(494f) Formation Kinetics and Flow Behavior of Semi-Clathrate Hydrate Slurry in a Flow Loop: Application for Cold Energy Transport and Distribution

The ever-increasing demand on space cooling has become a major contributor to the growth of electricity consumption in buildings. Phase change materials (PCMs) are attracting overwhelming attentions for their great potentials to improve the energy efficiency of cooling systems, being used as cold energy storage media or secondary refrigerants. Semi-clathrate hydrates such as tetra-n-butyl ammonium bromide (TBAB) hydrate stand out as their phase change temperatures (mostly between 5 °C to 27 °C) are suitable for air-conditioning applications, with high dissociation enthalpies owing to their H-bonded crystalline framework. To be employed for cooling applications, fundamental knowledge on the formation kinetics and flow behavior of semi-clathrate hydrate slurry in various processes of the cooling system is very needed.

In this work, a laboratory-scale flow loop was developed to investigate the flow behavior of TBAB hydrate slurry with various hydrate fractions. A 25 L stirred tank reactor with cooling jacket was employed for hydrate generation. To measure the hydrate formation kinetics, the electrical resistivity-based method developed in our previous bench-scale study was adopted and scaled up. Once hydrates were generated, the hydrate slurry was pumped into the flow loop for testing and then returned to the reactor for regeneration. The pressure drops and temperatures were monitored to analyze the flow behavior and heat transfer characteristics of TBAB hydrate slurry in the flow loop.

The results demonstrated that the efficient removal of heat generated by hydrate formation was the key to fast hydrate production. The deposition of hydrates on the inner reactor wall would cause a significant deterioration in the cooling efficiency and thus slow down the hydrate formation kinetics. This is a major challenge to be addressed to achieve efficient hydrate generation. In terms of the flow behavior, the apparent viscosity of TBAB hydrate slurry with different hydrate fractions were determined from the pressure drop and flow rate data. The frictional loss of TBAB hydrate slurry flowing through various pipe fittings were obtained and correlations were developed. These results could be employed to estimate the energy loss during the transport of TBAB hydrate slurry. The knowledge gained in this work is of great significance for the further development of efficient hydrate-based cooling systems.