High-Temperature Generation Beyond the Equilibrium by Self-Condensation Effect and Heat Storage Capacity in Absorption Heat Pump Using Lithium Bromide Crystal Slurry

抄録

A higher concentration of LiBr is effective in achieving an even higher performance in LiBr/water absorption heat pump (AHP), but crystal growth occurs and causes blocking fluid stream once the concentration reaches its saturation point. It was pointed that a fine particle slurry of LiBr crystal is formed under a super saturation condition when zeolite powder is suspended into the solution. Then the slurry possesses a potential to improve remarkably the output of heat. This paper proposes a concept of the self-condensation effect contributing to not only significantly higher temperature generation beyond the equilibrium for working in a heating-up mode of AHP but also enlargement of the heat capacity as a heat storage material. The adiabatic maximum temperature in the absorber was estimated based on thermodynamic equilibrium, energy and mass conservation, and the thermodynamic properties for different crystal concentrations in the slurry and evaporator temperatures assuming the case of a batch process in two columns consisting of absorber and evaporator. The slurry with higher crystal concentration than 0.3 kg-crystal/kg-slurry and 0.1 kg-crystal/kg-slurry has the potential to generate a maximum temperature of more than 150 °C under given evaporator temperature of 60 °C and 80 °C, respectively. In addition, the slurry can generate temperatures up to 80 °C with its heat storage capacity peaks at 1300 kJ/kg-slurry while the homogeneous solution heats up only to a low level of temperature at 65 °C with the heat storage capacity of 900 kJ/kg-solution, assuming that the initial temperatures of the solution and the evaporator are fixed at 25 °C and heat over 40 °C is utilized.