Synthesis and characteristics of hygroscopic phase change material: Composite microencapsulated phase change material (MPCM) and diatomite

Synthesis and characteristics of hygroscopic phase change material: Composite microencapsulated phase change material (MPCM) and diatomite

Accepted Manuscript Title: Synthesis and Characteristics of Hygroscopic Phase Change Material: Composite Microencapsulated Phase Change Material (MPCM...

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Accepted Manuscript Title: Synthesis and Characteristics of Hygroscopic Phase Change Material: Composite Microencapsulated Phase Change Material (MPCM) and Diatomite Author: Zhi Chen Menghao Qin Jun Yang PII: DOI: Reference:

S0378-7788(15)30008-6 http://dx.doi.org/doi:10.1016/j.enbuild.2015.05.033 ENB 5881

To appear in:

ENB

Received date: Revised date: Accepted date:

25-1-2015 19-5-2015 22-5-2015

Please cite this article as: Z. Chen, M. Qin, J. Yang, Synthesis and Characteristics of Hygroscopic Phase Change Material: Composite Microencapsulated Phase Change Material (MPCM) and Diatomite, Energy and Buildings (2015), http://dx.doi.org/10.1016/j.enbuild.2015.05.033 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Synthesis and Characteristics of Hygroscopic Phase Change Material:

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Composite Microencapsulated Phase Change Material (MPCM) and

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Diatomite

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Zhi Chen, Menghao Qin*, Jun Yang

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Division of Building Physics, School of Architecture and Urban Planning,

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Nanjing University, Nanjing 210093, China

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Tel: +86 25 83593020

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*Corresponding author: Prof. Menghao Qin

E-mail address: [email protected]

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Abstract: This paper prepared a new kind of hygroscopic phase change material using

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MPCM and diatomite. The composite can absorb/release not only thermal heat, but also

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moisture. The shell material of MPCM was prepared with methyl triethoxysilane

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(MTES) by sol–gel method, and a kind of alkane mixture was used as the core material.

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The diatomite was used as hygroscopic material. The morphology of the microcapsules

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and the diatomite were measured by the scanning electron microscopy (SEM). The

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thermal properties of MPCM and the composite MPCM/diatomite materials (CMPCM)

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were analyzed with differential scanning calorimetry (DSC). The thermal gravimetric

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analysis (TGA) was used to study the thermal stability of MPCM and CMPCM. The

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moisture transfer coefficient and moisture buffer value (MBV) of the diatomite and

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CMPCM were measured. The DSC results showed that the microcapsules were

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encapsulated in the SiO2 shell. The TGA results showed that the microcapsules and

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CMPCM have a good thermal stability. The measurements of the moisture transfer

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coefficient and moisture buffer value (MBV) of CMPCM, diatomite, gypsum board and

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wood showed that CMPCM has a better hygroscopic performance. The hygroscopic

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phase change material can moderate both the indoor temperature and moisture.

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Keywords: Microencapsulated phase change material; Silicon dioxide shell; Diatomite;

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Thermal energy storage material; Hygroscopic material; Building energy conservation

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1. Introduction

With the development of economy, energy demand is increasing quickly.

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Conventional fossil energy sources are limited, and the use of them lead to climate

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changes and environment pollution. Buildings account for about 40 percent of the

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world’s total energy consumption, and more than 30% of the primary energy consumed

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in buildings is for the heating and air-conditioning system [1]. In order to ensure

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adequate supplies of energy and to curtail the growth of CO2 emissions, it is essential

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that building energy consumption is significantly reduced [2,3]. One way this can be

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achieved is through the introduction of passive building design enabled by innovative

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sustainable building materials, for example the hygroscopic phase change material

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(HPCM).

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The indoor temperature, relative humidity and air quality are important

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environmental parameters of human comfort. To control the indoor environment at a

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comfort level, the internal sensible and latent heat loads must be removed by either

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active technologies (for example: air-conditioning, dehumidification system etc.) or

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passive strategies (for example: hygroscopic thermal energy storage materials, natural

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ventilation etc.) The research of coupled heat and moisture transfer in buildings and

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using passive strategies to create comfort indoor environment are timely and important

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research topics [4-6].

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The ambient temperature during a day is fluctuant. In summer, the temperature in

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daytime may be high during the daytime, so it’s not comfortable. But at night the

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temperature drops below the comfort temperature range. Phase change material (PCM)

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can absorb thermal energy when the temperature is high, and release thermal energy

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when temperature is low. The temperature of the phase change material is a constant

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during the phase change process. So using the phase change material to realize the

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regulation of temperature is an ideal way of energy saving [7-10]. But some

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disadvantages of the PCM limit the use of it, for example the low conductivity,

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super-cooling degree and the difference between the phase change temperature during

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heating and cooling.

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Microencapsulated Phase change material is a kind of shape stabilized phase

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change material [11]. The shell material of the microcapsules can prevent the leakage of

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phase change material in the phase change process, but also can improve the thermal

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conductivity of phase change materials, and reduce the super-cooling degree of phase

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change materials. Many preparation methods of microencapsulated phase change

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microcapsules have been developed [12, 13], but the shell material is usually organic

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material. Organic materials are usually flammable, and some shell material can release

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toxic substances. Studies on Preparation of shell material using inorganic material are

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not too many. Fang [14] and Chen [15, 16] prepared some microcapsules with SiO2 as

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shell material. He [17] developed a new silica encapsulation technique using sodium

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silicate precursor. Cao [18, 19] and Chai [20] prepared some microcapsules with TiO2

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as shell material.

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Relative humidity is related to human comfort and health closely [21].

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Experiments show that people feel most comfortable and are not easy to get disease

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when the relative humidity of the air is 50% - 60%. People may suffer from rheumatic

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and rheumatoid arthritis if working in high humidity areas for long time. When

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humidity is too low, dry air makes people skin chapped, and dry cough and hoarseness

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may occur [22-24]. In order to maintain a relatively stable relative humidity, air

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conditioning system is used to dehumidify or humidify the indoor environment.

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Humidity is also fluctuant during a day like temperature, so hygroscopic material can be

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used to regulate the indoor relative humidity, which can keep the indoor environment

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healthy, but also reduce energy demand [25]. However, the sorption and desorption

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process of the hygroscopic material are different, and the performance of the

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hygroscopic material is dependent on climate conditions, which all limit the real

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application of the hygroscopic material. There is a need to develop new materials or

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products with better hygrothermal performance for passive building applications. A hygroscopic phase change material was prepared in this paper. SiO2 prepared

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with MTES by sol–gel method was used as shell material of the microcapsules [15]. A

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kind of alkane mixture was used as core material. Diatomite has a good moisture

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sorption property, and it is a kind of healthy organic material. So the diatomite was used

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as hygroscopic material [26]. The composite microcapsules and diatomite material were

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prepared to be a composite thermal regulating and humidity controlling materials. The

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materials can effectively reduce the daily fluctuations of indoor air temperature and

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relative humidity. At the same time the microcapsule particles can improve the moisture

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sorption performance of the diatomite.

d 2. Experimental

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2.1 Materials

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Methyl triethoxysilane (Reagent grade, Tokyo chemical industry CO., LTD) was

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used as the precursor. Anhydrous ethanol (Reagent grade, Sinopharm Chemical Reagent

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Company) and distilled water were used as solvent. Hydrochloric acid (Reagent grade,

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Nanjing Chemical Reagent CO., LTD) and ammonia solution (Reagent grade, Nanjing

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Chemical Reagent CO., LTD) were used to control the PH degree. PCM (Industrial

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grade, Ruhr Technology Company) was used as core material. Sodium dodecyl sulfate

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(SDS) (Reagent grade, Shanghai Chemical Reagent CO., LTD) was used as oil–water

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emulsifier . The melting temperature and the latent heat of the alcane mixture are listed

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in Table 1. More detailed characteristics could be found in [26]. Diatomite (Industrial

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grade, Shanghai Liangjiang Titanium White Product Company) was used as

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hydroscopic material, the density is 0.47 g/cm3 (loose weight) (lit.), the specific surface

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area is 38m2/g, the pore volume is 0.6cm3/g and the porosity is 80%.

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2.2 Preparation of the PCM Oil/Water emulsion

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20g PCM and 2.5g SDS were added into 100ml distilled water in a beaker. The solution

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was heated at 35 ℃ to melt the phase change material. Then the temperature of the

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solution was maintained at 35 ℃ and the solution was stirred at a rate of 600 rpm for

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0.5 h with a magnetic stirrer. And then the temperature was maintained at 25 , and the

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solution was stirred for 0.5h.

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2.3 Preparation of the microencapsulated PCM with SiO2 shell

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20g MTES, 20g ethanol and 30ml distilled water were mixed in a beaker to form the

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solution. The PH degree of the MTES solution was controlled at 2–3 by using

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hydrochloric acid. Then the solution was stirred by a magnetic stirrer at 50 ℃ a rate of

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500 rpm for 20 min. Then the sol solution was gained as microencapsulation precursor

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with the hydrolysis reaction of the MTES. The temperature of the PCM micro-emulsion

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was maintained at 35℃ and stirred at a rate of 400 rpm. And the PH degree of the PCM

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micro-emulsion was maintained at 9-10 by adding ammonia solution. Then, the sol

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solution was added into the PCM micro-emulsion in drops. The emulsion was kept

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reacting and being stirred for 2 h. The condensation reactions between the methyl

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silicate and methyl silicate took place to form the SiO2 shell. And then the SiO2

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polymerized to build SiO2 shell on the surface of the PCM droplet in the polymerization

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process of the sol mixture. Finally, the filter paper was used to collect the microcapsules.

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And the microcapsules were washed with distilled water and dried in a low temperature

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vacuum oven at 0 ℃ for 24 h. The microencapsulated PCM composites were gained,

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and then named as MPCM.

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2.4 Preparation of the endothermal-hygroscopic material The diatomite was dried in a vacuum oven for 10 h at 100 ℃. Then 5g MPCM, 20g

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diatomite and 80g water were mixed in a beaker. The composites were stirred at a rate

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of 200 rpm at the room temperature for 5 min, and were formed as a brick. Then the

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composites were dried in a vacuum oven at 25 ℃ for 48 h. The MPCM/diatomite

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composites were acquired, and then were named as CMPCM. 20g diatomite and 40g

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water were mixed in a beaker, stirred at a rate of 200 rpm at the room temperature for 5

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min, and then also formed as a brick. The brick formed by single diatomite, gypsum and

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wood will be as the control samples for the CMPCM.

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3 Characterization of the MPCM/diatomite composites

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3.1 Morphology of the MPCM and diatomite

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The microstructure and morphology of the MPCM and diatomite were investigated by a scanning electronic microscope (SEM, S-3400NⅡ, Hitachi Inc., Japan). Fig. 1 shows the SEM profiles of the MPCM and the diatomite. As shown in Fig.

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1a, the microcapsules have a compact surface to encapsulate the PCM in the SiO2 shell,

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and the SiO2 shell can keep the PCM from leaking when the PCM is melted. The

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microcapsules have a spherical shape without edges or dents, and the size of the

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microcapsules is about 60-80µm. It can be seen from Fig.1b that the diatomite has a

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porous structure. There are many nano-pores in the particle of the diatomite, which

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make it absorb water vapor. Fig.2 shows the photos of the brick formed by CMPCM,

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the brick formed by single diatomite, gypsum and wood. It can be seen that the bricks

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are blocky structural integrity. The mass ratio of the MPCM and diatomite ensures that

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the brick of CMPCM is not too loose to be broken. When increasing the mass ratio of

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the MPCM to 30%, the brick will be likely to be broken.

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Fig. 1 Fig. 2

3.2 Thermal properties of the MPCM/diatomite composites A differential scanning calorimeter (Pyris 1 DSC, Perkin-Elmer) was used to

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measure the thermal properties of the MPCM/diatomite composites. The heating and

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cooling temperature rate was 5 ℃/min with a constant stream of argon at a flow rate of

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20 ml/min. The accuracy of temperature measurements was ±2 ℃ and the enthalpy

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accuracy was ±5%. The DSC results of the PCM, MPCM and CMPCM are shown in Fig.3, Fig.4 and

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Table 1. The thermal absorbing process is shown in Fig.3, and the thermal releasing

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process is shown in Fig.4. Table 1 shows the melting temperature, solidifying

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temperatures, latent heat and the super-cooling degree of the PCM, MPCM and

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CMPCM. As can be seen in Table 1, the melting and solidifying temperatures of the

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PCM are measured to be 28.1℃and 26.2℃, the melting and solidifying latent heat are

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145.7kJ/kg and 144.3kJ/kg, and the super-cooling degree is 1.9℃. The melting and

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solidifying temperatures of the MPCM are measured to be 27.2 ℃ and 26.7 ℃, the

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melting and solidifying latent heat are 94.4 kJ/kg and 89.6 kJ/kg, and the super-cooling

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degree is 0.5 ℃. The melting and solidifying temperatures of the CMPCM are measured

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to be 27.0 ℃ and 26.8 ℃, the melting and solidifying latent heat are 19.0 kJ/kg and

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18.4 kJ/kg, and the super-cooling degree is 0.3 ℃. It can be seen that the super-cooling

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degrees of MPCM and CMPCM is lower than that of the PCM, which makes the

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composite more suitable for building applications.

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The latent heat of the MPCM and CMPCM are lower than that of the PCM because

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the PCM and diatomite have no phase change process. Higher content of the PCM in

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the MPCM or CMPCM mean higher thermal heat storage capacity. The latent heat of

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the MPCM or the CMPCM is proportional to the content of the PCM. The mass ratio of

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the PCM can be calculated by the following Eq. (1):

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η=

∆H × 100 % ∆H PCM

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The η is the mass ratio of the PCM in MPCM or the CMPCM, the ∆H means the

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mean latent heat of the MPCM or the CMPCM, and the ∆HPCM represents the mean

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latent heat of the PCM. The mass ratios of the PCM in the MPCM and the CMPCM are

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shown in Table 1. The mass ratios of the PCM in the MPCM and the CMPCM are 63.4%

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and 12.9%.

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Fig.4

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Table 1

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3.3 Thermal stability of the MPCM/diatomite composites The thermo-gravimetric analyzer (Pyris 1 TGA, Perkin-Elmer) was used to

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investigate the thermal stability of the MPCM and CMPCM. The temperature in

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measurement is from 25 ℃ to 700 ℃. The heating rate is 20 ℃/min with a constant

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nitrogen stream, and the flow rate of nitrogen is 20 ml/min.

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Fig.5 presents the TGA curves of the PCM, MPCM and CMPCM. Table 2 shows

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the residual weight at 700 ℃ and the starting temperature of the maximum weight loss.

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It can be seen from Fig. 5 that there is a two-step thermal degradation process. When

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the temperature is between 130 ℃ and 250 ℃, the first step occurs, which is

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corresponding to the thermal degradation of the PCM. When the temperature is between

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250 ℃ and 700 ℃, the second step occurs, which is corresponding to the thermal

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degradation of the SiO2 molecular. The starting temperature of maximum weight loss

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for MPCM or CMPCM is higher than that of PCM, and this result means that the SiO2

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shell can protect the core material and act as a fire retardant to improve the kindling

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point. Fig.5

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Table 2

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3.4 Hygroscopic properties of the CMPCM and diatomite

In order to evaluate the hygroscopic performance (especially the moisture buffer

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ability) of the composite, both the moisture transfer coefficient and the moisture buffer

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value were measured. The former represents the rate of moisture transfer; the latter

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mainly represents the moisture buffer capacity in a dynamic RH variation. The sorption

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and desorption isotherms of the CMPCM were also measured.

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Moisture transfer in a porous building material can be analyzed using the so-called

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thermal–moisture analogy. The moisture diffusivity is analogous to the thermal

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conductivity in heat transfer process. The material used for humidity controlling should

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have a higher moisture transfer coefficient, which means that the material can quickly

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respond to the indoor relative humidity change. The mass ratio of the saturated moisture

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content to the diatomite is relatively high, can reach to 10% [26]. But the moisture

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transfer coefficient of a material which has large saturated moisture may be small,

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which means that the material may need to take a long time to absorb the water vapor.

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So the material cannot respond to the indoor relatively humidity quickly, and cannot act

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as a moisture controlling material. Moisture transfer coefficient can be defined by

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following Eq. (2): qm ∂RH ∂x

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λ=

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The λ is the moisture transfer coefficient, q m represents the flux of water vapor

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in a unit time and a unit area, RH means the relative humidity and x is the thickness of

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the material.

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The classic cup method was adopted to measure the moisture transfer coefficient of

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samples. Areas of 3*3cm on the two sides of the brick are exposed to make the water

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vapor transfer from the bottle to outside, and the other samples were also operated like

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this. The saturated NaCl solution is kept in the bottle to keep the relative humidity of the

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air in container as 75%. The relative humidity outside is maintained at 52%. The

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measurement accuracy of the relative humidity was ±2%.

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Fig.6

The moisture transfer coefficients of CMPCM and the diatomite are shown in Fig.6

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and Table 3. It can be seen that the moisture transfer coefficient of CMPCM is 5×10-8

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kg/(m ∙ s ∙ %RH). It is higher than that of others, which is mainly due to the fact that

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adding MPCM increases the porosity of CMPCM.

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Moisture buffer value is a characteristic of a material based on a period of moisture

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uptake/release. The practical moisture buffer value indicates the amount of water that is

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transport in or out a material per open surface during a certain period of time, when it is

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subjected to variations in relative humidity of surrounding air [27]. The moisture buffer

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value can be defined as Eq. (3): (3)

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The MBV is the moisture buffer value, the G is the moisture uptake of the material,

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MBV

The A is the area of the material surface to exchange moisture with the air, and ∆RH is

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the difference value between the high relative humidity and the low relative humidity.

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Fig.7 shows that there are two bottles containing some saturated salt solution. One

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bottle contains saturated KCl solution, which keeps the relative humidity inside at 88%.

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Another one contains saturated NaBr solution, which keeps the relative humidity inside

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at 62%. The sample hangs in the bottle with KCl solution, and then the bottle is sealed

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for 8 hours. Then the sample hangs in the bottle with NaBr solution, and the bottle is

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sealed for 16 hours. The process is alterative operated for at least 6 days. And the mass

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of the sample is measured with analytical balance.

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Fig.8 shows the mass change curves of the CMPCM, diatomite, wood and gypsum.

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The moisture buffer values of the samples are presented in Fig.9 and Table 4. It can be

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seen that the MBV of CMPCM is 1.57 g/m2∙%RH, which is much higher than that of

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others. Rode [28] classified the MBV using five different categories. The good class

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ranges from 1 g/m2∙%RH to 2 g/m2∙%RH. It can be seen that the MBV of CMPCM is

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within good class, and the MBV of other samples are all within limited class, which

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ranges from 0.2 g/m2∙%RH to 0.5 g/m2∙%RH. The microcapsules in CMPCM will

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increase the porosity of the composite, and consequently increase the moisture transfer

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coefficient of the composite. The CMPCM can absorb more water vapor in a given time (e.g. 8 h) than pure diatomite, which leads to a larger MBV as shown in Fig. 9. In addition, Fig. 10 shows that the sorption and desorption isotherms of the

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CMPCM are nearly linear in normal hygroscopic range (between 20% and 85% RH).

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The MBV could be regarded as a constant within this range for building application.

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Fig.8

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Fig.9

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Fig.10

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3.7 The effects of the CMPCM in buildings applications

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The CMPCM can be used in interior wallboard of buildings. The PCM in the

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composites can effectively reduce the daily fluctuations of indoor air temperatures and

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maintains it at the desired comfort level for a longer period of time. The hygroscopic

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material (diatomite) in the composites can regulate the relative humidity of the indoor

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environment by uptake/release moisture.

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A following example about the practical application is given to show how the

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CMPCM can be used to reduce the air conditioning load. An unventilated and insulated

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room has dimensions 4m×5m×3m= 60 m3. At the initial time, the indoor temperature is

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25 ℃, and the relative humidity is 50%. In the room is released 100g moisture per hour,

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and heat power is 1000W. To maintain the indoor temperature is below 27 ℃ and the

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relative humidity is below 60 %, how much will the air conditioning load be in 8 hours? If there is no CMPCM, the sensible heat load can be calculated from Eq. (4):

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  ∙ 8    ∙ 27    ∙ 25 ∙

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E" h ∙ $q& ∙ 8  SW ∙ 60%  SW" ∙ 50% ∙ V+

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The air conditioning load is from Eq. (6):

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The latent heat load can be calculated from Eq. (5):

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(5)

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Where E, is the sensible heat load, E" is the latent heat load and E is the total load

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of the air conditioning system. The q and q& are heat power and moisture releasing rate

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respectively. The c and c" are specific heat capacity of air at 27 ℃ and 25 ℃

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respectively. The ρ and ρ" are air density at 27 ℃ and 25 ℃ respectively. The SW

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and SW" are saturation water vapor concentration at 27 ℃ and 25 ℃ respectively. The

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h is the latent heat of water vapor. The V is the volume of the room, and the COP is the

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coefficient of performance of the air conditioning system [29]. The values of the

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parameters are listed in Table 5. It can be calculated that the E= 2.54 kWh.

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If the inner wall of the room is clad with A=54 m2 of the CMPCM and the

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thickness of the coating is d=2 cm [30]. The E456 represents the thermal heat absorbed

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by PCM, which can be calculated from Eq. (7):

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E456 α ∙ A ∙ d ∙ ρ56456 ∙ h56456

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Where, α is the ratio of the enthalpy available between the high and low

(7)

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temperatures by the total enthalpy, ρ56456 is the density of the CMPCM and h56456

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is the latent heat of the CMPCM, which are listed in Table 5. And the relative humidity RH in 8 hours can be calculated from Eq. (8):

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SW ∙ RH ∙ V - MBV ∙ RH  50% ∙ 100 ∙ A SW" ∙ 50% ∙ V - q& ∙ 8

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When α =20%, It can be determined that the E456 =0.74 kWh and RH=57.1%.

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It can be known that the relative humidity is always below 60% when the inner

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wall is clapped with CMPCM. So air condensation dehumidification is not needed. The

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air conditioning load is calculated from Eq. (9):

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It can be determined that the E; =2.09 kWh. The energy saving rate is 17.7%. Table 5

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In reality, the room experiences an air and heat change with outside environment, so the energy load should be investigated comprehensively.

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(9)

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(8)

4. Conclusions

This paper presents the synthesis, thermal properties and the hygroscopic

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properties of the MPCM/diatomite composites. The SiO2 prepared with MTES was used

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as the shell material, and a kind of alkane mixture was used as core material. The

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measurement results of thermal properties show that the melting temperature of

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CMPCM is 27.0℃ and the solidifying temperature is 26.8℃. The super-cooling degree

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of CMPCM is 0.3℃. The SiO2 shell can improve the thermal stability of the PCM. The

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measurement results of the hygroscopic properties show that the MPCM can improve

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the hygroscopic performance of CMPCM. The MBV of CMPCM is within good class.

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The overall hygrothermal performance of the composite is better than simple

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combination of two separate layers of PCM and diatomite. An example about practical

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application shows that the CMPCM can moderate both the indoor temperature and

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relative humidity. The CMPCM has the potential to be an energy saving material.

us

cr

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335

For future work, the performance and effect of the CMPCM in real building

342

applications under different climates will be studied by detailed experimental

343

measurements.

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344

Acknowledgements

te

346

d

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This work was supported by the National Natural Science Foundation of China

348

(Grant No. 51108229), and Research Fund for the Doctoral Program of Higher

349

Education of China (Grant No. 20130091110053).

350

Ac ce p

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[13] C.Y. Zhao, G.H. Zhang. Review on microencapsulated phase change materials

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[14] G.Y. Fang, Z. Chen, H. Li, Synthesis and properties of microencapsulated paraffin composites with sio2 shell as thermal energy storage materials, Chemical

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[15] Z. Chen, L. Cao, G. Fang, F. Shan, Synthesis and characterization of

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microencapsulated paraffin microcapsules as shape-stabilized thermal energy storage materials, Nanoscale and Microscale Thermophysical Engineering, 17 (2013) 112–123.

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microencapsulated stearic acid as composite thermal energy storage material in

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[18] L. Cao, F. Tang, G.Y. Fang, Preparation and characteristics of microencapsulated

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palmitic acid with TiO2 shell as shape-stabilized thermal energy storage materials,

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[19] L. Cao, F. Tang, G.Y. Fang, Synthesis and characterization of microencapsulated

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paraffin with titanium dioxide shell as shape-stabilized thermal energy storage

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materials in buildings, Energy and Buildings 72 (2014) 31–37.

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[20] L.X. Chai, X. Wang, D. Wu, Development of bifunctional microencapsulated phase change materials with crystalline titanium dioxide shell for latent-heat storage

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and photocatalytic effectiveness, Applied Energy 138, ( 2015), 661–674.

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[21] I. Andersen, J. Korsgaard, Asthma and the indoor environment: assessment of the

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health implications of high indoor air humidity, Environment International 12 (1984) 121–127.

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[23] J. Toftum, A.S. Jørgensen, P.O. Fanger, Upper limits of air humidity for preventing warm respiratory discomfort, Energy and Buildings 28 (1998)15–23. [24] J. Toftum, A.S. Jørgensen, P.O. Fanger, Upper limits for indoor air humidity to avoid uncomfortable humid skin, Energy and Buildings 28 (1998) 1–13.

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106, Pt. 2 (2000).

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endothermal-hydroscopic material, Energy and Buildings 86 (2015) 1–6.

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buildings, Journal of ASTM International 4 (2007) 1-12. [29] China Standard Association, GB 12021.3-2010, the minimum allowable value of

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[30] J. Y. Zhang, Z. Q. Chen, Application analogue simulation of diatomite-based humidity control building material, Journal of Southeast University 43 (2013) 840-844.

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Page 21 of 35

Table(s) with Caption(s)

Tables with Captions

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Table 1 DSC data of the PCM, MPCM and CMPCM Melting (5 ℃/min)

Encapsulation

Solidifying (5 ℃/min)

Sample ratio of the name

Latent heat

Latent heat

Temperature (℃)

PCM (%)

cr

Temperature (℃)

100. 0

28.1

145.7

MPCM

63.4

27.2

94.4

CMPCM

12.9

27.0

an

PCM

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(kJ/kg)

26.2

144.3

26.7

89.6

26.7

18.4

M

19.0

(kJ/kg)

PCM

130

0

175

38

175

88

Ac ce p

MPCM

CMPCM

Charred residue amount (%) (700 ℃)

T (℃)

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Samples

d

Table 2 TGA data of PCM, MPCM and CMPCM

Table 3 Moisture transfer coefficient of CMPCM, diatomite, gypsum and wood Samples

CMPCM

diatomite

gypsum

wood

5.00

2.75

1.54

0.79

moisture transfer coefficient -8

(10 kg/m ∙ s)

1

Page 22 of 35

Table 4 MBV of CMPCM, diatomite, gypsum and wood CMPCM

diatomite

gypsum

wood

1.57

0.33

0.26

0.40

MBV 2

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cr

(g/m ∙%RH)

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Samples

value

A (m2)

54

d (m)

0.02

ρ (kg/m3) ρ (kg/m3)

1.177 1.185

c (kJ/kg∙K)

value

SW (g/m3)

25.8 23

ρ (kg/m3) η (-)

650 12.9%

1.005

h (kJ/kg)

19

1.005

h (kJ/kg)

2434.4

COP (-)

3.5 [27]

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SW (g/m3)

Ac ce p

c (kJ/kg∙K)

parameter

M

parameter

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Table 5 The values of parameters for the CMPCM application

q (W)

1000

q (g/h)

100

2

Page 23 of 35

List of Figure Captions

List of Figure Captions

Fig.1 SEM photographs of the (a) CMPCM, (b) Diatomite

Fig.5 TGA curve of PCM, MPCM and CMPCM

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Fig.4 Solidifying DSC curve of PCM, MPCM and CMPCM

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Fig.3 Melting DSC curve of PCM, MPCM and CMPCM

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Fig.2 Photos of the (a) Wood, (b) CMPCM, (c) gypsum, (d) diatomite

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Fig.6 Moisture transfer coefficient of CMPCM, diatomite, wood and gypsum Fig.7 Photos of bottles containing saturated salt solution of (a) KCl, (b) NaBr

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Fig.8 Mass change curves of the CMPCM, diatomite, wood and gypsum

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Fig.9 MBV of the CMPCM, diatomite, wood and gypsum

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Fig.10 Sorption and desorption isotherms of the CMPCM

1

Page 24 of 35

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Figure(s)

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Fig. 1

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Fig. 2

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Fig. 3

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Fig. 4

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ed

Fig. 5

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ed

Fig. 6

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ed

Fig. 7

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Fig. 8

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Fig. 9

Page 33 of 35

0.11

sorption

0.09

desorption

0.08 0.07

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0.06 0.05

0.04 0.03

cr

Moisture content by mass (g/g)

0.10

0.02

0.00

0

20

40

60

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0.01

80

100

an

Relative humidity (%)

Ac

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ed

M

Fig. 10

Page 34 of 35

Highlights

Highlights

1. A new kind of hygroscopic phase change material was prepared. 2. The SiO2 shell can improve the thermal properties of the composite.

cr

4. The composite has a good hygrothermal performance.

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3. The SiO2 shell can prevent the melted phase change material from leaking.

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ed

M

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5. The composite can moderate both the indoor temperature and relative humidity.

Page 35 of 35