Fluidized bed ice slurry generator for enhanced secondary cooling systems

Abstract

Ice slurries are liquid solutions of a freezing point depressant in water, in which small ice crystals are present. Ice slurries are efficient secondary cooling fluids because they utilize the latent heat effect involved with the ice/water phase change. A high heat capacity is available at relatively constant temperatures, while ice slurries are also pumpable. Furthermore, ice slurries can be stored in tanks for later use, which allows for benefits of peak load reduction and also allows for shifting of cooling loads to the nighttime, when electricity tariffs are low and the primary cycle efficiency is high. Ice slurries may for example be utilized in air-conditioning, supermarket cooling and cooling in (food) industry. The objective of the research was to enhance secondary cooling system performance by using a fluidized bed ice slurry generator. The research was initiated because ice slurries, though efficient cold carriers, are not applied widely in secondary cooling systems yet, the main obstacle being the lack of an efficient ice slurry generator. In the research the heat and mass transfer processes in the fluidized bed ice slurry generator were studied in detail. An accurate heat transfer model was developed. Ice crystallization, ice adhesion and liquid/solid fluidization phenomena were investigated to determine the processes that are responsible for freeze-up of the ice slurry generator. Also the thermophysical properties of the ice slurries and their behavior in secondary cooling cycles were evaluated. The results were implemented in a dynamic simulation model in which the economic and energetic performance of the fluidized bed ice slurry generator could be evaluated in detail. It was shown that the novel technique may be a competitive option even in air-conditioning applications in the Netherlands.