Embed Size (px)
Citation preview
lable at ScienceDirect
Applied Thermal Engineering 66 (2014) 328e334
Contents lists avai
Applied Thermal Engineering
journal homepage: www.elsevier .com/locate/apthermeng
Thermo-physical stability of fatty acid eutectic mixtures subjected toaccelerated aging for thermal energy storage (TES) application
Hadi Fauzi a,c,*, Hendrik S.C. Metselaar a,*, T.M.I. Mahlia b, Mahyar Silakhori a
aDepartment of Mechanical Engineering, University of Malaya, Kuala Lumpur 50603, MalaysiabDepartment of Mechanical Engineering, Universiti Tenaga Nasional, Kajang 43000, Selangor, MalaysiacDepartment of Chemical Engineering, Syiah Kuala University, Banda Aceh 23111, Indonesia
h i g h l i g h t s
� The prepared MA/PA and MA/PA/SS were used as eutectic phase change materials (PCM).� Thermo-physical reliability of eutectic PCMs evaluated using a thermal cycling test.� MA/PA/SS has a great thermo-physical stability than MA/PA after 1500 thermal cycles.
a r t i c l e i n f o
Article history:Received 21 November 2013Accepted 5 February 2014Available online 14 February 2014
Keywords:Thermal propertiesThermal reliabilityChemical degradationVolume change
* Corresponding authors. Department of MechanicMalaya, Kuala Lumpur 50603, Malaysia. Tel.: þ60 379
E-mail addresses: [email protected],(H. Fauzi), [email protected] (H.S.C. Metselaar)
http://dx.doi.org/10.1016/j.applthermaleng.2014.02.011359-4311/� 2014 Elsevier Ltd. All rights reserved.
a b s t r a c t
The thermo-physical stability of fatty acids eutectic mixtures subjected to accelerated number ofmelting/solidification processes has been identified using thermal cycling test in this study. Myristic acid/palmitic acid (MA/PA) (70/30, wt.%) and myristic acid/palmitic acid/sodium stearate (MA/PA/SS) (70/30/5,wt.%) were selected as eutectic phase change materials (PCMs) to evaluate their stability of phasetransition temperature, latent heat of fusion, chemical structure, and volume changes after 200, 500,1000, and 1500 thermal cycles. The thermal properties of each eutectic PCMs measured by differentialscanning calorimetric (DSC) indicated the phase transition temperature and latent heat of fusion valuesof MA/PA/SS has a smallest changes after 1500 thermal cycles than MA/PA eutectic mixture. MA/PA/SSalso has a better chemical structure stability and smaller volume change which is 1.2%, compared to MA/PA with a volume change of 1.6% after 1500 cycles. Therefore, it is concluded that the MA/PA/SS eutecticmixture is suitable for use as a phase change material in thermal energy storage (TES) such as solar waterheating and solar space heating applications.
� 2014 Elsevier Ltd. All rights reserved.
1. Introduction
Every latent heat thermal energy storage (LHTES) system re-quires a suitable phase change material (PCM). A PCM in a LHTESsystem should possess desirable economic and thermo-physicalproperties to guarantee a long term utilization of the system [1].The stability of thermal properties, chemical structure and volumechange of phase change material (PCM) should be evaluated after alarge number of thermal cycles and this evaluation is essentialbefore applying the PCM in a latent heat thermal energy storage
al Engineering, University of674451; fax: þ60 [email protected].
4
(LHTES) system. This is to have a quality assurance of the long termperformance and economic feasibility of the LHTES system [2,3].
It has been noted that a comprehensive knowledge of thethermal properties and thermal reliability of a PCM should beverified by a thermal cycling test to assure the long term stabilitybefore applying it in a LHTES system [1,3]. The economic feasibilityof employing a latent heat storage material in a solar system de-pends on the life of the storage material. There should not be majorchange in the melting point and latent heat of fusionwith time dueto the melting/solidification cycles of the storage material [2,4].
Several studies reported on the thermal reliability of PCMs dueto their changes of thermal properties after a large number ofthermal cycles. Sari, 2003 [2] determined the thermal reliability ofstearic acid (SA), palmitic acid (PA), myristic acid (MA) and lauricacid (LA) subjected to 120, 560, 850 and 1200 thermal cycles andnoted that the melting temperature of those PCMs were almostconstant after 120 thermal cycles, and tend to decrease after 560
Nomenclature
Tm melting temperatureTf freezing or solidification temperatureDHf latent heat of fusionDHf,m latent heat of fusion on liquid phaseDHf,s latent heat of fusion on solid phasewt.% weight percentage
H. Fauzi et al. / Applied Thermal Engineering 66 (2014) 328e334 329
and after 1200 thermal cycles. A decrease in latent heat of fusionalso occurred with an increasing number of thermal cycles, but thedecrease was irregular. That melting temperature and latent heat ofSA show no regular degradation after 20, 50, 70, 100, 150, 200, 250and 300 thermal cycles was reported by Sharma et al., 1999 [5]. Inanother work, Sari and Kaygusuz, 2003 [6] reported the reductionof the latent heat of fusion of SA, PA, MA and LA as PCM in a shortterm period of 40 thermal cycles, middle term period of 410 ther-mal cycles, and long term period of 910 thermal cycles. The latentheat of fusion of those PCMs decreased irregularly with increasingthe number of thermal cycles.
Zhang et al., 2001 [7] evaluated the thermal stability of LA/PAand LA/SA eutectic mixtures and reported that the thermalproperties of the binary system were stable after 100 melting/solidification cycles. Karaipekli et al., 2009 [8] prepared the capricacid/stearic acid (CA/SA) eutectic mixture and reported thatthe changes in melting temperature and latent heat subjectedto 1000, 2000, 3000, 4000 and 5000 melting/solidificationcycles were irregular against the number of thermal cycles butacceptable for use in thermal application systems. Sari et al., 2004[3], Sari, 2005 [1], and Sari, 2006 [9] have evaluated the changesin the melting temperature and latent heat of fusion of someeutectic mixtures of fatty acids and identified that those eutecticPCMs have good thermal reliability in term of the changes intheir thermal properties respected to a large number of thermalcycles.
Many studies have been done on evaluating the thermal sta-bility of PCMs by cycling on a setup consisting of an electronic hotplate with a temperature controller, where the samples of PCMwere put in a stainless steel container with lid [4,10,11]. In theresearch on the thermal stability of PCM, different methods havebeen applied to conduct the thermal cycling test of PCMs thatconsisted of a thermostatic chamber with temperature controller[2,9,12e15]. Furthermore, the thermal cycling test methods wereimproved by connecting the thermocouples to a data logger or dataacquisition system to observe the actual changes of PCM temper-ature during the cycle [16,17]. Recently, we did a significantmodification on the thermal cycling test setup by integrating thevalve control system to ensure the continuity in a large numbers ofheating/cooling cycles as shown in Fig. 2.
Fig. 1. Thermal cycling chamber and capsule tubes samples; 1. Samples PCMs, 2. Heattransfer fluid.
In the present study, we evaluated the thermo-physical stabilityof MA/PA and MA/PA/SS eutectic mixtures subjected to 200, 500,1000, and 1500 melting/solidification cycles. The thermo-physicalstability of those eutectic PCMs included changes of phase transi-tion temperature and latent heat of fusion, chemical structure, andvolume changes of both eutectic PCMs after the thermal cyclingprocess.
2. Materials and methods
2.1. Materials
The eutectic mixtures of myristic acid/palmitic acid (MA/PA) andmyristic acid/palmitic acid/sodium stearate (MA/PA/SS) preparedby Fauzi et al. [18,19] were used as phase change material in thisstudy. A MA/PA eutectic mixture was prepared by blending singlecomponents of myristic acid (MA) (Acros Organic) and palmitic acid(PA) (Acros Organic) in composition ration 70/30 wt.% at 80 �C for20 min. The same composition of MA and PA was used to preparethe MA/PA/SS by addition of 5% sodium stearate (Sigma Aldrich)[18].
2.2. Thermal cycling test
The thermal cycling set-up was designed and assembled atEngineering Faculty, University of Malaya. The experimental setupconsists of a hot and a cold water circulation bath, a chamber in-tegrated with two sample capsule tubes (Fig. 1), thermocouplestype-J, automatic control valves, data acquisition, and PC. Thediameter and height of both capsule tubes were 27.5 mm and75 mm, respectively.
The thermal cycling test setup was used to evaluate the stabilityof thermal properties such as melting temperature Tm, latent heatof fusion DHf, and volume changes of PCMs during the heating/cooling cycles. 2 g both of eutectic mixtures of MA/PA and MA/PA/SS were placed in double cylindrical capsules made of Pyrex glasswith lid, the capsules were fixed into the chamber with circulatingwater as a heat transfer fluid (HTF) to transfer the heat to and fromthe PCMs. The phase transition temperatures of the PCMs weremeasured by thermocouples connected to a data acquisition systemto read and record the temperature data.
The temperature of HTF in the heating circulation bath was setat 65 �C, which is above the melting temperatures of both eutecticPCMs and the HTF in the cooling water circulation bath was set at25 �C, below the solidification temperature of both PCMs.
2.3. Stability of thermal properties
The thermal properties of MA/PA and MA/PA/SS eutectic mix-tures subjected to 200, 500, 1000 and 1500 cycles were evaluatedusing a Differential Scanning Calorimeter (DSC, Mettler Toledo,DSC1 Stare system) [18]. 6e8 mg of each eutectic PCM were placedin a sealed aluminum crucible pan and analyzed under heating andcooling at 5 �C/min. The melting temperature (Tm), was obtainedfrom the onset during heating while the solidification temperature(Tf), was obtained from the onset during cooling and the latent heatof fusion (DHf) was calculated as the area under the peak by nu-merical integration [20].
2.4. Chemical degradation analysis
Fourier transform infrared spectroscopy (FT-IR, Bruker IFS 66/S)was used to evaluate the degradation of chemical structure of MA/PA and MA/PA/SS eutectic mixtures subjected to a large number of
Fig. 2. Schematic diagram of thermal cycling test.
H. Fauzi et al. / Applied Thermal Engineering 66 (2014) 328e334330
thermal cycles. The eutectic PCMswere analyzed on a KBr disk withspectra in the frequency range of 4000e400 cm�1.
2.5. Volume change of PCMs
The volume changes both of MA/PA and MA/PA/SS eutecticmixtures were evaluated using the phase transition method inwhich the PCMs are placed into the same size tubes that are usedfor thermal cycling. The PCMs were heated to a constant temper-ature of 70 �C which is above their melting temperatures. Once thePCMs formed a homogenous liquid, the height of the PCMs in thetube was measured, and vice versa. The volume change was ob-tained from the difference in the height of PCMs between liquid andsolid state [16].
Table 1Thermal properties of MA/PA and MA/PA/SS eutectic mixtures with respect tothermal cycling number.
PCMs Thermal cyclingnumbers
Thermal properties
Tm (�C) DHf,m (J g�1) Ts (�C) DHf,s (J g�1)
MA/PA 0 46.73a,b 155.43a,b 44.76a,b 152.64a,b
200 45.98 180.21 45.17 188.01500 47.20 160.91 46.38 165.99
1000 46.19 191.32 45.92 199.111500 45.30 164.50 45.18 161.40
MA/PA/SS 0 41.81a,b 191.85a,b 41.00a,b 188.06a,b
200 42.06 192.53 41.88 193.54500 44.72 184.52 44.01 184.26
1000 44.30 180.80 43.80 184.741500 43.17 172.46 42.56 169.20
a Fauzi et al., Solar Energy, 2013.b Fauzi et al., Applied Thermal Engineering, 2013.
3. Results and discussion
3.1. Stability of thermal properties
Table 1 shows the phase transition temperature (Tm, Ts) andlatent heat of fusion (DHf,m, DHf,s) of MA/PA and MA/PA/SS eutecticmixtures as prepared and after 200, 500, 1000 and 1500 thermalcycles. It can be seen that MA/PA/SS has a lower melting temper-ature than MA/PA and a greater latent heat of fusion (DHf).
Fig. 3. DSC curves of MA/PA and MA/PA/SS eutectic mixtures subjected to 200 thermalcycles.
Fig. 4. DSC curves of MA/PA and MA/PA/SS eutectic mixtures subjected to 500 thermalcycles.
Fig. 6. DSC curves of MA/PA and MA/PA/SS eutectic mixtures subjected to 1500thermal cycles.
H. Fauzi et al. / Applied Thermal Engineering 66 (2014) 328e334 331
The DSC curves of MA/PA and MA/PA/SS eutectic mixturessubjected to 200, 500, 1000, and 1500 thermal cycles are shown inFigs. 3e6. The data in these figures and Table 1 show that changesoccurred in thermal properties of eutectic PCMs as the number ofthermal cycling increases. The phase transition temperature of MA/PA eutectic mixture decreased with an increasing number of ther-mal cycles while the phase transition temperature of MA/PA/SSincreases with an increasing number of thermal cycles. The meltingtemperature of MA/PA/SS subjected to thermal cycling shows anirregular increase but is still in the range of suitable phase transi-tion temperature for thermal energy storage application systems(40e45 �C). The changes of the melting temperature of MA/PA andMA/PA/SS are shown in Fig. 7. Fig. 8 show the changes in latent heatof fusion of MA/PA and MA/PA/SS eutectic mixtures. This reflectsthe data in Table 1 and indicates that the latent heat of fusion (DHf)of MA/PA eutectic mixture was increased irregularly after 200, 500,1000, and 1500 cycles. Whereas the DHf of MA/PA/SS shows mostlydecreases.
The other studies of thermal reliability of eutectic fatty acids asPCM, Zhang et al., 2001 [7] reported that the thermal properties of
Fig. 5. DSC curves of MA/PA and MA/PA/SS eutectic mixtures subjected to 1000thermal cycles.
lauric acid/palmitic acid (LA/PA) eutectic mixture was stable up to100 cycles. Sari et al., 2004 [3] evaluated the thermal reliability ofsome fatty acid eutectic mixtures such as lauric acid/stearic acid(LA/SA), myristic acid/palmitic acid (MA/PA), and palmitic acid/stearic acid (PA/SA). As shown in Table 2 they reported that thechanges in the Tm and DHf of those eutectic PCMs were irregularwhen subjected to 90, 180 and 360 thermal cycles and wereacceptable for a PCM that will be used in latent heat thermal energystorage (LHTES) applications. In another work, Sari, 2006 [9] alsoevaluated the thermal stability of LA/MA, LA/PA andMA/SA eutecticmixtures after 720, 1080 and 1460 thermal cycles and found thatthe thermal properties including Tm and DHf of both PCM eutecticmixtures tends to decrease with an increasing number of thermalcycles, but the amounts of decreasewere irregular andminor, thoseresult are shown in Table 3. The last work of thermal stability ofeutectic fatty acids as PCMwas conducted by Karaipekli et al., 2009[8] who observed the thermal stability of capric acid/stearic acid(CA/SA) subjected to 1000, 2000, 3000, 4000 and 5000 thermalcycles, the study revealed that the melting temperature (Tm) andthe latent heat of fusion (DHf) of CA/SA change irregularly during
Fig. 7. Changes on phase transition temperature of MA/PA and MA/PA/SS subjected tonumbers of thermal cycles.
Fig. 8. Changes on latent heat of fusion of MA/PA and MA/PA/SS subjected to numbersof thermal cycles. Fig. 9. FT-IR curves of un-cycled MA/PA and MA/PA/SS.
H. Fauzi et al. / Applied Thermal Engineering 66 (2014) 328e334332
the thermal cycling test, and they concluded that the results areacceptable for a PCM to be used for LHTES application.
Therefore, the changes of thermal properties such as meltingtemperature (Tm) and latent heat of fusion (DHf) of MA/PA and MA/PA/SS eutectic mixtures are in agreement with literature and wereacceptable for use in a thermal energy storage (TES) applicationsuch as solar water heating and solar space heating system up to atleast 1500 thermal cycles, corresponding to a 4 year utilizationperiod.
3.2. Chemical degradation analysis
The changes of thermal properties of fatty acid eutectic mixturesas PCM after a large number of heating/cooling cycles are caused bychanges in the chemical structures of PCM or the increasing
Table 2Thermal properties of LA/SA, MA/PA and PA/SA eutectic mixture after thermal cycling te
Eutectic PCMs Number of cycling test Melting temperature (Tm), �C
LA/SA 0 37.00a
90 36.56a
180 36.12a
360 37.36a
MA/PA 0 42.60a
90 42.04a
180 42.70a
360 42.40a
PA/SA 0 52.30a
90 53.43a
180 51.88a
360 53.58a
a Sari et al., Energy Conversion and Management, 2004.
Table 3Tm and DHf values of uncycled and 1460 cycled some fatty acids eutectic mixtures.
Eutectic PCMs Number of cycling test Melting temperature (Tm), �C
LA/MA 0 34.21a
1460 33.90a
LA/PA 0 35.20a
1460 34.80a
MA/SA 0 44.10a
1460 42.99a
a Sari, Energy Conversion and management, 2006.
amount of impurities contents (2e3, wt.%) in the fatty acids used inpreparation of the eutectic PCM [6,8,9,13,16]. The FT-IR curve inFig. 9 shows the spectra of as preparedMA/PA andMA/PA/SS whereall the peak were found at the same frequency. This means that theaddition of 5 wt.% sodium stearate (SS) in MA/PA (70/30, wt.%) didnot lead to any chemical reaction that changed the structure of MA/PA.
The spectra of as preparedMA/PA andMA/PA after 1500 thermalcycles are shown in Fig. 10. It can be seen that after 1500 thermalcycles a new peak appears at 3832.57 cm�1, which indicates theformation of hydrogen bonds after 1500 thermal cycles. Hydrogenbonding also occurred in as prepared and in cycled MA/PA/SSeutectic mixture at wavenumber 3805.20 cm�1 as show in Fig. 11. Awider different frequency band at MA/PA/SS compare to MA/PAafter 1500 thermal cycles is caused by the presence of sodium (Na)bonding at sodium stearate (SS) in the mixture. Therefore, it can be
st.
Changes of Tm, �C Latent heat of fusion (DHf), J g�1 Change of DHf, %
n.a 182.7a n.a�0.44a 171.4a �6.2a
�0.88a 149.8a �18a
0.36a 183.1a 0.2a
n.a 169.7a n.a�0.56a 157.4a �7.2a
0.10a 163.8a �3.5a
�0.20a 174.6a 2.9a
n.a 181.7a n.a1.31a 185.7a 2.3a
0.42a 175.5a �3.4a
1.28a 186.3a 2.5a
Changes of Tm, �C Latent heat of fusion (DHf), J g�1 Change of DHf, %
n.a 166.8a n.a�0.31a 170.8a 2.4a
n.a 166.3a n.a�0.40a 168.8a 1.5a
n.a 182.4a n.a�1.11a 184.2a 1.0a
Fig. 10. FT-IR curves of un-cycled MA/PA and MA/PA after 1500 melting/solidificationcycle numbers.
Table 4Volume change with phase transition of MA/PA and MA/PA/SS after 1500th thermalcycling test.
Eutectic PCMs Number of thermal cycles Volume change (%)
MA/PA 0 1.11500 1.6
MA/PA/SS 0 0.81500 1.2
H. Fauzi et al. / Applied Thermal Engineering 66 (2014) 328e334 333
concluded that the thermal properties of MA/PA and MA/PA/SSeutectic mixture changes irregularly when subjected to 200, 500,1000 and 1500 thermal cycles caused by changes in the chemicalstructures.
3.3. Volume changes of PCMs
The changes of volume of MA/PA and MA/PA/SS eutectic mix-tures upon solidification and melting were measured by the phasetransition method. Table 4 shows the comparison percentage ofvolume change between solid and liquid condition of as preparedMA/PA and MA/PA/SS as well as MA/PA and MA/PA/SS after 1500thermal cycles. The as prepared MA/PA and MA/PA/SS eutecticmixtures Inside the capsule tube shows the volume in liquid phaseof 22.81 ml and 22.75 ml while in solid phase these eutectic PCMshave a volume of 22.563 ml and 22.565 ml. After 1500 thermalcycles the MA/PA and MA/PA/SS eutectic mixture have a volume inliquid phase of 22.91ml and 22.82ml whereas their volume in solidphase were 22.545 ml and 22.546 ml, respectively. Therefore the asprepared MA/PA eutectic mixture decreases by 1.1% during
Fig. 11. FT-IR curves of un-cycled MA/PA/SS and MA/PA/SS after 1500 melting/solidi-fication cycle numbers.
solidification.Whereas as preparedMA/PA/SS changes only by 0.8%.After 1500 thermal cycles the volume change of both MA/PA andMA/PA/SS increased by 1.6% and 1.2%.
In a previous work, Matsui, et al., 2007 [16] have investigatedthe volume change of pure water (H2O), capric acid/lauric acid (CA/LA) and capric acid/lauric acid with 20 wt.% sodium oleate (CA/LA/SO). They reported that pure water has a volume expansion of 1.5%upon solidification. While CA/LA/SO has a volume contractionof �0.7% upon solidification and CA/LA contracted by �1.1%. Meh-ling and Cabeza, 2008 [21] mentioned that the volume changes ofselected PCM usually less than 10%. Therefore, in application ofLHTES system a container can fit the phase with the larger volume,the pressure is not changed significantly and consequently meltingand solidification of the storage material proceed at a constanttemperature. We can confirm that the volume expansion ofdeveloped eutectic PCMs in this study were small enough andacceptable in latent heat thermal application system.
4. Conclusions
The thermo physical stability of MA/PA and MA/PA/SS eutecticwas measured to evaluate the thermal properties stability, degra-dation of chemical structure, and changes of volume of botheutectic PCMs after 200, 500, 1000, and 1500 melting/solidificationcycles. The changes of melting point of MA/PA and MA/PA/SS wereirregular but of acceptable magnitude. The latent heat of fusion ofMA/PA/SS decreases by 10.1% after 1500 thermal cycles. Whereas,the latent heat of fusion of MA/PA increased irregularly by up to 6%after 1500 thermal cycles but stays below the latent heat of fusionof MA/PA/SS eutectic mixture. Identification of the chemicalstructure and changes of volume of MA/PA and MA/PA/SS eutecticmixtures after 1500 thermal cycles also showed that the MA/PA/SSperformed better than MA/PA. Therefore, from this study it can beconcluded that the MA/PA/SS has a better thermo-physical stabilitythan MA/PA eutectic mixture for at least 1500 thermal cycles, cor-responding to 4 years of utilization in a latent heat thermal energystorage system.
Acknowledgements
The authors acknowledge the Ministry of Higher Education andFaculty of Engineering, University of Malaya through High ImpactResearch grant (UM.R/HIR/MOHE/ENG/21-D000021-16001).
References
[1] A. Sarı, Eutectic mixtures of some fatty acids for low temperature solar heatingapplications: thermal properties and thermal reliability, Appl. Therm. Eng. 25(14e15) (2005) 2100e2107.
[2] A. Sarı, Thermal reliability test of some fatty acids as PCMs used for solarthermal latent heat storage applications, Energy Convers. Manage. 44 (14)(2003) 2277e2287.
[3] A. Sarı, H. Sarı, A. Önal, Thermal properties and thermal reliability of eutecticmixtures of some fatty acids as latent heat storage materials, Energy Convers.Manage. 45 (3) (2004) 365e376.
[4] A. Sharma, S.D. Sharma, D. Buddhi, Accelerated thermal cycle test of acet-amide, stearic acid and paraffin wax for solar thermal latent heat storageapplications, Energy Convers. Manage. 43 (14) (2002) 1923e1930.
H. Fauzi et al. / Applied Thermal Engineering 66 (2014) 328e334334
[5] S.D. Sharma, D. Buddhi, R.L. Sawhney, Accelerated thermal cycle test of latentheat-storage materials, Sol. Energy 66 (6) (1999) 483e490.
[6] A. Sarı, K. Kaygusuz, Some fatty acids used for latent heat storage: thermalstability and corrosion of metals with respect to thermal cycling, RenewableEnergy 28 (6) (2003) 939e948.
[7] J.-J. Zhang, J.L. Zhang, S.M. He, K.Z. Wu, X.D. Liu, Thermal studies on the solideliquid phase transition in binary systems of fatty acids, Thermochim. Acta 369(1e2) (2001) 157e160.
[8] A. Karaıpeklı, A. Sarı, K. Kaygusuz, Thermal properties and thermal reliabilityof capric acid/stearic acid mixture for latent heat thermal energy storage,Energy Sources, Part A 31 (3) (2009) 199e207.
[9] A. Sarı, Eutectic mixtures of some fatty acids for latent heat storage: thermalproperties and thermal reliability with respect to thermal cycling, EnergyConvers. Manage. 47 (9e10) (2006) 1207e1221.
[10] L. Shilei, Z. Neng, F. Guohui, Eutectic mixtures of capric acid and lauric acidapplied in building wallboards for heat energy storage, Energy Build. 38 (6)(2006) 708e711.
[11] M. Silakhori, M.S. Naghavi, H.S.C. Metselaar, T.M.I. Mahlia, H. Fauzi,M. Mehrali, Accelerated thermal cycling test of microencapsulated paraffinwax/polyaniline made by simple preparation method for solar thermal energystorage, Materials 6 (5) (2013) 1608e1620.
[12] M.N.R. Dimaano, A.D. Escoto, Preliminary assessment of a mixture of capricand lauric acids for low-temperature thermal energy storage, Energy 23 (5)(1998) 421e427.
[13] A. Karaipekli, A. Sari, K. Kaygusuz, Thermal properties and long-term reli-ability of capric acid/lauric acid and capric acid/myristic acid mixtures forthermal energy storage, Energy Sources, Part A 30 (13) (2008) 1248e1258.
[14] A. Sari, A. Karaipekli, K. Kaygusuz, Capric acid and myristic acid for latent heatthermal energy storage, Energy Sources, Part A 30 (16) (2008) 1498e1507.
[15] A. Sharma, S.D. Sharma, D. Buddhi, R.L. Sawhney, Thermal cycle test of urea forlatent heat storage applications, Int. J. Energy Res. 25 (5) (2001) 465e468.
[16] T. Matsui, M. Yoshida, H. Yamasaki, Y. Hatate, Thermal properties of multi-component fatty acids as solideliquid phase change materials for coolingapplications, Chem. Eng. Commun. 194 (1) (2007) 129e139.
[17] A. Shukla, D. Buddhi, R.L. Sawhney, Thermal cycling test of few selectedinorganic and organic phase change materials, Renewable Energy 33 (12)(2008) 2606e2614.
[18] H. Fauzi, H.S.C. Metselaar, T.M.I. Mahlia, M. Silakhori, H. Nur, Phase changematerial: optimizing the thermal properties and thermal conductivity ofmyristic acid/palmitic acid eutectic mixture with acid-based surfactants, Appl.Therm. Eng. 60 (1e2) (2013) 261e265.
[19] H. Fauzi, H.S.C. Metselaar, T.M.I. Mahlia, M. Silakhori, Sodium laurate en-hancements the thermal properties and thermal conductivity of eutectic fattyacid as phase change material (PCM), Sol. Energy 102 (2014) 333e337.
[20] J.W. Dodd, K.H. Tonge, B.R. Currell, Thermal Methods, 1987. Medium: X; Size:Pages: 360.
[21] H. Mehling, L. Cabeza, Basic thermodynamics of thermal energy storage, in:Heat and Cold Storage with PCM, Springer, Berlin Heidelberg, 2008, pp. 1e10.
