Enhancement of LiBr–Water Absorption Heat Pump Performance by Supersaturated Fine Crystal Slurry

概要

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The present study examined the use of supersaturated fine crystal slurry to improve the performance of LiBr–water absorption heat pump. To confirm the physical properties and heat transfer characteristics of the crystal slurry, measurements of particle size distribution and viscosity and a solution film heat transfer experiment were carried out. The effect of the presence of fine crystals on heat pump performance was analyzed by a heat and mass transfer model in the case where the solution flow forms a film in the absorber or regenerator. The particle size of crystal slurry (LiBr conc. 63.4%, adsorbent conc. 5.56%, temp. 25°C) ranged from 10 to 200 µm and the median size was 57.0 µm. The viscosity of same crystal slurry at 20°C was 1.67×10-2 Pa·s, and the higher amount of crystal resulted in higher viscosity but showed sufficient fluidity. Overall heat transfer coefficient was 107–893 W/(m2·K) when the flow rate of solution was in the range of 3.6×10-6 to 49.0×10-6 m3/s. Adsorbent suspended in the solution showed little effect on the heat transfer, but an increase in solution flow rate enhanced the overall heat transfer coefficient. The analysis based on the model developed revealed that the presence of fine crystal slurry advanced the vapor absorption rate up to 100% compared with that for crystal free solution.