ISSN Online: 2377-424X
International Heat Transfer Conference 12
Degassing during polymer processing
Аннотация
Degassing is a thermal separation process in order to remove low molecular solvents from mixtures of polymers.
Extruders with partly filled degassing zones are often used for this process. The two-phase flow of the polymer
and the degassing monomers and solvents is complex due to free surfaces. In film flow and two-phase bubbly
flow the polymer is heated by dissipation and cooled by evaporation of the low molecular solvent.
Temperature and concentration fields are difficult to predict in extruders because of the complex flow field. Therefore the experimental investigations are carried out in special designed apparatus with a similar flow field and in a transparent double screw extruder to investigate the different flow mechanisms.
In order to nucleate bubbles of the volatile component the polymers must be supersaturated and some kind of deformation must exist. The bubble nucleation is shear induced. The changes in concentration during two-phase bubbly flow result in decreasing temperatures. The mass transfer rates are increased due to the large inner surfaces of the bubbles in the foam and so is the cooling by evaporation. The heating by dissipation is low because of to the reduced viscosity of the foam compared to the single-phase polymer melt flow in thin films.
Temperature and concentration fields are difficult to predict in extruders because of the complex flow field. Therefore the experimental investigations are carried out in special designed apparatus with a similar flow field and in a transparent double screw extruder to investigate the different flow mechanisms.
In order to nucleate bubbles of the volatile component the polymers must be supersaturated and some kind of deformation must exist. The bubble nucleation is shear induced. The changes in concentration during two-phase bubbly flow result in decreasing temperatures. The mass transfer rates are increased due to the large inner surfaces of the bubbles in the foam and so is the cooling by evaporation. The heating by dissipation is low because of to the reduced viscosity of the foam compared to the single-phase polymer melt flow in thin films.