n-Tetradecane

Subscriber access provided by RYERSON UNIV

Article

Preparation and thermal performance of silica/n-tetradecane microencapsulated phase change material for cold energy storage Yutang Fang, Hao Wei, Xianghui Liang, Shuangfeng Wang, Xin Liu, Xuenong Gao, and Zhengguo Zhang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b01799 • Publication Date (Web): 09 Oct 2016 Downloaded from http://pubs.acs.org on October 16, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels 1

1 2

Preparation and thermal performance of silica/n-tetradecane microencapsulated phase change material for cold energy storage

3

Yutang Fang*, Hao Wei, Xianghui Liang, Shuangfeng Wang，Xin Liu, Xuenong

4

Gao, Zhengguo Zhang

5

Key Laboratory of Enhanced Heat Transfer and Energy Conservation of the Ministry

6

of Education, South China University of Technology, Guangzhou, 510640, People’s

7

Republic of China

8

*Corresponding author. Tel. /fax: +86-20-87113870

9

E-mail address: [email protected] (Yutang Fang)

10

Abstract: A novel silica (SiO2)/n-tetradecane (Tet) microencapsulated phase change

11

material (MEPCM) was synthesized by in-situ interfacial polycondensation. The

12

influences of the amount of the composite emulsifier and the mass ratio of n-

13

tetradecane and tetraethyl silicate on the MEPCM performance were systematically

14

investigated. The morphology, chemical structure and the composition of the

15

MEPCM were characterized by Scanning electron microscopy and Energy dispersive

16

X-ray spectrometer (SEM-EDS), Fourier transform infrared spectroscopy (FT-IR), X-

17

ray diffractometer (XRD), and its thermal performance and thermal stability were

18

measured by Differential scanning calorimeter (DSC) and Thermogravimetric

19

analyzer (TGA). The results showed that the n-tetradecane core material was

20

successfully encapsulated by silica shell material with encapsulation ratio of 62.04%.

21

The MEPCM had a melting enthalpy of 140.5 kJ kg-1 and thermal conductivity of

22

0.139 W m-1 K-1. Because of its excellent thermal performance and thermal stability,

23

silica/n-tetradecane MEPCM displays a good potential for cold energy storage.

24

Keywords: Microencapsulated phase change material; Silica shell; Cold energy

25

storage; Thermal performance; Thermal conductivity

ACS Paragon Plus Environment

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

2

26

1. INTRODUCTION

27

In recent years, energy problem has become the bottleneck of industrial development

28

and social progress due to the imminent energy shortage and the increase of greenhouse

29

emission 1. The technology of cold thermal energy storage (CTES), with the help of

30

phase change material (PCM), realizes the storage and transportation of cold thermal

31

energy. Because of high energy storage density and nearly isothermal behavior in phase

32

transition process, the CTES technology can improve energy efficiency, achieve peak

33

load shifting and reduce energy consumption 2, which has been widely applied to

34

industrial fields such as recovery and utilization of industrial waste energy 3, energy

35

conserving in building 4, electronic devices thermal control 5, and so on.

36

As a traditional PCM, water (ice) is used for CTES system due to the advantageous

37

features such as non-toxic, high energy storage density and bargain price. Tamasauskas

38

6

39

Compared with the heat pump system only using sensible storage, there was a 26%

40

reduction in operating energy consumption. However, in order to store cold energy, air-

41

conditioning system has to run below the phase change freezing point of water greatly

42

decreasing the coefficient of performance (COP) of refrigerator 7. Therefore, most of

43

researches for PCM focus on hydrates salt due to their more suitable phase transition

44

temperature and excellent latent heat storage capacity. However, a majority of inorganic

45

hydrate salts are prone to supercooling and phase separation, which limits their

46

application severely 8. What’s more, only few pure hydrates are known in the required

47

temperature range for air conditioning and cooling 9. Hence, the research expands to

et al. investigated the performance of a solar-assisted heat pump containing ice slurry.


Page 2 of 19

Page 3 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels 3

48

organic PCM due to their appropriate thermal properties and chemical stability. Among

49

them, n-tetradecane (Tet) is an attractive alternative due to the suitable phase transition

50

point in the range of 5-9 ℃ and little supercooling.

51

On the other hand, leakage problems caused by direct use of phase change materials

52

leading certain harm to energy storage system and environment 2. In order to prevent

53

undesirable problems, several methods have been developed to prepare PCM such as

54

encapsulated PCM 10 and form-stable PCM 11. Among these methods, the encapsulation,

55

which can enlarge heat transfer area and reduce the interference from surroundings, is

56

considered as one of the most widely used technique. Besides, organic shell materials,

57

such as polystyrene 12, melamine-formaldehyde resin 13 and urea-formaldehyde resin 14,

58

are widely employed for their prominent properties such as stability, durability and

59

flexibility. Fang et al.

60

nanoencapsulated phase change material (NEPCM) as latent functionally thermal fluid

61

(LFTF) for cold thermal energy storage. The results showed that the melting and

62

freezing point of the NEPCM was 4.04 and -3.43 ℃, respectively, which indicating it

63

is suitable for cold thermal energy storage. Fang et al.

64

nanoencapsulated n-tetradecane with urea and formaldehyde resin as shell material.

65

The results demonstrated that NEPCM had a latent heat storage capacity of 134.16 kJ

66

kg-1 and phase change temperature of 5.7 ℃ . Konuklu et al.

67

microencapsulated caprylic acid with different organic shell materials by coacervation

68

method. Qiu et al.

69

butylmethacrylate (BMA)-based copolymer shells. The DSC results shows the n-

17

7

synthesized a novel polystyrene/n-tetradecane composite

15

reported the synthesis of

16

fabricated

prepared the microcapsules of n-octadecane with different n-


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

4

70

octadecane content of the microencapsulated phase change material (MEPCM) with P

71

(BMA-co-MAA) has the highest latent heat of 144.3 kJ kg-1 and both the melting and

72

crystallization temperature of the PCM were altered by less than 1.0 ℃ after 1000

73

thermal cycles.

74

In spite of this, organic materials still have common drawbacks, such as flammability,

75

low mechanical strength and poor thermal conductivity. Zhang et al. 18 investigated the

76

heat storage characteristic of MEPCM slurry. The results showed that the heat storage

77

capacity increased with the increasing of mass concentration, while the completion time

78

increase more. So, there is an inherent requirement of high thermal conductivity shell

79

material for encapsulated PCM to enhance heat transfer performance. Usually, the

80

thermal conductivity of inorganic materials is significantly higher than that of the

81

organic ones. Moreover, they possess higher mechanical strength compared with

82

organic materials. Taguchi et al.

83

hybrid as shell. The obtained phase change material showed that incorporation of

84

inorganic particles in the shell could improve the thermal conductivity of the

85

microcapsules. Song et al.

86

phase change material for thermal energy storage. Yu et al. 21 successfully synthesized

87

calcium carbonate/ n-octadecane MEPCM and its thermal conductivity (1.264 W m-1

88

K-1 ) was higher than that of MEPCM with polymeric shell material (0.2 W m-1 K-1) 22.

89

Based on the mentioned above, investigations on tetradecane for cold energy are still

90

inadequate. Moreover, the microcapsules with inorganic shell materials for cold energy

91

storage have rarely been reported. In this study, by introducing in-situ interfacial

20

19

synthesized the microcapsules with SiC/polyurea

prepared capric-stearic acid@SiO2 microencapsulated


Page 4 of 19

Page 5 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels 5

92

polycondensation strategy, we attempted to synthesize microencapsulated n-

93

tetradecane with silica as shell material for cold energy storage, optimized the

94

polycondensation condition, and discussed its morphology, chemical structure,

95

composition and thermal performance.

96

2. EXPERIMENTAL SECTION

97

2.1. Materials

98

n-Tetradecane (Tet, AR), tetraethyl silicate (TEOS, CP), tween-80(CP), span-80 (CP),

99

polyvinyl alcohol (PVA, AR), acetic acid (HAc, AR), ethanol (AR) and sodium

100

chloride (NaCl, AR) were purchased by Tianjin Kemiou Chemical Reagents, China.

101

All chemicals were used as received without further purification.

102

2.2. Preparation of MEPCM

103

In a typical procedure, an oil phase mixture obtained by adding 10.0 g Tet and 0.75 g

104

composite emulsifier composed of span-80 and tween-80 with mass ratio of 1:1, and an

105

aqueous medium prepared by mixing 100 g deionized water and 1.5 g PVA together

106

were even mixed in a 250 ml beaker under the water bath of 25 ℃ and the speed of

107

500 rpm, then added dropwise 2 ml 2.5 mol L-1 NaCl solution for 30 min, a stable oil-

108

in-water (o/w) microemulsion was formed. Then, 0.3 g 10 wt% HAc

109

10.0 g TEOS added dropwise to the microemulsion, and the reaction was accomplished

110

at 55 ℃ and the speed of 300 rpm for 3 h. The resulting product recorded as SiO2/Tet

111

MEPCM was obtained by filtering, washing with ethyl alcohol and distilled water three


solution and

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 19

6

112

times and drying at low temperature sequentially. The encapsulation ratio (R) can be

113

determined from the following equation:

114

R=

115

Where ∆Hm,

116

tetradecane, respectively.

117

2.3. Characterization of MEPCM

118

The MEPCM was observed by a DM 2500P polarizing microscope (POM, Leica

119

Instrument Co., Germany). The morphology and surface element of the sample were

120

measured with an S-3700 scanning electron microscope and energy dispersive X-ray

121

spectrometer (SEM-EDS, Hitachi Co., Japan) with Au-target and accelerating voltage

122

of 15 kV, and its structure was recorded with a Vector 33 Fourier transform infrared

123

spectrometer (FT-IR, Bruker Instrument Co., Germany) in the range from 400 to 4000

124

cm-1 using KBr pellets. X-ray diffraction pattern of the solid powder sample was

125

obtained using D/max-ⅢA X-ray diffractometer (XRD, Rint Co., Japan) with Cu Kα

126

radiation at the radiation tube voltage of 40 kV, tube current of 40 mA and the scan

127

speed of 2° min-1. The thermal behavior of the MEPCM was carried out on Q20

128

differential scanning calorimeter (DSC,TA Instrument, USA) under N2 atmosphere at

129

a heating or cooling rate of 5 ℃ min-1 in the range of -30-40 ℃. About 10 mg sample

130

is used each time. Thermal conductivity was measured with a 2500s thermal constant

131

analyzer (Hot Disk Co., Sweden) using transient plane source (TPS) method

132

microcapsules and 0.5 g water glass were filled into mold to form two equivalent thin

133

films with the diameter of 2 cm and the Tet was in a liquid form. The sensor was

H m ,micro PCM  100% H m ,PCM micro-PCM,

(1)

∆Hm,

PCM

are melting enthalpy of the MEPCM and pure n-


23

. 10 g

Page 7 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels 7

134

sandwiched between two pieces of film supported by a background material. Thermal

135

conductivity of the microcapsules based on the average of three tests at room

136

temperature. The thermal stability of the dried MEPCM was evaluated using TG 209

137

thermogravimetric analyzer (TG, Nietzsche Co. Ltd., Germany) at a scanning rate of

138

10 ℃ min-1 under a nitrogen atmosphere.

139

3. RESULTS AND DISCUSSION

140

3.1. Influence of polycondensation condition

141

3.1.1. Amount of composite emulsifier

142 143 144

Fig. 1 Optical micrographs of the SiO2/Tet MEPCM with different amount of composite emulsifier: (a) 1.0 g, (b) 1.5 g, (c) 2.0 g and (d) 2.5 g

145


Energy & Fuels 8

150 120 -1

Enthalpy (kJkg )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 19

90 60 30 0 0.5

146 147

1.0

1.5

2.0

2.5

3.0

Amount of emulsifier (g) Fig.2 Effect of the amount of composite emulsifier on the enthalpy of SiO2/Tet MEPCM

148

The emulsifier can reduce microemulsion surface tension significantly, which is in

149

favor of SiO2 (shell) deposition on the oil droplets (core) surface and produces regular

150

spherical MEPCM. The optical micrographs of the MEPCM with different amount of

151

composite emulsifier are shown in Fig.1. When over dosage of emulsifier, composite

152

emulsifier seriously influenced phase change enthalpy of MEPCM. As shown in Fig.2,

153

as emulsifier of 1.5 g, the melting enthalpy of MEPCM reached 140.1 kJ kg-1, as

154

emulsifier of 2.5 g, though it could produce uniform and small MEPCM, the

155

microcapsules has a lower enthalpy (115.2 kJ kg-1). Therefore, the appropriate amount

156

of composite emulsifier was 1.5 g.


Page 9 of 19

9

157

3.1.2. Mass ratio of Tet/TEOS

30/70: 40/60: 50/50: 60/40:

2.5 2.0 1.5

Heat Flow (W/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

77.1 kJ/kg 107.5 kJ/kg 140.1kJ/kg 151.0 kJ/kg

1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 -40

-30

-20

-10

0

10

20

30

40

50

Temperature (°C)

158 159

Fig. 3 Effect of the mass ratio of Tet and TEOS on the enthalpy of SiO2/Tet MEPCM

160 161

Fig. 4 Optical micrograph of SiO2/Tet MEPCM synthesized at RTet/TEOS of 30/70

162

The mass ratio of Tet and TEOS (RTet/TEOS) influences phase change enthalpy of

163

microcapsules. As shown in Fig. 3, the enthalpy of the microcapsules increased with

164

the increase of RTet/TEOS. When RTet/TEOS of 30/70, high content SiO2 formed by

165

hydrolysis and condensation of TEOS led to some excess tiny SiO2 particles attached

166

on the surface of the microcapsules (Fig.4) and the decrease of encapsulation ratio. As


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 19

10

167

RTet/TEOS of 60/40, the melting enthalpy of MEPCM was 151.0 kJ kg-1. Since the

168

obtained SiO2 shell material was too thin to encapsulate Tet core material completely,

169

the stability of the microcapsules was inferior. Based on the above factors, the optimum

170

mass ratio of RTet/TEOS was 50/50.

171

3.2. Characterization of the SiO2/Tet MEPCM

172

3.2.1. SEM observation and EDS analysis

173 174

Fig.5 SEM photo and EDS spectrum of SiO2/Tet MEPCM

175

Table 1 EDS data of SiO2/Tet MEPCM Element

Weight/%

Atomic/%

C

58.09

68.21

O

28.50

25.12

Si

11.45

5.75

Others

1.96

0.91

176

The morphology of SiO2/Tet MEPCM was observed using scanning electron

177

microscopy (SEM). As shown in the Fig. 5(a), the synthesized MEPCM are spherical

178

particles with smooth and compact surface. Its particle size is about 2 μm.


Page 11 of 19

11

179

The EDS spectrum of the SiO2/Tet MEPCM was analyzed. As shown in Fig. 5(b),

180

obviously, the synthesized MEPCM contained C, O and Si element, among them, C

181

atom stemmed from n-tetradecane core and Si and O atom originated from SiO2. Table

182

1 shows the EDS analysis data of the SiO2/Tet MEPCM. The mass percent of C element

183

was 58.09%, and the total mass percent of both Si and O element was 39.95%.

184

3.2.2. Thermal performance

6

Endo

o

Tm:5.88 C

Tet

Hm:225.8kJ/kg

4

o

Tc:2.15 C

-1

Heat flow (W g )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Hc:225.4kJ/kg

2 0

o

-2

Tm:2.39 C Hm:140.1kJ/kg

-4

MEPCM

-6

Hc:139.9kJ/kg

-20 185 186

o

Tc:-0.39 C

-10

0

10

0

20

Temperature ( C) Fig. 6 DSC curves of SiO2/Tet MEPCM and n-tetradecane

187 188 189 190


30

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 19

12

191

Table 2 Comparison of encapsulation ratio of the MEPCM prepared with results in literature MEPCM

Latent heat(J/g)

Encapsulation ratio (%)

Reference

n-Tetradecan/polystyrene

98.71

44.7

7

n-Tetradecan/UF

134.16

60.0

15

n-Tetradecan /AS

113.5

51.5

24

n-Tetradecan /ABS

107.1

48.5

24

n-Tetradecan /PC

113.2

51.3

24

n-Tetradecan /SiO2

140.1

62.0

Present study

192

Fig.6 shows the DSC curves of SiO2/Tet MEPCM and pure n-tetradecane. The results

193

showed that the melting enthalpy of SiO2/Tet MEPCM and n-tetradecane was 140.1

194

and 225.8 kJ kg-1, respectively. Table 2 presents the comparison of the encapsulation of

195

MEPCM prepared in this study with different MEPCM in literature. The results indicate

196

that the of SiO2/Tet MEPCM prepared in this study are as high as those of organic shell

197

(about 120 kJ kg-1), which proving that the obtained MEPCM has good thermal storage

198

potential for cold energy storage. It could also be observed that the melting (Tm) and

199

the crystallization temperature (Tc) of the MEPCM was 2.39 and -0.39 ℃, respectively,

200

and the one of n-tetradecane was 5.88 and 2.15 ℃. Slight difference of the melting and

201

solidification points between the core material (Tet) and the MEPCM can be interpreted

202

that the thermal resistance of SiO2 shell delays the phase change process of the MEPCM.


Page 13 of 19

13

3.2.3. Thermal stability

0

100 MEPCM

80

-10

60

-20

40

Tet

-30

20

DTG/ %/min

203

TG/ %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

-40

0 0

100

200

300

400

500

-50

o

204

Temperature/ C

205

Fig. 7 TG and DTG curves of SiO2/Tet MEPCM

206

Fig.7 shows thermogravimetric (TG) and differential thermogravimetric (DTG) cures

207

of SiO2/Tet MEPCM and n-tetradecane. The TG results showed that n-tetradecane

208

exhibited the weight loss of 97.5% which resulted from gasification of n-tetradecane in

209

the range of 30 to 150℃, while MEPCM displayed the weight loss of 58.5%, which

210

corresponded to the core content in the range of 130 to 230℃. The initial and final

211

gasification temperature of MEPCM obviously lagged behind that of pure n-tetradecane.

212

Moreover, as shown from DTG, there existed a significant difference between their

213

gasification rates. The maximum gasification rate of n-tetradecane was -35.38% min-1

214

at 97 ℃ , while the one of MEPCM was only -15.50 % min-1 at 197 ℃ , which

215

demonstrating that silica has good protection to the n-tetradecane.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 19

14

216

3.2.4. Thermal conductivity

217

Table 3 Thermal conductivity of SiO2/Tet MEPCM with different mass ratio of RTet/TEOS RTet/TEOS

Thermal conductivity

g/g

/( W m-1 K-1)

100/0 a

0.098

60/40

0.125

50/50

0.139

40/60

0.144

30/70 50/50(RTet/PS) a

0.151 b

0.106

denotes pure n-tetradecane without SiO2,

b

denotes polystyrene (PS)/Tet MEPCM

218

Note:

219

synthesized at RTet/PS of 50/50 as reference 13

220

Although n-tetradecane has many advantages for cold energy storage, as organic phase

221

change material, it has inherent shortcomings such as low thermal conductivity. Table

222

3 shows the thermal conductivity of SiO2/Tet MEPCM with different mass ratio of Tet

223

and TEOS (RTet/TEOS). As shown in table 3, the thermal conductivity of pure n-

224

tetradecane was only 0.098 W m-1 K-1. When SiO2 encapsulated n-tetradecane, the

225

thermal conductivity of MEPCM markedly improved. With the decrease of the RTet/TEOS,

226

namely, the increase of the SiO2 content, thermal conductivity of MEPCM increased.

227

Such as RTet/TEOS was 50/50, the thermal conductivity of MEPCM reached 0.139 W m-

228

1

229

PS organic polymer as shell at the same content of n-tetradecane, respectively. It

230

confirms that the inorganic silica as shell plays an important role in enhancing heat

231

transfer performance of MEPCM.

K-1, which was 1.454 and 1.311 times than that of n-tetradecane, and MEPCM with


Page 15 of 19

15

470

2854

Transmittance

MEPCM

722

3.2.5. FT-IR analysis

1464

1084 1467 1360

3385

SiO2

4000

3500

3000

2854

Tet 2924

461

2925

721

232

1081

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

2500

2000

1500

1000

500

Wavenumber (cm-1)

233 234

Fig. 8 FTIR spectra of SiO2/Tet MEPCM

235

The FT-IR spectra of MEPCM, n-tetradecane and SiO2 are shown in Fig.8. In the

236

spectrum of n-tetradecane, the absorption peaks at 1467 cm-1and 1360 cm-1 were

237

corresponded to C-H bending vibration of –CH3, the ones at 2924 cm-1 and 2854 cm-1

238

were assigned to C-H stretching vibration of CH3– and –CH2. In addition, the

239

absorption peak at 721 cm-1 was associated with –CH2 in-plane rocking vibration. In

240

the spectrum of silica, the absorption peak at 3385 cm-1 was attributed to Si-OH

241

stretching vibration, the ones at 1084 cm-1 and 461 cm-1 can be found owing to Si-O-Si

242

symmetric and asymmetric stretching vibration. In the spectrum of SiO2/Tet MEPCM, all

243

the characteristic peaks existed in n-tetradecane and silica still appeared in the MEPCM.

244

No new significant peaks observed suggesting that no chemical interaction happens

245

between the components. These results indicate that n-tetradecane is encapsulated by

246

SiO2.


Energy & Fuels 16

247

3.2.6. XRD analysis

Intensity/ (a.u)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 19

0

10

20

30

40

50

/ ()

248 249

Fig.9 XRD spectrum of SiO2/Tet MEPCM

250

Fig.9 displayed the XRD pattern of the SiO2/Tet MEPCM. A wide disperse peak at

251

about 20°appeared which indicates that the obtained SiO2 shell displays amorphous

252

structure. Since n-tetradecane is no crystal liquid under test condition, there was no

253

characteristic peak in the spectrum.

254

4. CONCLUSIONS

255

Novel microencapsulated phase change material (MEPCM) with silica (SiO2) as shell

256

and n-tetradecane (Tet) as core for cold energy storage was successfully synthesized by

257

in-situ interfacial polycondensation. The obtained optimum conditions were 1.5 g

258

composite emulsifier and 50/50 RTet/TEOS. According to the FT-IR, XRD, SEM-EDS

259

analysis results, n-tetradecane was well encapsulated by SiO2 shell with encapsulation

260

ratio of 62.04%. Based on the results of DSC and TG, the MEPCM had melting

261

enthalpy of 140.1 kJ kg-1 and excellent thermal stability. Moreover, since excellent


Page 17 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels 17

262

thermal conductively of SiO2 shell, the thermal conductively of MEPCM reached 0.139

263

W m-1 K-1. It indicates that the synthesized SiO2/Tet MEPCM has considerable potential

264

for cold energy storage.

265

ACKNOWLEDGMENT

266

This work was supported by National Natural Science Foundation of China (No.

267

51536003, No.21471059).

268

REFERENCES

269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295

1. Agyenim, F.; Hewitt, N.; Eames, P.; Smyth, M., A review of materials, heat transfer and phase change problem formulation for latent heat thermal energy storage systems (LHTESS). Renewable & Sustainable Energy Reviews 2010, 14 (2), 615-628; (b) Karthikeyan, S.; Solomon, G. R.; Kumaresan, V.; Velraj, R., Parametric studies on packed bed storage unit filled with PCM encapsulated spherical containers for low temperature solar air heating applications. Energy Conversion & Management 2014, 78 (1), 74–80; (c) Sarı, A.; Alkan, C.; Biçer, A.; Altuntaş, A.; Bilgin, C., Micro/nanoencapsulated n -nonadecane with poly(methyl methacrylate) shell for thermal energy storage. Energy Conversion & Management 2014, 86 (10), 614-621; (d) Trigui, A.; Karkri, M.; Krupa, I., Thermal conductivity and latent heat thermal energy storage properties of LDPE/wax as a shape-stabilized composite phase change material. Energy Conversion & Management 2014, 77 (1), 586-596. 2. Liu, C.; Rao, Z.; Zhao, J.; Huo, Y.; Li, Y., Review on nanoencapsulated phase change materials: Preparation, characterization and heat transfer enhancement. Nano Energy 2015, 13, 814-826. 3. López-Sabirón, A. M.; Royo, P.; Ferreira, V. J.; Aranda-Usón, A.; Ferreira, G., Carbon footprint of a thermal energy storage system using phase change materials for industrial energy recovery to reduce the fossil fuel consumption ☆. Applied Energy 2014, 135, 616-624; (b) Deng, Y. Y.; Zhou, J. R.; Yao, N.; Yin, L., Recovery of Industrial Waste Heat. Building Energy Efficiency 2013. 4. Li, Y.; Sang, G.; Shi, H., Potential applications of phase-change materials (PCM) in building energy efficiency. Journal of New Materials for Electrochemical Systems 2014, 17, 123-127; (b) Feng, J. M.; Zhu, X. P.; Wang, P.; Luo, J. P. In Study on PCM Application in Old Building Energy Efficiency, 2013 Fifth International Conference on Measuring Technology and Mechatronics Automation, 2013; pp 1080-1083. 5. Alshaer, W. G.; Nada, S. A.; Rady, M. A.; Barrio, E. P. D.; Sommier, A., Thermal management of electronic devices using carbon foam and PCM/nano-composite. International Journal of Thermal Sciences 2015, 89, 79-86; (b) Gharbi, S.; Harmand, S.; Jabrallah, S. B., Experimental comparison between different configurations of PCM based heat sinks for cooling electronic components. Applied Thermal Engineering 2015, 87, 454–462. 6. Tamasauskas, J.; Poirier, M.; Zmeureanu, R.; Sunyé, R., Modeling and optimization of a solar assisted heat pump using ice slurry as a latent storage material. Solar Energy 2012, 86 (11), 3316-3325.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

18

296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336

7. Fang, Y.; Yu, H.; Wan, W.; Gao, X.; Zhang, Z., Preparation and thermal performance of polystyrene/ntetradecane composite nanoencapsulated cold energy storage phase change materials. Energy Conversion & Management 2013, 76 (12), 430–436. 8. Suwono, A.; Indartono, Y.; Irsyad, M.; Al-Afkar, I. In Application of calcium chloride as an additive for secondary refrigerant in the air conditioning system type chiller to minimized energy consumption, IOP Conference Series: Materials Science and Engineering, IOP Publishing: 2015; p 012035. 9. Kenisarin, M.; Mahkamov, K., Salt hydrates as latent heat storage materials: Thermophysical properties and costs. Solar Energy Materials and Solar Cells 2016, 145, 255-286. 10. Alkan, C.; Sarı, A.; Karaipekli, A., Preparation, thermal properties and thermal reliability of microencapsulated n-eicosane as novel phase change material for thermal energy storage. Energy Conversion and Management 2011, 52 (1), 687-692; (b) Pan, L.; Tao, Q.; Zhang, S.; Wang, S.; Zhang, J.; Wang, S.; Wang, Z.; Zhang, Z., Preparation, characterization and thermal properties of microencapsulated phase change materials. Solar Energy Materials and Solar Cells 2012, 98, 66-70; (c) Wu, C.-B.; Wu, G.; Yang, X.; Liu, Y.-J.; Liang, T.; Fu, W.-F.; Wang, M.; Chen, H.-Z., Preparation of microencapsulated medium temperature phase change material of Tris (hydroxymethyl) methyl aminomethane@ SiO 2 with excellent cycling performance. Applied Energy 2015, 154, 361-368. 11. Silakhori, M.; Metselaar, H. S. C.; Mahlia, T. M. I.; Fauzi, H.; Baradaran, S.; Naghavi, M. S., Palmitic acid/polypyrrole composites as form-stable phase change materials for thermal energy storage. Energy Conversion and Management 2014, 80, 491-497; (b) Zeng, J.-L.; Zheng, S.-H.; Yu, S.-B.; Zhu, F.-R.; Gan, J.; Zhu, L.; Xiao, Z.-L.; Zhu, X.-Y.; Zhu, Z.; Sun, L.-X., Preparation and thermal properties of palmitic acid/polyaniline/exfoliated graphite nanoplatelets form-stable phase change materials. Applied Energy 2014, 115, 603-609. 12. Sarı, A.; Alkan, C.; Döğüşcü, D. K.; Biçer, A., Micro/nano-encapsulated n-heptadecane with polystyrene shell for latent heat thermal energy storage. Solar Energy Materials and Solar Cells 2014, 126, 42-50; (b) Sarı, A.; Alkan, C.; Döğüşcü, D. K.; Kızıl, Ç., Micro/nano encapsulated n-tetracosane and n-octadecane eutectic mixture with polystyrene shell for low-temperature latent heat thermal energy storage applications. Solar Energy 2015, 115, 195-203. 13. Mohaddes, F.; Islam, S.; Shanks, R.; Fergusson, M.; Wang, L.; Padhye, R., Modification and evaluation of thermal properties of melamine-formaldehyde/n-eicosane microcapsules for thermoregulation applications. Applied Thermal Engineering 2014, 71 (1), 11-15; (b) Khakzad, F.; Alinejad, Z.; Shirin-Abadi, A. R.; Ghasemi, M.; Mahdavian, A. R., Optimization of parameters in preparation of PCM microcapsules based on melamine formaldehyde through dispersion polymerization. Colloid and Polymer Science 2014, 292 (2), 355-368; (c) Yin, D.; Ma, L.; Geng, W.; Zhang, B.; Zhang, Q., Microencapsulation of n-hexadecanol by in situ polymerization of melamine–formaldehyde resin in emulsion stabilized by styrene–maleic anhydride copolymer. International Journal of Energy Research 2015, 39 (5), 661-667. 14. Fayyad, E. M.; Almaadeed, M. A.; Jones, A., Preparation and characterization of urea– formaldehyde microcapsules filled with paraffin oil. Polymer Bulletin 2015, 1-16; (b) Xin, C.; Tian, Y.; Wang, Y.; Huang, X. a., Effect of curing temperature on the performance of microencapsulated low melting point paraffin using urea-formaldehyde resin as shell. Textile Research Journal 2013, 0040517513507367.


Page 18 of 19

Page 19 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels 19

337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365

15.Fang, G.; Li, H.; Yang, F.; Liu, X.; Wu, S., Preparation and characterization of nano-encapsulated ntetradecane as phase change material for thermal energy storage. Chem Eng J. Chemical Engineering Journal 2009, 153 (1), 217-221. 16.Konuklu, Y.; Unal, M.; Paksoy, H. O., Microencapsulation of caprylic acid with different wall materials as phase change material for thermal energy storage. Solar Energy Materials and Solar Cells 2014, 120, 536-542. 17.Qiu, X.; Lu, L.; Wang, J.; Tang, G.; Song, G., Preparation and characterization of microencapsulated n-octadecane as phase change material with different n-butyl methacrylate-based copolymer shells. Solar Energy Materials and Solar Cells 2014, 128, 102-111. 18.Zhang, Y.; Wang, S.; Rao, Z.; Xie, J., Experiment on heat storage characteristic of microencapsulated phase change material slurry. Solar Energy Materials and Solar Cells 2011, 95 (10), 2726-2733. 19.Taguchi, Y.; Morita, R.; Saito, N.; Tanaka, M., Formation of Pickering emulsion by use of PCM and SiC and application to preparation of hybrid microcapsules with interfacial polycondensation reaction. Polymers for Advanced Technologies 2015. 20.Song, S.; Dong, L.; Qu, Z.; Ren, J.; Xiong, C., Microencapsulated capric–stearic acid with silica shell as a novel phase change material for thermal energy storage. Applied Thermal Engineering 2014, 70 (1), 546-551. 21.Yu, S.; Wang, X.; Wu, D., Microencapsulation of n-octadecane phase change material with calcium carbonate shell for enhancement of thermal conductivity and serving durability: synthesis, microstructure, and performance evaluation. Applied Energy 2014, 114, 632-643. 22.Yu, R.; Ping, L. G.; Yan, L.; Lin, C. S.; Liang, W., Preparation and thermal properties of microencapsulated phase change material for enhancing fluid flow heat transfer. Heat Transfer—asian Research 2007, 36 (1), 28–37. 23. Ahadia, M.; Andisheh-Tadbira, M.; Tamb, M.; Bahrami, M., An improved transient plane source method for measuring thermal conductivity of thin films: Deconvoluting thermal contact resistance. International Journal of Heat & Mass Transfer 2016, 96, 371-380. 24. Yang, R.; Zhang, Y.; Wang, X.; Zhang, Y.; Zhang, Q., Preparation of n -tetradecane-containing microcapsules with different shell materials by phase separation method. Solar Energy Materials & Solar Cells 2009, 93 (10), 1817-1822.

366


n-Tetradecane

Recommend Documents