Non-evaporating black liquor falling film hydrodynamics

Knowledge of wave behaviour is a key factor for understanding heat transfer in falling film evaporators. Here the industrially important fluid black liquor has been examined, together with water which has been used as a reference. Notable results are that there are large local fluctuations in the film thickness; for instance at a Re number of 4100 in the black liquor falling film, the thickness varies between 0.2 and 8.0 mm. For the water falling film, both correlations (Brotz and Brauer) are mostly within the 95% confidence interval of the measured average film thickness. The black liquor film tends to be thicker than the film thickness calculated with the correlations, especially for higher Re numbers.