Hydrate slurry, crystallization, kinetic model
Hydrate slurry has been reported to be suitable secondary fluid for refrigeration and air-conditioning systems. The latent heat of CO2 hydrate is 387 kJ/kg under phase equilibrium condition of 7 Â°C and 30 bar. The utilization of CO2 hydrate slurry in air-conditioning systems is promising in improving the energy efficiency and shifting energy supply and demand load as well as relieving greenhouse effect caused by normal refrigerant like CFCs, HCFCs etc. The production of CO2 hydrate slurry in a coil heat exchanger is investigated in this study. Crystals are supposed to firstly form on the wall of the tube, generating a solid layer. The appearance of the solid layer increases the heat resistance from liquid to the refrigerant. Type-III antifreeze proteins have been added to the solution to better control the crystallization process of hydrate formation since AFPs have been proved to be an effective hydrate formation preventer which is environment friend. A kinetic model is developed based on the gas hydrate growth model of Skovborg and Rusmussen (1994), taking the mass transfer process to be the rate-control step. The diffusion coefficient of gas to liquid is investigated to be influenced by pressure, temperature and concentration of the hydrate formation preventer. Results show that the growth rate decreases with the increase of the concentration of AFPs while the thickness of the crystal layer doesnâ€™t show the same trend.