- Email: [email protected]
Ice storage system using water–oil mixture Discussion about influence of additive on ice formation process
International Journal of Refrigeration 25 (2002) 11–18 www.elsevier.com/locate/ijrefrig
Ice storage system using water–oil mixture Discussion about influence of additive on ice formation process Koji Matsumoto a,*, Yasuo Shiokawa b, Masashi Okada c, Tetsuo Kawagoe d, Chaedong Kang e a
Department of Precision Mechanics, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo, 112-8551 Japan b Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo, 112-8551 Japan c Department of Mechanical Engineering, Aoyama Gakuin University, 6-16-1 Chitosedai, Setagaya-ku, Tokyo, 157-8572 Japan d 757-4 Katakurachou, Kanagawa-ku, Yokohama, 221-0861 Japan e School of Mechanical and Aerospace Engineering (BK21), Seoul National University, #2305, 136-1 dong San 56-1, Shillim-Dong, Kwanak-Gu, Seoul 151-742, Korea Received 22 December 2000; received in revised form 22 February 2001; accepted 22 February 2001
Abstract Ice storage is one technique for effective use of thermal energy. So, many studies on slush ice as a thermal storage material have been done. We have also been studying a suspension (slush ice) made from an oil-water mixture by cooling and stirring. From our study results, it was found that an additive having both an amino group (-NH2) and a silanol group (-SiOH) was essential to form a suspension with high IPF without adhesion of ice to the cooling wall. Moreover, ice particles formed in the suspension were dispersed and granular, and did not stick to each other. In the present paper, we carried out experiments to clarify the characteristics of the suspension formation process. From a thermal analysis of the substance formed in the suspension by difference scanning calorimeter (DSC), it was found that the substance was not ice but a compound of ice and additive. Then, at a very small depression of freezing point (about 7 C) all water in the mixture could be frozen by using the additive. # 2001 Elsevier Science Ltd and IIR. All rights reserved. Keywords: Ice storage; Water; Oil; Mixture; Ice; Formation
Accumulation thermique sous forme de glace, utilisant un me´lange eau/huile Re´sume´ Le stockage de glace est une technique permettant l’utilisation efficace de l’e´nergie thermique et un grand nombre d’e´tudes ont e´te´ effectue´es afin d’approfondir les proprie´te´s des coulis de glace dans cette application. Les auteurs ont e´tudie´ une suspension (coulis) compose´e d’un me´lange d’huile et d’eau obtenu par un processus de refroidissement sous agitation. Cette e´tude a montre´ que l’ajout d’un additif posse´dant un groupe amine (-NH2) et un groupe hydroxyde de silicium (-SiOH) s’ave`re essentiel afin de cre´er une suspension a` IPF e´leve´ sans adhe´sion de la glace aux parois refroidissantes. En outre, les particules de glace qui se forment dans la suspension sont disperse´es et granulaires et n’ont pas tendance a` former des amas. Cette communication de´crit en particulier le processus de formation de la suspension. Les * Corresponding author. Tel.: +81-3-3817-1837; fax: +81-3-3817-1828. E-mail addresses: [email protected] u.ac.jp (K. Matsumoto), [email protected] (Y. Shiokawa), [email protected] (M. Okada), [email protected] (C. Kang). 0140-7007/01/$20.00 # 2001 Elsevier Science Ltd and IIR. All rights reserved. PII: S0140-7007(01)00024-X
12
K. Matsumoto et al. / International Journal of Refrigeration 25 (2002) 11–18
auteurs ont utilise´ une analyse thermique de la substance forme´e dans la suspension, a` l’aide de la calorime´trie par analyse diffe´rentielle : cette e´tude a montre´ que la substance forme´e est un me´lange de glace et d’un additif. Graˆce a` cette substance, on obtient une faible de´pression du point de fusion (environ 7 C) et on peut congeler toute l’eau dans le me´lange graˆce a` la pre´sence de l’additif. # 2001 Elsevier Science Ltd and IIR. All rights reserved. Mots cle´s : Accumulation thermique ; Eau ; Huile ; Me´lange ; Glace ; Formation
1. Introduction From the viewpoint of effective use of thermal energy, ice storage systems have attracted interest recently because of their high storage capacity per unit volume. Ice storage is classified into two types, static and dynamic. The dynamic type in particular has some excellent characteristics, and there have been many proposals for a formation technique for slush ice to be used as the thermal storage material. As slush ice has fluidity, a large amount of cooling energy can be transported with less pumping work. The dynamic type system can respond quickly to changes in the heat load because the ice particles have a large surface area. The technique where slush ice is formed by dissolution of the super-cooling state of solution is fairly widely used. Recently new slush ice formation techniques have been developed. The techniques are that ice formed on a cooling surface from ethylene glycol aqueous solution is removed by buoyancy force [1,2] or oscillation [3]. The values of the ice packing factor (IPF) in both techniques are, however, small. The authors also studied a new method of forming slush ice [4]. In this method a small amount of additive (silane-coupler) is added to a mixture of 10 vol.% siliconeoil and 90 vol.% water and the additive dissolves in water. The mixture (solution) was cooled with stirring in a vessel and changed into an ice-oil and water suspension. The suspension is also slush ice, which did not adhere to the cooling wall and had a high IPF. The ice-oil suspension remained in a state consisting of dispersed small particles even after the suspension was preserved for a long time in a freezing condition. In the present report, the same mixture as that described in the previous report [4] was cooled in a vessel with stirring and changed into a suspension. After the relationship between concentration of additive and freezing temperature of solution has been clarified, we discuss the measurement results for temperature, concentration of the suspension and mass of ice formed in the suspension, and we clarify the influence of additive on the ice formation process.
2. Experimental procedure 2.1. Experimental apparatus A schematic diagram of the experimental apparatus is shown in Fig. 1. The apparatus, experimental conditions and procedure are the same as used in the previous
report [4]. From this report [4], the use of a polymethylpentene (PMP) beaker as the experimental vessel was decided upon as the ice in the suspension hardly adheres to its inner wall at all. The inside diameter and height of the PMP beaker were 85 and 118 mm, respectively, which is a quarter of the beaker size in the previous report [4]. The diameter of the stirring wing was reduced to 60 mm with the change of beaker size. In order to cool the mixture, the beaker containing the mixture was soaked directly in a cold-type thermostatic bath filled with brine consisting of ethylene–glycol solution. T-type thermocouples of diameter 0.2 mm were used to measure temperature. The temperature of suspension was measured at about 3 cm below the suspension surface at the center of the beaker. The brine temperatures were measured at two positions in the thermostatic bath. The concentration of solution was measured by a refracting densitometer. 2.2. Water-additive solidus curve We thought that the relationship between the concentration of additive and freezing temperature of the solution had to be obtained in order to be able to consider the influence of the additive on the ice formation process. Therefore, an experiment for obtaining the water-additive solidus curve was carried out. In the previous report [4], it was found that a silane-coupler with an amino group (-NH2) which is a hydrophilic substance was effective as the additive. Typical examples of a hydrophilic substance are g-aminopropyltrimethoxy silane or g-aminopropyltriethoxysilane. The difference between them in the freezing process characteristics is very small. Therefore, in the present study, g-aminopropyltriethoxysilane was used and is referred to as the additive from now on. At first, a solution with a pre-determined initial concentration of additive was put into a test tube, and then the test tube was soaked directly in a cold-type thermostatic bath and cooled. The solution was periodically stirred during cooling in order to make the temperature distribution of the solution uniform. The temperature in the center part of solution was measured. After the solution had reached the maximum extent of super-cooling degree, the super-cooling state of the solution was dissolved. The temperature immediately after dissolution of super-cooling was defined as the freezing temperature of solution for the initial concentration. Similar experiments with various initial concentrations were carried out. In
K. Matsumoto et al. / International Journal of Refrigeration 25 (2002) 11–18
13
Fig. 1. Experimental apparatus. Fig. 1. Sche´ma de l’appareil expe´rimental.
order to confirm reproducibility of these experiments, experiments for each initial concentration were repeated several times.
ship between temperature and the amount of formed ice was clarified.
2.3. Ice formation experiment
3. Experimental results and discussion
A 450 cc mixture composed of 90 vol.% tap water and 10 vol.% silicone oil (kinematic viscosity= 110 4 m2/s, specific gravity=0.965 at 25 C [6]) was put into the PMP beaker. A 18cc (4 vol.% of the mixture) of additive (specific gravity=0.94 at 25 C [6]) was then added to the mixture. The additive dissolved in water making the mixture into a solution. The brine temperature was set to 10 C. The beaker containing the solution was soaked directly in a cold-type thermostatic bath and cooled with stirring, causing the solution to change into an ice– water–oil suspension. After the temperature of suspension reached a predetermined value, the suspension was transferred to another vessel (separation vessel) made of resin. This vessel was cylindrical in shape and tapered downward. In order to separate ice from the suspension, a net was stretched to the bottom of vessel. Separation was carried out for 60 min by vibrating the vessel. A mass of separated ice was equal to the amount of ice formed for the pre-determined temperature. Another vessel was set under the separation vessel in order to receive the separated liquid. The separation apparatus was placed in a cold-type thermostatic box which was set to 1 4 C as the formed ice was then prevented from melting or the solution was prevented from freezing. The amount of formed ice was measured for various temperatures and relation-
The relationship between the mass concentration of additive and freezing temperature is shown in Fig. 2. The * symbol in the figure represents the average value of several measurements for a certain concentration. The reproducibility of measurement values for each concentration was good. The solid line is a least square approximation of the average values. The suspension was able to be separated into ice and liquid. The relationship between separated ice (formed ice) and temperature is shown in Table 1. Measurements were carried out twice for each temperature, and the reproducibility of measurements was good. The 1.3 C value corresponds to the freezing temperature for the initial concentration of mixture (solution). By melting the ice, it was found that the ice was separated into two layers corresponding to ‘‘other substance’’ and water, respectively. Although it was thought that the water contained some additive, the amount of additive was neglected because it was very small. The liquid was also separated into two layers corresponding to ‘‘other substance’’ and water, respectively. The amount of additive in the water was also neglected in this case. Although ‘‘other substances’’ in the separated ice and liquid might also have contained some additive, both ‘‘other substances’’ were regarded as oil because the amount of additive was very small. The value of ‘‘other substance’’ in the liquid can
14
K. Matsumoto et al. / International Journal of Refrigeration 25 (2002) 11–18
Table 1 Amount of formed Ice (formed substance) Tableau 1 Quantite´ de glace forme´e (substance forme´e) Temperature ( C) 1.3
1.5
1.7
1.9
Separated liquid (g)
Separated Ice (g)
Recovery rate (%)
Water=394 Other=5.8 Water=395 Other=9.7
Ice=29 Other=28 Ice=30 Other=28
98.2
Water=257 Other=2.9 Water=257 Other=2.9
Ice=160 Other=40.5 Ice=156 Other=38.6
98.9
Water=222 Other=4.8 Water=220 Other=1.9
Ice=188 Other=47.3 Ice=198 Other=40.5
99.3
Water=193
Ice=223 Other=38.6 Ice=225 Other=33.8
Water=192 2.5
Water=95 Water=106
3.0
Water=58 Water=59
4.0
Water=34 Water=24
Ice=305 Other=43.4 Ice=306 Other=42.5 Ice=353 Other=36.7 Ice=345 Other=41.5 Ice=375 Other=46.3 Ice=393 Other=36.7
99.4
97.7
98.9 97.7 96.9 95.3 97.7 96.2 95.7 97.9 97.5
not be measured below 1.9 C. As the amount of formed ice increases with a drop in temperature, the amount of oil taken in among the ice particles increases. Therefore, the separation of ‘‘water’’ and ‘‘other substance’’ (oil) is impossible below 1.9 C. After the separated ice was placed into a graduated measuring cylinder and melted at room temperature, the mass of formed ice was calculated from the product of the specific gravity of water and the volume of water obtained by melting the separated ice. The mass of oil was also calculated from the product of the specific gravity of oil and the volume of ‘‘other substance’’. The ‘‘recovery rate’’ shown in Table 1 indicates the rate of the separated ice and liquid to the mass of the entire mixture (465.3 g). The reason why the ‘‘recovery rate’’ was less than 100% is that liquid or ice has been left in the separation vessel. As the minimum ‘‘recovery rate’’ was over 95%, it is likely that, most of suspension was separated into ice and liquid (water and oil). The variation in the concentration in solution with freezing was calculated from the masses of additive in the mixture and separated water shown in Table 1. The symbol ~ in Fig. 3 represents the calculated result. The approximated line in Fig. 2, that is, ‘‘the solidus curve’’, is also shown in Fig. 3. From the results shown in Fig. 3, it was found that, for identical concentrations, the values of the freezing temperature shown by ~ are larger than those indicated by the solidus curve, although the case of 1.3 C (temperature immediately after dissolution of super-cooling) is an exception. The difference between the values of freezing temperature shown by ~ and the solidus curve becomes increasingly large with rise in concentration. The measured concentration of the liquid phase during the freezing process of the solution is shown in Fig. 4. The symbol * and the solid line indicate the measured value and the solidus curve, respectively. The measured
Fig. 2. Relationship between concentration of additive and solidification temperature of solution.
Fig. 3. Comparison of calculated concentration with wateradditive solidus curve.
Fig. 2. Relation entre la concentration en additif et la tempe´rature de solidification de la solution.
Fig. 3. Comparaison de la concentration calcule´e avec la courbe de solidification du me´lange eau/additif.
15
K. Matsumoto et al. / International Journal of Refrigeration 25 (2002) 11–18
value is in approximate agreement with the solidus curve. From the results of Figs. 3 and 4, it is speculated that the amount of additive in the liquid phase decreases with freezing. Therefore, we will examine the speculation for its validity. The additive used in this study has a hydrolysis group which changes into a silanol group (-SiOH). The silanol group combines with ice by hydrogen bonding. As the amount of formed ice increases with freezing, the amount of additive which combines with the ice by hydrogen bonding also increases. Therefore, the amount of additive in the liquid phase decreases with freezing. A report on the hydrogen bond between the silanol group of additive and ice was also made by Saito et al. [5]. From Fig. 4, the following is speculated. The first substance formed when the solution freezes is merely ice because the measured concentration agrees well with the solidus curve. The additive combines with the ice by hydrogen bonding after the ice is formed. Finally, the formed substance becomes a compound of ice and additive. Next, the above speculation will be proved. A comparison of the amount of formed substance with the amount of ice calculated by the solidus curve is shown in Fig. 5. The symbols * and indicate the amount of formed substance and the amount of calculated ice, respectively. At 1.3 C (temperature immediately after dissolution of super-cooling), difference between both amounts is very small. However the difference becomes increasingly large during freezing. Finally, at 4 C, the amount of formed substance is larger than that of calculated ice by about 35%. The values of the latent heat of fusion of the formed substance measured by DSC (difference scanning calorimeter) are shown in Table 2. The average value is smaller than the latent heat of fusion of ice by about 25%.
Thermal analyses for three kinds of substance were carried out by DSC. Fig. 6(a) shows the melting curve of the ice in a formed mushy region by cooling an ethylene–glycol solution with an initial concentration of 10 wt.% to about 30 C. In this case, the freezing temperature at the initial concentration is 3.37 C [7]. Fig. 6(b) shows the melting curve of the formed substance obtained by the present method. In this case, the substance was formed under conditions such that it did not contain any moisture at all. The concentration of additive used was 12 wt.% and the freezing temperature for this concentration is 3.7 C. Fig. 6(c) shows the melting curve of formed ice obtained by cooling the distilled water to about 15 C. The freezing temperature for the initial concentration of cases in the Fig. 6(a) and (b) was adjusted to be almost the same value. In the case where the ethylene-glycol solution was used [Fig.6(a)], an endoergic reaction corresponding to the latent heat of fusion of ice in the mushy region appears dispersively with melting of the ice. On the other hand, in the case using additive [Fig. 6(b)], the distribution of the latent heat of fusion of the substance is relatively convergent. Also, in the case of Fig. 6(a), the melting finishes in the vicinity of the freezing temperature for the initial concentration of the ethylene–glycol solution, while, in the case of Fig. 6(b), the melting finishes in the
Fig. 5. Comparison of mass of formed substance with that of ice calculated by solidus curve. Fig. 5. Comparaison de la masse de la substance forme´e et de celle de la glace calcule´e a` l’aide de la courbe de solidification.
Table 2 Latent heat of fusion of formed substance Tableau 2 Chaleur latente de fusion de la substance forme´e
Fig. 4. Measured concentration of liquid region of suspension. Fig. 4. Concentration mesure´e de la re´gion liquide de la suspension.
No.
1
2
3
4
5
Average
L (kJ/kg)
246.1
273.7
237.8
240.3
234.8
246.5
16
K. Matsumoto et al. / International Journal of Refrigeration 25 (2002) 11–18
vicinity of the freezing temperature of water. From a comparison of the melting curve in Fig. 6(b) with the curves in Fig. 6(a) and (c), it is found that the shape of the curve in Fig. 6(b) is similar to that in Fig. 6(c) compared with Fig.6(a). If the concentration of additive is varied, there is no change in the above tendency. From the above discussions, it seems that the formed substance is not ice but a compound. Although, the latent heat of fusion of the substance is smaller than that of ice, it is large enough to act as a thermal storage material compared with the other substances. The ice shape was
made granular by stirring, and the silanol group (-SiOH) in the additive was combined with the ice by hydrogen bonding. Therefore, the substance was covered with the additive. The substances are hardly bonded together, enabling the granular ice to remain in a dispersed state for a long time. The variation in the amount of additive attached to the ice during freezing was calculated on the basis of the amount of separated water and the result shown in Fig. 4. The result of the calculation is shown in Fig. 7. There is little additive attached to the ice at 1.3 C (temperature immediately after dissolution of super-cooling), but the amount of additive attached to the ice increases with freezing. At 4 C, about 75% of the additive is attached to the ice. A photograph of a suspension with high IPF from the previous report [4] is shown in Fig. 8. In this case, gaminopropyltrimethoxysilane was used as the additive. As mentioned above, there is a striking similarity in the characteristics between g-aminopropyltrimethoxysilane andg-aminopropyltriethoxysilane. For the relationship between the amount of formed ice and temperature in particular, there is little difference betweeng-aminopropyltrimethoxysilane andg-aminopropyltriethoxysilane. The suspension was melted by a heater and the IPF value of the suspension was estimated by the electric energy supplied to the heater and the latent heat of fusion of ice (334 kJ/kg), considering the heat capacity of the beaker and sensible heats of ice, water and oil, where IPF= (mass of ice)/(total mass of mixture). The estimate showed that the IPF was 73%, but in spite of this value, there was hardly any observable water content in the suspension, which was like granular ice. When we consider that the suspension consisted of 90 vol.% water and 10 vol.% oil, it should have been possible to observe water content in the suspension. As before, we obtain the result that the formed suspension (substance) was a compound of ice and additive. Besides, considering this observation,
Fig. 6. (a) Melting curve of ice in mushy region obtained by cooling ethylene-glycol solution (10 wt.%, Tf= 3.37 C); (b) melting curve of formed substance (12 wt.%, Tf= 3.37 C); (c) melting curve of ice obtained by cooling distilled water. Fig. 6. (a) Courbe de la fusion de glace dans la re´gion fondante obtenue a` l’aide d’une solution d’e´thyle`ne glycol (10% , Tf = 3,37 C) : (b) courbe de fusion (12% , Tf = 3,37 C) ; (c) courbe de fusion de glace obtenue avec de l’eau distille´e.
Fig. 7. Variation in amount of additive attached to ice with freezing. Fig. 7. Quantite´ d’additif attache´ a` la glace suite a` la conge´lation.
K. Matsumoto et al. / International Journal of Refrigeration 25 (2002) 11–18
17
Fig. 9. Temperature-variation of IPF of suspension. Fig. 8. Photograph of suspension with high IPF at T= 7.1 C (using PMP beaker with -aminopropyltrimethoxysilane).
Fig. 9. Variation de la tempe´rature et de l’IPF de la suspension.
Fig. 8. Photo d’une suspension a` IPF (Ice Packing Factor) e´leve´ ou` T = 7,1 C (utilisant un be´cher PMP et du g-aminopropyletrime´thoxysilane).
there is quite a possibility that the suspension had no water content, and the IPF may therefore have been about 90% at that time. Namely, the latent heat of fusion of suspension must have become smaller than that of ice by about 20%. This result agrees approximately with Table 2. When no water content at all could be seen, the temperature of suspension was about 7.1 C. The relationship between the IPF of the suspension and temperature is shown in Fig. 9. The definition of IPF has already been mentioned and the dashed line in Fig. 9 corresponds to the case where all water freezes, at which time the IPF is 86.8%. From Fig. 9, it is found that the IPF is already over 80% at 4 C. Fig. 10 is a semilog-graph showing the variation in the amount of water during with freezing. The symbol * and solid line represent the measured values and least square approximation to the measured values, respectively. From extrapolation of the least square approximation, it was estimated that all water freezes at about 7 C. This estimation agrees well with the result obtained from Fig. 8. From Figs. 8–10, it seems that all water freezes in the neighborhood of 7 C. This freezing temperature which is necessary to freeze all water is much smaller than the eutectic temperature of a two-component solution, for example, ammonia solution (about 72 C) . Moreover, it is also observed that a granular and dispersive substance like ice having about 100% IPF can be formed by using a solution without oil. In the former methods based on freezing of the solution, it is impossible to form suspensions with high IPF (about 90%) at over 10 C because the freezing temperature is depressed due to concentration of the solution with freezing. In the method discussed in this paper,
Fig. 10. Variation in amount of water in suspension with freezing. Fig. 10. Quantite´ d’eau dans la suspension lors de la conge´lation.
the amount of g-aminopropyltriethoxysilane in the solution decreases with freezing because it combines with the formed ice by hydrogen bonding. Therefore, all water in the solution can be frozen at a very small depression of freezing point (about 7 C), so that an IPF of about 90% which is much greater than the value of IPF obtained by the former methods, can be realized. The above results seem extremely useful for engineering. Namely, forming a suspension with high IPF at a very small depression of freezing point, it is possible to decrease the injection power to a refrigerating machine, so that the coefficient of performance (COP) of the system may be expected to be improved remarkably. Moreover, the shape of the formed ice is granular. The ice is covered with the additive, so that the additive becomes coating. Therefore, the additive prevents ice particles from attaching together, and the ice is in a dispersive state which can be maintained for a long time.
18
K. Matsumoto et al. / International Journal of Refrigeration 25 (2002) 11–18
In the present method for ice formation, the 10 vol.% silicon–oil is used. The amount of oil can be reduced to zero, so that the value of IPF can be increased further. As a natural consequence, the IPF in the present method is much greater than that of the slush ice in the former methods. Moreover, the IPF is also greater than or equal to that of the hard ice layer formed on the cooling surface in the static-type system by using water. In ice storage system of the static type, the melting rate of ice is slow. However, it is expected that the melting rate of ice obtained by the present method can be much faster than that in the static system because ice particles do not attach together and the ice can be kept granular and in a dispersive state for long time. As shown in the previous report [4], if fluidity is required for the suspension which acts as the thermal storage material of the dynamic-type system, use of a suspension with low IPF is effective.
4. Conclusions 1. The formation process of a suspension with high IPF(about 90%) made from a water-oil mixture containing a small amount of g-aminopropyltri ethoxysilane, was clarified. 2. From thermal analysis of the formed substance by using DSC, it was found that the substance was a compound of ice and g-aminopropyltriethoxy silane. 3. For ice formation by using an water-oil mixture containing g-aminopropyltriethoxysilane, it was found that at a very small depression of freezing point (about 7) all water of the mixture (>90 vol.%) could be frozen. 4. The IPF value for the ice formation method in the present paper was larger than the maximum value in the static types of ice storage systems by using water.
Acknowledgements The authors wish to thank Dr. Takegoshi and Dr. Hirasawa who belong to Toyama University, Mr. Oda who was a graduate student of Aoyama Gakuin University and Mr. Ishikawa and Mr. Sawada who were the students of Chuo University, for their co-operation in this experiment. This study was supported financially by Chuo University as one of the 2000 Research Projects for Promotion of Advanced Research at Graduate School and by a subsidy of the Japan Society of the Promotion of Science under the ‘‘Research for the Future Program’’ (JPSP-RFTF97P01003, Fundamental Research on Thermal Energy Storage to Preserve Environment).
References [1] Hirata A, Nagasaka K, Ishikawa M. Crystal ice formation of solution and its removal phenomena at cooled horizontal solid surface (Part I: ice removal phenomena). Int J Heat Mass Transfer 2000;43(3):333–9. [2] Hirata T, Kato M, Nagasaka K, Ishikawa M. Crystal ice formation of solution and its removal phenomena at cooled horizontal solid surface (Part II: ice removal condition). Int J Heat Mass Transfer 2000;43(5):757–65. [3] Kawabe H, Fukusako S, Yamada M, Yanagita K. Continuous production characteristics of slush-ice by use of a horizontal oscillating cooled wall (in Japanese). Trans of JSRAE 1998;15(3):193–201. [4] Matsumoto K, Okada K, Kawagoe T, Kan C. Ice storage system with water-oil mixture (formation of suspension with high IPF). Int J Refrigeration 2000;23(5):336–44. [5] Saito T, Yabe A, Inada T, Zhang X, Tanaka M. Microscopic observation of ice crystal surface containing adsorbed silane coupling agents (in Japanese). Trans of JSME 1999;65(630):463–8. [6] Technical Report. A silane-coupler, Shinetsu Co.Ltd., 1996. [7] JSME data book. Thermophysical properties of fluid, 1997; 477.
Ice storage system using water–oil mixture Discussion about influence of additive on ice formation process Koji Matsumoto a,*, Yasuo Shiokawa b, Masashi Okada c, Tetsuo Kawagoe d, Chaedong Kang e a
Department of Precision Mechanics, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo, 112-8551 Japan b Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo, 112-8551 Japan c Department of Mechanical Engineering, Aoyama Gakuin University, 6-16-1 Chitosedai, Setagaya-ku, Tokyo, 157-8572 Japan d 757-4 Katakurachou, Kanagawa-ku, Yokohama, 221-0861 Japan e School of Mechanical and Aerospace Engineering (BK21), Seoul National University, #2305, 136-1 dong San 56-1, Shillim-Dong, Kwanak-Gu, Seoul 151-742, Korea Received 22 December 2000; received in revised form 22 February 2001; accepted 22 February 2001
Abstract Ice storage is one technique for effective use of thermal energy. So, many studies on slush ice as a thermal storage material have been done. We have also been studying a suspension (slush ice) made from an oil-water mixture by cooling and stirring. From our study results, it was found that an additive having both an amino group (-NH2) and a silanol group (-SiOH) was essential to form a suspension with high IPF without adhesion of ice to the cooling wall. Moreover, ice particles formed in the suspension were dispersed and granular, and did not stick to each other. In the present paper, we carried out experiments to clarify the characteristics of the suspension formation process. From a thermal analysis of the substance formed in the suspension by difference scanning calorimeter (DSC), it was found that the substance was not ice but a compound of ice and additive. Then, at a very small depression of freezing point (about 7 C) all water in the mixture could be frozen by using the additive. # 2001 Elsevier Science Ltd and IIR. All rights reserved. Keywords: Ice storage; Water; Oil; Mixture; Ice; Formation
Accumulation thermique sous forme de glace, utilisant un me´lange eau/huile Re´sume´ Le stockage de glace est une technique permettant l’utilisation efficace de l’e´nergie thermique et un grand nombre d’e´tudes ont e´te´ effectue´es afin d’approfondir les proprie´te´s des coulis de glace dans cette application. Les auteurs ont e´tudie´ une suspension (coulis) compose´e d’un me´lange d’huile et d’eau obtenu par un processus de refroidissement sous agitation. Cette e´tude a montre´ que l’ajout d’un additif posse´dant un groupe amine (-NH2) et un groupe hydroxyde de silicium (-SiOH) s’ave`re essentiel afin de cre´er une suspension a` IPF e´leve´ sans adhe´sion de la glace aux parois refroidissantes. En outre, les particules de glace qui se forment dans la suspension sont disperse´es et granulaires et n’ont pas tendance a` former des amas. Cette communication de´crit en particulier le processus de formation de la suspension. Les * Corresponding author. Tel.: +81-3-3817-1837; fax: +81-3-3817-1828. E-mail addresses: [email protected] u.ac.jp (K. Matsumoto), [email protected] (Y. Shiokawa), [email protected] (M. Okada), [email protected] (C. Kang). 0140-7007/01/$20.00 # 2001 Elsevier Science Ltd and IIR. All rights reserved. PII: S0140-7007(01)00024-X
12
K. Matsumoto et al. / International Journal of Refrigeration 25 (2002) 11–18
auteurs ont utilise´ une analyse thermique de la substance forme´e dans la suspension, a` l’aide de la calorime´trie par analyse diffe´rentielle : cette e´tude a montre´ que la substance forme´e est un me´lange de glace et d’un additif. Graˆce a` cette substance, on obtient une faible de´pression du point de fusion (environ 7 C) et on peut congeler toute l’eau dans le me´lange graˆce a` la pre´sence de l’additif. # 2001 Elsevier Science Ltd and IIR. All rights reserved. Mots cle´s : Accumulation thermique ; Eau ; Huile ; Me´lange ; Glace ; Formation
1. Introduction From the viewpoint of effective use of thermal energy, ice storage systems have attracted interest recently because of their high storage capacity per unit volume. Ice storage is classified into two types, static and dynamic. The dynamic type in particular has some excellent characteristics, and there have been many proposals for a formation technique for slush ice to be used as the thermal storage material. As slush ice has fluidity, a large amount of cooling energy can be transported with less pumping work. The dynamic type system can respond quickly to changes in the heat load because the ice particles have a large surface area. The technique where slush ice is formed by dissolution of the super-cooling state of solution is fairly widely used. Recently new slush ice formation techniques have been developed. The techniques are that ice formed on a cooling surface from ethylene glycol aqueous solution is removed by buoyancy force [1,2] or oscillation [3]. The values of the ice packing factor (IPF) in both techniques are, however, small. The authors also studied a new method of forming slush ice [4]. In this method a small amount of additive (silane-coupler) is added to a mixture of 10 vol.% siliconeoil and 90 vol.% water and the additive dissolves in water. The mixture (solution) was cooled with stirring in a vessel and changed into an ice-oil and water suspension. The suspension is also slush ice, which did not adhere to the cooling wall and had a high IPF. The ice-oil suspension remained in a state consisting of dispersed small particles even after the suspension was preserved for a long time in a freezing condition. In the present report, the same mixture as that described in the previous report [4] was cooled in a vessel with stirring and changed into a suspension. After the relationship between concentration of additive and freezing temperature of solution has been clarified, we discuss the measurement results for temperature, concentration of the suspension and mass of ice formed in the suspension, and we clarify the influence of additive on the ice formation process.
2. Experimental procedure 2.1. Experimental apparatus A schematic diagram of the experimental apparatus is shown in Fig. 1. The apparatus, experimental conditions and procedure are the same as used in the previous
report [4]. From this report [4], the use of a polymethylpentene (PMP) beaker as the experimental vessel was decided upon as the ice in the suspension hardly adheres to its inner wall at all. The inside diameter and height of the PMP beaker were 85 and 118 mm, respectively, which is a quarter of the beaker size in the previous report [4]. The diameter of the stirring wing was reduced to 60 mm with the change of beaker size. In order to cool the mixture, the beaker containing the mixture was soaked directly in a cold-type thermostatic bath filled with brine consisting of ethylene–glycol solution. T-type thermocouples of diameter 0.2 mm were used to measure temperature. The temperature of suspension was measured at about 3 cm below the suspension surface at the center of the beaker. The brine temperatures were measured at two positions in the thermostatic bath. The concentration of solution was measured by a refracting densitometer. 2.2. Water-additive solidus curve We thought that the relationship between the concentration of additive and freezing temperature of the solution had to be obtained in order to be able to consider the influence of the additive on the ice formation process. Therefore, an experiment for obtaining the water-additive solidus curve was carried out. In the previous report [4], it was found that a silane-coupler with an amino group (-NH2) which is a hydrophilic substance was effective as the additive. Typical examples of a hydrophilic substance are g-aminopropyltrimethoxy silane or g-aminopropyltriethoxysilane. The difference between them in the freezing process characteristics is very small. Therefore, in the present study, g-aminopropyltriethoxysilane was used and is referred to as the additive from now on. At first, a solution with a pre-determined initial concentration of additive was put into a test tube, and then the test tube was soaked directly in a cold-type thermostatic bath and cooled. The solution was periodically stirred during cooling in order to make the temperature distribution of the solution uniform. The temperature in the center part of solution was measured. After the solution had reached the maximum extent of super-cooling degree, the super-cooling state of the solution was dissolved. The temperature immediately after dissolution of super-cooling was defined as the freezing temperature of solution for the initial concentration. Similar experiments with various initial concentrations were carried out. In
K. Matsumoto et al. / International Journal of Refrigeration 25 (2002) 11–18
13
Fig. 1. Experimental apparatus. Fig. 1. Sche´ma de l’appareil expe´rimental.
order to confirm reproducibility of these experiments, experiments for each initial concentration were repeated several times.
ship between temperature and the amount of formed ice was clarified.
2.3. Ice formation experiment
3. Experimental results and discussion
A 450 cc mixture composed of 90 vol.% tap water and 10 vol.% silicone oil (kinematic viscosity= 110 4 m2/s, specific gravity=0.965 at 25 C [6]) was put into the PMP beaker. A 18cc (4 vol.% of the mixture) of additive (specific gravity=0.94 at 25 C [6]) was then added to the mixture. The additive dissolved in water making the mixture into a solution. The brine temperature was set to 10 C. The beaker containing the solution was soaked directly in a cold-type thermostatic bath and cooled with stirring, causing the solution to change into an ice– water–oil suspension. After the temperature of suspension reached a predetermined value, the suspension was transferred to another vessel (separation vessel) made of resin. This vessel was cylindrical in shape and tapered downward. In order to separate ice from the suspension, a net was stretched to the bottom of vessel. Separation was carried out for 60 min by vibrating the vessel. A mass of separated ice was equal to the amount of ice formed for the pre-determined temperature. Another vessel was set under the separation vessel in order to receive the separated liquid. The separation apparatus was placed in a cold-type thermostatic box which was set to 1 4 C as the formed ice was then prevented from melting or the solution was prevented from freezing. The amount of formed ice was measured for various temperatures and relation-
The relationship between the mass concentration of additive and freezing temperature is shown in Fig. 2. The * symbol in the figure represents the average value of several measurements for a certain concentration. The reproducibility of measurement values for each concentration was good. The solid line is a least square approximation of the average values. The suspension was able to be separated into ice and liquid. The relationship between separated ice (formed ice) and temperature is shown in Table 1. Measurements were carried out twice for each temperature, and the reproducibility of measurements was good. The 1.3 C value corresponds to the freezing temperature for the initial concentration of mixture (solution). By melting the ice, it was found that the ice was separated into two layers corresponding to ‘‘other substance’’ and water, respectively. Although it was thought that the water contained some additive, the amount of additive was neglected because it was very small. The liquid was also separated into two layers corresponding to ‘‘other substance’’ and water, respectively. The amount of additive in the water was also neglected in this case. Although ‘‘other substances’’ in the separated ice and liquid might also have contained some additive, both ‘‘other substances’’ were regarded as oil because the amount of additive was very small. The value of ‘‘other substance’’ in the liquid can
14
K. Matsumoto et al. / International Journal of Refrigeration 25 (2002) 11–18
Table 1 Amount of formed Ice (formed substance) Tableau 1 Quantite´ de glace forme´e (substance forme´e) Temperature ( C) 1.3
1.5
1.7
1.9
Separated liquid (g)
Separated Ice (g)
Recovery rate (%)
Water=394 Other=5.8 Water=395 Other=9.7
Ice=29 Other=28 Ice=30 Other=28
98.2
Water=257 Other=2.9 Water=257 Other=2.9
Ice=160 Other=40.5 Ice=156 Other=38.6
98.9
Water=222 Other=4.8 Water=220 Other=1.9
Ice=188 Other=47.3 Ice=198 Other=40.5
99.3
Water=193
Ice=223 Other=38.6 Ice=225 Other=33.8
Water=192 2.5
Water=95 Water=106
3.0
Water=58 Water=59
4.0
Water=34 Water=24
Ice=305 Other=43.4 Ice=306 Other=42.5 Ice=353 Other=36.7 Ice=345 Other=41.5 Ice=375 Other=46.3 Ice=393 Other=36.7
99.4
97.7
98.9 97.7 96.9 95.3 97.7 96.2 95.7 97.9 97.5
not be measured below 1.9 C. As the amount of formed ice increases with a drop in temperature, the amount of oil taken in among the ice particles increases. Therefore, the separation of ‘‘water’’ and ‘‘other substance’’ (oil) is impossible below 1.9 C. After the separated ice was placed into a graduated measuring cylinder and melted at room temperature, the mass of formed ice was calculated from the product of the specific gravity of water and the volume of water obtained by melting the separated ice. The mass of oil was also calculated from the product of the specific gravity of oil and the volume of ‘‘other substance’’. The ‘‘recovery rate’’ shown in Table 1 indicates the rate of the separated ice and liquid to the mass of the entire mixture (465.3 g). The reason why the ‘‘recovery rate’’ was less than 100% is that liquid or ice has been left in the separation vessel. As the minimum ‘‘recovery rate’’ was over 95%, it is likely that, most of suspension was separated into ice and liquid (water and oil). The variation in the concentration in solution with freezing was calculated from the masses of additive in the mixture and separated water shown in Table 1. The symbol ~ in Fig. 3 represents the calculated result. The approximated line in Fig. 2, that is, ‘‘the solidus curve’’, is also shown in Fig. 3. From the results shown in Fig. 3, it was found that, for identical concentrations, the values of the freezing temperature shown by ~ are larger than those indicated by the solidus curve, although the case of 1.3 C (temperature immediately after dissolution of super-cooling) is an exception. The difference between the values of freezing temperature shown by ~ and the solidus curve becomes increasingly large with rise in concentration. The measured concentration of the liquid phase during the freezing process of the solution is shown in Fig. 4. The symbol * and the solid line indicate the measured value and the solidus curve, respectively. The measured
Fig. 2. Relationship between concentration of additive and solidification temperature of solution.
Fig. 3. Comparison of calculated concentration with wateradditive solidus curve.
Fig. 2. Relation entre la concentration en additif et la tempe´rature de solidification de la solution.
Fig. 3. Comparaison de la concentration calcule´e avec la courbe de solidification du me´lange eau/additif.
15
K. Matsumoto et al. / International Journal of Refrigeration 25 (2002) 11–18
value is in approximate agreement with the solidus curve. From the results of Figs. 3 and 4, it is speculated that the amount of additive in the liquid phase decreases with freezing. Therefore, we will examine the speculation for its validity. The additive used in this study has a hydrolysis group which changes into a silanol group (-SiOH). The silanol group combines with ice by hydrogen bonding. As the amount of formed ice increases with freezing, the amount of additive which combines with the ice by hydrogen bonding also increases. Therefore, the amount of additive in the liquid phase decreases with freezing. A report on the hydrogen bond between the silanol group of additive and ice was also made by Saito et al. [5]. From Fig. 4, the following is speculated. The first substance formed when the solution freezes is merely ice because the measured concentration agrees well with the solidus curve. The additive combines with the ice by hydrogen bonding after the ice is formed. Finally, the formed substance becomes a compound of ice and additive. Next, the above speculation will be proved. A comparison of the amount of formed substance with the amount of ice calculated by the solidus curve is shown in Fig. 5. The symbols * and indicate the amount of formed substance and the amount of calculated ice, respectively. At 1.3 C (temperature immediately after dissolution of super-cooling), difference between both amounts is very small. However the difference becomes increasingly large during freezing. Finally, at 4 C, the amount of formed substance is larger than that of calculated ice by about 35%. The values of the latent heat of fusion of the formed substance measured by DSC (difference scanning calorimeter) are shown in Table 2. The average value is smaller than the latent heat of fusion of ice by about 25%.
Thermal analyses for three kinds of substance were carried out by DSC. Fig. 6(a) shows the melting curve of the ice in a formed mushy region by cooling an ethylene–glycol solution with an initial concentration of 10 wt.% to about 30 C. In this case, the freezing temperature at the initial concentration is 3.37 C [7]. Fig. 6(b) shows the melting curve of the formed substance obtained by the present method. In this case, the substance was formed under conditions such that it did not contain any moisture at all. The concentration of additive used was 12 wt.% and the freezing temperature for this concentration is 3.7 C. Fig. 6(c) shows the melting curve of formed ice obtained by cooling the distilled water to about 15 C. The freezing temperature for the initial concentration of cases in the Fig. 6(a) and (b) was adjusted to be almost the same value. In the case where the ethylene-glycol solution was used [Fig.6(a)], an endoergic reaction corresponding to the latent heat of fusion of ice in the mushy region appears dispersively with melting of the ice. On the other hand, in the case using additive [Fig. 6(b)], the distribution of the latent heat of fusion of the substance is relatively convergent. Also, in the case of Fig. 6(a), the melting finishes in the vicinity of the freezing temperature for the initial concentration of the ethylene–glycol solution, while, in the case of Fig. 6(b), the melting finishes in the
Fig. 5. Comparison of mass of formed substance with that of ice calculated by solidus curve. Fig. 5. Comparaison de la masse de la substance forme´e et de celle de la glace calcule´e a` l’aide de la courbe de solidification.
Table 2 Latent heat of fusion of formed substance Tableau 2 Chaleur latente de fusion de la substance forme´e
Fig. 4. Measured concentration of liquid region of suspension. Fig. 4. Concentration mesure´e de la re´gion liquide de la suspension.
No.
1
2
3
4
5
Average
L (kJ/kg)
246.1
273.7
237.8
240.3
234.8
246.5
16
K. Matsumoto et al. / International Journal of Refrigeration 25 (2002) 11–18
vicinity of the freezing temperature of water. From a comparison of the melting curve in Fig. 6(b) with the curves in Fig. 6(a) and (c), it is found that the shape of the curve in Fig. 6(b) is similar to that in Fig. 6(c) compared with Fig.6(a). If the concentration of additive is varied, there is no change in the above tendency. From the above discussions, it seems that the formed substance is not ice but a compound. Although, the latent heat of fusion of the substance is smaller than that of ice, it is large enough to act as a thermal storage material compared with the other substances. The ice shape was
made granular by stirring, and the silanol group (-SiOH) in the additive was combined with the ice by hydrogen bonding. Therefore, the substance was covered with the additive. The substances are hardly bonded together, enabling the granular ice to remain in a dispersed state for a long time. The variation in the amount of additive attached to the ice during freezing was calculated on the basis of the amount of separated water and the result shown in Fig. 4. The result of the calculation is shown in Fig. 7. There is little additive attached to the ice at 1.3 C (temperature immediately after dissolution of super-cooling), but the amount of additive attached to the ice increases with freezing. At 4 C, about 75% of the additive is attached to the ice. A photograph of a suspension with high IPF from the previous report [4] is shown in Fig. 8. In this case, gaminopropyltrimethoxysilane was used as the additive. As mentioned above, there is a striking similarity in the characteristics between g-aminopropyltrimethoxysilane andg-aminopropyltriethoxysilane. For the relationship between the amount of formed ice and temperature in particular, there is little difference betweeng-aminopropyltrimethoxysilane andg-aminopropyltriethoxysilane. The suspension was melted by a heater and the IPF value of the suspension was estimated by the electric energy supplied to the heater and the latent heat of fusion of ice (334 kJ/kg), considering the heat capacity of the beaker and sensible heats of ice, water and oil, where IPF= (mass of ice)/(total mass of mixture). The estimate showed that the IPF was 73%, but in spite of this value, there was hardly any observable water content in the suspension, which was like granular ice. When we consider that the suspension consisted of 90 vol.% water and 10 vol.% oil, it should have been possible to observe water content in the suspension. As before, we obtain the result that the formed suspension (substance) was a compound of ice and additive. Besides, considering this observation,
Fig. 6. (a) Melting curve of ice in mushy region obtained by cooling ethylene-glycol solution (10 wt.%, Tf= 3.37 C); (b) melting curve of formed substance (12 wt.%, Tf= 3.37 C); (c) melting curve of ice obtained by cooling distilled water. Fig. 6. (a) Courbe de la fusion de glace dans la re´gion fondante obtenue a` l’aide d’une solution d’e´thyle`ne glycol (10% , Tf = 3,37 C) : (b) courbe de fusion (12% , Tf = 3,37 C) ; (c) courbe de fusion de glace obtenue avec de l’eau distille´e.
Fig. 7. Variation in amount of additive attached to ice with freezing. Fig. 7. Quantite´ d’additif attache´ a` la glace suite a` la conge´lation.
K. Matsumoto et al. / International Journal of Refrigeration 25 (2002) 11–18
17
Fig. 9. Temperature-variation of IPF of suspension. Fig. 8. Photograph of suspension with high IPF at T= 7.1 C (using PMP beaker with -aminopropyltrimethoxysilane).
Fig. 9. Variation de la tempe´rature et de l’IPF de la suspension.
Fig. 8. Photo d’une suspension a` IPF (Ice Packing Factor) e´leve´ ou` T = 7,1 C (utilisant un be´cher PMP et du g-aminopropyletrime´thoxysilane).
there is quite a possibility that the suspension had no water content, and the IPF may therefore have been about 90% at that time. Namely, the latent heat of fusion of suspension must have become smaller than that of ice by about 20%. This result agrees approximately with Table 2. When no water content at all could be seen, the temperature of suspension was about 7.1 C. The relationship between the IPF of the suspension and temperature is shown in Fig. 9. The definition of IPF has already been mentioned and the dashed line in Fig. 9 corresponds to the case where all water freezes, at which time the IPF is 86.8%. From Fig. 9, it is found that the IPF is already over 80% at 4 C. Fig. 10 is a semilog-graph showing the variation in the amount of water during with freezing. The symbol * and solid line represent the measured values and least square approximation to the measured values, respectively. From extrapolation of the least square approximation, it was estimated that all water freezes at about 7 C. This estimation agrees well with the result obtained from Fig. 8. From Figs. 8–10, it seems that all water freezes in the neighborhood of 7 C. This freezing temperature which is necessary to freeze all water is much smaller than the eutectic temperature of a two-component solution, for example, ammonia solution (about 72 C) . Moreover, it is also observed that a granular and dispersive substance like ice having about 100% IPF can be formed by using a solution without oil. In the former methods based on freezing of the solution, it is impossible to form suspensions with high IPF (about 90%) at over 10 C because the freezing temperature is depressed due to concentration of the solution with freezing. In the method discussed in this paper,
Fig. 10. Variation in amount of water in suspension with freezing. Fig. 10. Quantite´ d’eau dans la suspension lors de la conge´lation.
the amount of g-aminopropyltriethoxysilane in the solution decreases with freezing because it combines with the formed ice by hydrogen bonding. Therefore, all water in the solution can be frozen at a very small depression of freezing point (about 7 C), so that an IPF of about 90% which is much greater than the value of IPF obtained by the former methods, can be realized. The above results seem extremely useful for engineering. Namely, forming a suspension with high IPF at a very small depression of freezing point, it is possible to decrease the injection power to a refrigerating machine, so that the coefficient of performance (COP) of the system may be expected to be improved remarkably. Moreover, the shape of the formed ice is granular. The ice is covered with the additive, so that the additive becomes coating. Therefore, the additive prevents ice particles from attaching together, and the ice is in a dispersive state which can be maintained for a long time.
18
K. Matsumoto et al. / International Journal of Refrigeration 25 (2002) 11–18
In the present method for ice formation, the 10 vol.% silicon–oil is used. The amount of oil can be reduced to zero, so that the value of IPF can be increased further. As a natural consequence, the IPF in the present method is much greater than that of the slush ice in the former methods. Moreover, the IPF is also greater than or equal to that of the hard ice layer formed on the cooling surface in the static-type system by using water. In ice storage system of the static type, the melting rate of ice is slow. However, it is expected that the melting rate of ice obtained by the present method can be much faster than that in the static system because ice particles do not attach together and the ice can be kept granular and in a dispersive state for long time. As shown in the previous report [4], if fluidity is required for the suspension which acts as the thermal storage material of the dynamic-type system, use of a suspension with low IPF is effective.
4. Conclusions 1. The formation process of a suspension with high IPF(about 90%) made from a water-oil mixture containing a small amount of g-aminopropyltri ethoxysilane, was clarified. 2. From thermal analysis of the formed substance by using DSC, it was found that the substance was a compound of ice and g-aminopropyltriethoxy silane. 3. For ice formation by using an water-oil mixture containing g-aminopropyltriethoxysilane, it was found that at a very small depression of freezing point (about 7) all water of the mixture (>90 vol.%) could be frozen. 4. The IPF value for the ice formation method in the present paper was larger than the maximum value in the static types of ice storage systems by using water.
Acknowledgements The authors wish to thank Dr. Takegoshi and Dr. Hirasawa who belong to Toyama University, Mr. Oda who was a graduate student of Aoyama Gakuin University and Mr. Ishikawa and Mr. Sawada who were the students of Chuo University, for their co-operation in this experiment. This study was supported financially by Chuo University as one of the 2000 Research Projects for Promotion of Advanced Research at Graduate School and by a subsidy of the Japan Society of the Promotion of Science under the ‘‘Research for the Future Program’’ (JPSP-RFTF97P01003, Fundamental Research on Thermal Energy Storage to Preserve Environment).
References [1] Hirata A, Nagasaka K, Ishikawa M. Crystal ice formation of solution and its removal phenomena at cooled horizontal solid surface (Part I: ice removal phenomena). Int J Heat Mass Transfer 2000;43(3):333–9. [2] Hirata T, Kato M, Nagasaka K, Ishikawa M. Crystal ice formation of solution and its removal phenomena at cooled horizontal solid surface (Part II: ice removal condition). Int J Heat Mass Transfer 2000;43(5):757–65. [3] Kawabe H, Fukusako S, Yamada M, Yanagita K. Continuous production characteristics of slush-ice by use of a horizontal oscillating cooled wall (in Japanese). Trans of JSRAE 1998;15(3):193–201. [4] Matsumoto K, Okada K, Kawagoe T, Kan C. Ice storage system with water-oil mixture (formation of suspension with high IPF). Int J Refrigeration 2000;23(5):336–44. [5] Saito T, Yabe A, Inada T, Zhang X, Tanaka M. Microscopic observation of ice crystal surface containing adsorbed silane coupling agents (in Japanese). Trans of JSME 1999;65(630):463–8. [6] Technical Report. A silane-coupler, Shinetsu Co.Ltd., 1996. [7] JSME data book. Thermophysical properties of fluid, 1997; 477.