- Email: [email protected]
expanded graphite composite phase change thermal energy storage material
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Energy Procedia 158 Energy Procedia 00(2019) (2017)4799–4804 000–000 www.elsevier.com/locate/procedia
10thth International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10 International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China
Experimental study on preparation of a novel foamed cement with Experimental study on preparation of aphase novel foamed cementenergy with The 15th International Symposium on District Heating and thermal Cooling paraffin/ expanded graphite composite change paraffin/ expanded graphite composite phase change thermal energy storage material storage material Assessing the feasibility of using the heat demand-outdoor Lifang Liu aa, Yue Qu aa, Tao Xu a,a, *, Jiayu Chen bb , Huijun Wuaa , Gongsheng Huangbb, Lifang Liu , Yue Qu , TaoXiaoqing Xu a *, long-term Jiayu Chen , district Huijun , Gongsheng , a temperature function for heat demandHuang forecast Zhou , Lixiu Yang aWu Xiaoqing Zhou a, Lixiu Yang a a a Engineering, Guangzhou b c Academy of Building Efficiency, of Civil Univers ity, Guangzhou510006, China c I. Andrića,b,c *, Energy A. and Pina P.School Ferrão , J. Fournier .,Kong, B. Tat Lacarrière , O. Le Corre Department Architecture Civil, Engineering, of Hong Cheeity, Avenue Kowloon, Hong Kong Academy ofofBuilding Energy Efficiency, School of City CivilUniversity Engineering, Guangzhou Univers Guangzhou510006, China a
ba
b Department of Architecture and Civil Engineering, City University of Hong Kong, Tat Chee Avenue Kowloon, Hong Kong 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 a
Abstract This study proposed a novel foaming cement heat preservation block with heat storage, peak clipping, and temperature This study proposed a novelsuch foaming cement heat preservationgraphite block with heat storage, peak clipping, andmaterial temperature adjustment functions . To produce cements, a paraffin/expansion composite phase change heat storage with adjustment functions . To produceof such paraffin/expansion graphite phaseThen change storage phase material with ℃ and aa enthalpy a Abstract phase transition temperature 41.9 cements, value of 207.6 J/g composite was prepared. the heat composite change amaterial phase transition temperature andexpanded a enthalpy value and of 207.6 J/g was Then the composite change (P CM) loaded paraffin ofat 41.9 44℃℃into graphite then was mixedprepared. cement uniformly. The porousphase structure of material (P CM) loaded paraffin at 44℃ into expanded graphite and then was mixed cement uniformly. The porous structure of the foamed cement has light weight and good heat preservation capacity so that then composite PCM can effectively store heat District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the the foamed cement has light weight and good heat preservation capacity so that then composite PCM can effectively store heat energy and shave the load peak. To investigate the characteristics of the proposed material, this focuses on the physical structure, greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat energy shave thechanged loadand peak. To investigate the characteristics ofthe thematerial proposed material, this of focuses on the physical thermal storage thermal insulation performance mass fractions PCM arefuture 10%、15%、20%、 sales. and Due to capacity the climate conditions and buildingwhen renovation policies, heat demand in the could structure, decrease, thermal storage capacity and thermal insulation performance when the material mass fractions of PCM are 10%、15%、20%、 25% and 30%. The experimental results show that with the increase of the mass fraction of PCM, the thermal storage capacity prolonging the investment return period. 25% and 30%. The experimental results show that with the increase of the mass fraction of PCM, the thermal storage and thermal insulation properties of the foamed cement increases. In addition, there is no chemical reaction between the materials. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heatcapacity demand and thermal insulation properties of the foamed cement addition, there no chemical reaction between the materials. The results The show a the proposed material has ainpotential in(Portugal), creatingInefficient thermal wall s. district forecast. district of Alvalade, located Lisbonincreases. was used as a isinsulation case study. The is consisted of 665 The results that showvary a theinproposed material has a potential in creating efficient thermal insulation s. buildings both construction period and typology. Three weather scenarios (low,wall medium, high) and three district Copyright © scenarios 2018 Elsevier All rights(shallow, reserved.intermediate, deep). To estimate the error, obtained heat demand values were wereLtd. developed ©renovation 2019 The Authors. Published by Elsevier Ltd. th Copyright © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the model, scientific committee of the 10and International compared withaccess resultsarticle from aunder dynamic heat demand previously developed validated byConference the authors.on Applied Energy This is an open the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) th Selection and peer-review under responsibility of the scientific committee of the 10 International Conference on Applied Energy (ICAE2018). The results under showed that when only weather change is considered, the margin error could be acceptable applications Peer-review responsibility of the scientific committee of ICAE2018 – The of 10th International Conferencefor onsome Applied Energy. (ICAE2018). (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation Keywords: change thermal storage material; Paraffin; Expanded on graphite; Foamed and cement scenarios,Phase the error value increased up to 59.5% (depending the weather renovation scenarios combination considered). Keywords: Phase change thermal storage material; Paraffin; Expanded graphite; Foamed cement The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and * Corresponding author. Tel.: 13925031066. renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the * Corresponding Tel.: 13925031066. E-mail address:author. [email protected] (T. Xu). coupled scenarios). The values suggested E-mail address: [email protected] (T. Xu). could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.
1. Introduction 1. Introduction © 2017 The Authors. Published by Elsevier Ltd. Building thermal aim theCommittee heat loss or heat 15th gainInternational from the interior of theonbuilding to the outside Peer-review underinsulations responsibility of to thereduce Scientific of The Symposium District Heating and Building thermal insulations aim to reduce the heat loss or heat gain from the interior of the building to energy the outside environment. Efficient insulations can effectively reduce the air-conditioning load and air-conditioning Cooling. environment. of Efficient insulations can effectively reduce thethermal air-conditioning and air-conditioning energy consumption a building [1]. Therefore, developing better insulationload building materials becomes one of consumption a building [1].Climate Therefore, Keywords: Heatof demand; Forecast; changedeveloping better thermal insulation building materials becomes one of 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. 1876-6102 Copyright © 2018 Elsevier Ltd. All rights Selection and peer-review under responsibility of thereserved. scientific committee of the 10th International Conference on Applied Energy (ICAE2018). 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.2019.01.717
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Lifang Liu et al. / Energy Procedia 158 (2019) 4799–4804 Author name / Energy Procedia 00 (2018) 000 –000
the most effective methods to reduce building energy [2]. In recent years, researchers found the traditional organic insulation materials have a few shortcomings, such as cracking [3], poor durability, flammability, and the toxic gases during combustion [4]. Therefore, it is inevitable to develop alternative materials that can overcomes these problems and maintain a high thermal insulation capacity [5]. As one of the ideal substitutions, foamed cement is a lightweight porous material made by adding bubbles that generated by chemical foaming agent in cement slurry [6]. Foamed cement is a typical building insulation material has been developed for years. It has excellent thermal insulation properties, as well as light weight, high adhesive force, good durability, excellent A-grade combustibility, and low carbon emission during production [7]. Based on these characteristics, researchers proposed to produce phase change thermal storage foamed cement by adding heat storage phase change material into foamed cement, as PCM has a large energy storage density and can maintain a constant temperature during the phase change process [8]. If such phase change thermal storage foamed cement can be applied to a building thermal insulation structure, it not only can provide necessary thermal insulation, but also play the role of heat storage. This can effectively shave the energy and temperate peak to stabilize the indoor temperature. In recent years, organic phase change materials (OPCMs) has attracted much attention in various applications for their excellence thermal storage properties. However, OPCMs suffers from the problems of liquid leakage and low thermal conductivity [9]. On the other hand, as paraffin is recognized as one of the most promising PCMs due to its large latent heat, low cost and its stable, nontoxic and noncorrosive properties [10]. Researchers used organic paraffin as PCM and expanded graphite as support structure and prepared the paraffin/expanded graphite composite phase change material. The porous adsorption property of expanded graphite can effectively solve the problem of paraffin wax leakage caused by phase change[11]. Chen et al. also proposed similar paraffin/expanded graphite composite phase change material with a mass ratio of EG of 20% (completely absorbed) to cool down the room temperature [12]. Based upon previous studies, this article first investigated the preparation of phase change thermal storage foamed cements with different mass fractions of composite PCM. Then this article studied the effects of adding different amounts of paraffin/expanded graphite composite PCM on the properties of foamed cements, including foamed cement microstructure, physical structure, heat storage capacity, and thermal conductivity. The research laid a foundation for the application of phase change thermal storage foamed cement in building thermal insulation structures. 2. Experiment description 2.1. Materials Paraffin (melting point Tm =44°C) was provided by Hangzhou Ruhr New Material Technology Co. Ltd. Expandable graphite (expansion ratio: 300ml/g, average particle size: 300µm) was supplied by the Qingdao Graphite Co. Ltd. Concentrated high efficiency cement foaming agent (QW-100) was produced by Zhengzhou Pengyi Chemical Building Materials Co. Ltd. Silicate 425 cement was produced by Haimen Conch Cement Co. Ltd. 2.2. Equipment The equipment to prepare the target materials includes a microwave oven (EG720FFI-NS, Midea, China), a electronic balance (WT5002N, Changzhou wantai balance instrument Co. Ltd.), a concrete accelerated curing box (HJ-84, Tianjin Luda Construction Equipment Co. Ltd.), a foaming machine (Yh-fp50, Guangzhou Yongsheng Construction Engineering Co. Ltd.), an electro-thermostatic blast oven (DGX-9243, Shanghai Foma Experimental Equipment Co. Ltd.), a scanning electron microscope (JSM-7001F, JEOL, Japan), an X-ray diffraction (PW3040/60, PANalytical,Netherlands), a differential scanning calorimeter (DSC2910, Ta Znstrument Inc company, USA) and a heating platform (DB - XAB ，Lichen Instruments).
Lifang Liu et al. / Energy Procedia 158 (2019) 4799–4804 Author name / Energy Procedia 00 (2018) 000–000
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2.3. Preparation of the composite PCM and foamed cement (1) Preparation of paraffin/expanded graphite composite PCM First, the expandable graphite powder should be dried in a vacuum drying oven at 65℃ for 16 hours. Put 2 to 3 g the dried expandable graphite into a ceramic crucible, and then place the crucible in a 700 W microwave oven and heat treated for 40 seconds to obtain expanded graphite. Pour the paraffin into a 400 mL glass beaker and place the beaker in a constant temperature water bath at 70 ℃ for 10 min. Add the expanded graphite to the beaker (the mass ratio of expanded graphite to paraffin is 2:8) and keep stirring and blending the mixture for 1 h. A composite phase change thermal storage material of paraffin/expanded graphite then can be obtained. (2) Preparation of phase change thermal storage foamed cement Take some cement into a beaker, add the paraffin/expanded graphite composite PCM (with the cement mass ratio of 10%, 15%, 20%, 25%, 30%) and mix them well. Add distilled water into to the beaker (with a cement mass ratio of 75%) and stir evenly. At this time, add air bubbles with a density of 50 kg/m 3 into the beaker and stirred evenly for about 10 seconds. Pour the uniform slurry into a 40*40*40 mm 3 mold, and then keep it at the room temperature for 24 hours. Place the module in a cement curing box at 40℃ for 3 days and then in a drying oven at 60℃ for 1.5 days until the weight of the foamed cement is constant, and then the phase change heat storage foamed cement is finally prepared. 3. Results and discussion
3.1. SEM analysis of foamed cement Fig. 1 shows the SEM image of the expanded graphite and paraffin/expanded graphite composite PCM. Fig. 2 shows the SEM image of phase change thermal storage foamed cement. Fig. 1(a) is an enlarged view of expanded graphite with an irregular honeycomb grid structure, which contains large amount crack-like and network-like micro holes for adsorbing organics [9]. Fig. 1(b) shows the expanded graphite that adsorbed paraffin and still maintains its original porous worm-like morphology. In the figure, paraffin was evenly adsorbed in the pores of expanded graphite and no block appear ed on the surface of expanded graphite. Fig. 2(a) is a cutaway view of foamed cement with bubbles. Fig. 2(b) is an enlarged view of the phase change thermal storage foamed cement. In the figure, the mixture of the composite phase change material and the cement can be clearly seen.
a
b
Paraffin. Pores.
Fig. 1. SEM images of the expanded graphite and paraffin/expanded graphite composite PCM: (a) EG(×2000); (b)Compos ite PCM( ×2000).
Author name Energy Procedia 00 (2018) –000 4799–4804 Lifang Liu/ et al. / Energy Procedia 158000 (2019)
44802
a
b
cement
Paraffin/expanded graphite PCM
Fig. 2. SEM images of the phase change thermal storage foamed cement : (a) Foaming cement (×60); (b)Foaming cement (×2000).
3.2. XRD analysis of Materials Fig . 3 shows the XRD patterns of the paraffin, expanded graphite, paraffin/expanded graphite composite PCM and the phase change thermal storage foamed cement. From the fig .3 (left), it can be seen that the strong peaks of pure paraffin and expanded graphite appear in the corresponding 2θ in the composite phase change materials respectively, and no other strong peaks appeared in the composite phase change material. The results indicats that the combination of material is a physical process and no chemical changes have occurred. Similarly, there is no chemical reaction between paraffin/expanded graphite composite PCM and cement in fig.3 (right). Therefore, paraffin/expanded graphite composite PCM and phase change thermal storage foamed cement can still maintain the phase change thermal storage properties and chemical properties of paraffin.
Fig. 3. XRD pattern of paraffin, expanded graphite, paraffin/expanded graphite composite PCM and phase change thermal storage foamed cement (left). XRD magnification of paraffin/expanded graphite composite PCM and phase change thermal storage foamed cement (right).
3.3. DSC analysis of Materials Fig. 4 (left) shows the DSC curve of the paraffin and paraffin/expanded graphite (mass ratio 80%:20%) composite PCM. There are two phase change peaks during the temperature rise process of paraffin from 20 to 60 °C, one is a solid-solid phase change peak around 40°C and the other is a solid-liquid phase change peak at about 45°C. The enthalpy values of the endothermic and exothermic processes of paraffins were similar, being 259.8 J/g and 259.5 J/g, respectively. Similarly, the DSC curve of paraffin/expanded graphite composite PCM also has two peaks during the temperature increase from 20 to 60 °C, the enthalpy of endothermic and exothermic heat of the composite PCM was reduced to 207.1 J/g and 207.6 J/g respectively . This is due to the reduction in the mass ratio of paraffin in composite PCM.
Lifang Liu et al. / Energy Procedia 158 (2019) 4799–4804 Author name / Energy Procedia 00 (2018) 000–000
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Fig. 4 (right) shows the DSC curves of phase change thermal storage foamed cement (The mass ratio of composite PCM and cement is 10%, 15%, 20%, 25%, 30%). Table 1 summaries the material features at different mass fractions. w is the composite PCM mass fraction; Ts/Te and Ts’/ Te’ are the melting and solidification temperature during the heat absorption and exothermic process, respectively. H1 and H2 are the absorption and exothermic values of the melting enthalpy, respectively. As can be seen from the figure, with the increase of the mass ratio of composite PCM, the enthalpy of the phase change thermal storage foamed cement also increases. However, the actual measured enthalpy is smaller than the theoretical value. This can be explained by the material loss during the preparation of the cement. Table 1. The tested phase change temperature and latent heat of the phase change thermal storage foamed cements with different mass fractions of composite PCM
w（wt%） 10% 15% 20% 25% 30%
Ts（℃） 36.9 36.9 39.7 39.6 40.3
Te（℃） 43.1 43.8 44.6 46.8 45.5
H1（J/g） 8.856 15.84 21.07 27.18 32.11
Ts’（℃） 38.6 42.1 43.1 42.7 42.7
Te’（℃） 33.0 30.5 29.8 32.0 38.5
H2(J/g) -7.798 -15.68 -20.58 -26.25 -29.6
Fig. 4. DSC curve of paraffin and composite PCM (left). DSC curve of phase change thermal storage foamed cement (right).
3.4. Thermal insulation capacity of the phase change thermal storage foam cement Fig. 5 shows the variation of the paraffin/expanded graphite composite PCM mass fractions ’ impacts on the thermal insulation capacity of the foamed cement. The figure shows the higher the content of the composite PCM, the higher the final temperature will be. This suggests that the material mass can enhance the thermal conductivity of the foamed cement. When the temperature is controlled within the threshold, additional paraffin/expanded graphite composite PCM can effectively delay the heat transfer and shave energy peak.
Fig.5. The temperature curves of phase change thermal foam cement
Lifang Liu et al. / Energy Procedia 158 (2019) 4799–4804 Author name / Energy Procedia 00 (2018) 000 –000
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The measurements above were performed at least three times and the results presented by averaging the measurements to cut down the measurement uncertainty [13]. 4. Conclusions This article mainly introduces the phase change heat storage foamed cement prepared from with paraffin, expanded graphite and portlandportland cement. The effects of paraffin/expanded graphite composite PCM mass fractions on the physical structure, thermal insulation performance and heat storage capacity of foamed cement were described in detail studied through in the experiments. (1) The paraffin/expanded graphite (mass ratio is 8:2) composite PCM is added to the foamed cement, and there is no paraffin leakage phenomenon. Adding The added paraffin can effectively improve the heat storage capacity. (2) The preparation and head absorbing process is physical process with no chemical reactions. Thus, the phase change thermal storage foamed cement can maintain the phase change and thermal storage properties and chemical properties of paraffin. (3) Adding more paraffin/expanded graphite composite phase change material can increase the heat storage capacity of foamed cement. As it can delay heat transfer and clip the heat peak during the phase transition, and the fluctuation indoor temperature can be reduced. Acknowledgements This work was supported by Guangzhou Science and Technology Program (201704030137), the Research Project of Guangdong Province (2017A050506058), and the Major Research Project of Guangdong Provincial Department of Education (No. 2016KZDXM035). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
Peng C, Wu H, Ding Y. Advances in the Study and Application of Thermal Insulation Materials for Building Efficiency[J]. Energy Conservation Technology, 2010,28(04): 332-335. Liang Y, Wu H, Huang G, et al. Thermal performance and service life of vacuum insulation panels with aerogel composite cores[J]. Energy & Buildings, 2017, 154 :606-617. Xu Z. Pondering on Prospects for Development of Building Energy Conservation Thermal Insulation Materials of Our Country[J]. Construction Energy Conservation, 2009, 26(3):75-82. Zhang M, Tian Q, Xu L, et al. Status and Prospects of Research on Foamed Cement[J]. Bulletin of the Chinese Ceramic Society, 2014,33(10):2547-2551. Yan Z. Foamed concrete is expected to become the preferred insulation material [J]. Concrete World, 2010(1):22-26. Li Q, Li G, Du C. Effects of modified polypropylene fibers on properties of foamed cement [J]. Acta Materiae Compositae Sinica, 2013, 30(3):14-20. Wang J, Pan C, Lin Y, Liu P, Tang A. Res earch progress in preparation technology of foamed cement insulation board[J]. Sichuan Building Materials, 2016, 42(1):19-21. Xu T, Li Y, Chen J, et al. Preparation and thermal energy storage properties of LiNO 3 -KCl-NaNO 3 /expanded graphite composite phase change material[J]. Solar Energy Materials & Solar Cells, 2017, 169:215-221. Liu X, Lin C, Rao Z. Diffusion and thermal conductivity of the mixture of paraffin and polystyrene for thermal energy storage: A molecular dynamics study[J]. Journal of the Energy Institute, 2016, 90(4) : 534-543. He B, Setterwall F. Technical grade paraffin waxes as phase change materials for cool thermal storage and cool storage systems capital cost estimation[J]. Energy Conversion & Management, 2002, 43(13):1709-1723. Zhang Z, Wang X, Fang X. Structure and Thermal Properties of Paraffin/Expanded Graphite Composite Phase Change Materials[J]. Journal of South China University of Technology (Natural Science Edition), 2006, 34(3):1-5. Chen C, Zhang H, Gao X, et al. Numerical and experimental investigation on latent thermal energy storage system with spiral coil tube and paraffin/expanded graphite composite PCM[J]. Energy Conversion & Management, 2016, 126:889-897. Yang J, Wu H, Huang G, et al. Modeling and coupling effect evaluation of thermal conductivity of ternary opacifier/fiber/aerogel composites for super-thermal insulation[J]. Materials & Design, 2017, 133(5) : 224-236.
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Energy Procedia (2018) 000–000 Available onlineatat00 www.sciencedirect.com Available online www.sciencedirect.com Energy Procedia 00 (2018) 000–000
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Energy Procedia 158 Energy Procedia 00(2019) (2017)4799–4804 000–000 www.elsevier.com/locate/procedia
10thth International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10 International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China
Experimental study on preparation of a novel foamed cement with Experimental study on preparation of aphase novel foamed cementenergy with The 15th International Symposium on District Heating and thermal Cooling paraffin/ expanded graphite composite change paraffin/ expanded graphite composite phase change thermal energy storage material storage material Assessing the feasibility of using the heat demand-outdoor Lifang Liu aa, Yue Qu aa, Tao Xu a,a, *, Jiayu Chen bb , Huijun Wuaa , Gongsheng Huangbb, Lifang Liu , Yue Qu , TaoXiaoqing Xu a *, long-term Jiayu Chen , district Huijun , Gongsheng , a temperature function for heat demandHuang forecast Zhou , Lixiu Yang aWu Xiaoqing Zhou a, Lixiu Yang a a a Engineering, Guangzhou b c Academy of Building Efficiency, of Civil Univers ity, Guangzhou510006, China c I. Andrića,b,c *, Energy A. and Pina P.School Ferrão , J. Fournier .,Kong, B. Tat Lacarrière , O. Le Corre Department Architecture Civil, Engineering, of Hong Cheeity, Avenue Kowloon, Hong Kong Academy ofofBuilding Energy Efficiency, School of City CivilUniversity Engineering, Guangzhou Univers Guangzhou510006, China a
ba
b Department of Architecture and Civil Engineering, City University of Hong Kong, Tat Chee Avenue Kowloon, Hong Kong 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 a
Abstract This study proposed a novel foaming cement heat preservation block with heat storage, peak clipping, and temperature This study proposed a novelsuch foaming cement heat preservationgraphite block with heat storage, peak clipping, andmaterial temperature adjustment functions . To produce cements, a paraffin/expansion composite phase change heat storage with adjustment functions . To produceof such paraffin/expansion graphite phaseThen change storage phase material with ℃ and aa enthalpy a Abstract phase transition temperature 41.9 cements, value of 207.6 J/g composite was prepared. the heat composite change amaterial phase transition temperature andexpanded a enthalpy value and of 207.6 J/g was Then the composite change (P CM) loaded paraffin ofat 41.9 44℃℃into graphite then was mixedprepared. cement uniformly. The porousphase structure of material (P CM) loaded paraffin at 44℃ into expanded graphite and then was mixed cement uniformly. The porous structure of the foamed cement has light weight and good heat preservation capacity so that then composite PCM can effectively store heat District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the the foamed cement has light weight and good heat preservation capacity so that then composite PCM can effectively store heat energy and shave the load peak. To investigate the characteristics of the proposed material, this focuses on the physical structure, greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat energy shave thechanged loadand peak. To investigate the characteristics ofthe thematerial proposed material, this of focuses on the physical thermal storage thermal insulation performance mass fractions PCM arefuture 10%、15%、20%、 sales. and Due to capacity the climate conditions and buildingwhen renovation policies, heat demand in the could structure, decrease, thermal storage capacity and thermal insulation performance when the material mass fractions of PCM are 10%、15%、20%、 25% and 30%. The experimental results show that with the increase of the mass fraction of PCM, the thermal storage capacity prolonging the investment return period. 25% and 30%. The experimental results show that with the increase of the mass fraction of PCM, the thermal storage and thermal insulation properties of the foamed cement increases. In addition, there is no chemical reaction between the materials. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heatcapacity demand and thermal insulation properties of the foamed cement addition, there no chemical reaction between the materials. The results The show a the proposed material has ainpotential in(Portugal), creatingInefficient thermal wall s. district forecast. district of Alvalade, located Lisbonincreases. was used as a isinsulation case study. The is consisted of 665 The results that showvary a theinproposed material has a potential in creating efficient thermal insulation s. buildings both construction period and typology. Three weather scenarios (low,wall medium, high) and three district Copyright © scenarios 2018 Elsevier All rights(shallow, reserved.intermediate, deep). To estimate the error, obtained heat demand values were wereLtd. developed ©renovation 2019 The Authors. Published by Elsevier Ltd. th Copyright © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the model, scientific committee of the 10and International compared withaccess resultsarticle from aunder dynamic heat demand previously developed validated byConference the authors.on Applied Energy This is an open the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) th Selection and peer-review under responsibility of the scientific committee of the 10 International Conference on Applied Energy (ICAE2018). The results under showed that when only weather change is considered, the margin error could be acceptable applications Peer-review responsibility of the scientific committee of ICAE2018 – The of 10th International Conferencefor onsome Applied Energy. (ICAE2018). (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation Keywords: change thermal storage material; Paraffin; Expanded on graphite; Foamed and cement scenarios,Phase the error value increased up to 59.5% (depending the weather renovation scenarios combination considered). Keywords: Phase change thermal storage material; Paraffin; Expanded graphite; Foamed cement The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and * Corresponding author. Tel.: 13925031066. renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the * Corresponding Tel.: 13925031066. E-mail address:author. [email protected] (T. Xu). coupled scenarios). The values suggested E-mail address: [email protected] (T. Xu). could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.
1. Introduction 1. Introduction © 2017 The Authors. Published by Elsevier Ltd. Building thermal aim theCommittee heat loss or heat 15th gainInternational from the interior of theonbuilding to the outside Peer-review underinsulations responsibility of to thereduce Scientific of The Symposium District Heating and Building thermal insulations aim to reduce the heat loss or heat gain from the interior of the building to energy the outside environment. Efficient insulations can effectively reduce the air-conditioning load and air-conditioning Cooling. environment. of Efficient insulations can effectively reduce thethermal air-conditioning and air-conditioning energy consumption a building [1]. Therefore, developing better insulationload building materials becomes one of consumption a building [1].Climate Therefore, Keywords: Heatof demand; Forecast; changedeveloping better thermal insulation building materials becomes one of 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. 1876-6102 Copyright © 2018 Elsevier Ltd. All rights Selection and peer-review under responsibility of thereserved. scientific committee of the 10th International Conference on Applied Energy (ICAE2018). 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.2019.01.717
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Lifang Liu et al. / Energy Procedia 158 (2019) 4799–4804 Author name / Energy Procedia 00 (2018) 000 –000
the most effective methods to reduce building energy [2]. In recent years, researchers found the traditional organic insulation materials have a few shortcomings, such as cracking [3], poor durability, flammability, and the toxic gases during combustion [4]. Therefore, it is inevitable to develop alternative materials that can overcomes these problems and maintain a high thermal insulation capacity [5]. As one of the ideal substitutions, foamed cement is a lightweight porous material made by adding bubbles that generated by chemical foaming agent in cement slurry [6]. Foamed cement is a typical building insulation material has been developed for years. It has excellent thermal insulation properties, as well as light weight, high adhesive force, good durability, excellent A-grade combustibility, and low carbon emission during production [7]. Based on these characteristics, researchers proposed to produce phase change thermal storage foamed cement by adding heat storage phase change material into foamed cement, as PCM has a large energy storage density and can maintain a constant temperature during the phase change process [8]. If such phase change thermal storage foamed cement can be applied to a building thermal insulation structure, it not only can provide necessary thermal insulation, but also play the role of heat storage. This can effectively shave the energy and temperate peak to stabilize the indoor temperature. In recent years, organic phase change materials (OPCMs) has attracted much attention in various applications for their excellence thermal storage properties. However, OPCMs suffers from the problems of liquid leakage and low thermal conductivity [9]. On the other hand, as paraffin is recognized as one of the most promising PCMs due to its large latent heat, low cost and its stable, nontoxic and noncorrosive properties [10]. Researchers used organic paraffin as PCM and expanded graphite as support structure and prepared the paraffin/expanded graphite composite phase change material. The porous adsorption property of expanded graphite can effectively solve the problem of paraffin wax leakage caused by phase change[11]. Chen et al. also proposed similar paraffin/expanded graphite composite phase change material with a mass ratio of EG of 20% (completely absorbed) to cool down the room temperature [12]. Based upon previous studies, this article first investigated the preparation of phase change thermal storage foamed cements with different mass fractions of composite PCM. Then this article studied the effects of adding different amounts of paraffin/expanded graphite composite PCM on the properties of foamed cements, including foamed cement microstructure, physical structure, heat storage capacity, and thermal conductivity. The research laid a foundation for the application of phase change thermal storage foamed cement in building thermal insulation structures. 2. Experiment description 2.1. Materials Paraffin (melting point Tm =44°C) was provided by Hangzhou Ruhr New Material Technology Co. Ltd. Expandable graphite (expansion ratio: 300ml/g, average particle size: 300µm) was supplied by the Qingdao Graphite Co. Ltd. Concentrated high efficiency cement foaming agent (QW-100) was produced by Zhengzhou Pengyi Chemical Building Materials Co. Ltd. Silicate 425 cement was produced by Haimen Conch Cement Co. Ltd. 2.2. Equipment The equipment to prepare the target materials includes a microwave oven (EG720FFI-NS, Midea, China), a electronic balance (WT5002N, Changzhou wantai balance instrument Co. Ltd.), a concrete accelerated curing box (HJ-84, Tianjin Luda Construction Equipment Co. Ltd.), a foaming machine (Yh-fp50, Guangzhou Yongsheng Construction Engineering Co. Ltd.), an electro-thermostatic blast oven (DGX-9243, Shanghai Foma Experimental Equipment Co. Ltd.), a scanning electron microscope (JSM-7001F, JEOL, Japan), an X-ray diffraction (PW3040/60, PANalytical,Netherlands), a differential scanning calorimeter (DSC2910, Ta Znstrument Inc company, USA) and a heating platform (DB - XAB ，Lichen Instruments).
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2.3. Preparation of the composite PCM and foamed cement (1) Preparation of paraffin/expanded graphite composite PCM First, the expandable graphite powder should be dried in a vacuum drying oven at 65℃ for 16 hours. Put 2 to 3 g the dried expandable graphite into a ceramic crucible, and then place the crucible in a 700 W microwave oven and heat treated for 40 seconds to obtain expanded graphite. Pour the paraffin into a 400 mL glass beaker and place the beaker in a constant temperature water bath at 70 ℃ for 10 min. Add the expanded graphite to the beaker (the mass ratio of expanded graphite to paraffin is 2:8) and keep stirring and blending the mixture for 1 h. A composite phase change thermal storage material of paraffin/expanded graphite then can be obtained. (2) Preparation of phase change thermal storage foamed cement Take some cement into a beaker, add the paraffin/expanded graphite composite PCM (with the cement mass ratio of 10%, 15%, 20%, 25%, 30%) and mix them well. Add distilled water into to the beaker (with a cement mass ratio of 75%) and stir evenly. At this time, add air bubbles with a density of 50 kg/m 3 into the beaker and stirred evenly for about 10 seconds. Pour the uniform slurry into a 40*40*40 mm 3 mold, and then keep it at the room temperature for 24 hours. Place the module in a cement curing box at 40℃ for 3 days and then in a drying oven at 60℃ for 1.5 days until the weight of the foamed cement is constant, and then the phase change heat storage foamed cement is finally prepared. 3. Results and discussion
3.1. SEM analysis of foamed cement Fig. 1 shows the SEM image of the expanded graphite and paraffin/expanded graphite composite PCM. Fig. 2 shows the SEM image of phase change thermal storage foamed cement. Fig. 1(a) is an enlarged view of expanded graphite with an irregular honeycomb grid structure, which contains large amount crack-like and network-like micro holes for adsorbing organics [9]. Fig. 1(b) shows the expanded graphite that adsorbed paraffin and still maintains its original porous worm-like morphology. In the figure, paraffin was evenly adsorbed in the pores of expanded graphite and no block appear ed on the surface of expanded graphite. Fig. 2(a) is a cutaway view of foamed cement with bubbles. Fig. 2(b) is an enlarged view of the phase change thermal storage foamed cement. In the figure, the mixture of the composite phase change material and the cement can be clearly seen.
a
b
Paraffin. Pores.
Fig. 1. SEM images of the expanded graphite and paraffin/expanded graphite composite PCM: (a) EG(×2000); (b)Compos ite PCM( ×2000).
Author name Energy Procedia 00 (2018) –000 4799–4804 Lifang Liu/ et al. / Energy Procedia 158000 (2019)
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b
cement
Paraffin/expanded graphite PCM
Fig. 2. SEM images of the phase change thermal storage foamed cement : (a) Foaming cement (×60); (b)Foaming cement (×2000).
3.2. XRD analysis of Materials Fig . 3 shows the XRD patterns of the paraffin, expanded graphite, paraffin/expanded graphite composite PCM and the phase change thermal storage foamed cement. From the fig .3 (left), it can be seen that the strong peaks of pure paraffin and expanded graphite appear in the corresponding 2θ in the composite phase change materials respectively, and no other strong peaks appeared in the composite phase change material. The results indicats that the combination of material is a physical process and no chemical changes have occurred. Similarly, there is no chemical reaction between paraffin/expanded graphite composite PCM and cement in fig.3 (right). Therefore, paraffin/expanded graphite composite PCM and phase change thermal storage foamed cement can still maintain the phase change thermal storage properties and chemical properties of paraffin.
Fig. 3. XRD pattern of paraffin, expanded graphite, paraffin/expanded graphite composite PCM and phase change thermal storage foamed cement (left). XRD magnification of paraffin/expanded graphite composite PCM and phase change thermal storage foamed cement (right).
3.3. DSC analysis of Materials Fig. 4 (left) shows the DSC curve of the paraffin and paraffin/expanded graphite (mass ratio 80%:20%) composite PCM. There are two phase change peaks during the temperature rise process of paraffin from 20 to 60 °C, one is a solid-solid phase change peak around 40°C and the other is a solid-liquid phase change peak at about 45°C. The enthalpy values of the endothermic and exothermic processes of paraffins were similar, being 259.8 J/g and 259.5 J/g, respectively. Similarly, the DSC curve of paraffin/expanded graphite composite PCM also has two peaks during the temperature increase from 20 to 60 °C, the enthalpy of endothermic and exothermic heat of the composite PCM was reduced to 207.1 J/g and 207.6 J/g respectively . This is due to the reduction in the mass ratio of paraffin in composite PCM.
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Fig. 4 (right) shows the DSC curves of phase change thermal storage foamed cement (The mass ratio of composite PCM and cement is 10%, 15%, 20%, 25%, 30%). Table 1 summaries the material features at different mass fractions. w is the composite PCM mass fraction; Ts/Te and Ts’/ Te’ are the melting and solidification temperature during the heat absorption and exothermic process, respectively. H1 and H2 are the absorption and exothermic values of the melting enthalpy, respectively. As can be seen from the figure, with the increase of the mass ratio of composite PCM, the enthalpy of the phase change thermal storage foamed cement also increases. However, the actual measured enthalpy is smaller than the theoretical value. This can be explained by the material loss during the preparation of the cement. Table 1. The tested phase change temperature and latent heat of the phase change thermal storage foamed cements with different mass fractions of composite PCM
w（wt%） 10% 15% 20% 25% 30%
Ts（℃） 36.9 36.9 39.7 39.6 40.3
Te（℃） 43.1 43.8 44.6 46.8 45.5
H1（J/g） 8.856 15.84 21.07 27.18 32.11
Ts’（℃） 38.6 42.1 43.1 42.7 42.7
Te’（℃） 33.0 30.5 29.8 32.0 38.5
H2(J/g) -7.798 -15.68 -20.58 -26.25 -29.6
Fig. 4. DSC curve of paraffin and composite PCM (left). DSC curve of phase change thermal storage foamed cement (right).
3.4. Thermal insulation capacity of the phase change thermal storage foam cement Fig. 5 shows the variation of the paraffin/expanded graphite composite PCM mass fractions ’ impacts on the thermal insulation capacity of the foamed cement. The figure shows the higher the content of the composite PCM, the higher the final temperature will be. This suggests that the material mass can enhance the thermal conductivity of the foamed cement. When the temperature is controlled within the threshold, additional paraffin/expanded graphite composite PCM can effectively delay the heat transfer and shave energy peak.
Fig.5. The temperature curves of phase change thermal foam cement
Lifang Liu et al. / Energy Procedia 158 (2019) 4799–4804 Author name / Energy Procedia 00 (2018) 000 –000
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The measurements above were performed at least three times and the results presented by averaging the measurements to cut down the measurement uncertainty [13]. 4. Conclusions This article mainly introduces the phase change heat storage foamed cement prepared from with paraffin, expanded graphite and portlandportland cement. The effects of paraffin/expanded graphite composite PCM mass fractions on the physical structure, thermal insulation performance and heat storage capacity of foamed cement were described in detail studied through in the experiments. (1) The paraffin/expanded graphite (mass ratio is 8:2) composite PCM is added to the foamed cement, and there is no paraffin leakage phenomenon. Adding The added paraffin can effectively improve the heat storage capacity. (2) The preparation and head absorbing process is physical process with no chemical reactions. Thus, the phase change thermal storage foamed cement can maintain the phase change and thermal storage properties and chemical properties of paraffin. (3) Adding more paraffin/expanded graphite composite phase change material can increase the heat storage capacity of foamed cement. As it can delay heat transfer and clip the heat peak during the phase transition, and the fluctuation indoor temperature can be reduced. Acknowledgements This work was supported by Guangzhou Science and Technology Program (201704030137), the Research Project of Guangdong Province (2017A050506058), and the Major Research Project of Guangdong Provincial Department of Education (No. 2016KZDXM035). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
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