Thermal compatibility of Sodium Nitrate/Expanded Perlite composite phase change materials

doi:10.1016/j.applthermaleng.2016.03.108

Applied Thermal Engineering

Volume 103, 25 June 2016, Pages 452-458

https://doi.org/10.1016/j.applthermaleng.2016.03.108 Get rights and content

Highlights

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Expanded Perlite/Sodium Nitrate composites hardly reported in thermal storage fields.
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The thermal compatibility and adsorption of Expanded Perlite were investigated.
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The thermo physic properties of composites were determined.
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The thermal stability and long term enthalpy changes of composites were investigated.

Abstract

The present work focused on the preparation and characterization of a new thermal storage material applied in thermal energy management. X-ray diffraction (XRD) results showed that Expanded Perlite (EP) has a good thermal stability varying from 300 °C to 900 °C. Morphology of scanning electron microscopy (SEM) revealed that sodium nitrate is uniformly encapsulated and embedded in the three-dimensional network structure of EP. Fourier transform infrared (FT-IR) spectroscopy indicated that the EP is physically combined with the nitrate salt. Thermo-gravimetric analysis (TGA) and differential Scanning Calorimeter (DSC) indicated that the composites have good thermal stability. The adsorption capacity of loose EP was 213.21%. When the EP mass fraction varying from 10% to 60%, thermal conductivity decreased with the content of EP increased, and the highest thermal conductivity is 1.14 W (m K)⁻¹ at 300 °C. SEM revealed the network structure of EP provided thermal conduction paths which enhanced the thermal conductivity of the composites. All results indicated that EP could be a good adsorption material to be applied in the thermal storage fields.

Introduction

Thermal energy storage comprise of sensible heat, latent heat and thermo-chemical storage. Some advantages of latent heat storage include large energy storage density, uniform storage temperature and compactness of size [1], [2]. Phase change materials (PCMs) use latent heat to store or release heat at constant temperature would be a more appropriate consideration for the small variation in volume during the solid–liquid transition, which is the most efficient thermal storage [3], [4]. Therefore phase change materials have been attracted much attention in thermal energy storage [5], [6], [7], [8]. Molten nitrate salts are being used as thermal energy storage and heat transfer media in thermal energy applications [9], [10]. Sodium nitrate seems to be a good material for the latent heat storage. Its latent heat is relatively high. Moreover it is a single component with a high commercial availability and is easier to manufacture than eutectic salt. However, the molten sodium nitrate belongs to the solid–liquid PCM, and special packaging is required to prevent the leakage during solid–liquid phase transition process. Meanwhile, the poor thermal conductivity and corrosion [11], [12], [13] also restricted the performance of thermal storage. Therefore, it is necessary to study the heat transfer, packing enhancement and long-term stability on thermal storage.

Recently a considerable amount of research has been carried out on the preparation of form-stable phase change materials without extra packaging. Some adsorbing materials have been investigated for thermal storage [14], [15], [16]. Expanded Perlite (EP) acts as an excellent insulator, both thermal and acoustical, resists fire and is classified as ultra-lightweight material [17], [18]. Meanwhile EP is spherical in shape, usually fluffy, highly porous due to a foam-like cellular internal structure. It exhibits an excellent adsorption with strong capillary force and surface tension with multiple pores so that sodium nitrate can be adsorbed easily in its pores. Therefore, this paper is aimed to investigate the preparation and characterization of sodium nitrate/EP composite thermal storage materials. Based on analysis of the composition, morphology, phase transition properties and thermo-physical properties, the work is focusing on investigation of the composite thermal storage materials in thermal storage application.

Section snippets

Materials

Sodium nitrate with purity ⩾99.0% is supplied by Beijing Chemical Reagent Company (Beijing, China), and used without further purification. EP is obtained by XinYang Shenda thermal insulation building material Co., Ltd, China (Henan, China) with average particle less than 1 mm, bulk density of 250 g/L, and pH of 6.5–7.5. The chemical constituents of EP are given in Table 1. The EP is dried at 105 °C for 24 h prior to experiment. Aluminum dihydrogen phosphate is purchased from Zhengzhou yucai

Morphology of EP

Morphology of EP is presented in Fig. 1. It showed that EP has a highly porous structure consisting of rough micro-pores which can demonstrate that this material could adsorb plenty of sodium nitrate. Fig. 1 presents spherical structure with a rich honeycomb structure which provides abundant pores for adsorption. Sodium nitrate, which was used in the study, could lead to corrosion of equipments of the thermal energy storage system, and construction of a barrier between salts and the system is

Conclusions

A new form-stable sodium nitrate/EP composite PCMs were prepared and investigated in this paper. The XRD results show that EP has a good thermal stability from 300 °C to 900 °C. The adsorption capacity of form-stable EP after heat treatment at 500 °C for 2 h is the highest, can reach 114.07%. Meanwhile the adsorption capacity of loose pure EP is 213.21%, it is higher than form-stable EP. The DSC results indicate that the latent heat of composite materials decreased as the time extended. The FT-IR

Acknowledgement

This work was supported by the National Science and Technology Support Program of China (No. 2012BAA05B06).

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Research PaperThermal compatibility of Sodium Nitrate/Expanded Perlite composite phase change materials

Highlights

Abstract

Introduction

Section snippets

Materials

Morphology of EP

Conclusions

Acknowledgement

Appl. Therm. Eng.

Sol. Energy Mater. Sol. Cells

Appl. Therm. Eng.

Carbon

Sol. Energy

Appl. Therm. Eng.

Appl. Therm. Eng.

Appl. Therm. Eng.

Appl. Therm. Eng.

Sol. Energy

Energy Proc.

Research Paper
Thermal compatibility of Sodium Nitrate/Expanded Perlite composite phase change materials