Nanofluids: An innovative phase change material for cold storage systems?

• A semi-analytical model of contact melting of a nanofluid phase change material is developed.
• Depending on the size and volume fraction an NEPCM may take longer to melt that the base fluid PCM.
• Even when melting is faster the energy release rate may be lower than the base fluid PCM.
• The size dependence may explain contradictory results in the literature.
• NEPCMs may not provide the anticipated improvements in energy storage and release.

An analytical approach is used to solve a contact melting problem where an alumina-water nanofluid is used as the phase change material. The mathematical model describing the process is reduced to three ordinary differential equations which are solved by means of the Heat Balance Integral Method. The melt front separating the solid and liquid constituents that possess different thermophysical problems (dependent on nanoparticle volume fraction) is tracked. The liquid height, solid height, total melt and melt rates are determined, as well as times to the onset of melting and melt completion. The results for both base fluid and nanofluid are compared, showing that the nanofluid phase change material may not be more efficient at releasing energy and that the efficiency is dependent on system size.