Current research work at the Institute of Fluid Mechanics at TU Dresden is concerned with the bubble interaction in a joining T-junction channel. Experimental techniques such as the fo-cused shadowgraph method in combination with image processing are mainly used. Due to the rectangular cross-section of the channels and the specific process parameters, the flow in the mixing area is highly three-dimensional, transient and transitional. A first focus of investi-gation is the description of the shape of deformed bubbles that break up eventually, with par-ticular attention being paid to deformation due to shear in one direction of motion. The bubbles under this strain are primarily stretched or compressed, resulting in a typical shape with axial symmetry along the major axis of the bubbles. With the aim of suitable modelling of the bubble behaviour in the flow, the volume-equivalent diameter proves to be the most suitable charac-teristic length measure. Due to the complexity of the flow, the simultaneous experimental de-termination of all quantities relevant for the bubble interaction is almost impossible. Therefore, the second part is dedicated to the qualification and use of numerical simulations for the de-termination of the variables of the continuous phase at the respective bubble position. This makes it possible, for example, to obtain information about the strain rate as an essential in-fluencing factor for the bubble deformation in the investigated regime.