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Rapid thawing of frozen food at room temperature
F LOOD & DRINK
R a p i d t h a w i n g o f f r o z e n f o o d at r o o m t e m p e r a t u r e Bulk t h a w i n g of frozen food stuffs such as r a w p r a w n s at a m b i e n t t e m p e r a t u r e c a n be a c h i e v e d e c o n o m i c a l l y using a G r a h a m oil sealed p i s t o n vac u u m p u m p b a c k e d by a Grah a m liquid ring v a c u u m p u m p in series. The v a p o u r p h a s e p r in ci p l e of h e a t t r a n s f e r is utilised by placing t h e frozen p r o d u c e into a chamber, preloaded into "wheel in" trolleys or by m a n u ally stacking. A w a t e r f i l l e d t r o u g h is h o u s e d in t h e b a s e of t h e c h a m b e r a n d indirectly h e a t e d by a s e p a r a t e p r i m a r y h o t w a t e r source circulated t h r o u g h imm e r s e d t u b e s a n d r e g u l a t e d to m a i n t a i n t h e w a t e r t r o u g h at a predetermined temperature n o r m a l l y b e t w e e n 14 a n d 21°C. Air is t h e n e v a c u a t e d from t h e c h a m b e r by t h e r o t a r y pist o n v a c u u m p u m p to an absolute p r e s s u r e of b e t w e e n 16 to 24 m b a r at which, t h e w a t e r in th e t r o u g h c o m m e n c e s to boil. The s t e a m / v a p o u r t h u s genera t e d e n v e l o p e s t h e frozen produce, w a r m i n g it by t h e t r a n s f e r of l a t e n t heat.
wATERTROUG~
OVERFLOW
and its smaller liquid ring backing p u m p is m o d e s t c o m p a r e d to an equivalent single liquid ring p u m p and air ejector system. The rotary p i s t o n c o m b i n a tion requires approximately 30% of t h a t for t h e air e j e c t o r / pumpset. The v a c u u m capability of t he a)At atmospheric pressure (1013 m b a r ) w a t e r boils at r o t a r y p i s t o n p u m p is such t h a t t h a w i n g t e m p e r a t u r e s less t h a n 100 ° (Sea level) b) In a v a c u u m of 250 milli- 14°C are possible w i t h o u t any b a r w a t e r will boil at 65°C. loss in p u m p i n g capacity. The (250 m b a r e q u a t e s to an alti- ai r e j e c t o r system is l i m i t e d 1. The oil sealed p i s t o n vat u d e of 31000 ft above sea level) b o t h on v a c u u m a c h i e v a b l e c u u m p u m p m a i n t a i n s a conand p u m p i n g speed. c) In a v a c u u m of 20 m b a r t i n u o u s s u p p l y o f s t e a m by Pre-condensers which require m a i n t a i n i n g t h e r e q u i r e d va- w a t e r will boil at I°C. (20 m b a r copious p r i m ar y cooling w a t e r to an a l t i t u d e of c u u m in t h e c h a m b e r w h i l s t e q u a t e s flow rates are not necessary with 16 miles above sea level) d r a w in g off u n c o n d e n s e d w a t e r the rotary piston v a c u u m p u m p v a p o u r t h a t h a s by-passed t h e The benefits of using t h e GT c o m b i n a t i o n unit. t h a w i n g p r o d u c e . T h e c o n - series oil sealed rotary p i s t o n The f u n c t i o n of t h e w a t e r d e n s e d s t e a m w h i c h h a s yielded v a c u u m p u m p an d its s m a l l e r sealed liquid ring backing p u m p its l a t e n t h e a t falls back into liquid ring backing p u m p are: is purely to t r a n s f e r w a t e r vath e b o t t o m trough. The p u m p i n g speed (capa- p o u r f r o m t h e r o t a r y p i s t o n 2. The oil sealed p i s t o n va- city) is c o n s t a n t from initial p u m p oil reservoir a nd therec u u m p u m p is able to h a n d l e c h a m b e r e v a c u a t i o n to t h e vac- fore need only be a t hi r d t he t h e s a t u r a t e d s t e a m w i t h o u t u u m d u t y p o i n t a t w h i c h capacity of t h e latter. Non r e t u r n valve V2 will o p e n e m u l s i f i c a t i o n of th e lube oil s t e a m g e n e r a t i o n f a c i l i t a t e s to allow s u r p l u s d i s c h a r g e d air by m a i n t a i n i n g this oil at a p r o d u c t thawing. E q u i v a l e n t systems using a to a t m o s p h e r e d u r i n g t he c ha mt e m p e r a t u r e o f 70 to 75°C, whilst t h e s m a l l e r liquid ring w a t e r sealed liquid ring v a c u u m b er evacuation. As t he p r e s s u r e backing p u m p m a i n t a i n s a va- p u m p only, w o u l d r e q u i r e an falls this valve will eventually c u u m in th e p i s t o n p u m p oil air e j e c t o r u p s t r e a m to achieve close t h u s allowing t he liquid r e s e r v o ir of b e t w e e n 250 an d t h e v a c u u m l e v e l s r e q u i r e d ring backing p u m p to c r e a t e t he 300 m b a r absolute. w h i ch in fact is c o u n t e r p r o d u c - n e c e s s a r y v a c u u m in t h e oil With th e Piston P u m p lube tive, as t h e p u m p n o w h a s r eser v o i r t h u s p r e v e n t i n g w a t e r oil r e s e r v o i r at 7 0 / 7 5 ° C an d to be grossly oversized to cope v a p o u r c o n d e n s i n g in same. e x p o s e d t o t h i s v a c u u m o f with t h e a d d i t i o n a l a t m o s p h e r i c Graham Precision Pumps Ltd, 2 5 0 / 3 0 0 m b a r a b s o l u t e , t h e air in-bleed t h r o u g h t h e ejec- The Forge, Forge Lane, Conw a t e r v a p o u r ( s t e a m ) is super- t o r nozzle. gleton, Cheshire CW12 4HQ, The combined power require- UK. Tel: + 4 4 1260 274721; h e a t e d such t h a t any carry over from t h e c h a m b e r is p r e v e n t e d m e n t of t h e Rotary Piston Pump Fax: + 4 4 1260 276965.
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WORLD PUMPS FEBRUARY 1997
from c o n d e n s i n g in t h e lube oil an d is t r a n s f e r r e d over to t h e L i q u i d Ring P u m p w h e r e it h a r m l e s s l y c o n d e n s e s in t h e p u m p sealing liquid w h i ch is also water. To clarify t h e b e h a v i o u r of H20 su b j ect ed to a v acu u m :
R a p i d t h a w i n g o f f r o z e n f o o d at r o o m t e m p e r a t u r e Bulk t h a w i n g of frozen food stuffs such as r a w p r a w n s at a m b i e n t t e m p e r a t u r e c a n be a c h i e v e d e c o n o m i c a l l y using a G r a h a m oil sealed p i s t o n vac u u m p u m p b a c k e d by a Grah a m liquid ring v a c u u m p u m p in series. The v a p o u r p h a s e p r in ci p l e of h e a t t r a n s f e r is utilised by placing t h e frozen p r o d u c e into a chamber, preloaded into "wheel in" trolleys or by m a n u ally stacking. A w a t e r f i l l e d t r o u g h is h o u s e d in t h e b a s e of t h e c h a m b e r a n d indirectly h e a t e d by a s e p a r a t e p r i m a r y h o t w a t e r source circulated t h r o u g h imm e r s e d t u b e s a n d r e g u l a t e d to m a i n t a i n t h e w a t e r t r o u g h at a predetermined temperature n o r m a l l y b e t w e e n 14 a n d 21°C. Air is t h e n e v a c u a t e d from t h e c h a m b e r by t h e r o t a r y pist o n v a c u u m p u m p to an absolute p r e s s u r e of b e t w e e n 16 to 24 m b a r at which, t h e w a t e r in th e t r o u g h c o m m e n c e s to boil. The s t e a m / v a p o u r t h u s genera t e d e n v e l o p e s t h e frozen produce, w a r m i n g it by t h e t r a n s f e r of l a t e n t heat.
wATERTROUG~
OVERFLOW
and its smaller liquid ring backing p u m p is m o d e s t c o m p a r e d to an equivalent single liquid ring p u m p and air ejector system. The rotary p i s t o n c o m b i n a tion requires approximately 30% of t h a t for t h e air e j e c t o r / pumpset. The v a c u u m capability of t he a)At atmospheric pressure (1013 m b a r ) w a t e r boils at r o t a r y p i s t o n p u m p is such t h a t t h a w i n g t e m p e r a t u r e s less t h a n 100 ° (Sea level) b) In a v a c u u m of 250 milli- 14°C are possible w i t h o u t any b a r w a t e r will boil at 65°C. loss in p u m p i n g capacity. The (250 m b a r e q u a t e s to an alti- ai r e j e c t o r system is l i m i t e d 1. The oil sealed p i s t o n vat u d e of 31000 ft above sea level) b o t h on v a c u u m a c h i e v a b l e c u u m p u m p m a i n t a i n s a conand p u m p i n g speed. c) In a v a c u u m of 20 m b a r t i n u o u s s u p p l y o f s t e a m by Pre-condensers which require m a i n t a i n i n g t h e r e q u i r e d va- w a t e r will boil at I°C. (20 m b a r copious p r i m ar y cooling w a t e r to an a l t i t u d e of c u u m in t h e c h a m b e r w h i l s t e q u a t e s flow rates are not necessary with 16 miles above sea level) d r a w in g off u n c o n d e n s e d w a t e r the rotary piston v a c u u m p u m p v a p o u r t h a t h a s by-passed t h e The benefits of using t h e GT c o m b i n a t i o n unit. t h a w i n g p r o d u c e . T h e c o n - series oil sealed rotary p i s t o n The f u n c t i o n of t h e w a t e r d e n s e d s t e a m w h i c h h a s yielded v a c u u m p u m p an d its s m a l l e r sealed liquid ring backing p u m p its l a t e n t h e a t falls back into liquid ring backing p u m p are: is purely to t r a n s f e r w a t e r vath e b o t t o m trough. The p u m p i n g speed (capa- p o u r f r o m t h e r o t a r y p i s t o n 2. The oil sealed p i s t o n va- city) is c o n s t a n t from initial p u m p oil reservoir a nd therec u u m p u m p is able to h a n d l e c h a m b e r e v a c u a t i o n to t h e vac- fore need only be a t hi r d t he t h e s a t u r a t e d s t e a m w i t h o u t u u m d u t y p o i n t a t w h i c h capacity of t h e latter. Non r e t u r n valve V2 will o p e n e m u l s i f i c a t i o n of th e lube oil s t e a m g e n e r a t i o n f a c i l i t a t e s to allow s u r p l u s d i s c h a r g e d air by m a i n t a i n i n g this oil at a p r o d u c t thawing. E q u i v a l e n t systems using a to a t m o s p h e r e d u r i n g t he c ha mt e m p e r a t u r e o f 70 to 75°C, whilst t h e s m a l l e r liquid ring w a t e r sealed liquid ring v a c u u m b er evacuation. As t he p r e s s u r e backing p u m p m a i n t a i n s a va- p u m p only, w o u l d r e q u i r e an falls this valve will eventually c u u m in th e p i s t o n p u m p oil air e j e c t o r u p s t r e a m to achieve close t h u s allowing t he liquid r e s e r v o ir of b e t w e e n 250 an d t h e v a c u u m l e v e l s r e q u i r e d ring backing p u m p to c r e a t e t he 300 m b a r absolute. w h i ch in fact is c o u n t e r p r o d u c - n e c e s s a r y v a c u u m in t h e oil With th e Piston P u m p lube tive, as t h e p u m p n o w h a s r eser v o i r t h u s p r e v e n t i n g w a t e r oil r e s e r v o i r at 7 0 / 7 5 ° C an d to be grossly oversized to cope v a p o u r c o n d e n s i n g in same. e x p o s e d t o t h i s v a c u u m o f with t h e a d d i t i o n a l a t m o s p h e r i c Graham Precision Pumps Ltd, 2 5 0 / 3 0 0 m b a r a b s o l u t e , t h e air in-bleed t h r o u g h t h e ejec- The Forge, Forge Lane, Conw a t e r v a p o u r ( s t e a m ) is super- t o r nozzle. gleton, Cheshire CW12 4HQ, The combined power require- UK. Tel: + 4 4 1260 274721; h e a t e d such t h a t any carry over from t h e c h a m b e r is p r e v e n t e d m e n t of t h e Rotary Piston Pump Fax: + 4 4 1260 276965.
I{
WORLD PUMPS FEBRUARY 1997
from c o n d e n s i n g in t h e lube oil an d is t r a n s f e r r e d over to t h e L i q u i d Ring P u m p w h e r e it h a r m l e s s l y c o n d e n s e s in t h e p u m p sealing liquid w h i ch is also water. To clarify t h e b e h a v i o u r of H20 su b j ect ed to a v acu u m :