Design and Structure Optimization of Plenum Chamber with Airfoil Baffle to Improve Its Outlet Velocity Uniformity in Heat Setting Machines

The plenum chamber of a heat setting machine is a key structure for distributing hot air to different air channels.Its outlet velocity uniformity directly determines the heating uniformity of textiles,significantly affecting the heat setting performance.In a traditional heat setting machine,the outlet airflow maldistribution of the plenum chamber still exists.In this study,a novel plenum chamber with an airfoil baffle was established to improve the uniformity of the velocity distribution at the outlet in a heat setting machine.The structural influence of the plenum chamber on the velocity distribution was investigated using a computational fluid dynamics program.It was found that a chamber with a smaller outlet partition thickness had a better outlet velocity uniformity.The structural optimization of the plenum chamber was conducted using the particle swarm optimization algorithm.The outlet partition thickness,the transverse distance and the longitudinal distance of the optimized plenum chamber were 20,686.2 and 274.6 mm,respectively.Experiments were carried out.The experimental and simulated results showed that the optimized plenum chamber with an airfoil baffle could improve the outlet velocity uniformity.The air outlet velocity uniformity index of the optimized plenum chamber with an airfoil baffle was 4.75%higher than that of the plenum chamber without an airfoil baffle and 5.98%higher than that of the conventional chamber with a square baffle in a commercial heat setting machine.

Investigation on the Structure and Performance of Polypropylene Sheets and Bi-axially Oriented Polypropylene Films for Capacitors

Polypropylene(PP) sheets are cast with various chill roll temperatures and rates, which are studied with differential scanning calorimetry, wide angel X-ray diffraction, scanning electronic microscopy and dielectric withstand voltage test system. The results show that increasing the chill roll temperature and cast rate can promote the increase of crystallinity and the growth of β-form. The PP sheets have asymmetric skin layer structures. The lower the chill roll temperature, the thicker the skin layer, the smaller the spherulite size. The electric breakdown strength(Eb) of PP sheets is mainly affected by the crystallinity but not the morphology. The PP sheets are further stretched to prepare bi-axially oriented PP(BOPP) films with various heat setting time. Our results indicate that the structure of PP sheets affects the properties of BOPP films. The as prepared BOPP films from the sheets cast at high chill roll temperature and rate have the highest crystallinity and Eb. Heat setting time has profound effect on the crystallinity and Eb, which increase first and then decrease with the heat setting time. It is expected that our study can provide guidance for optimizing process parameters.