CA2111831A1 - Improved cooling medium for use in a thermal energy storage system - Google Patents
Improved cooling medium for use in a thermal energy storage systemInfo
- Publication number
- CA2111831A1 CA2111831A1 CA 2111831 CA2111831A CA2111831A1 CA 2111831 A1 CA2111831 A1 CA 2111831A1 CA 2111831 CA2111831 CA 2111831 CA 2111831 A CA2111831 A CA 2111831A CA 2111831 A1 CA2111831 A1 CA 2111831A1
- Authority
- CA
- Canada
- Prior art keywords
- surfactant
- critical micelle
- micelle concentration
- energy storage
- thermal energy
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
- C09K5/02—Materials undergoing a change of physical state when used
- C09K5/06—Materials undergoing a change of physical state when used the change of state being from liquid to solid or vice versa
- C09K5/063—Materials absorbing or liberating heat during crystallisation; Heat storage materials
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
- C09K5/02—Materials undergoing a change of physical state when used
- C09K5/04—Materials undergoing a change of physical state when used the change of state being from liquid to vapour or vice versa
Abstract
The present invention provides a cooling medium for use in a thermal energy storage system comprising water, a guest molecule and a surfactant having a critical micelle concentration in an amount less than about twice said critical micelle concentration.
Preferably the critical micelle concentration is less than about 1x10-3M and more preferably between 1x10-4M and 1x10-6M. A
thermal energy storage unit which uses said cooling medium and a process for using said thermal energy storage unit are also disclosed.
Preferably the critical micelle concentration is less than about 1x10-3M and more preferably between 1x10-4M and 1x10-6M. A
thermal energy storage unit which uses said cooling medium and a process for using said thermal energy storage unit are also disclosed.
Description
WO93/~4t2 2 ~ 31 PCI~/US!~2/0!;368 .
I~RO~:D COOLIN~ P~EI)IlJM FOR IJ8~ l A
., T~R~ ENERGY 8TORAG~ ~Y8?EM
~ This application is a continuatisn-in-part of `,5 Application Serial No. 722,428, filed on June 27, 1992.
. B~ck~Qun~ Q~_~h~ Invent on Thermal energy storage 5ystems contain a`cooling ~ medium, which is frozen during the off peak, evening r hours. During ~he daytime, heat from the s~rrounding .~ 1~ area is us~d to ~elt the cooling mediu~. The ramoval of heat to drive the decomposition causes the surrounding ar~a to b~come cool~r.
U.S. Patent No. 4,540,501 discloses a the ~ al energy stor~ge system which u~es clathrates as the cooling ~ediu~. Clathrates are hydrates which use a non-sto~chio~etric number o~ uater molecules per guest molecule. Th~ guest moleculQ f~lls th~ interior of the lattice, stabilizing the clathrat~. This stabilization allows the watex lattic~ ~ructure to form at te~peratures si~nificantly higher than the temperature of ice fo~mation (0C). The ~uest ~ol~cul~ must be highly insoluble in water, and must have a molecular ~ize which is 1~8 than 7 ~.
The halogenated hydrocarbons which are used as ~he gue~t ~ol~cul~ are not water ~i~cible. Clathrates will not for~ unle~s the guest ~nd ~os~ (lat~ice) co~psund3 ~r~ in contact. In an ~ttempt to bri~g the gUB~t mol~cul~ and wat~r into closer contact, v~rious ~ur~n~tant~ bava been add~d. U.S. Patent No. 4,540,501 di~close~ using a nonionic ~luoro~ur~actant having the chemical ~onmula F(CF2CF2) ~-~CH2cH20 (CH2~H20) 0~ when the gue3t molecule i~ a refrigerant cho~en fro~ brominated, chlorinated ~n~ ~luorinated hydrocarbsns including CCl2F2, CCl3P, CBr~3, CHClzF~ CHClF2, CH~ClF and CH3CClF2.
U.S. Patent No. 4,821,79~ disclo~es the ~SR Or Zonyl~
Plsrosur~actants in amounts between 1 to 5000 ppm gener lly, and th~ use o~ Zonyl FSN with ~ W~93/ ~ 12 PCT/US92/0~
...
trichlorofluoromethane in the ~mount of about 200 to 300 ppm. Zonyl9 Fluorosurfactant and Unidyne DS-401 have been added to water-l,l,l-tetrafluoro~thane clathrate forming thermal energy storage medium in - 5 Foxma~ion of Gas Hydrate or I~e ~y ~i~ect-Contact Eva~ora~ion of CFC Alternatives, F. Isobe and Y.H.
Mori, Int. J. Re~rig., vol. 15, No. 3 (1992~, pgs.
137 - 142. Proc. Inter. SQC. Ener~y Convers. ~nq.
.~ Con~!, Akiya et al., 1991, 26th~6) 115-119 used two unspecifie~ surfactants in concentrations up to 500 ppm to enhance the rate of formation of the clathrate from a water ~ dichloro-1-fluoro~thane cooling medium.
., How~v~r, for the known guQst molecules relativ~ly l~rge quantities of ~ur~actant have been u~Qd (up ts and in eXcQss of 1000 ppm) and so~e of the guest ~olecule will a~sociat~ with the urfaetant inst2ad o~ forming a clathrat~ wlth ~atex. This decr~as~ khe ef~iciency of ~ha th~rmal en~rgy storage system.
~rior to the present inv~nti~n ther~ has been no teaching in the art of how to sQlect a surfactant for a particular cooling medium or how to determine the amsunt of ~urf~ctant which will in~urQ opti~u~ mixing ~ with a mlni~u~ of gue~t molecul~ a~ oci~tion.
t~ , 25 Furth~rmore, many of th9 guest mol~cul~ presently b~ing u~d ~re CFC ~uch as trichloro~luoromethane (CYC-ll). Th~ use o~ the~ eo~pound~ i~ beeoming di ~avor~d b¢eau~e o~ the detr~m~ntal ef~eet to the ozone layor. Thu~ it i9 a goal o~ th~ pre~ent invention to ~ind a ~oolng mediu~ wh~eh pO3~5 less of a thr~at to th~ ozone }ayer. Halohydroearbons such as HCFC-141~b) whieh eontain hydrog~n, and are believed to po8e le3s o~ ~ threat to the ozon~ layer, and are thus propo ed a8 ~he guest ~olecule in elathra~e formation aeeording to the present invention.
~,, ".
~ WO93/~Y2 PCT/~S92/~
I~RO~:D COOLIN~ P~EI)IlJM FOR IJ8~ l A
., T~R~ ENERGY 8TORAG~ ~Y8?EM
~ This application is a continuatisn-in-part of `,5 Application Serial No. 722,428, filed on June 27, 1992.
. B~ck~Qun~ Q~_~h~ Invent on Thermal energy storage 5ystems contain a`cooling ~ medium, which is frozen during the off peak, evening r hours. During ~he daytime, heat from the s~rrounding .~ 1~ area is us~d to ~elt the cooling mediu~. The ramoval of heat to drive the decomposition causes the surrounding ar~a to b~come cool~r.
U.S. Patent No. 4,540,501 discloses a the ~ al energy stor~ge system which u~es clathrates as the cooling ~ediu~. Clathrates are hydrates which use a non-sto~chio~etric number o~ uater molecules per guest molecule. Th~ guest moleculQ f~lls th~ interior of the lattice, stabilizing the clathrat~. This stabilization allows the watex lattic~ ~ructure to form at te~peratures si~nificantly higher than the temperature of ice fo~mation (0C). The ~uest ~ol~cul~ must be highly insoluble in water, and must have a molecular ~ize which is 1~8 than 7 ~.
The halogenated hydrocarbons which are used as ~he gue~t ~ol~cul~ are not water ~i~cible. Clathrates will not for~ unle~s the guest ~nd ~os~ (lat~ice) co~psund3 ~r~ in contact. In an ~ttempt to bri~g the gUB~t mol~cul~ and wat~r into closer contact, v~rious ~ur~n~tant~ bava been add~d. U.S. Patent No. 4,540,501 di~close~ using a nonionic ~luoro~ur~actant having the chemical ~onmula F(CF2CF2) ~-~CH2cH20 (CH2~H20) 0~ when the gue3t molecule i~ a refrigerant cho~en fro~ brominated, chlorinated ~n~ ~luorinated hydrocarbsns including CCl2F2, CCl3P, CBr~3, CHClzF~ CHClF2, CH~ClF and CH3CClF2.
U.S. Patent No. 4,821,79~ disclo~es the ~SR Or Zonyl~
Plsrosur~actants in amounts between 1 to 5000 ppm gener lly, and th~ use o~ Zonyl FSN with ~ W~93/ ~ 12 PCT/US92/0~
...
trichlorofluoromethane in the ~mount of about 200 to 300 ppm. Zonyl9 Fluorosurfactant and Unidyne DS-401 have been added to water-l,l,l-tetrafluoro~thane clathrate forming thermal energy storage medium in - 5 Foxma~ion of Gas Hydrate or I~e ~y ~i~ect-Contact Eva~ora~ion of CFC Alternatives, F. Isobe and Y.H.
Mori, Int. J. Re~rig., vol. 15, No. 3 (1992~, pgs.
137 - 142. Proc. Inter. SQC. Ener~y Convers. ~nq.
.~ Con~!, Akiya et al., 1991, 26th~6) 115-119 used two unspecifie~ surfactants in concentrations up to 500 ppm to enhance the rate of formation of the clathrate from a water ~ dichloro-1-fluoro~thane cooling medium.
., How~v~r, for the known guQst molecules relativ~ly l~rge quantities of ~ur~actant have been u~Qd (up ts and in eXcQss of 1000 ppm) and so~e of the guest ~olecule will a~sociat~ with the urfaetant inst2ad o~ forming a clathrat~ wlth ~atex. This decr~as~ khe ef~iciency of ~ha th~rmal en~rgy storage system.
~rior to the present inv~nti~n ther~ has been no teaching in the art of how to sQlect a surfactant for a particular cooling medium or how to determine the amsunt of ~urf~ctant which will in~urQ opti~u~ mixing ~ with a mlni~u~ of gue~t molecul~ a~ oci~tion.
t~ , 25 Furth~rmore, many of th9 guest mol~cul~ presently b~ing u~d ~re CFC ~uch as trichloro~luoromethane (CYC-ll). Th~ use o~ the~ eo~pound~ i~ beeoming di ~avor~d b¢eau~e o~ the detr~m~ntal ef~eet to the ozone layor. Thu~ it i9 a goal o~ th~ pre~ent invention to ~ind a ~oolng mediu~ wh~eh pO3~5 less of a thr~at to th~ ozone }ayer. Halohydroearbons such as HCFC-141~b) whieh eontain hydrog~n, and are believed to po8e le3s o~ ~ threat to the ozon~ layer, and are thus propo ed a8 ~he guest ~olecule in elathra~e formation aeeording to the present invention.
~,, ".
~ WO93/~Y2 PCT/~S92/~
2 ~ 3 ~
..,.
Descrip~i~n_Qf the Fi~u~e FIGURE 1 shows the relationship between the surfa~tant concentration and the sur~ace tension of , wat~r for the surfactant D~SC~.
- 5 Figure 2 shows the relation~hip between surfactant concentra~ion (DRSC~) and the interfacisl tension for l,l-dichlo~o-~-fluoroethane/wat~r 801ution.
- Detailed D~s~iDtion of the nv~ntion .
` ~The pre nt invention pro~des a cooling medium for ug2 in a ~her~al en~rgy tor~ge system comprising wat~r, a gu~t ~olecule ~nd a ~urfactant having a critical micelle concentration in an ~ount les~ than about ~wic~ th~ cr~tical micell~ concentration.
Pr~ferably ~h~ eriti~al ~icell~ conc~ntration i less than about lxlO'~ and mor~ pre~r~bly b~ween lx10-4M
and lxlO'q~. A thermal energy ~tor~ge uni~ which uses the cooling ~diu~ and a proG~s ~or u~ing the thermal ; energy storag~ unit ara also di~clo~ed.
The gu~st ~olecules Or ~he present in~ention may be any compound capabl~ o~ forming a cl~thra~ with ~ter.
Suitabl~ gues~ moleculas g~nerally hav~ an average diameter o~ le~s than about 7 A. Pr~f~rably, ~he guest molQcul~ re~rigerant salQctQd fro~ the group consistin~ o~ hydrochlorofluorocarbon~, hydro~luorocarbon~, and mixtur~3 th~reo~. Exa~ples of pr~orr~d ~ydrochloro~luorocarbon gu~3t molecules includs l-~luoro-1,1-dichloro~thane, 2nd chlsrodi~luoromethane. Exa~plQs o~ prQ~erred hydro~luorocarbon gue3t mol~cul~ include ~,1,1,2-tetra~luoroethane, 1,1,l-tri luoro~than~, di~luororm~th~ne, p~ntaflusro~thane, ~nd 1,?-dl~luoro~thana. ~he con~iguration o~ th~ th~r~al ~n~rgy storag~ gy~t~ o~ thB pr~s~nt inv~ntion is the similar to ~hat o~ U.S. patsn~ No. 4,540,501.
~ W0~3/~X P~T/~2~
.....
~ ~lii3~1 ~ . 4 ;~ To form a clathrate the guest molecule and water must be dissimilar and be in contact with each other.
~` the more intimate the contact, the more efficient the clathrate formation will be. Accordingly, emulsions of water and the guest molecule are highly desirable~
Cla~hra~es of the pre3ent in~en~ion ~re formed from the guest molecule, and water. Depending on the size of the guest molecule between 5 to 17 water molecules per -1 guest molecule are needed to ~orm a clathrate.
Preferably the amount of sach the guest molecùle and water is at 12ast equal to the ratio necessary to form clathrate. ~ore pr~farably, an 8XC~SS of water is used to ~aintain a -~lurry, and en~ure con~inuous a~d e~ficient h~t transfer. ~or exampl~, where HCFC-141(b~ is u~ed, 20 moles of wat~r is used for each 1mol~ o~ HCFC-141(b).
The concentration of fre~ surfactant in water af~ects th~ properties of th~ ~ter and particularly the ~uxfacQ tenRion, which i shown ~or DRSC~ in Figure 1. For mu}tipha~ syst~s, such ~s th~ guest molecule/w~ter mixtur~s which ar~ u ed in thermal energy storage systems th~ intQr~acial tansion between the gue3t molocule and water ~ay b~ mea~ured. The er~ect o~ DRSC at varying concentrations on a 1,1-, 25 d~chloro~ luoroethane/water i8 shown in Fiyure 2.
Th~ pr~psrtie~ of both solution chang~ rapidly b~tween about 25 ppm and a~out 125 ppm. B~yond that rang~ of conc~ntration, propQr~ies changa ~ora gradually. This narrow concentratîon range in which prop2rtie~ change rapidly is c~lled th~ critical ~icells concentration or cmc. A~t~r the cmc has be~n Qxc~Qd~d w~ter surface tension dQcreasQ only ~lightly by adding more sur~actant~ Because water-guest moleculs mixing increas~3 a3 the ~urf ace tension o~ water decreases, maximum water-guest molecule mixing i8 achiev~d n~ar :`'~ `i ;~: .l, .` 1 WO 93/00~1~ Prr/u~g2/o53~i8 3 ~
''`, , the cmc. Moreover, after about 200 ppm (twice the cmc~
~-i of the DRSC9 surfactant has been added there is virtually no change in ei~her the surface or ~: interfacial tension. Thus, regar~less of what . 5 surfactant i5 used, the optimum concentra~ion of surfactant necessary ~o provide maximum ~ixing is not gxeater th~n about twice ~ha critical micslle concentra~ion, preferably l~ss th~n about 1.5 times the c~c and most prefer~bly le~s th~n about the cmc. By . 10 - limitin~ th~ amount of surfactant u~d to less than , . ..
. about twice the cmc it is possible to use small amounts~s o~ surfactants, e~pecially if the critical micelle . concentration is s~all (les~ ~h~n abou~ 10-3M).
Each ~ur~actant ha~ a uniqu~ cm~, whi~h depends upon its ~tru~turQ. G~nQrally ~urfactants ~ith longer . hydrocarbon chains havs lower critic~l micell~
conc~n~ration~. The low~r th~ c~c, the 1~ surfactant i~ neeassary to achi~ve ~axi~um mixing. Thu~, pr~f~rably surfactants of ~h~ pr~l~nt invention have critical mic~ concsntrations w~ich ~r~ be}ow lxlO-~M, and pr2ferab1y..b4tw~n ~xlO-~ and.lxlO~~M. Critical :~ micelle conc~ntrations ~or many ~urf~ctants are listed ; in "cr~tical Mic~lls Concentrations o ~queous Suxf~ctant Syste~ by MuX~r~ and My3~1~ [NAt. Stand.
R~f. D~ta S~r., Nat. Bur. ~tand. (U.S) 36, Feb. 1971.
Many way~ o~ d~t~rmining th~ c~c o~ 3urfactant~ are ; d~cribed by Mukerje~ et al. ~oraover, b~c use the . pres~nt invent$on providQ~ a l~rg~ number o~ ~uitable surf~ct~nt3, surfaet~ntQ which produc~ only gradual ~ 30 chang~s in sur~ac~ or inter~acial tension ov~x varying .~ sur~actan~ concentratisn3, ~nd thu~ ha~e poorly definedCmC-Q are no~ preferred. An example o~ a surfactan~
having a poorly de~ined c~c is Zonyl~ FSN.
Mos~ prs~erably, a ~urfactant having a cmc less than lxlO-qM is u~ed in an amount about equal to or ~,4, :`g ~ W093/~12 PCT/~S92/05 8 ~ ~
slightly in excess of the cmc. By choosing surfactants ha~ing low ~mcs and limiting the amount of surfactant to the c~c, inefficiencies du2 to gu~st molec~le association with the aggregated surfactant and S competition b~tween th~ surfactan~ and guest molecule ~ay be mini~iz~d. ~hen any non-polar substance is in contact with water, the wat~r ~o}~cules beco~e arranged or organiz~d in a clu~tçr around ~he non-polar ~oi~ty.
It is belieYed that clathrates are formed by th~
crystallization of this clust~r. Si~ilarly, ~hen a ~urfactant is pr@sent, water ~olecules clus~er around the sur~actant, forming surfactant aggr~gat~s. This co~petition between the potential guest molecules and surfacta~t molQcules for wat~r ~olacul~s d~crea es the amount of cl~hrat~ which can ~ for~ad with a given : amount o~ w~ter ~olecule~. ThUB ~t iS pr~ferable t~
~ini~izs the a~o~t o~ ~ur~ac~nt u~d.
In ~o~ ~ituation8, it ~ny b~ de~irabla to exc~ed the c~c in order ~o acheiva ~ particul~r ~f~ct. When the cmc is ~ow, the concentration of sur~actant may ~till be qui*e low ~s co~pared to convention~l sur~ctant conc~ntration even though it is above the cmc. Thus, thQ competition b2~w~en the sur~actant and tha gu~t mol~cule is proportionataly l~s~ ~ev~re, even : , 25 nt conc~ntr~tions ~hich are ~bov~ th~ cmc. Thus, aur~ctant~ with cr$tical mic~ concentrations below ~bout lXlO'k ar~ prefe~ed.
An Qx~ple o~ a surf actant species uhic:h has been ~ound partic~larly e~fecti~a ~n ~nhancing emul~ion formation where HCFC-141(b) is u~ed as t~ guest molecule i~ surfactant DRSC (alkyl dimethyl benzyl ammonium salt Or oc~aphenyl pho~phoric acid ~
commQrcially aYailabl~ fro~ Allied-Signal, Inc.). The physical propQrtie~ of DRSCo ar~ 8hOWrl in Table 1, 3 5 below.
~' W~ ~3/00412 PCrlUS92/~36 ., 2~ 31 .. ..
.
Table 1 I .; _ -- - . _ _.
Surf actant BP Specif ic Vapor Sol O in H20 .j~ ( F) Gravity Press . at 2 5 C
. . ~ 2 5 - C mm Hgê 2 5 - C
DRSC~ 180~ 0 ~ 95 <1 Sol .
~ o ~ Hg ~ - , . .
The cmc for DRSC~ is between about 50 ppm and about 125 ppm, which was determined by measuring the sur~ace tension of water as increa~ing amounts o~ DRSC~
were added! Thus, less than a~out 200 pp~ of the DRSC~
is raquired to insure emulsion formation between water and ~he chosen guest molecul~. Prefer~bly less than 100 ppla DRSC 19 is used. The losses of the gu~st ms~lecule (HC:P'C 141(b)) due to as. ociation with the sur~ ac~ant d~ ::rea-ce as the aDlount of suriEactant us d is ..
dec~!aas~d~ ther~by incraasing t~ ~f~ici~ncy o~
clathrate formation, and ~ ther~al energy storage system.
Agitation is not required ts ensure clathrate formation of th~ cooling mediu~ o~ the ~resent invention. However, agitation may be used to further 2 0 encourag~ clathrate or~ation ~
Emul~ion~ f or~ed ~ccording to the present inYention ~r~ 3tabl~ at roo~a t~mp~rature, and remain eDIul~ d ~or as long 213 two d~ys ~ith mini~um lnag~. Th~ clathrat0 is form~d in a ~ rage tank/crystall~z~r. The pr~sure in the c:~stallizer i5 decre~d by me~ns of a co~pre~sor, ~ described in moxe d~tail in U.S. Patent No. 4,5~0,501, and heat is removed unt~l the temperature o~ ~ormation f or the clathratg is reach~d. The prsssure ~nd te~perature are 3 0 maintained until ~11 sf t~e clathrate i5 f ormed . The clathrate is circulated through the heat exchanger via the recirculatisn loop. Clathrate i5 circulated through the heat exchanger, decompos~d, and the water WQg3~12 PCT~US92/~5 `-;
~ 3 ~ 8 and guest molecule mixture is returned to the crystallizer.
Example . 5A solu~ion of DRSC~ ha~ing a concentration of 25 ppm was ~ade by adding 0.025 ml of DRSC~ to 1 li~er of w~ter~ 300 ml o~ the surfactant solution was poured into a 500 ml jar, and 30 ml of 141(b) was added. The jar was capped and shaXen vigorously ~or 1 minute. An emulsion f~r~ed in the jar, which W~5 stable and r~main~d emulsi~ied for two days without noticeable drainage.
The se led jar was placed in a fr~ezer at 40F. A
considerablQ amount of snow~lak~-like cryst~ls (the ~5 ~lathrat~) wa3 observsd in the ~ar a~ter 1.0 hour. The jar was lef~ in the ~r~ezQr overnight. By morning cry~tal$ had ~or~d in ~he ~ar, indicating that cla~hrate had ~orm~d.
,Accordingly, DRSCo, which h~ a lo~ emc, is a suitabl~ aid for clatbrat~ formation, for~ing clath-;ate .~ at low surfactant concentration~. Becau~ only a small amount of sur~actant i5 required (tWiCQ the cmc or 1~8s ), thers i~ less surfactant to as~ociate with the guQst molecule (here HCFC-141(b)), and thu~ the clathrat~ ~ormation proc~ss, and the ther~al en~rqy storag~ syst~m are mor~ e~ici~nt.
..,.
Descrip~i~n_Qf the Fi~u~e FIGURE 1 shows the relationship between the surfa~tant concentration and the sur~ace tension of , wat~r for the surfactant D~SC~.
- 5 Figure 2 shows the relation~hip between surfactant concentra~ion (DRSC~) and the interfacisl tension for l,l-dichlo~o-~-fluoroethane/wat~r 801ution.
- Detailed D~s~iDtion of the nv~ntion .
` ~The pre nt invention pro~des a cooling medium for ug2 in a ~her~al en~rgy tor~ge system comprising wat~r, a gu~t ~olecule ~nd a ~urfactant having a critical micelle concentration in an ~ount les~ than about ~wic~ th~ cr~tical micell~ concentration.
Pr~ferably ~h~ eriti~al ~icell~ conc~ntration i less than about lxlO'~ and mor~ pre~r~bly b~ween lx10-4M
and lxlO'q~. A thermal energy ~tor~ge uni~ which uses the cooling ~diu~ and a proG~s ~or u~ing the thermal ; energy storag~ unit ara also di~clo~ed.
The gu~st ~olecules Or ~he present in~ention may be any compound capabl~ o~ forming a cl~thra~ with ~ter.
Suitabl~ gues~ moleculas g~nerally hav~ an average diameter o~ le~s than about 7 A. Pr~f~rably, ~he guest molQcul~ re~rigerant salQctQd fro~ the group consistin~ o~ hydrochlorofluorocarbon~, hydro~luorocarbon~, and mixtur~3 th~reo~. Exa~ples of pr~orr~d ~ydrochloro~luorocarbon gu~3t molecules includs l-~luoro-1,1-dichloro~thane, 2nd chlsrodi~luoromethane. Exa~plQs o~ prQ~erred hydro~luorocarbon gue3t mol~cul~ include ~,1,1,2-tetra~luoroethane, 1,1,l-tri luoro~than~, di~luororm~th~ne, p~ntaflusro~thane, ~nd 1,?-dl~luoro~thana. ~he con~iguration o~ th~ th~r~al ~n~rgy storag~ gy~t~ o~ thB pr~s~nt inv~ntion is the similar to ~hat o~ U.S. patsn~ No. 4,540,501.
~ W0~3/~X P~T/~2~
.....
~ ~lii3~1 ~ . 4 ;~ To form a clathrate the guest molecule and water must be dissimilar and be in contact with each other.
~` the more intimate the contact, the more efficient the clathrate formation will be. Accordingly, emulsions of water and the guest molecule are highly desirable~
Cla~hra~es of the pre3ent in~en~ion ~re formed from the guest molecule, and water. Depending on the size of the guest molecule between 5 to 17 water molecules per -1 guest molecule are needed to ~orm a clathrate.
Preferably the amount of sach the guest molecùle and water is at 12ast equal to the ratio necessary to form clathrate. ~ore pr~farably, an 8XC~SS of water is used to ~aintain a -~lurry, and en~ure con~inuous a~d e~ficient h~t transfer. ~or exampl~, where HCFC-141(b~ is u~ed, 20 moles of wat~r is used for each 1mol~ o~ HCFC-141(b).
The concentration of fre~ surfactant in water af~ects th~ properties of th~ ~ter and particularly the ~uxfacQ tenRion, which i shown ~or DRSC~ in Figure 1. For mu}tipha~ syst~s, such ~s th~ guest molecule/w~ter mixtur~s which ar~ u ed in thermal energy storage systems th~ intQr~acial tansion between the gue3t molocule and water ~ay b~ mea~ured. The er~ect o~ DRSC at varying concentrations on a 1,1-, 25 d~chloro~ luoroethane/water i8 shown in Fiyure 2.
Th~ pr~psrtie~ of both solution chang~ rapidly b~tween about 25 ppm and a~out 125 ppm. B~yond that rang~ of conc~ntration, propQr~ies changa ~ora gradually. This narrow concentratîon range in which prop2rtie~ change rapidly is c~lled th~ critical ~icells concentration or cmc. A~t~r the cmc has be~n Qxc~Qd~d w~ter surface tension dQcreasQ only ~lightly by adding more sur~actant~ Because water-guest moleculs mixing increas~3 a3 the ~urf ace tension o~ water decreases, maximum water-guest molecule mixing i8 achiev~d n~ar :`'~ `i ;~: .l, .` 1 WO 93/00~1~ Prr/u~g2/o53~i8 3 ~
''`, , the cmc. Moreover, after about 200 ppm (twice the cmc~
~-i of the DRSC9 surfactant has been added there is virtually no change in ei~her the surface or ~: interfacial tension. Thus, regar~less of what . 5 surfactant i5 used, the optimum concentra~ion of surfactant necessary ~o provide maximum ~ixing is not gxeater th~n about twice ~ha critical micslle concentra~ion, preferably l~ss th~n about 1.5 times the c~c and most prefer~bly le~s th~n about the cmc. By . 10 - limitin~ th~ amount of surfactant u~d to less than , . ..
. about twice the cmc it is possible to use small amounts~s o~ surfactants, e~pecially if the critical micelle . concentration is s~all (les~ ~h~n abou~ 10-3M).
Each ~ur~actant ha~ a uniqu~ cm~, whi~h depends upon its ~tru~turQ. G~nQrally ~urfactants ~ith longer . hydrocarbon chains havs lower critic~l micell~
conc~n~ration~. The low~r th~ c~c, the 1~ surfactant i~ neeassary to achi~ve ~axi~um mixing. Thu~, pr~f~rably surfactants of ~h~ pr~l~nt invention have critical mic~ concsntrations w~ich ~r~ be}ow lxlO-~M, and pr2ferab1y..b4tw~n ~xlO-~ and.lxlO~~M. Critical :~ micelle conc~ntrations ~or many ~urf~ctants are listed ; in "cr~tical Mic~lls Concentrations o ~queous Suxf~ctant Syste~ by MuX~r~ and My3~1~ [NAt. Stand.
R~f. D~ta S~r., Nat. Bur. ~tand. (U.S) 36, Feb. 1971.
Many way~ o~ d~t~rmining th~ c~c o~ 3urfactant~ are ; d~cribed by Mukerje~ et al. ~oraover, b~c use the . pres~nt invent$on providQ~ a l~rg~ number o~ ~uitable surf~ct~nt3, surfaet~ntQ which produc~ only gradual ~ 30 chang~s in sur~ac~ or inter~acial tension ov~x varying .~ sur~actan~ concentratisn3, ~nd thu~ ha~e poorly definedCmC-Q are no~ preferred. An example o~ a surfactan~
having a poorly de~ined c~c is Zonyl~ FSN.
Mos~ prs~erably, a ~urfactant having a cmc less than lxlO-qM is u~ed in an amount about equal to or ~,4, :`g ~ W093/~12 PCT/~S92/05 8 ~ ~
slightly in excess of the cmc. By choosing surfactants ha~ing low ~mcs and limiting the amount of surfactant to the c~c, inefficiencies du2 to gu~st molec~le association with the aggregated surfactant and S competition b~tween th~ surfactan~ and guest molecule ~ay be mini~iz~d. ~hen any non-polar substance is in contact with water, the wat~r ~o}~cules beco~e arranged or organiz~d in a clu~tçr around ~he non-polar ~oi~ty.
It is belieYed that clathrates are formed by th~
crystallization of this clust~r. Si~ilarly, ~hen a ~urfactant is pr@sent, water ~olecules clus~er around the sur~actant, forming surfactant aggr~gat~s. This co~petition between the potential guest molecules and surfacta~t molQcules for wat~r ~olacul~s d~crea es the amount of cl~hrat~ which can ~ for~ad with a given : amount o~ w~ter ~olecule~. ThUB ~t iS pr~ferable t~
~ini~izs the a~o~t o~ ~ur~ac~nt u~d.
In ~o~ ~ituation8, it ~ny b~ de~irabla to exc~ed the c~c in order ~o acheiva ~ particul~r ~f~ct. When the cmc is ~ow, the concentration of sur~actant may ~till be qui*e low ~s co~pared to convention~l sur~ctant conc~ntration even though it is above the cmc. Thus, thQ competition b2~w~en the sur~actant and tha gu~t mol~cule is proportionataly l~s~ ~ev~re, even : , 25 nt conc~ntr~tions ~hich are ~bov~ th~ cmc. Thus, aur~ctant~ with cr$tical mic~ concentrations below ~bout lXlO'k ar~ prefe~ed.
An Qx~ple o~ a surf actant species uhic:h has been ~ound partic~larly e~fecti~a ~n ~nhancing emul~ion formation where HCFC-141(b) is u~ed as t~ guest molecule i~ surfactant DRSC (alkyl dimethyl benzyl ammonium salt Or oc~aphenyl pho~phoric acid ~
commQrcially aYailabl~ fro~ Allied-Signal, Inc.). The physical propQrtie~ of DRSCo ar~ 8hOWrl in Table 1, 3 5 below.
~' W~ ~3/00412 PCrlUS92/~36 ., 2~ 31 .. ..
.
Table 1 I .; _ -- - . _ _.
Surf actant BP Specif ic Vapor Sol O in H20 .j~ ( F) Gravity Press . at 2 5 C
. . ~ 2 5 - C mm Hgê 2 5 - C
DRSC~ 180~ 0 ~ 95 <1 Sol .
~ o ~ Hg ~ - , . .
The cmc for DRSC~ is between about 50 ppm and about 125 ppm, which was determined by measuring the sur~ace tension of water as increa~ing amounts o~ DRSC~
were added! Thus, less than a~out 200 pp~ of the DRSC~
is raquired to insure emulsion formation between water and ~he chosen guest molecul~. Prefer~bly less than 100 ppla DRSC 19 is used. The losses of the gu~st ms~lecule (HC:P'C 141(b)) due to as. ociation with the sur~ ac~ant d~ ::rea-ce as the aDlount of suriEactant us d is ..
dec~!aas~d~ ther~by incraasing t~ ~f~ici~ncy o~
clathrate formation, and ~ ther~al energy storage system.
Agitation is not required ts ensure clathrate formation of th~ cooling mediu~ o~ the ~resent invention. However, agitation may be used to further 2 0 encourag~ clathrate or~ation ~
Emul~ion~ f or~ed ~ccording to the present inYention ~r~ 3tabl~ at roo~a t~mp~rature, and remain eDIul~ d ~or as long 213 two d~ys ~ith mini~um lnag~. Th~ clathrat0 is form~d in a ~ rage tank/crystall~z~r. The pr~sure in the c:~stallizer i5 decre~d by me~ns of a co~pre~sor, ~ described in moxe d~tail in U.S. Patent No. 4,5~0,501, and heat is removed unt~l the temperature o~ ~ormation f or the clathratg is reach~d. The prsssure ~nd te~perature are 3 0 maintained until ~11 sf t~e clathrate i5 f ormed . The clathrate is circulated through the heat exchanger via the recirculatisn loop. Clathrate i5 circulated through the heat exchanger, decompos~d, and the water WQg3~12 PCT~US92/~5 `-;
~ 3 ~ 8 and guest molecule mixture is returned to the crystallizer.
Example . 5A solu~ion of DRSC~ ha~ing a concentration of 25 ppm was ~ade by adding 0.025 ml of DRSC~ to 1 li~er of w~ter~ 300 ml o~ the surfactant solution was poured into a 500 ml jar, and 30 ml of 141(b) was added. The jar was capped and shaXen vigorously ~or 1 minute. An emulsion f~r~ed in the jar, which W~5 stable and r~main~d emulsi~ied for two days without noticeable drainage.
The se led jar was placed in a fr~ezer at 40F. A
considerablQ amount of snow~lak~-like cryst~ls (the ~5 ~lathrat~) wa3 observsd in the ~ar a~ter 1.0 hour. The jar was lef~ in the ~r~ezQr overnight. By morning cry~tal$ had ~or~d in ~he ~ar, indicating that cla~hrate had ~orm~d.
,Accordingly, DRSCo, which h~ a lo~ emc, is a suitabl~ aid for clatbrat~ formation, for~ing clath-;ate .~ at low surfactant concentration~. Becau~ only a small amount of sur~actant i5 required (tWiCQ the cmc or 1~8s ), thers i~ less surfactant to as~ociate with the guQst molecule (here HCFC-141(b)), and thu~ the clathrat~ ~ormation proc~ss, and the ther~al en~rqy storag~ syst~m are mor~ e~ici~nt.
Claims (22)
1. A thermal energy storage system having a crystallizer compartment containing a clathrate forming cooling medium, a means for circulating the cooling medium through a heat exchanger and a means for lowering the temperature in said crystallizer compartment; the improvement comprising:
using as said clathrate forming cooling medium a mixture comprising water, a guest molecule and a surfactant in an amount which is less than about twice the upper value of said surfactant's critical micelle concentration range; wherein said amount is about 200 ppm or less.
using as said clathrate forming cooling medium a mixture comprising water, a guest molecule and a surfactant in an amount which is less than about twice the upper value of said surfactant's critical micelle concentration range; wherein said amount is about 200 ppm or less.
2. The thermal energy storage system of claim 1 wherein said surfactant is used in an amount up to about said surfactant's critical micelle concentration.
3. The thermal energy storage system of claim 1 wherein said critical micelle concentration is between about 1x10-4M and about 1x10-8M.
4. The thermal energy storage system of claim 1 or 3 wherein said guest molecule is selected from the group consisting of hydrochlorofluorocarbons and hydrofluorcarbons.
5. The thermal energy storage system of claim 1 or 3 wherein said guest molesule is a hydrochlorofluorocarbon s?
from the group consisting of 1,1-dichloro-1-flurorethan?
chlorod1fluoromethane.
from the group consisting of 1,1-dichloro-1-flurorethan?
chlorod1fluoromethane.
6. The thermal energy storage system of c?
wherein the surfactant is alkyl dimethyl benz?
octaphenyl phosphoric acid.
wherein the surfactant is alkyl dimethyl benz?
octaphenyl phosphoric acid.
7. The thermal energy storage system ?
wherein the amount of said surfactant used is le?
ppm.
wherein the amount of said surfactant used is le?
ppm.
8. A process for thermal energy storage wherein a cing medium is induced to form a clathrate, and heat is removed from the surroundings to melt the clathrate; the improvement comprising:
using as said cooling medium a mixture comprising water; a guest molecule and a surfactant having a critical micelle concentration less than about 1x10-3M in an amount less than twice the upper value of said critical micelle concentration range;
wherein said amount is about 200 ppm or less.
using as said cooling medium a mixture comprising water; a guest molecule and a surfactant having a critical micelle concentration less than about 1x10-3M in an amount less than twice the upper value of said critical micelle concentration range;
wherein said amount is about 200 ppm or less.
9. The process of claim 8 wherein said surfactant has a critical micelle concentration between about 1x10-4M and about 1x10 8M.
10. The process of claim 9 wherein said surfactant is alkyl dimethyl benzyl ammonium salt of octaphenyl phosphoric acid.
11. The process of claim 18 wherein the amount of said surfactant used is less than 200 ppm.
12. A cooling medium for use in a thermal energy storage system comprising water, a guest molecule and a surfactant having a critical micelle concentration in an amount is less than about twice the upper value said critical micelle concentration range;
wherein said amount is about 200 ppm or less.
wherein said amount is about 200 ppm or less.
13. The cooling medium of claim 22 wherein said critical micelle concentration is less than about 1x10-3M.
14. The cooling medium of claim 23 wherein said critical micelle concentration is between about 1x10-4M and about 1x10-?M.
.
.
15. The cooling medium of claim 24 wherein the surfactant is alkyl dimethyl benzyl ammonium salt of octaphenyl phosphoric acid.
I CLAIM:
I CLAIM:
16. A thermal energy storage system having a crystallizer compartment containing a clathrate forming cooling medium, a means for circulating the cooling medium through a heat exchanger and a means for lowering the temperature in said crystallizer compartment; the improvement comprising:
using as said clathrate-forming cooling medium a mixture comprising water, a guest molecule and a surfactant having a critical micelle concentration and the amount of surfactant is less than twice the upper values of the surfactant's critical micelle concentration range; wherein the surfactant is not Zonyl FSN.
using as said clathrate-forming cooling medium a mixture comprising water, a guest molecule and a surfactant having a critical micelle concentration and the amount of surfactant is less than twice the upper values of the surfactant's critical micelle concentration range; wherein the surfactant is not Zonyl FSN.
17. The thermal storage system of claim 16 wherein the critical micelle concentration of the surfactant is less than the lower value of the critical micelle concentration of Zonyl FSN.
18. The thermal energy storage system of claim 16 wherein said surfactant's critical micelle concentration is less than about 10-3M.
19. The thermal energy storage system of claim 16 wherein said critical micelle concentration is between about 1x10-4M and about 1x10-8M.
20. A process for thermal energy storage wherein a cooling medium is induced to form a clathrate, and heat is removed from the surroundings to melt the clathrate; the improvement comprising:
using as said cooling medium a mixture comprising water, a guest molecule and a surfactant having a critical micelle concentration less than about 1x10-3M in an amount less than twice the upper value of said critical micelle concentration range.
using as said cooling medium a mixture comprising water, a guest molecule and a surfactant having a critical micelle concentration less than about 1x10-3M in an amount less than twice the upper value of said critical micelle concentration range.
21. The process of claim 20 wherein said surfactant has a critical micelle concentration between about 1x10-4M and about 1x10-?M.
22. A cooling medium for use in a thermal energy storage system comprising water, a guest molecule and a surfactant having a critical micelle concentration range with an upper limit of less than 1x10-3M and present in an amount is less than about twice said critical micelle concentration range.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/722,428 | 1991-06-27 | ||
| US07/722,428 US5159971A (en) | 1991-06-27 | 1991-06-27 | Cooling medium for use in a thermal energy storage system |
| US89972292A | 1992-06-23 | 1992-06-23 | |
| US07/899,722 | 1992-06-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2111831A1 true CA2111831A1 (en) | 1993-01-07 |
Family
ID=27110592
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2111831 Abandoned CA2111831A1 (en) | 1991-06-27 | 1992-06-24 | Improved cooling medium for use in a thermal energy storage system |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0591430A1 (en) |
| JP (1) | JPH06508679A (en) |
| AU (1) | AU659663B2 (en) |
| CA (1) | CA2111831A1 (en) |
| WO (1) | WO1993000412A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1999029800A1 (en) * | 1997-12-11 | 1999-06-17 | Alliedsignal Inc. | A cold pack comprising an aqueous clathrate composition |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4332690A (en) * | 1979-04-23 | 1982-06-01 | Mitsubishi Denki Kabushiki Kaisha | Heat storage system comprising a phase change medium and a nucleating agent |
| US4540501A (en) * | 1984-09-12 | 1985-09-10 | The United States Of America As Represented By The United States Department Of Energy | Gas hydrate cool storage system |
| US4821794A (en) * | 1988-04-04 | 1989-04-18 | Thermal Energy Storage, Inc. | Clathrate thermal storage system |
| WO1993004139A1 (en) * | 1991-08-27 | 1993-03-04 | Allied-Signal Inc. | Improved thermal energy storage system and process for thermal energy storage and transfer |
-
1992
- 1992-06-24 CA CA 2111831 patent/CA2111831A1/en not_active Abandoned
- 1992-06-24 EP EP92914815A patent/EP0591430A1/en not_active Withdrawn
- 1992-06-24 AU AU22956/92A patent/AU659663B2/en not_active Ceased
- 1992-06-24 JP JP5501658A patent/JPH06508679A/en active Pending
- 1992-06-24 WO PCT/US1992/005368 patent/WO1993000412A1/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| JPH06508679A (en) | 1994-09-29 |
| AU2295692A (en) | 1993-01-25 |
| WO1993000412A1 (en) | 1993-01-07 |
| EP0591430A1 (en) | 1994-04-13 |
| AU659663B2 (en) | 1995-05-25 |
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