Research On Ammonia-water Bubble Absorption Behavior In An Air-cooled Vertical Finned Tube

A detailed description of the heat and mass transfer during ammonia-water bubble absorption in air-cooled vertical finned tube is presented. The tube is externally finned. The ammonia-water absorbent and ammonia vapor enter the absorber at the bottom and leave at the top. To obtain local values of some important parameters (temperature, molar ratio) and their variations along the tube, a thermal calculation based on the set parameters of the actual ammonia-water refrigeration cycle which is driven by waste heat is preformed. The calculation results are served as initial conditions of the vertical finned tube absorber inlet. A differential mathematical model for the heat and mass transfer is proposed based on mass and heat balances. Using the model, a numerical simulation is performed for the absorption process in the vertical air-cooled finned tube absorber.Through the conversion conditions of the flow model and the calculation results, local values of some important parameters such as temperature, model ratio, their variation along the absorber and the absorption length are obtained. There are three kinds of flow models during the absorption process, they are churn flow, slug flow, and bubble flow from the bottom to the top. The absorption velocity in churn flow and slug flow is faster than that in bubble flow. The interface temperature is very close to the bulk liquid temperature during the whole absorption process, so the bulk vapor thermal resistance is prominent in the total thermal resistance. Finally, when the solution circulation rates are constant, effect of the variable conditions of the absorber inlet upon the absorption behavior in the vertical air-cooled finned tube absorber is researched.Research on the heat and mass transfer behavior in the vertical air-cooled finned tube absorber which is driven by waste heat is advanced. So far, the research is in the theoretical analysis of phase. But the simulation results provide a reference for practical application. Owing to some superiorities of energy saving, quiet operation and small vibration, the ammonia-water bubble absorption system has some economic advantage and development space. Finally, to achieve better operation characteristics, some measures of optimization and improvement which include experiment verification, the other parameter variation (cooling air temperature, additives) of the absorber inlet and alternative refrigerants are proposed.