Direct contact PCM–water cold storage

Comfort cooling demand continues to increase throughout the world. Conventional cooling production results in high demand for electrical power during peak hours, leading to high emissions for producing cooling, and potential power shortages in electric grids. With a cold storage, the peak power demand is effectively managed and enables free-cooling. This paper examines one concept using phase change materials (PCM) for storing of cold, where the cold carrier (water) is in direct contact with the PCM. This is in order to enable high power for charging and discharging while providing a high storage capacity. A theoretical model highlights important design parameters for reaching large storage and power capacity. The capacity increases with the Packing Factor and temperature difference across the storage. For high power, the flow rate, temperature difference, and drop size is important parameters which is also verified in an experimental evaluation. The obtainable power is between 30 and 80 kW/m3 storage. Practical limitations of this concept are shown to be PCM–water bed expansion and non-uniform channeling due to asymmetric and unstable PCM shells.