Evaluation of different evaporator designs and concepts for sorption processes using water as refrigerant

Evaporation characteristics of water at low temperatures and pressures (5-30 °C, 870 - 4200 Pa) are of great interest for sorption processes. The work presents the experimental characterization of the evaporation performance measured on different market available and newly developed heat exchanger designs. Designs, experimental data, and performance evaluation criteria are described. As a central evaluation values the heat transfer coefficient and the volumetric UA-value are discussed for the different scales of samples. The focus is led on an alternating operation mode, where the same heat exchanger is used as condenser first and then changed to evaporation. Additionally the influence of a flooded operation is analyzed. The results illustrate that different designs and operation modes result into different time dependent performances. High UA-values are reached with the open, unflooded operation mode. Nevertheless the mass of refrigerant kept in the heat exchanger can be increased strongly by flooded operation.