Ethylene-Propylene Terpolymer-Modified Polyethylene-Based Phase

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Materials and Interfaces

Ethylene-propylene terpolymer modified Polyethylene based phase change material with enhanced mechanical and thermal property for building application Yanfeng Chen, Xiaojuan Wu, Yue Situ, Jian Liu, and Hong Huang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b04316 • Publication Date (Web): 04 Dec 2018 Downloaded from http://pubs.acs.org on December 4, 2018

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Industrial & Engineering Chemistry Research

Ethylene-propylene terpolymer modified Polyethylene based phase change material with enhanced mechanical and thermal property for building application Yanfeng Chen 1, Xiaojuan Wu 1, Yue Situ 1, Jian Liu 2*, Hong Huang 1**

1. School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, PR China 2. Key Laboratory of Distributed Energy Systems of Guangdong Province, Department of Energy and Chemical Engineering, Dongguan University of Technology, Dongguan 523808, PR China

*

Corresponding author. E-mail address: [email protected] (J. Liu)

**

Corresponding author. E-mail address: [email protected] (H. Huang)

ACS Paragon Plus Environment

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ABSTRACT: An enhanced mechanical and thermal property phase change composite was successfully prepared. A paraffin is absorbed by expanded graphite, and is confined by Polyethylene, Ethylene-propylene terpolymer is added and cross-linked to Polyethylene to improve mechanical and thermal property. Melting temperature and latent heat of the composite are 41.5 °C and 143.8 J g-1. The as-prepared composite shows 4-fold thermal conductivity, 8-fold tensile strength and 3-fold impact strength enhancement as compared to EG/paraffin. Further, thermal insulation property of the phase change composite was numerically investigated. The results show that low thermal conductivity and large thickness has an advantage on delaying increasing temperature of the roof in the daytime. The enthalpy has little effect on the temperature of the room, and the phase change composite with melting temperature of 40°C was most suitable for the building roof. The results show that the optimized phase change composite has great potential in building applications. KEYWORDS: Building energy; Phase change material; Thermal conductivity; Mechanical property; Thermal isolation

Abstract Graphics


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1. INTRODUCTION About 30–40% of primary energy is consumed by the building sector and is responsible for one-third of greenhouse gas emissions around the world 1. In buildings, a major portion of the energy is used by heating and cooling applications and it is estimated that 10–20% of this energy is used 2. Global concern of the environmental impacts of the fossil fuel usage has prompted the interest to search and use passive techniques for heating and cooling of the buildings 3. Thermal energy storage with phase change materials (PCMs) offers a high thermal storage density with a moderate temperature variation, and has attracted growing attention due to its important role in achieving energy conservation in buildings with thermal comfort 4. PCM with high heat of fusion, melting and solidifying at a certain temperature and are capable of storing and releasing large amount of thermal energy at a certain phase change temperature 5-8. The thermal energy is absorbed or released as the material changes its phase from solid to liquid or from liquid to solid. In building, the PCMs can be broadly used two types: active application of the PCM in building is walls

11

9

and passive

10

. The passive

, floors 12, and roof 13, the active utilization of the

PCM in building is the thermal accumulator integrated with the heat pump 14 or refrigerator 15. For the passive application of the PCM in building, the specific property of the PCM are desired: suitable phase change temperature, high latent enthalpy, good thermal property and mechanical property

16

. To gain high latent enthalpy and good thermal property of the PCM, the porous

materials such as expanded graphite 6, 17-20, expanded perlite 21, 22, CNT 23, 24 were used to absorbed the PCM to form phase change composite (PCC). Though the PCC has high thermal conductivity and enthalpy, the mechanical property is usually poor especially in solid-liquid process. The compression strength of the walls sharply decrease when integrated the PCC. To enhance the compression strength of the PCM, high density polyethylene (PE) was used to mix and extrude


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with the PCM, the PE based PCC has much higher compression strength than the PCM. Previous works show that the polymer based PCC such as the PE based PCC has great tensile strength and flexural modulus and could be moulded to difformity by injection and hot press

25, 26

. Unlike the

porous material based PCCs, the polymer based PCC crosslinking and twine the PCM with the macromolecular chain of polymer, the polymer based PCC has structural continuity. Hence, the polymer based PCC has great mechanical property especially when the temperature beyond the melting point. Previous works have been reported the PCC based building wall 27, 28, roof 29, 30 and floor 31, 32

, the PCC has great thermal insulation performance in passive application. Numerically method

was usually used to investigate the effect of phase change temperature, enthalpy and thermal conductivity on the thermal insulation performance of the PCC based building block 4. The previous works show that the phase change temperature of the PCC is dependent with the latitude of the building and the thermal conductivity play an important role on increasing the heat resistance of the PCC to obstruct the heat energy of the ambient. Although the works systematically investigate the performance of the PCC in building for passive application, the vast majority of the PCC was porous materials based material with poor mechanical property, which impeding the application of the PCC. Researchers used the Aluminum box

33, 34

or steel pipe

35

to encapsulate

the phase change materials to enhance the mechanical property and thermal property. Although the metal encapsulated PCC could be used as the floor, roof and wall in building, the cost of the PCC sharply increase to a high level. Inexpensive polymer based PCC should developed to enlarge the application in building. Hence, the thermal conductivity, enthalpy and phase change temperature of the polymer based PCC should be systematically investigated.


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In this work, an enhanced mechanical and thermal property PCC was successfully prepared. The paraffin is absorbed by expanded graphite, and the composite is confined by PE, 5% of the EPDM was added and cross-linked to the PE to improve the mechanical and thermal property. The as-prepared PCC has good mechanical property, high heat storage capacity and large thermal conductivity. Then, the thermal insulation performance of the PCC as building roof was systematically investigated with numerical method. The effect of thermal conductivity, enthalpy, thickness and phase change temperature on the thermal insulation property of the PCC was numerical simulated and optimized.

2. EXPERIMENTAL SECTION Materials. Technical grade paraffin (OP44) was purchased from Hangzhou Ruhr energy science and technology Co, Ltd. Expanded graphite (EG) was purchased from Qingdao Herita graphite product Co, Ltd. The high density polyethylene DMDA8920 (PE) was purchased from China National Petroleum Co, Ltd. The Ethylene-propylene terpolymer (EPDM) was purchased from The Dow Chemical Company. Preparation of phase change composites. The PCC was prepared by two steps. First, the OP44 was absorbed in the EG to form OP44/EG with the mass ratio is 9:1. Second, the OP44/EG was confined in the viscous high density PE with different mass fraction by open mill (XH-401, Dongguan Xihua Co., Ltd.). To improve the thermal conductivity and the mechanical property, EPDM was added and cross-linked to the PE when mixing in the open mill for 15 min. The mass ratio of the as-prepared samples is shown in Table 1. The as-prepared phase change composites OP44/EG/PE- EPDM were formed to blocks by hot-press (XH-406B, Dongguan Xihua Co., Ltd.).


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Table 1 Mass ratio of the as-prepared samples

a

Samples

OP44/EG a

PE

EPDM

OP44/EG/PE

70

30

0

OP44/EG/PE-EPDM

70

30

5

mass ratio of OP44/EG (OP44:EG =9:1) Characterizations of PCC. The morphology and microstructure of EG, OP44/EG,

OP44/EG/PE and OP44/EG/PE-EPDM were observed on a field emission scanning electron microscopy (SU8020, Hitachi). The structure of the composite was characterized by X-ray diffraction. The X-ray diffraction (XRD) patterns of the samples were carried out on X-ray diffractometer (D8 ADVANCE). Fourier transform-infrared (FTIR) spectra of the samples were measured on a Bruker Vector 33 spectrometer. The phase change temperature and latent heat of the samples were measured by a differential scanning calorimeter (Q20, TA). For DSC measurements, 5-8 mg for every sample was sealed in an aluminum pan for characterization at a heating rate of 10 °C min-1 under a constant stream of nitrogen at flow rate of 50 mL min-1. Thermogravimetric analysis (TGA) used a thermal analyzer (Q600 SDT, TA, URT100). The measurements were conducted by heating the samples from room temperature to 600 °C at a heating rate of 10 °C min-1 under nitrogen atmosphere with a flow rate of 100 mL min-1. The thermal conductivity of the composite was measured using a thermal constants analyzer (Hot Disk TPS 2500S, Hot Disk AB, Sweden). The tensile strength was measured using a universal mechanical testing analyser (Zwick/Roell Z020). The impact strength of the composite was measured using an impact tester (Zwick/HIT5.5P). The thermal isolation behavior of the PCC based roof was conducted in a manual climatic box (150×150×150 mm3). In this experiment, the PCC was placed on the roof of the simulated hexahedron house. The hexahedron house was loaded in manual climatic box, the temperature in the hexahedron box during these periods were


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recorded by K-type thermocouples and a data acquisition instrument (Agilent, 34970A), the measurement errors were ±1%. Numerical simulation of the PCC based roof. The numerical model of the phase change composite based roof was shown in Figure 1. The governing equation is given as Eq. (1)36:

ρ𝑐𝑝

𝜕𝑇 𝜕 2𝑇 𝜕 2𝑇 𝜕 2𝑇 =  × ( 2 + 2 + 2) 𝜕𝑡 𝜕𝑥 𝜕𝑦 𝜕𝑧

(1)

where T is temperature, , 𝑐𝑝 ,  are density, specific heat, and thermal conductivity, respectively.

Figure 1 The simulated model of the PCC based roof

For the phase change material, the enthalpy-porosity technique is used for modeling the solidification/melting process. The general heat conduction equation in PCM layer is given as Eq. (2):

𝜌𝑝𝑐𝑚 ×

𝜕𝐻 𝜕 2𝑇 𝜕 2𝑇 𝜕 2𝑇 = 𝑝𝑐𝑚 × ( 2 + 2 + 2 ) 𝜕𝑡 𝜕𝑥 𝜕𝑦 𝜕𝑧


(2)

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where H is enthalpy (J kg-1). The enthalpy of the material is computed as the sum of the sensible enthalpy (h) and the latent heat (H): 𝐻 = ℎ + 𝛽𝐿 𝑇

where h = ℎ𝑟𝑒𝑓 +∫𝑇

𝑟𝑒𝑓

(3)

𝑐𝑝 𝑑𝑇, and href is the reference enthalpy, Tref is the reference temperature, Cp

is the specific heat at constant pressure,  is the liquid fraction, and L is the latent heat of PCM. The liquid fraction of the PCM can be defined as: 0, 𝑇 − 𝑇𝑠 , β={ 𝑇𝑙 − 𝑇𝑠 1,

T < 𝑇𝑠 𝑇𝑠 < 𝑇 < 𝑇𝑙 𝑇 > 𝑇𝑙

where Ts is the temperature that the phase of PCM starts to change from solid to liquid, Tl is the temperature that the phase of PCM completely changed into liquid. For the surfaces exposed to the outside and inside air, the boundary condition are:

𝑘𝑜

𝜕𝑇 = ℎ𝑜 (𝑇𝑒 − 𝑇𝑜 ) 𝜕𝑥

(4)

𝑘𝑝

𝜕𝑇 = ℎ𝑖 (𝑇𝑖 − 𝑇𝑎 ) 𝜕𝑥

(5)

where ho and hi are the convective heat transfer coefficient of the exterior and interior surface, respectively, Te and Ta are the sol-air temperature and interior air temperature, respectively, To and Ti are the temperature on the outer surface and inner surface, respectively.


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3. RESULTS AND DISSCUSSION 3.1. Characterization of PCC The morphology and microstructure of PCC are observed by SEM. As shown in Figure 2, the EG (Figure 2a) consists of graphite sheets and abundant pores among them, offering a large pore volume for absorbing the OP44 at a high loading. When absorbed the OP44 in the pores of the EG by capillary force and surface tension, the OP44 filled the EG apparently (Figure 2b). The OP44/EG composite is mixed in the high density PE, Figure 2c shows that the OP44/EG was confined by linear chain of high density PE, while locality of the composite is coarse since the outspread linear chain of PE. As shown in Figure 2d, the linking chain of the PE is smooth after modifying the PE by vinyl and allyl chain of the EPDM, the surface trends to densification.

Figure 2 SEM of the prepared samples: (a) EG; (b) OP44/EG; (c) OP44/PE-EG; (d) OP44/EG/PE- EPDM


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To further confirm the structure of PCC, the XRD spectrums of the PCC are conducted, as shown in Figure 3. In the pattern of OP44, the strong diffraction peaks at 2θ =6.67, 9.78, 12.97, 16.17, 19.57, 19.95, 23.57 and 25.08°were caused by regular crystallization of the pure OP44 37, which are attributed to the diffractions of (110), (200) and other crystal planes. In the pattern of EG, there is only one sharp diffraction peak of 26.5°. The XRD pattern of the OP44/EG contains all the peaks of OP44 and EG, no new peaks are produced. The PE has two sharp diffraction peaks at 2θ=21.51 and 24.27°and the EPDM has no sharp diffraction peak. The XRD pattern of the OP44/EG/PE contains the peaks of OP44, EG and PE, while the peaks of OP44 were covered by PE, the intensity of the peaks below 2θ=20°declines. When modified by EPDM, the peaks of OP44/EG/PE-EPDM is similar to the OP44/EG/PE. The FT-IR spectrograms of the OP44 and based samples show the similar result (Figure 4), implying that the combination of the composite is a physical process.

PE EG EPDM OP44/EG/PE-EPDM OP44/EG/PE OP44/EG OP44

Intensity / a.u

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

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20

40

60

80

2q / degree

Figure 3 XRD patterns of the OP44 and based samples


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


Transmitance / %

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PE OP44 OP44/EG OP44/EG/PE-EPDM OP44/EG/PE EPDM EG

4000

3500

3000

2500

2000

1500

1000

500

Wavenumber / nm

Figure 4 FT-IR spectra of the OP44 and based samples

3.2. Melting−freezing behavior and stability of PCC The melting−freezing behavior of PCC is shown in Figure 5 (A) and Table 2. For the OP44, there are two endothermic peaks in the melting DSC curve and two exothermic peaks in the solidifying DSC curves. It is ascribed to different crystal transitions according to the XRD patterns. From Figure 5 (A), the solid−liquid melting peak and liquid−solid freezing peak were used to calculate the melting and freezing latent heat values, respectively. The melting and freezing temperature are measured to be 41.3 and 43.2 °C for the OP44 and 42.5 and 42.7 °C for OP44/EG and the melting and freezing latent heats are measured to be 240.3 and 239.4 J g-1 for OP44 and 215.8 and 213.9 J g-1 for OP44/EG, respectively. For OP44/EG/PE and OP44/EG/PE-EPDM, it exhibits the similar phase transition characteristics as that of OP44, the melting and freezing temperature are measured to be 40.5 and 42.3 °C for OP44/EG/PE and 41.5 and 41.1 °C for


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OP44/EG/PE-EPDM and the melting and freezing latent heats are measured to be 150.7 and 149.5 J g-1 for OP44/EG/PE and 143.8 and 143.2 J g-1 for OP44/EG/PE-EPDM, respectively. As shown in Figure 5 (B), TGA curves show that the accurate loading amount of OP44 in the OP44/EG/PE and OP44/EG/PE-EPDM are 61.7 and 58 %, which agrees with the DSC result.

(A) 6

(B) 100

4

OP44 OP44/EG OP44/EG/PE OP44/EG/PE-EPDM

80

2

Mass / %

Heat Flow / W g-1

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

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exotherm 0

60 40

endotherm -2

OP44 OP44/EG OP44/EG/PE OP44/EG/PE-EPDM

-4 10

20

30

40

20 0 50

60

70

100

Temperature / ℃

200

300

400

500

600

Temperature / ℃

Figure 5 Melting−freezing properties (A) and TGA (B) for OP44 and OP44 base composites Table 2 Melting−freezing properties for OP44 and OP44 base composites Samples

Tm/ ºC

△Hm/J g-1

Tf/ ºC

△Hf/J g-1

OP44

41.3

240.3

43.2

239.4

OP44/EG

42.5

215.8

42.7

213.9

OP44/EG/PE

40.5

150.7

42.3

149.5

OP44/EG/PE-EPDM

41.5

143.8

41.1

143.2

After 200 of heat/cool (10-80-10℃) cycling tests, the reversible stability of OP44/EG/PEEPDM was investigated by DSC and SEM. As shown in Figure 6, the morphology of the PCM is similar to that before heat/cool cycles, implying that the PCM has good stability. To further verify


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the revisable stability of the OP44/EG/PE-EPDM, the melting-freezing behavior was tested, as shown in Figure 7. As shown in Table 3, compared with 143.8 and 143.2 J g-1 before the cycles, the latent heats of melting and freezing are 143.5 and 142.7 J g-1 after 200 cycles, respectively, confirming good thermal cycling of the OP44/EG/PE-EPDM.

Figure 6 SEM image of OP44/EG/PE-EPDM before and after 200 cycles

2

Heat Flow / W g-1

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


Cycle 1 Cycle 200

1

0

-1

-2 10

20

30

40

50

60

70

Temperature / C

Figure 7 Melting−freezing properties of OP44/EG/PE-EPDM before and after 200 cycles


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Table 3 Melting−freezing properties for OP44/EG/PE-EPDM before and after 200 cycles

Cycles

Tm/ ºC

△Hm/J g-1

Tf/ ºC

△Hf /J g-1

Cycle 1

41.5

143.8

41.1

143.2

Cycle 200

41.3

143.5

41.1

142.7

3.3. Thermal conductivity of PCC The thermal conductivity of PCC were measured with the transient plane source method, an advanced technique evolving from the hot wire method. As shown in Figure 8, the thermal conductivity of the OP44 with the density of 860 kg m-3 is measured to be 0.382 W m-1 K-1, while the thermal conductivity of OP44/EG/PE is 1.52 W m-1 K-1 as the packing density of 820 kg m-3. Note that OP44/EG/PE has 3-fold higher thermal conductivity than OP44. When modified by EPDM, the OP44/EG/PE-EPDM shows the thermal conductivity of 2.2 W m-1 K-1, has 4-fold higher thermal conductivity than OP44. It is ascribed to the vinyl and allyl chain could unbind the linear chain of PE and divide the EG powder in the OP44/EG/PE-EPDM, the thermal path of the composite could be connected by the EG and the surface is smooth to gain low thermal resistance. It is indicated that the OP44/EG/PE-EPDM has an advantage of high thermal conductivity for the thermal management.


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2.5

Thermal conductivity / W m-1 K-1

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


2.0

1.5

1.0

0.5

0.0

OP44

OP44/EG/PE

OP44/EG/PE-EPDM

Figure 8 thermal conductivity of OP44 and OP44 base composites 3.4. Mechanical property of PCC The tensile strength and impact strength of PCC is show Figure 9. The tensile strength of OP44/EG is measured to be 0.54 MPa, while tensile strength of OP44/EG/PE is measured to be 5.06 MPa. Note that the tensile strength of OP44/EG/PE has 8-fold higher than OP44/EG, owing to the integration of PE has superior tensile strength. When adding 5% of the EPDM in the composite, the tensile strength of OP44/EG/PE-EPDM is measured to be 4.36 MPa, indicating the rigidity of the composite is lower and the suppleness is enhanced. The impact strength of OP44/EG is measured to be 0.58 KJ m-2, and the OP44/EG/PE is 1.53 KJ m-2, with 2-fold higher than OP44/EG. When adding 5% of EPDM in the composite, the OP44/EG/PE-EPDM is measured to be 2.24 KJ m-2, which is 3-fold higher than OP44/EG. The enhanced tensile strength and impact


15


strength of PCC indicating that the PCC is more suitable for building, thermal management systems.

2.4 5

Tensile strength / MPa

Tensile strength Impact strength

2.0

4 1.6 3 1.2 2

0.8

1

Impact strength / KJ m-2

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

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0.4

0

0.0

OP44/EG

OP44/EG/PE

OP44/EG/PE-EPDM

Figure 9 Mechanical property of OP44 and OP44 base composites 3.5 Thermal isolation behavior of the PCC based roof 3.5.1 Comparison of experimental and numerical results The thermal isolation behavior of the PCC based roof was investigated experimentally and numerically. In the manual climatic box, the temperature variation inside the hexahedron house was recorded and the results is shown in Figure 10. Without PCC on the roof, the experimental temperature inside the hexahedron house increase from 297 to 319 K from 0 to 25000 s, and decrease to 287.5 K since the time increase to 75000 s. Without PCC on the roof, the experimental temperature inside the hexahedron house increase from 297 to 316 K from 0 to 25000 s, and decrease to 288 K since the time increase to 75000 s. It is indicated that the temperature variation inside the hexahedron house with PCC was decrease 3.5 K in comparison with that has no PCC,


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the PCC could decrease the temperature inside the room in daytime and increase slightly the temperature at night by the thermal charge and discharge process of PCC. In addition, the thermal isolation of the PCC was numerically simulated, the results show that the numerical results trend consistently with the experimental data. The relative error between the experimental and numerical results is lower than 5%, implying that the numerical model could be used to systematically investigate the thermal performance of the PCC in building.

320 No PCM NUM With PCM NUM No PCM EXP With PCM EXP

315 310

Temperature / K

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


305 300 295 290 285 0

30000

60000

90000

120000

150000

180000

Time / s

Figure 10 Numerical and experimental thermal behavior of the PCC based roof 3.5.2 The effect of thermal conductivity The thermal insulation performance of PCC based roof with different thermal conductivity of the PCC was numerically investigated. As shown in Figure 11, the temperature of the PCC based roof increase in the daytime and decrease in the nightime. Interestingly, the highest temperature of the room increase with the thermal conductivity of the PCC in the daytime and decrease with the thermal conductivity in the nightime. The highest temperature of the room increase from 314.5 K


17


to 317.5 K with the thermal conductivity of the PCC increase from 0.05 to 3 W m-1 K-1 in the daytime, and the lowest temperature of the room decrease from 288.5 to 286 K since the thermal conductivity of the PCC increase from 0.05 to 3 W m-1 K-1. The results show that low thermal conductivity of the PCC is advantage of thermal insulation, the thermal conductivity of the PCC should be under 0.1 W m-1 K-1 to maintain the insulation property.

320 0.05 W m-1 K-1 0.1 W m-1 K-1 0.3 W m-1 K-1 0.5 W m-1 K-1 1 W m-1 K-1 3 W m-1 K-1

315

Temperature / K

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

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310 305 300 295 290 285 0

30000

60000

90000

120000

150000

180000

Time / s

Figure 11 Thermal insulation property and the liquid fraction of the PCC with different thermal conductivity 3.5.3 The effect of Enthalpy The effect of enthalpy on the thermal insulation performance was also investigated numerically. From Figure 12, we could clearly see that the temperature of the PCC decorative room with different enthalpy have a little variation. The enhancement of highest temperature of the PCC room is lower than 0.5 K, implying that the enthalpy of the PCC has little effect on the temperature of


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the room. Higher available enthalpy means larger energy is absorbed by PCC, while the higher available enthalpy could not delay the enhancement of the temperature. It is indicated that the exterior heat is much larger than the heat capacity of the PCC, the key to decrease the temperature of the room is to increase the thermal resistance of the room in the daytime. Obviously, decreasing the thermal conductivity of the PCC has an advantage of increasing the thermal resistance.

320

120 J g-1 140 J g-1 150 J g-1 160 J g-1

315

Temperature / K

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


310 305 300 295 290 285 0

30000

60000

90000

120000

150000

180000

Time /s

Figure 12 Thermal insulation property and the liquid fraction of the PCC with different enthalpy 3.5.4 The effect of thickness The effect of thickness on the thermal insulation performance was investigated, as shown in Figure 13. The temperature of the PCC decorative room decrease from 316.5 to 315 K as the thickness of the PCC increase from 15 to 30 mm. Although the liquid fraction of the PCC decrease with the thickness, the available enthalpy of the PCC increase with the thickness. The liquid


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fraction decrease from 0.5 to 0.36 as the thickness increase from 15 to 30 mm, while the relative available enthalpy of the PCC increase from 0.25 to 0.37. Increasing the thickness of the PCC has advantage of increasing the enthalpy and heat resistance of the PCC, the enthalpy has little effect on the thermal insulation performance of the room. The results indicating that increasing the thickness could slightly increase the heat resistance, while decreasing the thermal conductivity of PCC is the most effective way to improve the thermal insulation performance.

320

15 mm 20 mm 25 mm 30 mm

315

Temperature / K

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

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310 305 300 295 290 285 0

30000

60000

90000

120000

150000

180000

Time / s

Figure 13 Thermal insulation property and the liquid fraction of the PCC with different thickness 3.5.5 The effect of phase change temperature The effect of phase change temperature on the thermal insulation performance was investigated, as shown in Figure 14. The temperature of the PCC decorative room decrease from 318.5 to 316 K as the phase change temperature increase from 35 to 40 °C, then increase from 316 to 317 K


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since the phase change temperature of the PCC increase from 40 to 44 °C. The PCC with phase change temperature of 40 °C has the best thermal insulation performance. For the PCC of 35 °C, the ambient heat energy could melt the PCC totally within 10000 s, then the temperature of the PCC quickly increase to 318.5 K. For the PCC of 44 °C, the phase change temperature is too high for melting by ambient temperature, hence the liquid fraction of the PCC is minimum. The PCC with phase change temperature of 40 °C is the most suitable for the roof of the room, since the PCC was melted by ambient to delay the increasing temperature and could not penetrated by the ambient to maintain in lower temperature.

320 315

44 ℃ 40 ℃ 35 ℃

310

Temperature / K

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


305 300 295 290 285 0

30000

60000

90000

120000

150000

180000

Time / s

Figure 14 Thermal insulation property of the PCC with different phase change temperature 4. CONCLUSIONS


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A shape-stabilized PCC with enhanced mechanical property and thermal conductivity was prepared. The melting temperature and enthalpy of PCC is 41.5°C and 143.8 J g-1. The PCC has thermal conductivity of 1.5 W m-1 K-1, which is 3-fold higher than OP44. When adding 5% of the EPDM, the thermal conductivity increase to 2.2 W m-1 K-1. The tensile strength and impact strength of PCC was enhanced several-fold higher than OP44/EG composite. The thermal isolation performance of the PCC was experimentally and numerically investigated, and the PCC could decrease the temperature inside the room in daytime and increase the temperature at night. The effect of thermal conductivity, enthalpy, thickness and phase change temperature on the thermal insulation performance was also investigated numerically in this work. The results show that the thermal insulation property of the PCC decorative room increase with the thermal conductivity and decrease with the thickness. The enthalpy has little effect on the thermal insulation performance of the PCC (in the range of 120-160 J g-1), and the PCC of 40 °C has best thermal insulation performance among three PCC with different phase change temperature. The results shows that the polymer based PCC has enhanced mechanical property and thermal property, which is suitable for application in building.

ACKNOWLEDGMENT The authors gratefully thank the following funders for financial support of this work. Author Prof. Dr. Hong Huang received funding from National Nature Science Foundation of China Grant 51573058. Author Dr. Jian Liu received funding from Research Start-up Funds of Dongguan University of Technology Grant GC300502-40.


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