Investigating thermal properties of using nano-tubular ZnO powder in paraffin as phase change material composite for thermal energy storage

Accepted Manuscript Investigating thermal properties of using nano-tubular ZnO powder in paraffin as phase change material composite for thermal energy storage Nurten Şahan, Halime Paksoy PII:

S1359-8368(16)31649-3

DOI:

10.1016/j.compositesb.2017.06.006

Reference:

JCOMB 5112

To appear in:

Composites Part B

Received Date: 17 August 2016 Revised Date:

15 May 2017

Accepted Date: 10 June 2017

Please cite this article as: Şahan N, Paksoy H, Investigating thermal properties of using nano-tubular ZnO powder in paraffin as phase change material composite for thermal energy storage, Composites Part B (2017), doi: 10.1016/j.compositesb.2017.06.006. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

Investigating Thermal Properties of Using Nano-Tubular ZnO Powder in Paraffin as Phase Change Material Composite for Thermal Energy

Nurten Şahana*, Halime Paksoya

a

Cukurova University, Chemistry Department, Adana, 01330, Turkey

SC

a

RI PT

Storage

*Corresponding Author

Tel: +90 322 3386418 Fax: +90 322 3386070

Abstract

TE D

e-mail: [email protected]

M AN U

Nurten Sahan

The thermal energy storage (TES) in phase change materials (PCMs) plays an important

EP

role in energy management systems. Paraffin has found wide range of applications as a PCM due to its unique thermal and physical properties. In this study, nano zinc oxide in

AC C

tubular shape and powder form is synthesized for the first time in literature. The nano tubular- zinc oxide is used as an additive with 10%wt composition to paraffin to prepare a nanocomposite. The variations in thermo physical properties of paraffin in composite form were subjected to investigate by experimentally. Key words: Phase change materials; thermal energy storage; paraffin; nano-tubular zinc oxide.

1

ACCEPTED MANUSCRIPT 1. Introduction The renewable energy sources, energy conservation and energy storage applications have become more important than ever depending on increasing energy demand of the World and

RI PT

problems caused by existing sources. Countries are trying to find the best renewable energy technologies that suit their economic, climate and geographic conditions.

Solar energy

investments have taken a prominent place in the renewable energy sector. But uninterruptible

SC

usage of energy generated from natural and renewable sources is impossible. Thermal energy storage (TES) provides flexible solutions to store overproduced energy and to consume during

M AN U

the periods when energy is not available and transfer it to areas in need to increase energy efficiency of systems. TES is also a key technology to recover waste heat and regulate optimum temperatures of equipment, devices and buildings without using energy sources [1, 2].

TE D

TES techniques used are: sensible, latent, and thermochemical heat or any combination of these [3]. Latent and sensible heats are more commonly preferred techniques due to high efficiency and ease of integration into real TES systems.

EP

Phase-change materials (PCMs) are capable of storing and releasing latent heat at a certain

AC C

temperature when the material changes from solid to liquid, liquid-gas, solid–solid and vice versa. PCMs are classified as inorganic, organic and eutectic according to their chemical structures. Paraffin has been widely used as organic PCM; since it is non-corrosive, non-toxic, and cost-effective, has relatively high latent heat, and can be designed for a wide range of melting temperatures [4]. The main drawback of using paraffin is its low thermal conductivity, which cause inefficient charging and discharging performances in high power short term storage systems. Some examples of such short term storage systems are solar dryers [5], portable electronic devices[6] and air heat exchangers[7]. 2

ACCEPTED MANUSCRIPT Different techniques that use support with high conductivity materials such as metal, metallic foam, metal oxide, graphite, and carbon nanotubes have been conducted to enhance low thermal conductivity problems of organic PCMs [8-10].

RI PT

Combining nanomaterials with PCMs for various TES applications is attracting an everincreasing interest since their unique thermal, chemical and physical properties [11-13].

Zinc oxide (ZnO) is a semiconductor material with wide conductivity gap of 3.37 eV. With

SC

this property, it is widely applied in solar cells, gas sensors, laser, transistor, nano- generator,

M AN U

photo catalysis and photo detectors [14-18]. Besides, nano ZnO is biodegradable and has low toxicity that enables it to be used in drug delivery, gene delivery, biosensors applications [19]. Nano ZnO has high thermal conductivity with a value of 1.160 W/mK that can be used as an additive to increase thermal conductivity of paraffin. Being an inexpensive and environmental

TE D

friendly material make ZnO to be used in large TES applications economically [20]. The aim of this study was to develop nano ZnO powder in tubular shape and use it as an additive to enhance thermal properties of paraffin as PCM for TES applications. This will add

EP

a new application field to ZnO products in addition to its multiple benefits. Chemical and thermal properties of ZnO paraffin (ZnO-P) composite are investigated in comparison with

AC C

pure paraffin.

2. Materials and methods 2.1. Material

Zinc acetate [Zn (CH3COO) 2. H2O](Sigma Aldrich) and oxalic acid [H2C2O4.2H2O] (Sigma Aldrich) were used as main chemical components to synthesize nano-tubular zinc oxide powder by chemical technique [21]. For PCM –nano composite; paraffin 46-48 (Merck) was

3

ACCEPTED MANUSCRIPT selected as a phase change materials since it has medium temperature melting point and low cost compared to technical paraffin. 2.2. Preparation of Composite

RI PT

0.1 M zinc acetate [Zn (CH3COO)2.2H2O] and 0.15 M oxalic acid [H2C2O4.2H2O] precursor solutions were prepared by deionized water at room temperature. These molar ratios were selected to attain maximum yield following the recommendation given in previous study [21].

SC

At the first step, oxalic acid solution was added into zinc acetate solution drop by drop while

M AN U

constantly stirring at a rate of 1000 rpm for 12 h at room temperature. At the end of following reaction (Eqn. 1) zinc oxalate was obtained (

) .2

+



. 2

→

.2

+2

+2

(1)

The product was dried in the oven at 100 °C for 4 h followed by thermal treatment at 450°C

TE D

for 5 h in muffle furnace. Finally, white nano- tubular- zinc oxide powder is obtained after removal of water in the second step according to the reaction given in Eqn. 2: +

→

+2

+2

EP

.

Dispersion technique was used to prepare

(2) nano-tubular zinc oxide and paraffin

AC C

composite[22]. Nano-tubular zinc oxide at 10%wt was added in melted paraffin. The composite was first mixed with vortex followed by ultrasonic bath (35 kHz, 320 W) at constant temperature of 50°C for 3 h. in order to obtain a homogeneous distribution of additives in paraffin.

4

ACCEPTED MANUSCRIPT 2.4. Characterization The crystal structure of nano-tubular zinc oxide, paraffin and ZnO-P were determined by using X-ray diffraction – XRD (Rigaku Miniflex-2) over the 2 θ range from 20 - 80° at rate of

RI PT

2 °/min, using CuK radiation (λ = 1.5405 Å ). Morphologies of all samples were investigated by Scanning Electron Microscope (SEM, Zeiss Supra 55). All samples were observed at various magnifications after coating their surfaces with platinum. The chemical structures were verified with the Fourier Transform Infrared - FTIR (Perkin Elmer RX-1) at 400-4000

SC

cm-1 wavelength range with 16 scans. The latent heat and melting/solidification temperatures

M AN U

of pure paraffin and ZnO-P were determined by a differential scanning calorimeter (DSC, Hitachi High Tech, 7000X) in the temperature range of 30°C - 65°C at 5°C/min heating rate under a constant stream of nitrogen at flow rate of 30 mL/min. The temperature accuracy was ±0.1°C, and heat flow repeatability was 5 µW. 6-9 mg of samples were sealed in aluminum

TE D

pans. All DSC measurements were repeated three times for each sample. Characterization thermal stability was done by Simultaneous Thermal Analysis (STA, Perkin Elmer STA6000). The accuracy of weight loss in TGA is 0.02%.The analysis was performed in the

EP

temperature range of 30°C - 600°C at 20°C/min heating rate under a constant stream of nitrogen at flow rate of 20 mL/min.

AC C

3. Results and discussion 3.1 SEM

The morphologies of ZnO and ZnO-P were investigated with SEM to clarify structure of synthesized ZnO particles and also to identify any changes of ZnO nano particles as a result of the dispersing in paraffin technique. Fig. 1a shows the schematic diagram of 3-D structure of ZnO. In Fig.1b SEM images of ZnO at 50K magnification show that ZnO particles are stacked in tubular structure that is similar to the schematic diagram given in Fig. 1a ZnO

5

ACCEPTED MANUSCRIPT particles have uniform geometry with the size range of 40-70 nm as shown in Fig.1c at 100K magnifications. These tubular structures are packed together in a sponge-like shape with holes in between the tubes. Fig.1d belongs to SEM image of ZnO-P that shows ZnO nano particles

RI PT

are covered and smeared with waxy paraffin structure entirely and tubular structure was not

b

AC C

a

EP

TE D

M AN U

SC

affected after dispersion in paraffin.

6

SC

RI PT

ACCEPTED MANUSCRIPT

d

M AN U

c

Figure 1 .

The SEM image of a commercial nano ZnO powder at 50K is shown in Fig.2 [23]. As seen in this figure, particle sizes are larger and randomly distributed without any ordered packing or

TE D

holes. Comparing this image with the ones obtained in this study (Fig.1), it can be seen that a

AC C

EP

new structure of nano ZnO powder has been successfully synthesized in this study.

7

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

Figure 2.

TE D

3.2. XRD

Fig. 3 compares the XRD patterns of ZnO, paraffin and ZnO-P composite. The corresponding 2θ and intensity values are given in Table 1.The peaks shown in Fig.3 observed at 2θ = 21.75

EP

°, 23.36°, 41.45°, 76.92° that belongs to regular crystallization of paraffin. The 2θ peaks at 31.77°, 34.40°, 36.25°, 47.51°, 56.59°, 62.82°, 66.35°, 67.92°, 69.05°, 72.54° and 76.91° are

AC C

attributed to pure bulk ZnO which has hexagonal crystal structure (ICDD PDF card no: 00003-0888). The XRD pattern of our synthesized nano-tubular zinc oxide verifies that it consists of hexagonal zinc oxide and has single crystalline form.The ZnO-P composite possess all specific XRD peaks of two different components at lower intensity when comparing each other. The XRD results show that during preparing composite between all components of ZnO-P does not exhibit any chemical interaction in view of preserve their pure crystal lattice.

8

AC C

Table 1.

EP

Figure 3.

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

3.3. FTIR

Fig. 4 shows FTIR spectra of ZnO nanoparticles, paraffin and ZnO-P composite. FT-IR analyses were carried out in order to prove chemical structure of synthesized ZnO and find out any chemical changes in composite form. In FTIR spectrum of ZnO the main absorption peak observed at 430 cm-1 is attributed to ZnO stretching modes in agreement with

9

ACCEPTED MANUSCRIPT literature[24]. In addition, no other peaks that may be from impurities or water were detected. The paraffin comprises of hydrocarbons with the general formula CnH2n+2 , therefore FTIR peaks of paraffin with frequency of 2800–3000 cm-1 indicate the symmetrical stretching

RI PT

vibrations of –CH3 and –CH2 groups and the peaks at 1350–1470 cm-1 frequency are corresponding to deformation vibrations of –CH3 and –CH2 groups. The peaks at 720– 725 cm-1 belong to –CH2 rocking groups of the paraffin. The FTIR spectrum of ZnO-P composite

SC

includes all characteristics peaks of ZnO and paraffin that make up the composite at lower intensity. FTIR analysis results confirmed that between nano ZnO and paraffin does not cause

AC C

EP

TE D

M AN U

any chemical intermolecular interaction since there are no additional specific peaks.

Figure 4.

3.4. Thermal Properties

TGA and DSC methods were used to determine the influences of using nano ZnO on thermal stability and storage capacity of paraffin.TGA results of paraffin and ZnO-P are shown in Fig. 5. The paraffin and ZnO-P have typical one-step degradation at 183°C and 184°C,

10

ACCEPTED MANUSCRIPT respectively. The weight loss percentage of paraffin is zero showing that no residues remain, but for ZnO-P it stays at 10%. This residue is a result of nano-ZnO that was added to the composite at 10% composition. This also shows that even in the very small sample used for

RI PT

TGA analysis composition of nano ZnO was 10%, which indicates it was homogeneously distributed in paraffin. TGA results also demonstrated that ZnO is not degraded even at 600°C. DSC results given in Fig. 6 show that latent heat capacities and phase change range is

SC

158 J/g and 40-48°C for paraffin, while the same parameters are 146 J/g and 39-48°C for ZnO-P. Latent heat capacity of paraffin decreased by 7%, when 10% wt nano tubular ZnO

M AN U

was used in the composite. This decrement can be considered to be insignificant in comparison to many previous studies showing higher reduction of enthalpies with lower

AC C

EP

TE D

amount of additives in PCMs [25-28].

Figure 5.

11

M AN U

EP

TE D

a

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

b

Figure 6.

Conclusions In this study, ZnO with nano-tubular shape with hexagonal crystal structure in powder form is synthesized for the first time in literature. Paraffin composite was prepared with nano- tubular

12

ACCEPTED MANUSCRIPT ZnO by adding 10% wt in order to investigate effects on thermal and chemical performance of paraffin for TES applications. Experimental findings demonstrate that phase change range of paraffin remained the same, whereas thermal storage capacity is slightly reduced by 7%. In

RI PT

addition to this, ZnO is usually preferred in many solar and electronic applications due to its remarkable properties such as optical absorption and emission, conductivity, piezoelectricity, photo catalysis, and sensitivity to gases[29]. Moreover, the nano-tubular ZnO developed in

SC

this study can be a pioneer in increasing multi benefits of ZnO and open new application areas. ZnO can be used in different solar applications with PCMs, such as nano PCM slurry

M AN U

for solar dryers and heaters. Another area can be incorporation with PCM in textile materials that can be used in solar shelters to benefit from UV absorption properties and also to enhance photovoltaic activity [30]. The thermal stability and thermal conductivity of the composites should be determined in further studies.

TE D

Acknowledgements

The authors would like to acknowledge the support provided by TUBITAK under the Project No: 110M213 and thank Prof. Dr. Mustafa Gunes from Adana Science and Technology

AC C

References

EP

University for DSC analysis.

[1] Sarı A. Thermal energy storage characteristics of bentonite-based composite PCMs with enhanced thermal conductivity as novel thermal storage building materials. Energy Conversion and Management. 2016;117:132-41. [2] Casado J, Gutiérrez-Solana F, Carrascal I, Diego S, Polanco J, Hernández D. Fatigue behavior enhancement of short fiber glass reinforced polyamide by adding phase change materials. Composites Part B: Engineering. 2016;93:115-22.

13

ACCEPTED MANUSCRIPT [3] Lachheb M, Mustapha K, Fethi A, Sassi BN, Magali F, Patrik S. Thermal properties measurement and heat storage analysis of paraffin/graphite composite phase change material. Composites Part B: Engineering. 2014;66:518-25.

RI PT

[4] Akeiber H, Nejat P, Majid MZA, Wahid MA, Jomehzadeh F, Famileh IZ, et al. A review on phase change material (PCM) for sustainable passive cooling in building envelopes. Renewable and Sustainable Energy Reviews. 2016;60:1470-97.

SC

[5] Shalaby S, Bek M, El-Sebaii A. Solar dryers with PCM as energy storage medium: A review. Renewable and Sustainable Energy Reviews. 2014;33:110-6.

M AN U

[6] Alawadhi EM, Amon CH. PCM thermal control unit for portable electronic devices: experimental and numerical studies. IEEE Transactions on Components and Packaging Technologies. 2003;26(1):116-25.

[7] Lazaro A, Dolado P, Marín JM, Zalba B. PCM–air heat exchangers for free-cooling

TE D

applications in buildings: experimental results of two real-scale prototypes. Energy Conversion and Management. 2009;50(3):439-43. [8] Liu L, Su D, Tang Y, Fang G. Thermal conductivity enhancement of phase change

2016;62:305-17.

EP

materials for thermal energy storage: A review. Renewable and Sustainable Energy Reviews.

AC C

[9] Shin HK, Rhee K-Y, Park S-J. Effects of exfoliated graphite on the thermal properties of erythritol-based composites used as phase-change materials. Composites Part B: Engineering. 2016;96:350-3.

[10] Trigui A, Karkri M, Boudaya C, Candau Y, Ibos L. Development and characterization of composite phase change material: thermal conductivity and latent heat thermal energy storage. Composites Part B: Engineering. 2013;49:22-35.

14

ACCEPTED MANUSCRIPT [11] Kibria M, Anisur M, Mahfuz M, Saidur R, Metselaar I. A review on thermophysical properties of nanoparticle dispersed phase change materials. Energy Conversion and Management. 2015;95:69-89.

RI PT

[12] Sahan N, Paksoy HO. Thermal enhancement of paraffin as a phase change material with nanomagnetite. Solar Energy Materials and Solar Cells. 2014;126:56-61.

[13] Şahan N, Fois M, Paksoy H. Improving thermal conductivity phase change materials—a

SC

study of paraffin nanomagnetite composites. Solar Energy Materials and Solar Cells. 2015;137:61-7.

M AN U

[14] Sankapal BR, Gajare HB, Karade SS, Salunkhe RR, Dubal DP. Zinc oxide encapsulated carbon nanotube thin films for energy storage applications. Electrochimica Acta. 2016;192:377-84.

[15] Liu J, Zhang Z, Lv Y, Yan J, Yun J, Zhao W, et al. Synthesis and characterization of

TE D

ZnO NWAs/graphene composites for enhanced optical and field emission performances. Composites Part B: Engineering. 2016;99:366-72. [16] Akgül FA. Influence of Ti doping on ZnO nanocomposites: Synthesis and structural

EP

characterization. Composites Part B: Engineering. 2016;91:589-94. [17] Yakuphanoglu F. Transparent metal oxide films based sensors for solar tracking

AC C

applications. Composites Part B: Engineering. 2016;92:151-9. [18] Ghafari E, Feng Y, Liu Y, Ferguson I, Lu N. Investigating process-structure relations of ZnO nanofiber via electrospinning method. Composites Part B: Engineering. 2017;116:40-5. [19] Zhang Y, R Nayak T, Hong H, Cai W. Biomedical applications of zinc oxide nanomaterials. Current molecular medicine. 2013;13(10):1633-45.

15

ACCEPTED MANUSCRIPT [20] Olorunyolemi T, Birnboim A, Carmel Y, Wilson OC, Lloyd IK, Smith S, et al. Thermal conductivity of zinc oxide: from green to sintered state. Journal of the American Ceramic Society. 2002;85(5):1249-53.

RI PT

[21] Kanade K, Kale B, Aiyer R, Das B. Effect of solvents on the synthesis of nano-size zinc oxide and its properties. Materials Research Bulletin. 2006;41(3):590-600.

[22] Şahan N, Fois M, Paksoy H. The effects of various carbon derivative additives on the

SC

thermal properties of paraffin as a phase change material. International Journal of Energy Research. 2016;40(2):198-206.

M AN U

[23] Ohkawara H, Kitagawa T, Fukushima N, Ito T, Sawa Y, Yoshimine T. A Newly Developed Container for Safe, Easy, and Cost-effective Overnight Transportation of Tissues and Organs by Electrically Keeping Tissue or Organ Temperature at 3 to 6° C. Transplantation proceedings: Elsevier; 2012. p. 855-8.

TE D

[24] Uysal I, Severcan F, Evis Z. Characterization by Fourier transform infrared spectroscopy of hydroxyapatite co-doped with zinc and fluoride. Ceramics International. 2013;39(7):772733.

EP

[25] Teng T-P, Yu C-C. Characteristics of phase-change materials containing oxide nanoadditives for thermal storage. Nanoscale research letters. 2012;7(1):1.

AC C

[26] Wang J, Xie H, Xin Z, Li Y, Chen L. Enhancing thermal conductivity of palmitic acid based phase change materials with carbon nanotubes as fillers. Solar Energy. 2010;84(2):33944.

[27] Zhang L, Zhu J, Zhou W, Wang J, Wang Y. Thermal and electrical conductivity enhancement of graphite nanoplatelets on form-stable polyethylene glycol/polymethyl methacrylate composite phase change materials. Energy. 2012;39(1):294-302.

16

ACCEPTED MANUSCRIPT [28] Nourani M, Hamdami N, Keramat J, Moheb A, Shahedi M. Thermal behavior of paraffin-nano-Al 2O 3 stabilized by sodium stearoyl lactylate as a stable phase change material with high thermal conductivity. Renewable Energy. 2016;88:474-82.

RI PT

[29] Peng Y, Xu A-W, Deng B, Antonietti M, Cölfen H. Polymer-controlled crystallization of zinc oxide hexagonal nanorings and disks. The Journal of Physical Chemistry B. 2006;110(7):2988-93.

SC

[30] Becheri A, Dürr M, Nostro PL, Baglioni P. Synthesis and characterization of zinc oxide nanoparticles: application to textiles as UV-absorbers. Journal of Nanoparticle Research.

M AN U

2008;10(4):679-89.

Figure Captions

TE D

Figure 1 . a) Schematic view of ZnO tubular stucture b) SEM image of ZnO at 50K magnification c) SEM image of ZnO at 100K magnification d) SEM image of ZnO-P

EP

Figure 2. SEM image of commercial nano ZnO powder [16] Fig. 3. Comparison of XRD patterns of ZnO, paraffin and ZnO-P

AC C

Fig. 4. FTIR spectra a) comparing ZnO, paraffin and ZnO-P Fig. 5. TGA curves of paraffin and ZnO-P Fig. 6. DSC curves a) paraffin b) ZnO-P

17

ACCEPTED MANUSCRIPT

Tables

Sample

M AN U

ZnO

2θ (deg) 31.77 34.40 36.25 47.51 56.59 62.82 66.35 67.92 69.05 72.54 76.91 21.75 23.36 41.45 76.92 21.32 23.08 31.85 34.47 36.30 41.2 47.59 56.66 62.88 66.37 67.96 69.08 77.00

EP

TE D

Paraffin

AC C

ZnO-P

18

Height (cps) 2134 4520 10001 1804 3852 2663 465 2667 1278 201 339 2035 2165 3509 4156 794 537 1733 1097 2682 58 505 1018 696 114 698 366 70

SC

ZnO, paraffin and ZnO-P

RI PT

Table 1. XRD results of 2θ in degrees (deg) and height in counts per second (cps) for