and does not take into account influences of mixing temperature variations boundary conditions and resin flow channel cross section variations it has been found useful and a good approximation to describe process variables and design features the dimensionless expression at r 2 which applies to fixed or motionless systems can be converted into one applying for flowing systems such as polymer flow through die channels when we consider that for non cylindrical resin flow channels the approximation r 2a p is used where p is the wetted perimeter the following examples are included for the purpose of illustrating the invention and it is to be understood that the scope of the invention is not to be limited thereby for examples 1 to 8 the apparatus of fig1 is used equipped with the bleed tube 19 and bleed valve 20 whereby adjusting of the bleed valve 20 different temperature and heat transfer patterns can be independently established in the tube section transition zone and nozzle zone with the resulting effect observed and measured on spinning performance at various air volumes and pressures the die is a 12 cm long tube 1 having a 0 3175 cm inside diameter connected to a 0 1588 cm thick plate 2 into which 16 nozzles 3 are inserted.