Heat transfer

In a false twisting process for continuous filament yarn wherein substantially parallel filaments are fed into a false twisting device, the improvement comprising transferring heat between an advancing continuous filament yarn and a fluid prior to subjecting said yarn to a false twisting operation, said yarn being advanced in the direction of its longitudinal axis through two substantially non-twisting and non-interlacing fluid vortices generated by fluid streams tangentially and symmetrically arranged about the path of the advancing yarn, said vortices decaying freely in opposite co-axial directions from their point of generation to the point of escape into the atmosphere, whereby heat exchange is effected while maintaining the individual filaments of the yarn bundle in substantially parallel configuration, and then false twisting said yarn.