Effect of the Flow Rate of Water Dropping onto the Evaporator in an Absorption Chiller

Abstract

Two-dimensional numerical study on the heat transfer characteristics and on a vapor flow in an absorption chiller has been performed to investigate the effect of water flow rate dropping onto the evaporator in an absorption chiller using the liquid film models previously developed. The flow rate was changed in three steps from 7.98 to 79.8 x 10 -3 kg m -1 s -1 where the Reynolds number of liquid film ranged from 10 to 100. From the results, it was found that the evaporation and the heat transfer rates take peak values when the water dropped onto the evaporator reaches the bottom line of the evaporator cylinder bundle. The heat transfer was found to decrease severely with the flow rate after the peak mainly due to the thickening of the water liquid film. The pressure loss was also found to increase with the vapor flow velocity and it made the temperature difference between the saturation temperature and the heating temperature small. This was also partial cause on such severe decrease of the heat transfer rate after taking the peak value. From this, it was concluded that the optimum operating condition exists at the condition when the water just reaches the bottom line of the evaporator bundle.