E . Passo s , F . M eu n ie r an d J . C . Gian o la , Th erm o d y n a m ic

p e r f o r m a n c e i m p r o v e m e n t o f a n i n t e rm i t t e n t s o l a r p o w -

ered r e f r ig e ra t io n cy cle u s in g ad so rp t io n o f me th an o l o n

ac t iv a ted ca rb o n . Heat R ec oveo , Sy s ems 6, 258 (1986).

4 . K . S r id h ar , S tu d y o f ac t iv a ted ca rb o n /m eth an o l p a ir s

with relevance to ice ma king . Thesis No . ET-87-2, A sian

In s t i tu e o f Tech n o lo g y , B an g k o k (1 98 7 ).

5 . M. Po lyani , In : M. Sm isek and S. Cerney , Act ive Carbon

Mam~[acture, Properties and Application (edited by M.

Smisek and S. Cerney ), pp . 17 161 . Elsev ier . Am sterd am

(1970).

6 . M . M . D u b in in an d V . A. As tak h o v , Adv. Chem.Ser. 102,

69 (1970).

7 . M . Po n s an d Ph . Gren ie r , A p h en o men o lo g ica l ad so rp -

t io n equ i l ib r iu m law ex t r ac ted f ro m ex p er imen ta l an d

th eo re t i ca l co n s id era t io n s ap p l i ed to th e ac t iv a ted ca rb o n

an d me th an o l p a i r. A ccep ted b y Carbon (1986).

8 . Z . Lav an an d W . M . W o rek , Per so n a l co mmu n ica t io n

(1986).

Adsorptive Properties of Activated Charcoal Methanol Combinations

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