Phase Change Materials for Low Temperature Energy Storage Applications

Contact Dr Keith Garzoli: Keith.Garzoli@anu.edu.au

Phase Change Materials (PCMs) store energy by changing phase from solid to liquid (i.e. melting) and releasing heat by changing phase from liquid to solid (i.e. freezing). Phase change materials provide a large heat capacity over a limited temperature range. They act a little like an isothermal reservoir of heat. A range of PCMs are being evaluated, all with a melt/freeze temperature of about 40oC. The choice of the most appropriate PCM is based on a number of factors, including cost, latent and sensible heat, and thermal conductivity in both the liquid and solid phases and its effect on the overall thermal performance of the complete system.

Improved Thermal Fluids using Phase Change Slurries

Contact: Dr Mike Dennis, Mike.Dennis@anu.edu.au

Two problems with using large quantities of PCM material (paraffin wax in this case) are its poor thermal conductivity and its large volumetric change between phases.

Effective heat exchange with the PCM requires a large surface area to volume ratio in the PCM heat exchanger. One way to achieve this is to break the PCM into small particles and wrap each particle in its own heat exchange surface. This process is called micro-encapsulation. This technology has been used by others to embed PCM material into wall boards for houses and into concrete.

ANU is extending this technology to develop water based slurries of PCM material. This way, heat can be transferred into the PCM with the aid of convection as well as conduction. Furthermore, the phase change slurry (PCS) has a very high heat capacity and so is able to improve the performance of thermodynamic systems by stabilising the operating conditions.

Our research involves making PCS with predictable properties and carrying out testing on the solutions. Such fluids are not commercially available.

Granulated phase change wax

Prototype PCM energy storage module

Microscope images of uPCM