Performance Analysis Of Absorption Refrigeration Cycle Using Two Working Pairs And Study Of Falling Film Evaporation

Lithium bromide absorption refrigeration system has exceptional advantages in utilizing solar energy which is a source of clean energy and one of readily available forms of renewable energy. However, the low solar energy collecting efficiency of vacuum tube or flat plate solar collector along with insufficient time for refrigeration in the daytime has impeded its applications. The loow grade solar energy driven two stage absorption refrigeration exploiting LiCI-H2O solution rather than LiBr-H2O solution as working fluid for high pressure stage loop has been presented in this paper aiming to tackle with above problems. The thermodynamic performance of the cycle has been investigated with variable operation conditions. An experimental setup with inner heat source has been designed and built, then the heat and mass transfer performance of lithium chloride-water solution film outside the vertical tube has been experimentally and theoretically studied in the system.The flow chart of novel refrigeration cycle has been described, thus thermodynamic performance between the novel cycle using two working fluids and traditional cycle has been compared. It has been revealed that the low grade solar energy driving the absorption chiller can be extended to 55-75? and the maximal COP can reach up to 0.47 owning to two working fluids. The thermodynamic performance of the cycle and solution gas-emission scope have been investigated and evaluated with variable operation conditions such as driven heat temperature, evaporation temperature, condensation temperature and intermediate pressure. The theoretical study indicates that the appropriate intermediate pressure at which the COP of the system achieves maximum lies mainly between 2.5kPa and 4.0kPa.An experimental setup for LiCl-H2O solution evaporation has been designed and built referring to related design manual. The functions and key design points of experimental setup have been expounded especially the body of falling film generator. The operating procedure of the experiment setup has been briefly covered, and equipment has been adjusted.The mass transfer performance of LiCl-H2O solution film has been experimentally studied on the test bench The solution film is in wavy laminar flow (Re=500?900) under the experimental conditions. The maximum generation rate is 11.7 g/(m2·s) for LiCl-H2O solution and maximum temperature difference is 6.3? for heat source. The mass transfer performance of solution film and temperature difference of heat source have been examined under variable heat source temperature and flow, solution concentration, generation pressure and solution flow, which provide key parameters for the generation model of LiCl-H2O solution.Atheoretical model of heat transfer for LiCl-H2O solution film generation based on finite volume method is firstly developed. Temperature distribution and concentration distribution of solution have been obtained using calculated program. Based on the experimental data measured under the variable operation condition, convective heat transfer coefficients for LiCl-H2O solution is about lies between 1500 and 2300 W/(m2·K), and rises as the solution film Re increases. Moreover, the rib tube or surface treatment tube has been suggested for heat transfer enhancement aiming to increase heat source temperature difference and solution gas-emission scope.