MICROWAVE DRYING OF RESIN IMPREGNATED PAPER by SHUSUKE MINAMI B. Eng., Hiroshima U n i v e r s i t y , 1961 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department of CHEMICAL ENGINEERING We accept t h i s t h e s i s as conforming t o the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA February., 1970 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y , I f u r t h e r a g r e e t h a ^ p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Depar tment o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Depar tment o f The U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, Canada Date fif*/3, i ABSTRACT. A p i l o t s c a l e machine was designed and c o n s t r u c t e d to allow study of the continuous microwave d r y i n g at 2 .45 GHz of paper impregnated with water or with phenol formaldehyde r e s i n . T h i s equipment c o u l d d e l i v e r microwave power at l e v e l s up 2 . 9 0 KW. Resin impregnated paper d r i e d by microwaves showed b e t t e r r e s i n d i s t r i b u t i o n , a b r a s i o n r e s i s t a n c e , and i n t e r n a l bond s t r e n g t h when compared to s i m i l a r papers d r i e d i n a hot a i r n a t u r a l con-v e c t i o n oven. No s i g n i f i c a n t d i f f e r e n c e s i n t e n s i l e s t r e n g t h , s t r e t c h , Young's modulus, or bending s t r e n g t h were observed. A q u a n t i t a t i v e method f o r the d e t e r m i n a t i o n of r e s i n d i s -t r i b u t i o n was d e v i s e d . O v e r a l l e f f i c i e n c i e s f o r the microwave d r y i n g based on power input to the microwave power supply were of the order of 50 to 70%. i i TABLE OF CONTENTS Page ABSTRACT • i LIST OF TABLES. . v LIST OF FIGURES • ••• • v i l ACKNOWLEDGEMENTS '. l x I - INTRODUCTION. . ... 1 I I - REVIEW OF PREVIOUS WORK 4 1 . . D rying Mechanism ^ q 2 . B a s i c s of Microwave D r y i n g ? ~\ f. 3 . R e s i n D i s t r i b u t i p n Measurement I I I - APPARATUS 2 0 20 1 . Process 2 . Paper D r i v i n g System.... 2 0 3 . R e s i n Impregnator 4 . V e n t i l a t i o n System .... 2 6 5 . Surface Thermocouples 2 6 6 . Microwave Generator and Power Supply System 2 8 7 . Microwave A p p l i c a t o r . . . " . . . . . . . 3 0 8 . D i r e c t i o n a l Power Meter.. 3 1 9 . Water Load 3 1 1 0 . S h i e l d i n g and R a d i a t i o n Leakage 3 2 IV - EXPERIMENTAL.. ,. 3 4 1 . Base Paper and Resin 3 4 2 . Start-Up. and Shut-Down of the Microwave Power Supply System 3 4 3 . Procedure f o r Drying Experiments 3 5 i i i Page 4. T e n s i l e S trength Measurement.. 37 5. Paper Bending Test 39 6. I n t e r n a l Bond Test . .. 1 | 1 7. Surface Abrasion T e s t . . . . . . . . . ^3 8. Q u a n t i t a t i v e Resin D i s t r i b u t i o n Measurement ^ a) Pretreatment of Samples..... ^ b) Resin Content A n a l y s i s - S u l f u r i c A c i d Method . 1 + 8 c) Resin Content A n a l y s i s - H y d r o f l u o r i c A c i d Method . 51 V - RESULTS AND DISCUSSION 5^ 1. D r y i n g Experiments 5 4 a) Drying of Paper Wetted with Water 54 b) Drying o f Resin Impregnated Paper 6 l c) Convective D r y i n g E f f e c t 67 2. Product Q u a l i t y Tests '.. 67 - a) Tension Tests 67 b) I n t e r n a l Bond Test . 6 9 c) Surface Abrasion Test 72 d) Paper Bending Test 75 3. R e s i n D i s t r i b u t i o n . . 75 k. Product Appearance , 8 0 VI - CONCLUSIONS...: 8 5 VII - REFERENCES...'. -.- 8 6 V I I I - NOMENCLATURE 8 9 i v Page APPENDIX A Power Meter C a l i b r a t i o n . .. A - 1 APPENDIX B Rotameter C a l i b r a t i o n B - l APPENDIX C Thermocouple C a l i b r a t i o n C" 1 APPENDIX D O r i f i c e Meter D - 1 APPENDIX E Sample C a l c u l a t i o n f o r Heat Balance... E - l L I S T OF TABLES TABLE Page I S u l f u r i c a c i d T r e a t m e n t D a t a f o r Base P a p e r , P u r e R e s i n , and R e s i n I m p r e g n a t e d P a p e r ^ I I H y d r o f l u o r i c A c i d T r e a t m e n t D a t a f o r Base P a p e r , P u r e R e s i n , and R e s i n I m p r e g n a t e d P a p e r 5 2 I I I D r y i n g D a t a f o r Wet P a p e r 5 5 IV A p p l i c a t o r E f f i c i e n c y f o r Wet P a p e r D r y i n g 5 6 V D r y i n g D a t a f o r R e s i n I m p r e g n a t e d P a p e r 6 2 VI A p p l i c a t o r E f f i c i e n c y f o r R e s i n I m p r e g n a t e d P a p e r D r y i n g 6 3 V I I C o n v e c t i v e E f f e c t o f V e n t i l a t i o n A i r 6 8 V I I I T e n s i o n T e s t D a t a ( T e n s i l e B r e a k i n g S t r e n g t h ) 7 0 IX T e n s i o n T e s t D a t a ( S t r e t c h ) 7 0 X T e n s i o n T e s t D a t a (Young's M o d u l u s ) 7 1 XI I n t e r n a l Bond T e s t D a t a 7 3 X I I S u r f a c e A b r a s i o n T e s t D a t a 7 3 X I I I P a p e r B e n d i n g T e s t D a t a 7 6 XIV R e s i n C o n t e n t D i s t r i b u t i o n 7 7 XV R e s i n P i c k - u p o f M i c r o w a v e D r i e d P r o d u c t s 7 8 APPENDIX A - l a Power M e t e r C a l i b r a t i o n D a t a (Low Range) A - 8 A - l b Power M e t e r C a l i b r a t i o n D a t a ( H i g h Range) A - 9 A - 2 a S t a r t - u p Time f o r Microwave G e n e r a t o r ( V a r i a c S e t t i n g i n H i g h Range : 7 5 ) A - 1 0 A - 2 b S t a r t - u p Time f o r M i c r o w a v e G e n e r a t o r ( V a r i a c S e t t i n g i n H i g h Range : 1 3 0 ) A - 1 0 A - 2 c S t a r t - u p Time f o r M i c r o w a v e G e n e r a t o r ( V a r i a c S e t t i n g i n Low Range : 7 0 ) A - l l V I Page B - l Rotameter C a l i b r a t i o n Data B_2 C - l S u r f a c e Thermocouple C a l i b r a t i o n Data C-2 C-2 Thermocouple C a l i b r a t i o n Data C-2 v i i LIST OF FIGURES F i g u r e Page 1 Plane-wave T r a n s m i s s i o n i n t o L o s s y M a t e r i a l 12 2 Flow Sheet o f Apparatus 21 3 Assembly Drawing o f Apparatus 22 4 Photographs o f Apparatus 23&24 5 S u r f a c e Thermocouple 27 6 A s s e m b l i n g o f S u r f a c e Thermocouples 27 7 W i r i n g Diagram o f Power Supply System 29 8 Load - E l o n g a t i o n Curve . 38 9 Paper Bending T e s t e r ' 40 10 M e t a l B l o c k s f o r I n t e r n a l Bond Test 42 11 Aluminium D i s c f o r S e c t i o n i n g 45 12 E x p e r i m e n t a l Set-up o f S e c t i o n i n g 45 13 D r y i n g Curves f o r Base Paper 47 14 D r y i n g Curves f o r R e s i n 49 15 D r y i n g Curves f o r R e s i n Impregnated Paper 50 16 M o i s t u r e Content v e r s u s Power G e n e r a t i o n ( D r y i n g o f Water Wetted Paper) 58 17 R e l a t i v e M o i s t u r e Content v e r s u s Power G e n e r a t i o n ( D r y i n g o f Water Wetted Paper) 59 18 Absorbed Energy v e r s u s P o s i t i o n ( D r y i n g o f Water Wetted Paper) 60 19 R e l a t i v e M o i s t u r e Content v e r s u s Power G e n e r a t i o n ( D r y i n g o f R e s i n Impregnated Paper) 64 20 Absorbed Energy v e r s u s P o s i t i o n ( D r y i n g o f R e s i n Impregnated Paper) 65 21 S u r f a c e A b r a s i o n Rate v e r s u s A b r a s i o n C y c l e s 74 22 R e s i n Content D i s t r i b u t i o n 79 23 Photographs o f R e s i n Impregnated Papers 82 V I 1 1 APPENDIX . Page A - l Power G e n e r a t i o n v e r s u s Power M e t e r R e a d i n g k-2 Power G e n e r a t i o n v e r s u s S u p p l y C u r r e n t A - 3 Power G e n e r a t i o n v e r s u s V a r i a c S e t t i n g . A - 4 Power S u p p l y E f f i c i e n c y v e r s u s Power A _ g G e n e r a t i o n A -5 S t a r t - u p Time f o r M i c r o w a v e G e n e r a t o r A - 7 B - l R o t a m e t e r C a l i b r a t i o n C u r v e B _2 i x ACKNOWLEDGMENT I w i s h t o t h a n k Dr. R. B r a n i o n , u n d e r whose d i r e c t i o n t h i s s t u d y was c o n d u c t e d , f o r h i s g u i d a n c e and encoura g e m e n t t h r o u g h -out t h i s work. I a l s o w i s h t o t h a n k Dr. W.A.G. Vo s s ( D e p a r t m e n t o f E l e c t r i -c a l E n g i n e e r i n g , t h e U n i v e r s i t y o f A l b e r t a ) f o r h i s c o n s u l t a t i o n and g u i d a n c e i n t h e c o n s t r u c t i o n and o p e r a t i o n o f t h e a p p a r a t u s . S i n c e r e a p p r e c i a t i o n i s due t o R e i c h h o l d C h e m i c a l s (Canada) L i m i t e d , and Dr. R.C. V a s i s h t h , i t s R e s e a r c h D i r e c t o r , f o r t h e i r h e l p i n many p h a s e s o f t h i s work. P a r t i c u l a r l y , I w i s h t o t h a n k Mr. K. T a k a h a s h i , n o t o n l y f o r h i s t e c h n i c a l a d v i c e , b u t a l s o f o r h i s encoura g e m e n t i n p r i v a t e l i f e . T hanks a r e a l s o due t o t h e F a c u l t y o f F o r e s t r y o f t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , f o r use o f t h e i r f a c i l i t i e s , and t h e work shop o f t h e C h e m i c a l E n g i n e e r i n g Department f o r t h e i r c o n s t r u c t i o n o f t h e a p p a r a t u s . P a r t i c u l a r l y , I w i s h t o t h a n k Mr. E. Szabo who was i n c h a r g e o f t h e e l e c t r i c a l p a r t o f t h i s a p p a r a t u s . I am i n d e b t e d t o t h e N a t i o n a l R e s e a r c h C o u n c i l o f Canada and t h e C h e m i c a l E n g i n e e r i n g Department o f t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a f o r f i n a n c i a l s u p p o r t . 1 I - INTRODUCTION Recently the application of microwave power to I n d u s t r i a l heating and drying processes has become economically feasible i n certain industries and i s approaching economic f e a s i b i l i t y i n others. This r e s u l t s from the development of high e f f i c i e n c y and high power microwave generators of improved s t a b i l i t y . These generators are available at much lower unit costs re-l a t i v e to e a r l i e r designs. The advantages that microwave heating and drying have over conventional heating and drying arise from the fact that micro-waves penetrate i n s t a n t l y to a s i g n i f i c a n t depth i n the material being heated and generate heat i n t h i s material throughout the volume which has been penetrated. In conventional heating and drying methods heat i s transferred into the material being dried from the suface into the bulk of the material. Heat i s f i r s t transferred to the surface by conduction, convection or radiation. In such a process the highest temperatures are at the surface and a temperature gradient within the material i s unavoidable. The conduction process which transfers heat into the material i s r e l a t i v e l y slow. To speed up t h i s process more severe conditions may be applied to the surface, e.g. increased a i r temperatures i n hot a i r drying, increased platen temperatures i n conduction heating, or increased radiation in t e n s i t y i n radiant heating. These more severe conditions may damage the surface and cause product defects such as surface cracks. In microwave heating the heat i s generated i n t e r n a l l y , thus the surface conditions are no more severe than those i n -side the bulk of the material. In fact the surface temperature 2 i s u s u a l l y the lowest. Depending on the a b s o r p t i v e c h a r a c t e r -i s t i c s of the m a t e r i a l being heated a l e s s steep temperature grad i e n t may be e s t a b l i s h e d . Another f e a t u r e of microwave h e a t i n g which i s p a r t i c u l a r l y important i n d r y i n g i s s e l e c t i v e h e a t i n g of water. Water mole-c u l e s because of t h e i r h i g h l y p o l a r s t r u c t u r e are able to s t r o n g l y absorb microwave energy. Thus i n the d r y i n g of paper, water' absorbs microwave energy and i s heated but c e l l u l o s e i s more or l e s s t r a n s p a r e n t to microwaves and thus does not absorb much energy from them. In an i n d u s t r i a l l a m i n a t i n g o p e r a t i o n such as plywood manufacture the glue l a y e r s c o u l d be heated up w i t h -out having to heat up the bulk of the wood because the wood can transmit. much of the microwave r a d i a t i o n . T h i s s e l e c t i v e h e a t i n g e f f e c t a l s o c o n t r i b u t e s to a s o r t of s e l f r e g u l a t i o n of h e a t i n g which i s e s p e c i a l l y important i n a c h i e v i n g a uniform and l e v e l moisture p r o f i l e . Thus micro-waves act upon the wet areas and ignore the dry areas. T h i s c o u l d be of great s i g n i f i c a n c e i n paper manufacture where the l e v e l moisture p r o f i l e s across paper machines, which are necessary to give uniform r e e l s of paper, are achieved by over-d r y i n g most of the sheet to remove the wettest s t r e a k s . T h i s study i s concerned with u s i n g microwave energy i n an attempt to improve the p r o p e r t i e s of p h e n o l i c r e s i n impregnated paper by microwave d r y i n g . At present t h i s m a t e r i a l i s d r i e d i n a c onventionalyhot gas,forced c o n v e c t i o n oven. Convention-, a l l y d r i e d r e s i n impregnated paper has a tendency to be r a t h e r b r i t t l e . When these papers are used as;,overlays f o r plywood, p a r t i c l e board e t c . e x c e s s i v e f l e x i n g of the underlay m a t e r i a l may cause cracks i n the o v e r l a y . T h i s has been a t t r i b u t e d to an uneven r e s i n d i s t r i b u t i o n which i s b e l i e v e d to be caused by r e s i n m i g r a t i o n d u r i n g d r y i n g i n the f o r c e d c o n v e c t i o n d r y i n g process. Heat i s applied, to the s u r f a c e causing the water suspending the r e s i n emulsion to evaporate. . To leave the sheet t h i s water migrates to the s u r f a c e and c a r r i e s with i t r e s i n molecules which polymerize f a s t e r at the s u r f a c e than i n the i n t e r i o r due to the higher temperature. T h i s h i g h l y polymerized r e s i n cannot d i f f u s e back i n t o the sheet and hence the i n t e r i o r of the sheet tends t o have a lower r e s i n r content than the s u r f a c e . In microwave d r i e d paper the h o t t e s t l o c a t i o n i s at the centre o f the sheet and thus p o l y m e r i z a t i o n would be most r a p i d t h e r e . T h i s would counteract the tendency to move toward the s u r f a c e with the e v a p o r a t i n g water because the r e s i n molecules would, on a t t a i n i n g a c e r t a i n degree of p o l y m e r i z a t i o n , drop out of suspension. T h i s a n a l y s i s would seem to be v a l i d d u r i n g the constant r a t e p e r i o d of d r y i n g and the f i r s t f a l l i n g r a t e p e r i o d . There i s a l s o a certain advantage i n microwave d r y i n g d u r i n g the f a l l i n g r a t e p e r i o d s i n that the c e l l u l o s e does not have to be heated up i n order to evaporate the water because the heat i s s e l e c t i v e l y generated i n the water. In t h i s study phenol-formaldehyde impregnated paper i s d r i e d u s i n g a 2.5 kw meanderline, microwave d r i e r under v a r i o u s c o n d i t i o n s . The q u a l i t y of t h i s product i s compared with the q u a l i t y of f o r c e d c o n v e c t i o n d r i e d papers produced commercially and i n the l a b o r a t o r y . Some u s e f u l data f o r the microwave d r y i n g process i s a l s o obtained. 4 I I - REVIEW OF PREVIOUS. WORK . 1. D r y i n g Mechanism ( 1 2 ) E a r l y w o r k e r s 5 i n t h e f i e l d o f d r y i n g d i v i d e d t h e d r y i n g p r o c e s s i n t o two s t a g e s , t h e c o n s t a n t r a t e s t a g e , w h e r e i n t h e r a t e o f e v a p o r a t i o n i s c o n s t a n t , and t h e f a l l i n g r a t e s t a g e i n w h i c h t h e r a t e o f e v a p o r a t i o n d e c r e a s e s w i t h d e c r e a s i n g m o i s t u r e c o n t e n t . The c o n s t a n t r a t e p e r i o d was, and i s s t i l l , b e l i e v e d t o be e v a p o r a t i o n f r o m a c o n t i n u o u s , u n b r o k e n f i l m o f w a t e r on t h e s u r f a c e o f t h e m a t e r i a l b e i n g d r i e d . When s u f f i c i e n t w a t e r has been e v a p o r a t e d d r y s o l i d b r e a k s t h r o u g h t h i s s u r f a c e f i l m ; t h e r a t e o f d r y i n g d e c r e a s e s ; t h i s i s t h e f a l l -i n g r a t e p e r i o d . . I n t h i s e a r l y work i t was p r o p o s e d t h a t w a t e r moves by d i f f u s i o n f r o m t h e i n t e r i o r o f t h e s o l i d t o t h e s u r f a c e and t h a t as more and more w a t e r i s e v a p o r a t e d t h i s d i f f u s i o n e n c o u n t e r s more and more r e s i s t a n c e . • (3) I n 1937 C e a g l s k e and Hougen v ' f o u n d t h a t t h e m o i s t u r e p r o f i l e w h i c h t h e y measured d i d n o t f i t t h e p r o f i l e t h a t t h e y c a l c u l a t e d on t h e b a s i s o f a d i f f u s i o n mechanism when d r y i n g beds o f s a n d . They e x p l a i n e d t h e s e r e s u l t s by i n t r o d u c i n g a c a p i l l a r y f l o w mechanism as o p p o s e d t o a d i f f u s i o n mechanism f o r t h e movement o f w a t e r . Thus w a t e r was assumed t o move f r o m t h e i n t e r i o r o f t h e s o l i d t o t h e s u r f a c e u n d e r t h e i n f l u e n c e o f s u r f a c e t e n s i o n f o r c e s i n the c a p i l l a r i e s . (4) C o r b e n and N e w i t t p r o p o s e d i n 1955 a t h e o r y o f d r y i n g b a s e d on a s e r i e s o f s t u d i e s on p o r o u s and n o n - p o r o u s m a t e r i a l s . U s i n g t h e c a p i l l a r y t h e o r y , mechanisms were p u t f o r w a r d f o r t h e c o n s t a n t r a t e p e r i o d and t h e f i r s t and s e c o n d f a l l i n g r a t e p e r i o d s . D u r i n g t h e c o n s t a n t r a t e p e r i o d s u r f a c e w a t e r i s e v a p o r a t e d ; 5 t h i s i s t h e f i r s t w a t e r t o be removed i n most d r y i n g p r o c e s s e s . F u r t h e r d r y i n g e x p o s e s t h e p o r e s i n t h e m a t e r i a l . T hese p o r e s l e a d i n t o t h e i n t e r i o r o f t h e s o l i d . At t h e i r mouths p e n d u l a r r i n g s o f w a t e r a r e p r e s e n t . When a l l t h e s e e x t e r n a l p o r e s a r e e x p o s e d and o n l y p e n d u l a r w a t e r r i n g s r e m a i n on t h e s u r f a c e t h e r i n g s s t a r t t o c o n t r a c t c a u s i n g more o f t h e p o r e s t o be opened. As t h e p e n d u l a r r i n g s c o n t r a c t i n c r e a s i n g l y n a r r o w p o r e s a r e e x p o s e d l e a d i n g t o g r e a t e r c a p i l l a r y s u c t i o n s . E v e n - " t u a l l y a s t a g e w i l l be r e a c h e d when t h e p e n d u l a r r i n g s a r e i n -c a p a b l e o f t r a n s f e r r i n g s u f f i c i e n t w a t e r t o t h e s u r f a c e f r o m t h e i n t e r i o r t o r e p l a c e t h a t w h i c h has been e v a p o r a t e d . Here t h e c o n s t a n t r a t e p e r i o d ends and t h e f a l l i n g r a t e p e r i o d b e g i n s . When w a t e r c a n no l o n g e r be removed by t h e m e n i s c u s r e c e d i n g i n t o s m a l l e r p o r e s f u r t h e r e v a p o r a t i o n o c c u r s by d i f f u s i o n o f w a t e r out o f t h e s o l i d . T h i s i s t h e s e c o n d f a l l -i n g r a t e p e r i o d . B o t h c a p i l l a r y and d i f f u s i o n mechanisms may o c c u r s i m u l t a n e o u s l y i n some m a t e r i a l s . The k i n d o f m a t e r i a l d e t e r m i n e s w h e t h e r c a p i l l a r y e f f e c t s o r d i f f u s i o n c o n t r o l t h e r a t e o f m o i s t u r e e v a p o r a t i o n . I n p o r o u s m a t e r i a l s c a p i l l a r y s u c t i o n i s most i m p o r t a n t ( e . g . beds o f s a n d ) , whereas i n n o n - p o r o u s m a t e r i a l s ( e . g . g e l a t i n e and o t h e r f o o d s ) d i f f u s i o n c o n t r o l s . I n o t h e r s i t u a t i o n s t h e d r y i n g e quipment has an i n f l u e n c e on t h e mechanism by w h i c h w a t e r i s moved f r o m t h e i n t e r i o r o f t h e s o l i d t o t h e s u r f a c e . I n t h e c o n v e n t i o n a l p a p e r d r y i n g p r o c e s s t h e wet s h e e t i s p r e s s e d a g a i n s t steam h e a t e d c y l i n d e r s . D r e s h f i e l d and H a n w / have r e p o r t e d an e v a p o r a t i o n - c o n d e n s a t i o n mechanism f o r t h i s k i n d o f d r y i n g . I n t h i s mechanism w a t e r i s b e l i e v e d t o e v a p o r a t e a t 6* o r n e a r t h e s u r f a c e where t h e h e a t i s b e i n g s u p p l i e d ; t h a t i s a t t h e s h e e t c y l i n d e r i n t e r f a c e . However, t h i s w a t e r c a n n o t e s c a p e t h r o u g h t h i s s u r f a c e w h i c h i s e f f e c t i v e l y s e a l e d by t h e m e t a l c y l i n d e r . The w a t e r v a p o u r t h e n moves t o t h e o p p o s i t e , c o o l e r s i d e o f t h e s h e e t where i t c o n d e n s e s . The e n e r g y r e -l e a s e d i n c o n d e n s a t i o n t h e n c o n t r i b u t e s t o t h e e n e r g y r e q u i r e d t o v a p o u r i z e w a t e r a t t h e s u r f a c e away f r o m t h e c y l i n d e r . The w a t e r i s s u p p o s e d t o m i g r a t e e i t h e r by d i f f u s i o n o r c a p i l l a r i t y . T h i s e v a p o r a t i o n - c o n d e n s a t i o n mechanism i s most p r o b a b l e when t h e s y s t e m i s s u b j e c t t o l a r g e t e m p e r a t u r e g r a d i e n t s s u c h a s . o c c u r i n d r y i n g by c o n t a c t w i t h a h o t s u r f a c e . A p p l y i n g * (6) t h i s mechanism Harmathy t h e o r e t i c a l l y s i m u l a t e d v a r i o u s d r y i n g p r o c e s s e s and showed t h a t t h e e v a p o r a t i o n - c o n d e n s a t i o n mechanism was t h e g o v e r n i n g mechanism o f d r y i n g d u r i n g t h e f a l l i n g r a t e p e r i o d . (6) Harmathy's p a p e r i s one o f a number o f p a p e r s w h i c h have a p p e a r e d r e c e n t l y and w h i c h a r e m a i n l y c o n c e r n e d w i t h computer (7 V s i m u l a t i o n o f d r y i n g p r o c e s s e s . Kauh has u s e d a n u m e r i c a l s o l u t i o n o f t h e d i f f u s i o n e q u a t i o n i n an a t t e m p t t o p r e d i c t a d r y i n g c u r v e u s i n g a d i f f u s i o n m o i s t u r e movement mechanism. A l t h o u g h a s u c c e s s f u l p r e d i c t i o n was c l a i m e d and good agreement between e x p e r i m e n t a l and c a l c u l a t e d r e s u l t s r e p o r t e d , t h e a p p l i -c a b i l i t y o f . t h i s k i n d o f s o l u t i o n w i l l be l i m i t e d s i n c e t h e d i f f u s i o n mechanism i s n o t a l w a y s t h e g o v e r n i n g one. F o r h o t s u r f a c e d r y i n g , s u c h as i s u s e d i n t h e s t e a m c y l i n d e r d r y i n g o f p a p e r , N i s s a n e t a l i ^ ' ^ ' ' ^ have n u m e r i c -a l l y s o l v e d t h e F o u r i e r h e a t c o n d u c t i o n e q u a t i o n t o g e t t h e t e m p e r a t u r e p r o f i l e i n p a p e r and i t s d r y i n g r a t e c u r v e . They assumed c o n d u c t i v e h e a t t r a n s f e r t h r o u g h t h e s h e e t and e v a p o r a t i o n 7 from the s i d e of the paper o p p o s i t e the c y l i n d e r - The tem-pe r a t u r e p r o f i l e was c a l c u l a t e d assuming a u n i f o r m m o i s t u r e content p r o f i l e . In Nissan's work the o p e r a t i o n of the d r y e r was d i v i d e d i n t o f o u r phases; 1) where the paper sheet f i r s t c o n t a c t s the c y l i n d e r ; 2) where the paper i s c o n t a c t i n g the c y l i n d e r and i s covered by the f e l t ; 3) where the sheet i s a g a i n exposed on one s i d e and 4) where the paper sheet i s between c y l i n d e r s . The f o l l o w i n g e q u a t i o n was s o l v e d 3 2T 1 3T 3x z a 30 D i f f e r e n t boundary c o n d i t i o n s a p p r o p r i a t e to t h e . v a r i o u s r e g i o n s were used. These were I n i t i a l c o n d i t i o n T = f ( x ) f o r 0 = 0 Phase 1 and 3 I *1) =;,_ HiX ( T _ T j V 3r ) r = 0 k \ 1 c xr=o' /3T \ = _ H2X ( - T ) - 4 - 6 5 H 2 X ( Y l - y )T, V 3 r / _ k 1 r=i a ; k K y 1 y a ; i b r= 1 Phase 2 /3T\ = _ H i X ( _ v V3r ) k v c 1 r = o J \ ' r = 0 dvJ k ^ r = i f' k v y i y f ; b r= 1 8 Phase 4 (f) HiX k (T - T ) a r = o H'.65HiX k r=o H 2X (T - T ) r=i a 4.65H 2X k k Comparing t h e i r n u m e r i c a l s o l u t i o n s w i t h e x p e r i m e n t a l measurements they concluded t h a t heat was indeed t r a n s f e r r e d through the sheet by c o n d u c t i o n alone i f the c y l i n d e r temperature was below the b o i l i n g p o i n t of water. They noted t h a t c o n v e c t i v e heat t r a n s f e r became of i n c r e a s i n g importance as the temperature r o s e . T h i s suggested the presence of an evaporation-conden-s a t i o n mechanism^''"^. (12) Snowv improved upon t h i s k i n d of a n a l y s i s by n u m e r i c a l l y solving the heat and mass t r a n s f e r equations s i m u l t a n e o u s l y . In h i s work he added a term to the heat c o n d u c t i o n e q u a t i o n to a l l o w f o r the e v a p o r a t i o n - c o n d e n s a t i o n mechanism. He s o l v e d The f i r s t term on the r i g h t hand s i d e r e p r e s e n t s conductive heat t r a n s f e r and the second r e p r e s e n t s e v a p o r a t i o n - c o n d e n s a t i o n heat t r a n s f e r . The a p p r o p r i a t e mass t r a n s f e r e q u a t i o n used was In t h i s e q u a t i o n the f i r s t term on the r i g h t hand s i d e r e -p r e s e n t s the r a t e of flow of l i q u i d water by c a p i l l a r y a c t i o n . Ps(M) i s the c a p i l l a r y s u c t i o n e x e r t e d on l i q u i d water by the 9 capi l laries in the paper having moisture content M. kq(M) represents the conductance of the paper for l iquid water. This term was determined empirically. The second -te'ra on the right hand side represents the rate of flow of water vapour which contributes to the evaporation-condensation heat and mass transfer. K r is calculated from the theory of molecular diffusion of water in a i r . Although the solutions of these equations rely on empirically determined coefficients which no doubt vary from material to material, Snows* analysis seems to give good results and his method should be tested on a wider range of materials. 2. Basics of Microwave Drying There have not been many papers published on the subject of microwave drying and even fewer on the microwave drying of paper. Most of the latter are concerned with the economic feas ib i l i ty of introducing microwave drying into papermaking. A number of papers have appeared which are concerned with the experimental determination of the die lectr ic properties of the material to be dried. Because of the.internal heat generation in the material being dried by microwave techniques the drying mechanism may be different than that found in conventional drying. However, as far as is known no research has been done on the mechanism . of moisture removal in microwave drying. (13) Goerz and Jol ly have done an economic feas ib i l i ty analy-sis on the use of a meanderline waveguide drier for instal lat ion on a conventional paper machine. They predicted significant (14)" savings but this conclusion has been cr i t i c i zed by Gardner 10 who q u e s t i o n s t h e c o s t f i g u r e s t h e y a s s i g n e d t o c o n v e n t i o n a l d r y i n g . T h e a d v a n t a g e s c i t e d b y G o e r z a n d J o l l y i n c l u d e a m o r e u n i f o r m m o i s t u r e p r o f i l e , a h i g h e r o v e r a l l m o i s t u r e c o n t e n t , a n d a s u b s t a n t i a l l y r e d u c e d d r i e r l e n g t h . D a m s k e y , H a n k i n a n d S t e p h a n s e n v J ' h a v e p r e s e n t e d a n o t h e r e c o n o m i c a n a l y s i s o f m i c r o w a v e a p p l i c a t i o n t o c o n v e n t i o n a l p a p e r -m a k i n g b y u s i n g c o m p u t e r s i m u l a t i o n t e c h n i q u e s . I n t h e i r w o r k t h e y c o m p u t e d t h e r e l a t i v e p r o f i t a b i l i t y o f u s i n g m i c r o w a v e e q u i p m e n t o v e r c o n v e n t i o n a l e q u i p m e n t i n p a p e r m a k i n g a n d p a p e r c o a t i n g . T h e f o l l o w i n g a s s u m p t i o n s w e r e m a d e : - 1 ) m i c r o w a v e d r y i n g p r o d u c e s a l e v e l m o i s t u r e p r o f i l e w i t h a h i g h e r a v e r a g e m o i s t u r e c o n t e n t ; 2 ) t h e i n c r e a s e d d r y i n g c a p a c i t y p r o v i d e d b y m i c r o w a v e m e t h o d s p e r m i t s h i g h e r p a p e r m a c h i n e o r c o a t i n g m a c h i n e s p e e d s . T h e i r e c o n o m i c m o d e l i n d i c a t e s a b e t t e r r e t u r n o n i n v e s t e d c a p i t a l f o r m i c r o w a v e d r y i n g o v e r c o n v e n t i o n a l d r y -i n g . M o r e e x p e r i m e n t a l d a t a i s n e c e s s a r y i n a n a c c e s s i b l e f o r m b e f o r e o n e c o u l d c o m p e t e n t l y d e s i g n o r s e l e c t a m i c r o w a v e d r i e r f o r p a p e r m a n u f a c t u r e . ~ M i c r o w a v e d r i e r s o r h e a t e r s e m p l o y h i g h f r e q u e n c y e n e r g y i n t h e r a n g e 3 0 0 MHz t o 30GHz ( 3 0 0 x 1 0 6 c y c l e s / s e c . t o 30 x 1 0 ^ c y c l e s / s e c ) . I n o r d e r t o p r e v e n t i n t e r f e r e n c e w i t h m i c r o w a v e c o m m u n i c a t i o n s s y s t e m s t h e f o l l o w i n g f r e q u e n c i e s h a v e b e e n a s s i g n e d : f o r i n d u s t r i a l , m e d i c a l , a n d s c i e n t i f i c u s e . F r e q u e n c y Wave L e n g t h MHz i n c h e s 8 9 0 - 9^0 . 1 3 . 0 2 4 0 0 - 2500 4.9 5 7 2 5 - 5 8 7 5 •: 2.0 2 2 , 0 0 0 - 2 2 , 2 5 0 0.24 I I The choice of frequency depends on s e v e r a l f a c t o r s . I n -d u s t r i a l equipment f o r d r y i n g i s only a v a i l a b l e f o r 915 MHz and 2450 MHz. High f r e q u e n c i e s promote hig h e r power d i s s i p a t i o n but the depth of p e n e t r a t i o n i n t o the m a t e r i a l i s g r e a t e r f o r low f r e q u e n c i e s . In the present work a 2450 MHz generator was used. At microwave frequencies, e l e c t r o m a g n e t i c energy i s ab-sorbed by means of a r e l a x a t i o n phenomenon or d i e l e c t r i c a f t e r e f f e c t . T h i s i s caused by the motion of the d i e l e c t r i c mole-cul e s i n response to an a p p l i e d a l t e r n a t i n g f i e l d . The motion c o n s i s t s of a d i s t o r t i o n of the molecular s t r u c t u r e . Thus the bond angles and i n t e r a t o m i c d i s t a n c e s i n the molecule are d i s -t o r t e d from t h e i r e q u i l i b r i u m p o s i t i o n by the f i e l d . The p o l a r molecules a l s o t r y to a l i g n themselves wi t h the f i e l d . But as the f i e l d d i r e c t i o n i s c o n t i n u a l l y changing the molecules are c o n t i n u a l l y d i s t o r t i n g and r e a l i g n i n g r e s u l t i n g i n energy d i s s i p a t i o n and p r o d u c t i o n of heat. When a microwave i s t r a n s m i t t e d i n t o a d i e l e c t r i c m a t e r i a l the i n c i d e n t power d e n s i t y (Pj_) c a r r i e d by the wave i s r e l a t e d to the e l e c t r i c f i e l d d e n s i t y by P i = — — 2 V where n 0 i s the i n t r i n s i c impedance of f r e e space. At the s u r f a c e . o f a d i e l e c t r i c m a t e r i a l i n a microwave f i e l d some of the i n c i d e n t energy i s r e f l e c t e d back towards the source and the remainder (P^.) Is t r a n s m i t t e d i n t o the m a t e r i a l . A t t e n u a t i o n theory, d e s c r i b e s how the e l e c t r i c f i e l d d e n s i t y i s attenuated i n the d i e l e c t r i c m a t e r i a l . Prom t h i s theory i t can be shown t h a t the power c a r r i e d by the microwaves i s decreased 12 Figure 1. Plane-wave Transmission into Lossy Material 1 3 to — of i t s surface, value i n a distance d where e v d = 1_ 2a = 1.5x10 10 (Trf/Ptana) -1 (cm ) a = attenuation constant of the material e'= d i e l e c t r i c constant f = frequency tan 6 = loss factor e = e' - j e " = e'(1 - j t a n S ) e = complex p e r m i t t i v i t y e"= d i e l e c t r i c loss factor The equation-sdes:cribing the amounts of power absorbed, re-f l e c t e d and transmitted for lossy d i e l e c t r i c s are generally com-plex and d i f f i c u l t to apply because the c h a r a c t e r i s t i c constants e' and tan 6 are temperature dependent. For materials which are th i n enough that the e l e c t r i c f i e l d density (Et) can be assumed to be constant i n them the absorbed power i s obtained from In order to evaluate the power dissipated i n microwave heat-ing or drying processes the d i e l e c t r i c constants' and the loss factor tan6 of the p a r t i c u l a r material at the p a r t i c u l a r frequency being used must be known. These values as well as being temperature dependent are also composition dependent. In P = 5 5 . 6 xlO _ l i |E. 2fe'tan<5 (watts/cm ) 14 d r y i n g one- o f t h e components i s w a t e r w h i c h has a r e l a t i v e l y l a r g e l o s s f a c t o r , t h u s the e' and t a n 6 f a c t o r s o f the wet m a t e r i a l depend on t h e m o i s t u r e c o n t e n t . Some e m p i r i c a l r e l a t i o n s f o r t h e s e p a r a m e t e r s have,been (16) r e p o r t e d . Voss a f t e r p r o c e s s i n g t h e e x p e r i m e n t a l d a t a o f s e v e r a l w o r k e r s has s u g g e s t e d t h e f o l l o w i n g e q u a t i o n s r e l a t i n g t h e d i e l e c t r i c c o n s t a n t and t h e l o s s f a c t o r f o r w a t e r t o tem-p e r a t u r e and f r e q u e n c y TtanS = 1 . 8 2 x l 0 " 9 f - 1.2 w £^ = 55 ± 10 % a t 9 - 10 GHz £ ' = 8 7 - 0.36T a t 2 - 3 GHz (T=temperature °K) (17) L e w i n has p r e s e n t e d t h e f o l l o w i n g e q u a t i o n t o d e s c r i b e t h e d i e l e c t r i c b e h a v i o u r o f a compound m a t e r i a l . T h i s e q u a t i o n r e s t s on a s e m i - t h e o r e t i c a l b a s i s e = e' - je" = ei-[ 1 + ?L £2 + 2 e i _ p £2 - e i £ i = complex p e r m i t t i v i t y o f component 1 ( d r y s o l i d ) £2 = complex p e r m i t t i v i t y o f component 2 ( w a t e r ) p = _-w P l P2 P i w = d e n s i t y o f component 2 = d e n s i t y o f component 1 = mass r a t i o o f component 2 t o component 1 15 S u b s t i t u t i n g G i = e i - J e " and , r e a r r a n g i n g and c o l l e c t i n g r e a l and I m a g i n a r y p a r t s g i v e s t h e d i e l e c t r i c c o n s t a n t e 1 and the l o s s f a c t o r e" o f the wet m a t e r i a l as e » = (1-F)(1+2F)( e ^ 2 + £ ^ 2 ) + ( 4 + F + 4 F 2 ) e k i + 2 ( l - F ) ( 2 + F ) £ l 2 {eHl-F)+e 1(2+F)} i^-(F-l)2 e»2 „ = 9Fe 2e' 2' { e ^ ( l - F ) + £ l ( 2 + F ) } ^ _ ( P _ i ) ^ e ^ 2 e"= The a p p l i c a t i o n o f Lewin's e q u a t i o n s t o m i x t u r e s has not been (l8) c o m p l e t e l y s u c c e s s f u l . I n Lewin's a n a l y s i s i t was assumed t h a t the two components were s i m p l y mixed w i t h o u t i n t e r a c t i o n . But i n many m a t e r i a l s such as c e l l u l o s e , w ater m o l e c u l e s are a c t u a l l y bonded t o t h e s o l i d s by f o r example, hydrogen bonds. These b i n d i n g f o r c e s a f f e c t the d i e l e c t r i c l o s s b e h a v i o u r . (19) Asami has d e v e l o p e d an e m p i r i c a l e x p r e s s i o n f o r the d i e l e c t r i c p e r m i t t i v i t y o f m i x t u r e s when bondi n g a f f e c t s a r e pre-s e n t . I n h i s e q u a t i o n s an e m p i r i c a l c o n s t a n t n i s i n t r o d u c e d which r e p r e s e n t s t h e m i x i n g c o n d i t i o n . H i s e q u a t i o n i s e 16 Voss tasted this equation with some experimental data obtained for wet wood and found good agreement. Although only certain frequencies are allowed for industrial microwave use by law these may not necessarily be the optimum frequencies for a particular drying or heating process since the die lectr ic behavour of materials is frequency dependent. De Loor^2(^V studied frequency effects on the die lectr ic behaviours of heterogeneous systems containing water and related the mechanism of microwave absorption to frequency. It is only recently that experimental data for use in designing pract ical microwave drying and heating processes have become available. For the microwave drying of wood Voss ; measured the die lectr ic constant and loss factor at 9-21 GHz. (21) Similar work at 2.45 GHz was done by Tinga . In the latter work the die lectr ic constants of several kinds of wood were measured as functions of temperature at various moisture contents. (22) Leidigh, Stephansen, and Stolte v A investigated the microwave absorption properties of paper at 2.45 GHz. They presented values of the die lectr ic constant and loss factor as functions of temperature and moisture content. More data is necessary before confident design or assessment of large scale industrial systems is feasible for the non equipment manufacturer. 3. Resin Distribution Measurement It has been postulated that non uniform resin distribution is a contributing factor to some of the defects found in resin im-pregnated papers. : Thus some method of observing or, preferably, • measuring the uniformity of resin distribution is necessary to confirm the postulate. 17 In order to study the resin distribution through the thick-ness of the sheet i t Is necessary to section the sheet somehow. After sectioning the resin distribution may be considered by (24 V one of four methods . . 1) microscopy 2) extraction and analysis 3) auto radiographic analysis 4 ) direct chemical analysis There are several possible ways of sectioning a sheet of paper into layers. These include using a microtome, scotch tape, a sheet sp l i t t er , sandpaper, or a lathe. " The microtome gives too l i t t l e sample; scotch tape w i l l not work on resin im-pregnated paper,neither w i l l the Beloit sheet sp l i t t er ; sand-paper contains phenolic resin which might affect subsequent analysis so we chose to use a lathe. So far the microscopic method for observing resin d i s t r i -(25) bution has not been made quantitative. Crosby and Marton ' have studied the mechanism of resin penetration into laminating papers. They dyed phenolic resins prior to impregnation and then observed the resin distribution after drying the sheet,under a light microscope;embedding i t in a polyamide mounting medium and sectioning by microtome. Dyes should be chosen so that they exert minimal effects on the properties or behaviour of the res in. (23) Takahashi, Vasishth, and Cote v J / have developed a method for ob-serving the resin distribution in a sheet of resin impregnated paper. Their technique involves soaking the dried and cured paper in hydrofluoric acid which dissolves a l l the cellulose leaving 18 behind the r e s i n s k e l e t o n . I t a l s o would leave behind l i g n i n but as the base papers were made from bleached k r a f t pulp the amount of l i g n i n would be s m a l l . T h i s r e s i n s k e l e t o n was then c a r e f u l l y washed, embedded i n a mounting medium and s e c t i o n e d on a microtome. Microphotographs showed the r e s i n d i s t r i b u t i o n and a more uniform d i s t r i b u t i o n was observed with microwave d r i e d papers. E x t r a c t i o n of the r e s i n f o l l o w e d by chemical or p h y s i c a l a n a l y s i s of the r e s i d u e or of the e x t r a c t has been used as a method f o r d e t e r m i n i n g the t o t a l r e s i n content of paper s h e e t s . These c o u l d be adapted to the d e t e r m i n a t i o n of a' r e s i n d i s t r i -b u t i o n i n a sheet a f t e r i t has.been s e c t i o n e d but does not seem t o have been so a p p l i e d p r e v i o u s l y . For p h e n o l i c r e s i n s a v a r i e t y o f s o l v e n t s have been proposed-cyclohexane, n - b u t a n o l , (26) dimethyl-formamide, acetone, or molten naphthol . The samples are weighed be f o r e and a f t e r e x t r a c t i o n and the r e s i n content determined by d i f f e r e n c e g r a v i m e t r i c a l l y . C o l o r i m e t r i c a n a l y s i s of the e x t r a c t c o u l d a l s o be u s e f u l . However, one i s not c e r t a i n of the s o l u b i l i t y of the r e s i n s a f t e r a v a r i e t y of c u r i n g p r o c e s s e s . Another s o r t of e x t r a c t i o n process i s d i s s o l u t i o n of the c e l l u l o s e a f t e r h y d r o l y s i s w i t h a c i d , f i l t e r i n g and weighing the (27) r e s i d u e . S e i f e r t used t h i s approach, m o d i f y i n g the Klason ( 2 8 ) l i g n i n d e t e r m i n a t i o n method '. In h i s method the c e l l u l o s e was d i s s o l v e d i n s u l f u r i c a c i d , and the l i g n i n removed with sodium c h l o r i t e . The r e s i n i s the r e s i d u e which was weighed to g i v e the r e s i n content. T h i s method was confirmed as being reasonably a c c u r a t e i n the present study. 19 Hydrolysis of c e l l u l o s e i n s u l f u r i c acid i s rather slow, the whole' analysis required about two days. E t t l i n g and (29) Adams reported that t h i s kind of analysis could be speeded up using chlorosulfohic acid instead of s u l f u r i c acid. They reported successful r e s u l t s i n measuring the r e s i n content of p a r t i c l e board. However, Berkeley^ 0^ t r i e d this.method and found i t impossible to use for r e s i n impregnated papers as he could not f i l t e r , or centrifuge o f f the residue. In the present work chlorosulfonic acid was t r i e d and abandoned because of i t s violent reaction with the r e s i n . In the present work acid hydrolysis of c e l l u l o s e was brought about, using hydrofluoric acid. In the auto radiographic method radioactive labels are i n -troduced into the r e s i n before impregnation. After drying and curing the sheet i s sectioned and the r e s i n content determined by a Geiger counter or by auto radiography. The method requires some elaborate equipment. The direct chemical method depends on the chemical analysis of a p a r t i c u l a r chemical component of the r e s i n . For example Kjeldahl analysis to get the nitrogen content allows c a l c u l a t i o n of the urea formaldehyde ormelamine formaldehyde r e s i n content. However, as phenolic resins contain only carbon, hydrogen, and oxygen which are pr e c i s e l y the components of c e l l u l o s e t h i s method cannot be used for determining the d i s t r i b u t i o n of t h i s r e s i n . 20 III - APPARATUS For this work a 2-. 5 kw microwave drier-res in impregnator was constructed. A schematic diagram of the equipment is pre-sented in figure 2; an assembly drawing is presented in figure 3 . Figures 4 a to 4 d are photographs of the equipment. 1 . Process Figure 2 provides a flow sheet or outline of the process. Base paper is f i r s t dipped into the resin solution and then drawn through the squeeze ro l lers into the microwave applicator. The paper passes through slots in the waveguide wall into the interior of the waveguide where the microwave energy is absorbed. It then passes out of the f i r s t waveguide and into the second one etc. After the f ina l waveguide the paper passes through the drive ro l l s and either is ripped ..off or is wound on a winder. The waveguides are ventilated to fac i l i ta te the removal of water. The microwave system consists of a microwave generator (magnetron), a meander line (series of U bends) waveguide, a power meter and a water load. The antenna of the magnetron is coupled to the waveguide at the dry paper end of the machine. The water load is coupled to the wet end. Thus the microwaves propagate from the dry end to the wet end. However, the micro-wave-paper flow is not truly counter current but is in a sort of counter current-cross flow combination. 2. Paper Driving System As shown in the assembly drawing (figure. 3 ) the paper driving system consists of a 1 / 4 HP electric motor driving a paper driving ro l l er through a reduction gear and a chain drive. Guide rol lers VENT SYMBOL Figure 2. Flow Sheet of Apparatus AIR DUCT MAGNETRON NO. QUANT. NAME AND REQ'D SPECIFICATION 1 4 MICROWAVE APPLICATOR EW3-WGSC 2 1 POWER METER EW3-DPM3 3 1 WATER LOAD EW3-WL25 4 1 RAW PAPER ROLL 5 1 PRODUCT PAPER ROLL 6 1 DRIVE ROLL 4"0D. Cr PLATED 7 1 PRESS ROLL Z"OD. MS-8 2 SQUEEZE ROLL 3"0D. Cr PLATED 9 3 GUIDE ROLL 4n0D. Cr PLATED 10 18 PILLOW BLOCK 3/4" SHAFT 1 1 1 MOTOR 115V I/4HP 1725 RPM 12 1 REDUCTION GEAR DIMENSIONS— INCHES Figure 3 Assembly Drawing of Apparatus 23 Figure 4 b Back View of Apparatus Figure 4 c S h i e l d i n g of Apparatus Figure 4d Control Panel • • • 25 c a r r y t h e -paper f r o m t h e f e e d r o l l t h r o u g h t h e r e s i n p a n and sq u e e z e r o l l s t o t h e w a v e g u i d e . T h e r e a r e t h r e e s p e e d s a t w h i c h t h e p a p e r c a n p a s s t h r o u g h t h e m a c h i n e . The s p e e d c an be v a r i e d by means o f 3 s p e e d p u l l e y s on t h e motor and on t h e g e a r box. The a v a i l a b l e s p e e d s are'0.354, 0.812, and I.67 m e t e r s / m i n . I n o r d e r t o m a i n t a i n a c o n s t a n t t e n s i o n on t h e p a p e r a s i m p l e s l i p t y p e c l u t c h i s . i n s t a l l e d on t h e p a p e r w i n d i n g r o l l . T h e r e i s a l s o ' p r o v i s i o n f o r a f r i c t i o n b r a k e on t h e f e e d r o l l but i n t h i s work i t was n e v e r n e c e s s a r y t o use i t . A l l t h e g u i d e r o l l e r s were c o n s t r u c t e d o f chromium p l a t e d c o p p e r p i p e (4" O.D. S t a n d a r d Copper P i p e ) ; t h e s q u e e z e r o l l e r s were a l s o c o n s t r u c t e d o f chromium p l a t e d c o p p e r p i p e (3" O.D. S t a n d a r d Copper P i p e ) . 3. R e s i n I m p r e g n a t o r The r e s i n i m p r e g n a t i o n s y s t e m c o n s i s t s o f a r e s i n pan, a d i p p i n g box and two s q u e e z e r o l l s . The r e s i n pan i s 22" x 15" x 10" h i g h ; a n d i s made o f p o l y -v i n y l c h l o r i d e . I t c a n h o l d up t o 4 g a l l o n s ' o f r e s i n s o l u t i o n and has a d r a i n i n t h e b o t t o m f o r r e m o v i n g t h e r e s i n . The d i p p i n g box i s 21" x 13" x 6" h i g h , a g a i n i t i s o f p o l y v i n y l c h l o r i d e . Two 2" p o l y v i n y l c h l o r i d e p i p e s ( c u t i n h a l f ) a r e w e l d e d t o t h e b o t t o m o f t h i s d i p p i n g box. Thus t h e p a p e r i s d r a g g e d u n d e r t h e s u r f a c e o f t h e r e s i n i n t h e r e s i n p a n , o v e r t h e two p i p e s on t h e d i p p i n g box and out o f t h e r e s i n . The d e p t h o f i m m e r s i o n o f t h e p a p e r c a n be a d j u s t e d by l o n g , t h r e a d e d r o d s w h i c h a r e a t t a c h e d t o t h e d i p p i n g box. The d e p t h o f p e n e t r a t i o n a l l o w s some v a r i a t i o n o f t h e i m p r e g n a t i o n t i m e . The i m p r e g n a t e d p a p e r t h e n goes t h r o u g h t h e s q u e e z e r o l l s . These two squeeze r o l l s are c o n s t r u c t e d of 3" o u t s i d e diameter, chrome p l a t e d , copper p i p e s . The pressure a p p l i e d t o the r e s i n impregnated sheet can be v a r i e d by moving weights along l e v e r arms a t t a c h e d t o the movable r o l l . Passage through the squeeze r o l l s makes the r e s i n d i s -t r i b u t i o n more uniform and squeezes excess r e s i n from the paper. The amount of r e s i n p i c k up can be c o n t r o l l e d by a d j u s t i n g the pressure between the squeeze r o l l s . 4. V e n t i l a t i o n System In order to t r a n s f e r mass i n the form of water from the paper being d r i e d i t i s of course necessary to v e n t i l a t e the waveguide.. A l s o i f the water content of the a i r i n the wave-guide i s too high water condenses i n s i d e the waveguide and d r i p s c a using a r c i n g which c o u l d l e a d t o f i r e s . A i r e nters through the s l o t s i n the waveguides and i s sucked out through the v e n t i l a t i o n p o r t s on the waveguide bends by a t u r b i n e type f a n . The flow r a t e of a i r ' i n the exhaust duct can be measured by an o r i f i c e p l a t e i n s t a l l e d i n the duct on the d e l i v e r y s i d e of the f a n . Wet and dry bulb temperatures of the a i r l e a v i n g the waveguide were a l s o measured by a psychro-meter mounted i n the duct on the s u c t i o n s i d e of the fan. 5. Surface Thermocouples A set of thermocouples was c o n s t r u c t e d t o measure the s u r -face temperature of the paper. For such s u r f a c e temperature measurements the thermocouple should be i n good contact with the s u r f a c e and heat l o s s e s from the thermocouple j u n c t i o n should be minimized.- Therefore the thermocouples (40 gauge copper-constantan) were embedded i n 3/4" x 2" x 1/16" s t r i p s of p o l y e t h y l e n e as shown i n f i g u r e 5. Thus the thermocouple j u n c t i o n 27 1/6 <|>x3 BRASS ROD =5s mm -\ao ALUMINIUM BAR lj-xi--22 t n. ij i l l ACRYLIC RESIN BLOCK 30 GAGE COPPER-CONSTANTAN PAPER POLYETHYLENE * SHEET V t -—' t ro| > 1 0 p 1 P2 p e n e t r a t i o n depth i n c i d e n t e l e c t r i c f i e l d d e nsity t r a n s m i t t e d e l e c t r i c f i e l d densuty frequency mixing c o n d i t i o n absorbed power density i n c i d e n t power density t r a n s m i t t e d power density weight r a t i o of component 2 to component 1 a t t e n u a t i o n constant complex p e r m i t t i v i t y complex p e r m i t t i v i t y of component 1 complex p e r m i t t i v i t y of component 2 d i e l e c t r i c constant d i e l e c t r i c constant of water d i e l e c t r i c l o s s f a c t o r i n t r i n s i c wave impedance of free space density of component 1 density of component 2 cm volts/m volts/m Hz • (-) watts/cm watts/cm^ 3 watts/cm -1 m farads/m farads/m farads/m farads/m farads/m farads/m 3 7 7 ohms 3 gr/cm 3 gr/cm A - l APPENDIX A Power Meter C a l i b r a t i o n The c r y s t a l type forward and reverse power meter (EIMAC EW3 - D P M 3 ) was c a l i b r a t e d using the water load as a c a l o r i m e t e r . This power meter was mounted i n the waveguide between the microwave a p p l i c a t o r and the water load. To c a l i b r a t e the power meter the microwave power l e v e l was set a some value and the c o o l i n g water flow rate through the water load and i t s i n l e t and o u t l e t temperatures were recorded. The power consumed was c a l c u l a t e d from the temperature r i s e and correlated with the d i f f e r e n c e between the forward and reverse power meter readings. T o t a l supply current and V a r i a c s e t t i n g were a l s o recorded f o r correlation with the energy absorbed i n the water load. The data obtained are recorded i n Table A-I. In f i g u r e A - l the net power absorbed i s p l o t t e d against the d i f f e r e n c e between forward and reverse power meter reading. Two d i f f e r e n t curves r e s u l t e d one f o r each range of the power supply. Since the behaviour of the water load and the power meter should not depend on the power supply c i r c u i t to the magnetron t h i s was unexpected. The only explanation that comes to mind i s that some mismatching between the magnetron and the waveguide occurs when the range switch i s changed or that the power meter i s some-how a f f e c t e d by t h i s change. The net power-absorbed i s p l o t t e d against t o t a l supply current i n f i g u r e A-2 and against Variac s e t t i n g i n f i g u r e A-3. Thus these parameters can a l s o be used as power generation i n d i c a t o r s as w e l l as the power meter. T o t a l power su p p l i e d was c a l c u l a t e d from the t o t a l supply k-2 current and supply voltage assuming the supply voltage was 115 v. The e f f i c i e n c y of the microwave power generator was then c a l c u l a t e d and p l o t t e d i n f i g u r e A-4. The o v e r a l l e f f i c i e n c y of the complete d r y i n g process i s the product of power supply e f f i c i e n c y and d r y i n g e f f i c i e n c y . Figure A-5 shows the time r e q u i r e d f o r the microwave generator system to achieve steady s t a t e . In c o l l e c t i n g the data f o r these curves the Variac s e t t i n g and the c o o l i n g water flow rate were maintained constant. The f i g u r e shows that about 2 hours are re q u i r e d to reach steady sta t e a f t e r s w i t c h i n g on the magnetron. Curves a and c were obtained when the magnetron was on continuously and curve b was obtained when the magnetron was switched on, a reading taken, and then turned o f f u n t i l the next reading was made. Data f o r the curves of f i g u r e A-5 are given i n Table A - I I . A-3 POWER METER READING (kw) (FORWARD—REVERSE) Figure A - l . Power Generation versus Power Meter Reading A-4 30 •ZL 2-0 o fe o 10 UJ CL 0 0 10 20 30 SUPPLY CURRENT (amp) Figure A-2. Power Generation versus Supply Current B I 8 0 50 100 VARIAC SETTING (-) Figure A-3. Power Generation versus Var i a c S e t t i n g a- 0 10 2 0 3 0 POWER GENERATION (kw) Figure A-4V Power Supply E f f i c i e n c y versus Power Generation A-7 1-5-g < 0 o 0 5 o 0 — O " VARIAC SETTING 75 (H RANGE) b / A VARIAC SETTING 130 A (H RANGE) A J / A —• / n^CT VARIAC SETTING 70 / (L RANGE) 20 0 30 60 90 TIME ( m i n ) Pigure A-5. Start-up Time f o r Microwave Generator TABLE A - l a POWER METER CALIBRATION DATA (LOW RANGE) POWER METER WATER WATER TEMPERATURE POWER VARIAC SUPPLY SUPPLY EFFICI-READING (kw) PLOW RATE (°C) GENERATION SETTING CURRENT POWER ENCY FORWARD REVERSE (kg/hr) INLET OUTLET (kw) (-) (amp) (kw) (%) 0.100 0.000 41.0 12.2 15.0 0.13 99 — — — 0.200 0.002 41.0 12 . 2 18.3 0.26 90 3.0 0.35 75.4 0.300 0.003 41.7 - 12.2 20.8 0.41 80 5.0 0.58 70.7 0.400 0 .005 41.7 12.2 23.5 0.55 72 6.5 0.75 73.5 0.500 0.010 41.2 12.2 26.6 0.71 . 62 7.8 0.90 78.9 0.600 0.010 41.7 12 .2 29-9 0.86 '54 • 9.1 1.05 81.9 o. 700 0.015 42.0 12.2 32.3 0.98 46 10.4 . 1.20 81.7 0.800 0. 020 41.7 12.0 34.5 1.09 38 11.5 1.32 82.6 0.900 0.020 42.0 12.0 37.2 1.23 31 12.6 1.45 84.8 1. 000 0.025 43.0 12.0 39.1 1.35 20 13.8 1.59 84.9 > I co TABLE A-lb POWER METER CALIBRATION (HIGH RANGE) POWER METER WATER WATER TEMPERATURE POWER VARIAC SUPPLY SUPPLY EFFICI-READING (kw) FLOW RATE (°C) GENERATION SETTING CURRENT POWER ENCY FORWARD REVERSE (kg/hr) INLET OUTLET (kw) (-) (amp) (kw) (*) 1. 000 0. 030 40.2 12.2 44.2 1.50 123 16.5 1.90 78.9 1.100 0.040 39.5 12.2 47.0 1.61 118 17.5 2.01 80.1 1. 200 0.45 39-5 12.2 49.9 1.76 113 18.6 2 .14 82.2 1.300 0.050 39-2 12.2 52.9 1.87 108 19.5 2.24 83.5 1.400 0.055 39.2 12.2 56.2 2. 02 101 20.5 2.36 85.6 1. 500 0.060 39.5 12.2 58.5 2.14 • 95 21.5 2.47 86.6 1.600 0.065 40.8 12.2 59.7 2.26 90 22.5 2.59 87.3 1.700 0.070 40.4 12 .2 62 .2 2. 36 85 23.2 2.67 88.4 1. 800 0.070 39.5 12.2 64.5 ' 2.44 80 24.0 2.76 88.4 1.900 0.070 39.5 12 .2 67.7 2.59 75 25.0 2.88 89.9 2.100 0.065 40.2 12.2 70.9 2.69 68 26.6 3.06 87.9 2.200 0.065 41.5 12.5 72.5 2.77 64 27. 2 3-12 88.8 2.300 0.075 40.2 13.2 74.6 2.9o 57 27.6 3.17 91.8 2.400 0.075 40.2 13.2 76.4 2.98 53 28.2 3-24 92.0 A-10 TABLE A-2a START-UP TIME FOR MICROWAVE GENERATOR (VARIAC SETTING IN HIGH RANGE 75) TIME POWER METER READING (kw) SUPPLY CURRENT (min) , FORWARD . REVERSE.. DIFFERENCE. (amp) 0 1.13 0.03 1.10 18.1 10 1.26 0.04 1.22 19.3 20 1.35 0.04 1. 31 20.1 30 1.40 0. 04 1.36 20.6 50 1.49 0.05 1.44 21. 7 70 1.52 0.05 1.47 22.3 100 1.52 0.05 1.47 22.5 120 1.52 0.05 1.47 22.5 TABLE A-2b START-UP TIME FOR MICROWAVE GENERATOR (VARIAC SETTING IN HIGH RANGE 130) TIME POWER METER READING (kw) SUPPLY CURRENT (min) FORWARD REVERSE DIFFERENCE (amp) 0 0.20 0.0 0.20 5.1 5 0.32 0.0 0.32 6.4 10 0.43 0.01 0.42 7-8 20 0.53 0.01 0.52 9-7 30 "0.65 0.02 0.63 11.4 40 0.75 0.02 0.73 12.8 50 0.85 0.02 0.83 14.8 60 0.90 0.03 0.87 14.8 70 0.93 0.03 0 .90 15.0 80 0.96 0.03 0.93 15.5 90 0.98 0.03 0.95 15.9 100 0.99 0.03 O.96 15.9 110 1.02 0.03 0.99 16.5 A - l l TABLE A-2c. START-UP TIME FOR MICROWAVE GENERATOR (VARIAC SETTING IN LOW RANGE 70). TIME POWER METER READING (kw) SUPPLY CURRENT (min) FORWARD REVERSE DIFFERENCE (amp) 0 0.10 0.0 0.10 3.0 10 0.13 0.0 0.13 • 3-5 20 0.24 0.0 0.24 4.5 30 0.26 0.0 0 .26 4.5 40 0. 30 0.0 0.30 5.0 60 0.32 0.01 •' 0.31 • 5-5 70 0.34 0.01 0.33 5-5 80 0.35 0.01 0.34 5-7 90 0.35 0.01 0.34 5.8 110 0.37 0 .02 0.35 6.1 130 0.37 0.02 0.35 6.0 B APPENDIX B Rotameter Calibration Figure B - l and Table B-I are the data collected for calibrating the Brooks Rotameter R-6-15A used in controll ing the cooling water flow rate. This was done for two water tem-peratures 12°C and 1 7 ° C No temperature effect was observed. B -2 TABLE B - l ROTAMETER CALIBRATION DATA ROTAMETER WATER PLOW WATER SETTING RATE (kg/hr) TEMP.(°C) 2 5 . 2 3 . 4 1 7 . 0 3 1 . 5 5 . 3 1 7 . 0 42 . 0 8 . 6 1 7 . 0 5 4 . 0 1 2 . 1 1 7 . 0 61 . 5 14 . 4 1 7 . 0 7 2 . 0 1 7 . 8 1 7 . 0 84 . 0 2 2 . 0 1 7 . 0 9 6 . 0 2 5 - 7 1 7 . 0 1 0 2 . 0 2 8 . 0 1 7 . 0 1 1 3 . 5 3 2 . 6 1 7 . 0 124 . 5 3 6 . 2 1 7 - 0 1 3 4 . 0 3 9 . 6 1 7 . 0 2 2 . 0 2 . 5 1 2 . 0 3 7 - 0 7 . 0 1 2 . 0 5 4 . 2 1 2 . 0 1 2 . 0 6 9 . 7 1 6 . 9 1 2 . 0 8 8 . 5 2 3 - 0 1 2 . 0 1 0 3 . 0 2 8 . 2 1 2 . 0 1 1 5 . 0 3 3 . 1 12 . 0 1 2 5 . 0 3 5 . 4 1 2 . 0 1 3 7 - 0 40 . 2 1 2 . 0 Figure B - l . Rotameter C a l i b r a t i o n Curve APPENDIX C C-l Thermocouple C a l i b r a t i o n The copper constantan thermocouples were c a l i b r a t e d using a quartz thermometer. The c a l i b r a t i o n data i s presented i n Tables C-I and. C-II. The maximum e r r o r due to reading of the recorder chart was estimated to be - 0 . 2°C. C-2 TABLE C - l SURFACE THERMOCOUPLE CALIBRATION DATA (THERMOCOUPLE NO.1 TO NO.5) TEMPERATURE POTENTIAL DIFFERENCE (mV) ( ° c ) . N O . l NO. 2 N0.3 NO. 4 NO. 5 11.1 0.44 0,44 . 0.44 0.44 0.44 19.9 0.78 0.78 . 0.78 0.7.8 0.78 29.8 1.18 1.18 1.18 1.18 1.18 4Q. .5 1.63 1.63 1.63 1.63 1.63 50.7 2.06 2.06 2.06 2.06 . 2.06 60.6 2.49 2.49 2.48 2. 49 2 49 70.4 2.90 2.90 2.90 2.90 2.90 81.2 2.39 2.39 2.38 2.39 2.38 91.1 3.85 3.85 3.83 3.85 3.85 96.0 4.07 4.07 4.07 4.07 4.05 TABLE C-2 THERMOCOUPLE CALIBRATION DATA (THERMOCOUPLE NO. 6 TO NO'. 9 ) TEMPERATURE POTENTIAL DIFFERENCE (mV) (°C) NO. 6 NO. 7 • NO. 8 NO. 9 21.2 0.87 0.86 0.86 0.86 30.0 1.24 1.23 1.23 1.23 40.1 1.67 1.65 1.65 1.65 50.1 2.11 2.10 2.09 2.09 60.0 2.55 2.55 2.54 2.53 70.1 2.99 2.99 2.97 2.97 80.0 . 3.48 3.46 3-45 3.43 90.0 3.95 3.93 3.91 3.88 APPENDIX D O r i f i c e Meter A three i n c h standard o r i f i c e meter was i n s t a l l e d i n the e x i t l i n e from the fan which v e n t i l a t e d the waveguide. This was used to set the a i r flow r a t e . . The a i r flow rates were c a l c u l a t e d from W = KA 0 V 2 S C (Pi - P 2 ) P 0 where K = discharge c o e f f i c i e n t . (-) 2 A 0= cross s e c t i o n a l area of the o r i f i c e ( f t ) p0= density of the f l u i d at the o r i f i c e (gm/cm^) W = mass flow r a t e (lb/sec) P 1 - P 2 = pressure drop"across the o r i f i c e = 2.048Ah op b Q ( l b f / f t 2 ) A h 0 = manometer l e v e l d i f f e r e n c e (cm) P.bo manometer f l u i d density (gm/cm^) The o r i f i c e discharge c o e f f i c i e n t s were taken from the t h e s i s (34) of Galloway who used and c a l i b r a t e d t h i s p a r t i c u l a r o r i f i c APPENDIX E Sample C a l c u l a t i o n f o r Heat Balance Sample c a l c u l a t i o n was done f o r experiment No. 3 of r e s i n impregnated paper d r y i n g t e s t . (1) Power Input C a l c u l a t i o n forward power from power meter = 1.20 kw reverse power from power meter = 0.05-kw d i f f e r e n c e of forward-reverse power = 1.15 kw power generation = 1.75 kw (from f i g u r e A - l) (2) Moisture Content and Resin P i c k up C a l c u l a t i o n paper feed speed = 21.24 m/hr width of paper web = 0.4l m p density of paper = 0.201 kg/m paper feed r a t e = (21.24)(0.4l)(0.201)=1. 75 kg/h moisture content and r e s i n p i c k up at p o s i t i o n 5 (wet end) concentration of r e s i n s o l u t i o n = 33-67$ weight of wet sample = 11.20 gr weight of oven d r i e d sample = 6.09 gr evaporated water = 11.20 - 6.09 = 5-11 gr weight of r e s i n = ( ° j ^ 3 ^ ^ 1 1 ) = 2.59 gr weight of paper = 11.20 - (5-11+2.59) 3.50. gr 2 59 i r e s i n p i c k - u p = 2 5 0 = 0-74 g r / g r - p a p e r 5 11 m o i s t u r e c o n t e n t = i.' nr. x 100 = 146.0 % 3 • 50 . m o i s t u r e c o n t e n t and r e s i n p i c k up at p o s i t i o n 4 weight o f sample = 4.46 gr weight o f oven d r i e d sample = 2.48 gr weight o f water = 4.46-2.48 = 1.98 g r r e s i n p i c k - u p =0.74 (from wet end data) ? 48 weight o f paper = 1 Q ^ = 1.43 gr m o i s t u r e c o n t e n t = J743" x 1 0 0 = 138.4 % S i m i l a r c a l c u l a t i o n was done f o r each p o s i t i o n . R e s u l t s were g i v e n as f o l l o w s : -P o s i t i o n 1 2 3 4 5 sample weight 6.11 5.73 7.54 4.46 11.20 oven d r i e d weight 5.49 3-91 4.24 2.48 6.09 weight o f water 0.62 1.82 3-30 1.98 5.H weight of r e s i n 2.33 1.66 1.80 1.05 2.59 weight o f paper . 3.16 2.25 2.44 1.43 3-50 r e s i n p i c k - u p - ' - - - 0.74 m o i s t u r e c o n t e n t 19.6 80.8 135.2 138.4 • 146.0 E-3 (3) Energy C a l c u l a t i o n f o r Evaporation evaporation at p o s i t i o n 1 (dry end waveguide) moisture content d i f f e r e n c e = O..808 - 0.196 = 0.612 kg-water/kg-paper water evaporation = (0.612)(1.75) = 1.07 kg/hr paper temperature at p o s i t i o n 5 = 23-0°C paper temperature at p o s i t i o n 1 = 72.3°C s p e c i f i c heat of water = 1.0 kcal/(kg)(°C) heat of v a p o r i z a t i o n . o f water = 555 k c a l / k g (at 72.3°C) energy f o r evaporation = (1.07) {(1.0)(72.3 - 59.4) + 555} = 609 k c a l / h r S i m i l a r c a l c u l a t i o n was done f o r each p o s i t i o n . Results were given as f o l l o w i n g : -Waveguide Water Energy f o r No. Evaporation Evaporation (kg/hr) ( k c a l / h r ) • 1 dry 1.071 609 2 0.952 505 3 0.056 53 4 wet 0.133 97 t o t a l 2.212 1261 (4) Energy C a l c u l a t i o n for, Sensible Heat s p e c i f i c heat of paper = 0.30 kcal/(kg)(°C) s p e c i f i c heat of r e s i n = 0.40 kcal/(kg)(°C) (assumed) E-4 paper t e m p e r a t u r e at p o s i t i o n 5 =23.0 °C paper t e m p e r a t u r e at p o s i t i o n 1 = 72.3 °C s e n s i b l e heat o f paper = (1. 7 5 ) ( 0 . 3 0 ) ( 7 2 . 3 - 23.0) = 25.9 k c a l / h r s e n s i b l e heat o f r e s i n = ( 1 . 7 5 ) ( 0 . 7 4 ) ( 0 . 4 0 ) ( 7 2 . 3 - 23.0) = 2 5 -5 k c a l / h r s e n s i b l e heat o f w a t e r i n p r o d u c t = (1.75)(0.196)(1.0)(72.3 - 23.0) 13.5 k c a l / h r t o t a l s e n s i b l e heat 25.9 + 25.5 + 13.5 64.9 k c a l / h r (5) E f f i c i e n c y o f A p p l i c a t o r energy i n p u t = (1.75)(860.5 ) = 1.505 k c a l / h r (1 kw = 860.5 k c a l / h r ) e f f i c i e n c y based on e v a p o r a t i o n 1,261 ' 1,505 x 100 = 83.8 % e f f i c i e n c y based on t o t a l energy a b s o r p t i o n 1,261 + 64.9 1,505 x 100 = 88.0 %