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1 Korean Chem. Eng. Res., Vol. 45, No. 4, August, 2007, pp { / o m mš om m Š mq ÇPeter Englezos*Çlk **Ç **, l o rž e r qr 30 *Department of Chemical and Biological Engineering, University of British 2216 Main Mall, Vancouver, British Columbia V6T 1Z4, Canada ** ne t 3 (2007 3o 18p r, o 5p }ˆ) Morphology of Methane/Propane Clathrate Hydrate Crystal Ju Dong Lee, Peter Englezos*, Yong Seok Yoon and Myungho Song**, Advanced Manufacturing Technology team, Korea Institute of Industrial Technology, san 30, Jangjeon-dong, Geumjeong-gu, Busan , Korea *Department of Chemical and Biological Engineering, University of British Columbia, 2216 Main Mall, Vancouver, British Columbia, V6T 1Z4, Canada **Department of Mechanical Engineering, Dongguk University, 3-ga, Pil-dong, Choong-gu, Seoul , Korea (Received 18 March 2007; accepted 5 May 2007) k h ˆ/ Ž ~p r p p k s l eˆ rp q p l m. r k n kp ~ v l nkp eˆ, m p p m p l p l pr ov p p rp, p, q p p l m. e s l p p p p ~m k~p l p ˆ eq lp, p n l p r p l p p l p p p p q r k p q m. }l q r p, r qp s l p ˆ v p ƒvl p v (dendrite)p }p q v v p m. k~ ml l o r(floating crystals) p Ž ~, Ž o Ž k ˆ p, p qp Ž ~ ˆ v rpl. p ƒvl o r le v p }p q m. p p rp q p l (memory effect; p p l k~l qp p~ s qs ) m p tep m. Abstract Morphology of methane/propane clathrate hydrate crystal was investigated under different undercooling conditions. After the water pressurized with compound guest gas was fully saturated by agitation, medium within the vessel was rapidly undercooled and maintained at the constant temperature while the visual observations using microscope revealed detailed features of subsequent crystal nucleation, migration, growth and interference occurring within liquid pool. The growth of hydrate was always initiated with film formations at the bounding surface between bulk gas and liquid regions under all tested experimental conditions. Then a number of small crystals ascended, some of which settled beneath the hydrate film. When undercooling was relatively small, some of the settled crystals slowly grew into faceted columns. As the undercooling increased, the downward growth of crystals underneath the hydrate film became dendritic and occurred with greater rate and with finer arm spacing. The shapes of the floating crystals within liquid pool were diverse and included octahedron and triangular or hexagonal platelet. When the undercooling was small, the octahedral crystals were found dominant. As the undercooling increased, the shape of the floating crystals also became dendritic. The detailed growth characteristics of floating crystals are reported focused on the influences caused by undercooling and memory effect. Key words: Morphology, Gas Hydrate, Undercooling, Floating Crystal, Dendrite To whom correspondence should be addressed. songm@dgu.edu 400

2 1. d r p p (p d p p ) om d lp eq 1930 l rp l p ep eq m, p e kp l l } l dp k p pl p. opp s p dm p l p p l q o o p p v l [1] oo d p e p q o p p p p lr l e p l eq l [2]. p, 1960 Makogonp p q p e k m Š l }lp sq ˆ p p p p p e [3], p ~r l v qop ˆ p p l ep s lm. Makogon[4] Kvenvolden[5]p ˆ p p e rm m Š vll o l pp s p m 3 l m. q v r e p m l, p p ˆ v p q l p ˆp l v p q rp r l o, ˆ }l d l qs q p 2 [5, 6]., p p k }l dl ~r d v p k }l dl rp o m k rq s p p rrp }l dp rq p t p pp [7, 8], l m dp p ˆ l d, p p ~ l ll rp k r r r m l vr rp rq, vr p ˆ }l ˆ p p l tp ˆ p p r rp e l ep vt p [9-12]. d p p q p p p lv p~ sp (cavity) l r qp d q r~p. r q(guest molecule)m s pq q(host molecule) pl r q p šp qn v kp q p r l p p p r tn s p. p p e p q }ov v kp qm pq qp pr p v k (non-stoichiometric). p p rp rr k p q lp kr l p m p m l ~ ˆ ov. v v p p p v q ˆ, lˆ,, p ˆ l 100s p p [13, 14]. d p p p r s t ql r, k v s p sl s-i s-iim, o sl s-h p [15, 16]. v v r d p p l vep sp l q r l pp [2, 13], rl p p rp vr p p pn km sp l tep. d p p p p er rl s p q p r l q rp erp l v r p rp rp. p, v ˆ/ Ž r p p rp q 401 r p p p m p p pr nk ~p d r p. p l, p p l X r NMR p pn q l tp er l m ll r, l r vp r er l [17]. p er l ~ pn l p p p r s nl qp rop p r p m. p p p p s m p p p er l p k v q l sm rp rp pn l p p p p vp pp p., p p p l l n }} q n rn, q lp p op ~rp p ol p p p q p l., qll sq p rp p p l p er p m q lp p p rp l l. ˆ (morphology)p p p m p e t p p p k l ep, r p p l p q v l kp [18, 19]. ˆ l p p p p e sm er p l r r. m, p p v vp o Œ, o l v r r p r r p. p er p e p p p, rq,, l rp l rp q p. e, ˆ p d p p p m, p p m q p pq er p p f, p p pn p ˆ } l v, rq (GTS; gas to solid technology)[20] l vrrp l. k e ˆ l, ~ ˆp ql krp, k~ p ˆ m p, tp q l ˆ p p p p t p l. Lee [17]p n l p p p r p ~ mlp v p p p qp l m, Sakaguchi and Mori[21] s-ii p p HCFC-141b(CH 3 CCl 2 F)m H 2 O edšl lrq k v (polyvinylpyrrolidone) - ˆ(polyvinyl-caprolactam)p p p rp ql l qn l m. p e er p p p s l m l q tl p q e p l l rp q r [14, 22-24]. l l ˆ Žp nkp q p p rp qp k (undercooling) s l m. e l n q er }l dp p 90.5 vol.% ˆ 9.5 vol.% Žp ~p. p d s l p p s-ii p k r p [25-29]. l ~/k~ l q p p p o q ˆ r r, v sp q r rp q., k~ ml Korean Chem. Eng. Res., Vol. 45, No. 4, August, 2007

3 402 pt Ë Peter EnglezosËon Ë l l ~/k~ p m q o r(floating crystal)p p p nl r p p m. 2. m l l n e q p vp Fig. 1l ˆ l. d p p p p pl n p v (polycarbonate plastic, Lexan) qp t p l p ov d p d dž qp o k. s n m rl p e sl mr q sp n p 10 mm p Œ k l n ok p p m. sp p m e rl p s p msm edšp l vr eˆ. t p p o p, t p v p 25 mm p v p kp v p. t p l p n p p p 37 mmm 25 mmp r p ˆ. e t n p kp ov krp o p vtp p p } m. m v kp m p o m n v p n l m. p t 15 mm, 25 mmp v }p p p ˆp. t p l n p v 37 mmm 25 mmp eop ˆ. v p p p t p n p p n p p. p v 114 mm p 44 mmp d p ddž o l t p v 37.2 mm p 22 mmp o r p. p ov o p n p r p l p Ž ptp m p m. p p p n 3 mm d p d dž p p ov, pl sq l ~ ˆp q n tp n m. tp l k l p d p o e } m. p l n p ~ k ~ mlp m r p T lr p p. pq qp p tp p p l l. sp m p lr n l r m. s p m p vp r n tn pqp. e l Nikon rq n 300 m p o pl p o o p n l sp n l s t p l s m., p ol e n o p p tep l m. prp p o n p l q r (magnetic bar) sp n l q p m. e t m m p CCD (Sony, DXC-390) q (Nikon, SMZ 1000) vˆ (Nikon, Coolpix 5400) n l m. e p t rp p. r n p d m v mr r p s, k 25 cc p p p (n ) l tp. pl sp m rl l p p m r m l p, p p r o ~ n l 1 MPa p p k p v k v e rp 3 p m. p p rp qp nk t qp l p l r m p. e l o e p t rl nkp e. l n e p r o m e p Fig. 2 l ˆ l. m e p l }ov n l p tp n m r m l ep Fig. 1. Photograph of optical test vessel. o45 o k Fig. 2. Result of preliminary experiment to determine the saturation time with methane/propane gas.

4 ˆ/ Ž r p p rp q 403 Table 1. Experimental conditions for experimental runs with two hours stanby time Experiment T exp P exp (MPa) C final (1) (%C1) T tri T T down (2) (min) Gas phase composition measured after experimental run Elapsed time until the first appearance of downward crystal since hydrate film formation (1) (2) Fig. 3. Transient change of temperature during preparation stages and experimental run. 1 eq m. el n e p 1 p p. n p k p sp m p p k p 2.48 MPa ~ v edšp q r k p m. n kp q v n r eq k 30 p l nkp l p p k v v kk. m e l e p l nk rp 60 p v m. r p, l (memory effect) l p p e v o p rveˆ e k e l nkp m m k p Fig. 3l rp ˆ l. Fig. 3 l, T tri p p - ~-nk(h-v-l)p 3 p k l p s 3 m p. n ed Šp e t vp m l k p T tri. vp m (T exp ) 3 m p l p p s p m p l s p l p. e l, rp p p rp q p rl l ( p p l k~l qp p~ s qs ) l rp r m. p rp Fig. 3l ˆ m p k 1e k vp m m 10 K ov p p m vp m m (T tri ) 3 K p m o v p p. l l r tl v rp nkp p l p p p m ne p e s l 40 p p. p p p rp mr v p p, p 2e 10 p e (stanby time)p. l nkp n po p p s p s erl rp p v o e (induction time)p o pl. l v kp nk(fresh liquid solution)p n n s l pl 1t r vp o e p n m. l nkp n n e l p p s p s 2e p l p p rp eq Table 2. Experimental conditions for supplementary experimental runs with 10 minutes stanby time Experiment T exp P exp (MPa) GC final (1) (%C1) m. r Fig. 3l ˆ e r t n ~p p d (Varian p CP-3800) n l p e p m. ~ p t r t pl p p p r t l rm o l pr m. r t n ~ p ˆ Žp n pl t p n ~m nkp v m k l ps. e s l p p e p s erl r p ~ t ˆp s Table 1 Table 2l m. 3. y T tri T (1) Gas phase composition measured after experimental run 3-1. /h m m mš o m p rl ~ ml k~ mlp }l ˆ/ Ž d p p rp q p. rl p e s p r Table 1l nk m. Table 1p 3 m (T tri ) n k (P exp ) e s e l r ~p p CSMHYD [13]p n l p, ( T) T tri m n vp m (T exp ) p rp ( T=T tri T exp ). e l p p p p ~ ml k~ ml pp (p /k )l p ˆ eq l. p p p p q rp qp l v l rp q v v (arm spacing)p m. Fig. 4 p q experiment 1( T = 15.2 K)p /k l p p qp vp. p p p p le /k l p ˆ eq lp r~ p 30 r n l. p m k 1 l s ˆp r(spicular crystal)p p p Korean Chem. Eng. Res., Vol. 45, No. 4, August, 2007

5 404 pt Ë Peter EnglezosËon Ë Fig. 6. Flange-like crystal developed at the tip of downward crystals during experiment 2. Fig. 4. Photographic images near bounding surface between gas and liquid regions taken at different elapsed times during experiment 1 (15.2 K undercooling). Fig. 7. Transient change in vertical extent of downward growing hydrate crystals at different undercooling conditions. Fig. 6. Crystal tip development during experiment 2. Fig. 5. Photographic images near bounding surface between gas and liquid regions taken at different elapsed times during experiment 2 (13.7 K undercooling). p k p qp eq m. e p l q r p ˆ v p }p q r m. rp q ˆ t v p lr p v rp q rp q ˆp. Experiment 1p n /k p l m o r (floating crystal)p plp q rl r p l o. Fig. 5 experiment 2( T = 13.7 K)p v p. p p p l rp q p r r p experiment 1 o v p l q rp m q r m k ˆp o rp l. p e l e p o45 o k v p p rp p ˆ Fig. 6l ˆ l. v rp t q v p l kp Ž kp r p l, m p pž v q q ˆ m. p n experiment 3( T=8.7K) e t p p p rp q p o m q rp m q experiment 2l l n m. p /k p q rp q l m p r rp r o p p e p e t m p p p t vp q r l Fig. 7l ˆ l. p p p q rp q e k p pr ( T)p v. rp r q q l l. p l ˆ/ Ž p p rp q p sp l [30, 31]l rp p ˆ ˆ p p rp ˆ rp lt. l l rp n p l, p k~ mlp l /k p m o rp p. Fig. 5l ˆ m p o rp ˆl

6 ˆ/ Ž r p p rp q 405 Fig. 8. Photographic images near bounding surface between gas and liquid regions taken at different elapsed times during experiment 4 (3.2 K undercooling). Fig. 9. Photographic images of floating crystals taken at different elapsed times during experiment 5 (13.7 K undercooling). v p k pp p l p t v p q v v r(equiaxed orthogonal dendritic crystal) d p p p p p l p p t v p q v v r(equiaxed skewed dendritic crystal)p. Fig. 5p (b)m (d)l m p e l v v o r p p /k p m p v v o rp t e l l. o rl q p e m p rl. q qp s p experiment 4( T=3.2K)l /k p p p p vr q rp qp pl v kkp e o rp q p m. p p k 350 k k p o r p v rp /k l m. pp p v (Fig. 8)l p p o rp p ~ p o Ž ~ kp v p p 30l 40 µmp o v p k 0.7 mm/min r m. Fig. 8p (b) p qp n p p l r o r t (faceted column)p ˆ q dp. v r p q n qk 7e p l p 1 mm p pl l om p pl p e l k~ml p l m k p p o r p l. o rp q p o e p m, o rp, kp n l e (stanby time)p m l v p kk. rl e l r wp e (10 )p l lp v e s p Table 2l nk m. Fig. 9 experiment 5 t k~mlp l m v v o r p p /k p p } l l q q ˆ lt v p. o r p m r q mp, t v 2 v (secondary arm) p t vm v p m (Fig. 9(a)). p o rp t v p d mp p Fig. 10. Photographic images of floating crystals taken at different elapsed times during experiment 6 (8.1 K undercooling). p l v 1 mm p p q m., p o r p ~ q t v q p v kp n q l. e p o r p /k p p p l r q kp qp m (Fig. 9(b)). p r qp experiment 6p n p p l v v r p m experiment 5l l r m (Fig. 10(a)). e p v l } l r o rp t v tl lv q n p t v rp q m (Fig. 10(b)) p 2 v q eq l r lvp m (Fig. 10(c)). e l ˆp r p }l eq m (Fig. 10(d)). p v v r p p l q p t vm t v pr t vm p q 2 v p lv. v v r le l q ˆ. v v v v k~ mlp l d o rp o. p t v p p k 0.2 mmp o Korean Chem. Eng. Res., Vol. 45, No. 4, August, 2007

7 406 pt Ë Peter EnglezosËon Ë rp n k 1 mm/minp d t v p p k 1.2 mmp rp k 4 mm/minp m. o r p d p p m nkp l p l p r r p l p l r. o rp k~ mlp k rp qp (isotropic)p ov v /k l r p qp. p p p p p q rp p p pr nk tp q l p p q p qkv p Ž. v, o r p p l q rp q l p, Fig. 9(b)m 10(d)l ˆ p l n l v o rp n qs l ppp k p. l m p o rl p p p rp q q Ž p lt p. ˆ p p o rp op lp n kp l r ˆ q l p p o p q e p /k k~ mlp o rp m. p p l t k~ m lp q k l p p Ž ~ Ž o Ž kp rp. k~mll o r p rp r q p l v n ep m. q tn ep Ž ~ sp p p rp vrl t v q m v v p q Ž o Ž kp rp v v p q ep. v v p 2 v t v v p ov Žl v v p 2 v pr t vm p q m. edš p r qp n(3.2 K p ) p p rp v p v r p v k~mlp m. p o rp Ž ~ ˆ v rp k om m m e p l ˆ/ Ž p p rp q l p r p [32]p on l p. l l p p rp k~ ˆp pq q lp rp ql p p r nkp q p p l m., p o l q p s p n p r m. /k ( p l nl sq ) }p nkp nkp r k q p. v, m kv n v pr ~ mlp p qp p p l k~ ml p r nkp q v. p n vp m p p p p p /k l r v. er n p n kp r, /k l p p p }l rp t l p rp l l r p p p o p s p s l p. l p n n t op p rq l p p rp p /k l p o45 o k p p eq l o rp /k l e p e l p p p eqp /k l p ˆ ep. p p rp p p l ql n p m p ˆ v k. v, p p /k l p (heterogeneous nucleation) p v l rp qp s l p p p eq, k~ ml l rp p n p (homogeneous nucleation) p l q r p pl v k p l m rp l l q p. pr p q r o rp ˆp k~ ml l v p }p q. p p rp qp vp p r v rl. p p p q pr nkp r, m tlv k l pr v k nkp l., qp p p nkp q l p p /k~ l pr nk l l lv p q p v (Fig. 11(d)). el, p p rp qp o qlp p e p p /k~ l pr nk l l lv p m m (Fig. 11(c)). n l p p /k~ t p p qp v l l r q. rp rp q p p l l pr nk p m m p t p l p. Fig. 11l p k q r o rp l (A)m (B)l pr nkp m m q p Fig. 11. Temperature and concentration profile near coner (A) and flat (B) surface of hydrate crystal.

8 l ˆ l. Fig. 11p (a)m (b)l, r p m q p r p rp rp lt. Fig. 11(d)l ˆ q p l pr nkp ( A) l pr nkp ( B). l qp nkp rp p m l p p s p s., Fig. 11(c)l ˆ m l pr nkp m ( A) l pr nkp m ( B). v, p p /k~ l r ( x) lv nkl T A T B C A C B., p p l pr nkp l pr nkl l m m l p p r l nl n q kr p k. p qp krp p p /k~ Ž p rp s l q qt r p p v p. l p (coner effect) [32]. e l o rp l q p p l k q p p ~ q p n v p }p p q. k p p l lv nk r ˆ p p p (driving force)p v l p p rp kr qp n v p. Murowchickm Barnes[33] e p l ~ rp q ˆ m m r l m p ep r p s p p s l v rp qp p., ˆ/ Ž r p p rp q 407 p rp qp n p p p p l Fig. 11l m m s p p l p lp p. p p rp p l lp pr q, o rp nl k~ ml l Ž p Ž ˆ o v p. p p l k q r p r qp n p ˆ v p v q v lp q p lp Fig. 8l ˆ q ˆ q p. 4. ˆ/ Ž dp r p p rp qp k s l m. e s l p p p qp ~m k~ mlp l p ˆ eq l. p l v }l p q r n l m l p o r p q p Fig. 12 l p nl r k l nk m. p ƒvl q rp v p v p }p q v vp p m. e p l q rp q v ˆ q p p p p Žp ˆ q. p rp qp n p p p q rp p v kkp Ž ~ ˆp o r p p l m p p l l. p Fig. 12. Morphology diagram as function of undercooling. (a1) Faceted column. (a2) Downward crystals with branches. (a3) More compact downward crystals. (b1) Octahedra and polyhedral platelets. (b2) Equiaxed orthogonal and skewed dendrites (b3) Multi-branched orthogonal and skewed dendrites. Korean Chem. Eng. Res., Vol. 45, No. 4, August, 2007

9 408 pt Ë Peter EnglezosËon Ë t p t p q m. o rp p l e p wp n p l. o rp Ž ~ s Žp o Ž p k ˆ v, Ž ~p q k p Žpmp o Ž ˆp o rp q qk. o rp p p l p v q p n t v q m v p }p m. p p rp q p p p l pr k~ mll qll p lr l p vr k erp m m p sp l m q p m. p p rp ˆl l pn kl r p p lrr vr ~ nkl m p s n q lk. l qq vop p lr pl. o45 o k y 1. Hammerschmidt, E. G., Formation of Gas Hydrate in Natural Gas Transmission Lines, Ind. Eng. Chem., 26(8), (1934). 2. Englezos, P., Reviews: Clathrate Hydrates, Ind. Eng. Chem. Res., 32(7), (1993). 3. Makogon, Y. F., Hydrate formation in Gas-Bearing Layer in permafrost Conditions, Gas Industry Journal, 5, 14-15(1965). 4. Makogon, Y. F., Natural Gas Hydrate: The State of Study in the USSR and Perspectives for Its Use, Third Chemical Congress of North America, June, Toronto, Canada(1988). 5. Kvenvolden, K. A., Methane Hydrate - A Major Reservoir of Carbon in the Shallow Geosphere?, Chemical Geology, 71(1), (1988). 6. Makogon, Y. F., Russia s Contribution to the Study of Gas Hydrates, Annals N.Y. Acad. Scie., 715, (1994). 7. Englezos, P. and Lee, J. D., Gas Hydrate: A Cleaner Source of Energy and Opportunity for Innovative Technologies, Korean J. Chem. Eng., 22(5), (2005). 8. Lee, H., Lee, J., Kim, D. Y., Park, J., Seo, Y.-T., Zeng, H., Moudrakovski, I. L., Ratcliffe, C. I. and Ripmeester, J. A. Tuning Clathrate Hydrates for Hydrogen Storage, Nature, 434(7034), (2005). 9. Lee, J. W., Chun, M.-K., Lee, K. M., Kim, Y. J. and Lee, H., Phase Equilibria and Kinetic Behaviour of CO 2 Hydrate in Electrolyte and Porous Media Solutions: Application to Ocean Sequestration of CO 2, Korean J. Chem. Eng., 19(4), (2002). 10. West, O. R., Tsouris, C., Lee, S., McCallum, S. D. and Liang, L., Negatively Buoyant CO 2 -Hydrate Composite for Ocean Carbon Sequestration, AIChE J., 49(1), (2003). 11. Seo, Y.-T. and Lee, H., Structure and Guest Distribution of the Mixed Carbon Dioxide and Nitrogen Hydrates As Revealed by X-ray Diffraction and 13C NMR Spectroscopy, J. Phys. Chem. B, 108(2), (2004). 12. Seo, Y.-T., Moudrakovski, I. L., Ripmeester, J. A., Lee, J.-W. and Lee, H., Efficient Recovery of CO 2 from Flue Gas by Clathrate Hydrate Formation in Porous Silica Gels, Environmental Science and Technology, 39(7), (2005). 13. Sloan, E. D., Clathrate Hydrates of Natural Gases, 2nd ed., Marcel Dekker, New York(1998). 14. Ripmeester, J. A., Hydrate Research-From Correlations to a Knowledge-based Discipline. The Importance of Structure, Annal. N.Y. Acad. Scie., 912, 1-16(2000). 15. Ripmeester, J. A., Tse, J. S., Ratcliffe, C. I. and Powell, B. M., A New Clathrate Hydrate Structure, Nature, 325(6100), (1987). 16. Ripmeester, J. A. and Ratcliffe, C. I., Xenon-129 NMR Studies of Clathrate Hydrates: New Guests for Structure II and Structure H, J. Phy. Chem., 94(25), (1990). 17. Lee, J. D., Susilo, R. and Englezos, P., Methane-ethane and Methane-propane Hydrate Formation and Decomposition on Water Droplets, Chemical Engineering Science, 60(15), (2005). 18. Makogon, Y. F., Hydrates of Natural Gas, Chapter 2, Penn Well, Tulsa, Oklahoma(1981). 19. Sugaya, M. and Mori, Y. H., Behaviour of Clathrate Hydrate Formation at the Boundary of Liquid Water and A Fluorocarbon in Liquid or Vapor State, Chemical Engineering Science, 51(13), (1996). 20. Thomas, S. and Dawe, R. A., Review of Ways to Transport Natural Gas Energy from Countries Which do not Need the Gas for Domestic Use, Energy, 28(14), (2003). 21. Sakaguchi, H., Ohmura, R. and Mori, Y. H., Effect of Kinetic Inhibitor on the Formation and Growth of Hydrate Crystals at a Liquid-liquid Interface, J. Crystal Growth, 247(3-4), (2003). 22. Udachin, K. A., Ratcliffe, C. I. and Ripmeester, J. A., Single Crystal Diffraction Studies of Structure I, II and H Hydrates: Structure, Cage occupancy and Composition, Journal of Supramolecular Chemistry, 2(4-5), (2002). 23. Koh, C. A., Towards a Fundamental Understanding of Natural Gas Hydrates, Chem. Soc. Rev., 31(3), (2002). 24. Sloan, E. D., Clathrate Hydrate Measurements: Microscopic, Mesoscopic, and Macroscopic, J. Chemical Thermodynamics, 35(1), 41-53(2003). 25. Subramanian, S., Ballard, A. L., Kini, R. A., Dec, S. F. and Sloan, E. D., Evidence of Structure II Hydrate Formation from Methane+ethane Mixtures, Chemical Engineering Science, 55(11), (2000a). 26. Subramanian, S., Ballard, A. L., Kini, R. A., Dec, S. F. and Sloan, E. D., Structural Transitions in Methane+ethane Gas Hydratespart I: Upper Transition Point and Applications, Chemical Engineering Science, 55(23), (2000b). 27. Ballard, A. L. and Sloan, E. D., Structural Transitions in Methane+ethane Gas Hydrates-part II: Modeling beyond Incipient Conditions, Chemical Engineering Science, 55(23), (2000). 28. Takeya, S., Kamata, Y., Uchida, T., Nagao, J., Ebinuma, T., Narita, H., Hori, A. and Hondoh, T., Coexistence of Structure I and II Hydrates Formed from a Mixture of Methane and Ethane Gases, Can. J. Phys., 81(1-2), (2003). 29. Uchida, T., Moriwaki, M., Takeya, S., Ikeda, I. Y., Ohmura, R., Nagao, J., Minagawa, H., Ebinuma, T., Narita, H., Gohara, K.

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44(3)-16.fm Korean Chem. Eng. Res., Vol. 44, No. 3, June, 2006, pp. 270-276 지능형헬스케어욕조시스템개발을위한온수온도변화 r ~r l o l l e l 561-756 r rte v v 1 664-14 (2006 3o 9p r, 2006 6o 20p }ˆ) Change of the Warm Water emperature for