Kinetic and rheological studies of CO2 semi-clathrate hydrates for cold storage air-conditioning systems

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Cold storage air-conditioning, as an advocated energy-saving technology, offers a mean to alleviate the peak load on electricity grids and utilize power in the off peak period. CO2 hydrate slurry is well suited for use as secondary refrigerant for cold storage applications, since it can be generated by CO2 injection in a cold aqueous solution (non-mechanical) and has a large thermal storage capacity due to the large dissociation enthalpy of CO2 hydrate (501~507 kJ kg-1). However, in many cases CO2 clathrate hydrates cannot achieve equilibrium within an adapted pressure range and temperature range for cold storage systems. The main aim of this project is to lower the equilibrium pressure of CO2 hydrates by forming CO2 semi-clathrate hydrates using aqueous solutions of additives, such as TBAB, TBPB and TBAF. The testing system is indicated in Fig. 1, which consists of a hydrate reactor cell, gas supply, a cooling/heating source and data gathering facility.

CO2 hydrate equilibrium testing system

Fig. 1. CO2 hydrate equilibrium testing system.

Solar air-conditioning system

Fig. 2. Solar air-conditioning system with a CO2 hydrate cold storage.

Specifically, the equilibrium conditions CO2 semi-clathrate hydrates and the induction time at different concentrations of additive solution are obtained during the formation process. The influencing factors on formation and dissociation behaviour of CO2 hydrates are investigated. The rheological properties of the formed CO2 hydrates are tested by an external circulating system. Furthermore, the application of an optimized CO2 hydrate cold storage will be developed in air-conditioning system by means of simulation, as is illustrated in Fig. 2.

References

  1. M. Dennis, I. Doemland, and L. Hou. Status and Prospects of Solar Cooling in Australia. In Proceedings of the 49th Annual Conference of the Australian Solar Energy Society, Sydney, 30 November–2 December, 2011.

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  2. L. Hou and M. Dennis. Evaluation of HVAC cold storage using TRNSYS under Australian conditions. In Proceedings of INNOSTOCK2012—The 12th International Conference on Energy Storage, Lleida, Spain, 16–19 May, 2012.

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