Heat Transfer Study And Entropy Generation Analysis On Direct Contact Ice Slurry Generator

Ice slurry has been widely utilized in fishery, surgery and ice storage air conditioning system due to its excellent cold storage capacity and flowing property. Ice storage technology has been intensively studied in recent years. Ice slurry production procedures were introduced in and aboard firstly. Direct contact method was emphasized. Using volatile refrigerant would inevitably cause contamination to the water solution and an inconvenience of separation of the two fluids. A novel ice slurry generation system consisting of two direct contact heat exchangers was brought out, adopting immiscible air as the secondary refrigerant.In terms of this ice slurry generation system, the following three aspects were studied sequentially:1. A partial differential equation was established regarding the heat transfer process between a single cold air bubble and the ice generation solution. The dimensionless excess temperature profile was obtained by solving the equation numerically. The thickness of thermal boundary layer variation with the bubble radius and bubble velocity was discussed. Furthermore, the correlation on Nusselt number regarding Reynolds number and Prandtl number was derived.2. The correlation on Nusselt number for single air bubble was generalized to bubble group to study the heat transfer characteristics of the ice slurry generator, in regard to the volumetric heat transfer coefficient. The volumetric heat transfer coefficient was calculated under different cold air volume flow rate with different ethylene glycol water solution. A comparision between the calculation results and the experimental results was made. A relative error less than±20%shows the credibility of the method.3. Based on the single bubble heat transfer correlation, an entropy generation analysis was made considering the heat transfer process. The dimensionless entropy generation number in terms of Reynolds number was obtained. It was found that an optimal Reynolds number exsists, which would contribute a minimum dimensionless entropy generation number.