Experimental study on absorption characteristics of a falling film absorber with micro-scale NH3/LiNO3 liquid film

2022 
Abstract This study proposed a novel micro-scale falling film absorber with its experimental data on a complete absorption refrigeration system. Micro-scale liquid-distributor has been carefully designed and manufactured by special techniques. An experimental system for absorption refrigeration has been established to test the novel absorber. This unique absorber applies ammonia/lithium nitrate as working pair which is considered to own application potential for small-scale absorption refrigeration units. Experimental analysis has been done under various of working conditions for making contrasts. Relationships between significant working parameters and absorption parameters have been discussed. Under series of working conditions, absorption rates ranging from 1.2 to 2.6×10-3 kg/(m2·s) have been obtained. Approach to equilibrium factor which characterize the perfection of absorption process ranges from 0.5 to 0.98 while absorption ratio ranges from 0.02 to 0.12. With the increase of Reynolds number from 3 to 52, the mass transfer coefficient rises from 12 to 98×10-6m/s and Sherwood number ranges from about 30 to 60 respectively. According to the analysis, absorption pressure potential and cooling water temperature are two major factors which enhance the absorption intensity. Absorption pressure potential and inlet solution subcooling degree owns nearly linear relationship with parameters such as absorption rate, absorption ratio and approach to equilibrium factor. However, normalized absorption rate and approach to equilibrium factor gain negative correlations with absorption pressure potential and Reynolds number respectively. Effects of inlet solution flowing features on absorption performance are distinguished under different working condition series. In general, solution flowing intensity inside absorber is a positive factor for absorption process. All the experimental results reveal that, this micro-scale falling film absorber has its priority on absorption perfection and absorption rate for per unit of mass transfer area. Compact structure makes it more valuable for further research and application on small-scale absorption refrigeration unit with the working pair of ammonia/lithium nitrate.
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