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Julia Aman, Turbulence and Energy Laboratory, Centre for Engineering Innovation, University of Windsor
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Paul Henshaw, Ph.D., P.E., Turbulence and Energy Laboratory, Centre for Engineering Innovation, University of Windsor
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David S-K Ting, Ph.D., P.E., Turbulence and Energy Laboratory, Centre for Engineering Innovation, University of Windsor
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The core components of vapor absorption refrigeration systems (VARSs) are the absorber, generator, condenser and evaporator. A pump is a critical component of a VARS to circulate the refrigerant–absorbent solution from the low pressure absorber to the high pressure generator. High quality mechanical/electrical energy is required to run this pump. Furthermore, the electrical pump is exposed to the high temperature corrosive solution. A thermally-driven bubble pump, which can be powered by waste heat or solar thermal energy, offers a simple and efficient technique for lifting a liquid from lower to higher levels, after which it can flow by gravity. In the vapor absorption refrigeration cycle, a bubble pump can be used to lift the solution from the absorber to the generator and also desorb the refrigerant vapor for achieving the necessary cooling effect. The performance of a VARS strongly depends on the bubble pump parameters. So the proper modelling and analysis of bubble pump parameters is a crucial to maximize the cycle performance. Extensive theoretical and experimental research has been performed in order to use the bubble pump for VARS. Some analyses have been developed based on air-lift pumps, some did not consider friction factor effects, two-phase flow, or the gas void fraction. Laminar flow is assumed and heat loss was not included for these analytical models. Beside these factors, thermophysical properties (such as specific heat, heat of vaporization, density, viscosity, surface tension) of the solution are also important for the evaluation of bubble pump performance as well as the overall performance of it in refrigeration systems. In this study, an analytical model of a bubble pump characteristics was developed and experimental work was conducted in order to use this pump in a VARS. In the simulation model, two-phase turbulent flow with heat loss, friction, surface tension effects and other thermophysical properties was considered. The model was validated by operating the bubble pump with water at atmospheric conditions. The bubble pump performance was investigated with tube diameters of 6 to 10 mm and lifting ratios (the ratio of the height of the liquid in the tube to the tube length) of 0.6 to 0.8, and at different heat inputs. Experimental results agreed with theoretical within 14%. The maximum liquid flow rate was obtained during slug flow at 180 watts heat input, a lifting ratio of 0.8, and tube diameter of 10 mm.
