VISUALIZATION AND DETERMINATION OF LOCAL MASS-TRANSFER AT SOLID WALLSIN LIQUID FLOW

A method for visualization and determination of local and integral mas s transfer coefficients at solid walls in liquid flow is presented. Th e method is based on chemisorption of a dye at a surface coated with p olyamide. This res;its in a colour intensity distribution which corres ponds to the local mass transfer: a high mass transfer rate results in a high colour intensity and vice versa. Chromatographic foils and pol yamide membranes are used for the coating of the surface. This method allows the investigation of surface flow phenomena in channels with wa ll suction by using membranes. The experimental method based on convec tive mass transfer in liquid flow allows the investigation of flow phe nomena near the wall in various apparatuses for heat and mass transfer . There are new possibilities for research of mass transfer in gas-liq uid flow and systems with free surfaces, for example stirred reactors. The method can also be used for the analysis of mixing behaviour and residence time distribution. The quantification of the local mass tran sfer coefficient is made by optical measurements of the resulting colo ur intensity distribution. This is made by remission photometry or dig ital image processing. The application of different CCD-cameras and sc anning systems is explained. The correlation between the optical measu rement and the transferred mass is evaluated in simple but effective c alibration experiments. Some examples of investigations show the pract icability of the method. (C) Elsevier, Paris.