140 research outputs found
Investigation of the effects of fillers in polymer processing
Get PDFThe addition of fillers has become a common method of improving the performance of composites. Therefore, many types of fillers are commercially available while several other types are being investigated. The understanding of the effect of additives on the processing and product quality is crucial for manufacturing products economically and with the desired qualities. This study focuses on investigating the possible effects of graphene and fumed silica nanoparticle fillers on polymer processing and product properties. Three polymeric materials were processed with these two fillers via a mini-Lab twin screw extruder to obtain a better dispersion, and then the properties of samples produced were explored with a number of different testing techniques (e.g., tensile testing, SEM, DSC and rheometer). Firstly, the Young's modulus of amorphous materials was strongly affected by the filler content, while crystalline materials were not that sensitive to the filler content/level. The Young's modulus of Polystyrene-based polymer nanocomposites (PNCs) with 8 wt.% fillers at 200 ℃ and 50 rpm was found to be of approximately 1786 MPa. Also, as clearly recognized by the SEM images and one glass transition temperature (Tg) value rather than two Tg values, it can be ensured that the particles are finely dispersed within PNCs regardless the filler type/content. And then, the rheological results further confirmed that the properties of PNCs are affected by the filler content and set conditions, while the Tg of PNCs was mainly dependent on the matrix and have slightly influenced by the degree of filler dispersion. Moreover, the energy demand was also explored during all the experimental trials for possible comparison and indicated that the energy consumption increased with the fillers content but the magnitude of increase was different with different polymer type
Mechanical and thermal properties of Graphene nanoplatelets-reinforced recycled polycarbonate composites
Get PDFNanocomposites have received significant interest in recent years, as they offer improved properties compared to conventional materials for various applications. Among many available nanofillers, graphene nanoplatelets (GNP) have shown promising results for polymer-based nanocomposite applications. This paper investigates the mechanical and thermal properties of GNP-reinforced virgin and recycled polycarbonate (PC) nanocomposites blended via a twin-screw extruder. Effects of various key processing parameters such as filler concentration, processing speed, barrel/die set temperature, and PC type (virgin and recycled) on the reinforced composites were examined. Mechanical properties were characterised by tensile testing, while thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to characterise the thermal properties. The results show that the processing speed and barrel/die set temperature have a slight influence, while the filler concentration significantly affects the properties of PC/GNPs composites. The Young's modulus and yield strength were enhanced with increasing GNP loading, where the maximum enhancement of Young's modulus was obtained as ∼33% for virgin-PC/GNP and ∼39.5% for recycled-PC/GNP composites at 10 wt.-% GNP loading. However, the failure strain was reduced with the increased GNP loading for both virgin and recycled PC/GNP composites. Embedding GNP into the PC matrix only slightly influenced the thermal stability and glassy transition temperature (Tg). The highest thermal stability for virgin PC/GNP composites was observed with 1 wt.-% (2.74% increase with respect to virgin PC), while for recycled PC/GNP, it was observed with 10 wt.-% (2.42% increase with respect to recycled PC) GNP loading. Under the same GNP loading, recycled PC-based composites showed lower thermal stability than virgin PC-based composites. The Tg evaluated from DSC showed a rise under 1 wt.-% GNP for virgin PC/GNP and decrease afterwards with higher filler loading, while an irregular variation for recycled PC/GNP was observed
Modelling of Heat Exchangers with Computational Fluid Dynamics
Get PDFHeat transfer is one of the major aspects of machineries, devices and industrial processes for maintaining their functionality and also for achieving better product quality. Hence, different types of heat exchangers are used in these applications with the purpose of removal of extra process/device heat to maintain them in desirable working temperatures. However, the size of a heat exchanger is a key consideration for any type of process or device as it decides the size of the machine/device or of the processing plant. This study aims to study the design of a heat exchanger theoretically and then to use computational fluid dynamics to optimize its performance. For design purposes, a counter flow heat exchanger was considered and its length was calculated with the LMTD method while the pressure drop and energy consumption were also calculated with the Kern method. Then, a computational model of the same heat exchanger was developed with ANSYS and then this was extended to six different models by changing its parameters for the optimization purposes. Also, these models were used to analyse the heat transfer behaviour, mass flow rates, pressures drops, and flow vortices of the shell and tube flows inside the heat exchanger. Theoretical and CFD results showed only a 1.05% difference in terms of the cooling performance of the hot fluid. The axial pressure drop showed positive correlations with both the overall heat transfer coefficient and pumping power. Overall, CFD modelling gave a promising outlook for design and optimization of heat exchangers
A Novel Soft Sensor for Real-Time Monitoring of the Die Melt Temperature Profile in Polymer Extrusion
Get PDFPolymer extrusion is the most fundamental technique for processing polymeric materials, and its importance is increasing due to the rapid growth of worldwide demand for polymeric materials. However, the process thermal monitoring is experiencing several problems resulting in poor process diagnostics and control. Most of the existing process thermal monitoring methods in industry only provide point/bulk measurements, which are less detailed and low in accuracy. Physical thermal profile measurements across the melt flow may not be industrially compatible due to their complexity, access requirements, invasiveness, etc. Therefore, inferential thermal profile monitoring techniques are invaluable for obtaining detailed, accurate, and industrially compatible measurements and, hence, to achieve improved process control. In this paper, a novel soft sensor strategy is proposed to predict the real-time temperature profile across the die melt flow in polymer extrusion for the first time in industry or research. It is capable of determining the melt temperature at a number of die radial positions only based on six readily measurable process parameters. A comparison between the simulation results of the novel melt temperature profile prediction soft sensor and the experimental measurements showed that the soft sensor can predict the real-time melt temperature profile of the die melt flow with good accuracy. Therefore, this will offer a promising solution for making real-time melt temperature profile measurements noninvasively in polymer extrusion, and also, it should be applicable to other polymer processes only with a few modifications. Moreover, this technique should facilitate in developing an advanced process thermal control strategy
Improving the performance of shell-and-tube heat exchangers by the addition of swirl
Get PDFHeat exchanger is a component which is used to transfer the heat from one medium to another efficiently. Generally, they occupy a large space compared to other components and such bulky designs are not attractive in the modern industrial applications due to several constraints. Therefore, it is invaluable to develop compact heat exchangers but with the improved performance. In this work, an investigation was made on the possibility of reducing the size of a shell-and-tube heat exchanger by addition of swirl. Swirl was generated by using a twisted-tape which inserted inside tube and the effects of these tapes on the heat transfer rate and pressure drop were theoretically studied. The results showed that a half-length regular spaced twisted-tape insert gave the lowest Nusselt number while a full-length twisted-tape insert gave the maximum Nusselt number and hence the highest rate of heat transfer. The length of the heat exchanger could be reduced by 13.3% with a full-length twisted tape and this would be result in 6.8% of reduction of the fabrication cost. Therefore, addition of swirl into the fluid flow should help to design compact and low cost heat exchanges with improved performance but the pressure drop increased leading to an increase of the required pumping power. A prototype shell-and-tube heat exchanger was designed and fabricated based on the theoretical results. Studies are underway to experimentally investigate the overall effectiveness of the use of twisted-tape inserts for enhancing the heat transfer rate by considering all the related benefits and drawbacks
A Novel Model-Based Controller for Polymer Extrusion
Get PDFExtrusion is a fundamental technique of processing polymeric materials, and the thermal homogeneity of the process melt output is a major concern for high-quality extruded products. Therefore, accurate process thermal monitoring and control are highly invaluable for product quality control. However, most of the industrial extruders use conventional thermocouples whose measurements are limited to a single point and are highly influenced by barrel metal wall temperature. It has shown that the melt temperature varies considerably with the die radial position, and hence, point-based measurements are not sufficient to determine the actual thermal stability across the melt flow. Therefore, thermal control techniques based on such point/bulk measurements may be limited in performance. In addition, the majority of process thermal control methods are based on linear models and are not capable of dealing with process nonlinearities. In this study, a review of the previous work relating to extruder melt temperature control is presented while identifying their limitations. A novel model-based control approach is then proposed to control the polymer extrusion process incorporating a melt temperature profile prediction soft sensor and fuzzy logic. The results show that the proposed controller is good in achieving the desired average melt temperature across the melt flow while minimizing the melt temperature variance. The adjustments made by the controller to the manipulated variables confirmed that it has the capability of adjusting the suitable variables, depending on the different situations encountered. Therefore, this will be a promising alternative to linear control techniques and control techniques based on point/bulk thermal measurements which are common in the present industry
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