Clathrate hydrate technology for cold storage in air conditioning systems

Clathrate hydrate is an attractive technology for cold storage applications. It offers a high cold storage density and elevates the phase change temperature compared to water. It offers better heat transfer properties and improved cyclic stability compared to eutectic salts. This paper reviews previous work on clathrate hydrates as phase change materials (PCMs) for cold storage air conditioning applications. Three aspects have been focused on: the characteristics of clathrate hydrates, modification of clathrate hydrate properties, and practical utilization of clathrate hydrates as cold storage media. Specifically, refrigerant clathrate hydrates, CO2 hydrates, hydrocarbon clathrate hydrates and multi-component clathrate hydrates are introduced. Technologies to decrease equilibrium pressure, increase dissociation enthalpy, accelerate formation process, decrease supercooling extent and enhance gas solubility are summarized. Clathrate hydrates based cold storage air conditioning systems that transport cooling in a manner of fixed container as well as in hydrate slurry are reviewed, and optimizing methods of system performance are studied. Finally, four features of clathrate hydrates, namely the self-preservation effect, memory effect, gas conversion and hydrate structure transformation are discussed.