Characteristic study of steam maldistribution in horizontal-tube falling film evaporators

The maldistribution of steam inlet velocity of a large horizontal-tube falling film evaporator was investigated with numerical simulation using the distributed parameter model (DPM) to provide essential design of falling film evaporator. Empirical correlations were obtained through experimental studies on the falling film evaporation outside a single horizontal tube, the condensation inside the tube and the inter-tube vapor flow across a tube bundle to conduct the three-dimensional simulation of the evaporator. The maldistribution of tube-side steam on tube row and column directions were analyzed with the brine inlet salinity ranging from 30 g/kg to 60 g/kg and the brine inlet spray density from 0.05 kg/m·s to 0.09 kg/m s. The Brine boiling point elevation (BPE) and the inter-tube vapor flow resistance were taken into account in the model. Considering the self-compensation characteristic between the heat flux and steam inlet velocity of the tubes, the maldistribution of heat flux was presented to analyze the maldistribution of tube-side steam inlet velocity. The simulation results exhibit the decreasing trend of the tube-side steam inlet velocity non-uniformity along the tube row direction with the increment in the brine inlet spray density and the decrement in the brine inlet salinity. Along the tube column direction, the non-uniformity of steam inlet velocity increases with the increment of brine inlet spray density and the decrement of brine inlet salinity.