Watten 1987 Aquacultural-Engineering

7/28/2019 Watten 1987 Aquacultural-Engineering

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Aq uacultural Engineering6 (1987) 127-140

Com parative Hydraulics o f a Rectangular Cross-flowRearing U nitB a r n a b y J . W a t te n a n d L . T o d d B e c k

Pennsylvania Pow er and Light Co. , De partm ent of Technology and E nerg y Assessment,Brurmer Is land A qua culture Project, PO B ox 221, York Ha ven , Pennsylvania 17 370,U S A

A B S T R A C TThe cross-flow rearing unit described was designed to provide completelym ixe d f lo w reactor (CM FR) behavior in a standard rectangular vesselwith little required tan k modification. W at er is distributed u nifor m lyalong o ne side o f the vessel, via a manifold, a nd is collected in a draingutter asse m bly running the length o f the opposite side . The influent isjetted directly at the water surface with sufficient force to establish rotarycirculation about the longitudinal axis. Hydraulic characteristics of thetan k are identi fied base d on a n analysis of residence t ime distribution an dare com pa red with those established fo r standard rectangular an d circu-lar tanks o f eq ua l l iquid capacity (1"715 mS). Results confirm the cross-f low tank is operating as a C M FR b oth wi th an d wi thou t ish present . Thistan k type appears particularly s uited fo r high density culture applicationsrequiring m inim al f low. Specific advantages include: (1) a ho m oge neo uscon tent, (2) self-cleaning prop erties, (3) efficient use o f wa ter supp lies a n dpressure, (4) velocity control, an d (5) the flexib ility o f operating as a plugflo w type rearing un it during f lushing or f ish handling operations.

N O M E N C L A T U R ECCiCminCoACmaxAquacuhural Engineering 014 4-86 09/8 7/S0 3.50 --Publishers L td. England, 1987. Printed in G rea t Britain

Tracer concentrat ion in e f f luent above normal supply leve l (mgliter- l )T racer concen trat ion in e f f luent at t ime i (mg l i ter- ~Tracer concentrat ion in inf luent fo l lowing step down (mgliter- 1)Tracer concentrat ion in inf luent above normal supply leve l (mgliter- l )M axim um change (negative) in trace r con cen trat ion (mg l iter -1)

127Elsevier Applied Science


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128 B.J. W a t t e n , L . T o d d B e c kDD]IuLLQt .tVO 20

Dispersion c o e f f i c i e n t ( m 2 s - 1)Ve sse l d i spe r s ion num be r , d im e n s ion le s sCh arac te r i s t ic length (m)V olum etr ic f low ra te ( l it er s m in - l )T i m e ( m in )V / Q , t he o r e ti c a l m e a n r e t e n t ion t im e (m in )C a lc u la t e d m e a n r e t e n t ion t im e (r ain )V olum e of l iqu id in tank ( li te rs )F lu id ve loc i ty (m s-x )V a r ia nc e a bou t ic ( m i r l 2 )t/i, n o r m a l i z e d t im e , d i m e n s i o n l e s s

I N T R O D U C T I O NRe searc h a t the Bru nn er I s land fac il i ty i s d i rec ted tow ards es tab l i sh ingthe m os t a ppr op r i a t e t e c hno logy f o r u t i li z ing the r m a l e f f lue n t f o r a qua -c u l tu r e pu r pose s . P r im a r y e m p ha s i s ha s be e n p la c e d o n the h igh de ns i tycul ture of channe l ca t f i sh ( Ic ta lurus punctatus) , hybr id s t r ipe d ba ss( M oro ne saxat il is x M oro ne chrysops ) and t i lap ia ( Oreo chrom is aureus )i n r a c e wa ys r e c e iv ing supp ly wa te r supe r sa tu r a t e d w i th d i s so lve d oxyge n(DO) (Wat ten and Beck , 1985) . The raceways used , measur ing 3 .1 mwide x 1 .1 m dee p x 61 m long , were or ig ina l ly des igned to s imu la te theper form anc e o f a p lug f low reac tor (PFR) ; i.e . wa te r in t rodu ced in to theve sse l a t one e nd m ove s th r ough i t w i th c ons ta n t a nd un i f o r m ve loc i tya nd i s d i sc ha r ge d a t t he oppos i t e e nd . A l though the r e c t a ngu la r sha peof fe r s the advantages of ease of f lush ing and f i sh handl ing (P iper et al.,1982) , ve loc i t ie s a re charac te r i s t ica l ly low resu l t ing in f i sh wi th poors t a m ina (B ur r ows a nd C he n owe th , 1970) . M or e im por t a n tly , a g r a d ie n tin D O a nd f i sh m e ta bo l i te s i s e s t a b l ishe d a long the long i tud ina l ax is o fthe tank promot ing d ispar i ty in f i sh d is t r ibu t ion , f i sh qua l i ty (Bur rowsa nd C he nowe th , 1970) a nd , a s e v ide nc e d in p r oduc t ion t r i a l s r e c e n t lycon duc ted a t our fac il ity , mo r ta l i ty and growth . Th e ex ten t of thegradien t e s tab l i sh ed is p rop or t ion a l to the f i sh b iom ass present (Weste rsand Prat t, 1977) . Th us , th i s po ten t ia l p rob lem is of pa r t icu la r con cern inh igh dens i ty cu l ture appl ica t ions .Ci rcu la t ing rea r ing uni t s , inc luding the Swed ish (P ipe r et al., 1982) ,c i r c u la r ( La r m oye ux et al., 1973) a nd B ur r ows type s ( B ur r ows a ndC he nowe th , 1970) , a r e ope r a t e d a s c om ple te ly m ixe d f low r e a c to r s( C MFR) a nd a s suc h a vo id the p r ob le m s ou t l ine d a bove . Wa te r i n t r o -duc ed un de r pre ssure es tab l i shes a c i rcu la ting f low which , in addi t ion tom a in ta in ing a hom o ge ne o us c on te n t, p r ov ide s ( P ipe r et al., 1982): (1)


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Hydraulics o f a rectangular cross-flow rearing unit 1 2 9s e l f -c l e a n i ng p ro pe r t i e s , (2 ) e f f ic i e n t u s e o f a v a i l a b l e w a t e r s upp l i e s, a n d(3 ) v e l o c i ty c o n t r o l . T h e c r o s s- f lo w t a n k d e s c r i b e d h e r e w a s d e s i g n e d t oo f f e r t h e h y d r a u l i c c h a r a c t e r i s t i c s o f a C M F R y e t r e t a i n t h e d e s i r a b l er e c t a n g u l a r s h a p e o f t h e r a c e w a y s c u r r e n t l y i n u s e. T h e d e s i g n w a si n t e n d e d t o p r o v i d e a n a l te r n a ti v e t o t h e B u r r o w s - ty p e r a c e w a y m o d i fi -c a t i o n t h a t , a t o u r f a c il it y, w a s c o n s i d e r e d u n e c o n o m i c a l i n t e rm s o f b o t hc o n s t r u c t i o n a n d e n e r g y r e q u ir e m e n t s .In t h i s pa pe r , t he hydra u l i c c ha ra c t e r i s t i c s o f t he c ros s - f l ow t a nk a r ei d e n t i fi e d b a s e d o n a n a n a l y si s o f r e s i d e n c e t i m e d i s t r ib u t i o n . D a t a a r ec o m p a r e d w i t h t h o s e e s t a b l i s h e d f o r s t a n d a r d r e c t a n g u l a r a n d c i r c u l a rt a nks o f e qua l l i qu i d c a pa c i t y . To t e s t t he hypo t he s i s t ha t f i s h i n f l ue nc eh y d r a u l i c b e h a v i o r , p e r f o r m a n c e w a s a s s e s s e d b o t h w i t h a n d w i t h o u tc h a n n e l c a t fi sh p r e s e n t i n e a c h t a n k t y p e. I n a d d i t io n , c o r r e l a t i o n ise s t a b l is h e d a m o n g c r o s s- f lo w v e lo c it y , o p e r a t i n g p r e s s u re , a n d f l o w r a te .

T A N K D E S I G NT h e c r o s s- f lo w t a n k is re c t a n g u l a r w i t h a d e p t h - t o - w i d t h r a t io o f a b o u t 1t o 1 (F ig . 1 , Ta nk B) . W a t e r is d i s t r i bu t e d un i fo rm l y a l ong t he l e ng t h o fo n e s i d e o f t h e t a n k , v i a a m a n i f o l d , a n d i s c o l l e c t e d i n a d r a i n g u t t e r

S ID E IE W S E N DV I E W S I N F L U E N T- I ,, 3 3 ~ 00 m T R A C E R r l

. . . . . S U P P L Y A N I F O L D I T H / ' i" T ; ~ :t E ~ : 'i~ : ~ii ::::[ I.(k :m S T A N D IF E 1 5 x 7.g m m D Ik H O L E S , .~ T A N K A

D S F ~ , - - - 7 3 .7 c m - - ~iS U P PL Y A N IF O L D IT H 2 xS ~ m m I k H O L E S ~ . .. ~ . T R A C E R ~ I~ _ _ T T T T T T T ~ . T T T T T T T . . ~ r IN F L U E N T~ %

| ~ . ~ t 7 ,6 mD R A I N A L U E I | ~ J~ : ~ i ~ - ' - R E A R L O O R R A I N ,' ,Ir "

F i g . 1 . D i m e n s i o n s o f t h e r e c t a n g u l a r t e st t a n k s. T a n k A r e p r e s e n t s t h e c o n v e n t i o n a lo r p l u g - f l o w c o n f i g u r a t i o n . T a n k B r e p r e s e n t s t h e c r o s s o r c o m p l e t e l y m i x e d f l o w c o n -f i g u ra t io n . N o t e t h a t t h e s i d e v ie w o f T a n k B ' s s u p p l y m a n i f o l d h a s b e e n d e p i c t e d a b o v e

i ts t ru e p o s i t i o n i n th e t a n k . T h e e f f lu e n t s a m p l e p o i n t i s m a r k e d D S P .


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130 B.J. Wat ten , L . Tod d Be cka s s e m b l y r u n n i n g t h e l e n g t h o f t h e o p p o s i t e s id e . T h e i n f l u e n t is j e t t e dd i r e c t l y a t t he w a t e r s u r f a c e w i th s u f f i c ie n t fo rc e t o i n duc e ro t a ry c i r c u l a -t i o n a b o u t t h e l o n g i t u d i n a l a x is . T h e c o n t e n t s o f th e t a n k a r e i n t e n d e d t ob e h o m o g e n e o u s w i t h w a t e r m i x in g i n th e c i r c u m f e r e n t ia l b u t n o t l o n g i-t u d i n a l d i r e c ti o n . T h e r e f o r e , u n l i k e a l t e rn a t i v e C M F R d e s ig n s , d i s s o lv e do r s u s p e n d e d m a t t e r i n t r o d u c e d a t o n e p o i n t w i ll n o t n e c e s s a r i l y p a s st h r o u g h o r c i r c u l a t e a m o n g t h e e n t i r e g r o u p o f f i sh i n th e v e s se l.

I t w a s a l s o i n t e n d e d t h a t t h e c r o s s - f lo w v e l o c i ty w o u l d b e s u f fi c ie n t t os c o u r s o l id s f r o m t h e t a n k f l o o r a l l o w i n g t h is m a t e r i a l to b e p u r g e d c o n -t i n u o u s l y w i t h th e t a n k o v e r fl o w . O v e r f l o w e x it s t h e t a n k t h r o u g h a s e ri eso f s ta n d p i p e s w h i c h p r o j e c t d o w n w a r d f r o m t h e d r a i n g utte r." T h e s t a n d -p i p e s e x t e n d t o a d e p t h a t w h i c h t h e r o t a t i n g c o n t e n t s a r e f l o w i n gu p w a r d s i n a v e r ti c a l d i r e c t io n , t h u s e l i m i n a t in g t h e n e e d f o r s o l id s t om a k e a b r u p t c h a n g e s i n d i r e c t i o n p r i o r t o b e i n g p u r g e d . O v e r f l o w c o l -l e c t e d i n t h e g u t t e r i s d i s c h a r g e d t h r o u g h a d a m w a l l a t t h e r e a r o f t h et a n k . T h e c o n t e n t s o f th e t a n k a r e d r a i n e d c o m p l e t e l y b y o p e n i n g a g a tev a l v e p o s i t i o n e d i n t h e d a m a t fl o o r le v el . W h e n f i s h a r e t o b e c r o w d e dwi th a s c r e e n , o r i f t he t a nk i s t o be f l u s he d , a s t a ndp ipe i s i n s e r t e d i n ther e a r f l o o r d r a i n t o m a i n t a i n t h e w a t e r l e v e l b e l o w t h e d r a i n g u t t e ra s s e m b l y . W i th t h is d r a i n c o n f i g u r a t io n , t h e c r o s s - fl o w t a n k c a n t h e n b ec o n v e r t e d f r o m C M F R t o a P F R t y p e r e a r i n g u n i t b y d i v e r t i n g w a t e rf r o m t h e s id e - m o u n t e d m a n i f o l d to a n a u x i li a r y d i f fu s e r ( n o t s h o w n inF ig . 1 ) po s i t i one d a t t he h e a d e nd o f t he ve s s e l.

M A T E R I A L S A N D M E T H O D SBackgroundH y d r a u l i c b e h a v i o r i s e v a l u a t e d h e r e , a s i n p r e v i o u s r e a r i n g u n i t st u d ie s( B u r r o w s a n d C h e n o w e t h , 1 9 5 5 ; H u g h e s e t a l . , 1 9 7 4 ; B u r l e y a n dK l a ps is , 1 9 8 5 ), u s i n g m e t h o d o l o g y d e v e l o p e d b y D a n c k w e r t s ( 1 9 5 3 ) t oc h a r a c t e r i z e n o n - i d e a l f l o w w i t h i n p r o c e s s r e a c t o r s . T h e a n a l y s i sr e q u i r e s a p u l s e o r s t e p c h a n g e i n a n i n f l u e n t ( n o n - r e a c ti v e ) t r a c e r c o n -c e n t r a t i o n . M o n i t o r i n g t h e r e s p o n s e o f t h e e f f l u e n t a n d d e v e l o p i n g ar e c t a n g u l a r - c o o r d i n a t e p l o t o f t r a c e r c o n c e n t r a t i o n v e r s u s t i m ee s t a b l i s h e s t h e e x i t - a g e d i s t r i b u t i o n o f m a t e r i a l f l o w i n g t h r o u g h t h eve s s e l . F rom the s e da t a f l ow a nom a l i e s , s uc h a s s ho r t c i r c u i t i ng , c a n beiden t i f i ed as we l l a s the v a r iab les to, a2 an d D / p L . fc r e p r e s e n t s t h e m e a nr e s i d e n c e t i m e o f a f l u i d e l e m e n t w i t h i n t h e r e a c t o r w h e r e a s c r~ r e p re -s e n t s th e d i s p e r s i o n a b o u t t h e m e a n . W i t h a s te p d o w n i n t r a c e r c o n c e n -t ra t ion , f~ an d 02 a re c a lcu la ted as fo l low s (Le ven sp ie l , 1979) :


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Hyd raulics o f a rectangular cross-flow rearing unit 131

o ( C m i n - C i) d tic= ACmR~ ( 1 )

2 [ t ( f mi n- C ,)dt2 JO -2a = - t c (2)ACm~

At c less than the theoretical retention time l establishes the presence ofstagnant regions within the reactor. The extent of these regionsexpressed as a fraction of the reactor's total liquid volume is one minusthe quotient of fc/L A ~ greater than f is not in accord with the Law ofConservation of Matter and as such is used as an indicator of error inanalytical procedure (Levenspiel, 1979, 1985).The degree of axial dispersion, or mixing within a reactor is charac-terized by the dimensionless group D / / u L . This group, termed the vesseldispersion number, ranges in value from zero for ideal plug flow toinfinity for completely mixed flow reactor behavior. In the case of avessel operating with turbulent flow within its restricted inlet and outlet,D / / u L is related to a 2 as follows (Levenspiel, 1979):

2U~ 2 = 2 ( D / I u L ) - 2 ( D / l a L )2[ 1 - e - uL/D] (3)tAnalysesThe dimensions of the three tank types evaluated are given in Figs 1 and2. All tanks were constructed of fiberglass with a similar finish. Theliquid capacity of each tank was set at 1.715 m 3 prior to the stocking oftest fish. Calibration was achieved by transferring water from one tank toanother and adjusting standpipes accordingly. The resultant operatinglevels in the cross-flow, rectangular and circular tanks were, respectively,68-6, 66.0 and 65.9 cm. Water from an elevated reservoir flowed bygravity into each tank at a rate of 52.7 liters min- 1 providing a retentiontime, L of 32.5 min. Flow rate was measured using a stopwatch and con-tainer of known capacity.Residence time distribution was identified based on the response ofeach tank type to a reduction in tracer concentration from one steadyvalue to another. Chloride was used as the non-reactive tracer. A 0"315 NNaC1 solution was dispersed in the water supply pipe of each tank at a


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132 B. J . Wat ten, L. To dd B ec k

TRACERt

SUPPLYMANIFOLOWITH ~T lm-~kr ~ , , a t , ~ . s - . . ~ n ' ,. . . . . . . i

F ig . 2 . D im ens ions o f t he c ir cu l a r t e s t t ank r ep resen t ing the conven t i ona l comp le t e lymixed f low con f igurat ion . T he inf luent i s d i rec ted tan gent ia l ly a t an angle of 83* f rom thehor i zona l . T he e f f l uen t s ample po in t is mark ed DS P .

r a t e t h a t p r o v i d e d a 1 - 1 . 5 f o l d i n c r e a s e in C I - c o n c e n t r a t i o n a b o v e t h en o r m a l i n f l u e n t l e v e l o f 9 " 3 m g l i t e r - 1 . T h e b r i n e w a s d i s p e r s e d i m m e -d i a t e l y u p s t r e a m o f a s e ri e s o f i n t e r n a l b a f fl e p la t e s w h i c h s e r v e d t o m i xt h e b r i n e w i t h t h e i n f l u e n t j u s t p r i o r t o d i s t r ib u t i o n . B r i n e f l o w w a sp r o v i d e d b y a p e r i s t a l t i c p u m p o p e r a t i n g a t a c o n s t a n t s p e e d . A s t e pd o w n i n t r a c e r c o n c e n t r a t io n w a s i n it ia t e d o n c e c o n s t a n t a n d e q u a l C 1 -c o n c e n t r a t i o n s w e r e e s t a b l i s h e d i n b o t h t h e i n f l u e n t a n d e f f l u e n t . T h es t e p d o w n w a s a c h i e v e d b y t e r m i n a t i n g b r i n e f l o w a n d t h u s r e t u r n i n gi n f l u e n t C 1 - c o n c e n t r a t i o n s t o th e n o r m a l w a t e r s u p p l y le v el . S a m p l e s o ft h e i n f l u e n t a n d e f f lu e n t w e r e t h e n t a k e n a t p e r i o d i c i n t e r v a ls fo r C 1 -a n a ly s i s. C h l o r i d e c o n c e n t r a t i o n s w e r e d e t e r m i n e d b y t i tr a t i o n u s i n g t h ea r g e n to m e t r ic m e t h o d ( A P H A , 1 9 75 ).

T r a c e r t e s t s c o n d u c t e d w i t h f i s h p r e s e n t i n t h e t a n k s w e r e i n i t i a t e db e t w e e n 2 3 . 0 0 a n d 2 4 . 0 0 h t o m i n i m i z e o u t si d e d is tu r b a n c e s . E a c h t a n kw a s s t o c k e d o n 1 3 J u l y 1 9 8 4 w i t h 4 9 . 4 k g o f c h a n n e l c a t f i s h a v e r a g i n g2 3 .7 c m i n f o r k l e n g t h a n d 1 5 9 g i n w e i g h t. T h e f is h w e r e f e d a p e l le t e df e e d a t a r at e c o r r e s p o n d i n g t o 2 % o f th e i r b o d y w e i g h t o n e a c h o f th ef i rs t 4 d a y s o f a 5 - d a y a c c l i m a t i o n p e r i o d . T r a c e r c u r v e s w e r e e s t a b l i s h e di n d u p l i c a t e f o r t a n k s w i t h a n d w i t h o u t f i s h p r e s e n t . W a t e r t e m p e r a t u r e


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Hydr aulics of a rectangular cross-flow rearing unit 133d u r i n g a ll t e s ts r a n g e d b e t w e e n 2 8 . 9 a n d 2 9 -4 C . F o l lo w i n g d a t a c o l le c -ti o n f~, a 2, a n d D/lzL w e r e c a l c u l a t e d b a s e d o n e q n s ( 1 ) -( 3 ). A n a l y s i s o fv a r i a n c e w a s u s e d t o c o m p a r e m e a n v a lu e s o f t h e f ac t o rs m e a s u r e d .C o r r e l a t i o n a m o n g m e a n c r o s s- f lo w v e l o ci ty , f lo w r a te , a n d o p e r a t i n gp r e s s u r e w a s o b t a i n e d b y m e a s u r i n g th e t i m e r e q u i re d f o r d y e t o t ra v e l3 0 c m f r o m a p o i n t p e r p e n d i c u l a r t o , a n d 2 5 c m f r o m , t h e d r a i n g u t t e rs id e o f t h e t a n k . T h e d y e w a s d i s p e r s e d a t a d e p t h o f 5 c m a t f o u r p o i n t sa l o n g t h e le n g t h o f t h e v e ss e l. A m a n o m e t e r w a s u s e d t o m e a s u r e s ta t icp r e s s u r e w i t h i n t h e i n l e t m a n i f o l d a t e a c h o f t h e f lo w r a t e s t e s te d .

R E S U L T SR e s u l t s o f t h e c h l o r i d e t r a c e r t e s t s h a v e b e e n p l o t t e d i n F i g . 3 u s i n g an o r m a l i z e d v a l u e o f t im e ( 0 ) a n d t r a c e r c o n c e n t r a t i o n (C/Co).N o r m a l -i z e d t i m e i s o b t a i n e d b y d i v i d i n g t h e o b s e r v e d t i m e t b y t h e t h e o r e t i c a lr e t e n t i o n t i m e L T h e l a tt e r, i, is c a lc u l a t e d b y d i v i d i n g th e c a l i b r a t e d t a n kvo lum e by f l ow ra t e . I n t hos e t e s ts i nvo lv ing f is h , a c on ve r s ion f a c to r o f0 . 9 8 2 l it e rs k g - ~ b i o m a s s w a s u s e d t o c o r r e c t t h e c a l i b r a t e d t a n k v o l u m ef o r t h e v o l u m e d i s p l a c e d b y t h e t o t a l b i o m a s s p r e s e n t . T h e c o n v e r s i o nf a c to r u s e d r e p r e s e n t s t h e m e a n o f a se r ie s o f i n d i v id u a l m a s s - v o l u m em e a s u r e m e n t s ( s a m p l e s iz e = 1 2 ; S D = 0 .0 2 1 ). T h e p e r f o r m a n c e o f t h ec ros s - f l ow a nd c i r c u l a r t a nks , a s i nd i c a t e d by t he c lo s e f i t o f t he da t a t ot h e t h e o r e t i c a l r e s p o n s e c u r v e s ( F i g . 3 ) , a p p r o x i m a t e s t h a t o f a n i d e a lC M F R i n w h i c h a n o n - r e a c t iv e t ra c e r i s b e i n g p u r g e d . F u r t h e r e v i d e n c eo f C M F R b e h a v i o r is p r o v i d e d b y c al cu l at ed D/~uLvalues of oo (Table1 ). T h e r e s p o n s e o f th e r e c t a n g u l a r t a n k , h o w e v e r , d e v i a t e d c o n s i d e r a b l yf r o m t h a t p r e d i c t e d f o r a n i d e a l P F R ( F i g . 3 ) . D/juL va lue s e s t a b l i s he df o r t h i s t a n k t y p e a v e r a g e d 0 . 4 2 2 ( S D = 0 . 0 5 7 ) a n d 0 - 6 82 ( S D -- 0 .1 1 7 ) ,r e s p e ct iv e l y , f o r t e s ts c o n d u c t e d w i t h a n d w i t h o u t fi sh ; v a l u e s w h i c h c o n -f i rm a h igh de g re e o f m ix ing w i th in t he ve s se l . T he e f f e c t o f fi s h on D/IaLwa s no t s t a t is t i c a l ly s i gn i f i c a n t (P > 0 .05 ) .T a b l e 1 p r o v i d e s a c o m p a r i s o n o f th e r a t i o f c / t e s t a b l is h e d f o r e a c h o fthe t h re e t a nk t ype s . N o te t ha t fc i n t he r e c t a ng u l a r t a n k wa s ve ry c lo s e tot h e t h e o r e t i c a l r e t e n t i o n t im e w h e r e a s i~ i n b o t h m i x e d f lo w t a n k s r e p r e -s e n t s 7 3 - 8 4 % o f t h e s a m e . A n a l y s i s o f v a r i a n c e i n d i c a t e s t h e t a n k t y p eef fec t on U t i s h igh ly s i gn i f ic a n t ( P < 0 . 01 ) . I t c a n a l s o b e s e e n t ha t t hep r e s e n c e o f f i sh i n t h e m i x e d f l o w t a n k s r e s u l t e d i n a m o d e r a t e r e d u c t i o ni n ~ / f w h i l e i n th e r e c t a n g u l a r t a n k a n i n c r e a s e w a s o b s e rv e d . T h e e f fe c to f f i sh on t h i s r a t io , how e ve r , w a s no t s i gn i f ic a n t a t t he 9 5 % c on f ide n c el eve l. F u r the r i n s pe c t i on o f T a b l e 1 r e ve a l s t ha t va r ia nc e , a s ind i c a t e d bythe ra t io o f c r : /fc, wa s g re a t e r i n t a nk t e s ts n o t i nvo lv ing f i s h t ha n i n t e st s i n


8/14

134 B. J . Wat ten, L. To dd Be ck1 . 0 " * -

i 0 J . ~ RE .c 'rN~U ~RAN K THEORETICALFR I~PON~E0 , I F

i 0 . 4 - , - .

. s . A e0 . 0 " , = s . , : ,1 . 0 ~

' f ' E l l CROSSLO W AN Ki O J l- ' ~ / THEORETICALM FR ESPONSEI X ~ C lC o= e~e~0 .4 - " , , ~ ,

m IO ~ , , ,1 0f f 0 .8 CIRCULARANKU - J \ / T HE OR E T ICA LMFR ESPONSEI ~ * C / C = ""0 . 0 o . s 1 . 0 1 . 5 2 .o ~ 3 . 0 3 . s

N O m A U Z E O 'n Z E , U i - - e .Fig. 3. Sum mary of the chloride tracer studies co nd uc ted with and without 49.4 kg ofchannel catfish present in each tank type. Data plotted represent the mean of twoobservations.

w h i c h fi sh w e r e p r e s e n t . A s e x p e c t e d , v a r i a n c e w a s a l s o g r e a t e r in t h em i x e d f lo w t a n k s t h a n i n th e r e c t a n g u l a r t a n k . B o t h f i sh a n d t a n k t y p ee f fe c ts o n v a r i a n c e W e re s ig n i fi c an t ( P < 0 - 05 ) b u t w e r e n o t c o r r e l a t e d(P > 0-05).

F i g u r e 4 g iv e s a c o m p a r i s o n o f th e s u r f a c e v e l o ci ty m e a s u r e d i n t h ec r o s s- f lo w t a n k w i th t h a t p r e d i c t e d f o r a n i d e al P F R o f th e s a m e d i m e n -s i o n s. N o t e t h a t a t a g i v e n f lo w r a t e, t h e s u r f a c e v e l o c i t y m e a s u r e d i s7 . 3 - 8 . 7 t im e s th a t p r e d i c t e d f o r t h e P F R . T h e i n c r e a s e in v e l o c it y w i t h in


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Hydraulics o f a rectangular cross-flow rearing unit 135T A B L E 1Resid enc e Tim e Distr ibution Characterist ics SD of Thr ee E xperim ental Tanks (Ana-lyses we re perfo rm ed with and without 49.4 kg of chan nel catfish p resent in each tank

type)V ariable Tank type

Circular Cross-flow RectangularM ean residen ce t ime, f (min)with fish 24-4 + 1"5 23"2 without fish 25"8 + 0.6 27-4 M ean rat io, icl[(%)a

with fish 77"3 4-7 73-4 without fish 79.3 1.7 84-4 M ean variance, o 2 (min2)with f ish 58 1.4+ 9.5 63 5.2 without fish 676 .0 _+ 65 .0 799 -5 _+Mean ratio o~-/~ min)with fish 18.4 0"3 20-1 without fish 20 .8 2.0 24.6 ___M ean dispersion num ber, D / u Lwith fish ozwithout fish

0-6 31"50-61-6 30"61"81"8 99"71"85"0 94"25"41 5 " 8 5 1 5 ' 1 1 9 - 074" 8 591" 5 113- 80"5 16'30"62-3 18-23-5

0"42 _+ 0"060"63+0"12"The theoretical retention t ime for tanks with and without f ish present was 31.6 and32.5 m in, respectively.

t h e c r o s s - f lo w t a n k h a s b e e n e s t a b l i s h e d w i t h a m i n i m a l p r e s s u r e h e a dr e q u i r e m e n t .

D I S C U S S I O NR e s u l t s o f t h e a n a l y s is o f r e s i d e n c e t im e d i s t r i b u t i o n c o n f i r m t h e c r o s s -f lo w v e s se l is o p e r a t i n g a s a m i x e d - f l o w r e a c t o r w i t h p e r f o r m a n c e e q u i -v a l e n t t o t h a t o f a s t a n d a r d c i r c u la r t an k . U n l i k e t h e B u r r o w s - t y p er e c t a n g u l a r r e a r in g u n it ( B u r r o w s a n d C h e n o w e t h , 1 9 70 ) , C M F Rb e h a v i o r h a s b e e n a c h i e v e d w i t h li t t le r e q u i r e d t a n k m o d i f i c a t i o n . A d d i -t io n a ll y , t h e p o w e r r e q u i r e d t o m a i n t a i n m i x in g is k e p t to a m i n i m u m b yj e t ti n g w a t e r a t l o w v e l o c i t y a l o n g t h e e n t i r e l e n g t h o f t h e v e s se l . F o x a n dG e x ( 1 9 5 6 ) , i n s tu d i e s a d d r e s s i n g t h e s i n g le p h a s e b l e n d i n g o f l iq u i ds ,d e m o n s t r a t e d t h a t a l o w v e l o c it y j e t w i l l p r o d u c e e q u i v a l e n t m i x i n gr e s u lt s w i th l e ss p o w e r t h a n is r e q u i r e d w i t h a h i g h v e l o c i t y j e t u n d e rc o n d i t i o n s o f e q u a l f l ow .


10/14

1 3 6 B . J . W a t t e n , L . T o d d B e c k

ca

>:9

u' l

5.~-

4 . 0 0 -

3 . 0 0 -

2.1~-

1.00-

ClIOSSFLOWTANK

.3 em

IOF.~LPLUGFLOWTANK

. o ~ 5 r ~ o ~ s Io ~ oFLOW RATE. LITER/MIN

Fig. 4. Com parison of velocity obtained in the cross-flow tank with that predicted foran ideal PFR of the sam e dimensions.D ata plotted represent the mean of measurementstaken at fo ur locations. Static pressures within the inlet man ifold (cm ) are given also.

A s n o t e d e a rl ie r , th e d i f fe r e n c e b e t w e e n m e a n r e s i d e n c e ti m e , to, a n dt h e o r e t i c a l r e t e n t i o n t i m e , L is a m e a s u r e o f t h e s t a g n a n t r e g i o n w i th i n af lo w r e a c to r ( D a n c k w e r ts , 1 9 5 3 ) . B u r r o w s a n d C h e n o w e t h ( 1 95 5 ) ,e m p l o y i n g a s t i m u l u s - r e s p o n s e a n a l y s is w i t h o u t fi sh , i d e n t i f i e d fc w i t h i n ar a c e w a y P F R a s w e l l a s a c i rc u l a r a n d F o s t e r - L u c a s t y p e C M F R . tce s t ab l is h e d fo r t h e C M F R v e ss e ls w e r e c o m p a r a b l e , r e p r e s e n t i n g 8 8 a n d8 3 % o f L re s p e c t i v e ly , fc e s t a b l i s h e d f o r t h e r a c e w a y P F R , h o w e v e r , in d i -c a t e d t h e e n t i r e t a n k v o l u m e w a s a c ti ve . S im i l ar r es u lt s w e r e o b t a i n e d i nt h e p r e s e n t s t u d y . T h e f~ d e r i v e d f o r t h e c r o ss - fl o w a n d c i rc u l a r C M F Ra v e r a g e d 8 2 % o f f w h i le tc w i t h i n t h e P F R w a s a g a i n g re a te r , r e p r e s e n t -i n g 9 4 % o f L R e s u l t s o f b o t h s t u d ie s i n d i c a t e th e i n a c ti v e r e g io n w i th i n aC M F R w i ll b e l a rg e r t h a n t h a t o f a P F R , s u g g e s ti n g i n f e ri o r h y d r a u l i cp e r f o r m a n c e .

T h e l o c a t i o n o f t h e i n a c t i v e a re a , h o w e v e r , a s w e l l a s its e x t e n t , m u s ta ls o b e c o n s i d e r e d . D e a d a r ea s i n a r e ct a n g u la r P F R d e v e l o p a l o n g f ~ e db o u n d a r i e s (B u r ro w s a n d C h e n o w e t h , 1 9 5 5 ). D e c o m p o s i t i o n p r o d u c t s


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Hydraulics o f a rectangular cross-flow rearing unit 137o f e x c r e m e n t a n d d e b r i s a c c u m u l a t in g in t h e s e a r e a s w i ll h a v e a d e t r i-m e n t a l e f fe c t o n w a t e r q u a l i ty a n d m a y a d v e r s e ly a ff e c t p r o d u c t i o n . C o n -ve r s e ly , r e la t i ve l y h i gh ve l oc i t i e s a r e p r e s e n t ne a r fLxed bo un da r i e s o f t hec i rc u l a r C M F R . T h e d e a d a r e a f o r m e d is a to r u s, o r d o u g h n u t s h a p e d ,a n d is r o t a t in g s lo w l y a b o v e a c u r r e n t m o v i n g r a d ia l ly o v e r t h e t a n k f l o o rt o w a r d t h e c e n t e r o u t l e t ( B u r ro w s a n d C h e n o w e t h , 1 9 5 5 ; L a r m o y e u x e tal . , 1 9 7 3 ) . T h i s i n a c t iv e r eg i o n , u n l i k e t h a t o f t h e P F R , c o n t r i b u t e s t o t h es e l f -c l e a n i ng p ro pe r t i e s o f t he ve s s e l a nd a s s uc h i s no t e n t i r e l y und e s i r -a b le . Q u i e s c e n t c o n d i t i o n s w i th i n t h e d e a d a r e a p r o m o t e t h e s e tt li n g o fp a r t i c u l a te m a t t e r. S o l id s d r o p p i n g o u t o f t h e r e g i o n a r e p i c k e d u p b y t h er a d ia l c u r r e n t a n d t r a n s p o r t e d t o t h e d i s ch a r g e s c re e n ( L a r m o y e u x e t a l . ,1 9 7 3 ). T h e i n a c ti v e r e g i o n o f t h e c r o s s - fl o w t a n k s i m i la r ly p r o m o t e s t h ep u r g i n g o f p a r ti c u la t e s. D y e s tu d i e s h a v e e s ta b l i sh e d t h e p r e s e n c e o f al ow ve l o c i t y c o re ro t a t i ng a bo u t t he l on g i t ud i na l a x is o f t he ve s s el . S o l i d sd r o p p i n g o u t o f t h is r e g i o n a r e s w e p t b y t h e c r o s s- f lo w c u r r e n t p r e s e n t a tt a n k b o u n d a r i e s t o w a r d s s t an d p i p e s p r o je c t in g d o w n w a r d f r o m t h ed ra i n gu t t e r a ss e mbl y .C h a n n e l c a t f i s h , u n d e r t h e c o n d i t i o n s t e s t e d , h a d l i t t l e e f f e c t o nh y d r a u l i c p e r f o r m a n c e ( F ig . 3 ). D / # L a n d i c va l ue s e s t a b l i s he d w i t h a ndw i t h o u t fi sh w e r e n o t d i f f e r e n t ( P > 0 "0 5). T h e p r e s e n c e o f f is h d i d , h o w -e ve r , r e s u l t i n a m od e ra t e bu t s t a ti s ti c a ll y s i gn if i c an t r e d uc t i on i n o2/~ c.T h e r e d u c t i o n o b s e r v e d m a y b e t h e r e su l t o f fi sh s w im m i n g i n a n d o u t o fd e a d r e g io n s w i t h i n t h e v e ss el . T h i s m o v e m e n t w o u l d p r o b a b l y i n c r e a set h e d e g r e e o f i n t e r c h a n g e b e t w e e n t h e a c t i v e a n d i n a c ti v e a r e a s t h e r e b yr e d u c i n g t h e t i m e r e q u i r e d t o p u r g e t h e t r a c e r c o m p l e t e l y f r o m t h e ta n k .D i f f e r e n c e s b e t w e e n r e p l i c a te d e t e r m i n a t i o n s o f u E / fc , a s m e a s u r e d b yt h e c o e f f i c i e n t o f v a r ia t io n , d e c r e a s e d f r o m a m e a n o f 1 2 . 7 % w i t h o u t f is hto 2 .6% w i th fi sh presen t , sugg es t ing fi sh ac tiv i ty w i th in a vesse l ma y a l soa c t t o s t a b il iz e hyd ra u l i c be ha v i o r .T h e u n u s u a l f l o w p a t t e r n p r o v i d e d b y t h e c r o ss -f lo w d e s ig n d o e s n o ta p p e a r t o a d v e r s e ly a f f e c t f is h b e h a v i o r . R e su l ts o f p r e l i m i n a r y p r o d u c -t i o n t r i a l s c o n d u c t e d i n d u p l i c a t e w i t h i n e a c h o f t h e t h r e e t a n k t y p e se v a l u a t e d h e r e a r e g i v e n i n T a b l e 2 . F l o w r a t e a n d b a c k g r o u n d w a t e rq u a l i ty v a r i a b le s m o n i t o r e d a r e s u m m a r i z e d i n T a b l e 3 . N o t e t h a t f e e dc o n v e r s i o n i n t h e c r o s s- fl o w a n d r e c t a n g u l a r P F R w e r e s im i la r, a v e r a g in g1-64 kg f e e d pe r kg ne t ga i n , w h i l e c onve r s i on i n t he c i r c u l a r t a nk w a ss ig n i fi ca n t ly h i g h e r ( P < 0 - 0 5 ) , a v e r a g in g 1 .8 6 k g p e r k g n e t g a in . C o n -ve r s e l y , s t a t i s t i c a l a na l ys e s i nd i c a t e e nd i ng me a n l e ng t h a nd w e i gh ta c h i e v e d i n t h e c r o s s - f l o w a n d c i r c u l a r C M F R w e r e n o t d i f f e r e n t( P > 0 - 0 5 ) b u t w e r e g r ea t er ( P < 0 . 0 5 ) t h a n th a t o b t a i n e d i n t h e r ec t-a n g u l a r P F R . I n c r e a s e d f i s h g r o w t h i n C M F R v e r s u s P F R t y p e r e a r i n gu n i t s h a s a l s o b e e n o b s e r v e d b y J o h n s o n a n d G a s t i n e a u ( 1 9 5 2 ) a n d


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1 3 8 B . J . Watten , L . Tod d Be ckT A B L E 2

R e s u lt s o f a P r o d u c t i o n T r i al C o n d u c t e d i n D u p l i c a t e W i t hi n E a c h o f T h r e e T a n k T y p e s( T a n k s w e r e s t o c k e d o n 2 4 A u g u s t 1 9 8 4 , w i t h 1 3 . 6 k g o f h y b r i d s t r i p e d b a s s ( M o r o n esaxatilis x Morone chrysops) a v e r a g i n g 2 5 . 3 g in w e i g h t a n d 1 1 5 m m i n t o t a l le n g t h . F i s hw e r e f e d a p el le t c o n t a i n i n g 3 8 % p r o t e i n ad l ib i tum t h r e e t i m e s p e r d a y d u r i n g a 7 0 - d a yc u l t u r e p e r i o d . D a t a a r e e n d i n g m e a n s + s t a n d a r d d e v i a ti o n s . S u b s a m p l e s iz e is d es i g -n a t e d a s N . V a l u e s in th e s a m e r o w p o s s e s s i n g a c o m m o n l e t te r d o n o t d i ff e r a t t h e 9 5 %

c o n f i d e n c e l e v e l )Variable Tan k type

Circular Cross-flow Rec tang ularM e a n t o t a l l e ng t h (m m ) ( N = 6 4 - 6 7 )M e a n i n d i v i d u a l w e i g h t (g )

( N = 6 4 - 6 7 )M e a n c o n d i t i o n c o n s t a n t a ( K x 10 3)

( N - - 6 4 - 6 7 )M e a n d a il y g ai n (m g d a y - ~)F e e d f e d ( k g )T o t a l h a r v e s t w e i g h t (k g )F e e d c o n v e r s i o n (k g f e e d / n e t w e i g h t

ga in )S u r v i v a l ( % )

1 8 8 4 , a 1 8 2 + l , a 1 7 2 + 1 ,b89.4 ___6.2 , a 79 .6 + 2-0 , a 65 .4 + 0 .3 , b1 2.8 + 0 . 3 , a 1 2 . 6 + 0 . 2 , a 1 2 . 4 _ 0 . 1 , a9 1 7 _ + 8 8 a 7 7 6 + 3 0 a 5 7 3 + 4 b

49 .9 + 6 .2 , a 38"3 + 0"20, a 29-3 + 0 .7 , b40"5 _+ 3-9 , a 37"3_+ 0-14 , a 31 "5 +0 "5 , b1 " 8 6 _ 0 . 0 4 , a 1 "6 2 + 0 . 0 1 , b 1 .6 5 + 0 - 0 9 , b83.9 + 2 .3 , a 87 .2 + 2 .4 , a 89 .4 + 1 .8 , a

" K = ( W t / L3) 1 0 0 w h e r e W = f i n al m e a n w e i g h t (g ); L = f i na l m e a n t o t a l le n g t h ( cm ) .

Burrows and Chenoweth (1970) . S t ress imposed by env i ronmenta l con-di t ions can manifes t i t se l f in mortal i ty ra te , changes in body condi t ion,and body compos i t i on (E s ch and Hazen , 1980 ; Fage r l und et a l . , 1981 ).Prox imate ana lyses (AOAC, 1975) conducted on whole f i sh samplestaken a t harves t d id no t revea l d i f fe rences in body compos i -t ion among the th ree t ank types (P> 0 .05) ; nor d id t ank type in f luencef i s h cond i t i on (P>0 .05) a s i ndexed by t he p ropo r t i ona l cons t an t K(Table 2) . A t rend towards h igher mortal i ty in CMFR rear ing uni ts i sevident in Table 2 , but again tank-type effects were not s igni f icant(P>0"05) . These resul ts , a l though not def in i t ive, suggest s t ress levelswi thin ea ch tank type a re s imilar.In summary, s tudies descr ibed here have demonst rated the feas ibi l i tyof es tab l i sh ing CMFR behav ior in a rec tangular t ank by in t roducingw ater uni form ly along one s ide of the vessel, v ia a man ifold , and col lect -ing the overf low along the length of the opposi te s ide. The rectangularcross-f low tank appears par t icular ly sui ted for h igh densi ty cul ture


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Hy draulics of a rectangular cross-flow rearing unit 139T A B L E 3Flow Rate and W ater Q ual i ty (a .m. samples) M oni tored D ur ing a P roduct ion Tr ialCon ducted in Du pl icate W ithin Eac h of Th ree Tank Types (Data are m eans _+ s tandard

deviations. Sam ple size is designated as N)V ariable Ta nk type

Circular Cross-f low RectangularM ea n effluent dissolved 0 2(mg litre -j ) (N -- 70) M ean tank dissolved N , + A r(% saturation) (N = 10) hM ean effluent tem per ature (C)(N = 70) ~Mean effluen t N H : N (mg l i t r e - l)( U = 9 ) oM ean effluent N H3 -N (m g l itre -~)( N = 9 )'Mean ef fluent pH (N = 9)~M ean f low rate ( l iters m in- 1) (N = 140)d

6.2+0.1 6.3+0.1 6.5_+0.11 0 4 .9 _ + 0 .2 1 0 6 - 0 _ + 0 . 4 1 0 4 .6 _ + 0 .4

27_+0 27+0 27_+00.43 _+ 0.09 0.35 _+ 0.01 0-26 _+ 0"000.0 2_ +0 .00 0.02 _+0 .01 0.01 _+ 0.007 . 82_+ 0 . 05 7 . 8 3 _ + 0 . 0 0 7 .88-+ 0.0160.9_+0.07 60.1 _+ 0.21 60-9 _+ 0.0

"Analyses perform ed us ing s tandard m ethods (AP HA , 1975) .~'Values based on an E C O M odel ES-2 W eiss Saturometer .' Calculated using disassociation con stants fro m Em erso n et al. (1975)., /Measured using a s topw atch and con tainer of know n capacity.

a p p l i c a t i o n s r e q u i r i n g m i n i m a l flo w . T h e c o n t e n t s o f t h e ta n k h a v e b e e ns h o w n t o b e h o m o g e n e o u s . T h u s , u n d e s i r a b l e g ra d i e n t s in D O a n d f is hm e t a b o l i t e s a l o n g t h e l e n g t h o f t h e v e ss e l a r e a v o i d e d . A d d i t i o n a l a d v a n -t a g e s i n c l u d e : ( 1 ) s e l f - c l e a n i n g p r o p e r t i e s , ( 2) v e l o c i t y c o n t r o l , ( 3 ) e f fi -c i e n t u s e o f a v a i la b l e w a t e r s u p p l y a n d p r e s s u r e , a n d (4 ) t h e f l ex i bi li ty o fo p e r a t i n g a s a P F R d u r i n g f lu s h in g a n d f is h h a n d l i n g o p e r a t io n s . F u r t h e rr e s e a r c h is b e i n g c o n d u c t e d o n l a r g e - s c a l e u n i t s to e s t a b l is h t h e e f f e c ts o fr o u n d i n g t h e b o t t o m c o r n e r s o f t h e t a n k a s w e ll as to d e t e r m i n e t h e o p t i -m u m p o s i t io n o f t h e in l et m a n i f o l d a n d d r a i n g u t t e r a s s e m b l ie s .

A C K N O W L E D G E M E N T SW e t h a n k D . R o t t i e r s a n d C . J o h n s o n o f t h e U S F i s h a n d W i ld l if eS e rv i c e , N a t i o n a l F i s h e r y R e s e a r c h a n d D e v e l o p m e n t L a b o r a t o r y ,W e l ls b o r o , P e n n s y l v a n i a , f o r p e r f o r m i n g t h e p r o x i m a t e a n a l y se s .


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140 B.J. Watten, L. To dd BeckR E F E R E N C E S

A O A C ( 19 7 5 ). Official M etho ds o f Ana lysis (12th Ed n) , A ssoc ia t ion of Off ic ia lAna ly t i ca l Chem is ts , W ash ing ton DC .A P H A (1 97 5 ). Standard Methods for the Exam inat ion of Water and Wastewater( 14 th Edn) , A m er i can Pub l i c Hea l t h Assoc i a t ion , New Y ork , 1193 pp .Bu rley, R. & Klapsis , A . (1985 ) . Flo w d is t r ibut ion s tudies in fish rear ing tanks.Pa r t 2 - Ana lys i s o f hydrau l ic pe r fo rm ance o f 1 m squa re tanks. A q u a -cultural En gineering, 4 , 1 1 3 - 3 4 .Bur rows , R . E . & Ch enow e th , H . H. ( 1955) . Eva lua t i on o f th r ee t ypes o f f ishr ea r ing pon ds . U S F i sh and W i ld l if e Serv ice, Resea rch Repor t , W ash ing tonDC , 39 , 29 pp .Bu r rows , R. E . & C hen ow eth , H. H. (1970) . T he rec tangular ci rcu la ting rear ingp o n d . Prog. Fish-Cu lt., 3 2 , 6 7 - 8 0 .D anckw er t s , E V. (1953) . Co nt inuo us flow systems - - d i s t r ibut ion of res idenc et imes. Chem. EngngSci . , 2 , 1 -18 .Emerson, K. , Russo , R. C. , Lund, R. E . & Thurs ton , R. B. (1975) . Aqueousam m on ia equi l ibr ium ca lcula tions : e f fec t of pH and tem pera ture . J . Fish. Res.Bd Can., 3 2 , 2 3 7 9 - 8 3 .Esch , G. W . & H azen , T . C. (1980) . S tress a nd bo dy co nd i t ion in a pop ula t ion ofla rgemouth bass : impl ica t ions for red-sore d i sease . Tran s. A m . Fish. Soc.,1 0 9 , 5 3 2 - 6 .Fa ger lund, V . H . M ., Mc B ride, J . R. & Stone, E . T. (198 1 ). St ress-related effectso f ha t che ry r ea r i ng dens i t y on coho sa lmon . Tran s. A m . Fish. Soc., 110,6 4 4 - 9 .Fox, E. & Gex, V. (1956) . Single-phase blending of l iquids . A I C h E , 2 (4) ,5 3 9 - 4 4 .Hughes, J . T. , Shleser , R. A. & Tchobanoglous, G. (1974) . A rear ing tank forlobs te r l a rvae and o th er aqua t ic spec ies . P rog. Fish-Cult., 3 6 , 1 2 9 - 3 2 .Johnson , H. E . & Gas t i neau , A . C . ( 1952) . A compar i son o f t he g rowth o ff inger l ing ch inoo k sa lmon rea red in pond s , t roughs an d c i rcu la r t anks. Prog.

Fish-Cult., 14 (2), 76-8 .Larm oyeu x, J. D., P iper, R. G. & C hen ow eth , H. H . (1973) . Evalua t ion of ci rcu-la r t anks for sa lmo nid product ion . P rog. Fish-Cult., 3 5 , 1 2 2 - 3 1 .Levenspie l , O. (1979) . The Chemical Reactor Omnibook , Oregon Sta te Univ .B oo k Stores Inc., Corvall is , O reg on .Levensp i e l, O . ( 1985) . Co m m en t on m ean r e s iden ce t ime i n fl ow systems.Chem.Engng Sci., 40, 1614.Piper , R. G. , McElwain, I . B. , Orme, L. E. , McCraren, J . E, Fowler , L. G. &Leo nard , J . R. (1982) . Fish Hatchery Management, US Dept . o f the In te r ior ,F i sh and W i ld l i fe Serv ice, W ashington DC , 51 7 pp .W atten, B . J . & B eck, L. T. (1985 ) . M od el ing gas transfer in a u- tube ox ygenab sorp t ion system: effects of off-gas recycling. Aquacultural Engineering, 4,2 7 1 - 9 7 .Westers , H. & Prat t , K. M. (1977) . Rat ional design of hatcher ies for intensivesa lmonid cul ture , based on metabol i t e charac te r i s t i cs . P rog. Fish-Cult., 39 ,1 5 7 - 6 5 .

Watten 1987 Aquacultural-Engineering

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