Experimental Study on Latent Heat Storage Characteristics of W/O Emulsion by Ultrasonic Wave Impression

doi:10.4236/ojfd.2013.32A008

Paper Menu >>

Journal Menu >>

Open Journal of Fluid Dynamics, 2013, 3, 48-54

http://dx.doi.org/10.4236/ojfd.2013.32A008 Published Online July 2013 (http://www.scirp.org/journal/ojfd)

Experimental Study on Latent Heat Storage

Characteristics of W/O Emulsion by Ultrasonic

Wave Impression

Shin-ichi Morita1, Yasutaka Hayamizu1, Akihiko Horibe2, Naoto Haruki2,

Hideo Inaba3, Issei Higashi4

1Department of Mechanical Engineering, Yonago National College of Technology, Yonago, Japan

2Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan

3Shujitsu University, Okayama, Japan

4Edit Inc., Fukuoka, Japan

Email: [email protected]

Received May 24, 2013; revised June 1, 2013; accepted June 8, 2013

which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

The flowable latent heat storage material like Oil/Water type emulsion, microencapsulated latent heat material-water

mixture or ice slurry, etc., is enabled to transport the latent heat in a pipe. Supercooling phenomenon of the dispersed

latent heat storage material in continuous phase is obstructed by a latent heat storage. The latent heat storage rates of

dispersed waterdrops in W/O (Water/Oil) emulsion are investigated experimentally in this study. The waterdrops in

emulsion have the diameter within 3 - 25 μm, the averaged diameter of waterdrops is 7.3 μm and the standard deviation

is 2.9 μm. Supercooling release of waterdrops in emulsion is examined by short time impressing of the ultrasonic. The

direct contact heat exchange method is chosen as the phase change rate evaluation of waterdrops in W/O emulsion. The

supercooled temperature is set as parameters of this study. The previous obtained experimental result, as the condition

without impressing ultrasonic wave, showed that the 35 K or more degree from melting point brings 100% latent heat

storage rate of W/O emulsion. It is clarified that it is possible to reduce 20 K of supercooling degree by impressing the

ultrasonic.

Keywords: Heat Storage; Latent Heat; W/O Emulsion; Direct Contact Heat Exchange; Ultrasonic

1. Introduction

Recently, much attention has been paid to research on the

latent heat storage system. Using of ice heat storage sys-

tem brings an equalization of electric power demand,

because it will be solved that the electric-power-demand-

concentration on day-time of summer by the air condi-

tioning. The flowable latent heat-storage system can

scale down the pipe size due to the augmentation of the

transported heat. Slurry type latent heat-storage (phase

change material) system is one of the available cooling

systems, which can take the place of the sensible (water)

heat-storage system. Phase change emulsion [1] and

phase change microcapsule slurry [2], clathrate hydrate

slurries [3] etc. are mentioned as a typical slurry type

latent heat storage substance. It is known that a super-

cooling phenomenon disturbs a latent heat-storage [4,5].

A supercooling rate increases with reduction of disper-

sion droplet diameter except for the microencapsulated

latent heat storage substance [6]. Some studies of super-

cooling by bulk water have been reported. The pure wa-

ter layers were cooled from upper side by five kinds of

copper cooling surfaces (electrolytic polished, nickel-

plated, buffed, porous, gold-plated copper disks) under

various cooling rate (0.05 - 0.5 K/s), and the degrees of

supercooling at the appearance of dendritic ice were

measured by A. Saito, et al. [7]. As a result, the porous

surface showed the lowest degree of supercooling. S.

Okawa, et al. [8] investigated the effect of the electric

field on freezing of supercooled water, experimentally. It

was found that supercooled water freezes instantly by

applying the electric charge at the voltage less than 100

VDC. The experimental results indicated that ultrasonic

vibration strongly promotes the freezing of supercooled

water, for both pure water and tap water by T. Inada, et

al. [9]. Furthermore, they found that ultrasonic vibration

S.-I. MORITA ET AL. 49

is also effective for making ice slurry. H. Inaba, et al. [10]

reported the supercooling degree for the test tap water

sample that was set in test tubes. The supercooling de-

gree was decreased with an increase in the mass ratio of

ice nucleating substance. However, it was clarified that

the supercooling degree for each test sample increased by

repeating the process of freezing and melting. T. Ho-

zumi, et al. [11] studied the mechanism of the freezing of

the supercooled water under the effect of the ultrasonic

wave. It was shown that the impression of the ultrasonic

wave (0.28 W/cm2) brought the generation of ice nuclea-

tion on every experimental condition. All of these inves-

tigations were carried out by using the bulk water.

The freezing of waterdrop in W/O emulsion brings

volume expansion. T. Inada et al. [12] measured the

amount of freezes of the waterdrop in a W/O emulsion

by microscope observation on the cooling rate of 0.067

K/sec. The counting of freeze numbers of the fine water-

drops is one of methods of measuring the degree of su-

percooling in W/O emulsion. However, this method does

not measure the amount of latent heat storages itself. H.

Inaba and S. Morita [13] showed the cold heat-release

characteristics of emulsion by air-emulsion direct contact

heat exchange method. By the same method, S. Aoyama

and H. Inaba [14] described that the direct contact heat

exchange characteristic between ice (averaged diameter

3.10 mm) and hot air. It can be said that the direct con-

tact heat exchange method is the effective method for

measuring the amount of latent heat storage. This study

shows the experimental results of the latent heat-storage

rate (supercooling rate of dispersed waterdrops) of the

water in oil (W/O) emulsion by direct contact heat ex-

change method.

P. Schalbart et al. [15] investigated the low-energy

emulsification method of Oil-in-Water (O/W) emul-

sions that have a narrow droplet size distribution in the

range of 200 - 250 nm. These nano-emulsions of tet-

radecane in water showed stability against sedimentation

and creaming for more than 6 months and low viscosity

(2 - 4 times than that of water). The mass percentages of

the nano-emulsion are 20% tetradecane, 6% surfactant

and 74% water. The waterdrops of this research are ex-

isted in 3 - 25 μm in diameter, and the average diameter

is 7.3 μm and the standard deviation is 2.9 μm. It is

thought that the stabilization of a nano-emulsion exceeds

a microemulsion. In this research, it is adopted from the

reason that micro-emulsion is easy to produce and close

to utilization. It was found that the emplacement of the

phase-change materials (PCMs) has no effect on the heat

transfer inside the emulsion. Test emulsion set as an ex-

pected temperature was supplied to the heat storage tank,

and it cooled with the low cooling rate. Authors’ previ-

ous research [16], as the condition without impressing

ultrasonic, showed that the 35 K or more degrees from

melting point brings 100% latent heat storage rate of

W/O emulsion. The supercooled temperature and the

cooling rate are set as parameters of this study. The

evaluation is performed by comparison between the re-

sults of this study and the past one.

2. Experimental Apparatus and Procedure

2.1. Test Emulsion

Figure 1 shows the external appearance and the micro-

graph (×400) of test emulsion. The emulsion has fluidity,

even if the dispersed water particles are the solid phase.

Test W/O emulsion consists of tap water as dispersed

phase, silicon oil as continuous phase and surfactant. The

silicone oil of continuous phase is used TSF451-10

(Momentive Performance Materials Holdings Inc.). The

emulsification is carried out by nonionic surfactant (DKS

NL-Dash403: Daiichi kogyo seiyaku CO. Ltd.). The

mass composition ratio of test emulsion is tap water 5%,

silicon oil 94% and surfactant 1%. The specific heat of

the emulsion used for data evaluation is calculated using

the additive property law. The base data of water and

silicon oil is used publication data [17,18]. The specific

heat of surfactant is used the actual value that measured

by water calorimeter. For example, the specific heat of an

emulsion is 1.90 kJ/(kg·K) at 298 K. The diameter of

distributed waterdrops (N = 300) in test emulsion exists d

= 3 - 25 μm, the average diameter of dm = 7.3 μm and

standard deviation is S = 2.9 μm. The stable time of test

emulsion is at least 210 minutes, so that the cooling of

experiment is carried out within the stable time.

2.2. Experimental Apparatus

Figure 2 shows the schematic diagram of experimental

apparatus for measuring latent heat storage rate of emul-

sion by direct contact heat exchange method. Experi-

mental apparatus consists of the test section and the hot

air supply line. The air supplied from a compressor is

sent to the test section through a surge tank, an air-dryer,

a heater, and a flow meter. Dried hot air is sent to the

10μm

Figure 1. Appearance and micrograph of emulsion.

S.-I. MORITA ET AL.

φ100

173

120°

146

AA'

Section view A-A'

Ultrasonic transduce

Test sectionComp.

Sg.

AA'

Pressure gauge

Surge tank

Compressor

Bubbling deviceAir dryer

Heater

Flowmeter

Thermo couple

●

Comp.

Sg.

Air bubbles

Acrylic resin

TestW/O Emulsion

Test section

Air

Ultrasonic transducer

Figure 2. Experimental apparatus.

Table 1. Experimental conditions.

bubbling device that set in the bottom of the test section.

The generated air bubble is directly heat exchanged by

contact with a test sample. The inlet air temperature is

fixed to 303 K. The heat quantity is calculated by a dif-

ference between inlet and outlet air temperature. All tem-

perature measurement is performed by K-type thermo

couples which have diameter 0.18 mm. The test section

is made of transparent acrylic resin, and it has an inner

diameter 100 mm, a height 550 mm and 10 mm in thick-

ness. The 3 units of ultrasonic transducer (Alex Corpora-

tion, ultrasonic oscillator NMS150-3FP, the oscillating

frequency 28, 50 or 80 kHz, max. output 150 W) are at-

tached to the acrylics cylinder pipe. The whole of test

section is stored in a low-temperature-controlled room,

and is made into the structure which prevents the influ-

ence by the temperature change by freezer on-off by

covering with thermal insulation. Table 1 indicates the

experimental conditions of this study.

Frequency of ultrasonic f 28, 50, 80 kHz

Air mass flow Ga 0.06465 kg/min

Air pressure P 0.1 MPa

Inlet air temperature Tain 303 K

Initial temp. of emulsion Tei 283 ± 0.5 K

Temp. of freezer Tf 233 K

Cooling rate uc 0.0015 - 0.0045 K/sec

Height of emulsion Z 173 mm

Degree of supercooling ΔT 5 - 20 K

Adding time of ultrasonic τu 20 sec

6) Measure the data and calculate the quantity of heat.

The experiment of this research is conducted by the

following procedures. 2.3. Quantity of Heat Storage Calculation

1) Set 233 K in a temperature control room; Figure 3 shows the time history of test emulsion tem-

perature on experiment. The variation of temperature is

shown from the emulsion set time into test section. The

temperature of an emulsion decreases with time and

reaches the melting point of water 273 K in about 800

seconds. The ultrasonic is impressed 20 seconds when

the emulsion temperature reaches to 268 K. Test emul-

sion is continuously cooled till reach to the supercooling

2) Set sample into the test section;

3) Cool the sample below to the melting point of the

latent heat storage material;

4) Impress the ultrasonic wave at 268 K (20 sec, 75%

of 150 W × 3 units) and keep cooling;

5) Heat exchange by the temperature controlled dry air

at the test section;

S.-I. MORITA ET AL. 51

255

260

265

270

275

280

285

290

295

02000 4000 6000 800010000

[K]

Time τ[sec]

273

=5 [mass%]

=3600 [sec]

= 20 [sec]

f = 28 [kHz]

ΔT =10 [K]

=0.0029 [K/sec]

add ultrasonic

air bubbling start

latent heat stora

Latent heat release

Impress

ultrasonic

Figure 3. Time history of Te.

degree 10 K (263 K) in about 4800 seconds. Test emul-

sion’s mass used for the experiment is me = 1.5 kg and

the temperature controlled room temperature is set Tf =

233 K. The cooling rate uc of this research is about uc =

0.0015 - 0.0045 K/sec. After the completion of cooling, a

bypass line is changed and the dried air (303 K) is flowed

to air bubbling device in test section. The temperature of

test emulsion rises by jet of an air bubble. The constant

temperature near the melting point of the water resulting

from latent heat release is observed in about 8200 -

10,000 seconds.

The amount of latent heat storages is measured with

the measurement data at the time of heat release. The

exchanged heat quantity of air is calculated by Equation

(1), in which the mass flow rate of air Ga, specific heat

Cpa and the temperature difference of inlet and outlet air

(Tain − Taout). The sensible heat of test emulsion is derived

by Equation (2), in which specific heat of emulsion Cpe,

mass of emulsion me and temperature difference of emul-

sion by time step (Ti − Ti − 1). The quantity of latent heat

storage of emulsion is calculated by Equation (3). The

amount of theoretical latent heat of dispersed water in

emulsion is expressed by Equation (4). All condition of

this experiment is carried out by C = 5 mass% and me =

1.5 kg, so that the theoretical latent heat of test emulsion

is calculated Qlt = 25 kJ by using latent heat of ice Qm =

333.7 kJ/kg. Equation (5) is defined as the latent heat

storage rate of emulsion.





totapaain aout

QGCTT

 (1)



speeii-

QCmTT





(2)

ltots

QQ Q (3)

lte m

100QC mQ (4)

llt

100QQ



 (5)

The measurement accuracy of the experiment was au-

thorized in advance by using the silicone oil as the test

sample. The accuracy approval experiment of the direct

heat exchange method was conducted 6 times by carry-

ing out 10 K temperature rise of the silicone oil. These

pre-experimental results showed the calorimetric meas-

urement accuracy ±1.7% of this research of a sensible

heat base. It is checked by previous test that the amounts

of sample heating by ultrasonic impression (20 seconds),

is less than 3% (0.75 kJ) of the latent heat of emulsion.

3. Experimental Results and Discussions

Latent Heat Storage Rate of Test W/O Emulsion

Figure 4 indicates the variation of the quantity of latent

heat storage Ql of test W/O emulsion with the supercool-

ing degree ΔTsc on each cooling rate uc. The quantity of

latent heat storage Ql of test W/O emulsion increases

with increasing of the supercooling degree ΔTsc. The

solid line in a figure shows the averaged value by the

experimental data of this study. The maximum line and

minimum line by an experimental value are shown in the

figure with the dashed line. It seems that the correlation

with a cooling rate is not seen as for the amount of latent

heat storages. A loose increase is observed until the

amount of latent heat storages reaches the supercooling

degree of about ΔTsc = 3 K. In supercooling degree 3 - 12

K, the rate of increase of the amount of latent heat stor-

ages is large.

Figure 5 shows the relationship between the number

of freezed waterdrops in test emulsion, that converted

from the amount of latent heat storage, and the super-

cooling degree. The number of freeze waterdrops is in-

creased with increasing of the supercooling degree.

Table 2 is indicated the achievements of passed re-

searches about bulk supercooling water. As for the re-

search on bulk water, the influence about the type of wa-

ter, the heat transfer surface, the volume, the cooling rate

has been considered and the method of supercooling re-

lease.

Figure 6 shows the variation of probability of freezing

φ with the supercooling degree ΔTsc. Probability of freez-

ing φ is calculated by probability distribution function for

the purpose of performing comparison with the data of

other researchers about supercooling release of bulk wa-

ter. The broken and chain lines in a figure show the re-

sults of the bulk water of (a) Okawa et al.: Electricity (b)

Inada et al.: Ultrasonic and (c) Inaba et al.: Ice nucleat-

ing substance. The data of (b) Inada et al. is the result of

tap water by using the ultrasonic impressing. The data of

surface and a cooling rate. The W/O emulsion’s prob-

ability of freezing φ reaches to about 100% in the super-

cooling degree ΔTsc of more than 15 K. As compared with

the same conditions of bulk water, it is understood that

the supercooling degree of a W/O emulsion is large and

it is difficult to carry out a latent heat storage.

S.-I. MORITA ET AL.

579 111315171921

N[-]

ΔT

[K]

(×10

)

Freezed

Non-Freezed

0510 15 20 25 30 35

[kJ]

ΔT

[K]

■u

=0.0015-0.002 [K/sec]

▲u

=0.002-0.0025 [K/sec]

●u

=0.0025-0.003 [K/sec]

◇u

=0.003-0.0035 [K/sec]

□u

=0.0035-0.004 [K/sec]

△u

=0.004-0.0045 [K/sec]

○u

=0.0045-0.005 [K/sec]

Max data

Min data

Averaged data

Figure 4. Variation of Ql with ΔTsc. Figure 5. Relationship between N and ΔTsc.

Table 2. Achievement of passed researches on bulk water.

Authors Ref. Water type Heat transfer surface Vol. cm3ΔTsc KUc K/sec Supercooling release method

(a) Okawa et al. [8] Pure water Acrylic/Water 0.005 4 - 6 0.0037 Electricity

(b) Inada et al. [9] Tap water Copper/Water 1.3 1.5 - 4.50.039 - 0.049Ultrasonic

(d) Oil/Water 1.0 3 - 7 - Piston

(e) Oil/Water/Oil 0.05 4 - 10 - Piston

(f) Polypropylene/Water1.0 2 - 9 0.0017 Ultrasonic

(g)

Hozumi et al. [11] Ultra pure water

Glass/Water 100 3 - 5 - Waterdrop

Figure 6. Relationship between φ and ΔTsc.

Figure 7 indicates the relationship between φ and ΔTsc

on each experimental condition of impressing or without

impressing the ultrasonic. It is clarified that it is possible

to reduce 20 K of supercooling degree by impressing the

ultrasonic wave.

release of W/O emulsion by ultrasonic impression, and

the following conclusions were obtained:

1) It is suggested that the W/O emulsion’s probability

of freezing by using ultrasonic reaches to about 100% in

the supercooling degree of more than 15 K.

2) It is clarified that as compared with the same condi-

tions of bulk water, the supercooling degree of a W/O

emsion is large.

4. Conclusions

It was performed by experimental study of supercooling

S.-I. MORITA ET AL. 53

Figure 7. Variation of φ with ΔTsc.

It is revealed that ultrasonic impression is the method

of supercooling release of W/O emulsion.

REFERENCES

[1] H. Inaba and S.-I. Morita, “Fundamental Study of Cold

Heat Storage System of O/W-Type Emulsion Having

Cold Latent Heat Dispersion Material (2nd Report, Flow

and Cold Heat-Storage Characteristics of Emulsion in a

Coiled Double-Tube Heat Exchanger),” JSME Interna-

tional Journal Series B: Fluids and Thermal Engineering,

Vol. 60, No. 572, 1994, pp. 1422-1429.

doi:10.1299/kikaib.60.1422

[2] H. Inaba, A. Horibe, H. Tsukamoto and M.-J. Kim, “Heat

Storage Characteristics of Latent Microcapsules Using

Hot Air Bubbles by Direct Contact Heat Exchange,”

JSME International Journal Series B: Fluids and Thermal

Engineering, Vol. 66, No. 645, 2000, pp. 1487-1494.

doi:10.1299/kikaib.66.1487

[3] H. Kumano, A. Saito, S. Okawa and Y. Goto, “Study on

Fundamental Characteristics of TBAB Hydrate Slurry,”

JSME International Journal Series B: Fluids and Thermal

Engineering, Vol. 72, No. 724, 2006, pp. 3089-3095.

[4] J. P. Bedecarrats, J. Castaing-Lasvignottes, F. Strub and J.

P. Dumas, “Study of a Phase Change Energy Storage Us-

ing Spherical Capsules. Part 1 Experimental Results,”

Energy Conversion and Management, Vol. 50, No. 10,

2009, pp. 2527-2536.

doi:10.1016/j.enconman.2009.06.004

[5] J. P. Bedecarrats, J. Castaing-Lasvignottes, F. Strub and J.

P. Dumas, “Study of a Phase Change Energy Storage Us-

ing Spherical Capsules. Part 2 Numerical Modeling,” En-

ergy Conversion and Management, Vol. 50, No. 10, 2009,

pp. 2537-2546. doi:10.1016/j.enconman.2009.06.003

[6] R. Yang, H. Xu and Y. P. Zhang, “Preparation, Physical

Property and Thermal Physical Property of Phase Change

Microcapsule Slurry and Phase Change Emulsion,” Solar

Energy Materials & Solar Cells, Vol. 80, No. 4, 2003, pp.

405-416. doi:10.1016/j.solmat.2003.08.005

[7] A. Saito, Y. Utaka, A. Tamaki, K. Matsuzawa and S.

Kajikawa, “On the Freezing Process with Supercooling

(Measurements of the Heat Transfer Surface Effects on

the Maximum Degree of Supercooling, and the Statistical

Analyses),” JSME International Journal Series B: Fluids

and Thermal Engineering, Vol. 54, No. 502, 1988, pp.

1439-1466. doi:10.1299/kikaib.54.1439

[8] S. Okawa, A. Saito and T. Harada, “Experimental Study

on the Effect of the Electric Field on the Freezing of the

Supercooled Water,” Transactions of the Japan Society of

Refrigerating and Air Conditioning Engineers, Vol. 14,

No. 1, 1997, pp. 47-55.

[9] T. Inada, X. Zhang, A. Yabe, M. Tanaka and Y. Kozawa,

“Active Control of Freezing of Supercooled Water by Ul-

trasonic Vibratio,” JSME International Journal Series B:

Fluids and Thermal Engineering, Vol. 65, No. 683, 1999,

pp. 3455-3460. doi:10.1299/kikaib.65.3455

[10] H. Inaba, K. Takeya and T. Asano, “Study on Ice Forma-

tion in Still Supercoold Water with Ice Nucleating Sub-

stance,” Transactions of the Japan Society of Refrigerat-

ing and Air Conditioning Engineers, Vol. 11, No. 3, 1994,

pp. 277-287.

[11] T. Hozumi, A. Saito and S. Okawa, “Study on the Mecha-

nism of the Freezing of the Supercooled Water under the

Effect of the Ultrasonic Wave,” Transactions of the Ja-

pan Society of Refrigerating and Air Conditioning Engi-

neers, Vol. 16, No. 2, 1999, pp. 147-156.

[12] T. Inada, T. Koyama, F. Goto and T. Seto, “Loss of

Ice-Nucleating Activity of Silver Iodide by Synthetic

Polymers,” Proceedings of 48th National Heat Transfer

Symposium of Japan, Okayama, 1-3 June 2011, pp. 443-

444.

[13] H. Inaba and S.-I. Morita, “Fundamental Study of Cold

Heat Storage System of O/W-Type Emulsion Having

Cold Latent Heat Dispersion Material (3rd Report, Cold

Heat-Release Characteristics of Emulsion by Air-Emul-

sion Direct-Contact Heat Exchange Method),” JSME In-

ternational Journal Series B: Fluids and Thermal Engi-

neering, Vol. 61, No. 583, 1995, pp. 1149-1156.

doi:10.1299/kikaib.61.1149

[14] S. Aoyama and H. Inaba, “Fundamental Study on Cold

S.-I. MORITA ET AL.

Energy Release by Direct Contact Heat Exchange be-

tween Ice Water Slurry and Hot Air,” JSME Interna-

tional Journal Series B: Fluids and Thermal Engineering,

Vol. 67, No. 654, 2001, pp. 514-521.

doi:10.1299/kikaib.67.514

[15] P. Schalbart, M. Kawaji and K. Fumoto, “Formation of

Tetradecane Nanoemulsion by Low-Energy Emulsifica-

tion Methods,” International Journal of Refrigeration,

Vol. 33, No. 8, 2010, pp. 1612-1624.

doi:10.1016/j.ijrefrig.2010.09.002

[16] S.-I. Morita, Y. Hayamizu, A. Horibe, N. Haruki and H.

Inaba, “Experimental Study on Latent Heat Storage Char-

acteristics of W/O Emulsion,” Journal of Thermal Sci-

ence, Vol. 22, No. 2, 2013, pp. 145-151.

doi:10.1007/s11630-013-0605-2

[17] “Data Sheet of Silicone Oil TSF451-10,” Momentive

Society of Mechanical Engineering, “JSME

Performance Materials Holdings Inc., Columbus, 2007,

pp. 4-11.

[18] The Japan

Data Book Heat Transfer,” 5th Edition, Maruzen Com-

pany, Limited, Tokyo, 2009, 291 pp.