Experiment on a Continuous Heat Regenerative Adsorption Refrigerator Using Spiral Plate Heat Exchanger as Adsorbers

8/13/2019 Experiment on a Continuous Heat Regenerative Adsorption Refrigerator Using Spiral Plate Heat Exchanger as Ads

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Pergamon Applied Therm al Engineering Vol. 18, Nos. 1-2, pp. 13-23, 1998~) 1997 Published by Elsevier Science Ltd.All rights reserved. Printed in Great BritainPII: S1 35 9-4 31 1(9 7)0 00 38 -0 1359-4311/98 19.00 + 0.00

E X P E R I M E N T O N A C O N T I N U O U S H E A TR E G E N E R A T I V E A D S O R P T I O N R E F R I G E R A T O R U S I N GS P I R A L P L A T E H E A T E X C H A N G E R A S A D S O R B E R S

R . Z . W a n g J . Y . W u Y . X . X u Y . T e n g a n d W . S h iI n s t i t u t e o f R e f r i g e r a t i o n a n d C r y o g e n i c s , S h a n g h a i J i a o T o n g U n i v e r s i t y , S h a n g h a i 2 0 00 30 , C h i n a

Received 18 Apri l 1997)A b s t r a c t - - S p i r a l p l a t e h e a t e x c h a n g e r s w e r e p r o p o s e d t o b e u s e d a s a d s o rb e r s , a n d a p r o t o t y p e h e a tr e g e n e r a t i v e a d s o r p t i o n r e f r i g e r a t o r u s i n g t h e a c t i v a t e d c a r b o n - m e t h a n o l p a i r w a s d e v e l o p e d a n d t e s t e d .T h e a d s o r p t i o n s y s t e m u s i n g 1 2 k g a c t i v a t e d c a r b o n h a s a c y c l e t i m e o f 4 0 r a i n ., m e a n w h i l e 1 4 k g i c ep e r d a y w a s m a d e . . ) 1 99 7 P u b l i s h e d b y E l s e v i e r S c i e n c e L t d .K e y w o r d s - - A d s o r p t i o n re f r i g e r a t o r , h e a t r e g e n e r a ti v e , s p i r a l p la t e h e a t e x c h a n g e r , a c t i v a t e d c a r b o n ,m e t h a n o l .

I N T R O D U C T I O NS o l id s o r p t i o n r e f r i g e r a ti o n ( o r h e a t p u m p ) h a s r e c e i v e d m u c h a t t e n t i o n i n r ec e n t y ea r s ; v a r i o u sk i n d s o f s o r p t i o n r e f r ig e r a t o r s a n d h e a t p u m p s w e r e d e v e l o p e d , m o s t l y o f a c t i v a te d c a r b o n -m e t h a n o l , z e o l i te - w a t e r , C a C 1 2 -N H 3 , a n d h y d r i d e - h y d r o g e n p a ir s . I n t e r m i t t e n t t y p e f o r s o l are n e r g y a p p l i c a t i o n s [ 1], h e a t r e g e n e r a t i v e c y c le [2 ] a n d c a s c a d e s y s t e m [3 ] w e r e d e v e l o p e d . N e wt h e r m o d y n a m i c c y c l e s , s u c h a s t h e r m a l w a v e c y c l e [ 4 ] a n d c o n v e c t i v e t h e r m a l w a v e c y c l e [ 5 ] ,w e r e p r o p o s e d f o r p o s s ib l e 'f u tu r e p o te n t i a ls . T h e r e n e w e d i n t e r e s t in t h e s t u d y o f a d s o r p t i o n r e -f r i g e ra t i o n is b a s e d u p o n t h e v a r i o u s a d v a n t a g e s o f t h e s y s te m s s u c h as n o n - C F C s p r o b l e m s ,c o s t -e f f ec t iv e , s i m p li c it y in c o n s t r u c t i o n , n o n e e d f o r s o l u t i o n p u m p s a n d m e a n w h i l e t h e y c a n b ed r i v e n d i r e c t l y b y l o w g r a d e e n e r g y .

F o r r e al a p p l i c a t i o n p u r p o s e s , c o n t i n u o u s h e a t r e g e n e r a t i v e a d s o r p t i o n c y c le is u s u al l y t a k e n ,h o w e v e r t h e d e v e l o p m e n t o f t h e a d s o r b e r is c r it ic a l . A g o o d d e s ig n o f t h e a d s o r b e r s h o u l d h a v es e v e r a l a d v a n t a g e s s u c h a s g o o d h e a t t r a n s f e r i n a d s o r p t i o n b e d ( t h u s t h e a d s o r p t i o n / d e s o r p t i o nt i m e c a n b e s h o r t e n e d , t h e s y s te m c a n b e c o m p a c t f o r a c e rt a i n p o w e r ) , s m a l l m a s s o f m e t a l t oe n s u r e i t s c o s t -e f f e c t iv e n e s s . S e v e r a l t y p e s o f h e a t e x c h a n g e r s h a v e b e e n s e l e c te d a s a d s o r b e r ss u c h a s s h e l l a n d t u b e h e a t e x c h a n g e r [ 6 ] , f l a t p i p e h e a t e x c h a n g e r [ 7 ] , f l a t p l a t e h e a t e x c h a n g e r[8 ] a n d p l a t e - f in h e a t e x c h a n g e r [ 9 ]. R e c e n t l y w e d e v e l o p e d a s p i r a l p l a t e h e a t e x c h a n g e r f o r t h ea d s o r b e r a n d t h e e x p e r i m e n t s h a v e s h o w n g o o d r e s u l t s .

D E S I G N O F A N A D S O R B E RT h e k e y p o i n t f o r th e d e s ig n o f a n a d s o r b e r i s r e la t e d t o t h e h e a t a n d m a s s t r a n s f e r i n t he

a d s o r p t i o n b e d . T h e t h e r m a l r e s i s ta n c e o f a d e s o r p t i o n o r a n a d s o r p t i o n p r o c e s s o c c u r s in :1. t h e c o n v e c t i v e h e a t t r a n s f e r b e t w e e n t h e r m a l f l u id a n d m e t a l l i c s e a li n g w a ll ;2 . t h e t h e r m a l c o n d u c t i o n t h r o u g h t h e m e t a l l i c s e a l i n g w a l l ;3 . t h e c o n t a c t r e s i s t a n c e b e t w e e n t h e m e t a l l i c s e a l i n g w a l l a n d t h e a d s o r b e n t ;4 . t h e th e r m a l c o n d u c t i o n i n th e a d s o r b e n t b e d .T h e t h e r m a l r e s i s t a n c e o f it e m ( 1 ) c a n b e r e d u c e d b y i n c r e a s i n g t h e f l o w s p e e d o f t h e t h e r m a lf lu id , t h u s i t p l ay s a l i tt l e ro l e i n t h e wh o le v a lu e . I t em ( 2 ) c an b e n eg lec t e d i f t h e wa l l t h i ck n e ssis v e r y l o w - a s l o w a s p o s s i b l e i f t h e s t r e n g t h c a n b e g u a r a n t e e d . T h e m a i n c o n t r i b u t i o n s t o t h et o t a l t h e r m a l r e s i s t a n c e a r e i t e m s ( 3 ) a n d ( 4 ) . T h u s b y i m p r o v i n g t h e r m a l c o n t a c t b e t w e e n t h e

13


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14 R . Z . W a n g e t a l .

l

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(2 > 0 6F i g . 1 . S h e l l a n d t u b e h e a t e x c h a n g e r a s a n a d s o r b e r . I t h e r m a l f lu i d i n ; 2 t h e r m a l fl u id o u t; 3 c o n n e c -

t i o n t o c o n d e n s e r ; 4 f i ns ; 5 c o i l t u b e ; 6 c o n n e c t i o n t o e v a p o r a t o r .

metallic sealing wall and the adsorbent and by improving the thermal conductance of the adsor-bent bed the total heat transfer between the thermal fluid and the adsorbent can be improved.However the mass transfer in an adsorbent bed should not be neglected as the diffusion andpermeation of adsorbate through an adsorption bed may go very slowly.Various types of heat exchangers have been used in adsorption systems such as shell andtube heat exchanger [6] flat pipe heat exchanger [7] flat plate heat exchanger [8] and plate-finheat exchanger [9]. Figures 1 2 and 3 show the designs.

Shell and tube type is simple in structure and cheap which was widely used in air-condition-ing engineering. Its main disadvantage as an adsorber is the large thermal resistance between

F i g . 2 . F l a t - p i p e t y p e a d s o r b e r . I t h e r m a l f lu i d f lo w c b a n n e l~ 2 a d s o r b e n t e m b e d d e d .


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7

F i g . 3. P l a te t y p e a d s o r b e r i n c l u d i n g p la t e - fi n h e a t e x c h a n g e r a s a n a d s o r b e r ) . 1 , a d s o r b e n t e m b e d d e d ;2 , t h e r m a l f l u i d p a s s a g e ; 3 m e t a l l i c s e a l i n g w a l l .

adsorbent and fins [6]; The flat-pipe type [7] seems to be effective in solving heat transfer pro-blems, the pressure difference between the adsorbent bed and thermal fluid may bring good ther-mal contact between adsorbent and metallic wall, meanwhile the thermal conduction in the bedcan also be improved, however specific manufacture techniques are needed, and a big tempera-ture difference will occur along the bed, meanwhile the pressure drop of thermal fluid is veryhigh [10]. Plate-type adsorber [8,9] could be a good solution to overcome the various thermalresistances, the mass production is also market ready, especially plate-fin heat exchanger, whichis usually vacuum brazed and made of aluminum, can be a very good adsorber for refrigerationor heat pump applications. The reported cycle time for a heat regenerative silica gel-water heatpump is 12 minute s possible [9], however this type of adsorber is very expensive.

An economic compromise between mass and heat transfer improvements inside the bed mustbe found, and an adsorber should be simple, efficient and cheap. We designed a spiral plate typeadsorber for the purpose, as spiral plate heat exchanger is market ready and widely applied in

2

3

4

E x p e r i m e n t o n a c o n t i n u o u s h e a t r e g e n e r a t i v e a d s o r p t i o n r e f r i g e r a t o r 1 5

5 6F i g . 4 . S p i r a l p l a t e t y p e a d s o r b e r . I , s p i r a l p l a t e ; 2 , v a p o r o u t l e t ; 3 , s o l i d a d s o r b e n t ; 4 , f lu i d fl o w p a s -s a g e ; 5 , t h e r m a l f l u i d o u t ; 6 , t h e r m a l f l u i d i n ; 7 , s u p p o r t r o d .


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16 R.Z. Wang e t a lc h e m i c a l e n g i n e e r i n g f o r i ts c o m p a c t n e s s a n d e f fi c ie n t i n h e a t t r a n s f e r . F i g u r e 4 s h o w s t h e s t r u c -t u r e o f t h e a d s o r b e r .

S P I R A L P L A T E A D S O R B E RT h e a d s o r b e r i s c o n s t r u c t e d b y t w o p a r a l le l s t a in l e s s s te e l w e l d e d p l a t e a t t h e t w o e n d s , t h e n

t u r n e d i n a s p i r a l li n e , t h e b o t t o m e n d i s w e l d e d a n d s e a l e d b y a f l a t p l a t e , w h i l e t h e u p p e r e n di s f a c e d t o a f l a n g e t o e m b e d a d s o r b e n t . T h e s u p p o r t r o d i s u s e f u l d u r i n g t h e s p i r a l - t u r n i n g p r o -c e ss , th e s p a c e b e t w e e n t h e t u r n e d s p i ra l p l a t e is t h u s u s e d f o r a d s o r b e n t s p a c e . A n o r m a l s p i r alp l a t e h e a t e x c h a n g e r h a s t w o f l o w p a ss a g e s , u s e d f o r h e a t e x c h a n g e b e t w e e n f lu id -1 a n d f lu i d -2 ;h o w e v e r f o r a s p i r a l p l a t e a d s o r b e r , o n l y o n e p a s s a g e i s u s e d f o r t h e r m a l f l u i d f l o w , t h e o t h e rs i d e p a s s a g e i s s e a l e d a n d u s e d f o r t h e a d s o r b e n t b e d , t h e u p p e r p l a t e f l a n g e s u p p l i e s t h e f l o wc h a n n e l f o r a d s o r p t i o n a n d d e s o r p t i o n p r oc e ss e s.

A s s h o w n i n F i g . 4 , th e h e a t t r a n s f e r b e t w e e n t h e t h e r m a l f l ui d a n d t h e a d s o r b e n t b e d iss o m e t h i n g l i k e f l a t - p i p e t y p e a n d f l a t - p l a t e t y p e . B e s i d e s t h e a d v a n t a g e s f o r f l a t - p i p e a n d f l a t -p l a t e t y p e a d s o r b e r s , t h e o t h e r m a i n a d v a n t a g e s o f s p i ra l p l a t e ty p e a d s o r b e r a r e:1. c o m p a c t s iz e, sm a l l h e a t t r a n s f e r t e m p e r a t u r e d i f f e re n c e , p o s s i b i li t y f o r m o r e u n i f o r m t e m -

p e r a t u r e d i s t r ib u t i o n , a n d e a s e t o c o n t r o l t h e t e m p e r a t u r e f i el d;2 . t h e s u p p o r t r o d s a r e u s e d f o r m a n u f a c t u r i n g p r o c e s s , in r e a l o p e r a t i o n , t h e y s e rv e as f in s t o

i m p r o v e t h e t h e r m a l c o n d u c t i o n i n t h e a d s o r b e n t b e d ;3 . h i g h h e a t t r a n s f e r d e n s i t y ;4 . t h e v o l u m e o f th e a d s o r b e n t b e d w i ll in c r e a s e m o r e s l o w l y i f c o m p a r e d w i t h t h e p l a te a r e a

i n c r e a s e ;5 . e a s e f o r m a n u f a c t u r i n g ;6 . c h e a p t o o b t a i n a n d r e a d y in m a r k e t .

T h u s w e o r d e r e d t w o s p i ra l p l a t e h e a t e x c h a n g e r s w i t h l i tt le m o d i f ic a t i o n s . T h e s p i ra l s p a c ef o r a n a d s o r b e n t b e d o f 6 k g a c t i v a t e d c a r b o n is 1 8 m m , a n d t h e s p i r a l p l a t e a r e a is 2 m 2. 2 0s t ai n l es s s t e el s c re e n c o n s t r u c t e d t u b e s w e r e i n s e r t e d i n t o t h e a d s o r b e n t b e d f o r m a s s t r a n s f e ri m p r o v e m e n t p u r p o s e .

F u l l e r e t a l r e c e n t ly t r ie d a t h e o r e t i c a l m o d e l f o r a s p i r a l p l a te a d s o r b e r , a n d m o d e l e d i t f o r at h e r m a l w a v e h e a t re g e n e r a t i v e a d s o r p t i o n h e a t p u m p . G o o d r e s u l t s a r e s h o w n [ 11 ]. O u r w o r k

Cooling WaterThrottlingValve Evaporator

)Condenser Receiver

puanp Ice box

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p CoolingWater

t>< 1 ]~

Adsorber2

Fig. 5. Schem atic of a prototype h eat regenerativeadsorption refrigerator.

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Experim ent on a continuou s heat ~Fegenerative adsorption refrigerator 7i s t h e f ir st tr y t o u s e s u c h k i n d o f a d s o r b e r i n a p r o t o t y p e a d s o r p t i o n s y s t e m , w h i c h m a y b r i n gs o m e m e a n i n g f u l r e s u l t s .

A D S O R P T I O N S Y :S T E M

A p r o t o t y p e c o n t i n u o u s h e a t r e g e n e r a ti v e a d s o r p t i o n r e f r i g e r a to r u s in g a c t iv a t e d c a r b o n -m e t h a n o l w a s d e v e l .o p e d , a n a r r a n g e m e n t o f a t y p i c a l , th e r m a l w a v e t y p e w a s p r e v i o u s l y t ri e d ,h o w e v e r n o g o o d r e s u l t s ~ e r e f o u n d [ 1 2 ] . W e h a v e i m p r o v e d t h e a d s o r p t i o n s y s t e m , i n w h i c ht h e t w o a d s o r b e r s a r e i n d e p e n d e n t l y o p e r a t e d f o r h e a t in g o r c o o l i n g e x c e p t th e g o - b e t w e e n h e a tr e c o v e r y p r o c e s s . F i g u r e 5 s h o w s t h e w h o l e u n i t a n d m e a s u r i n g s e n s o r s. T h e s y s t e m h a s t w oa d s o r b e r s , o n e c o n d e n s e r a n d . on e e v a p o r a ~ o r , a r e c e i v e r is i n s t a ll e d f o r t h e o b s e r v a t i o n o f re -f r i g e r a n t f l o w i n t h e s y s t e m . A n i c e b o x i s u s e d i n w h i c h s a l t - w a t e r h e a t t r a n s f e r f l u i d t a k e s h e a tt o t h e e v a p o r a t o r . F i g u r e 6 s h o w s t h e a r r a n g e m e n t o f t e m p e r a t u r e s e n s o rs i n t h e s p ir a l p l a t ea d s o r b e n t b e d ( i n s e r t e d i n t h e m i d d l e o f th e b e d h e i g h t ) .

T h e c o n n e c t i o n s o f th e t w o a d s o r b e r s t o th e c o n d e n s e r a n d e v a p o r a t o r a r e b y f o u r v a c u u mv a l v es , w h i c h k e e p o n e a d s o r b e r w h e n r e g e n e r a t e d b e i n g c o n n e c t e d t o t h e c o n d e n s e r a n d t h eo t h e r a d s o r b e r w h e n c o o l e d fo r a d s o r p t i o n c o n n e c t e d t o t h e e v a p o r a t o r . H e a t i n g to a n a d s o r b e ris c o n t r o ll e d b y a c o m p u t e r , t h e m e a s u r e d d a t a o f e v e r y s e n so r is s h o w n o n t h e d i s p la y o f c o m -p u t e r , w h i c h d e m o n s t r a t e s t h e w h o l e s y s t e m ( S c r e e n 1 ), t h e t e m p e r a t u r e f ie ld s o f a d s o r b e r - 1( S c r e e n 2 ) a n d a d s o r b e r - 2 ( S c r e e n 3 ) , t h e t e m p e r a t u r e v s t i m e c u r v e s o f t h e a d s o r b e n t b e d ( a v e r -a g e ) a n d t h e t h e r m a l f l u id f lo w i n / o u t ( S c r e e n 4 ), a n d a l s o th e p r e s s u r e v e r s u s t i m e c u r v e s o fa d s o r b e r s ( S c r e e n 5 ). T h e d a t a a c q u i s i t i o n s y s t e m m a k e s u s p o s s i b le to r e a d a ll t h e d a t a f r o mt h e d o c u m e n t d a t a f i l e s .

E X P E R I M E N T SH e a t t r a n sf e r o f s p ir a l p l a t e a d s o r b e r

H e a t t r a n s f e r f r o m t h e r m a l f lu id t o a d s o r p t i o n b e d i s c r it ic a l f o r a n a d s o r b e r , t h e p e r f o r m a n c eo f s p ir a l p l a t e a d s o r b e r c a n b e t e s te d f r o m r e a l o p e r a t i o n . A t y p i c a l r u n s h o w n i n F i g . 7 , i nw h i c h c u r v e 1 a n d 2 re p r e s e n t t h e r m a l f lu id i nl et t e m p e r a t u r e a n d a v e r a g e b e d t e m p e r a t u r e r e-s p e c ti v e ly . T h e e x p e r i m e n t a l r e s u lt s i n d ic a t e t h a t t h e a d s o r p t i o n b e d t e m p e r a t u r e f o l l o w s th et h e r m a l f l u i d i n l e t t e m p e r a t u r e q u i t e w e l l .

T h e e x p e r i m e n t a l c y c le ti m e i s 4 0 m i n , w h i c h i n c lu d e s h e a t i n g , c o o l i n g a n d h e a t r e c o v e r y p r o -c e s s e s .

Fig. 6. The arrangement of thermocouples in an adsorption bed. 1, thermal fluid in; 2, temperature sen-sors; 3, activated carbon; 4, therm al fluid out.


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18 R. Z. Wang e t a l120100

v 8 0N 6 0~ 4 0

2 00

l thermal fluid inlet temperature2 average bed temperature

i2 / :.,.. Ni

0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0T i m e s e c )

Fig. 7. Adsorption bed temperature vs. thermal fluid inlet temperature for one adsorber.Desorption speed of adsorption bed

The desorption speed of an adsorber can be estimated from the desorbed gas mass vs timecurve. A typical experimental test is shown in Fig. 8. For the measurement the throttl ing valveis closed the desorbed methanol from one adsorber is condensed in the condenser the con-densed liquid is accumulated in the glass receiver in which the liquid quantity can be indicated.This measurement is performed after the full water in the ice box was iced. The desorptionspeed curve indicates that a desorption time of 15-20 min is expected for the real operation ofthe system as the desorption occurs mainly in this period.

ycle timeCycle time for a real adsorption system depends on three processes: adsorpt ion heat recoveryand desorption. Figure 8 indicated the desorption speed however adsorp tion speed is impossibleto measure in this real system.

In the air conditioning operat ion condition it seems tha t adsorption goes more fast than des-orption however it will be different for refrigeration conditions especially for very low evapor-ation pressures. In the real operation heat recovery process is about 3-5 rain this time could beshorter if the thermal fluid lines had larger flow capacity.

3

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~ 1 0 0~D

0 0 4 0 0 8 0 0 1 2 0 0T i m e s e c )

Fig. 8. Desorption speed of an adsorber for a maximum desorption temperature of 110 C.


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Experiment on a continuous hea t regenerative adsorption refrigerator 1912

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1- for 40 minutes cycle time2- for 60 minutes cycle time

. . . . i . . . . ~ . . . . i . . . . i . . . . i . . . . i . . . . i . . . .0 2000 4000 6000 8000T i m e s e e )

Fig. 9. Co oling effect with differen t cycle times. 1-cycle im e for 40 min ; 2-cycle im e for 60 min.T h e o p t i m i z e d c y c l e t i m e f o r r e f ri g e r a t i o n e ff e c t w a s t e s t e d i n w h i c h t h e i c e b o x h a s n o h e a t

l o a d . T h e s a l t - w a t e r c o o l a n t t e m p e r a t u r e w a s m e a s u r e d f o r t h r e e o p e r a t i o n c y c l e t im e 4 0 r a in6 0 r a in a n d 8 0 m i n . F i g u r e s 9 a n d 1 0 s h o w s t h e c o o l i n g s p e e d o f t h e c o o l a n t . F o r e a c h o p e r a t i o nt h e r e is a t e m p e r a t u r e j u m p w h i c h is c a u s e d b y h e a t l e a k a g e a n d c o n d u c t e d h e a t f r o m t h e c o o l -a n t p u m p . I n o r d e r to g e t m a x i m u m c o o l in g s pe e d t h e c o o l a n t p u m p i s s h u t - d o w n d u r i n g h e a tr e c o v e r y p r o c e s s . F o r t h e s a m e in i ti a l c o n d i t i o n s a n d s a m e o p e r a t i o n t i m e p e r i o d t h e la s t c o o l -a n t t e m p e r a t u r e c a n b e c o m p a r e d a s s h o w n i n F ig . 9 a n d F i g. 1 0 w e c a n se e 4 0 m i n c y c l e t i m ei s a l i tt le b i t b e t t e r t h a n 6 0 m i n c y c l e t i m e a n d m u c h b e t t e r t h a n t h a t o f 8 0 m i n . T h i s r e s u l tc o u l d b e a l so e s t i m a t e d f r o m t h e m e a s u r e d r a t e o f m e t h a n o l d e s o r p t i o n s h o w n i n F ig . 8.

I n r e a l r e f r i g e r a ti o n o p e r a t i o n t h e c y c le t i m e 4 0 m i n w a s c h o s e n .I c e - m a k i n g t e s t

T w o e x p e r i m e n t a l c o n d i t i o n s h a v e b e e n t e st e d t o m a k e i ce w i t h t h e a d s o r p t i o n r e f r i g e r a t o r .Te s t 1 A f t e r t h e a d s o r p t i o n r e f r i g e r a t o r re a c h e d n o r m a l o p e r a t i o n c o n d i t i o n 1 5.5 k g w a t e r

w i t h a t e m p e r a t u r e o f 29 .8 C w a s f i ll ed i n t o t h e i c e b o x t h e e x p e r i m e n t a l c o n d i t i o n s a r e ;a d s o r p t i o n t e m p e r a t u r e 2 5 C c o n d e n s i n g t e m p e r a t u r e 2 2 C e v a p o r a t i o n t e m p e r a t u r e - 1 5 C

12- for 40 minutes cycle time

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42

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0 2000 4000 6000 8000Time (sec)

F i g . 1 0 . C o o l i n g e f f e c t w i t h d i f f e r e n t c y c l e t i m e s l - c y c l e t i m e f o r 4 0 m i n : 2 - c y c l e t i m e f o r 8 0 m i n .


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20 R. Z. Wang e t a l3 02 52 O

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i - - - : : ' - - ~ - ' ~ -

0 4 0 0 0 8 0 0 0 12 0 0 0 1 6 0 0 0Time s ec )Fig. 11. Refrigeration effect o f the ads orp tio n system for the first 5 h of test 1. 1, wate r temp era ture inthe ice box, 2, coolant temperature.

d e s o r p t i o n t e m p e r a t u r e 1 00 C . T h e f i rs t 5 h r e f r i g e r a t i o n e f f e c t c a n b e s h o w n i n F i g . l l , i nw h i c h c u r v e I r e p r e s e n t s m e a s u r e d w a t e r t e m p e r a t u r e i n t h e i c e b o x , c u r v e 2 r e p r e s e n t s t h e s a l tw a t e r c o o l a n t ) t e m p e r a t u r e . F i g u r e 11 s h o w s t h a t i t t a k e s a b o u t 1 2 0 0 0 s t o s t a r t w a t e r -i c et r a n s f o r m a t i o n , h o w e v e r a s u b - c o o l in g i s n e e d e d t o i n it i at e t hi s tr a n s f o r m a t i o n . D u r i n g t h ew a t e r - i c e t r a n s f o r m a t i o n p e r i o d , b o t h o f t h e c o o l a n t a n d w a t e r t e m p e r a t u r e a r e n e a r l y c o n s t a n t .T h e l a s t 5 h f o r t h e o p e r a t i o n i s s h o w n i n F i g . 1 2, i n w h i c h t h e s t o p p o i n t r e p r e s e n t s 2 4 h o f r e-

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- 1 0 . . . . , . . . . , . . . . , , - , , . . . .0 4 0 0 0 8 0 0 0 1 2 0 0 0 1 6 0 0 0 2 0 0 0 0T i m e ( s e e )

Fig. 12. Re|Yigeration effect of the ads orp tion system for the last 5 h of test 1. 1, ice temperat ure, 2,coolant temperature.


9/11

E x p e r i m e n t o n a c o n t i n u o u s h e a t r e g e n e r a t i v e a d s o r p t i o n r e f r i g e r a t o r 2 1

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0 2 0 0 0 6 0 0 0 1 0 0 0 0 1 4 0 0 0 1 8 0 0 0T i m e s e c )

F i g . 1 3 . R e f r i g e r a t i o n e f fe c t o f t h e a d s o r p t i o n s y s t e m f o r t h e f i rs t 5 h o f t e s t 2 . 1 w a t e r t e m p e r a t u r e i nt h e i c e b o x 2 c o o l a n t t e m p e r a t u r e .

f r i g e r a ti o n , t h e r e m a i n e d w a t e r w a s w e i g h t e d a s 0. 9 k g , th u s t h e o n e d a y i c e m a d e b y t h e m a -c h i n e i s 1 4.6 k g , t h e i ce h a s a t e m p e r a t u r e o f - 3 .7 C .

W i t h a c yc l e t i m e o f 4 0 m i n a n d t h e a b o v e o p e r a t i o n c o n d i t i o n s , t h e m e a s u r e d d e s o r b e dm e t h a n o l f o r t h e t w o b e d s is 50 0 m l .

Test 2 T h e s a m e o p e r a t i o n t e s t w a s p e r f o r m e d b u t w i t h d i f f e r e n t o p e r a t i o n c o n d i t i o n s . I n t h i st e s t, 1 4 k g w a t e r w i t h a t e m p e r a t u r e o f 2 9 .8 C w a s f i ll ed i n t o t h e i c e b o x a f t e r t h e a d s o r p t i o nr e f r i g e r a t o r r e a c h e d t h e n o r m a l o p e r a t i o n c o n d i t i o n . T h e e x p e r i m e n t a l c o n d i t i o n s a r e : a d s o r p -t i o n t e m p e r a t u r e 3 0 ~ C , c o n d e n s i n g t e m p e r a t u r e 3 0 ~ C, e v a p o r a t i o n t e m p e r a t u r e - 13 .5 C , d e s o -r p t i o n t e m p e r a t u r e 1 01 .5 C . T h e f i rs t 5 h a n d t h e l a s t 2 h r e f r i g e r a t i o n e f f e c t s a r e s h o w n i nF i g . 1 3 a n d F i g . 1 4 r e s p e c t i v e l y .

W i t h a c y c le ti m e o f 4 0 m i n a n d t h e a b o v e o p e r a t i o n c o n d i t i o n s , t h e m e a s u r e d d e s o r b e dm e t h a n o l f o r t h e t w o b e d s i s 4 2 0 m l . T h e m e a s u r e d r e m a i n e d w a t e r i n th e i c e b o x a t 2 4 h r e -f r i g e r a t i o n w a s 0 . 7 5 k g , t h u s t h e 2 4 h r e f r i g e r a t i o n y i e l d s 1 3 .2 5 k g i c e .

D I S C U S S I O N ST h e a b o v e e x p e r i m e n t s w e r e ta k e n i n t h e p r o t o t y p e a d s o r p t i o n s y s t e m , in w h i c h s o m e

i m p r o v e m e n t s s h o u ld b e f u r t h e r m a d e .T h e l in e d i a m e t e r f o r t h e t h e r m a l f l u id l o o p is c r it ic a l f o r t h e s p e e d o f a d s o r p t i o n , d e s o r p t i o n

a n d h e a t r e c o v e r y p r o c e s s e s , t h e 0 . 4 i n . l in e is a li tt le b i t s m a l l e r , i f t h e d i a m e t e r i s l a r g e r t h a n0 . 6 i n . th e c y c l e t i m e c o u l d b e f u r t h e r s h o r t e n e d , e s p e c i a l l y th e t i m e f o r h e a t r e c o v e r y p r o c e s s ;T h e l in e d i a m e t e r f o r m e t h a n o l a n d t h e o p e n n e s s o f c o n n e c t i n g v a l v e s a r e a ls o cr i ti c a l f o ra d s o r p t i o n a n d d e s o r p t i o n s p e e d s .

A s h e ll a n d t u b e t y p e h e a t e x c h a n g e r a r r a n g e d h o r i z o n t a l l y w a s u s e d a s a n e v a p o r a t o r , w h i c hs e r v e s a s a f l o o d e d t y p e e v a p o r a t o r , t h e d i a m e t e r o f t h e s h e ll is 1 4 c m , i f t h e f u l l t u b e s h e a te x c h a n g e r w e r e u s e d f o r h e a t t r a n s f e r b e t w e e n e v a p o r a t i n g m e t h a n o l i n t h e sh e ll a n d t h e c o o l a n ti n th e t u b e s, t h e n a m a x i m u m t e m p e r a t u r e d i f f e re n c e o f 7 C w o u l d o c c u r i n t h e e v a p o r a t i n g


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stop o f operationi i I i } i i I i i i i i i ~0 2 0 0 0 4 00 0 6 00 0 8 0 0 0 1 0 0 0 0

Time see)F i g . 1 4. R e f r i g e r a t i o n e f f e c t o f t h e a d s o r p t i o n s y s t e m f o r t h e l a s t 2 h o f t e s t 2 . l i c e t e m p e r a t u r e 2c o o l a n t t e m p e r a t u r e .

m e t h a n o l f o r a n e v a p o r a t i o n t e m p e r a t u r e o f - 1 0 C , t h o u g h i t w o u l d n o t b e s o s e r io u s f o r a i r-c o n d i t i o n i n g p u r p o s e . I n t h e e x p e r i m e n t s o n l y 1 / 3 h e a t t r a n s f e r a r e a w a s u se d a b o u t 1 /3 tu b e si m m e r s e d i n li q u id ) , t h u s i c e - m a k i n g w a s p o s s i b le h o w e v e r i t f o r m e d a b o t t l e -n e c k f o r h e a tt r a n s f e r , w h i c h m a d e t h e e v a p o r a t o r n o t m a t c h t h e m a c h i n e r e f r i g e r a t i o n p o w e r .

T h e h e a t e x c h a n g e r i n t h e i c e b o x i s a l s o c r i t i c a l f o r t h e i c e m a k i n g . W e t r i e d s e v e r a l t y p e sa n d s iz e s o f h e a t e x c h a n g e r s s u c h a s c o i l - tu b e h e a t e x c h a n g e r , a n d n o r m a l a i r - c o o l e d c o n d e n s e r ,b i g h e a t t r a n s f e r a r e a y i e l d ed g r e a t i ce p r o d u c t i o n .

I f i t is c o m p a r e d w i t h a ir c o n d i t i o n i n g A C ) o p e r a t i o n c o n d i t i o n , t h e r e f r ig e r a t i o n o p e r a t i o nc o n d i t i o n i s m o r e d i f fi c u lt t o r e a c h , n o t o n l y c a u s e d b y h e a t l e a k s b u t a l s o c a u s e d b y lo n ga d s o r p t i o n t i m e . I n t h e A C c o n d i t i o n s , a d s o r p t i o n i s f a s t e r t h a n d e s o r p t i o n , b u t i n t h e r e f r i g e r -a t i o n c o n d i t i o n s , a d s o r p t i o n i s s l o w e r t h a n d e s o r p t i o n .

C y c l e t im e i s i m p o r t a n t f o r a n a d s o r p t i o n s y s t em , b u t i t is u s u a ll y c o n t r a d i c t e d t o C O P o f th es y s t e m . A d s o r p t i o n r e f r i g e r a t i o n i s a t y p i c a l d y n a m i c s y s t e m , d y n a m i c a d s o r p t i o n a n d d e -s o r p t i o n , t h e n o r m a l s t e a d y s t a t e e v a l u a t i o n o f C O P a n d s p e ci fi c p o w e r d e n s i ty m i g h t b e f a rd e v i a t e d f r o m r e a l o p e r a t i o n s .

T h e d e s i g n o f a n a d s o r b e r s h o u l d c o n s i d e r t h e m a ss r a t i o b e t w e e n m e t a l a n d a d s o r b e n t . I no u r s y s t e m , t h e a d s o r b e r w a s t a k e n f r o m a s t a n d a r d u s e d f o r h e a t t r a n s f e r i n c h e m i c a l e n g in -e e r i n g , h o w e v e r i ts fl a n g e is s p e c i a ll y m a d e w h i c h i s u s e d f o r c h a n g i n g a d s o r b e n t . E a c h a d s o r -b e r h a s a w e i g h t o f 7 0 k g m a i n l y t h e t w o u p p e r f l an g e s ) a n d o n l y 6 k g a c t i v a t e d c a r b o nf il le d , l a r g e a m o u n t o f s e n s i b le h e a t i s w a s t e d t o h e a t t h e s t a i n l e s s s te e l c h a m b e r i t s el f, w h i c hc a u s e s a l s o a l o w C O P v a l u e . T h e r e a l m a c h i n e d o e s n o t n e e d t h e f l a n g e s l i k e t h i s p r o t o t y p es y s t e m , w h i c h m a y s h o w b e t t e r p e r f o r m a n c e r e s u l t s . T h e f u r t h e r w o r k s h o u l d c o n s i d e r t h eh e a t c a p a c i t y i n f l u e n c e o n s y s t e m p e r f o r m a n c e [ 1 3 ] , t h e s p i r a l p l a t e a d s o r b e r s h o u l d b e s p e c i f i -c a l l y m a n u f a c t u r e d .

T h e r e c e n t w o r k s h o w s t h e a d s o r p t i o n r e f r i g e r a t o r c a n m a k e i ce m o r e t h a n 1 k g p e r d a y p e rk g a c t i v a t e d c a r b o n . H o w e v e r , i f t h e p r e v i o u s l y m e n t i o n e d i m p r o v e m e n t s a r e d o n e w e ll , i tw o u l d b e e x p e c t e d t o h a v e a s p e c i fi c i c e m a k i n g p o w e r d e n s i t y o f 2 - 4 k g i ce p e r d a y p e r k g a c ti -v a t e d c a r b o n .


11/11

E x p e r i m e n t o n a c o n t i n u o u s h e a t r e g e n e r a t iv e a d s o r p t i o n r e f r ig e r a t o r 2 3R E S U L T S

T h e p r ev i o u s s t u d i e s s h o w t h e f o l l o w i n g .1 . Sp i ra l p la te hea t exchanger i s su i t ab le fo r adsorp t ion r e f r igera t ion sys tem to be used as an

ad s o r b e r . T h e g o o d h ea t t r an s f e r p r o p e r t i e s en s u r e s h o r t cy c le t i m e f o r ad s o r p t i o n s y s tem snow i t i s ver i f i ed tha t a 40 min cyc le t ime i s poss ib le .

2 . T h e co n s t r u c t ed a d s o r p t i o n r e f r i g e r a t o r u s in g ac t iv a t ed ca r b o n - m e t h an o l c an m ak e i c e p r o p -e r ly . T h e e x p e r i m en t a l r e s u lt s s h o w t h e s y s t em can m a k e m o r e t h an 1 k g i ce p e r k g ad s o r b en to n e d ay . T h e ex p ec t ed i ce m ak i n g p o w er d en s i t y w i ll b e 2 -4 k g i ce p e r k g ad s o r b en t o n e d a ya f t e r t h e f u r t h e r i m p r o v em en t .

Ac k now l e dge m e n t s - - Th i s w o r k w a s s u p p o r t e d b y S h a n g h a i S c i e n c e S t a r P r o g r a m . T h e a u t h o r s a l s o t h a n k t h e S h u g u a n gT r a i n i n g P r o g r a m o f S h a n g h a i E d u c a t i o n C o m m i s s i o n, t h e T r a n s - C e n t u r y T r a i n in g P r o g r a m F o u n d a t i o n f o r t h e T a le n t so f S E D C a n d t h e E d u c a t i o n F o u n d a t i o n o f Y . D . H o u .

R E F E R E N C E S1 . M. Pons a nd J . J . Gu i l l e mi no t , De s i gn o f a n e xpe r i me n t a l s o l a r - powe r e d s o l i d - a ds o r p t i on i c e ma ke r . T r a n s . A S M E(J . Solar Energy Engg. ) 108, 332 -337 1986).2 . N . Dous s , F . E . M e un i e r a nd L . M. Sun , P r e d i c t i ve mod e l a nd e xpe r i m e n t a l r e s u l ts f o r a t wo- a ds o r be r s o l id a ds o r p -t i o n h e a t p u m p . Ind. Eng, Chem. Res. 27 2) , 310 -316 1988).3 . F . M e u n i e r a n d N . D o u s s , P e r f o r m a n c e o f a d s o r p t i o n h e a t p u m p s : a c t i v e c a r b o n - m e t h a n o l a n d z e o l i t e- w a t e r p a i r s.A S H R A E T r a n s . , 267-274 1990).4 . S . V . S h e l t o n a n d W . J . W e p f e r , S o l i d - V a p o r h e a t p u m p t e c h n o l o g y . I n lEA Heat Pump Conf . , Tokyo, pp . 525-535,1990.5 . R . E . C r i t o p h , F o r c e d c o n v e c t i o n e n h a n c e m e n t o f a d s o r p t i o n c y c le s. Heat Recovery Sys tems and CHP 14 4) , 34 3-350 1994).6 . G . R e s t u cc i a , V . R e c u p e r o , G . C a c c i o l a a n d M . R o t h m e y e r , Z e o l i t e h e a t p u m p f o r d o m e s t i c h e a ti n g . Energy Int. J.13, 333 -342 1988).7 . D . I . Tc h e r ne v a n d D . T . Em e r s on , H i gh e ff ic ie ncy r e ge ne r a t i ve z e o l i t e he a t pum p . A S H R A E T r a n s . , 94, 1988).8 . G . C a c c i o l a , G . C a m m a r a t a , A . F i c h e r a a n d G . R e s t u c ci a , A d v a n c e s o n i n n o v a t i v e h e a t e x c h a n g er s in a d s o r p t i o n

h e a t p u m p s . I n Proc. Syrup. Solid Sorption Refrigeration, Par is , pp . 221-226 1992).9 . H . Y a n g i , F . K o m a t u , N . I n o a n d Y . Y o k a m o t o , P r o t o t y p e t e s t o f a d s o r p t i o n r e f r i g e r a to r u s in g s il i ca g e l -w a t e rpa i r s . I n Proc. Syrup. Solid Sorption Refrigeration, Pa ris, pp. 117-122 1992).1 0 . G . C a c c i o l a a n d G . R e s t u c c i a , P r o g r e s s o n a d s o r p t i o n h e a t p u m p s . H e at Re c ov e r y Sy s t e m s and C H P 14 4 ) , 40 9 -420 1994).11 . T . A . F u l l e r , W. J . We pf e r , S . V . She l t o n a nd M+ W. E l li s, A t w o- t e m pe r a t u r e mo de l o f t he r e ge ne r a t i ve s o l i d - va po rh e a t p u m p . Trans. A S M E (J . Energy Res . Technol .) 116, 29 7-3 04 1994).1 2. R . Z . W a n g , Y . T e n g a n d J . Y . W u , A c o n t i n u o u s h e a t r e g e n e r a t iv e a c ti v e c a r b o n - m e t h a n o l r e f r i g e r a to r u s i n g s p i r a lp l a t e h e a t e x c h a n g e r a s a d s o r b e r s , I n Proc. In t , Ab-Sorpt ion Heat Pum p C onf 96, Mont r e a l , Se p t e mbe r 16 - 21 ,Vol . 1 , pp . 587 -59 4 1996).1 3. Y . T e n g , R . Z . W a n g a n d J . Y . W u , S t u d y o f t h e f u n d a m e n t a l s o f a d s o r p t i o n s y s te m s . Appl. Thermal Engng 17 4),327 - 338 1997 ) .

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