Advantages and potentials of a blown film cooling system with a complete housing of the tube formation zone

In a prior work, a novel cooling approach for the blown film application was developed, called Multi-Jet. In contrast to a conventional cooling ring, this alternative cooling system guides the air vertically on the film surface, using several slit nozzles over the whole tube formation zone. In addition, the bubble expansion zone is surrounded by a housing. In this context, the cooling jets penetrate the boundary sublayer on the film surface that is developed by the fast flowing cooling air. The advantage of the housing can been seen in the disablement of the interaction of the cooling jet and the static ambient air. Besides the exhausting of the monomer loaded air, the housing allows to realize a heat recovery of the warmed cooling air. In this paper, an experimental and numerical investigation of the novel cooling system is shown. Here a comparison is done for several different process conditions with and without the use of the housing for the tube formation zone. By the means of a CFD-simulation, the cooling air flow phenomena and the heat exchange behavior can be made visible and compared with the experimental data. The stability and efficiency of the different process conditions of the film contours are experimentally measured. Moreover, questions about the possible amount and the temperature level of the dissipated heat are discussed.