Analysis of yarn tension in air-jet nozzles

In the insertion of yarns by air-jet, the yarn acceleration in the jet nozzle is one of the important factors. The present investigation is planned to discuss the yarn tension mechanism in nozzles as follows. 1) Air flow rate and its velocity in nozzles are measured experimentally. 2) The drag force acting on different kinds of yarns according to yarn structure and count is measured. The yarn tension obtained is compared with the theoretical value calculated from the drag coefficient based on the Reynolds number. The results obtained were as follows. 1) An increase of the bore size of the induction nozzle provided in the jet nozzle increases the air flow rate inducted by driving flow. The maximum bore size was 3 mm. 2) The induced flow rate reached a limited value in spite of increasing the driving pressure. 3) The applied tension on the yarn in a jet reached a limited value in spite of increasing the length of the acceleration pipe. 4) The yarn tension calculated from equation based on the isentropic flow of compressible fluid and the air drag in the nozzle were in agreement with those obtained experimentally.