dispersion of vapor from liquid natural gas spills

7/28/2019 Dispersion of Vapor From Liquid Natural Gas Spills

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Journal of Wind Engineering and Industrial Aerodynamics, 1 0 ( 1 9 8 2 ) 1 - - 1 9 1E l se v ie r S ci e n ti f ic P u b li s hi n g C o m p a n y , A m s t e r d a m - - P r i n te d i n T h e N e t h e r l a n d s

D I S P E R S I O N O F V A P O R F R O M L I Q U I D N A T U R A L G A S S P I L L S - -E V A L U A T I O N O F S I M U L A T I O N I N A M E T E O R O L O G I C A L W I N DT U N N E L : F I V E - C U B I C - M E T E R C H I N A L A K E S P I L L S E R I E S

R . N . M E R O N E Y a n d D .E . N E F FFluid Mec hanics and W ind Engineering, Civil Engineering Depa rtment, Colorado StateUniversity, CO (U.S.A.)(Rece ived June 1 , 1981 ; a ccep t ed i n r ev is ed fo rm S ep t em ber 7 , 198 1 )

S u m m a r yA se r ie s o f s i x - cub i c -me te r l iqu id n a tu r a l ga s (LN G) sp il ls w e re pe r fo rm ed i n 1978 a tt he Ch ina L ake N ava l W eapons Cen t e r , CA. A pa ra l le l s e t o f mod e l ed spi ll s we re s imu la t edin me teo ro log i ca l w ind - tunne l f a c il it ie s t o p rov id e f ie l d - te s t p l ann ing i n fo rm a t ion , t o ex -t end t he va lue o f t he l im i t ed s e t o f fi e ld me asu rem en t s c a r ri ed ou t , and t o eva lua t e t hecon cep t o f phys i ca l mode l i ng o f LN G p lum e d i spe r s ion a s a p r ed i c ti ve haza rd ana ly s i s t o o l

N o m e n c l a t u r eMM RRF rF r fS GR e

m a s s r a t i o , p s Q / p a U a L 2m o m e n t u m r a t io , p s Q 2 / p a U aL 4v o l u m e f l u x ra t io , Q / U a L 2d e n s i m e t r ic F r o u d e n u m b e r , U a 2 / g [ ( p s - - P a ) / P a ] Lf lu x F r o u d e n u m b e r , U a 3 L / g [ ( p s - - P a ) / P a ] Qs p e c i f i c g r a v i t y , p s / P aR e y n o l d s n u m b e r , Q / v L 2

I n t r o d u c t i o nR e c e n t e f f o r t s to e x p a n d t h e w o r l d ' s n a tu r a l g a s s u p p l y i n c l u d e t h e t r an s -

p o r t o f n a t u r a l g a s i n a l i q u id s t a t e f r o m d i s t a n t g a s f ie ld s . U n f o r t u n a t e l y ,s t o r a g e a n d t r a n s p o r t o f l i q u id n a t u r a l g a s m a y i n v o l v e a r e l a t i v e l y la r g e e n -v i r o n m e n t a l r is k . T o t r a n s p o r t l i q u id n a t u r a l g a s ( L N G ) , i t is m a i n t a i n e d int h e l i q u i d s t a t e a t - - 1 6 2 C . A t th i s t e m p e r a t u r e , i f a s t o r a g e t a n k o n a s h ip o ro n l a n d w e r e t o r u p t u r e a n d t h e c o n t e n t s s p i ll o u t o n t o t h e e a r t h ' s s u r f a c e ,r a p i d b o i l i n g o f t h e L N G w o u l d e n s u e , a n d t h e l i b e r a t i o n o f a p o t e n t i a l l yf l a m m a b l e v a p o r w o u l d r e s u l t . P a st s t u d ie s h a v e d e m o n s t r a t e d t h a t a c o l dL N G v a p o r p l u m e r e m a i n s n e g a t i v e l y b u o y a n t f o r m o s t o f i t s l i f e t i m e [ 1 , 2 ] .A h a z a r d o u s m i x t u r e w i l l t h e r e f o r e e x t e n d d o w n w i n d a t g r o u n d l e ve l u n t i lt h e a t m o s p h e r e h a s d i l u t e d t h e L N G v a p o r b e l o w t h e l o w e r f l a m m a b i l i t y

0 3 0 4 - 3 9 0 8 / 8 2 / 0 0 0 0 - 0 0 0 0 / $ 0 2 . 7 5 1 9 8 2 E l se v ie r S c i en t if i c P u b l is h in g C o m p a n y


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l im i t ( a l o c al c o n c e n t r a t i o n o f m e t h a n e l es s t h a n 5 % b y v o l um e } .L i q u i d n a t u r a l g a s w a s sp i ll e d in sm a l l a m o u n t s o n t o a p o n d a t t h e C h i n a

L a k e N a v al W e a p o n s C e n te r , C A , d u r in g 1 9 7 8 , t o e x a m i n e t h e p h y s i c s o fL N G p l u m e d i s p e r s io n b e h a v i o r . A p ar a ll e l w i n d - t u n n e l m o d e l p r o g r a m w a sp e r f o r m e d in t h e m e t e o r o lo g i c a l w i n d t u n n e l o f C o l o r a d o S t a t e U n i v e r s it yt o p r o v i d e f i e ld - t e s t p l a n n i n g i n f o r m a t i o n , t o e x t e n d t h e v a l u e o f t h e l i m i t e ds e t o f fi e ld m e a s u r e m e n t s , a n d t o e v a l u a t e t h e c o n c e p t o f p h y s i c a l m o d e l i n go f L N G p l u m e d i s p e r s i o n a s a p r e d i c t iv e h a z a r d a n a l y si s t o o l . T h e m e a s u r e -m e n t r e su l ts d e s c r i b e d h e r e i n p r o v i d e d a f o u n d a t i o n f o r t h e i n t e r p r e t a t i o n o ft e r ra i n e f f e c t s i n t h e f i e ld e x p e r i m e n t s a n d a n e x p l a n a t i o n f o r c o n c e n t r a t i o nv a g a r i e s n o t i c e d i n t h e f i e l d d a t a d u r i n g w i n d d i r e c t i o n v a r i a t i o n . W i n d - t u n n e ll a b o r a t o r y m e a s u r e m e n t s p e r m i t a d e g re e o f c o n t r o l o f s a f e ty a n d o f m e t e o -r o l o g i c a l, s o u r c e a n d s i te v a r i a b l e s n o t o f t e n f e a s i b l e o r e c o n o m i c a t f u ll sc a le .N o n e t h e l e s s , s a t i s f a c t o r y s i m u l a t io n o f th e b e h a v i o r o f d e n s e p l u m e s i s n o ts t r a i g h t fo r w a r d ; a d i s c u s s io n o f s o m e o f t h e p r o b l e m s a s s o c i a t e d w i t h t h i sa p p r o a c h f o l l o w s .L a b o r a t o r y s im u l a t i o n o f d e n s e p l u m e s r e s u l t i n g f r o m c r y o g e n i c s p i l l s

P h y s i c a l m o d e l i n g i n w i n d t u n n e l s r e q u i r e s c o n s i d e r a t i o n o f th e p h y s i c s o ft h e a t m o s p h e r i c s u r fa c e la y e r a s w e l l a s t h e d y n a m i c s o f p l u m e m o t i o n .R e l i a b l e c ri te r ia f o r s i m u l a t in g t h e p e r t i n e n t p h y s i c a l p r o p e r t i e s o f t h e a t m o -s p h e r ic b o u n d a r y l a y e r ha v e b e e n d e m o n s t r a t e d b y s e v er a l i n v e s ti g a to r s [ 3 ,4 ] . F r e q u e n t l y , p a r t ia l s i m u l a t io n s u f f ic e s w h e n t h e t e s t d o m a i n is l i m i t e d int i m e a n d s p a c e . S p e c i f ic p r o b l e m s a s s o c i a t e d w i t h t h e d i s p e r s io n o f c o l dn a t u r a l g a s p l u m e s h a v e b e e n p r e v i o u s l y d i s c u s se d b y M e r o n e y e t a l. [ 5 , 6 ] .P r i o r e x p e r i e n c e : d e n s e g a s - p l u m e s i m u l a t i o nA n u m b e r o f c o n t r o l le d l a b o r a t o r y e x p e r i m e n t s h a v e b e e n c o n d u c t e dp r e v i o u s l y t o e v a l u a t e t h e s i g ni fi c a nc e o f d e n s i t y f o r d is p e r s io n o f g a s e o u sp l u m e s . S a k a g a m i a n d K a t o [ 7 ] m e a s u r e d d i f f u s i o n a n d v a p o r r is e f r o m as m a l l ( 5 1 0 c m ) L N G w e ll i n t h e f l o o r o f a w i n d t u n n e l o f c r o s s- s e c t io n5 0 5 0 c m a n d l e n gt h 2 0 0 c m . T h e y c o n f i r m e d a t e n d e n c y f o r t h e g as tor e m a i n c o n c e n t r a t e d a t g r o u n d l ev el . B o y l e a n d K n e e b o n e [ 8 ] r e le a s e d L N Go n w a t e r , p r e - c o o l e d m e t h a n e , a n d p r o p a n e i n a s p e c i a l l y b u i l t a s b e s t o s - w a l lw i n d t u n n e l o f c r o s s -s e c t io n 1 . 5 1 . 2 m a n d l e n g t h 5 m . N o a t t e m p t w a sm a d e t o s c a le t h e a t m o s p h e r i c s u r f a c e - la y e r v e l o c i t y p r o fi le o r t u r b u l e n c e . I tw a s c o n c l u d e d t h a t r e le a se o f p r o p a n e a t r o o m t e m p e r a t u r e s i m u l a t e d a nL N G s pi ll q u i t e w e l l, b u t t h e p r e - c o o l e d m e t h a n e r e le a s e s lo f t e d , s u g g e st in gt o t h e a u t h o r s i n c o r re c t r e le a s e te m p e r a t u r e o r e x a g g er a te d h e a t t r a n sf e rf r o m t h e g r o u n d s u rf a ce . H o o t an d M e r o n e y [ 9 ] a n d H a l l e t a l . [ 1 0 ] c o n s id -e r e d g r o u n d -l e v e l, p o i n t - s o u r c e r e l e a s es o f h e a v y g a s e s i n w i n d t u n n e l s . H o o ta n d M e r o n e y f o u n d t h a t r e le a s i ng g a se s w i t h s p e c i f i c g r a v i t i e s a s g r e a ~ a s 3 . 0o n l y s li gh tl y s h if t e d th e d e c a y o f m a x i m u m c o n c e n t r a t i o n w i t h d i s t a n ce ,d e s p i t e s i g n i fi c a n t l y d i f f e r e n t p l u m e c r o s s - s e c t i o n s . H a l l e t al. c o n s i d e r e d


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t r a n s i e n t a n d c o n t i n u o u s r e l e a se s o n a r o u g h s u r f a c e ( p l u m e h e i g h t a s a f u n c -t i o n o f r o u g h n e s s h e i g h t ) a n d o n u p h i l l a n d d o w n h i l l s lo p e s . H a l l r e p o r t e ds h a ll o w , w i d e p l u m e s w h o s e s h a p e s w e r e c o n s i d e r a b l y a l t e r e d b y 1 in 1 2g r o u n d - s l o p e s .

T e s t s w e r e c o n d u c t e d b y N e f f e t al. [ 1 1 ] in w i n d - t u n n e l f a c i li ti e s t oe v a l u a t e t h e r a t e o f d i s p e rs i o n a n d t h e e x t e n t o f d o w n w i n d h a z a r d s a s s o c i a t e dw i t h t h e r u p t u r e o f ty p i c a l , l ar ge L N G s t o ra g e ta n k s . C o n c e n t r a t i o n a n d t e m -p e r a t u r e m e a s u r e m e n t s , a n d p h o t o g r a p h i c r e c o r d s , w e r e o b t a i n e d f o r d i ff e r-e n t w i n d s p e e d s , w i n d d i r e c t i o n s a n d c o n s t a n t b o i l - o f f r a te s , u n d e r b o t hn e u t r a l a n d s t a b le a t m o s p h e r i c s t ra t if ic a t io n s . S u b s e q u e n t m e a s u r e m e n t s b yM e r o n e y e t a l. [ 1 2 ] e x a m i n e d t r a n s i e n t r e le a s e s in s im i l a r c o n f i g u r a t i o n s a sw e l l a s d e n s e p l u m e s o n u p h i l l s l o p e s, a n d b u o y a n t p l u m e l i f t- o f f s i t u a ti o n s .D i f f e r e n t m o d e l r el e as e g as e s w e r e u s e d t o s i m u l a t e t h e b e h a v i o r o f t h e c o l dm e t h a n e p l u m e - - h e a v y i s o t h e r m a l g a s m i x t u r e s (C O 2 , F r e o n - 1 2 a n d a i r, o ra r g o n ) o r l ig h t c o l d m i x t u r e s ( H e a n d N 2 ) .T h e s e l a t t e r m e a s u r e m e n t s s u g g e s te d t h d t h e a t tr a n s f e r e f f e c t s m a y b es m a l l o v e r t h e s i g n i f ic a n t t i m e s c a le s ; h e n c e , g a s d e n s i t y s h o u l d b e a d e q u a t e -l y s i m u l a t e d b y u si n g i s o t h e r m a l h i g h - m o l e c u l a r - w e i g h t g a s m i x t u r e s , d u r i n gm o d e r a t e w i n d s . V i s u a l i z a t i o n o f s im i l a r t e s t s f o r th e r a n g e o f m o d e l s c a l esu s e d { 1 : 1 3 0 t o 1 : 6 6 6 ) i n d i c a t e d s i m i la r p l u m e g e o m e t r i e s . T h e c o n c e n t r a -t i o n r e s u l t s f o r t h e d i f f e r e n t m o d e l s c al es ag r e e d t o w i t h i n t h e e x p e r i m e n t a la c c u r a c y o f -+ 2 0 % . S i m i la r l y , r e p e a t e d i d e n t ic a l t e s t s a l so s h o w e d g o o d a g re e -m e n t ; h e n c e , t h e R e y n o l d s n u m b e r m u s t p l a y a m i n o r p a r t i n t h e d en s e -g a sd i s p e r s i o n s i t u a t i o n s c o n s i d e r e d .T h e m a j o r p r a c ti c a l l im i t a t io n s t o a c c u r a t e w i n d - t u n n e l s i m u l a t io n o f L N Gd i s p e r s i o n a r e o p e r a t i o n a l c o n s t r a i n t s , p a r t i c u l a r ly t h e i n a b i l it y t o o b t a i n as t e a d y w i n d p r o f i l e o r t o s i m u l a t e a c c u r a t e l y a t m o s p h e r i c t u r b u l e n c e a t t h el o w e s t w i n d s p e e d s o f in t e r e st , a n d R e y n o l d s n u m b e r c o n s t r a i n t s ( as y e ts o m e w h a t i ll - d e fi n e d ) a s s o c i a t e d w i t h t h e p r o p e r s c a l in g o f n e a r - f ie l d t u r b u -l e n ce . W h e n c o m b i n e d w i t h e s t i m a t e s o f t h e r e st r a in t o f p l u m e e x p a n s i o n b yt h e t u n n e l s id e -w a ll s, th e s e c o n s i d e r a t i o n s p e r m i t t h e d e v e l o p m e n t o f a p e r-f o r m a n c e e n v e l o p e f o r a p a rt ic u l a r w i n d - t u n n e l f a c il it y ; e x a m p l e s o f s u c he n v e l o p e s h a v e b e e n g iv e n b y M e r o n e y e t a l. [ 5 ] .P a r t ia l s im u l a t i o n c r it er ia : d e n s e g a s p l u m e s

C o n s i d e r in g t h e d y n a m i c s o f g a s e o u s p l u m e b e h a v i o r , e x a c t s i m i l it u d e re -q u i r e s th e s i m u l t a n e o u s e q u i v a le n c e o f m as s, m o m e n t u m f lu x a n d v o l u m ef l u x r a t i o s, d e n s i m e t r i c F r o u d e n u m b e r , R e y n o l d s n u m b e r , a n d sp e c if icg r a v it y (s e e N o m e n c l a t u r e ) . C o n s i d e r a t i o n o f v a r ia b l e - p r o p e r t y , n o n - i de a lg a se s a n d t h e t h e r m a l b e h a v i o r o f t h e p l u m e m i x t u r e i n t r o d u c e s a d d i t io n a lc o n s t r a i n t s o n v a r i a t io n s i n t h e s p e c i f ic h e a t c a p a c i t y [ 1 3 ] .F o r a p l u m e w h o s e t e m p e r a t u r e , m o l e c u l a r w e i g h t, a n d s p e c if ic h e a t a r ea ll d i f f e r e n t f r o m t h a t o f th e a m b i e n t a i r, w h i c h is t h e c a s e f o r a c o l d n a t u r a lg a s p l u m e , t h e c o n s t r a i n t o f e q u i v a l e n c e i n t h e v a r i a t i o n o f t h e s p e c i f i cg r a v i t y u p o n m i x i n g m u s t b e r e la x e d s l i gh t ly i f a ga s d i f f e r e n t f r o m t h a t o f


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t h e p r o t o t y p e is t o b e u s e d f o r m o d e l i n g . C a l c u l a t io n s f o r e q u i v a l e n t c o l d o ri s o t h e rm a l d e n s e p l u m e s u s i n g a s i n gl e -b o x m o d e l , s u c h a s t h o s e u s e d b y F a y[ 1 4 ] a n d M e r o n e y a n d c o - w o r k e r s [ 1 5 ] , r e v ea l o n l y s m a l l p e r t u r b a t i o n s int h e p r e d i c t e d c o n c e n t r a t io n s .

A r e a s o n a b l y c o m p l e t e s i m u l a t i o n m a y b e o b t a i n e d in s o m e s i tu a t io n s e v e nw h e n a m o d i f i e d i n it ia l s p e c i f i c g a s r a t i o is s t i p u l a t e d . B y i n c r e a si n g t h es p e c if ic g r a v i ty o f t h e m o d e l g a s c o m p a r e d t o t h e p r o t o t y p e g as , t h e r e f e r e n c ev e l o c i t y o v e r t h e m o d e l is i n c r e a s e d . I t i s d i f f i c u l t t o g e n e r a t e a f l o w s i m i la rt o t h a t o f t h e a t m o s p h e r i c b o u n d a r y l a y e r in a w i n d t u n n e l o p e r a t e d a t v e r yl o w w i n d s p e e d s . T h u s t h e e f f e c t o f m o d i f y i n g t h e m o d e l ' s s p e ci fi c g ra v i t ye x t e n d s t h e r a n g e o f f lo w s i tu a t io n s w h i c h c a n b e m o d e l e d a c c u r a t e l y . M e r o n e ye t a l. [ 1 6 ] a n d I s y u m o v a n d T a n a k a [ 1 7 ] f o u n d t h a t F r o u d e n u m b e r a n dv o l u m e f l u x e q u a l i t y p r o v i d e d c o n s e r v a t i v e g r o u n d - le v e l c o n c e n t r a t i o n s f o rb u o y a n t p l u m e s . S k i n ne r a n d L u d w i g [ 1 8 ] o b t a i n e d s i m ila r, e l e v a te d p l u m et r a je c t o r i e s w h e n f lu x F r o u d e n u m b e r a n d m o m e n t u m r a t i o eq u i va l e nc e sw e r e r e q u i r e d .S c a l in g o f t h e e f f e c t s o f h e a t t r a n s f e r b y c o n d u c t i o n , c o n v e c t i o n , r a d i a ti o n ,o r l a t e n t h e a t re le a se f r o m e n t ra i n e d w a t e r v a p o r c a n n o t b e r e p r o d u c e d w h e nt h e m o d e l s o u r c e ga s a n d e n v i r o n m e n t a re is o th e r m a l . F o r t u n a t e l y , f o r L N Gp l u m e s d is p e r s in g i n a n o n c a l m e n v i r o n m e n t , t h e e f f e c t s o f h e a t t r a n s f e r b yc o n d u c t i o n , c o n v e c t i o n , a n d r a d i a t i o n f r o m t h e s u r r o u n d i n g s a r e s u f f i c i e n t l ys m a ll t h a t t h e p l u m e b u o y a n c y r e m a i n s e s s en t ia l ly u n c h a n g e d [ 1 2 ] . T h e in -f l u e n c e o f l a te n t h e a t r e le a se b y m o i s t u r e u p o n t h e p l u m e ' s b u o y a n c y i s af u n c t i o n o f t h e q u a n t i t y o f w a t e r v a p o r p r e s e n t i n t h e p l u m e a n d o f th eh u m i d i t y o f t h e a m b i e n t a t m o s p h e r e . S u c h p h a s e- c h a n ge e f f e c t s o n p l u m eb u o y a n c y c a n b e v e r y p r o n o u n c e d in s o m e p r o t o t y p e s i t u a ti o n s w h e r e la rg ea m o u n t s o f w a t e r v a p o r a re e n tr a in e d . F o r t u n a t e l y t h e C h i n a L a k e s i te h a sv e r y l o w h u m i d i ty .T h e m o d e l i n g o f t h e p l u m e R e y n o l d s n u m b e r is r e la x e d in all p h y s ic a lm o d e l s tu d i e s . T h i s p a r a m e t e r is t h o u g h t t o b e o f s m a l l i m p o r t a n c e , s in c e t h ep l u m e ' s c h a r a c t e r w il t b e d o m i n a t e d b y b a c k g r o u n d a t m o s p h e r i c t u r b u l e n c es o o n a f t e r i ts e m i ss io n . B u t , i f o n e w e r e i n t e r e s t e d i n p l u m e b e h a v i o r n e a rt h e s o u r c e , th e n s te p s w o u l d h a v e b e ta k e n t o i n s ur e t h a t t h e m o d e l ' s p l u m ew a s f u l l y tu r b u l e n t .S i m u l a t i o n o f t h e C h i n a L a k e L N G s pi ll p l u m eT h e b u o y a n c y o f a p l u m e f r o m a n L N G s pil l is a f u n c t io n o f b o t h t h em o l e f r a c t i o n o f m e t h a n e a n d t e m p e r a t u r e . I f t h e p l u m e e n t r a i n s a ir a d i a b a ti c -a l ly , th e n i t w i l l r e m a i n n e g a t i v e l y b u o y a n t f o r i t s e n t i r e l i f e t im e . A r e l e a s e o fa n i s o t h e r m a l h i g h . m o l e c u l a r - w e i g h t g a s w i ll b e h a v e i n a s im i l ar m a n n e r t o ac o l d p l u m e e n t r a in i n g a ir a d i a b a t i c a l ly , w i t h i n s m a l l v a ri a t io n s d u e t o d i f fe r .e n c e s b e t w e e n t h e s p e c if ic h e a t c a p a c i t ie s o f t h e s o u r c e g a s a n d a ir ( se e :d is c u s-s io n in p r e c e d i n g s e c t i o n ) . H e n c e , t o s i m p l i f y l a b o r a t o r y p r o c e d u r e s , t h ee q u a l i t y o f m o d e l a n d p r o t o t y p e s p ec if ic g ra v it i es w a s r e la x e d s o t h a t p u r ea r g o n c o u l d b e u s e d a s th e s o u r c e g a s. O t h e r h i g h . m o l e c u l a r - w e i g h t g a s m i x -


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tures are possible; however, argon prod uces a favorable signal- to-noise rat iofor the concentrat ion probes used (see below) . The equivalence of momentumflux rat ios is not physically signif icant for a ground source released at lowflow rates over a large area (as was the case for LNG released on the ChinaLake test pond); hence, model condit ions were st ipulated on the basis ofequivalence between dens imetr ic Froude numbers and volume f lux rat ios .Undis tor te d scal ing of the veloci ty com pon ent s was maintained, which im-plies und istor ted scaling of source strength.

Since the thermally variable prototype gas was simulated by an isothermals imulat ion gas , the concentrat ion measurements obtained in the model mustbe adjusted to the equivalent concentrat ions that would be measured in thefield. This scaling is necessary because the number of moles released in a coldme tha ne plume is larger than the n umb er of moles released in an isothermalplume of equivalent volume source strength. Ideal-gas law behavior leads to therelationship which is derived in [13] :Xp = Xm/[Xm (1 - - X m ) T s / T a ]where Xm is the volume (or mole fraction) measured during the model tests ,T s is the tem per atu re of the LNG source un der f ield condit ions, and T a isthe ambient ai r temperature under f ield condi t ions .

The full-scale source boil-off rate per unit area over the t ime du rati on of aspil l of LNG on water is highly unpredictable. As there were no data on thevariable areas and volumes used in the different LNG tests conducted atTABLE 1Prototype conditionsaCharacteristic Test No.

18 19 20 21Release diameter, D (m) 20 20 20 20Total release volume, VLNG(m 3) 4.39 5.2 4.5 4.2VLN G (at boil-off temperature) (m 3) 1000 1184.5 1025 956.7Spill duration, At (s) 67 59 77 53Boil-off rates, ~ (kg s -~) 27.7 37.4 24.8 33.6Q (at boil:of f temperature) (m ~ s -~) 14.9 20.1 13.3 18.0Wind speed, U, at a height of 2 m (m s-1) 6.7 5.1 12.4 4.9Wind direction 214 260 256 224 Stability (Pasquill--Gifford category) C C--D C CHumidity (%) 16 29 15 21Reynolds number, U D /v, at a heightof 2mFroude number, U2/g(Ap/p )D, at aheight of 2 m 0.42 0.24 1.42 0.22

8.8X 104 6.7X 106 1.6X 107 6.4)< 106

aTb.o. = 111.63 K; PLNG = 422.63 kg m-3; PNG (at boil-off temperature) = 1.86 kg m-~;Va= 1.526 X 10-s m2s -l; pa= 1.186 kg m 3.


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China Lake, the source conditions were appro ximat ed by assuming ast eadyboil-off ate for the duration of the Spill ve ra constant area: rototype a n dmo de l conditions are specified n Tables I an d 2.

T A B L E 2M o d e l c o n d i t i o n s aC h a r a c t e r is t ic T e s t N o .

18 19 20 21R e l e a s e d i a m e t e r , D ( c m ) 2 3 . 5 2 3 . 5 2 3 . 5 2 3 . 5T o t a l r e le a s e v o l u m e , V ( c m s ) 1 6 2 5 1 9 2 9 1 6 6 9 1 5 5 8Bo i l -o f f du r a t i on , a t ( s ) 8 . 7 7 .7 10 ,8 6 .9Bo i l -o f f r a t e , Q ( cm ~ s - ' ) 186 251 166 225Spec i f i c g r av i t y 1 .38 1 .38 1 .38 1 .38Wind speed , U , a t a he igh t o f 1 .3c m ( c m s - ' ) 6 0 4 6 1 1 2 4 4Wind d i r ec t i o n 214 260 256 2 2 4 Stab i l i t y (Pasqu i l l - -G i f fo rdc a t e g o r y ) D D D DR e y n o l d s n u m b e r , - U D / v , a t a h e i g h to f 2 . 4 c m 9 , 4 0 0 7 , 1 0 0 1 7 , 2 0 0 6 , 9 0 0F r o u d e n u m b e r , U:/g(Ap/p)D, a t ahe igh t o f 2 .4 cm 0 .42 0~24 1 .43 0 .23apA r = 1 .65 kg m-~ ; l eng th s ca l e r a t i o (LS) = 85 ; (U a ) m = [ (SGra - 1 ) / ( S G p - 1 ) ] W ( l l L S ) 1/2(U a)p ; t m = [ ( S G p - 1 ) ] ( S G m - 1)] w ( 1 / L S ) ~ / " t p ; q m = [ (S G m ~- 1 ) / ( S V p 1)] v ' ( 1 ] L S ) ~/~Q p ; L m = ( 1 / L S ) L p .L a b o r a t o r y m e t h o d o l o g y

S i m u l a t i o n m e t h o d s r e q u i r e d t o p r o d u c e a m o d e l a t m o s p h e r i c b o u n d a r yl a y e r h a v e b e e n d e s c r i b e d i n s o m e d e t a i l b y C e r m a k [ 3 ] . S p e c ia l p r o c e d u r e sa n d e q u i p m e n t r e q u i r e d f o r m e a s u r e m e n t s o f d e n s e p l u m e s a r e d e s c r i b e d i nM e r o n e y e t a l. [ 5 , 6 ] .W i n d - t u n n e l f a c i l i t y

T h e e n v i r o n m e n t a l w i n d t u n n e l ( E W T ) a t C o l o r a d o S t a t e U n i v e r s i t y w a su s e d f o r t h e L N G - s p i l l t e s t s e r ie s . T h i s w i n d t u n n e l , d e s i g n e d e s p e c i a l l y t os t u d y a t m o s p h e r i c f l o w p h e n o m e n a , i n c o r p o r a t e s s p e e i a l f e a t u r e s s u c h a s a na d j u s t a b l e c e i li ng , r o t a t i n g t u r n t a b l e s , t r a n s p a r e n t b o u n d a r y w a l ls , a n d al o n g t e s t - s e c t i o n ( 3 .6 m w i d e 2 .1 m t a ll 1 7 . 4 m l o n g ) t o p e r m i t r e p r o d u c -t i o n o f m i c r o m e t e o r o l o g i c a l b e h a v i o r a t l a rg e r s c a l es . M e a n w i n d s p e e d s o f0 . 1 5 - - 1 2 m s - ' c a n b e o b t a i n e d i n t h e E W T . B o u n d a r y - l a y e r d e p t h s 1 m t h i c ko v e r t h e d o w n s t r e a m 6 m c a n b e o b t a i n e d b y u s in g v o r t e x g e n e r a t o r s a t t h et e s t - s e c t i o n e n t r a n c e a n d s u r f a c e r o u g h n e s s o n t h e f l o o r . T h e f l e x ib l e te s t-s e c t i o n r o o f o f t h e E W T is a d j u s t a b l e i n h e i g h t t o p e r m i t t h e l o n g i t u d i n a l


7/19

p r e s s u re g r a d i e n t t o b e s e t a t z e r o . F o r t h e p r e s e n t t e s t s , t h e v o r t e x g e n e r a t o r sa t th e t u n n e l ' s e n t r a n c e w e r e f o l l o w e d b y 1 0 m o f s m o o t h f l o o r , a n d a 3 ma p p r o a c h r a m p t o a m o d e l o f t h e t o p o g r a p h y a t t h e C h i n a L a k e s i t e .Models1 : 8 5 a n d 1 : 1 7 0 s ca le m o d e l s o f t h e C h i n a L a k e t o p o g r a p h y w e r e c o n -s t r u c t e d f o r u se in t h e E W T . T h e t o p o g r a p h i c r e l i e f o f t h e C h i n a L a k e s it e iss h o w n i n Fi g . 1 . A c y l i n d r i c a l p l e n u m m a n u f a c t u r e d w i t h a p e r f o r a t e d u p p e rp l a t e w a s c e n t e r e d in t h e m i d d l e o f t h e t e s t - s i t e p o n d . T h e s o u r c e g as , a rg o n ,s t o r e d i n a h i g h - p r e s s u r e c y l i n d e r , w a s d i r e c t e d t h r o u g h a s o l e n o i d v a lv e , af l o w m e t e r , a n d o n t o t h e c i r c u l a r -a r ea s o u r c e m o u n t e d i n t h e m o d e l p o n d . A l ls o u r c e r e l ea s e c o n d i t i o n s w e r e s t e p f u n c t i o n s ; t h u s , t h e i r p r o f i le s c a n b er e c r e a t e d f r o m t h e d a t a in T a b l e 1 .

" , ~ o '., ~ , 7 ; o ,

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. . . . . - , , w , )r e fe re n c e ~ \ ~ / ,' ~ ~ o , e v o t io n 2 m ~ !

Y2 0 3 o r e

S W u ~ ~ J( 2 2 5 ) S c a l eF i g . 1 . T o p o g r a p h y o f C h i n a L a k e t e s t s i t e .


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Wind profiles and turbulence measurernentsV e l o c i t y p ro f i l e m e a s u r e m e n t s a n d r e f e r e n c e w i n d s p e e d c o n d i t i o n s w e r e

o b t a i n e d u s in g a T h e r m o - S y s t e m s I n c. (T S I ) M o d e l 1 0 5 0 a n e m o m e t e r a n d aT S I M o d e l 1 2 1 0 h o t - f i l m p r o b e . T u r b u l e n c e m e a s u r e m e n t s w e r e m a d e w i t ht h is s y t e m f o r t h e l o n g it u d i n a l v e l o c i t y c o m p o n e n t a n d w i t h a T S I s p l it -f il mp r o b e c o n n e c t e d t o tw o T S I 1 0 5 0 a n e m o m e t e r s f o r b o t h l o n g it u d in a l a n dv e r t ic a l c o m p o n e n t m e a s u r e m e n t s . S i n ce t h e v o l ta g e re s p o n s e s o f t h e s ca n e m o m e t e r s a r e n o n l i n e a r w i t h r e s p e c t to v e l o c i ty , a m u l t i p o i n t c a l i b r a t io no f s y s t e m - r e s p o n s e v e r s u s v e l o c i t y w a s u t i li z e d f o r d a t a r e d u c t i o n .Concentration measurements

T h e c o n c e n t r a t i o n s o f m e t h a n e p r o d u c e d d u r in g a n L N G s pil l a re in h e re n t -l y t i m e d e p e n d e n t . I t is n e c e s s a r y t o h a v e a f r e q u e n c y r e s p o n s e t o c o n c e n t r a -t i o n f l u c t u a t i o n s o f a t l e a s t 5 0 H z t o is o l a te p e a k s o f m e t h a n e c o n c e n t r a t i o ng r e a te r t h a n 5 % b y v o l u m e ( t h e l o w e r f la m m a b i l i t y l im i t ( L F L ) o f m e t h a n ei n a i r) ; h e n c e , a n a s p i r a t i n g h o t . f i l m p r o b e w a s u s e d f o r th i s s t u d y ( s e e F i g. 2 )

z t u JO e t a d A

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z T W O a l u m i n a c o a I e ~ n o t f l l rP s e n s o r s( 5 0 ~ r n a l a

1 2~ v a c u u r r ~

c o : n e c b o r ~ . .

0 . 4 6 c m Dl a ~ , ,4

4 6 C r F~

C j_- i ~ - -- 1 4 c m . . . . ~ 1x U e t a l ~ A

Fig. 2. Hot-fi lm aspirating c onc entrat ion-p robe .T h e b a s ic p r in c i p le s g o v e r n i n g t h e b e h a v i o r o f s u c h a p r o b e h a v e b e e n

d i sc u s se d b y B l a c k s h e a r a n d F i n g e r so n [ 1 9 ] , B r o w n a n d R e b o l l o [ 2 0] K u r e t s k y [ 2 1 ] , a n d J o n e s a n d W i l so n [ 2 2 ] . A v a c u u m s o u r c e s u f f i c ie n t t oc h o k e t h e f l o w t h r o u g h t h e s m a l l o ri f i c e j u s t d o w n w i n d o f th e s e ns in g e le -m e n t s w a s a p p l ie d . O n l y o n e o f th e t w o f i l m s in th i s s p e ci a l p r o b e w a s a na c t i ve e l e m e n t f o r t h e m e a s u r e m e n t s o f c o n c e n t r a t i o n in t h e p r e s e n t s t u d y .


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This film was operated in constant-t emperatu re mode at a temp eratu reabove tha t of the ambie nt air. A feedback amplifier maintai ned a constant-overheat resistance through ad justme nt of the heating current. A change inoutput voltage from this sensor circuit corresponds to a change in heat trans-fer between the hot wire and the sampling environment.The hea t transf er rate fr om a ho t cylindrical film to a gas flowing over itdepends primarily upon the film diameter, the t empera ture difference betweenthe film and the gas, the ther mal co nduc tivi ty and viscosity of the gas, andthe gas velocity [ 22]. For a film in an aspirated probe w ith a sonic throat ,the gas velocity can be expressed as a fun cti on of the ra tio o f the prob e cross-sectional a~ea at the film position to the area at the thro at, the specific heatratio, and the speed of sound in the gas. The latte r two parameters, as well asthe thermal conducti vity and viscosity of the gas, mentio ned earlier, aredeterm ined by the gas composit ion and temperature. Hence, for a fixedprobe geo metry and film temperature, the heat transfer rate, or the relatedvoltage drop across the film, is a fun cti on onl y of the gas comp osit ion andtemperature. Since all tests performed in this study were for an isothermalflow situation, the film's response was a function only of gas composition.For probe calibration, argon--air mixtures of kno wn compositions werepassed through a heat exchanger to condit ion the gas to the tunnel tempera-ture. These known c ompositions were produced from bottles of pure argonand pure air passed through a Matheson gas proportioner, or were drawnfrom a bottle of prepared gas composition provided by Matheson Labora-tories. F or an overheat ratio (temperature of film/ambien t temperature ) of1.75, the voltage drop varies monotonically with argon concentration. Higheroverheat ratios led to failure.

The effective sampling area of the probe inlet is a func tion of th e prob easpiration rate and of the distr ibutio n of approach velocities of the gases tobe sampled. A calcu lation of t he effective sampling area during all tests sug-gested that this area was always less than the area of the probe inlet, 1.88 cm:.Thus the resolution of the c oncent ration mea surements as applied to theChina Lake site is ~ 1.6 m 2.

The travel time from the sensor to the sonic choke limits the upper fre-quency response of the probe. At high frequencies the correlation betweenconcen tration fluctuations and velocity fluctuations (velocity fluctuationsare a result of the changes of sonic velocity with concentration) at the sensorbegins to decline. Wilson and Netterville [24] examined the operating charac-teristics of similar, small, aspirated concentration-sen sors. The y calibratedtheir sensors dynam ica lly and f oun d a flat response to ~ 200 Hz. The CSUaspirated probe was expected to have an electronic upper frequency responseof 1000 Hz, but, to improve signal-to-noise characteristics, the signal wasfiltered at 200 Hz. This is well above the e xpecte d frequenc ies of concentra-tion fluctuations.

The errors caused by the assumption of piecewise linearity between calibra-tion points in the reduction of the concentration data are approximately the


10/19

10co mpo ne nt value (per cent argon) + 75%. The errors caused by calibrationchanges du et o temperature drif t are ~0.1% of the compo nent value perdegree centigrade. Since the tunnel temperature varies at most by + 5C duringa given test period, the ma ximu m error due to te mpera ture drift wou ld be0.5% of the c omp on en t value. Final accumulate d errors result in a confide ncelevel of + 0,8% met ha ne at measure d levels near 2.5%.T e s t p r o g r a m r e s u l t s

Summaries of the pro to ty pe and model test conditions for the LNG spilltests 18, 19, 20 and 21 performed during the fall of 1978 at the China LakeNaval Weapons Center are prese nted in Tables 1 and 2, respectively. Alldimensions reported for the wind-tunnel results are in the equivalent full scalevalues. The coordinate origin for all figures is the LNG spill point (see Fig. 1).The positive x-axis is in the d irec tion o f the prevailing wind.Characteristics of the modeled boundary layer

Measurements of the approach-flow characteristics were obtained for themodel flow over the China Lake scale topography. These characteristic lengthand velocity scales should be comparabl e with those exp ecte d to occur overthe China Lake site. Counihan [25] has summarized the values of aerodynamicroughness z0, longitudinal-ve locity integral length scale Ax, and t he power-lawindex 1/n that may be expected to occur in the atmosphere. Table 3 com-pares values of these quantities as cited by Couni han and values scaled upfrom the model tests. Figures 3 and 4 show the profiles of mean velocity andlocal turbulence intensity, respectively. Profile measurements were not avail-able for the field measurements.

TABLE 3Summary of approach-flow characteristicsParameter Field data a Model valuesz 0 (m) 0.01 -0 .15 0.0171/n 0.143-0.167 0.18Ax (m) at a height of 2 m 12.0 --30.0 14.5Az (m) at a height of 2 rn 1 --2 5.1aSee ref. 25.

Test series resultsThe China Lake boil-off rate, boil -off durat ion, and wind speed for theLNG tests 18 and 19 were simulated in the ~ using:a smo oth floor~ Th esame tests were then repe ated , but this t ime the to pogr aphy of the China


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1 1

16

N

N

u ( z ) z o.1,L N G - 1 8 U ( Z r e f ) = 6 7 m / s1 2 - L N G - 1 9 O ( Z r e t ,) = 5 1 m / sL N G - 2 0 Q ( Z r e f ) = 1 2 4 r n / s e~lO8 LNG-21 U (Zre f)= 49 m/s / e

64 *"# ~ l * ' ' ] i2 "

e

0 0.5 1.0 1.5U ( z ) / 0 ( z ,, , , )F i g . 3 . V e l o c i t y p r o f i l e s .

1614 Zre = 2 meters1210

"~7~- 6 N

2

I _ I ~ ~0 0 0 .0 5 0 .1 0 0 .1 5 0 . 2 0 0 . 2 5 0 .3 0a ,,(Z) /O Z )F ig . 4. L o c a l l o n g i t u d i n a l t u r b u l e n c e i n t e n s i t y p r o fi l e .

0 . 3 5

L a k e s i te w a s i n c lu d e d * . T h o r o u g h c o n c e n t r a t i o n m e a s u r e m e n t s d o w n w i n dw e r e o b t a i n e d f o r th e s e f o u r t e s t s . A s u m m a r y o f t h e t e s t c o n d i t i o n s f o r th ef o u r te s t s is p r e s e n t e d i n T a b l e 2 . C o m p a r i s o n s b e t w e e n t h e s i m i l a r t e s t s , o n e* U n f o r t u n a t e l y , t h e w i n d d i r e c t i o n s p r o v i d e d b y t h e f i e l d in v e s t i g a to r s w e r e i n e r ro r .T h e s e t w o t e s t s w e r e r e - r u n i n a f in a l t e s t s er ie s.


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1 2

p e r f o rm e d w i t h t he m o d e l t o p o g r a p h y a n d o n e p e r f o r m e d u s i n g a s m o o t hf l o o r , r e v e a l e d t h a t t h e d i s p e r s i o n :at t h e C h i n a L a k e s i t e i s g r e a t e r t h a n w o u l db e e x p e r i e n c e d i f t h e s p i ll o c c u r r e d i n a v e r y s m o o t h a n d f l a t a r ea .

F i n a l ly , c o n c e n t r a t io n m e a s u r e m e n t s d o w n w i n d w e r e o b t a in e d f o r t h es i m u l a t e d L N G f i e ld t e st s 1 8 , 1 9 , 2 0 , a n d 2 1 . A s u m m a r y o f t h e f ie l d c o n d i -t i o n s s i m u l a t e d is p r e s e n t ed i n T a b l e 1 . A s u m m a r y o f t h e m o d e l c o n d i t i o n sf o r t h e s e t e s t s is p r e s e n t e d i n T a b l e 2 . G r o u n d - l e v e l p e a k c o n c e n t r a t i o n c o n -t o u r s f o r e a c h t e s t ar e s h o w n in F ig . 5 - - 8 . T h e s e c o n t o u r l in e s w e r e p r o d u c e d

Test-run No. LNG-18(No of grid points=18)circled numbers are LLL field values

" \ : o % , o s ; , I ] ) )\ ' \ , \ ' , ,

. . . . . . . .

6 - ' - 2 ' o . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0 30 4Q 5Q 60 70 80 90 100 110 120 130 140China lake scale (m)F i g . 5 . M o d e l t e st 1 8 : g r o u n d c o n t o u r p l o t o f p e a k c o n c e n t r a t i o n .

Test-run No. LNG-19(No of g rid points =12 )circled numbers ape LLL field values

A _ Ii i 1406 l o 2 0 3 b ' ; o d o ~ d o ' l & ~ l b 1 ~ o 1300O China lake scale (m)F i g. 6 . M o d e l t e s t 1 9 : g r o u n d c o n t o u r p l o t o f p e a k c o n c e n t r a t io n .


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T e s t r u n N O. L N G -2 Q( N o o f g r i d p o i n ts = 4 7 )c i r c l e d n u m b e r s a r e L L L f i e l d v d l u e s

~ 1 0

13

i i i i io 1 ~ ~ o d o ' 4 o d o 4 0 ~ o ~ o0 10 0 1110 120China lake sca le (m )Fig. 7. Model test 20: ground contour plot of peak concentration.

l i1 3 0 1 4 0

T e s t r u n N o L N G -2 1(No. o f g r id po in t s =91 )c ir c le d n u m b e r s a r e L L L f i e l d va l u e s~ / ~ ~ Test \ \ . ! I I I 1 ~

O t ~ I 2 1 0 I I 5 1 0 I I I I I L I I I1 0 0 4 0 6 0 7 0 8 0 9 0 1 0 0 1 10 1 2 0 1 3 0 1 4 0China lake scale (m )Fig. 8. M odel test 21 : ground con tour plot of p eak concen tration.

b y h a n d i n t e r p o l a t i o n b e t w e e n 1 8 t o 9 1 g r id p o i n t s o v er t h e m o d e l . T h e g rids p a c in g w a s v a rie d f r o m e x p e r i m e n t t o e x p e r i m e n t t o r e f le c t e x p e c t e d p l u m eb e h a v i o r . A s u m m a r y o f t h e t i m e s o f a r riv al, p e a k c o n c e n t r a t i o n s a n d p a s s ag eo f t h e p lu m e , a n d t h e m a x i m u m p e a k c o n c e n t r a t i o n s o b s e r v e d is t a b u l a t e d inr e f . 1 3 .C o m p a r i s o n w i t h f ie ld d a t a

A s p a r t o f t h e C h i n a L a k e f i e ld - t e s t s er ie s , f ie l d c o n c e n t r a t i o n m e a s u r e -


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14ments were obtained over two in depen dent mea sure ment grids. The NavalWeapons Test Center established a grid of ten diffe rent concentration-mea-surement stations, and the Lawrence Livermore Laboratory (LLL) providedeight towers with a variety of conce ntrat ion sampling equi pmen t [25]. Theprimary purpose of the LLL grid was sensor evaluation. Both these grids areindicated in Fig. 1.The degree to which data modele d physically correlate with values ob-tained in the field is dependent upon the approximations assumed in theformulation of the model and upon the inherent randomness of atmosphericdiffusion processes. The assumptions emp loyed in the c onstruct ion of thephysical model of LNG vapor dispersion at t he Naval Weapons Test Centerwere discussed above. The randomness of wind directions and velocities inthe atmosphere is such that a single time-realization for a fixed point in spaceis insufficient to describe the complete probability distribution of peak con-centra tions that may be observed at that point. Witho ut ensemble-averagingof similar tests in the field, the values fo un d during a single realization mayrange over a limited portio n of an un kno wn probability distribution. Pasquill[ 27] note d th at in ma ny circumstances of practical interest the unc erta intyfoun d between cont inuou s releases of gaseous plumes may be at best 10--50% in the average and a factor of two or more for individual data [26]. Inaddition to the small-scale effects of local randomness, the atmo sphere haslarge-scale variations which lead to meandering of the mean plume motion.These large-scale meanderings are not mode led in wind tunnels, and lead tothe primary source of discrepancy between model and field concentrationmeasurements.The Naval Weapons Test Center grid consisted of ten different concentra-tion sensors. These instrume nts were all of the catalytic combus tion typ e.The principle o f opera tion of these ins truments is that a hot catalytic fila-ment causes methane passing over it to oxidize, and the rise in temperaturedue t o the reaction changes the electrical resistance of the filament. Thesedetectors are accurate only for low (below 7%), slowly varying methaneconcentrations.Table 4 compares peak concentrations observed in the field at the NavalWeapons test grid points with those obtaine d for the wind-tunnel model.This comparison is in general quite poor. There are several factors which mayacc ount for this scatter in comparable da ta over several orders of magnitude.The y are: (1} the mean wind direction specified for each wind-tunn el testmay have been in error, owing to the large shifts in wind direction during thefield experiments; (2) the f luctuat ions in direction tha t occurred during the

+ ofield tests were as large as -5 0 (physical mode ling of large wind-d irect ionfluctuations is not possible in a wind tunnel); (3) the wind speed observed inthe field changed by as much as -+1.8 m s-1 during the tests (this amount offluc tuati on can accou nt for variation by ~ 50% in measured, conc entra tionvalues); (4) the peak con cent ration fluctuat ions in the field tests were t oorapid for the catalytic sensors torespond; (5) the field concentrations were


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15

T A B L E 4Summary o f peak conce n t r a t i on da t a a t t es t -po in t l oca t i ons fo r mode l and f ie ld exper i -m e n t sLoca t ion Tes t No. 18 Tes t No. 19 Tes t No. 20 Tes t No. 21

Field Model Field Model Field Model Field ModelC h i n a L a k eN a v a l W e a p o n sG r i d

1 >5 % 5.9 >5% 0 1.6% 0 1.6% 192 >5 % 5.3 >5 % 0 1.0 0 1.6% 24.73 >5 % 4.1 0.7 5 0 0 0 0.7 10. 64 >5 % 4.0 >5 % 0 0 0 1.6% 17.75 0.7 3.6 0 0 0 0 0.6 12. 36 0 1.7 0 0 0 0 0.3 6.17 4.0 7.6 0 0 0 0 2.1 4.38 0 6.4 0 0 0 0 0 10 .89 0 0 >5 % 20.8 2.4% 8.8 0 4.0

10 0.3 0 >5 % 0 1.8% 2.5 0 1.5L a w r e n c eL i v e r m o r eL a b . G r i d

1 42.5 >40 .0 a 46 .0 >50. 0 a 22 .0 >20. 0 a 64 .0 >50. 0 a2 41 .0 >40 .0 33 .0 -50 . 0 35 .0 -19 . 0 36 .0 >50. 03 23 .0 -32 .0 26 .0 -10 . 0 - - - 0 33 .0 -35 . 04 38.0 - 7.0 21.0 -15 .0 11.0 - 2.5 34.0 -2 5. 05 - - - - - 0 - - - 0 2 8 . 0 - 2 7 . 0

6 -- 16.4 - 8 12.7 5 - 0.8 10.5 -1 0. 07 -- 0.0 ~ 0 0.6 ~ 0 5.3 ~1 2. 08 -- 8.1 - 0 1.9 - 0 -- - 5.0

a Approx ima te va lues on ly ; mode l da t a were no t ob t a ined a t t he equ iva l en tmore grid si tes. Lawrence Liver -

too large for the catalytic sensors to respond; and (6) the approximations usedin simulating the LNG field-test series were too weak to achieve propersimulation.

The Lawrence Livermore Laborator y obtained conce ntratio n time historiesat a variety of different heights on their eight towers equipped with concen-trati on sensors [2 6]. Several diffe rent types of sensors were employe d. Eachof these de tec tor responses was verified by simultaneous grab-bag samplingof the gases flowing over the sensor. This techniq ue provides an ac curateme tho d of verifying that the dif fere nt sensors' responses were correct. Thepeak field concentrations obtained from the lowest sensor elevation at each ofthe eight towers are summarized together with approximate model values inTable 4. Since the res ponse times of the various instruments utilized byLawrence Livermore Laboratory (grab samplers, thermocoupling aspirated


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16batherometers, infrared analyzers, etc.) were only several seconds, concentra-tions were essentially measured instantane ously. A peak conce ntratio n isdefined as the maximum value detected during the nonstationary variationof the plume conc entr atio n as it passes a given sampler. Nonsta tionary windcondition s made any analysis of arrival time, departure time, or mean con-centr ation meaningless.

Multiple plume-release replication s over the China Lake mo del revealedthat peak concentrations were reproducible to within a small range (+5%};hence this proper ty was chosen for the mod el/fie ld comparisons despite theuncertainties outlined early in this section [27]. Since flamma bility dependsupon instantaneous stochiometric composition, peak concentrations werealso of ma xim um interest to the sponsor. As concen tration s over the modelwere not obtained at the Lawrence Livermore grid sites, the values noted formodel equivalents are only approximate. These values were obtained by in-terpolation of the hand-drawn ground-level peak concentration contours inFigs. 5 8. On these figures the circled numbe rs are the peak conc entr ati onsobserved in the field on the Lawrence Livermore grid.

The correlation between the Lawrence Livermore data and the model datais generally superior to t hat between the Naval Weapons Test Center data andthe model data. There remain, however, a number of sampling points wherepoor agreement exists. Considering each model test p oint individually forcase 18, reas onably compar able results, i.e. within 50% of the field values,are found for the near-field grid points 1, 2, and 3, and poor comparison forgrid point four. The reason for these discontinuities in field/mo del com-parisons may be any combination of the factors mentioned previously. Inthis case the differences appear to be caused by the small number of measure-ment locations in both field and model tests, and the variability of wind direction in the field.For case 19 the quality of the comparison between the model and fielddata is not as good. The decays of concentr ation with distance from thesource appear to agree, but the directions of the plume appear to be differ-ent. This result suggests a difference between the wind direction in the fielddata and th at modeled. Here again, as in case 18, an insufficient numbe r ofmodel or field measurement locations were used to define the concentrationfield properly.In case 20 the comparison between the field and model results again ap-pears poor. The laboratory model predicts that at the higher wind speed(12.4 m s-1 at 2 m) f or this case, the LNG p lume has very little lateral spread,whereas the field mea surem ents showed significant conce ntrati ons at largedistances from the plume's mean axis. This suggests large variation in thewind direct ion or an error in the mean wind direction. For this test and test21 a sufficient num ber of meas ureme nt locations were used to define themodel ground-level contours properly, i,e. 47 and 91 points, respectively. Ofthe f our tests modeled, test 21 shows the greatest comparability between themode l and field results. All measur emen t locations can be considered to give


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17a c c e p t a b l e c o m p a r a b i l i t y c o n s i d e r i n g t h e v a r ia t i o n o f w i n d d i r e c t i o n a n dv e l o c i t y in t h e f i e ld a n d t h e i n s u f f i c i e n t n u m b e r o f f i e ld d a t a p o i n t s .C o n c l u s i o n s

A s e ri es o f s i x - c u b i c - m e t e r l iq u i d n a t u r a l g a s ( L N G ) s p i l ls w e r e p e r f o r m e di n 1 9 7 8 a t t h e C h i n a L a k e N a v a l W e a p o n s C e n t e r , C A . A p a r a l l e l se t o fm o d e l e d s p i ll s w e r e s i m u l a t e d i n m e t e o r o l o g i c a l w i n d - t u n n e l f a c il i t i e s t op r o v i d e f i e ld - t e s t p l a n n i n g i n f o r m a t i o n , t o e x t e n d t h e v a l ue o f t h e l i m i t e ds e t o f f ie ld m e a s u r e m e n t s , a n d t o e v a l u a t e th e c o n c e p t o f p h y s ic a l m o d e l i n go f L N G p l u m e d i s p e r s i o n a s a p r e d i c t i v e h a z a r d a n a ly s i s t o o l . C o m p a r i s o n o fm e a s u r e m e n t s o v e r 1 : 1 7 0 a n d 1 : 8 5 s c al e m o d e l s o f t h e C h i n a L a k e s it ew i t h f i e l d m e a s u r e m e n t s r e v e a l e d t h a t : ( a) w h e n t h e w i n d f i e ld c o n d i t i o n sw e r e n e a r l y s t a t i o n a r y , t h e r e s u l t a n t p l u m e s t r u c t u r e w a s r e p r o d u c e d b y th em o d e l p l u m e w i t h i n f ie ld i n s t r u m e n t r e s o l u t io n ; ( b ) m e a s u r e m e n t s m a d e o v e r1 : 1 7 0 a n d 1 : 8 5 s ca le m o d e l s p r o d u c e d s i m i la r c o n c e n t r a t i o n v a r i a t i o n sw h e n s c a le d b y t h e d e n s i m e t r i c F r o u d e n u m b e r ; a n d ( c ) t o p o g r a p h y e f f e c t sa r e s ig n i f ic a n t . M o d e s t h i ll s lo p e s o f 1 : 1 0 c a n d e t a i n d e n s e p l u m e s a n dr e d u c e t h e l o n g i t u d i n a l d i s t a n c e s c o v e r e d b e f o r e d i l u t i o n t o t h e l o w e r f l a m -m a b i l i t y l i m i t o f f l a m m a b l e g a s es . S h a l lo w v a l le y s a n d g o r g e s c h a n n e l t h ep l u m e a n d s u s t a i n h i g h c o n c e n t r a t i o n s .A c k n o w l e d g m e n t s

T h e a u t h o r s w i s h t o a c k n o w l e d g e t h e f i n a n c ia l s u p p o r t o f t h e U . S . C o a s tG u a r d , D e p a r t m e n t o f T r a n s p o r t a t i o n C o n t r a c t D O T - C G - 7 5 2 7 9 - A .R e f e r e n c e s

1 R . N . M e r o n e y a n d D . E . N e f f , B e h a v i o r o f n e g a ti v e ly b u o y a n t g a s p l u m e s e m i t t e df rom an LN G spil l, P roc . 6 th Aus t r a l a s . Hydrau l . F lu id M ech . Conf . , Ade l a ide ,Aus t r a l i a , December 5 - -9 , 1977 , pp . 472 - -475 .2 A m e r i c a n G a s A s s o c i a ti o n , L N G S a f e t y P r o g r a m , I n t e r i m R e p o r t o n P h a s e I I W o r k ,R e p o r t o n A m e r i c a n G a s A s s o c ia t io n P r o j e c t I S - 3 -1 , B a t te l le C o l u m b u s L a b o r a t o r ie s ,O H , 1 9 7 4 .3 J .E . Ce rmak , Ap p l i ca t i ons o f fl u id me chan i c s to w ind eng inee r ing , a F r e em an Scho l a rlec ture , J . F lu id Eng. , Ser . 1 , 97 (1975) 9- -38 .4 J .E . Ce rm ak , Ap p l i ca t i on o f w ind t unne l s t o i nves t iga t i on o f w ind eng inee r ing p rob -l ems , Am. In s t . Ae ronau t . As t ronau t . J . , 10 (1979 ) 679 - -690 .5 R .N . M eroney , D .E . N e f f and J .E . Ce rm ak , Wind t unne l s imu la t i on o f LN G sp i ll s,P roc . Am . Gas Assoc . T ransm i s s ion Conf ., Mon t r ea l , Canada , M ay 8 - -10 , 1978 , pp .T 2 1 7 - - T 2 2 3 .6 R .N . M eroney , Phys i ca l mo de l i ng o f a tm osp he r i c d i spe r s ion o f heavy ga se s r e l ea seda t t he g roun d o r f r om sho r t s t a cks , P roc . 10 th In t . Tech . Mee t . - on A i r Po l l u t i onM o d e l i n g a n d I t s A p p l i c a t io n , R o m e , O c t o b e r 2 3 - - 2 6 , 1 9 7 9 , p p . 6 8 9 - - 6 9 9 .7 J . S a k a g a m i a n d M . K a t o , D i f f u s io n a n d v a p o u r ri se o f m e t h a n e v a p o u r f r o m a r ea lsou rce i n a ir s t r e am, Na t . Sc i. Rep . O chano mizu Un ive r s i t y , J apan , 19 (2 ) ( 1968 )59---66.


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18

8 G.J. Boyle and A. Knee bone , Labor atory Inves tigation into the Characteristics ofLNG Spills on Water, Evapo ratio n, Spreading and Vapor Dispersion, Shell ResearchLtd., Report to American Petroleum Institute , March 19 739 T.G. Hoot and R.N. Meroney, The behavior of negatively buo ya nt stack gases, 67thAnn . Meet. Air Pol lut ion Contr ol Association, Denver, CO, Jun e 9 13, 1973, Pap. No.74-210.10 D.J. Hall, C.F. Barrett and M.O. Ralph, Experim ent s on a Model of an Escape ofHeavy Gas, Warren Spring Labor ator y Rep. LR217 (AP), Dep art ment of Trade andIndus try (U.K.).11 D.E. Neff, R.N. Meroney and J.E. Cermak, Wind Tun nel Study of the NegativelyBuo yan t Plume Due to an LNG Spill, Flui d Mech. Wind Eng. Rep. CER76-77DEN~RNM-JEC22, Colorado State University, For t Collins, CO. Also P.T. Harsha, LNGSafety Program Topical Report: Wind Tunnel Tests of Vapor Dispersion from LandFacilities, R & D Associates, CA, RDA-TR -1100-00 2, for Am. Gas Assoc. Project,IS-128-1, August 1976 (available from Natl. Tech. Inf. Serv., Springfield, VAk12 R.N. Meroney, D.E. Neff, J.E. Cermak and M. Megahed, Dispersion of Vapor from

LNG Spills -- S imul atio n in a Meteorological Wind Tun nel , Report prepared forR & D Associates, CA, Fluid Mech. Wind Eng. Rep. CER76-77RNM-JEC-MM57,Colorado Stat e University, Fort Collins, CO. Also Liquified Natural Gas Wind-Tunn elSimulati on and Ins trum enta tion Assessments, U.S. Dept. of Energy Rep. SAN/W1364-01, Cont rac t No. EE-77-C-03-1364, April 1978 (available from Natl Tech. Inf. Serv.,Springf ield, VA ).13 D.E. Neff and R.N. Meroney, Dispersion of Vapor from LNG Spills -- Sim ulat ion in aMeteorological Wind Tun ne l of Spills at Chin a Lake Naval Weapons Center, CA. FluidMech. Wind Eng. Rep. CER78-79DE N-RNM41, Colorado State University, For tCollins, CO; U.S. Coast Guard, Dept. o f Transpo rtati on. Cont ract DOT CG-75279-A(available from Natl. Tech. Inf. Serv., Springfield, VA).14 J.A. Fay, Grav itatio nal spread and dilu tio n of heavy vapor clouds, 2nd Int. Syrup.on Stratified Flows, Tro ndhe im, Norway, June 24--27, 1980, pp. 421 494.15 A. Lohmeyer , R.N. Meroney and E.J. Plate, Model investigations of the spreading ofheavy gases released from an inst anta neous volume source at the gr ound, Proc. 1 lt hNATO/CCMS Int. Tech. Meet. on Air Pol lut ion Modeling and Its Applic ations. Am-sterdam, The Netherlands, November 25--28, 19 80 pp. 303--320.16 R.N. Meroney, J.E. Cermak and B.T. Yang, Modeling of atmospheric transpo rl andfumigation at sharefines, Boundary Layer Meteorol., 9 (1975) 69--90.17 N. Isyumov and H. Tanaka, Wind tun nel modelling of stack gas dispersion -- Difficul-ties and appro ximat ions , in J.E. Cermak (Ed.), Proc. 5th I nt. Conf. on Wind Engineer-ing, Fort Collins, CO, U.S.A., Jul y 9--14 , 1979, Pergamon, Oxford.18 G.T. Skinner and G.R. Ludwig, Physical Modeling of Dispersion in the Atmos pheri cBound ary Layer, Calspan Advanced Technolog y Center, Calspan Rep. No. 201, May1978.19 P.L. Blackshear, Jr. and L. Finger son, Rapid response heat flux probe for high tem-perature gases, Am. Rocket Soc. J., 32 (1962) 1709--1715.20 G.L. Brown and M.R. Rebollo, A small, fast response probe to measure comp osi tionof a binary gas mixture, Am. Inst. Aeronaut. Astronaut. J., 10 (1972) 649--752.

2 1 W . H . K u r et s k y , O n t h e U s e o f a n As pi ra ti ng H o t - F i l m A n e m o m e t e r f o r t h e I ns ta nt an e.o u s M e a s u r e m e n t o f T e m p e r a t u r e , T he s is , M . M e c h . E n g . , U n iv e rs i ty o f M in n e s o t a ,Minneapolis.

2 2 B . G . J o n e s a n d R . J . W i ls o n, G a s c o n ce n tr a ti o n m e a s u r e m e n t s w i t h a t e m p e r a t u r ec o m p e n s a t e d a s pi r at i ng p r o be , P r o c . 6 t h B i e nn . S y r up . o n T u r b u l e n c e , U n i ve r s it y o fM i s so u r i, R o l la , O c t o b e r 1 9 7 7 , p p . 2 0 5 - - 2 1 0 .

2 3 J. M c Q u a i d a n d W . W r i gh t , T h e r e s p o ns e o f a h o t w i re a n e m o m e t e r i n f l o w s o f g a smixtures, Int. J. Heat and Mass Transfer, 16 (1973) 819--828.24 D.J. Wilson and D.D.J. Netterville, A fast-response, heated -eleme nt con cen tra tio ndetector for wind tunnel applications, J. Wind Eng. Ind. Aerodyn., 7 (1981) 55--64.


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19

25 J. Counih an, Adiabat ic atmospheric bo und ary layers: a review and analysis of datafrom the period 1880--1972, Atmos. Environ., 9 (1975) 871--905.26 R.P. Koopma n, B.R. Bowman and D.L. Ermak, Data and Calculations of Dispersionon 5 m 3 LNG Spill Tests, Lawrence Livermore L aboratory, University of California,Livermore, CA, Rep. UCRL-52876 (available from Natl. Tech. Inf. Serv., Springfield,VA).27 F. Pasquill, Atmosphe ric Diffusion, Van Nostrand, Londo n.28 R.N. Meroney, D.E. Neff and K.M. Kothari, Behavior of LNG Vapor Clouds: Teststo Define the Size, Shape and Stru cture of LNG Vapor Clouds, Ann. Rep. 19 79 -1980, Gas Research Insti tute, Chicago, IL; Rep. No. GRI 7910073, Contract No.5014-352-0203 (available from Natl. Tech. Inf. Serv., Springfield, VA).

dispersion of vapor from liquid natural gas spills

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