Naret Intawong

Design and construction of photo-conductive light pressure sensor for highly viscous fluids

A new pressure sensor based on the use of a light dependent resistor (LDR) is introduced in this article; the sensor being called photo-conductive light pressure (PLP) sensor. The sensor uses a mechanical system to transmit pressure from the fluid system to a filter pin, causing it to move. The displacements of the filter pin due to the applied pressure allow different amounts of light, sent out by a light emitting diode (LED), to reach a light dependent resistor (LDR). By direct calibration, the resistance changes are converted into electrical voltage and thus real pressure value. The proposed sensor is found to be simple to use and reliable, low in cost and is recommended suitable for pressure measurements of highly viscous fluid systems. The sensor proposed in this work gives a maximum pressure range of 100 bar and shows high repeatability and accuracy in the obtained results with a sensitivity, a sensitivity error and a response time of 6.62 mV/bar, 0.15% FS and 1.66 s FS, respectively.

Flow properties and entrance corrections of polymer melts by a mobile barrel capillary rheometer

This paper investigates the flow properties and entrance corrections of a polyethylene melt in a capillary rheometer that features the possibilities of moving either the piston or the barrel, the latter mode being novel in operation. The paper mainly aims to investigate the variations in the flow properties and the entrance corrections due to the mode of operation. It is found that the flow properties and entrance corrections are dependent on the mode of operation and the die sizes used in the capillary rheometer, this being thought to be associated with the flows occurring in the capillary rheometer.

Effects of Roller Speed, Die Temperature, Volumetric Flow Rate, and Multiple Extrusions on Mechanical Strength of Molten and Solidified LDPE under Tensile Deformation

An experimental rig coupled with a high speed data-logging and recording system and a personal computer was specially designed and constructed for the real-time measurement of mechanical strength (in terms of drawdown force) as a function of volumetric flow rate and roller speed for virgin low-density polyethylene (LDPE) and reprocessed LDPE during a filament stretching process. The effect of the number of extrusion passes for the reprocessed LDPE was our main interest. The experimental rig was connected to the end of a single-screw extruder, which was used to melt and extrude the polymers. The LDPE filaments were then solidified and collected for studying the mechanical properties. The mechanical strength of the virgin LDPE and reprocessed LDPE were investigated in both molten and solidified states. The mechanical strengths of the virgin and reprocessed LDPEs under these two states are discussed and compared in terms of change in magnitude under a wide range of processing conditions (volumetric flow rate, die temperature, and roller speed). The results suggested that in the molten state the drawdown force for LDPE melts was dependent on volumetric flow rate, die temperature, roller speed, and the number of reprocessing passes. The drawdown force being affected by the number of reprocessing passes could be explained by molecular degradation and gelation effects when using high volumetric flow rates. In the solidified state, the tensile properties of the solidified LDPE increased with roller speed. The effect of the number of extrusion passes for the solidified LDPE was similar to that for the molten LDPE. In the case of volumetric flow rates, the mechanical properties of the solidified LDPE decreased with increasing volumetric flow rate, whereas those of the molten LDPE exhibited the opposite effect. Thus, the mechanical strength of the molten LDPE could not always be used to assess the mechanical properties of the solidified LDPE.

An Experimental Apparatus for Measurement of Elongational Flow Properties for LDPE Melt and the Effect of Testing Conditions

An experimental rig was designed and constructed for melt strength measurement and was assembled at the end of a single screw extruder used for the production of low-density polyethylene (LDPE) melt. The experimental rig was coupled with a high speed data logging system and a personal computer for the real-time measurement of melt strength. The molten LDPE was extruded through a capillary die, forming a continuous filament before being pulled down by speed-adjustable mechanical rollers until the filament failed. A digital camera was used for measuring the actual extrudate size at failure point. The drawdown forces as a function of volumetric flow rate from the extruder, roller speed, die temperature and take-up style were of interest in this study. It was found that the experimental rig could be used for accurate measurement of the mechanical strength for the LDPE melt. The experimental results suggested that the melt strength of LDPE was dependent upon the volumetric flow rate through the die from the screw extruder, roller speed, and the take-up style. For ladder-step take-up, increasing roller speed resulted in non-linear increases in the drawdown forces, the drawdown force changes being associated with the molecular disentanglement and elastic resistances of the branched LDPE melt. The drawdown forces of the LDPE melt measured under the rapid speed take-up method were 40–60% greater than those tested under the ladder-step speed take-up method, depending on the volumetric flow rate used in the screw extruder. The tensile viscosity of the LDPE melt was found to decrease slightly with strain rate and die temperature in the testing conditions used in this work.

Flow visualization & extrudate swell behavior of natural rubber compound in annular die capillary rheometer

This research aims to study the flow pattern and extrudate swell properties of a Natural Rubber (NR) compound in a constant shear rate capillary rheometer, using two types of annular die: convergent annular and divergent annular. Results revealed that flow patterns that occurred in the barrels of both types of annular dies were significantly different, especially the vortex flow at the barrel wall and at the die entrance. This difference in flow pattern significantly affected both diameter swell and thickness swell of the NR compound. It was also found that thickness swell was higher than diameter swell in every test condition. This difference could be explained by analysis of the complex flow pattern at the die entrance.

Moderation of Entrance Pressure Drop and Extrudate Swelling of Wood Fiber/Polypropylene Composites Melt in Rotating-Die Extrusion Process

A novel rotating-die system was proposed to moderate the elastic swelling for molten polypropylene (PP) and wood/polypropylene (WPP) composite. The results suggested that the neat PP and WPP melts followed the psuedoplastic non-Newtonian pattern. The rotation of the die could moderate the extrusion load and entrance pressure drop. The die rotation effect appeared to be very pronounced for the PP with high wood contents and high extrusion rates. The decreases in extrusion load and entrance pressure drop were related with reductions of melt viscosity due to shear heating effect. The results practically implied that use of the rotating die system could increase the productivity in the extrusion process. In terms of elastic swelling, in all cases, it was found that the swelling ratio of neat PP and WPP melt composite increased with increasing shear rate, but for any given shear rates, the addition of wood particles and the use of rotating die caused decreases in swell ratio of the melts, the wood content being more well-defined than the die rotating speed.