organic composite phase change material for cold thermal energy storage

organic composite phase change material for cold thermal energy storage

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Energy Procedia 158 Energy Procedia 00(2019) (2017)5305–5310 000–000 www.elsevier.com/locate/procedia

10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10th International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China

Performance study on expand graphite/organic composite phase Performance study on expand graphite/organic The 15th International Symposium on District Heatingcomposite and Cooling phase change material for cold thermal energy storage change material for cold thermal energy storage Assessing the feasibility heat demand-outdoor a, of using the b a Zhou Sunxia,b , Zhang Xuelai *, Liu Sheng , Li Yuyang , Xu Xiaofengaa a, a,b b a Zhou Sunxi , Zhang for Xuelai *, Liu Shengdistrict , Li Yuyang Xiaofengforecast temperature function a long-term heat, Xu demand Cool Storage Technology Institute,Shanghai Maritime University,Shanghai 201306, China a

a Cool StorageCenter Technology Institute ,Shanghai Maritime University Shanghai 201306,100097 China,China Vegetable Research ,Beijing Academy of Agriculture and Forestry, Sciences ,Beijing a,b,c a a b c b Vegetable Research Center ,Beijing Academy of Agriculture and Forestry Sciences,Beijing 100097,China b

I. Andrić a

*, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Correc

IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal

b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France Abstract c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France Abstract Octanoic-myristic acid binary eutectic mixture (OA-MA) was prepared as a base liquid. A novel shaped composite PCM of OAOctanoic-myristic acid binary eutectic mixture mass (OA-MA) was prepared as a base A novel shaped composite of OAMA/expanded graphite (EG) with an optimum ratio (OA-MA:EG=93:7) wasliquid. prepared by uniformly absorbing PCM OA-MA into MA/expanded graphite with an micro optimum mass ratio (OA-MA:EG=93:7) preparedmicroscopy by uniformly absorbing OA-MA into the porous structure of (EG) the EG. The structure was observed by scanningwas electronic (SEM). The phase change Abstract the porous structure of the Themeasured micro structure was observed scanning electronic microscopy (SEM). phaseconstant change temperature and latent heatEG. were by DSC.The thermalbyconductivity was measured by Hot DiskThe thermal temperature and latent heat were measured by DSC.The thermal conductivity was measured by Hot Disk thermalThe constant analyzer. Besides, the thermal cycling tests was carried out for 100 times to validate the stability of OA-MA/EG. phase District Besides, heating networks are commonly addressed in the literature as onetoofvalidate the most solutions for decreasing the analyzer. the thermal cycling waslatent carried outwas for 146.1 100 times theeffective stability of OA-MA/EG. phase change temperature of OA-MA was 7.1tests ℃, the heat J/g, and the thermal conductivity was 0.2971 The W/(m·K). greenhouse gas emissions from was the building sector. These systems require high investments which are returned through the heat change temperature of OA-MA 7.1 ℃, the latent heat was 146.1 J/g, and the thermal conductivity was 0.2971 W/(m·K). After adding the 7 % EG, the phase change temperature of OA-MA/EG was 6.8 ℃, the latent heat was 136.3 J/g, and the sales.adding Due to changed climate conditions and building renovation policies, heat demand in thewas future could After thethe 7 % EG,0.9975 the phase change of than OA-MA/EG latenttests heat J/g, decrease, and the ℃, the thermal conductivity was W/(m·K), 2.36temperature times higher OA-MA. was The 6.8 thermal cycling showed136.3 that OA-MA/EG prolonging the investment return period. thermal conductivity 0.9975 W/(m·K), 2.36All times thermalPCM cycling OA-MA/EG composite PCM has awas good thermal reliability. the higher results than showOA-MA. that the The composite has tests greatshowed prospectthat in the practical The main scopehas of thisgood paper is to assess the feasibility of using the heat – outdoor temperature function in forthe heatpractical demand composite thermal reliability. All the results show that demand the composite PCM has great prospect applicationPCM to medicala refrigerated transportation system which temperature range is 2~8 ℃. forecast. The districtrefrigerated of Alvalade, located in Lisbon (Portugal), was used as isa 2~8 case℃. study. The district is consisted of 665 application to medical transportation system which temperature range buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district Copyright © 2018 Elsevier Ltd. All rights reserved. © 2019 The Published by Elsevier Ltd. intermediate, deep). To estimate the error, renovation scenarios wereLtd. developed (shallow, obtained heat demand values were Copyright © Authors. 2018 Elsevier All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) compared with results from a dynamic heat demand model, previously developed and validated by the authors. th Selection and peer-review under responsibility of the scientific committee of the 10 International Conference on Applied Energy (ICAE2018). Peer-review under responsibility of the scientific committee of ICAE2018 – The of 10th International Conferencefor onsome Applied Energy. The results showed that when only weather change is considered, the margin error could be acceptable applications Energy (ICAE2018). (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation Keywords: phase change materials;thermal conductivity; organic; cyclic stability; cold storage scenarios,phase the error increased up to 59.5% organic; (depending the weather and renovation scenarios combination considered). Keywords: changevalue materials;thermal conductivity; cycliconstability; cold storage The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and 1.decrease Introduction scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the 1.renovation Introduction coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and The rapid development socialestimations. economy and technology has led to a dramatic increase in energy consumption. improve the accuracy of heatof demand

ThePCM rapidtodevelopment of social economy andintechnology has and led to a dramatic increase in energy consumption. Using solve the contradiction of energy terms of time space is one of the effective ways to alleviate Using PCM to solve the contradiction of energy in terms of time and space is one of the effective ways to systems, alleviate energy at present [1].by Nowadays, PCM has been widely used in latent heat thermal energy storage © 2017shortage The Authors. Published Elsevier Ltd. energy shortage at present [1]. Nowadays, PCM has been widely used in latent heat thermal energy storage systems, Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel.: +021-38282925; fax: +021-38282925. * Corresponding Tel.: +021-38282925; fax: +021-38282925. E-mail address:author. [email protected] Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected]

1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. 1876-6102 Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10th International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility the scientific Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018). 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.642

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such as energy saving in buildings [2], solar thermal storage [3], food and medicine cooling [4]. Therefore, the development of high-efficiency PCM is of great significance, and of course, also is the focus of research. Organic PCMs have the advantages of low super cooling, non-toxic, high latent heat, small corrosion and good thermal cycling stability[5], having great potential for application. Taguchi et al. [6] prepared pentadecane methyl methacrylic acid micro-capsule with a phase change temperature of 9.5 ℃ and latent heat of 97 J/g. Zuo et al. [7] developed a caprylic - dodecanol composite PCM with a minimum eutectic point of 6.5 ℃ and a latent heat of 171.1 J/g. However, the thermal conductivity of organic PCMs is generally low. Various research groups have done a lot of research on enhancing the thermal conductivity of organic PCMs. Huang et al. [8] studied the citric - palmitic stearic acid/EG composite PCMs, when the mass ratio was 13:1, the melting and solidification temperatures were 28.9 °C and 16.3 °C, the latent heat were 137.4 J/g and 141.5 J/g. Sharma et al. [9] found that the thermal conductivity of palmitic acid was increased by 80 % after adding TiO2 with a ratio of 5 wt%. The above studies do not involve binary organic PCMs for medical refrigerated transportation systems at 2 to 8 ℃. Furthermore, they did not carry out a complete cool storage and discharge experiment after the cycle. The aim of this paper is to study the novel binary organic PCM OA-MA/EG, which can be used in medical refrigerated transportation systems at 2~8 ℃ . In order to enhance the thermal conductivity of OA-MA, EG with micrometer-scale grid structure was used as additive. EG is worm-like and its surface has micrometer-scale grid structure, which can adsorb OA-MA, and improves the thermal conductivity through the overlap of itself. Nomenclature PCM EG SEM OA-MA DSC

phase change material expanded graphite scanning electronic microscopy octanoic-myristic acid binary eutectic mixture differential scanning calorimetry

2. Experimental 2.1. Experimental preparation Preparation of OA-MA: Both OA and MA were analytical reagents. EG was 80 mesh with an expansion rate of 250 ml/g. OA and MA were weighed by electronic analytical balance and placed in beaker of 100 ml. Notably, the mass ratio of OA and MA was determined as 87:13 in this study. Then, the beaker was heated to 30 ℃ and mixed by magnetic stirring apparatus for 30 minutes to guarantee the uniformity. The solutions with the mass of 47.5 g, 47 g, 46.5 g, 46 g, 45.5 g, and 45 g were prepared for the experiment. Preparation of EG: EG was expanded in an electric box-type resistance furnace with a temperature of 700 ℃. The duration of expansion process was set to 10 minutes. The SEM micrographs of EG was demonstrated in Fig.1. Comparing Fig.1 (a) with Fig.1 (b), it is clear that the surface of EG is relatively smooth before being expanded, while the surface of EG has a clear porous structure after expansion at a high temperature . The porous structure in expanded EG contributes to adsorbing more base liquid, which can enhance the thermal conductivity.

Fig.1. SEM micrographs (a) EG without expansion (b) EG (c) OA-MA/EG



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Preparation of OA-MA/EG: OA-MA with a ratio of 87:13 was used as the base fluid, and EG was used as the matrix to prepare six groups of PCMs. The proportions of EG in the six groups were 5 %, 6 %, 7 %, 8 %, 9 % and 10 % respectively. Firstly, weighing OA-MA 47.5 g, 47 g, 46.5 g, 46 g, 45.5 g, 45 g in a beaker, and heating on a magnetic stirrer to 40 ℃, then stirring 30 minutes to make it mix uniformity. After that, weighing the EG 2.5 g, 3.0 g, 3.5 g, 4.0 g, 4.5 g, and 5 g, adding to the OA-MA mixed solution with a mass ratio of 87:13, respectively. The prepared OA-MA/EG was stirred every half an hour for a total of six times to make it mixed uniformly. 2.2. Experimental methods

2.2.1 The optimal ratio of EG The greater content of OA-MA, the greater latent heat of the composite PCM. In this paper, the maximum adsorption ratio of EG to OA-MA mixed solution was defined as the optimal ratio of OA-MA to EG. 0.2 g OAMA/EG composite PCM with different proportion of EG was weighed on the filter paper with an electronic analytical balance, and record the total mass of OA-MA/EG and filter paper. The samples were placed in an electrothermal blowing dry box at 50 ℃ for 60 minutes. By comparing the mass before and after drying, the optimal proportion of EG was qualitatively determined by the smallest mass loss. 2.2.2 Cold storage and discharge experiment The experiment was conducted with two low-temperature thermostat baths, one of it was maintained at -15 ℃ and another was kept at 25 ℃. Samples were cooled in a low-temperature thermostat bath with the temperature of 15 ℃. The temperature of the material was measured by thermocouple and recorded by an Agilent temperature-time recorder. When the temperature is near -15 ℃, the beaker was quickly removed and placed in another lowtemperature thermostat bath with the temperature of 25 ℃. 2.2.3 Measurement of phase change temperature and latent heat Experiments for testing phase change temperature and latent heat were performed by DSC. Liquid nitrogen was used to cool the PCM and nitrogen vapor was used as protective gas and purge gas. Indium was performed as a reference material for calibration. The temperature was in the range of -20 to 30 ℃ and the purge gas flow rate was 20 ml/min. The protective gas flow rate was 60 ml/min and heating and cooling rate was 5 K/min. 2.2.4 Measurement of thermal conductivity TPS2500s thermal constant analyzer was used to test the thermal conductivity. Before testing, the machine was turned on and preheated for 30 minutes. The C5465 probe was inserted into the middle of the mixed solution, the vertical distance from the probe center to the liquid level and beaker wall were recorded. In order to avoid the influence of indoor air flow, the test probe and beaker was closed inside a container. 2.2.5 Testing of material stability OA-MA/EG (30 g) was weighed by electronic analysis balance scale and then put it into the high and low temperature alternating test box. The temperature range of high and low temperature alternating test box was -40 ~60 ℃. The period of stability test was 60 minutes and totally 100 cycles were conducted. 3. Results and discussion 3.1. The optimal proportion of EG The comparison of weight changes of the composite PCM before and after drying are shown in Table 1. It can be clearly seen from the table that the mass loss rate of composite PCM with EG mass ratio of 5 % and 6 % were 13.70 % and 11.20 % respectively. The insufficient amount of EG caused the PCM to fail to absorb completely and the quality loss rate was high. The mass loss rates of composite PCMs containing 7 %, 8 %, 9 % and 10 % EG were between 5.50% and 5.60%, and the mass loss rate was almost equal and stable. Therefore, when the mass ratio of OA-MA to EG was 93:7, the adsorption effect showed the best, and it was defined as the optimal ratio of OA-MA to EG. Fig.1(c) is a SEM image of OA-MA/EG containing 7 % EG, compared with Fig. 1(b), it made OA-MA filled

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better. Table1 Quality changes of OA-MA/EG before and after drying EG quality ratio (%)

Pre-drying quality (g)

Dry quality (g)

Loss of quality (g)

Loss rate (g)

5

0.2

0.1726

0.0274

13.70%

6

0.2

0.1776

0.0224

11.20%

7

0.2

0.1888

0.0112

5.60%

8

0.2

0.1889

0.0111

5.55%

9

0.2

0.1890

0.0110

5.50%

10

0.2

0.1889

0.0111

5.55%

3.2. Phase change temperature and latent heat DSC results of OA-MA and OA-MA/EG are shown in Fig.2. The phase change temperature of OA-MA/EG was 6.8 ℃, which was reduced by 0.3 ℃ compared to OA-MA. The latent heat of OA-MA was 136.3 J/g, which was reduced 9.1J/g compared to OA-MA. This because EG only acts as a skeleton without phase transformation in the composite PCM and does not contribute to its latent heat. The proportion of EG (7 wt%) matches the decrease of the latent heat of 6.7 %. (a)

(b)

Fig. 2. (a) DSC curve of OA-MA (b) DSC curve of OA-MA/EG

3.3. Thermal conductivity of OA-MA/EG Thermal conductivity is an important factor affecting the use of PCM. Higher thermal conductivity can speed up the cold storage and discharge of materials and improve the utilization of materials. The step-cooling curves of OAMA and OA-MA/EG are shown in Fig.3. In the process of sensible heat release, when the temperature dropped from 5 to -5 ℃, OA-MA/EG took 4 minutes, and OA-MA took 11.5 minutes. The addition of EG increased the cooling rate of sensible heat by 187.5 %. After adding EG, since the EG in the OA-MA matrix can overlap with each other, a perfect thermally conductive mesh structure was formed, the heat conduction mode was improved, and the thermal conductivity was increased. During the absorption of latent heat, when the temperature increased from 10 ℃ to 12 ℃, OA-MA/EG took 5.3 minutes, and OA-MA took 9.8 minutes. The addition of EG increased the melting rate of OA-MA by 84.9 %. In the period of latent heat release, when the temperature declined from 8 to 6 ℃, OAMA/EG took 6.8 minutes and OA-MA took 70.8 minutes. The addition of EG improved the release rate of OA-MA latent heat by 941.2 %. After adding EG, OA-MA was divided into several small units to increase contact area of materials. EG can not only increase the thermal conductivity, but also greatly enhance the coagulation and nucleation rate. The thermal conductivity of the OA-MA and OA-MA/EG were measured as 0.2971 W/(m·K) and 0.9975 W/(m·K), respectively. The addition of EG increased the thermal conductivity by 2.36 times. The results showed that it is an effective way to enhance the thermal conductivity of PCMs by adding EG. And obviously, OA-MA/EG has a wider application space.



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Fig.3. Step cooling curve of OA-MA and OA-MA/EG

3.4. Thermal reliability of OA-MA/EG Stability is an important performance indicator of PCM. DSC results of OA-MA/EG before and after cycles are shown in Fig.4(a). After 100 cycles, the phase change temperature was 6.9 ℃, which was 0.1 ℃ higher than before the cycle;the latent heat was 136.8 J/g. In general, there is no regular change in the latent heat of fatty acids before and after cycling[10]. The latent heat of OA-MA/EG increased 0.5 J/g after cycling , this may be the error caused by the experimental instrument. In any case, the latent heat and phase change temperature of OA-MA/EG did not change obviously,with good stability. Cold storage and discharge curves before and after 100 cycles of OA-MA/EG are shown in Fig.4(b). In the phase of sensible heat release, when the temperature decreased from 5 to -5 ℃, the rate of sensible cooling was decreased by 37.5 % after 100 cycles. During the stage of latent heat release, when the temperature decreased from 8 to 6 ℃, the release rate of latent heat was reduced by 29.4 % after 100 cycles. During the phase of latent heat absorption, when the temperature increased from 10 to 12 ℃, the absorption rate of melting latent heat decreased by 26.4 % after 100 cycles. The thermal conductivity of OA-MA/EG after 100 cycles was 0.7736 W/(m·K), which decreased by 22.4 % compared with that before cycling. After circulation, the mass loss rate was 6.61 % which was greater than the mass loss rate range 5.50 to 5.60 %. The reason for the sensible heat, latent heat and thermal conductivity of OA-MA/EG are less than those before the cycling, was that a small part of the OA-MA spill from the EG, which makes the network structure of the EG cut off and then causes heat transfer to become slower. (a)

(b)

Fig.4. (a) DSC test results after 100 cycles of OA-MA/EG (b) Cold storage and discharge curves before and after 100 cycles of OA-MA/EG

4. Conclusion (1) A new low-temperature composite PCM OA-MA/EG used in medical refrigerated transportation system with temperature range of 2~8 ℃ has been developed. The optimal mass ratio of EG was determined as 7 % for OA-MA

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by electrothermal blowing dry box. The phase change temperature of OA-MA/EG was 6.8 ℃ and the latent heat was 136.3 J/g. (2) The thermal conductivity of OA-MA was increased 2.36 times after addition of EG. Compared to the base solution, the cooling rate of sensible heat of OA-MA/EG was increased by 187.5 %, the heat absorption rate of latent heat was increased by 84.9 % and the release rate of latent heat was increased by 941.2 %.The addition of EG not only increased the thermal conductivity of OA-MA but also enhanced the nucleation rate of OA-MA. (3) Both the phase change temperature and latent heat of the OA-MA/EG were not changed obviously after 100 cycles of cold storage and discharge contrast experiment. Due to the stable thermal storage and discharge properties of the material, the newly developed OA-MA/EG can maintain stable thermodynamic properties in practical application. Acknowledgements This study benefits from financial support of the Key Program of Shanghai Science and Technology Commission (Grant No. 16040501600) and National Natural Fund Project (Grant No. 51376115). References [1] Liu R L, Huang X M. Development of cold storage air conditioning technology and promotion of power grid migration and peak filling[J]. Energy Saving Technology, 2004, 22(1):39-41. [2] Laaouatni A, Martaj N, Bennacer R, et al. Phase change materials for improving the building thermal inertia[J]. Energy Procedia, 2017, 139:744-749. [3] Kapsalis V, Karamanis D. Solar thermal energy storage and heat pumps with phase change materials[J]. Applied Thermal Engineering, 2016, 99:1212-1224. [4] Kahwaji S,Johnson M B, Kheirabadi A C,et al. Fatty acids and related phase change materials for reliable thermal energy storage at moderate temperatures[J]. Solar Energy Materials & Solar Cells, 2017,167:109-120. [5] Murillo D C. Refrigerated container versus bulk: evidence from the banana cold chain[J]. Maritime Policy & Management, 2015,42(3):228245. [6] Taguchi Y, Yokoyama H, Kado H, et al. Preparation of PCM microcapsules by using oil absorbable polymer particles[J]. Colloids & Surfaces A Physicochemical & Engineering Aspects, 2007, 301(1):41-47. [7] Zuo J, Li W, Weng L. Thermal performance of caprylic acid/1-dodecanol eutectic mixture as phase change material (PCM)[J]. Energy & Buildings, 2011,43(1):207-210. [8] Huang X, Cui Y D, Yin G, et al. Preparation and thermal properties of lanthanic- palmitic - stearic acid/expanded graphite energy storage composite phase change materials[J]. Material Review, 2017, 31(14):52-56 . [9] Sharma R K, Ganesan P , Tyagi V V , et al. Thermal properties and heat storage analysis of palmitic acid-TiO2, composite as nano-enhanced organic phase change material (NEOPCM)[J]. Applied Thermal Engineering, 2016, 99:1254-1262. [10] Tian S L, Zhang D, Xiao D, et al. Experimental study on thermal cycling behavior of fatty acid phase change energy storage materials[J]. Development and Application of Materials, 2006, 21(1):9-12.