Novel form-stable phase change material composite for high-efficiency room temperature control

Significance Statement

Latent thermal energy storage facilities containing phase change material have been the subject of great interest in matters regarding cooling energy saving in modern office buildings and residential homes. State of the art thermal energy storage systems for interior items such as tiles and furnishing require the material matrix to transfer heat rapidly between the adjacent phase change materials and the indoors. Thermal energy systems developers offer a wide variety of phase change material composites. However, for most of these materials, the high thermal conductivity counterbalances the phase change material volume capacity and material form stability above the phase change materials’ melting point. A novel aluminum matrix with open ultrathin pores and the developed surface area has been seen as a probable solution to this long-awaited dilemma.

In a recent paper published in Solar Energy Materials and Solar Cells research group of Prof. Ben Y.B. Chan from the Hong Kong University of Science and Technology proposed to develop a new form of stable phase change material composite that would be used to control the room temperature with high efficiencies. The researchers adopted aluminum for their study and focused on exploring the sintering process and porosity control in its nanoflakes. They aimed at providing a viable description for the preparation and key properties of the new aluminum composite matrix. They also hoped to show that the new material could be prepared economically using conventional powder metallurgy procedures.

The cold isostatic pressing route was employed to compress the aluminum nanoflakes into cylindrical compacts. The obtained compacts were then exposed to rapid heating (40 ºC/min) and annealing (1 min at 600ºC) in industrial grade flowing nitrogen where partial sintering was achieved. To impart the partially sintered nanoflakes with thermal mass, they used coconut oil as bio-based phase change material with a melting point of about 24ºC.

The authors of this paper observed that the developed pore surface in the partially sintered compact of the aluminum nanoflakes acts to durably incorporate and store bio-based phase change materials, such as the coconut oil used, within extremely narrow pore channels of sizes less than 150 nm. As noted the rapid heat treatment durably bonds the compacted aluminum nanoflakes without causing the material structure distortion. It allows the flawless fabrication of large scale tiles and plates. The material structure was observed can deliver a thermal conductivity of up to 120 W/mK, which stands unrivaled amongst known PCM composites. Herein, the composite has been seen to demonstrate satisfactory form-stability in the constant testing conditions.

In sum, this lightweight (1.8-2.3 g/cm3) composite has been proven that it can be effectively used to cover the entire building interior due to its highly efficient absorption and drain rate of excessive indoor heat to the building mass. The aluminum matrix electroconductivity has also been observed that it could allow rational radiant heating upon demand through the straightforward passage of electricity from an external connected system.

Novel form-stable phase change material composite for high-efficiency room temperature control (Advances in Engineering)

 

Key Highlights

  1. The material and its fabrication method have been protected with a US Prov. Pat. Application. So, it is now on the way to commercial success.
  2. It can be shaped in a desired form through conventional powder metallurgy methods.
  3. Affordable due to rapid heat processing in nitrogen at moderate temperatures (below 600ºC). Meanwhile, Al nanoflakes can be reasonably prepared via traditional ball milling of micrometric Al particles in stearic acid (~1 wt%). The method allows making large scale plates without flaws.
  4. The material can deliver energy efficiency in both cold and hot climate. Due to the thermal conductivity and thermal mass, heat energy (excessive or lacking) is rapidly managed throughout the material covered walls, floors, and ceiling.
  5. 95% Recyclable.

Reference

Andrey A. Chernousov, Ben Y.B. Chan. Novel form-stable phase change material composite for high-efficiency room temperature control. Solar Energy Materials and Solar Cells 170 (2017) 13–20

The Hong Kong University of Science and Technology, Department of Civil and Environmental Engineering, Clear Water Bay Road, Hong Kong, Hong Kong SAR

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