To dimension an air-cooling-system for a blown film extrusion line, the computational fluid dynamics has been established. For more than ten years the institute for product engineering is engaged in this topic. Within the dissertation of D. Wolf and B. Feron the technical bases were set to improve the capacity of a cooling-system within the blown film-production by means of numerical methods. Because the convective heat transfer is the major cooling value inside the tube formation zone, J. Spirgatis used the fluid simulation in his work to investigate more precisely all occurrences in the cooling air. Due to the demonstrative display of path lines, temperature and pressure distribution within the domain, the computation helps to increase the understanding of the tight linkage between cooling airflow and film reaction. Generated results indicate that shortly above the first airflow guidance the free jet interacts with the ambient air. This interaction first of all leads to an absorption of the ambient air into the free jet, which causes an expansion of the free jet volume in extrusion direction. Furthermore macroscopic eddies and vortexes occur, due to fact that they accumulate to lager eddies they have the opportunity to interact with the hot melt of the tube formation zone. On the basis of this insight, a completely new air flow guidance has been developed. This system provides a controlled guidance of the main flow due to the venture-effect and the interaction of the ambient air can be affected purposefully. To develop a new air flow guidance, the use of a CFD-simulation tool is very helpful. None the less the simulation comes to its limitations, if the influence of the cooling air on the instable film should be considered. Due to this limitation, in a project supported by the German research department (DFG), the institute of engineering and plastic machinery has developed a process model. This model describes the tube formation zone numerically. By use of the CFD-simulation in combination with the numerical description, an iterative calculation of the state of equilibrium between the cooling air and the film is accomplished. The results of the first calculations show that this combination works quite well. Thus the basis is set up and further investigation will be made to gain a better prediction of the film contour.