Testing of a Falling-Film Evaporator for Adsorption Chillers

In this work, the performance of an innovative evaporator based on water falling film was investigated. The studied evaporator has been equipped with a recirculation system to maximise the wetted surface. Tests have been carried out in a lab-scale adsorption unit connected to a test bench recently realised at Politecnico di Milano labs for evaluating heat transfer performances under realistic operating conditions. Several ad/desorption cooling cycles were performed, setting different liquid refrigerant initial contents (0.9-1.5 kg), different chilled water inlet temperatures (7-20o C) and flow rates (200-1000 L/h) and different adsorbent bed temperatures (25-30o C). Evaporation performance has been determined in delivered cooling capacity. Moreover, the experimental data were used to calculate the overall evaporator heat transfer conductance (UA). Experiments showed how the heat duty peaks are mainly due to the thermal level of the chilled water that enters the evaporator, not the water content inside it because this value only affects the duration of the process. Instead, the UA value does not depend on the evaporator inlet chilled water temperature and initial mass content inside the evaporator. UA is 540-570 W/K for temperatures of chilled water entering the evaporator, equal to 10-20o C, and mass of refrigerant of 0.9-1.5 kg.