Experimental study on heat and mass transfer performance of a falling film absorber

The objective of this study is to evaluate the performance of a falling film absorber for absorption refrigeration machines. Experiments with smooth and enhanced tubes were conducted to measure the heat transfer coefficient of this component in a wide range of mass flow rates, at temperature levels corresponding to an absorption chiller application case. The aim of this study is to experimentally clarify the absorption phenomenon of smooth and enhanced tubes in a wide range of mass flow rates, which would then be useful in designing absorption systems. Regarding the working medium, LiBr-H₂O solution was used as the absorbent and water as the refrigerant. Additionally, 1-ocatanol was added as a surfactant. The experimental apparatus consists of 10 horizontal tubes, a distributer, and a desorber. A falling film absorber is that absorption falls from the distributer to the horizontal tubes, which are surrounded by water vapor. The flowing behavior of the absorptive solution on horizontal tubes influences heat and mass transfer coefficient. The mass flow rate and shape of the tube has influence on the flowing behavior. Hence, the experiment was conducted in a wide range of mass flow rate and using different tubes with smooth or enhanced surfaces. The heat transfer coefficient was calculated from the heat transfer rate. As a result, the differences in the heat transfer performance of the absorber for each kind of tube were clarified. It was concluded that the shape of the tube significantly influences the heat transfer coefficient.